JP2013015632A - Polarization conversion element and image display apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED To improve the resolution of an image displayed by an image display device. To solve the above problems, an image display device of the present invention comprises:
A polarization conversion element that selectively converts the polarization of incident light into first polarization or second polarization;
A polarization separation element that transmits the first polarized light emitted from the polarization conversion element and reflects the second polarized light;
A first light modulation element on which light of the first polarization transmitted through the polarization separation element is incident;
A second light modulation element on which the second polarized light reflected by the polarization separation element is incident;
[Selection] Figure 1

Description

  The present invention relates to a polarization conversion element and an image display apparatus using the same, and more particularly to an image display apparatus capable of displaying a parallax image for stereoscopic viewing and a polarization conversion element used therefor.

  Conventionally, as a technology of an image display apparatus capable of stereoscopic viewing, Patent Document 1 discloses that the polarization direction of projection light is switched between 0 degrees and 90 degrees between a prism that synthesizes RGB color light and a projection lens. A configuration in which a liquid crystal cell is arranged is disclosed. Patent Document 2 discloses a configuration in which a liquid crystal cell that switches the polarization direction of projection light between clockwise circular polarization and counterclockwise circular polarization is disposed between a prism that synthesizes RGB color light and a projection lens. Has been.

JP-A-2005-065055 JP-A-2005-115276

  However, in the inventions described in Patent Documents 1 and 2, since the liquid crystal cell is disposed in the projection optical path that sensitively affects the imaging performance, the resolution of the projected image is lowered.

  It is an object of the present invention to provide a polarization conversion element capable of displaying an image with reduced resolution and an image display apparatus using the polarization conversion element.

In order to solve the above problems, an image display device according to the present invention provides:
A polarization conversion element that selectively converts the polarization of incident light into first polarization or second polarization;
A polarization separation element that transmits the first polarized light emitted from the polarization conversion element and reflects the second polarized light;
A first light modulation element on which light of the first polarization transmitted through the polarization separation element is incident;
It has the 2nd light modulation element in which the light of the 2nd polarization reflected from the polarization separation element enters.

  In addition, a polarization conversion element that selectively converts the polarization of incident light into the first polarization or the second polarization constitutes one aspect of the present invention.

  An image display device to which the projection optical system is detachably mounted also constitutes one aspect of the present invention.

  The present invention provides a polarization conversion element that selectively changes the direction of polarization in an illumination optical path and emits it, or an image display device that can display a high-resolution image by performing polarization conversion using the polarization conversion element. it can.

Configuration diagram of Embodiment 1 of the present invention Enlarged view of the PBS array of the present invention Front view of the liquid crystal element of the present invention Optical path diagram when polarized light is converted to P-polarized light in the polarization conversion element of the present invention Optical path diagram when polarized light is converted to S-polarized light in the polarization conversion element of the present invention Explanatory drawing of switching of the polarization state in Embodiment 1 of the present invention Enlarged view of another form of PBS array of the present invention Configuration diagram of Embodiment 2 of the present invention Explanatory drawing of the switching of the polarization state in Embodiment 2 of this invention Configuration diagram of Embodiment 3 of the present invention Explanatory drawing of the switching of the polarization state in Embodiment 3 of this invention

(Embodiment 1)
FIG. 1 shows a configuration diagram of an image projection apparatus according to Embodiment 1 of the present invention. The light emitted from the light source 1 is reflected by the reflector 2 and divided into a plurality of light beams by the first fly-eye lens 3 to form a plurality of light source images in the vicinity of the second fly-eye lens 4 and the PBS array 5. To do. The plurality of light beams forming the light source image are converted into a predetermined polarization state by passing through the PBS array 5 and the liquid crystal element 6 (phase conversion element). Then, the light beam that has passed through the liquid crystal element 6 passes through the condenser lens 7 and the polarization separation element 8 to reflect the image display element 9 (first light modulation element) or the image display element 10 (second image). The light modulation element) is uniformly illuminated. Which of the image display elements 9 and 10 is illuminated depends on the polarization state converted by the PBS array 5 and the liquid crystal element 6. Hereinafter, the PBS array 5 and the liquid crystal element 6 are collectively referred to as a polarization conversion element. The illumination optical system is from the light source 1 to the condenser lens 7.

