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CMOS-compatible all-optical modulator based on thesaturable absorption of graphene

Yi Wang, Hong Wang, Ningning Yang, limin chang, Chaobiao Zhou, Shiyu Li, Meng Deng, Zhen-Wei Li, Chi Zhang, Zhi-Yong Li, and Qiang Liu

DOI: 10.1364/PRJ.380170 Received 11 Oct 2019; Accepted 16 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: Graphene resting on silicon-on-insulator platform offers great potential for optoelectronic devices. In thepaper, we demonstrate all-optical modulation on the graphene-silicon hybrid waveguides (GSHWs) withtens of micrometers in length. Owing to strong interaction between graphene and silicon strip waveguideswith compact light confinement, the modulation depth reaches 22.7% with a saturation thresholddown to 1.38 pJ per pulse and a 30-m-length graphene pad. A response time of 1.65 ps is verified by apump-probe measurement with an energy consumption of 2.1 pJ . The complementary metal-oxide semiconductor(CMOS) compatible GSHWs with the strip configuration exhibit great potential for ultrafastand broadband all-optical modulation, indicating that two-dimension materials have become a complementarytechnology to promote the silicon photonic platform.

Self-accelerated optical activity in free space induced by Gouy phase

Peng Li, Xinhao Fan, Dongjing Wu, Sheng Liu, Yu Li, and Jianlin Zhao

DOI: 10.1364/PRJ.380675 Received 18 Oct 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: Optical activity (OA), is the rotation of the polarization orientation of the linearly polarized light as it travels through certain materials that are of mirror asymmetry, including gases or solution of chiral molecules such as sugars and proteins, as well as metamaterials. The necessary condition for achieving OA is the birefringence of two circular polarizations in material. Here, we propose a new kind of self-accelerated OA in free space, based on the intrinsic Gouy phases induced mode birefringence of two kinds of non-diffracting beams. We provide a detailed insight into this kind of self-accelerated OA by analyzing angular parameters, including angular direction, velocity, acceleration, and even the polarization transformation trajectory. As the Gouy phase exists for any wave, this kind of self-accelerated OA can be implemented in other waves beyond optics, from acoustic and elastic waves to matter waves.

Synergistic effects of electric-field-enhancement and charge-transfer based SERS study in Ag₂S quantum dots/plasmonic bow-tie nanoantenna composite system

Subhash Singh, Bin Wang, Chen Zhao, Huanyu Lu, Tingting Zou, ZHI YU, Chaonan Yao, Xin Zheng, Jun Xing, Yuting Zou, Cunzhu Tong, WEILI YU, Bo Zhao, and Chunlei Guo

DOI: 10.1364/PRJ.383612 Received 20 Nov 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: Localized surface plasmonic resonance (LSPR) of nanostructures and the interfacial charge transfer (CT) of semiconductor materials play essential roles in the optical and photo-electronic property study. In this article, a composite substrate of Ag₂S quantum dots (QDs) coated plasmonic Au bow-tie nanoantenna (BNA) arrays with metal-insulator-metal (MIM) configuration was built to study the synergistic effect of LSPR and interfacial CT using surface-enhanced Raman spectroscopy (SERS) in near-infrared (NIR) region. The Au BNA arrays structure with large enhancement of localized electric field (E-field) and broad enhanced spectral region strongly enhanced the Raman signal of adsorbed p-aminothiophenol (PATP) molecules owing to the coupling of LSPR. The as-prepared Au BNA arrays structure facilitated enhancements of the excitation as well as the emission of Raman signal simultaneously, which was proved by finite-different-time-domain (FDTD) simulation. Moreover, Ag₂S semiconductor QDs were introduced into BNA/PATP system to further enhance Raman signals, which benefited from the interfacial CT resonance in BNA/Ag₂S-QDs/PATP system. As a result, the Raman signals of PATP in BNA/Ag₂S-QDs/PATP system were strongly enhanced under 785 nm laser excitation due to the synergetic effect of E-field enhancement and interfacial CT. Furthermore, the SERS polarization dependence effects of BNA/Ag₂S-QDs/PATP system were also investigated. This study establishes a correlation of synergetic effect of interfacial CT and E-field enhancement for SERS applications and provides guidance for the development of SERS study on semiconductor QDs based plasmonic substrates, and can be further extended to other material-nanostructure systems for various optoelectronic and sensing applications.

Dielectric metalens-based Hartmann-Shack array for high-efficiency optical multi-parameter detection system

Jinsong Xia, Yuxi Wang, Zhaokun Wang, Xing Feng, Ming Zhao, Cheng Zeng, Guangqiang He, Zhen Yu Yang, and Yu Zheng

DOI: 10.1364/PRJ.383772 Received 22 Nov 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: The real-time measurement of the polarization and phase information of light is very important and desirable in optics. Metasurfaces can be used to achieve flexible wavefront control and can therefore be used to replace traditional optical elements to produce a highly integrated and extremely compact optical system. Here, we propose an efficient and compact optical multi-parameter detection system based on a Hartmann-Shack array with 2×2 sub-array metalenses. This system not only enables the efficient and accurate measurement of the spatial polarization profiles of optical beams via the inspection of foci amplitudes but also measures the phase and phase-gradient profiles by analysing foci displacements. In this work, details of the design of the elliptical Si pillars for metalens are described, and we achieve a high average focusing efficiency of 48% and a high spatial resolution. The performance of the system is validated by the experimental measurement of 22 scalar polarized beams, an azimuthally polarized beam, a radially polarized beam and a vortex beam. The experimental results are in good agreement with theoretical predictions.

Frequency-tuning induced state transfer in optical microcavities

Gui Lu Long, Xu-Sheng Xu, H. Zhang, xiang-yu kong, and Min Wang

DOI: 10.1364/PRJ.385046 Received 03 Dec 2019; Accepted 14 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: Quantum state transfer in optical microcavities plays an important role in quantum information processing, and is essential in many optical devices, such as optical frequency converter and diode. Existing schemes are effective and realized by tuning the coupling strengths between modes. However, such approaches are severely restricted due to the small amount of strength that can be tuned and the difficulty to perform the tuning in some situations, such as on-chip microcavity system. Here, we propose a novel approach that realizes the state transfer between different modes in optical microcavities by tuning the frequency of an intermediate mode. We showed that for typical functions of frequency-tuning, such as linear and periodic functions, the state transfer can be realized successfully with different features. To optimize the process, we use gradient descent technique to find an optimal tuning function for the fast and perfect state transfer. We also showed that our approach has significant nonreciprocity with appropriate tuning variables, where one can unidirectionally transfer a state from one mode to another, but the inverse direction transfer is forbidden. This work provides an effective method for controlling the multimode interactions in on-chip optical microcavities via simple operations and it has practical applications in all-optical devices.

