Contents
2021
Volume: 9 Issue 3
20 Article(s)
Special Issue on DEEP LEARNING IN PHOTONICS
Monte Carlo simulation fused with target distribution modeling via deep reinforcement learning for automatic high-efficiency photon distribution estimation
Jianhui Ma, Zun Piao, Shuang Huang, Xiaoman Duan, Genggeng Qin, Linghong Zhou, and Yuan Xu
Particle distribution estimation is an important issue in medical diagnosis. In particular, photon scattering in some medical devices extremely degrades image quality and causes measurement inaccuracy. The Monte Carlo (MC) algorithm is regarded as the most accurate particle estimation approach but is still time-consuming, even with graphic processing unit (GPU) acceleration. The goal of this work is to develop an automatic scatter estimation framework for high-efficiency photon distribution estimation. Specifically, a GPU-based MC simulation initially yields a raw scatter signal with a low photon number to hasten scatter generation. In the proposed method, assume that the scatter signal follows Poisson distribution, where an optimization objective function fused with sparse feature penalty is modeled. Then, an over-relaxation algorithm is deduced mathematically to solve this objective function. For optimizing the parameters in the over-relaxation algorithm, the deep Q-network in the deep reinforcement learning scheme is built to intelligently interact with the over-relaxation algorithm to accurately and rapidly estimate a scatter signal with the large range of photon numbers. Experimental results demonstrated that our proposed framework can achieve superior performance with structural similarity >0.94, peak signal-to-noise ratio >26.55 dB, and relative absolute error <5.62%, and the lowest computation time for one scatter image generation can be within 2 s.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000B45 (2021)
Deep compressed imaging via optimized pattern scanning | On the Cover
Kangning Zhang, Junjie Hu, and Weijian Yang
The need for high-speed imaging in applications such as biomedicine, surveillance, and consumer electronics has called for new developments of imaging systems. While the industrial effort continuously pushes the advance of silicon focal plane array image sensors, imaging through a single-pixel detector has gained significant interest thanks to the development of computational algorithms. Here, we present a new imaging modality, deep compressed imaging via optimized-pattern scanning, which can significantly increase the acquisition speed for a single-detector-based imaging system. We project and scan an illumination pattern across the object and collect the sampling signal with a single-pixel detector. We develop an innovative end-to-end optimized auto-encoder, using a deep neural network and compressed sensing algorithm, to optimize the illumination pattern, which allows us to reconstruct faithfully the image from a small number of measurements, with a high frame rate. Compared with the conventional switching-mask-based single-pixel camera and point-scanning imaging systems, our method achieves a much higher imaging speed, while retaining a similar imaging quality. We experimentally validated this imaging modality in the settings of both continuous-wave illumination and pulsed light illumination and showed high-quality image reconstructions with a high compressed sampling rate. This new compressed sensing modality could be widely applied in different imaging systems, enabling new applications that require high imaging speeds.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000B57 (2021)
Backpropagation through nonlinear units for the all-optical training of neural networks
Xianxin Guo, Thomas D. Barrett, Zhiming M. Wang, and A. I. Lvovsky
We propose a practical scheme for end-to-end optical backpropagation in neural networks. Using saturable absorption for the nonlinear units, we find that the backward-propagating gradients required to train the network can be approximated in a surprisingly simple pump-probe scheme that requires only simple passive optical elements. Simulations show that, with readily obtainable optical depths, our approach can achieve equivalent performance to state-of-the-art computational networks on image classification benchmarks, even in deep networks with multiple sequential gradient approximation. With backpropagation through nonlinear units being an outstanding challenge to the field, this work provides a feasible path toward truly all-optical neural networks.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000B71 (2021)
Research Articles
