Polarization characteristics of vertical-cavity surface-emitting lasers with tilted waveguide region

Abstract

Control of the polarization state for vertical-cavity surface-emitting lasers (VCSELs) is one of the critical issues for polarization sensitive optical systems. In conventional VCSEL structures, the nearly degenerated orthogonal polarization states with fundamental mode are observed at and above threshold. However, in the absence of the selectivity of a polarization state, unstable polarization switching occurs and results in an excess intensity noise by mode hopping. A stable polarization operation over wide current range is required for low noise applications. Several attempts have been made to control the polarization of VCSELs.[1-3] A birefringent metal/dielectric polarizer on the top distributed Bragger reflector (DBR)[1] and an anisotropic gain medium of fractional-layer superlattice structure[2] were introduced. Choquette et al. [3] examined anisotropic transverse cavity like rhombus- or dumbbell-shape and obtained strong polarization selectivity for a specific direction. In this work, we propose a simple method to control the polarization direction by tilted-etching of laser pillar. This structure can select a single dominant polarization state with an electric field perpendicular to the tilted direction. We also demonstrate switching of the two polarized beams in form of 2x4 array in which a switching unit consists of a pair of laser devices tilted with different directions.