He Wen

Multimode optical fibers, with their high spatial-mode capacity, present a promising platform for high-fidelity image transmission. However, environmental instabilities and complex input patterns often result in intricate speckle outputs, complicating accurate image reconstruction. In this work, we encode grayscale images through orbital angular momentum (OAM) mode superpositions and achieve high-fidelity reconstruction using a ResNet-based decoding network. By incorporating transfer learning, the model demonstrates strong generalization across different wavelengths and spectral linewidths, attaining a reconstruction accuracy of up to 99%. Furthermore, we develop an attention-enhanced DoubleU-Net to reconstruct complex images with rich edge structures. Experimental results verify that OAM filtering substantially enhances edge fidelity, improving the reconstruction accuracy by approximately 4% over the non-OAM case, reaching a final accuracy of 95%. These findings open avenues toward high-dimensional optical information processing, multimode fiber communications, and advanced computational imaging.

To address signal blockage challenges associated with the millimeter-wave (mmWave) band, we explore the potential of reconfigurable intelligent surfaces (RIS) to enhance performance of integrated sensing and communication (ISAC) systems. Unlike most studies assuming continuous phase control, we consider the more practical scenario of discrete phase-shifted RIS. Simulation results show that RIS in mmWave ISAC systems can mitigate blockage by building a virtual line-of-sight (LOS). Besides, we present the trade-off analysis of communication and radar performance using discrete phase-shifted RIS, comparing the continuous and discrete phase configurations in terms of mean square error (MSE) and normalized sideband power (NSP).

This paper presents a photonic-assisted full-duplex Integrated Sensing and Communication (ISAC) system. The system integrates radar and communication functionalities by processing OFDM waveforms on a real-time FPGA platform within a time-division duplex (TDD) framework. A carriermultiplexed frequency-division duplexing (FDD) scheme enables simultaneous uplink and downlink transmission. A single-fiber radio-over-fiber (RoF) link supports bidirectional transmission by employing phase modulation (PM) for the downlink and intensity modulation (IM) for the uplink. This cost-effective and stable platform simultaneously supports video streaming and realtime radar echo detection, achieving 82.368 Mbps bidirectional communication and 5-meter radar ranging. Furthermore, we demonstrate the system's potential for urban safety and fire inspection applications through intelligent vehicle-based inspection and rapid rescue scenarios, leveraging shared sensing and communication data.

Multi-plane Light Conversion (MPLC) based mode sorters stand out for high mode count, high mode purity, low crosstalk, and flexibility, but generally require number of phase masks 1∼2 times of the mode count. There are few exceptions that the number of masks is significantly reduced in sorting Hermite-Gaussian (HG) or orbital angular momentum (OAM) beams thanks to the special mode structure and the corresponding geometric input layout. However, linearly-polarized (LP) modes in fiber are out of these exceptions for the more complex mode structure compared to that of HG or OAM modes. In this paper, we explore the possibility to construct LP mode sorters with fewer phase masks. We used trial-and-error approaches from multiple aspects to improve the performance of LP mode sorters, such as optimizing the geometric input layout to account for phase shift characteristics of liquid crystal, modifying algorithm to obtain smooth phase patterns, and improving beam alignment to reduce performance degradation. Finally, we experimentally demonstrate a 10-LP mode sorter with 7 phase masks using a liquid crystal on silicon (LCoS) spatial light modulator (SLM), achieving insertion loss of -3.6 dB, mode-dependent loss of -5.6 dB and 1-dB bandwidth of 50 nm. The results indicate that LP-mode sorters with moderate performance can be effectively constructed by LCoS SLMs. LCoS SLMs are preferred in laboratory use for their flexibility and ease of rapidly constructing MPLC-based mode sorters, which can adapt to fibers with various refractive index profiles.

Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of − 1.6    dB , mode-dependent loss of 4.7 dB, and average total mode crosstalk of − 4.4    dB . Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

We propose and experimentally demonstrate high-speed operation of random-channel cryptography (RCC) in multimode fibers. RCC is a key generation and distribution method based on the random channel state of a multimode fiber and multi-dimension to single-dimension projection. The reciprocal intensity transmittance of the channel shared between the two legitimate users is used to generate and distribute correlated keys. In previous work, RCC's key rate-distance product was limited by the speed of light. In this work, we show that adding a fast modulator at one end of the channel decouples the key rate and distance, resulting in a significant improvement in the key rate-distance product, limited only by the fiber's modal dispersion. Error-free transmission at a key rate-distance product of 64.7 Mbps $ \times $ 12 km, which is seven orders of magnitude higher than the previous demonstration, was achieved. The proposed method's security arises from a fundamental asymmetry between the eavesdroppers’ and legitimate users’ measurement complexity.

We present a few-mode frequency-modulated receiver for light detection and ranging (LiDAR). We show that using a few-mode local oscillator (LO) with spatial modes at different frequencies at the receiver can significantly improve the performance of the LiDAR detection range. A preferred receiver architecture features LO modes with unequal frequency separations based on optical orthogonal codes (OOC) to allow range detection via cross correlation. The required signal-to-noise ratio (SNR) for the frequency-modulated continuous wave (FMCW) LiDAR decreases with the number of LO modes. This receiver can have a potential impact in the area of automotive LiDARs.

Mode-selective fiber lasers have advantages in a number of applications. Here we propose and experimentally demonstrate a transverse mode-selective few-mode Brillouin fiber laser using the mode-selective photonic lantern. We generated the lowest three orders of linearly polarized (LP) modes based on both intramodal and intermodal stimulated Brillouin scattering (SBS). Their slope efficiencies, optical spectra, mode profiles, and linewidths were measured.

We propose a Hermite–Gaussian (HG) mode-demulti-plexing hybrid (MDH) for coherent detection of mode-division multiplexed signals. The MDH, which performs multiple functionalities, including demultiplexing, local oscillator splitting, and optical 90-deg mixing, is realized based on the multi-plane light conversion technique. An isosceles right triangle output layout is employed to reduce the number of phase masks to fewer than the number of modes, significantly simplifying the construction of the MDH. A 10-Hermite–Gaussian (HG) mode MDH with only five phase masks is demonstrated by numerical simulation, achieving an insertion loss (IL) and mode dependent loss as low as − 2.3 and 1.7 dB, respectively. The IL was further reduced to − 1.5 d B through optimization of MDH parameters, such as the beam waists of the input HG modes and the output spots.