JP2007225744A - Polarization converting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization converting element that can efficiently convert non-polarized light into linearly polarized light and that is excellent in productivity, and to provide a liquid crystal projector or a liquid crystal display using the element. <P>SOLUTION: The polarization converting element is obtained by laminating a polarization separating layer which separates non-polarized light at 0° incident angle into linearly polarized light T<SB>1</SB>exiting in an almost normal direction and linearly polarized light T<SB>2</SB>exiting in an oblique direction with respect to the normal line, and a polarization controlling layer which almost completely converts the polarization state of the linearly polarized light T<SB>1</SB>into the polarization state of the linearly polarized light T<SB>2</SB>and which does not convert the polarization state of the linearly polarized light T<SB>2</SB>for 50% or more but transmits the light. The obtained polarization converting element is disposed in front of a light source to obtain a liquid crystal projector or a liquid crystal display device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarization conversion element and a liquid crystal display device using the same. More specifically, the present invention relates to a polarization conversion element that can efficiently convert non-polarized light into linearly polarized light and is excellent in productivity, and a liquid crystal projector or liquid crystal display using the polarization conversion element.

As a polarizer used in a liquid crystal display device, iodine-based or dye-based dichroic polarizing elements are often used. Such a dichroic polarizing element generates linearly polarized light by absorbing only one of the two orthogonally polarized light components and not transmitting it, and transmitting the other polarized light component. Since the dichroic polarizing element generates linearly polarized light by utilizing light absorption, in principle, the upper limit of the light transmittance is 50%.
Therefore, in a liquid crystal display device using a dichroic polarizing element, only half or less of the light emitted from the light source can be used.

In order to increase the utilization efficiency of light emitted from the light source, a method of converting the polarization of light from the light source has been proposed.
For example, in Patent Document 1, a layer that separates an unpolarized beam into two linearly polarized components that are orthogonal to each other and a vertically incident polarized component maintain its polarization direction and are incident at a non-perpendicular angle. A polarization element comprising a polarization rotation layer that rotates the polarization direction of the polarization component is disclosed, and the polarization rotation layer having such a function is such that the axis of the uniaxially oriented molecule is normal to the layer. It is stated that this is achieved by being positioned in a plane that forms an angle θ with respect to the surface.
Patent Documents 2 and 3 disclose a polarization conversion film comprising a polarization separation layer that separates unpolarized incident light into two orthogonally polarized light beams and a polarization conversion layer that converts the polarization state of linearly polarized light. It has been disclosed that a birefringent compound tilted with respect to the film surface is used as the polarization conversion layer. This polarization conversion layer has a function of converting the polarization state of linearly polarized light incident at an angle without converting the polarization state of linearly polarized linearly incident light.

Japanese National Patent Publication No. 10-505435 Japanese Patent Laid-Open No. 2004-77899 JP 2004-77900 A

However, according to the study by the present inventors, the inventions described in Patent Documents 1 to 3 are extremely capable of rotating the polarization state of linearly polarized light that is obliquely incident on the polarization rotation layer or the polarization conversion layer by 90 °. It turned out to be difficult. In addition, it is difficult for industrial production to align a birefringent compound or a liquid crystal compound in an inclined manner with respect to the layer surface, and it is also possible to adjust the relationship between thickness, refractive index, and molecular tilt orientation angle. It is difficult in production. Therefore, the conventional polarization conversion element has low polarization conversion efficiency and low productivity, so the production cost is high.
An object of the present invention is to provide a low-cost and highly productive polarization conversion element capable of efficiently converting non-polarized light into linearly polarized light, and a liquid crystal projector or liquid crystal display using the same.

As a result of studies conducted by the present inventor to achieve the above-described object, linearly polarized light T ₁ that emits light having no incident angle of 0 degrees of polarization in a substantially normal direction and linearly polarized light T that emits in an oblique direction with respect to the normal line. A polarization separating layer that divides into _two and a linearly polarized light T ₁ that is emitted in a substantially normal direction is converted into a polarization state of a linearly polarized light T ₂ almost completely and is emitted obliquely with respect to the normal. A polarization conversion element capable of efficiently converting non-polarized light into linearly polarized light can be efficiently produced at low cost by combining with a polarization control layer that transmits light without converting the polarization state of the polarized light T ₂ by 50% or more. And the present invention has been completed based on this finding.

