Low-loss, low-power, MOSCAP optical phase shifter on an InP membrane platform

We demonstrate a low-loss and low-power InP MOSCAP optical phase shifter. The device features a MOSCAP structure formed by placing a metal electrode on top of an InP membrane waveguide, separated by a 700-nm-thick gate oxide. Voltage application induces electron accumulation at the surface of the InP waveguide, modulating the refractive index. By exploiting the large electron-induced refractive index change and the low free carrier absorption in InP, a modulation efficiency (V_π·L) of 1.08 V·cm and an additional optical loss of 0.27 dB/π are obtained, despite the use of the thick gate oxide. Furthermore, the thick gate oxide suppresses leakage current, enabling low power operation of 11.5 pW/π.