Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-07-13
2001-12-18
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S631000
Reexamination Certificate
active
06331916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a virtual image optical system suitable for use in view finders of video cameras, head mount displays or the like. In particular, the present invention relates to a virtual image optical system using a reflective spatial light modulator.
2. Description of the Related Art
The spatial light modulator (SLM) is a device which is applied to be supplied with a video signal and to modulate light on every pixel on the basis of image data of the video signal.
The spatial light modulators can be classified into a transmission type which modulates light transmitted by the spatial light modulator and a reflection type which modulates light reflected by the spatial light modulator. The virtual image optical system of the present invention uses the latter reflective spatial light modulator.
The spatial light modulators use liquid crystal, digital micro mirrors, or the like. Especially, spatial light modulators using liquid crystal are referred to as liquid crystal spatial light modulators.
The liquid crystal can be classified to twisted nematic mode type, birefringence mode type, and light dispersion mode type, and light absorption mode type.
As typically used liquid crystal, there are TN liquid crystal using the twisted nematic (TN) operation mode of the twisted nematic mode type, STN liquid crystal using the super twisted nematic (STN) operation mode of the birefringence operation mode type, and FLC liquid crystal using the ferroelectric liquid crystal (FLC) operation mode.
By referring to
FIG. 1
, the structure and operation principle of a reflective spatial light modulator using the TN liquid crystal or the STN liquid crystal will now be described.
A TN or STN liquid crystal reflective spatial light modulator
90
includes a pair of electrode portion, a liquid crystal material
95
inserted between the electrode portion, and a lower reflector
96
.
The upper electrode portion includes a glass substrate
91
A, a transparent electrode
92
A disposed inside (under) the glass substrate
91
A, and an alignment layer
93
A disposed inside (under) the transparent electrode
92
A. The lower electrode portion includes a glass substrate
91
B, a transparent electrode
92
B disposed inside (on) the glass substrate
91
B, and an alignment layer
93
B disposed inside (on) the transparent electrode
92
B.
A polarizer
94
A is disposed outside (on) the glass substrate
91
A of the upper electrode portion. An analyzer
94
B is disposed outside (under) the glass substrate
91
B of the lower electrode portion.
Directions of the polarization of the two polarizers
94
A and
94
B are perpendicular to each other.
Each of the alignment layers
93
A and
93
B has a function of aligning the alignment direction of molecules of the liquid crystal material
95
. The alignment direction of the alignment layer
93
A disposed in the upper electrode portion is parallel to the polarization direction of the polarizer
94
A disposed in the upper electrode section. The alignment direction of the alignment layer
93
B disposed in the lower electrode portion is parallel to the polarization direction of the analyzer
94
B disposed in the lower electrode portion.
In other words, the alignment directions of the two alignment layers
93
A and
93
B are perpendicular to each other.
FIG. 1A
shows a voltage non-application state in which a voltage is not applied to each of the transparent electrodes
92
A and
92
B.
FIG. 1B
shows a voltage application state in which a voltage is applied to each of the transparent electrodes
92
A and
92
B.
In the voltage non-application state of
FIG. 1A
, the alignment of molecules of the liquid crystal material
95
comes in a twisted state. In the voltage application state of
FIG. 1B
, molecules of the liquid crystal material
95
come in a aligned state in the vertical direction.
In the case of TN liquid crystal, the twist angle of molecules in the voltage non-application state is 90 degrees.
In the voltage non-application state of
FIG. 1A
, polarized light
97
A fed from the upper polarizer
94
A is rotated in direction of the polarization by passing through the liquid crystal material
95
.
Therefore, this polarized light
97
B is passed through the lower polarizer
94
B and arrives at the reflector
96
.
In the same way, polarized light
97
C reflected by the reflector
96
is rotated in direction of the polarization by passing through the liquid crystal material
95
, and the polarized light
97
C is passed through the upper polarizer
94
A.
In other words, the polarized light
97
C returns to the same path as the incident light.
In the voltage application state of
FIG. 1B
, the polarized light
97
A fed from the upper polarizer
94
A is not rotated in direction of the polarization by passing through the liquid crystal material
95
.
Therefore, this polarized light cannot be passed through the lower polarizer
94
B, and does not arrive at the reflector
96
.
In other words, reflected light for the incident light is not obtained.
By referring to
FIGS. 2A
to
2
C, the structure and operation principle of a reflective spatial light modulator using FLC will now be described.
An FLC reflective spatial light modulator
100
includes a pair of electrode portions, and a liquid crystal material
105
inserted between the electrode portions.
The upper electrode portion includes a glass substrate
101
A, a transparent electrode
102
A disposed inside (under) the glass substrate
101
A, and an alignment layer
103
A disposed inside (under) the transparent electrode
102
A. The lower electrode portion includes a silicon substrate
101
B, an aluminum electrode
102
B disposed inside (on) the silicon substrate
101
B, and an alignment layer
103
B disposed inside (on) the aluminum electrode
102
B.
The aluminum electrode
102
B functions as a reflective layer as well.
A polarizer
104
is disposed outside (on) the glass substrate
101
A of the upper electrode portion.
FIG. 2A
shows a first voltage direction state in which a voltage in a first direction is applied to each of the transparent electrode
102
A and the aluminum electrode
102
B.
FIG. 2B
shows a second voltage direction state in which a voltage in a second direction is applied to each of the transparent electrode
102
A and the aluminum electrode
102
B.
As shown in
FIG. 2C
, the liquid crystal material
105
does not exhibit a birefringence effect to the incident polarized light in the first voltage direction state, but the liquid crystal material
105
exhibits a birefringence effect to the incident polarized light in the second voltage direction state.
In the first voltage direction state of
FIG. 2A
, the liquid crystal material
105
does not exhibit a birefringence effect, and consequently the polarized light
107
A fed from the polarizer
104
is passed through the liquid crystal material
105
and arrives at the aluminum electrode (reflective layer)
102
B without changing the state of polarization.
The polarized light
107
B reflected by the aluminum electrode (reflective layer)
102
B is passed though the liquid crystal material
105
again and arrives at the polarizer
104
without changing the state of polarization.
In other words, the light having the same polarization state as that of the incident light returns to the polarizer
104
.
As a result, exit light is obtained from the polarizer
104
.
On the other hand, in the second voltage direction state of
FIG. 2B
, the polarized light
107
A fed from the polarizer
104
is subjected to a birefringence effect when it is passed through the liquid crystal material
105
, and consequently linearly polarized light is changed to circularly polarized light.
The circularly polarized light is reflected by the aluminum electrode (reflective layer)
102
B and thus the rotation direction of the circularly polarized light
107
B becomes reverse.
The circularly polarized light
107
B with reverse rotation direction is subjected to a birefringence effect when it is passed through the liquid cr
Frommer William S.
Frommer & Lawrence & Haug LLP
Mack Ricky
Sony Corporation
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