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Accepted papers to appear in an upcoming issue

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A polarization-insensitive silicon waveguide crossing based on multimode interference couplers

Yaocheng Shi and Jingye Chen

Doc ID: 347696 Received 08 Oct 2018; Accepted 12 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: A polarization-insensitive waveguide crossing based on multimode interference (MMI) couplers is proposed and demonstrated on silicon-on-insulator (SOI) platform. By utilizing two orthogonal MMIs, the footprint of the device is about μm× μm. The proposed device, easily fabricated with only one fully-etched step, is characterized with low insertion losses (< 1.5 dB) and low crosstalks (< -25 dB) for both TE- and TM- polarizations from 1520 nm to 1610 nm band.

Soliton content in the standard optical OFDM signal

Egor Sedov, Alexey Redyuk, Mikhail Fedoruk, A Gelash, Leonid Frumin, and Sergei Turitsyn

Doc ID: 347646 Received 09 Oct 2018; Accepted 11 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Nonlinear Schrödinger equation (NLSE) is often used as a master path-average model for fiber-optic transmission lines. In general, NLSE describes the co-existence of dispersive waves and soliton pulses. Propagation of signal in such a nonlinear channel is conceptually different from linear systems. We demonstrate here that the conventional orthogonal frequency-division multiplexing (OFDM) input optical signal at powers typical for modern communication systems might have soliton components statistically created by the random process corresponding to the information content. Applying Zakharov-Shabat spectral problem to a single OFDM symbol with multiple sub-carriers we quantify the effect of statistical soliton occurrence in such an information-bearing optical signal. Moreover, we observe that at signal powers optimal for transmission OFDM symbol incorporates multiple solitons with high probability. The considered optical communication example is relevant to a more general physical problem of generation of coherent structures from noise.

Quadratic Soliton Combs in Doubly-Resonant Second-Harmonic Generation

Tobias Hansson, Pedro Parra-Rivas, Martino Bernard, François Leo, Lendert Gelens, and Stefan Wabnitz

Doc ID: 347379 Received 03 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We report a theoretical investigation of quadratic frequency combs in a dispersive second-harmonic generation cavity system. We identify different dynamical regimes and demonstrate that the same system can exhibit both bright and dark localized cavity solitons in the absence of a temporal walk-off.

Pulsating soliton with chaotic behavior in a fiber laser

Zhi-Wei Wei, Meng Liu, Shu-Xian Ming, Aiping Luo, Wen-Cheng Xu, and Zhi-Chao Luo

Doc ID: 342661 Received 17 Aug 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: The pulsating behavior of solitons is one of the interesting dynamics in dissipative nonlinear systems. It was theoretically predicted that the chaotic soliton could exist in the soliton pulsation process. Herein, we reported on the experimental evidence of the pulsating soliton with chaotic behavior in an ultrafast fiber laser. By virtue of dispersive Fourier transformation (DFT) method, the chaotic behavior of soliton pulsation is visualized by the fact that the mode-locked spectrum collapses abruptly in an unpredictable way during the pulsating process. The obtained results provide the first experimental demonstration of the chaotic behavior in the pulsating soliton, which would also give some new insights into the soliton pulsation dynamics in dissipative systems.

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity

Xinliang Zhang, Gaoneng Dong, and Yilun Wang

Doc ID: 348868 Received 22 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40 dB and a peak loss as low as 0.6 dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption and higher contrast, comparing to that involving Lorentzian resonance. For example, under signal trains of 2.5 Gb/s, switching energy with a contrast of 3 dB for Fano case is 113 fJ, which is 8-dB smaller than that for Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67 dB to 9.53 dB.

Nonlinear frequency conversion and manipulation of vector beams

Haigang Liu, Hui Li, Yuanlin Zheng, and Xianfeng Chen

Doc ID: 349213 Received 25 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Vector beams have been extensively investigated in recent years because of its fascinating vector character across the beam transverse section, which is demonstrated to be useful for optical micro-manipulation, optical micro-fabrication, optical communication, single molecule imaging, and so on. To date, it is still a challenge to realize nonlinear frequency conversion and manipulation of such vector beams because of the polarization sensitivity in most of nonlinear processes. Here, in our experiment, second-harmonic vector beams are generated by using three-wave mixing processes, which occur in two orthogonal placed nonlinear crystals, and the vector property is recognized by using a Glan-Taylor polarizer. This nonlinear frequency conversion process enables vector beams to be obtained at new wavelengths, and opens up new possibilities for all-optical switching and manipulation of vector beams.

Novel silicon nanoparticles based broadband optical modulators for solid-state lasers

Xinyang Liu, Kejian Yang, Shengzhi Zhao, Tao Li, Wenchao Qiao, Yaling Wang, Lei Guo, Yiran Wang, hongkun nie, Baitao Zhang, and Jingliang He

Doc ID: 346959 Received 28 Sep 2018; Accepted 09 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Motivated by the tremendous success of carbon nanomaterials in acting as optical nonlinear modulator, in this paper, the optical nonlinearity of its counterpart, silicon nanoparticles (SiNPs), is investigated. For the first time, the nonlinear optical property of SiNPs in 1μm and 2μm wavelength bands is observed. Its practical modulation performance was investigated by employing SiNPs as saturable absorber (SA) in pulsed lasers and the fabrication process, surface morphology, linear and nonlinear optical response property of the prepared SiNPs-SA were presented. Based on the SiNPs-SA, the formed Q-switched Nd:LuAG laser could generate laser pulses with shortest duration of 490 ns at ~1 μm and ~2 μm laser pulses with shortest duration of 453 ns were delivered from a Q-switched Tm:YAP laser, which shows that the SiNPs could be employed as a promising broadband SA for near- and mid-infrared spectral region.

Aperiodic Vogel spirals for broadband optical wave focusing

Taotao Zhao, Yanwen Hu, Shenhe Fu, Xiaonan Li, Yi-Kun Liu, Hao Yin, Zhen Li, Juntao Li, and Zhenqiang Chen

Doc ID: 347335 Received 02 Oct 2018; Accepted 09 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We demonstrate both experimentally and numerically a new type of hole array structures which exhibit optically diffractive focusing phenomenon. The hole arrays are designed based on the aperiodic Vogel spirals. In contrast to periodic and quasi-periodic hole arrays that contain discrete Bragg peaks in reciprocal space, the Vogel spiral hole arrays have particularly continuous Fourier components with circular symmetry, which enables optical wave focusing into a diffraction-limited hotspot for a wide range of incident wavelengths. We further demonstrate that the diffracted fields contain local orbital angular momentum leading to rotations of the diffractive circular rings around the center, although the total orbital angular momentum is zero.

Fiber optic refractive index sensors through spectral detection of Rayleigh backscattering in a chemically etched MgO-based nanoparticle-doped fiber

Marzhan Sypabekova, Sanzhar Korganbayev, Wilfried Blanc, Takhmina Ayupova, Aliya Bekmurzayeva, Madina Shaimerdenova, Kanat Dukenbayev, Carlo Molardi, and Daniele Tosi

Doc ID: 348705 Received 18 Oct 2018; Accepted 09 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We demonstrate and experimentally validate a fiber-optic refractive index (RI) sensor obtained by simply etching a high-scattering MgO-based nanoparticle-doped single-mode fiber in hydrofluoric acid (HF). The fiber has 32.3 dB stronger Rayleigh scattering than a standard fiber, allowing a detection of scattering spectral signatures with an optical backscatter reflectometer (OBR) even when the core is exposed to the outer refractive index. The obtained sensitivity is 1.53 nm/RIU (RI units), measured by correlating the scattering spectra. We prove the possibility of implementing a distributed RI detection (7 locations spaced by 1 mm). The fabrication method for this RI sensor is simplified as it simply requires etching in a HF bath, without the need of inscribing reflective elements or fabricating microstructures on the fiber.

1 W dual-end-pumped Ho:YAG MOPA system and its application to a mid-infrared ZGP2 OPO

Benrui Zhao, baoquan yao, Chuanpeng Qian, gaoyou liu, Yi Chen, Ruixue Wang, Tongyu Dai, and Xiaoming Duan

Doc ID: 349325 Received 26 Oct 2018; Accepted 09 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: A high efficiency and brightness Ho:YAG master-oscillator power-amplifier (MOPA) system dual-end-pumped by Tm:YLF lasers was demonstrated. The maximum output power of 1 W at wavelength of 2090.7 nm was achieved with pulse repetition frequency (PRF) of 10 kHz and pulse width of 22.9 ns, corresponding to pulse energy of .1 mJ and peak power of ~1 MW. The extraction efficiency of the amplifier system was more than 60%. The beam quality factor M2 was measured to be ~1.05. Using the Ho:YAG MOPA system as pump source, the ZGP2 (ZGP) optical parametric oscillator (OPO) delivered an output power of 110 W, corresponding to slope efficiency of 62%.

Compact highly efficient 2.1-W continuous-wave mid-IR Fe:ZnSe coherent source pumped by Er:ZBLAN fiber laser

Andrey Pushkin, Ekaterina Migal, Hiyori Uehara, Kenji Goya, Shigeki Tokita, M. Frolov, Yuriy Korostelin, Vladimir Kozlovsky, Yan Skasyrsky, and Fedor Potemkin

Doc ID: 351238 Received 07 Nov 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We report the compact and robust coherent source operating in mid-IR based on Fe:ZnSe chalcogenide gain medium optically pumped by Er:ZBLAN fiber laser. The output power of 2.1 W with 59% slope efficiency with respect to absorbed pump power at liquid nitrogen cooling is achieved. We show that strong re-absorption at high pump power and iron ion doping concentrations leads to the continuous tuning of central wavelength from 4012 to 4198 nm. Robustness of high power Er:ZBLAN fiber laser combined with prominent spectroscopic properties of Fe:ZnSe media pave the way for the development of reliable tunable CW mid-IR sources for scientific and industrial purposes.

Generation of telecom-band correlated photon pairs in different spatial modes using few-mode fibers

Cheng Guo, Jie Su, Zhenzhen Zhang, Liang Cui, and Xiaoying Li

Doc ID: 346327 Received 19 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We experimentally demonstrate the production of photon pairs at 1555 nm in LP01 mode and at 1566.8 nm in LP11 mode, respectively, via the spontaneous intermodal four-wave mixing in a 100-m-long few-mode fiber. We achieve a coincidence to accidental-coincidence ratio of 28, which clearly indicates the existence of quantum correlation. We also discuss the contribution of spontaneous Raman scattering to the background noise of photon pairs. Our source of photon pairs, compatible with the low-loss multiplexing and de-multiplexing components for space division multiplexing optical fiber communication, can be used for generating higher-dimensional entanglement.

