Gratings for distributed feedback lasers formed by selective epitaxial growth

The implementation of state-of-the-art semiconductor lasers with distributed feedback (DFB), and the optimization of the DFB resonator for specific operating characteristics, require, in many cases, a grating with carefully tailored, slowly varying parameters along the cavity axis. A change in the corrugation pitch and incorporation of discrete phase shifts along the cavity may be implemented by E-beam lithographic methods, and by changes in the geometrical parameters of the laser waveguide. A change in the coupling strength, |κ|, is more difficult to realize. Recently, a novel method for fabricating a DFB laser with two discrete values of |κ| in different sections of the laser cavity, was demonstrated, but the extension of this method to arbitrary variations in |κ| along the laser is not straightforward. Selective organometallic vapor phase epitaxy (OMVPE) on masked substrates is an attractive option for epitaxial layer deposition with controllable thickness variations. Both the growth rate and the composition of ternary or quaternary layers are determined by the mask geometry. In this work, a novel method for the formation of DFB gratings is demonstrated, relying on selective OMVPE growth. The method does not require semiconductor etching, and furthermore it allows for a controlled variation of |κ| along the laser cavity