WO2010029817A1 - Light source device and image display device - Google Patents

Abstract

A light source device is provided with a first edge surface; a second edge surface opposite to the first edge surface, wherein the second edge surface is inclined with respect to the first edge surface in the case of a view from the vertical direction with respect to a plane intersecting the first and second edge surfaces, respectively; a crystal (4) that generates harmonics of light incident through the first edge surface; a coherent light supply means that makes a plurality of coherent light rays with different wavelengths travel in parallel with each other in the plane and incident on the first edge surface; and a multiplexing means that multiplexes a plurality of second harmonics that are outputted from the second edge surface and have different wavelengths, wherein phase matching for the generation of the harmonics in the crystal (4) is continuously carried out in directions intersecting the respective light ray axes of the plurality of the coherent light rays.

Description

Light source device and image display device

The present invention relates to a light source device that generates a second harmonic light beam and an image display device including the same.

Projection type that illuminates a planar image display element such as a liquid crystal light valve with incoherent light from a light source such as a halogen lamp or high-pressure mercury lamp, and enlarges and projects the image formed on the image display element on the screen with a projection lens Image devices are known.

This type of projection-type image projection apparatus uses an incoherent light source, so that power consumption is large and the brightness of the display image is small.

Also, the wavelength band of incoherent light sources is wide. For this reason, it is difficult to realize a display with a wide chromaticity range in a structure in which incoherent light sources are used as light sources of red, green, and blue colors.

Furthermore, in a structure using a planar image display element such as a liquid crystal light valve, it is difficult to reduce the size of the apparatus because the projection optical system becomes large.

Furthermore, since the image formed on the image display element is formed using a projection lens, the focus is achieved only within the focal depth of the projection lens. For this reason, the user must adjust the focus according to the installation position of the screen.

Therefore, there has been proposed a compact image projection apparatus that is portable and portable and does not require focus adjustment within a certain projection range. For example, Patent Document 1 (US Pat. No. 6,921,170) discloses an image display device that includes a laser light source that is a coherent light source, and that projects and displays an image on a screen by scanning with the laser beam from the laser light source. It is disclosed.

However, in the image display device as described above, noise on speckles called speckle is generated due to the coherence of the laser beam. Speckle is a nuisance when observing a display and degrades image quality.

Speckle can be reduced by widening the wavelength width of the laser beam and reducing the coherence. As a method of widening the wavelength width, there is a method of widening the wavelength width by causing a longitudinal multimode oscillation in a semiconductor laser. However, since there is no semiconductor laser having a green wavelength (530 nm) at present, normally, infrared light of 1060 nm is converted into the second harmonic using a nonlinear optical crystal, A green laser beam is obtained.

When the second harmonic is generated using a nonlinear optical crystal, if the condition that the crystal length is an integral multiple of the coherent length Lc represented by the following Equation 1, that is, the phase matching condition, is not satisfied, The conversion efficiency to waves is reduced.

Lc = λ / (4 · (ns-nf)) (Formula 1)
Here, λ is the wavelength of the incident fundamental wave, nf is the refractive index of the incident fundamental wave, and ns is the refractive index of the second harmonic.

Further, even in a crystal having a domain-inverted structure for each coherent length Lc, the second harmonic is not satisfied unless the phase matching condition (in the case of a crystal having a domain-inverted structure, it may be referred to as quasi phase matching). Conversion efficiency is reduced. For this reason, when the second harmonic is generated using a laser light source having a wavelength width, wavelength conversion is performed only at a specific wavelength that satisfies the phase matching condition (pseudo phase matching condition). Becomes narrower.

Patent Document 2 (Japanese Patent Laid-Open No. 2007-073552) and Patent Document 3 (Japanese Patent Laid-Open No. 2005-352393) describe methods for satisfying the phase matching condition for a light source having a wavelength width. The wavelength conversion element provided with the wavelength conversion area | region which consists of is described.

FIG. 1 is a schematic diagram showing the configuration of the wavelength conversion element described in Patent Document 2. FIG. This wavelength conversion element has a crystal 101 having a plurality of domain-inverted periodic structures 102a to 102e. The polarization inversion periodic structures 102a to 102e have a periodic structure in a direction from the incident end face side to the outgoing single face side, and the period of each polarization inversion is different. Light having different wavelengths is incident on each of the polarization inversion periodic structures 102a to 102e, and second harmonics corresponding to the incident wavelengths are generated by wavelength conversion.

FIG. 2 is a diagram for explaining the wavelength conversion element described in Patent Document 3. The figure indicated by the arrow 100A is a top view of the wavelength conversion element, and the figure indicated by the arrow 100B is a cross-sectional view of the wavelength conversion element. This wavelength conversion element has a branching waveguide 103a, a synthetic waveguide 103b, and a region 104 having a plurality of domain-inverted periodic regions provided between these waveguides.

A laser beam having a wavelength width is branched into a plurality by the branching waveguide 103 a, and the branched laser beam is incident on each polarization inversion periodic region of the region 104. In each domain inversion period region of the area 104, only a component satisfying each domain inversion period and the phase matching condition (pseudo phase matching condition) in the laser beam is converted into the second harmonic. The laser beam of each wavelength converted into the second harmonic in each polarization inversion period region of the region 104 is synthesized by the synthesis waveguide 103b, and as a result, a second harmonic laser beam having a wavelength width can be obtained. .

In addition to the above, Patent Document 4 (Japanese Patent Laid-Open No. 10-325970) and Patent Document 5 (Japanese Patent Laid-Open No. 06-2006) are provided with spectroscopic means for efficiently converting a laser beam having a wavelength width into a second harmonic laser beam. -160926).

FIG. 3 is a schematic diagram showing a configuration of a wavelength conversion device provided with the spectroscopic means described in Patent Document 4. This wavelength converter includes prisms 105a and 105b, concave mirrors 106a and 106b, and a crystal 107.

