Grating-Assisted Directional Coupler in Lithium Niobate for Tunable Mode Filtering

We propose a long-period grating assisted directional coupler in lithium niobate (LN) for the realization of electro-optic tunable mode filtering functionality. Our typical device, fabricated with the annealed proton-exchange process and designed for filtering out the fundamental mode in a two-mode LN waveguide, achieves a maximum mode extinction ratio of 29 dB at 1551.7 nm wavelength and a -20 dB bandwidth of similar to 2.5 nm with an electrical wavelength tuning sensitivity of 0.182 nm/V.