Volume: 11 Issue 2
26 Article(s)

Export citation format
Nonlinear photonics with metasurfaces
Polina Vabishchevich, and Yuri Kivshar
Nonlinear optics is a well-established field of research that traditionally relies on the interaction of light with macroscopic nonlinear media over distances significantly greater than the wavelength of light. However, the recently emerged field of optical metasurfaces provides a novel platform for studying nonlinear phenomena in planar geometries. Nonlinear optical metasurfaces introduce new functionalities to the field of nonlinear optics extending them beyond perturbative regimes of harmonic generation and parametric frequency conversion, being driven by mode-matching, resonances, and relaxed phase-matching conditions. Here we review the very recent advances in the rapidly developing field of nonlinear metasurface photonics, emphasizing multi-frequency and cascading effects, asymmetric and chiral frequency conversion, nonperturbative nonlinear regimes, and nonlinear quantum photonics, empowered by the physics of Mie resonances and optical bound states in the continuum.
Photonics Research
  • Publication Date: Jan. 30, 2023
  • Vol. 11, Issue 2, B50 (2023)
Research Articles
Holography, Gratings, and Diffraction
High-speed rendering pipeline for polygon-based holograms
Fan Wang, Tomoyoshi Ito, and Tomoyoshi Shimobaba
As an important three-dimensional (3D) display technology, computer-generated holograms (CGHs) have been facing challenges of computational efficiency and realism. The polygon-based method, as the mainstream CGH algorithm, has been widely studied and improved over the past 20 years. However, few comprehensive and high-speed methods have been proposed. In this study, we propose an analytical spectrum method based on the principle of spectral energy concentration, which can achieve a speedup of nearly 30 times and generate high-resolution (8K) holograms with low memory requirements. Based on the Phong illumination model and the sub-triangles method, we propose a shading rendering algorithm to achieve a very smooth and realistic reconstruction with only a small increase in computational effort. Benefiting from the idea of triangular subdivision and octree structures, the proposed original occlusion culling scheme can closely crop the overlapping areas with almost no additional overhead, thus rendering a 3D parallax sense. With this, we built a comprehensive high-speed rendering pipeline of polygon-based holograms capable of computing any complex 3D object. Numerical and optical reconstructions confirmed the generalizability of the pipeline.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 313 (2023)
Imaging Systems, Microscopy, and Displays
Super-resolution computed tomography imaging spectrometry
Lei Yuan, Qiang Song, Hecong Liu, Kevin Heggarty, and Weiwei Cai
Computed tomography imaging spectrometry (CTIS) is a snapshot spectral imaging technique that relies on a limited number of projections of the target data cube (2D spatial and 1D spectral), which can be reconstructed via a delicate tomographic reconstruction algorithm. However, the restricted angle difference between the projections and the space division multiplexing of the projections make the reconstruction suffer from severe artifacts as well as a low spatial resolution. In this paper, we demonstrate super-resolution computed tomography imaging spectrometry (SRCTIS) by assimilating the information obtained by a conventional CTIS system and a regular RGB camera, which has a higher pixel resolution. To improve the reconstruction accuracy of CTIS, the unique information provided by the zero-order diffraction of the target scene is used as a guidance image for filtering to better preserve the edges and reduce artifacts. The recovered multispectral image is then mapped onto the RGB image according to camera calibration. Finally, based on the spectral and the spatial continuities of the target scene, the multispectral information obtained from CTIS is propagated to each pixel of the RGB image to enhance its spectral resolution, resulting in SRCTIS. Both stimulative studies and proof-of-concept experiments were then conducted, and the results quantified by key metrics, such as structural similarity index measurement and spectral angle mapping have suggested that the developed method cannot only suppress the reconstruction artifacts, but also simultaneously achieve high spatial and spectral resolutions.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 212 (2023)
Instrumentation and Measurements
Nanoscale electric field sensing using a levitated nano-resonator with net charge | Editors' Pick
