Low Voltage Optical Modulator Using Electrooptically Induced Phase Gratings

An optical modulator with square phase gratings, which are induced by a mosaic structure of electrooptic crystals, is proposed. Analysis and experiments show its utility and the possibility of fabricating it by binding several crystals. An experimental device is built by an array structure using eight 0.9(z) x 0.9(y) x 12.5(x)-mm LiNbO(3) rods. Its 100% modulation voltage is 68 V, and its capacitance is 18 pF. Experimental results, such as modulation transfer function and angle of diffraction, agree well with the analysis, and the farfield patterns obtained are fairly good. This type of modulator offers a low voltage operation, which is about 40% of that of a conventional one for LiNbO(3)crystals. Furthermore, it has the advantage of insensitivity to temperature change.