Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
2000-03-06
2002-01-22
Font, Frank G. (Department: 2877)
Coherent light generators
Particular beam control device
Modulation
C372S024000, C372S101000, C372S108000, C372S098000, C372S100000, C372S092000
Reexamination Certificate
active
06341136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical beam deflector. The optical beam deflector can be used, for example, for generating a scanning beam in a laser beam scanning apparatus, and the laser beam scanning device can be used in recording, reading, and displaying information, laser radar, intersatellite communication, and the like.
2. Description of the Related Art
Conventionally, the following techniques are proposed for optical beam deflectors:
(1) Laser Beam Deflectors Using Microlens Array
(a) W. Goltsos, and M. Holz, “Agile Beam Steering Using Binary Optics Microlens Arrays,” Optical Engineering, vol. 29 (1990), 1392.
(b) T. D. Milster and J. N. Wong, “Modeling and Measurement of Micro-Optic Beam Deflector,” in “Design, Modeling, and Control of Laser Beam Optics,” SPIE Proceedings, vol. 1625 (1992), 78-83.
In the techniques disclosed in the above references (a) and (b), two microlens arrays are provided in a telescope arrangement, and an incident laser beam is deflected by displacing one of the two microlens arrays in the direction perpendicular to the light axis. However, these techniques have the following drawbacks.
(i) Distributions of amplitudes and phases of the deflected beam are inequable, i.e., the deflected beam is not a single-peaked beam. Luminous energy of portions of the laser beam which are diffracted in directions other than the desired direction of deflection is lost, quality of the light beam is deteriorated, and performance of apparatuses utilizing the optical beam deflector is impaired.
(ii) Since the deflection is realized by mechanical displacement of the microlens array, it is not possible to perform agile, stable, and reliable scanning by using the above optical beam deflectors.
(2) Laser Beam Deflectors Using Liquid Crystal Phase Modulator Array
R. M. Matic, “Blazed Phase Liquid Crystal Beam Steering,” SPIE Proceedings, vol. 2120 (1994), 194-205.
In the technique disclosed in the above reference, an incident laser beam is deflected in a desired direction by providing a distribution of phase modulation over the crosssection of the laser beam by using an array of optical phase modulators. However, due to use of only one array of optical phase modulators, this technique has the following drawbacks.
(i) Dead spots or stripe-shaped electrode areas of the array of optical phase modulators cause loss of luminous energy, and deform the wavefront of an output laser beam.
(ii) The maximum deflection angle is determined by a maximum gradient of the phase distribution, which is further determined by a pitch of the electrodes and the maximum phase difference achieved by each optical phase modulator in the array of optical phase modulators. Therefore, in order to increase the maximum deflection angle, the maximum gradient of the phase distribution has to be increased. That is, it is necessary to decrease the pitch of the electrodes, or to increase the maximum phase difference achieved by each optical phase modulator.
However, when the pitch of the electrodes is decreased, a considerable amount of phase distortion is generated at edge portions of the array of optical phase modulators, and it becomes impossible to realize a desired stepwise phase distribution. In addition, in order to increase the above maximum phase difference achieved by each optical phase modulator, it is necessary to thicken each optical phase modulator. However, when each optical phase modulator is thickened, a large driving voltage is needed, and response becomes slow.
Therefore, it is difficult to increase the maximum deflection angle with the above technique.
(3) Laser Beam Scanning Radiating Apparatus Using Laser Resonator
U.S. Pat. No. 5,600,666 discloses a laser beam scanning and radiating apparatus which generates and scans a laser beam by using a laser resonator.
However, in the above laser beam scanning and radiating apparatus, resonator mirrors must be a phase conjugate mirror. Nevertheless, usually, a passive optical element such as a mirror can achieve the optical phase conjugation only approximately. Therefore, the use of the resonator mirrors causes loss of luminous energy. In addition, the laser beam scanning and radiating apparatus using a laser resonator has a complex construction.
Further, active elements such as nonlinear optical crystals are expensive, and cannot realize a stable phase-conjugate element.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an optical beam deflector which causes neither loss of luminous energy nor deformation of wavefront, has no limit of the maximum deflection angle, guarantees agile, stable, and reliable movement of a beam, has a simple construction, and is inexpensive.
According to the present invention, a crosssection of an incident optical (e.g., laser) beam is divided into a plurality of first micro crosssections, a plurality of phases of the optical beam in the first micro crosssections are respectively modified so that a desired phase gradient is realized over the crosssection of the optical beam, and thereafter the crosssection of the optical beam is further divided into a plurality of second micro crosssections, and a plurality of phases of the optical beam in the second micro crosssections are respectively modified so that the optical beam as a whole is finally directed in a desired direction of deflection or to a desired point.
More concretely, the optical beam deflector according to the first aspect of the present invention contains an array of lenses which collect a first plurality of portions of an incident optical beam into a plurality of spots, respectively; an array of first optical phase modulators which modulate, at or in vicinities of the plurality of spots, phases of the first plurality of portions of the optical beam; a first Fourier transform lens which performs Fourier transformation on the optical beam output from the array of first optical phase modulators to generate a second plurality of portions of the optical beam; an array of second optical phase modulators which modulate phases of the second plurality of portions of the optical beam; an array of second Fourier transform lenses which collect the second plurality of portions of the optical beam after the phases of the second plurality of portions are modulated by the array of second optical phase modulators, and perform inverse Fourier transformation on the second plurality of portions of the optical beam; and a driving unit which drives the arrays of first and second optical phase modulators so that the second plurality of portions of the optical beam which exit from the array of second Fourier transform lenses as a whole are directed in a desired direction of deflection or to a desired point.
In the optical beam deflector according to the first aspect of the present invention, a first plurality of portions of an incident optical beam are collected, by the array of lenses, respectively into a plurality of spots. The phases of the first plurality of portions of the optical beam are modulated by the array of first optical phase modulators at or in vicinities of the plurality of spots. Fourier transformation is performed by the first Fourier transform lens on the optical beam output from the array of first optical phase modulators, to generate a second plurality of portions of the optical beam. The phases of the second plurality of portions of the optical beam are modulated by the array of second optical phase modulators. The second plurality of portions of the optical beam, after the phases of the second plurality of portions are modulated by the array of second optical phase modulators, are collected by the array of second Fourier transform lenses, and inverse Fourier transformation is performed on the second plurality of portions of the optical beam. The driving unit drives the arrays of first and second optical phase modulators so as to realize appropriate phase distributions over the arrays of first and second optical phase modulators, respectively. Thus, the second plurality of
Font Frank G.
Fuji Photo Film Co. , Ltd.
Rodriguez Armando
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