Extinction Ratio Improvement of Lithium Niobate Modulators for Quantum Communication Systems

A method for photorefractive trimming of lithium niobate integrated optical modulators was developed. An improvement in the extinction ratio in a Mach-Zehnder (MZ) modulator by photorefractive precision adjustment of its couplers was achieved. An increase in the extinction ratio by 18 dB (from 30 to 48 dB) was demonstrated.