JP2010152178A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device capable of reducing the number of speckles while keeping high quality of image. <P>SOLUTION: This image display device includes a light source 10 emitting light, a half mirror 30 arranged on an optical path of the light L emitted from the light source 10 and separating the light L into a first beam La and a second beam Lb, a scanning optical system 50 for scanning the first beam La and the second beam Lb in the two dimensional direction on a screen 1000 to draw an image, and a phase modulating means 40 arranged on the optical path of light from the light source 10 to the scanning optical system 50 and changing phase of the second beam Lb by time by controlling length of the optical path related to the second beam Lb. The scanning optical system 50 applies each of the first beam La and the second beam Lb on the same drawing point X on the screen 1000 at different angles of incidence θa, θb. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image display device.

  In recent years, projectors (image display devices) using a laser light source have been developed with the increase in output of semiconductor lasers and the appearance of blue semiconductor lasers. Since this type of projector has a narrow wavelength range of the laser light source, the color reproduction range can be sufficiently widened, and the size and the number of components can be reduced. This has great potential as a next-generation projector.

  However, when displaying on a projector using a laser light source, a phenomenon called so-called speckle occurs in which light spots and dark spots are distributed in a striped pattern or a spotted pattern due to light interference caused by a scatterer such as a screen. There is a case.

  Speckle causes an adverse effect such as giving glare to an observer and giving an uncomfortable feeling when viewing an image. In particular, since laser light is highly coherent (coherent) light, speckle is likely to occur. In addition to the laser light source, speckle problems similarly occur when an LED is used as the light source, and in recent years, even in the case of a lamp light source, the coherence of light has been increased by shortening the arc. . Therefore, a technique for removing speckle has become important.

  As means for reducing speckle, for example, the following method is known. One is a method of making speckle patterns difficult to see by generating speckles of a plurality of patterns using light having low coherence (incoherent) with each other and simultaneously superimposing a plurality of speckles. There is (Method 1).

  For example, in Patent Document 1, by utilizing the fact that polarized lights having different polarization directions are incoherent, the laser light emitted from the light source is separated into two polarized lights, and phase modulation is applied to one polarized light. Image formation is performed using the synthesized light. In this way, it is proposed that speckles caused by two polarized lights are superposed and averaged to reduce speckles.

The other is a method of suppressing speckle generation itself by reducing the coherence of laser light used for image formation (Method 2). For example, in Patent Document 2, a laser beam used for image formation is transmitted through a birefringence diffuser plate having a plurality of regions having different refractive indexes, so that the wavefront of the laser beam (a surface formed by connecting points that have the same phase). Is disturbing. By doing in this way, the coherence (spatial coherence) of the wave of a spatially different part in a laser beam is reduced, the coherence of a laser beam is reduced, and generation | occurrence | production of a speckle is suppressed.
JP 2005-234156 A JP 2005-62114 Gazette

  However, the above method has the following problems.

  In the above method 1, the ratio at which the speckle contrast (the difference in luminance between the darkest part and the brightest part in the speckle pattern) is reduced is determined according to the number of speckle patterns to be superimposed. It is known from theoretical and experimental results that when n speckle patterns are superimposed, the speckle contrast is 1 / √n. Therefore, in the method of Patent Document 1 in which the speckle pattern caused by the two polarizations is superimposed, the speckle contrast is reduced only to 1 / √2 times (about 0.7 times), which is satisfactory as a speckle countermeasure. is not.

  In Patent Document 2, the wavefront of the emitted laser light is disturbed by spatially applying phase modulation to reduce speckle. However, according to such a method, the quality of the laser light is reduced, and the projection screen is reduced. The beam spot diameter at the top increases. In a scanning projector, when the beam spot diameter is increased, the image resolution is lowered, so that the speckle is reduced but the image quality is greatly lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides an image display device capable of reducing speckles while maintaining high image quality.

  In order to solve the above problems, an image display device of the present invention includes a light source that emits light, and a separating unit that is disposed on an optical path of the light emitted from the light source and separates the light into a plurality of separated lights. A plurality of the separated lights in a two-dimensional direction on the projection surface to draw an image; and a light path of the light from the light source to the scanning means. Phase modulation means for temporally changing the phase of the separated light by controlling the optical path length, and the scanning means each of the separated lights at the same drawing point on the irradiated surface at different incident angles. Irradiating.

  According to this configuration, first, each separated light interferes at a drawing point irradiated at a different incident angle to form interference fringes. Here, since each incident angle of the separated light changes with scanning, the distance from the scanning unit of each separated light to the drawing point changes. Therefore, the pattern of interference fringes generated changes with scanning.

  Further, the phase modulation means has a function of controlling the optical path length of the separated light. The “optical path length” is a product of a geometric length along a path and a refractive index when a light ray travels along a path between two points in a medium having a constant refractive index. When a light beam passes through a plurality of media having different refractive indexes in the path, the overall optical path length is the sum of the optical path lengths obtained for each medium.

