The high frequency, wideband acousto-optic light deflector is an excellent candidate in many EW systems such as radar warning receivers and communications signal processing. In order to provide such needs, broad bandwidth acousto-optic Bragg cells for the gigahertz frequency range are developed. To track Bragg angle for broadband operation, a phased array design is employed and therefore its performance needs to be well understood, especially at microwave frequencies. In this paper we propose a new acoustic phased array transducer model. A microwave model for conversion of an RF signal to an acoustic beam is presented. The model is based on calculating the phased array transducer interdigital capacitance from coupled transmission lines theory. We also discuss the impact of other transmission line effects at electromagnetic wavelengths. The microwave phased array transducer model is then used to predict the behavior of the electrode voltages and currents and of the overall capacitance.
In this paper we review the development of phased-array transducer AO Bragg cell technology. It is shown that certain acoustic modes may be preferred for high dynamic range applications. The design and analysis of phased array transducers is also discussed and the mathematical formalism is generalized. Some experimental results using RF sputtered piezoelectric film transducers are presented.
The acousto-optic (AO) filter interaction is unique in acousto-optics because of its ability to operate with large acceptance angles or field of view. The device can deflect a constant wavelength with a fixed drive signal over a range of incidence angles; however, resolution broadening occurs as the acceptance angle is increased. This paper presents a particular AOTF design which achieves a large field of view with no resolution broadening.
A new, and potentially very important, class of crystals, the mercurous halides were synthesized about a decade ago by Barta in Czechoslovakia. Mercurous chloride, Hg2C12, is the most highly developed of these, and its photo-elastic properties were described by Silvestrova2 in the Soviet Union. This crystal possesses certain unique acousto-optic properties, making it highly desirable for certain signal processing applications requiring very long delay Bragg cells.
A 32 channel acousto-optical Bragg cell has been developed and evaluated for optical computing applications. This device was designed based on a computer model and was verified in an optical computing system. The Bragg Cell has 1000 resolvable spots per channel, diffraction efficiency of 40%/watt and -0d13 channel to channel isolation. The design and evaluation of this device allow for the prediction of a higher performance multi channel Bragg cell.
Attractive correlation system performance potential is possible using magneto-optic spatial light modulators (SLM) to implement binary phase-only reference filters at high rates, provided the correlation performance of such reduced-information-content filters is adequate for the application. In the case studied here, the desired filter impulse response is a rectangular shape, which cannot be achieved with the usual binary phase-only filter formulation. The correlation application problem is described and techniques for synthesizing improved filter impulse response are considered. A compromise solution involves the cascading of a fixed amplitude-only weighting mask with the binary phase-only SLM. Based on simulations presented, this approach provides improved impulse responses and good correlation performance, while retaining the critical feature of real-time variations of the size, shape, and orientation of the rectangle by electronic programming of the phase pattern in the SLM. Simulations indicate that, for at least one very challenging input scene clutter situation, these filters provide higher correlation signal-to-noise than does "ideal" correlation, i.e. using a perfect rectangle filter response.
A proof-of-principle, fully dynamic, hybrid digital optical correlator has been built and successfully tested in a real-world non-cooperative target recognition environment provided by the U.S. Army. Preliminary test results have demonstrated the feasibility of using the LIGHT-MODTm, a patented and trademarked product of Litton Data Systems, as the key component in a fieldable non-cooperative target recognition system.
An architecture for a real-time signal correlation based on optical joint transform correlation is proposed. Two parallel on-plane acousto-optic (AO) cells and a liquid crystal light valve (LCLV) are employed to produce crosscorrelation of two electrical signals. Arranging two AO cells on the same plane, this architecture can be implemented in a compact form. The proposed architecture has a capability of performing parallel multiple crosscorrelations by adding AO cells on the input plane. The theoretical analysis and preliminary experimental results are presented.
The use of a deformable mirror device (DMD) as an input spatial light modulator and/or as a phase-only spatial filter in a coherent optical correlator is investigated. Both Vander Lugt and joint transform correlator geometries are analyzed, and the results of computer simulations using a simplified phase device model are presented. Detailed geometrical and diffraction models of Texas Instruments' cantilever beam DMD are developed and used to simulate an input phase device in a Vander Lugt correlator. The results are encouraging for those interested in using the DMD for image correlation applications.