The excitation laser light (λ2) is split into laser light having a wavelength range of λ1 to λ2 by the prism 105a. A concave mirror 106a is disposed in the traveling direction of the laser light dispersed by the prism 105a, and a crystal 107 is disposed in the traveling direction of the laser light condensed by the concave mirror 106a.

The crystal 107 performs wavelength conversion on the incident laser light. A concave mirror 106b is disposed in the traveling direction of the laser light (second harmonic) wavelength-converted by the crystal 107, and a prism 105b is disposed in the traveling direction of the laser light condensed by the concave mirror 106b.

In the above wavelength conversion device, the incident angle of the laser beam dispersed by the prism 105a to the crystal 107 varies depending on the wavelength λ. For this reason, the optical path length which passes through the crystal | crystallization 107 in each of the laser beam of each wavelength differs. By setting the optical path length of the laser light having each wavelength separated so as to satisfy the phase matching condition, light having different wavelengths can be efficiently converted into the second harmonic by one crystal.

FIG. 4 is a schematic diagram showing a configuration of a wavelength conversion element provided with the spectroscopic means described in Patent Document 5. This wavelength conversion element includes a prism 108 and a crystal 109. Laser light from the laser diode (LD) 110 is split by the prism 108, and the split laser light of each wavelength enters the crystal 109. As in the case shown in FIG. 3, the incident angle of the dispersed laser light on the crystal 109 differs depending on the wavelength, and therefore the optical path lengths of the laser light of each wavelength passing through the crystal 109 are different. Therefore, by setting the optical path length of the split laser light of each wavelength so as to satisfy the phase matching condition (pseudo phase matching condition), light with different wavelengths can be efficiently converted to the second harmonic with one crystal. can do.

In the above-described wavelength conversion element, the laser light of each wavelength is not condensed at one point, so that it is possible to maintain the resistance to the incident light intensity.

As described above, the image display device described in Patent Document 1 has a problem in that speckles are generated, thereby reducing the image quality.

Patent Documents 2 to 5 can reduce speckle by satisfying the phase matching condition for a light source having a wavelength width. However, those described in Patent Documents 2 to 5 have the following problems.

In the wavelength conversion element described in Patent Document 2, the second harmonic generated in each of the polarization inversion periodic structures 102a to 102e is not synthesized as a coaxial beam. Such a configuration is difficult to apply to an image display apparatus that scans with a laser beam as described in Japanese Patent Application Laid-Open No. H10-228707.

In the wavelength conversion element described in Patent Document 3, only the component satisfying the phase matching condition (pseudo phase matching condition) of the laser light from the light source becomes the second harmonic in each polarization inversion period region of the region 104. Converted. Therefore, although a laser beam (second harmonic) having a wavelength width can be obtained, the conversion efficiency to the second harmonic is lowered.

In the wavelength conversion device described in Patent Document 4, since the beam is focused at one point in the crystal, depending on the crystal material, sufficient resistance to incident light intensity may not be obtained. For example, when a lithium niobate (LiNO ₃ ) crystal is used as the second harmonic generation crystal, its light resistance is 0.5 (W / mm ² ). Therefore, for example, when the beam condensing diameter is 0.1 mm (beam area 0.0079 mm ² ), the incident light intensity that the crystal can withstand is 3.9 mW or less, and the incident light intensity is high as in an image display device. It is difficult to deal with things.

In the wavelength conversion element described in Patent Document 5, since the principal light of each wavelength that has been dispersed diverges while passing through the crystal, the light that condenses each wavelength of light after passing through the crystal and synthesizes it into one beam. A system is required. Since such an optical system is generally large, when the wavelength conversion element described in Patent Document 5 is applied to an image display device, it is difficult to reduce the size of the device.

An object of the present invention is to solve the above-mentioned problems, and to provide a light source device that generates a second harmonic light beam having a large light resistance, a small size and a light weight and having a wavelength width, and an image with less speckle noise using the same. It is to provide a display device.

In order to achieve the above object, the light source device of the present invention comprises:
A second end face provided with a first end face and a second end face opposed to the first end face, when viewed from a direction perpendicular to a plane intersecting each of the first end face and the second end face; Is inclined with respect to the first end face, and generates an optical harmonic wave of light incident from the first end face;
A coherent light supply means for making a plurality of coherent lights having different wavelengths collimated so as to travel in parallel in the plane enter the first end face;
Combining means for combining a plurality of second harmonics having different wavelengths output from the second end face;
The phase matching for generating the harmonics in the optical crystal is continuously taken in the direction intersecting with the respective beam axes of the plurality of coherent lights.

The image display device of the present invention has the above light source device and means for scanning an external screen with a second harmonic light beam output from the light source device.

FIG. 2 is a schematic diagram showing a configuration of a wavelength conversion element described in Japanese Patent Application Laid-Open No. 2007-073552. FIG. 3 is a diagram for explaining a wavelength conversion element described in JP-A-2005-352393. FIG. 3 is a schematic diagram showing a configuration of a wavelength conversion device including a spectroscopic unit described in Japanese Patent Laid-Open No. 10-325970. FIG. 2 is a schematic diagram showing a configuration of a wavelength conversion element including a spectroscopic unit described in Japanese Patent Laid-Open No. 06-160926. It is a schematic diagram which shows the structure of the light source device which is the 1st Embodiment of this invention. It is a schematic diagram which shows the polarization inversion structure of the crystal | crystallization of the light source device shown to FIG. 5A. It is a schematic diagram which shows the structure of each lens of the light source device shown to FIG. 5A. It is a schematic diagram which shows the structure of the light source device which is the 2nd Embodiment of this invention. It is a figure for demonstrating the range of the oscillation wavelength of the laser group of the light source device shown to FIG. 6A. It is a schematic diagram which shows the structure of the light source device which is the 3rd Embodiment of this invention. It is a figure for demonstrating the range of the oscillation wavelength of the laser group of the light source device shown to FIG. 7A. It is a block diagram which shows the structure of the image display apparatus carrying the light source device shown to FIG. 7A. It is a schematic diagram which shows the structure of the light source device which is the 4th Embodiment of this invention. It is a block diagram which shows the structure of the image display apparatus carrying the light source device shown to FIG. 8A.

