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Molecular strong-field approximation for photodetachment of electrons from homonuclear diatomic molecular anions

Dejan Milosevic, Azra Gazibegovic-Busuladzic, Dino Habibovic, and Mustafa Busuladzic

DOI: 10.1364/JOSAB.383916 Received 25 Nov 2019; Accepted 17 Jan 2020; Posted 17 Jan 2020  View: PDF

Abstract: Molecular strong-field approximation is applied to above-threshold detachment of homonuclear diatomic molecular negative ions.Differences between the photodetachment amplitudes for neutral diatomic molecules and diatomic anions, both for direct and rescattered electrons, are examined. Numerical results for the photoelectron spectra of C$_{2}^{-}$ molecular anion for different intensities and wavelengths of a linearly polarized laser field and different molecular anion orientations are shown and discussed. Two-center destructive interference minima (suppression regions) in the rescattering part of the photoelectron spectra are observed. For molecules with molecular orientation defined by the angle $\theta_L$ with respect to the laser-field polarization axis, these minima manifest as two parallel straight lines in the distribution of the photoelectron yield presented in the photoelectron momentum plane. These lines make the angle $90^\circ -\theta_L$ with the momentum component parallel to the laser-field polarization axis. Focal-averaged photoelectron spectra are also presented and analyzed.

Universal DV-CV interaction mechanism for deterministic generation of entangled hybridity

Sergey Podoshvedov and Mikhail Podoshvedov

DOI: 10.1364/JOSAB.380268 Received 11 Oct 2019; Accepted 16 Jan 2020; Posted 17 Jan 2020  View: PDF

Abstract: We propose a general approach for the implementation of the hybrid entangled states consisting of continuous variable (CV) and discrete variable (DV) states. Peculiarities of DV-CV interaction mechanism on the beam splitter with arbitrary parameters is key for the for the birth of the entangled hybridity provided that some measurement event is registered in auxiliary mode. We show that the CV states forming output entangled state can consist exclusively of either even or odd Fock states. Various input CV states including Schrodinger cat state (SCSs) are used at the input of the beam splitter where they mix with delocalized single photon. We show the hybrid entanglement generation is observed at any values of the experimental parameters used. Degree of the hybrid entanglement is evaluated. Conditions for generating the maximally entangled hybridity are established.

Transmission Characteristics of Double Fiber Ring with Fiber Bragg Grating

Biswajit Ghosh and SANJOY MANDAL

DOI: 10.1364/JOSAB.383167 Received 14 Nov 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: The Z domain model of double fiber ring (DR) with a uniform fiber Bragg grating (FBG) incorporated using two optical couplers and a DRFBG configuration using three optical couplers is developed. The developed mathematical model is used to determine the transmission response. The performance of double ring with FBG using two optical couplers is compared with previously measured results and is found to be in very close agreement. A similar DRFBG structure with three optical couplers is proposed. By proper optimization of FBG reflectivity and power coupling ratios, a narrow FWHM (Full width at half maximum) with virtually zero crosstalk is achieved. Compared with the double ring configuration using two optical couplers, the proposed structure yields a higher finesse giving much better spectral selectivity. The performance of the proposed structure as strain sensor is investigated using the delay line signal processing technique in Z domain. The detection resolution of strain variation is much enhanced.

Anisotropic two-photon absorbers measured by the Z-scan technique and its application in laser beam shaping

Gu Bing, Yueqiu Hu, Bo Wen, Changgui Lu, Guanghao Rui, jun He, and Yiping Cui

DOI: 10.1364/JOSAB.383899 Received 25 Nov 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: We investigate anisotropic two-photon absorption (TPA) effects excited by both scalar and vectorial optical fields. Firstly, we present the anisotropic TPA coeffi-cient, which depends on the anisotropy coefficient, the dichroism coefficient, the crystal orientation angle, as well as the ellipticity of the polarized ellipse. Secondly, we develop the elliptically polarized light Z-scan technique for characterizing ani-sotropic two-photon absorbers, which is demonstrated experimentally. Lastly, we present the laser beam shaping of vectorial optical fields with Gaussian intensity distribution into flat-top profile through anisotropic TPA effects. It is shown that the anisotropic TPA offers a new avenue to manipulate the intensity distribution of the polarization-structured light field, which may find interesting applications in beam shaping, optical limiting, and photodetection.

Enhanced second-harmonic generation from L-shaped AlGaAs nanoantennas

Tao Zeng, Ling Guo, Long Xu, and Tiancheng Han

DOI: 10.1364/JOSAB.356071 Received 23 Oct 2019; Accepted 15 Jan 2020; Posted 17 Jan 2020  View: PDF

Abstract: Nanostructured materials offer many advantages over bulk materials in nonlinear optical phenomena. For example, the subwavelength scale allows the neglect of phase matching issues. Also, the ability to control tight confinement and large resonant enhancement of electromagnetic fields results in higher nonlinear frequency conversion efficiencies than bulk materials. Compared with plasmonic nanostructures, high-index dielectric nanoparticles render larger mode volumes and show great promise for enhanced nonlinear optical processes. In this work, we present resonantly enhanced second-harmonic generation (SHG) from L-shaped AlGaAs nanoantennas. By tuning the nanostructure thickness, arm length and width, the overlap of resonances at fundamental and second harmonic wavelength can be realized with any pump wavelength in a broad near-infrared spectral region. We predict SHG efficiency exceeding 4 × 10-3 with pump intensity of 1 GW/cm2 at two representative pump wavelengths of 1675 nm and 1800 nm. Our findings are valuable in the applications involving all-dielectric nanoantennas, such as efficient sensing and single biomolecule tracking microscopy.

Research on photonic crystal fiber based on surface plasmon resonance sensor with segmented silver-Titanium dioxide film

Hairui fang, Chenjing Wei, Dong Wang, Long Yuan, Jiao Shengxi, Zhiyu Bao, and Han-Rui Yang

DOI: 10.1364/JOSAB.373395 Received 26 Jul 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: A photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) sensor coated with segmented silver-Titanium dioxide (Ag-TiO₂) film is proposed for microfluid refractive index sensing. The sensing properties of the designed sensor are analyzed numerically by full-vectorial finite element method (FEM). The results display that the wavelength sensitivity can be tuned by the thickness of the TiO₂ film and segmented number and angle of Ag-TiO₂ film. It is observed that an average sensitivity of 6329 nm/RIU for the refractive index range from 1.330 to 1.360 and a maximum wavelength sensitivity of 10600 nm/RIU with a high resolution of 9.43×10¯⁶ RIU can be achieved in the sensing range from 1.350 to 1.355. In addition, it also shows a maximum amplitude sensitivity of 763.2262 RIU¯¹, which can be applied to the field of chemical and biological analysis.

Phase modulation of multiple optomechanically induced transparency in an optomechanical system with multiple mechanical resonators

Ying-Jian Zhu, Cheng-Hua Bai, Tie Wang, Dong-Yang Wang, Shou Zhang, and Hong-Fu Wang

DOI: 10.1364/JOSAB.378791 Received 24 Sep 2019; Accepted 15 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: We investigate the change of width of transparency windows and the amplification of the probe output spectrum in an optomechanical system with multiple mechanical resonators. Via exhibiting the probe output spectrum of the system, we find that the number of transparency windows is explicitly decided by the number of mechanical resonators with different frequencies. Meanwhile, we discuss the effect of cavity decay rate on the width of the transparency windows. Moreover, we also investigate the absorption and amplification phenomena under different detuning parameters and the amplification phenomenon of the probe output spectrum can be observed via properly choosing the phase of the pump field. These interesting phenomena can also be exploited to investigate the optical switch and frequency comb generation.