Measurement of high pressure and high temperature using a dual-cavity Fabry-Pérot interferometer created in cascade hollow-core fibers

Zhang Zhe, Jun He, Bin Du, Fengchan Zhang, Kuikui Guo, and Yiping Wang

Doc ID: 346526 Received 21 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: A compact dual-cavity Fabry-Perot interferometer (DC-FPI) sensor is proposed and demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) spliced with a hollow-core fiber (HCF). The HC-PBF, which has low transmission loss, was used as the first FPI cavity and also acted as a bridge between the lead-in single-mode fiber (SMF) and the HCF. The HCF was used as the second FPI cavity and also acted as a micro gas inlet into the first FPI cavity. A DC-FPI sensor with different cavity lengths of 226 and 634 μm in the first FPI and the second FPI was created. Both gas pressures ranging from 0–10 MPa and temperatures ranging from 100–800 °C were measured using the DC-FPI sensors together with a fast Fourier transform (FFT) and phase demodulation algorithm. Experimental results showed that the first FPI cavity was gas-pressure sensitive but temperature insensitive, while the second FPI cavity was temperature sensitive but gas-pressure insensitive. A high gas-pressure sensitivity of 1.336 μm/MPa and a temperature sensitivity of 17 nm/°C were achieved in the DC-FPI sensor. Moreover, the cross sensitivity between the gas pressure and temperature was calculated to be ~−15 Pa/°C and ~0.3 °C/MPa. The proposed DC-FPI sensors provide a promising candidate for the simultaneous measurement of high pressures and high temperatures at some precise locations.

Generation of broadband near-field optical spots using thin film silicon waveguide with gradually changing thickness

Kaifeng Zhang, Shin-ichi Taniguchi, and Takehiro Tachizaki

Doc ID: 347462 Received 17 Oct 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We developed a thin film silicon waveguide with gradually changing thickness for generating a near-field optical spot. Theoretical studies show that the surface plasmons that are resonantly excited on the waveguide generate a hot spot with a wide spectral range. We experimentally confirmed generation of the near-field hot spot using continuous waves at 850 nm and 660 nm wavelengths. This waveguide which can generate the enhanced electric field by normal incident of the excitation beam under situations of the practical use is promising for broadband near-field optical technologies.

Non-diffracting linear-shift point-spread function by focus-multiplexed computer-generated hologram

Tomoya Nakamura, Shunsuke Igarashi, Yuichi Kozawa, and Masahiro Yamaguchi

Doc ID: 341864 Received 21 Aug 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: An Airy beam can be used to implement a non-diffracting self-bending point-spread function~(PSF), which can be utilized for computational 3D imaging. However, the parabolic depth-dependent spot trajectory limits the range and resolution in rangefinding. In this Letter, we propose a novel pupil-phase-modulation method to realize a non-diffracting linear-shift PSF. For the modulation, we use a focus-multiplexed computer-generated hologram, which is calculated by multiplexing multiple lens-function holograms with 2D sweeping of the foci. With this method, the depth-dependent trajectory of the non-diffracting spot is straightened, which improves the range and resolution in rangefinding. The proposed method was verified by numerical simulations and optical experiments. The method can be applied to laser-based microscopy, time-of-flight rangefinding, and so on.

Femtosecond fiber Bragg grating fabrication with adaptiveoptics aberration compensation

Julian Fells, Patrick Salter, Matthew Woolley, Stephen Morris, and Martin Booth

Doc ID: 342972 Received 22 Aug 2018; Accepted 07 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We present fiber Bragg gratings (FBGs) fabricated using adaptive optics aberration compensation for the first time. The FBGs are fabricated with a femtosecond laser by the point-by-point method using an air-based objective lens, removing the requirement for immersion oil or ferrules. We demonstrate a general phase correction strategy that can be used for accurate fabrication at any point in the fiber cross-section. We also demonstrate a beam shaping approach that nullifies the aberration when focused inside a central fiber core. Both strategies give results which are in excellent agreement with coupled-mode theory. An extremely low wavelength polarization sensitivity of 4 pm is reported.

mJ-level, kHz-rate, CPA-free linear amplifier for 2 µm ultrashort laser pulses

Moritz Hinkelmann, Bastian Schulz, Dieter Wandt, Uwe Morgner, Maik Frede, Joerg Neumann, and Dietmar Kracht

Doc ID: 346692 Received 02 Oct 2018; Accepted 07 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: The generation of mJ-level ultrashort laser pulses at a wavelength of 2.05 μm in a compact CPA-free linear amplifier based on Holmium-doped YLF gain medium is presented. More than 100 MW of pulse peak power has been achieved. We show capabilities of this laser amplifier from 1 kHz up to 100 kHz repetition rate. A detailed numerical description supports the experimental work and verifies the achieved results.

Controlling Dipole Transparency with Magnetic Fields

Stephen Hughes and Girish Agarwal

Doc ID: 346315 Received 21 Sep 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: We describe how magnetic fields can be exploited to control dipole-induced transparency in quantum dot cavity systems. Coupling a linearly-polarized microcavity mode to two spin charged exciton states of a single quantum dot, we demonstrate how cavity-mediated interference and magnetic-field resonance shifts can be utilized to control the transmission of light and on-chip photons, in both magnitude and phase. In particular, we show a triple resonance feature, which also survives with weakly coupled cavities, as long as one operates in the good cooperativity regime. The central peak, which is mediated by the applied magnetic field, is shown to exhibit spectral squeezing. We also demonstrate how the magnetic field allows five regions in which the phase changes by $2\pi$ over a small frequency window, where a possible phase gate could be implemented.

Exceptional points for photon pairs bound by nonlinear dissipation in cavity arrays

Mark Lyubarov and Alexander Poddubny

Doc ID: 347417 Received 08 Oct 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: We study theoretically the dissipative Bose-Hubbard model describing array of tunneling-coupled cavities with non-conservative photon-photon interaction. Our calculation of the complex energy spectrum for the photon pairs reveals exceptional points where the two-photon states bound by nonlinear dissipation are formed. This improves fundamental understanding of the interplay of non-Hermiticity and interactions in the quantum structures and can be potentially used for on-demand nonlinear light generation in photonic lattices.

Beam shifting technique for speckle reduction and flow rate measurement in optical coherence tomography

Chen Chaoliang, weisong shi, Ryan Deorajh, NHU NGUYEN, Joel Ramjist, Andrew Marques, and Victor Yang

Doc ID: 346428 Received 20 Sep 2018; Accepted 06 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: In this letter, we proposed a beam shifting optical coherence tomography (BSOCT) scheme for speckle reduction and flow rate calculation of blood flow, where variations of speckle pattern and Doppler angle were generated by parallel shifting of the sample beam incident on objective lens. The resultant OCT images could then be averaged for speckle noise reduction and simultaneously analyzed for flow rate measurement. The performance of the proposed technique was verified by both phantom and in vivo experiments.

Strong magnetochiral dichroism in chiral/magnetic layered heterostructures

Aristi Christofi

Doc ID: 348518 Received 17 Oct 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: In the present work we propose a nonreciprocal heterostructure which combines magnetism and chirality in a simple, easy to fabricate design and exhibits at least two orders of magnitude larger magnetochiral dichroism, compared to other proposed metamaterials. This effect stems from the simultaneous lack of time-reversal and space inversion symmetries and is enhanced by collective slow-photon modes originating from the strong bending of the photonic bands at the Brillouin zone boundaries. We investigate the optical properties of this bianisotropic multilayer heterostructure, consisting of consecutive bilayers of chiral and magnetic materials, embedded in air, and discuss associated photonic band structure and transmission/absorption spectra obtained by means of full electrodynamic calculations.

Dynamic mode-switchable optical vortex beams using acousto-optic mode converter

JIAFENG LU, Linghao Meng, Fan Shi, Xiaomin Liu, Zhengqian Luo, Peiguang Yan, Liangjin Huang, Fufei Pang, Tingyun Wang, Xianglong Zeng, and Pu Zhou

Doc ID: 345314 Received 10 Sep 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We propose a dynamic scheme to realize mode-switchable generation of LP11a/b modes and ±1-order orbital angular momentum (OAM) modes simultaneously, which are induced by an acoustically-induced fiber grating driven by a radio frequency modulation. LP11a/b mode degeneration in a few-mode fiber is induced by the geometric irregularity of optical fibers. A dual-wavelength resonance of mode coupling from LP01 to LP11a/b modes is found based on the combined effects of optical and acoustic birefringence. Within the configuration of CW intra-cavity laser output, we experimentally demonstrate a fast-switchable generation of LP11a/b modes and optical vortex beams with ±1-order OAM at a switching speed up to 4.3 kHz. This approach has potential applications in mode division multiplexing, particle manipulation, stimulated emission depletion microscopy and quantum information science.

Ultrafast thulium fiber laser system emitting more than 1kW of average power

Christian Gaida, Martin Gebhardt, Tobias Heuermann, Fabian Stutzki, Cesar Jauregui, and Jens Limpert

Doc ID: 346379 Received 20 Sep 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: In this letter we report on the generation of 1060 W average power and a compressed pulse energy of 13.2 µJ from an ultrafast thulium-doped fiber chirped-pulse-amplification system. The compressed pulse duration of 265 fs at 80 MHz pulse repetition rate results in a peak power of 50 MW spectrally centered at 1960 nm. Even though the average heat-load in the fiber core is as high as 98 W/m, we confirm diffraction-limited beam quality of the compressed output. Furthermore, the evolution of the RIN-noise with increasing average output power has been measured to verify the absence of transversal mode instabilities. This system represents a new average power record for thulium-doped fiber lasers (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality in general, even considering single-channel ytterbium-doped fiber amplifiers.

Micro-lensed optical fiber probe for surface-enhanced Raman scattering measurements​

Karolina Milenko, Silje Fuglerud, Snorre Kjeldby, Reinold Ellingsen, Astrid Aksnes, and Dag Hjelme

Doc ID: 345650 Received 12 Sep 2018; Accepted 06 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We present the fabrication and characterization of a novel sensing configuration based on surface-enhanced Raman scattering (SERS) and two micro-lensed optical fibers. The first micro-lensed fiber is used to excite surface plasmon resonance in a gold film deposited over a mono-layer of nano-sphere surface (AuFON) and the second lensed fiber is used to collect the SERS signal. The sensing capabilities of the fabricated device is demonstrated by measuring different concentrations of rhodamine 6G in water solution.

Bright and efficient quantum dot light emitting diodes with double light emitting layers

Qin Zhang, Chun Chang, Weifeng Zhao, Qingcheng Li, Feng Li, Xiao Jin, Feng Zhao, Zhongping Chen, and Qinghua Li

Doc ID: 342754 Received 23 Aug 2018; Accepted 06 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We demonstrate high bright and efficient light emitting diodes (QLEDs) with 60 nm-thick double quantum dot light emitting layers (D-EMLs) based on the poly(p-phenylene benzobisoxazole) precursors (pre-PBO). This structure distributes the charge balance by blocking electrons. The D-EMLs QLEDs exhibit significantly improvement in brightness, efficiency and stability. The external quantum efficiency (EQE) and luminance of D-EMLs QLEDs show 170 % and 48 % enhancement compared with single light emitting layer (S-EML), respectively. The efficiency roll-off of D-EMLs QLEDs is only 16 % of that of S-EML up to 10 V.

Liquid crystal based polarization volume grating applied for full-color waveguide displays

Yishi Weng, Yuning Zhang, Jingyi Cui, Ao Liu, Zhongwen Shen, Xiaohua Li, and bao wang

Doc ID: 346571 Received 24 Sep 2018; Accepted 06 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: In this letter, we demonstrated the polarization volume grating (PVG) based couplers for a double-layer waveguide display to realize a full-color near-eye display. The polarized interference exposure with photo-alignment methods was employed to generate a birefringent spiral configuration with two-dimensional periodicity in a chiral-dopant reactive mesogen material. Such a structure presents a unique high efficient single-order Bragg diffraction with polarized selectivity. The prepared PVG-couplers exhibit over 80% diffraction efficiency with large diffraction angles at spectra of blue (457 nm), green (532 nm) and red (630 nm). The demonstrated waveguide prototype showed a full-color display with a diagonal FOV of around 35°. The overall optical efficiency was measured as high as 91.4 cd/m2 per lumen with a transparency of 72% for ambient light.

