Electro-optic single-sideband modulator integrated with branch-line coupler of miniaturized configuration prepared on LiNbO3 substrate

The branch-line coupler (BC) circuit of miniaturized configuration using periodically installed open circuit stabs was designed onto an electro-optic (EO) crystal, LiNbO₃, substrate at 10 GHz. The operation as the 90 degree hybrid was confirmed at around the center frequency by the experiment. By using this BC circuit as the signal power divider, we proposed a compact EO single sideband (SSB) modulator. The SSB modulator was designated and fabricated for 1550 nm light wavelength. In the experiment, the optical SSB signal with the sideband suppression ratio of about 30 dB was observed.