JP2007033676A - Polarized light converting optical element, optical modulation module, and projection type image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inexpensive polarized light converting optical system having less degradation in the performance with time. <P>SOLUTION: The polarized light converting optical system includes at least a polarized light separating means 1 to separate two orthogonal polarized light components from each other, and a polarized light varying means 2 to vary a polarization state, and is capable of aligning the polarization state of exiting light into one direction independent of the polarization state of incident light, wherein at least either the polarized light separating means 1 or the polarized light varying means 2 has a fine rugged structure with a pitch shorter than the wavelength used. Since at least either the polarized light separating means 1 or the polarized light varying means 2 is fabricated by using a fine rugged structure smaller than the wavelength, the system can be inexpensively mass-produced by means of nano-scale imprinting, photolithography or the like, while the stability of performances with time can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarization conversion optical element that aligns the polarization direction of light from a randomly polarized light source, a light modulation module using the polarization conversion optical element, and a projection type image display apparatus using the light modulation module.

  In a conventional projection type image display device such as a projector, a discharge lamp such as a high-pressure mercury lamp or a metal halide lamp is used as a light source. Light from the light source is guided to a light valve such as a liquid crystal, and light modulated by the light valve is projected. Projected onto the screen by a lens. At this time, the light incident on the liquid crystal needs to be linearly polarized light that vibrates in a single direction. However, since the light from the discharge lamp is randomly polarized, the light used in the liquid crystal is from the discharge lamp. The light utilization efficiency is deteriorated because the light is less than half of the light. Therefore, a “polarization conversion optical system” that aligns the polarization direction of light from the light source in one direction is necessary. Conventionally, as such a polarization conversion optical system, a polarization beam splitter and a phase difference as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2002-23106) and Patent Document 2 (Japanese Patent Laid-Open No. 2002-244221) are used. A polarization conversion optical system combining plates is used. A typical structure example is shown in FIG.

  In FIG. 14, light from a discharge lamp (not shown) is converted into substantially parallel light by a reflector (not shown), and the light collected by the microlens arrays 201 and 202 enters the polarization beam splitter 203 and passes through the polarization beam splitter 203. The polarized light is rotated 90 ° by a λ / 2 plate (phase difference plate) 204 and incident on a superimposing lens (not shown). The light reflected by the polarizing beam splitter 203 is bent 90 ° by a mirror 205. And enters a superimposing lens (not shown). The light incident on the superimposing lens is superimposed on a light valve such as a liquid crystal (not shown), and the light valve such as a liquid crystal is uniformly irradiated with linearly polarized light having a uniform polarization direction.

Japanese Patent Laid-Open No. 2002-23106 Japanese Patent Application Laid-Open No. 2002-244211 Mool C. Gupta and S. T. Peng, “Diffraction characteristics of surface-relief gratings”, Appl. Opt., Vol. 32, No. 16 (1993)

  In the polarization conversion optical system in FIG. 14, the polarization beam splitter 203 is usually realized by a multilayer film structure in which a large number of optical films having different refractive indexes are stacked on a substrate. A polarizing beam splitter using this multilayer film structure is expensive due to many man-hours and the necessity of vacuum deposition. Furthermore, since the inside of the projector is very hot and the polarization conversion optical system is used in a high temperature environment, there is a problem that the performance deteriorates with time due to the occurrence of microcracks or the like. In order to enhance the polarization separation function, a larger number of optical films are required, and it is difficult to achieve both high performance and low cost. Further, there is a problem that it is difficult to control the film thickness of each layer and it is difficult to realize a desired polarization separation function.

  In addition, the λ / 2 plate (retardation plate) 204 is often realized using a polymer, but the retardation plate using a polymer is also vulnerable to heat, like the polarizing beam splitter. Therefore, the performance deteriorates over time.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polarization conversion optical system that is small in performance deterioration with time and low in cost, a light modulation module using the polarization conversion optical system, and the light An object of the present invention is to provide a projection type image display apparatus using a modulation module.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention has at least polarization separating means for separating two orthogonal polarization components and polarization changing means for changing the polarization state, and polarization of the emitted light regardless of the polarization state of the incident light. In a polarization conversion optical system capable of aligning states in one direction, at least one of the polarization separation unit and the polarization change unit has a fine concavo-convex structure with a pitch shorter than a wavelength to be used. (Claim 1).

The second means of the present invention has a reflection means and a phase change means in the polarization conversion optical system of the first means, and the polarization separation means is one linearly polarized light component of two orthogonal linearly polarized light. And the other linearly polarized light component is transmitted, and the reflected linearly polarized component is reflected by the reflecting means and passed through the phase changing means (claim 2). ).
The third means of the present invention has a reflecting means and a phase changing means in the polarization conversion optical system of the first means, and the polarization separating means is one of two orthogonal linearly polarized lights. The polarized light component is reflected and the other linearly polarized light component is transmitted, and the transmitted linearly polarized light component is reflected by the reflecting means and passed through the phase changing means. Item 3).