Instrumentation and Measurements
Photonic smart bandage for wound healing assessment
Arnaldo Leal-Junior, Jingjing Guo, Rui Min, António José Fernandes, Anselmo Frizera, and Carlos Marques
Chronic wounds affect around 2% of the world population with an annual multi-billion dollar cost to the healthcare system. This background pushes the development of new therapies and procedures for wound healing and its assessment. Among them, the potential of hydrogen (pH) assessment is an important indicator of the wound healing stage and condition. This paper presents the development of the first optical fiber-embedded smart wound dressing for pH assessment. An intrinsically pH-sensitive optical fiber is fabricated using a polydimethylsiloxane (PDMS) precursor doped with rhodamine B dye. Raman and Fourier transform infrared (FTIR) spectroscopies are performed in order to verify the presence of rhodamine B and PDMS in the fiber samples. Then, the fiber is embedded in gauze fabric and hydrocolloid wound dressing. In addition, such low Young’s modulus of PDMS fiber enables its use as a highly sensitive pressure sensor, where the results show that the fiber-embedded bandage can measure pressures as low as 0.1 kPa with a high linearity in the range of 0 to 0.3 kPa. The smart bandage is subjected to different pH, which resulted in a wavelength shift of 0.67 nm/pH when the absorption peak at 515 nm was analyzed. Furthermore, pH increase leads to linear decrease of the transmitted optical power (R2 of 0.998), with rise and fall times below 20 s and 30 s, respectively. Therefore, the proposed optical fiber-embedded smart bandage enables the simultaneous assessment of pressure and pH on the wound region.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000272 (2021)
Lasers and Laser Optics
Real-time collision dynamics of vector solitons in a fiber laser
Kangjun Zhao, Chenxin Gao, Xiaosheng Xiao, and Changxi Yang
Particle-like structures of solitons, as a result of the balance between dispersion and nonlinearity, enable remarkable elastic and inelastic soliton collisions in many fields. Despite the experimental observation of temporal vector-soliton collisions in birefringent fibers, collision dynamics of vector solitons in fiber lasers have not been revealed before, to the best of our knowledge. Here, the real-time spectral evolutions of vector solitons during collisions in a dual-comb fiber laser, which generates vector solitons with slightly different repetition rates, are captured by a time-stretch dispersive Fourier transform technique. We record the whole process of vector-soliton collisions, including the formation of weak pulses induced by cross-polarization coupling, opposite central wavelength shifts of both vector solitons, distinct intensity redistribution and dissipative energy, and gradual recovery to initial states. Furthermore, extreme collisions with strong four-wave mixing sidebands are observed by virtue of coherent coupling between the orthogonal polarization components of vector solitons. Numerical simulations match well with the experimental observations. The experimental and numerical evidences of vector-soliton collision dynamics could give insight into the understanding of nonlinear dynamics in fiber lasers and other physical systems, as well as the improvement of laser performance for application in dual-comb spectroscopy.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000289 (2021)
Structured laser beams: toward 2-μm femtosecond laser vortices
Yongguang Zhao, Li Wang, Weidong Chen, Pavel Loiko, Xavier Mateos, Xiaodong Xu, Ying Liu, Deyuan Shen, Zhengping Wang, Xinguang Xu, Uwe Griebner, and Valentin Petrov
Structured ultrashort-pulse laser beams, and in particular eigenmodes of the paraxial Helmholtz equation, are currently extensively studied for novel potential applications in various fields, e.g., laser plasma acceleration, attosecond science, and fine micromachining. To extend these prospects further, in the present work we push forward the advancement of such femtosecond structured laser sources into the 2-μm spectral region. Ultrashort-pulse Hermite– and Laguerre–Gaussian laser modes both with a pulse duration around 100 fs are successfully produced from a compact solid-state laser in combination with a simple single-cylindrical-lens converter. The negligible beam astigmatism, the broad optical spectra, and the almost chirp-free pulses emphasize the high reliability of this laser source. This work, as a proof of principle study, paves the way toward few-cycle pulse generation of optical vortices at 2 μm. The presented light source can enable new research in the fields of interaction with organic materials, next generation optical detection, and optical vortex infrared supercontinuum.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000357 (2021)
