JP5794442B2 - Projection-type image display device - Google Patents

Description

  The present invention relates to an illumination device that uses coherent light such as laser light, a projection-type image display device that illuminates a light modulation element using the coherent light as a light source, and projects an image on a screen, and to these The present invention relates to an optical device.

  2. Description of the Related Art A projector (projection-type image display device) is known in which illumination light from a light source is imaged using a light modulation element (micro display) such as liquid crystal or MEMS and projected onto a screen. Among such projectors, a projector using a white light source such as a high-pressure mercury lamp as the light source is known, and an image obtained by illuminating a two-dimensional light modulation element such as a liquid crystal is magnified by a projection optical system. The image is projected above.

  However, high-intensity discharge lamps such as high-pressure mercury lamps have a relatively short life and need to be frequently replaced when used in projectors. In addition, there is a drawback that the apparatus itself is increased in size. Furthermore, the specification of a high-pressure mercury lamp that uses mercury is not preferable from the viewpoint of environmental load. In order to eliminate such drawbacks, a projector using laser light as a light source has been proposed. The semiconductor laser has a longer life than a high-pressure mercury lamp or the like, and the entire apparatus can be reduced in size.

  Thus, since the laser beam expected as the next-generation light source of the projector is excellent in straightness, it is considered that the light incident efficiency can be improved as compared with the LED or the like. However, when laser light is used as a light source, there is a drawback that speckle noise is generated due to high coherence and it is difficult to view an image.

  Speckle noise is speckled noise caused by interference of light scattered from minute irregularities on the surface of the irradiation object when coherent laser light is used as the light source. As well as causing physiological discomfort to the observer. In order to reduce this speckle noise, various attempts have been made, such as vibrating the diffusion plate through which the laser beam passes, expanding the wavelength spectrum of the laser spectrum, and vibrating the screen itself that is the target of the laser beam irradiation. . As an attempt to reduce such speckle noise, Patent Document 1 discloses a non-speckle display device that reduces speckle noise by rotating a diffusion element through which coherent light passes.

Japanese Patent Laid-Open No. 6-208089

  However, in the speckle noise reduction method disclosed in Patent Document 1, speckle noise (interference pattern) generated before reaching the diffusing element can be averaged, but the incident ray angle from the diffusion center to the screen is on the screen. Since it is invariant at any point, the light scattering characteristic of each point on the screen becomes constant, and as a result, there is a problem that the effect of removing speckle noise generated on the screen is hardly obtained.

Such speckle caused by coherent light is a problem not only in a projection-type image display device (projector) that uses coherent light as a light source but also in various illumination devices that use coherent light.

  The first object of the present invention is to provide an illumination device that suppresses speckles generated when coherent light is used as a light source, and a projection-type image display device using such an illumination device. Furthermore, an object of the present invention is to effectively illuminate an illuminated area and to improve the light utilization efficiency in such an illumination device and projection type image display device. Further, the object is to uniformly illuminate the entire illuminated area by illuminating the illuminated area under substantially the same conditions.

A projection-type image display device according to the present invention includes:
A light source that emits coherent light;
An optical scanning unit that scans coherent light emitted from the light source;
A light modulation element having an image forming region on which an image is formed;
Beam shaping means provided between the light source and the optical scanning unit;
An optical path conversion system set so that coherent light scanned by the optical scanning unit illuminates the image forming region over time;
A projection optical system that projects an image of the light modulation element onto a screen,
The beam shaping means uniformizes the intensity distribution of the cross section of the coherent light from the light source on the surface in the vicinity of the optical scanning unit,
The optical path conversion system is arranged such that the surface in the vicinity of the optical scanning unit is conjugate to the light modulation element surface of the light modulation element,
The incident angle of coherent light incident on each point of the image forming region varies with time.

Furthermore, in the projection type image display device according to the present invention,
The beam shaping means transforms the cross-sectional shape of the coherent light from the light source into the shape of the light modulation element,
The optical path conversion system is characterized in that the aperture of the coherent light is adjusted so as to illuminate at least a part of the image forming area in the light modulation element.