Nonlinear self-channeling of high-power lasers through controlled atmospheric turbulence

Gregory DiComo, Michael Helle, Dmitri Kaganovich, Andreas Schmitt-Sody, Jennifer Elle, and Joseph Penano

DOI: 10.1364/JOSAB.384137 Received 28 Nov 2019; Accepted 14 Jan 2020; Posted 16 Jan 2020  View: PDF

Abstract: High-power laser beams are demonstrated to resist the spreading effects of atmospheric turbulence over a 180 meter-long path. This “nonlinear self-channeling” behavior occurs when nonlinear self-focusing balances diffraction, maintaining the beam radius at a size smaller than the inner scale or coherence radius of turbulence, over the length of propagation. Nonlinear self-channeling is shown to persist into the strong turbulence regime. However, the turbulence-induced increase in beam wander remains unchanged.

Terahertz pulse induced femtosecond optical second harmonic generation in transparent media with cubic nonlinearity

Sergey Bodrov, Yuri Sergeev, Alexey Korytin, Ekaterina Burova, and Andrey Stepanov

DOI: 10.1364/JOSAB.384841 Received 02 Dec 2019; Accepted 13 Jan 2020; Posted 13 Jan 2020  View: PDF

Abstract: Second harmonic (SH) generation of femtosecond laser radiation induced by a short terahertz pulse in a layer of isotropic medium with cubic nonlinearity was investigated. A comprehensive 1D theory of SH field dynamics with allowance for different propagation velocities of interacting terahertz, fundamental and SH pulses was developed. In particular, it was shown that for media with a coherent length of the fundamental and second optical harmonics smaller than the walk-off length of the fundamental optical and THz pulses, a SH radiation signal is generated only when the fundamental optical and terahertz pulses overlap near the entrance and exit surfaces of the nonlinear layer rather than when the pulses are superimposed in the bulk. The prediction was verified experimentally by using a 3-mm thick fused quartz. Good agreement between the theory and the experiment was demonstrated.

Spacing-Dependent Electromagnetically Induced Transparency with two nuclear ensembles inside an x-ray planar cavity

Xinchao Huang, Lin-Fan Zhu, Xinchao Huang, Wenbin LI, and Xiang-Jin Kong

DOI: 10.1364/JOSAB.377328 Received 05 Sep 2019; Accepted 12 Jan 2020; Posted 13 Jan 2020  View: PDF

Abstract: The x-ray planar cavity-two nuclear ensembles system with flexible configurations are studied theoretically. A concise transfer matrix method is developed to solve the system analytically, and the changing of spacing between the two nuclear ensembles is reflected as the phase changing of the propagation matrices. A periodic characteristic as a function of the spacing is observed, and the system shows an electromagnetically induced transparency (EIT)-like effect when the first ⁵⁷Fe layer locates at node position, while the EIT-like effect is completely suppressed when the first ⁵⁷Fe layer locates at antinode. It indicates that the phase difference be-tween the two nuclear ensembles plays a key role for the coupling field. This kind of phase manipulation will rich the approaches of quantum control in x-ray regime.

Quantum teleportation with hybrid entangled resources prepared from heralded quantum states

Karina Garay-Palmett, Fernando Rojas, and Francisco Dominguez Serna

DOI: 10.1364/JOSAB.377687 Received 11 Sep 2019; Accepted 09 Jan 2020; Posted 10 Jan 2020  View: PDF

Abstract: In this work we propose the generation of a hybrid entangled resource (HER) and its further application in a quantum teleportation scheme from an experimentally feasible point of view. The source for HER preparation is based on the four wave mixing process in a photonic crystal fiber, from which one party of its output bipartite state is used to herald a single photon or a single photon added coherent state. From the heralded state and linear optics the HER is created. In the proposed teleportation protocol Bob uses the HER to teleport qubits with different spectral properties. Bob makes a Bell measurement in the single photon basis and characterizes the scheme with its average quantum teleportation fidelity. Fidelities close to one are obtained for qubits in a wide spectral range. The work also includes a discussion about the fidelity dependence on the geometrical properties of the medium through which the HER is generated. An important remark is that no spectral filtering is employed in the heralding process, which emphasizes the feasibility of this scheme without compromising photon flux.

Enhanced responsivity of co-hyperdoped silicon photodetectors fabricated by femtosecond laser irradiation in mixed SF₆/NF₃ atmosphere

Shengxiang Ma, Liu Xiaolong, Sun Haibin, Zhao Yang, Hu Yue, Xi-Jing Ning, Li Zhao, and Jun Zhuang

DOI: 10.1364/JOSAB.374044 Received 06 Aug 2019; Accepted 09 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: Co-hyperdoped silicon is fabricated on single crystalline Si substrate by using femtosecond-laser pulses in a mixed gas of SF₆ and NF₃ with different ratios. With the increase of the proportion of NF3 in the mixed gas, the co-hyperdoped silicon shows increased crystallinity but decreased sub-bandgap absorption. Photodetectors are fabricated based on these samples without high-temperature thermal annealing. With the increase of the proportion of NF3, the photoelectric response firstly increases then decreases. Photodetectors based on the co-hyperdoped (NF₃/SF₆, 35/35 kPa) material without high-temperature thermal annealing demonstrate high performances on photoresponsivity (6 A∙W-1@−5 V for 1050 nm) which is an order of magnitude higher compared with the photodetector made from S-hyperdoped silicon. Moreover, the device could response to 1310 nm light with a photoresponsivity of 2 mA∙W−1.

Continuous-Variable Quantum Key Distribution Based on Faster-Than-Nyquist Scheme

Duan Huang, Yaxi Pan, Ling Zhang, and Ying Guo

DOI: 10.1364/JOSAB.381689 Received 01 Nov 2019; Accepted 08 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: In previous continuous-variable quantum key distribution (CV-QKD) systems, the transmission rate is limited by Nyquist criterion. Since the data symbols transmit without inter symbol interference (ISI) under this limitation, how to improve the secret key rate is still a notoriously hard problem. Faster-than-Nyquist (FTN) technology has been viewed as a potential technique in future communication systems because of its higher spectrum efficiency and faster symbol rate. In this paper, a CV-QKD system based on FTN is proposed. The transmission of FTN system is simulated, then we analyze the Mazo limit and the constrained capacities of the system, and finally compare the secret key rate of FTN signals and Nyquist signals. Our proposed scheme is especially beneficial for the high-speed scenario. Simulation results demonstrate such a CV-QKD system can increase channel capacity, and enhance key rate, it can also improve the safe transmission distance of CV-QKD.

