JP2013167661A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces speckle noise.SOLUTION: An image forming apparatus includes: a laser light source that emits laser light; a light diffusion element 20 that diffuses the light from the laser light source; a light modulation element that modulates the laser light diffused by the light diffusion element; and a projection optical system that projects the light modulated by the light modulation element. The light diffusion element 20 has a conical shape; an inclined surface 21 of the conical shape is a diffusion surface that diffuses light; and the diffusion surface has the diffusion degree to incident light that gradually decreases as being separated from an apex of the conical shape.

Description

  The present invention relates to an image forming apparatus including a light diffusing element that diffuses light from a light source.

  In recent years, image forming apparatuses such as projectors and displays have been required to have higher performance. For example, in studies on high performance projectors, laser light sources are attracting attention as light sources with a wide color gamut and high efficiency. One of the characteristics of the laser light source is high coherence. However, due to the influence of this high coherence, the light diffused on the screen when the image is projected interferes on the retina of the eye, and speckle noise that is particulate noise is generated. As a result, there is a problem that image quality deteriorates.

  In order to obtain an image with reduced speckle noise, it is necessary to reduce the coherence of the light source. A commonly used method for reducing coherence is to insert a light diffusing element such as a diffusing plate into the optical system to spatially modulate the phase of the light source so that light can be transmitted. A measure to reduce the coherence is required (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 6-208089

  However, while the diffusing means described in Patent Document 1 can obtain a despeckle effect, the light diffusing element diffuses light uniformly, so that when viewed in an illumination area in a plane perpendicular to the optical axis, the illumination area The light is diffused similarly in the vicinity of the boundary. At this time, if the light near the boundary of the boundary region in the illumination region is diffused greatly, the light is not incident on the light modulator that is the illumination target, and there is a problem in that the illumination efficiency decreases.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 An image forming apparatus according to this application example modulates a laser light source that emits laser light, a light diffusion element that diffuses light from the laser light source, and laser light diffused by the light diffusion element. A light modulation element; and a projection optical system that projects light modulated by the light modulation element. The light diffusion element has a conical shape, and the conical slope of the conical shape diffuses light. The diffusion surface is characterized in that the degree of diffusion with respect to incident light gradually decreases as the distance from the vertex of the conical shape increases.

According to this application example, the light diffusing element has a conical shape, and the degree of diffusion with respect to incident light gradually decreases as the distance from the apex of the cone gradually increases, so that the vicinity of the optical axis has the strongest diffusion. As a result, the amount of light near the center of the donut-shaped non-diffracted beam emitted from the prism having a conical shape is averaged by diffusion, the diffusion away from the optical axis is weakened, the aperture size of the light modulation element, and It is possible to suppress the occurrence of light loss at the entrance pupil of the projection lens.
Therefore, it is possible to provide an image forming apparatus having a light diffusing element capable of reducing speckle noise while suppressing light loss.

  Application Example 2 In the image forming apparatus according to the application example, it is preferable that the light diffusing element is formed by joining a plurality of diffusing members having different diffusion degrees so as to have the conical shape.

  According to this application example, by using a combination of a plurality of diffusing members having different diffusion degrees, it is possible to form a conical light diffusing element having a gradually different diffusion degree from the apex position of the light diffusing element. In addition, the degree of diffusion of each diffusing member forming the conical light diffusing element can be freely selected. Therefore, the degree of diffusion is optimized according to the optical system configuration of the image forming apparatus to be used, thereby reducing the illumination efficiency. It is possible to form a suppressed optimal light diffusing element.

  Application Example 3 In the image forming apparatus according to the application example, it is preferable that the light diffusing element includes a rotation mechanism that rotates the light diffusing element.

  According to this application example, the speckle reduction effect can be improved by time superposition of speckle noise by rotating the light diffusing element. In addition, since the luminance unevenness due to the diffusion unevenness of the light diffusing element can be averaged, the noise component reduction effect of the projected image is increased, whereby a beautiful image with little noise can be projected.

  Application Example 4 In the image forming apparatus according to the application example, it is preferable that the light diffusing element includes a vibration mechanism that vibrates the light diffusing element.

  According to this application example, it is possible to improve the speckle reduction effect by temporally superimposing speckle noise by vibrating the light diffusing element. In addition, since the luminance unevenness due to the diffusion unevenness of the light diffusing element can be averaged, the noise component reduction effect of the projected image is increased, whereby a beautiful image with little noise can be projected.