Thus, according to the present invention,
(1) polarized light separation layer to linearly polarized light T ₁ and the normal to emit a substantially normal direction without light polarization of the incident angle of 0 degrees to separate linearly polarized T ₂ emitted in an oblique direction, and a direction substantially normal It is converted almost completely polarization state of the linearly polarized light T ₂ the polarization state of the linearly polarized light T ₁ emitted to, without conversion and normal to the polarization state of the linearly polarized light T ₂ emitted in an oblique direction of 50% or more A polarization conversion element comprising a polarization control layer that transmits the light.
(2) The polarization separation layer is composed of an optically isotropic prism array having a plurality of V grooves on the surface, and a uniaxial birefringent layer,
All the grooves of the prism array are almost parallel,
Refractive index and n _i of the material forming the prism array, is substantially equal to the refractive index n _o for ordinary light of the material forming the birefringent layer, the polarization conversion element according to (1).
(3) The polarization conversion element according to (2), wherein the V-groove direction of the prism array and the optical axis direction of the birefringent layer are substantially parallel.
(4) The polarization conversion element according to any one of (1) to (3), wherein the polarization control layer has an in-plane retardation of approximately ½ of the wavelength of incident light.
(5) the polarization control layer, the in-plane slow axis is tilted 40 to 50 degrees from the polarization direction of linearly polarized light T _1, wherein (1) to the polarization conversion according to any one of (4) element.

(6) the polarization control layer, the refractive index in the in-plane slow axis direction n _x, when the direction of the refractive index perpendicular thereto and n _y, the refractive index in the thickness direction and ^{_{n z, (n x 2 +}} n The polarization conversion element according to any one of (1) to (5), wherein an absolute value of a difference between _y ² ) / 2 and _nz ² is 0.004 or more.
(7) The exit angle of the linearly polarized light T _{2 from} the polarization separation layer is set to be equal to or greater than the minimum angle of the incident angle θ _{i that is} transmitted as it is without converting the linearly polarized light T ₂ by 50% or more by the polarization control layer. The polarization conversion element according to any one of (1) to (6).
(8) The polarization conversion element according to any one of (1) to (7), further including a prism or a lens.
(9) A light source that generates a beam, a polarization conversion element according to any one of (1) to (8), a liquid crystal cell, an analyzer, and a projection lens system in order in the optical path of the beam A liquid crystal projector.
(10) The liquid crystal projector according to (9), wherein a polarizer is further disposed between the polarization conversion element and the liquid crystal cell.
(11) A liquid crystal display in which a backlight, the polarization conversion element according to any one of (1) to (8), a polarizer, a liquid crystal cell, and an analyzer are arranged in this order.
Is provided.

  When non-polarized light is incident on the polarization conversion element of the present invention from a substantially vertical direction, the intensity of one linearly polarized light and the intensity of the other linearly polarized light are significantly different (that is, having a high degree of polarization). Come out. Furthermore, since the utilization factor of incident light is high and various sizes and shapes can be easily manufactured, a high brightness image can be obtained by using the polarization conversion element of the present invention for a liquid crystal projector or a liquid crystal display. Obtainable.

The polarization conversion element of the present invention includes a polarization separation layer that separates linearly polarized light T ₁ that emits non-polarized light with an incident angle of 0 degrees in a substantially normal direction and linearly polarized light T ₂ that emits in an oblique direction with respect to the normal, The polarization state of the linearly polarized light T ₁ emitted in the substantially normal direction is converted into the polarization state of the linearly polarized light T ₂ almost completely, and the polarization state of the linearly polarized light T ₂ emitted in the oblique direction with respect to the normal is 50 It comprises a polarization control layer that transmits without being converted by more than%.

