Liquid crystal cells – elements and systems – Liquid crystal optical element – Beam dividing switch formed from liquid crystal cell
Utility Patent
1998-08-24
2001-01-02
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal optical element
Beam dividing switch formed from liquid crystal cell
C359S245000
Utility Patent
active
06169594
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a beam deflector for deflecting a beam of electromagnetic energy and more particularly to (1) a beam deflector that comprises at least one mated pair of arrays of microprisms that can selectively change the angle of a beam of light for use in scanning light beams from and on an object spaced from the array, (2) a method of making the beam deflector, and (3) a scanner using the beam deflector that is capable of one-dimensional, two-dimensional or three-dimensional scanning, such as for use in laser radar or other scanning and imaging applications.
BACKGROUND OF THE INVENTION
In the past, it has been known to use a microprism array to selectively change the angle of a beam of light passing through the array. One such array is disclosed in an article entitled
Free
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space optical interconnections with liquid
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crystal microprism arrays,
Katsuhiko Hirabayashi, Tsuyoshi Yamamoto, and Masayasu Yamaguchi, Vol. 34, No. 14,
Applied Optics,
May 10, 1995. However, one drawback of the disclosed array is that it uses undesirably large microprisms, limiting how fast the array can react to change the angle of light passing through it. Moreover, a further drawback is that the disclosed beam that passes through the array has to have a diameter less than the size of one of its microprisms which is about 100 microns which thereby limits its use for large area distortion-free scanning. Still further, by the array using such a large diameter beam, the array is unsuitable for use in an image or object scanner because its resolution would be extremely poor. As a result, the disclosed array is impractical for commercial applications, such as optical interconnections and optical switches disclosed, because these applications require much higher switching speeds than what the array will provide. Due to the relatively slow switching speed of the array and the poor resolution that results from the rather large size, i.e. large pitch, microprism used, the array cannot be used for scanning applications (1) where an object remote from the array is being scanned with the beam, or (2) where light from an object or source remote from the array is being scanned.
In the past, scanners have been made up of mirrors and motors that quickly and precisely move or vibrate the mirrors to position a light beam emitted from a light source. However, such mechanical systems have a less than desirable scanning speed because the inertia of each moving object slows scanning.
More recently, the need to rapidly scan and steer a beam of light energy, typically from a laser, has led to the development of optical systems with low rotational or translational inertia because movement of mechanical components is kept to a minimum. Examples of these developments include deformable mirror arrays based on integrated circuit technology, a binary optics microlens array concept based on the mechanical movement of a complementary pair of microlens arrays, a liquid crystal scanner based on diffraction using liquid crystal phase gratings, and a conical beam scanner and collector based on a holographic plate.
Unfortunately, all of these developments have drawbacks and limitations. For example, the deformable mirror scanner is costly to manufacture, is limited to small apertures and low scanning speeds, and, perhaps worst of all, can only scan a single dimension. The microlens array requires a special aspheric structure and non-planar movement to achieve acceptable beam collimation quality. In addition, the microlens array requires complex high voltage and bulky piezoelectric mechanical drivers for non-planar movement and is limited to relatively slow kilohertz scanning speeds. The liquid crystal diffractive beam deflectors are, at best, experimental and have small diffraction angles, less than optimal diffraction efficiencies, and a great deal of noise. Lastly, rotating holographic optical elements or plates are also undesirably limited to one-dimensional conical scanning, as the beam is emitted only along the surface of a cone, which therefore requires in-plane rotation of the holographic optical elements.
What is needed is a device that can efficiently change the direction of light without the apparatus having to move. What is further needed is a microprism array capable of changing the direction of a beam of light from an object having a large diameter without distorting the beam sufficiently quickly so as to be suitable for commercial applications. What is also needed is a beam deflector that can be used in scanners that scans light from a light source as well as light received from an object. What is still further needed is a microprism array suitable for use in a scanner using a source of light that scans an object or series of objects located remote from the array. What is additionally needed is a microprism array that can be used in a scanner capable of two-dimensional scanning or three-dimensional scanning. What is still additionally needed is a scanner that has no moving parts and which can be used to scan terrain, images, retinas, as well as any other object or indicia capable of being scanned.
SUMMARY OF THE INVENTION
A beam deflector composed of a pair of mated prism arrays with one of the arrays comprised of a material having a refractive index that remains substantially constant and the other of the arrays comprised of a material having a refractive index that can be selectively varied. During operation, a field that is either an electric field or a magnetic field is selectively applied to the array of variable refractive index material to control the angle a beam is deflected as it passes through the beam deflector. The field intensity, flux or flux density is controlled by selective application of voltage to terminals of the beam deflector. The flux lines of the field preferably extend generally parallel to the length of the variable refractive index prism. The beam deflector preferably does not move during operation.
Each array comprises a prism having a height, a width, and a length longer than either its height or width. Each prism preferably has a generally triangular cross-section that can comprise a right triangle. Each prism has a face disposed toward the incoming beam, a face from which the beam exits after it passes through the prisms, and a sidewall face. To quickly respond to the presence or absence of a field or a change in the field, the variable refractive index prism has a height no greater than about 20 &mgr;m such that it is a microprism that responds within about 100 &mgr;s. In other preferred embodiments, prism heights smaller than 15 &mgr;m and preferably smaller than 10 &mgr;m are preferred for responding as fast as about 30 &mgr;s or faster. The variable refractive index prism also has an apex angle between about 10° and about 60° and can have its refractive index varied as much as 0.15-0.3, typically about 0.2, so as to deflect the beam by an angle of as much as 30° or more. Preferably, the refractive index is selectively variable such that the beam can be deflected accurately to within an angular resolution of about 0.5 milliradians. The refractive index of the variable refractive index prism is selectively variable so it can match the refractive index of the constant refractive index prism such that the beam is not deflected as it passes through. Each variable refractive index prism preferably is made of a liquid crystal material that is a nematic liquid crystal material or preferably is a ferroelectric crystal material.
Preferably, each array is comprised of a plurality of pairs of microprisms with the microprisms of one array received between the voids between adjacent microprisms of the other array such that the mated arrays preferably have a generally rectangular cross-section. The array comprised of variable refractive index microprisms is disposed such that the beam passes through it before passing through the array of constant refractive index microprisms.
The mated arrays preferably are disposed between a pair of panes with an electri
Aye Tin M.
Savant Gajendra D.
Dudek James A.
Nilles & Nilles S.C.
Physical Optics Corporation
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