Piezoelectric light beam deflector

Details Piezoelectric light beam deflector Piezoelectric light beam deflector

2000-12-15

2001-09-25

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With support

C359S824000, C359S298000

Reexamination Certificate

active

06295171

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to light direction control, and more particularly, to techniques for the dynamic control of light propagation direction.
2. The Prior Art
Dynamic control of light beam propagation direction is a fundamental technique in optics. Direct applications include projection displays, entertainment, advertisement, laser printers, laser detection systems, laser scanning, optical communications, laser machining, etc. Electromechanical devices have been the most frequently used light scanners in commercial products. Electromechanical methods use a rotating reflector or a rotating refractor driven by an electromechanical mechanism for changing light direction. The most important limitations of the electromechanical scanner include slow speed, bulky size, and the deficiencies inherent in complex electromechanical mechanisms. These limitations are intrinsic due to the nature of mechanical movement at a macro-dimensional scale.
Piezo-electric devices are able to induce small geometric changes on a sub-millimeter scale. Note that there is a significant difference between the macro-dimensional scale and the sub-millimeter scale. These difference extend beyond merely size; they represent different principles of operation and different methods of fabrication. When an electric signal is appropriately applied on a piezoelectric material, such as PZT (Lead Zirconate Titanite), a small dimensional change is induced. The dimensional change is generally in the range of from 1 micrometer (&mgr;m) to 500 &mgr;m. Piezoelectric actuators are based on such sub-millimeter scale processes. The most notable features of the sub-millimeter scale devices include high speed, miniature size, and simple device structure.
In the prior art, there are two types of piezoelectric light beam deflectors, the simple type and the mechanically enhanced type. Simple piezoelectric light deflectors can produce a small deflection angle ranging from 0.01° to several degrees. They are essentially piezoelectric light deflectors without enhancement. Since the deflection angles produced by the simple piezoelectric deflectors are too small for many practical applications, U.S. Pat. Nos. 3,981,566 and 4,025,203 and other prior art publications disclose mechanically enhanced piezoelectric mechanisms. Mechanically enhanced devices further extended the deflection angle to as large as about 15°. However, mechanically enhanced devices suffer from reduced speed and very delicate mechanical mechanisms at the macro-dimensional scale. The deficiencies of the mechanically enhanced piezoelectric light deflectors are on par with those of other electromechanical devices, while sacrificing the unique advantages of the simple piezoelectric process. Mechanically enhanced piezoelectric light deflectors have proved incapable of competing with other conventional electromechanical light deflectors for commercial applications.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a geometric optical lens system capable of providing a large output deflection angle for dynamic control of light beam direction.
Another object is to provide a dynamic light beam deflector based on the use of simple piezoelectric actuators. Such a deflector provides a large deflection angle with a simple structure characteristic of piezoelectric devices. The present system eliminates deficiencies associated with macro-electromechanical devices.
The light beam deflector of the present invention comprises an initial dynamic beam deflector, which imparts a small initial deflection &thgr;
0
, and a beam deflection amplifier, which increases the initial small deflection &thgr;
0
to an output deflection &thgr;. The light beam deflector is for use with a light source, such as a laser, light-emitting diode, or optical fiber, and conventional optics to appropriately modify the light output to meet the requirements of the initial beam deflector.
The initial beam deflector employs a piezoelectric actuator to control the amount of deflection in several embodiments. The first embodiment comprises a pair of positive geometric optical lenses with parallel axes and a piezoelectric actuator. The lenses are separated by a distance equal to the sum of their focal lengths f
1
+f
2
. The actuator is affixed to one lens such that the actuator can move the lens, either one- or two-dimensionally, in a plane parallel to the other lens. When the lens axes are separated by a distance d, the incident light beam will be deflected by an angle &thgr;
0
=d/f
2
. The angle &thgr;
0
can typically range up to about 5°.
The second embodiment of the initial deflector is essentially the same as the first embodiment except that a mirror is placed close to the back surface of the second lens. With this arrangement, the deflection angle &thgr;
0
=2d/f
1
.
The third embodiment is essentially the same as the first embodiment except that the positive second lens is replaced by a negative lens. Because the focal length of the second lens is less than zero, the distance between the lenses is f
1
−|f
2
|. The initial deflection angle &thgr;
0
=d/f
2N
. One characteristic of the third embodiment is that there exists no real focal point of the light beam. This may be advantageous if the power of the light beam is extremely high.
The fourth embodiment of the initial deflector is essentially the same as the third embodiment except that a mirror is placed close to the back surface of the negative lens. With this arrangement, the deflection angle &thgr;
0
=2d/f
2
.
The fifth embodiment of the initial beam deflector comprises a mirror rigidly affixed to a piezoelectric actuator, which tilts the mirror, producing a change in the orientation of the mirror.
The beam deflection amplifier multiplies the initial deflection angle &thgr;
0
by an amplification factor A to result in a full deflection angle &thgr;
0
A=&thgr;, where A>1. There are five preferred embodiments. The first embodiment comprises a Keplerian telescope lens system first stage and a negative lens system second stage. The most important criteria for achieving a large output deflection angle is to make sure that the first stage output light beam always angles away from the optical axis after crossing the optical axis between the two stages.
The second embodiment comprises a Galilean telescope lens system first stage and a negative lens system second stage. The most important criteria for achieving a large output deflection angle is to make sure that the first stage output light beam always angles away from the optical axis, without crossing the optical axis between the two stages.
The third embodiment uses a standard telescope lens system alone, either a Keplerian and Galilean telescope lens systems. They both comprise two lenses with different focal lengths where the amplification factor is basically determined by the ratio of the focal length of the two lenses.
The fourth embodiment replaces the single second lens of the first stage with a compound lens system. Examples of such compound systems include the Huigenian, Ramsden, Kellner, RKE, Orthoscopic, Plossl, and Erfle eyepieces.
The fifth embodiment is the lens system as disclosed in the U.S. Pat. application Ser. No. 09/503,828, which can provide an output deflection angle approaching ±90°.
Other objects of the present invention will become apparent in light of the following drawings and detailed description of the invention.


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Glöckner et al., Micro-opto-mechanical Beam Deflector

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