JPH06313810A - Polarizing-converting-combining element - Google Patents

Abstract

PURPOSE:To provide a polarizing-converting-combining element dissolving problems on image multiplication and phase difference. CONSTITUTION:A polarized light converting-combining element is provided with a polarizing-separating, element 1 for separating incident light into two linear polarized light mutually orthogonal in the polarized direction, at least a pair of reflecting faces for changing the optical path of the linear polarized light, and a prism cubic pair 7 formed by holding a TN-type liquid crystal thin layer 4 for changing the polarized direction of the linear polarized light, between prisms 5, 6. The optical path length of the respective polarized light 8s, 8p, separated by the polarizing-separating element 1, until reaching the interface of the TB-type liquid crystal thin layer 4 through the prisms 5, 6 after being reflected by the reflecting faces 2a, 3a is set in such a way as to be the same. The refractive indexes of the respective prisms 5, 6 and TN-type liquid crystal thin layer 4 are set in such a way that one polarized light 8s incoming from one interface of the TN-type liquid crystal thin layer 4 is transmitted through the TN-type liquid crystal thin layer 4 and that the other polarized light 8p incoming from the other interface is totally reflected by this interface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization conversion / synthesis element that can be used in an image display device using a liquid crystal panel.

[0002]

2. Description of the Related Art In a projection type image display device using a liquid crystal panel, linearly polarized light is applied to the liquid crystal panel, spatial phase modulation of the polarized light is performed by the liquid crystal panel, and then projected on a screen to display an enlarged image. it's shown. Here, since the light emitted from the light source for projection is generally unpolarized light, it is necessary to polarize the unpolarized light into linearly polarized light by an optical element and then irradiate the liquid crystal panel.

Conventionally, as an optical element for polarizing such unpolarized light into linearly polarized light, by absorbing linearly polarized light vibrating in a specific direction, linearly polarized light vibrating in a direction orthogonal thereto is obtained. So-called polarizers are known. However, since such a polarizer removes unnecessary linearly polarized light, the amount of light reaching the screen is halved, which is disadvantageous for obtaining a bright image.

Therefore, the incident unpolarized light is orthogonalized to 2
After splitting into one linearly polarized light, the polarization direction of one linearly polarized light is rotated by 90 ° to match the polarization direction of the other linearly polarized light, and these two linearly polarized lights are combined to obtain the output light. Various polarization conversion synthesizing elements with improved strength have been developed. For example, in Japanese Unexamined Patent Publication No. 4-156420, as shown in FIG. 5, unpolarized incident light 90 emitted from a light source 81 and composed of an S-polarized component 90s and a P-polarized component 90p has their polarization directions orthogonal to each other. A polarization splitting element 82 for splitting the two linearly polarized light, that is, an S polarized light 91s and a P polarized light 92p, a polarization conversion element 83 for changing the polarization direction of the linearly polarized light, and an optical path changing element 84 for changing the optical path of the linearly polarized light. There is disclosed a polarization conversion / combining element including and. In this polarization conversion / combination element, the polarization separation element 8
2, a polarization beam splitter is used, a reflection mirror is used as the optical path changing element 84, and an optical rotation film, that is, a TN type liquid crystal film is used as the polarization conversion element 83.

The two linearly polarized lights separated by the polarization separating element 82 (S-polarized light 91s and P-polarized light 92)
In p), the traveling direction of one linearly polarized light (S-polarized light 91s) is changed by the optical path changing element 84 so as to coincide with the traveling direction of the other linearly polarized light (P-polarized light 92p), and this optical path is changed. The polarization direction of one linearly polarized light (S-polarized light 91s) is changed by the polarization conversion element 83 to the other linearly polarized light (P
It is converted so as to match the polarization direction of the polarized light 92p) and P
The polarized light is 91p. As a result, two linearly polarized light (P-polarized light 9
The 1p, P-polarized light 92p) is emitted from the respective emission end faces 80a, 80b in the same plane of the polarization conversion / combination element adjacent to each other.