  Since the optical path length of the separated light that passes through the phase modulation means changes, the phase is relatively shifted compared to the separated light that does not pass through the phase modulation means. This phase shift can be temporally changed by controlling the phase modulation means. Then, the interference fringes generated by the interference of the separated light change with time, and the speckle pattern generated by the irradiation of the separated light also changes.

  The various speckle patterns resulting from the change in interference fringes accompanying the change in the incident angle of the separated light and the change in the speckle pattern resulting from the phase modulation of the separated light are caused by the observer of the display image. It will be superimposed on the retina. Therefore, it is possible to obtain an image display device that allows the observer to recognize the light as uniform light and realize speckle reduction.

In the present invention, the phase modulation means is disposed on at least one of the plurality of optical paths of the separated light, and the phase modulation means is configured to refract the medium through which the separated light passes in the optical path of the separated light. It is desirable to change the rate.
According to this configuration, the optical path length of the separated light can be changed by changing the refractive index, and the phase of the separated light can be favorably modulated. Therefore, it is possible to obtain an image display device that can generate various speckle patterns satisfactorily and suppress speckles.

In the present invention, the phase modulation unit includes an electro-optic material whose refractive index changes with respect to light transmitted through the phase-modulation unit and a voltage supply unit that applies a voltage to the electro-optic material. Is desirable.
According to this configuration, it is possible to achieve a desired phase modulation speed by electrical control, and an image display apparatus that can suppress speckles well can be obtained.

In the present invention, the electro-optic material is preferably a ferroelectric crystal.
According to this configuration, it is possible to realize a high-speed phase modulation speed, and it is possible to provide an image display device that suppresses speckles satisfactorily.

In the present invention, the electro-optic material is preferably a liquid crystal material.
According to this configuration, it is possible to realize a high phase modulation speed corresponding to the response speed of a liquid crystal material such as liquid crystal molecules, and an image display apparatus that can suppress speckles can be obtained.

In the present invention, the phase modulation means has a concavo-convex plate having a concavo-convex surface and irradiated with the separated light, and swings the concavo-convex plate in a direction intersecting the optical axis of the separated light, or the separated light. It is desirable to have drive means for rotating around a rotation axis set in a direction parallel to the optical axis.
According to this configuration, since the optical path length when the separated light passes through the concavo-convex plate changes according to the thickness of the concavo-convex plate at the position where it passes through the concavo-convex plate, the separated light undergoes phase modulation. Therefore, phase modulation according to the total number of changes of the unevenness that changes per unit time is possible, and an image display device that suppresses speckles well can be obtained. In addition, for example, when the concavo-convex plate is formed of a resin material, the phase modulation means can be mass-produced at low cost by using a technique such as thermal transfer, and thus an image display device capable of suppressing speckles at a low manufacturing cost is provided. be able to.

In the present invention, it is preferable that the phase modulation means is disposed on at least one of the optical paths, and the phase modulation means changes a geometric distance in the optical path of the separated light.
According to this configuration, the optical path length of the separated light can be controlled by changing the geometric distance in the optical path of the separated light by mechanical control without using a relatively expensive optical member. Therefore, it is possible to modulate speckles by modulating the phase of the separated light with an inexpensive configuration and giving fluctuations to the state of interference fringes.

In the present invention, the phase modulation unit is disposed on an optical path between the light source and the separation unit, and has a refractive index anisotropic in the same direction as the polarization directions of two polarized lights in the light emitted from the light source. And the separation means separates the light into the two separated polarized lights, and the two separated light polarization directions in the optical path of the separated light from the separation means to the scanning means. It is desirable to have phase difference plates having the same polarization direction.
According to this configuration, the light emitted from the light source is preliminarily phase-modulated into a polarization component in a specific direction and then separated. Therefore, the structure after separating the light can be simplified, and the apparatus can be miniaturized. Further, an image display device capable of suppressing speckles regardless of the polarization direction of light can be obtained.

In the present invention, the phase modulation means includes an electro-optic material in which a relative refractive index in the two directions changes according to a voltage applied to the phase modulation means, and a voltage supply means for applying a voltage to the electro-optic material. Is desirable.
According to this configuration, it is possible to achieve a desired phase modulation speed by changing the voltage to be applied, and it is possible to obtain an image display device that suppresses speckles satisfactorily.

In the present invention, the electro-optic material is preferably a ferroelectric crystal.
According to this configuration, it is possible to realize a high-speed phase modulation speed, and it is possible to provide an image display device that suppresses speckles satisfactorily.

