Hybrid Integrated Frequency-Modulated Continuous-Wave Laser With Synchronous Tuning

We report a wavelength widely-tunable hybrid integrated external cavity laser (ECL) with synchronous tuning to achieve a large frequency chirp bandwidth and high chirp linearity. Si ₃ N ₄ Vernier microring resonators (MRRs) in the ECL function as an optical bandpass filter to offer strong wavelength selectivity and fast frequency tunability. The wavelength tuning range is 56 nm, the maximum output optical power is 22.5 mW, the minimum intrinsic linewidth is 2.9 kHz, and the static frequency sweep bandwidth is 56 GHz. A frequency-modulated continuous-wave (FMCW) signal is generated under synchronous modulation with a chirp bandwidth of 7.68 GHz at a 1 kHz repetition rate, much larger than that produced by modulating the phase shifter or the Vernier filter alone. A chirp linearization method based on a non-uniform sampling algorithm and an iterative learning algorithm is employed to reduce the chirp nonlinearity to 1.02×10 ^-7 , allowing for a detection resolution of 2.47 cm.