US Government As Represented by the Secretary of the Army

Andree N Filipov

Norman J Berg

Richard N Johnson

Michael W Casseday

Norman J Berg, Deceased

Christopher N Winslow

This invention relates to an acousto-optic time-integrating correlator for rocessing broadband Doppler-shifted signals. The present invention uses a conical lens telescope to compensate, in one dimension, for the differences in the absolute values of Doppler shift occurring in broadband signals. A laser light beam is expanded to a sheet beam using a conventional beam expander. The sheet beam is split and redirected using a modified Koster's prism. The two sheet beams are them directed toward a SAW device. The SAW device contains two tilted transducers. The inputs to the SAW device are counterpropagating A Doppler-shifted sheet beam and an undiffracted sheet beam are processed by respective conical lens telescopes. The outputs of the conical lens telescopes are combined with associated unprocessed sheet beams and combined by respective modified Koster's prisms and imaged onto respective two-dimensional photodetectors. The output of one photodetector is subtracted from the other to reduce offsets. Three alternate embodiments are also disclosed which show how a conical lens telescope can be used to improve the broadband performance of prior art approaches that use cylindrical lenses.

Accusto-optic time-integrating correlator for processing broadband

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

An analog-to-digital converter is disclosed providing high speed operation or high resolution analog signal data. The converter utilizes the repetitive nature of the data by converting a portion of the signal corresponding to the changing component of the data. A smaller number of bits of information is thus converted from analog-to-digital form than is needed to represent the data. In addition to savings in hardware, a significant saving in conversion time is provided. The cancellation of static components of a radar signal moreover provides, within the system, a clutter-free signal.

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Silver Spring, MD, United States of America

Andree N Filipov