JP2010224311A - Laser light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser light source device for effectively reducing speckle contrast without using a mechanical sliding part in particular. <P>SOLUTION: The laser light source device (100) has: a laser light source (110) for emitting laser light; a liquid crystal modulation element (120) for controlling a polarizing state of the laser light emitted from the laser light source (110); a polarizing beam splitter (130) for branching the laser light whose polarizing state is controlled by the liquid crystal modulation element (120) into P polarization (230) and S polarization (240) to have an optical path difference to be propagated so as to be composed thereafter; a first rectangular prism (140); and a second rectangular prism (150). The liquid crystal modulation element (120) controls the polarizing state of the laser light by electrically controlling at least one of birefringence and optical rotation for the laser light on each of a plurality of areas dividing an radiation range of the laser light emitted from the laser light source (110). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser light source device used as a light source of a display device, for example.

  In recent years, attempts to use a laser light source as a light source of a display device such as a projection device have become active. Laser light has a narrow wavelength width and high color purity. The laser light source is a device that is smaller, has a higher output, and has a longer lifetime than a general lamp light source. Therefore, by adopting the laser light source, it is possible to achieve a wide color gamut, thinning, high brightness, and long life of the display device.

  On the other hand, laser light has a feature that a bright and dark pattern called speckle noise is easily imaged on the retina of an observer. Speckle noise (hereinafter simply referred to as “speckle”) is caused by high coherence characteristics (coherence) of laser light. In particular, in the case of a display application, that is, when laser light is converted into planar light and used for video output, speckles are observed superimposed on the video, causing a problem of video degradation. appear.

  Therefore, for example, Patent Document 1 and Patent Document 2 describe a technique for reducing speckle of laser light by superimposing a plurality of speckle patterns.

  The apparatus described in Patent Document 1 divides laser light into two light components by a polarizing beam splitter (PBS), and these two light components are equal to or greater than the coherence length (coherence distance) of the laser light. Synthesize after propagation with optical path difference. That is, the laser light is converted into combined light of two light components that do not interfere with each other. Thereby, the integration effect of two speckle patterns can be obtained, the coherence characteristic can be reduced, and the speckle density ratio (speckle contrast) can be reduced.

  The apparatus described in Patent Document 2 uses a half mirror to divide and synthesize laser light.

  Further, for example, Patent Literature 3 and Patent Literature 4 describe a technique for reducing speckle of laser light by superimposing a plurality of speckle patterns on a time average basis.

  The apparatus described in Patent Document 3 moves the irradiation position of the laser beam on the irradiation surface at a high speed by rotating the variable angle mirror, and changes the speckle pattern with time. Thereby, an integration effect of a plurality of speckle patterns can be obtained, the coherence characteristic can be lowered, and the speckle contrast can be reduced.

The apparatus described in Patent Document 4 uses a VA (vertical alignment) liquid crystal element to change the speckle pattern by performing phase modulation that changes only the phase without changing the polarization state of the laser light. .
JP 2001-296503 A JP 2000-223396 A JP-A-63-100461 JP 2007-163702 A

  However, since the technique described in Patent Document 3 requires a mechanical sliding part such as a variable angle mirror and its driving device, there is a problem in the reliability, life and quietness of the device.

  Since each technique described in Patent Document 1, Patent Document 2, and Patent Document 4 does not require a mechanical sliding portion, such a problem does not occur.

  However, in the techniques described in Patent Document 1 and Patent Document 2, since speckles for each light component are in a fixed state, it is difficult to sufficiently reduce speckle contrast.

  In the technique described in Patent Document 4, the integration effect is low, and it is difficult to sufficiently reduce the speckle contrast. This is apparent from the fact that there are many residual speckles, although the phase information is modulated when laser light is transmitted through a rotating lenticular lens.

  Therefore, it is conceivable to combine the technique described in Patent Document 1 or Patent Document 2 and the technique described in Patent Document 4. However, only the phase modulation is performed for each divided light component, and it is difficult to sufficiently reduce the speckle contrast.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a laser light source device capable of effectively reducing speckle contrast without using a mechanical sliding portion.

  In the laser light source device of the present invention, a polarization state is controlled by a light source unit that emits laser light, a polarization state control unit that controls a polarization state of the laser light emitted from the light source unit, and the polarization state control unit. Further, a branching unit for branching the laser light into a first polarization component and a second polarization component, and an optical path difference between the first polarization component and the second polarization component branched by the branching unit. The polarization state control means is configured to combine the laser light for each of a plurality of areas obtained by dividing the irradiation range of the laser light emitted from the light source unit. The polarization state of the laser beam is controlled by electrically controlling at least one of birefringence and optical rotatory power.