As another polarization converting / combining element, Japanese Patent Laid-Open No. 3-10219 discloses a non-polarized incident light which is emitted from a light source 81 and is composed of an S-polarized component and a P-polarized component, as shown in FIG. A polarization separation element 82 for separating 90 into two linearly polarized lights whose polarization directions are orthogonal to each other, that is, an S-polarized light 91s and a P-polarized light 92p, and a P-polarized light 91p by changing the polarization direction of one S-polarized light 91s. Polarization conversion element 8
3, one of the P-polarized light 91p and the other P-polarized light 92
Optical path changing elements 84a and 84b for changing the optical path of p to make the traveling directions the same and to guide the polarized lights 91p and 92p to the luminous flux synthesizing body 85 described later while providing a predetermined space therebetween in a direction perpendicular to the traveling direction. , 84c and a light flux synthesizing body 85 that synthesizes the light fluxes of the two linearly polarized lights (91p, 92p). The light flux synthesizing body 85 is perpendicular to the incident surface 85a that is substantially perpendicular to the incident direction of the light flux, and is orthogonal to the arranging direction of the two light fluxes, and at an angle of approximately 45 ° with respect to the incident directions. First and second stepped surfaces 85b, 85 having a plurality of inclined reflecting surfaces and rising surfaces that are substantially parallel to the incident direction.
and a transparent body having a high transmittance having c.

Then, only one light beam (91p) of the two light beams is incident on the incident surface 85a, and the light beam (91p) incident on the incident surface 85a is in the light beam synthesizing body 85 in the incident direction. It passes through and is reflected by each reflecting surface of the second step-shaped surface 85c to become a large number of divided light beams, further passes through the light flux combining body 85 in the emission direction, and is emitted from the first step-shaped surface 85b as an emission surface. . The other light beam (92p) of the two light beams directly enters the first step-shaped surface 85b without passing through the incident surface 85a, is reflected by each reflection surface of the first step-shaped surface 85b, and is reflected in a large number. It is emitted as a divided light beam. Thus, the above two light fluxes (91p, 92p) are
The luminous flux combiner 85 illuminates the liquid crystal display panel 86 as a combined luminous flux in which the divided luminous fluxes of the respective luminous fluxes are alternately arranged, that is, a combined luminous flux having a uniform luminance distribution.

[0008]

However, in the conventional polarization conversion / combination element disclosed in Japanese Patent Laid-Open No. 4-156240, two linearly polarized light beams are separated and emitted from the emission end face. As described above, when the incident light to which the information is input is used, there is a disadvantage that two images appear.

Further, in the conventional polarization conversion / combining element disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-10219, the light beam combining member 8 is used.
Since two light fluxes are combined by 5, there is no problem that two images as described above appear. However, one of the two light fluxes (91p) has passed through the light flux synthesis body 85, and the other light flux (92p) has not passed through the light flux synthesis body 85. For this reason, the optical path lengths of the two light fluxes (the product of the length l of the streak in which light travels and the refractive index n in the medium having the refractive index n) are different. When the optical path length of each light flux is different in this way, the difference in perspective occurs due to the phase difference,
Especially, a problem occurs in the case of motion images.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polarization conversion / synthesis element which can be polarized without causing a decrease in light quantity and which solves the problems of multi-image and phase difference. To do.

[0011]

A polarization conversion / combining element of the present invention which solves the above-mentioned problems, and a polarization separating element for separating incident light into two linearly polarized light whose polarization directions are orthogonal to each other, and the linearly polarized light. At least a pair of reflecting surfaces that change the optical path of the linearly polarized light, and a prism cubic pair formed by sandwiching a TN type liquid crystal thin layer that changes the polarization direction of the linearly polarized light between a pair of prisms. An optical path from the polarization separation element until one of the linearly polarized lights changes its optical path by reflection on one of the reflecting surfaces and reaches one interface of the TN type liquid crystal thin layer through the one prism. And the other linearly polarized light separated by the polarization separation element changes its optical path by being reflected by the other reflecting surface and passes through the other prism to the other interface of the TN type liquid crystal thin layer. As the optical path length from the polarizing beam splitter to reach are the same, the polarization separating element,
Each reflecting surface and the prism cubic pair are set,
One of the linearly polarized light, which is arranged and is incident from one interface of the TN type liquid crystal thin layer, is transmitted through the TN type liquid crystal thin layer and is incident from the other interface of the TN type liquid crystal thin layer. Of the TN liquid crystal thin layer, and the refractive index of each prism is set so that the linearly polarized light is totally reflected at the other interface of the TN liquid crystal thin layer. is there.

