Through-glass programmable coupler made of liquid crystal tilted gratings for optical interferometry

This work presents the development of a programmable optical system based on tunable tilted liquid crystal gratings designed to work within the infrared (IR) spectrum. The proposed system has a total footprint of a few mm2, and the grating is obtained between two stacked BK7 glass substrates forming a multilayer system. The scope of such configuration is to guide light inside an optical channel made on the upper surface of the bottom BK7 glass (i.e. buried inside the glass stack). Alternatively, by applying an external voltage, it enables the activation of a secondary path, configured as a Mach-Zehnder interferometer (MZI), by steering light through the top glass and coupling it inside two optical channels made on the upper surface of the system. At the end of the secondary path, light is steered back to the internal waveguide through the top glass and recoupled towards the output of the system. The Finite-Difference Time-Domain (FDTD) simulations, validate the optical coupling of an out-of-plane light beam coming from above to the bottom arm of the MZI using a liquid crystal tilted grating structure, providing a promising foundation for the development of a versatile, compact and programmable Mach-Zehnder interferometer suitable for optical communications systems and optical biosensing.