According to a fourth means of the present invention, in the polarization conversion optical system of any one of the first to third means, at least the polarization separation means and the polarization changing means are configured to be parallel to each other. (Claim 4).
According to a fifth means of the present invention, in the polarization conversion optical system of any one of the first to fourth means, the polarization separation means and the polarization change means are integrated on a single optical element. (Claim 5).
Further, a sixth means of the present invention is the polarization conversion optical system according to any one of the first to fifth means, wherein the same surface of a single optical element is divided into a plurality of areas, and the divided areas are divided. The polarization separation means and the polarization change means are formed in each of the above (claim 6).

According to a seventh means of the present invention, in the polarization conversion optical system of any one of the second to sixth means, the reflecting means and the polarization changing means are integrated on a single optical element. (Claim 7).
According to an eighth means of the present invention, in the polarization conversion optical system of any one of the second to seventh means, the reflection means, the polarization separation means, and the polarization changing means are on a single optical element. (Claim 8).

  According to a ninth means of the present invention, in the polarization conversion optical system of the first means, the polarization separation means bends and transmits one linearly polarized light component of two orthogonal linearly polarized light and transmits the other straight line. The traveling direction of two orthogonal linearly polarized light is separated so that the polarization component is transmitted as it is, and one component of the separated linearly polarized light is transmitted through the polarization changing means and rotated by 90 °. The other component of the separated linearly polarized light is bent once again by the optical path deflecting unit, and the traveling direction of the linearly polarized component transmitted through the polarization changing unit and the linearly polarized component transmitted through the optical path deflecting unit is substantially parallel. It is comprised so that it may become (Claim 9).

According to a tenth means of the present invention, in the polarization conversion optical system according to the ninth means, the optical path deflecting means has a fine concavo-convex structure with a pitch shorter than the wavelength to be used.
According to an eleventh means of the present invention, in the polarization conversion optical system of the ninth or tenth means, the polarization changing means and the optical path deflecting means are integrated on a single optical element. (Claim 11).

A twelfth means of the present invention is a light modulation module, comprising: a light source; a polarization conversion optical system of any one of the first to eleventh means; and a light modulation means for modulating the intensity distribution of the light source. (Claim 12).
According to a thirteenth means of the present invention, in the light modulation module of the twelfth means, the light source is a light emitting diode (LED).
Further, the fourteenth means of the present invention is the light modulation module of the twelfth or thirteenth means, wherein the light source is an LED array, and one of the first to eleventh ones corresponding to one LED of the LED array. A polarization conversion optical system as one means is provided (claim 14).

  A fifteenth means of the present invention is a projection-type image display device, a light modulation module of any one of the twelfth to fourteenth means, and a projection lens that projects the intensity distribution of the light modulation module onto an image plane. (Claim 15).

  In the polarization conversion optical system according to the first to third means of the present invention, since at least one of the polarization separation means and the polarization change means is realized by using a fine concavo-convex structure of a wavelength or less, nanoimprinting or photo Not only can it be produced in large quantities at low cost by means such as lithography, but also the stability of performance over time can be improved.

In the polarization conversion optical system of the fourth means of the present invention, since the polarization separation means and the polarization change means are configured in parallel, the polarization conversion optical system can be downsized.
Further, in the polarization conversion optical system of the fifth and sixth means of the present invention, since the polarization separation means and the polarization change means are integrated, high stability is achieved by reducing relative positional fluctuations over time. Cost reduction can be realized by omitting the alignment process and reducing the number of parts.

In the polarization conversion optical system of the seventh means of the present invention, since the reflecting means and the polarization changing means are integrated, high stabilization by reducing the relative position variation with time and the omission of the alignment process and parts Cost reduction can be realized by reducing the number of points.
In the polarization conversion optical system of the eighth means of the present invention, since the reflection means, the polarization change means, and the polarization separation function are integrated, it is possible to achieve high stabilization by reducing relative positional fluctuations over time. Cost reduction can be realized by omitting the alignment process and reducing the number of parts.

In the polarization conversion optical system of the ninth and tenth means of the present invention, at least one of the polarization separation means and the polarization change means is realized by using a fine structure having a wavelength equal to or less than the wavelength. Not only can it be produced in large quantities at low cost by means such as lithography, but also the stability of performance over time can be improved.
Further, in the polarization conversion optical system of the eleventh means of the present invention, since the polarization changing means and the polarization separating means are integrated, high stabilization by reduction of relative position variation with time and alignment process can be achieved. Cost reduction can be realized by omission or reduction of the number of parts.

In the light modulation module of the twelfth means of the present invention, a highly stable and low-cost light modulation module can be realized by using a polarization conversion optical system that has stable performance over time and is low in cost. it can.
In the light modulation modules of the thirteenth and fourteenth means of the present invention, a light modulation module with low power consumption can be realized by using an LED as the light source.

  In the projection image display apparatus of the fifteenth means of the present invention, a highly stable and low-cost light modulation module is used, so that a highly stable and low-cost projection image display apparatus can be realized.

  Embodiments of a polarization conversion optical system according to the present invention, a light modulation module using the same, and a projection type image display device using the light modulation module will be described in detail with reference to the drawings.