Polarization-driven spin precession of mesospheric sodium atoms

Felipe Pedreros, Domenico Bonaccini Calia, Dmitry Budker, Mauro Centrone, Joschua Hellemeier, Paul Hickson, Ronald Holzloehner, and Simon Rochester

Doc ID: 342138 Received 13 Aug 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We report experimental results on the first on-sky observation of atomic spin precession of mesospheric sodium driven by polarization modulation of a continuous-wave laser. The magnetic resonance was remotely detected from the ground by observing the enhancement of induced fluorescence when the driving frequency approached the precession frequency of sodium in the mesosphere, between 85 km and 100 km altitude. The experiment was performed at La Palma, and the uncertainty in the measured Larmor frequency (~260 kHz) corresponded to an error in the geomagnetic field of 0.4 mG. The results are consistent with geomagnetic field models and with the theory of light-atom interaction in the mesosphere.

Precise control of evanescent scattering by self-assembled ferromagnetic particles for optical sensing with tunable sensitivity

Hau Ping Chan, Binghui Li, and Kazi Rony

Doc ID: 343101 Received 24 Aug 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We propose an optical sensing platform that uses evanescent scattering through precise manipulation of self-assembled ferromagnetic particle columns. The movement of column tips can be dynamically controlled down to a submicron range by an external actuation, namely, magnetic field, for interacting with evanescent wave propagation along an optical waveguide that causes a change in its output intensity for optical sensing. To demonstrate the idea, an AC current sensor with only a 5 mm interaction length is proposed and realized. Furthermore, its sensitivity is tunable within 9–20 dB/A by varying a DC-biased signal. The platform shows favorable signal reversibility, stability, broadband operation, and real-time response.

Open-loop Fiber-optic gyroscope with a double sensitivity employing a polarization splitter and Faraday rotator mirror

Weiran Wu, Ke Zhou, Chengjie Lu, and Tuohua Xian

Doc ID: 346866 Received 27 Sep 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: In this letter, a novel open-loop fiber-optic gyroscope configuration is proposed to increase the gyro’s sensitivity. In the proposed configuration light waves propagate twice along the same fiber coil in two Orthonormal polarization direction by employing a polarization-maintaining Faraday rotator mirror (PM-FRM) and a polarization beam splitter/combiner (PSC). The reciprocity of the configuration has been verified in theory. The Allan variance analysis of the gyro prototype exhibits 0.03⁰/h bias stability over 5.5h in the laboratory environment

Signal-to-noise ratio improvement of photonic time-stretch coherent radar enabling high-sensitivity ultrabroad W-band operation

Na Qian, Weiwen Zou, Siteng Zhang, and Jianping Chen

Doc ID: 348456 Received 16 Oct 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: The signal-to-noise ratio (SNR) of the photonic time-stretching receiver in the photonic time-stretch coherent radar (PTS-CR) system is theoretically analyzed. According to the analysis based on the Erbium-doped fiber amplifier (EDFA) characteristic, it is found that the SNR is dominantly determined by the input optical power of EDFA. With the improvement of the SNR of the photonic time-stretching receiver, the radar detection sensitivity is consequently enhanced. Furthermore, a PTS-CR system operating at W band with the ultrabroad bandwidth of 12 GHz is experimentally enabled, leading to the range resolution of ~1.48 cm.

Overcoming quantum limit 3 μm Er: YGG crystal lasers by balancing energy transfer and thermal effects

Li You, Dazhi Lu, Zhongben Pan, Haohai Yu, Huaijin Zhang, and jiyang wang

Doc ID: 348589 Received 18 Oct 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: By balancing the energy transfer and thermal effects, we demonstrate efficient erbium-doped yttrium gallium garnet (Er:YGG) crystal lasers at the wavelength of 2.8-2.9 μm for the first time to the best of our knowledge. Associated with the influence of doping concentration on the energy transfer and thermal effects, the Er3+ doping concentration was optimized to be 10 at.%, and with the optimized crystal, the maximum continuous-wave (CW) output power was 1.38W, corresponding to the slope efficiency of 35.4% overcoming the quantum limits. The thermal effects during the laser process were discussed. We believe that this work should be helpful for optimizing the erbium-doped gain for the 3 μm laser and the development of 3 μm lasers.

Richardson-Lucy deconvolution of time histograms forhigh-resolution Non-Line-of-Sight imaging based onback-projection method

chenfei jin, Jiaheng Xie, Siqi Zhang, Zijing Zhang, and Yuan Zhao

Doc ID: 342020 Received 10 Aug 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: Non-Line-of-Sight (NLoS) imaging is a new developing technique with wide applications in recent years. At present it is difficult for NLoS imaging to acquire a high resolution reconstruction with back projection. We present a novel back projection based on Richardson-Lucy deconvolution of time histograms for high resolution NLoS imaging. In our method, the backscattering photons from LoS scene are used as the essential for the deconvolution of time histogram but not removed as the interference, and then all deconvoluted time histograms are back projected into the space to form a high resolution NLoS reconstruction. The simulated and experimental results demonstrate the reconstructions of NLoS objects with high resolution for our method. Our method also indicates a good ability to restore NLoS objects under high noise level.

70 micron diameter optical probe for Common Path Optical Coherence Tomography in air and liquids

Marica Marrese, Hidde Offerhaus, Erik Paardekam, and Davide Iannuzzi

Doc ID: 344359 Received 27 Aug 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: We investigate and validate a novel method to fabricate ultrathin optical probes for Common-Path OCT. The probes are obtained using a 65 μm barium titanate microsphere inserted into an inward concave cone chemically etched at the end of a single mode fiber. We demonstrate that the high refractive index (n =1.95) of the barium titanate microspheres allows one to maintain high sensitivity even while imaging in liquids, reaching a sensitivity of 87 dB. Thanks to its low cost, flexibility, and ease of use, the probe holds promise for the development of a new generation of ultrathin needle-based OCT systems.

Optical detection of ultrasound by lateral shearing interference of a transparent PDMS thin film

Supannee Learkthanakhachon, Suejit Pechprasarn, and Michael Somekh

Doc ID: 340903 Received 06 Aug 2018; Accepted 04 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A lateral shearing interferometric technique combined with a \SI{11.6}{\micro\meter} Polydimethylsiloxane (PDMS) transparent thin film is proposed and demonstrated for optical detection of ultrasound. We experimentally report the device change of reflectivity with pressure of \SI{5.1e-7}{\per\Pa}, 9.5 times more sensitive than the critical angle based sensor, 31 times more sensitive than the surface plasmon based sensor and comparable to the Fabry-Perot sensor. The objective lens based angle scanning characterization setup inspired from a laser scanning system allows direct comparison between the PDMS sensor and critical angle based sensor by adjusting the incident angle with a scanning mirror, thereby eliminating optical and electronics system dependence. The sensing element is easily fabricated through spin coating and the detection element incorporated into an existing optical system with minimum modification.

Step-index High Absorption Yb-doped Large-mode-area Fiber with Ge-doped Raised Cladding

Raghuraman Sidharthan, Junhua Ji, Kang Jie Lim, Huiting Serene Lim, Huizi Li, Jian Wei Lua, Yanyan Zhou, Chun Ho Tse, Daryl Ho, Yue Seng, Song-Liang Chua, and Seongwoo Yoo

Doc ID: 345845 Received 13 Sep 2018; Accepted 04 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: We report an all-solid large mode area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing highly Ytterbium-doped P:Al core and Germanium-doped cladding. The fiber provides core absorption of ~1200 dB/m at 976 nm with a low 0.07 core NA thanks to the raised Ge cladding. Furthermore, matched profiles of P and Al across core is successfully obtained with high concentration of Yb2O3 above 0.4 mol%. The fiber characteristics are routinely achievable by the conventional modified chemical vapor deposition with a solution doping technique. Highly efficient laser with >100 W output power, 86% slope efficiency with respect to launched pump power and a mean M2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode.

Ultrafast tunable modulation of light polarization at THzfrequencies

Vincent Juve, Gwenaelle Vaudel, Zoltán Ollmann, Janos Hebling, Vasily Temnov, Vitalyi Gusev, and Thomas Pezeril

Doc ID: 346267 Received 27 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Controlling light polarization is one of the most essen-tial routines in modern optical technology. Since thedemonstration of optical pulse shaping by spatial lightmodulators and its potential in controlling quantum re-action path, it paved the way to many applications ascoherent control of photoionization process or as po-larization shaping of Terahertz (THz) pulses. Here weevidenced efficient non-resonant and noncollinear χ( 2 )-type light-matter interaction in femtoseconds polar-ization sensitive time-resolved optical measurements.Such nonlinear optical interaction of visible light andultra-short THz pulses leads to THz modulation of vis-ible light polarization in bulk LiNbO 3 crystal. Theoret-ical simulations based on the wave propagation equa-tion capture the physical processes underlying this non-linear effect. Apart from the observed tunable polar-ization modulation at ultra-high frequencies of visiblepulses, this physical phenomenon can be envisaged inTHz depth-profiling of materials.

Universal quantum gate with hybrid qubits in circuit QED

Chui-Ping Yang, Zhen-Fei Zheng, and Yu Zhang

Doc ID: 346890 Received 26 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Hybrid qubits have recently drawn intensive attention in quantum computing. We here propose a method to implement a universal controlled-phase gate of two hybrid qubits via two three-dimensional (3D) microwave cavities coupled to a superconducting flux qutrit. For the gate considered here, the control qubit is a microwave photonic qubit (particle-like qubit), whose two logic states are encoded by the vacuum state and the single-photon state of a cavity, while the target qubit is a cat-state qubit (wave-like qubit), whose two logic states are encoded by the two orthogonal cat states of the other cavity. During the gate operation, the qutrit remains in the ground state; therefore decoherence from the qutrit is greatly suppressed. The gate realization is quite simple, because only a single basic operation is employed and neither classical pulse nor measurement is used. Our numerical simulations demonstrate that with current circuit QED technology, this gate can be realized with a high fidelity. The generality of this proposal allows to implement the proposed gate in a wide range of physical systems, such as two 1D or 3D microwave or optical cavities coupled to a natural or artificial three-level atom. Finally, this proposal can be applied to create a novel entangled state between a particle-like photonic qubit and a wave-like cat-state qubit.

Multipass nonlinear pulse compression from 1.3 ps to 41 fs at 18 mJ energy

Martin Kaumanns, Vladimir Pervak, Dmitrii Kormin, Vyacheslav Leshchenko, Alexander Kessel, Moritz Ueffing, Yu Chen, and Thomas Nubbemeyer

Doc ID: 347510 Received 05 Oct 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Nonlinear compression of laser pulses with tens of millijoule energy in a gas-filled multipass cell is a promising approach to realize the next generation femtosecond sources. For the first time we demonstrate nonlinear compression of pulses with over 18 mJ of energy at 5 kHz repetition rate from 1.3 ps to 41 fs in an argon filled Herriott cell. In addition to the large compression factor, the output beam has an outstanding quality and excellent spectral homogeneity. Furthermore we discuss prospects to scale the energy to the 100 mJ level in the near future.