[0012]

In the polarization converting / combining element of the present invention, the unpolarized light incident on the polarization separating element is separated into two linearly polarized lights whose polarization directions are orthogonal to each other. One linearly polarized light is reflected by one reflecting surface, changes its optical path, and enters from one prism of the prism cubic pair to one interface of the TN type liquid crystal thin layer. The other linearly polarized light is reflected by the other reflecting surface, changes its optical path, and enters the other interface of the TN type liquid crystal thin layer from the other prism of the prism cubic pair.

In the polarization conversion / combining element of the present invention,
By adjusting the refractive index of the TN type liquid crystal thin layer of the prism cubic pair and each prism, one linearly polarized light incident on one interface passes through the TN type liquid crystal thin layer and the other incident on the other interface. The linearly polarized light is totally reflected at the other interface of the TN type liquid crystal thin layer. This can be performed by adjusting the refractive index of the TN type liquid crystal thin layer and each prism so that total reflection does not occur at the one interface and total reflection occurs at the other interface. That is, at the one interface, when the refractive index of one prism is n _P1 and the apparent refractive index of the liquid crystal on the one interface side is n _L1 , the incident angle is 45 degrees, so n _P1 sin45 ° ≦ It may be set so as to satisfy n _L1 sin 90 ° (a). On the other interface, when the refractive index of the other prism is n _P2 and the apparent refractive index of the liquid crystal on the one interface side is n _L2 , the incident angle is 4
Since it is 5 degrees, it may be set so as to satisfy n _P2 sin45 ° ≧ n _L2 sin90 ° (b). In this way, by adjusting the refractive index of the TN type liquid crystal thin layer and each prism,
One linearly polarized light incident from one interface passes through the TN type liquid crystal thin layer, and the other linearly polarized light incident from the other interface is totally reflected by the other interface. At this time, when the one linearly polarized light passes through the TN type liquid crystal thin layer, the polarization direction thereof is changed by 90 ° and totally reflected at the other interface of the TN type liquid crystal thin layer. The same direction as the direction. The linearly polarized lights whose polarization directions are the same as each other pass through the other prism and are emitted as one beam.

Here, in the polarization conversion / combining element of the present invention,
The polarization splitting element, each reflecting surface, and the prism cubic pair are arranged so that the linearly polarized lights separated by the polarization splitting element have the same optical path length from the polarization splitting element until reaching the interface of the TN type liquid crystal thin layer. Are set and arranged. For this reason, the linearly polarized light emitted from the prism cubic pair has a longer optical path length by the amount of one linearly polarized light passing through the TN type liquid crystal thin layer. For example, the optical path lengths through which the linearly polarized light passes through the polarization conversion / synthesis element of the present invention can be made substantially the same. Therefore, the polarization conversion / combination element of the present invention can eliminate the deviation of the phase difference due to the difference in the optical path length of each linearly polarized light, and can emit the light with the original phase difference.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. The polarization conversion / combination element of this embodiment includes a polarization molecular element 1, a pair of right-angled prisms 2 and 3 having reflective films 2a and 3a formed on the surface corresponding to the hypotenuse of the cross-sectional shape, and a TN type liquid crystal thin layer 4. The prism cubic pair 7 is composed of a pair of right-angled prisms 5 and 6 sandwiched therebetween. The reflection films 2a and 3a of the right-angle prisms 2 and 3 correspond to the reflection surfaces of the present invention.

The polarization splitting element 1 is a mirror that attaches two right-angle prisms having the same shape and the same material, and transmits the P-polarized light 8p and reflects the S-polarized light 8s on the attachment surface (mirror processing surface 1a). It is a polarized beam splitter that has been processed. The S-polarized light 8s reflected by the mirror processing surface 1a is emitted from the emission end face 11, the P-polarized light 8p passing through the polarization separation element 1 is emitted from the emission end face 12, and both linearly polarized lights are orthogonal to each other. Emit in the direction.