  According to the present invention, since the ratio of two light components giving an optical path difference can be electrically controlled for each divided area, speckle contrast is effectively reduced without using a mechanical sliding part. Can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a plan view showing the configuration of the laser light source apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, the laser light source device 100 includes a laser light source 110, a liquid crystal modulation element 120, a polarization beam splitter 130, a first right-angle prism 140, and a second right-angle prism 150.

  Hereinafter, in each figure, the right direction in the horizontal direction of the paper, which is the normal direction of the main surface of the liquid crystal modulation element 120, is the positive direction of the Z axis, and the upward direction in the vertical direction of the paper is the positive direction of the Y axis. Of the directions orthogonal to these directions, the depth direction in the drawing is the positive direction of the X axis. Further, the terms P-polarized light and S-polarized light are used with reference to the polarization separation surface of the polarization beam splitter described later.

  The laser light source 110 emits laser light. Here, it is assumed that the laser light source 110 emits the laser light 210 in the positive direction of the Z axis. The laser light 210 is assumed to be P-polarized light that vibrates in the Y-axis direction.

  The liquid crystal modulation element 120 is arranged in the positive direction of the Z-axis as viewed from the laser light source 110, enters the laser light 210 emitted from the laser light source 110, converts it into the laser light 220, and emits it in the positive direction of the Z-axis. To do.

  At this time, the liquid crystal modulation element 120 electrically controls at least one of birefringence and optical rotation with respect to the laser light 220 for each area (hereinafter referred to as “divided area”) obtained by dividing the irradiation range of the laser light 210. . Thereby, the liquid crystal modulation element 120 can control the polarization state of the laser light 220. Specifically, the liquid crystal modulation element 120 can emit, for example, a laser beam 220 obtained by converting all or part of the P-polarized component of the laser beam 210 into an S-polarized component. Hereinafter, in the laser light 220 emitted from the liquid crystal modulation element 120, the P-polarized component is simply referred to as “P-polarized light”, and the S-polarized component is simply referred to as “S-polarized light”. The configuration of the liquid crystal modulation element 120 will be described later.

  The polarization beam splitter 130 splits the laser light 220 emitted from the liquid crystal modulation element 120 into P-polarized light 230 and S-polarized light 240. Specifically, the polarizing beam splitter 130 emits the P-polarized light 230 in the positive direction of the Z-axis by the transmission action, and converts the S-polarized light 240 into the Y-axis by the transmission action and the reflection action at the polarization separation surface 131. The light is deflected in the positive direction and emitted.

  The first right-angle prism 140 and the second right-angle prism 150 combine the P-polarized light 230 and the S-polarized light 240 emitted from the polarization beam splitter 130 after propagating them with an optical path difference. Specifically, the first right-angle prism 140 and the second right-angle prism 150 cause the S-polarized light 240 to propagate through the predetermined optical path length by the action of reflection, and then return to the polarization separation surface 131 of the polarization beam splitter 130 again. Make it incident. The predetermined optical path length is preferably longer than the coherence length of the laser light 210 emitted from the laser light source 110. In the present embodiment, it is assumed that the predetermined optical path length is equal to or longer than the coherence length of the laser beam 210. Also, an arbitrary optical path difference can be set by setting the positions of the first right-angle prism 140 and the second right-angle prism 150 in the Y-axis direction.

  The position where the S-polarized light 240 re-enters the polarization beam splitter 130 is a position where the S-polarized light 240 is first reflected on the polarization separation surface 131. The direction of incidence of the S-polarized light 240 on the polarization beam splitter 130 is the positive direction of the Y axis, that is, the direction in which the S-polarized light 240 is first emitted from the polarization separation surface 131. As a result, the polarization beam splitter 130 deflects the re-incident S-polarized light 240 from the same position as the P-polarized light 230 in the positive direction of the Z-axis by the action of reflection on the polarization separation surface 131 and emits it. As a result, the P-polarized light 230 and the S-polarized light 240 are combined again in a state where an optical path difference equal to or greater than the coherence length of the laser light 210 is generated, and is emitted as the laser light 250.

