JP2009229729A - Polarization element and projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization element which successfully maintains polarization separation characteristics. <P>SOLUTION: The polarization element 5 includes a first prism 51 having an emission side inclined surface 512 inclined to a luminous flux incident side end surface 511, a second prism 52 having a luminous flux emission side end surface 521 parallel to the luminous flux incident side end surface and an incident side inclined surface 522 inclined to the luminous flux emission side end surface and parallel to the emission side inclined surface and a polarization element body 53 provided on the emission side inclined surface. Each prism is disposed in a state where the emission side inclined surface and the polarization element body are separated at a prescribed interval. The first prism satisfies a relation of a formula α≤sin<SP>-1</SP>(1/n<SB>d</SB>)-β when an inclined angle formed by the luminous flux incident side end surface and the emission side inclined surface, a refractive angle formed by refracting an incident luminous flux by the first prism and a refractive index of the first prism are denoted as α, β and n<SB>d</SB>, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing element and a projector.

Conventionally, there has been known a projector including a light source device, a light modulation element that modulates a light beam emitted from the light source device according to image information to form image light, and a projection optical device that enlarges and projects the image light. Yes.
In such projectors, polarizing elements that transmit predetermined linearly polarized light and remove other light beams from the incident light beam are usually arranged on the light beam incident side and light beam emission side of the light modulation element (liquid crystal panel). (For example, see Patent Document 1).
In the projector described in Patent Document 1, a reflection-type polarizing element is used as the exit-side polarizing element disposed on the light beam exit side of the liquid crystal panel, improving the light resistance and heat resistance of the exit-side polarizing element, and An unnecessary light flux reflected by the side polarizing element is not incident on the liquid crystal panel.
Specifically, the exit side polarization element includes a first prism having a triangular cross section having a light beam incident side end surface orthogonal to the optical axis of the incident light beam, and an exit side inclined surface inclined with respect to the light beam incident side end surface; A second prism having a triangular cross section having a light beam exit side end surface parallel to the side end surface and an incident side inclined surface that is inclined with respect to the light beam exit side end surface and faces the exit side inclined surface, and is interposed between the inclined surfaces. A reflective polarizing plate. Then, the unnecessary light beam reflected by the reflective polarizing plate is totally reflected at the light beam incident side end surface of the first prism and proceeds in a direction avoiding the liquid crystal panel.

International Publication WO01 / 055778

By the way, for example, when the first prism, the reflective polarizing plate, and the second prism are arranged in close contact with each other, there are the following problems.
That is, the reflection-type polarizing plate generally splits into two linearly polarized light beams whose polarization directions are orthogonal to each other, transmits one linearly polarized light, and reflects some of the linearly polarized light. Absorbs heat and generates heat.
Then, when the heat of the reflective polarizing plate is transmitted to the first prism and thermal distortion occurs in the first prism, it proceeds in the first prism due to the influence of the phase difference generated by the internal stress due to the thermal distortion. The polarization direction of the light beam is disturbed.
That is, the polarization direction of the light beam to be transmitted through the reflective polarizing plate is disturbed in the first prism, so that a part of the light beam is reflected by the reflective polarizing plate or the light beam to be reflected by the reflective polarizing plate. When the direction is disturbed in the first prism, there is a problem that a part of the light beam is transmitted through the reflective polarizing plate, and the polarization separation characteristic of the exit side polarization element is deteriorated.

  An object of the present invention is to provide a polarizing element and a projector that can maintain good polarization separation characteristics.

The polarizing element of the present invention is a polarizing element that transmits predetermined linearly polarized light out of an incident light beam, and includes a light beam incident side end surface on which a light beam is incident and an exit side inclined surface that is inclined with respect to the light beam incident side end surface. A first prism having a light beam emission side end surface parallel to the light beam incident side end surface, a second prism having an incident side inclined surface inclined with respect to the light beam emission side end surface and parallel to the emission side inclined surface, The first linearly polarized light that is provided on the incident-side inclined surface and transmits the first linearly polarized light out of the light flux that has passed through the first prism and whose polarization direction is orthogonal to the first linearly polarized light is the first. A polarizing element body that reflects toward the prism, wherein each of the prisms is disposed with the exit-side inclined surface and the polarizing element body spaced apart from each other by a predetermined distance, and the first prism is configured to receive the light flux Side end face and the injection side The inclination angle between the slope alpha, the angle of refraction the incident light beam is refracted by the first prism beta, the refractive index of the first prism when a n _d, the following relationship of equation (1) It is formed so that it may satisfy | fill.

In the present invention, the polarizing element includes a first prism, a second prism, and a polarizing element body. The polarizing element body is provided on the incident-side inclined surface of the second prism, and each prism is disposed in a state in which the exit-side inclined surface and the polarizing element body are separated by a predetermined distance. As a result, an air layer having a high heat insulating effect is interposed between the polarizing element body and the first prism. For this reason, heat conduction from the polarizing element body to the first prism can be effectively suppressed.
Therefore, the thermal distortion of the first prism due to the influence of heat generation of the polarizing element body can be suppressed, and the polarization separation characteristics of the polarizing element can be maintained well.