1 Laser (fundamental wave)
2 Spectral grating 3, 5 Lens 4 Crystal 6 Combined grating

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 5A is a schematic diagram illustrating a configuration of the light source device according to the first embodiment of the present invention.

Referring to FIG. 5A, the light source device includes a laser 1 that emits laser light (fundamental wave) having a wavelength width, a spectral grating 2, a lens 3, a crystal 4, a lens 5, and a multiplexing grating 6.

Laser 1 is a longitudinal multimode semiconductor laser, and its output light (fundamental wave) has a center wavelength λ of 1060 nm, a wavelength interval dλ of 1 nm, and a wavelength width of 20 nm. The laser light output from the laser 1 is split by the spectroscopic grating 2.

The grating interval Λ of the spectral grating 2 is 1.1 μm, and the laser beam from the laser 1 is dispersed at an angle θ. The angle θ is, for example, 0.2 °. The light beam split by the spectroscopic grating 2 enters the lens 3.

The focal length f of the lens 3 is 30 mm, and the aperture is 3 mm. The principal rays of the light beams of the respective wavelengths separated by the spectral grating 2 are collimated by the lens 3. The interval X between the light beams of the respective wavelengths collimated by the lens 3 is 100 μm. These collimated light beams having respective wavelengths are condensed in the crystal 4 in parallel.

The crystal 4 is made of LiNO ₃ to which MgO is added and has nonlinear optical characteristics. The exit surface of the crystal 4 is inclined with respect to the incident surface, and the shape of the crystal 4 when viewed from a direction perpendicular to the surface intersecting the entrance / exit surface is a wedge shape. When light (fundamental wave) having a wavelength of 1060 nm is incident on the crystal 4, the difference (ns−nf) between the refractive index ns of the second harmonic and the refractive index nf of the incident fundamental wave in the crystal 4 is 0.039. . The coherent length Lc at a wavelength of 1060 nm given by the above-described Equation 1 is 6.8 μm.

In the crystal 4, the crystal length of the portion of the collimated light beam of each wavelength through which the light having the center wavelength of 1060 nm passes is 6.8 mm, which is the coherent length Lc (Lc = 6.8 μm) at the wavelength of 1060 nm. ) 1000 times longer.

The coherent length Lc changes in proportion to the wavelength of the incident light according to the above-described equation 1. When the coherent length Lc changes by 6.4 nm at a wavelength difference of 1 nm, the crystal length that satisfies the phase matching condition changes by 6.4 μm, which is 1000 times the amount of change of the coherent length Lc at a wavelength difference of 1 nm. Therefore, by setting the inclination angle α of the exit surface with respect to the entrance surface to 3.66 ° so that the crystal length is changed by 6.4 μm with respect to the light having a wavelength difference of 1 nm paralleled at intervals of 100 μm, The phase matching condition of the light of the wavelength can be satisfied.

The light of each wavelength transmitted through the crystal 4 and converted into the second harmonic enters the lens 5. The focal length f of the lens 5 is 30 mm, and the aperture is 3 mm. The light beam of each wavelength from the crystal 4 is collected by the lens 5 and enters the multiplexing grating 6.

The multiplexing grating 6 is disposed at the condensing point of the lens 5. The grating interval of the multiplexing grating 6 is 0.55 μm, which is ½ of the grating interval Λ of the spectral grating 2. The multiplexing grating 6 combines the light beams (second harmonics) of the respective wavelengths from the crystal 4 so that the respective principal rays coincide on the same axis. Laser light (second harmonic wave) 7 synthesized by the multiplexing grating 6 is used as output light of the light source device.

FIG. 5A shows the spectral distribution of the laser beam (second harmonic) 7. According to this distribution, the laser beam (second harmonic wave) 7 has a wavelength width, its center wavelength is 530 nm, which is a half value of the wavelength λ of the fundamental wave, and the wavelength interval is the fundamental wave. It is 0.5 nm which is a half of the wavelength interval dλ.

Note that the crystal 4 may have a domain-inverted structure. FIG. 5B schematically shows the polarization inversion structure of the crystal 4. As shown in FIG. 5B, the crystal 4 has a polarization inversion portion 8 in which spontaneous polarization is spatially inverted from the incident surface side to the output surface side. The inversion period of the polarization inversion unit 8 is twice the coherent length of the incident laser light. For example, if the coherent length of laser light (fundamental wave) with a wavelength of 1060 nm is Lc, the inversion period of the portion where the laser light (fundamental wave) of the polarization inversion unit 8 is incident is twice as long as the coherent length Lc. . Thereby, the amplitude of the second harmonic can be increased.

In the polarization inversion unit 8 shown in FIG. 5B, the “+” side region and the “−” side region are alternately arranged from the incident surface side, and viewed from a direction perpendicular to the surface intersecting with the incident / exit surface. The “+” side region and the “−” side region each have a wedge shape. When the total number of “+” side regions and “−” side regions is A (when the crystal length is A times the coherent length Lc), the incident side in each of the “+” side region and the “−” side region The inclination angle of the polarization boundary surface (or exit surface) on the exit side with respect to the polarization interface surface (or entrance surface) is shown in FIG. 5B when the exit surface tilt angle α with respect to the entrance surface of the crystal 4 is 3.66 °. (In FIG. 5B, abbreviated as A = 4, but actually A = 1000), each of the “+” side region and the “−” side region The inclination angle of the outgoing polarization interface (or outgoing surface) with respect to the incoming polarized interface (or incoming surface) is 0.00366 °, which is 1 / A of 3.66 °.

