Mode control in VCSELs using guided-mode resonant filters

Abstract

The vertical-cavity surface-emitting laser (VCSEL) by now has almost completely supplanted the edge-emitting laser in the data communication market. Although there are a number of reasons behind this, including superior beam shape, wafer-level testing prior to dicing, ease of packaging, improved reliability, and much lower drive current, one particular advantage is that the VCSEL has one longitudinal mode and multiple transverse modes with relatively narrow spectral bandwidth (~<2 nm). The latter property assures excitation of multiple guided modes in large core graded-index fiber (typically, either 50 µm or 62.5 µm diameter), thus minimizing one of the dominant noise sources in optical data communications - modal noise. However, there are very many other applications, such as optical storage, sensing, and barcode scanning, where operation in the ftindamental single mode with polarization control is required. Several methods have been proposed to achieve lasing in only the lowest-order transverse mode; most involve some form of spectral or spatial filtering. Here, we report on our continuing efforts [1,2] to use the combined spectral, spatial, and polarization selective properties of Wang and Magnusson's guided-mode resonant filter [3,4] to provide modal control in VCSELs.