Velocity matched electro-optic phase modulator for wide optical sideband generation

A novel ultrafast and high effective electro-optic phase modulator is reported, in which the velocity matching between light group velocity and microwave phase velocity is achieved by using a higher-order mode of the microstrip line on an electro-optic crystal. This modulator can be used for long interaction length, hence an enormously wide optical sideband with low microwave power can be obtained. In an experiment using a modulator with a 20 mm long modulating electrode on the LiTaO₃ crystal, wide optical sideband spectra of 680 GHz (FWHM) were generated at 16.2 GHz modulation frequency.