Broadband blue emission from ZnO amorphous nanodomains in zinc phosphate oxynitride glass

Muzhi Cai, weim mao, Laurent Calvez, Jean Rocherulle, Hong-li Ma, Ronan Lebullenger, Xiang-Hua Zhang, Shiqing Xu, and Junjie Zhang

Doc ID: 345573 Received 11 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Zn-O amorphous nanostructure in a glass matrix shows unique optical properties. However, although Zn-O amorphous nanostructure can be formed in some settled multi-component silicate glasses, the intensity of its emission is extremely weak. Here, we report a novel and simple zinc phosphate oxynitride glass which can display strong broadband blue emission with a short decay time due to the Zn-O amorphous nanostructure in the glass matrix. The result implies that the glass topological constraints are the key to forming Zn-O amorphous nanostructure. The findings contribute to a deeper understanding of the formation of Zn-O amorphous nanostructure in zinc containing glass.

Bandwidth-tunable, FSR-free, microring-based, SOI filter with integrated contra-directional couplers

Ajay Mistry, Mustafa Hammood, Hossam Shoman, Lukas Chrostowski, and Nicolas Jaeger

Doc ID: 345710 Received 14 Sep 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A silicon-on-insulator, bandwidth (BW)-tunable, free spectral-range (FSR) free, microring resonator (MRR)-based filter is experimentally demonstrated. The device achieves an FSR-free response at its through and drop ports by using a grating-assisted coupler in one coupling region of the MRR and achieves a nonadjacent channel isolation, (nAi), for 400 GHz WDM, greater than 26.7 dB. A thermally tunable Mach Zehnder Interferometer-based coupling scheme is also utilized to compensate for fabrication variations and enable the BW tunability of the filter. The BW of the filter can be continuously tuned from 25 GHz to 60 GHz while maintaining an nAi greater than 26.7 dB. We also show that the phase response at the minor notches in the through port of the filter are suppressed.

Stokes mode Raman random lasing in a fully biocompatible medium

Venkata Siva Gummaluri, Sivarama Krishnan, and Vijayan C

Doc ID: 348317 Received 16 Oct 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: We demonstrate for the first time, Raman random lasing in a continuous-wave (CW) excited, completely biocompatible and biodegradable carrot medium naturally composed of fibrous cellulose scattering medium and rich carotene Raman gain medium. CW laser induced photoluminescence(PL) threshold and linewidth analysis at the Stokes modes of carotene show a characteristic lasing action with threshold of 130 W/cm2 and linewidth-narrowing with mode Q factor up to 1300. Polarization study of output modes reveals that lasing mode mostly retains the source polarization state. A neat and interesting linear temperature dependence of emission intensity is also discussed. Easy availability, bio-compatibility, excitation dependent emission wavelength selectivity and temperature sensitivity are hallmarks of this elegant Raman laser medium with a strong potential as an optical source for applications in bio-sensing, imaging and spectroscopy.

Super smooth surface demonstration and the physical mechanism of CO2 laser polishing of fused silica

Ting He, Chaoyang Wei, Zhigang Jiang, Yuanan Zhao, and Jianda Shao

Doc ID: 340010 Received 22 Aug 2018; Accepted 02 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: This paper reports on the results of experiments aimed at obtaining high-quality super-smooth surfaces, by investigating the laser polishing of fused silica. A maximum reduction in root mean square (RMS) roughness to 0.156 nm was achieved, and laser-polished surfaces exhibited virtually no micro defects or damage. Subsequent analysis using a multi-physics numerical model revealed the underlying physical mechanism of laser polishing of fused silica. The model simulated the surface smoothing process of laser polishing and demonstrated the effects of surface tension, Marangoni effect, light pressure, and gravity in the process. It was found that the surface tension dominates the surface smoothing process and it is a critical factor for achieving sub-nanometer micro roughness of laser polishing of fused silica. Additionally, the model was successfully applied to predict the residual surface roughness of laser polishing, which is in good agreement with the experimental results.

Enhancing the dynamic range of phase-sensitive optical coherence elastography by overcoming speckle decorrelation

Bing Pan, Bo Dong, and Yun Zhang

Doc ID: 346038 Received 17 Sep 2018; Accepted 02 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: Phase-sensitive optical coherence elastography (PhS-OCE) is a high-sensitivity optical method for measuring internal displacement fields of semi-transparent materials. Although the displacement measurement sensitivity of PhS-OCE reaches sub-nanometer level, the dynamic range of the measured displacements is limited to micrometers due to displacement-induced speckle decorrelation. In this letter, a displacement tracking method is developed to overcome this limitation. The method uses subset-based match approach and takes the noise number of phase difference map as the match quality, which can effectively track both axial and lateral displacements. For validation, phase changes inside polymer samples due to the displacements produced by the temperature/mechanical load changing were measured. The results show that many previously undetectable mechanical behaviors can be quantitatively detected after enhancing the dynamic range by applying the proposed method.

Coherent perfect absorber and laser for nonlinear waves in optical waveguide arrays

Vladimir Konotop, Dmitry Zezyulin, and Herwig Ott

Doc ID: 340368 Received 24 Jul 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A localized non-Hermitian potential can operate as a coherent perfect absorber or as a laser for nonlinear waves. The effect is illustrated for an array of optical waveguides, with the central waveguide being either active or absorbing. The arrays situated to the left and to the right from the center can have different coupling constants and different Kerr nonlinearities. The result can be further generalized to a setup with the central waveguide carrying an additional nonlinear dissipation or gain and to the two-dimensional waveguide arrays with embedded one-dimensional absorbing or lasing sub-arrays.

A multifocal multiphoton volumetric imaging technique for high speed time-resolved FRET imaging in vivo

Simon Poland, Grace Chan, James Levitt, Nikola Krstajic, Ahmet Erdogan, Robert Henderson, Maddy Parsons, and Simon Ameer-Beg

Doc ID: 345100 Received 06 Sep 2018; Accepted 01 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: In this paper we will discuss the development of a multifocal multiphoton fluorescent lifetime imaging system where 4 individual fluorescent intensity and lifetime planes are acquired simultaneously, allowing us to obtain volumetric data without the need for sequential scanning at different axial depths. Using a phase-only SLM with an appropriate algorithm to generate a holographic pattern, we project a beamlet array within a sample volume of a size, which can be pre-programmed by the user. We demonstrate the capabilities of the system to image live-cell interactions. Whilst only 4 planes are shown, this technique can be rescaled to a large number of focal planes enabling full 3D acquisition and reconstruction.

Three-dimensional direct laser written achromatic multi-component micro lenses

Michael Schmid, Simon Thiele, Alois Herkommer, and Harald Giessen

Doc ID: 345260 Received 24 Sep 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Femtosecond 3D printing is an important technology for manufacturing of nano- and microscopic optical devices and elements. However, most structures in the past have been created using only one photoresist at a time, thus limiting potential applications. In this paper we successfully demonstrate the combination of two different photoresists, namely IP-S and IP-Dip, to realize multi-component three-dimensional direct laser written optics. We use the combination of IP-S and IP-Dip to correct chromatic aberrations and to realize an achromatic axicon. In a second step we demonstrate the first three-dimensional direct laser written Fraunhofer doublet. We characterize their optical properties and measure the substantial reduction of chromatic aberrations. We outline the possibilities and benefits of creating three-dimensional direct laser written multi-component structures for micro-optics.

Degeneracy in the Diffraction of Orbital Angular Momentum Carrying Beams

Surendra Singh, Emily Walla, Chitra Shaji, and Reeta Vyas

Doc ID: 344600 Received 30 Aug 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Symmetry constraints on the far field diffraction of Laguerre-Gauss vortex beams by planar aperture arrays with N-fold rotational symmetry are considered. The experiments reveal a simple structure for the diffraction pattern and high degree of degeneracy in its dependence on the orbital angular momentum index of the incident beam in agreement with analytical and numerical results.

Photoluminescence Enhancement and Ultrafast Relaxation Dynamics in A Novel Low-dimensional Heterostructure: Effect of Plasmon-Exciton Coupling

runlin miao, Yiwen Zhang, Yuxiang Tang, Jie You, Yanbin Zhang, Lei Shi, and Tian Jiang

Doc ID: 346251 Received 18 Sep 2018; Accepted 31 Oct 2018; Posted 02 Nov 2018  View: PDF

Abstract: In this work, we present an in-depth study on the low-dimensional heterostructure comprising the monolayer (ML) WS2 and 1D plasmonic photonic crystal (PPC). The stable-state photoluminescence (PL) experiments are employed to study the optical and electrical properties of WS2 films with and without PPC. In addition, the angle-resolved reflectance and PL microscopy measurements are used to identify the coupling effect between the ML WS2 and 1D PPC. Furthermore, by means of the femtosecond pump-probe experiments, the relaxation time of this newly-proposed heterostructure is extracted to be 0.69ps, 18.84ps, 885.62ps. Importantly, the relaxation process of the weak plasmon-exciton effect is also revealed in the hybrid structure for the first time.

Polarization mediated coherent and incoherent Bessel-moiré generation

Jayeta Banerjee and Mina Ray

Doc ID: 330449 Received 27 Apr 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: We demonstrate an efficient approach for investigation of polarization states of Bessel beam along the propagation direction. Furthermore, we propose a method to generate Bessel-moiré using Birefringent Lens and Wollaston prism. The analysis showed that experimentally generated incoherent moiré pattern is analogous to theoretically simulated pattern. Moreover, we verified that inhomogeneous polarization states of Bessel beam is still present in Bessel-moiré along its propagation direction. Our observation of Bessel-moiré due to mechanical vibration depicts the fact that incoherent moiré is stable, whereas coherent moiré is sensitive to external vibration only along its propagation direction.

Directional invisibility by genetic optimization

Emre Bor, Ceren Babayigit, Hamza Kurt, Kestutis Staliunas, and Mirbek Turduev

Doc ID: 342235 Received 13 Aug 2018; Accepted 31 Oct 2018; Posted 01 Nov 2018  View: PDF

Abstract: In this study, the novel design of a directional optical cloaking by genetic algorithm is proposed and realized experimentally. Three-dimensional finite-difference time-domain method is combined with the genetic optimization approach to generate the cloaking structure for directional cloaking of a cylindrical object made of perfectly electrical conductor (PEC) by suppressing the undesired scattered fields around the PEC object. The optimization algorithm designs the permittivity distribution of the dielectric polylactide material to achieve an optical cloaking effect. Experimental verification of the designed cloaking structure is performed at microwave frequencies where the proposed structure is fabricated by 3D printing technique. The imperfect conformal mapping due to large scale permittivity distribution and the compensation of the remaining scattering due to small scale permittivity distribution are the basic physical mechanisms of the proposed optical cloaking.

Sculpting complex polarization singularity networks

Eileen Otte and Cornelia Denz

Doc ID: 340659 Received 25 Jul 2018; Accepted 31 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Polarization singularities in vectorial light fields have become an important tool for different cutting-edge applications as in information processing with integer information units. However, even though vectorial singularities naturally form configurations of multiple singular points, up to now only rather simple, mostly cylindrical vector beams including single central singularities have been considered. Here, we demonstrate the customization of extended singularity networks embedded in a class of complexly polarization structured fields based on general Ince-Gaussian modes, namely Ince-Gaussian vector modes. Contributing to fundamental singular optics, our investigations evince the conservation of tailored singularity arrangements upon propagation, whereby respective modes enlarge the range of stable vectorial fields, paving the way to information technologies with a significantly enhanced number of degrees of freedom.

