Taperless Si hybrid optical phase shifter based on a metal-oxide-semiconductor capacitor using an ultrathin InP...

We propose a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter using an ultrathin InP membrane, which allows us to eliminate the III-V taper required for mode conversion between Si and hybrid waveguides. We numerically revealed that thinning a III-V membrane can reduce the insertion loss of the phase shifter while maintaining high modulation efficiency because the optical phase shift is induced by carrier accumulation at the MOS interface. We experimentally demonstrated the proposed optical phase shifter with an ultrathin InP membrane and achieved the modulation efficiency of 0.54 Vcm and the insertion loss of 0.055 dB. Since the taperless structure makes the hybrid integration easier and more flexible, the hybrid MOS optical phase shifter with an ultrathin III-V membrane is promising for large-scale Si programmable photonic integrated circuits.