Photonic cavity enhanced high-performance surface plasmon resonance biosensor

Guishi Liu, Xin Xiong, weicheng shi, Yaofei Chen, Wenguo Zhu, Huadan Zheng, JianHui Yu, Nur Hidayah Azeman, Yunhan Luo, Zhe Chen, and Shiqi Hu

DOI: 10.1364/PRJ.382567 Received 15 Nov 2019; Accepted 14 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: Herein we propose a novel strategy to enhance the surface plasmon resonance (SPR) by introducing a photonic cavity into a total-internal-reflection architecture. The photonic cavity, which is comprised of a photonic crystal, defect layers, and an Au film, enables Fabry-Pérot (FP) resonances in the defect layers to excite a narrow SPR mode in the metallic surface, as well as increase the electric field intensity and penetration depth in the evanescent region. The fabricated sensor exhibits 5.7-fold increase in the figure of merit and a higher linear coefficient, as compared with the conventional Au-SPR sensor. The demonstrated PC/FB cavity/metal structure presents a new design philosophy for SPR performance enhancement.

Integrated beam steering by using tunable, narrow linewidth hybrid lasers in Si3N4 photonics platform

Yeyu Zhu, siwei zeng, and Lin Zhu

DOI: 10.1364/PRJ.382852 Received 08 Nov 2019; Accepted 13 Jan 2020; Posted 13 Jan 2020  View: PDF

Abstract: Chip-scale, tunable narrow linewidth diode lasers based on quantum-dot RSOAs at 1.3 µm are demonstrated through hybrid integration in silicon nitride photonics platform. The hybrid laser linewidth is around 85 kHz and the tuning range is around 47 nm. Then, a fully integrated beam steerer is demonstrated by combining the tunable diode laser with a waveguide surface grating. Our system can provide beam steering of 4.1° in one direction by tuning the wavelength of the hybrid laser. Besides, a wavelength tunable triple-band hybrid laser system working at ~1 µm, ~1.3 µm, and ~1.55 um bands is demonstrated for integrated wide-angle beam steering in a single chip.

Optimizing interleaved p-n junction to reduce energy dissipation in silicon slow-light modulators

Marco Passoni, Dario Gerace, Liam O'Faolain, and Lucio Andreani

DOI: 10.1364/PRJ.382620 Received 11 Nov 2019; Accepted 12 Jan 2020; Posted 13 Jan 2020  View: PDF

Abstract: Reducing power dissipation in electro-optic modulators is a key step for widespread application of silicon photonics to optical communication. In this work, we design Mach-Zehnder modulators in the Silicon-on-Insulator platform, which make use of slow light in a waveguide grating and of a reverse-biased p-n junction with interleaved contacts along the waveguide axis. After optimizing the junction parameters, we discuss the full simulation of the modulator in order to find a proper tradeoff among various figures of merit such as modulation efficiency, insertion loss, cutoff frequency, optical modulation amplitude, and dissipated energy per bit. Comparison with conventional structures (with lateral p-n junction and/or in rib waveguides without slow light) highlights the importance of combining slow light with the interleaved p-n junction, thanks to the increased overlap between the travelling optical wave and the depletion regions. As a surprising result, the modulator performance is improved over an optical bandwidth that is much wider than the slow-light bandwidth.

Ultra-broadband reflector using double-layer subwavelength gratings

Jinlong Zhang, Shuaikai Shi, Hongfei Jiao, Xiaochuan Ji, Zhanshan Wang, and Xinbin Cheng

DOI: 10.1364/PRJ.382941 Received 14 Nov 2019; Accepted 10 Jan 2020; Posted 13 Jan 2020  View: PDF

Abstract: Double-layer high contrast subwavelength gratings that are separated by a dielectric space layer were investigated to achieve ultra-broadband reflection. The reflection phase of subwavelength gratings and the propagation phase shift between two gratings were manipulated to expand reflection bandwidth by properly stacking two reflective gratings. The high-reflector exhibits >58% fractional band in the near infrared was designed. Then, this reflector was prepared using laser interference lithography and ion beam planarization, where an ultra-broadband reflection was achieved with reflectance exceeding 97% over a 950nm in the near infrared region.

Performance characteristics of AlGaN tunnel junction light emitting diodes

Ayush Pandey, Walter Shin, Jiseok Gim, Robert Hovden, and Zetian Mi

DOI: 10.1364/PRJ.383652 Received 18 Nov 2019; Accepted 07 Jan 2020; Posted 07 Jan 2020  View: PDF

Abstract: AlGaN is the material of choice for high efficiency deep UV light sources, which is the only alternative technology to replace mercury lamps for water purification and disinfection. At present, however, AlGaN-based mid and deep UV LEDs exhibit very low efficiency. Here, we report a detailed investigation of the epitaxy and characterization of AlGaN tunnel junction LEDs operating at ~265 nm, which have the potential to break the efficiency bottleneck of deep UV photonics. A thin GaN layer was incorporated between p+ and n+-AlGaN to reduce the tunneling barrier. By optimizing the thickness of the GaN tunnel junction width and the thickness of the top n-AlGaN contact layer, we demonstrate AlGaN deep UV LEDs with a maximum external quantum efficiency (EQE) of ~11% and wall-plug efficiency (WPE) of ~7.6% for direct on-wafer measurement. It is also observed that the devices exhibit severe efficiency droop under very low current densities, which is explained by the low hole mobility, due to the hole hopping conduction in the Mg impurity band, and the resulting electron overflow.

Quantum versus optical interaction contribution to giant spectral splitting in a strongly-coupled plasmon-molecules system

Bo Wang, Xian-Zhe Zeng, and Zhiyuan Li

DOI: 10.1364/PRJ.375135 Received 12 Aug 2019; Accepted 06 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: The vacuum Rabi splitting, which stems from a single photon interaction with a quantum emitter (a single atom, molecule, or quantum dot), is a fundamental quantum phenomenon. Intrinsically this effect is reflected in the internal energy splitting of quantum emitter state, while extrinsically it is reflected by the spectral splitting in either photoluminescence, or fluorescence, or scattering, or absorption spectrum. Many reports have claimed that using J-aggregates coupling to highly localized plasmon can produce giant Rabi splitting (in scattering spectra) which is proportional to √N, where N is the number of excitons in J-aggregates, and this splitting originate purely from quantum interaction between excitons and plasmons. In this work, we show that compared with the photoluminescence or fluorescence, which is a sign of molecular internal states and can really reflect the molecular energy-level splitting, the scattering spectra is far more sensitive to the surrounding matter. The giant spectral splitting stems both from the quantum interaction of single-molecule with plasmons (Rabi splitting) and from the classical optical interaction of multiple molecules with plasmons. We develop a Lorentzian model to describe molecules and plasmon and find that the collective optical interaction is dominant to generate the giant splitting (in scattering spectra), which is also proportional to √N, upon the quantum interaction of single-molecule Rabi splitting. Simply speaking, the observed giant spectral splitting is not a pure quantum Rabi splitting effect, but rather a mixture contribution from the large spectral modulation by the collective optical interaction of all molecules with plasmons and the modest quantum Rabi splitting of single-molecule strongly coupled with plasmons

Broadband supercontinuum generation in nitrogen-rich silicon nitride waveguides using a 300 mm industrial platform.