By the way, since an air layer is interposed between the first prism and the polarizing element main body, it is introduced into the first prism as compared with the configuration in which the first prism and the polarizing element main body are in close contact with each other. Light flux (hereinafter referred to as transmitted light) to be transmitted to the polarizing element body via the boundary surface between the inclined surface and the air layer (hereinafter referred to as the first boundary surface) is likely to be reflected at the first boundary surface, and the light utilization efficiency Will be reduced. In particular, when the inclination angle α is increased more than necessary, the incident angle to the first boundary surface is also increased, so that transmitted light is easily reflected on the first boundary surface.
In the present invention, since the first prism is formed so as to satisfy the relationship of Expression (1) (hereinafter referred to as transmission conditions), the incident angle to the first boundary surface is reduced, and the transmitted light is transmitted to the first boundary surface. The light can be transmitted without being reflected, and the light utilization efficiency can be improved.

  In the polarizing element of the present invention, it is preferable that the first prism is formed so as to satisfy the relationship of the following formula (2).

By the way, the incident angle at which the second linearly polarized light is introduced into the first prism and is incident on the boundary surface between the light incident side end surface and the air layer (hereinafter referred to as the second boundary surface) and the inclination angle α have a correlation. There is something. Specifically, as the inclination angle α is decreased, the incident angle at which the second linearly polarized light is incident on the second boundary surface is decreased. When the first prism is formed so as to satisfy the transmission condition, if the inclination angle α is reduced more than necessary, the incident angle of the second linearly polarized light on the second boundary surface is also reduced. The second linearly polarized light is easily transmitted without being totally reflected at the second boundary surface, and is incident on an optical element such as a liquid crystal panel disposed on the upstream side of the optical path of the polarizing element.
In the present invention, since the first prism is formed so as to satisfy the relationship of the formula (2) (hereinafter, total reflection condition), the incident angle to the second boundary surface is increased, and the second linearly polarized light is Can be totally reflected at the second boundary surface, and it is possible to prevent the second linearly polarized light from entering the optical element disposed on the upstream side of the optical path.

In the polarizing element of the present invention, it is preferable that an antireflection film corresponding to the tilt angle is formed on the exit side inclined surface.
In the present invention, an antireflection film corresponding to an inclination angle, that is, an incident angle at which transmitted light enters the first boundary surface is formed on the exit side inclined surface. Thus, in addition to forming the first prism so as to satisfy the transmission condition, it is possible to transmit the transmitted light without reflecting it at the first boundary surface by forming the antireflection film. The effect can be suitably achieved.

A projector according to the present invention includes a light source device, a light modulation element that modulates a light beam emitted from the light source device according to image information to form image light, and a projection optical device that enlarges and projects the image light. The projector includes the polarizing element described above.
In the present invention, since the projector includes the polarizing element described above, the projector can enjoy the same operations and effects as the polarizing element described above.
In addition, since the projector includes a polarizing element that can maintain the polarization separation characteristic satisfactorily, the image quality of the projected image can be maintained satisfactorily.

The projector of the present invention includes a light guide optical system that guides the light beam emitted from the light source device to the polarization element, and the light guide optical system has an incident angle of 20 with respect to a light beam incident side end surface of the polarization element. It is preferable that the light beam is incident at a temperature of less than or equal to °.
Incidentally, since the refraction angle β depends on the incident angle θ to the light incident side end face, the tilt angle α defined by the transmission condition and the total reflection condition depends on the incident angle θ. When the first prism is formed so as to satisfy the transmission condition and the total reflection condition, if the incident angle θ exceeds 20 °, the range of the inclination angle α defined by the expressions (1) and (2) is extreme. The first prism becomes difficult to process.
In the present invention, the projector includes a light guide optical system that causes the light beam emitted from the light source device to enter the light beam incident side end surface of the polarizing element with an incident angle θ of 20 ° or less. Accordingly, when forming the first prism so as to satisfy the transmission condition and the total reflection condition, the range of the inclination angle α defined by the expressions (1) and (2) can be set to a manufacturable range. .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[Main components of the projector]
FIG. 1 is a diagram schematically showing a schematic configuration of a projector 1 in the present embodiment.
The projector 1 modulates a light beam emitted from a light source according to image information to form image light, and enlarges and projects the formed image light on a screen (not shown). As shown in FIG. 1, the projector 1 is roughly configured by an optical unit 3, a projection lens 4 as a projection optical device, and an exterior housing 2 that houses the optical unit 3 and the projection lens 4 and constitutes an exterior. ing.
Although not specifically illustrated, each of the projector 1 and the cooling unit provided with a cooling fan or the like for cooling the inside of the projector 1 in a space other than the optical unit 3 and the projection lens 4 in the exterior housing 2. It is assumed that a power supply device that supplies power to the constituent members, a control device that controls operations of the constituent members of the projector 1, and the like are arranged.

