Digitally Controlled Phase Shifter Using an SOI Slot Waveguide With Liquid Crystal Infiltration

We demonstrate a phase shifter using a silicon slot waveguide infiltrated with liquid crystal. For a 1-mm long device we achieve $73\pi $ phase shift with a 5 V voltage, with a voltage-length product of 0.0224 $\text{V}\cdot $ mm $\sim 1$ V. We drive the phase shifter with a digital 1 V, duobinary pulsewidth-modulated signal, or a 1 V frequency-modulated signal. This enables direct digital CMOS control of an analog optical phase shifter.