Christian Lafforgue, Sylvain Guerber, Joan Manel Ramirez, Guillaume Marcaud, Carlos Alonso-Ramos, Xavier Le Roux, Delphine Marris-Morini, Eric Cassan, Charles BAUDOT, Frederic Boeuf, Sébastien Crémer, Stephane Monfray, and Laurent Vivien

DOI: 10.1364/PRJ.379555 Received 02 Oct 2019; Accepted 05 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: We report supercontinuum generation in nitrogen-rich silicon nitride waveguides fabricated through back-end CMOS compatible processes on a 300 mm platform. By pumping in the anomalous dispersion regime at a wavelength of 1200 nm, two-octaves spanning spectra covering the visible and near-infrared ranges, including the O-band, were obtained. Numerical calculations showed that the nonlinear index of nitrogen-rich silicon nitride is within the same order of magnitude than that of stoichiometric silicon nitride despite the lower silicon content. Nitrogen-rich silicon nitride then appears to be a promising candidate for nonlinear devices compatible with back-end CMOS processes.

Passively Q-switched and femtosecond mode locked Erbium-doped fiber laser based on 2D palladium disulfide (PdS2) saturable absorber

Ping Kwong Cheng, Chun-Yin Tang, Xinyu Wang, Longhui Zeng, and Yuen Tsang

DOI: 10.1364/PRJ.380146 Received 11 Oct 2019; Accepted 05 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: Stable Q-switched and mode-locked erbium-doped fiber laser (EDFL) are firstly demonstrated by using the novel layered PdS2, a new member of group 10 transition metal dichalcogenides, based saturable absorbers (SA). Self-started Q-switched operation at 1567 nm was achieved with a threshold pump power of 50.6 mW. The modulation ranges of pulse duration and repetition rate were characterized as 12.6 - 4.5 µs and 17.2 - 26.0 kHz, respectively. Meanwhile, a mode-locked EDFL was also obtained with a pump power threshold of 106.4 mW. The achieved pulse duration is 803 fs, corresponding to center wavelength of 1564 nm and 3.7 nm 3dB bandwidth. To the best of our knowledge, the achieved pulse duration of the mode-locked EDFL in this work is the narrowest compared with all others group 10 TMDs SAs based lasers.

Two-photon interference between continuous-wave coherent photons temporally separated by days

Han Seb Moon, DANBI Kim, Jiho Park, Jung Take, and Heonoh Kim

DOI: 10.1364/PRJ.376993 Received 04 Sep 2019; Accepted 02 Jan 2020; Posted 03 Jan 2020  View: PDF

Abstract: An understanding of the phenomenon of light interference forms the kernel underlying the discovery of the nature of light from the viewpoints of both classical physics and quantum physics. Here, we report on two-photon interference with temporally separated continuous-wave (CW) coherent photons by using a temporal post-selection method with an arbitrary time delay. Although the temporal separation (of the order of days) between the photons is considerably longer than the coherence time of the light source, we observe the Hong–Ou–Mandel (HOM) interference of the pairwise two-photon state. Furthermore, we experimentally demonstrate the HOM interference observed in one of the interferometer-output modes by using only one single-photon detector for a large temporal separation.

Microbubble resonators combined with digital optical frequency comb for high-precision air-coupled ultrasound detectors

Jingshun Pan, Bin Zhang, Zhengyong Liu, xin zhao, Yuanhua Feng, Lei Wan, and Zhaohui Li

DOI: 10.1364/PRJ.376640 Received 02 Sep 2019; Accepted 30 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: This paper describes a fast and high accuracy optical technique combining high-Q microbubble resonators (MBRs) with a digital optical frequency comb (DOFC) for air-coupled ultrasound detection. Each comb line of DOFC provides one sampling, enabling this technique to capture complete ultrasound-induced spectral changes including intensity and phase responses of the MBR with femtometer resolution and sub-microsecond response time. As a demonstration, a high Q (~2x107) MBR combined with the DOFC is used for detection of air-coupled ultrasound at 165 kHz and noise equivalent pressure in air as low as 4.4 mPa/√Hz is achieved. Moreover, it can acquire a fast and full spectral changes including multi-responses peaks from multiple MBRs to directly monitor the precise spatial location of the ultrasonic source. This approach has the potential to 3D air-coupled photoacoustic and ultrasonic imaging with high fidelity.

All-optical tuning of a diamond micro-disk resonator on silicon

Paul Hill, Charalambos Klitis, Benoit Guilhabert, Marc Sorel, erdan Gu, Martin D. Dawson, and Michael Strain

DOI: 10.1364/PRJ.372358 Received 12 Jul 2019; Accepted 26 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: High quality integrated diamond photonic devices have previously been demonstrated in applications from non-linear photonics to on-chip quantum optics. However, the small sample sizes of single crystal material available, and the difficulty in tuning its optical properties, are barriers to the scaling ofthese technologies. Both of these issues can be addressed by integrating micron scale diamond devices onto host photonic integrated circuits using a highly accurate micro-assembly method. In this work a diamond micro-disk resonator is integrated with a standard single mode silicon-on-insulator waveguide, exhibiting an average loaded Q-factor of 3.1×10^4 across a range of spatial modes, with a maximum loaded Q-factor of 1.06×10^5. The micron scale device size and high thermal impedance of the silica interface layer allow for significant thermal loading and continuous resonant wavelength tuning across a 450 pm range using a mW level optical pump. This diamond-on-demand integration technique paves the way for tunable devices coupled across large scale photonic circuits.

Brillouin wavelength-selective all-optical polarization conversion

Diego Samaniego and Borja Vidal

DOI: 10.1364/PRJ.371513 Received 01 Jul 2019; Accepted 26 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: The manipulation of the polarization properties of light in guided media is crucial in many classical and quantum optical systems. However, the capability of current technology to finely define the state of polarization of particular wavelengths is far from the level of maturity in amplitude control. Here, we introduce a light-by-light polarization control mechanism with wavelength selectivity based on the change of the phase retardance by means of stimulated Brillouin scattering. Experiments show that any point on the Poincaré sphere can be reached from an arbitrary input state of polarization with little variation of the signal amplitude (< 2.5 dB). Unlike other Brillouin processing schemes, the degradation of the noise figure is small (1.5 dB for a full 2π rotation). This all-optical polarization controller can forge the development of new polarization-based techniques in optical communication, laser engineering, sensing, quantum systems and light-based probing of chemical and biological systems

In-depth investigation and applications of novel silicon photonics microstructures supporting optical vorticity and waveguiding for ultra narrowband near-infrared perfect absorption

Roy Avrahamy, Moshe Zohar, Mark Auslender, Benjamin Milgrom, Shlomo Hava, and Rafi Shikler