On the other hand, the right-angled prism 2 has a reflection film 2a.
Is attached to the emission end face 11 of the polarization separation element 1 so that the light is parallel to the mirror processing surface 1 a of the polarization separation element 1. The other right-angled prism 3 also has its reflection film 3a parallel to the mirror processing surface 1a of the polarization separation element 1.
It is attached to the emission end face 12 of the polarization separation element 1.
Each of the reflection films 2a and 3a is formed by performing aluminum vacuum deposition processing. The right angle prisms 2 and 3 are
The same shape and the same material are used, and the exit end face 21 of one right-angle prism 2 and the exit end face 31 of the other right-angle prism 3 are orthogonal to each other.

In the prism cubic pair 7, the TN type liquid crystal thin layer 4 is parallel to the reflection films 2a and 3a of the right angle prisms 2 and 3 and is flush with the mirror processing surface 1a of the polarization separation element 1. As described above, one right-angle prism 5 is attached to the emission end face 21 of the right-angle prism 2, and the other right-angle prism 6 is attached to the emission end face 31 of the right-angle prism 3. Then, a horizontal alignment treatment film (not shown) in the direction perpendicular to the paper surface of FIG. 1 is formed on the bonding surface of one of the right-angle prisms 5, and the bonding surface of the other right-angle prism 6 of FIG. A horizontal alignment treatment film (not shown) parallel to the paper surface is formed. Further, the TN type liquid crystal thin layer 4 is formed by enclosing nematic liquid crystal in a hermetically sealed space having a thickness of about 10 μm formed by sealing the peripheral portion thereof with an epoxy adhesive. The rectangular prisms 5 and 6 have the same shape and the same material.

Here, the refractive index of one of the rectangular prisms 5 is n _p1, and the refractive index of the other rectangular prism 6 is n _p2 .
Let n _L1 be the apparent refractive index of the liquid crystal at the interface of the TN type liquid crystal thin layer 4 on one side of the right-angle prism 5, and let the apparent refraction of the liquid crystal at the interface of the other side of the TN type liquid crystal thin layer 4 on the right-angle prism 6 be. Let the rate be n _L2 . At this time, in the polarization conversion / combining element of the present example, n _P1 sin 45 ° ≦ n _L1 sin 90 ° (a) is set so that incident light is not totally reflected at the one interface. Further, in order to totally reflect the incident light on the other interface, n _P2 sin45 ° ≧ n _L2 sin90 ° (b) is set.

Specifically, the apparent refractive index n _L1 of the liquid crystal at the one interface is that the incident light incident on the one interface is the S-polarized light 8 s, as will be described later, and the apparent refractive index n _L1 at the one interface is Since the alignment direction of the liquid crystal molecules is the same as the vibration direction of the S-polarized light 8s, the refractive index n of the liquid crystal with respect to extraordinary light is n.
It becomes _e . Further, the apparent refractive index n _L2 of the liquid crystal at the other interface is that the incident light incident on the other interface is P-polarized light 8p, and the alignment direction of the liquid crystal molecules at the other interface is as described later. 4 in the same direction as the vibration direction of this S-polarized light 8s
Since an angle of 5 ° is formed, assuming that the refractive index of the liquid crystal with respect to ordinary light is n _o , it becomes (n _e + n _o ) / 2. Here, when n _e = 1.60 and n _o = 1.40, n _L1 = n _e = 1.60, n _L2 = (n _e + n _o ) /2=1.50 Further, the above formula (a ), N _P1 sin 45 ° ≦ 1.60 sin 90 ° ∴n _P1 ≦ 2.26 Further, from the above formula (b), n _P2 sin 45 ° ≧ 1.50 sin 90 ° ∴2.12 ≦ n _P2 , and n _p1 = n _{Since it is p2} , it is set to satisfy 2.12 ≦ n _P1 = n _P2 ≦ 2.26.

The operation of the polarization conversion / combining element of this embodiment having the above-mentioned structure will be described below. First, when the unpolarized light 8 enters the polarization separation element 1, it is separated into S-polarized light 8s and P-polarized light 8p. That is, one S-polarized light 8s
Is reflected by the mirror processing surface and emitted from the emission end face 11,
The other P-polarized light 8p passes through the mirror processing surface and is emitted from the emission end surface 12.