  The laser light 250 emitted from the laser light source device 100 is given an expansion action and a diffusion action by a subsequent optical system, and reaches, for example, a diffusion surface such as a diffusion plate of the projection apparatus.

  According to the laser light source device 100 having such a configuration, the laser light 250 with reduced coherence can be generated, and speckle noise observed on the diffusion surface can be reduced. Further, the electrical control of the liquid crystal modulation element 120 can easily change the ratio of the P-polarized light 230 and the S-polarized light 240 for each divided area.

  Next, the configuration and operation of the liquid crystal modulation element 120 will be described.

  As a driving method of the liquid crystal modulation element 120, various methods capable of imparting a polarization rotation action to transmitted light can be employed. Examples of such a driving method include a TN (twisted nematic) method, a VA method, and an IPS (in-plane switching) method.

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the TN liquid crystal modulation element 120.

  As shown in FIG. 2, the TN liquid crystal modulation element 120 includes a pair of glass substrates 121 and 122 that are spaced apart from each other. The glass substrates 121 and 122 have a pair of transparent electrodes 123 and 124 disposed on the surfaces facing each other (hereinafter referred to as “inside”), and a pair of alignment films 125 and 126 disposed further inside. Respectively. A liquid crystal layer 127 is formed between the alignment film 125 and the alignment film 126 by filling and sealing the liquid crystal.

  The groove direction of the alignment film 125 and the groove direction of the alignment film 126 are orthogonal to each other. Here, the groove direction of the alignment film 125 is the Y-axis direction, and the groove direction of the alignment film 126 is the X-axis direction. That is, the groove direction of the alignment film 125 arranged on the side on which the laser beam 210 is incident coincides with the polarization direction of the laser beam 210.

  Therefore, the liquid crystal modulation element 120 continuously rotates the liquid crystal molecules in the liquid crystal layer 127 from the alignment film 125 side to the alignment film 126 side at an angle corresponding to the magnitude of the voltage applied to the transparent electrodes 123 and 124. The polarization direction of the laser light 220 can be rotated.

  Further, the rotation angle of the polarization direction in the liquid crystal modulation element 120 (hereinafter referred to as “deflection rotation angle”) is 90 degrees at the maximum. Therefore, the liquid crystal modulation element 120 can convert P-polarized light into S-polarized light or light including both components of P-polarized light and S-polarized light at a predetermined ratio. Alternatively, the liquid crystal modulation element 120 can output P-polarized light as it is.

  The transparent electrodes 123 and 124 can control the voltage to be applied for each of the divided areas. Therefore, the liquid crystal modulation element 120 can arbitrarily change the ratio of the P-polarized light and the S-polarized light of the laser light 220 for each divided area.

  Note that the above-described TN liquid crystal modulation element or the like rotates the polarization by optical rotation and outputs a substantially linearly polarized laser beam 220.

  FIG. 3 is a schematic diagram illustrating an example of the configuration of the IPS liquid crystal modulation element 120, and corresponds to FIG.

  As shown in FIG. 3, the IPS liquid crystal modulation element 120 does not have a transparent electrode disposed on the exit side glass substrate 122. In the IPS liquid crystal modulation element 120, the groove direction of the alignment film 126 on the emission side is parallel to the alignment film 125 on the incident side. Also with such a liquid crystal modulation element 120, the ratio of the P-polarized light and the S-polarized light of the laser light 220 can be arbitrarily changed for each divided area.

  Note that the IPS liquid crystal modulation element or the like described above performs polarization rotation by birefringence and outputs elliptically polarized laser light 220. In these methods, the ratio of the P-polarized light and the S-polarized light of the laser light 220 can be arbitrarily changed by changing the axial direction of the elliptically polarized light.

  The configuration of the liquid crystal modulation element 120 of the present embodiment is different from the configuration of a conventional liquid crystal modulation element used in a liquid crystal display device such as a television. This is because the conventional liquid crystal modulation element is intended to control the amount of light transmitted for each pixel, whereas the liquid crystal modulation element 120 of the present embodiment is intended to control the polarization state of the laser light 210. It is.

  Here, for reference, an example of the configuration of a conventional liquid crystal modulation element will be described.

  FIG. 4 is a schematic diagram showing a configuration of a conventional liquid crystal modulation element, and corresponds to FIG. Here, a TN color liquid crystal modulation element will be described as an example.

