Surface emitting (SE) lasers and their application in VLSI optical interconnect networks are considered. In particular, the advantages provided by SE lasers in optical interconnect circuits and monolithic integration are discussed. Some of the requirements, such as wavelength stability, power dissipation, emission angle, size, etc. are compared with respect to conventional laser diodes. It is noted that the operation of SE lasers will be critically dependent on the properties of the feedback reflectors. Experimental measurements of reflection spectra on AIGaAs/GaAs multilayer reflectors and InAlAs/InGaAs etalons formed with molecular beam epitaxy (MBE) are presented.

We report the first implementation of fiber optics at 11 GHz in an experimental satellite communication EHF/SHF research terminal for airborne applications. Signal-to-noise and bit-error-rate were measured to characterize the system after a 100-m-long fiber optic link replaced a 4 ft long coaxial cable to enable X-band signal remoting.

Large-signal modulation of a laser diode generates harmonics which can be exploited in applications such as indirect optical injection locking of millimeter wave local oscillators in optically controlled phased array antennas. Under large-signal modulation, the output harmonic content of laser diodes with and without reflective coating on the back facet is analyzed on the basis of the rate equations and is compared with the experimental results over 2-6 GHz. The utilization of these harmonics in the optical injection locking of millimeter wave oscillators has also been demonstrated for two 21.5GHz free-running FET oscillators. Finally a comparison has been made between the laser diode and FET nonlinearities. Experiments reveal that the laser nonlinearity has a greater contribution to the locking range than that of the FET.

In this paper the functional system aspects of a phased array system are discussed. Certain areas within a radar system can use optical processing techniques to gain advantages in processing speed, and a reduction in size, weight, and power. In one case in particular optical techniques will become an enabling technology.

Interdigitated photodetectors of various geometries have been fabricated on GaAlAs/GaAs heterostructure material. Optical response characteristics of these devices have been examined at both dc and microwave frequencies. The microwave response, at frequencies to 8 GHz, was studied by illuminating the devices with the output of an internally modulated GaAlAs diode laser. Results of these measurements are presented and compared with that of GaAs photoconductors.

Optoelectronic switching employs a hybrid optical/electronic principle to perform the switching function and is applicable for either analog broadband or high-bit rate digital switching. The major advantages of optoelectronic switching include high isolation, low crosstalk, small physical size, light weight, and low power consumption. These ad-vantages make optoelectronic switching an excellent candidate for on-board satellite switching. This paper describes a number of optoelectronic switching architectures. System components required for implementing these switching archi-tectures are discussed. Performance of these architectures are evaluated by calculating their crosstalk, isolation, inser-tion loss, matrix size, drive power, throughput, and switching speed. Technologies needed for monolithic optoelectronic switching are also identified.

Fiber optics provide numerous attractive features to various EHF phased-array antennas. This paper presents some critical fiber optic components/subsystems for EHF array applications, including 21 GHz fiber optic links, microminiature switching matrices, low loss fiber optic delay line on miniature spools, and low cost lxN fiber distribution couplers.

Over the last six years NASA Lewis Research Center has carried out a program aimed at the development of advanced monolithic microwave integrated circuit technology, principally for use in phased-array antenna applications. Arising out of the Advanced Communications Technology Satellite (ACTS) program, the initial targets of the program were chips which operated at 30 and 20 GHz. Included in this group of activities were monolithic power modules with an output of 2 watts at 20 GHz, variable phase shifters at both 20 and 30 GHz, low noise technology at 30 GHz, and a fully integrated (phase shifter, variable gain amplifier, power amplifier) transmit module at 20 GHz. Subsequent developments are centered on NASA mission requirements, particularly space station communications systems and deep space data communications.In addition, more recent programs investigate advanced materials, such as power high electron mobility (HEMT) devices, pseudomorphic (InGaAs) monolithic microwave integrated circuits (MMIC's), and the interface between GaAs MMIC and high speed fiber optic systems.'

GaAs circuits for use in a fully monolithic 1 Gb/s optical controller have been developed and tested. The circuits include photodetectors, transimpedence amplifiers and 1:16 demultiplexers that can directly control the phase of MMIC phase shifters. The entire chip contains approximately 300 self-aligned gate E/D-mode MESFETs. The MESFETs have one micron-wide gate and the E-mode FETs typically have transconductance of 200 ms/mm. Results of simulations and tests are reported. Also, the design and layout of the fully monolithic chip is discussed.

The architectural and algorithmic design aspects of a digital optical processor for high performance adaptive radar array beam forming have been studied. Device research to provide the required integrated optics processor elements has been initiated. The design concept has advantages of modularity and expandability, as well as inherent embodiment of the primary advantages of optical computing: parallelism and interconnection capability. With successful device development, the design has the potential to provide all-optical adaptive radar processors having commanding and enduring advantages over electronically-implemented competitors, and capable of meeting far term radar performance requirements.