Correlation gating quantifies optical properties of dynamic media in transmission mode

Dawid Borycki, Oybek Kholiqov, and Vivek Srinivasan

Doc ID: 341134 Received 13 Aug 2018; Accepted 31 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Quantifying light transport in turbid media is a long-standing challenge. This challenge arises from the difficulty in experimentally separating unscattered, ballistic light from forward scattered light. Correlation gating is a new approach that numerically separates light paths based on statistical dynamics of the optical field. Here we apply correlation gating with interferometric near-infrared spectroscopy (iNIRS) to separate and independently quantify ballistic and scattered light transmitted through thick samples. First, we present evidence that correlation gating improves isolation of ballistic light in an intrinsically dynamic medium with Brownian motion. Then, from a single set of iNIRS transmission measurements, we determine the ballistic attenuation coefficient and group refractive index from the time-of-flight resolved static intensity, and we determine the reduced scattering and absorption coefficients from the diffusive part of the time-of-flight resolved dynamic intensity. Finally, we show that correlation gating can isolate ballistic light in intrinsically static media in which motion is induced externally. Thus, for the first time, key optical properties of a turbid medium can be derived from a single set of transmission measurements.

Suspended low-loss germanium waveguides for the longwave-infrared.

Ahmed Osman, Milos Nedeljkovic, J. Soler Penades, Yangbo Wu, Zhibo Qu, Ali Khokhar, Kapil Debnath, and Goran Mashanovich

Doc ID: 345563 Received 11 Sep 2018; Accepted 30 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Germanium is a material of high interest for midinfrared (MIR) integrated photonics due to its CMOS compatibility and its wide transparency window covering the 2–15 mm spectral region exceeding the 4 and 8 μm limit of the Silicon-on-Insulator (SOI) platform and Si material respectively. In this Letter, we report suspended germanium waveguides operating at a wavelengthof 7.67 μm with a propagation loss of 2.6 ± 0.3 dB/cm. To our knowledge, this is the first demonstration of low-loss suspended germanium waveguides at such a long wavelength. Suspension of the waveguide is achieved by defining holes alongside the core providing access to the buried oxide layer and the underlying Si layer so that they can be wet etched using HF and TMAH respectively. Our MIR waveguides create a new path towards long wavelength sensing in the fingerprint region.

Frequency comb up- and down-conversion in a synchronously-driven χ² optical microresonator

Simon Herr, Victor Brasch, Jan Szabados, Ewelina Obrzud, Yuechen Jia, Steve Lecomte, Karsten Buse, Ingo Breunig, and Tobias Herr

Doc ID: 344979 Received 04 Sep 2018; Accepted 29 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: Optical frequency combs are key to optical precision measurements. While most frequency combs operate in the near-infrared regime, many applications require combs at mid-infrared, visible or even ultra-violet wavelengths. Frequency combs can be transferred to other wavelengths via nonlinear optical processes, however, this becomes exceedingly challenging for high-repetition rate frequency combs. Here, it is demonstrated that a synchronously driven high-Q microresonator with a second-order optical nonlinearity can efficiently convert high-repetition rate near-infrared frequency combs to visible, ultra-violet and mid-infrared wavelengths providing new opportunities for microresonator and electro-optic combs in applications including molecular sensing, astronomy, and quantum optics.

Off-site and on-site vortex solitons in space-fractional photonic lattices

Xueming Liu and Xiankun Yao

Doc ID: 345022 Received 06 Sep 2018; Accepted 29 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: We address the existence and stability of off-site and on-site vertex solitons with unit topological charge in space-fractional Kerr lattices. In contrast to the reported ordinary Kerr lattices, vortex solitons in the proposed fractional-space lattices are stable only in the intermediate region of propagation constant, and this region widens rapidly with the increase of Lévy index. Under the same Lévy index, the stability range of on-site vortices is larger than that of off-site ones. Especially, for on-site vortex solitons, the upper edge of stability range appears at where the maximum of soliton power is located, which provides an effective way to identify the stability range of on-site vortices. Our results extend the study of vortex solitons into space-fractional systems and deepen the understanding of Kerr lattices in fractional dimensions.

Optical injection locking at sub nano-Watt powers

Ravikiran Kakarla, Jochen Schroeder, and Peter Andrekson

Doc ID: 346875 Received 28 Sep 2018; Accepted 29 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: We demonstrate optical injection locking (OIL) at record low injection power of -65dBm using EDFA based pre-amplification and an electrical phase locked loop (PLL). Investigating the phase noise characteristics of OIL we find that at low injection powers the slave laser linewidth and injection ratio strongly influence the phase noise of the locked slave output. By introducing an EDFA pre-amplifier, the minimum locking power for OIL is reduced. Moreover using this pre-amplifier we find that there exists an optimum injection power into the slave where the output phase noise is minimized and is below the noise without EDFA. We evaluate an OIL based pump recovery in a phase sensitive amplifier (PSA) receiver system aimed at free space communications.

Sensitivity-enhanced ultrafast optical tomography by parametric- and Raman-amplified temporal imaging

Lingxiao Yang, Sheng Wang, Jiqiang Kang, Pingping Feng, Chi Zhang, Bowen Li, and Kenneth Kin-Yip Wong

Doc ID: 343124 Received 24 Aug 2018; Accepted 28 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: To overcome the speed limitation of conventional optical tomography, temporal imaging technique has been integrated with optical time-domain reflectometry (OTDR) to realize the ultrafast temporally-magnified (TM) tomography. In this paper, the sensitivity of TM tomography has been further enhanced using optical parametric amplification (OPA) and distributed Raman amplification (DRA), and this technique is named as temporally-encoded, amplified and magnified (TEAM) tomography. As a result, a 78-dB sensitivity has been realized, comparable to ultrafast optical coherence tomography (OCT) systems. In addition, an 86.7-μm axial resolution can be realized across 67.5-mm imaging range. To demonstrate the significance of the sensitivity improvement, tomographic imaging of a cm-thick phantom is provided at an A-scan rate of 44 MHz.

Free-Running Mode-Locked Laser Based Dual-Comb Spectroscopy

Md Imrul Kayes, Nurmemet Abdukerim, Alexandre Rekik, and Martin Rochette

Doc ID: 346581 Received 24 Sep 2018; Accepted 27 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: We present a real-time dual-comb spectrometer operated from a bi-directional mode-locked fiber laser in the wavelength range of 1.9 μm. Two pulsed signals emitted from a common cavity ensures mutual coherence and common mode noise rejection. The resulting spectrometer operates without any complex electronic feedback system.

Multi-carrier channeled polarimetry for photoelastic modulator systems

Andrey Alenin, Farhana Bashar, Michael Gehm, and J. Scott Tyo

Doc ID: 346727 Received 25 Sep 2018; Accepted 26 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Photoelastic modulator-based polarimeters use multi-carrier modulation schemes that are more complicated than the single carriers of rotating optics. Current state-of-the-art reconstruction implementations favor mathematical simplicity by using significantly abridged subsets of channels. In this Letter, we extend our generalized channeled polarimetry principles to address the challenges associated with multi-carrier modulation schemes. We demonstrate the performance forfeited by existing systems through the use of an incomplete set of information channels, as well as propose a set of more optimal system parameters that achieve better reconstruction noise characteristics. The overall improvement corresponds to an up to a factor of six better sensitivity.

Narrowing spectral linewidth in passively mode-locked solid-state lasers

Tzu-Lin Huang, S. C. Li, C. H. Tsou, Hsing-Chih Liang, K. F. Huang, and Yung-Fu Chen

Doc ID: 346968 Received 28 Sep 2018; Accepted 25 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: A novel scheme to realize a mode-locked laser with narrow spectral linewidth is demonstrated by exploiting a reflected Fabry-Perot cavity to introduce intense Fabry-Perot effect. Stable continuous-wave mode-locked operation is achieved with the repetition rate of 48 MHz and the maximum average output power of 2.6 W under an incident pump power of 11.9 W. The mode-locked pulse width is systematically investigated by varying the optical thickness of the reflected Fabry-Perot cavity. The pulse duration is experimentally found to be in a range from 0.8 ns to 2.6 ns. Experimental results reveal that the reflected Fabry-Perot cavity is the key factor leading to the pulse generation in nanosecond regime. This work is believed to provide a promising method for generating optical pulses with narrow spectral linewidth.

Optical rectification of a 100 W average power mode-locked thin-disk oscillator

Frank Meyer, Negar Hekmat, Samira Mansourzadeh Ashkani, Felix Fobbe, Farhad Aslani, Martin Saraceno, and Clara Saraceno

Doc ID: 347364 Received 04 Oct 2018; Accepted 25 Oct 2018; Posted 01 Nov 2018  View: PDF

Abstract: We demonstrate THz generation at MHz repetition rate by optical rectification in GaP crystals, using excitation average power levels exceeding 100 W. The laser source is a state-of-the-art diode-pumped Yb:YAG SESAM-mode-locked thin-disk laser, capable of generating 580 fs pulses at an average power up to 120 W and a repetition rate of 13.4 MHz directly from a one-box oscillator, without the need for any extra amplification stages. In this first demonstration, we measure a maximum THz average power of 78 µW at a central frequency of 0.8 THz. Our result shows that optical rectification of state-of-the-art high average power ultrafast sources in nonlinear crystals is within reach, and paves the way towards high average power, ultrafast laser pumped THz sources.

Dispersion Engineering of Hyperbolic Plasmons in Bilayer 2D Materials

Maturi Renuka, Xiao Lin, zuojia wang, Lian Shen, Bin Zheng, Huaping Wang, and Hongsheng Chen

Doc ID: 346675 Received 08 Oct 2018; Accepted 25 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: Recent progress on anisotropic 2D materials brings new technologies for directional guidance of hyperbolic plasmons. Here, we investigate the plasmonic modes in twisted bilayer 2D materials. Calculated dispersion curves show that two hyperbolas split as the twisted angle increases. The topological transition from closed ellipses to open hyperbolas is achieved by varying the frequency, indicating switching between highly directional and omnidirectional plasmons. These findings will provide potential applications in the design of tunable field effect transistors and waveguides.

Light field-based absolute phase unwrapping

Xiaoli Liu, Zewei Cai, Zhizhen Chen, Qijian Tang, Bruce Gao, Giancarlo Pedrini, Wolfgang Osten, and Xiang Peng

Doc ID: 342021 Received 09 Aug 2018; Accepted 24 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Ambiguity caused by wrapped phase is an intrinsic problem in fringe projection-based 3D shape measurement. Among traditional methods for avoiding phase ambiguity, spatial phase unwrapping is sensitive to sensor noise and depth discontinuity, and temporal phase unwrapping requires additional encoding information that leads to increase of image sequence acquisition time or reduction of fringe contrast. Here, we report a novel method of absolute phase unwrapping based on light field imaging. In a recorded light field under structured illumination, i.e., a structured light field, a wrapped phase-encoded field can be retrieved and resampled in diverse image planes associated with several possible fringe orders in a measurement volume. Then, by leveraging phase consistency constraint in the resampled wrapped phase-encoded field, correct fringe orders can be determined to unwrap the wrapped phase without any additional encoding information. Experimental results demonstrated that the proposed method was suitable for accurate and robust absolute phase unwrapping.

