Development of a through-glass programmable optical interferometer made of liquid crystal tilted gratings

This work introduces a novel programmable optical device based on electrically-tunable tilted liquid-crystal gratings (TLCG), obtained on two stacked BK7 glasses, covering a total footprint of a few mm2. The primary light path follows a straight optical channel made on the upper surface of the bottom glass through double ion exchange method. The application of a voltage between the indium tin oxide (ITO) contacts patterned on the BK7 inner surfaces enables a secondary path since tilted gratings form in liquid crystal wells. Therefore, light is redirected through the top glass and coupled to two parallel optical channels, forming a multilayer Mach-Zehnder Interferometer (MZI) pattern. Finite-Difference Time-Domain (FDTD) simulations at 1550 nm wavelength confirm the light's routing through the MZI secondary path. A highly-focused light beam is steered out of the plane when the designed TLCG structures, placed on top of the primary path, are electrically activated. Furthermore, the optical coupling of an out-of-plane light beam coming from underneath to the upper MZI arms is successfully proven using glass-etched tilted grating structures. These findings mark promising foundations in developing a simple, cost-effective, versatile, compact and programmable MachZehnder interferometer suitable for optical biosensing and optical communications systems.