Calculated wavelength sensitivity of lithium niobate switches

A method is presented for calculating the wavelength sensitivity for electrooptic guided-wave stitches that work by mode interference, including directional-coupler and balanced-bridge switches. The method relies on a coupled-mode theory, using measured wavelength sensitivity of the coupling. Crosstalk is taken as the bandwidth-limiting property and is calculated by expanding in bandwidth. It is found that the wavelength sensitivity depends on the coupler gap, the amount of coupling, and the electrode configuration. Numerical examples show that switches with proper design can exhibit better than 25 dB of crosstalk with a 100-μm bandwidth. Modulators have a still wider bandwidth