Influence of lateral waveguide and grating layouts on the diffraction efficiency of distributed Bragg reflectors

Wavelength stabilized diode lasers, such as distributed Bragg reflector (DBR) lasers, are required for many different applications. A tool for manufacturing of DBR gratings is electron beam lithography, a flexible technology with high reproducibility. The resolution enables the realization of low-order gratings with high reflectivities. For a recent process of 1030 nm DBR lasers, numerical simulations for infinitely wide gratings predicted that diffraction efficiencies > 90% can be obtained (Fig. 1, left). However, measurements for processed ridge waveguide lasers showed a significant loss of output power through the anti-reflection coated rear facet [1]. Based on the ratio of output power measured at both facets, the experimentally obtained DBR diffraction efficiencies were only half the values obtained from the numerical simulations using the CAvity Modelling FRamework tool (CAMFR, http://camfr.sourceforge.net/). In comparison, high diffraction efficiencies were measured for broader DBR ridge waveguide lasers. For diode lasers, low DBR diffraction efficiencies may result in increased laser thresholds and reduced electro-optical efficiencies. In case of DBR tapered diode lasers low diffraction efficiencies may even cause a poor spatial mode filtering, significantly limiting the diffraction limited output power of such devices.