Shaocong Zhu, Zhenhai Fu, Xiaowen Gao, Cuihong Li, Zhiming Chen, Yingying Wang, Xingfan Chen, and Huizhu Hu
The nanomechanical resonator based on a levitated particle exhibits unique advantages in the development of ultrasensitive electric field detectors. We demonstrate a three-dimensional, high-sensitivity electric field measurement technology using the optically levitated nanoparticle with known net charge. By scanning the relative position between nanoparticle and parallel electrodes, the three-dimensional electric field distribution with microscale resolution is obtained. The measured noise equivalent electric intensity with charges of 100e reaches the order of 1 μV⋅cm-1⋅Hz-1/2 at 1.4×10-7 mbar. Linearity analysis near resonance frequency shows a measured linear range over 91 dB limited only by the maximum output voltage of the driving equipment. This work may provide an avenue for developing a high-sensitivity electric field sensor based on an optically levitated nano-resonator.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 279 (2023)
Optical multi-imaging–casting accelerator for fully parallel universal convolution computing
Guoqing Ma, Junjie Yu, Rongwei Zhu, and Changhe Zhou
Recentlycorresponding author guidelines for details."?>, optical computing has emerged as a potential solution to computationally heavy convolution, aiming at accelerating various large science and engineering tasks. Based on optical multi-imaging–casting architecture, we propose a paradigm for a universal optical convolutional accelerator with truly massive parallelism and high precision. A two-dimensional Dammann grating is the key element for generating multiple displaced images of the kernel, which is the core process for kernel sliding on the convolved matrix in optical convolutional architecture. Our experimental results indicate that the computing accuracy is typically about 8 bits, and this accuracy could be improved further if high-contrast modulators are used. Moreover, a hybrid analog–digital coding method is demonstrated to improve computing accuracy. Additionally, a convolutional neural network for the standard MNIST dataset is demonstrated, with recognition accuracy for inference reaching 97.3%. Since this architecture could function under incoherent light illumination, this scheme will provide opportunities for handling white-light images directly from lenses without photoelectric conversion, in addition to convolutional accelerators.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 299 (2023)
Lasers and Laser Optics
Multi-wavelength random fiber laser with a spectral-flexible characteristic
Sicheng Li, Jiangming Xu, Junrui Liang, Jun Ye, Yang Zhang, Xiaoya Ma, Jinyong Leng, and Pu Zhou
In past decades, multi-wavelength lasers have attracted much attention due to their wide applications in many fields. In this paper, we demonstrate a multi-wavelength random fiber laser with customizable spectra enabled by an acousto–optic tunable filter. The operating wavelength range can be tuned from 1114.5 to 1132.5 nm with a maximal output power of 5.55 W, and spectral channel tuning can also be realized with a maximal number of five. The effect of gain competition and the interaction between Raman gain and insertion loss are also analyzed. Furthermore, the output spectra can be ordered by radiating appropriate radio frequency signals to the acousto–optic tunable filter. This work may provide a reference for agile shape spectrum generation and promote multi-wavelength random fiber laser practicability in sensing, telecommunications, and precise spectroscopy.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 159 (2023)
Self-synchronized temporal-spectral characterization system for revealing ultrafast fiber laser dynamics
Yulong Cao, Zhenghu Chang, Qiang Wu, Jingsheng Huang, Laiyang Dang, Ai Liu, Yiyang Luo, Ligang Huang, Wei Huang, Lei Gao, and Tao Zhu