A system is described which consists of an acousto-optic Bragg cell, a Fourier transform lens, a vidicon detector, and a digital Fourier transform. This simple system has potential for processing wide bandwidth signals with significant time-bandwidth capability. Time delays were observed between two nearly identical signals of arbitrary wave shape and found to conform with the theory. Experimental results for three types of signals are presented: narrow pulse, FM chirp, and white noise; the results of which conform with the theory.
The explosive growth of computer technology in recent years has precipitated an equally dramatic growth in the market for nonimpact electronic printers. One of the most popular methods for implementing a high quality nonimpact electronic printer is to integrate a laser scanner with a xerographic copier/duplicator. The subject of this article is a discussion of alternative optical scanner architectures, including both traditional designs which are well represented in the marketplace, and also more exotic designs configured with spatial light modulators, designs which to date have had scant penetration into the marketplace but which can offer superior image quality.
This paper reviews the theory of multifrequency acousto-optic (AO) interaction in Bragg cells. The non-linear response is caused by multiple linear AO diffractions, elasto-optic and acoustic nonlinearities. A unified theory is presented that determines the intermodulation products in AO Bragg cells. The various diffraction processes are analyzed with Feynman diagram techniques.
A recent breakthrough in the growth of excellent quality single crystal thallium arsenic selenide (TAS) on a production basis has made it possible to build an electronically controlled acousto optic tunable filter (AOTF) capable of operating in the infrared. Such a filter with integral ultrasonic transducer can be used in place of mechanical filter wheels, spinning gas cells, moving mirrors, diffraction gratings and mechanical light choppers. The TAS AOTF produces an electronically controllable narrow band infrared filter capable of being tuned to any infrared frequency desired. It provides a chopped and tuned IR source that can be directed across the stack on any combustion process to measure the concentrations of CO, CO2, SO2, C2H6, CH4, NO, NO2, H2O, etc., simultaneously.
We have overcome the frequency limitations of traveling wave electro-optic modulators (TWEOMs) through the use of a noncollinear interaction. We derive the efficiency of the device and show that this electro-optic modulator may also be used as a Bragg cell.
Traditionally the Sagnac fiber-optic sensor has been used to make measurements of rotation. By utilizing acousto-optic modulators to provide a frequency difference between the counterpropagating light beams in the sensing coil other environmental disturbances can be measured with high accuracy. A discussion of the various configurations used to cause a frequency difference between the counterpropagating light beams is given. A description of a laboratory model using one of these configurations is discussed and data demonstrating the ability to measure environmental disturbances accurately is presented.
High power lasers have been used successfully in scanning systems for direct production of printing plates and cylinders. The modulation of these lasers has posed severe technical challenges due to the high optical powers involved, combined with demanding requirements for modulation bandwidth, amplitude and beam pointing stability, and beam profile quality. Solutions to these problems are presented for two systems in current production. In both systems, a combination of careful system design and state of the art modulator design and manufacture has been necessary to achieve success in meeting the demanding system specifications.
The utilization of acousto-optic devices for producing stable picosecond pulses is dis-cussed. Incorporating a highly resonant modelocker in a CW YAG laser, pulse-widths of less than 40 ps were generated at ten watts of average power. In addition a very stable pulse compressor system is described which uses a travelling wave loss modulator to provide 3 ps pulses of 532 nm light at 750 milliwatts of average power and less than 5% peak to peak noise.
The object of ellipsometry is to determine the complex ratio ρ (ρ=tanifi exp(i&) ) of the reflected or transmitted polarization state parameters. Ellipsometry has traditionally been used as a tool for measuring the optical constants (n,k) of a surface, or when given the optical constants of the substrate, to determine some property such as the thickness of a thin film. The operation of a Photo Elastic Modulator (PEM) type ellipsometer is described in Mueller matrix terms. The phase shift (6) between orthogonal polarization components and the relative amplitude ratio (tan b) is contained in the Mueller matrix elements and can be obtained via combinations of measlired matrix elements using no mechanical motion. Polarization modulation ellipsometry offers a fast automatic means for obtaining the Mueller matrix for an optical component or system. A computer controlled implementation is described along with simple algorithms to extract the ellipsometric constants. Experimental results for a low phase shift "standard" reflector are given.