FIG. 2 is a schematic diagram illustrating a schematic configuration of a projector using the light diffusing element according to the first embodiment. FIG. 3 is a cross-sectional view of the light diffusing element according to the first embodiment. The schematic diagram which shows the rotation mechanism of the light-diffusion element which concerns on the modification 1. FIG. The schematic diagram which shows the vibration mechanism of the light-diffusion element which concerns on the modification 2. FIG. FIG. 6 is a schematic diagram illustrating a configuration of a monitor device according to a second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each member is made different from the actual scale so that each layer and each member can be recognized.

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating a schematic configuration of a projector as an image forming apparatus according to the first embodiment. FIG. 2 is a sectional view of the light diffusing element.
First, a schematic configuration of the projector 100 according to the first embodiment will be described.

As shown in FIG. 1, the projector 100 includes laser light sources 10R, 10G, and 10B, a light diffusing element 20, liquid crystal light valves (light modulation elements) 30R, 30G, and 30B, a projection lens (projection optical system) 40, and the like. ing.
The laser light sources 10R, 10G, and 10B are single light sources or light sources arranged in an array, and include a laser light source 10R that emits red light, a laser light source 10G that emits green light, and a laser light source that emits blue light. 10B.

The light diffusing element 20 has a conical shape as shown in FIG. 2, and the conical slope 21 is a diffusing surface for diffusing light. The degree of diffusion by the element is weakened as the distance from the optical axis L increases, and the vicinity of the optical axis L has the highest diffusion.
Specifically, the light diffusing element 20 is formed in a conical shape by joining a plurality of diffusing members 20a, 20b, and 20c having different diffusion degrees with an optical adhesive or the like.
Thus, by using a combination of a plurality of diffusing members 20a, 20b, and 20c having different diffusing degrees, it is possible to form a conical light diffusing element 20 having gradually different diffusing degrees from the apex position of the light diffusing element 20. it can. In addition, since it is possible to freely select the diffusion degree of each of the diffusion members 20a, 20b, and 20c forming the conical light diffusion element 20, the diffusion degree is optimized in accordance with the configuration of the optical system of the image forming apparatus to be used. Thus, it is possible to form the optimal light diffusion element 20 in which a decrease in illumination efficiency is suppressed.
The light diffusing element 20 is arranged so that the apex of the conical shape faces the light traveling direction.

The liquid crystal light valves 30R, 30G, and 30B spatially modulate the diffused laser light.
The projection lens 40 projects the light modulated by the liquid crystal light valves 30R, 30G, and 30B.
The projector 100 can include a cross dichroic prism (color light combining means) 35 that combines the light emitted from the liquid crystal light valves 30R, 30G, and 30B and guides the light to the projection lens 40.

  Thus, the projector 100 diffuses the light emitted from the laser light sources 10R, 10G, and 10B by the light diffusing element 20, and enlarges the image formed by the liquid crystal light valves 30R, 30G, and 30B with the projection lens 40. Can be projected onto a screen (display surface) 45.

  In the above example, the transmissive liquid crystal light valves 30R, 30G, and 30B are used as the light modulation elements. However, a light valve other than the liquid crystal may be used, or a reflective light valve may be used. Examples of such a light valve include a reflective liquid crystal light valve and a digital micromirror device. Further, the configuration of the projection optical system is appropriately changed depending on the type of light valve used.

As described above, according to the projector 100 according to the present embodiment, the following effects can be obtained.
Since it is known that the beam emitted from the conical light diffusing element 20 is a non-diffracted beam, the beam is not diffracted and the spread of the beam due to propagation can be suppressed. However, since the beam shape is a donut shape, the amount of light in the vicinity of the central hole is averaged by diffusion, and the diffusion away from the optical axis is weakened so that the openings of the liquid crystal light valves 30R, 30G, and 30B are opened. , And the occurrence of light loss at the entrance pupil of the projection lens 40 is suppressed. As a result, it is possible to provide a bright projector 100 with less noise that achieves both speckle reduction and light quantity loss reduction.

(Modification 1)
Next, Modification 1 of the first embodiment will be described. In this modification, a rotation mechanism for rotating the light diffusing element is added. For this reason, a rotation mechanism is demonstrated in detail here.
3A and 3B are schematic views showing the rotation mechanism of the light diffusing element according to the modification 1. FIG. 3A is a cross-sectional view in a plane parallel to the optical axis, and FIG. It is sectional drawing in a vertical surface.

The rotation mechanism 50 of the conical light diffusing element 20 includes a holding frame 51 that holds the light diffusing element 20, a rotation motor 52, and the like.
The holding frame 51 that holds the light diffusing element 20 has a shape surrounding the conical shape of the light diffusing element 20, and protects it from an impact applied to the light diffusing element 20. Further, the outer periphery of the holding frame 51 has a gear structure in which a tooth shape is formed. The rotation motor 52 is disposed at a position adjacent to the holding frame 51, and transmits the rotational motion of the rotation motor 52 to the holding frame 51 having a tooth shape on the outer periphery via a gear, thereby rotating the light diffusing element 20.
As described above, in the first modification, in addition to the spatial phase modulation according to the first embodiment, a speckle reduction mechanism by temporal phase modulation by rotational motion can be provided.