Optical and Photonic Materials
Influence of substrate misorientation on the emission and waveguiding properties of a blue (In,Al,Ga)N laser-like structure studied by synchrotron radiation microbeam X-ray diffraction
A. Kafar, A. Sakaki, R. Ishii, S. Stanczyk, K. Gibasiewicz, Y. Matsuda, D. Schiavon, S. Grzanka, T. Suski, P. Perlin, M. Funato, and Y. Kawakami
In this work, we study how an epitaxial laser-like (or superluminescent diode-like) structure is modified by intentional changes of the substrate misorientation in the range of 0.5°–2.6°. The 40 μm×40 μm test structure with misorientation profiling was fabricated using multilevel photolithography and dry-etching. The local structural parameters were measured by synchrotron radiation microbeam X-ray diffraction, with the sampling area of below 1 μm×1 μm. We directly obtained the relation between the misorientation and indium content in the quantum well, changing from 9% to 18%, with a high resolution (small misorientation step). We also show a good agreement of local photoluminescence emission wavelength with simulation of transition energy based on synchrotron radiation microbeam X-ray diffraction (SR-XRD) data and estimated Stokes shift. We observe that the substrate misorientation influences also the InGaN waveguide and AlGaN cladding composition. Still, we showed through simulation of the optical confinement factor of a full laser diode structure that good light guiding properties should be preserved in the whole misorientation range studied here. This proves the usefulness of misorientation modification in applications like broadband superluminescent diodes or multicolor laser arrays.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000299 (2021)
Highly efficient ultraviolet high-harmonic generation from epsilon-near-zero indium tin oxide films
Wendong Tian, Fei Liang, Dazhi Lu, Haohai Yu, and Huaijin Zhang
High-harmonic generation in the ultraviolet region is promising for wireless technology used for communications and sensing. However, small high-order nonlinear coefficients prevent us from obtaining high conversion efficiency and functional photonic devices. Here, we show highly efficient ultraviolet harmonic generation extending to the fifth order directly from an epsilon-near-zero indium tin oxide (ITO) film. The real part of the annealed ITO films was designed to reach zero around 1050 nm, matching with the central wavelength of an Yb-based fiber laser, and the internal driving electric field was extremely enhanced. A high energy conversion efficiency of 10-4 and 10-6 for 257.5 nm (fourth-order) and 206 nm (fifth-order) ultraviolet harmonic generation was obtained, which is at least 2 orders of magnitude higher than early reports. Our results demonstrate a new route for overcoming the inefficiency problem and open up the possibilities of compact solid-state high-harmonic generation sources at nanoscale.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000317 (2021)
Solution-processed lead-free bulk 0D Cs3Cu2I5 single crystal for indirect gamma-ray spectroscopy application
Qiang Xu, Juan Wang, Qindong Zhang, Xiao Ouyang, Maheng Ye, Weiting Xie, Xuewen Yan, Deyuan Li, Xiaoping Ouyang, Xiaobing Tang, and Xiaodong Zhang
Bulk scintillators that are with high density, low cost, and fine pulse-height energy spectral resolution, and are non-hygroscopic and user friendly, are desired for high-energy gamma-ray spectroscopy application. Recently, low-cost solution-processed perovskite nanoscintillators have been demonstrated with outstanding performances for indirect low-energy X-ray detection; however, the stability and thickness are not suitable for high-energy gamma-ray detection. Here, we report scintillation performances of a low-cost solution-processed bulk 0D Cs3Cu2I5 single crystal. The self-trapped exciton emission results in a large Stokes shift (109 nm) that is reabsorption free. A broad X-ray excited emission matches well with the sensitivity of a silicon photodiode. The unique Cs+ surrounded isolated [Cu2I5]3- cluster scintillator provides ultra-stability in air and strong radiation hardness under high-dose gamma-ray exposure from a 60Co source. This solution-processed Cs3Cu2I5 scintillator is expected with low-cost and has detection performances comparable to commercial alkali-halide scintillator products.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000351 (2021)