[Embodiment 1 (embodiment of first and second means)]
As a first embodiment of the present invention, an embodiment of a polarization conversion optical system is shown in FIG. The polarization conversion optical system shown in FIG. 1A includes a polarization separation unit 1, a polarization changing unit 2, and a reflection unit 3. Specifically, the polarization separation unit 1 is a reflective polarization beam splitter, The polarization changing means 2 is composed of a retardation plate, and the reflecting means 3 is composed of a mirror. In FIG. 1A, in the polarization conversion optical system of the present embodiment, a polarization separation means (polarization beam splitter) 1, a phase change means (phase difference plate) 2, and a reflection means (mirror) 3 are arranged substantially in parallel. The incident light is incident on the polarization separation means (polarization beam splitter) 1 at an angle.

  Next, the operation principle of the polarization conversion optical system shown in FIG. 1 will be described. In FIG. 1A, incident light that is randomly polarized light is first separated into two linearly polarized light (S-polarized light and P-polarized light) by a reflective polarization beam splitter 1. In FIG. 1A, the polarization separating means 1 is a polarizing beam splitter that reflects S-polarized light and transmits P-polarized light. However, it may be a polarizing beam splitter that reflects P-polarized light and transmits S-polarized light. The light reflected by the polarization beam splitter 1 enters the phase difference plate 2, the polarization state is changed by the phase difference plate 2, and then the polarization state is changed again by the phase difference plate 2 by reflection by the mirror 3. After that, the light is incident on the polarization beam splitter 1 again. Here, if the retardation plate 2 is designed so that the retardation plate 2 functions as a λ / 2 wavelength plate (λ / 4 wavelength plate on one side) in a reciprocating manner with respect to the incident light, the polarizing beam splitter is first prepared. Since the polarization direction of the light transmitted through 1 matches the polarization direction of the light transmitted through the phase difference plate 2, the optical system as shown in FIG. 1A aligns the polarization direction of the light from the light source in one direction. It can function as a “polarization conversion optical system”.

  As shown in FIG. 1, it is best to arrange the polarization beam splitter 1, the phase difference plate 2, and the mirror 3 so as to be parallel, but it is not always necessary to be parallel, and the polarization conversion optical system is increased in size. Although there is a demerit, it is possible to realize an equivalent function.

  Here, in the polarization conversion optical system as shown in FIG. 1A, it is preferable to control the divergence angle of the incident light using a lens or the like so that the incident light is not blocked by the mirror. This is shown in FIG. In FIG. 1B, the incident light is drawn so as to be converted into a convergent light beam by the lens 4. However, if it is not shielded by the mirror 3, it does not need to be a convergent light beam, and may be a parallel light beam or a divergent light beam.

  As the reflective polarization beam splitter 1, a wire grid polarization beam splitter may be used. FIG. 2 shows a typical structure of the wire grid type polarization beam splitter. In FIG. 2, a fine grid structure in which a metal 1b such as aluminum is formed (embedded) is formed on a transparent substrate 1a. By making the microgrid structure below the wavelength order, it can function as a reflective polarization beam splitter. Polarized light parallel to the fine line direction of the microgrid structure is reflected and polarized light in the orthogonal direction is transmitted. To do.

  As another configuration example that functions as a reflective polarization beam splitter, Non-Patent Document 1 (Mool C. Gupta and STPeng, “Diffraction characteristics of surface-relief gratings”, Appl. Opt., Vol. 32, No. 1). 16 (1993)), it is possible to reflect one polarized light and transmit the other light using a fine concavo-convex structure of a wavelength or less.

  The common point between the two types of polarizing beam splitters described above is that a fine concavo-convex structure with a wavelength or less is used. For example, a wire grid type polarization beam splitter as shown in FIG. 2 can be used to produce the structure as described above, using the photolithography technique, and the reflection type described in Non-Patent Document 1 described above. The polarizing beam splitter can be manufactured using nanoimprinting technology or the like, and both can be manufactured in large quantities at low cost. Furthermore, since both of the above two types of polarizing beam splitters realize the polarizing beam splitter function due to the structure of the element itself, performance deterioration with time is very small even when used in a high temperature environment. Good stability. Therefore, by using the configuration of this embodiment, it is possible to realize a polarization conversion optical system that is low in cost and very stable in performance over time.

  Next, FIG. 3 shows an example in which the retardation film 2 is configured using a fine concavo-convex structure having a wavelength or less. When the fine concavo-convex structure 2b of a wavelength or less is formed on the substrate 2a to realize the configuration as shown in FIG. 3, strong birefringence occurs depending on the polarization direction. Therefore, an arbitrary phase delay amount can be realized by controlling the period and depth of the fine concavo-convex structure 2b and the fill factor (ratio of the convex area to the concave area of the fine concavo-convex structure). A board can be obtained.

  FIG. 1 shows an embodiment in which the light passes through the retardation plate 2 twice. The light transmitted through the polarizing beam splitter 1 is first transmitted through the polarizing beam splitter 1 and then again. The phase difference plate 2 is designed so as to cause a phase change of λ / 2 in a reciprocating manner before being incident on 1. Further, an optical system that passes only once before or after reflection by the mirror 3 may be realized, but it is preferable that the retardation plate 2 pass twice. This is because by passing the phase difference plate 2 twice, it is sufficient to function as a λ / 4 plate in one pass, and the amount of phase change caused by passing the phase difference plate 1 once can be reduced. The aspect ratio of the fine concavo-convex structure 2b (the ratio between the pitch and the depth of the fine concavo-convex structure 2b) can be reduced, and the fabrication becomes easy.