In the present invention, the electro-optic material is preferably a liquid crystal material.
According to this configuration, it is possible to realize a high phase modulation speed corresponding to the response speed of a liquid crystal material such as liquid crystal molecules, and an image display apparatus that can suppress speckles can be obtained.

In the present invention, the phase modulation means includes a concavo-convex plate that has refractive index anisotropy in the two directions and has a concavo-convex surface and is irradiated with the separation light, and the concavo-convex plate is an optical axis of the separation light. It is desirable to have driving means for swinging in a direction intersecting with the rotation axis or rotating around a rotation axis set in a direction parallel to the optical axis of the separated light.
According to this configuration, since the optical path length when the separated light passes through the concavo-convex plate changes according to the thickness of the concavo-convex plate at the position where it passes through the concavo-convex plate, the separated light undergoes phase modulation. Therefore, phase modulation according to the total number of changes of the unevenness that changes per unit time is possible, and an image display device that suppresses speckles well can be obtained.

In the present invention, it is desirable that the modulation speed of the phase modulation means is higher than a drawing speed at which a plurality of the separated lights draw the drawing points.
The “drawing point” is an irradiation area on the projection surface corresponding to one pixel which is the minimum unit constituting the display image. According to this configuration, since a plurality of speckle patterns can be obtained while drawing the same pixel, it is possible to provide an image display device that can suppress speckles more by superimposing these speckle patterns. it can.

In the present invention, it is preferable that the scanning unit is provided corresponding to each of the separated lights.
According to this configuration, it becomes easy to independently control the incident angle of each separated light, and an image display device that can suppress speckles can be obtained.

[First Embodiment]
The image display apparatus according to the first embodiment of the present invention will be described below with reference to FIGS. In all the drawings below, the film thicknesses and dimensional ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is a schematic perspective view showing an image display device 1 of the present embodiment. As shown in the figure, an image display device 1 scans a laser light source 10 that emits laser light, a relay optical system 20 composed of a plurality of lenses, and a laser beam on a screen (projected surface) 1000 to draw an image. An optical system (scanning means) 50 is provided. A half mirror (separating means) 30, a reflecting mirror 35, and a phase modulating means 40 are arranged on the optical path in the relay optical system 20.

  The laser light source 10 includes a semiconductor laser element that emits red light, a semiconductor laser element that emits green light, and a semiconductor laser element that emits blue light, although the detailed structure thereof is not shown. The light emitted from the three semiconductor laser elements is synthesized by a color synthesis element such as a dichroic prism, and the synthesized light L is emitted from the laser light source 10. Laser light emitted from each laser element is coherence light with high coherence. Laser light has high spatial coherence and is emitted as a nearly perfect plane wave.

  The relay optical system 20 of the present embodiment includes one collimating lens 22 on which the light L is incident and two condenser lenses 24. The light L emitted from the laser light source 10 is collimated by the collimator lens 22, branched as described later, and subjected to phase modulation, and then condensed by the condenser lens 24. The relay optical system 20 can be changed as appropriate according to the configuration of the image display device. For example, when the parallelism of light emitted from the light source is extremely high, the relay optical system can be simplified or omitted. The collimating lens 22 and the condenser lens 24 may be an optical system composed of a plurality of lenses.

  The light L that has passed through the collimating lens 22 included in the relay optical system 20 enters a half mirror 30 that is a beam splitter disposed on the optical path, and the first beam (separated light) La and the second beam (separated light) Lb. Fork. Both the first beam La and the second beam Lb formed by separating the light L that is a plane wave are plane waves.

  The second beam Lb is incident on the phase modulation means 40 via the reflection mirror 35. The phase modulation means 40 changes the phase of the second beam Lb over time by changing the optical path length of the entire second beam Lb while maintaining high spatial coherence in the second beam Lb (the wavefront remains plane). Change. As a result, the phase of the second beam Lb temporally changes with respect to the phase of the first beam La that was in phase.

  Here, the phase modulation means 40 of the present embodiment changes the optical path length of the second beam Lb by changing the refractive index of the medium through which the second beam Lb is transmitted when the second beam Lb is transmitted. It has a configuration. In the present embodiment, a liquid crystal element is used as the phase modulation means 40.

  FIG. 2 is a schematic cross-sectional view of the liquid crystal element 100 used in the present embodiment. As shown in the figure, the liquid crystal element 100 has a positive dielectric anisotropy sandwiched between a pair of glass substrates 112 and 113 bonded via a sealant 111 and a pair of glass substrates 112 and 113. A liquid crystal layer 116 containing liquid crystal molecules, a pair of electrodes 117 and 118 that are disposed on the inner surfaces of the pair of glass substrates 112 and 113 and apply a voltage to the liquid crystal layer 16, and alignment films 119 and 120 on the electrodes 117 and 118. And. The alignment films 119 and 120 are subjected to an alignment process in which the liquid crystal molecules in the liquid crystal layer 116 are randomly aligned in the initial alignment state.