Wavelength tunable gain-switched fiber laser around 1.7-μm-band and its application to spectroscopic photoacoustic imaging

Can Li, Jiawei Shi, Xiaojing Gong, Cihang Kong, Zhi-Chao Luo, Liang Song, and Kenneth Kin-Yip Wong

Doc ID: 345579 Received 11 Sep 2018; Accepted 24 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Recently demonstrated bond-selective photoacoustic imaging has revealed the importance of 1.7-μm laser sources, which are currently accessed through nonlinear conversion from shorter wavelengths with compromised performances. In this letter, we demonstrate a gain-switched thulium-doped fiber laser with continuous tuning from 1690 nm to 1765 nm by using an electrically driven acousto-optical tunable filter. Micro-joule laser pulses with a shot-to-shot intensity variation of 1.6% and a pulse duration of 150 ns are achieved. The laser source is then harnessed to implement a photoacoustic microscopy system, of which the lateral resolution is estimated to be 17.8 μm by scanning a resolution target. The photoacoustic spectra of butter, rapeseed oil, and adipose tissue are measured and show a consistent absorption peak of around 1720 nm. Photoacoustic microscopy imaging of the adipose tissue demonstrates a desirable optical absorption contrast of lipids and the superiority of the laser for spectroscopic photoacoustic detection.

Polarization-multiplexed multiplane display

Shin-Tson Wu, Guanjun Tan, Tao Zhan, Yun-Han Lee, and Jianghao Xiong

Doc ID: 342783 Received 22 Aug 2018; Accepted 23 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We demonstrate a polarization-multiplexed multi-plane display system for near-eye applications. A polarization-sensitive Pancharatnam-Berry phase lens is implemented to simultaneously generate two focal depths. A spatial polarization modulator is utilized to direct the two images to designated focal planes. Based on this design, a dual focal plane display system is constructed. The vergence-accommodation conflict is suppressed successfully without increasing space and time complexities.

Localized chaos of elliptically polarized cavity solitons in broad-area VCSEL with a saturable absorber

Krassimir Panajotov and Mustapha Tlidi

Doc ID: 348393 Received 16 Oct 2018; Accepted 23 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We introduce a spin-flip model for a broad-area Vertical-Cavity Surface-Emitting Laser (VCSEL) with a saturable absorber. We demonstrate simultaneous existence of orthogonally linearly polarized and elliptically polarized cavity solitons. We show that polarization degree of freedom leads to period doubling route to spatially localized chaos of the elliptically polarized cavity solitons.

Color image identification and reconstruction using artificial neural networks on multi-mode fiber images, towards an all optic design

Nadav Shabairou, Eyal Cohen, Omer Wagner, dror malka, and Zeev Zalevsky

Doc ID: 343115 Received 05 Sep 2018; Accepted 22 Oct 2018; Posted 24 Oct 2018  View: PDF

Abstract: The rapid growth of applications, which rely on artificial neural networks concepts, give rise to their demands in a staggering pace. New type of hardware that can support these requirements is needed, and optical artificial neural networks fit well for the task. Inherently, could be optical artificial neural networks are faster, had larger bandwidth and produce less heat than their electronic implementations.Here we propose the design of an optical artificial neural network based imaging system that has the ability to self-study image signals from an incoherent light source in different colors. Our design consists of a combination/tailoring between a multi-mode fiber and a multi-core optical fiber realizing a neural network. We show that the signals, transmitted through the multi-mode fiber, can be used for image identification purposes and can also be reconstructed using artificial neural networks with a low number of nodes. An all-optic solution can then be achieved by realizing these networks with the multi-core optical neural network fiber.

Soliton compression in a multipass cell

gaëtan jargot, Nour Daher, Loïc Lavenu, Xavier Delen, Nicolas Forget, Marc Hanna, and Patrick Georges

Doc ID: 340161 Received 18 Jul 2018; Accepted 22 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We demonstrate soliton compression of short-wavelength infrared pulses in a multipass cell containing a plate of silica. Nonlinear propagation in the cell in the anomalous dispersion regime results in the generation of 14 µJ 22 fs pulses at 125 kHz repetition rate and 1550 nm wavelength. Periodic focusing inside the cell allows to circumvent catastrophic self-focusing, despite an output peak power of 440 MW well beyond the critical power in silica of 10 MW. This technique allows straightforward energy scaling of self-compression setups, and control over the spatial manifestation of Kerr nonlinearity. More generally, multipass cells can be used to perform, at higher energy levels, temporal manipulations of pulses that have been previously demonstrated in waveguides.

Effects of Photonic Crystal structures on the Imaging Properties of a ZnO:Ga Image Converter

mengxuan xu, Liang Chen, Bo Liu, Zhichao Zhu, Feng Huang, Wei Zheng, Chaohui He, and Xiaoping Ouyang

Doc ID: 341629 Received 14 Sep 2018; Accepted 21 Oct 2018; Posted 22 Oct 2018  View: PDF

Abstract: We investigate the effects of photonic crystal structures on radiation imaging properties of ZnO:Ga image converter. Results shows photonic crystal structures can regulate luminescence distribution and spatial resolving power, which is caused by the light extraction and the defect scattering of photonic crystal structures. The present investigation confirm photonic crystals can improve the imaging properties of existing image converters and propose a new coupling mode between photonic crystal image converter and back-end optical devices, which is beneficial to the application of photonic crystals in the field of radiation imaging.

Performance enhancement of an optical high-order QAM channel by adding correlated data to robust neighboring BPSK or QPSK channels

Yinwen Cao, Kaiheng Zou, Peicheng Liao, Ahmed Almaiman, Ahmad Fallahpour, Fatemeh Alishahi, Amirhossein Mohajerin Ariaei, Changjing Bao, Ari Willner, DMITRY STARODUBOV, Moshe Tur, and Alan Willner

Doc ID: 342711 Received 21 Aug 2018; Accepted 21 Oct 2018; Posted 22 Oct 2018  View: PDF

Abstract: We numerically simulate and experimentally demonstrate an approach to potentially enhance the performance of a high-order quadrature-amplitude-modulation (QAM) channel by adding correlated data to other robust binary-phase-shift-keyed (BPSK) or quadrature-phase-shift-keyed (QPSK) channels. The correlated data are introduced by optically multiplying the BPSK or QPSK channels, already modulated with their own data, by the target high-order QAM data of the same baudrate. After joint detection and signal processing, a ~3-dB optical signal-to-noise ratio (OSNR) improvement is observed in simulations for a target channel modulated with formats from 4QAM (QPSK) to 256QAM. We also experimentally demonstrate the scheme for a QPSK or a 16QAM target channel using BPSK correlated channels. A ≥2-dB OSNR improvement is experimentally observed using both single and double correlated channels.

Orbit-induced localized spin angular momentum in tight focusing of linearly polarized vortex beams

Panpan Yu, Qian Zhao, Xin-Yao Hu, Yinmei Li, and Lei Gong

Doc ID: 342375 Received 15 Aug 2018; Accepted 21 Oct 2018; Posted 23 Oct 2018  View: PDF

Abstract: Optical spin-orbit interaction has gained much interest recently due to its universality and importance in modern photonics. In this Letter, we theoretically demonstrate that orbit-induced spin angular momentum (SAM) conversion can occur in tight focusing of spin-free linearly polarized vortex beams (LPVBs). By analysis of the local polarization states that are associated with the SAM density, we attribute the occurrence of such conversion to the helical-phase-induced change in polarization states of the focused field. Particularly, the local SAM density can be further regulated by altering the sign and value of OAM in the incident LPVBs as well as their polarization orientations. Our work contributes to a more comprehensive picture of the optical spin-orbit coupling, which may benefit applications of optical microscopy and trapping.

An efficient post-processing technique for fabricating SNAP microresonators with sub-angstrom precision by femtosecond laser

Yu Qi, Du Yueqing, Xu Zuowei, Peng Wang, zhen zhang, zece zhu, Haoran Cao, Misha Sumetsky, and Xuewen Shu

Doc ID: 346217 Received 19 Sep 2018; Accepted 21 Oct 2018; Posted 24 Oct 2018  View: PDF

Abstract: We demonstrated the sub-angstrom precise correction of surface nanoscale axial photonics (SNAP) micro-resonators by the femtosecond (fs) laser post-processing technique for the first time. The internal stress can be induced by fs laser inscriptions in the fiber, causing nanoscale effective radius variation (ERV). However, the obtained ultra-precise fabrication usually undergoes multiple tries. Here, we propose a novel post-processing technique based on fs laser that significantly reduces the ERV errors and improves the fabrication precision without iterative corrections. The post-exposure process is achieved at the original exposure locations with using lower pulse energy than that in the initial fabrication process. The results show that the ERV is nearly proportional to the pulse energy of the post-exposure process. The slope of the ERV versus the pulse energy is 0.07 Å/nJ. The maximum of the post-processed ERV can reach 8.0 Å. The repeatability was experimentally verified by accomplishing the correction on three SNAP microresonators with the precision of 0.75 Å. The developed fabrication technique with fs laser enables SNAP microresonators with new breakthrough applications for optomechanics and filters.

Non-evolving spatial coherence function

Aristide Dogariu and CRISTIAN ACEVEDO

Doc ID: 347526 Received 08 Oct 2018; Accepted 21 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: We present a general model for the spatial coherence function of random fields created by scattering elliptical, perfect vortex beams. Remarkably, as opposed to the free-space propagation of typical random fields, there are regimes were the spatial coherence function does not evolve. We demonstrate analytically, numerically, and experimentally that both the size and the shape of the spatial correlations can be precisely controlled in a manner that is independent of the propagation distance.

Monochromatic NIR UC emission in Tm3+/Yb3+ co-doped GdVO4 phosphor: Effect of Bi3+ ion concentration and pump power of diode laser

abhishek dwivedi, Devendra Kumar, and S Rai

Doc ID: 334376 Received 08 Jun 2018; Accepted 20 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Tm3+/Yb3+/Bi3+ co-doped GdVO4 phosphor sample has been synthesized using high temperature solid state reaction technique. The X-ray diffraction patterns reveal pure phase formation and crystalline behavior of the synthesized samples. Intense blue and NIR upconversion (UC) emissions have been observed on excitation with 980 nm diode laser. It is found that addition of Bi3+ ion to the phosphor reduces the intensity of blue emission and enhances the NIR emission intensity to the extent so that NIR emission is nearly monochromatic [(INIR/IBlue) ~ 14]. This ratio is further improved upto 70 times [almost monochromatic] by varying the pump power of the diode laser. This value is observed for the composition GdVO4: 0.01Tm3+, 0.05Yb3+, 0.10Bi3+ phosphor at 1.0 W pump power. Thus this sample can be used as a cheap source of monochromatic ‘Red LED’ and also in bioimaging.OCIS Keywords: Optical materials (Materials), Rare-earth-doped materials (Materials), Energy transfer (Physical optics), Luminescence (Physical optics), Emission (Spectroscopy), Fluorescence, laser-induced (Spectroscopy)

Ultrafast Switching of Photoemission Electron Through Quantum Pathways Interference in Metallic Nanostructure

Peng Lang, Boyu Ji, Xiaowei Song, Yingping Dou, Haiyan Tao, Xun Gao, Zuoqiang Hao, and Jingquan Lin

Doc ID: 344337 Received 29 Aug 2018; Accepted 20 Oct 2018; Posted 22 Oct 2018  View: PDF

Abstract: The localized photoemission electron originated from the plasmonic ‘hot spots’ in metallic bowtie nanostructure can be separately switched ‘on’ and ‘off’ by adjusting the relative time delay between two orthogonally polarized laser pulses. The demonstrated femtosecond timing, nanometric spatial switching of multiphoton photoemission results from the interference of quantum pathways. Energy resolved measurement of the photoemission electrons further shows that the quantum pathways interference mechanism applies to control all the liberated electrons. The experimental results also show that the probability of electron emission through quantum pathways from a plasmonic ‘hot spot’ is determined by the localized emission response to the two incident laser pulses. These findings are of importance for controlling photoemission in ultrahigh spatiotemporal resolution in metallic plasmonic nanostructure.

