JP4165179B2 - Illumination device and image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to an illumination device for illuminating a spatial light modulation element in an image display device and an image display device configured using the illumination device.
[0002]
[Prior art]
Conventionally, a spatial light modulation element such as a liquid crystal panel or a so-called “DMD element” is illuminated by a lighting device, and transmitted light or reflected light from the spatial light modulation element is projected onto a screen by a projection lens. An image display device (optical projector) has been proposed.
[0003]
Currently, high-intensity discharge lamps such as metal halide lamps and high-pressure mercury lamps are mainly used as light sources for illumination devices in such image display devices. However, these light sources have several problems as described below.
[0004]
That is, the high-intensity discharge lamp has a short life. For example, the lifetime of a 150 W class high-pressure mercury lamp that is currently most often used as a light source for a projection projector is about 1500 to 3000 hours. Therefore, in an image display apparatus using such a light source, the lamp must be frequently replaced.
[0005]
In an image display device using such a light source, normally, white light is separated into three primary colors by a dichroic mirror or the like, then spatially modulated for each color component, and synthesized again to produce a color image. Is configured. Therefore, in such an image display device, the configuration of the optical system from the illumination device to the projection lens is complicated, and the light use efficiency cannot be increased.
[0006]
In order to solve these problems, an attempt has been made to use a semiconductor laser as a light source of an illumination device. The semiconductor laser has a practically sufficient life, and the monochromaticity of the emitted light is good, so that a large color reproduction region can be realized.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 06-208089
[Problems to be solved by the invention]
By the way, in the illumination device using the semiconductor laser as the light source as described above, a problem of speckle noise occurs. Generally, when an observer appreciates an image projected on a screen by an image display device, an image is formed on the observer's retina by overlapping reflected light from each region of the projected image. . At this time, the unevenness with a height of about the wavelength or more on the screen causes the reflected light reflected from different areas on the screen to overlap with each other in a complicated phase relationship, and the light emitted from the semiconductor laser has high coherency. Since they have (coherence), they interfere with each other. Such interference causes random intensity changes, that is, speckle noise. By forming such speckle noise, the image quality of the display image is degraded.
[0009]
Speckle noise is a common problem when using laser light having coherency as illumination, and various attempts have been made so far to reduce speckle noise. For example, a configuration using a fiber bundle has been proposed. This fiber bundle is composed of a plurality of optical fibers, and the optical path length difference between the optical fibers is longer than the coherent length of the laser light used as the illumination light or about the coherent length. When coherent light is incident from one end of such a fiber bundle, the light emitted from the other end is non-interfering. By using the light emitted from the other end of the fiber bundle as illumination light, coherency of the entire illumination system can be reduced, and speckle noise on the screen can be reduced.
[0010]
However, such a configuration causes the following problems. That is, in such a fiber bundle, since the light beams that have passed through different optical fibers are each non-interfering, the more the number of optical fibers, that is, the greater the number of divided light beams, the more the illumination light that is combined. Coherency can be reduced. Here, it is assumed that a fiber bundle composed of n optical fibers is used. In general, in a semiconductor laser having a single mode power spectrum, the typical spectrum width of emitted light is about 100 MHz, and the coherent length c is on the order of several meters. Then, in order to obtain non-interfering illumination light using this fiber handle, the difference in length between the shortest optical fiber and the longest optical fiber is nxc [m]. For example, when the number n of optical fibers is 50 and the coherent length c is 1 m, the length of the longest optical fiber is 50 m or more.
[0011]
Such an optical system including a fiber bundle composed of a large number of optical fibers having different optical path lengths has a considerably large volume and weight, leading to an increase in the size of the entire image projection apparatus. End up.
[0012]
On the other hand, as another configuration for reducing speckle noise, a configuration using a rotating diffusion plate or the like has been proposed. In this configuration, a diffusion plate that is rotated at high speed and transmits the illumination light is disposed on the optical path of the illumination light emitted from the semiconductor laser. The diffusion plate is rotated at a high speed, thereby splitting an interference pattern generated by illumination light that is coherent light, and this interference pattern, that is, speckle noise, moves around on the screen at high speed.
[0013]
That is, in this configuration, speckle noise does not actually disappear, but it looks as if speckle noise has disappeared.