  The conventional liquid crystal modulation element 10 includes a pair of polarizing plates 11 and 12 and a color filter 13 arranged in crossed Nicols in addition to the configuration of the liquid crystal modulation element 120 of the present embodiment shown in FIG. Further, the conventional liquid crystal modulation element 10 has a crosstalk preventing means (not shown) such as a black matrix arranged so as to surround each pixel in order to prevent crosstalk of light between the pixels and improve the contrast of the image. Z). With this configuration, the conventional liquid crystal modulation element 10 can change the polarization state of light transmitted through the area corresponding to each pixel, for example, in units of subpixels.

  As is clear from a comparison between FIG. 2 and FIG. 4, the liquid crystal modulation element 120 of the present embodiment includes polarizing plates 11 and 12, a color filter 13, and crosstalk that are necessary in the conventional liquid crystal modulation element 10. There is no prevention means.

  The reason why the polarizing plate 11 is not provided is that the laser light 210 having a single polarization direction is used as the incident light. The reason why the polarizing plate 12 is not provided is to change the polarization direction of the emitted light. The reason for not having the crosstalk prevention means is that it is not necessary to prevent the crosstalk.

  As described above, the liquid crystal modulation element 120 of the present embodiment can be manufactured at low cost because the number of parts can be reduced as compared with the conventional liquid crystal modulation element 10.

  Further, in the conventional liquid crystal modulation element 10, the substantial aperture ratio is less than 100% due to the influence of the black matrix or the like, but the liquid crystal modulation element 120 of the present embodiment has a substantial aperture ratio of almost 100%. And a very high transmittance can be realized.

  Further, the transmittance of the liquid crystal modulation element 120 of the present embodiment is about 3.75 times the transmittance of the conventional liquid crystal modulation element 10 even when the black matrix is not considered. This is a numerical value when the incident light is white laser light, the transmittance of the polarizing plate 11 is 80%, the attenuation of the amount of light in the color filter 13 is 1/3, and the polarizing plate 12 is not disposed. The reason why the polarizing plate 12 is not disposed is that when the polarizing plate 12 is disposed, only linearly polarized light is emitted.

  Next, the control of the polarization state by the liquid crystal modulation element 120 and the effect thereof will be described.

  FIG. 5 is a schematic diagram illustrating an example of a state of polarization state control by the liquid crystal modulation element 120. Here, the polarization direction of the laser light 220 when the liquid crystal modulation element 120 is viewed from the positive direction side of the Z axis (hereinafter referred to as “polarization direction after modulation”) is shown.

  As shown in FIGS. 5A and 5B, the light transmission region 300 of the liquid crystal modulation element 120 is divided into a plurality of divided areas in the XY plane. The liquid crystal modulation element 120 has a configuration in which the polarization rotation angle can be individually set for each divided area 310. That is, in the liquid crystal modulation element 120, one or more pairs of transparent electrodes are arranged for each divided area 310, and a voltage applied to the transparent electrode is controlled for each divided area 310. In general, when the polarization direction of light rotates, the phase is also modulated.

  The laser beam 210 incident on the liquid crystal modulation element 120 can be considered as an aggregate of a plurality of minute laser beams that are continuous in the irradiation range (transmission range) 211 of the laser beam 210 and have the respective divided areas 310 as the irradiation ranges. Therefore, by performing modulation for each divided area 310, it is possible to perform polarization state control with a high degree of freedom for the entire emitted laser light 220.

  This polarization state control includes control as to how much the minute laser light transmitted through which divided area 310 is converted into S-polarized light. The polarization state control also includes control as to how much the phase state of each minute laser beam is changed as a side effect.

  Here, the modulated polarization directions 311 of the divided areas 310 shown in FIG. 5A are orthogonal to each other between the adjacent divided areas 310. In this case, if the transient state caused by the response speed of the liquid crystal is ignored, the adjacent divided areas 310 always have an optical path difference equal to or greater than the coherence length. Therefore, no interference occurs between the minute laser beams in the adjacent divided areas 310, and speckle can be reduced as compared with the case where the modulated polarization directions 311 are matched between the adjacent divided areas 310. .

  Further, the liquid crystal modulation element 120 may repeat, for example, an operation of alternately switching between the state illustrated in FIG. 5A and the state illustrated in FIG. The modulated polarization direction 311 of each divided area 310 shown in FIG. 5A and the modulated polarization direction 312 of the corresponding divided area 310 in FIG. 5B are orthogonal to each other. In this case, if the transient state due to the response speed of the liquid crystal is ignored, two speckle patterns are observed on the diffusion surface. In this case, if the repetition period is set to a human eye afterimage time (about 1/30 second) or less, the speckle pattern is observed in a state where the two patterns are integrated, and as a result, speckle is further reduced. Can do.

