Photonic Generation of Broadband Coherent LFM Microwave Waveforms Based on Phase-Locked Tunable Integrated Lasers

We propose and demonstrate a novel scheme for generating broadband and high-coherence linear frequency-modulated (LFM) waveforms based on heterodyne beating of two real-time phase-locked tunable lasers. The generation scheme comprises two hybrid integrated self-injection locked lasers in a master- slave configuration. By controlling the integrated high-Q microring resonator (MRR) external cavities through heaters and a piezoelectric transducer (PZT), the lasers can achieve broadband frequency linear sweeping and ultrafast tuning, respectively. Combined with an optical phase-locked loop (OPLL) and a standard intermediate frequency LFM (IF-LFM) reference signal, the slave laser can maintain real-time phase locking with the master laser. In the experiment, multiple coherence beat LFM signals with reconfigurable center frequency, bandwidth, and temporal period are generated, with a time- bandwidth product (TBWP) of up to $2.44 \times 10^{8}$ . The performance in terms of the signal linearity and pulse-to-pulse coherence is characterized. Moreover, we conduct a dechirp ranging experiment using the generated signals in different frequency bands (C-, X-, Ku-, and K-bands) and successfully demonstrate the high-precision-ranging capability. Featuring a simple structure, a broad operation bandwidth, high phase coherence, and flexible reconfiguration, the proposed signal generation scheme is expected to play an important role in real-world radar application scenarios.