5B includes a “+” side electrode and a “+” side electrode and a “+” side region on a plane intersecting the incident / exit plane of the crystal 4 and a region corresponding to each of the “+” side region and the “−” side region. This can be realized by forming a “−” side electrode and applying a voltage between the “+” side electrode and the “−” side electrode. The shapes of the “+” side electrode and the “−” side electrode are similar to the shapes of the corresponding “+” side region and “−” side region. That is, for each of the electrodes on the “+” side and the “−” side, the inclination angle of the exit end with respect to the entrance end is a value obtained by dividing the inclination angle α by A (for example, 0.00366 °). Is done. Such an electrode can be formed using a photolithography process known as a semiconductor manufacturing process. For example, a comb-shaped electrode may be employed as the electrode.

According to the light source device of the present embodiment, it is possible to improve the tolerance to the incident light intensity by collimating the light of each wavelength to be incident on the crystal 4.

In addition, since the principal ray of each wavelength of light does not diverge within the crystal 4, the aperture of the lens 5 that is a condenser lens can be reduced. Thereby, a small and lightweight light source device can be provided as a light source for generating a second harmonic light beam having a wavelength width.

The display image with less speckle noise can be provided by applying the light source device of the present embodiment to an image display device that scans a laser beam.

In the light source device of this embodiment, LiNO ₃ is used as the nonlinear optical material for forming the crystal 4, but instead, various nonlinear optical materials such as BBO, LBO, CLBO, and KTP may be used.

Further, if the collimated light of each wavelength satisfies the phase matching condition (pseudo phase matching condition), the size of the crystal 4 and the inclination angle α of the exit surface with respect to the entrance surface can be any value. Good.

The laser 1 used as the fundamental wave may be of any center wavelength as long as it oscillates in the longitudinal multimode. For example, the laser 1 may be a super luminescent diode.

If the fundamental wave incident on the spectral grating 2 is combined into one beam by the multiplexing grating 6 and satisfies the condition for phase matching with the crystal 4, the spectral grating 2 and the multiplexing grating 6 The lattice spacing, the focal lengths and the apertures of the lenses 3 and 5 may be any values.

In place of the spectral grating 2 and the combining grating 6, a refractive index dispersion means such as a prism may be used.

A concave mirror may be used instead of the lenses 3 and 5.

Further, each of the lenses 3 and 5 may be composed of a combination of a convex lens 2001 and a concave lens 200 as shown in FIG. 5C. According to this configuration, since the lenses 3 and 5 can be configured with an optical system having a short focal length, the size can be reduced.

Further, in the light source device using the wedge-shaped crystal 4 (or the wedge-shaped polarization inversion structure) as in the present embodiment, means for moving the crystal 4 in the movement direction 9 may be provided. According to this configuration, it is possible to continuously adjust the phase matching for each wavelength by moving the crystal 4 in the moving direction 9. Here, the moving direction 9 is a direction that intersects the principal ray of each wavelength that is split by the spectroscopic grating 2 and collimated by the lens 3.
(Second Embodiment)
FIG. 6A is a schematic diagram illustrating a configuration of a light source device according to a second embodiment of the present invention.

Referring to FIG. 6A, the light source device is different from the light source device of the first embodiment in that a laser group 11 is used in place of the laser 1 and the spectral grating 2 in the configuration shown in FIG. 5A. In FIG. 6A, the same components as those of the light source device of the first embodiment are denoted by the same reference numerals.

The laser group 11 includes 2N + 1 lasers having different oscillation wavelengths arranged in parallel. For convenience, FIG. 6A shows a laser 11a having an oscillation wavelength λ, a laser 11b having an oscillation wavelength of (λ + N · dλ), and a laser 11c having an oscillation wavelength of (λ−N · dλ). Yes. The oscillation wavelength λ of the laser 11a is 1060 nm. Here, N is a positive integer, and dλ is 1 nm, for example. According to this condition, N lasers whose oscillation wavelengths are shifted by 1 nm from the oscillation wavelength λ of the laser 11a located at the center are arranged in parallel on both sides of the laser 11a.

FIG. 6B shows the range of the oscillation wavelength of the laser group 11 when N is 10. In this example, the laser group 11 includes 21 lasers, and the wavelength range of laser light output from each laser is 1050 nm to 1070 nm as a whole. The interval between the laser beams from each laser (the interval between the optical axes) is 100 μm, and the beam diameter is 100 μm (beam area 0.0079 mm ² ).

The laser light of each wavelength from the laser group 11 is a parallel light bundle, and is incident on the crystal 4 in parallel. The output of each laser constituting the laser group 11 is 3 mW, and the energy of laser light incident on the crystal 4 from the laser group 11 is 63 mW in total.

Since the laser light of each wavelength is incident on the crystal 4 in parallel at intervals of 100 μm, the incident energy density is 0.38 W / m ² . This value is smaller than 0.5 W / m ² which is the light resistance of the lithium niobate (LiNO ₃ ) crystal. Therefore, the structure using the laser group 11 can improve the tolerance to the incident light intensity. Note that a longitudinal mode single semiconductor laser or a super luminescent diode is used for each wavelength of the laser constituting the laser group 11.

According to the light source device of this embodiment, it is possible to improve resistance to incident light intensity by arranging a plurality of lasers having different wavelengths in parallel and allowing laser light from each laser to enter the crystal in parallel. It is.