A novel optical arithmetic element, based on combinatorial logic, is described. A combined use of residue arithmetic and truthtable optimization techniques is shown to yield a highly efficient design. A unique array-processing architecture is shown which computes most of the common primitive linear-algebra processes without iteration. Several possible all-optical far-term implementations of the arithmetic element are discussed.

Optical look-up tables (LUT's) 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 LUT's.

Gram-Schmidt orthogonalization of a set of vectors is carried out in a Residue Number System. Two problems usually present in RNS computations - singularity of transformations and the occurrence of isotropic vectors (i.e., nonzero vectors whose length is zero) - are properly handled. It is shown how these developments can be used together with optical look-up tables (LUTs) to solve adaptive beam nulling problems.

Optical LUTs were designed to perform algebraic operations in residue arithmetic. Also, a technique for factoring LUTs that significantly reduces the hardware and provides a second level of parallelism has been developed. This paper explains the notion of table factorization, illustrates it with an example and discusses the use made of it in solving linear algebraic equations.

A Residue Number System (RNS) modulo (6+5i) multiplier/accumulator computer utilizing factored look-up tables (LUTs) is presented. The inner product computer computes the inner product of two n dimensional complex integer vectors. The general features of the 200 MHz multiplier/accumulator is described. A discussion of the design of the inputs, the multiplier, the accumulator, the optical fiber decoder interconnections and the distributed clock is included. An architecture is given as an example. Finally, a fabricated modulo (6 + Si) multiplier (photo included) is described which demonstrates the validity of the concept.

This paper details the use of linear algebraic optical processors for narrowband and wideband adaptive phased array radar (APAR) applications. A general APAR scenario is explained, outlining the need for improvements in processor performance which optical processing techniques can provide. We then analyze the optical architecture and its implementation including negative base encoding for bipolar data, AC-coupled inputs for linearity and temperature stability, matrix partitioning for handling large matrices, and bit partitioning for improved accuracy. A new block Toeplitz processing algorithm for wideband processing is presented. Results of an inverse covariance matrix updating algorithm are shown.

An analog optical matrix-vector processor with 10-bit accuracy is described. The operating mode of the various components of the system and the system architecture are reviewed. The system is capable of handling bipolar and complex-valued data with no loss in throughput. Various applications of this architecture and initial laboratory data and simulation results are provided. Applications addressed include: finite impulse response filters, two high/low accuracy algorithms and systems for solving linear algebraic equations, a correlation cancellation loop processor and new algorithms and architectures for the discrete and continuous steepest descent algorithms and solutions, plus preconditioning algorithms and associated techniques for these systems, and finally constrained LAE solutions for reduced accuracy processors (using ridge regression techniques).

The use of the Bimodal Optical Computer (BOC) in determining the weights for an adaptive phased array radar is introduced. Interference canceling is presented for two cases: first assuming the direction of the jammer is known, secondly no a priori information is assumed. Effect of the jammers on the array pattern is shown for up to four jammers.

A wide bandwidth (1 GHz) RF channelizer device based on the separation and focussing of bulk acoustic waves is the subject of this report. This device is relatively simple in design and has a very high dynamic range potential. Device design issues and analytical modelling results are discussed.

As a starting point for understanding the utility of focused acoustic wave devices it is useful to consider the operation of the electromagnetic antenna array. The aperture of the array can be considered as the aperture of a large camera lens. If such a lens were present, the electromagnetic radiaton received by the array would be imaged in the focal plane at a point corresponding to the location of the source. This concept is illustrated in Figure(1). The widely used parabolic dish antenna is a limited embodiment of this principle with a single image point or beam on the reflector axis. In the case of an array the antenna elements in the aperture sample the fields at discrete points (really smaller subapertures) and use various methods of combining the resulting signals to form approximations to the "images" at various angular locations or beam directions. In most cases it is simply not practical to put a physical lens or imaging reflector in the aperture location and place real sensors (feed horns) at the image points. Acoustic wave devices can be used to reduce the scale of the problem so that wave imaging approaches to beam forming become practical. Suppose that an array of acoustic radiating elements is arranged in a manner that exactly corresponds to the physical arrangement of the electromagnetic array elements. That is; the frequency is the same and the acoustic radiator spacing measured in acoustic wavelengths is identical to the electromagnetic element spacing measured in electromagnetic wavelengths. Under these circumstances the acoustic wave reconstructed from the aperture samples is a scaled replica of the electromagnetic wave incident on the array. The scale factor is equal to the ratio of the electromagnetic wave velocity to the acoustic wave velocity. This ratio is typically on the order of ten to the power five for useful acoustic materials. The possibility of forming an image of the far field source distribution becomes much more attractive when this scale factor is applied. This paper will deal with the design parameters of such an imaging system for a modest size (on the order of 10 X 10 elements) two dimensional array operating in the low gHz range.