  FIG. 6 is a schematic diagram showing the speckle integration effect.

When a plurality of speckle patterns are observed in an integrated state, as the number of speckle patterns to be integrated increases, the finally observed speckle decreases. Further, the smaller the correlation between the speckle patterns to be integrated, the higher the effect of speckle reduction. For example, as shown in FIG. 6, when speckle patterns P _{1 to} P _N of _N patterns are integrated, a speckle pattern P in which luminance levels are averaged is obtained.

  Further, as the distribution of the polarization direction of the laser beam 220 loses its temporal periodicity and spatial periodicity, that is, as it becomes more random, the number of speckle patterns integrated increases and the observed speckle decreases. To do. Therefore, for example, the liquid crystal modulation element 120 changes the polarization rotation angle of each divided area 310 while shifting the phase at the same period, or changes the polarization rotation angle at a different period. The liquid crystal modulation element 120 may change the polarization rotation angle of each divided area 310 in an aperiodic and different pattern, for example.

  Next, a specific example of the control content of the liquid crystal modulation element 120 will be described.

  The liquid crystal modulation element 120 changes the angle at which the polarization direction of incident light is rotated (hereinafter referred to as “polarization rotation angle”) for each divided area in a range from 0 degrees to a predetermined angle of 90 degrees. Further, the liquid crystal modulation element 120 is configured so that the polarization component ratio between the P-polarized light 230 and the S-polarized light 240 of the emitted laser light 220 is approximately 1: 1. Further, all the divided areas of the liquid crystal modulation element 120 have the same size.

  As a specific example, two driving methods will be described.

  The first is a driving method in which the liquid crystal modulation element 120 switches the polarization direction after modulation between two values of 0 degrees or 90 degrees as shown in FIG. However, the liquid crystal modulation element 120 may randomly divide the divided area in which the polarization direction after modulation is 0 degrees (or the divided area in which the polarization direction after modulation is 90 degrees) to be approximately half of all the divided areas. select.

  The second is a driving method in which the liquid crystal modulation element 120 changes the rotation angle within a range of plus or minus 45 degrees with reference to a state in which the laser light 210 is rotated 45 degrees in all areas.

  Specifically, for example, the liquid crystal modulation element 120 divides the light transmission region 300 into H areas each composed of a plurality of divided areas, and creates a pair of divided areas in the divided areas. The liquid crystal modulation element 120 modulates one divided area constituting the pair to 45 + α (t) degrees and modulates the other divided area to 45−α (t) degrees. Here, α (t) is a function of time t. Thereby, the ratio of the S-polarized light and the P-polarized light of the laser light 220 emitted from the liquid crystal modulation element 120 is always 1: 1 and constant. If the ratio is other than 1: 1, the reference angle may be other than 45 degrees.

  With such a driving method, the liquid crystal modulation element 120 causes the laser beam 220 to be incident on the polarization separation surface of the polarization beam splitter 130 in a state where the ratio of S polarization and P polarization is equal, thereby reducing coherence, and The speckle pattern can be generated and superimposed on a time average basis.

  In the above two driving methods, the range of the polarization rotation angle and the ratio of the P-polarized light 230 and the S-polarized light 240 are not limited to the above contents. Further, the liquid crystal modulation element 120 may change with time how to take the H divided areas and how to form a pair in each divided area.

  Further, the liquid crystal modulation element 120 may control the polarization state of the laser light 220 in accordance with the luminance of the image. For example, the liquid crystal modulation element 120 uses the laser beam 220 so that speckles at the same level are always observed in a dark scene (the luminance of the laser beam 210 is low) and a bright scene (the luminance of the laser beam 210 is high). Control the polarization state of. In general, speckle is more noticeable and more conspicuous as the image brightness is higher. Therefore, such control can reduce a sense of incongruity due to a change in speckle strength.

  Specifically, for example, the liquid crystal modulation element 120 is configured so that the ratio of the S-polarized light that works in the direction of reducing the speckle of P-polarized light becomes smaller in time average in a dark scene than in a bright scene. Controls the polarization rotation angle. Such control may be effective in reducing the power consumed by the liquid crystal modulation element 120.