  Light that has entered the image display elements 9 and 10 and whose polarization state has been changed is incident on the polarization separation element 8 again, and is directed toward the projection lens 11 (projection optical system), and returned to the light source 1 side. Separated. If the light toward the projection lens 11 is image light, the image light is magnified by the projection lens 11 and projected onto the screen (projected surface). The projection lens 11 can be detached from the image display apparatus main body.

  The PBS array 5 is composed of a plurality of PBSs 21 (polarization separation surfaces) and a light shielding plate 22 as shown in FIG. The plurality of PBSs 21 are inclined at approximately 45 degrees with respect to the incident surface of the polarization conversion element, and are arranged in the x-axis direction (specific direction) in FIG.

  The liquid crystal element 6 is disposed on the exit side of the PBS array 5, that is, on the condenser lens 7 side. In other words, the PBS array 5 and the liquid crystal element 6 are arranged in order from the light source side to the image display element side. The polarization conversion element 5 is an element that can convert the polarization state of light emitted from the light source 1 into P-polarization (first polarization) or S-polarization (second polarization). Furthermore, it is possible to selectively control whether the polarization is P polarization or S polarization. In this specification, P-polarized light and S-polarized light are defined with reference to the polarization separation surface of the polarization separation element 8.

  The liquid crystal element 6 has a plurality of liquid crystal cells, and when the front surface is a surface having the optical axis of the condenser lens 7 as a normal line, a strip-shaped liquid crystal cell 23 (first liquid crystal cell) as shown in FIG. The liquid crystal cells 24 (second liquid crystal cells) are alternately arranged along the x-axis direction (along a specific direction). Of the polarized light separated by the PBS 21, a liquid crystal cell 23 is disposed on an optical path through which S-polarized light passes, and a liquid crystal cell 24 is disposed on an optical path through which P-polarized light passes. Further, the short side directions of the strip-shaped (rectangular) liquid crystal cells 23 and 24 are arranged in parallel with the x-axis direction.

  The liquid crystal element 6 is an element that can control the phase difference applied to incident light by applying a voltage, and can change the phase of the incident light. Hereinafter, means for controlling the phase difference given to the incident light by the liquid crystal element 6 is referred to as control means. When unpolarized light passing through the PBS array 5 and the liquid crystal element 6 is to be aligned with P-polarized light, a voltage is applied so that the phase difference given to the incident light of the liquid crystal cell 23 shown in FIG. 23 is applied. On the other hand, a voltage is applied to the liquid crystal cell 24 so that the phase difference given to the incident light by the liquid crystal cell 24 becomes zero. Alternatively, in the state where no voltage is applied to the liquid crystal cell 24, when the phase difference applied to the incident light is zero, no voltage is applied.

  As a result, as shown in FIG. 4, the non-polarized light that has passed through the PBS array 5 and the liquid crystal element 6 is converted into P-polarized light, passes through the polarization separation element 8, and illuminates the image display element 10. Of the light whose polarization state has been changed by the image display element 10, the S-polarized component is reflected by the polarization separation element 8 and guided to the projection lens 11 as image light. Then, it is magnified by the projection lens 11 and projected onto the screen.

  When unpolarized light passing through the PBS array 5 and the liquid crystal element 6 is to be aligned with S-polarized light, a voltage is applied so that the phase difference given to the incident light of the liquid crystal cell 24 shown in FIG. 24. On the other hand, the liquid crystal cell 23 does not give a phase difference to the incident light. As a result, as shown in FIG. 5, the unpolarized light that has passed through the PBS array 5 and the liquid crystal element 6 is converted into S-polarized light, reflected by the polarization separation element 8, and illuminates the image display element 9. Of the light whose polarization state has been changed by the image display element 9, the P-polarized component passes through the polarization separation element 8 and is guided to the projection lens 11 as image light. Then, it is enlarged by the projection lens 11 and projected onto the screen.