  As a merit of realizing the retardation plate 2 using the fine concavo-convex structure 2b of a wavelength or less, the phase change is realized by the structure of the element itself, similar to the polarizing beam splitter 1, so that it can be used in a high temperature environment. However, there is very little performance deterioration with time and stability is good.

[Embodiment 2 (embodiment of first and third means)]
As a second embodiment of the present invention, another embodiment of the polarization conversion optical system is shown in FIG. In FIG. 4A, incident light that is randomly polarized light is first transmitted through one of the linearly polarized light components and reflected from the other linearly polarized light component by the reflective polarization beam splitter 1 that is a polarization separating means. . In FIG. 4A, a polarizing beam splitter that reflects S-polarized light and transmits P-polarized light is used. However, a polarizing beam splitter that reflects P-polarized light and transmits S-polarized light is used. It may be used. The light transmitted through the polarization beam splitter 1 is reflected by the mirror 3, passes through the polarization beam splitter 1 again, passes through the phase difference plate 2, and the polarization state is changed. At this time, if the phase difference plate 2 is designed as a λ / 2 plate, a “polarization conversion optical system” capable of aligning the polarization direction of randomly polarized light in one direction can be obtained.

  In FIG. 4A, the light that has passed through the phase difference plate 2 before entering the polarization beam splitter 1 is not successfully polarized and converted, so that the incident light is incident using the lens 4 as shown in FIG. 4B. It is preferable that the light divergence angle is controlled so as to be incident only on the polarization beam splitter 1. In FIG. 4B, it is drawn as if it has been converted into a convergent light beam by the lens 4, but it is not necessarily a convergent light beam. .

  As shown in FIG. 4, it is best to arrange the polarization beam splitter 1, the phase difference plate 2, and the mirror 3 so as to be parallel, but it is not always necessary to be parallel, and the polarization conversion optical system is increased in size. Although there is a demerit, it is possible to realize an equivalent function.

[Example 3 (Examples of the fourth and fifth means)]
In the first or second embodiment described above, the polarization separating means 1 such as a polarizing beam splitter and the polarization changing means 2 such as a phase difference plate are preferably configured to be parallel (fourth). Means). By doing so, it is possible to reduce the size of the polarization conversion optical system.

  In the first and second embodiments, the polarization separating means (polarizing beam splitter) 1 and the polarization changing means (phase difference plate) 2 are preferably formed integrally on a single optical element. As a result, there is no performance degradation due to relative position fluctuations over time and stability can be further improved over time. Cost reduction by reduction or the like can be realized.

  FIG. 5 shows an example in which a polarizing beam splitter and a phase difference plate are configured using a fine concavo-convex structure of a wavelength or less and integrated on a single optical element. In FIG. 5A, a polarizing beam splitter 11 formed using a fine concavo-convex structure of a wavelength or less is formed on one surface (incident surface side) of a single substrate 10, and the other surface (exit surface side) is formed. FIG. 5B is an example of an optical element 13 having a retardation plate 12 formed using a fine uneven structure having a wavelength or less. FIG. 5B shows a fine uneven structure having a wavelength or less on one surface of a single substrate 20. An example of an optical element 23 formed by superposing a polarizing beam splitter 21 realized by using and a phase difference plate 22 realized by using a fine concavo-convex structure of a wavelength or less is shown. The operation principle of the polarization conversion optical system using the optical elements 13 and 23 shown in FIGS. 5A and 5B is the same as that in FIG.

[Example 4 (Example of sixth means)]
As a fourth embodiment of the present invention, in FIG. 6, the polarization separation means (polarization beam splitter) and the polarization change means (phase difference plate) of the polarization conversion optical system are integrated on a single optical element. Another embodiment is shown.
6A and 6B, the same surface of the substrate 30 of the single optical element 33 (or 34) is divided into a plurality of regions, and the polarized light separating means ( A polarization beam splitter) 31 and a polarization changing means (phase difference plate) 32 are formed. Here, FIG. 6A shows that light having the same direction of linearly polarized light is obtained in the direction of transmission through the polarization conversion optical system, and the operating principle is the same as in FIG. FIG. 6B shows the operation principle similar to that of FIG. 4, in which light with the same direction of linearly polarized light is obtained in the direction reflected by the polarization conversion optical system. 6A and 6B, on one surface of a single substrate 30, a fine concavo-convex structure having a subwavelength functioning as the polarizing beam splitter 31 and a fine concavo-convex structure having a subwavelength functioning as the phase difference plate 32 are provided. Are formed by dividing the region.

[Example 5 (Example of the seventh means)]
As a fifth embodiment of the present invention, FIG. 7 shows an example of an optical element in which a mirror of a polarization conversion optical system and a retardation plate using a fine concavo-convex structure of a wavelength or less are integrated. By integrating the mirror and phase difference plate on the same substrate, there is no performance degradation due to relative position fluctuation over time, etc., and it is possible not only to further improve the stability over time, but also to be integrated. By doing so, it is possible to realize cost reduction by omitting the alignment process and the like and reducing the number of parts.
Furthermore, in the polarization conversion optical system using this optical element, it passes through the retardation plate of the fine concavo-convex structure twice, so the aspect ratio of the fine concavo-convex structure can be reduced, and the production becomes easy. Cost reduction can be realized.

