The invention relates to optical processing apparatus in general, and more particularly to integrated optics, e.g., to a solid-state device in which guided light is modulated by electrical control means as in the field of electronics.
It has been recognized for many years that optical devices can advantageously be used to process information in a mono- or bi-dimensional format. This results from the Fourier transform properties of certain optical systems. This capability has been put to use for performing complex operations such as spectrum analysis, correlation, convolution and image enhancement.
A definite superiority of optical processing lies in the ability to simultaneously operate upon many information channels, or bits, so that processing can proceed at great speed and often an output can be derived in real time with relatively little system complexity.
Developments in integrated optics have further increased the interest in optical processing methods. In particular thin-film techniques applied to light waveguides have made possible a high degree of miniaturization of optical devices. The next step was to interface the optics to the integrated electronic components of the system, in which a common substrate may be shared by both optical and electronic components, e.g., silicon. Optical signal processing in a thin-film wave guide is accomplished with some form of modulation or deflection of the beam of light. To this end, integrated optic modulation or deflection has been developed in three parallel modes of modulating or deflecting light traveling in a thin-film waveguide: (1) the electrooptic effect, (2) the magneto-optic effect and (3) the acousto-optic effect. A shortcoming of the first two modes is that the waveguide material must be either an electro-optic, or a magneto-optic material. Consequently, they do not lend themselves to integration on a common substrate. In contrast, the acousto-optic effect occurs in all materials and a waveguide suitable for deposition on a silicon substrate may be chosen. Two types of acousto-optic interactions are possible. One consists in using an acoustic surface wave. A drawback lies in that the interaction is limited in bandwidth by attenuation and in time resolution by the travel time of the acoustic wave across the light beam (in the order of one microsecond). The second mode consists in using bulk acoustic waves for modulating guided light. This method, described in the Article "Bulk Acoustic Wave Interaction with Guided Optical Waves" by G. B. Brandt, M. Gottlieb and J. J. Conroy in Applied Physics Letters, Vol. 23, No. 2, July 15, 1973 pp. 53-54, uses a configuration in which the acoustic wave propagates normally to the light guide. This technique, as further described in U.S. Pat. No. 3,856,378 of Gerald B. Brandt and Milton Gottlieb, provides on a common substrate for passing ultrasonic acoustic waves, either longitudinal or shear bulk waves, through one or several parallel optical channels.
Integrated optics technology has become more and more promising for the field of high-data-rate communication, in particular for surface and space applications. With increased complexity analagous to solid-state technology in the field of electronics, several functions have been added on a common substrate. Typical of the progress made is the device described by Gary E. Marx, Milton Gottlieb and Gerald B. Brandt in IEEE Journal on Solid State Circuits, Vol. SC-12, No. 1 of February 1977, pp. 10-13 entitled "Integrated Optical Detector Array, Waveguide, and Modulator Based on Silicon Technology". An integrated optical (IO) hybrid circuit has been fabricated, as explained in the article, by coupling on a common silicon substrate an IO modulator and a photo-detector array. It uses the aforementioned interaction between guided light and bulk acoustic waves. A transducer element operates on an optical waveguide to deflect the guided light onto a linear array of p-n junction photodiode detectors formed on the silicon substrate common to the transducer element, the optical waveguide and the photo-detectors. The present invention takes advantage of the existing technology, it also takes inspiration from phased-array radar technology.
Phased-array radar has been developed in the direction of a fully integrated microwave circuit. See "Microwave Semiconductor Devices" by H. V. Shurmer, pp. 215-217 published in 1971 by John Wiley & Sons. By analogy with the phased-array radar technique, the prior art shows that an A/D converter has been conceived by coupling a light beam deflector with an array of photoelectric detectors. See "Electrooptic Phased-Array Light Beam Deflector with Application to Analog-to-Digital Conversion" by P. Saunier, C. S. Tsai, I. W. Yao and Le T. Nguyen, a paper presented at the Topical Meeting on Integrated and Guided Wave Optics, Jan. 16-18, 1978, Salt Lake City, Utah under the sponsorship of The Optical Society of America (Tu C.sub.2- 1 to 4). However, this paper does not show the use of bulk acoustic waves, nor a fully integrated solid-state device. This is also the case with U.S. Pat. No. 4,058,722 of Henry F. Taylor.
An object of the present invention is to provide a solid-state light deflector using acoustic wave interaction with guided light.
Another object of the present invention is to provide a monolithic A/D converter using the interaction of acoustic waves with guided light to convert analog signals into digital signals.