Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-06-03
2002-10-22
Chang, Audrey (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S015000, C385S016000, C385S018000, C385S019000, C385S025000, C385S030000, C385S031000, C385S036000, C385S047000, C385S048000
Reexamination Certificate
active
06470115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an optical switching element (light valve) used for optical communication and optical computation. The invention also relates to an optical switching element used in an optical storage device, an optical printer, an image display device, etc., and particularly in an image display device.
2. Description of Related Art
A conventional optical switching element comprises a liquid crystal. As shown in a schematic configuration of
FIG. 16
, a conventional optical switching element
900
comprises polarizers
901
and
908
, glass plates
902
and
903
, transparent electrodes
904
and
905
, and a liquid crystal
906
or
907
, so that when a voltage is applied between the transparent electrodes, the direction of liquid crystal molecules is changed to rotate the surface of polarization, resulting in optical switching. A conventional image display device comprises a liquid crystal panel having such optical switching elements (liquid crystal cells) arranged in a two-dimensional form, in which the direction of liquid crystal molecules is controlled by adjusting the applied voltage to achieve grayscale.
However, a liquid crystal has low responsiveness, and is operated at a response speed of only several milliseconds. Therefore, it is difficult to apply an optical switching element comprising a liquid crystal to optical communication, optical computation, an optical memory device such as hologram memory, an optical printer, and the like. Also, an optical switching element comprising a liquid crystal is subject to that problem that the utilization efficiency of light deteriorates due to polarizers.
Higher image quality has recently been demanded in image display devices, and thus there has been a demand for an optical switching element which permits more precise display of grayscale than an optical switching element using a liquid crystal.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an optical switching element which permits high speed response with low loss of light. Another object of the invention is to provide an image display device which can be relatively simply manufactured with high yield, and which permits color display with high resolution at low cost. A further the object of the present invention is to provide an image display device which permits thinning of an optical system for illumination and which has precise grayscale characteristics.
In order to achieve the objects, the present invention provides an optical switching element comprising a light guide which permits extraction of light when a transmissive extraction surface is brought into contact with the light guide, and extraction of leaking evanescent light when the extraction surface is brought near the light guide at a distance of half a wavelength, preferably ¼ wavelength, therefrom, whereby light can be turned on and off at high speed by finely moving a light extraction unit provided with the extraction surface for about a wavelength or less. Namely, in accordance with the optical switching element of the present invention, the light guide has a total reflection surface capable of transmitting light by total reflection, and the light extraction unit has the transmissive extraction surface which can be moved between a first position at not more than the extraction distance from the total reflection surface, where evanescent light leaks, and a second position at not less than the extraction distance therefrom. Since the optical switching element is capable of extracting evanescent light, it does not necessarily require adhesion (close contact) to the total reflection surface of the light guide, and exhibits high reliability. An off state is caused by movement from the first position to the second position at a distance of about a wavelength from the total reflection surface, and it is thus possible to provide an optical switching element which can be operated at high speed. Also, in the off state, light from the light guide is totally reflected without leaking, and thus an optical switching element having high contrast can be provided.
In the optical switching element, the light extracted by the extraction surface may be appropriately processed by an emission member so that the light can be output to the outside, thereby permitting on-off operations. For example, at least one of an emission surface and a reflection surface at a different angle from the total reflection surface may be provided on the emission member so that the light extracted by the light extraction unit can be output to the outside. As such an emission member, a micro prism or micro lens can be used for efficiently outputting the light extracted by the extraction surface to the outside. As the emission member, it is possible to use an optical element having the shape of a truncated cone or truncated pyramid which expands in the emission direction. The use of such an optical element enables a further increase in the efficiency of light extraction, and the direction of the extracted light to be close to the direction perpendicular to the total reflection surface of the light guide.
Also a light scattering body can be used as the emission member o that the extracted light can be emitted to the outside by scattering by the emission member. Further, as the emission member, a member which can emit light by extracted light, for example, a member which uses ultraviolet light as light to be transmitted to the light guide unit, and which contains a fluorescent agent emitting light when the ultraviolet light is applied thereto, can be used.
Further, an optical switching element can be provided in which wavelength selectivity is imparted to the light extraction unit to develop different colors. For this purpose, the extraction surface or the emission member may be provided to function as a color filter, a material having wavelength selectivity may be used as a scattering material or a light emitting agent.
The light extraction unit may be a transmissive type in which extracted light is guided to the side opposite to the extraction surface. Such a transmissive extraction unit is disposed on the light emission side with respect to the light guide unit to function as an optical switching element. On the other hand, the light extraction unit may be a reflective type in which extracted light is guided to the extraction surface side, and such a reflective light extraction unit is disposed on the side opposite to the light emission side with respect to the light guide unit to function as an optical switching element. Also the light extraction unit may be an emissive type which emits light by the light extracted by the extraction surface. In cases where the extracted s scattered, or the light emitted by extracted light is emitted, a light absorbing layer is disposed on the side opposite to the emission side with respect to the light guide unit to absorb extraneous light, thereby improving contrast.
Further, a non-movable light processing unit may be provided on the emission side where the light extracted by the light extraction unit is emitted, and provided with a wavefront converting function, a wavelength selecting function or a light emitting or scattering function in place of the emission member having a scattering or wavelength selecting function and provided on the light extraction unit for switching operations. By providing such a light processing unit, it is possible to simplify the configuration of the light extraction unit, facilitate movement due to a decrease in the operation load, and enable high-speed switching operations.
In such an optical switching element, the light extraction unit may be separately supported so that it can be moved at a proper distance from the light guide. Where a thin film is laminated on the light guide with spacers therebetween, and the light extraction unit is supported by the thin film, it is possible to maintain an appropriate distance from the light guide, and unitize the light extraction unit
Chang Audrey
Curtis Craig
Oliff & Berridge PLC.
Seiko Epson Corporation
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