Strong magnetic field enhancement and magnetic Purcell effect in dielectric disk-ring composite nanocavity

Yang Yang, bofeng zhu, and Haitao Dai

DOI: 10.1364/JOSAB.382711 Received 11 Nov 2019; Accepted 08 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: All-dielectric nanocavity with low dissipative absorption brings new opportunities for efficiently enhancing and confining the optical magnetic field. Recently, high-index dielectric nanodisk with internal magnetic dipole (MD) mode has become prominent forefront candidate in accelerating spontaneous decay of MD transitions in quantum emitters (known as magnetic Purcell effect). In this paper, we numerically investigate a dielectric disk-ring composite nanocavity, which is capable of achieving one order of magnitude stronger enhancement of magnetic field than a single disk. Multipole decomposition analysis further reveals the ultra-high enhancement is attributed to the huge MD radiation originating from the near-field (radiative) coupling between MD mode and electric quadrupole (magnetic octupole). More importantly, numerical result also indicates such composite nanocavity supports stronger Purcell effect than a single disk under the excitation of an MD emitter, which can be verified by theoretical calculations. Further simulation demonstrates the better tolerance of composite nanocavity on larger hole dimension, thereby reducing the experimental difficulties in both structure fabrication and emitter loading. Besides, the magnetic local density of states is also calculated through a theoretical approach. This presented design could open a promising avenue beyond the individual disk cavity for light−matter interactions in magneto-optical domain.

Enhanced extinction ratios of metasurface polarizers by surface-plasmon interference

Hiroyuki Kurosawa and Shin-ichiro Inoue

DOI: 10.1364/JOSAB.382875 Received 12 Nov 2019; Accepted 08 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: A numerical study demonstrates that an ultra-high extinction ratio of ≥ 3 × 10^9 is possible in a metasurface polarizer. The metasurface has stacked complementary structures with an air-hole array. From Babinet’s principle, this kind of metasurface is known to have a high extinction ratio exceeding 10^4. In this paper, numerical calculations reveal that Babinet’sprinciple incorporating destructive interference between localized and propagating surface plasmon polariton resonances is key in the enormous enhancements in the extinction ratio. Moreover, this study shows that an asymmetry in the complementary structures plays a crucial role in the fine-adjustments of the interference. As a result, an extremely low transmittanceis realized, leading to an ultrahigh extinction ratio of ≥ 3 × 10^9 in the O-band. An analytical study confirms that the low transmittance associated with ultra-high extinction ratios originates from the destructive interference. Such ultra-high performances are wavelength-tunable by a simple scaling of the metasurface and a fine adjustment of the interference. In the C-band, theultra-high extinction ratio exceeds 200 × 10^9. This study reveals the numerical and theoretical design criteria for ultra-high extinction ratios in metasurface polarizers.

Cascaded nonlinearities in high power femtosecond optical parametric oscillator.

Ignas Stasevicius, Giedrius Martynaitis, and Mikas Vengris

DOI: 10.1364/JOSAB.383595 Received 18 Nov 2019; Accepted 08 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: Femtosecond optical parametric oscillator (OPO) pumped by second harmonic of Yb: KGW solid state oscillator was investigated. Comparison between LBO and BBO crystals was carried out with particular attention to the impact of phase mismatch on pulse characteristics. The phase mismatch induces cascaded nonlinearity which acts as effective nonlinear refractive index. Negative group delay dispersion (GDD) of the resonator and effective nonlinear refractive index allows soliton formation with varying pulse durations. Z-scan experiment was used to determine nonlinear refractive indices under conditions identical to those in the oscillator cavity. Unexpectedly, the signs of nonlinear refraction as measured by Z-scan and indirectly observed in optical parametric oscillator proved to be opposite. This sign reversal could be interpreted in terms of the competing cascaded nonlinearities corresponding to self-phase modulation and cross-phase modulation between the signal and the pump pulses in the nonlinear OPO crystal.

Berry-phase-based quantum gates assisted by transitionless quantum driving

Shifan Qi and Jing Jun

DOI: 10.1364/JOSAB.381706 Received 31 Oct 2019; Accepted 07 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: We propose a novel proposal for geometric quantum gates using three- or two-level systems, in which a controllable variable, the detuning between the driving frequency and the atomic energy spacing, is introduced to realize geometric transformations. In particular, we can have two instantaneous eigenstates with opposite eigenvalues constituting a closed loop in the parameter space. The accumulated dynamical phase is then exactly cancelled when the loop is completed, which is beyond the traditional parallel-transport restriction. We apply the transitionless quantum driving method to enhance the speed and the fidelity of geometric gates. Gate fidelity under decoherence is also estimated.

Metamaterial nonlinear and polarization-dependent bi-frequency THz switch

Nahid Sharifi and Nosrat Granpayeh

DOI: 10.1364/JOSAB.380364 Received 16 Oct 2019; Accepted 07 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: In this work, we propose a novel metamaterial structure with two concentric split ring resonators. The splits are filled by photoconductive Si. So, by illuminating the structure by an oblique optical pump with wavelength of 800 nm, in addition to the normal THz signal wave, excites the structure by variation of the Si conductivity. Also, by changing in the direction of the incident TE wave by ${{90}^{\circ }}$, the transmission frequency will be changed. Therefore, the structure operates as a switch at two switching windows at two normal polarization. The response time of the photoconductive switch is less than 3 ps. The substrate was replaced by a more cost effective and flexible material, polyimide, to achieve even more exciting results in broadening the switching windows. Also, the response time of this switch is less than 1 ps. At last, for verification of the simulation results, a circuit model of photoconductive switch was proposed, the results of switch comply very well with the simulation results. The proposed switch can be used in fast optical systems and networks.

A composite nanostructured design for dynamic control of metasurface holograms

Juan Liu, Shiqi Jia, Ata Ur Rahman Khalid, and Dapu Pi

DOI: 10.1364/JOSAB.381642 Received 28 Oct 2019; Accepted 07 Jan 2020; Posted 09 Jan 2020  View: PDF

Abstract: Metasurface holograms that can be dynamically controlled have attracted wide attention and been realized in many ways. In particular, the phase change materials (PCMs) that can be switched into amorphous and crystalline states at high speed by external thermal stimulation is one of the most promising candidates to break the limitations of material properties and fixed structures. Here, we propose a metasurface hologram which aims to realize a dual display that can reconstruct different images by annealing thermal stimulation. The designed metasurface incorporates alternated chalcogenide PCMs cubes and sector columns which possess uniform amplitude and full 2π phase coverage. Simplicity and compactness make this metadevices easily be integrated into various devices such as memory storage, augmented reality, anti-counterfeiting, and so on.

Broadband graphene/hBN modulators based on Si3N4 waveguide

Xiaoying He, Jiale Su, and chong li

DOI: 10.1364/JOSAB.382091 Received 31 Oct 2019; Accepted 07 Jan 2020; Posted 07 Jan 2020  View: PDF

Abstract: For exploring a strong electro-optic effect from graphene/hBN structure, here a comprehensive study for investigating the integrated broadband graphene/hBN modulators had been presented. Two representative configurations with Si3N4 waveguide had been compared, focusing on optimizing the hBN thickness, waveguide width and height, and graphene size to balance their performances. It was found that 200-μm long devices with 65-nm hBN thickness allow for ~ 80 GHz modulation bandwidth, 35.4 dB extinction ratio and over 700 nm operation spectral range. Compared to the ridge Si3N4 waveguide, the buried Si3N4 waveguide was more suitable as optical waveguide for graphene/hBN modulator to obtain large modulation depth of ~0.17 dB/μm and large operation spectral range from 750 to ~ 1640 nm.

