Fabrication and Optimization of the 45° Micro-mirrors for 3-D Optical Interconnections

This report experimentally demonstrated the fabrication and optimization of 45° micro-mirror forming process in the polymer waveguide layer for optical interconections. The fluorinated acrylate waveguide is consisted of stacking of the lower cladding, core and upper cladding layer. The guide core (70 um × 70 um) is fabricated by the soft molding method and the cladding layers are fabricated by spin-coating. The mirrors are fabricated by mechanical dicing using a 90° diamond dicing blade. The characteristics of the mirror, i.e., angle, surface quality and reflectivity are critical in achieving an efficient optical coupling of the active devices and the waveguide to form a 3-D optical interconnection. Scanning electron microscopy (SEM) and white light interferometer were used for the characterization of micro-mirror. The quality of the micro-mirror, which affecting the optical coupling in the polymer waveguide is of crucial for the success of the optical interconnections. The roughness and angle of mirror is important criteria in achieving an efficient optical coupling. Mirror surface roughness, measured by white-light interferometer, is of 316 nm with standard deviation of 0.006. The angle of the mirror which was measured by SEM and the white-light interferometer, met the requirement of 45 ± 1°. Larger angle tolerance will diversify the laser beam, lose its verticality and off targeting the photo-detector. In order to meet the performance specification, tighter process control and optimization of the dicing parameters are required to minimize the optical transmission loss. Detailed of each process are discussed in this paper.