Broadband and Polarization-Independent Efficient Vertical Optical Coupling With 45° Mirror for Optical I/O of Si Photonics

Efficient, broadband, and polarization-independent optical input/output (I/O) coupling of silicon photonics chips is significant for its practical application, and single-mode vertical optical I/O coupling will be necessary for high-density optical I/O connections required in future high-performance computing systems. We demonstrated such optical coupling using a 45° mirror, which was integrated by a cost-effective dicing technique with a polishing process. The 45° mirrors were integrated into Si-rich silica (SiOx) waveguides on a Si substrate. To evaluate the light beam profile, which was important factor for the single-mode optical coupling, we measured near field patterns and far field patterns of light beams reflected by the 45° mirror. Owing to the polishing process, high-quality single-mode beams were successfully obtained as the vertical optical output. Using the fabricated 45° mirrors, the efficient single-mode vertical optical coupling with loss penalty of around 0.3 dB was demonstrated. The wavelength-dependent loss was less than 0.6 and 0.2 dB for TE and TM polarization, respectively. The polarization-dependent loss was also very small and it was less than 0.2 dB in 1500-1600 nm.