DOI: 10.1364/PRJ.375802 Received 23 Aug 2019; Accepted 25 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: We propose a novel concept of designing silicon-photonics structures for perfect near-infrared light-absorption based on subwavelength metasurfaces. The emphasis of this study is an in-depth investigation of various physical mechanisms behind the ~ 100% ultra narrowband record peak absorptance of the designed structures, comprising ultrathin silicon absorber layers. The electromagnetic power transport, described by the Poynting vector is innovatively explored, which shows combined vortex and crossed-junction two-dimensional waveguide like flows, as outcomes of optical field singularities. These flows, though peculiar for each of the designed structures, turn out to be the ultimate keys to the perfect resonant optical absorption. The electromagnetic fields show tight two-dimensional confinement, sharp vertical confinement of the resonant-cavity type combined with a lateral one within an artificial microcavity, set by the metasurface patterning period. The design involves solely, silicon oxide, silicon nitride, and silicon used as ultra-thin photo-absorber, that are well compatible with silicon-on-insulator microelectronics. In these structures, a silicon-absorbing layer and its oxide environment are confined between two subwavelength metasurfaces. The design concept and its outcomes meet the enormous challenges of ultrathin absorber for minimum noise and ultra-narrowband absorptance spectrum while constraining the structure to be overall very thin for planar integration. With these materials and such objectives, the proposed designs prove indispensable, as the standard approaches fail to achieve the above goals, mainly because of a very low absorption coefficient of silicon over the near-infrared range. The performance tolerances with respect to the allowed fabrication errors in the metasurfaces' patterning are tested. Fair tolerability while maintaining high absorptance peak, along with a controllable deviation off the central-design wavelength, is shown. Various applications for the proposed structures are suggested and analyzed, which include, but are not limited to: precise photodetectors for focal plan array imaging systems and on-chip integrated silicon photonics, high-precision spectroscopic chemical and angular-position sensing, and wavelength-division multiplexing.

Ultraviolet-to-Microwave Room Temperature Photodetectors Based on Three-dimensional Graphene Foams

Yifan Li, Yating Zhang, yu yu, Zhiliang Chen, Qingyan Li, Tengteng Li, Jie Li, Hongliang Zhao, Quan Sheng, Feng Yan, Zhen Ge, Yuxin Ren, Yongsheng Chen, and Jian-Quan Yao

DOI: 10.1364/PRJ.380249 Received 15 Oct 2019; Accepted 25 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: Highly sensitive broadband photo detection is of critical importance to many applications. However, it is a great challenge to realize broadband photo detection by using a single device. Here, we report photodetectors (PDs) based on three-dimensional (3D) graphene foam (GF) photodiodes with asymmetric electrodes, which show an ultra-broadband photo response from ultraviolet to microwave for wavelengths ranging from 102 to 106 nm. Moreover, the devices exhibit a high photoresponsivity of 103 A W−1, fast response time of 43 ms and 3 dB bandwidth of 80 Hz. The high performance of the devices can be attributed to the photothermoelectric (PTE) (Seebeck) effect in the 3D GF photodiodes. The excellent optical, thermal, and electrical properties of 3D GFs offer a superior basis for the fabrication of PTE-based PDs. This work paves the way to realize ultra-broadband and high sensitivity PDs operated at room temperature.

First-photon imaging via a hybrid penalty

Mingjie Sun, Xin-Yu Zhao, xiao peng, and Li-Jing Li

DOI: 10.1364/PRJ.381516 Received 25 Oct 2019; Accepted 24 Dec 2019; Posted 03 Jan 2020  View: PDF

Abstract: First-photon imaging is a photon-efficient, computational imaging technique which reconstructs an image by recording only the first-photon arrival event at each spatial location and then optimizing the recorded photon information. The optimization algorithm plays a vital role in image formation. A natural sparse scene can be reconstructed by maximum likelihood of all spatial locations constrained with a sparsity regularization penalty, and different penalties lead to different reconstruction. The l1-norm penalty of wavelet transform reconstructs major features but blurs edges and high-frequency details of the image. The total variational penalty preserves edges better, however, it induces ‘staircase effect’ which degrades image quality. In this work, we proposed a hybrid penalty to reconstruct better edge features while suppressing ‘staircase effect’ by combining wavelet l1-norm and total variation into one penalty function. Results of numerical experiments indicate that the proposed hybrid penalty reconstructed better images, which have an averaged root mean squared error 14.29% and 11.38% smaller than those of the images reconstructed by using only wavelet l1-norm and total variation penalty, respectively. Practical experimental results are in a good agreement with the numerical ones, demonstrating the feasibility of the proposed hybrid penalty. Having been verified in first-photon imaging system, the proposed hybrid penalty can be applied to other Poisson noise removal optimization problems.

Ultra-broadband nanophotonic phase shifter based on subwavelength metamaterial waveguides

David Gonzalez-Andrade, José Luque-González, J. Gonzalo Wangüemert-Pérez, Alejandro Ortega-Moñux, Pavel Cheben, I. Molina-Fernández, and Aitor Velasco

DOI: 10.1364/PRJ.373223 Received 19 Jul 2019; Accepted 24 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: Optical phase shifters are extensively used in integrated optics not only for telecom and datacom applications, but also for sensors and quantum computing. While various active solutions have been demonstrated, progress in passive phase shifters is still lacking. Here, we present a new type of ultra-broadband 90° phase shifter, which exploits the anisotropy and dispersion engineering in subwavelength metamaterial waveguides. Our Floquet-Bloch calculations predict a phase shift error below ±1.7° over an unprecedented operation range from 1.35 µm to 1.75 µm, i.e. 400 nm bandwidth covering the E, S, C, L and U telecommunication bands. The flat spectral response of our phase shifter is maintained even in the presence of fabrication errors up to ±20 nm, showing greater robustness than conventional structures. Our device was experimentally demonstrated using standard 220-nm-thick SOI wafers, showing a fourfold reduction in the phase variation compared to conventional phase shifters within the 145 nm wavelength range of our measurement setup. The proposed subwavelength engineered phase shifter paves the way for novel photonic integrated circuits with an ultra-broadband performance.

User-independent optical path length compensation scheme with sub-ns timing resolution for 1×N quantum key distribution network system

Byung Kwon Park, Min Ki Woo, Yong-Su Kim, Young-Wook Cho, Sung Moon, and Sang-Wook Han

DOI: 10.1364/PRJ.377101 Received 05 Sep 2019; Accepted 23 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: Quantum key distribution (QKD) networks are promising solutions for secure communication. Beyond conventional point to point QKD, we developed 1×N QKD network systems with a sub-ns resolution optical path length compensation scheme. With a practical plug & play QKD architecture and compact timing control modules based on a field programmable gate array (FPGA), we achieved long-term stable operation of a 1×64 QKD network system. Using this architecture, 64 users can simultaneously share secret keys with one server without using complex software algorithms and expensive hardware. We successfully demonstrated the working of a 1×4 QKD network system using the deployed fiber network of a metropolitan area.

High power hybrid GaN-based green laser diodes with ITO cladding layer

Lei Hu, Xiaoyu Ren, Jianping Liu, Aiqin Tian, Lingrong Jiang, Siyi Huang, Wei Zhou, liqun zhang, and Hui Yang

DOI: 10.1364/PRJ.381262 Received 23 Oct 2019; Accepted 22 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: Green laser diodes (LDs) still perform worst among visible and near infrared spectrum range, which is called the ‘green gap’. Poor performance of green LDs is mainly related to p-type AlGaN cladding layer, which on one hand imposes large thermal budget on InGaN quantum wells (QWs) during epitaxial growth, and on the other hand has poor electrical property especially when low growth temperature has to be used. We demonstrate in this work that hybrid LD structure with indium tin oxide (ITO) p-cladding layer can achieve threshold current density as low as 1.6 kA/cm2, which is only one third of that of conventional LD structure. The improvement is attributed to two benefits that are enabled by ITO cladding layer. One is the reduced thermal budget imposed on QWs by using ITO p-cladding layer, and another is increasing hole concentration since low Al content p-AlGaN cladding layer can be used in hybrid LD structures. Moreover, the slope efficiency is increased by 25% and the operation voltage is reduced by 0.6 V for hybrid green LDs. As a result, 400 mW high power green LD has been obtained. These results indicate hybrid LD structure can pave the way towards to high-performance green LDs.

