Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-04-17
2003-04-15
Kim, Robert H. (Department: 2882)
Optical waveguides
With optical coupler
Switch
C385S019000, C385S016000, C359S223100
Reexamination Certificate
active
06549694
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switching element capable of deflecting incident light in two ways, and an optical switching apparatus and an image display apparatus employing the optical switching element.
2. Description of the Related Art
Recently, a display has been playing an important role as an image device for image information. As an element for the display, and elements for optical communication, an optical storage apparatus, an optical printer, a request for developing an optical switching element achieving fast operation has been increased. Conventionally, as those kinds of the elements, an element employing liquid crystal, an element employing a micromirror, an element employing diffraction grating and so on have been used. An example of the element employing liquid crystal is shown in FIG.
1
. An example of the element employing the micromirror is shown in
FIGS. 2A
to
5
. An example of the element employing diffraction grating is shown in FIG.
6
.
The optical switching element employing crystal liquid (
FIG. 1
) is provided with a pair of deflection boards
101
a,
101
b,
a pair of glass substrates
102
a,
102
b,
transparent electrodes
103
a,
103
b,
103
c,
103
d,
and crystal liquid
104
sealed between the pair of the glass substrates
102
a
and
102
b.
In the optical switching element, voltage is applied to the transparent electrodes
103
a,
103
b,
103
c,
and
103
d
to control orientation of crystal liquid molecules and rotate a deflection face, thereby carrying out switching.
However, the liquid crystal has poor fast-response characteristics. Even one having fast response exhibits only a few milli-seconds. For this reason, liquid crystal is considerably difficult to be applied to those optical storage apparatuses, which are required fast response, such as optical communication, optical calculation, optical storage apparatus such as holographic memory, an optical printer and so on. Additionally, in the optical switching element employing the liquid crystal, the pair of the deflection boards are necessary, which decreases effective use of light. Further, the liquid crystal can not resist strong light, so that switching can not be conducted by light having high energy density such as strong laser light. Especially, in the case of using the display, higher quality image is required. However, in the current optical switching element employing the liquid crystal, disadvantages such as inaccuracy in gradation indication begin to appear.
In the optical switching element employing the micromirror, as typified by DMD (digital micromirror device) manufactured by Texas Instruments Incorporated (U.S.), many specific examples have already existed. As its structure, there are two types: one supporting the micromirror with a single hand (
FIGS. 2A
,
2
B, and
3
), and the other supporting the micromirror with two hands (
FIGS. 4A
,
4
B and
5
). As a method for driving the micromirror, there are a method using electrostatic attraction, a method using piezoelectric elements, a method using thermo actuator and so on. Although there are differences in the structure, the method for driving and so on, as its function, switching of incident light is performed by controlling the angle of the micromirror, which is rather simple.
Here, the micromirror using the electrostatic attraction will be described as an example. As the driving principle of the micromirror, the case where the micromirror is supported with the single hand (
FIGS. 2A
,
2
B and
3
) is as follows; Potential difference is given between a micromirror
105
and a driving electrode
106
, which generates electrostatic attraction to incline the micromirror
105
. When the given potential difference is eliminated, the previous condition gets back by spring strength of a hinge
105
a
supporting the micromirror
105
.
In the case where the micromirror is supported with two hands (
FIGS. 4A
,
4
B, and
5
), the same potential difference is generated between the micromirror
108
and a pair of electrodes
107
a,
107
b
oppose to the micromirror
108
. Under this condition, for example, voltage applied to the electrode
107
a
becomes low, on the other hand, voltage applied to the electrode
107
b
becomes high, which occurs unbalance in electrostatic attraction generated between the electrodes
107
a,
107
b
and the micromirror
108
respectively, thereby inclining the micromirror
108
.
The light is switched based on the following conditions. In the case of the micromirror supported with the single hand (
FIGS. 2A
,
2
B, and
3
), under a condition where the micromirror
105
is not inclined with respect to incident light P
100
, reflection light advances in a P
101
direction, on the other hand, in a condition where the micromirror
105
is inclined with respect to the incident light P
100
, the reflection light advances in a P
102
direction. In the case of the micromirror supported with two hands (
FIGS. 4A
,
4
B, and
5
) as the same manner, under a condition where the micromirror
108
is inclined in one direction with respect to the incident light Ploo, the reflection light advances in a P
103
direction, on the other hand, under a condition where the micromirror
108
is inclined in the other direction, the reflection light advances in a P
104
direction.
However, response speed of the above-mentioned switching is a few micro-seconds in many cases, which is not enough to achieve fast switching. In the optical switching element employing the micromirror, an angle capable of deflecting light (angle difference between two of the reflection light is twice as large as a mechanical mirror angle of deviation). However, in the case where the optical switching element is used for the display, for obtaining high contrast, angle differences between the two reflection light P
103
and P
104
must be wider, thereby the response speed becomes slower.
In the optical switching element employing diffraction grating (FIGS.
6
A and
6
B), as disclosed in Translated National publication of Patent Application No. Hei 10-510374, with electrostatic attraction caused by potential difference between a movable mirror
109
a
and a lower electrode
110
a,
a ribbon-like movable mirror having a light reflection face moves in a quarter wavelength of the incident light P
100
. This produces an optical path difference in a half wavelength between a ribbon-like static mirror
109
b
and the movable mirror
109
a,
thereby generating diffraction light, and then the reflection light is switched between a zero diffraction light P
105
direction and a linear diffraction light P
106
direction. At this moment, with the reason that the optical path difference is controlled within a half wavelength, intensity of the linear diffraction light P
106
can be controlled. In the optical switching element employing diffraction grating, only the extremely lightweight ribbon-like mirror is moved in a small distance, which can perform switching of the light, therefore, its response is fast. For this reason, the optical switching element employing diffraction grating is suitable for the fast switching.
However, for generating light diffraction, at least the two ribbon-like mirrors are necessary, and for enhancing effective use of the light, the four mirrors or more are necessary, specifically, the six ribbon-like mirrors are necessary. For this reason, in the case of using the ribbon-like mirrors arranged in linear, a whole size is difficult to be realized miniaturization. The linear diffraction light is generated with certain angles in two directions symmetrical with respect to the optical axis of the zero diffraction light. Therefore, for using the linear diffraction light, this requires a complicated optical system used for converging the above-mentioned light, advancing in two directions, into single light. Ideally, the reflection face of the static mirror
109
b
and the reflection face of the movable mirror
109
a
must be positioned on the same plane in a condition wh
Hane Kazuhiro
Hara Masaki
Hori Kazuhito
Makino Takuya
Sano Naoki
Barber Therese
Frommer William S.
Frommer & Lawrence & Haug LLP
Kessler Gordon
Kim Robert H.
LandOfFree
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