Optical heterodyne detector

Details Optical heterodyne detector Optical heterodyne detector

1989-11-16

1991-06-18

Eisenzopf, Reinhard J.

Telecommunications

Receiver or analog modulated signal frequency converter

Signal selection based on frequency

350 367, G02F 100

Patent

active

050254880

ABSTRACT:
Nonlinear optical devices and techniques are used to provide heterodyne detection for coherent optical communications. Heterodyne detection is achieved by matching the wave front of a local oscillator beam with the wave front of a received optical signal. Precise wave front matching provides high heterodyne efficiency and a wide field of view. In one embodiment, the received signal and a reference beam of the same frequency are directed into a nonlinear medium to form a volume hologram that contains the spatial information of the received signal. The reference beam is alternated with a local oscillator beam that has the same wave front and is parallel to the reference beam but at a different frequency. The hologram matches the wave fronts of the signal beam and the local oscillator beam to produce a large heterodyne signal. In an alternative embodiment, the received signal beam and the local oscillator beam are directed into a mutually pumped phase conjugator (MPPC). The MPPC generates a spatial phase conjugate of the oscillator beam that carries the temporal characteristics of the signal beam. A beam splitter combines the information carrying phase conjugate beam with a phase conjugate of the pure local oscillator beam returned by a phase conjugate mirror. The two phase conjugate beams arrive at the plane of a photodetector with precisely the same wave front and direction. The matched wave fronts produce high heterodyne efficiency, and the automatic tracking feature of the phase conjugators provides a wide field of view.

REFERENCES:
patent: 3610932 (1971-10-01), Morse et al.
patent: 4442455 (1984-04-01), Huignard et al.
patent: 4761059 (1988-08-01), Yeh et al.
patent: 4911537 (1990-03-01), Ewbank
Morimoto et al., "A Picosecond Optical Gate using Photo-Induced Grating", Japanese Journal of Applied Physics, vol. 20, No. 6, Jun. 1981, pp. 1129-1133.
J. Shamir et al., "Wavefront Conjugation and Amplification for Optical Communication Through Distorting Media", Applied Optics, vol. 27, No. 14, pp. 2912-2914, Jul. 15, 1988.

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