Mechanical driving mediated slow light in quadratically coupled optomechanical systems

Cheng Jiang, Yongchao Zhang, Kexun Yan, Zhangyin Zhai, Xintian Bian, Zuo Fen, and Hualing Yu

DOI: 10.1364/JOSAB.383220 Received 14 Nov 2019; Accepted 06 Jan 2020; Posted 07 Jan 2020  View: PDF

Abstract: We theoretically study the controllable optical response in an optomechanical system with membrane-in-the-middle geometry, where the cavity mode is coupled to the square of the position of the membrane. When the optical cavity is driven by a strong control field and the movable membrane is excited by a weak coherent mechanical driving field, the optical response of the system can be detected by applying a weak probe field to the optical cavity. Due to the additional mechanical driving field, more complex interference exists in this optomechanical system. Under the two-phonon resonance condition, the probe transmission can be larger than unity or suppressed to be zero because of the interference effect, which is dependent on the phase difference of the applied fields. We show that the transmission coefficient and group delay of the probe field can be controlled flexibly by the power of the control field, the amplitude and phase of the mechanical driving field, and the environment temperature. Our results provide a flexible route to control the light propagation based on the quadratically coupled optomechanical system.

Fiber motion-insensitive fiber-based polarization-sensitive optical coherence tomography for optic axis determination

Zenghai Lu and Cheng Liu

DOI: 10.1364/JOSAB.376808 Received 03 Sep 2019; Accepted 05 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: Polarization-sensitive optical coherence tomography (PS-OCT) is widely used to image fibrous biological tissues providing additional image contrast compared to intensity-based OCT including birefringence and optic axis orientation information. Here a theoretical and experimental analysis of the effect of the system fiber on determination of optic axis orientation using a previously reported algorithm based on the angle between Stokes vectors on the Poincaré sphere in fiber-based PS-OCT experimentally confirms that the algorithm only works correctly when the parameters of the system fiber are kept constant during the imaging acquisition of each frame. To extend the use of the algorithm to situations in which the parameters of the system fiber are varied among A-scans/image frames, which is true when the OCT probe scanning does move the sample arm fiber, we propose the use of polarization maintaining fiber (PMF) with a special polarization axis orientation as the sample arm fiber for extracting optic axis orientation using fiber-based PS-OCT systems. The use of the PMF makes the system insensitive to variations of the sample fiber birefringence for determining optic axis orientation by automatically removing the offset ambiguity from each A-scan. we demonstrated that the proposed method is capable of extracting the relative optic axis orientation correctly when the PMF birefringence is varied among A-scans due to external disturbances to the system fibers, provided that the polarization axis orientation (slow or fast) of the PMF is kept constant (or a recommended orientation variation of <2°) during the measurement.

Abnormal evolution dynamics of erupting solitons in dissipative systems

Xianqiong Zhong, Jiameng XU, Bo Wu, and Ke Cheng

DOI: 10.1364/JOSAB.378534 Received 23 Sep 2019; Accepted 04 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: Evolutions of initial finite energy Airy pulse pairs with different initial relative phases and time separations are numerically investigated in the erupting soliton parameter region of the cubic-quintic complex Ginzberg-Laudau equation governed dissipative system. It shows that, before evolving to the final erupting solitons, all of the Airy pulse pairs will experience a special soliton dynamics called erupting soliton molecules which consist of two or more branches of erupting solitons. Moreover, the number and structures of the sub-erupting solitons vary with different initial relative phases and time separations. Before forming the finally single erupting solitons, these sub-erupting solitons may merge for one moment and separate for the next. The merging or separating position as well as the erupting positions of every sub-erupting solitons may vary with the propagation distance. The evolution dynamics of the final erupting solitons also vary with different initial relative phases and time separations.

Tunable optical bistability in multi-mode optomechanical system

Zhen Wang, Cheng Jiang, Yong He, Chang-Ying Wang, and Heng-Mei Li

DOI: 10.1364/JOSAB.380207 Received 15 Oct 2019; Accepted 04 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: The optical bistability have been studied theoretically in a multi-mode optomechanical system with two mechanical oscillators independently coupled to two coupled cavities respectively. It is found that the multi-mode optomechanical system allows one to control the optical bistability in a much more flexible way. Specifically, the bistable behavior of the mean intracavity photon number in one cavity can be tuned by the strength and frequency of the pump laser beam driving another cavity. And meanwhile, it is also found that the coupling between the two cavities and the coupling between mechanical oscillators and cavities can effectively affect the optical bistability behavior in a sensitive manner. Moreover, the mechanical steady-state position exhibit clear bistability in the situation of relative lower phonon number, and it exhibit more controllability as well. The investigation on optical bistability in multi-mode optomechanical system shall have promising applications in optical quantum computing and quantum information processing.

Planar optical glass-slide based DMA sensor with cresol red /TiO2 composite thin film

Nuerguli Kari, Lili Wang, patima nizamidin, Shawket Abliz, and Abliz Yimit

DOI: 10.1364/JOSAB.382710 Received 08 Nov 2019; Accepted 03 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: Cute dimethylamine (DMA) sensor was fabricated with cresol-red (CR) and titanium dioxide (TiO2) composite thin film as guiding layer coated on the surface of tin diffused planar glass slide. UV-Vis spectrum before and after analyte exposure, light-guided optical detections at room temperature were investigated. Experimental results show that this sensing system was not only fast-to-response (6 seconds), also rapid-to-recover within recovery time 21 seconds (0.004 mg/m3). Besides, detection is available for DMA solution as low concentration as 0.0008 mg/m3 reversibly with signal to noise ratio (S/N) 5.29, being stable for one month at ambient temperature.

A carbon-based molecular spin-photovoltaic device

Sara Zamani and Rouhollah Farghadan

DOI: 10.1364/JOSAB.375695 Received 19 Aug 2019; Accepted 03 Jan 2020; Posted 06 Jan 2020  View: PDF

Abstract: We generate a spin-polarized current in hexagonal zigzag graphene nanoflake (hZGNF) with integrating the photovoltaic and spin-dependent transport effects. We consider three different hZGNF configurations and simulate their spin-photovoltaic properties using two probe model, in the presence of ferromagnetic contacts as well as the magnetization of zigzag edges. Our results reveal acceptable spin-dependent quantum efficiency, full optical spin polarization and also good optically induced magnetoresistance up to 900% which can be modified by adjusting the photon energy and under the variation of configuration and also introducing monovacancy. Interestingly, switching the magnetization of ferromagnetic contacts can approximately invert the spin characteristic of the photocurrent, and so the sign of optical spin polarization. Our findings may be provided an efficient way to enhance radiation-induced magnetoresistance in carbon-based molecular junctions.

Laser frequency locking with subnatural linewidth spectroscopy

Guo-qing Yang, xu-xing geng, qi yu, shang-qing liang, Yifu Zhu, guang-ming huang, and Gaoxiang Li

DOI: 10.1364/JOSAB.380337 Received 14 Oct 2019; Accepted 02 Jan 2020; Posted 03 Jan 2020  View: PDF

Abstract: We demonstrate a simple technique to lock the frequency of a laser to an atomic transition with a new technique of the subnatural linewidth spectroscopy. The coupled rubidium system exhibits an enhanced absorption spectrum of the probe beam with a subnatural linewidth. Comparing with other techniques with an additional laser, our scheme only utilizes a single laser which will be locked. The observed spectroscopic linewidth is down to about 3.5 MHz. The laser frequency fluctuation is about 226 kHz after locking on. The demonstrated scheme offers a convenient and low-cost technique for laser frequency stabilization and related precision measurements.

