A photonic system based on a two-channel structure is proposed to realize the simultaneous measurement of angle-of-arrival (AOA) and Doppler-frequency-shift (DFS) of microwave signal without direction ambiguity. The unambiguous AOA measurement can be acquired by recording the power of the output intermediate frequency (IF) signal and output radio frequency (RF) signal from two channels. The DFS can be determined from the frequency of the IF signal. Estimated experimental results show that a −66.44° to 66.44° AOA measurement with errors of less than ±2.2° and an unambiguous DFS measurement with errors of ±0.6 Hz are implemented.

We propose a microwave photonic frequency measurement scheme based a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM) and frequency -to-time mapping. A compact frequency measurement system is guaranteed thanks to the use of a single modulator, and multi-tone measurement ability is achieved due to the principle of frequency-to-time mapping. In the proposed scheme, the unknown microwave signal is mixed with a linearly chirped microwave signal with the help of the DP-DDMZM, and the mixing product is selected by an electrical bandpass filter to achieve frequency-to-time mapping. Single and multi-tone microwave frequency measurement are successfully demonstrated in the experiment, and the measurement errors are less than ± 3 MHz.

We report a novel temperature sensor based on a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) and temperature-to-time mapping. In the proposed scheme, a narrow bandpass electrical filter is inserted into the FDML OEO cavity. The temperature information is mapped to the time interval of the output pulses due to the temperature-sensitive bidirectional scanning property of the FDML OEO. Compared with other OEO-based temperature sensors, the proposed scheme avoids the needs of wideband electrical spectrum analyzers, since the temperature-sensitive output pulses can be interrogated using a low-speed oscilloscope working under sub-Nyquist sampling condition. In the proof-of-concept experiment, a high sensitivity of 8.166 μs/°C and resolution of 0.03°C is achieved, demonstrating a good temperature sensing performance.

A compact photonics-assisted scheme for short-time Fourier transform (STFT) is proposed and experimentally demonstrated. In the proposed scheme, a periodic chirp signal and an electrical bandpass filter (BPF) are applied to achieve a sliding window function. At the same time, the BPF is utilized to realize frequency-to-time mapping and obtain the frequency-domain information in each time window. The STFT can be realized by splicing the frequency-domain information corresponding to different time windows into a two-dimensional time-frequency graph. Experimentally, STFTs of various time-varying microwave signals are demonstrated, where a frequency resolution of 100 MHz, a time resolution of 0.1 μ s, and a real-time measurement range from 1 to 9.7 GHz are separately realized. In addition, the measurement range is only limited by the bandwidth of the applied periodic chirp signal and the center frequency of the BPF. Furthermore, the proposed scheme avoids additional processing latency compared to dispersion-based STFT schemes, which ensures great real-time performance.

We propose a photonic scheme to generate binary phase-coded microwave pulses and dual-chirp microwave waveforms without baseband-modulated signals (background noise) based on a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM) which contains x-DDMZM and y-DDMZM at two different polarization states. A radio frequency (RF) signal from a microwave source is transferred into two differential RF signals and employed into one arm of x-DDMZM and one arm of y-DDMZM, while a baseband signal from an arbitrary waveform generator is divided by an electronic coupler and then driven into the two other arms of DP-DDMZM. By adjusting the phase differences between the x-DDMZM and the y-DDMZM, binary phase-coded pulses and dual-chirp signals without baseband-modulated signals are generated. The proposed scheme can eliminate the interference caused by baseband-modulated signals, and satisfy different radar applications for different frequency bands. Experimental results show that phase-coded signals at 15 GHz with the bit rates of 1 Gb/s and 2 Gb/s and dual-chirp signals at 10 GHz and 15 GHz with the time durations of 0.5 s are successfully generated. The reported scheme is well analyzed in theory and verified by experiment.

We propose a microwave photonic scheme to generate rectangular and triangular waveforms by external modulation. Different from previous works, the duty circle of the generated waveforms in our scheme is freely tunable. The main structure is based on a Mach-Zehnder modulator and a tunable optical delay line. By power splitting and time-delay tuning on two polarization branches, triangular or rectangular waveforms can be obtained by the superposition of beating signals. Moreover, the RF modulation index in this work is unfixed, which increases the flexibility of the system. The proposed scheme is theoretically analyzed and experimentally verified. The triangular and rectangular waveforms at repetition rates of 4 and 5 GHz are successfully generated.