Three-dimensional (3D) imaging radar is an advanced sensor applied in space surveillance and target recognition for supplying 3D geometric features and supporting visualization. However, high 3D resolution requires both broadband operation and a large 2D aperture, which are difficult and complex for conventional radars. This paper presents a photonics-enabled distributed multiple-input and multiple-output (MIMO) radar with a centralized architecture. By use of photonic multi-dimensional multiplexing, multi-channel signal generation and reception are implemented on a shared reference signal in a central office, enabling a highly coherent network with a simple structure. Additionally, a sparse array and a synthetic aperture are combined to efficiently reduce the required transceivers, further weakening the dilemma between system complexity and angular resolution. A 4×4 MIMO radar is established and evaluated in field tests. A high-resolution 3D image of a non-cooperative aircraft is obtained, in which rich details are displayed. From a comparison with electronics-based radar, significant resolution improvement is observed. The results verify the superior imaging capability and practicability of the proposed radar and its great potential to outperform conventional technologies in target classification and recognition applications.

基于光学微腔的集成光频梳具有光谱宽、谱线间隔大、体积小等优势，为微波光子系统带来了新的发展机遇。近年来涌现了多种基于微腔光梳的微波光子应用，包括高质量微波信号产生、微波光子信号处理、真延时微波波束形成等，具有相位噪声低、可重构能力强、奈奎斯特带宽大等优异性能，展现了集成微腔光梳在微波光子领域的广阔应用前景。

A photonic approach to concurrently measure the angle-of-arrival (AOA) and the chirp rate of a linear frequency modulated (LFM) signal is proposed and experimentally demonstrated. The measurement is achieved by estimating the differential frequency of a two-tone signal output by a dual-parallel Mach–Zehnder modulator and an additional asymmetry Mach–Zehnder interferometer. Experiments show that the AOA and the chirp rate are measured simultaneously, with an AOA measurement error of ±0.1° at an signal-to-noise ratio (SNR) of 9.6 dB. When the SNR is -10.4 dB, the AOA error is ±1.3°, and the chirp rate, measured as 210.2±1.5Hz/ps, has a standard deviation of 0.7%. The measured chirp rate agrees well with the real LFM signal.

Microcomb generation with simultaneous χ(2) and χ(3) nonlinearities brings new possibilities for ultrabroadband and potentially self-referenced integrated comb sources. However, the evolution of the intracavity field involving multiple nonlinear processes shows complex dynamics that are still poorly understood. Here, we report on strong soliton regulation induced by fundamental–second-harmonic (FD-SH) mode coupling. The formation of solitons from chaos is extensively investigated based on coupled Lugiato–Lefever equations. The soliton generation shows more deterministic behaviors in the presence of FD-SH mode interaction, which is in sharp contrast with the usual cases where the soliton number and relative locations are stochastic. Deterministic single soliton transition, soliton binding, and prohibition are observed, depending on the phase-matching condition and coupling coefficient between the fundamental and second-harmonic waves. Our finding provides important new insights into the soliton dynamics in microcavities with simultaneous χ(2) and χ(3) nonlinearities and can be immediate guidance for broadband soliton comb generation with such platforms.

A broadband photonic analog-to-digital converter (ADC) for X-band radar applications is proposed and experimentally demonstrated. An X-band signal with arbitrary waveform and a bandwidth up to 2 GHz can be synchronously sampled and processed due to the optical sampling structure. In the experiment, the chirp signal centered at 9 GHz with a bandwidth of 1.6 GHz is sampled and down-converted with a signal-to-noise ratio of 7.20 dB and an improved noise figure. Adopting the photonic ADC in the radar receiver and the above signal as the transmitted radar signal, an X-band inverse synthetic aperture radar system is set up, and the range and cross-range resolutions of 9.4 and 8.3 cm are obtained, respectively.

We present the investigation on deformation of orbital angular momentum (OAM) modes in bending ring-core fibers (RCFs) with different structure sizes through numerical and experimental studies. The effective refractive index differences of even and odd fiber eigenmodes, which constitute OAM±1,1 modes, induced by RCF bending and their impacts on the OAM±1,1 mode intensity distributions are analyzed. Bending experiments are also carried out on three different RCFs, and the results match well with simulation values. It is found that RCFs with smaller inner and outer radii show preferable tolerance to the fiber bending.

A highly linear W-band receiver front-end based on higher-order optical sideband (OSB) processing is proposed and experimentally demonstrated. Two-tone analysis shows that by manipulating higher-order OSBs, the third-order intermodulation distortion (IMD3) introduced by optoelectronic components (mainly modulators) in the receiver front-end can be further suppressed, and a 9 dB improvement of the ratio of the fundamental and IMD3 can be attained. In the experiment, the spurious-free dynamic range of the W-band receiver front-end is up to 122.1 dB·Hz2/3, with improvement by 9 dB compared with that of only processing the five OSBs.