Method of making distributed feedback laser having spatial variation of

Abstract

A distributed feedback (DFB) laser is made with a spatially graded optical coupling (.kappa.) between its diffraction grating and its active layer by means of selective area epitaxial growth of the epitaxial layer from which the grating is formed. More specifically, the epitaxial layer is formed on a major surface of a semiconductor substrate on which a mask, such as a silicon dioxide mask, has been formed. The mask has a pair of segments spaced apart by a fixed distance, the segments having spatially variable widths. Advantageously the epitaxial layer has a refractive index that is different from that of the substrate at the operating wavelength of the laser. The epitaxial layer is then etched into stripes. In this way the heights of the resulting grating stripes will be spatially variable, and so will the coupling .kappa. between the grating and the active layer. In this way, the properties of the optical output of the laswer can be adjusted. Advantageously also, the spacer layer and the substrate have the same refractive indices at the operating wavelength of the laser, whereby accurate control over the depth of the etching is not required.