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This paper reports the realization of integrated acousto-optic (AO) device modules that combine a wideband AO Bragg cell, an ion-milled Bragg diffraction grating, and a titanium-indiffused protonexchanged waveguide lens in a Y-cut LiNbO(3) substrate, 1 x 8 x 16 mm(3) in size, to perform optical heterodyning, and their application to rf signal processing. These integrated AO heterodyne modules have demonstrated the capabilities for channelized detection of the amplitude, the frequency, and the phase of wideband rf signals and thus the capability to perform interferometric rf spectral analysis with significantly improved performances over the conventional AO Bragg cells. The single-unit (basic) modules have provided single-tone simultaneous and two-tone third-order spurious-free dynamic ranges of 51 and 40 dB, respectively, and a bandwidth of 205 MHz centered at 350 MHz at the optical wavelength of 0.6328 microm, the optical power of 1.0 mW, and the drive power of 50 mW/rf signal input. Furthermore the dual-unit modu es that consist of a pair of identical basic heterodyne devices in the same LiNbO(3) waveguide substrate, also 1 x 8 x 16 mm(3) in size, have been constructed and used to measure the angle of arrival of the rf signals.

No 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.