The optical unit 3 optically processes the light beam emitted from the light source device 31 under the control of the control device to form image light corresponding to the image information. The optical unit 3 includes a light source device 31, an illumination optical device 32, a color separation optical device 33, a relay optical device 34, an optical device 35, and illumination light in which these optical components 31 to 35 are set inside. And an optical component housing 36 disposed at a predetermined position with respect to the axis Ax.
As illustrated in FIG. 1, the light source device 31 includes a light source lamp 311, a reflector 312, and the like. In the light source device 31, the light beam emitted from the light source lamp 311 is aligned in the emission direction by the reflector 312, and is emitted toward the illumination optical device 32.

  As shown in FIG. 1, the illumination optical device 32 includes a first lens array 321, a second lens array 322, a polarization conversion element 323, and a superimposing lens 324. The light beam emitted from the light source device 31 is divided into a plurality of partial light beams by a plurality of small lenses (not shown) constituting the first lens array 321, and a plurality of small lenses 322 A constituting the second lens array 322. An image is formed in the vicinity of (see FIG. 6). Each partial light beam emitted from each small lens 322 </ b> A of the second lens array 322 is incident so that its central axis (principal ray) is perpendicular to the incident surface of the polarization conversion element 323. It is emitted as one type of linearly polarized light. A plurality of partial light beams emitted from the polarization conversion element 323 as linearly polarized light and passed through the superimposing lens 324 are superimposed on three liquid crystal panels 351 described later of the optical device 35.

As shown in FIG. 1, the color separation optical device 33 includes two dichroic mirrors 331 and 332 and a reflection mirror 333, and the dichroic mirrors 331 and 332 and the reflection mirror 333 emit the light from the illumination optical device 32. It has a function of separating a plurality of partial light beams into three color lights of red, green, and blue.
As shown in FIG. 1, the relay optical device 34 includes an incident side lens 341, a relay lens 343, and reflection mirrors 342 and 344, and color light separated by the color separation optical device 33, for example, red light, is optical device 35. Of the liquid crystal panel 351R on the red light side, which will be described later.

  The optical device 35 modulates an incident light beam according to image information to form image light. As shown in FIG. 1, the optical device 35 includes three field lenses 350, three incident-side polarizing elements 352, and three liquid crystal panels 351 (light on the red light side) as light modulators in order from the optical path front side. A liquid crystal panel 351R, a green light side liquid crystal panel 351G, and a blue light side liquid crystal panel 351B), three emission-side polarizing elements 5, and a cross dichroic prism 354 as a color synthesizing optical device.

The field lens 350 converts each partial light beam emitted from the illumination optical device 32 into a light beam parallel to the central axis (principal ray).
The incident side polarization element 352 transmits only linearly polarized light having a polarization direction substantially the same as the polarization direction aligned by the polarization conversion element 323 out of the light flux that has passed through the field lens 350. The incident-side polarizing element 352 may be composed of an absorptive polarizer that transmits linearly polarized light with a predetermined polarization direction and absorbs linearly polarized light with a polarization direction orthogonal to the predetermined polarization direction. Or you may comprise with a reflection type polarizer similarly to the polarizing element main body 53 mentioned later.

Although not specifically shown, the liquid crystal panel 351 is a transmissive liquid crystal panel, and is enclosed in a plurality of liquid crystal cells (pixels) arranged in a matrix based on a drive signal from the control device. The alignment direction of the liquid crystal molecules is changed to modulate the polarization direction of the linearly polarized light emitted from the incident side polarization element 352.
The exit-side polarizing element 5 transmits only the first linearly polarized light having a polarization direction orthogonal to the transmission axis of the incident-side polarizing element 352 out of the light flux emitted through the liquid crystal panel 351.
The configuration of the exit side polarization element 5 will be described later.

The cross dichroic prism 354 synthesizes the color lights transmitted through the exit-side polarization elements 5 to form image light (color image). The cross dichroic prism 354 has a substantially square shape in plan view in which four right-angle prisms are bonded together, and two dielectric multilayer films are formed on the interface where the right-angle prisms are bonded together. These dielectric multilayer films transmit G-color light emitted from the liquid crystal panel 351G and transmitted through the exit-side polarization element 5, and transmit R and B-color light emitted from the respective liquid crystal panels 351R and 351B and transmitted through the exit-side polarization elements 5. reflect. In this way, the color lights are combined to form a color image.
The projection lens 4 is configured as a combined lens in which a plurality of lenses are combined, and enlarges and projects the image light emitted from the optical device 35 on the screen.

