JP2005077545A - Polarization conversion optical system, its manufacturing method and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-shaped polarization conversion element which is improved in the positioning accuracy of an optical element, and to provide a method for manufacturing the polarization conversion optical element. <P>SOLUTION: A microlens array 4 is previously formed, and nearly collimated beams of light are made incident on a 1st microlens array at a prescribed incident angle, and then the polarization conversion element is formed by using the beams of light converged by the microlens array; positioning of the microlens array and the polarization conversion element is performed automatically; the element is accurately formed, thus, the miniaturization and the thick reduction can be attained. The polarization conversion optical system is provided with a polarized light separating element, the microlens array and the polarization conversion element, and wherein the microlens array and the polarization conversion element are positioned with prescribed accuracy, so that such a problem is eliminated where the miniaturization and the thickness reduction of the polarizing conversion element could not be attained, because the positioning accuracy of the microlens array and the polarizing conversion element is stringent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention splits incident unpolarized or partially polarized light into two angularly separated outgoing beams with different polarization states and converts the polarization direction of one polarized light to substantially fully polarized light. The present invention relates to a polarization conversion optical system for conversion, and a projection display device incorporating such a polarization conversion optical system.

  Many projection display devices using liquid crystal or the like need to be illuminated by linearly polarized light in one direction. When such devices operate with unpolarized or partially polarized light, the light must be converted to unidirectional linearly polarized light before entering the optical system.

  One method for converting non-polarized light to unidirectional linearly polarized light is the well-known linear polarizer. Ideally, a linear polarizer transmits linearly polarized light in one direction without loss and completely absorbs linearly polarized light in an orthogonal direction, so that non-polarized light incident on the polarizer is converted into completely linearly polarized light. While such a linear polarizer is a simple means of generating linearly polarized light, it is disadvantageous in that it has low efficiency. Due to absorption in the polarizer or reflection at the surface of the polarizer, such a linear polarizer is ideally only 50% efficient and in practice is in the range of 40-45%.

  Another means for converting non-polarized light to polarized light is a polarization conversion optical system. In the polarization conversion optical system, incident light that is already in a desired polarization state is transmitted without change. Incident light in a polarization state orthogonal to the desired polarization state is converted to light in the desired polarization state without being blocked.

  The polarization conversion optical system includes a polarization separation element that separates incident non-polarized light or partially polarized light, and light in one polarization state is spatially or angularly separated from light having orthogonal polarization states. It is emitted from. The polarization conversion optical system also includes a polarization conversion element that converts one polarization state of components emitted by the polarization separation element.

  As an example, FIG. 22 shows a polarization conversion optical system 105 in which a first microlens array 101, a second microlens array 102, a polarization beam splitter 103, and a half-wave plate 104 are combined. The light beam condensed by the microlens array is transmitted through the polarization beam splitter, the P-polarized light is transmitted, and the S-polarized light is reflected. The transmitted P-polarized light is rotated by 90 ° with a half-wave plate, converted to S-polarized light, and then emitted from the polarization conversion optical system. On the other hand, the S-polarized light reflected by the polarization beam splitter is further reflected by the 45-degree mirror 106 and emitted from the polarization conversion optical system. Therefore, the light beam emitted from the polarization conversion optical system is converted into one polarization state.

As another example, FIG. 23 shows a polarization conversion optical system in which a wedge-shaped polarization separation element 111, a microlens array 112, and a half-wavelength element 113 are combined. In the wedge-shaped polarization separation element 111, the wedge-shaped portion is formed of a material having a different refractive index depending on the polarization direction, and the emission angle varies depending on the polarization direction of the light beam incident on the wedge-shaped polarization separation element 111, so that polarization separation is possible. The light beams emitted from the wedge-shaped polarization separation element 111 are condensed by the microlens array 112, but are condensed at different points because the incident angles to the microlens array are different between S-polarized light and P-polarized light. For example, if the half-wavelength element 113 is disposed in the vicinity of the point where the P-polarized light is condensed, the P-polarized light is converted to S-polarized light, and all the light beams emitted from the polarization conversion optical system become S-polarized light. In this system, a microlens array is further added to include a wedge-shaped polarization separation element 121, a first microlens array 122, a second microlens array 123, and a half-wavelength element 124 as shown in FIG. It can be.
JP 2002-228840 A (publication date: August 14, 2002)

  However, in the case of the polarization conversion optical system shown in FIG. 22, the polarization beam splitter is manufactured by laminating a bulk material and cutting it in the direction of 45 degrees, so the thickness in the optical axis direction cannot be reduced, and the entire polarization conversion optical system There was a problem of increasing. In addition, it is difficult to manufacture a polarizing film and a microprism to reduce the size of the polarizing beam splitter in an array.