  FIG. 3 is an explanatory diagram showing how the liquid crystal element 100 is driven. As shown in FIG. 3A, when no application is made to the electrodes 117 and 118 of the liquid crystal element 100, the liquid crystal molecules LC having refractive index anisotropy are randomly oriented in the plane direction. Therefore, the refractive index of the liquid crystal layer 116 with respect to the second beam Lb transmitted through the liquid crystal element 100 is an average value of the two refractive indexes of the liquid crystal molecules LC.

  As shown in FIG. 3B, when applied to the electrodes 117 and 118, the major axis of the liquid crystal molecules LC is aligned in the direction of the electric field generated between the electrodes. Therefore, the refractive index of the liquid crystal layer 116 with respect to the second beam Lb transmitted through the liquid crystal element 100 is the refractive index in the minor axis direction of the liquid crystal molecules LC.

  Therefore, in the liquid crystal element 100, the refractive index with respect to the light transmitted through the liquid crystal layer 116 changes according to the voltage applied to the electrodes 117 and 118. The second beam Lb passes through the phase modulation unit having such a liquid crystal element 100, so that the phase modulation unit gives the same phase change to the entire second beam Lb.

  The first beam La and the second beam Lb that has undergone phase modulation by the phase modulation means 40 are incident on the condensing lenses 24A and 24B disposed on the respective optical paths and are condensed. Corresponding scanning optical systems 50A and 50B are provided for the respective condensed lights.

  The scanning optical system 50 includes the first deflection mirror 50a that changes the optical axes of the first beam La and the second beam Lb in the main scanning direction on the surface of the screen 1000, and the optical axes of the first and second beams. And a second deflecting mirror 50b that changes the surface of the screen 1000 in the sub-scanning direction. For example, the main scanning direction is a horizontal direction on the screen 1000, and the sub-scanning direction is a vertical direction orthogonal to the horizontal direction on the screen 1000.

  Examples of the scanning optical system 50 include a configuration in which a micro mechanical mirror formed by a MEMS technique or the like is used for the first deflection mirror 50a, and a galvano mirror or the like is used for the second deflection mirror 50b. Further, the figure shows a state in which the scanning optical system 50 is configured by two mirrors. However, for example, two drive shafts are set for one mirror, and one MEMS can perform two-dimensional scanning. A mirror may be used.

The scanning optical systems 50A and 50B irradiate the same drawing point X on the screen 1000 to the first beam La and the second beam Lb. The operations of the scanning optical systems 50A and 50B are synchronized with each other, and the drawing point X, which is a beam irradiation point, is scanned in the main scanning direction and the sub scanning direction, respectively, to form a display image. At this time, since the light La and Lb are scanned by different scanning optical systems 50, they enter the drawing point X from different azimuth angles and enter the drawing point X at different incident angles θa and θb. In addition, since scanning is performed by the scanning optical systems 50 independent from each other, the incident angles of the light beams La and Lb can be easily controlled.
The image display device 1 of the present embodiment has the above configuration.

  Next, after explaining the principle of speckle generation as a problem, the principle of speckle reduction according to the present invention will be described with reference to the drawings.

  Speckle mainly occurs in a scene where coherent light is irradiated onto an uneven surface. Assuming that the screen is irradiated with laser light, which is coherent light, the laser light that has reached the screen is scattered by unevenness on the screen surface and reaches the retina of the observer. At this time, the unevenness of the screen has a sufficiently large amplitude with respect to the wavelength of the laser beam, and gives random phase modulation from −π to π in the laser beam. Although these lights form an image on the retina, the laser beams that have undergone random phase modulation interfere with each other, resulting in interference fringes with very high contrast. This interference fringe is a defect that is called speckle and is observed.

  The image display apparatus 1 according to the present embodiment realizes speckle reduction as follows. FIG. 4 is a schematic diagram showing the effect of the image display device 1. In the figure, the light L emitted from the laser light source 10 and the optical paths of the first beam La and the second beam Lb are indicated by alternate long and short dash lines, and wavefronts of the respective lights are indicated by line segments orthogonal to the respective optical paths.

  In the image display device 1, the first beam La and the second beam Lb are simultaneously irradiated onto the drawing point X on the screen 1000 from different angles using the scanning optical systems 50 </ b> A and 50 </ b> B. At this time, the beams are plane waves having coherence with each other and intersect at the drawing point X to interfere with each other. As a result, an interference fringe IF is generated on the screen.

  Here, since the incident angles of the first beam La and the second beam Lb change with scanning, the distance from the scanning means of each separated light to the drawing point X changes. Therefore, the pattern of the generated interference fringe IF changes with scanning.

