Low power optical phase shifter using liquid crystal actuation on a silicon photonics platform

Abstract

Low-power and compact phase shifters are crucial for large photonic circuits, both to cope with variability and to create programmable waveguide circuits scaling to thousands of tuning elements. This work demonstrates a liquid crystal phase shifter where there is a lateral silicon electrode "rail" on one side of the waveguide core. Using this architecture, a strong quasi-static electric field E actuation can be applied over the gap, which is filled with liquid crystal cladding material, with modest voltages. Because the mode is largely confined in the waveguide, optical losses are limited, compared to earlier experiments with slot waveguides. The liquid crystal is deposited locally on three different device variations using inkjet printing. The local deposition avoids unwanted interference of the liquid crystal with other optical components such as grating couplers. Measurements show similar trends as simulations of the liquid crystal orientations. For one device with a length of 50 µm, a phase shift of almost 0.9π is shown at 10 VRMS. We also discuss the challenges with this first demonstration of this phase shifter geometry using a silicon side-rail as an electrode.