Giant enhancements of high-order upconversion luminescence enabled by multiresonant hyperbolic metamaterials
Haofei Xu, Zhimin Zhu, Jiancai Xue, Qiuqiang Zhan, Zhangkai Zhou, and Xuehua Wang
Photonic nanostructures with resonant modes that can generate large electric field (EF) enhancements are applied to enhance light-matter interactions in nanoscale, bringing about great advances in both fundamental and applied science. However, a small hot spot (i.e., the regions with strong EF enhancements) and highly inhomogeneous EF distribution of the resonant modes usually hinder the enhancements of light-matter interactions in a large spatial scale. Additionally, it is a severe challenge to simultaneously generate multiple resonant modes with strong EF enhancements in a broadband spectral range, which greatly limits the capacity of a photonic nanostructure in boosting optical responses including nonlinear conversion, photoluminescence, etc. In order to overcome these challenges, we presented an arrayed hyperbolic metamaterial (AHMM). This AHMM structure is applied to simultaneously enhance the three-photon and four-photon luminescence of upconversion nanoparticles. Excitingly, the enhancement of the three-photon process is 1 order of magnitude larger than previous records, and for the enhancing four-photon process, we achieve an enhancement of 3350 times, greatly beneficial for overcoming the crucial problem of low efficiency in near infrared light upconversion. Our results demonstrated a promising platform for realizing giant enhancements of light-matter interactions, holding potential in constructing various photonics applications such as the nonlinear light sources.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000395 (2021)
Optical Devices
Observation of a manifold in the chaotic phase space of an asymmetric optical microcavity
Yan-Jun Qian, Qi-Tao Cao, Shuai Wan, Yu-Zhong Gu, Li-Kun Chen, Chun-Hua Dong, Qinghai Song, Qihuang Gong, and Yun-Feng Xiao
Chaotic dynamics in optical microcavities, governed dominantly by manifolds, is of great importance for both fundamental studies and photonic applications. Here, we report the experimental observation of a stable manifold characterized by energy and momentum evolution in the nearly chaotic phase space of an asymmetric optical microcavity. By controlling the radius of a fiber coupler and the coupling azimuth of the cavity, corresponding to the momentum and position of the input light, the injected light can in principle excite the system from a desired position in phase space. It is found that once the input light approaches the stable manifold, the angular momentum of the light experiences a rapid increase, and the energy is confined in the cavity for a long time. Consequently, the distribution of the stable manifold is visualized by the output power and the coupling depth to high-Q modes extracted from the transmission spectra, which is consistent with theoretical predictions by the ray model. This work opens a new path to understand the chaotic dynamics and reconstruct the complex structure in phase space, providing a new paradigm of manipulating photons in wave chaos.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000364 (2021)
Terahertz wave avalanche breakdown transistor for high-performance switching
Weijun Wang, Liang-Hui Du, Jiang Li, Pei-Ren Tang, Changlin Sun, Songlin Chen, Jun Wang, Zhao-Hui Zhai, Zhipeng Gao, Ze-Ren Li, Jianquan Yao, Furi Ling, and Li-Guo Zhu
There is still a lack of high-performance terahertz (THz) modulators with wide operation bandwidth and large modulation depth due to the underlying physics limitation behind existing approaches. Meanwhile, for many applications, simple compact THz modulators working straightforward in the transmission mode are also highly desired. Here, we demonstrate a THz modulator with a maximal transmission-amplitude modulation depth of 99.9% (switching ratio of 1000) based on a commonly used silica-on-silicon structure. Different from those reported graphene or metamaterials enhanced proposals, the device we proposed works within a reversible avalanche breakdown region of silicon that has not been studied yet and has the potential to modulate/switch THz waves efficiently. Further, we proved that the modulation depth exceeds 97% in the frequency range from 0.2 to 1 THz in the experiment. The simplicity and generality of this new type of near-perfect THz modulator will undoubtedly attract lots of attention of researchers in the near future due to its potential to be engineered into integrated devices.