Single crystal films of the bismuth substituted iron garnets have been grown by liquid phase epitaxial (LPE) procedures onto GGG or CMZGGG substrates. For switchable devices, both the optical figure of merit, defined by θ/α (0 = Faraday rotation and a= optical loss) and the magnetic properties must be controlled. We have prepared films of the type BixRE3-xFe5-yGay012 on GGG (ao = 12.383A) substrates with figures of merit greater than 1°/pm or 2°/dB at 550 nm. Single rare earths (RE) or combinations of Tm, Yb, Lu, or Y are used with 0.4 <x <0.6 and 0.8 <11. <1.2. The anisotropy field Ht, magnetization 4TrMs, and collapse field must be low to obtain switching. The optical figure of merit can be doubled by employing substrates of CMZGGG (a0 = 12.495A) to incorporate more Bi. Films of the type BixTmyGdzY3-x-y-zFe5-tGat012 were prepared by LPE growth. These films approach 4°/db at 550 nm, had also a high Curie point of 170°C, and fulfilled all magnetic parameters for switching. Switchable films are useful for structured devices such as displays, printers, modulators, pattern recognition, or cross bar switches. Many of these have been prepared with 64 to 128K independent elements. If the highest figure of merits are desired and mag-netic parameters are not critical, the amount of Bi can be increased further by using NdGG (ao = 12.51A) (or other high ao substrates such as GdScGG (a0 = 12.55A). These films are prepared in 1 - 10μm thicknesses but can be grown up to 50 - 400pm by single or multiple film methods. Thus high absolute rotations of 45 - 90° can be obtained. Such films may be used in optical isolators for fiber optics at 1.30 - 1.50μm where low insertion loss is required. The consistent growth of both low resonant linewidth (AH) and high Bi films for optical guided wave and magnetostatic wave interactions is still a challenge.
High-frequency acousto-optic modulators have been developed for single-mode fibers. Gradient index (GRIN) lenses are used to couple the acousto-optic device to the input and output fibers. A new device interaction geometry using birefringent diffraction is proposed to achieve wideband coupling to single-mode fibers.
Diffraction of guided light by magnetostatic waves generated in ferri.magnetic garnets is emerging as a promising new technology for optical signal processing in integrated optics format. Here the design and fabrication criteria for producing suitable single-mode waveguides in an YIG-GGG structure are investigated. A complete analysis of the optical propagation in multilayer waveguides is presented, and the need of further experimental investigations of LPE-grown doped YIG layers is discussed.
Wideband guided wave magneto-optic (MO) modulation by magnetostatic surface waves (MSSW) in Yttrium Iron Garnet (YIG) - Gadolinium Gallium Garnet (GGG) has been demonstrated in a noncollinear coplanar interaction geometry. Excitation of the MSSW and efficient MO interaction at 1.152 and 1.302 μm optical wavelengths were accomplished over a wide frequency range of 3 to 7 GHz by linear electronic tuning of the dc magnetic field from 500 to 1700 Gauss. The mode conversion efficiency for 1.302 μm optical wavelength was measured to be 8.13% at 1.00 watt rf drive power. Theoretical analysis and experimental results both show that the mode conversion in this noncollinear configuration is caused by a combination of Faraday and Cotton-Mouton effects induced by the dc magnetic field and the MSSW. Such interaction configuration should result in a number of integrated optic devices for wideband communication and signal processing applications at electronically tunable microwave carrier frequencies.
The propagation modes in a five-layer magnetooptical waveguide have been calculated as a function of the permeability and permitivity tensors of the material. TE-TM mode conversion caused by magnetic linear birrefringence has been studied for a plane magnetooptic wave guide consisting in a three-layer thin film epitaxially grown on a substrate and placed in the air, where the active element corresponds to the top layer. This structure makes it possible to obtain single mode propagation and mode conversion between different modes, which is of great interest in the making of optical devices (1). A relation between the thickness of the active layer and the width and refraction indexes of the intermediate layers in order to obtain single mode conversion has been established. Calculations were performed for wavelenghts of 1.152 μm.