Furthermore, the projection type image display device according to the present invention is:
A light source that emits coherent light;
An optical scanning unit that scans coherent light emitted from the light source;
A light modulation element having an image forming region on which an image is formed;
Beam shaping means provided between the light source and the optical scanning unit;
An optical path conversion system set so that coherent light scanned by the optical scanning unit illuminates the image forming region over time;
A projection optical system that projects an image of the light modulation element onto a screen,
The beam shaping means transforms the cross-sectional shape of the coherent light from the light source into the shape of the light modulation element,
The optical path conversion system adjusts the aperture of the coherent light so as to illuminate at least a part of the image forming area in the light modulation element,
The incident angle of coherent light incident on each point of the image forming region varies with time.

Furthermore, in the projection type image display device according to the present invention,
The beam shaping means includes a beam expander.

  According to the illuminating device of the present invention, the illumination light emitted from the optical path changing system irradiates the illuminated area at different angles in time by scanning the coherent light with the optical scanning unit. It is possible to make the speckles generated in the invisible state invisible to the observer. Furthermore, in the projection type image display apparatus of the present invention, speckles generated on the screen can be effectively suppressed by irradiating the screen at different angles in time.

The figure which shows the structure of the projection type video display apparatus provided with the illuminating device which concerns on embodiment of this invention. The figure which shows the structure of the illuminating device which concerns on embodiment of this invention. The figure which shows the structure of the optical scanning part (variable diffraction type element) which concerns on other embodiment of this invention. The figure which shows the mode of the structure and phase change of the optical scanning part (phase modulation element) which concern on other embodiment of this invention. The figure which shows the mode of the phase change in the optical scanning part (phase modulation element) which concerns on other embodiment of this invention.

  Now, an illumination device and a projection display apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a projection-type image display device including an illumination device according to an embodiment of the present invention. Note that the drawings described below are schematic views and may differ from actual shapes, dimensions, and arrangements.

  The projection-type image display device 10 according to the present embodiment includes an illumination device 20, a light modulation element 31 for forming an image, a projection optical system 32 that projects an image formed by the light modulation element 31 onto a screen 41, and the like. ing. In the figure, the screen 41 on which an image is projected is an XY plane, and an axis perpendicular to the XY plane is a Z axis. As the screen 41, either a reflective screen for observing an image reflected by the screen 41 or a transmissive screen for observing an image transmitted through the screen 41 can be used.

  The illuminating device 20 of this embodiment includes a light source 11, an optical scanning unit 15, and an optical path conversion system 21. The optical device referred to in the present invention includes the light scanning unit 15 and the optical path conversion system 21 excluding the light source 11 from the illumination device 20.

  As the light source 11, various laser devices such as a semiconductor laser device that emits laser light as coherent light are used. The coherent light emitted from the light source 11 illuminates the optical scanning unit 15. In addition, it is preferable to provide beam shaping means for uniforming the intensity distribution in the cross-sectional direction of the coherent light emitted from the light source 11. As a design example, a beam shaping unit is provided so as to be uniform on the surface in the vicinity of the optical scanning unit, and the illumination region is set by setting the optical path conversion system 21 so that the surface and the light modulation element surface are conjugated. It becomes possible to illuminate with uniform intensity. Further, the beam shaping means may be one that makes the intensity uniform and at the same time changes the cross-sectional shape of the laser beam into the shape of the light modulation element. Further, the aperture of the coherent light to be emitted may be adjusted by a beam expander according to various conditions such as the size of the image forming area of the light modulation element 31 as the illuminated area and the enlargement ratio of the optical path conversion system 21.

The optical scanning unit 15 is an optical element that temporally changes the direction of coherent light emitted from the light source 11. In the present embodiment, a galvanometer mirror capable of rotating the reflecting surface around the rotation center Ra is used. In addition, a polygon mirror and a MEMS scanner may be used as the movable mirror device that mechanically rotates the movable mirror. In addition to the movable mirror device, a variable diffractive element or a phase modulation element that changes the emission direction by electrically changing a diffraction condition may be used. Since such an element does not have a movable part unlike a movable mirror device, it is possible to reduce the process burden during manufacturing or maintenance. Details will be described later.