Duecorresponding author guidelines for details."?> to the electronic bottleneck limited real-time measurement speed of common temporal-spectral detection and the particle-like nature of optical soliton enabled nonrepeatable transient behaviors, capturing the ultrafast laser pulses with unknown times of arrival and synchronously characterizing their temporal-spectral dynamic evolution is still a challenge. Here, using the Raman soliton frequency shift based temporal magnifier and dispersive Fourier transform based spectral analyzer, we demonstrate a self-synchronized, ultrafast temporal-spectral characterization system with a resolution of 160 fs and 0.05 nm, and a recording length above milliseconds. The synchronized nonlinear process makes it possible to image full-filled temporal sub-picosecond pulse trains regardless of their arrival times and without extra pump lasers and photoelectric conversion devices. To demonstrate the significance of this improvement, a buildup dynamic process of a soliton laser with a complex breakup and collisions of multisolitons is visually displayed in the spectral and temporal domains. The soliton dynamic evolution processes observed by our characterization system are in one-to-one correspondence with the numerical simulation results. We believe this work provides a new multidimensional technique to break the electronic bottleneck to gain additional insight into the dynamics of ultrafast lasers and nonlinear science.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 173 (2023)
Controlled generation of picosecond-pulsed higher-order Poincaré sphere beams from an ytterbium-doped multicore fiber amplifier
Kunhao Ji, Di Lin, Ian A. Davidson, Siyi Wang, Joel Carpenter, Yoshimichi Amma, Yongmin Jung, Massimiliano Guasoni, and David J. Richardson
Higher-order Poincaré sphere (HOPS) beams with spatially variable polarization and phase distributions are opening up a host of unique applications in areas ranging from optical communication to microscopy. However, the flexible generation of these beams with high peak power from compact laser systems remains a challenge. Here, we demonstrate the controlled generation of HOPS beams based on coherent beam combination from an Yb-doped multicore fiber (MCF) amplifier. Using a spatial light modulator to adaptively adjust the wavefront and polarization of the signals seeded into the individual cores of the MCF various structured beams (including cylindrical vector beams and first- and second-order vortex beams) were generated with peak powers up to 14 kW for ∼92 ps pulses.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 181 (2023)
Nanophotonics and Photonic Crystals
Photon counting reconstructive spectrometer combining metasurfaces and superconducting nanowire single-photon detectors
Jingyuan Zheng, You Xiao, Mingzhong Hu, Yuchen Zhao, Hao Li, Lixing You, Xue Feng, Fang Liu, Kaiyu Cui, Yidong Huang, and Wei Zhang
Faint light spectroscopy has many important applications such as fluorescence spectroscopy, lidar, and astronomical observations. However, the long measurement time limits its application to real-time measurement. In this work, a photon counting reconstructive spectrometer combining metasurfaces and superconducting nanowire single-photon detectors is proposed. A prototype device was fabricated on a silicon-on-insulator substrate, and its performance was characterized. Experiment results show that this device supports spectral reconstruction of mono-color lights with a resolution of 2 nm in the wavelength region of 1500–1600 nm. Its detection efficiency is 1.4%–3.2% in this wavelength region. The measurement time required by the photon counting reconstructive spectrometer was also investigated experimentally, showing its potential to be applied in scenarios requiring real-time measurement.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 234 (2023)
Nonlinear Optics
Classical imaging with undetected photons using four-wave mixing in silicon core fibers
M. Huang, D. Wu, H. Ren, L. Shen, T. W. Hawkins, J. Ballato, U. J. Gibson, M. Beresna, R. Slavík, J. E. Sipe, M. Liscidini, and A. C. Peacock
Undetected-photon imaging allows for objects to be imaged in wavelength regions where traditional components are unavailable. Although first demonstrated using quantum sources, recent work has shown that the technique also holds with classical beams. To date, however, all the research in this area has exploited parametric down-conversion processes using bulk nonlinear crystals within free-space systems. Here, we demonstrate undetected-photon-based imaging using light generated via stimulated four-wave mixing within highly nonlinear silicon fiber waveguides. The silicon fibers have been tapered to have a core diameter of ∼915 nm to engineer the dispersion and reduce the insertion losses, allowing for tight mode confinement over extended lengths to achieve practical nonlinear conversion efficiencies (∼-30 dB) with modest pump powers (∼48 mW). Both amplitude and phase images are obtained using classically generated light, confirming the high degree of spatial and phase correlation of our system. The high powers (>10 nW) and long coherence lengths (>4 km) associated with our large fiber-based system result in high contrast and stable images.
