Continuously variable delay lines

Details Continuously variable delay lines Continuously variable delay lines

1992-05-27

1993-09-21

Arnold, Bruce Y.

Optical: systems and elements

Optical modulator

Light wave temporal modulation

359285, 359305, 359306, 359308, 359314, 359560, 385 7, 385 10, G02F 111, G02F 133, G02B 2746

Patent

active

052473880

ABSTRACT:
An acousto-optic apparatus is described that varies the time delay of electrical signals over a continuum of delays. In the preferred embodiment, a light source, which can be either coherent or incoherent, emits an optical beam that is focused into an acousto-optic cell. An input electrical signal is used to drive the acousto-optic cell which, in turn, modulates the focused optical beam. Portions of the input optical beam are modulated and diffracted at angles proportional to the frequencies and phases contained in the input electrical signal. By appropriately choosing the cone of angles at which the light is focused into the acousto-optic cell, the diffracted optical beam can be made to overlap with portions of the undiffracted, unmodulated optical beam. All of the light exiting the acousto-optic cell is then collected onto a device for detection. Optical photomixing of the diffracted beam and the undiffracted beam is performed in order to derive the input electrical signal with a time delay. The approach to generating a continuously variable delay maintains a true time delay of the input electrical signal on its electrical carrier frequency, and does not suffer the limitations imposed by only time delaying the modulation envelope of the input electrical signal. Since all optical beams travel exactly the same physical path, the present invention is robust to mechanical or thermal variations unlike inferior acousto-optic approaches for implementing time delay.

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patent: 5187487 (1993-02-01), Riza
"An acousto-optic modulator for a CO.sub.2 laser rangefinder using heterodyne detection"; Optical and Quantum Electronics 12; No. 5 Sep. 1980 p. 419.
Anthony Vanderlugt, "Accousto-Optic Devices", Optical Signal Processing pp. 289-297, 1992 (distributed at least as early as 1988).
M. J. Brienza, "Variable Time Compression, Expansion, and Reversal of RF Signals by Laser-Acoustic Techniques", Applied Physics Letters, vol. 12, No. 5, pp. 181-184 (Mar. 1968).
M. J. Brienza and A. J. DeMaria, "Continuously-Variable Ultrasonic-Optical Delay Line", Applied Physics Letters, vol. 9, No. 8, pp. 312-314 (Oct. 1966).

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