  Optical phase shifters are essential elements in photonic integrated circuits
(PICs) and function as a direct interface to program the PIC. Non-volatile
phase shifters, which can retain information without a power supply, are highly
desirable for low-power static operations. Here a non-volatile optical phase
shifter is demonstrated by driving a III-V/Si hybrid metal-oxide-semiconductor
(MOS) phase shifter with a ferroelectric field-effect transistor (FeFET)
operating in the source follower mode. Owing to the various polarization states
in the FeFET, multistate non-volatile phase shifts up to 1.25{\pi} are obtained
with CMOS-compatible operation voltages and low switching energy up to 3.3 nJ.
Furthermore, a crossbar array architecture is proposed to simplify the control
of non-volatile phase shifters in large-scale PICs and its feasibility is
verified by confirming the selective write-in operation of a targeted FeFET
with a negligible disturbance to the others. This work paves the way for
realizing large-scale non-volatile programmable PICs for emerging computing
applications such as deep learning and quantum computing.