  The optical scanning unit 15 of the present embodiment has a rotation center Ra in the Y-axis direction, and performs one-dimensional scanning that scans coherent light in the XZ plane. Either one-dimensional scanning or two-dimensional scanning may be used for the light scanning. In any case, it is necessary to scan the incident surface of the optical path conversion system 21 and to sufficiently illuminate the illuminated area as a result.

  The coherent light incident from the light source 11 becomes scanning light La whose direction changes temporally in the optical scanning unit 15 and enters the optical path conversion system 21. In the figure, the states of the scanning light La (t1) and La (t2) near the outermost end are shown, but actually the scanning light La passes between La (t1) and La (t2). It will move continuously or intermittently over time.

  The optical path conversion system 21 is an optical element that illuminates an image forming area as an illuminated area with the scanning light La emitted from the optical scanning unit 15. The scanning light La optically scanned by the optical scanning unit 15 illuminates the illuminated area through this optical path conversion system 21 so as to overlap with time. In particular, in the present embodiment, the optical path conversion system 21 constantly illuminates the entire image forming region of the light modulation element 31 as the illuminated region regardless of the scanning position of the light scanning unit 15. Improvements are being made. Further, by constantly illuminating the image forming area with parallel light or substantially parallel light, each point of the image forming area is illuminated under the same conditions, and for example, the entire image forming area can be illuminated uniformly. It has become.

  The light modulation element 31 is a display having an image forming area in which an image is formed based on a video signal. In this embodiment, a transmissive liquid crystal display element is used. As the light modulation element 31, in addition to such a transmission type, a reflection type such as MEMS can be used. The illumination light Lb from the optical path conversion system 21 enters the light modulation element 31 while changing the incident angle with time, and is converted into the modulated light Lc based on the image displayed in the image forming area.

  The projection optical system 32 enlarges and converts the modulated light Lc from the light modulation element 31 into the image reproduction light Ld and projects it onto the screen 41. In the present embodiment, a diaphragm 33 is provided downstream of the projection optical system 32.

  Now, the principle and the like of the illumination device 20 which is a main configuration for suppressing speckles in the projection display apparatus 10 will be described in detail. FIG. 2 is a diagram illustrating a configuration of the illumination device 20 according to the embodiment of the present invention, and is a diagram illustrating a state of illumination by the optical path conversion system 21.

  As shown in FIG. 2, the scanning light La (t1) at time t1 enters the optical path conversion system 21 and illuminates light Lb (illuminating at least a part of the image forming region in the light modulation element 31). After being converted to t1), the area is illuminated. Similarly, the scanning light La (t2) at time t2 is converted into illumination light Lb (t2) by the optical path conversion system 21, and then illuminates at least a part of the image forming region. As shown in this figure, the illuminating device 20 illuminates the entire image forming area while temporally changing the incident angle with respect to the illuminated area.

The optical path conversion system 21 in the present embodiment is composed of a first light collecting element 21a and a second light collecting element 21b. As shown in the figure, the first light collecting element 21a has a front focal length of F1_a,
The rear focal length is F1_b, and the rotation center Ra of the optical scanning unit 15 is located at the front focal position. On the other hand, in the second condensing element 21b, the front focal length is F2_a, the rear focal length is F2_b, and the incident surface of the light modulation element 31 is located at the rear focal position. And the back focal position of the 1st condensing element 21a is arrange | positioned so that it may be located in the front focal position of the 2nd condensing element 21b.

  As the 1st condensing element 21a and the 2nd condensing element 21b, what is necessary is just to have a function which has a condensing function, and a lens, a concave mirror, etc. are used. You may implement | achieve with the hologram element, diffraction element, etc. which have an equivalent function. Moreover, you may implement | achieve by these combination. In addition, the optical path conversion system 21 only needs to have a function such that the scanned coherent light illuminates the illuminated region over time. In addition to the combination of condensing elements, a plurality of mirrors and a plurality of prisms are used. It may be realized by a plurality of light guide elements, an optical fiber array, or the like.