Exceptional points and the ring laser gyroscope

Luke Horstman, Ning Hsu, James Hendrie, David Smith, and Jean-Claude Diels

DOI: 10.1364/PRJ.369521 Received 10 Jun 2019; Accepted 20 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: An equivalence is made between the exceptional points proposed by the field of non-Hermitian quantum mechanics and the dead-band observed in laser gyroscopes. The sensitivity enhancement near this exceptional point is plagued by increased uncertainty due to a broadening of the beat-note bandwidth. Also, near the dead-band the gyroscope response is caused by Rabi intensity oscillations, and not solely by a phase modulation. Finally, a distinction is made between conservative and non-conservative coupling.

Second harmonic generation using d₃₃ in periodically poled lithium niobate microdisk resonators

Zhenzhong Hao, Li Zhang, Mao Wenbo, Ang Gao, Xiaomei Gao, Feng Gao, Fang Bo, Guoquan Zhang, and Jingjun Xu

DOI: 10.1364/PRJ.382535 Received 08 Nov 2019; Accepted 19 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: A fabrication process allowing for the production of periodically poled lithium niobate (PPLN) photonic devices with any domain patterns and unit size down to 200 nm is developed by combining semiconductor fabrication techniques and piezo-force-microscopy (PFM) tips polarization. Based on this fabrication process, PPLN microdisk resonators with quality factors of 8×10⁴ were fabricated from a Z-cut lithium niobate film. The second harmonic generation (SHG) utilizing d₃₃ in the whole cavity was demonatrated in a PPLN microdisk with a 2-µm-spatial-period raidal domain pattern. The SHG conversion efficiency was measured to be 1.44×10¯⁵ mW¯¹. This work paves the way to fabriate complex PPLN photonic devices and to obtain efficient nonliear optical effects that have wide applications in both classical and quantum optics.

Ultrafast polarization-dependent all-optical switching of germanium-based metaphotonic devices

Xin Zheng, HAO SUN, Yuze Hu, Jie You, junhu zhou, HENGZHU LIU, and Tang Yuhua

DOI: 10.1364/PRJ.380446 Received 17 Oct 2019; Accepted 18 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: Metamaterials play an important role in the modulation of amplitude and group delay at terahertz (THz) regime, on account of its optical properties which are rare in natural materials. Here, an ultrafast anisotropic switch of plasmon-induced transparency (PIT) effect is experimentally and numerically demonstrated by metamaterial devices composed of two pairs of planar split ring resonators (SRRs) and a pair of closed ring resonators (CRRs). By integrated with germanium (Ge) film, a recovery time of 3 ps and a decay constant of 785 fs are realized in the metadevice. Stimulated by the exterior optical pump, the PIT windows at different frequencies are switched-off with an excellent property of slow light, for vertical and horizontal THz polarizations, respectively, realizing an astonishing modulation depth as high as 99.06%. This work provides a new platform for ultrafast anisotropic metadevices tunable for amplitude and group delay.

A 3-D integrated photonics platform with deterministic geometry control

Jerome Michon, Sarah Geiger, Juejun Hu, Kathleen Richardson, Claudia Goncalves, Xinqiao Jia, Hongtao Lin, and Lan Li

DOI: 10.1364/PRJ.375584 Received 20 Aug 2019; Accepted 18 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: 3-D photonics promises to expand the reach of photonics by enabling both the extension of traditional applications to non-planar geometries and adding novel functionalities that cannot be attained with planar devices. Available material options and device geometries are, however, limited by current fabrication methods. In this work, we pioneer a method allowing for placement of integrated photonic device arrays at arbitrary pre-defined locations in 3-D using a fabrication process that capitalizes on the buckling of a 2-D pattern. We present theoretical and experimental validation of the deterministic buckling process demonstrating implementation of the technique to realize what we believe to be the first fully-packaged 3-D integrated photonics platform. Application of the platform for mechanical strain sensing is further demonstrated.

Effects of Coupling and Phase Imperfections in Programmable Photonic Hexagonal Waveguide Meshes

Iman Zand and Wim Bogaerts

DOI: 10.1364/PRJ.376227 Received 10 Sep 2019; Accepted 18 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: We present a study of the effect of the imperfections on the transmission and crosstalk in programmable photonic mesh circuits consisting of tunable couplers and phase shifters. The many elements in such a mesh can generate a multitude of parasitic paths when the couplers and phase shifters deviate even slightly from their nominal value. Performing Monte-Carlo simulations, we show that small stochastic imperfections in the phase and coupling (<1.0 %) can introduce unwanted interferences and resonances and significantly deteriorate the frequency response of the circuit. We also demonstrate that in the presence of imperfections the programming strategy of the unused couplers can reduce effects of such parasitics.

A Hybrid Waveguide Scheme for Silicon-based Quantum Photonic Circuits with Quantum Light Sources

Lingjie Yu, Chenzhi Yuan, Renduo Qi, Yidong Huang, and Wei Zhang

DOI: 10.1364/PRJ.376805 Received 09 Sep 2019; Accepted 16 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: We propose a hybrid silicon waveguide scheme trying to solve the pump light induced noise problem in some application scenarios of quantum photonic circuits with quantum light sources. The scheme is composed of strip waveguide and shallow-ridge waveguide structures. It utilizes the difference of biphoton spectra generated in these two types of waveguides by spontaneous four wave mixing (SFWM). By proper pumping setting and signal/idler wavelength selection, the impact of noise photons generated by SFWM in the shallow-ridge waveguide part can be avoided. The generation of desired photon pairs is limited in the part of strip waveguide. On the other hand, the shallow-ridge waveguide part has no contribution on these photon pairs. Hence, it could be used to realize various linear operation devices for pump light and quantum state manipulations. Dispersion tailoring is conducted for the optimization of waveguide dispersion characteristics and corresponding biphoton spectra. The feasibility of this scheme is verified by theoretical analysis and primary experiment. Two applications are proposed and analyzed, showing its great potential on silicon-based quantum photonic circuits.

Effective suppression of photodarkening effect in high power Yb-doped fiber amplifiers by H2-loading

Rui-ting Cao, Gui Chen, Yisha Chen, Zhilun Zhang, Xianfeng Lin, bin dai, Luyun Yang, and Jinyan Li

DOI: 10.1364/PRJ.381208 Received 30 Oct 2019; Accepted 16 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: The radical suppression of photodarkening effect and laser performance deterioration via H2-loading were demonstrated in high power Yb-doped fiber amplifiers. The photodarkening loss at equilibrium was 114.4 dB/m at 702 nm in the pristine fiber, while it vanished in the H2-loaded fiber. To obtain a deeper understanding of the impact of photodarkening on laser properties, the evolution of the mode instability threshold and output power in fiber amplifiers was investigated. After pumping for 300 min, the mode instability threshold of the pristine fiber dropped from 770 W to 612 W and the periodic fluctuation of output power became intense, finally reaching 100 W. To address the detrimental effects originated from photodarkening, H2-loading was applied in contrast experiments. The output power remained stable and no sign of mode instability was observed in the H2-loaded fiber. Moreover, the transmittance at 638 nm confirmed the absence of photodarkening effect. The results pave the way for the further development of high power fiber lasers.

