Countless waveguides have been designed based on four basic bends: circular bend, sine/cosine bend, Euler bend (developed in 1744) and Bezier bend (developed in 1962). This paper proposes an n-adjustable (NA) bend, which has superior properties compared to other basic bends. Simulations and experiments indicate that the NA bends can show lower losses than other basic bends by adjusting n values. The circular bend and Euler bend are special cases of the proposed NA bend as n equals 0 and 1, respectively. The proposed bend are promising candidates for low-loss compact photonic integrated circuits.

A practical two-dimensional beam steering solid-state system based on the synthesis of one-dimensional wavelength tuning and a one-dimensional optical phased array is demonstrated and investigated. The system incorporates an integrated multiple-channel-interference widely tunable laser, an integrated 32-channel optical phased array, an offline phase error correction unit, and home-made control electronics. The introduction of the integrated tunable laser avoids the traditional bulky light source fed into the optical phased array, making the architecture promising to be miniaturized. In addition, a calibration method based on particle swarm optimization is proposed and proved to be effective to correct the phase errors existing in the arrayed channels and improve the emitted far-field quality. Other practical aspects, such as high-speed control and cost, are taken into the consideration of the system design as well. Under the control of home-made electronics, the laser exhibits a tuning range of 50 nm with a 44 dB side-mode suppression ratio, and the system presents the characteristics of low divergence ( 0.63 ∘ × 0.58 ∘ ), high side-lobe suppression ratio ( > 10 d B ), and high-speed response ( < 10 µ s time constant) in an aliasing-free sweeping range of 18 ∘ × 7 ∘ .

A dual-band reconfigurable microwave photonic transceiver chip for synthetic aperture radar is proposed and demonstrated on silicon photonic platform. Study deep into material level is conducted to establish the relation between nonlinear mechanisms in silicon and the performance of the system-on-chip. Guided by the theoretical model, rational paralleled photonic circuit architecture and a series of control strategies, including waveform predistortion, linearity optimization and thermal crosstalk compensation, are put forward to realize a practical and high-performance photonic radar transceiver. RF characterizations indicate that the chip is capable to generate broadband C-band or Ku-band radar signal with low phase deviation on the order of 10 ^-7 . It can also conduct stretch processing in both bands with high spurious free dynamic range exceeding 100 dB·Hz ^2/3 . A radar system taking the photonic chip as core is established to serve the function of two-dimensional imaging. Resolutions at centimeter level and high peak to side lobe ratios are achieved and in consistent with theoretical values. To the best of our knowledge, this work realizes superior analog frequency-conversion signal processing and imaging quality in comparison with previous works.

A microwave photonic (MWP) radar system with improved signal-to-noise ratio (SNR) performance is proposed and experimentally demonstrated. By improving the SNR of echoes through properly designed radar waveforms and resonant amplification in the optical domain, the proposed radar system can detect and image weak targets that were previously hidden in noise. Echoes with a common low-level SNR obtain high optical gain and the in-band noise is suppressed during resonant amplification. The designed radar waveforms, based on random Fourier coefficients, reduce the effect of optical nonlinearity while providing reconfigurable waveform performance parameters for different scenarios. A series of experiments are developed to verify the feasibility of the SNR improvement of the proposed system. Experimental results show a maximum SNR improvement of 3.6 dB with an optical gain of 28.6 dB for the proposed waveforms over a wide input SNR range. From a comparison with linear frequency modulated signals in microwave imaging of rotating targets, significant quality enhancement is observed. The results confirm the ability of the proposed system to improve SNR performance of MWP radars and its great application potential in SNR-sensitive scenarios.

An active integrated broadband photonics multi-beamformer using optical true-time delay induced Blass matrix is designed and demonstrated. The multi-beamformer is constructed on a standard silicon-on-insulator platform, incorporating on-chip modulator array and photodetector array alongside a broadband multi-beamforming network. The network utilizes a Blass matrix architecture based on optical true-time delay to precisely control the power and delay of input microwave signals. Furthermore, wavelength division multiplexing technology achieved by multi-wavelength lasers is used to decouple the signals from different channels, enabling the simultaneous multi-beamforming. Radio-frequency characterizations indicate that the active integrated broadband photonic multi-beamformer is capable of covering the frequency range up to Ku-band and realizes five beams directed at 0${}^{\circ }$, $\pm$ 20${}^{\circ }$, and $\pm$ 40${}^{\circ }$ by 4 input channels. Experimental measurements demonstrate good agreement with designed parameters, validating the compatibility and feasibility of this beamformer for large-scale antenna arrays in radar and wireless communications systems.