As an emerging topic, photonic‐assisted microwave measurements with distinct features such as wide frequency coverage, large instantaneous bandwidth, low frequency‐dependent loss, and immunity to electromagnetic interference, have been extensively studied recently. In this article, we provide a comprehensive overview of the latest advances in photonic microwave measurements, including microwave spectrum analysis, instantaneous frequency measurement, microwave channelization, Doppler frequency‐shift measurement, angle‐of‐arrival detection, time–frequency analysis, compressive sensing, and phase‐noise measurement. A photonic microwave radar, as a functional measurement system, is also reviewed. The performance of the photonic measurement solutions is evaluated and compared with the electronic solutions. Future prospects using photonic integrated circuits and software‐defined architectures to further improve the measurement performance are also discussed. image

The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fibre networks, such as urban structure imaging, ocean seismic detection, and safety monitoring of underground embedded pipelines. This work demonstrates a scheme of integrated sensing and communication in an optical fibre (ISAC-OF) using the same wavelength channel for simultaneous data transmission and distributed vibration sensing. The scheme not only extends the intelligent functionality for optical fibre communication system, but also improves its transmission performance. A periodic linear frequency modulation (LFM) light is generated to act as the optical carrier and sensing probe in PAM4 signal transmission and phase-sensitive optical time-domain reflectometry (Φ-OTDR), respectively. After a 24.5 km fibre transmission, the forward PAM4 signal and the carrier-correspondence Rayleigh backscattering signal are detected and demodulated. Experimental results show that the integrated solution achieves better transmission performance (~1.3 dB improvement) and a larger launching power (7 dB enhancement) at a 56 Gbit/s bit rate compared to a conventional PAM4 signal transmission. Meanwhile, a 4 m spatial resolution, 4.32-nε/ $$\sqrt {Hz}$$H z strain resolution, and over 21 kHz frequency response for the vibration sensing are obtained. The proposed solution offers a new path to further explore the potential of existing or future fibre-optic networks by the convergence of data transmission and status sensing. In addition, such a scheme of using shared spectrum in communication and distributed optical fibre sensing may be used to measure non-linear parameters in coherent optical communications, offering possible benefits for data transmission.

Nowadays, the microwave photonics (MWP) concept has been evolved from laboratory tests to practical applications, and related techniques have been widely deployed in many fields including such as wireless communications, medicine, sensing, radars, electronic warfare, and space explorations. In this paper, we concentrate on the featured applications of MWP in the high-speed railways (HSRs), an emerging field and massive market, and an overview about our recent work is presented. The radio-over-fiber based wireless communications in high-mobility scenarios, photonic-assisted electromagnetic interference detection along HSR lines, and fiber sensing for safety protection of railways are investigated systematically in our group. Experiments are then performed to verify the basic functionalities of the three MWP-enabled systems mentioned above. In particular, field trials have been successfully implemented along two in-service HSR lines located in Southwest China, i.e., the Chengdu–Chongqing and the Chengdu–Mianyang–Leshan HSR lines. With these results and achievements, we can expect more MWP-enabled striking applications in the HSR field in near future.

We propose and experimentally demonstrate a photonic approach to the measurement of the time-difference-of-arrival (TDOA) and the angle-of-arrival (AOA) of a microwave signal. In the proposed system, the TDOA and the AOA are equivalently converted into a phase shift between two replicas of a microwave signal received at two cascaded modulators. The light wave from a CW laser is externally modulated by the microwave signal at the first modulator, which is biased to suppress the optical carrier, leading to the generation of two first-order sidebands, which are further modulated by the phase-delayed microwave signal at the second modulator. Two optical components at the carrier wavelength are generated. The total power at the carrier wavelength is a function of the phase shift due to the coherent interference between the two components. Thus, by measuring the optical power, the phase shift is estimated. The AOA is calculated from the measured phase shifts. In our experiment, the phase shift of a microwave signal at 18 GHz from $-160°$ to 40° is measured with measurement errors of less than $\pm 2.5°$.

A novel millimeter-Wave (mm-Wave) joint radar and communication (JRC) system based on photonic spectrum-spreading phase-coding is proposed. The key to the proposed system is the convergence of photonic microwave phase-coding and spectrum-spreading multiplexing techniques. Phase-coding enables the generation of wideband mm-Wave JRC signal, leading to both high range resolution (< 3.5 cm) for radar detection and high capacity (>1 Gb/s) for wireless communication. The spectrum-spreading multiplexing orthogonalizes the radar signal and communication data, highly reducing mutual interferences. In addition, the spectrum-spreading multiplexing is able to improve both peak sidelobe ratio (PSR) for radar and anti-jamming/anti-noise performance for communication. In the proof-of-concept experiments, a JRC phase-coding signal at 35 GHz is generated. For a 5-Gb/s coding rate, the signal-to-noise ratio (SNR) margin is improved by around 13.8 dB for wireless communication below the pre-forward error correction (FEC) limit, while the PSR reaches ~12 dB for radar. Moreover, the impact of spreading gain on the communication capacity has been discussed, revealing that an optimized spreading gain should be set to balance the radar and communication performances.

We propose a fully digital programmable optical frequency comb (OFC) generation scheme based on binary phase-sampling modulation, wherein an optimized bit sequence is applied to phase modulate a narrow-linewidth light wave. Programming the bit sequence enables us to tune both the comb spacing and comb-line number (i.e., number of comb lines). The programmable OFCs are also characterized by ultra-flat spectral envelope, uniform temporal envelope, and stable bias-free setup. Target OFCs are digitally programmed to have 19, 39, 61, 81, 101, or 201 comb lines and to have a 100, 50, 20, 10, 5, or 1 MHz comb spacing. As a demonstration, a scanning-free temperature sensing system using a proposed OFC with 1001 comb lines was also implemented with a sensitivity of 0.89°C/MHz.