Abstract

An integrated-optics standing-wave surface-acoustic-wave modulator (SWSAWM) for optical communications is being investigated. This novel modulation method, which has been described previously,¹ was used to upconvert a color TV video signal to TV channel 4 by generating a 70-MHz subcarrier with a Ti-LiNbθ3 modulator. Prisms were used to couple light in and out of the waveguide. A photodetector placed at one of the diffracted beams received the upconverted signal. An ordinary TV receiver recovered the original video signal. Picture quality was good. The phase of the acoustooptically generated subcarrier could be changed by changing the phase relationship between the rf signals driving the two inter-digital transducers. The standing wave nature of the modulator was also demonstrated by the frequency dependence of the diffracted optical power. Nonlinearities in surface acoustic wave generation and/or acoustooptic diffraction caused sub-carrier distortion on high diffraction efficiencies. This effect is being examined theoretically and experimentally to determine its influence on system performance. Subcarrier generation at higher frequencies (600 MHz and above) is also being explored.

© 1988 Optical Society of America