A deep learning model for ultrafast multi-frequency optical property extractions for Spatial Frequency Domain Imaging (SFDI)

Yanyu Zhao, Deng Yue, Feng Bao, Hannah Peterson, Raeef Istfan, and Darren Roblyer

Doc ID: 345807 Received 14 Sep 2018; Accepted 20 Oct 2018; Posted 24 Oct 2018  View: PDF

Abstract: Spatial frequency domain imaging (SFDI) is emerging as an important new method in biomedical imaging due to its ability to provide label-free, wide-field tissue optical property maps. Most prior SFDI studies have utilized 2 spatial frequencies (2-fx) for optical property extractions. The use of more than 2 frequencies (multi-fx) can vastly improve the accuracy and reduce uncertainties in optical property estimates for some tissue types, but has been limited in practice due to the slow speed of available inversion algorithms. We present a deep learning solution that eliminates this bottleneck by solving the multi-fx inverse problem 300× – 100,000× faster, with equivalent or improved accuracy compared to competing methods. The proposed deep learning inverse model will help to enable real-time and highly-accurate tissue measurements with SFDI.

Dual-mode phase and fluorescence imaging with a confocal laser scanning microscope

Gerd Nienhaus, Juanjuan Zheng, Chao Zuo, and Peng Gao

Doc ID: 348365 Received 16 Oct 2018; Accepted 19 Oct 2018; Posted 23 Oct 2018  View: PDF

Abstract: We present dual-mode phase and fluorescence imaging in a confocal laser scanning microscopy (CLSM) system. For phase imaging, the depth of field (DOF) of the CLSM system is extended by fast axial scanning with a tunable acoustic gradient index of refraction (TAG) lens. Under transillumination, intensity images of the sample are recorded at a few different defocusing distances. The phase image is reconstructed from these intensity images by using the transport-of-intensity equation (TIE). The 3D fluorescence image is obtained by 3D confocal scanning of the sample. The dual-mode images with pixel-to-pixel correspondence yield complementary quantitative structural and functional information. Combination of the two imaging modalities enables standalone determination of the refractive index of live cells.

Two dimensional photon-electronic spectroscopy for excited state population detection

Long Xu, Hui Dong, and Libin Fu

Doc ID: 344938 Received 05 Sep 2018; Accepted 19 Oct 2018; Posted 19 Oct 2018  View: PDF

Abstract: Atomic excitation to excited states in strong laser field is the key to high-order harmonic generation below ionization threshold, yet remains unclear mainly due to the lack of proper detection methods. We propose a two-dimensional photon-electron spectroscopy technique to reconstruct population of excited states with the second delayed laser pulse. The technique utilizes Fourier transformation to separate ionization from different excited states to different position on the spectrum. With the advantage of the separation, we provide a scheme to reconstruct populations on different excited states after the first pulse. The scheme is validated by high-precision population reconstruction of helium and hydrogen atoms.

Measurement of the vortex spectrum in a vortex-beam array without cuts and gluing of the wavefront

Alexander Volyar, BRETSKO Mihail, Akimova Yana, and Egorov Yuriy

Doc ID: 340301 Received 23 Jul 2018; Accepted 19 Oct 2018; Posted 22 Oct 2018  View: PDF

Abstract: We presented a new method for measuring the squares of the amplitudes and phases of partial vortex-beams in a complex beam array in real time. The method is based on measuring the high-order intensity moments and analyzing the solutions of a system of linear equations. Calibration measurements have shown that the measurement error at least for an array of 10-15 beams does not exceed 4%. When measuring beams with different fractional topological charge of optical vortices, we revealed a sharp decrease in the OAM for small deviations of the topological charge from the integer order, which is associated with a sharp increase in the number of integer-order vortices. The application of this approach e.g. for the terabit-information processing in optical fibers provides significant advantages in comparison with the traditional diffraction methods and opens up additional possibilities of information compressor when modulating not only the OAM but also phases of partial beams

Demonstration of a 10-Mbit/s quantum communication link by encoding data on two Laguerre-Gaussian modes with different radial indices

Kai Pang, Cong Liu, Guodong Xie, Yongxiong Ren, Zhe Zhao, Runzhou Zhang, Yinwen Cao, Jiapeng Zhao, haoqian song, Hao Song, Long Li, Ari Willner, Moshe Tur, Robert Boyd, and Alan Willner

Doc ID: 341638 Received 06 Aug 2018; Accepted 18 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We experimentally demonstrate a 10-Mbit/s free-space quantum communication link using data encoding on orthogonal Laguerre-Gaussian (LG) modes with the same azimuthal index but different radial indices. Data encoding on two LGℓp modes (i.e., for ℓ = 0, we encode [“0”, “1”] as [p = 0, p = 1], and for ℓ = 1, we encode [“0”, “1”] as [p = 0, p = 1]) is demonstrated by employing directly modulated laser diodes and helical phase holograms. The quantum symbol error rate (QSER) of < 5 % is achieved at an encoding rate of 10 Mbit/s. Moreover, the influence of the circle radius (R) of the receiver phase pattern on registered photon rates and QSERs is investigated. Our results show that a receiver phase pattern whose R does not match the beam size of the LG modes would induce higher crosstalk between the two encoded quantum branches.

Mapping complex polarization states of light on a solid

Mariam Alameer, Ashish Jain, Mitra Rahimian, Hugo Larocque, Paul Corkum, Ebrahim Karimi, and Ravi-Bhardwaj Vedula

Doc ID: 346986 Received 28 Sep 2018; Accepted 17 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Polarization states of light, represented by different points on a Poincar\'e sphere, can be readily analyzed for a Gaussian beam by a combination of waveplates and polarizers. However, this method cannot be extended to higher order Poincar\'e spheres and complex polarization patterns produced by coherent superpositions of vector vortex beams. We demonstrate visualization of complex polarization patterns by imprinting them on to a solid surface in the form of periodic nano-gratings oriented parallel to the local structure of the electric field of light. We design unconventional surface structures by controlling the superposition of vector vortex beams. Our method is of potential interest to the production of sub-wavelength nano-structures.

Cavity induced tunable perfect infrared absorption in imprinted coupled complementary hole-disk array

alireza safaei, Sushrut Modak, Abraham Vázquez-Guardado, Daniel Franklin, and Debashis Chanda

Doc ID: 344258 Received 29 Aug 2018; Accepted 17 Oct 2018; Posted 17 Oct 2018  View: PDF

Abstract: Photonic microcavity coupling of a subwavelength hole-disk array, a two-element metal/dielectric composite structure with enhanced extraordinary transmission, leads to 100% coupling of incident light to the cavity system and subsequent absorption. This light-funneling process arises from the temporal and spatial coupling of the broadband localized surface plasmon resonance on the coupled hole-disk array and the photonic modes of the optical cavity, which induces spectral narrowing of the perfect absorption of light. A simple nanoimprint lithography-based large area fabrication process paves the path towards practical implementation of plasmonic cavity-based devices and sensors.

Cascaded downconversion interface to convert single-photon-level signals at 650 nm to the telecom band

Vahid Esfandyarpour, Carsten Langrock, and Martin Fejer

Doc ID: 342897 Received 28 Aug 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We present a device for two-step downconversion of single-photon-level signals at 650 nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7 nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange (RPE) periodically poled lithium niobate waveguide and a 2.19-μm pump laser. We achieved 99% depletion efficiency for each stage, corresponding to an internal conversion efficiency of 63% at the optimum pump power for the complete cascaded process.

Efficient design of random metasurfaces

Hadiseh Nasari, Matthieu Dupre, and Boubacar Kante

Doc ID: 343216 Received 27 Aug 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: Random media introduce large degrees of freedom in device design and can thus address challenges in manipulating optical waves. Wave shaping with metasurfaces has mainly utilized periodic or quasi-periodic grids, and, the potential of random arrangement of particles for devices has only come under investigation recently. The main difficulty in pursuing random metasurfaces is the identification of the degrees of freedom that optimize their efficiencies and functions. They can also encode information using the statistics of particles distribution. We propose a phase-map that accounts for the statistical nature of random media. The method takes into account effects of random near-field couplings that introduce phase errors by affecting the phase shift of elements. The proposed approach increases the efficiency of our random metasurface devices by up to ~20%. This work paves the way towards the efficient design of random metasurfaces with potential applications in highly secure optical cryptography and information encoding.

Efficient Perfectly Vertical Grating Coupler for Multi-Core Fibers Fabricated with 193-nm DUV Lithography

Yeyu Tong, Wen Zhou, and Hon Tsang

Doc ID: 345258 Received 07 Sep 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We proposed a novel high-efficiency, low-reflection and fabrication-tolerant perfectly vertical grating coupler (PVGC) with a minimum feature size >200 nm to allow for fabrication using the 193-nm deep-ultraviolet (DUV) lithography. The structural parameters of PVGC were optimized by a genetic optimization algorithm. Simulations predicted the coupling efficiency to be −2.0 dB (63.0%) and the back reflections less than −20 dB in the wavelength range of 1532 nm to 1576 nm. The design was fabricated in a multi-project wafer (MPW) run for silicon photonics and a coupling efficiency of −2.7dB (53.7%) with a 1-dB bandwidth of 33 nm is experimentally demonstrated. The measured back reflection is less than −16 dB over the C-band. The PVGC occupies a compact footprint of 30×24 µm2 and can be interfaced with the multi-core fibers for future space-division-multiplexing networks.

Efficiency increase of distributed feedback Raman fiber lasers by dynamic control of the phase shift

Sébastien Loranger and Raman Kashyap

Doc ID: 340668 Received 27 Jul 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Π-phase-shifted distributed feedback (DFB), ultra-long fiber Bragg gratings (FBG) with Raman gain have been shown to be excellent ultra-narrow single-frequency (SF) lasers which can be operated at any wavelength. However, these lasers have shown unusually low slope-efficiency (1-10 %), while theoretical simulations predict a much higher (30-60 %) number. We believe this poor performance is due to a thermally induced phase shift inside the FBG due to absorption of the high intensity of the signal oscillating in the cavity. To compensate for this, a thermally controlled dynamic phase-shift is proposed to increase efficiency, after lasing first occurs. We show here an increase in the slope efficiency of a factor of 4 and an increase in the total output efficiency by a factor of 6.5 with 6 Ws of pump power by reducing the phase shift once the laser begins oscillating.

