Stable Microwave Signal Generation by Heterodyning Dual Lasers Injection-Locked to a Single Microring Resonator

We present a photonic integrated microwave signal generation approach using a dual self-injection-locked (DSIL) laser. The DSIL laser integrates two commercially available distributed feedback (DFB) lasers with a single silicon nitride (Si₃N₄) microring resonator (MRR), exhibiting a high quality-factor (Q-factor) of approximately 2 × 10⁶. By sharing one resonator, both lasers simultaneously achieve self-injection locking, and their frequency fluctuations become highly synchronized. Each self-injection-locked (SIL) laser exhibits integral line widths of 2.3 kHz and 2.4 kHz, highlighting the strong noise suppression that results from high Q-factor resonator feedback. This enables the generation of a heterodyne microwave signal at 13.38 GHz with a narrow line width of about 8.75 kHz. The phase noise of the 13.38 GHz carrier frequency generated by the DSIL architecture is below −85 dBc/Hz at 30 kHz offset, which is more than 30 dB lower than that of a 15 GHz microwave signal produced by heterodyning two independent SIL lasers. Over a 10 h measurement period, the microwave signal at 13.38 GHz exhibits a frequency drift of less than 900 kHz (approximately 67 ppm at 10 h), representing a significant advancement for chip-scale approaches without external frequency stabilization. This stability corresponds to a minimum Allan deviation of 4.9 × 10^–7 at a 1 s averaging time, which is 83 times lower than that of independent SIL lasers. Our results underscore the potential of leveraging large-perimeter resonators, low-loss wide waveguides, and precise phase control to realize compact, ultrastable microwave sources for emerging microwave applications, such as next-generation wireless communications and radar.