Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-03-26
2001-08-21
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S263000, C359S254000, C359S250000
Reexamination Certificate
active
06278540
ABSTRACT:
TECHNICAL FIELD
The present invention relates to manipulation of an optical beam, and more specifically to optical filtering and beam steering.
BACKGROUND
An optical beam can be manipulated to obtain desired effects for various applications. One type of optical manipulation is color filtering. For example, the spectral composition of a beam can be filtered by using an optical wavelength filter to obtain light of a desired wavelength or within a certain wavelength range. Optical color filters can produce color images in display systems such as liquid crystal displays (“LCDs”) in projectors, laptop computers, and camcorders.
Many conventional optical color filters operate based on absorption. Such a filter transmits light of a desired color and absorbs light of other colors. In a color LCD, three different absorbing color filters can be implemented in the three adjacent pixel cells to form one color pixel. Such filters are lossy since only about one third of a white beam is actually used for color display. This low efficiency significantly reduces the image brightness for a given light source.
Color wheels are also absorbing color filters. As the wheel spins, a white beam is intercepted and absorbed by different absorbing materials on the wheel. Thus, different colors can be obtained in the transmitted light. In addition to the above absorption loss of light, a color wheel can also be prone to mechanical failure because of tear and wear of the moving wheel.
Another common type of optical manipulation is beam steering where the direction of an optical beam is steered in a controlled manner. For example, laser vector displays and laser video projectors use beam scanners to scan laser beams at high speeds to form images. One type of beam scanners are based on a mirror or a prism engaged to a moving device such as a galvanometer. Such scanners are relatively slow due to the inertia of the galvanometer and the attached optical element. Wear and tear of the galvanometer associated with the motion of the galvanometer also adversely affect the reliability and durability of such beam scanners.
Therefore, there exists a need for efficient color filters and for reliable beam scanners without moving parts.
SUMMARY
The present disclosure provides a non-absorbing tunable optical color filter and an optical scanner without a moving part based on total internal reflection.
An optical interface between two different transparent dielectric materials is used to effect total internal reflection from a high-index material with a refractive index of n
H
to a low-index material with a refractive index of n
L
. The critical angle, &thgr;
C
, for the total internal reflection is a function of n
L
when the n
H
is a fixed constant: &thgr;
C
=sin
−1
(n
L
H
). Hence, control and adjustment of n
L
can be used to control and adjust the condition of the total internal reflection for a beam incident to the interface near a predetermined critical angle.
According to one embodiment, a device operable to change a property of an optical beam may include a first transparent optical element having an optical surface coated with a transparent conducting layer and a layer of electro-optic material formed over the transparent conducting layer. The electro-optic material has a refractive index which is smaller than that of the first optical element when biased at a first voltage and is substantially equal to that of the first optical element when biased at a second voltage.
The device includes a plurality of independent transparent electrodes formed over the electro-optic material to divide the layer of electro-optic material into a plurality of pixels. A control circuit is coupled to bias each electrode relative to the transparent conducting layer between the first and second voltages to either effect total internal reflection on an incident beam in the first transparent optical element or to transmit the incident beam.
The above device may be configured as a tunable color filter by incorporating a non-absorbing filter in each pixel. The filter can be formed over the electrode in each pixel to transmit light of a selected color associated with that pixel and reflect light of other colors.
In addition, the above device may be used to effect an optical scanner to shift the position of an incident beam from one pixel to another by properly controlling the bias voltages on the pixels.
The total internal reflection and the index control based on the electro-optic effect are combined in a special way to provide high-speed optical control without moving parts. In addition, the use of non-absorbing color filters significantly increases efficiency of color filtering over conventional absorbing color wheels and dye filters and provides new color display techniques for many applications including notebook computers.
These and other aspects and advantages of the present invention will become more apparent in light of the following detailed description, the accompanying drawings, and the claims.
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California Institute of Technology
Epps Georgia
Fish & Richardson P.C.
Thompson Timothy
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