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

Summary form only given. 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.In this work we therefore analyse the effect of lateral ridge waveguide and grating layout changes on the obtained grating diffraction efficiency. In order to determine the diffraction efficiency, 2 mm and 4 mm long 1030 nm DBR lasers with an asymmetric super large optical cavity vertical layer structure, previously applied for tapered lasers, were manufactured. Intrinsic wavelength stabilization is obtained with 1 mm long 3rd and 7th order DBR gratings. Three different lateral layouts are compared, including lasers with straight waveguide and grating, linear adiabatic waveguide [2] and straight grating, and straight waveguide and linear adiabatic grating. The adiabatic layouts are selected in order to obtain high diffraction efficiencies similar to broad devices and a good spatial mode filtering [3]. For each layout the diffraction efficiencies are obtained by measuring the optical output power emitted through the rear and the front facets of unmounted devices.