Deep-etched distributed Bragg reflector lasers with curved mirrors. Experiments and modeling

A semiconductor laser with deep-etched distributed Bragg reflectors (DBRs) supporting a planar Gaussian mode has been experimentally and theoretically studied. A 90-μm-long laser with two-groove DBRs has a low threshold current of 7 mA and a maximum side mode suppression of 17.6 dB under continuous operation. The laser resonator supports a mode that closely resembles the desired planar Gaussian mode. The reflectivities of the deep-etched DBRs were experimentally determined using broad area devices, and the reflection, transmission, and scattering properties of the DBRs were simulated using a finite-difference time-domain model. The simulations show that deep grooves, covering the full transverse extent of the guided mode, are needed to maximize the reflectivity and to minimize the scattering loss. A beam-propagation model was used to simulate the laser resonator. The simulations (as well as the experiments) show that the laser is sensitive to thermal effects. Thermal lensing narrows the mode waist, and therefore increases the spatial hole burning in the center of the resonator where the intensity is at its maximum. At high drive currents, this leads to a degradation of the spatial mode quality. The simulations also indicate that a laser with optimized DBRs (one one- and one two-groove DBRs with an etch depth of 1 μm) would have a threshold current less than 2 mA and support a high-quality planar Gaussian mode to an output power of 9 mW under continuous operation