We numerically investigated the optical output characteristics in two kinds of optical waveguide coupled high-index-contrast subwavelength grating VCSELs (HCG-VCSELs) that couple the laser output to the in-plane waveguide, operating at a 1.55-µm region. One is the transverse electric (TE) HCG, and the other is the transverse magnetic (TM) HCG. In a waveguide coupled HCG without a cavity structure, the out-coupling efficiency to the waveguide strongly depends on the intensity of the incident light at the starting edge of the waveguide. In a waveguide coupled HCG-VCSEL, the ratio of the waveguide output to the optical power inside the active region is determined also by the intensity of the resonant mode at the waveguide edge. The TE-HCG-VCSEL exhibited an almost 30 times larger waveguide output power while the quality factor of the laser cavity is 1/3, compared to those in the TM-HCG-VCSEL. The single mode condition was satisfied for the waveguide of the TE-HCG-VCSEL while the first order mode was allowed for that of the TM-HCG-VCSEL. Positioning the mesa edge at the waveguide edge within 1-µm accuracy results in waveguide outputs of about 0.7 and 0.02% of that inside the active region for TE- and TM-HCG-VCSEL, respectively.

We review our research progress of multi-port optical switches based on the silicon photonics platform. Up to now, the maximum port-count is 32 input ports×32 output ports, in which transmissions of all paths were demonstrated. The switch topology is path-independent insertion-loss (PILOSS) which consists of an array of 2×2 element switches and intersections. The switch presented an average fiber-to-fiber insertion loss of 10.8 dB. Moreover, -20-dB crosstalk bandwidth of 14.2 nm was achieved with output-port-exchanged element switches, and an average polarization-dependent loss (PDL) of 3.2 dB was achieved with a non-duplicated polarization-diversity structure enabled by SiN overpass waveguides. In the 8×8 switch, we demonstrated wider than 100-nm bandwidth for less than -30-dB crosstalk with double Mach-Zehnder element switches, and less than 0.5 dB PDL with polarization diversity scheme which consisted of two switch matrices and fiber-type polarization beam splitters. Based on the switch performances described above, we discuss further improvement of switching performances.