[Configuration of exit-side polarizing element]
FIG. 2 is a diagram schematically showing the configuration of the exit-side polarizing element 5. Specifically, FIG. 2 is a perspective view of the exit-side polarizing element 5 as viewed from above.
As shown in FIG. 2, the exit side polarization element 5 is disposed on the light beam exit side of the first prism 51 and the second prism 52 having the same shape and refractive index as the first prism 51. And a polarizing element body 53.
The first prism 51 is a triangular prism having a right-angled triangular cross section.
The first prism 51 is arranged such that an end surface (light beam incident side end surface) 511 corresponding to one side other than the hypotenuse having a right-angled triangular section is located on the light beam incident side and orthogonal to the illumination optical axis Ax. The That is, the first prism 51 has an end surface (emission side inclined surface) 512 corresponding to the hypotenuse having a right-angled triangular cross section located on the light beam exit side and a plane orthogonal to the illumination optical axis Ax (light beam incident side end surface 511). It will be arranged in an inclined state.

  In the first prism 51, an antireflection film 512 </ b> A is formed on the exit side inclined surface 512. This antireflection film 512A is in accordance with an inclination angle formed by the light beam incident side end face 511 and the emission side inclined surface 512 (inclination angle of the emission side inclined surface 512 with respect to the illumination optical axis Ax), that is, to the emission side polarizing element 5. Are formed in accordance with the incident angle incident on the exit-side inclined surface 512 after traveling through the first prism 51 in a state parallel to the illumination optical axis Ax.

  The polarizing element body 53 is provided on an incident-side inclined surface 522 described later in the second prism 52, transmits the first linearly polarized light, and the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light. It is composed of a reflective polarizer that reflects light. In the present embodiment, the polarizing element main body 53 has a configuration in which a large number of fine linear ribs such as aluminum are formed in parallel on the incident-side inclined surface 522, although the specific illustration is omitted. Then, the polarizing element body 53 transmits linearly polarized light (first linearly polarized light) having a perpendicular polarization direction in the direction in which the linear rib extends, and linearly polarized light (secondly polarized light having a parallel polarization direction). Of linearly polarized light).

  In the second prism 52, an end surface (incident side inclined surface) 522 corresponding to a hypotenuse having a right-angled triangular section is positioned on the light beam incident side, and the polarizing element body 53 is parallel to the outgoing side inclined surface 512 while the polarizing element body 53 is in the outgoing side inclined surface 512. Are spaced apart from each other by a predetermined distance. In other words, the second prism 52 has an end surface (light beam exit side end surface) 521 corresponding to the other side excluding a hypotenuse having a right-angled triangular cross section, located on the light beam exit side, and orthogonal to the illumination optical axis Ax (light beam incident side end surface 511). In parallel).

[The optical path of the light beam emitted from the exit side polarization element]
FIG. 3 is a diagram schematically showing the optical path of the light beam emitted from the exit-side polarizing element 5. Specifically, FIG. 3 is a longitudinal sectional view of the exit-side polarizing element 5.
In FIG. 3, the antireflection film 512A is not shown for convenience of explanation. The same applies to the following figures.
In FIG. 3, for the sake of simplicity, the light beam L <b> 1 through the liquid crystal panel 351 travels in a direction parallel to the illumination optical axis Ax, that is, in a direction orthogonal to the light beam incident side end surface 511. Shall.
The light beam L1 is introduced into the first prism 51 through the air layer, refracted at the boundary surface between the emission-side inclined surface 512 and the air layer (hereinafter referred to as the first boundary surface B1), and directed toward the polarizing element body 53. proceed. The light beam L1 is separated by the polarizing element body 53 into the first linearly polarized light L11 and the second linearly polarized light L12.

The first linearly polarized light L11 passes through the polarization element body 53, is emitted through the second prism 52, and is introduced into the cross dichroic prism 354. At this time, the first linearly polarized light L11 travels in substantially the same direction as the traveling direction of the light beam L1 incident on the light beam incident side end surface 511.
On the other hand, the second linearly polarized light L <b> 12 is reflected by the polarizing element body 53 toward the light beam incident side, refracted at the first boundary surface B <b> 1, and introduced into the first prism 51. The second linearly polarized light L12 is totally reflected at the boundary surface between the light beam incident side end surface 511 and the air layer (hereinafter referred to as the second boundary surface B2), and is emitted from the light beam incident side end surface 511 and the emission of the first prism 51. The light is emitted from an end surface 513 that intersects the side inclined surface 512. That is, the second linearly polarized light L12 is emitted in a direction that avoids the liquid crystal panel 351 (in the present embodiment, upward). Although not specifically shown, an antireflection film for preventing the reflection of the second linearly polarized light L12 is formed on the end surface 513.

  In the present embodiment, the first prism 51 satisfies the transmission condition for transmitting the light beam L1 without reflecting it at the first boundary surface B1, and all the second linearly polarized light L12 is transmitted at the second boundary surface B2. The shape as shown below is set so as to satisfy the total reflection condition to be reflected.