  As described above, the liquid crystal element 6 is arranged on the emission side of the PBS array 5. Then, the control means controls the phase difference given to the incident light by the liquid crystal cells 23 and 24 of the liquid crystal element 6 to selectively switch the polarization state of the polarized light emitted from the polarization conversion element. It is possible to control the polarization state of the light projected on the screen.

  The illumination light illuminates the image display elements 9 and 10 alternately by controlling so that the polarization state converted by polarization control is switched between P-polarized light and S-polarized light at a predetermined timing. An example is shown in FIG. t1, t2, t3... t6 indicate a table of timings at which the polarization state is switched.

  An image modulated by the image display element 9 and projected via the projection lens 11 is used as an image for the right eye (parallax image), and an image modulated by the image display element 10 and projected via the projection lens 11 is left. Let it be an image for an eye (parallax image). A viewer can see a three-dimensional image (video) by observing this image through polarized glasses.

  As described above, according to the present invention, since a liquid crystal element or the like is not arranged in the projection optical path that sensitively affects the imaging performance, an image (video) with a high resolution (resolution) can be projected.

  In this embodiment, the projection optical path is between the image display elements 9 and 10 and the projection surface, and the illumination optical path is an optical path from the light source 1 to the polarization separation element 8. The image display element and the projection surface are conjugated with each other, and an image formed by the image display element is formed on the projection surface. Therefore, if a liquid crystal element or the like is placed in the projection optical path, the influence of aberrations Appears directly as a blur in the projected image. On the other hand, since the illumination light is intended to illuminate the image display element, even if the liquid crystal element 6 is arranged in the illumination optical path as in the present invention, the resolution is not lowered.

  When a 2D image is projected, non-polarized light is emitted without performing polarization conversion by the polarization conversion element, and both the image display elements 9 and 10 are illuminated by the non-polarized light. At this time, the image display elements 9 and 10 modulate incident light based on the same image signal. Thereby, since the energy which illumination light gives to each image display element is disperse | distributed compared with the case where one image display element is illuminated, an image display element can be used over a long period of time.

  As another form when projecting a 2D image, similarly to the case of projecting a 3D image, the polarization conversion element alternately converts the incident light into P-polarized light and S-polarized light. The image display elements 9 and 10 modulate incident light based on the same image signal. As described above, the illumination light can be incident on different image display elements by switching the state of the polarized light emitted at a predetermined timing. Thereby, the burn-in of the image display element can be reduced.

  Furthermore, when a laser light source is used as the light source 1, it is possible to vary the polarization direction of the projection light that illuminates the screen by varying the polarization direction of the light beam emitted from the polarization conversion element with time. Become. As a result, the speckle noise generated on the screen can be reduced. The above-described advantages in the case of projecting a 2D image can be similarly obtained in the following embodiments.

  In the first embodiment, the polarization conversion element in which the liquid crystal element 6 having the PBS array 5 and the liquid crystal cells 23 and 24 is integrally formed as shown in FIGS. 2 and 3 has been described. However, the present invention is not limited to this, and as shown in FIG. 7, a liquid crystal element is disposed as a separate body at the rear stage (condenser lens side) of a general PBS array (polarization conversion element) having a light shielding plate 25 and a phase difference plate 26. However, the same function can be obtained.

(Embodiment 2)
FIG. 8 shows a configuration diagram of Embodiment 2 of the present invention. The difference from the first embodiment is that color separation is performed using a dichroic mirror 38, and the light source 1 to the condenser lens 7 are the same as in the first embodiment.