  With such an optical arrangement of the first condensing element 21a and the second condensing element 21b, the parallel or substantially parallel coherent light incident from the light source 11 is always parallel to the entire predetermined region of the light modulation element 31. It is possible to illuminate with substantially parallel illumination light Lb. In the present embodiment, a predetermined area illuminated by the illumination light Lb is set as an image forming area in the light modulation element 31. By constantly illuminating the entire image forming area, the light use efficiency can be improved. Furthermore, by using the parallel or substantially parallel illumination light Lb, each point in the image forming region can be illuminated under the same conditions.

  The optical path conversion system 21 has been described as being configured by the first condensing element 21a and the second condensing element 21b. However, the configuration of the optical path conversion system 21 is not limited to this embodiment, and the scanning light La What is necessary is just to illuminate at least a part of the image forming area as the illuminated area and to illuminate the entire image forming area over time as the optical scanning unit 15 performs the optical scanning.

  Returning to FIG. 1, the modulated light Lc modulated by the light modulation element 31 is magnified by the projection optical system 32 and projected onto the screen 41 as the image reproduction light Ld, and the reflected or transmitted image is observed by the observer. Let At this time, the coherent light diffused on the surface of the screen 41 interferes with each other to cause speckle. However, in this embodiment, since the coherent light is scanned by the optical scanning unit 15, as a result, the incident angle of the image reproduction light Ld projected on the screen 41 is changed with time, and this speckle is very effectively conspicuous. It is lost.

  At the point P1 on the screen shown in FIG. 1, for example, the video reproduction light Ld (t1) at time t1 and the video reproduction light Ld (t2) at time t2 are irradiated at different incident angles. The same applies to other points P2 shown in the figure and other points not shown, and the image reproduction light Ld projects an image on the screen 41 while changing the incident angle with time. Therefore, speckles formed on the screen in a very short time are averaged in time within the visual response time by the image reproduction light Ld being irradiated at different incident angles depending on the time, and projected onto the screen 41. This is not sufficiently conspicuous for an observer who observes an image.

  The speckles observed by the observer are not only speckles generated due to the scattering of coherent light on the screen 41 as described above, but also those generated on various optical elements of the projection display apparatus 10. is there. This speckle is projected on the screen 41 via the light modulation element 31 and is observed by the observer. In the present embodiment, the scanning light La scans the optical path conversion system 21 so that speckles generated in various optical elements of the projection display apparatus 10 can be made inconspicuous.

  As described above, in the present embodiment in FIGS. 1 and 2, the movable mirror device using the galvano mirror has been described for the optical scanning unit 15, but a variable diffraction element or a phase modulation element having no movable part is used. It is also possible to do. FIG. 3 is a diagram illustrating a configuration of an optical scanning unit (variable diffraction element) according to another embodiment of the present invention, and FIG. 4 illustrates an optical scanning unit (phase modulation element) according to another embodiment of the present invention. ) And the state of phase change. FIG. 5 is a view showing the state of phase change in an optical scanning unit (phase modulation element) according to another embodiment of the present invention.

  The optical scanning unit 15 in FIG. 3 is an embodiment using a variable diffractive element, and in this embodiment, an amplitude modulation type liquid crystal element is used as the variable diffractive element. The liquid crystal element constituting the optical scanning unit 15 forms a diffraction grating with the liquid crystal 151. By changing the diffraction angle by changing the pitch of the diffraction grating formed by the liquid crystal 151 with time, the emission direction of the coherent light incident from the light source 11 can be changed with time. In the present embodiment, by making the coherent light incident obliquely with respect to the incident surface of the optical scanning unit 15, it is possible to escape the zero-order light and emit the diffracted light in the normal direction of the element.

  In addition to the liquid crystal element, an optical element that modulates the phase of light passing therethrough may be used as the variable diffraction element. Alternatively, a micromirror device that modulates the phase of the reflected light can be used.

  The optical scanning unit 15 in FIG. 4 is an embodiment using a phase modulation element, and in this embodiment, a liquid crystal element that modulates only the phase is used. FIG. 4A is a diagram showing this configuration example, and the optical scanning unit 15 includes a liquid crystal layer 152 sealed between transparent substrates 153 and 154. The liquid crystal layer 152 is provided with a pixel electrode 152a and a common electrode 152b provided for each part, and the phase of transmitted light can be changed by changing the refractive index over time for each part. It has become.