  In addition, the first beam La and the second beam Lb are spatially in phase until reaching the phase modulation means 40, but phase modulation is given to the second beam Lb that passes through the phase modulation means 40. . Therefore, the wavefront WFb of the second beam Lb varies between, for example, WF1 illustrated by a solid line and WF2 illustrated by a wavy line.

  Then, the interference fringe IF generated by the interference between the wavefront WFa of the first beam La and the wavefront WFb of the second beam Lb, for example, generates IF1 illustrated by a solid line when the wavefront WFa and the wavefront WF1 interfere with each other, and the wavefront WFa When the wavefront WF2 interferes with the wavefront WF2, it changes and fluctuates so as to generate IF2 shown by a wavy line. Due to the change (fluctuation) of the interference fringe IF, the speckle pattern generated by the irradiation with the first beam La and the second beam Lb also varies.

  The speed of change of the interference fringe IF mainly corresponds to the phase modulation speed by the phase modulation means 40. As an example, when displaying an image at a frame rate of 30 Hz using the image display device 1, when the phase modulation means 40 modulates the phase of the second beam Lb at a modulation speed equal to or higher than the frame rate, 30 is displayed for 1 second. The speckle pattern generated in each of the images is different. Therefore, the speckle pattern generated for each image can be superimposed to make it difficult to recognize the speckle pattern.

  In the present embodiment, the liquid crystal element 100 is used as the phase modulation means 40. When a general cholesteric liquid crystal is used as a liquid crystal molecule included in the liquid crystal element, a response speed of about 1 MHz can be obtained, and thus modulation much faster than the frame rate is possible. Therefore, the generated interference fringes IF can be changed at high speed, and various speckle patterns are superimposed on the retina of the observer.

  As described above, various interference fringes caused by changes in the incident angles of the first beam La and the second beam Lb and various speckle patterns caused by the phase modulation of the second beam Lb are caused. By superimposing the speckle pattern, the observer recognizes it as uniform light and realizes a reduction in speckle.

  According to the image display device 1 having the above configuration, it is possible to realize an image display device capable of realizing speckle reduction and displaying a high-quality image.

  In the present embodiment, a liquid crystal element is used as the phase modulation means 40. Therefore, it is possible to realize a high-speed phase modulation speed corresponding to the response speed of the liquid crystal molecules included in the liquid crystal element, and the image display device 1 with favorable speckle suppression can be obtained.

  In this embodiment, a laser light source is used as a light source for emitting coherent light. However, as long as the coherent light can be emitted, the LED is not limited to a laser light source, and an LED is used as a light source or a short arc lamp light source. Can also be used.

  Further, in the present embodiment, the phase modulation means 40 is arranged on the optical path of the second beam Lb, but of course, it may be arranged on the optical path of the first beam La. Further, since the phase modulation means 40 is intended to relatively change the phase of the first beam La and the second beam Lb, it is arranged only on the optical path of the second beam Lb in this embodiment. However, as long as the purpose is achieved, it may be arranged on both optical paths.

  In the present embodiment, the two scanning optical systems 50A and 50B that are synchronized are used. However, the present invention is not limited to this. For example, one scanning optical system including two reflecting mirrors corresponding to the scanning optical systems 50A and 50B is used so that the separated light beams through the two reflecting mirrors are respectively irradiated to the same drawing point on the screen. By performing the operation, drawing similar to drawing using two synchronized scanning optical systems may be performed.

  In the present embodiment, the front type image display device has been described. However, any image display device that employs a scanning projection method can be applied to a rear projection type.

  In the present embodiment, a liquid crystal element is used as the phase modulation means 40, but the present invention is not limited to this.

  For example, when the image display apparatus 1 is used to display an image with an output resolution of SVGA (800 × 600) and a frame rate of 30 Hz, a different speckle pattern for each pixel of the image is displayed. When formed, a smoother image display becomes possible. In order to realize such phase modulation, a phase modulation speed of about 15 MHz (30 × 800 × 600 = 14400000 Hz) is required.

  However, as described above, when the liquid crystal element 100 is used as the phase modulation means 40, only a modulation speed of about 1 MHz can be realized, and thus the calculated modulation speed cannot be realized. When such high-speed phase modulation is required, a ferroelectric crystal can be used as the phase modulation means.

FIG. 5 is a schematic diagram of the phase modulation means 42 using a ferroelectric crystal. The phase modulation means 42 includes a ferroelectric crystal (electro-optic material) 210, transparent electrodes 217 and 218 sandwiching the ferroelectric crystal 210, and a power source (voltage supply means) 230 connected to the transparent electrodes 217 and 218. ,have. As the ferroelectric crystal, LiNbO ₃ or KTiOPO ₄ (KTP) can be used.

  It is known that a ferroelectric crystal changes its polarization inversion structure due to an electric field applied from the outside and changes its refractive index (electro-optic phenomenon). By utilizing this phenomenon, the phase modulation means 42 using a ferroelectric crystal can realize a phase modulation speed of several hundred MHz or more.