  In the case of the system shown in FIG. 23, if the microlens array is to be thinned, that is, the focal length must be shortened, the half-wavelength element is accordingly small and it is necessary to form them at a narrow interval. 24, it is difficult to align the two. Furthermore, in the system shown in FIG. 24, the positions of the three bodies of the first microlens array, the second microlens array, and the half-wavelength element are set. There is a problem that it is necessary to arrange with high accuracy, and further, alignment is difficult, and it is impossible to reduce the thickness.

  The thickness of the polarization conversion optical system having the microlenses, polarization separation elements, and the like prepared by the above-described prior art is as large as several tens of millimeters, which has been an obstacle especially for mounting on a direct view type panel. Also, when trying to make these thin, cracks occurred or the strength was insufficient. Further, in manufacturing, each optical element has to be produced by pasting it, which requires labor.

  In view of the above problems, an object of the present invention is to provide a thin polarization conversion element having a good alignment accuracy of an optical element and a method for manufacturing the same.

In order to solve the above problems, the present invention has the following configuration.
The method for manufacturing a polarization conversion optical system according to the present invention includes a polarization separation element, a microlens array, and a polarization conversion element, the macrolens array and the polarization conversion element are positioned with a predetermined accuracy, and the microlens array is formed in advance. And a step of making a substantially parallel light incident on the microlens array at a predetermined incident angle and forming a polarization conversion element using the focused light from the microlens array.

  The step of forming the polarization conversion element includes a step of changing an incident angle of a light beam incident on the microlens array and modulating an irradiation intensity or an irradiation time in accordance with the incident angle. .

  Further, the microlens array has two sets, and the other microlens may be formed using focused light from the microlens array. Further, the polarization separation element may be formed by using focused light from a microlens array.

  The polarization conversion optical system according to the present invention includes a polarization separation element, a microlens array, and a polarization conversion element. The macrolens array and the polarization conversion element are positioned with a predetermined accuracy and are incident on the microlens array. A microlens array or a polarization conversion element different from the microlens array is formed by light. The entire thickness of the polarizing optical system is several mm or less, more preferably 0.2 mm or less.

  Furthermore, the liquid crystal display device of the present invention includes a backlight unit having a light source and a light guide plate, a polarization separation element, a microlens array, and a polarization conversion element, and the macrolens array and the polarization conversion element are positioned with a predetermined accuracy. A polarization conversion optical system, and a liquid crystal panel, and a polarization conversion optical system in which a microlens array or a polarization conversion element different from the microlens array is formed by light incident on the microlens array It is characterized by that. The directivity of the backlight unit is preferably ± 10 degrees or less in terms of a half-value angle.

  According to the present invention, in the polarization conversion optical system, since the alignment accuracy between the microlens array and the polarization conversion element or between the microlens arrays is greatly improved, each can be formed small, and thus can be reduced in thickness. Thus, it can be mounted on a thin display device or the like that could not be mounted conventionally, and the light use efficiency is improved.

  Examples of the present invention will be described below.

  1 and 2 are configuration diagrams of a polarization conversion optical system according to this embodiment. It comprises a wedge-shaped prism 1, a polarization separation material 2, a lens base 3, a microlens array 4, a resin layer 5, and a half-wavelength element 7.

  After the randomly polarized visible light beam enters the wedge prism, it is refracted at the interface between the wedge shape of the wedge prism and the polarization separation material. Here, since the P-polarized light and the S-polarized light have different refractive indexes in the polarization separation material, the P-polarized light is refracted and separated in the arrow direction of FIG. 1, and the S-polarized light is separated in the arrow direction of FIG. Each polarized light is incident on the microlens array at a different incident angle and is condensed on Qa and Qb, respectively. Here, a half-wavelength element 7 is formed in the vicinity of Qa, and the P-polarized light is converted into S-polarized light by the half-wavelength element and is emitted from the polarization conversion optical system. On the other hand, since there is no ½ wavelength element in the vicinity of Qb, it is emitted as S-polarized light. Therefore, in the polarization conversion optical system, it is possible to convert a randomly-polarized light beam into a unidirectional linearly polarized light, and instead of absorbing or reflecting P-polarized light, it is converted to S-polarized light, so that the conversion efficiency is high, Less light loss.

