Anastasios P. Goutzoulis

Hybrid electronic fiber optic wavelength-multiplexed system for true time delay steering of phased array antennas

A hybrid electronic fiber optic true time-delay steering architecture is presented which retains the highly hardware compressive property of an earlier all-optical approach and introduces the economical advantages of electronics at every level possible without compromising overall performance. The architecture is particularly suited to large arrays where maximum advantage can be taken of the hardware compression. A detailed design based on this architecture is described for steering a linear, 16-element, L -band (0.7- to 1.4-GHz) array in transmit mode over a scan angle of ±20 deg with a delay resolution of 6 bits (0.63 deg). An analysis of the expected performance of the design is given together with progress toward the fabrication of the prototype system, which includes the first iteration electronic binary delay line subsystem and a single-segment, high-fidelity, directly modulated DFB laser diode fiber optic link. The experimental data from these modules is in agreement with the performance predicted from the analysis.

Optical processing with residue LED/LD lookup tables

Position-coded modulo m lookup tables (LUTs) with gate complexities equal to m(2), 2m, and 4 radicalm are discussed. The design of practical miniaturized LUTs is described along with results obtained from a prototype 7 x 7 laser diode LUT. A factored m(2) LUT technique that achieves large dynamic range is presented. Several LUT performance issues are also discussed.

Systolic time-integrating acousto-optic binary processor

An optical processing system performs matrix-matrix, matrix-vector, and vector-vector multiplication. Element product formation is accomplished by the time integration of a detector array which converts light signals into electrical signals. Inner products are formed by the spatial integration of a cylindrical lens which focuses modulated light onto the detector array. Modulation of the light is accomplished by bit-serial modulation of the light sources with one element value in twos complement form, and by bit-serial modulation of an acousto-optic cell by the other element value in twos complement form. A multi-channel systolic embodiment permits a complete vector quantity formation without the need to enter modulation data separately for each inner product of the vector.

Hardware-compressive 2-D fiber optic delay line architecture for time steering of phased-array antennas.

The requirements for true time steering of phased array antennas are reviewed, and the resulting delay line hardware requirements are discussed. Two hardware-compressive fiber optic delay line architectures are then briefly described and quantitatively compared. The basics of phased array antenna partition are then presented. Based on these principles a delay-compressive and element-compressive 2-D fiber optic delay line architecture is described, and its basic characteristics and capabilities are discussed.

High-performance acousto-optic materials - Hg2Cl2 and PbBr2

New results achieved with recently grown Hg2Cl2 and PbBr2 crystals are described. With an optimized crystal growth technique Hg2Cl2 crystals were grown that show a significantly reduced acoustic attenuation compared to prior crystals, from 13.4 to 8 dB/μs-GHz2. These crystals allow the development of Hg2Cl2 Bragg cells with time-bandwidth product figures in the 5100 to 6900 range, frequency operation as high as that for Te02, and resolution about 25% higher than TeO2 for similar crystal lengths. PbBr2 crystals were also grown that exhibit a large figure of merit (M2 550) with an attenuation coefficient of 12 dB/μs-GHz2. This material may be the choice for infrared devices where large diffraction efficiencies are needed.

Residue arithmetic techniques for optical processing of adaptive phased array radars

Residue arithmetic techniques which can be implemented optically are investigated for applicability to adaptive phased array radar processors. It is shown that neither the bit-serial nor the bit-parallel convolutional methods can compete favorably with emerging digital electronic techniques but that specialized forms of residue arithmetic processors may hold great potential in this area. We present a brief review of the salient features of residue arithmetic and illustrate Gauss reduction of linear systems by a procedure that is amenable to optical implementation. We discuss the details of a direct algorithm based on Gram-Schmidt orthogonalization which allows solution of large linear systems in residue arithmetic without the excessive growth of the principal modulus that is usually encountered in this approach. A pipelined architecture for performing this algorithm is also described.

Prototype position-coded residue look-up table using laser diodes

Abstract A prototype residue-arithmetic, position-coded, look-up table has been fabricated using laser diodes. It utilizes a 7x7 array of discrete laser diodes which are driven via an interlaced electrode grid. Optical addition takes place through the use of fiber-optic, resilient-ferrule connectors. Experimental results show that operation exceeding 250 MHz (RZ data) or 500 MHz (NRZ data) is possible with low cross-talk. Current pulse reflections represent a potentially major problem.

Devices made from vapor-phase-grown mercurous chloride crystals

Abstract Preliminary test results of optical signal processing and acousto-optic tunable devices built from mercurous chloride crystals are described. Experimentally determined tuning curves for acousto-optic tunable filters for the laser wavelengths of 0.633, 3.39, and 10.6 μm were in excellent agreement with the theoretical curve.

Digital electronics meets its match (acoustooptic devices)

The promise shown by acoustooptic (AO) spectrum analyzers and correlators in field-test prototypes for radar, communications and electronic-warfare surveillance is discussed. The principle of operation of AO devices is explained, and its use for correlation and convolution is examined. Two types of Bragg cell (the basic AO component) are described: surface-acoustic-wave (SAW) and bulk cells. The use of a 2-D AO correlator (i.e. one that moves its output beam over an array of photodetectors rather than a single line) in a spread-spectrum receiver is presented to exemplify the use of AO devices.<<ETX>>

Fabrication and characterization of mercurous chloride acoustooptic devices

Mercurous chloride crystals, recently synthesized in large good optical quality boules by vapor deposition, have been characterized as to their unusual acoustooptic properties. This material offers the potential for superior performance Bragg cells for signal processing and tunable filters. We have developed fabrication techniques to overcome severe problems associated with its high chemical reactivity, designed transducer structures, and built and tested a number of devices.