Heralded universal quantum computing on electron spins in diamond nitrogen-vacancy centers assisted by low-Q microtoroidal resonators

Ming Li, Xin Wang, Jia-Ying Lin, and Mei Zhang

DOI: 10.1364/JOSAB.376940 Received 03 Sep 2019; Accepted 31 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: Heralded universal quantum gates can largely decrease the quantum resource consumed in the integration of a multi-qubit quantum circut. Here we present a scheme for heralded universal quantum computing, including the constuction of the CNOT gate, the Toffoli gate, and the Fredkin gate on the electron spins in diamond nitrogen-vacancy (NV) centers assisted by low-Q microtoroidal resonators. These quantum gates can achieve unity fidelity as the infidelity induced by the imperfect nonlinear interaction is transferred into the photon loss. The clicks on different single-photon detectors can either herald the success of the quantum gates or instruct an immediate recycling procedure even without reinitializing the NV centers. Besides the heralding, this scheme is also more realistic observing that the non-monochromatic auxiliary photon and the inhomogeneous NV centers have no adverse impact on the performance. The high fidelity and efficiency with experimental parameters show that the scheme is feasible with current technology.

Frequency and time-domain analyses of multiple reflections and interference phenomena in a metamaterial absorber

Nilotpal -, Aman -, Somak Bhattacharyya, and P. Chakrabarti

DOI: 10.1364/JOSAB.381191 Received 23 Oct 2019; Accepted 30 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: The theory of absorption of infrared radiation based on the formation of antiparallel surface current in a metamaterial absorber appears to be invalid when the thickness of the dielectric material in the structure is increased by an integral multiple of a half-wavelength. The absorption characteristics repeat itself with an increase of each integral multiple of a half-wavelength, despite the fact that the surface current components for an odd value of integers are parallel to each other. This contradicts the theory of absorption based on the formation of antiparallel surface current. The reason for this uncertainty in surface current has been well explored in this paper, wherein we demonstrate theoretically the principle of absorption in a metamaterial structure based on the principle of multiple reflection and interference model. For the validation of occurrence of multiple reflection phenomenon involved in the absorption, time-domain analysis of metamaterial absorber under normal as well as oblique incidence have been simultaneously analyzed. The time of occurrence of each reflection obtained numerically using inverse chirp-Z transform is found to be in good agreement with the results obtained analytically.

Plasmonic enhanced microcrystalline silicon solar cells

Uttam Kumawat, Kamal Kumar, Sumakesh Mishra, and Anuj Dhawan

DOI: 10.1364/JOSAB.378946 Received 02 Oct 2019; Accepted 29 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: This paper describes the enhanced performance of the microcrystalline silicon (μc-Si) thin-film solar cells due to the incorporation of plasmonic nanostructures. Finite-Difference Time Domain (FDTD) numerical modeling is used to calculate the optical properties of the solar cells such as the absorption and the short circuit current density (Jsc). In this paper, two dimensional (2D) periodic arrays of various geometries of plasmonic nanostructures such as nano-rings, nano-discs, nano-hemispheres, nano-cubes are employed at the back side of the solar cells to increase the absorption for the longer wavelengths of the incident light, where most of the photons remain unharvested due to extremely low absorption coefficients of μc-Si material. These plasmonic nanostructures are compared in terms of the solar cell performance and it is found that the 2D periodic arrays of nano-rings show significant absorption enhancement at multiple wavelengths, thereby leading a substantial enhancement in the Jsc. An enhancement of 35% in the Jsc is obtained when a 2D periodic arrays of plasmonic nano-rings is present at the back side of the solar cell, which is higher than that of the μc-Si solar cells having arrays of plasmonic nanostructures of other geometries (i.e. nano-discs, nano-cubes, nano-hemispheres). It is observed that the enhancement in the absorption is attributed to the enhanced electromagnetic fields in the active layer due to several localized surface plasmon (LSP) modes that are excited in the plasmonic nanostructures at different wavelengths. Moreover, the effect of the thickness of the spacer layer (the layer between metal back-reflector and plasmonic nanostructure arrays) on the performance of different plasmonic solar cells is examined.

Picosecond synchronously-pumped optical parametric oscillator based on chirped quasi-phase matching

Guillaume Walter, Delphine Descloux, Jean-Baptiste Dherbecourt, Jean-Michel Melkonian, Myriam Raybaut, Cyril Drag, and Antoine Godard

DOI: 10.1364/JOSAB.380605 Received 15 Oct 2019; Accepted 28 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: We investigate and model a picosecond synchronously pumped optical parametric oscillator (OPO) based on an aperiodically poled lithium niobate (APPLN) nonlinear crystal with a chirped quasi-phase-matching (QPM) grating. We observe remarkable spectral features with an asymmetric OPO spectrum consisting of a main peak with lower side-lobes. Depending on the sign of the QPM chirp rate, the side-lobes are located either on the red or on the blue side of the main peak. Meanwhile, side-bands develop in the depleted pump spectrum. We attribute these features to cascaded sum-/difference-frequency generation processes which are quasi-phase matched at different positions in the APPLN crystal. A terahertz-generation cascading effect is also observed and characterized at high pump power.

Gap solitons in PT-symmetric lattices with fractional-order diffraction

Lei Li, Huagang Li, Wen Ruan, Feng-Chun Leng, and xiaobing luo

DOI: 10.1364/JOSAB.376975 Received 11 Sep 2019; Accepted 27 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: We investigate new types of gap solitons in a periodic parity-time symmetric lattice with fractional-order diffraction. Both the fundamental and diople solitons in the first and second gaps are discussed. It is found that the fractional-order diffraction can not only stabilize low-power dipole PT solitons in the first gap under focusing nonlinearity but also help to get the stable dipole PT solitons in the second gap under defocusing nonlinearity. Additionally, the influence of the strength ω¡ of the gain-loss component on the properties of solitons is also analysed. It is shown that increasing ω¡ is unfavorable to the stability of fractional fundamental solitons, especially for the second gap. While for fractional dipole solitons, the increase of ω¡ may lead to destabilization of them in the first gap but stabilization of them in the second gap.

Multiple band frequency locking in acousto-optic system with optoelectronic feedback

Sergey Mantsevich, Andrey Voloshin, Grigory Slinkov, Ekaterina Kostyleva, and Vladimir Balakshy

DOI: 10.1364/JOSAB.384519 Received 28 Nov 2019; Accepted 26 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: In this paper we introduce and analyze both experimentally and theoretically multiple band frequency locking that becomes possible in acousto-optic (AO) system with optoelectronic feedback. This effect is observed in a system combining a collinear acousto-optic cell and positive electronic feedback. Feedback signal is formed with optical heterodyning effect that occurs at the AO cell output and takes place in the special regime of collinear AO diffraction. It is shown for the first time that frequency locking is possible in this system when connecting external RF generator not only in one band near the self-oscillations frequency, but in several bands. The existence of as much as 9 frequency locking bands was predicted. The number of frequency locking bands and their width depends on the feedback gain and RF generator signal magnitude.

