Analysis and design of cylindrically symmetric surface emitting DBR lasers

Abstract

In optical fiber communications, long-distance, low -interference communication links have been realized through the development of both low-loss, single-mode fibers and high output power single-mode diode lasers. Three configurations of surface emitting DBR (Distributed Bragg Reflector) lasers that have cylindrical symmetry and operate in a single mode are designed in this research. All lasers of this type are capable of lasing at a single frequency and of generating high output power through normal surface emission. Coupled mode theory is employed to analyze the effective reflectivity resulting from the grating and to thereby set up the threshold condition. Cavity mode discrimination ability is carefully investigated by studying the threshold gain of each mode in a cavity designed for a specific mode. In one of the configurations, a judicious modification has been introduced into the cavity design to ensure stable single mode operation; for this configuration the far-field power distribution of the surface emitting laser is studied. Unlike other designs, our design shows a far-field power distribution that has an oval shape with divergence angle close to the diffraction limit. This is a major improvement. Details of realizing the modification on refractive index and techniques for fabrication of the circular grating are discussed.