FIG. 7A-1 shows an example of the optical element 40 in which a metal is formed on the back surface of the substrate 41 on which the retardation plate 42 using the fine concavo-convex structure is formed, and is caused to act as the mirror 43. a-2) shows a configuration example of a polarization conversion optical system using the optical element 40. Since the principle of operation of this polarization conversion optical system is the same as that in FIG. 1, its description is omitted here.
FIG. 7B-1 is an example of the optical element 50 in which a metal is formed on the fine concavo-convex structure formed on the substrate 51 to act as the mirror 53, and FIG. 2 shows a configuration example of a polarization conversion optical system using the optical element 50. Since the principle of operation of this polarization conversion optical system is the same as that in FIG. 1, its description is omitted here.
In the above example, a mirror is used as the reflecting means. However, total reflection may be used as the reflecting means.

[Embodiment 6 (Embodiment of Eighth Means)]
As a sixth embodiment of the present invention, FIGS. 8A and 8B show an example in which a polarization beam splitter 61, a phase difference plate 62, and a mirror 63 are integrated on the same optical elements 64 and 65. FIG. In this way, by integrating all the optical components used on a single optical element, it is possible to greatly reduce performance degradation due to relative position fluctuations over time, and further improve stability over time. In addition to being able to be made, by forming them in an integrated manner, it is possible to realize cost reduction by omitting the alignment process and reducing the number of parts.

In FIG. 8A, a mirror 63 is further integrated on an optical element 64 having a configuration in which a polarization beam splitter 61 and a retardation plate 62 are formed on the same substrate (or spacer) 60 as in FIG. 6A. FIG. The principle of operation of the polarization conversion optical system using this optical element 64 is the same as that shown in FIG.
Further, in FIG. 8B, similarly to FIG. 6B, a mirror 63 is further integrated on an optical element 65 having a configuration in which a polarizing beam splitter 61 and a retardation plate 62 are formed on the same substrate (or spacer) 60. FIG. Since the principle of operation of the polarization conversion optical system using this optical element 65 is the same as that in FIG. 4, the description thereof is omitted here.

[Example 7 (Examples of ninth to eleventh means)]
As a seventh embodiment of the present invention, FIG. 9 shows another embodiment of the polarization conversion optical system. First, the operation principle of the polarization conversion optical system will be described with reference to FIG. Randomly polarized light from a light source (not shown) is separated in the traveling direction of two orthogonal linearly polarized light components by the polarization separating means 71 (in the figure, the P-polarized light travels straight and the S-polarized light travels with its optical path bent. Among the separated linearly polarized light components, the folded polarized light component is bent by the optical path deflecting unit 73 and proceeds. That is, the polarization separation means 71 in FIG. 9A is a transmission type polarization beam splitter. On the other hand, the linearly polarized light component that has been transmitted straight through the polarization separation means 71 is transmitted through the phase difference plate (λ / 2 plate) 72, so that the polarization direction is rotated by 90 °. At this time, it is preferable that the traveling direction of the linearly polarized light component transmitted through the phase difference plate 72 and the linearly polarized light component bent by the optical path deflecting unit 73 is substantially parallel.

  Here, the transmission type polarization beam splitter 71, the phase difference plate 72, and the optical path deflecting unit 73 are preferably configured using a fine uneven structure having a wavelength equal to or less than the wavelength, and as a result, a high-temperature environment such as the inside of the projector apparatus. In use, the performance deterioration with time is very small and the stability is good.

  FIG. 9B shows an example in which a transmission type polarization beam splitter is configured using a fine concavo-convex structure of a wavelength or less. Next, the principle of operation will be described. In FIG. 9B, the fine concavo-convex structure is formed at a pitch equal to or smaller than the wavelength, the width of the convex portion varies depending on the location, and the height of the convex portion is set to 2π with respect to the wavelength used. deep. When two types of linearly polarized light (1) and (2) are incident on a polarizing beam splitter having such a structure as shown in the figure, the linearly polarized light parallel to the groove (linearly polarized light of (2)) is grooved. Since the height of 2π is 2π, it feels like there is no groove, so it passes through as it is. When linearly polarized light perpendicular to the groove (linearly polarized light of (1)) is incident, the width of the convex portion varies depending on the location. In the case of FIG. 9B, the left side of the paper feels a higher refractive index, On the other hand, the refractive index is felt low. Therefore, FIG. 9B is equivalent to a prism as shown in FIG. 9C, and one linearly polarized light is transmitted as it is as shown in FIG. 9B, but the other linearly polarized light is bent. To Penetrate. In addition, said phenomenon is a phenomenon which appears when the pitch of a fine concavo-convex structure becomes below a wavelength.

Here, since the incident light other than the polarization separation means is not converted in polarization, as shown in FIG. 9D, the light incident on the polarization conversion optical system is polarized and separated by controlling the divergence angle by the lens 75 or the like. It needs to be incident only on the means. 9 (a) and 9 (d) show an embodiment in which the light incident on the light other than the polarization separation means 71 is shielded by the light shielding plate 74. However, as shown in FIG. 9 (d), the lens 75 is used. For example, the light shielding plate 74 is not necessarily required when light is incident only on the polarization separation means 71 using the above-described technique.
In addition, about the optical path deflection | deviation element 73 comprised using the fine concavo-convex structure below a wavelength, it is realizable by setting it as the structure similar to FIG.9 (b).