First, the transmission conditions will be described.
FIG. 4 is a diagram for explaining the transmission conditions. Specifically, FIG. 4 is a view of the first prism 51 as viewed from the side.
In addition, as the incident light beam L1 to the first prism 51, an incident angle range is determined by an optical system (light guide optical system 6 described later) disposed on the upstream side of the optical path of the exit side polarization element 5. Therefore, hereinafter, the description will be made assuming that the incident light beam L1 is incident on the light beam incident side end surface 511 at the incident angle θ.
Further, for convenience of explanation, the incident light beam L1 is incident on the light beam incident side end surface 511 from the lower side, that is, from the side where the distance between the light beam incident side end surface 511 and the exit side inclined surface 512 is small. It will be explained as a thing.

Here, the refraction angle of the light beam L1A that is refracted at the second boundary surface B2 by the light beam L1 incident on the light beam incident side end surface 511 at the incident angle θ is defined as β.
The refraction angle beta, the refractive index of air 1, if the refractive index of the first prism 51 and the n _d, is represented by the following formula from the Snell's law (3).

Further, since the first prism 51 is disposed such that the light beam incident side end surface 511 is orthogonal to the illumination optical axis Ax, the light beam L1A is inclined by the light beam incident side end surface 511 and the exit side inclined surface 512. When α is α, the light enters the first boundary surface B1 at an angle of α + β.
The transmission condition for transmitting the light beam L1A without reflecting at the first boundary surface B1 is expressed by the following formula (4) from Snell's law.

In the above description, since the incident light beam L1 is incident on the light beam incident side end surface 511 from the lower side, the light beam L1A is incident on the first boundary surface B1 at an angle of α + β. Conversely, when the incident light beam L1 is incident on the light beam incident side end surface 511 from the upper side, that is, from the side where the separation between the light beam incident side end surface 511 and the exit side inclined surface 512 is large, at an incident angle θ. The light beam L1A enters the first boundary surface B1 at an angle α−β.
However, since the incident angle (α + β) at the lower incidence is larger than the incident angle (α−β) at the upper incidence, the transmission condition of Expression (4) in which the incident angle of the light beam L1A is defined by α + β is satisfied. If it is satisfied, all the light beams L1A are transmitted without being reflected by the first boundary surface B1.

Next, total reflection conditions will be described.
FIG. 5 is a diagram for explaining the total reflection condition. Specifically, FIG. 5 is a view of the first prism 51 as viewed from the side.
In addition, the refraction angle of the second linearly polarized light L12A obtained by refracting the second linearly polarized light L12 reflected by the polarizing element body 53 at the first boundary surface B1 is the exit side inclined surface 512 and the incident side inclined surface. Since the light beam L1A is reflected on the first boundary surface B1, the reflection angle is the same as that of the light beam L1A. For this reason, in FIG. 5, for convenience of explanation, the second linearly polarized light L12A is illustrated as being reflected by the first boundary surface B1.
For convenience of explanation, the description will be made assuming that the incident light beam L1 is incident on the light beam incident side end surface 511 from the upper side at an incident angle θ.

Since the incident light beam L1 is upward incident, the light beam L1A is incident on the first boundary surface B1 at an angle of α-β as described above. In addition, the refraction angle of the second linearly polarized light L12A is the same as the reflection angle when the light beam L1A is reflected by the first boundary surface B1 as described above, and is an angle α−β. Furthermore, since the traveling direction of the light beam L1 ′ incident on the light beam incident side end surface 511 at the incident angle 0 ° and the normal line Nm of the light beam incident side end surface 511 are parallel, the second linearly polarized light L12A is With respect to the surface B2, the angle of 2α−β is obtained by adding the refraction angle (α−β) of the second linearly polarized light L12A to the incident angle α at which the light beam L1 ′ is incident on the first boundary surface B1.
Then, the total reflection condition in which the second linearly polarized light L12A is totally reflected at the second boundary surface B2 is expressed by the following formula (5) from Snell's law.

In the above description, since the incident light beam L1 is incident upward, the second linearly polarized light L12A is incident on the second boundary surface B2 at an angle of 2α−β. On the other hand, when the incident light beam L1 is downward incident, the second linearly polarized light L12A is incident on the second boundary surface B2 at an angle of 2α + β.
However, since the incident angle (2α−β) at the upper incidence is smaller than the incident angle (2α + β) at the lower incidence, an expression defining the incident angle of the second linearly polarized light L12 by 2α−β. When the total reflection condition (5) is satisfied, all the second linearly polarized light L12A is totally reflected at the second boundary surface B2.

  As described above, the first prism 51 is set so that the inclination angle α falls within the ranges of the expressions (4) and (5).

