Abstract

The conventional acousto-optic (AO) Bragg cell rf receiver is known to suffer from two limitations: limited dynamic range and incapability for phase measurement. To increase the dynamic range and to facilitate the phase measurement, we must use optical heterodyning detection. Most related works have been carried out using bulk AO Bragg cells¹ in which a number of beam splitters, mirrors, and wedges were configured into a Mach-Zehnder interferometer to facilitate the required functions of beam splitting, directing, combination, and filtering for the signal and reference beams. To overcome the problems of vibrations and thermal fluctuations and subwavelength alignment tolerances required, a so-called modified Mach-Zehnder interferometer was explored recently. This expoloration was accomplished by using integrated-optic (IO) architecture² in which a pair of proton-exchanged gratings were used as the beam splitting, directing, and combining elements. A relatively low dynamic range of 30 dB was measured owing to excessive optical losses from the gratings and the propagation in the waveguide. In this paper we present a simple IO architecture that utilizes wideband cascaded AO and electrooptic (EO) Bragg diffractions in Y-cut LiNbO₃ planar waveguide to perform efficient and wideband heterodyning detection. The results obtained thus far suggest a new architecture for the realization of wideband IO interferometric rf spectrum analyzers.

© 1990 Optical Society of America