  Here, as shown in FIG. 9A, both the phase difference plate 72 and the optical path deflecting means 73 are formed using a fine concavo-convex structure of a wavelength or less, and are formed as an optical element integrated on a single substrate. It is good to do. By integrating the phase difference plate 72 and the optical path deflecting unit 73 on a single optical element, the phase difference plate 72 and the optical path polarizing unit 73 can be manufactured in a lump, thereby realizing cost reduction. In addition, the relative position fluctuation between the phase difference plate 72 and the optical path deflecting unit 73 can be greatly reduced over time, so that the performance over time can be stabilized.

[Embodiment 8 (Embodiments of the 12th to 14th means)]
As an eighth embodiment of the present invention, FIG. 10 shows an embodiment of a light modulation module configured using the polarization conversion optical system of the present invention. FIG. 10A is an example in which the polarization direction is converted into linearly polarized light in a single direction by the polarization conversion optical system 85 of the present invention using a discharge lamp 81 such as a high pressure mercury lamp or a metal halide lamp as a light source. FIG. 10B shows an example in which a light emitting diode (LED) 91 is used as a light source, light from the LED 91 is incident on a polarization conversion optical system 93, and the polarization direction is converted into linearly polarized light in a single direction. FIG. 10C shows an example in which one polarization conversion optical system 93 is provided for each LED 91 using an LED array 98 in which a plurality of LEDs 91 are arranged as a light source.

  First, the light modulation module in FIG. 10A will be described. The randomly polarized light beam emitted from the discharge lamp 81 is converted into substantially parallel light by the reflector 82 and then divided into a plurality of light beams by the lens arrays 83 and 84, and the divided light beam is polarized by the polarization conversion optical system 85. The direction is converted to linearly polarized light in a single direction. The split luminous flux that is linearly polarized light in a single direction is superimposed on the liquid crystal panel 88 by the superimposing lens 86 and illuminated uniformly. Here, the field lens 87 plays a role of allowing the split light beam to enter the liquid crystal panel 88 as substantially parallel light.

Next, for the light modulation module of FIG. 10B, the randomly polarized light beam emitted from the LED 91 is converted into a convergent light beam by the lens 92 and converted into a single linearly polarized light by the polarization conversion optical system 93. The light is divided into a plurality of light beams by the lens array 94 and superimposed on the liquid crystal panel 97 by the superimposing lens 95 to illuminate the liquid crystal panel 97 uniformly. Here, the field lens 87 plays a role of allowing the split light beam to enter the liquid crystal panel 88 as substantially parallel light.
In FIG. 10B, the light from the LED 91 is converted into a convergent light beam by the lens 92, when the light beam from the LED 91 is incident on the polarization conversion optical system 93 without being blocked by the mirror 3 or the like. It is not always necessary to use the lens 92. If the polarization conversion optical system 93 is disposed near the light emitting point, polarization conversion can be performed without light loss due to light shielding or the like without using a lens. Is possible.

Next, with respect to the light modulation module of FIG. 10C, the randomly polarized light beam emitted from each LED 91 of the LED array 98 is converted into a single linearly polarized light by the polarization conversion optical system 93 and then the lens array 94. The light beam is divided into a plurality of light beams and is superimposed on the liquid crystal panel 97 by the superimposing lens 95 to illuminate the liquid crystal panel 97 uniformly. Here, the field lens 87 plays a role of allowing the split light beam to enter the liquid crystal panel 88 as substantially parallel light.
In the light modulation module of FIG. 10C, the intensity of illumination light on the liquid crystal panel 97 can be increased by adopting the same configuration for the plurality of LEDs 91.

As described above, in the conventional polarization conversion optical system shown in FIG. 14, the polarization beam splitter 203 configured with a multilayer film structure is usually used, which is not only expensive but also vulnerable to heat. There is a problem that the performance deteriorates over time due to microcracks or the like generated by using in a high temperature environment. In addition, in order to enhance the polarization separation function, since a larger number of optical films are required, it is difficult to achieve both high performance and low cost, and it is difficult to control the film thickness of each layer. There is also a problem that it is difficult to realize the separation function.
In addition, the λ / 2 plate (retardation plate) 204 used in FIG. 14 is often realized using a polymer, but the retardation plate using a polymer is also the same as the polarizing beam splitter described above. Similarly, there is a problem that the performance deteriorates over time due to the disadvantage of being weak against heat.

  In contrast, in the polarization conversion optical system of the present invention, as described in Examples 1 to 7, the function as a polarization beam splitter is realized by using only a fine uneven structure of a wavelength or less without using a multilayer film structure. The wire grid type polarization beam splitter of FIG. 2 can be manufactured using photolithography technology or the like, and the polarization beam splitter described in Non-Patent Document 1 can be manufactured using nanoimprinting technology or the like, Both can be produced inexpensively. Furthermore, both of the two types of polarizing beam splitters described above have realized the polarizing beam splitter function with a fine concavo-convex structure, so even when used in a high temperature environment, there is very little deterioration in performance over time, Good stability. Therefore, by using the polarization conversion optical system of the present invention, it is possible to realize a light modulation module that is low in cost and has good performance stability over time.

