  Chip-scale, high-energy optical pulse generation is becoming increasingly
important as we expand activities into hard to reach areas such as space and
deep ocean. Q-switching of the laser cavity is the best known technique for
generating high-energy pulses, and typically such systems are in the realm of
large bench-top solid-state lasers and fiber lasers, especially in the long
wavelength range >1.8 um, thanks to their large energy storage capacity.
However, in integrated photonics, the very property of tight mode confinement,
that enables a small form factor, becomes an impediment to high energy
application due to small optical mode cross-section. In this work, we
demonstrate complementary metal-oxide-semiconductor (CMOS) compatible,
rare-earth gain based large mode area (LMA) passively Q-switched laser in a
compact footprint. We demonstrate high on-chip output pulse energy of >150 nJ
in single transverse fundamental mode in the eye-safe window (1.9 um), with a
slope efficiency ~ 40% in a footprint of ~9 mm2. The high energy pulse
generation demonstrated in this work is comparable or in many cases exceeds
Q-switched fiber lasers. This bodes well for field applications in medicine and
space.
