Optical beam steering device

Details Optical beam steering device Optical beam steering device

1991-10-21

1994-09-27

Bovernick, Rodney B.

Coherent light generators

Raman laser

372 22, H01S 330

Patent

active

053512502

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to an optical beam steering device, and in particular to a device for steering high power light beams.
2. Discussion of Prior Art
Optical beam steering devices are well-known in the prior art. Typical electro-mechanical devices involve a moving mirror employed to deflect a light beam. This suffers from the disadvantage that the energy required to rotate such a mirror is proportional to the fifth power of the mirror diameter (D.sup.5). High power light beams require large diameter steering mirrors so that the power density at the mirror surface is less than a damage threshold. In consequence, high power beam steering requires a bulky and expensive moving mirror assembly.
Acousto-optical and electro-optical beam steering devices are also known in the prior art. The former comprises a piezo-electric block in which acoustic waves interact with a light beam to produce steering. The latter comprises an electro-optical waveguide array which is an optical analogue of a radar phased array. Beam steering is achieved by varying the bias voltage on (and thereby the phase change induced by) individual waveguides. However, the power handling capacity of each of these devices is severely restricted. It is orders of magnitude below that required to accommodate high power laser beams.


SUMMARY OF THE INVENTION

It is an object of the invention to provide an alternative form of beam steering device.
The present invention provides an optical beam steering device comprising means for steering a low power light beam, and phase conjugating means arranged to receive the steered low power beam and to generate a high power phase conjugate thereof.
The invention provides the advantage that high power light beam steering is produced with the aid of steering means operating on a low power beam, since the phase conjugate beam direction is governed by that of the steered beam. This makes it possible to employ conventional steering devices only suitable for low powers to control the direction of a much higher power beam. Furthermore, by virtue of the use of phase conjugating means, degradation in the optical quality of the low power beam by optical components is counteracted in the high power beam.
In a preferred embodiment, the phase conjugating means incorporates a Brillouin four wave mixing cell and pumping means for providing the cell with counterpropagating laser pump beams having frequencies appropriate to produce four wave mixing in combination with the steered low power beam. The pumping means may also incorporate a laser arranged to provide both the pump beams and the low power beam. The laser output may be divided between first and second Brillouin scattering cells arranged to provide a first pump beam and the low power beams respectively, these beams having frequencies decremented by .delta..upsilon..sub.A and .delta..upsilon..sub.B respectively from that of the laser, and a second pump beam may be provided by a third Brillouin scattering cell arranged to receive the first pump beam after transmission through the four wave mixing cell and to return it thereto with a further frequency decrement .delta..upsilon..sub.B. The first pump beam may be amplified prior to input to the four wave mixing cell.
The phase conjugating means may alternatively incorporate a Brillouin amplifier and a stimulated Brillouin scattering cell.
The low power beam steering device may incorporate one of following: mirror, the mirror being arranged adjacent to a common focal plane of the telescope and lens, and reflectivity surface disposed in a focal plane of focussing means.


BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention might be more fully understood, examples thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic block diagram of an optical beam steering device of the invention;
FIGS. 2, 3 and 4 schematically illustrate low power beam steering means for use in the FIG. 1 device;


REFERENCES:
patent: 4493085 (1985-01-01), Valley
patent: 4500855 (1985-02-01), Feinberg
patent: 4633103 (1986-12-01), Hyman et al.
patent: 4778261 (1988-10-01), Boyd et al.
patent: 4794344 (1988-12-01), Johnson
patent: 4812682 (1989-03-01), Holmes
patent: 4853528 (1989-08-01), Byren et al.
patent: 4934779 (1990-06-01), Dunning
Ackerman et al.; "Improved Performance from Noncollinear Pumping in a High-Reflectivity Brillouin-Enhanced Four-wave Mixing Phase Conjugator"; IEEE J. of Quantum Electronics; vol. 25, No. 3; Mar. 1989; pp. 479-483.
IEEE Journal of Quantum Electronics, vol. 25, No. 3, Mar. 1989, A. M. Scott et al. "A Review of Brillouin-Enhanced Four-Wave Mixing", pp. 438-459 International Search Report.

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