Further, since the chief rays of the laser light of each wavelength do not diverge within the crystal 4, the aperture of the condenser lens can be reduced, and as a result, a light source that generates a second harmonic light beam having a wavelength width that is small and lightweight. Can be realized.

Further, by applying the light source device of the present embodiment to an image display device that scans a laser beam, a display image with less speckle noise can be provided.

In the light source device of this embodiment, LiNO ₃ is used as the nonlinear optical material for forming the crystal 4, but various nonlinear optical materials such as BBO, LBO, CLBO, and KTP may be used instead.

The size of the crystal 4 and the inclination angle of the exit surface with respect to the entrance surface may be set to any values as long as the parallelized light of each wavelength satisfies the phase matching condition (pseudo phase matching condition).

If the incident fundamental wave is synthesized into one beam by the multiplexing grating 6 and satisfies the condition that the phase matching with the crystal 4 is satisfied, each grating interval of the multiplexing grating 6, the focal length of the lens 5, and the like. The aperture may have any value.

Instead of the multiplexing grating 6, a refractive index dispersion means such as a prism may be used.

A concave mirror may be used instead of the lens 5.
(Third embodiment)
FIG. 7A is a schematic diagram illustrating a configuration of a light source device according to a third embodiment of the present invention.

Referring to FIG. 7A, the light source device is different from the light source device of the second embodiment in that a modulation element group 21 is added to the configuration shown in FIG. 6A. In FIG. 7A, the same reference numerals are given to the same components as those of the light source device of the second embodiment.

The laser group 11 includes N lasers having different oscillation wavelengths arranged in parallel. In FIG. 7A, for convenience, a laser 11a having an oscillation wavelength λ, a laser 11b having an oscillation wavelength of [λ + (N / 2) · dλ], and an oscillation wavelength of [λ− (N / 2-1) · dλ And a laser 11c given in FIG. The oscillation wavelength λ of the laser 11a is 1060 nm, and N is a positive integer.

The modulation element group 21 is composed of N modulation elements provided in each of the lasers of each wavelength constituting the laser group 11. For example, an acousto-optic element is used as the modulation element. Each laser constituting the laser group 11 and each modulation element constituting the modulation element group 21 correspond one-to-one. By controlling each modulation element, on / off control of laser light of each wavelength is performed.

FIG. 7B shows the oscillation wavelength range of the laser group 11 when N is 8. In this example, the laser group 11 includes eight lasers, and the wavelength range of laser light output from each laser is 1057 nm to 1064 nm as a whole. The interval between laser beams from each laser is 100 μm, and the beam diameter is 100 μm. The wavelength interval is 1 nm.

The weight of the laser beam output from each laser is weighted at a different rate. Specifically, the ratio to the laser beam having a wavelength of 1060 nm is 128, the ratio to the laser beam having a wavelength of 1061 nm is 64, the ratio to the laser beam having a wavelength of 1059 nm is 32, the ratio to the laser beam having a wavelength of 1062 nm is 16, and the laser beam having a wavelength of 1058 nm is used. Intensity weighting is performed with a ratio of 8 to a laser beam having a wavelength of 1063 nm, a ratio of 4 to a laser beam having a wavelength of 1057 nm, and a ratio of 1 to a laser beam having a wavelength of 1064 nm.

By performing the weighting as described above, it is possible to stably supply a multi-gradation image in digital video. More specifically, when an image composed of a plurality of pixels is displayed with 256 gradations, the modulation element group 21 selects a laser combination corresponding to the luminance of the pixel for each pixel. For example, for a pixel whose luminance data is 160, a laser with a ratio of 128 (wavelength 1060 nm) and a laser with a ratio of 32 (wavelength 1059 nm) are selected. Thus, by performing laser selection control for each pixel, a multi-gradation image can be stably supplied.

In the above laser selection control, there are pixels where only one laser is selected depending on the brightness. However, it is rare that one laser having the same wavelength is selected at the same time in all pixels. Further, since the luminance of the pixel changes according to the video signal, it is rare that a state where only one laser is selected continues for a long time. Therefore, in the laser selection control described above, speckle noise may occur partially and instantaneously when viewed in the entire image, but the effect of such speckle noise on image quality is small. .

FIG. 7C is a block diagram showing a configuration of an image display device equipped with the light source device of the present embodiment. Referring to FIG. 7C, the main part of the image display device includes a color synthesis optical system 31, a blue light source 32, a red light source 33, a light source device 51, a signal processing device 52, and scanning means 53.

The light source device 51 is the light source device shown in FIG. 7A and is used as a green light source. The blue light source 32 and the red light source 33 are composed of vertical multimode semiconductor lasers. The wavelength of the blue light source 32 is 445 nm, the wavelength of the red light source 33 is 645 nm, and both output collimated laser light.

The color synthesis optical system 31 includes first and second dichroic mirrors. The first dichroic mirror is disposed at a position where the laser light (red) from the red light source 33 and the laser light (green) from the light source device 51 intersect. The laser light from the light source device 51 passes through the first dichroic mirror. The laser light from the red light source 33 is reflected by the first dichroic mirror so as to be directed in the same direction as the laser light (transmitted light) from the light source device 51.

The second dichroic mirror is disposed at a position where the laser light (red / green) from the first dichroic mirror and the laser light (blue) from the blue light source 32 intersect. The laser light from the first dichroic mirror passes through the second dichroic mirror. The laser light from the blue light source 32 is reflected by the second dichroic mirror so as to be directed in the same direction as the laser light (transmitted light) from the first dichroic mirror. Laser light (red / green / blue) from the second dichroic mirror is supplied to the scanning means 53.