(Polarized light separation layer)
The polarized light separating layer constituting the present invention has a function of separating light having no incident angle of 0 degrees into linearly polarized light T ₁ that emits light in a substantially normal direction and linearly polarized light T ₂ that emits in an oblique direction with respect to the normal. (The substantially normal direction means that the error angle from the normal direction is within 10 °). The polarization directions of the linearly polarized light T ₁ and the linearly polarized light T ₂ are orthogonal to each other.
As an example of the polarization separation layer, a layer composed of a prism array and a birefringent layer can be given. For example, it can have a structure as shown in FIG. The prism array has a plurality of V-grooves in a shape in which elongated triangular prisms are laid down on one surface, and all the grooves are substantially parallel. From the viewpoint of increasing the light collection efficiency by the prism or lens described later, it is preferable that the apex angles of the plurality of convex portions formed by the grooves of the prism array are substantially the same. In the present invention, “substantially parallel” means that the error angle from parallel is within 5 °.
In Figure 1, the polarization separating layer has a refractive index n _i isotropic prism array 11 made of a material, the refractive index anisotropy in the groove of the prism array _{Δn = n e -n o (n} e ≠ n of _o ) It is made of a uniaxial birefringent layer 12 embedded with a uniaxial material. Here, n _e and n _o are the extraordinary light and the refractive index for ordinary light of the uniaxial material 12.
Further, n _o and is substantially equal in magnitude (in this case, the n _i, as described later, when the linearly polarized light T ₁ is is perpendicularly incident on the polarized light separation layer, so that the polarization is straight ahead, n the size of the _o and _{n i} may be equal). At this time, if a uniaxial material is embedded so that the optical axis of the birefringent layer 12 is parallel to the groove direction of the prism array, the refractive index in the direction perpendicular to the groove direction of the polarization separation layer becomes constant (= _ni ). The refractive index with respect to the direction parallel to the groove direction changes at the contact surface between the prism array 11 and the birefringent layer 12.
Therefore, as shown in FIG. 5, when linearly polarized light T ₁ having a polarization direction orthogonal to the groove direction is perpendicularly incident on the polarization separation layer, the polarization goes straight as it is (this “straight forward” This means that the error angle from the straight line is within 10 °). When linearly polarized light T ₂ having a polarization direction parallel to the groove direction is incident on the polarization separating layer, refraction at the interface of the prism array 11 and the birefringent layer 12 (or reflected) to its polarization proceeds in an oblique direction .

Light no polarization it can be considered as linearly polarized light component T ₁ having a polarization direction orthogonal to the groove direction, and a composite of linearly polarized light component T ₂ having a polarization direction parallel to the groove direction. When unpolarized light enters the polarization separation layer at an incident angle of 0 degree, the linearly polarized light component T ₁ having a polarization direction orthogonal to the groove direction travels straight as it is and is emitted in a substantially normal direction according to the above principle.
On the other hand, the linearly polarized light component T ₂ having a polarization direction parallel to the groove direction is refracted (or reflected) at the contact surface between the prism array 11 and the birefringent layer 12 and is emitted obliquely with respect to the normal line. In this way, unpolarized light can be separated into two linearly polarized light components, and the traveling direction of the linearly polarized light can be changed according to the state of polarization.

Angle linearly polarized light T ₂ is emitted, the difference in refractive index n _i of the refractive index n _e and isotropic material uniaxial material 12, and on the apex angle of the prism array. In this polarization separation layer, since polarization separation is performed using refraction (or reflection), light can be efficiently condensed by a prism or a lens, which will be described later, and can be preferably used. In addition, if polarization separation due to diffraction occurs in this polarization separation layer, the light collection efficiency may be reduced. Therefore, the pitch of the prism array (the distance between the apexes of adjacent apex angles of the prism array) should be reduced so as not to cause diffraction as much as possible. ) Is preferably sufficiently large with respect to the wavelength of the incident light.

  The material constituting the prism array 11 is not particularly limited as long as it is a transparent and optically isotropic material. Examples of such a material include glass and polymer. From the viewpoint of obtaining a polarization conversion element having a large area, a transparent optically isotropic polymer is preferably used.

  The material constituting the uniaxial material 12 is not particularly limited as long as it is a cured product that is transparent and optically uniaxial. Examples of such a material include a material obtained by curing nematic liquid crystal. A birefringent layer can be formed by applying nematic liquid crystal to the grooves of the prism array, orienting the molecular axes so as to be parallel to the groove direction, and then curing.