[0014]
However, in this configuration, polished glass or the like is used as the diffusion plate, so that the light use efficiency is lowered. In addition, since the diffusion plate is mechanically driven, there is a possibility that the driving sound becomes loud, and there is a problem in long-term reliability. Furthermore, when such a configuration is specifically incorporated into an illumination optical system, specific proposals such as where to install it, what kind of properties and size should be used are as follows. Little has been done.
[0015]
Therefore, the present invention is proposed in view of the above circumstances, using coherent light as illumination light, without increasing the size of the apparatus configuration, and without causing a decrease in light utilization efficiency, It is an object of the present invention to provide an illumination device in which the generation of speckle noise is suppressed, and to provide an image display device configured to include such an illumination device.
[0016]
[Means for Solving the Problems]
In order to solve the above-described problems, an illumination device according to the present invention is a coherent light source group including a plurality of semiconductor lasers that emit a coherent light beam in a visible light region, supported by a thermally supported laser support base. And a temperature control element that controls the temperature of each semiconductor laser that is thermally connected via the laser support base, and a control means that controls the operation of the temperature control element, the semiconductor laser emitting light At the same time, the laser support substrate cools the semiconductor laser by the temperature control element, the control means controls the operation of the temperature control element, and the temperature control element The temperature of each semiconductor laser varies depending on the difference in the thermal distance to each other, and coherent light beams with different wavelengths are emitted from each semiconductor laser. To Isa.
[0017]
An image display apparatus according to the present invention includes a coherent light source group including a plurality of semiconductor lasers that are supported by laser support bases that are thermally connected to each other and emit a coherent light beam in a visible light region, and the coherent light source. Controls the temperature of each of the semiconductor lasers that are thermally connected via the laser support substrate and the spatial light modulator that is illuminated by the luminous flux emitted from the group, the imaging means that forms an image of the spatial light modulator A temperature control element that controls the operation of the temperature control element, and the semiconductor laser generates heat by emitting light and heats the laser support base. At the same time, the laser support base The semiconductor laser is cooled by an element, and the control means controls the operation of the temperature control element, and the difference in thermal distance from the temperature control element. By, at different temperatures of the semiconductor lasers to emit coherent light beam of different wavelength from the semiconductor laser.
[0018]
In the illuminating device and the image display device according to the present invention, the temperature of each semiconductor laser is made different so that the wavelengths of the light beams emitted from these semiconductor lasers are different, and the coherency of the light beams emitted from the coherent light source group as a whole is reduced. The generation of speckle noise on the surface to be illuminated such as a spatial light modulator is suppressed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
The illumination device according to the present invention is a device that guides a coherent light beam emitted from a light source to an illuminated surface through an optical element such as a collimator lens. The image display apparatus according to the present invention guides a coherent light beam emitted from a light source to a spatial light modulation element serving as an illuminated surface via an optical element such as a collimator lens, and forms an image serving as an imaging unit. An image (virtual image or real image) of the spatial light modulator is formed by the optical system.
[0021]
In these illumination devices and image display devices, a coherent light source group including a plurality of coherent light sources is used as a light source. As shown in FIG. 1, this coherent light source group is composed of, for example, nine (CAN) type semiconductor lasers 1A, 1B, and 1C that are coherent light sources.
[0022]
As the light source of the image display device, the oscillation wavelength of each semiconductor laser is in the visible light region of 380 nm to 780 nm. For example, for red, it is conceivable to use laser light having a wavelength of about 650 nm. However, it is not necessary for all the nine semiconductor lasers 1A, 1B, and 1C to emit light having the same oscillation wavelength at the same temperature, three of which are 640 nm, the other three are 650 nm, and the remaining three are 660 nm. It is preferable to emit light beams having slightly different wavelengths, such as emitting light of a wavelength.
[0023]
These can-type semiconductor lasers 1A, 1B, and 1C are supported by the laser support base 2 and are thermally connected to each other. As a material forming the laser support base 2, for example, a metal material having an appropriate thermal conductivity such as copper, silver, gold, or aluminum can be used. The laser support base 2 is further installed on the base 4.