  FIG. 4B is a diagram showing a basic type of phase change, and the phase distribution is shown in a form corresponding to the configuration diagram of FIG. By changing the bias applied to the pixel electrode 152a with time, for example, a phase distribution as shown at times t1 and t2 can be formed. In such a phase distribution, as shown in FIG. 4A, the scanning light La (t1) can be deflected to the state of the scanning light La (t2) at the time t1, and at the time t2. In practice, the direction of the scanning light La can be changed in multiple steps or continuously by changing the phase state of t1 and the phase state of t2 in multiple steps or continuously.

  FIG. 5 is a diagram showing another form of phase change, in which the deflection condition is changed over time by changing the phase distribution into a kinoform type, that is, by changing a pattern that repeats from 0 to 2π over time. As in the case of FIG. 4B, the deflection direction is changed. This figure shows the phase distribution corresponding to the configuration diagram of FIG. 4A, as in FIG. 4B, and FIG. 5A shows the phase state at time t1, and FIG. 5 (e) shows the phase state at time t2. Coherent light incident from the light source 11 is deflected by temporally changing the phase shape between FIGS. 5A to 5E and 5E to 5A. The phase distribution may be a Fresnel lens type set in a range other than 0 to 2π.

  As described above, when the phase modulation element is used in the optical scanning unit 15, the zero-order light is not generated unlike the case where the variable diffraction element is used, so that the light use efficiency is improved. Further, as shown in the figure, it is possible to make coherent light incident perpendicular to the incident surface of the optical scanning unit 15.

As described above, according to the present embodiment, an illumination device in which speckle noise is not noticeable, and a projection-type image that can provide an image in which speckle noise is not noticeable by illuminating the light modulation element 31 with the illumination device. A display device can be provided. In particular, in this embodiment, the light utilization efficiency is improved by illuminating the light scanned by the light scanning unit 15 via the optical path conversion system 21.

  Note that the present invention is not limited to these embodiments, and embodiments configured by appropriately combining the configurations of the respective embodiments also fall within the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Projection type image display apparatus 11 ... Light source 15 ... Optical scanning part 151 ... Liquid crystal 152 ... Liquid crystal layer 152a ... Pixel electrode 152b ... Common electrode 153, 154 ... Transparent base material 21 ... Optical path conversion system 21a ... 1st condensing element 21b ... Second light collecting element

Claims (4)

A light source that emits coherent light;
An optical scanning unit that scans coherent light emitted from the light source;
A light modulation element having an image forming region on which an image is formed;
Beam shaping means provided between the light source and the optical scanning unit;
An optical path conversion system set so that coherent light scanned by the optical scanning unit illuminates the image forming region over time;
A projection optical system that projects an image of the light modulation element onto a screen,
The beam shaping means uniformizes the intensity distribution of the cross section of the coherent light from the light source on the surface in the vicinity of the optical scanning unit,
The optical path conversion system is arranged such that the surface in the vicinity of the optical scanning unit is conjugate to the light modulation element surface of the light modulation element,
An incident angle of coherent light incident on each point of the image forming region changes with time. In the projection type video display device according to claim 1,
The beam shaping means transforms the cross-sectional shape of the coherent light from the light source into the shape of the light modulation element,
The projection type image display apparatus, wherein the optical path conversion system adjusts a diameter of coherent light so as to illuminate at least a part of an image forming region in the light modulation element. A light source that emits coherent light;
An optical scanning unit that scans coherent light emitted from the light source;
A light modulation element having an image forming region on which an image is formed;
Beam shaping means provided between the light source and the optical scanning unit;
An optical path conversion system set so that coherent light scanned by the optical scanning unit illuminates the image forming region over time;
A projection optical system that projects an image of the light modulation element onto a screen,
The beam shaping means transforms the cross-sectional shape of the coherent light from the light source into the shape of the light modulation element,
The optical path conversion system adjusts the aperture of the coherent light so as to illuminate at least a part of the image forming area in the light modulation element,
An incident angle of coherent light incident on each point of the image forming region changes with time. In the projection type video display device according to any one of claims 1 to 3,
The beam shaping means includes a beam expander.

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