  • Publication Date: Jan. 10, 2023
  • Vol. 11, Issue 2, 137 (2023)
Spatially engineered nonlinearity in resonant metasurfaces | On the Cover
Anna Fedotova, Mohammadreza Younesi, Maximilian Weissflog, Dennis Arslan, Thomas Pertsch, Isabelle Staude, and Frank Setzpfandt
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 252 (2023)
Optical and Photonic Materials
Multiband metamaterial emitters for infrared and laser compatible stealth with thermal management based on dissipative dielectrics
Kun Yu, Wei Zhang, Mengdan Qian, Peng Shen, and Yufang Liu
The modulation of thermal radiation in the infrared region is a highly anticipated method to achieve infrared sensing and camouflage. Here, a multiband metamaterial emitter based on the Al/SiO2/Al nanosandwich structure is proposed to provide new ideas for effective infrared and laser-compatible camouflage. By virtue of the intrinsic absorption and magnetic resonance property of lossy materials, the thermal radiation in the infrared region can be rationally modulated. The fabricated samples generally present low emissivity (ε3–5 μm=0.21, ε8–14 μm=0.19) in the atmospheric windows to evade infrared detection as well as high emissivity (ε5–8 μm=0.43) in the undetected band for energy dissipation. Additionally, the laser camouflage is also realized by introducing a strong absorption at 10.6 μm through the nonlocalized plasmon resonance of the SiO2 layer. Moreover, the fabricated emitter shows promising prospects in thermal management due to the good radiative cooling property that is comparable to the metallic Al material. This work demonstrates a multiband emitter based on the metasurface structure with compatible infrared-laser camouflage as well as radiative cooling properties, which is expected to pave new routes for the design of thermal radiation devices.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 290 (2023)
Physical Optics
Multiplication and division of orbital angular momentum beams by Fermat’s spiral transformation
Zishuai Zeng, Zihao Pang, Keming Pan, Jia Xu, and Daomu Zhao
Optical geometrical transformation is a novel and powerful tool to switch orbital angular momentum (OAM) states in modern optics. We demonstrate a scheme to operate multiplication and division in OAM by Fermat’s spiral transformation. The characteristics of the output beams in the case of integer and fraction OAM operations are presented in detail. Additionally, the power weight of the output OAM modes and the interference patterns of the output beams are reported to confirm the expected ability of OAM mode conversion by Fermat’s spiral transformation. We further investigate the evolution of OAM beams in operations theoretically and experimentally. This work provides a practical way to perform an optical transformation mapping on OAM beams. It can find application in optical communications with larger OAM mode numbers as well as quantum information in high-dimensional systems.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 165 (2023)
Gap solitons in parity–time symmetric moiré optical lattices
Xiuye Liu, and Jianhua Zeng
Parity–time (PT) symmetric lattices have been widely studied in controlling the flow of waves, and recently, moiré superlattices, connecting the periodic and non-periodic potentials, have been introduced for exploring unconventional physical properties in physics, while the combination of both and nonlinear waves therein remains unclear. Here, we report a theoretical survey of nonlinear wave localizations in PT symmetric moiré optical lattices, with the aim of revealing localized gap modes of different types and their stabilization mechanism. We uncover the formation, properties, and dynamics of fundamental and higher-order gap solitons as well as vortical ones with topological charge, all residing in the finite bandgaps of the underlying linear-Bloch wave spectrum. The stability regions of localized gap modes are inspected in two numerical ways: linear-stability analysis and direct perturbance simulations. Our results provide an insightful understanding of soliton physics in combined versatile platforms of PT symmetric systems and moiré patterns.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 196 (2023)
Virtual metasurfaces: reshaping electromagnetic waves in distance
Ruichao Zhu, Jiafu Wang, Yajuan Han, Yuxiang Jia, Tonghao Liu, Tianshuo Qiu, Sai Sui, Yongfeng Li, Mingbao Yan, Shaobo Qu, and Cheng-Wei Qiu
Metasurface has provided unprecedented freedoms in manipulating electromagnetic (EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface (VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles (TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 203 (2023)
Symmetry-protected third-order exceptional points in staggered flatband rhombic lattices
Yingying Zhang, Shiqiang Xia, Xingdong Zhao, Lu Qin, Xuejing Feng, Wenrong Qi, Yajing Jiang, Hai Lu, Daohong Song, Liqin Tang, Zunlue Zhu, Wuming Liu, and Yufang Liu