Effect of partially coherent pump on the spatial and spectral profiles of down converted photons

Bhaskar Kanseri and PREETI SHARMA

DOI: 10.1364/JOSAB.376565 Received 03 Sep 2019; Accepted 24 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: We report a theoretical study of spatial and spectral profiles of the twin photons generated with the pump beam having partially spatially coherent nature. These profiles are simulated for both type-I and type-II spontaneous parametric down conversion in collinear and non-collinear configurations and found to be highly dependent on the choice of beam waist and transverse correlation length of the pump beam. It is found that by suitable choice of coherence length and size of pump beam, the asymmetry in spatial geometry of down converted photons and the spectral width can be modified. Owing to partial spatial coherence nature, these biphoton beams might offer more robustness against losses compared to their fully coherent counterparts, and thus could yield high success rate in the free space quantum communication and in quantum key distribution.

Composite gyroscope with high sensitivity in the low-velocity region and no dead zone

Weiguo Jiang, Yundong Zhang, Jinfang Wang, Kai Ma, Fuxing Zhu, Guo Yi, and He Tian

DOI: 10.1364/JOSAB.377838 Received 17 Sep 2019; Accepted 24 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: In order to solve the problems of low sensitivity for traditional Interference fiber optic gyroscopes at low velocity and the existence of measurement dead zone for Slow-light gyro, a composite fiber optic gyroscope whose fiber coil consists of Sagnac loop and resonant loop is proposed in this paper. Since it combines the characteristics of the two gyroscopes, Composite gyro can meet the requirements of high sensitivity at low rotation velocity and no measurement dead zone. The relative sensitivity in the low-velocity and high-velocity region can be flexibly adjusted by tuning the length ratio of the Sagnac loop and resonant loop, to meet the practical application requirement. We also investigate the effects of loss and coupling coefficient on gyroscope's sensitivity to optimize parameters and achieve optimal sensing performance.

Nanoparticle-Laser Interaction: Computation ofSize Reduction and Thermal Conductance atSolid-Vapor Interface

Hadi Movahedinejad, Hamid Nadjari, and Amir Farahbod

DOI: 10.1364/JOSAB.378973 Received 30 Sep 2019; Accepted 24 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: Laser interaction with water-immersed metal nanoparticle can bring about a condition such that a bubble is generated and the nanoparticle is evaporated. This phenomenon is strongly dependent on the laser parameters and the nanoparticle size. In this study, we simulated the behavior of gold nanoparticle and its surrounding medium during interaction with nanosecond pulsed laser by considering nanoparticle size reduction, the variations of the nanoparticle absorption cross section and the variations of thermal conductance at the nanoparticle-bubble interface.Results show that the bubble dynamics under low energy and long pulse width laser (so that do not cause to evaporate) depends strongly on the nanoparticle temperature behavior, while under higher laser energy it is dependent on the amount of nanoparticle size reduction. Moreover, by comparing the nanoparticle thermal behavior with experimental data, we were able to estimate the thermal conductance at the nanoparticle-bubble interface. This simulation not only leads to the nanoparticle size control but also helps to understand heat transfer processes in nanoscale.

Theoretical investigation of pulse-to-pulse instabilities in synchronously pumped femtosecond optical parametric oscillator

Viktorija Tamuliene, Mikas Vengris, and Valdas Sirutkaitis

DOI: 10.1364/JOSAB.380350 Received 14 Oct 2019; Accepted 23 Dec 2019; Posted 24 Dec 2019  View: PDF

Abstract: Singly resonant synchronously pumped optical parametric oscillator (SPOPO) based on the experimental set-up of K. Ivanauskiene et. al. (2019) [1] is studied theoretically. Stable, oscillatory and chaotic operation modes of the SPOPO are investigated. The need of the self- and cross-phase modulation terms in the theoretical model for the explanation of the instabilities is demonstrated. The theoretical values of the wavelengths of the signal spectrum maxima are found. The evidence of chaos by the calculation of the Lyapunov exponent is provided. The possibilities to avoid the instabilities are discussed.

Performance Analysis of Quantum Key Distribution in Underwater Turbulence Channels

Amir Hossein Fahim Raouf, majid safari, and Murat Uysal

DOI: 10.1364/JOSAB.376267 Received 26 Aug 2019; Accepted 22 Dec 2019; Posted 02 Jan 2020  View: PDF

Abstract: The current literature on quantum key distribution (QKD) is mainly limited to the transmissions over fiber optic, atmospheric or satellite links and are not directly applicable to underwater environments with different channel characteristics. In this paper, we analyze the quantum bit error rate (QBER) performance of the well-known BB84 protocol in underwater channels. As path loss model, we consider a modified version of Beer-Lambert formula which takes into account the effect of scattering. We derive a closed-form expression for the wave structure function to determine the average power transfer over turbulent underwater path and use this to obtain an upper bound of QBER. Based on the derived QBER bound, we present the performance of BB84 protocol in different water types including clear, coastal and turbid water and under different atmospheric conditions such as clear, hazy and overcast. We further investigate the effect of system parameters such as aperture size and detector field-of-view on QBER performance.

Guided-mode resonance filter optimal inverse design using one- and two- dimensional grating

yaser khorrami, Davood Fathi, and Raymond Rumpf

DOI: 10.1364/JOSAB.380094 Received 08 Oct 2019; Accepted 21 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: We propose an optimized method for the inverse design of guided-mode resonance (GMR) filters using one- and two- dimensional (1D & 2D) grating structures. This work for 2D state is based on developing the effective permittivity of 1D grating structures along three orthogonal axes to predict the physical dimensions of the structure, for the first time. Also, we compare three optimization methods to reach the optimized conditions based on the characteristics of multilayer structures. Both the transfer matrix method (TMM) and the rigorous coupled-wave analysis (RCWA) are used to simulate and show the reflection and transmission of the proposed 2D GMR filters. Results show that, insensitivity to polarization, the best accuracy in the resonance location design and a high quality factor can be achieved for both the rectangular and cylindrical structures as the ideal 2D GMR filters. Also, the effect of each layer thickness on the resonance location and the full width at half maximum (FWHM) is illustrated. Finally, we investigate three different reasons for decreasing the FWHM of the output reflection of the GMR filters.

Multi-channel Photonic bandgap consequences in one-dimensional linear, exponential and hyperbolic graded index photonic crystals

Bipin Singh, Ashish Bijalwan, Praveen Pandey, and Vipul Rastogi

DOI: 10.1364/JOSAB.381681 Received 07 Nov 2019; Accepted 21 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: We present the structuring of different graded index materials in the form of one-dimensional (1-D) photonic crystals (PCs) for highly efficient light trapping and controlling photonic devices in terms of tuned and controlled photonic band gap (PBG) performances. We consider hyperbolic, exponential and linear refractive index variation in the graded index layer. We systematically study the influence of structural and grading parameters on band gap performances for two different graded photonic crystal (GPC) structures formed by stacking different graded-index layers. Compared with conventional PCs, the GPC band gaps can be changed and tuned by the refractive index profile of the graded index layer. We show that the number of band gaps increases with graded index layer thickness and the band gap frequencies can be tuned by the grading profiles. We also study the influence of stacking pattern and grading profiles on band gap, phase shift, group velocity and delay time, and field distribution. The proposed GPC configurations facilitate the design of reflectors, multi-channel filters, detectors, and other photonic devices. The study may also provide the basis of understanding of the influence of graded index materials on the PBG characteristics in the GPCs.