  Such a phase modulation means 42 can temporally change the refractive index of the region through which the incident light Lb passes in accordance with the electric field applied. Then, the optical path length of the light Lb changes according to the change in the refractive index, and the phase of the light Lb with respect to the phase of the light La changes.

  In addition, when the above-described phase modulation means 42 is used, when the above-described image is displayed, it is possible to perform phase modulation a plurality of times while rendering the same pixel. As a result, it is possible to display a high-quality image with further reduced speckles. If the refractive index is changed by applying a voltage, the crystal used for the phase modulation means may not be a ferroelectric substance.

  Further, the phase modulation means may be configured as shown in FIG. FIG. 6 is a schematic diagram showing another example of the phase modulation means. 6A is a cross-sectional view showing a concavo-convex plate for controlling the optical path length, and FIGS. 6B and 6C are schematic views showing a device configuration of phase modulation means using the concavo-convex plate. .

  The phase modulation means includes a transparent uneven plate 300 having a cross-sectional structure as shown in FIG. The concavo-convex plate 300 is formed using a forming material having a refractive index n and having eight steps. The size W of each step unit 300s is set larger than the beam diameter WL of the second beam Lb. In the figure, the step changes stepwise, but the change in the step between the adjacent step portions 42s may be random.

Further, the value H in the thickness direction (height direction) between the thickest step portion and the thinnest step portion is H = λ / (n−n ₀ ) (λ: of the second beam) Wavelength, n ₀ : Refractive index of environmental gas, in case of air ≈ 1), and a phase difference from 0 to 2π is given in the second beam Lb.

  Such an uneven plate 300 can be formed using, for example, an acrylic resin (n≈1.5). When a transparent resin is used, it is possible to mass-produce concavo-convex plates having the same shape by thermal transfer at low cost, and the manufacturing cost can be reduced.

  FIG. 6B is a schematic diagram of the phase modulation means 44 that performs phase modulation by swinging the above-described concavo-convex plate. The phase modulation means 44 includes a concavo-convex plate 300A having a substantially rectangular shape in plan view, and eccentric plates (drive means) 310 are attached to both ends of one side of the concavo-convex plate 300A.

  The eccentric plate 310 is connected to the concavo-convex plate 300 via a connection pin 312, and a drive device (drive means) 320 such as a rotary motor is connected to a connection portion 314 that is different from the arrangement position of the connection pin 312. Yes. The rotation center axis of the eccentric plate 310 is set so as to overlap the connection portion 314.

  As long as the two eccentric plates 310 can be driven synchronously, one drive device 320 may be provided in common with respect to the two eccentric plates 310, and may be provided for each of the two eccentric plates 310. It may be done. Electric power is supplied to the driving device 320 from the power source 330.

  Such a phase modulation means 44 drives the drive device 320, whereby the eccentric plate 310 rotates around the rotation center axis overlapping the connecting portion 314, and the uneven plate 300A swings. The position of the beam spot S of the second beam Lb irradiated to the concavo-convex plate 300A changes with the swing of the concavo-convex plate, and the second beam Lb is at the step portion of the concavo-convex plate 300A at the irradiation position of the beam spot S. Phase modulation is applied according to the thickness.

  In such a phase modulation means 44, assuming that the width of the step portion of the concavo-convex plate 300A is 1 mm, the distance between the center of the connection pin 312 and the center of the connection portion 314 is 2 mm, and the rotational speed of the eccentric plate 310 is 100 Hz, it is about 1 kHz. A phase modulation speed of (2 × 2π × 100≈1260 Hz) can be realized.

  FIG. 6C is a schematic view of the phase modulation means 46 that performs phase modulation by rotating the above-described concavo-convex plate. The phase modulation means 46 includes an uneven plate 300B having a substantially circular shape in plan view, and a shaft 316 is attached to the center of the uneven plate 300A. A driving device 320 such as a rotary motor and a power source 330 are connected to the shaft 316.

  Such a phase modulation means 46 drives the driving device 320 to rotate the concavo-convex plate 300 </ b> B around the rotation axis R set so as to overlap the shaft 316. The position of the beam spot S of the second beam Lb irradiated to the concavo-convex plate 300B changes with the rotation of the concavo-convex plate, and the second beam Lb is the thickness of the step portion of the concavo-convex plate 300B at the irradiation position of the beam spot S. As a result, it undergoes phase modulation.

  In such a phase modulation means 46, assuming that the distance from the center of the shaft 316 to the center of the beam spot S is 3 mm and the rotation speed of the concavo-convex plate 300B is 200 Hz, the center of the beam spot S is about 3.8 kHz (3 × 2π). × 200≈3770 Hz) phase modulation speed can be realized.