Higher-order exceptional points (EPs), which appear as multifold degeneracies in the spectra of non-Hermitian systems, are garnering extensive attention in various multidisciplinary fields. However, constructing higher-order EPs still remains a challenge due to the strict requirement of the system symmetries. Here we demonstrate that higher-order EPs can be judiciously fabricated in parity–time (PT)-symmetric staggered rhombic lattices by introducing not only on-site gain/loss but also non-Hermitian couplings. Zero-energy flatbands persist and symmetry-protected third-order EPs (EP3s) arise in these systems owing to the non-Hermitian chiral/sublattice symmetry, but distinct phase transitions and propagation dynamics occur. Specifically, the EP3 arises at the Brillouin zone (BZ) boundary in the presence of on-site gain/loss. The single-site excitations display an exponential power increase in the PT-broken phase. Meanwhile, a nearly flatband sustains when a small lattice perturbation is applied. For the lattices with non-Hermitian couplings, however, the EP3 appears at the BZ center. Quite remarkably, our analysis unveils a dynamical delocalization-localization transition for the excitation of the dispersive bands and a quartic power increase beyond the EP3. Our scheme provides a new platform toward the investigation of the higher-order EPs and can be further extended to the study of topological phase transitions or nonlinear processes associated with higher-order EPs.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 225 (2023)
Quantum Optics
Noisy quantum gyroscope | Editors' Pick
Lin Jiao, and Jun-Hong An
Gyroscope for rotation sensing plays a key role in inertial navigation systems. Developing more precise gyroscopes than the conventional ones bounded by the classical shot-noise limit by using quantum resources has attracted much attention. However, existing quantum gyroscope schemes suffer severe deterioration under the influence of decoherence, which is called the no-go theorem of noisy metrology. Here, by using two quantized optical fields as the quantum probe, we propose a quantum gyroscope scheme breaking through the constraint of the no-go theorem. Our exact analysis of the non-Markovian noise reveals that both the evolution time as a resource in enhancing the sensitivity and the achieved super-Heisenberg limit in the noiseless case are asymptotically recoverable when each optical field forms a bound state with its environment. The result provides a guideline for realizing high-precision rotation sensing in realistic noisy environments.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 150 (2023)
On-chip generation of hybrid polarization-frequency entangled biphoton states | Spotlight on Optics
S. Francesconi, A. Raymond, R. Duhamel, P. Filloux, A. Lemaître, P. Milman, M. I. Amanti, F. Baboux, and S. Ducci
We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement, allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation. Our AlGaAs device is based on type-II spontaneous parametric downconversion in a counterpropagating phase-matching scheme in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization–frequency entangled photons at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong–Ou–Mandel interference (raw visibility 70.1%±1.1%) of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization–frequency space.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 270 (2023)
Silicon Photonics
16-channel photonic–electric co-designed silicon transmitter with ultra-low power consumption
Jingbo Shi, Ming Jin, Tao Yang, Haowen Shu, Fenghe Yang, Han Liu, Yuansheng Tao, Jiangrui Deng, Ruixuan Chen, Changhao Han, Nan Qi, and Xingjun Wang
A hybrid integrated 16-channel silicon transmitter based on co-designed photonic integrated circuits (PICs) and electrical chiplets is demonstrated. The driver in the 65 nm CMOS process employs the combination of a distributed architecture, two-tap feedforward equalization (FFE), and a push–pull output stage, exhibiting an estimated differential output swing of 4.0Vpp. The rms jitter of 2.0 ps is achieved at 50 Gb/s under nonreturn-to-zero on–off keying (NRZ-OOK) modulation. The PICs are fabricated on a standard silicon-on-insulator platform and consist of 16 parallel silicon dual-drive Mach–Zehnder modulators on a single chip. The chip-on-board co-packaged Si transmitter is constituted by the multichannel chiplets without any off-chip bias control, which significantly simplifies the system complexity. Experimentally, the open and clear optical eye diagrams of selected channels up to 50 Gb/s OOK with extinction ratios exceeding 3 dB are obtained without any digital signal processing. The power consumption of the Si transmitter with a high integration density featuring a throughput up to 800 Gb/s is only 5.35 pJ/bit, indicating a great potential for massively parallel terabit-scale optical interconnects for future hyperscale data centers and high-performance computing systems.