Photonics Research
  • Publication Date: Mar. 09, 2021
  • Vol.9 Issue, 3 03000370 (2021)
Saturation efficiency for detecting 1550 nm photons with a 2 × 2 array of Mo0.8Si0.2 nanowires at 2.2 K
Feiyan Li, Hang Han, Qi Chen, Biao Zhang, Han Bao, Yue Dai, Rui Ge, Shuya Guo, Guanglong He, Yue Fei, Shuchao Yang, Xiaohan Wang, Hao Wang, Xiaoqing Jia, Qingyuan Zhao, Labao Zhang, Lin Kang, and Peiheng Wu
Amorphous materials are attractive candidates for fabricating the superconducting nanowire single-photon detectors (SNSPDs) due to their superior tolerance and scalability over crystalline niobium nitride. However, the reduced superconducting transition temperature degenerates both operating temperature and saturation efficiency. Herein, the SNSPD (6.5 nm thickness and 50 nm width) based on the amorphous Mo0.8Si0.2 film with a high optical absorption coefficient demonstrates close-to-unity intrinsic detection efficiency for 1550 nm photons from 75 mK to 2.2 K. Further, a high-performance array SNSPD with optimized 90 nm-width wires is also demonstrated. As-fabricated uniform 4-pixel SNSPD exhibits a saturation plateau for the photon counts at 2.2 K, which overcomes the limitation of operation at low temperature (1 K) for traditional amorphous SNSPDs. Coupled with superior intrinsic quantum efficiency, highly efficient photon counts, and low dark count ratio, this detector paves a way for achieving high efficiency and superior yield for large array systems.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000389 (2021)
Quantum Optics
Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system | Editors' Pick
Yuan Zhou, Dong-Yan Lü, and Wei-You Zeng
We propose what we believe is a novel proposal for realizing a quantum C-NOT logic gate, through fabricating an interesting hybrid device with a chiral photon-pulse switch, a single nitrogen-vacancy (NV) center, and an optical microcavity. Three major different practical routes on realizing a chiral photon emitter are discussed, which can implement a chiral control unit via the nonreciprocal emitter–photon interactions, so-called “propagation-direction-dependent” emission. With the assistance of dichromatic microwave driving fields, we carry out the relevant C-NOT operations by engineering the interactions on a single NV spin in a cavity. We note that this logic gate is robust against practical noise and experimental imperfection, and this attempt may evoke wide and fruitful applications in quantum information processing.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000405 (2021)
Surface Optics and Plasmonics
Birefringent transmissive metalens with an ultradeep depth of focus and high resolution
Jiaran Qi, Yongheng Mu, Shaozhi Wang, Zhiying Yin, and Jinghui Qiu
Depth of focus (DOF) and transverse resolution define the longitudinal range and definition of the focusing lens. Although metasurface axilenses and light-sword metalenses with radial and angular modulations can elongate the DOF, these approaches have inherent limitations in being reliable only for small numerical aperture (NA) cases, which in turn compromises the transverse resolution for the given aperture dimension. To conquer this limitation, we propose and experimentally demonstrate a birefringent metalens, achieving an ultradeep DOF of 41λ in terms of the total scattered field, corresponding to a record-breaking wide NA range from 0.14 to 0.7. Meanwhile, the diffraction limited focal spot size in this NA range can guarantee acquisition of images with high resolution. A hybrid methodology is proposed that utilizes both the accuracy of holography in electromagnetic field reconstruction and the polarization multiplexing to double the DOF. A stratified transmissive meta-atom is utilized to encode a pair of independent phase profiles in two orthogonal polarization channels. Furthermore, we combine the generalized scattering matrix with the multipole expansion theory for the first time to elucidate the mechanism of maintaining high transmittance and widening the transmission phase coverage by using the multilayered structure. The proposed metalens provides a competitive platform for devising high-resolution deep DOF systems for imaging and detection applications.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000308 (2021)