The signal processing device 52 receives the video signal 54 from an external device such as a personal computer. The video signal 54 includes bit information related to video of each color of red (R), green (G), and blue (B). The signal processing device 52 generates a signal for intensity-modulating the laser beam corresponding to each color (wavelength) based on the bit information regarding the RGB color images of the video signal 54. Specifically, in the signal processing device 52, the bit information regarding the green (G) video is converted into a signal for driving each modulation element of the light source device 51, and the bit information regarding the blue (B) and red (R) video. Are converted into signals for intensity-modulating the blue light source 32 and the red light source 33, respectively. The blue light source 32 and the red light source 33 are modulated by controlling current drive.

In each of the light source device 51, the blue light source 32, and the red light source 33, when intensity modulation is performed in accordance with a signal from the signal processing device 52, RGB modulated light 56 is supplied from the color synthesis optical system 31 to the scanning unit 53. The scanning unit 53 scans the screen with the RGB modulated light 56 supplied from the color synthesis optical system 31. The scanning of the RGB modulated light 56 by the scanning unit 53 is performed in synchronization with the synchronization signal 55 output from the signal processing device 52, and a display image 57 is displayed on the screen.

The image definition is 1280 horizontal pixels and 1024 vertical pixels. The scanning unit 53 includes a resonant micromechanical scanning element for performing horizontal scanning and a galvanometer mirror for performing vertical scanning. The drive frequency of the resonant micromechanical scanning element is, for example, 31 KHz. The galvanometer mirror is driven by a sawtooth wave, and the drive frequency is, for example, 60 Hz.

The intensity modulation of the laser beam is performed every 12.7 ns in synchronization with the scanning element. Thereby, the light of the brightness | luminance according to a pixel value is obtained.

Also in the light source device of this embodiment, a light source that generates a second harmonic light beam having a small wavelength and a wide wavelength range can be provided. In addition, an image display device including the light source device of the present embodiment can provide an image display with less speckle noise and good gradation reproduction characteristics.

The light source device of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate. For example, the laser intensity modulation in the blue light source 32 and the red light source 33 may be performed by performing pulse width modulation within the time for scanning one pixel.

The image definition may be set appropriately. However, the scanning frequency of the scanning element and the modulation frequency of the laser are frequencies corresponding to the image definition.

The modulation element used in the modulation element group may be other than the acousto-optic element. For example, various optical modulators such as an electro-optic crystal, a Mach-Tunda type waveguide modulation element, and a MEMS modulation element may be used as the modulation element.
(Fourth embodiment)
FIG. 8A is a schematic diagram illustrating a configuration of a light source device according to a fourth embodiment of the present invention.

Referring to FIG. 8A, the light source device has an infrared laser group 41, modulation element groups 42a to 42c, a crystal 43, a lens 44, a multiplexing grating 45, a blue laser group 46, and a red laser group 47.

The infrared laser group 41, the modulation element group 42a, the crystal 43, the lens 44, and the multiplexing grating 45 are the laser group 11, the modulation element group 21, the crystal 4, the lens 5, and the multiplexing grating shown in FIG. 7A. Same as 6. The light source device of the present embodiment is different from the light source device of the third embodiment in that modulation element groups 42b and 42c, a blue laser group 46, and a red laser group 47 are added to the configuration shown in FIG. 7A. .

Each of the infrared laser group 41, the blue laser group 46, and the red laser group 47 has N lasers with different oscillation wavelengths arranged in parallel, and the oscillation wavelengths of the lasers are as shown in FIG. 7A. It is the same relationship. However, the oscillation wavelength λ of the laser arranged at the center of the infrared laser group 41 is 1060 nm, the oscillation wavelength λ of the laser arranged at the center of the blue laser group 46 is 445 nm, and the center of the red laser group 47 is The oscillation wavelength λ of the arranged laser is 645 nm. N is a positive integer.

The modulation element group 42b is composed of N modulation elements provided in each of the lasers of the respective wavelengths constituting the blue laser group 46. For example, an acousto-optic element is used as the modulation element. Each laser constituting the blue laser group 46 and each modulation element constituting the modulation element group 42b correspond one-to-one. By controlling each modulation element, on / off control of laser light of each wavelength is performed.

The modulation element group 42 c is composed of N modulation elements provided for each of the lasers of each wavelength constituting the red laser group 47. For example, an acousto-optic element is used as the modulation element. Each laser constituting the red laser group 47 and each modulation element constituting the modulation element group 42c have a one-to-one correspondence. By controlling each modulation element, on / off control of laser light of each wavelength is performed.

The multiplexing grating 45 is supplied from the infrared laser group 41 via the modulation element group 42a, the crystal 43 and the lens 44, and from the blue laser group 46 via the modulation element group 42b. The laser beam (blue) and the laser beam (red) supplied from the red laser group 47 via the modulation element group 42c are combined to generate one white laser beam.

Also in the present embodiment, in the infrared laser group 41, the blue laser group 46, and the red laser group 47, the intensity of the laser light output from each laser is weighted at a different rate. For example, when the infrared laser group 41, the blue laser group 46, and the red laser group 47 are each composed of eight lasers, the following intensity weighting is performed.

In the infrared laser group 41, the ratio to the laser beam having a wavelength of 1060 nm is 128, the ratio to the laser beam having a wavelength of 1061 nm is 64, the ratio to the laser beam having a wavelength of 1059 nm is 32, the ratio to the laser beam having a wavelength of 1062 nm is 16, and the wavelength is 1058 nm. Intensity weighting is performed with a ratio of 8 for the laser light of 4, a ratio of 4 for the laser light of wavelength 1063 nm, a ratio of 2 for the laser light of wavelength 1057 nm, and a ratio of 1 for the laser light of wavelength 1064 nm.