[0024]
Semiconductor lasers have extremely sensitive characteristics to temperature, and it is known that various characteristics such as laser oscillation current value, light emission efficiency, maximum oscillation output, and oscillation wavelength change with increasing temperature. ing. Therefore, in order to operate the semiconductor laser stably, it is necessary to design the semiconductor laser so as to keep the temperature constant by using a thermoelectric element or the like.
[0025]
In this illumination device, the Peltier element 3 is used to keep the temperature of each semiconductor laser at a predetermined temperature. The Peltier element 3 is installed in a state of being sandwiched between the base 4 and the laser support base 2. That is, the Peltier element 3 and each of the semiconductor lasers 1A, 1B, and 1C are in a state of being thermally connected via the laser support base 2. That is, the semiconductor lasers 1A, 1B, and 1C generate heat by emitting light and heat the laser support base 2. At the same time, since the laser support base 2 is cooled by the Peltier element 3, the semiconductor lasers 1A, 1B, and 1C are cooled. The semiconductor lasers 1A, 1B, and 1C are maintained at a temperature at which the amount of heat generated by the semiconductor lasers 1A, 1B, and 1C and the cooling capability of the Peltier element 3 are balanced.
[0026]
In this way, each of the semiconductor lasers 1A, 1B, and 1C is maintained at a predetermined constant temperature, and can be operated stably. In this coherent light source group, all the semiconductor lasers 1A, 1B, 1C are not maintained at the same temperature, but differ depending on the difference in the thermal distance (the length of the heat conductor) to the Peltier element 3. Maintained at temperature. That is, the Peltier element 3 is arranged so that the thermal distances are different from those of the nine semiconductor lasers 1A, 1B, and 1C, and the semiconductor lasers 1A, 1B, and 1C have different temperature distributions.
[0027]
That is, in this coherent light source group, among the nine semiconductor lasers 1A, 1B, and 1C, the temperature T _{A of} the three semiconductor lasers 1A farthest from the Peltier element 3 and the next 3 away from the Peltier element 3 and the temperature T _B of the number of semiconductor lasers 1B, the temperature T _C of the nearest three semiconductor laser 1C to Peltier element 3, has a relationship that the following conditions are met.
[0028]
T _A > T _B > T _C
Therefore, even if these nine semiconductor lasers 1A, 1B, and 1C are all the same type of semiconductor lasers, they emit light beams having different wavelengths according to the temperature difference.
[0029]
In this way, the semiconductor lasers 1A, 1B, and 1C emit light beams having different wavelengths, thereby reducing the coherency of the entire emitted light beam from the coherent light source group, and the entire illumination device or image as described later. As a display device, generation of speckle noise on the surface to be illuminated can be suppressed.
[0030]
Further, the coherent light source group in the illumination device and the image display device may be configured by using a plurality of semiconductor laser chips 5 and modularizing these semiconductor laser chips 5 as shown in FIG. In the embodiment shown in FIG. 2, nine semiconductor laser chips 5 are housed in a housing-like package 7 and modularized to form a coherent light source group.
[0031]
In this coherent light source group, as shown in FIG. 3, each semiconductor laser chip 5 is joined to the side surface portion of the metal block 6 by solder, silver paste, or the like. It is installed on the base block 9. That is, a plurality of metal blocks 6 are arranged in parallel on the base block 9, and the semiconductor laser chip 5 is bonded to each side surface portion of each metal block 6.
[0032]
The metal block 6 is generally formed of copper in consideration of the viewpoint of improving heat dissipation from the semiconductor laser chip 5. Similar to the metal block 6, the base block 9 to which the plurality of metal blocks 6 are joined is formed of a material having high thermal conductivity.
[0033]
Each of the semiconductor lasers 5 emits a light beam toward the opened one end side of the package 7, that is, in a direction substantially perpendicular to the main surface portion of the base block 9, as indicated by an arrow L in FIGS. It is installed to do.
[0034]
The package 7 is an outer casing for protecting the plurality of semiconductor lasers 5, and at the same time, has a role of a heat sink. The base block 9 is installed on the bottom surface of the package 7.