  • Publication Date: Jan. 10, 2023
  • Vol. 11, Issue 2, 143 (2023)
Blazed subwavelength grating coupler
Rongxiang Guo, Shujiao Zhang, Haoran Gao, Ganapathy Senthil Murugan, Tiegen Liu, and Zhenzhou Cheng
Short-wavelength mid-infrared (2–2.5 μm wave band) silicon photonics has been a growing area to boost the applications of integrated optoelectronics in free-space optical communications, laser ranging, and biochemical sensing. In this spectral region, multi-project wafer foundry services developed for the telecommunication band are easily adaptable with the low intrinsic optical absorption from silicon and silicon dioxide materials. However, light coupling techniques at 2–2.5 μm wavelengths, namely, grating couplers, still suffer from low efficiencies, mainly due to the moderated directionality and poor diffraction-field tailoring capability. Here, we demonstrate a foundry-processed blazed subwavelength coupler for high-efficiency, wide-bandwidth, and large-tolerance light coupling. We subtly design multi-step-etched hybrid subwavelength grating structures to significantly improve directionality, as well as an apodized structure to tailor the coupling strength for improving the optical mode overlap and backreflection. Experimental results show that the grating coupler has a recorded coupling efficiency of -4.53 dB at a wavelength of 2336 nm with a 3-dB bandwidth of ∼107 nm. The study opens an avenue to developing state-of-the-art light coupling techniques for short-wavelength mid-infrared silicon photonics.
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 189 (2023)
High sideband suppression silicon single sideband modulator integrated with a radio frequency branch line coupler
Penghui Xia, Hui Yu, Mingxiang Yang, Naidi Cui, Haijun Liao, Qiang Zhang, Zhilei Fu, Qikai Huang, Nannan Ning, Zhujun Wei, Xiaoqing Jiang, and Jianyi Yang
We demonstrate a single-chip silicon optical single sideband (OSSB) modulator composed of a radio frequency (RF) branch line coupler (BLC) and a silicon dual-parallel Mach–Zehnder modulator (DP-MZM). A co-design between the BLC and the DP-MZM is implemented to improve the sideband suppression ratio (SSR). The modulator has a modulation efficiency of VπLπ∼1.75 V·cm and a 3 dB electro-optical (EO) bandwidth of 48.7 GHz. The BLC can generate a pair of RF signals with equal amplitudes and orthogonal phases at the optimal frequency of 21 GHz. We prove through theoretical calculation and experiment that, although the BLC’s performance in terms of power balance and phase orthogonality deteriorates in a wider frequency range, high SSRs can be realized by adjusting relevant bias phases of the DP-MZM. With this technique, the undesired sidebands are completely suppressed below the noise floor in the frequency range from 15 GHz to 30 GHz when the chip operates in the full carrier OSSB (FC-OSSB) mode. In addition, an SSR >35 dB and an carrier suppression ratio (CSR) >42 dB are demonstrated at 21 GHz in the suppressed carrier OSSB (SC-OSSB) mode.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 329 (2023)
Mechanisms of enhanced sub-bandgap absorption in high-speed all-silicon avalanche photodiodes
Yuan Yuan, Wayne V. Sorin, Di Liang, Stanley Cheung, Yiwei Peng, Mudit Jain, Zhihong Huang, Marco Fiorentino, and Raymond G. Beausoleil
All-silicon (Si) photodiodes have drawn significant interest due to their single and simple material system and perfect compatibility with complementary metal-oxide semiconductor photonics. With the help from a cavity enhancement effect, many of these photodiodes have shown considerably high responsivity at telecommunication wavelengths such as 1310 nm, yet the mechanisms for such high responsivity remain unexplained. In this work, an all-Si microring is studied systematically as a photodiode to unfold the various absorption mechanisms. At -6.4 V, the microring exhibits responsivity up to ∼0.53 A/W with avalanche gain, a 3 dB bandwidth of ∼25.5 GHz, and open-eye diagrams up to 100 Gb/s. The measured results reveal the hybrid absorption mechanisms inside the device. A comprehensive model is reported to describe its working principle, which can guide future designs and make the all-Si microring photodiode a promising building block in Si photonics.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 337 (2023)
Self-calibrating microring synapse with dual-wavelength synchronization
