Electro-optic SSB modulator with 90° hybrid directly prepared onto LiNbO3 substrate

Optical single-sideband (SSB) modulation is theoretically realised by applying two modulation signals with a 90° phase difference to the dual-electrode type electro-optic (EO) modulator. A branch-line coupler (BC) as the microwave 90° hybrid was directly prepared on the EO modulator substrate, LiNbO₃, to create two modulation signals from a single input signal. Output ports of the BC were connected to the modulation electrodes on the substrate. Thereby, an EO optical SSB modulator was realised with a single-tip and a small-sized configuration. The SSB modulator was designed and fabricated for around 10 GHz modulation frequency and 1550 nm light wavelength. The optical SSB modulation operation with a sideband suppression ratio of more than 20 dB was confirmed by the experiment.