Another example of the polarization separation layer constituting the present invention is a birefringent diffraction grating. As shown in FIG. 2, the birefringent diffraction grating is composed of a rectangular uneven grating 11 made of an isotropic material and a birefringent layer 12 made of an anisotropic material embedded in the recess. .
Since the anisotropic material exhibits birefringence, ordinary light (for example, a polarization component that vibrates in the x-axis direction in FIG. 2) and extraordinary light (for example, a polarization component that vibrates in the y-axis direction in FIG. 2) and The refractive index is different. Accordingly, due to the action of the periodic grating, the diffraction efficiency of the generated diffracted light also differs between ordinary light and extraordinary light, and polarization separation can be achieved by adjusting the refractive index and the grating shape. Incidentally, anisotropic material, to the extraordinary refractive index of the light n _e and ordinary index of refraction n _o, usually n _e> n _o, the polarization direction anisotropic material of the extraordinary light in this case the slow axis of the made birefringent layer 12, the polarization direction is the fast axis of the ordinary light (the slow axis and the fast axis in the case of n e _{<n o} is replaced, respectively.).

As another example of the polarization separation layer, an H ⁺ ion exchange region optical diffraction grating having a period is formed on the main surface of a lithium niobate crystal plate (JP-A-5-249308, JP-A-6-18817). JP-A-6-27320); having a dielectric layer on the bottom surface of a periodic groove provided on the main surface of a crystal substrate having optical anisotropy (JP-A-2-156205) A cholesteric liquid crystal spiral axis arranged parallel to the cell plate (Appl. Phys. Lett. 1997, 71, 1350-1352); a polarization separation layer disclosed in JP-A-2004-77899, etc. It is done.

(Polarization control layer)
The polarization control layer converts the polarization state of the linearly polarized light T ₁ emitted in a direction approximately normal to the almost complete polarization state of the linearly polarized light T _2, and with respect to the normal of the linearly polarized light T ₂ emitted in an oblique direction It has a function of transmitting without changing the polarization state by 50% or more, preferably 80% or more, more preferably 90% or more.
The polarization control layer having such a function may have any optical anisotropy as described below.
First, in order to almost completely transparent to convert the polarization state of the linearly polarized light T ₂ the polarization state of the linearly polarized light T ₁ emitted in a direction approximately normal, the polarization control layer, whose plane retardation, the incident light Is preferably approximately ½ of the wavelength (note that approximately ½ is 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.49 to 0.51. Means the range.) Plane retardation is the difference between the direction of the refractive index n _y perpendicular to the refractive indices n _x and slow axis in the in-plane slow axis direction is obtained by multiplication of the average thickness d. Further, it is preferable that the in-plane slow axis of the polarization control layer is inclined 40 degrees to 50 degrees to the polarization direction of the linearly polarized light T _1, and more preferably are inclined 45 degrees.
The polarization control layer having such a configuration, the linearly polarized light T ₁ is incident from a direction approximately normal, the polarization direction is rotated 90 degrees. Conversion of the linearly polarized light T _{1 to} the linearly polarized light T ₂ is almost completely performed. Specifically, it is preferable that 98% or more of the incident linearly polarized light T ₁ is converted to the linearly polarized light T ₂ .

On the other hand, normal to the diagonal direction in the polarization state of the linearly polarized light T ₂ emitted 50% or more, preferably 80% or more, in order to transmit without converting more preferably 90% or more, the polarization control layer has a thickness direction of the refractive index n _z is the refractive indices n _x and n _y in the plane, it is preferable to satisfy the following relationship.
First, the polarization control layer of the present invention, the in-plane slow axis direction of the refractive index n _x, the direction of the refractive index n _y perpendicular _thereto, the refractive index n _z in the thickness direction, n _x> n _y> n _z, or it is preferably _{n z> n x> n y} . Moreover, the absolute value of the difference between ( _nx ² + _ny ² ) / 2 and _nz ² is preferably 0.004 or more, and more preferably 0.007 or more.

