Passband-flattened acousto-optic polarization converter

Abstract

A passband-flattened acousto-optic polarization converter (100) in which two acoustic waveguides (14, 20) are formed in a substrate and a separated by a small gap (18) such that the two acoustic waveguides act as a directional coupler in which acoustic power is transferred back and forth. An interdigitated transducer (12) launches a surface acoustic wave in the first acoustic waveguide, and an optical waveguide is formed in the middle of the second waveguide. A partial acoustic absorber (27) is formed over both acoustic waveguides at a crossover length at a distance from the transducer equal to the point at which the acoustic wave has transferred from the first to the second waveguides and back again. The partial absorber absorbs most of the acoustic amplitude with the attenuated acoustic amplitude being coupled back again to the second acoustic waveguide but at an opposite sign. A complete absorber (26) is formed over both acoustic waveguides at a distance from the transducer equal to approximately twice the crossover length such that the attenuated acoustic wave following the partial absorber and transferred to the second acoustic waveguide again transfers back to the first acoustic waveguide. The optical signal is exposed to an acoustic signal that increases to a maximum, decreases and then increases and decreases again with a smaller magnitude and reversed sign. The resultant frequency response has a significantly flattened shape for improved performance of the converter for use as a an optical switch or filter.