Quantification of losses in bent waveguides within DBR-RW laser diodes emitting at 785 nm

Abstract

An experimental study of straight and bent distributed Bragg reflector (DBR) ridge waveguide (RW) lasers and Fabry–Pérot (FP) RW lasers emitting at 785 nm is presented. To determine the losses introduced by the bent waveguides within DBR-RW lasers, different laser designs were manufactured and characterized. The bent waveguides investigated here within DBR-RW laser diodes are sine-shaped S-bends. S-bends with three different lateral offsets are manufactured. The experimental characterization of FP lasers and the straight DBR-RW lasers with different coatings at the rear facet enables a rough estimation of the losses caused by the DBR grating and the determination of the DBR reflectivity. Furthermore, additional losses in the bent DBR-RW lasers caused by the S-bend (i.e. radiation and scattering losses) are quantified by comparing them to the straight DBR-RW lasers. Within the active resonator, the S-bend losses amount to α Bend = 0.6 cm−1 (α Bend = 0.5 dB) for the smallest manufactured lateral S-bend offset H = 40 μm. For both straight and bent DBR-RW lasers spectrally narrow single-mode emission is obtained. A lateral beam width of 3.8 μm (using second moments) and a lateral far-field angle of about 18° and 19.5° (using second moments) for the straight and S-bend DBR-RW are measured, respectively. This gives a lateral beam propagation ratio of 1.2 and 1.3 (using second moments) for straight and S-bend DBR-RW, respectively. The radiation loss in dependency of the lateral S-bend offset is simulated and compared to experimentally estimated S-bend losses for bent DBR-RW lasers (H = 40 μm, H = 60 μm and H = 70 μm).