  Further, for example, the liquid crystal modulation element 120 may control the polarization rotation angle of each divided area so that the number of speckle patterns integrated in a dark scene is smaller than that in a bright scene. The number of speckle patterns can be controlled, for example, by changing the temporal periodicity and spatial periodicity of the polarization rotation angle distribution.

  In general, the laser light has a Gaussian distribution or its cross section is deformed into an ellipse, so that the light intensity differs between the divided areas within the irradiation range of the laser light 210. Therefore, the liquid crystal modulation element 120 also considers the difference in the light intensity of the laser light in each divided area, and the rotation angle of each divided area so that the S-polarized light intensity and the P-polarized light intensity of the laser light 220 are substantially equal. Is preferably controlled. Such control can be easily realized, for example, by taking the above-described divided area sufficiently small.

  As described above, according to laser light source device 100 according to the present embodiment, it is possible to selectively reduce the coherence at an arbitrary position in the cross section of the laser light emitted from laser light source 110. Further, by modulating this temporally, a plurality of speckle patterns can be generated, and speckle can be reduced by the effect of integration.

  In general, for speckles that occur when a diffused surface is irradiated with coherence light such as laser light, changes in each part of the beam pattern (intensity distribution in the laser light cross section) and each part of the observed speckle pattern It is difficult to quantify the correspondence with changes. Also, the observed speckle pattern varies depending on the observation position and the pupil diameter of the observer.

  Therefore, the observation conditions that can reduce speckle are limited by the superposition of a plurality of static beam patterns performed by the apparatus described in Patent Documents 1 to 4.

  In laser light source apparatus 100 according to the present embodiment, individual beam patterns to be superimposed can be made more complicated, and the range of observation conditions for reducing speckle can be expanded.

  Further, speckles that are generated when light is scattered after the laser light source device 100 by control using a simple element in which a polarizing plate is removed from a general monochrome liquid crystal modulation element can be used as a mechanical sliding part. And can be greatly reduced.

  Further, since the liquid crystal modulation element can electrically control the polarization state of the laser beam for each divided area, the speckle reduction can be easily realized.

  By the way, while the beam light output from the apparatus described in Patent Document 4 has the same polarization direction, the beam light output from the laser light source apparatus 100 according to the present embodiment has a state in which the polarization direction is not uniform. Become.

  However, the projection system at the rear stage of the laser light source device 100 does not use a device that needs to maintain the polarization such as a liquid crystal display element, but a DMD (digital micromirror device), a two-dimensional MEMS (micro electro mechanical systems) scanner, or the like. If it is not necessary to maintain the polarization, the light guide efficiency does not deteriorate. In the apparatus described in Patent Document 4, only the VA method using a nematic liquid crystal as a liquid crystal modulation element can be adopted. However, the laser light source device 100 according to the present embodiment uses a TN method, an IPS method, or the like. A liquid crystal modulation element can be used, which is advantageous in versatility.

  The first right-angle prism 140 and the second right-angle prism 150 that function as a light guide optical system for the purpose of generating an optical path difference of the laser light 210 may be replaced with four mirrors. In some cases, the mirror can reduce the material cost for configuring the optical system. However, the right-angle prism has the advantages that the reflectivity of the laser beam 210 is generally better and the arrangement and adjustment of the arrangement when configuring the optical system are simple.

  Further, as this series of branching section, light guiding optical system, and combining section (polarizing beam splitter 130, first right-angle prism 140, second right-angle prism 150), a half mirror or beam splitter is used as a polarization beam splitter. A configuration of a Michelson interferometer or a Mach-Zehnder interferometer arranged in place of 130 can be adopted. Further, this series of device units may be configured by replacing two polarization beam splitters and one right-angle prism as in the example described in Patent Document 1.

(Modification of Embodiment 1)
When attempting to obtain high-luminance planar light with the laser beam 210 having a small diameter, the light density when passing through the liquid crystal modulation element 120 increases, and the liquid crystal modulation element 120 may be damaged. In order to effectively reduce speckle with the laser beam 210 having a small diameter, it is necessary to make the divided area very small in order to arrange a sufficient number of divided areas in the irradiation range. It may be disadvantageous in terms of rate (aperture ratio).

  Therefore, the diameter of the laser beam 210 may be enlarged using an enlargement optical system, and the laser beam 210 with the enlarged diameter may be incident on the liquid crystal modulation element 120.