  Further, as shown in FIGS. 10B and 10C, the light modulation module using the LED 91 or the LED array 98 as a light source has a high power-to-light conversion efficiency of the LED, and is very advantageous for low power consumption. It is. Further, since the LED is very thin, it is advantageous for miniaturization. However, since the light from the LED is randomly polarized, the polarization conversion optical system 93 is necessary for effective use of the light. Therefore, by using the polarization conversion optical system of the present invention, an optical modulation module with low power consumption can be realized.

[Embodiment 9 (Embodiment of Fifteenth Means)]
As a ninth embodiment of the present invention, FIGS. 11 to 13 show a configuration example of a projection type image display apparatus (for example, a liquid crystal projector) configured by a light modulation module using the polarization conversion optical system of the present invention and a projection optical system. Show.
First, the configuration and operation will be described with reference to FIG. This liquid crystal projector includes a light modulation module having the configuration described in the eighth embodiment, and a projection optical system including a projection lens that projects the intensity distribution of the light modulation module onto an image plane. Randomly polarized light emitted from the LED array (herein referred to as an LED array) is converted into a single linearly polarized light by the polarization conversion optical system 102 of the present invention. At this time, the divergence angle of the LED is controlled by a lens or the like so that there is no light loss in the polarization conversion optical system 102. Thereafter, the light is divided into a plurality of light beams by the lens array 103. The plurality of light beams are superimposed on the liquid crystal panels 112R, 112G, and 112B by the superimposing lens 104. A field lens (not shown) is arranged in front of each liquid crystal panel 112R, 112G, 112B so that the liquid crystal panel is illuminated with substantially parallel light.

  In the light source 101, LED arrays of three colors of red (R), green (G), and blue (B) are simultaneously mounted on one substrate, and a lens and a polarization conversion optical system 102 are provided for each LED. ing. With this configuration, the light source unit can be downsized and the entire projector can be downsized. The light transmitted through the superimposing lens 104 is decomposed for each color by the color light separation optical system. First, the light transmitted through the superimposing lens 104 is transmitted by the dichroic mirror 105, and the red component is transmitted and the other components are reflected. The red component transmitted through the dichroic mirror 105 is reflected by the mirror 111 and applied to the red liquid crystal panel 112R. For the light other than the red light component reflected by the dichroic mirror 105, the green component is reflected by the dichroic mirror 106 and the blue component is transmitted. The green component reflected by the dichroic mirror 106 is applied to the green liquid crystal panel 112G. The blue component transmitted through the dichroic mirror 106 is irradiated to the blue liquid crystal panel 112B through the lenses 107 and 109 and the mirrors 108 and 110.

  As described above, the R, G, and B colors are guided to the corresponding liquid crystal panels 112R, 112G, and 112B, respectively. Then, after being modulated for each color by the liquid crystal panels 112R, 112G, and 112B, synthesized by the synthesis prism 114, and projected onto a screen (not shown) by the projection optical system 113 including a projection lens and the like.

The example of FIG. 11 is a configuration example of a so-called “three-plate type” liquid crystal projector, and includes liquid crystal panels 112R, 112G, and 112B corresponding to R, G, and B, respectively.
On the other hand, FIG. 12 includes R, G, and B LED arrays 101R, 101G, and 101B, polarization conversion optical systems 102R, 102G, and 102B, and a single liquid crystal panel 112, and R, G, and B are time-divisionally divided. This is an example of a liquid crystal projector configured by using a so-called “field sequential method” in which the liquid crystal panel 112 is switched sequentially and in synchronization therewith. One of the merits of using an LED as the light source is that the LED can be switched ON / OFF at high speed, so that a field sequential method can be used, and the liquid crystal panel 112 can be shared by R, G, and B. It is possible to achieve downsizing and cost reduction.

  In FIG. 12, the R, G, and B LED arrays 101R, 101G, and 101B are provided as separate substrates. However, as shown in the configuration example of FIG. It is desirable to mount colored LEDs. By making it like FIG. 13, since further size reduction and cost reduction are realizable, it is the most suitable.

  11 to 13 are configured using a transmission type polarization conversion optical system as shown in FIG. 1, but are configured using a reflection type polarization conversion optical system as shown in FIG. You can also.