  Next, a manufacturing method of the polarization conversion optical system according to the present embodiment will be described with reference to FIGS. In this manufacturing method, a ½ wavelength element is accurately formed with respect to the position of each microlens array by using the condensing function of the microlens array. First, the microlens array sheet 8 is stuck on the wedge-shaped prism 1 (FIG. 3). The wedge-shaped prism is manufactured by a 2P (Photo-Polymerization) method using a stamper, and the microlens array sheet 8 includes a lens base 3, a microlens array 4, and a resin layer 5. Similarly to the wedge-shaped prism 1, the lens base 3 It is molded by the 2P method using a high refractive index resin and is further flattened by the resin layer 5. Next, the wedge-shaped prism 1 and the microlens array sheet 8 are joined via the polarization separation material 2 (FIG. 4). At this time, the oblique angle δ of the wedge is determined by the relationship between the refractive index nw of the wedge prism, the refractive index np for the P-polarized light and the refractive index ns for the S-polarized light. Liquid crystal is used as the polarization separation material. Subsequently, a karcite or quartz thin plate 10 is attached on the lens base 3 (FIG. 5), and a negative resist 11 is applied thereon (FIG. 6). P-polarized exposure light that is substantially parallel from the wedge prism 1 side. Is incident at a right angle, the light is condensed at point Qa in FIG. 7, and the negative resist near Qa is exposed. Thereafter, development is appropriately performed to remove the unexposed portion of the negative resist (FIG. 7), and wet etching is performed using the remaining resist as a mask (FIG. 8). In the exposure, the remaining area of the negative resist is adjusted by the exposure time. If necessary, the exposure area of the negative resist is optimized by changing the incident angle of the exposure light to the polarization conversion optical system and scanning. Can do. With the above manufacturing method, the polarization conversion optical system of the present invention is obtained (FIG. 9). The polarized light separating material is not limited to the above materials, and other materials such as a resin material may be used as long as they have polarization characteristics.

  Here, the focal length of the microlens is about 50 μm to 1 mm, and if it becomes smaller than 50 μm, the influence of diffraction is exerted, so that the production accuracy is deteriorated, and if it exceeds 1 mm, the merit produced by this production method is reduced. In order to make the whole thickness thinner, it is preferable to set the thickness to 50 μm to 100 μm. The lenses are arranged in a close-packed square, and the lens pitch is about 10 μm to 1 mm, more preferably an array configuration of 10 μm to 100 μm.

  According to the present invention, since the microlens and the half-wavelength element can be accurately aligned, the pitch of the microlens can be set to be small, that is, the focal length can be set small. Can be made thinner. The polarization conversion optical system produced in this way takes a sheet-like appearance, and the overall thickness mainly depends on the thickness of the lens base. The thickness of the lens base is about 50 to 100 μm, and the thicknesses of the other microlens array and the wedge-shaped prism are about 50 μm, respectively. Therefore, the total thickness can be formed to several millimeters. In the case of forming the thinnest, it can be suppressed to about 0.2 mm or less. As a result, it can be mounted on a direct-view type liquid crystal panel, which has been impossible in the past, and the light utilization efficiency can be significantly improved.

  FIG. 10 shows a schematic configuration of a direct-view type liquid crystal display using the polarization conversion optical system according to the present invention. It has a light source 12, a light guide plate 13, a polarization conversion optical system 14, and a liquid crystal panel 15. With this optical system, the light utilization efficiency has been improved to 1.5 to 2.0 times the conventional efficiency. In addition, a scattering plate, a lens sheet, a reflection sheet, etc. (not shown) may be disposed as necessary. At this time, when the light source and the light guide plate are collectively referred to as a backlight unit, it is better that the directivity of the light beam emitted from the backlight unit is high, that is, the intensity distribution is around 0 degree with respect to the light guide plate. It is desirable that the half-value angle is ± 10 degrees or less. As a result, the incident angle of the light beam incident on the sheet-like optical element constituting the polarization conversion optical system is maximized in the vicinity of 0 degrees, and the polarization conversion efficiency is increased.