[0035]
Each semiconductor laser chip 5 emits a laser beam by being injected with carriers. Carrier supply to each semiconductor laser chip 5 is performed from the outside through a metal wire 8 drawn outward from the side surface portion of the package 7 via an external circuit board (not shown). The carrier supplied through the metal wire 8 is supplied to each semiconductor laser 5 through each metal block 6.
[0036]
Also in this coherent light source group, the Peltier element 11 is used to keep the temperature of each semiconductor laser chip 5 at a predetermined temperature. The Peltier element 11 is mounted and installed on the support plate 10 in a state of being sandwiched between the base block 9 and the bottom surface portion of the package 7. That is, the Peltier element 11 and each semiconductor laser chip 5 are in a state of being thermally connected via the base block 9. That is, the semiconductor laser chip 5 generates heat by emitting light and heats the base block 9. At the same time, since the base block 9 is cooled by the Peltier element 11, the semiconductor laser chip 5 is cooled. The semiconductor laser chip 5 is maintained at a temperature at which the amount of heat generated by the semiconductor laser chip 5 and the cooling capability of the Peltier element 11 are balanced.
[0037]
In this way, each semiconductor laser chip 5 is kept at a predetermined constant temperature and can operate stably. In this coherent light source group, all the semiconductor laser chips 5 are not maintained at the same temperature, but, for example, the three semiconductor laser chips 5A, 5B, and 5C are maintained at different temperatures. That is, the Peltier element 11 sets the semiconductor laser chips 5A, 5B, and 5C to different temperature distributions.
[0038]
That is, in the coherent light source group, nine semiconductor laser chip 5A, 5B, among 5C, and the temperature T _A of the first three semiconductor laser chip 5A, the second three semiconductor laser chip 5B and the temperature T _B, and the temperature T _C of the third three semiconductor laser chip 5C, has a relationship that the following conditions are met.
[0039]
T _A > T _B > T _C
Therefore, even if all of these nine semiconductor laser chips 5A, 5B and 5C are semiconductor laser chips having the same characteristics of the same type, they emit light beams having different wavelengths depending on the temperature difference. Become.
[0040]
In this way, each semiconductor laser chip 5A, 5B, 5C emits light beams having different wavelengths, thereby reducing the coherency of the entire emitted light beam from the coherent light source group, and the entire illumination device as described later, or As an image display device, generation of speckle noise on the illuminated surface can be suppressed.
[0041]
In the coherent light source group configured as described above, as shown in FIG. 4, the temperature rises in the relationship between the wavelength of the emitted light beam from the semiconductor lasers 1A, 1B, 1C or the semiconductor laser chip 5 and the temperature. As the wavelength becomes longer, the relationship becomes longer. For example, a semiconductor laser that emits a light beam with a wavelength of 654 nm at 0 ° C. emits a light beam with a wavelength of 658 nm at 25 ° C., emits a light beam with a wavelength of 665 nm at 50 ° C., and emits a light beam with a wavelength of 667 nm at 75 ° C. It will be emitted. When light beams having different wavelengths are emitted at the same time as described above, coherency is reduced as compared with light beams having a single wavelength.
[0042]
And the illuminating device which concerns on this invention which has a coherent light source group of the above structures guides the light beam which the coherent light source group emitted, for example to the to-be-illuminated surface which is a spatial light modulation element, as shown in FIG. The illuminated surface is illuminated. When the surface to be illuminated is a spatial light modulation element, the image (virtual image or real image) of the spatial light modulation element is formed by an imaging optical system serving as an imaging means. An image display apparatus according to the above is configured.
[0043]
In other words, this image display device has three colors of light source: red (hereinafter referred to as “R”), green (hereinafter referred to as “G”), and blue (hereinafter referred to as “B”). Three sets of coherent light source groups 12R, 12G, and 12B that emit light of different colors are included.
[0044]
The R, G, and B coherent lights emitted from the respective coherent light source groups 12R, 12G, and 12B are converted into parallel light beams by the collimator lenses 13R, 13G, and 13B, respectively. The R light beam is reflected by a mirror (or a dichroic mirror that reflects only R light) 14R, and passes through a dichroic mirror 14G that reflects only G light and a dichroic mirror 14B that reflects only B light. The G light flux is reflected by the dichroic mirror 14G that reflects only the G light, and passes through the dichroic mirror 14B that reflects only the B light. The B light flux is reflected by the dichroic mirror 14B that reflects only the B light. In this way, the R, G, and B color lights are combined and incident on the condenser lens 15.
