US Government As Represented by the Secretary of the Army

Michael W Casseday

Norman J Berg

Irwin J Abramovitz

John N Lee

Andree N Filipov

An acousto-optic diffraction and signal mixing device. A laser light beam is expanded and shaped into a sheet beam which is directed across the surface of an acousto-optic medium. Four acoustic transducers are disposed on the acousto-optic medium, two at each end of the medium. Each acoustic transducer is supplied with a signal to be propagated on the surface of the acousto-optic medium. The first two signals diffract the sheet beam to produce a first product diffracted beam of light containing the product of the first two signals. The second two signals diffract the sheet beam to produce a second product diffracted beam of light containing the product of the second two signals.

Acousto-optic diffraction and signal mixing device

A device for processing signals to obtain a multi-product, time integrated, correlated output signal. A laser light beam is expanded and shaped into a sheet beam which is directed across the surface of an acousto-optic medium. Four acoustic transducers are disposed on the acousto-optic medium, two at each end of the medium. Each acoustic transducer is supplied with a signal to be propagated on the surface of the acousto-optic medium. The first two signals diffract the sheet beam to produce a first, product diffracted beam of light containing the product of the first two signals. The second two signals diffract the sheet beam to produce a second product diffracted beam of light containing the product of the second two signals. The two product diffracted beams are rotated so that they are orthogonal to each other, and then combined. A time integrating photodetecting means is disposed in the path of the combined beam for generating a multi-product, time integrated, correlated output signal.

Multi-product acousto-optic time integrating correlator

An acousto-optic architecture is provided for simultaneously obtaining time integration correlation and power spectrum analysis. A laser beam is expanded and split into first and second beams. The first beam is diffracted by a first acousto-optic Bragg cell, and the second beam is diffracted by a second acousto-optic Bragg cell. The diffracted first beam is split into third and fourth beams, and the diffracted second beam is split into fifth and sixth beams. A first Fourier transform lens system is placed in the path of the third beam, and a first photodiode detector array is placed at the back focal plane of the lens system. A second Fourier transform lens system is placed in the path of the sixth beam, and a second photodiode detector array is placed at the back focal place of the lens system. The fourth and fifth beams are combined and the combined beam is split into seventh and eighth beams. A first Schlerin spatial filter is disposed in the path of the seventh beam for filtering undiffracted light from it. A second Schlerin spatial filter is disposed in the path of the eighth beam for filtering undiffracted light from it. A third photodiode detector array is disposed in the output of the first Schlerin spatial filter, and a fourth detector is disposed in the output of the second Schlerin spatial filter. The outputs of the first and second photodiode detector arrays are proportional to the power spectral density of the signals S.sub.1 (t) and S.sub.2 (t), which are respectively applied to the first and second Bragg cells. These outputs are resolved to a limit determined by the time aperture of the Bragg cells and are time averaged over the integration period of the array. The output of the third photodiode detector array is proportional to the correlation of the bandpass signals S.sub.1 (t)cos .omega..sub.a t offset by the frequency .omega..sub.o and in a compressed, shifted time frame. The output of the fourth photodiode detector array is proportional to the correlation of the bandpass signals S.sub.1 (t)cos .omega..sub.a t and S.sub.2 (t)cos .omega..sub.a t offset by the frequency .omega..sub.o, but in a more restricted delay range than that of the third photodiode detector array.

Multi-function acousto-optic signal processor

A method and device for processing spread-spectrum and other wideband comications and radar signals to obtain three and four product correlated signals. A laser beam is split and shaped into first and second sheet beams. The first beam is directed to a first acousto-optic medium where it is doubly diffracted by first and second signals. The second beam is directed to a second acousto-optic medium which is spatially rotated 90.degree. relative to the first acousto-optic medium where the second sheet beam is either singly diffracted by a third signal or doubly diffracted by a third signal and a fourth signal. The diffracted sheet beams are shaped into square beams, combined and directed to a photodiode area array.

Three and four product surface-wave acousto-optic time integrating

An acousto-optic time integrating two-dimensional frequency scanning correlator for cross-correlating signals which are separated in frequency. Two coherent light beams which are derived from the same laser are fed across respective Bragg cells, one cell having the signal A(t) cos .omega..sub.A t propagating thereacross and the other cell having the signal B(t) cos .omega..sub.B t propagating thereacross. The respective output beams are comprised in the x direction and expanded in the y direction and are made incident on an acousto-optical correlator device having chirp signals counter-propagating thereacross. The optical output is fed to a time-integrating photodiode array which provides an output signal corresponding to the cross-correlation of A(t) and B(t). In a further embodiment, the two Bragg cells are replaced by a single Bragg cell and beams having different polarizations are fed thereacross. In a still further embodiment, only a single crystal is used which has the A(t) and B(t) signals, as well as the chirp signals, counter-propagating thereacross.

Acousto-optic time integrating frequency scanning correlator

A highly efficient time integrating acousto-optic correlator which determs the time difference of arrival of the signals being correlated as well as the center frequency and bandwidth of the signals. A surface acoustic wave delay line is provided with two counter-propagating surface acoustic waves with wavefronts tilted with respect to each other. Two laser beams are directed across the propagating waves with an angle of 4.theta..sub..beta. between them where .theta..sub..beta. is the Bragg angle, so that one beam interacts primarily with one propagating wave while the other beam interacts primarily with the other wave. The modulated optical beams are directed to a time-integrating photodetector means which provides a signal output corresponding to the correlation function.

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Washington, DC, United States of America

Michael W Casseday