High-Power Distributed Feedback Lasers With Surface Gratings: Theory and Experiment

Semiconductor lasers with integrated surface gratings are known to operate with narrow spectra as well as high power and efficiency. In this paper, we present a theoretical description of DFB lasers with 80th-order waveguide gratings, fabricated by etching narrow grooves into the epitaxial layer structure. The passive gratings are simulated by mode expansion and S-matrix algorithm yielding the reflection and transmission matrices in dependence on wavelength for given parameters of the grating, such as residual layer thickness and width of the grooves. The lasing condition is solved by constructing a round-trip operator and singular-value deposition for the calculation of lasing wavelength and threshold gain. A fast simulation of DFB lasers is performed within the framework of coupled-wave theory using adapted coupling coefficients. GaAs based ridge-waveguide and narrow-stripe broad-area lasers with integrated surface gratings are experimentally shown to emit output powers of 0.6 W into a single spectral line Δλ_FWHM <; 30 pm) and > 5 W into a spectrum with width Δλ_95% ≈ 0.8 nm, respectively.