  The dichroic mirror 38 transmits G light (green wavelength band light, first color light), B light (blue wavelength band light, second color light) and R light (red wavelength band light, third color light). ) Is reflected. The light reflected by the dichroic mirror 38 is only R light by the wavelength-selective phase plate 39, the polarization direction of which is rotated by approximately 90 degrees, and the B light and R light are rotated by the first polarization separation element 40 (polarization beam splitter). To be separated. Thereafter, among the light whose polarization state has been changed by the image display element 42 and the image display element 41, the image light is projected through the first polarization separation element 40 and the synthesis prism 43 (color synthesis element, optical path synthesis element). The image is enlarged and projected on the screen by the lens 11. The combining prism 43 has a characteristic of reflecting G light regardless of the polarization direction and transmitting R light and B light regardless of the polarization direction.

  Which of B light and R light reflected by the dichroic mirror 38 illuminates the image display element 42 and the image display element 41 depends on whether the unpolarized light is P-polarized in the PBS array 5 and the liquid crystal element 6 (polarization conversion element). Depending on whether the light is converted to S-polarized light or S-polarized light. If the polarized light is converted into P-polarized light by the polarization conversion element, the R light enters the image display element 42 and is projected on the screen as P-polarized image light. At this time, the B light enters the image display element 41 and is projected onto the screen as S-polarized image light. On the other hand, when the light is converted into S-polarized light by the polarization conversion element, the light is incident on the image display element 41 and is projected on the screen as S-polarized image light. At this time, the B light enters the image display element 42 and is projected onto the screen as P-polarized image light. In the second embodiment, the image display elements illuminated by the R light and the B light are switched depending on the polarization direction to which the polarization conversion is performed.

  The same applies to the G light transmitted through the dichroic mirror 38. When the light is converted into P-polarized light, it is incident on the image display element 47 and projected onto the screen as S-polarized image light. On the other hand, when the light is converted to S-polarized light, it is incident on the image display element 46 and projected onto the screen as P-polarized image light.

  Here, assuming that P-polarized image light is incident on the right eye and S-polarized image light is incident on the left eye, the image display elements 42 and 46 correspond to the right eye, and the image display elements 41, 47 corresponds to the left eye. FIG. 9 shows a relationship table between the timing at which the polarization conversion element switches the polarization state of the emitted light and the color light incident on each image display element.

(Embodiment 3)
FIG. 10 shows a configuration diagram of Embodiment 3 of the present invention. The steps from the light source 1 to the condenser lens 7 are the same as those in the first embodiment. The light transmitted through the dichroic mirror 58 that transmits R light and G light and reflects B light is separated by a dichroic mirror 59 that transmits R light and reflects G light. The R light transmitted through the dichroic mirror 59 illuminates the image display element 61 or the image display element 62 via the polarization separation element 60. The image light reflected by the image display element 61 or 62 is reflected by the cross prism 63 and enlarged and projected on the screen via the projection lens 64.

  The G light is reflected by the dichroic mirror 59 and then illuminates the image display element 66 or the image display element 67 via the polarization separation element 65. The image light reflected by the image display elements 66 and 67 passes through the cross prism 63 and is enlarged and projected on the screen via the projection lens 64.

  The B light is reflected by the dichroic mirror 58 and then illuminates the image display element 71 or the image display element 72 via the mirror 68, the relay lens 69, and the polarization separation element 70. The image light reflected by the image display element is reflected by the cross prism 63 in the same manner as the R light and G light, and is enlarged and projected on the screen via the projection lens 64. The cross prism 63 has a first color separation surface for R light transmission, G light transmission, and B light reflection, and a second color separation surface for R light reflection, G light transmission, and B light transmission.

  In the third embodiment, similarly to the second embodiment, two image display elements are arranged with respect to the polarization separation element arranged between the condenser lens 7 and the image display element. Which of the two image display elements is illuminated depends on the polarization direction in which the polarization is converted by the PBS array 5 and the liquid crystal element 6 (polarization conversion element). FIG. 11 shows a relationship table between the timing at which the polarization conversion element switches the polarization state of the emitted light and the color light incident on each image display element.