[Range of incident angle θ]
In the present embodiment, the optical component 32 to 34 and 350 to 352 (light guide optical system 6) disposed on the upstream side of the light path of the exit side polarization element 5 has a range of the incident angle θ as shown below. Is set.
6 and 7 are diagrams for explaining the range of the incident angle θ. Specifically, FIG. 6 is a diagram schematically illustrating the optical path of the light beam L1 that is emitted from the light source device 31 and is incident on the exit-side polarizing element 5. FIG. 7 is an enlarged view of a part of FIG. 6 and shows only the microlens ML and the exit-side polarizing element 5 (first prism 51).
In FIG. 6, for convenience of explanation, the second lens array 322, the polarization conversion element 323, the superimposing lens 324, the field lens 350, among the light guide optical system 6 constituted by the optical components 32 to 34 and 350 to 352. Only the liquid crystal panel 351 is shown.

In FIG. 6, the liquid crystal panel 351 includes a plurality of microlenses ML that are provided according to a plurality of pixels and narrow the incident light beam L1 to the plurality of pixels. In FIG. 6, for convenience of explanation, only two of the plurality of microlenses ML are illustrated.
Further, in FIG. 6, in order to indicate the angle at which the incident angle θ is maximized, the light beam L1 is emitted from the small lens 322A on the outermost periphery (lower side in FIG. 6) of the second lens array 322, and the polarization conversion element A partial light beam that is incident on the exit-side polarizing element 5 is adopted through the micro lens ML on the outermost periphery (upper side in FIG. 6) of the H.323, superimposing lens 324, field lens 350, and liquid crystal panel 351.

As shown in FIG. 6, the field lens 350 converts the partial light beam L1 into a light beam parallel to the central axis A (principal light beam), so that all the partial light beams L1 are incident on the liquid crystal panel 351 at an incident angle θ. ₁ is incident.
As shown in FIG. 6, the incident angle θ ₁ is the distance D from the superimposing lens 324 to the liquid crystal panel 351 (microlens ML), and the superimposing lens 324 has an outer edge from the central axis A of the partial light beam L1 (in FIG. , the length to the outer edge of the upper side) in the case of the d _1, represented by the following equation (6).

Then, as shown in FIG. 7, the maximum angle with respect to the straight line Ax ′ parallel to the illumination optical axis Ax when the partial light beam L1 is converged by the microlens ML is θ ₂ , and the diameter dimension of the microlens ML is d ₂ ( 6), when the focal length of the microlens ML is f, the following equation (7) can be derived.

Here, the maximum incident angle θ is the same as the angle θ ₂ as shown in FIG. Therefore, the maximum incident angle θ is expressed by the following formula (8) from formulas (6) and (7).

In the present embodiment, the incident angle θ is set to 20 ° or less by appropriately setting the distance D, the length dimension d ₁ , the diameter dimension d ₂ , and the focal length f in the light guide optical system 6. .
In the above description, the liquid crystal panel 351 has the configuration including the microlens ML. However, in the configuration without the microlens ML, d ₂ / 2f is omitted in the equation (8). Therefore, in the case of the configuration no microlens ML is the guiding optical system 6, the distance D and the length d ₁ only appropriate, by setting, to the incident angle θ to 20 ° or less.

The embodiment described above has the following effects.
In the present embodiment, the exit side polarization element 5 includes a first prism 51, a second prism 52, and a polarization element body 53. The polarizing element body 53 is provided on the incident-side inclined surface 522 of the second prism 52, and each of the prisms 51 and 52 is disposed in a state where the exit-side inclined surface 512 and the polarizing element body 53 are separated from each other by a predetermined interval. The Thus, an air layer having a high heat insulating effect is interposed between the polarizing element body 53 and the first prism 51. For this reason, heat conduction from the polarizing element body 53 to the first prism 51 can be effectively suppressed.
Therefore, the thermal distortion of the first prism 51 due to the influence of heat generation of the polarizing element body 53 can be suppressed, and the polarization separation characteristics of the exit side polarizing element 5 can be maintained well.
In addition, since the polarization separation characteristic of the exit side polarization element 5 can be maintained satisfactorily, the image quality of the projection image projected from the projector 1 can be maintained satisfactorily.

Further, since the first prism 51 is formed so as to satisfy the transmission condition of Expression (4), the incident angle at which the light beam L1A enters the first boundary surface B1 is reduced, and the light beam L1A is converted into the first boundary surface B1. The light can be transmitted without being reflected, and the light utilization efficiency can be improved.
Furthermore, since the first prism 51 is formed so as to satisfy the total reflection condition of Expression (5), the incident angle at which the second linearly polarized light L12A enters the second boundary surface B2 is increased, and the second The linearly polarized light L12A can be totally reflected at the second boundary surface B2, and the second linearly polarized light L12A can be prevented from entering the liquid crystal panel 351 disposed on the upstream side of the optical path.