  Since the phase modulation speed possible with the phase modulation means 44 and 46 is several tens of times the frame rate or higher, a speckle pattern is superimposed between display images to display an image with reduced speckle. Can do.

[Second Embodiment]
FIG. 7 is an explanatory diagram of an image display apparatus according to the second embodiment of the present invention. The image display device of this embodiment is partially in common with the image display device of the first embodiment. The difference is that the phase modulation means changes the path length, which is the geometric length of the optical path of the second beam. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  Here, the phase modulation means 60 of the present embodiment is configured to change the optical path length of the second beam Lb by changing the path length, which is the geometric distance of the path (optical path) of the second beam Lb. It has become.

  As shown in the figure, the phase modulation means 60 included in the image display apparatus 2 of the present embodiment has two mirrors 62 and 63 installed on a drive stage 61. The second beam Lb separated by the half mirror 30 is reflected by the mirrors 62 and 63 and then enters the condenser lens 24 </ b> B via the reflection mirror 37. In the figure, the mirrors 62 and 63 each reflect the second beam Lb at an angle of 90 °, and reflect in the direction in which the second beam Lb is incident.

  The drive stage 61 is controlled by an electrostatic actuator (not shown) and reciprocally vibrates in the optical axis direction of the second beam Lb incident on the mirror 62. With this vibration, the path of the second beam Lb continuously changes with a width that is twice the amplitude AM of the vibration. Thereby, the optical path length of the second beam Lb changes and the phase is modulated.

  On the screen 1000, the first beam La, which is a plane wave scanned by the corresponding scanning optical systems 50A, 50B, and the second beam Lb, which is a phase-modulated plane wave, interfere with each other to generate interference fringes. Similar to the embodiment, the interference fringes are time-varying with the phase modulation of the second beam Lb, so that a plurality of interference fringes are superimposed on the retina of the observer.

  Here, the laser beam used for image display has a wavelength in the visible light region and is about 650 nm at the longest. Therefore, even if the amplitude AM is a value several times as large as 650 nm (for example, several μm), a sufficiently large path difference is generated with respect to the wavelength of the second beam Lb.

  For example, if the drive stage 61 is configured to reciprocate at a speed of 100 μm / s, a path difference corresponding to a wavelength of about 150 cycles (100,000 / 650≈150) per second is generated. On the screen, the brightness of the interference fringes varies about 150 times per second, and interference fringes with different patterns are generated. By superimposing these various interference fringes, the observer is recognized as an image with reduced speckles.

  According to the image display device 2 configured as described above, the optical path length of the second beam Lb can be controlled by changing the path length by mechanical control. The speckle can be suppressed by modulating the phase and giving fluctuations to the state of the interference fringes.

[Third Embodiment]
FIG. 8 is an explanatory diagram of an image display apparatus according to the third embodiment of the present invention. The image display device of this embodiment is partially in common with the image display device of the first embodiment. The difference is that phase modulation is performed before the light emitted from the laser light source is separated into two. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  As shown in the figure, in the image display device 3 of the present embodiment, the linearly polarized light Lp emitted from the laser light source 11 is collimated through the collimator lens 22 and arranged on the lower side of the collimator lens 22. Incident on the means 70.

  The phase modulation means 70 has different refractive indexes in two directions orthogonal to the optical path of the linearly polarized light Lp and orthogonal to each other, and one of the different refractive indexes is anisotropically adjustable. This is a sexual phase modulation element. A liquid crystal element is used for the phase modulation means 70 of the present embodiment, and the refractive index difference in two directions is controlled by the voltage applied to the electrodes. The linearly polarized light Lp is modulated into circularly polarized light Lc by being incident so as to be in a direction of 45 ° with respect to the two orthogonal directions.

  Thereafter, the circularly polarized light Lc is separated into a first beam La that is a p-polarized component and a second beam Lb that is an s-polarized component by a polarizing beam splitter (separating means) 32. The second beam Lb is incident on the phase difference plate 72 which is a λ / 2 plate disposed on the optical path via the reflection mirror 25, and the polarization direction is rotated by 90 ° to become p-polarized light. As the phase difference plate 72, for example, calcite having an appropriate thickness can be used.

  On the screen 1000, the first beam La, which is a plane wave scanned by the corresponding scanning optical systems 50A, 50B, and the second beam Lb, which is a phase-modulated plane wave, interfere with each other to generate interference fringes. Similar to the embodiment, the interference fringes are time-varying with the phase modulation of the second beam Lb, so that a plurality of interference fringes are superimposed on the retina of the observer.

  According to the image display device 3 having the above-described configuration, the emitted linearly polarized light Lp is preliminarily subjected to phase modulation to a polarization component in a specific direction and then separated. Therefore, the configuration after the polarizing beam splitter 32 can be simplified, and the apparatus can be miniaturized.