  As another embodiment, the liquid crystal element 6 is controlled to give a phase difference of λ / 4 to each of the P-polarized light and the S-polarized light separated by the PBS array 5 to emit the polarization conversion element. The direction of polarization of the light beam can be aligned with clockwise circularly polarized light or counterclockwise circularly polarized light. Then, by arranging the λ / 4 plate at the subsequent stage (on the condenser lens side) of the liquid crystal element 6, the polarization direction of the light beam incident on the polarization conversion element can be aligned with P-polarized light or S-polarized light. In this way, the polarization state of the light beam emitted from the polarization conversion element may be switched every time.

  Note that a polarization conversion element that is disposed between the light source and the light modulation element and selectively converts the polarization of incident light into the first polarization or the second polarization also constitutes one aspect of the present invention. Thereby, since the polarization conversion element is disposed in the illumination optical path, an image with higher resolution can be displayed. When this polarization conversion element is used in an image display apparatus having the constituent elements described in the first to third embodiments, a more preferable form is obtained. The component includes a polarization separation element that transmits the first polarization light emitted from the polarization conversion element and reflects the second polarization light, and a first polarization light that is transmitted through the polarization separation element. And a second light modulation element on which the light of the second polarization reflected by the polarization separation element is incident.

1 Light source 5 PBS array 6 Liquid crystal element 9, 10 Image display element

Claims (9)

A polarization conversion element that selectively converts the polarization of incident light into first polarization or second polarization;
A polarization separation element that transmits the first polarized light emitted from the polarization conversion element and reflects the second polarized light;
A first light modulation element on which light of the first polarization transmitted through the polarization separation element is incident;
An image display device comprising: a second light modulation element on which light of the second polarization reflected by the polarization separation element is incident. The polarization conversion element includes a polarization separation surface that separates light according to polarization, and
A phase conversion element that converts the phase of each light separated by the polarization separation surface;
The image display device according to claim 1, wherein the polarization of incident light is selectively converted into the first polarization or the second polarization by changing a phase converted by the phase conversion element. The phase conversion element is a liquid crystal element capable of controlling a phase difference applied to incident light,
The image display device according to claim 2, wherein the liquid crystal element gives different phase differences to the first polarized light and the second polarized light separated by the polarization separation surface. . The liquid crystal element has a first liquid crystal cell and a second liquid crystal cell,
The first liquid crystal cell and the second liquid crystal cell are alternately arranged along the incident surface of the polarization conversion element,
The first liquid crystal cell is disposed on an optical path of the light of the first polarization separated by the polarization separation surface,
The second liquid crystal cell is disposed on an optical path of the light of the second polarization separated by the polarization separation surface,
When the polarization conversion element controls the polarization state of the light emitted from the polarization conversion element to be the first polarization, the phase difference that the first liquid crystal cell imparts to the incident light becomes zero. The second liquid crystal cell controls the phase difference imparted to the incident light to be λ / 2,
When controlling the polarization state of the light emitted from the polarization conversion element to be the second polarization, the first liquid crystal cell is controlled so that the phase difference imparted to the incident light is λ / 2, The image display device according to claim 3, wherein the second liquid crystal cell controls the phase difference applied to incident light to be zero.   5. The image display device according to claim 1, wherein the polarization conversion element alternately converts the polarization of incident light into a first polarization or a second polarization. 6. Having a light source,
The image display device according to claim 1, wherein the light source is a laser light source.   The image display apparatus according to claim 1, wherein the first light modulation element and the second light modulation element modulate incident light based on the same image signal.   8. The projection optical system according to claim 1, further comprising a projection optical system that projects image light modulated by the first light modulation element and the second light modulation element onto a projection surface. 9. Image display device.   A polarization conversion element that is disposed between the light source and the light modulation element and selectively converts the polarization of incident light into the first polarization or the second polarization.

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