FIG. 8 is a diagram showing the relationship between the upper limit and the lower limit of the tilt angle α with respect to the incident angle θ when the refractive index _nd is 1.8.
In FIG. 8, the range of the inclination angle α when the incident angle θ is 20 ° is 22.8 ° ≦ α ≦ 22.4 °. This is the limit angle range that can be manufactured in consideration of crossing during processing. When the incident angle θ is further increased, the range of the inclination angle α is further reduced, and the processing of the first prism 51 becomes difficult. Further, when the incident angle θ is 20.5 °, the range of the inclination angle α does not exist. That is, when the incident angle θ exceeds 20 °, the inclination angle α that simultaneously satisfies the expressions (4) and (5) cannot be substantially realized.
As a first prism 51, a refractive index _{n d} of a general glass material is 1.4 to 1.8. Equation (3) to (5) than the refractive index _{n d} the smaller the difference between the upper and lower limits (the range of the inclination angle alpha) for the greater refractive index than the refractive index of 1.8 1.4 to 1 The range of allowable incident angle θ becomes larger in .5. However, the amount is very small, and even when the refractive index is 1.4 to 1.5, if it exceeds 21 °, it is almost the limit.
In the present embodiment, the projector 1 includes a light guide optical system 6 that causes the light beam L1 emitted from the light source device 31 to be incident on the light beam incident side end surface 511 of the emission side polarizing element 5 with an incident angle θ of 20 ° or less. Accordingly, when forming the first prism 51 so as to satisfy the transmission condition and the total reflection condition, the range of the inclination angle α defined by the equations (3) to (5) can be set to a manufacturable range. it can.

  Further, an antireflection film 512A corresponding to the inclination angle α, that is, the incident angle at which the light beam L1A is incident on the first boundary surface B1 is formed on the emission side inclined surface 512. Thus, in addition to forming the first prism 51 so as to satisfy the transmission condition, the antireflection film 512A is formed so that the light beam L1A can be transmitted without being reflected by the first boundary surface B1. The effect that it is possible can be achieved suitably.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
In the embodiment, the first prism 51 is formed so as to satisfy the transmission condition and the total reflection condition. However, the present invention is not limited to this, and the first prism 51 may be formed so as to satisfy only the transmission condition.
In the above-described embodiment, when the exit-side polarizing element 5 is incorporated into the projector 1, the prisms 51 and 52 may be separately incorporated into the projector 1. The prisms 51 and 52 may be incorporated into the projector 1 in an integrated state in advance. It does not matter as a configuration.

  In the above embodiment, the light emission side end face 521 of each exit side polarization element 5 is fixed to the cross dichroic prism 354 with an adhesive or the like, and the cross dichroic prism 354 and each exit side polarization element 5 are integrated. I do not care. Similarly, each liquid crystal panel 351, each incident side polarization element 352, and each field lens 350 may be integrated with the cross dichroic prism 354.

In the embodiment, the prisms 51 and 52 may have different shapes. The prisms 51 and 52 may be made of different materials (different refractive indexes).
For example, the shape of the end surface 513 of the first prism 51 may be formed so that the second linearly polarized light L12 totally reflected by the second boundary surface B2 is incident perpendicularly.
In each of the embodiments described above, the emission side inclined surface 512 is positioned on the light beam emission side so that the second linearly polarized light L12 is emitted upward, and is on a plane (light beam incident side end surface 511) orthogonal to the illumination optical axis Ax. However, the present invention is not limited to this, and as long as the liquid crystal panel 351 is avoided, the emission side inclined surface 512 may be inclined in any direction, up, down, left, or right.

In the embodiment, the configuration of the polarizing element body 53 is not limited to the configuration described in the embodiment, and any configuration may be used as long as it is a reflective polarizer.
For example, as the polarizing element main body 53, a polymer-type layered polarization in which an organic material having refractive index anisotropy (birefringence) such as a polarization separation element formed of a dielectric multilayer film or a liquid crystal material is laminated in layers. A plate, an optical element that combines a λ / 4 phase difference plate and a circularly polarized light reflecting plate that separates unpolarized light into clockwise circularly polarized light and counterclockwise circularly polarized light, and reflected polarized light using Brewster's angle. You may employ | adopt the optical element isolate | separated into transmitted polarized light, or the hologram optical element using a hologram.

  Further, when the polarizing element body 53 is formed in a rectangular shape as a whole, it is preferable that the long side is inclined with respect to the illumination optical axis Ax in a state parallel to the light beam incident side end surface 511 and the light beam emission side end surface 521. With such a configuration, when the polarizing element body 53 is tilted as described above when tilted at the same tilt angle α, the rectangular short side has the light beam incident side end surface 511 or the light beam exit side. The thickness dimension along the illumination optical axis Ax in the entire exit-side polarizing element 5 can be reduced as compared with the configuration in which the tilt is made with respect to the illumination optical axis Ax in a state parallel to the end surface 521.