Fabrication-tolerant Fourier transform spectrometer on silicon with broad bandwidth and high resolution

ang li, Jordan Davis, Andrew Grieco, Naif Alshamrani, and Yeshaiahu Fainman

DOI: 10.1364/PRJ.379184 Received 02 Oct 2019; Accepted 16 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [1]. We retrieve abroadband spectrum (7 THz around 193 THz) with 0.11 THz or sub nm resolution, more than3 times higher than previously demonstrated [1]. Moreover, it effectively solves the issue offabrication variation in waveguide width, which is a common issue in silicon photonics. The structure is a balanced Mach-Zehnder-Interferometer with 10 cm long serpentine waveguides.Quasi-continuous optical path difference (OPD) between two arms is induced by changing effective index of one arm using integrated heater. The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguide at the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss leads to higher spectral efficiency, larger dynamic range and better signal-noise-ratio. Also, for the first time, we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a fabrication tolerant device. This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile platforms.

“Periodic” soliton explosions in a dual-wavelength mode-locked Yb-doped fiber laser

Meng Liu, Ti-Jian Li, Aiping Luo, Wen-Cheng Xu, and Zhi-Chao Luo

DOI: 10.1364/PRJ.377966 Received 16 Sep 2019; Accepted 16 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: We report the “periodic” soliton explosions induced by intracavity soliton collisions in a dual-wavelength mode-locked Yb-doped fiber laser. Owing to the different group velocities of the two wavelengths, the mode-locked solitons centered at different wavelengths would periodically collide with each other. By using the dispersive Fourier transformation (DFT) technique, it was found that each collision would induce one soliton explosion, but none of them would be identical. Therefore, this phenomenon was termed as “periodic” soliton explosions. In addition, the dissipative rogue waves (DRWs) were detected in the dual-wavelength mode-locked state. The experimental results would be fruitful to the communities interested in soliton dynamics and dual-comb lasers.

Enhancement of Femtosecond Laser Induced Surface Ablation via Temporal Overlapping Double Pulses Irradiation

ZHENYUAN LIN, Lingfei Ji, and Minghui Hong

DOI: 10.1364/PRJ.379254 Received 30 Sep 2019; Accepted 14 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: This paper reports the physical phenomenon of the temporal overlapping double femtosecond laser induced ablation enhancement at different time delays. Detail thermodynamic modeling demonstrates the ablation enhancement is highly depended on the first pulse’s laser fluence. In the case of the first pulse laser fluence higher than material’s ablation threshold, the ablation enhancement is attributed to optical absorption modification by the first pulse ablation. While the first pulse laser fluence lower than the material’s ablation threshold, the first pulse induced melting leads to much higher absorption of the second pulse laser. However, for the case of the first pulse laser fluence even lower than melting threshold, the ablation enhancement decreases obviously with time delay. The results of the temporal overlapping double femtosecond laser ablation of poly(ε-caprolactone) (PCL) are in good agreement with the theory predict.

Super-resolution compressive spectral imaging via two-tone adaptive coding

Chang Xu, Ting Xu, Ge Yan, Xu Ma, Yuhan Zhang, Xi Wang, Feng Zhao, and Gonzalo Arce

DOI: 10.1364/PRJ.377665 Received 10 Sep 2019; Accepted 14 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: Coded apertures with random patterns are extensively used in compressive spectral imagers to sample the incident scene in the image plane. Random samplings, however, are inadequate to capture the structural characteristics of the underlying signal due to the sparse and structure nature of sensing matrices in spectral imagers. This paper proposes a new approach for super-resolution compressive spectral imaging via adaptive coding. In this method, coded apertures are optimally designed based on a two-tone adaptive compressive sensing (CS) framework to improve the reconstruction resolution and accuracy of the hyperspectral imager. A liquid crystal tunable filter (LCTF) is used to scan the incident scene in the spectral domain to successively select different spectral channels. The output of the LCTF is modulated by the adaptive coded apertures and then projected onto a low-resolution detector array. The coded apertures are implemented by a digital micromirror device (DMD) with higher resolution than that of the detector. Due to the strong correlation across the spectra, the recovered images from previous spectral channels can be used as a-priori information to design the adaptive coded apertures for sensing subsequent spectral channels. In particular, the coded apertures are constructed from the a-priori spectral images via a two-tone hard thresholding operation that respectively extracts the structural characteristics of bright and dark regions in the underlying scenes. Super-resolution image reconstruction within a spectral channel can be recovered from a few snapshots of low-resolution measurements. Since no additional side information of the spectral scene is needed, the proposed method does not increase the system complexity. Based on the mutual-coherence criterion, the proposed adaptive CS framework is proved theoretically to promote the sensing efficiency of the spectral images. Simulations and experiments are provided to demonstrate and assess the proposed adaptive coding method.

Subwavelength imaging and detection using adjustable and movable droplet microlenses

Xixi Chen, Tianli Wu, Zhiyong Gong, Yuchao Li, Yao Zhang, and Baojun Li

DOI: 10.1364/PRJ.377795 Received 19 Sep 2019; Accepted 14 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: We developed adjustable and movable droplet microlenses consisting of a liquid with a high refractive index. The microlenses were prepared via ultrasonic shaking in deionized water and the diameter of the microlenses ranged from 1 to 50 μm. By stretching the microlenses, the focal length can be adjusted from 13 to 25 μm. With the assistance of an optical tweezer, controllable assembly and movement of microlens arrays were also realized. The results showed that an imaging system combined with droplet microlenses provided a resolution of ~80 nm and an effective numerical aperture of 4.19 under white-light illumination. Using the droplet microlenses, fluorescence emission at 550 nm from CdSe@ZnS quantum dots were efficiently excited and collected. Moreover, Raman scattering signals from a silicon wafer were enhanced by ~19 times. The presented droplet microlenses may offer new opportunities for flexible liquid devices in subwavelength imaging and detection.

Laser Cooling Characterization of Yb-Doped ZBLAN Fiber as a Platform for Radiation-Balanced Lasers

Arash Mafi, Mostafa Peysokhan, Esmaeil mobini souchelmaei, Arman Allahverdi, and Behnam Abaie

DOI: 10.1364/PRJ.380615 Received 14 Oct 2019; Accepted 11 Dec 2019; Posted 13 Dec 2019  View: PDF

Abstract: Recent advances in power scaling of fiber lasers are hindered by the thermal issues, which deteriorate the beam quality. Anti-Stokes fluorescence cooling has been suggested as a viable method to balance the heat generated by the quantum defect and background absorption. Such radiation-balanced configurations rely on the availability of cooling-grade rare-earth-doped gain materials. Herein, we perform a series of tests on a ytterbium-doped ZBLAN optical fiber to extract its laser cooling-related parameters and show that it is a viable laser cooling medium for radiation-balancing. In particular, a detailed Laser Induced Modulation Spectrum (LITMoS) test is performed to highlight the transition of this fiber to the cooling regime as a function of the pump laser wavelength. Numerical simulations support the feasibility of a radiation-balanced laser, but highlight that practical radiation-balanced designs are more demanding on the fiber material properties, especially on the background absorption, than are solid-state laser cooling experiments.