  Another embodiment will be described with reference to FIGS. 11 and 12 show a wedge-shaped prism 21, a polarization separation material 22, a first microlens array 23, a first resin layer 24, a lens base 25, a second microlens array 26, a second resin layer 27, and a half wavelength. It consists of the element 28. Since the microlens array has a two-layer structure, the second microlens array functions as a so-called relay lens and has an action of refracting a light beam incident from the first microlens to the inside. Therefore, the spread of the light beam can be suppressed.

  After the randomly polarized visible light beam enters the wedge prism, it is refracted at the interface between the wedge shape of the wedge prism and the polarization separation material. Here, since the P-polarized light and the S-polarized light have different refractive indexes in the polarization separation material, the P-polarized light is refracted and separated in the arrow direction of FIG. 11, and the S-polarized light is separated in the arrow direction of FIG. Each polarized light enters the microlens array at a different incident angle, passes through the second microlens array, and is condensed on Qc and Qd, respectively. Here, a half-wave element is formed centering on Qc, P-polarized light is converted to S-polarized light, and emitted from the polarization conversion optical system. On the other hand, since there is no half-wavelength element in the vicinity of Qd, it is emitted as S-polarized light. Therefore, in the polarization conversion optical system, it is possible to convert a randomly-polarized light beam into S-polarized light. Instead of absorbing or reflecting P-polarized light, the light is converted into S-polarized light. Few.

  Next, a manufacturing method of the polarization conversion optical system according to the second embodiment will be described with reference to FIGS. In this manufacturing method, the second microlens array and the ½ wavelength element are accurately formed with respect to the position of each microlens array by using the condensing function of the first microlens array. First, the first microlens array 23 is formed on the lens base 25 by the 2P method (FIG. 13). It is desirable to use a resin having a high refractive index for the lens portion. A first resin layer 24 is formed on the first microlens array 23 and planarized (FIG. 14). Further, an ultraviolet curable resin 26 is applied with a predetermined thickness on the surface of the lens base 25 opposite to the surface on which the first microlens array 23 is formed, and substantially parallel ultraviolet light for exposure is applied from the first microlens array 23 side. Is incident at a predetermined angle, and the ultraviolet curable resin 26 is cured using the light condensing function of the first microlens array 23 (FIG. 15). The ultraviolet curable resin 26 used here desirably has a high refractive index. The exposure light is condensed by the first microlens array and is condensed at the point Ra, and the portion is cured by a thickness corresponding to the exposure amount. When the incident angle to the first microlens array is changed, the condensing point Ra moves, and the second microlens array 27 can be formed by appropriately changing the incident angle and the exposure intensity or scanning speed (see FIG. 16). Thereafter, the wedge prism 21 is bonded to the first lens base through the polarization separation material 22 (FIGS. 17 and 18). After the second resin layer 28 is formed on the second microlens array and flattened, a thin sheet 30 of karcite or quartz is applied on the second resin layer, and a negative resist 31 is applied thereon (see FIG. FIG. 19). When a P-polarized parallel light beam, which is substantially perpendicular to the first lens base, is incident as exposure light, the exposure light is condensed at a point Ua, and the negative resist in the vicinity thereof is exposed. Thereafter, development is appropriately performed to remove the unexposed portion of the negative resist (FIG. 20), and wet etching is performed using the remaining resist as a mask (FIG. 21). In the exposure, the remaining area of the negative resist is adjusted by the exposure time. If necessary, the exposure area of the negative resist is optimized by changing the incident angle of the exposure light to the polarization conversion optical system and scanning. Can do.

  In addition, although a karcite or quartz thin plate is used as the half-wave element 29, for example, a polymer material may be provided with birefringence, and in this case, the thickness can be further reduced. . Instead of the negative resist, it is also possible to use a positive resist. Furthermore, as the polarization separation material, liquid crystal is used, but other materials may be used as long as the refractive index changes depending on the polarization direction. There is no change in the effect of the present application even with a polymer material having optical anisotropy, or with other materials such as crystals.

