Optical waveguides – Temporal optical modulation within an optical waveguide – Electro-optic
Reexamination Certificate
1999-05-20
2001-02-13
Lee, John D. (Department: 2874)
Optical waveguides
Temporal optical modulation within an optical waveguide
Electro-optic
C385S014000
Reexamination Certificate
active
06188808
ABSTRACT:
GOVERNMENT INTEREST
The invention described herein may be manufactured, used, sold, imported and licensed by or for the Government of the United States of America without the payment to us of any royalty thereon.
FIELD OF THE INVENTION
This invention relates generally to the field of micro-electronics and more particularly to the monolithic integration of opto-electronic signal processing structures for use in photonic systems.
BACKGROUND OF THE INVENTION
In recent years, artisans have made significant advances in fabricating and using opto-electronic integrated circuits. These improved circuits, which often contain passive and active optical devices, have found significant applications in a number of fields including optical computing and communications. The use of opto-electronic circuits in many systems can result in significant cost savings, increased circuit speeds, reduced physical size and power requirements, increased reliability, as well as other improvements. As such, those concerned with the development of photonic systems in such fields as radar, communications and computing have recognized the need for improved techniques of constructing opto-electronic circuits.
Specifically, conventional phased-array antenna systems have been successfully demonstrated for transmitting and receiving microwave energy in communication and radar systems. A phased-array antenna is an antenna with two or more driven elements. The elements are fed with a certain relative phase, and they are spaced at a certain distance, resulting in a directivity pattern or beam that exhibits gain in some directions and little or no radiation in other directions. Although phased arrays may have fixed beams, they usually contain rotatable or steerable beams. Of course, an antenna structure may be physically moved to effect beam steering, however, in a phased-array antenna, beam steering is usually accomplished by simply varying the relative signal phase being fed to the antenna elements.
Although prior art phased-array antennas have served the purpose, they have not proved entirely satisfactory for use in many microwave communication and/or radar systems. To obtain sufficient radar resolution, phased-array antennas employed with some microwave radars require that as many as a thousand antenna elements be arrayed to produce a sufficiently narrow beam. Since many long-range communication systems also require narrow antenna beams, they often have antenna arrays with hundreds of antenna elements. While the size of microwave antenna arrays having several hundred or even a thousand antenna elements can be relatively small, the signal processing circuits connected to these antenna arrays often become prohibitively large and expensive to manufacture. Thus, artisans have recognized the need for reducing the size and cost of many signal processing circuits by using an optically controlled microwave system.
SUMMARY OF THE INVENTION
A general purpose of this invention is to provide a technique of fabricating a monolithically integrated circuit by growing a network of interconnected active and passive optical waveguide devices on a substrate in a single selective epitaxial growth step.
A specific aspect of the invention comprises an optical signal processor for optical phase distribution and microwave beam forming. A network of interconnected optical waveguide devices are built on a semiconductor substrate. The optical waveguide devices comprise optical beam splitters, optical amplifiers and optical phase shifters. A gain control circuit connects to the optical amplifiers for amplifying optical energy propagating through the optical amplifiers. A phase-shift control circuit connects to the phase shifters for controlling the relative phases of two optical beams with orthogonal polarization.
A more specific aspect of the present invention comprises a microwave system having a photonically controlled phased-array microwave/millimeter wave antenna. The system comprises an optical signal processor formed from a monolithically integrated semiconductor structure having a network of interconnected waveguide devices. The waveguide network includes optical beam splitters, optical amplifiers and optical phase shifters. Phase-locked master and slave lasers generate two orthogonal light beams having a difference frequency that corresponds to the microwave/millimeter wave carrier frequency of the phased-array antenna. The lasers feed the optical signal processor which performs beam splitting, optical amplifying and phase shifting functions. The optical signal processor has a plurality of optical outputs equal in number to the number of antenna elements. A polarizer at the outputs and an array of optical fibers transmit these optical outputs to diode detectors that generate microwave signals which feed the phased-array antenna. The optical waveguides are fabricated in a single selective epitaxial growth step on a semiconductor substrate.
The exact nature of this invention, as well as other objects and advantages thereof, will be readily apparent from consideration of the following specification relating to the annexed drawings.
REFERENCES:
patent: 5233673 (1993-08-01), Vali et al.
patent: 5307073 (1994-04-01), Riza
patent: 5411895 (1995-05-01), Hsu
patent: 5485014 (1996-01-01), Jain et al.
patent: 5811830 (1998-09-01), Dubey et al.
Dutta Mitra
Pamulapati Jagadeesh
Shen Paul H.
Zhou Weimin
Lee John D.
O'Meara John M.
Song Sarah U.
The United States of America as represented by the Secretary of
Zelenka Michael
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