Mid-infrared photonic crystal waveguides in yttrium aluminium garnet crystal fabricated by femtosecond-laser writing and phosphoric acid etching

Jin-Man Lv, BinBin Hong, Yang Tan, Feng Chen, Javier Vazquez de Aldana, and Guo Ping Wang

DOI: 10.1364/PRJ.380215 Received 14 Oct 2019; Accepted 10 Dec 2019; Posted 13 Dec 2019  View: PDF

Abstract: We demonstrate a method to fabricate a photonic-crystal structure in a single-crystal. At first, tracks with a periodic arrangement were written inside the yttrium aluminum garnet (YAG) crystal via femtosecond laser inscription. Then, the tracks were etched by the phosphoric acid (H3PO4) forming the hollow structures, similar to a photonic-crystal structure. The evolution of the microstructure of tracks was investigated in detail. The function of this photonic-crystal structure was analyzed by the transmission matrix method, the finite-difference beam propagation method and the plane wave expansion method which indicate the proposed photonic-crystal waveguide effectively operates in quasi-single-mode pattern in the mid-infrared wavelength range. Furthermore, the experimental results prove that the photonic crystal waveguide exhibit excellent guiding performance at a mid-infrared wavelength of 4 μm with low losses of ~0.5 dB/cm.

High energy all-fiber gain-switched thulium-doped fiber laser for volumetric photoacoustic imaging of lipids

Can Li, Jiawei Shi, Xiatian Wang, boquan wang, Xiaojing Gong, Liang Song, and Kenneth Kin-Yip Wong

DOI: 10.1364/PRJ.379882 Received 07 Oct 2019; Accepted 03 Dec 2019; Posted 04 Dec 2019  View: PDF

Abstract: We demonstrate a high-energy all-fiber short wavelength gain-switched thulium-doped fiber laser for volumetric photoacoustic (PA) imaging of lipids. The laser cavity is constructed by embedding a short piece of gain fiber between a pair of fiber Bragg grating (FBG). Through utilizing three pairs of FBG with operation wavelength at 1700 nm, 1725 nm and 1750 nm, respectively, three similar lasers are realized with a cavity length of around 25 cm. Under a maximum pump energy of 300 μJ at 1560 nm, laser pulse energies of 58.2 μJ, 66.8 μJ and 75.3 μJ are respectively achieved with a minimum pulse width of <16.7 ns at a repetition rate of 10 kHz. Volumetric imaging of lipids is validated through scanning a piece of fatty beef with a PAM system incorporated with the newly developed source, and a lateral resolution of 18.8 μm and an axial resolution of 172.9 μm are achieved. Moreover, the higher shooting speed of the developed source can potentially allow for increasing at twice the frame rate of current intravascular PA imaging.

Real-time, in-situ probing of Gamma radiation damage with packaged integrated photonic chips

Qingyang Du, Jerome Michon, Bingzhao Li, Derek Kita, Danhao Ma, Haijie Zuo, Shaoliang Yu, Tian Gu, Anuradha Agarwal, Mo Li, and Juejun Hu

DOI: 10.1364/PRJ.379019 Received 02 Oct 2019; Accepted 03 Dec 2019; Posted 04 Dec 2019  View: PDF

Abstract: Integrated photonics is poised to become a mainstream solution for high-speed data communications and sensing in harsh radiation environments such as outer space, high-energy physics (HEP) facilities, nuclear power plants, and test fusion reactors. Understanding the impact of radiation damage in optical materials and devices is thus a prerequisite to building radiation-hard photonic systems for these applications. In this paper, we report real-time, in-situ analysis of radiation damage in integrated photonic devices. The devices, integrated with an optical fiber array package and a baseline-correction temperature sensor, can be remotely interrogated while exposed to ionizing radiation over a long period without compromising their structural and optical integrity. We also introduce a method to deconvolve the radiation damage responses from different constituent materials in a device. The approach was implemented to quantify Gamma radiation damage and post-radiation relaxation behavior of SiO2-cladded SiC photonic devices. Our findings suggest that densification induced by Compton scattering displacement defects is the primary mechanism for the observed index change in SiC. Additionally, post-radiation relaxation in amorphous SiC does not restore the original pre-irradiated structural state of the material. Our results further point to the potential of realizing radiation-hard photonic device designs taking advantage of the opposite signs of radiation-induced index changes in SiC and SiO2.

Distributed curvature sensing based on bending loss resistant ring-core fiber

li shen, Hao Wu, Can Zhao, Lei Shen, Rui Zhang, Weijun Tong, Songnian Fu, and Ming Tang

DOI: 10.1364/PRJ.379178 Received 02 Oct 2019; Accepted 28 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: A theoretical and experimental study on curvature sensing using Brillouin optical time-domain analyzer (BOTDA) based on the ring-core fiber (RCF) is reported. Brillouin gain spectrum (BGS) of the RCF is investigated, and Brillouin frequency shift (BFS) dependence on temperature and strain is calibrated. We theoretically analyze the fiber bending induced BFS and peak Brillouin gain variation for the RCF through a numerical simulation method, and the RCF is revealed to have a high curvature sensitivity. Distributed curvature sensing is successfully demonstrated with the bending radius ranging from 0.5 cm to 1.5 cm, corresponding to BFS variation from 32.90 MHz to 7.81 MHz. The RCF takes the advantage of great bending loss resistance and the maximum macro-bending loss at the extreme bending radius of 0.5 cm is less than 0.01 dB/turn. Besides, the peak Brillouin gain of the RCF is discovered to vary significantly in response to fiber bending, which is expected to be another parameter for distributed curvature determination. The results imply that the RCF is a promising candidate for highly sensitive distributed curvature measurement, especially with sharp bending circumstances.

Strong mechanical squeezing in optomechanical system based on Lyapunov control

Biao Xiong, Xun Li, Shi-Lei Chao, Zhen Yang, Wen-Zhao Zhang, Weiping Zhang, and Ling Zhou

Doc ID: 373535 Received 24 Jul 2019; Accepted 26 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We propose a scheme to generate the strong squeezing of mechanical oscillator in an optomechanical system through Lyapunov control. A frequency modulation of mechanical oscillator is designed via Lyapunov control method. We show that the variance of the mechanical position decreases with time evolution, which results in the strong mechanical squeezing. What's more, the squeezing is largely immune to the thermal noise so that we can obtain squeezing beyond the 3-dB limit even at room temperature.

