Broad-band traveling-wave modulator using a LiNbO 3 optical waveguide

A traveling-wave electrooptic phase modulator using a Ti-in-diffused LiNbO 3 optical waveguide was designed and constructed with emphasis placed on broad-band operation. As a microwave waveguide, a coplanar parallel stripline of aluminum with characteristic impedance of 48 Ω was fabricated on the crystal surface. The electrodes are 1.5 μm thick, 1 cm long, and 60 μm apart. The modulator was tested at 0.63 μm over a bandwidth of 7.5 GHz. For 250-mW drive power, the measured phase-modulation index was 1 rad up to about 3 GHz and reduced to 0.5 tad at 7.5 GHz.