Monolithically integrated narrow-bandwidth disk laser on thin-film lithium niobate

Integrated on-chip microdisk lasers have attracted great attention as a light source of compact size, low lasing threshold and narrow bandwidth. However, challenges remain unresolved in terms of single mode operation at high output power while maintaining the ultra-narrow bandwidth. In this work, we demonstrate monolithically integrated on-chip single-frequency disk lasers coupled with bus-waveguides fabricated by photolithography assisted chemo-mechanical etching. Owing to the long cavity lengths (e.g., 409 μm and 1 mm) for high optical gain and high-Q mode regulation for suppressing multimode lasing, a disk laser with a narrow linewidth of 0.11 MHz and a maximum output power of 62.1 μW has been achieved at room temperature. These two values are about one order of magnitude better than the best results previously reported on monolithically integrated LN microlasers.