A statistical-driven model for efficient analysis of few-photon transport in waveguide quantum electrodynamics

Yuecheng Shen, Ruiqi Cui, and Dian Tan

DOI: 10.1364/JOSAB.380142 Received 09 Oct 2019; Accepted 20 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: Understanding transport properties in quantum nanophotonics plays a central role in designing few-photon devices yet suffer from a longstanding extensive computational burden. In this work, we propose a statistical-driven model with a tremendously eased computational burden based on the deep understanding of few-photon spontaneous emission process. By utilizing phenomenological statistical-driven inter-photon offset parameters, the proposed model expedites the transport calculation with a three-order-of-magnitude enhancement of speed in contrast to conventional first-principle simulations. We showcase the two-photon transport computation benchmarked by the rigorous analytical approach. Our work provides an efficient tool for designing few-photon nano-devices, and significantly deepens the understanding of correlated quantum many-body physics.

Ground-state cooling of a magnomechanical resonator induced by magnetic damping

Ming-Song Ding, Li Zheng, and Chong Li

DOI: 10.1364/JOSAB.380755 Received 17 Oct 2019; Accepted 20 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: Quantum manipulation of mechanical resonators has been widely applied in fundamental physics and quantum information processing. Among them, cooling a mechanical system to its quantum ground state is regarded as a key step. In this work, we propose a scheme which one can realize ground-state cooling of resonator in a cavity magnomechanical system. The sys-tem consists of a microwave cavity and a small ferromagnetic sphere, in which phonon-magnon coupling and cavity photon-magnon coupling can be achieved via magnetostrictive interaction and magnetic dipole interaction, respectively. Within experimentally feasible parameters, we demonstrate that the extra magnetic damping can be utilized to achieve ground-state cooling of the magnomechanical resonator via a effective dark-mode interaction. The magnomechanical cooling mainly coming from the magnon-phonon interaction terms. We further illustrate the optimal cooling can be obtained by adjusting the external magnetic field.

Transient Grating Measurements at Ultra-Low Probe Power

Baozhu Lu, Mykola Abramchuk, Fazel Tafti, and Darius Torchinsky

DOI: 10.1364/JOSAB.377545 Received 11 Sep 2019; Accepted 20 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: We report on an ultra-low probe-power transient grating apparatus with probing based on a laser diode pulser, digital delay generator and data acquisition card. The electronic triggering of the diode pulser permits measurement of arbitrarily slow laser-induced dynamics using pulses of probe light with average power ~5 nW, significantly lower than currently used by continuous wave measurement. Our method also allows for flexibility in selection of the probe wavelength limited only by availability of low threshold current laser diodes. Examples of Impulsive Stimulated Thermal Scattering measurements are presented on liquid isopropanol, single crystal solid CrCl₃ and a thin film of Cu vapor deposited on a Si substrate, demonstrating the flexibility of the technique.

Comparative Study of Condensate fraction of Balanced and Imbalaced Uniform Fermionic System in The BEC-BCS Crossover

Imrana Ashraf, Shahzeb Aziz, Sidra Jamil, and abdul Rahman

DOI: 10.1364/JOSAB.377423 Received 10 Sep 2019; Accepted 19 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: In this paper, we have made comparative study of Condensate fraction of balanced and imbalanced two component uniform fermionic systems in the BEC-BCS crossover. We have used extended BCS equations to calculate condensate of cooper-pairs as a function of chemical potential, gap energy in a balanced system using Path integral approach. While in an imbalanced system the same equation has been derived as a function of average chemical potential, imbalanced chemical potential, gap energy and temperature . The condensate fraction in a balanced fermi system varies with interaction parameter whereas its behavior in an imbalanced system changes with interaction parameter and polarization, in different regimes. In specific, the effect of polarization on condensate fraction has been studied in an imbalanced system for odd values of polarization. Finally, we compared the fraction of condensate for both the systems analytically and graphically, it has been found that in an imbalanced system it decreases with increasing polarization and almost vanishes for higher values of polarization in the BEC regime.

Entanglement dynamics of moving qubits in a common environment

Sare Golkar, Mohammad K. Tavassoly, and A Nourmandipour

DOI: 10.1364/JOSAB.379261 Received 02 Oct 2019; Accepted 19 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: In this paper, we provide an analytical investigation of the entanglement dynamics of moving qubits dissipating into a common and (in general) non-Markovian environment for both weak and strong coupling regimes. We first consider the case of two moving qubits in a common environment and then generalize it to an arbitrary number of moving qubits. Our results show that when the system evolves from an initially entangled state, the amount of the initial entanglement decreases and finally disappears after a finite interval of time due to the environmental effects. Moreover, we show that the movement of the qubits has a constructive role in the protection of the initial entanglement. In a sense, in this case, we observe a Zeno-like effect due to the velocity of the qubits. On the other hand, we show how a stationary state of entanglement may be achieved when we consider the case in which at least one of the moving qubits is initially in the ground state. Surprisingly, we illustrate that when we extend the number of moving qubits with the same velocity, the stationary state of the qubits does not depend on the velocity of qubits as well as the environmental properties. This means that in this condition the stationary state of entanglement depends only on the number of moving qubits.

Patterned laser induced graphene for terahertz wave modulation

Zongyuan Wang, Guocui Wang, liu guang, Bin Hu, Juan Liu, and Yan Zhang

DOI: 10.1364/JOSAB.383324 Received 13 Nov 2019; Accepted 18 Dec 2019; Posted 23 Dec 2019  View: PDF

Abstract: Laser-induced graphene (LIG) has received a large amount of attention because of its superior properties of high electrical conductivity, high thermal stability and conductivity, simple synthesis, and low-fabrication cost of patterned structures. However, most studies on LIG are focused on electrical applications. In this work, we first examine the effect of the substrate on LIG generated on polyimide and then fabricate the patterned-LIG structures including gratings and Fresnel zone plates for terahertz (THz)-wave modulations. The functions of the structures are experimentally demonstrated by a THz focal plane imaging system. It is anticipated that LIG-based structures could widen the application of THz technology.

Alexandrite: an attractive thin-disk laser material alternative to Yb:YAG?

Umit Demirbas and Franz Kaertner

DOI: 10.1364/JOSAB.380140 Received 09 Oct 2019; Accepted 17 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: Yb:YAG thin-disk (TD) technology has enabled construction of laser/amplifier systems with unprecedented average/peak powers, and became the work-horse of many scientific investigations. On the other hand, for some applications, the narrow emission bandwidth of Yb:YAG limits its potential, and search for alternative broadband TD gain media, with suitable thermo-opto-mechanical parameters is ongoing. Alexandrite gain medium has broad emission spectrum centered around 750 nm and possesses thermo-mechanical strength that even outperforms Yb:YAG. Using high-brightness red diodes as pump sources, continuous-wave (cw) output powers above 25 W has already been demonstrated using rod type Alexandrite crystals in compact/simple cavities. In this work, we have numerically investigated power scaling potential of cw Alexandrite lasers in TD geometry to the first time. Using a detailed laser model, we have numerically compared potential cw laser performance of Yb:YAG, Ti:Sapphire, Cr:LiSAF, Cr:LiCAF and Alexandrite thin disk lasers (TDLs) under similar conditions, and show that among the investigated transition metal doped gain media, Alexandrite is the best alternative to Yb:YAG in power scaling studies at room temperature (RT). Our analysis further demonstrated that Ti:Sapphire could also potentially be a good alternative TD material, but only at cryogenic temperatures. As a strong drawback, we have seen that, compared to Yb:YAG, achievable laser gain is relatively low in both Alexandrite and Ti:Sapphire, which then requires usage of low-loss cavities with small output coupling, for efficient cw operation.

