Fabrication of Embedded 45-Degree Micromirror Using Liquid-Immersion Exposure for Single-Mode Optical Waveguides

A new integration technique of a 45-degree micromirror providing a vertical coupling between a free-space wave and a guided wave in a dielectric-glass waveguide for high-density intra-board optical interconnection was described. A planar waveguide consisting of a 4-μm-thickness GeO :SiO guiding core layer and a 2-μm-thickness SiO cladding layer on an SiO substrate was used for characterization of the micromirror. A trench with 8-μm depth and 8-μm width was formed in the waveguide by using a dry etching technique. A photoresist filling the trench was exposed at an angle of 45 degrees in the water to give a 45-degree taper in the trench. Au was evaporated on the taper to give high-reflection micromirror. An excess loss due to the micromirror insertion was estimated to be about 2 dB by comparing insertion losses of waveguides with and without the micromirror.