It is a figure which shows one Example of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of a polarization conversion optical system. It is a figure which shows an example of the polarization separation means used for the polarization conversion optical system of this invention, Comprising: It is a schematic perspective view of a wire grid type polarization beam splitter. It is a figure which shows an example of the phase difference plate used for the polarization conversion optical system of this invention, Comprising: It is a schematic perspective view of the phase difference plate comprised using the fine concavo-convex structure below a wavelength. It is a figure which shows another Example of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of a polarization conversion optical system. It is a figure which shows an example of the optical element used for the polarization conversion optical system of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of an optical element which integrated the polarization separation means and the polarization change means on the board | substrate. It is a figure which shows another example of the optical element used for the polarization conversion optical system of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of an optical element which integrated the polarization separation means and the polarization change means on the same surface of a board | substrate. is there. It is a figure which shows another example of the optical element used for the polarization conversion optical system of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of an optical element which integrated the polarization change means and the mirror on the board | substrate. It is a figure which shows another example of the optical element used for the polarization conversion optical system of this invention, Comprising: It is a figure which shows the structural example of the optical element which integrated the polarization separation means, the polarization change means, and the mirror on the board | substrate. It is a figure which shows another Example of this invention, Comprising: It is explanatory drawing of a structure and operation | movement of a polarization conversion optical system. It is a figure which shows the structural example of the light modulation module comprised using the polarization conversion optical system of this invention. It is a schematic block diagram which shows an example of the projection type image display apparatus (liquid crystal projector) comprised using the polarization conversion optical system of this invention. It is a schematic block diagram which shows another example of the projection type image display apparatus (liquid crystal projector) comprised using the polarization conversion optical system of this invention. It is a schematic block diagram which shows another example of the projection type image display apparatus (liquid crystal projector) comprised using the polarization conversion optical system of this invention. It is a figure which shows an example of the conventional polarization conversion optical system.

Explanation of symbols

1, 11, 21, 31, 61, 71: Polarization separation means (polarization beam splitter)
2, 12, 22, 32, 42, 52, 62, 72: Polarization changing means (retardation plate)
3, 43, 53, 63: Mirror 4, 75: Lens 73: Optical path deflecting means 81: Discharge lamp 82: Reflector 83, 84, 94, 103: Lens array 85, 93, 102: Polarization converting optical system 86, 95, 104: Superimposing lens 87, 96: Field lens 88, 97, 112: Liquid crystal panel 91: Light emitting diode (LED)
98: LED array 113: Projection optical system (projection lens, etc.)

Claims (15)

It has at least a polarization separation means that separates two orthogonal polarization components and a polarization change means that changes the polarization state, and can align the polarization state of the emitted light in one direction regardless of the polarization state of the incident light. In a polarization conversion optical system,
At least one of the polarized light separating means and the polarized light changing means has a fine concavo-convex structure with a pitch shorter than the wavelength to be used. The polarization conversion optical system according to claim 1,
A reflection means and a phase change means, wherein the polarization separation means is configured to reflect one of two orthogonal linearly polarized light components and to transmit the other linearly polarized light component; The polarization conversion optical system characterized in that the linearly polarized light component is reflected by the reflecting means and passes through the phase changing means. The polarization conversion optical system according to claim 1,
A reflection means and a phase change means, wherein the polarization separating means is configured to reflect one of the two orthogonally polarized light components and to transmit the other linearly polarized light component; The polarization conversion optical system characterized in that the linearly polarized light component is reflected by the reflecting means and passes through the phase changing means. In the polarization conversion optical system according to any one of claims 1 to 3,
At least the polarization separation unit and the polarization changing unit are configured to be parallel to each other. In the polarization conversion optical system according to any one of claims 1 to 4,
The polarization conversion optical system, wherein the polarization separation means and the polarization change means are integrated on a single optical element. The polarization conversion optical system according to any one of claims 1 to 5,
A polarization conversion optical system, wherein the same surface of a single optical element is divided into a plurality of regions, and the polarization separation unit and the polarization change unit are formed in each of the divided regions. In the polarization conversion optical system according to any one of claims 2 to 6,
The polarization converting optical system, wherein the reflecting means and the polarization changing means are integrated on a single optical element. In the polarization conversion optical system according to any one of claims 2 to 7,
The polarization converting optical system, wherein the reflecting means, the polarization separating means, and the polarization changing means are integrated on a single optical element. The polarization conversion optical system according to claim 1,
The polarization separation means separates the traveling direction of two orthogonal linearly polarized light so that one of the two orthogonally polarized light is bent and transmitted, and the other linearly polarized light is transmitted as it is. One component of the separated linearly polarized light is transmitted through the polarization changing means and the polarization direction is rotated by 90 °, and the other component of the separated linearly polarized light is bent once again by the optical path deflecting means. In addition, the polarization conversion optical system is configured such that the traveling directions of the linearly polarized light component transmitted through the polarization changing unit and the linearly polarized light component transmitted through the optical path deflecting unit are substantially parallel to each other. In the polarization conversion optical system according to claim 9,
The polarization conversion optical system, wherein the optical path deflecting unit has a fine concavo-convex structure with a pitch shorter than a wavelength to be used. The polarization conversion optical system according to claim 9 or 10,
The polarization conversion optical system, wherein the polarization changing unit and the optical path deflecting unit are integrated on a single optical element.   An optical modulation module comprising: a light source; the polarization conversion optical system according to claim 1; and an optical modulation unit that modulates an intensity distribution of the light source. The light modulation module according to claim 12,
The light modulation module, wherein the light source is a light emitting diode (LED). The light modulation module according to claim 12 or 13,
12. The light modulation module according to claim 1, wherein the light source is an LED array, and the polarization conversion optical system according to claim 1 is provided corresponding to one LED of the LED array. 15. A projection-type image display device comprising: the light modulation module according to claim 12; and a projection lens that projects an intensity distribution of the light modulation module onto an image plane.

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