查看更多>>摘要：? 2021 Elsevier B.V.In order to achieve a new kind of optical transistor model, we construct a parity-time (PT) symmetry coupled cavity structure. The gain cavity G is made of semiconductor InGaAsP doped with quantum well and the loss cavity is made of the same material as G but periodically inserted by graphene sheets. Through a parameter optimizing, the structure reaches the PT-symmetry pole state with a huge transmittance. The voltage on the graphene sheets as an input signal can modulate the pole state and results in an amplification output of transmittance. Through proper static working points, the structure can achieve the amplification in phase, out phase and of doubling frequency.
查看更多>>摘要：? 2021 The AuthorsHigh-speed photonic networks using digital signal processing (DSP) techniques are flourishing nowadays to meet the high-bandwidth requirements of modern bandwidth-thirsty applications in a cost-effective manner. However, the additional latency introduced by DSP is hindering the latency-critical applications. In this paper, a FPGA-based real-time low-latency four-level pulse amplitude modulation (PAM-4) receiver including digital adaptive equalization (DAE) is designed and implemented by using a latency-reducing parallel architecture. The DSP-introduced latency in the receiver end is analyzed in detail. As for DAE parallel implementation, a novel re-allocation scheme is proposed to cope with the issue of the dependency of the output on the successive input samples, and a look-ahead computation technique is introduced to improve the adaptive update efficiency. A real-time PAM-4 receiver is demonstrated in an experimental fiber link with 2.5 Gbit/s data rate for the performance evaluation. Compared with offline processing with MATLAB, the BER performance has little deterioration at 7% FEC limit of 1 × 10?3. With the help of the proposed deep-parallel technique, the DSP-introduced latency is reduced to 0.4μs on average, which better meets the requirements of latency-sensitive user cases in 5G networks. Furthermore, the real-time PAM-4 receiver could be flexibly reconfigured for various scenarios with low-latency requirements, and the latency-efficient parallel technique as well as the latency analysis method can also be extended to high-speed hardware implementation for data rates up to 100 Gbit/s or more.
查看更多>>摘要：? 2021 Elsevier B.V.A toluene-ethanol filled dual-core photonic crystal fiber (PCF) based on surface plasmon resonance effect is designed for temperature sensing. The toluene with higher refractive index is injected into the central air hole in order to support the core mode. In contrast, the ethanol, whose refractive index is lower, is injected into the sideward air hole coated by gold film to support the mode induced by surface plasmon polariton. The resonance characteristics of surface plasmon in the designed PCF are numerically investigated by using finite element method. It is shown that the influences of structure parameters on temperature sensing performance are different. On the other hand, the resulting resonance wavelength of the spectrum of confinement loss moves to longer wavelength to satisfy the phase matching when the detective temperature is increased. After optimizing structure parameters, the sensitivity of temperature sensor can reach 6.32 nm/°C in the range from 10 °C to 70 °C, indicating its potential applications in temperature measurement with wide temperature range.
查看更多>>摘要：? 2021 Elsevier B.V.To broaden the range of working frequency of the metasurface in the THz band, a flexible metasurface based on the parylene-C film was proposed. The metasurface is composed of elliptical split-ring units with different opening gaps. Elliptical split-ring units with different arrangement can work as 2D beam deflector, 3D beam deflector or vortex generator. The 2D beam deflector modulate THz waves with deflection angles (38°–13.5°) in the broad frequencies (0.6–1.6 THz), whereas the 3D beam deflector can realize beam deflection in 3D space, and the vortex beam generator can modulate THz wave as stable vortex beams carrying orbital angular momentum (OAM) in the broad frequencies (0.8–1.4 THz). The simulation results illustrate that the proposed flexible metasurface exhibits broadband effect in THz range, which promotes the application of flexible metasurfaces in the fields of THz optical field modulation and THz communication.
查看更多>>摘要：? 2021 Elsevier B.V.We propose a system that realizes optical image hiding under low light and reconstructs secret images through deep learning. Based on the improved Mach–Zehnder interferometer system, the light intensity of the two optical paths of the reference light and the object light is adjusted by the neutral density filter (NDF) until the light intensity ratio is 1:15, which constitutes the experimental system of optical image hiding under low light field in this article. The interference hologram collected by the CCD is used as the training data set of the neural network, and the neural network model is continuously optimized. Finally, the optimized neural network model reconstructs the secret image with high quality. The proposal of this scheme reduces the embedding depth of the secret image, making the secret image less noticeable. In addition, the results of optical experiments and simulated test results of different light intensity ratios show that the scheme has certain feasibility and effectiveness.
查看更多>>摘要：? 2021 Elsevier B.V.Spot size converters (SSCs) are essential optical components that connect waveguides with different modal spot sizes for adiabatic light coupling. However, previous SSCs usually suffer from large sizes or limited coupling efficiencies, which are not conducive to develop large-scale and high-density photonic integrated circuits (PICs). Herein, we theoretically study an ultra-compact SSC with a footprint of only 1×2 μm2. The design is based on topologically optimized digital metamaterials, which is implemented by using a genetic algorithm. The device shows a transmission of ?0.11 dB for TE0-mode spot size conversion with a 1-dB bandwidth of 600 nm. Moreover, the device supports the spot size conversion for TE0-mode and TM0-mode simultaneously with a transmission of more than ?2 dB. With the high transmission, wide spectral bandwidth, and ultra-compact footprint, the device is expected to open a new avenue to boost the development of PICs.
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