  In the present embodiment, a liquid crystal element is used as the phase modulation means 40. However, the present invention is not limited to this. In addition, for example, an electro-optic material such as a ferroelectric crystal having biaxial refractive index anisotropy can be used.

  In the present embodiment, the laser light source 11 emits linearly polarized light. However, even a light source that emits circularly polarized light can be used similarly. Further, it may be a normal laser beam having vibrations in all directions instead of polarized light having a vibration direction in a specific direction.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

1 is a schematic perspective view showing an image display device according to a first embodiment of the present invention. It is explanatory drawing which shows the phase modulation means of 1st Embodiment. It is explanatory drawing which shows the phase modulation means of 1st Embodiment. It is the schematic which shows the effect of the image display apparatus of 1st Embodiment. It is the schematic which shows the other example which concerns on the phase modulation means of 1st Embodiment. It is the schematic which shows the other example which concerns on the phase modulation means of 1st Embodiment. It is explanatory drawing of the image display apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the image display apparatus which concerns on 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2, 3 ... Image display apparatus 10, 11 ... Laser light source (light source), 30 ... Half mirror (separation means), 32 ... Polarization beam splitter (separation means) 40, 42, 44, 46, 60, 70 ... Phase modulation means, 50, 50A, 50B ... scanning optical system (scanning means), 100 ... liquid crystal element, 210 ... ferroelectric crystal (electro-optic material), 300, 300A, 300B ... uneven plate, 320 ... drive device (drive) Means), 330 ... power source (voltage supply means), 1000 ... screen (projected surface), L ... light, La ... first beam (separated light), Lb ... second beam (separated light), Lp ... linearly polarized light, LC: liquid crystal molecule (liquid crystal material, electro-optic material), X: drawing point, θa, θb: incident angle,

Claims (14)

A light source that emits light;
A separating unit disposed on an optical path of light emitted from the light source, and separating the light into a plurality of separated lights;
Scanning means for drawing an image by scanning a plurality of the separated lights in a two-dimensional direction on a projection surface;
A phase modulation unit that is arranged in the optical path of the light from the light source to the scanning unit, and that temporally changes the phase of the separated light by controlling an optical path length related to the plurality of separated lights,
The image display apparatus, wherein the scanning unit irradiates each of the separated lights onto the same drawing point on the irradiated surface at different incident angles. The phase modulation means is disposed on at least one of the plurality of optical paths of the separated light,
The image display apparatus according to claim 1, wherein the phase modulation unit changes a refractive index of a medium through which the separated light is transmitted in an optical path of the separated light. The phase modulation means includes an electro-optic material that changes a refractive index with respect to light that is transmitted through the phase modulation means,
The image display apparatus according to claim 2, further comprising a voltage supply unit that applies a voltage to the electro-optic material.   The image display device according to claim 3, wherein the electro-optic material is a ferroelectric crystal.   The image display apparatus according to claim 3, wherein the electro-optic material is a liquid crystal material. The phase modulation means has a concavo-convex plate having a concavo-convex surface and irradiated with the separated light
Drive means for swinging the concavo-convex plate in a direction crossing the optical axis of the separated light or rotating around a rotation axis set in a direction parallel to the optical axis of the separated light. The image display device according to claim 2. The phase modulation means is disposed on at least one of the plurality of optical paths of the separated light,
The image display apparatus according to claim 1, wherein the phase modulation unit changes a geometric distance in an optical path of the separated light. The phase modulation means is disposed on an optical path between the light source and the separation means, and has a refractive index anisotropy in the same direction as the polarization directions of two polarized lights in the light emitted from the light source,
The separation means separates the light into the separated light that is the two polarized lights,
2. The image display according to claim 1, further comprising: a phase difference plate that sets the polarization directions of the two separated lights in the same polarization direction in an optical path of the separated light from the separating unit to the scanning unit. apparatus. The phase modulation means includes an electro-optic material in which a relative refractive index in the two directions changes depending on a voltage applied to itself.
The image display apparatus according to claim 8, further comprising a voltage supply unit that applies a voltage to the electro-optic material.   The image display device according to claim 9, wherein the electro-optic material is a ferroelectric crystal.   The image display device according to claim 9, wherein the electro-optic material is a liquid crystal material. The phase modulation means has a refractive index anisotropy in the two directions and has a concavo-convex surface and is irradiated with the separated light.
Drive means for swinging the concavo-convex plate in a direction crossing the optical axis of the separated light or rotating around a rotation axis set in a direction parallel to the optical axis of the separated light. The image display device according to claim 8.   13. The image display device according to claim 1, wherein a modulation speed of the phase modulation unit is higher than a drawing speed at which the plurality of separated lights draw the drawing points.   The image display apparatus according to claim 1, wherein the scanning unit is provided corresponding to each of the separated lights.

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