Tunable self-injection locked green laser diode.

We report, to the best of our knowledge, the first employment of a self-injection locking scheme for the demonstration of a tunable InGaN/GaN semiconductor laser diode. We have achieved a 7.11 nm (521.10-528.21 nm) tunability in a green color with different injection currents and temperatures. The system exhibited mode spectral linewidth as narrow as ∼69 pm and a side mode suppression ratio as high as ∼28 dB, with a maximum optical power of ∼16.7 mW. In the entire tuning window, extending beyond 520 nm, a spectral linewidth of ≤100 pm, high power, and stable performance were consistently achieved, making this, to the best of our knowledge, the first-of-its-kind compact tunable laser system attractive for spectroscopy, imaging, sensing systems, and visible light communication.

375-nm ultraviolet-laser based non-line-of-sight underwater optical communication.

For circumventing the alignment requirement of line-of-sight (LOS) underwater wireless optical communication (UWOC), we demonstrated a non-line-of-sight (NLOS) UWOC link adequately enhanced using ultraviolet (UV) 375-nm laser. Path loss was chosen as a figure-of-merit for link performance in this investigation, which considers the effects of geometries, water turbidity, and transmission wavelength. The experiments suggest that path loss decreases with smaller azimuth angles, higher water turbidity, and shorter wavelength due in part to enhanced scattering utilizing 375-nm radiation. We highlighted that it is feasible to extend the current findings for long distance NLOS UWOC link in turbid water, such as harbor water.