Broadband continuous frequency-tunable narrow-linewidth laser based on self-injection locking to a miniaturized Fabry-Perot cavity

We demonstrate a 1550 nm external-cavity diode laser (ECDL) based on a high-Q miniaturized Fabry-Pérot (FP) cavity, achieving a wide mode-hop-free continuous frequency-tuning range, which holds significant application value in fields such as frequency-modulated continuous-wave (FMCW) ranging and radar. By minimizing the feedback loop length and employing a piezoelectric transducer (PZT) to scan the cavity length, the continuous frequency-tuning range exceeds 30 GHz at a repetition rate of 100 Hz, with frequency-tuning nonlinearities of 1.7% and 1.9% for the up-scan and down-scan phases, respectively. When the scanning frequency is increased to 10 kHz, the continuous frequency-tuning range remains above 10 GHz. The 3 dB linewidth is narrowed to 10 kHz, while the laser volume is only 3 mL. Through synchronous adjustment of both the feedback loop and FP cavity phases, the continuous frequency-tuning range can be expanded to 50 GHz, with a corresponding frequency-tuning nonlinearity of 2.0%. By increasing the Q-factor of the FP cavity (>10⁶), the linewidth is further narrowed to 2.8 kHz, and the high-Q FP cavity demonstrates significant suppression of frequency noise.