Adaptive signal processing presents extremely demanding requirements to current signal processing hardware. In this paper Signed-Digit arithmetic techniques are evaluated for applicability in adaptive signal processing architectures. It is shown that signed-digit arithmetic offers the advantage of parallelism in computation without the accompanying conversion problems of the residue arithmetic representation. A brief overview of the basic features of signed-digit arithmetic are presented with structures for addition and multiplication. It has been shown that these primitives can be used for matrix operations, including least-square minimization. In optical implementations of residue arithmetic architectures, look-up tables are generally used, which can also be used for a signed-digit implementation.

The use of a high accuracy optical processor to obtain the optimal solution for the weight vector in the Adaptive Phased Array Radar (APAR) problem is discussed. This optical system is a multi-channel, acousto-optic architecture which obtains high accuracy results through the encoding of the numerical data as bit streams which are processed optically. The actual accuracy is based upon the number of bits used for processing and is controlled through software. Experimental results obtained using the laboratory optical processing system are presented for several APAR signal environments. These experiments demonstrate that the optical processing system is capable of yielding weight vectors nearly identical to the optimal solution.

A conceptual space-fed architecture is presented that may offer potential advantages over conventional constrained-feed approaches. Fiber or free space optics may be used to control switching functions, distribute signals, achieve beam steering, or injection lock impact avalanche and transmit time (IMPATT) diodes. Fiber optics and monolithic optical technology may reduce weight, size, power, and cost if the high performance required for signal distribution to array elements is achieved.

Lightwave circuits have a number of advantages over conventional metallic conductors for both analog and digital signal distributions in a phased array antenna. Potential architectures and system issues involved in implementing a fiber optic based EHF subarray will be discussed.

A low cost, high performance microwave fiber optic link was demonstrated at 2.2 and 6.9 GHz using 1.4 GHz heterodyne laser diode and multimode fiber/connectors, achieving signal-to-noise ratios of 115 and 97.5 dB/Hz.

This work concerns intself with the analytical investigation into the feasibility of optical processor based beamforming for microwave array antennas. The primary focus is on systems utilizing the 20/30 GHz communications band and a transmit configuration exclusively to serve this band. A mathematical model is developed for computation of candidate design configurations. The model is capable of determination of the necessary design parameters required for spatial aspects of the microwave "footprint" (beam) formation. Computed example beams transmitted from geosynchronous orbit are presented to demonstrate network capabilities.

Using MMICs in phased-array applications above 20 GHz requires complex RF and control signal distribution systems. Conventional waveguide, coaxial cable, and microstrip methods are undesirable due to their high weight, high loss, limited mechanical flexibility and large volume. An attractive alternative to these transmission media, for RF and control signal distribution in MMIC phased array antennas, is optical fiber. Presented are potential system architectures and their associated characteristics. The status of high frequency opto-electronic components needed to realize the potential system architectures is also discussed. It is concluded that an optical fiber network will reduce weight and complexity, and increase reliability and performance, but may require higher power.

This paper describes a wideband electro-optic direction finding (DF) processor employing an array of laser diodes, an array of photodetectors, and a network of fiber optic delay lines. This DF filter offers a potential operational bandwidth in excess of 10 GHz and allows for multiple, simultaneous beam angular responses with peaks which are independent of frequency. Two eight-laser, two-beam laboratory test model DF devices, one utilizing multimode optical fiber and the other single-mode fiber, were constructed. These experimental optical beamforming filters are operable in the 100-2000 MHz frequency range and can simultaneously monitor two angles of arrival. Experiments were performed to determine the two system's sensitivity, dynamic range, angular resolution, and frequency response. It is concluded from theoretical and experimental results obtained that the multimode DF device is slightly superior in performance to the single-mode system due to the higher throughput optical power levels possible with multimode systems. Further, it is concluded that this fiber optic beamforming processor can be a useful device for ultra-wideband DF.

The phased array is a type of microwave antenna which has a number of individual radiating elements with spacings of elements of about a wavelength . Higher frequency antenna systems may require smal1er dimensions, so a modular approach with both amplification and signal control at each element can be envisioned for future phased arrays. Coaxial systems can be replaced by fiberoptic systems which are light, smal1, rugged, have 1arge bandwidths and are immune to EMI/EMP signals. The recently developed InGaAsP buried heterostructure 1aser is suitable for high frequency modulation and optical coupling to a fiber for transmission, and a high speed InGaAs photodetector is suitable as a receiver and microwave demodulator. This study concerns the direct modulation of a 1.3μm InGaAsP vapor phase regrown buried heterostructure 1aser (VPR-BH). The modulated signal, after coupling to a multimode 3μm optical fiber, is detected and demodulated by a 20-22GHz bandwidth InGaas photodetector.