Variable groove depth grating waveguide couplers (VGDGWCs) can be used to couple light into or out of planar waveguides. In principle an out-coupled light beam with any arbitrary irradiance profile can be obtained. VGDGWCs that produce out-coupled beams exhibiting a Gaussian irradiance profile are examined in this report. An expression for the grating groove depth variation necessary to produce Gaussian beams from VGDGWCs is derived. The design of a VGDGWC using two different materials for the host planar waveguide is presented. The designs are optimized with a consideration of the waveguide materials, the fabrication process, and the out-coupled beam quality. Two methods, that utilize ion etching to fabricate VGDGWCs are presented. Each method operates by limiting the cross sectional area of an ion beam. A scanning slit is used for one method and a moving variable width aperture is employed for the second. The ion etching process for each of the fabrication methods is characterized by a series of ion beam etching experiments. The results from the ion beam etching experiments are used to optimize the fabrication process. The variable width aperture fabrication method in combination with a post etching process, is found to produce the optimum results. The measured irradiance profile and the wavefront quality of the out-coupled beams from the fabricated VGDGWCs are compared to theory. The variable width aperture fabrication method is found to produce out-coupled beams with a nearly perfect Gaussian irradiance profile. The measured wavefront quality of out-coupled beams shows good agreement with theory.
展开▼
