Measurement of the residual amplitude modulation in annealed proton-exchanged waveguide electro-optic phase modulators

Polarization-resolved, multi-parameter measurements are performed on the residual amplitude modulation generated in annealed proton-exchanged waveguide electro-optic phase modulators operating at 1064 nm. The residual amplitude modulation consists of multiple independent components resulting from the interference of the strong, guided extraordinary light with weak, non-guided lights propagating along different paths inside the modulator. Among these components, several temperature-sensitive ones are observed, with their half-wave temperatures and voltages ranging from 0.07 to 0.5°C and 1.60 to 2.50 V, respectively. Notably, a portion of residual amplitude modulation (∼1200<i>p</i><i>p</i><i>m</i>) is found to be insensitive to temperature variations. The corresponding temperature-insensitive components, with half-wave voltages that vary from 1.71 to 2.90 V, are attributed to a subset of the weak, non-guided extraordinary lights whose transmission paths are close to the waveguide. When temperature-insensitive components dominate, stable feedback control of residual amplitude modulation can be achieved using a single channel that operates by adding a bias voltage to the modulation signal. The current approach can be adopted to assist the development of new waveguide-type electro-optic modulators that, to our knowledge, will benefit a variety of precision measurements relying on optical phase modulation of ultra-high purity.