This relationship will be described in more detail with reference to FIG. When linearly polarized light T ₂ that with respect to the normal of the polarization control layer is incident obliquely passes through the polarization control layer, and those coming out remains the same polarization state as linearly polarized light T _2, the polarization state of the linearly polarized light T ₁ Some of them come out after being converted. The intensity of the component exiting remain in the same state as linearly polarized T ₂ I may be represented by the number 1. A, B, and δ in Equation 1 are expressed by Equation 2.

_{Here, n x, n y, n} z is a refractive index in the in-plane slow axis direction of the polarization control layer (x-direction) to which the direction orthogonal in the plane (y-direction), the thickness direction (z-direction) And d is the layer thickness. a _{ζ = n i sinθ i, θ} i is the incident angle of the polarization control layer of the linearly polarized light _{T 2, n i} is the refractive index of the incident side. The incident angle theta _i, since linearly polarized light T ₂ is the same as the angle at which emitted from the polarization separating layer, constituting the birefringent layer of the polarization separation layer, the refractive index n _e and isotropic material 11 uniaxial material 12 Depending on the difference in the refractive index n _i and the shape of the prism array or grating. The refractive index n _i of the incident side, when a polarized light separation layer and the polarization control layer are laminated in close contact without the intervention of an air layer in the polarization conversion device of the present invention, n _i is the prism array of the polarization separating layer or This is the refractive index of the isotropic material forming the grating.

When linearly polarized light T ₂ is incident on the polarization control layer, the polarization control layer speed, is divided into two unique light waves having different propagation directions. k _z1 and k _z2 are z components of the wave number vectors of the two _{eigenwaves, and} are expressed by Equation 3. Here, λ is the wavelength of incident light.

数１によると、ｃｏｓδが１の時に、強度Ｉは最大値の１となる。すなわち、直線偏光Ｔ２が偏光状態を維持したまま透過したことになる。

According to Equation 1, when cos δ is 1, the intensity I has a maximum value of 1. That is, the linearly polarized light T2 is transmitted while maintaining the polarization state.

The value of δ at which cos δ becomes 1 is obtained from Equation 2 and Equation 3. Note that there are a plurality of solutions δ obtained from Equations 2 and 3, and in any solution, the intensity I of the linearly polarized light T ₂ can be set to 1, so the degree of freedom in designing the polarization control layer is very high. high.
In order to increase the light utilization efficiency of the light source in a liquid crystal projector or a liquid crystal display and use it practically, cos δ = 1, that is, I = 1 is not required, and the intensity I may be increased as much as possible. When cos δ is −1, I becomes A / (A + B). In order for A to become a large value, it is derived from _Equation ² that the condition is that the difference between ( _nx ² + _ny ² ) / 2 and _nz ² is large.

FIG. 4 is a diagram showing the relationship between θ _i and the intensity I of the linearly polarized light T ₂ based on the calculation formula. It shows that the incident angle increases toward the right side of the axis indicating the incident angle. When the absolute value of the difference between (n _x ² + _ny ² ) / 2 and _nz ² is large in the solid line, the absolute value of the difference between ( _nx ² + _ny ² ) / 2 and _nz ² is small in the solid line Is the case.
In the solid line, it can be seen that the linearly polarized light T ₂ having the incident angle θ ₂ is transmitted as it is without being converted by the polarization control layer. As can be seen from the broken line, the linearly polarized light T ₂ having the incident angle θ ₄ is transmitted as it is without being converted by the polarization control layer. From this, by making the exit angle of the linearly polarized light T ₂ separated by the polarization separation layer equal to or greater than the minimum angle of the incident angle θ _{i that} transmits the linearly polarized light T ₂ of the polarization control layer as it is without being converted. It can be seen that a preferable polarization conversion element with high conversion efficiency can be constructed. The minimum angle is, for example, an intermediate angle between θ ₁ and θ _{2 in} the solid line in FIG. 4 and an angle near θ _{3 in} the broken line in FIG. At least, the incident angle theta _i which is transmitted through the linear polarization T ₂ of the polarization control layer without converting 50% or more _(the incident angle theta _i, it is possible to more present) when the minimum angle or more of the A preferable polarization conversion element with high conversion efficiency can be configured.

