Multi-wavelength hybrid laser with side-coupled Fabry-Perot silicon nitride resonators

We demonstrate a hybrid external cavity laser incorporating an integrated side coupled Fabry-Perot (SC-FP) resonator realised on a silicon nitride platform and coupled to a semiconductor optical amplifier. The SC-FP resonator achieves loaded quality factors of up to 6.5 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> with on-resonance reflectivity reaching 57%. The hybrid laser exhibits multi-wavelength emission aligned to the SC-FP resonances, with multiple longitudinal modes of the hybrid cavity competing within each resonance. When isolating single resonances, we observe coherent pulse trains with corresponding radiofrequency linewidth as narrow as ∼3 kHz. The system spontaneously generates multiple identical pulse profiles within the laser cavity, effectively multiplying the repetition rate. These results establish SC-FP resonators as promising wavelength-selective reflectors for compact, multi-wavelength hybrid laser systems with potential applications in frequency comb generation for telecommunication and precision spectroscopy.