Junwei Cheng, Zhenming He, Yuhao Guo, Bo Wu, Hailong Zhou, Teyan Chen, Yixin Wu, Wenwei Xu, Jianji Dong, and Xinliang Zhang
corresponding author guidelines for details."?>As a resonator-based optical hardware in analog optical computing, a microring synapse can be straightforwardly configured to simulate the connection weights between neurons, but it faces challenges in precision and stability due to cross talk and environmental perturbations. Here, we propose and demonstrate a self-calibration scheme with dual-wavelength synchronization to monitor and calibrate the synaptic weights without interrupting the computation tasks. We design and fabricate an integrated 4×4 microring synapse and deploy our self-calibration scheme to validate its effectiveness. The precision and robustness are evaluated in the experiments with favorable performance, achieving 2-bit precision improvement and excellent robustness to environmental temperature fluctuations (the weights can be corrected within 1 s after temperature changes 0.5°C). Moreover, we demonstrate matrix inversion tasks based on Newton iterations beyond 7-bit precision using this microring synapse. Our scheme provides an accurate and real-time weight calibration independently parallel from computations and opens up new perspectives for precision boost solutions to large-scale analog optical computing.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 347 (2023)
Interpulse stimulation Fourier-transform coherent anti-Stokes Raman spectroscopy
Minjian Lu, Yujia Zhang, Xinyi Chen, Yan Li, and Haoyun Wei
Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two ∼100-fs pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 357 (2023)
Surface Optics and Plasmonics
Transmissive metasurface for multi-channel and full-polarization modulation of electromagnetic wavefronts
Linda Shao, Zhenfei Li, Jialin Feng, Jin Zhang, Hongyu Shi, Xudong Bai, and Weiren Zhu
Metasurfaces have great potential for flexible manipulation of electromagnetic wave polarizations and wavefronts. Here, we propose a general method for achieving independent wavefront manipulation in a single polarization-multiplexing transmissive metasurface. As a proof of concept, we design a transmission-type anisotropic metasurface for independent wavefront manipulation in full-polarization channels. An x-polarized wave transmitted through such a metasurface could be converted into four outgoing beams with delicately designed polarization states that converge to specific positions for holographic imaging. The measured results are in good agreements with simulated ones, verifying the independent wavefront manipulations with arbitrary polarization conversions. Compared with the existing traditional meta-devices with single-polarization modulation, we achieve polarization-multiplexed metasurfaces with mixed polarization and phase control, which can greatly improve the functional richness of the system.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 245 (2023)
Plasmonic bound states in the continuum for unpolarized weak spatially coherent light | Editors' Pick
Zhuo Wang, Yao Liang, Jiaqi Qu, Mu Ku Chen, Mingjie Cui, Zhi Cheng, Jingcheng Zhang, Jin Yao, Shufan Chen, Din Ping Tsai, and Changyuan Yu
Plasmonic resonances empowered by bound states in the continuum (BICs) offer unprecedented opportunities to tailor light–matter interaction. However, excitation of high quality-factor (Q-factor) quasi-BICs is often limited to collimated light at specific polarization and incident directions, rendering challenges for unpolarized focused light. The major hurdle is the lack of robustness against weak spatial coherence and poor polarization of incident light. Here, addressing this limitation, we demonstrate sharp resonances in symmetric plasmonic metasurfaces by exploiting BICs in the parameter space, offering ultraweak angular dispersion effect and polarization-independent performance. Specifically, a high-Q (≈71) resonance with near-perfect absorption (>90%) is obtained for the input of unpolarized focused light covering wide incident angles (from 0° to 30°). Also, giant electric and magnetic field enhancement simultaneously occurs in quasi-BICs. These results provide a way to achieve efficient near-field enhancement using focused light produced by high numerical aperture objectives.
  • Publication Date: Feb. 01, 2023
  • Vol. 11, Issue 2, 260 (2023)