Edward C. Malarkey

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.

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.

Diamond-Machined Geodesic Lenses In LiNbO3

The application of single point diamond turning to the fabrication of aberration-corrected, aspheric geodesic lenses in LiNb03 for use in integrated optics is reported. F/5 lenses with useful apertures of 4 mm and 5 mm have been produced. Lens profile accuracies ranging between 1.5 and 3 pm total indicator reading and depth accuracies of 0.25 to 2.0 μm have been achieved. The machined surfaces require only light polishing, which produces little effect on the figure accuracy, to remove residual machining marks. Waveguides grown by Ti-indiffusion are found to be characterized by very low scattering losses. Optical image spot sizes of 1.35 to 2.23 times diffraction-limited have been measured for input beam widths of 1.0 to 3.28 mm for a lens in which the edge rounding has not been incorporated into the aspheric correction. The edge rounding has been included in the correction for subsequent lenses.

Photosensor Array For Integrated Optical Spectrum Analyzer Systems

A silicon photodiode array with 50 dB dynamic range has been developed for integrated optical spectrum analyzer systems. The device consists of 140 pixels on a 12 micrometer pitch. Each pixel can be addressed within a period of 2μseconds. The device is butt coupled to an integrated optical waveauide spectrum analyzer circuit fabricated from lithium niobate.

Geodesic Lens Performance Characteristics

The position of the focal plane, the intensity profile of the first diffraction spot and power losses have been measured for geodesic lenses in Ti-indiffused LiNb03 waveguides. It was intended for the focal plane of a geodesic lens to be situated at a waveguide edge; experimental results have shown that this was achieved to a tolerance of better than 12 im with two of the measured focal planes coinciding with the waveguide edge to within the +2 Inn accuracy of the measurement techniaue. Scans of the intensity profiles of focused diffraction spots have been made for one and two lens systems; the spot sizes in both cases were found to be <1.15 times the diffraction limit at F/12. Throughput losses in geodesic lenses ranged from 2.5 to 17 dB - the larger losses occurring in lenses with small edge rounding and large corrected regions. An analytical program was initiated to determine the various mechanisms responsible for power loss. A simplified model indicates that a significant loss is due to mode mismatch in the vicinity of the edge rounding.

Advanced Integrated Optic Rf Spectrum Analyzer

Efforts to improve upon the reported dynamic range of newly developed integrated optical RF spectrum analyzers center about two separate components. One of these is an efficiently coupled, high power, single mode, narrow-beam-spread GaAlAs laser diode and the other is the photodiode array with its associated read-out circuitry. Recent attempts to realize improvements in both of these components are described, as are the design changes in the spectrum analyzer necessitated by the characteristics of available laser diodes.

Advances In Integrated Optical Spectrum Analyzers

The operating characteristics of a hybrid integrated optical spectrum analyzer and the results of a design analysis performed to permit the development of an improved device are discussed. The existing device incorporates a LiNbO3 substrate, which contains a Ti-indiffused optical waveguide, two near-diffraction-limited geodesic waveguide lenses, and a two-element surface acoustic wave transducer array, and a butt-coupled photodiode array. The optical source is either an end-fire or butt-coupled laser. This unit has been shown to operate over a 400 MHz bandwidth with a resolution which varies from 5.3 MHz for an optical wavelength of 0.6328 μm to 4.0 MHz for 0.83 μm.

Theory Of Geodesic Lenses

The geometrical theory of axially symmetric geodesic lenses is discussed. An algorithm was developed and used to obtain the optimal shape of a lens that is corrected for spherical aberrations. The effects of lens surface distortions on the performance characteristics are determined. For a lens to be near diffraction limited it was found that its ideal shape must be maintained to within 10-4 X lens diameter.

Operational characteristics of an optically implemented microwave frequency synthesizer

A multistage optically implemented microwave frequency synthesizer has been designed and fabricated. The concept and implementation are described with emphasis on operational characteristics of a prototype 3-stage unit. The synthesizer is designed as an optical analogue of the mix-and-divide approach to frequency synthesis taking advantage of the single-sideband, supressed-carrier modulation produced by the Bragg acousto-optic interaction and the sum- only or difference-only mixing of optical heterodyne detection without the need for any in- stage passband filtering. The synthesizer exhibits a 500 MHz bandwidth and completely switches and settles stably upon a new frequency within 250 nanoseconds. Phase noise was measured to be less than -130 dBc/Hz at 10 KHz offset from the carrier.

Optical Adaptive Beamforming Using Residue Number Systems (RNSs) And Gauss Elimination

Optical look-up tables (LUTs) are used for solving the Adaptive Beamforming problem in a quadratic (Complex) Residue Number System, QRNS. It is shown that QRNS is isomorphic to the usual RNS arithmetic so that real moduli implementations can be used. In QRNS, a system of linear equations can appear singular when the determinant is a multiple of one of the moduli used in the representation. It is shown that this apparent singularity can be avoided and that the singular-like system of equation can be solved uniquely in spite of the apparent singularity. An example is given to illustrate the technique of solving singular-like QRNS systems of equations. The optical implementation of QRNS arithmetic uses Second Factorization which is shown to significantly reduce the number of optical components needed in the LUTs.