One S-polarized light 8s enters one rectangular prism 2, is reflected by the reflection film 2a while maintaining S-polarized light, and is emitted from the emission end face 21. Then, the light enters the right-angled prism 5 of the prism cubic pair 7 and enters the one interface with the TN liquid crystal thin layer 4 at an incident angle of 45 °. At this time, since the incident light is set not to be totally reflected on this one interface as described above, the S-polarized light 8s passes through the TN type liquid crystal thin layer 4 while converting the polarization direction by 90 °. Then, it is converted into P-polarized light 8 p ′, passes through the other right-angle prism 6, and is emitted from the prism cubic pair 7.

On the other hand, the other P-polarized light 8p enters the other right-angle prism 3, is reflected by the reflection film 3a while maintaining the P-polarized light, and is emitted from the emission end face 31. Then, it is incident on the other right-angled prism 6 of the prism cubic pair 7, and TN
The light is incident on the other interface with the type liquid crystal thin layer 4 at an incident angle of 45 °. At this time, since the incident light is totally reflected on the other interface as described above, the P-polarized light 8p becomes P
Reflects while maintaining polarization. Then, the P-polarized light 8p passes through the other right-angle prism 6 and is emitted from the prism cubic pair 7.

As described above, in the polarization conversion / combining element of this embodiment, the P-polarized light can be emitted as one beam, and even when the information-inputted light such as an image is used as the incident light, The inconvenience that two images appear does not occur. Here, in the polarization conversion / combining element of the present embodiment, the right-angle prisms forming the polarization separating element 1 are formed of the same shape and the same material, and the right-angle prisms 2, 3 are formed.
Also, 5 and 6 are formed of the same shape and the same material, respectively, and one of the S-polarized light 8 separated by the polarization separation element 1
The optical path lengths from the polarization separation element until s and the other P-polarized light 8p reach the respective interfaces of the TN type liquid crystal thin layer 4 are set to be the same. Therefore, the polarized lights 8p and 8p ′ (8
In s), the optical path length becomes longer as much as one polarized light 8p ′ (8s) passes through the TN type liquid crystal thin layer 4, but since this TN type liquid crystal thin layer 4 is an extremely thin layer of about 10 μm. ,
The polarization conversion / combination element of this embodiment is used for each polarized light 8s (8
The optical path lengths through which p ′) and 8p pass can be made substantially the same. Therefore, the polarization conversion / combining element of this embodiment is
The deviation of the phase difference due to the difference in the optical path length of each linearly polarized light can be eliminated, and the light can be emitted with the original phase difference. As a result, the polarization conversion / combining element of the present embodiment does not cause a perspective shift due to the phase difference even in the case of incident light to which the information of the operation image is input.

In the above embodiment, each prism 2, 3
Although the example of forming the other side of the present invention by the reflection films 2a and 3a has been described above, the reflection films 2a and 3a can be formed by adjusting the refractive indexes of the prisms 2 and 3 so as to satisfy the condition of total reflection. Instead, it can be used as the reflecting surface of the present invention.
In addition, one polarized light 8p ′ (8s) and the other polarized light 8p
In order to completely eliminate the deviation of the optical axis and the deviation of the optical path length between and, the following design method can be used.

Since one polarized light 8s passes through the liquid crystal layer 4, it is refracted as shown in FIG. The other polarized light 8p is
It is reflected at the interface between the prism 6 and the liquid crystal layer 4. The refractive indices n _p1 and n _p2 of the prisms 5 and 6 are 2.12 ≦ n _p1 and n _p2 ≦
Since it is 2.26 and the refractive index n _e = 1.6 of the liquid crystal layer 4, one polarized light 8 s is shifted upward by ΔL when passing through the liquid crystal layer 4. On the other hand, the other polarized light 8p should be reflected at the point 0 (center of the liquid crystal layer 4) in FIG. 3 without the liquid crystal layer 4, but is actually reflected at the point 0 '(interface of the liquid crystal layer 4). It deviates from the original optical axis by ΔL '. Therefore, as it is, one polarized light 8s (8
Between p ′) and the other polarized light 8p, the optical axis is deviated by ΔL ′ + ΔL.