  By the manufacturing method described above, the alignment accuracy of the microlens array and the polarization conversion element, or the first microlens array and the second microlens array can be improved, and the interval or focal length of the microlens array can be reduced. As a result, the polarization conversion optical system can be reduced in size and thickness.

It is sectional drawing of the polarization conversion optical system which shows the Example of this invention. It is sectional drawing of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a block diagram of the display apparatus carrying the polarization conversion optical system which shows the Example of this invention. It is sectional drawing of the polarization conversion optical system which shows the 2nd Example of this invention. It is sectional drawing of the polarization conversion optical system which shows the 2nd Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is a manufacturing flowchart of the polarization conversion optical system which shows the Example of this invention. It is explanatory drawing which shows a prior art example. It is explanatory drawing which shows a prior art example. It is explanatory drawing which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wedge-shaped prism 2 Polarization separation material 3 Lens base 4 Micro lens array 5 Resin layer 7 1/2 wavelength element 12 Light source 13 Light guide plate 14 Polarization conversion optical system 15 Liquid crystal panel

Claims (10)

A method of manufacturing a polarization conversion optical system having a polarization separation element, a microlens array, and a polarization conversion element, wherein the macro lens array and the polarization conversion element are positioned with a predetermined accuracy,
A step of forming a first microlens array in advance, a substantially parallel light incident on the first microlens array at a predetermined incident angle, and using a focused light from the first microlens array, a polarization conversion element A process for producing a polarization conversion optical system, comprising the step of forming 2. The polarization conversion optical system according to claim 1, wherein the step of forming the polarization conversion element makes an incident angle of a light beam incident on the microlens array variable, and an irradiation intensity or an irradiation time corresponding to the incident angle. The method of manufacturing a polarization conversion optical system according to claim 1, further comprising a step of forming a polarization conversion element. A method of manufacturing a polarization conversion optical system having a polarization separation element, two sets of microlens arrays, and a polarization conversion element, wherein the first macrolens array and the second microlens array are positioned with a predetermined accuracy. ,
A step of forming the first microlens array in advance, a substantially parallel light incident on the first microlens array, and the shape of the second microlens array is formed using the focused light from the first microlens array. A method for manufacturing a polarization conversion optical system, comprising the step of forming. 4. The polarization conversion optical system according to claim 3, wherein the step of forming the second microlens array makes the incident angle of the light beam incident on the first microlens array variable, and corresponds to the incident angle. 4. The method of manufacturing a polarization conversion optical system according to claim 3, further comprising the step of modulating the irradiation intensity or the irradiation time to form a second microlens array. A polarization conversion optical system having a polarization separation element, two sets of microlens arrays, and a polarization conversion element, wherein the first macro lens array, the second microlens array, and the polarization conversion element are positioned with a predetermined accuracy. A method,
Forming a first microlens array in advance, and entering a substantially parallel light into the first microlens array, and forming a polarization conversion element using the focused light from the first microlens array. A manufacturing method of a polarization conversion optical system characterized by the above. 6. The polarization conversion optical system according to claim 5, wherein in the step of forming the polarization conversion element, an incident angle of a light beam incident on the first microlens array is variable, and an irradiation intensity corresponding to the incident angle. 6. The method of manufacturing a polarization conversion optical system according to claim 5, further comprising a step of modulating the irradiation time to form a polarization conversion element. A polarization conversion optical system having a polarization separation element, a microlens array, and a polarization conversion element, wherein the macro lens array and the polarization conversion element are positioned with a predetermined accuracy;
7. The polarization conversion optical system using the manufacturing method according to claim 1, wherein a microlens array or a polarization conversion element different from the microlens array is formed by light incident on the microlens array. 8. The polarization conversion optical system according to claim 7, wherein the thickness of the entire polarization optical system is several 0.2 mm or less. A backlight unit having a light source and a light guide plate; a polarization conversion optical system having a polarization separation element, a microlens array, and a polarization conversion element; and the macro lens array and the polarization conversion element are positioned with a predetermined accuracy; and a liquid crystal A liquid crystal display device having a panel,
A liquid crystal display device comprising a polarization conversion optical system in which a microlens array or a polarization conversion element different from the microlens array is formed by light incident on the microlens array. 10. The liquid crystal display device according to claim 9, wherein the directivity of the backlight unit is ± 10 degrees or less in half value angle.

Images