[0045]
The light beam incident on the condenser lens 15 is collected by the condenser lens 15 and becomes diffused light via the relay lens 16 and enters the collimator lens 17. The collimator lens 17 causes the incident light beam to enter the spatial light modulator 18 as a parallel light beam. In this way, the spatial light modulation element 18 is illuminated. A light beam that illuminates the spatial light modulation element 18 and is modulated in accordance with an image signal displayed by the spatial light modulation element 18 is projected onto a screen 20 by a projection lens 19 that is an imaging optical system.
[0046]
Although FIG. 5 shows the transmissive spatial light modulator 18, a reflective spatial light modulator can be used instead of the transmissive spatial light modulator 18.
[0047]
【The invention's effect】
As described above, in the illuminating device and the image display device according to the present invention, the temperatures of the respective semiconductor lasers forming the coherent light source group are made different so that the wavelengths of the light beams emitted by these semiconductor lasers are different, and the coherent light source group As a whole, the coherency (coherence) of the light flux emitted from the light source is reduced, and the generation of speckle noise on the illuminated surface such as a spatial light modulator is suppressed.
[0048]
That is, the present invention provides a lighting device in which the generation of speckle noise is suppressed without using a semiconductor laser as the illumination light, without increasing the size of the device, and without causing a decrease in light utilization efficiency. In addition, an image display device configured to include such an illumination device can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a coherent light source group serving as a light source in an illumination device and an image display device according to the present invention.
FIG. 2 is a perspective view showing another example of the configuration of the coherent light source group.
3 is an exploded perspective view showing the configuration of the coherent light source group shown in FIG. 2; FIG.
FIG. 4 is a graph showing a relationship between an oscillation wavelength and a temperature in a semiconductor laser forming the coherent light source group.
FIG. 5 is a side view showing configurations of an illumination device and an image display device according to the present invention.
[Explanation of symbols]
1A, 1B, 1C semiconductor laser, 3,11 Bertier element, 5, 5A, 5B, 5C semiconductor laser chip, 13R, 13G, 13B collimator lens, 18 spatial light modulator, 19 projection lens, 20 screen

Claims (6)

A coherent light source group consisting of a plurality of semiconductor lasers that are supported by thermally supported laser support substrates and emit a coherent light beam in the visible light region ;
A temperature control element for controlling the temperature of each semiconductor laser in a state of being thermally connected via the laser support base ;
Control means for controlling the operation of the temperature control element,
The semiconductor laser generates heat by emitting light and heats the laser support base. At the same time, the laser support base cools the semiconductor laser by the temperature control element,
The control means controls the operation of the temperature control element, varies the temperature of each semiconductor laser according to a difference in thermal distance to the temperature control element, and emits coherent light beams having different wavelengths from each semiconductor laser. Lighting device. 2. The illumination device according to claim 1, wherein each of the semiconductor lasers emits light having the same oscillation wavelength at the same temperature. The illumination device according to claim 1, wherein the temperature of the plurality of semiconductor lasers increases as the distance from the temperature control element increases. A coherent light source group consisting of a plurality of semiconductor lasers that are supported by thermally supported laser support substrates and emit a coherent light beam in the visible light region ;
A spatial light modulation element illuminated by a light beam emitted from the coherent light source group;
An imaging means for forming an image of the spatial light modulator;
A temperature control element for controlling the temperature of each semiconductor laser in a state of being thermally connected via the laser support base ;
Control means for controlling the operation of the temperature control element,
The semiconductor laser generates heat by emitting light and heats the laser support base. At the same time, the laser support base cools the semiconductor laser by the temperature control element,
The control means controls the operation of the temperature control element, varies the temperature of each semiconductor laser according to a difference in thermal distance to the temperature control element, and emits coherent light beams having different wavelengths from each semiconductor laser. Image display device.   5. The image display device according to claim 4, wherein each of the semiconductor lasers emits light having the same oscillation wavelength at the same temperature. The image display device according to claim 4, wherein the temperature of the plurality of semiconductor lasers increases as the distance from the temperature control element increases.

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