High gain in dual pass rod type fiber amplifier.

Jean-François LUPI, METTE JOHANSEN, Mattia Michieletto, Simon Christensen, and Jesper Laegsgaard

DOI: 10.1364/JOSAB.381433 Received 24 Oct 2019; Accepted 17 Dec 2019; Posted 18 Dec 2019  View: PDF

Abstract: Single pass amplification using rod-type fibers has become a common route to pulsed laser sources around 1030 nm with high average and peak power. Averagepower scaling is currently limited by the dynamic thermo-optic phenomenon of ’transverse mode instability’ (TMI). In comparison, double-pass amplifier configurations have not been extensively studied. Recent theoretical and experimental work has shown both static and dynamic mode degradation phenomena, including an unexpected nonlinear polarization rotation effect. Here we present new results obtained with a modified setup using polarization filtering between the first and the second pass. We obtain up to 113 W output power, i.e. more than 40 dB of amplification from a single amplifier module seeded by 10 mW of 20 ps/20 MHz/1030 nm pulses. We observe excellent beam quality and polarization extinction ratio. Finally,we investigated a wide range of seed powers and report a strong increase of static mode deformation threshold with decreasing seed power. The experimental results are corroborated by numerical simulations.

Strain and Temperature Discrimination Based on A Sagnac Interferometer with Three Sections of HBFs

Zhichao Ding and Zhongwei Tan

DOI: 10.1364/JOSAB.381089 Received 21 Oct 2019; Accepted 14 Dec 2019; Posted 16 Dec 2019  View: PDF

Abstract: Abstract—We present an all-fiber sensor for simultaneous measurement of temperature and strain by inserting three sections of high birefringence fibers in a Sagnac interferometer. The proposed sensor employs only one type of high birefringence fiber and is easy fabrication. The dips in the transmission spectrum show different sensitivities to temperature and strain, strain and temperature discrimination is obtained by monitoring the wavelength shift of two different dips. The sensitivities for strain and temperature are measured to be −1.582nm/°C and 6.8 pm/με, and discriminative errors for strain and temperature are ±0.07 °C and ±19.7 με. The proposed sensor with high sensitivity, simple configuration, and low cost is suitable for strain and temperature sensing applications.

A photon-conserving generalized nonlinear Schrödinger equation for frequency-dependent nonlinearities

Juan Bonetti, Nicolas Linale, Alfredo Sanchez, Santiago Hernandez, Pablo Fierens, and Diego Grosz

DOI: 10.1364/JOSAB.377891 Received 03 Oct 2019; Accepted 13 Dec 2019; Posted 16 Dec 2019  View: PDF

Abstract: Pulse propagation in nonlinear waveguides is most frequently modeled by resorting to the generalized nonlinear Schrödinger equation (GNLSE). In recent times, exciting new materials with peculiar nonlinear properties, such as negative nonlinear coefficients and a zero-nonlinearity wavelength, have been demonstrated. Unfortunately, the GNLSE may lead to unphysical results in these cases since, in general, it does not preserve the number of photons and, in the presence of a negative nonlinearity, predicts a blueshift due to Raman scattering. In this paper, we put forth a modified GNLSE that can be used to model the propagation in media with an arbitrary, even negative, nonlinear coefficient. This novel photon-conserving genereralized nonlinear Schrödinger equation (pcGNLSE) ensures preservation of the photon number and can be solved by the same tried and trusted numerical algorithms used for the standard GNLSE. Finally, we compare results for soliton dynamics in fibers with different nonlinear coefficients obtained with the pcGNLSE and the GNLSE.

Z-Scan and Eclipsing Z-Scan Analytical Expressions for Instantaneous Optical Nonlinearities

Magnus Pereira and Ricardo Correia

DOI: 10.1364/JOSAB.376541 Received 30 Aug 2019; Accepted 12 Dec 2019; Posted 13 Dec 2019  View: PDF

Abstract: Analytical expressions for Gaussian-beam Z-Scan and Eclipsing Z-Scan signals are obtained in a unified format in the case of instantaneous third-order optical nonlinearities. Considering optically thin media in the presence of both nonlinear refraction and nonlinear absorption, the Gaussian decomposition method is applied to express the normalized transmittance through an aperture or a disk in terms of a sum of heterodyne and homodyne contributions. The expressions presented are also valid for arbitrary circularly symmetric real ABCD post-sample optical systems.

Supercontinuum decoherence due to XPM-assisted Raman amplification in normal dispersion fibers for polarization or wavelength offset pulses

James Feehan and Jonathan Price

DOI: 10.1364/JOSAB.379563 Received 02 Oct 2019; Accepted 09 Dec 2019; Posted 11 Dec 2019  View: PDF

Abstract: We report the importance of cross-phase modulation (XPM) effects on supercontinuum coherence degradation in all-normal dispersion (ANDi) fiber due to Raman amplification of quantum noise. This extends recent scalar results showing that Raman amplification of quantum noise occurs most strongly at the leading edge of a pulse. Simulations of a high-energy pump pulse co-propagating with a low-energy probe show that non-phase-matched parametric Raman amplification stimulated by XPM within the probe by the pump is a previously unreported mechanism through which a pump pulse can degrade the coherence of a co-propagating signal. By investigating numerous fiber and pulse parameters, we show consistently that for weak probe pulses the XPM from the pump is the dominant influence on the probe decoherence. We show that because XPM operates in the time domain and depends on the temporal overlap between the pump and probe, the faster decoherence at the pump leading edge means that the probe coherence is reduced most effectively when the probe has a higher group velocity. This is achieved either when an orthogonally-polarized probe is aligned to the fast axis of the fiber, or when a co-polarized probe has a longer central wavelength. We show that this effect occurs for a large birefringence range, and that the faster rate of decoherence for co-propagating signals with a higher group velocity occurs in both polarization maintaining (PM) and non-PM ANDi fibers.

Dual-Image Multiple-beam Fringes of Equal Chromatic Order for dynamic characterisation of fibres

Mohammed Raslan and A. A. Hamza

DOI: 10.1364/JOSAB.375944 Received 21 Aug 2019; Accepted 05 Dec 2019; Posted 16 Dec 2019  View: PDF

Abstract: In this article, we present a modification of one of the common systems for producing multiple-beam fringes of equal chromatic order, FECO. This modification allows us to capture two FECO patterns of different polarisations simultaneously during dynamic investigations of fibres. Using this modified system, the dispersion curves in case of parallel and perpendicular polarisations can be measured simultaneously. Also, dispersion of birefringence values along the visible spectrum can be calculated using a single FECO pattern.

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