USA As Represented by Secretary of the Navy

Anthony E Spezio

Edward M Alexander

Hal L Levitt

John N Lee

Gordon W Anderson

Brian Krantz

Timothy N Reynolds

Saurabh Dalal

A phase tracking multichannel apparatus includes a plurality of optical transmitters, an optical multiplexer, a common optical link, and a user electronics. RF signals having different phases are received and are output on separate RF channels, each of which is coupled to an optical transmitter. RF-modulated optical output signals are then output to the optical multiplexer to produce a multiplexed output signal. The multiplexed signal is applied to a common optical link that at its output substantially maintains the phase separation of RF modulation components on optical carriers as received at its input. The optical output of the common optical link is then applied to an optical signal receiving system, such as an optical demultiplexer and a plurality of photodetectors. By multiplexing all of the optical signals onto the common optical fiber, all signals transmit the same path and, therefore, have the same time and phase delay. The phase tracking is preserved because all of the signals experience the same optical or expansive properties of the common optical fiber. A typical use would be to transmit multiple RF signals from an antenna array to a remote RF phase measuring receiver, such as a RF direction finding system.

Phase tracking multichannel link

A system for extracting the complex Fourier coefficients from an unknown RF signal to classify the RF signal is disclosed. The extraction system utilizes optical signal processing in combination with the generation of electronic timing and control signals. The system employs an optical processor comprising a Bragg cell to yield the Fourier coefficients including the amplitude, phase and frequency parameters thereof. The system further includes a parallel arrangement that provide for parallel processing to reduce the computational time needed to determine the complex Fourier coefficients including the amplitude, phase and frequency parameters thereof.

Complex Fourier coefficient extractor

A apparatus and method for coherently stretching or compressing signals of nterest, i.e. without loss of information. A first, or tapping, Bragg cell has an acoustic signal launched in it which is modulated onto a laser carrier. The signal of interest is launched into a second, or signal, Bragg cell, and is similarly modulated onto the carrier exiting the first Bragg cell. Upon demodulation, the resultant signal, is the convolution of the two acoustic signals in the respective Bragg cells, but whose duration is either stretched or compressed according to the relative velocity between the acoustic signals in the two Bragg cells, and by the magnification of optics between the two cells. If the signal in the first Bragg cell is of such a short duration that it is effectively an impulse, the resultant signal is a coherently stretched or compressed replica of the signal launched into the second Bragg cell, i.e. the signal of interest.

Apparatus and method for coherent acousto-optic signal width modification

A signal filter, and method of signal filtering, in which an optical signal s spatially dispersed according to frequency, and undesired frequencies blocked out. In an embodiment, a Bragg cell receives a (typically microwave) signal, and transduces it to an acoustic signal. A light source, e.g. a laser diode, directs light through the acoustic signal in a known manner so as to produce an optical output which is spatially dispersed according to frequency. A programmable spatial light modulator blocks out unwanted frequency components. Upon removal of the optical carrier, e.g. by heterodyning the spatial light modulator's output with a reference signal from the light source, the components can be recombined into a resultant filtered signal. The invention can be used as a repeater, a military electronic countermeasure, in environments which have large amounts of electromagnetic clutter but in which one does not want the clutter repeated. The spatial light modulator can be programmed to pass only frequency components in which one is interested, thus blocking the clutter from the repeated signal.

Method and apparatus for signal filtering

A circuit link, and method for using link, for self initializing any device peratively connected to the link. An input signal is split into two portions, one of which is delayed so that the undelayed signal can transverse the circuit link before the delayed signal. A pair of quadrature splitters are operatively connected to one another to split and combine the undelayed and delayed signals in their turns, and recombine them in their turns, in a manner effective to cause one of the circuit link's outputs to be nonzero responsive to the delayed signal, and zero responsive to the undelayed signal, with the opposite result on the other circuit output. The undelayed signal is thus available to initialize any device requiring initialization, and the delayed signal, unperturbed by any such device, is thus available for use as the circuit link's ultimate output. The circuit is especially useful with frequency selective limiters (FSL's), which are commonly used as channelizers in multichannel communication systems, and which are ineffective before initialization.

Self-initializing circuit link

An image processing system and method are provided which use a selectively ccessed detector array comprised of subarrays. Regions of image activity are located within the detection array through readout of the activity determining elements. Each subarray is evaluated to determine whether any image activity has been detected by the corresponding subarray. Data is only read for the active subarrays. Thus, the activity indicator allows efficient transfer of relevant data from the detector array without requiring previous information. This results in reduced data flow and generally shorter readout cycles. The activity determination can be a non-destructive process so that data contained in the detection array remains available for sensor readout. This eliminates the need to perform one detector exposure cycle to determine activity and a second cycle to read out data from the detector.

Selective readout of a detector array

A 3 or more - dimensional optical processor for simultaneously processing ree or more parameters from a coherent emitter via an acoustic Bragg cell. For a 3-D processor, two separate antenna arrays (azimuth and elevation) are connected to excite two sets of acoustic transducer arrays on one edge of the Bragg cell. Multiplexing is achieved by the appropriate choice of the transducer array apertures. One transducer array set may have a narrow aperture to produce one wide first grating lobe pattern or a fraction thereof in a given focal plane (nonredundant imaging). The other transducer array set may have a wider transducer array aperture to produce a plurality of smaller second grating lobes within the first grating lobe pattern in the focal plane (redundant imaging). One coordinate axis of the focal plane represents the frequency of the emitter. The other coordinate provides the elevation parameter for that frequency emitter by measuring the position of the nonredundant lobe relative to the center boresight axis. The azimuth parameter is then obtained for that frequency emitter by measuring the position of the small redundant lobe closest to the centroid of the nonredundant lobe relative to its null position for that particular redundant lube.

Multi dimensional instantaneous optical signal processor

An optical downconverter with very wide bandwidth operable to separately ically downconvert individual spectrum sections of an RF spectrum, comprising the steps of modulating an optical carrier with the RF spectral width to be downconverted, spatially separating via optical gratings the different sections of the spectrum of the optical carrier sidebands into a plurality of optical channels, generating a different phase-coherent optical local oscillator signal for each optical channel at an appropriate frequency such that the difference between the LO frequency and the particular spectrum section on the given optical channel is equal to a predetermined difference frequency; and mixing each optical channel with its appropriate frequency L.O. and detecting the difference frequency resulting therefrom.

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Laurel, MD, United States of America

Anthony E Spezio