Monolithically Integrated Wavelength Locked and High-Brightness Laser Diodes

This thesis presents the fabrication and characterization of high brightness laser diodes with monolithically integrated wavelength locking. The work focuses on two wavelength ranges, 1.5 µm and 1.18 µm, relevant to specific application targets. The lasers emitting around 1.5 µm are primarily aimed at eye-safe LIDAR (light detection and ranging, a group of 3D scanning technologies) applications. 1.18 µm wavelength region is important for frequency doubling into yellow–orange wavelength range. These wavelengths have especially medical applications and are practically unreachable with direct emission using current semiconductor material technology.

Application requirements are approached using two component variants: tapered distributed Bragg reflector laser diodes (tapered DBR-LDs) and broad area DBR-LDs. In both variants, the wavelength locking DBR element is integrated monolithically on the same chip as the active region, enabling smaller component assembly footprints and cost-effective fabrication. Tapered DBR-LDs comprise three sections: tapered mode expansion and power amplification section, ridge waveguide section providing lateral mode filtering, and DBR grating section providing longitudinal mode filtering. Broad area DBR-LDs comprise wide active region and DBR grating. The tapered design provides better beam quality for the applications where a Gaussian beam is required, while the broad area design provides higher output power and easier device operation with a reduced beam quality.

1.18 µm tapered DBR-LDs reached a continuous wave (CW) output power of 4.04 W, while 1.5 µm tapered and broad area DBR-LDs reached pulsed peak output powers of 4.6 W and 6.1 W, respectively. Wavelength locking reduced temperature change induced wavelength drift to 0.1 nm/◦C and spectral full width at half-maximum to 0.3 nm or below. The results are compared quantitatively to results published by others. At the time of publication, these results progressed the state of the art in their own respective categories and have served as the stepping stone for further research and results in the field of high-brightness, wavelength locked lasers.