As described above, by adjusting the relationship of n _x, n _y and n _z, it is possible to the conditions of the above equation, the polarization control layer, for example, simple, such as stretching a transparent resin film It can be easily obtained by a manufacturing method. The polarization control layer constituting the present invention is compared with the conventional polarization rotation layer and polarization conversion layer that cannot be obtained unless the refractive index, film thickness, molecular orientation direction, etc. are adjusted with high accuracy. Easy to manufacture.

  In the polarization conversion element of the present invention, the polarization separation layer and the polarization control layer may be simply stacked, or may be sandwiched by a frame or the like, or bonded or melted so that no air layer is interposed between both layers. It may be laminated by wearing.

  The polarization conversion element of the present invention may further include a prism or a lens. Since the light traveling direction is divided into two in the polarization separation layer, by including a prism or lens, the polarized light component emitted in an oblique direction from the polarization control layer is condensed, and most of the polarized light is substantially normal. Can be directed.

  The polarization conversion element of the present invention can be used for a liquid crystal projector or a liquid crystal display. The liquid crystal projector includes a light source that generates a beam, a polarizer, a liquid crystal cell, an analyzer, and a projection lens system that are arranged in the optical path of the beam. The polarization conversion element of the present invention can be used as a polarizer of a liquid crystal projector, and can also be installed between a light source and a polarizer. Polarizers and analyzers are, for example, uniaxially stretched by adsorbing dichroic substances such as iodine and dichroic dyes on hydrophilic polymer films such as polyvinyl alcohol films and ethylene vinyl acetate partially saponified films. Can also be used.

  In addition, the liquid crystal display has a backlight, a polarizer, a liquid crystal cell, and an analyzer arranged in order. The polarization conversion element of the present invention can be used as a polarizer of a liquid crystal display, and can also be installed between a backlight and a polarizer closer to the backlight.

Examples 1-5
A transparent resin (ZEONOR1420 manufactured by Nippon Zeon Co., Ltd., refractive index n _i = 1.53) was dried at 100 ° C. for 5 hours and supplied to an injection molding machine to obtain a prism array sheet having a pitch of 50 μm and an apex angle of 45 degrees. . Nematic liquid crystal (refractive index n _o = 1.532 for ordinary light, refractive index n _e = 1.751 for extraordinary light) is applied to the grooves of the prism array sheet, and the molecules of the nematic liquid crystal are aligned in the groove direction. To obtain a polarized light separation film (polarized light separation layer). When the non-polarized light beam having an incident angle of 0 degree and a wavelength of 550 nm is irradiated on the liquid crystal layer side of the polarization separation film, the ordinary light is emitted from the prism array sheet side in a substantially normal direction, and the abnormal light is emitted from the normal line. The light was emitted in a direction inclined by 1 degree.

A transparent resin (manufactured by Zeon Corporation, ZEONOR1420: refractive index n _i = 1.53) was dried at 100 ° C. for 5 hours, introduced into an extruder, and a film was obtained using a T-die. This film was stretched to obtain anisotropic films (polarization control layers) 1 to 5 having refractive indexes _nx , _ny and _nz shown in Table 1. The refractive index is a value measured with an ellipsometer (M-2000, manufactured by JA Woollam).

  On the prism array sheet side of the polarization separation film, the anisotropic films 1 to 5 are arranged so that the in-plane slow axis (x direction) is inclined 45 degrees with the groove direction of the polarization separation film prism array. Then, the respective layers were laminated to obtain polarization conversion elements 1 to 5, respectively.

Unpolarized light beams having an incident angle of 0 degree and a wavelength of 550 nm were irradiated to the polarization separation film side of these polarization conversion elements 1 to 5. Using an analyzer to determine the percentage F1 of the emission amount of the polarization component T ₁ of the direction perpendicular to the groove direction of the prism with respect to the emission amount of the polarization component T ₂ of the horizontal direction to the groove direction of the prism. The results are shown in Table 2. It can be seen that by the polarization conversion element of the present invention, most of the unpolarized light beam is converted into the polarization component T ₂ in the direction horizontal to the groove direction of the prism.