Further, as described in the above embodiment, when the polarizing element body 53 has a configuration in which a large number of fine linear ribs such as aluminum are formed in parallel, the polarizing element body 53 is formed as shown below. It is preferable to incline.
For example, in consideration of maintaining the characteristics of the polarizing element body 53, it is preferable to incline the polarizing element body 53 about the transmission axis (axis perpendicular to the extending direction of the linear rib). That is, when tilted as described above, when the polarizing element body 53 is viewed from the light beam incident side, the pitch of each linear rib is the same as the state in which the linear rib is not tilted. Can be maintained.
For example, when considering the transmission efficiency at the first boundary surface B1 and the reflection efficiency at the second boundary surface B2, the polarizing element body around the absorption axis (axis parallel to the extending direction of the linear rib) 53 is preferably inclined. That is, when tilted as described above, a light beam having the same polarization direction as the first linearly polarized light L11 to be transmitted through the polarizing element body 53 out of the light beam L1 is P-polarized light on the first boundary surface B1. Therefore, the reflection at the first boundary surface B1 can be suppressed and the transmission efficiency can be improved. In addition, since the second linearly polarized light L12 is incident on the second boundary surface B2 as S-polarized light, transmission through the second boundary surface B2 can be suppressed and reflection efficiency can be improved.

In the above-described embodiment, the configuration of the polarizing element according to the present invention is used for the exit-side polarizing element 5. However, the configuration is not limited to this, and the polarizing element 352 may be used.
In the embodiment, the example of the three-plate projector 1 provided with three liquid crystal panels 351 has been described. However, the configuration is not limited to this, and the configuration provided with only one liquid crystal panel 351 and the configuration provided with two liquid crystal panels 351 are provided. Alternatively, a configuration in which four or more liquid crystal panels 351 are provided may be employed.
In the embodiment, only the example of the front projection type projector has been described, but the present invention is also applicable to a rear type projector that includes a screen and performs projection from the back side of the screen.

  The present invention can maintain the polarization separation characteristics well, and therefore can be used for a polarizing element of a projector used in presentations and home theaters.

FIG. 2 is a diagram schematically showing a schematic configuration of a projector in the embodiment. The figure which shows typically the structure of the output side polarizing element in the said embodiment. The figure which shows typically the optical path of the light beam inject | emitted from the output side polarizing element in the said embodiment. The figure for demonstrating the permeation | transmission conditions in the said embodiment. The figure for demonstrating the total reflection conditions in the said embodiment. The figure for demonstrating the range of the incident angle in the said embodiment. The figure for demonstrating the range of the incident angle in the said embodiment. The figure for demonstrating the range of the inclination-angle in the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Projector, 4 ... Projection lens (projection optical apparatus), 5 ... Output side polarization element, 6 ... Light guide optical system, 31 ... Light source device, 51 ... 1st prism 52 ... second prism, 53 ... polarizing element body, 351 ... liquid crystal panel (light modulation element), 511 ... light-incident-side end surface, 512 ... exit-side inclined surface, 512A,. Antireflection film, 521... End face on the light emission side, 522... Inclined surface on the incident side, L1... Incident light flux, L11 ... the first linearly polarized light, L12. light.

Claims (5)

A polarizing element that transmits predetermined linearly polarized light in the incident light beam,
A first prism having a light beam incident side end surface on which a light beam is incident, and an exit side inclined surface inclined with respect to the light beam incident side end surface;
A second prism having a light beam emission side end surface parallel to the light beam incident side end surface, and an incident side inclined surface inclined with respect to the light beam emission side end surface and parallel to the emission side inclined surface;
The second linearly polarized light, which is provided on the incident-side inclined surface and transmits the first linearly polarized light out of the light flux passing through the first prism and whose polarization direction is orthogonal to the first linearly polarized light, is A polarizing element body that reflects toward one prism;
Each of the prisms is disposed in a state in which the exit side inclined surface and the polarizing element body are separated by a predetermined distance,
The first prism is
Eggplants inclination angle between the light-incident surface and the exit-side inclined surface alpha, the angle of refraction the incident light beam is refracted by the first prism beta, the refractive index of the first prism when a n _d ,

A polarizing element characterized by being formed so as to satisfy the above relationship. The polarizing element according to claim 1,
The first prism is

A polarizing element characterized by being formed so as to satisfy the above relationship. The polarizing element according to claim 1 or 2,
In the exit side inclined surface,
A polarizing element, wherein an antireflection film corresponding to the tilt angle is formed. A projector comprising: a light source device; a light modulation element that modulates a light beam emitted from the light source device according to image information to form image light; and a projection optical device that magnifies and projects the image light,
A projector comprising the polarizing element according to claim 1. The projector according to claim 4, wherein
A light guide optical system for guiding a light beam emitted from the light source device to the polarizing element;
The light guide optical system is:
It is set so that the light beam is incident at an incident angle of 20 ° or less with respect to the light beam incident side end surface of the polarizing element.
A projector characterized by that.

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