Super Contrast-Enhanced Darkfield Imaging of Nano Objects through Null Ellipsometry

Seongkeun Cho, Janghwi Lee, Hyungu Kim, Seulgi Lee, Akinori Ohkubo, Jungchul Lee, Taehyun Kim, Sangwoo Bae, and Wondon Joo

Doc ID: 342860 Received 23 Aug 2018; Accepted 11 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: We rediscover the null ellipsometry principle as for an outstanding image-contrast enhancement method for darkfield imaging. Simply by adding polarizers, compensators and a PD sensor to a conventional dark-field imaging system and applying null principle, Si nano-cylinder structures as small as D20nm (H20nm) on non-patterned wafer and gap defects as small as 14.6nm and bridge defects as small as 21.9nm in size on 40nm Line and 40nm Space pattern (H40nm) which are invisible in conventional darkfield imaging can be distinguished from scattered noise. As far as we are concerned, no method has been successful for identifying such small non-metal (silicon) nanoscale-objects with such low magnification (X20) optics.

Vector beam generation from vertical cavity surface emitting lasers

Yuichi Kozawa, Yuki Nara, Naoto Jikutani, Yasuhiro Higashi, and Shunichi Sato

Doc ID: 346630 Received 24 Sep 2018; Accepted 11 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: Radially and azimuthally polarized beams in a single transverse mode are generated from a commercially available VCSEL in an external cavity with a birefringent rutile lens, of which c-axis is parallel to the optical axis of the cavity, to select favorable polarization. In addition, a vector Bessel-Gaussian beam is generated from a VCSEL, which is fabricated to oscillate with a linear polarization in a fixed direction in free-running, in the same way using the external cavity. These results clearly show potential ability of VCSELs to generate vector beams, which will be essential to the space-division multiplexing in the future optical communication.

Broadband main OPCPA amplifier at 808 nm wavelength in high deuterated DKDP crystals

Xiao Liang, Xinglong Xie, Cheng Zhang, Jun Kang, Qingwei Yang, Ping Zhu, Ailin Guo, Haidong Zhu, Shunhua Yang, Ziruo Cui, Meizhi Sun, and Jianqiang Zhu

Doc ID: 346732 Received 27 Sep 2018; Accepted 10 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: The optical aperture of ultrashort extreme intensity laser facilities, which reach 10 Petawatt, will be beyond several hundred millimeters. DKDP is by now the only nonlinear crystal that can be grown to such diameter and used in the main Optical Parametric Chirped Pulse Amplification (OPCPA) amplifier of such laser system. Here, at the signal wavelength of 808 nm for the first time, we experimentally present a broadband OPCPA system which consists of a pre-amplifier in BBO crystals and a main OPCPA amplifier in two 95% deuterated DKDP crystals. The final amplified spectrum exceeding 50 nm and the compressed pulse duration of 27 fs have been proved. The conversion efficiency of main OPCPA amplifier reached 24 % and a net signal gain of 13 was obtained. For high energy OPCPA amplifier, the influence due to partial absorption on the idler pulses in DKDP crystal is theoretically analyzed. The results indicate the potential utilization of high deuterium DKDP for the main OPCPA amplifiers in multi-Petawatt laser system at 808 nm wavelength.

Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser

Ying Han, J. Partington, Rabi Chhantyal-Pun, Manju Henry, O. Auriacombe, T. Rawlings, Lian He Li, James Keeley, M. Oldfield, N. Brewster, R. Dong, Paul Dean, Giles Davies, Brian Ellison, Edmund Linfield, and Alex Valavanis

Doc ID: 344578 Received 31 Aug 2018; Accepted 10 Oct 2018; Posted 07 Nov 2018  View: PDF

Abstract: A multimode self-mixing terahertz-frequency gas absorption spectroscopy is demonstrated based on a quantum cascade laser. A double-metal device configuration is used to expand the laser’s frequency tuning range and a precision-micromachined external waveguide module is used to enhance the optical feedback. Methanol spectra are measured using two laser modes at 3.362 THz and 3.428 THz simultaneously, with more than 8 absorption peaks resolved over a 15 GHz bandwidth, which provide the minimum detectable absorption coefficient of 2.7×10-4 cm−1 and 4.9×10−4 cm−1, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth and duty cycle significantly.

Further Emission Efficiency Improvement of a Commercial-quality Light-emitting Diode through Surface Plasmon Coupling

Chun-Han Lin, Chia-Ying Su, Yu-Feng Yao, Ming-Yen Su, Hsin-Chun Chiang, Meng-Che Tsai, Wei-Heng Liu, Charng-Gan Tu, Yean-woei Kiang, Chih-Chung Yang, Feng-Wen Huang, Chi-Ling Lee, and Ta-Cheng Hsu

Doc ID: 337912 Received 04 Jul 2018; Accepted 09 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: It is usually believed that surface plasmon (SP) coupling is practically useful only for improving the performance of a light-emitting diode (LED) with a low intrinsic internal quantum efficiency (IQE). In this letter, we demonstrate that the performance of a commercial-quality blue LED with a high IQE (>80 %) can still be significantly improved through SP coupling based on a surface Ag nanoparticle (NP) structure. The performance improvement of such an LED is achieved by increasing the Mg doping concentration in its p-AlGaN electron blocking layer to enhance the hole injection efficiency such that the p-GaN layer thickness can be significantly reduced without sacrificing its electrical property. In this situation, the distance between surface Ag NPs and quantum wells is decreased and hence SP coupling strength is increased. By reducing the distance between the surface Ag NPs and the top quantum well to 66 nm, the IQE can be increased to almost 90 % (an ~11 % enhancement) and the electroluminescence intensity can be enhanced by ~24 %.

Fast Raman spectral mapping of highly fluorescing samples by time-gated spectral multiplexed detection

Christopher Corden, Dustin Shipp, Pavel Matousek, and Ioan Notingher

Doc ID: 335878 Received 11 Sep 2018; Accepted 07 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We present a time-gated Raman micro-spectroscopy technique suitable for fast Raman mapping of samples eliciting large laser-induced fluorescence backgrounds. To achieve the required time resolution for effective fluorescence rejection, a pico-second pulsed laser and a single photon avalanche diode were used. A module consisting of a spectrometer, digital micromirror device (DMD) and two prisms was used for high-resolution spectral filtering and multiplexing, required for a high chemical specificity and short integration times. With this instrument, we demonstrated time-gated Raman imaging of highly fluorescent samples, achieving acquisition times as short as 3 minutes for 40x40 pixels resolution images.

Laser speckle contrast imaging of blood flow in deep brain using microendoscopy

Ming Chen, Wen Dong, songlin huang, shen gui, Zhihong Zhang, Jinling Lu, and Pengcheng Li

Doc ID: 338725 Received 13 Jul 2018; Accepted 06 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: Dysfunctions of blood flow circulation locating in deep brain below the cortex may be involved in many brain diseases. However, the limitation of light penetration hinders detection of blood flow in deep brain tissue in vivo. Therefore, we present a gradient index (GRIN) lens based laser speckle contrast imaging system to perform time-lapse blood flow detection in deep brain. Hemodynamic changes in thalamus of the mouse models of acute hypoxia and transient middle cerebral artery occlusion (tMCAo) were conducted as validation.

Free-beam spectral self-compression at supercritical peak powers

Alexander Mitrofanov, Maxim Nazarov, Aleksandr Voronin, Dmitry Sidorov-Biryukov, Vladislav Panchenko, and Aleksei Zheltikov

Doc ID: 335567 Received 18 Jun 2018; Accepted 05 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: We demonstrate free-beam spectral self-compression of ~100-GW femtosecond laser pulses due to self-phase modulation (SPM) in a transparent dielectric. While all the earlier studies of SPM-induced spectral narrowing have been performed using optical fibers, experiments and simulations presented in this paper show that this type of spectral transformation can be implemented as a part of a full three-dimensional field-waveform dynamics and can be extended to peak powers ~10^5 times higher than the critical power of self-focusing. With a properly chosen initial chirp, spectral self-compression is accompanied by pulse compression, providing spectral--temporal mode self-compression as a whole.

Image reversal reactive immersion lithography improves the detection limit of focal molography

Andreas Frutiger, Yves Blickenstrofer, Cla Tschannen, Andreas Reichmuth, Christof Fattinger, and Janos Vörös

Doc ID: 341991 Received 04 Sep 2018; Accepted 29 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: Focal molography is a label-free optical biosensing method that relies on a coherent pattern of binding sites for biomolecular interaction analysis. Reactive immersion lithography (RIL) is central to the patterning molographic chips but has potential for improvements. Here, we show that applying the idea of image reversal to RIL enables the fabrication of coherent binding patterns of increased quality (i.e., higher analyte efficiency). Thereby the detection limit of focal molography in biological assays can be improved.

Microwave photonic multiband filter with independently tunable passband spectral properties

Qidi Liu, Mable Fok, and Jia Ge

Doc ID: 336395 Received 27 Jun 2018; Accepted 26 Sep 2018; Posted 26 Sep 2018  View: PDF

Abstract: Multiband RF filters with independently controllable passbands are an essential component in dynamic multiband RF communications. Unfortunately, even a fixed multiband RF filter without the capability to adjust the passband properties individually is very difficult to achieve using either RF electronics or microwave photonic technologies. In microwave photonic approaches, the critical limitation is the close relationship between passbands – the tuning of one passband will lead to a change in another, hindering the ability to independently control each passband. In this article, a programmable microwave photonic multiband filter with full control of amplitude, frequency, bandwidth, group delay slope, and spectral shape of each passband has been experimentally demonstrated. A multiband filter design algorithm has also been developed, which considers each RF passband as an individual, then uses inverse Fourier transform and filter design rule to determine the corresponding optical parameters, and combines a series of shaped cosine functions to achieve the desired RF properties.

339-J high-energy Ti:sapphire chirped-pulse amplifier for 10-PW laser facility

Li Wenqi, Zebiao Gan, Lianghong Yu, Cheng Wang, Yanqi Liu, zhen guo, Lu Xu, Min Xu, Yin Hang, Yi Xu, Jianye Wang, Pei Huang, He Cao, Bo Yao, Xiaobo Zhang, Lingru Chen, Yunhai Tang, Shuai Li, Xingyan Liu, Shanming Li, Mingzhu He, Dingjun Yin, Xiaoyan Liang, Yuxin Leng, Ruxin Li, and Zhizhan Xu

Doc ID: 341663 Received 09 Aug 2018; Accepted 17 Sep 2018; Posted 24 Oct 2018  View: PDF

Abstract: We report on the laser pulse output of 339 J centered at 800 nm from a chirped-pulse amplification (CPA) Ti:sapphire laser system at the Shanghai Superintense Ultrafast Laser Facility. The experimental results demonstrated that the parasitic lasing as well as the transverse amplified spontaneous emission of the homemade 5-mm-diameter Ti:sapphire final amplifier were suppressed successfully via the temporal dual-pulse pumped scheme and the index-matching liquid cladding technique. The maximum pump-to-signal conversion efficiency of 32.1% was measured for the final amplifier. With the compressor transmission efficiency of 64% and the compressed pulse duration of 21 fs obtained for the sample light at a lower energy level, this laser system could potentially generate a compressed laser pulse with a peak power of 10.3 PW. The experimental results represent significant progress with respect to the CPA laser.

Photonics in highly dispersive media: The exact modal expansion

Frederic Zolla, Andre Nicolet, and Guillaume Demesy

Doc ID: 338174 Received 09 Jul 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: We present exact modal expansions for photonic systems including highly dispersive media. The formulas, based on a simple version of the Keldysh theorem, are very general since both permeability and permittivity can be dispersive, anisotropic, and even possibly non reciprocal. A simple dispersive test case where both plasmonic and geometrical resonances strongly interact exemplifies the numerical efficiency of our approach.

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