All-dielectric metasurface for fully resolving arbitrary beams on a higher-order Poincaré sphere
Hui Yang, Zhenwei Xie, Guanhai Li, Kai Ou, Feilong Yu, Hairong He, Hong Wang, and Xiaocong Yuan
Characterizing the amplitude, phase profile, and polarization of optical beams is critical in modern optics. With a series of cascaded optical components, one can accurately resolve the optical singularity and polarization state in traditional polarimetry systems. However, complicated optical setups and bulky configurations inevitably hinder future applications for integration. Here, we demonstrate a metadevice that fully resolves arbitrary beams on a higher-order Poincaré sphere (HOPS) via a single-layer all-silicon metasurface. The device is compact and capable of detecting optical singularities and higher-order Stokes parameters simultaneously through a single intensity measurement. To verify the validity of the proposed metadevice, different beams on HOPS0,0 and HOPS1,-1 are illuminated on the metadevices. The beams are fully resolved, and the reconstructed higher-order Stokes parameters show good agreement with the original ones. Taking the signal-to-noise ratio into account, the numerical simulations indicate that the design strategy can be extended to fully resolve arbitrary beams on HOPS with order up to 4. Because of the advantages of compact configuration and compatibility with current semiconductor technology, the metadevice will facilitate potential applications in information processing and optical communications.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000331 (2021)
Control of the harmonic near-field distributions by an active metasurface loaded with pin diodes
Jin Yang, Jun Chen Ke, Mao Chen, Ming Zheng Chen, Jun Yan Dai, Jian Feng Chen, Rui Yang, Jun Wei Wu, Qiang Cheng, and Tie Jun Cui
Recent advances of space-time-coding digital metasurfaces demonstrate powerful capabilities in the generation of nonlinear harmonics and the accurate control of the corresponding wavefronts. However, to date the near field manipulation and the experiment characterization are still not explored. In this paper, we propose a space-time-digital coding metasurface to realize accurate manipulation of the near fields at the fundamental and +1st (-1st) harmonics simultaneously, by properly controlling the initial phase and time delay of the time varying reflectivity. A novel mapping system is established to measure the nonlinear near field distributions of multiharmonics. Both the simulation and experimental results demonstrate the validity of the proposed method.
Photonics Research
  • Publication Date: Feb. 24, 2021
  • Vol.9 Issue, 3 03000344 (2021)
Optical fiber SPR biosensor complying with a 3D composite hyperbolic metamaterial and a graphene film
Can Li, Jinjuan Gao, Muhammad Shafi, Runcheng Liu, Zhipeng Zha, Dejun Feng, Mei Liu, Xuejian Du, Weiwei Yue, and Shouzhen Jiang
In the present study, an optical fiber surface plasmon resonance (SPR) biosensor was developed for measuring time- and concentration-dependent DNA hybridization kinetics. Its design complies with a 3D Au/Al2O3 multilayer composite hyperbolic metamaterial (HMM), a graphene film, and a D-shaped plastic optical fiber. According to the numerical simulation and the experimental demonstration, the SPR peak of the designed biosensor can be effectively altered in the range of visible to near-infrared by varying the HMM structure. The sensitivity of the appliance was shown to achieve a value of up to 4461 nm/RIU, allowing its applicability for bulk refractive index sensing. Furthermore, a biosensor designed in this work displayed high-resolution capability (ranging from 10 pM to 100 nM), good linearity, and high repeatability along with a detection limit down to 10 pM, thus suggesting a vast potential for medical diagnostics and clinical applications.
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000379 (2021)
Ultrafast Optics
Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions | Editors' Pick
Zachary N. Coker, Xiao-Xuan Liang, Allen S. Kiester, Gary D. Noojin, Joel N. Bixler, Bennett L. Ibey, Alfred Vogel, and Vladislav V. Yakovlev
Photonics Research
  • Publication Date: Mar. 02, 2021
  • Vol.9 Issue, 3 03000416 (2021)

About the Cover

A new deep compressed imaging modality enables high speed image acquisition and high fidelity object reconstruction.