Comparative Examples 1-5
An anti-parallel alignment nematic liquid crystal cell in which nematic liquid crystal is sealed between two glass substrates (pretilt angles are a: about 15 degrees, b: about 30 degrees, c: about 45 degrees, d: about 60 degrees, and e: 5 types of about 75 degrees). The sealed nematic liquid crystal had a refractive index of 1.4816 for ordinary light and a refractive index of 1.5805 for extraordinary light.
On the prism array sheet side of the polarization separation film, the antiparallel alignment nematic liquid crystal cells a to e are arranged so that the liquid crystal alignment surface is parallel to the groove direction of the prism array of the polarization separation film, and laminated respectively. Polarization conversion elements a to e were obtained, respectively.
Unpolarized light beams having an incident angle of 0 degree and a wavelength of 550 nm were irradiated on the polarization separation film side of these polarization conversion elements a to e. Using an analyzer to determine the percentage F2 of the emission amount of the polarization component T ₂ of the horizontal direction to the groove direction of the prism with respect to extraction intensity of the polarization components T ₁ of the direction perpendicular to the groove direction of the prism. The results are shown in Table 3. In the polarization conversion element it is understood that they are not completely converted into the polarization component T _1.

The figure which shows an example of the polarization separation layer which comprises this invention. The figure which shows another example of the polarization separation layer which comprises this invention. The figure which shows the principle of the polarization control layer which comprises this invention. The figure which shows the relationship between the incident angle of a polarization control layer, and polarization | polarized-light transmission intensity. The figure which shows the principle of the polarization conversion element of this invention.

Explanation of symbols

11: Layer made of isotropic material 12: Layer made of anisotropic (uniaxial) material T ₁ : Linearly polarized light component perpendicular to the groove (normal light)
T ₂ : Linearly polarized light component parallel to the groove (abnormal light)
3: Anisotropic film 4: Beam light A: Polarization separation layer B: Polarization control layer

Claims (11)

A polarization separation layer that separates linearly polarized light T ₁ that emits non-polarized light with an incident angle of 0 degrees in a substantially normal direction and linearly polarized light T ₂ that is emitted obliquely with respect to the normal, and a polarization state of the linearly polarized light T ₁ the converted almost completely polarization state of the linearly polarized light T _2, and the polarization state of the linearly polarized light T ₂ without converting 50% or more, the polarization conversion element comprising a polarization control layer which transmits. The polarization separation layer is composed of an optically isotropic prism array having a plurality of V grooves on the surface, and a uniaxial birefringent layer,
All the grooves of the prism array are almost parallel,
The refractive index n _i for ordinary light of the material forming the prism array, is substantially equal to the refractive index n _o for ordinary light of the material forming the birefringent layer, the polarization conversion element according to claim 1.   The polarization conversion element according to claim 2, wherein the V-groove direction of the prism array and the optical axis direction of the birefringent layer are substantially parallel.   The polarization conversion element according to any one of claims 1 to 3, wherein the polarization control layer has an in-plane retardation of approximately ½ of the wavelength of incident light. The polarization control layer, the in-plane slow axis is tilted 40 to 50 degrees from the polarization direction of linearly polarized light T _1, the polarization conversion element according to any one of claims 1 to 4. The polarization control layer, when the refractive index in the in-plane slow axis direction n _x, it the refractive index n _y in the direction perpendicular in the _plane, the refractive index in the thickness direction is ^{_{n z, (n x 2 +}} n _y ²⁾ / 2 and the absolute value of the difference between _n ^{z 2} is equal to or greater than 0.004, the polarization conversion element according to any one of claims 1 to 5. The exit angle from the polarization separating layer of the linearly polarized light T _2, and the linearly polarized light T ₂ by the polarization control layer to less than the minimum angle of the incident angle theta _i which is transmitted through without conversion 50% or more, claim 1 The polarization conversion element according to any one of 6.   The polarization conversion element according to claim 1, further comprising a prism or a lens.   A liquid crystal projector comprising: a light source that generates a beam; and the polarization conversion element according to claim 1, a liquid crystal cell, an analyzer, and a projection lens system arranged in that order in the optical path of the beam.   The liquid crystal projector according to claim 9, wherein a polarizer is further arranged between the polarization conversion element and the liquid crystal cell. A liquid crystal display in which a backlight, the polarization conversion element according to claim 1, a polarizer, a liquid crystal cell, and an analyzer are arranged in order.

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