  According to the rotation mechanism 50 of the light diffusing element 20 according to the first modification, the diffusion pattern by the light diffusing element 20 can be changed with time by the rotation of the light diffusing element 20, and therefore, within the integration time of the eyes. It is possible to increase the effect of reducing speckle noise by superimposing speckle patterns generated on the surface.

(Modification 2)
Next, a second modification of the first embodiment will be described. In this modification, a vibration mechanism for vibrating the light diffusing element is added. For this reason, a rotation mechanism is demonstrated in detail here.
4A and 4B are schematic views showing a rotation mechanism of the light diffusing element according to the modification 2. FIG. 4A is a cross-sectional view in a plane parallel to the optical axis, and FIG. It is sectional drawing in a vertical surface.

The vibration mechanism 60 of the conical light diffusing element 20 includes a holding frame 61 that holds the light diffusing element 20, a vibration source 62, and the like.
The holding frame 61 that holds the light diffusing element 20 has a shape surrounding the conical shape of the light diffusing element 20, and protects the vibration from being directly transmitted from the vibration source 62 to the light diffusing element 20. However, when the vibration is weak enough not to damage the light diffusing element 20, the holding frame 61 may not be provided. The vibration source 62 includes a holding frame 61 or a piezoelectric element disposed at a position directly adjacent to the light diffusing element 20. The vibration source 62 is vibrated by controlling the voltage applied to the piezoelectric element from the power source 63, and the vibration is transmitted by bringing the vibration source 62 into contact with the holding frame 61 to vibrate the light diffusing element 20.
Thus, in the second modification, in addition to the spatial phase modulation according to the first embodiment, a speckle reduction mechanism by vibration can be provided.

  According to the vibration mechanism 60 according to the second modification, the speckle pattern generated within the integration time of the eye is superimposed by changing the diffusion state of the light diffusion element 20 with time by the vibration of the light diffusion element 20. It is possible to increase the effect of reducing speckle noise.

(Embodiment 2)
Next, a monitor device as an image forming apparatus according to the second embodiment will be described.
FIG. 5 is a schematic diagram showing the configuration of the monitor device.

A monitor device 200 according to the second embodiment includes a laser light source 10, a light diffusing element 20, a projection lens 40, an imaging unit 70, and the like. The subject illuminated by the laser light source 10, the light diffusing element 20, and the projection lens 40 is imaged by the imaging unit 70.
Also in the monitor device 200 having such a configuration, the light diffusing element 20 described in the first embodiment, the first modification, and the second modification can be used.

  According to the monitor device 200 according to the present embodiment, since the light diffusing element 20 is provided, the light source device emits light with low coherence, and the subject is irradiated with bright light without uneven brightness. Therefore, the imaging unit 70 can capture the subject clearly.

  DESCRIPTION OF SYMBOLS 10, 10R, 10G, 10B ... Laser light source, 20 ... Light diffusing element, 21 ... Conical slope, 20a, 20b, 20c ... Diffusing member, 30R, 30G, 30B ... Liquid crystal light valve as light modulation element, 40 ... Projection optics Projection lens as a system, 50: rotating mechanism, 51: holding frame, 52 ... rotating motor, 60 ... vibrating mechanism, 61 ... holding frame, 62 ... vibration source, 63 ... power source, 70 ... imaging unit, 100 ... image forming apparatus As a projector, 200... A monitor device as an image forming apparatus.

Claims (4)

A laser light source that emits laser light;
A light diffusing element for diffusing light from the laser light source;
A light modulation element for modulating the laser light diffused by the light diffusion element;
A projection optical system for projecting the light modulated by the light modulation element,
The light diffusing element has a conical shape, and the conical slope of the conical shape is a diffusing surface for diffusing light, and the diffusing surface gradually decreases in the degree of diffusion with respect to incident light as it moves away from the apex of the conical shape. An image forming apparatus characterized by comprising: The image forming apparatus according to claim 1, wherein the light diffusing element is formed by joining a plurality of diffusing members having different diffusion degrees so as to have a conical shape. The image forming apparatus according to claim 1, wherein the light diffusing element includes a rotation mechanism that rotates the light diffusing element. The image forming apparatus according to claim 1, wherein the diffusing element includes a vibration mechanism that vibrates the light diffusing element.

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