To prevent this point, the reflecting surface of the prism 2 may be displaced by (ΔL '+ ΔL) as shown in FIG. As a result, one polarized light 8p ′ and the other polarized light 8p
The optical axis with p coincides perfectly. Further, in this case, regarding the optical path length, if one polarized light 8p ′ (8s) has a relative axis with the other polarized light 8p, assuming that the refractive index of the prism 2 is n _p , {(ΔL + ΔL ′) · n _p } is short, and the prism cubic pair 7 has { _ne · l−n _p1 (ΔL + Δ
L ')} Long. That one polarizing beam 8p '(8s) {than the other polarized light 8p is _{n e · l- (ΔL + ΔL} ') (n p1
+ N _p )} is long.

Therefore, in order to make the optical path lengths of the polarized light 8p '(8s) on one side and the polarized light 8p on the other side completely coincide with each other, the polarization separating element 1 and the rectangular prism 3 or the rectangular prism 3 are required. Between Prism Cubic vs. 7
It is conceivable to form a transparent film having a predetermined refractive index in order to completely adjust the optical path difference. Alternatively, the refractive index of the prism 2 or 3 may be changed to a predetermined value for adjustment.

[0029]

As described in detail above, the polarization conversion / combination element of the present invention uses the TN type liquid crystal thin layer as an optical path conversion element and a polarization conversion element, whereby each linearly polarized light separated by the polarization separation element is used. It is possible to emit these linearly polarized lights as one beam while making the optical path lengths of the lights equal.
Therefore, there is no inconvenience that two images appear when the information-input light such as an image is used as the incident light. Further, since each linearly polarized light can be emitted with the original phase difference as it is, even in the case of the incident light to which the information of the operation image is input, the perspective shift due to the phase difference does not occur.

[Brief description of drawings]

FIG. 1 is a plan view showing a polarization conversion / combination element of this embodiment.

FIG. 2 is a perspective view showing a polarization conversion / combination element of this embodiment.

FIG. 3 is an explanatory diagram showing a shift of an optical axis in the polarization conversion / combination element of the present embodiment.

FIG. 4 is an explanatory diagram showing that the polarization conversion / combining element of this embodiment completely eliminates the deviation of the optical axis.

FIG. 5 is a plan view showing a conventional polarization and polarization combining element.

FIG. 6 is a plan view showing another conventional polarization and polarization combining element.

[Explanation of symbols]

Reference numeral 1 is a polarization separation element, 2a and 3a are reflection films as reflection surfaces, 4 is a TN type liquid crystal thin layer, 5 and 6 are right angle prisms, and 7 is a prism cubic pair.

Claims (1)

[Claims] 1. A polarization separation element for separating incident light into two linearly polarized lights whose polarization directions are orthogonal to each other, at least a pair of reflecting surfaces for changing an optical path of the linearly polarized light, and a polarization direction of the linearly polarized light. And a prism cubic pair formed by sandwiching a TN type liquid crystal thin layer between a pair of prisms, wherein one of the linearly polarized light beams separated by the polarization beam splitting element is reflected by one of the reflecting surfaces and its optical path is changed. And the optical path length from the polarization separation element until reaching one interface of the TN type liquid crystal thin layer through one of the prisms,
Until the other linearly polarized light separated by the polarization separating element changes its optical path by reflection on the other reflecting surface and reaches the other interface of the TN type liquid crystal thin layer via the other prism. The polarization splitting element, each of the reflecting surfaces and the prism cubic pair are set and arranged so that the optical path length from the polarization splitting element is the same, and from one interface of the TN type liquid crystal thin layer. One of the incident linearly polarized lights passes through the TN type liquid crystal thin layer, and
Refraction of the TN type liquid crystal thin layer of the prism cubic pair and each prism so that the other linearly polarized light incident from the other interface of the N type liquid crystal thin layer is totally reflected at the other interface of the TN type liquid crystal thin layer. A polarization conversion / synthesis element characterized in that the ratio is set.