Multi-frequency self-injection locking of a FSR-tunable multimode laser diode

This study presents the controllable multi-frequency self-injection locking regimes realization with an original experimental setup composed of a reflective semiconductor optical amplifier, an external feedback mirror, and a high-Q chip-scale Si₃N₄ ring microresonator. Our findings demonstrate the conditions of multiple modes' simultaneous locking being analogous to Vernier effect. We varied the free spectral range of the external-cavity laser by its length tuning, enabling the robust generations from 1 to 4 self-injection locked narrow lines on demand, that is important for optical telecommunications, and photonic-based microwave and THz sources.