In the blue laser group 46, the ratio to the laser beam having a wavelength of 445 nm is 128, the ratio to the laser beam having a wavelength of 446 nm is 64, the ratio to the laser beam having a wavelength of 444 nm is 32, the ratio to the laser beam having a wavelength of 447 nm is 16, and Intensity weighting is performed with a ratio of 8 for laser light, 4 for laser light with a wavelength of 448 nm, 2 for laser light with a wavelength of 442 nm, and 1 for laser light with a wavelength of 449 nm. In this case, a longitudinal mode single semiconductor laser that oscillates at a wavelength of about 440 nm is used as the laser of each wavelength.

In the red laser group 47, the ratio to the laser beam having a wavelength of 645 nm is 128, the ratio to the laser beam having a wavelength of 646 nm is 64, the ratio to the laser beam having a wavelength of 644 nm is 32, the ratio to the laser beam having a wavelength of 647 nm is 16, and the wavelength is 643 nm. Intensity weighting is performed, with the ratio to the laser light being 8, the ratio to the laser light having a wavelength of 648 nm is 4, the ratio to the laser light having a wavelength of 642 nm is 2, and the ratio to the laser light having a wavelength of 649 nm is 1. In this case, a longitudinal mode single semiconductor laser that oscillates at a wavelength of 640 nm is used as the laser of each wavelength.

By weighting as described above, it is possible to stably supply a multi-gradation image in a digital color image. More specifically, in each of the infrared laser group 41, the blue laser group 46, and the red laser group 47, for each pixel, a laser combination corresponding to the luminance of the pixel is selected by the modulation element group. As a result, a multi-gradation image can be stably supplied for each of the red, green, and blue images.

FIG. 8B is a block diagram showing a configuration of an image display device equipped with the light source device of the present embodiment. Referring to FIG. 8B, the main part of the image display device includes a light source device 51, a signal processing device 52, and scanning means 53. The light source device 51 is the light source device shown in FIG. 8A.

The signal processing device 52 receives the video signal 54 from an external device such as a personal computer. The video signal 54 includes bit information related to video of each color of red (R), green (G), and blue (B). The signal processing device 52 generates a signal for intensity-modulating the laser beam corresponding to each color (wavelength) based on the bit information regarding the RGB color images of the video signal 54. Specifically, the bit information regarding the green (G) video is converted into a signal for driving the modulation element group 42 a provided in the infrared laser group 41. Bit information relating to the blue (B) video is converted into a signal for driving the modulation element group 42 b provided in the blue laser group 46. Bit information relating to the red (R) video is converted into a signal for driving the modulation element group 42 c provided in the red laser group 47.

When each of the modulation element groups 42 a to 42 c is driven in accordance with a signal from the signal processing device 52, the RGB modulated light 56 is supplied from the light source device 51 to the scanning unit 53. The scanning unit 53 scans the screen with the RGB modulated light 56 supplied from the light source device 51. The scanning of the RGB modulated light 56 by the scanning unit 53 is performed in synchronization with the synchronization signal 55 output from the signal processing device 52, and a display image 57 is displayed on the screen.

The image definition is 1280 horizontal pixels and 1024 vertical pixels. The scanning unit 53 includes a resonant micromechanical scanning element for performing horizontal scanning and a galvanometer mirror for performing vertical scanning. The drive frequency of the resonant micromechanical scanning element is, for example, 31 KHz. The galvanometer mirror is driven by a sawtooth wave, and the drive frequency is, for example, 60 Hz.

The intensity modulation of the laser beam is performed every 12.7 ns in synchronization with the scanning element. Thereby, the light of the brightness | luminance according to a pixel value is obtained.

Also in the light source device of this embodiment, a light source that generates a second harmonic light beam having a small wavelength and a wide wavelength range can be provided. In addition, an image display device including the light source device of the present embodiment can provide an image display with less speckle noise and good gradation reproduction characteristics.

The light source device of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate. For example, the image definition may be set as appropriate. However, the scanning frequency of the scanning element and the modulation frequency of the laser are frequencies corresponding to the image definition.

The modulation element used in the modulation element group may be other than the acousto-optic element. For example, various optical modulators such as an electro-optic crystal, a Mach-Tunda type waveguide modulation element, and a MEMS modulation element may be used as the modulation element.

According to an aspect of the present invention, a light source device includes a first end surface and a second end surface that faces the first end surface, and is perpendicular to a plane that intersects each of the first and second end surfaces. The second end face is inclined with respect to the first end face when viewed from any direction, an optical crystal that generates harmonics of light incident from the first end face, and in the plane A plurality of coherent light beams having different wavelengths, which are collimated so as to travel in parallel, are incident on the first end face; and a plurality of second harmonics having different wavelengths output from the second end face. A means for combining the waves, and the phase matching for generating the harmonics in the optical crystal is continuously taken in a direction intersecting with the respective beam axes of the plurality of coherent lights. .

In the above light source device, the coherent light supply means includes means comprising the laser 1, the spectral grating 2 and the lens 3 described in the first embodiment, and the laser group 11 described in the second and third embodiments. This corresponds to the infrared laser group 41 described in the fourth embodiment.

The coherent light supply means includes a laser light source, a spectroscopic means for spectroscopically splitting the laser light from the laser light source, and a first lens for collimating the principal rays of each wavelength split by the spectroscopic means. Also good. The spectroscopic means may be a diffraction grating or a prism.

The coherent light supply means may be composed of a plurality of laser light sources having different oscillation wavelengths, and the laser light from each laser light source may be collimated so as to travel in parallel in the plane.

The laser light source or the plurality of laser light sources may be a longitudinal multimode semiconductor laser or a super luminescent diode.

It may further include a modulation means for individually modulating the intensity of each wavelength of laser light from a plurality of laser light sources. Weighting may be applied to the intensity of laser light output from a plurality of laser light sources at different rates.