Thermometry strategy developed based on fluorescence contrast driven by varying excitations in codoped LiNbO₃

Siwei Long, Shaopeng Lin, Decai Ma, Yunzhong Zhu, Huashan Li, and Biao Wang

Doc ID: 373633 Received 26 Jul 2019; Accepted 26 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We proposed a novel optical thermometry strategy (FIR-Ex) based on the fluorescence intensity ratio (FIR) between two radiations associated with the same emission peak but different excitation wavelengths, in contrast to the traditional approach (FIR-Em) that depends on the FIR at varying emission wavelengths. The temperature dependent FIR within the FIR-Ex strategy arises from the different charge/energy evolution routes, rather than the distribution of thermally coupled levels within the FIR-Em strategy. Considerable diversity in thermal behaviors and luminescence mechanisms were demonstrated by analyzing the 618 nm red emission in Pr³+ doped congruent LiNbO₃ (Pr:CLN) under 360 nm and 463 nm excitations. The temperature sensitivity was further improved via Mg²+ codoping due to the optimization of charge dynamics and energy transfer processes. Given its wide detection scope, relatively high absolute sensitivity at low temperature, and high tunability of temperature sensitivity, the FIR-Ex strategy is promising for developing optical temperature sensing materials with high performance.

Microcrystals Modulated Exciton-Polariton Emissions from Single ZnO@ZnO:Ga Microwire

Mingming Jiang, Wangqi Mao, Jiaolong Ji, Peng Wan, Xiangbo Zhou, and Caixia Kan

Doc ID: 374101 Received 30 Jul 2019; Accepted 25 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: Due to the outstanding surface-to-volume ratio, highly smooth surface and well-defined crystal boundary, semiconducting micro/nanocrystals have been utilized as pivotal platform to fabricate multifunctional optoelectronic devices, such as super resolution imaging, solar concentrators, photodetectors, light-emitting diodes (LEDs), lasers, etc. Especially, the micro/nanocrystal being foreseen as the key elements can be employed to tailor the fundamental optical and electronic transport properties of the integrated hetero/homostructures. Herein, ZnO microcrystals decorated pre-synthesized Ga-doped ZnO microwire (ZnO@ZnO:Ga MW) was prepared. The single ZnO@ZnO:Ga MW can be utilized to construct optically pumped Fabry-Perot (F-P) mode microlasers, with the dominating lasing peaks centered in the violet spectral region. In particular, stabilized exciton-polariton emissions from single ZnO@ZnO:Ga MW based heterojunction diode can also be realized. The deposited ZnO microcrystals can facilitate the strong coupling of F-P optical modes with excitons, leading to the formation of exciton-polariton features in the ZnO@ZnO:Ga MW. Therefore, it can be anticipated that the waveguiding lighting behavior and energy-band alignment of ZnO microcrystals sheathed ZnO:Ga MW radial structures are extremely attractive for potential application that hammer at semiconducting microstructures based optoelectronic devices, such as micro-LEDs, laser microcavities, waveguides, photodetectors, etc.

Erbium-doped TeO2-coated Si3N4 waveguide amplifiers with 5 dB net gain

Henry Frankis, Hamidu M. Mbonde, Dawson Bonneville, Chenglin Zhang, Richard Mateman, Arne Leinse, and Jonathan Bradley

Doc ID: 379031 Received 27 Sep 2019; Accepted 25 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We demonstrate 5 dB net gain in an erbium-doped tellurium-oxide-coated silicon-nitride waveguide . The amplifier design leverages the high refractive index and high gain in erbium-doped tellurite glass and ultra-low losses and mature, reliable and low cost fabrication methods of silicon nitride waveguide technology. We show that the waveguide platform demonstrates low background propagation losses of 0.25 dB/cm based on a ring resonator device with a Q factor of 1.3×10⁶ at 1640 nm. We measure 5 dB peak net gain at 1558 nm and > 3 dB of net gain across the C-band in a 6.7-cm-long waveguide for 35 mW of launched 1480 nm pump power. Gain per unit length of 1.7 and 1.4 dB/cm is measured in a 2.2-cm-long waveguide for 980 and 1480 nm pump wavelengths, respectively. These results demonstrate a promising approach for the monolithic integration of compact erbium-doped waveguide amplifiers on silicon nitride chips and within silicon-based photonic integrated circuits.

Quantum Nonreciprocality in Quadratic Optomechanics

xun wei xu, Yanjun Zhao, Hui Wang, Hui Jing, and Aixi Chen

Doc ID: 371416 Received 02 Jul 2019; Accepted 25 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We propose to achieve nonreciprocal quantum control of photons in quadratic optomechanical (QOM) system based on directional nonlinear interactions. We show that by optically pumping the QOM system in one side, an effective QOM coupling can be enhanced significantly in that side, but not for the other side. This, contrary to the intuitive picture, allows the emergence of nonreciprocal photon blockade in such optomechanical devices with weak single-photon QOM coupling. Our proposal opens up the prospect of exploring and utilizing quantum nonreciprocal optomechanics, with applications ranging from single-photon nonreciprocal devices to on-chip chiral quantum engineering.

Broadband on-chip photonic spin Hall element via inverse design

Zhenwei Xie, Ting Lei, Haodong Qiu, Zecen Zhang, Hong Wang, and Xiaocong Yuan

Doc ID: 374260 Received 31 Jul 2019; Accepted 20 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: The photonic spin Hall effect plays an important role in photonic information technologies, especially in on-chip spin Hall devices. However, conventional devices suffer from low efficiency or narrow bandwidth, which prevents their practical application. Here, we introduce a spin Hall device using inverse design to achieve both high efficiency and broadband. Spin-dependent light separation is enabled by a 2.4-μm circular device with 100-nm pixels. The photonic spin Hall element is fabricated on silicon on an insulator wafer compatible with a standard integrated photonic circuit. The spin light is detected and emitted with an efficiency of up to 22% and 35%, respectively, over a 200-nm bandwidth at optical wavelength. The inversely designed spin Hall device will greatly benefit optical computing, optical sensing, optical communications, and other ultrafast or broadband photonic spin-related applications.

Revealing the Underlying Mechanisms Behind TE Extraordinary THz Transmission

Suzanna Freer, Miguel Camacho, Sergei Kuznetsov, Rafael R. Boix, Miguel Beruete, and Miguel Navarro-Cia

Doc ID: 373664 Received 25 Jul 2019; Accepted 09 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Transmission through seemingly opaque surfaces, so-called extraordinary transmission, provides an exciting platform for strong light-matter interaction, spectroscopy, optical trapping and colour filtering. Much of the effort has been devoted to understanding and exploiting TM extraordinary transmission, while TE anomalous extraordinary transmission has been largely omitted in the literature. This is regrettable from a practical point of view since the stronger dependence of the TE anomalous extraordinary transmission on the array’s substrate provides additional design parameters for exploitation. To provide high-performance and cost-effective applications based on TE anomalous extraordinary transmission, a complete physical insight on the underlying mechanisms of the phenomenon must be first laid down. To this end, resorting to a combined methodology including quasi-optical Terahertz (THz) time-domain measurements, full-wave simulations and Method of Moments analysis, subwavelength slit arrays under s-polarized illumination are studied here, filling the void in the literature. This work reveals unequivocally the leaky-wave role of the grounded-dielectric slab mode mediating in the TE anomalous extraordinary transmission and provides the necessary frame to design practical high-performance THz components and systems.

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