The optical crystal corresponds to the crystal 4 described in the first to fourth embodiments. The optical crystal has a domain-inverted structure in which spontaneous polarization is spatially inverted from the first end surface toward the second end surface, and a direction perpendicular to the plane of each polarization region of the domain-inverted structure The shape when viewed from above may be a wedge shape. The inversion period of the domain-inverted structure may continuously change in a direction intersecting with each light axis of the plurality of coherent lights in the plane.

The multiplexing means corresponds to the means including the lens 5 and the grating 6 described in the first to fourth embodiments. The multiplexing means combines the second lens for collecting the second harmonic light output from the second end face of the optical crystal and the second harmonic light from the second lens. You may have a diffraction grating or a prism to wave.

The light source device further includes another light source that generates light having a wavelength different from the wavelengths of the plurality of coherent lights, and the multiplexing unit includes the second harmonic light and the other light source. You may combine light. Other light sources correspond to the red light source and blue light source described in the third embodiment, and the red laser group and blue laser group described in the fourth embodiment.

The light source device may include a moving unit that moves the optical crystal in a direction intersecting with each light axis of the plurality of coherent lights in the plane. According to this configuration, the following effects can be obtained.

Generally, the oscillation wavelength of a laser light source varies depending on the manufacturing rod. For example, there is a manufacturing variation in which an oscillation wavelength of a laser light source in one rod is 1060 nm and an oscillation wavelength of a laser light source in another rod is 1063 nm. Since the oscillation wavelength varies in this way, for example, in a wavelength conversion element having a waveguide structure as shown in FIG. Efficiency is reduced. According to the light source device including the moving means described above, even if the oscillation wavelength of the laser light source varies, it is possible to accurately adjust the phase matching for each wavelength by moving the optical crystal.

According to another aspect of the present invention, an image display device includes the above-described light source device and means for scanning an external screen with a second harmonic light beam output from the light source device.

According to another aspect of the present invention, an image display device includes: a light source device including the above-described modulation unit; a signal processing unit that controls the modulation unit of the light source device according to an input video signal; and the light source device. Means for scanning the external screen with the output second harmonic light beam.

According to the light source device of the present invention described above, the coherent light of each wavelength is made parallel to each other and incident on the optical crystal, so that it is possible to improve resistance to incident light intensity.

In addition, since the principal ray of each wavelength does not diverge in the optical crystal, the aperture of the condensing lens constituting the multiplexing means can be reduced. Thereby, a small and lightweight light source device can be provided as a light source for generating a second harmonic light beam having a wavelength width.

According to the image display device of the present invention, a display image with less speckle noise can be provided by using the light source device that generates the second harmonic light beam having the above-described wavelength width.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and operation of the present invention without departing from the spirit of the present invention.

This application claims priority based on Japanese Patent Application No. 2008-232254 filed on Sep. 10, 2008, the entire disclosure of which is incorporated herein.

Claims (15)

A second end face provided with a first end face and a second end face opposed to the first end face, when viewed from a direction perpendicular to a plane intersecting each of the first and second end faces; Is inclined with respect to the first end face, and generates an optical harmonic wave of light incident from the first end face;
Coherent light supply means for making a plurality of coherent lights having different wavelengths collimated to travel in parallel in the plane enter the first end face;
Combining means for combining a plurality of second harmonics having different wavelengths output from the second end face;
The light source device, wherein phase matching for generating the harmonics in the optical crystal is continuously taken in a direction intersecting with the respective light axis of the plurality of coherent lights. The optical crystal has a domain-inverted structure in which spontaneous polarization is spatially inverted from the first end surface toward the second end surface, and a direction perpendicular to the plane of each polarization region of the domain-inverted structure The light source device according to claim 1, wherein the light source device has a wedge shape when viewed from above. The light source device according to claim 2, wherein an inversion period of the polarization inversion structure continuously changes in a direction intersecting with each light axis of the plurality of coherent lights in the plane. The coherent light supply means includes
A laser light source;
A spectroscopic means for splitting laser light from the laser light source;
The light source device according to any one of claims 1 to 3, further comprising a first lens for collimating chief rays of respective wavelengths separated by the spectroscopic means. The light source device according to claim 4, wherein the spectroscopic means is formed of a diffraction grating or a prism. The light source device according to claim 4 or 5, wherein the laser light source is a longitudinal multimode semiconductor laser or a super luminescent diode. The coherent light supply means includes a plurality of laser light sources having different oscillation wavelengths, and the laser light from each laser light source is collimated so as to travel in parallel in the plane. 4. The light source device according to any one of items 3. The light source device according to claim 7, wherein the plurality of laser light sources are longitudinal multimode semiconductor lasers or superluminescent diodes. The light source device according to claim 7 or 8, further comprising modulation means for individually modulating the intensity of laser light of each wavelength from the plurality of laser light sources. The light source device according to claim 9, wherein weighting is performed at different ratios with respect to the intensities of the laser beams output from the plurality of laser light sources. The multiplexing means is
A second lens for collecting the second harmonic light output from the second end face of the optical crystal;
11. The light source device according to claim 1, further comprising a diffraction grating or a prism for combining the second harmonic light from the second lens. And further comprising another light source that generates light having a wavelength different from the wavelength of the plurality of coherent lights,
The light source device according to any one of claims 1 to 11, wherein the multiplexing unit combines the second harmonic light and the light from the other light source. The light source device according to any one of claims 1 to 12, further comprising a moving unit that moves the optical crystal in a direction intersecting with each light axis of the plurality of coherent lights in the plane. . A light source device according to any one of claims 1 to 13,
An image display device comprising means for scanning an external screen with a second harmonic light beam output from the light source device. A light source device according to claim 9 or 10, and
Signal processing means for controlling the modulation means of the light source device in accordance with an input video signal;
An image display device comprising means for scanning an external screen with a second harmonic light beam output from the light source device.

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