  FIG. 7 is a plan view showing the configuration of the magnifying optical system and its periphery.

  As shown in FIG. 7, the magnifying optical system 160 is disposed between the laser light source 110 and the liquid crystal modulation element 120, expands the laser light 210 emitted from the laser light source 110, and converts the expanded laser light 210 into liquid crystal. The light is incident on the modulation element 120. The magnifying optical system 160 includes, for example, first and second convex lenses 161 and 162.

  By providing such a magnifying optical system 160, speckle can be reduced while preventing damage to the liquid crystal modulation element 120 by the laser light 210 even when the diameter of the laser light 210 is small.

(Embodiment 2)
FIG. 8 is a plan view showing the configuration of the laser light source apparatus according to Embodiment 2 of the present invention.

  As shown in FIG. 8, the laser light source device 100a according to the second embodiment of the present invention has the first right-angle prism 140 and the second right-angle prism 150 at positions different from those of the laser light source device 100 according to the first embodiment. It is arranged. Specifically, the first right-angle prism 140 and the second right-angle prism 150 are configured so that the S-polarized light 240 is detected from the position where the S-polarized light 240 is first reflected in the polarization separation surface 131 of the polarization beam splitter 130. Are arranged at positions and orientations for incidence at different positions.

  Here, the position of the first right-angle prism 140 is shifted from the position in FIG. Thereby, the incident position of the S-polarized light 240 with respect to the first right-angle prism 140 is shifted, and the re-incident position (re-reflecting position) of the S-polarized light 240 to the polarization separation surface 131 is shifted.

  As shown in FIG. 8, the polarization separation surface 131 is arranged in a direction that bisects the positive direction of the Y axis and the positive direction of the Z axis, and the second right-angle prism 150 is shifted in the negative direction of the Z axis. In this case, the S-polarized light 240 is shifted in the negative direction of the Y axis with respect to the P-polarized light 230. As a result, the P-polarized light 230 and the S-polarized light 240 are combined into one laser beam 250 in a state where the optical axes of the P-polarized light 230 and the S-polarized light 240 are shifted in the Y-axis direction.

  In FIG. 8, the laser light 250 finally emitted from the laser light source device 100a is in a state where the P-polarized light and the S-polarized light are not overlapped, but may be partially overlapped. Further, both the first right-angle prism 140 and the second right-angle prism 150, or only the first right-angle prism 140 are appropriately moved in the Z-axis direction, so that the S-polarized light 240 re-enters the polarization separation surface 131. The position may be shifted.

  According to such a configuration, in addition to the speckle reduction effect described in the first embodiment, it is possible to control which part of the cross section of the laser light 210 is translated to a predetermined position. In addition, the selection of the part to be translated can be changed with time. Thereby, the spatial coherence of the laser beam 210 can also be reduced. That is, the laser beam 250 having various beam patterns can be output, and speckle can be further reduced.

  Further, in this embodiment, the coherence length of the laser light 210 is extremely long, and a sufficient optical path difference cannot be generated by the polarization beam splitter 130, the first right-angle prism 140, and the second right-angle prism 150. It is also effective in some cases. That is, since the position of the P-polarized light 230 and the position of the S-polarized light 240 are shifted, the coherence characteristic can be reduced.

(Modification of Embodiment 2)
The irradiation range of the laser light 250 output from the laser light source device 100a of the present embodiment is larger than the irradiation range of the laser light 250 output from the laser light source device 100 of the first embodiment. In addition, the intensity distribution of the laser light 250 output from the laser light source device 100 a of the present embodiment is non-uniform compared to the intensity distribution of the original laser light 210. Therefore, a uniformizing optical system for reducing the irradiation range of the laser beam 250 and making the intensity distribution of the laser beam 250 uniform may be disposed on the optical path of the laser beam 250.

  FIG. 9 is a plan view showing an example of the configuration of the homogenizing optical system.

  As shown in FIG. 9, the homogenizing optical system 170 includes an entrance side lens 171, an exit side lens 172, and a rod lens 173. The rod lens 173 is disposed between the entrance side lens 171 and the exit side lens 172.

  The incident side lens 171 makes the laser beam 250 emitted from the polarization beam splitter 130 incident, and makes the narrowed laser beam 250 incident on the rod lens 173.

  The rod lens 173 propagates the incident laser beam 250 while repeating total internal reflection, and causes the laser beam 250 to enter the exit side lens 172. The exit side lens 172 collimates the incident laser beam 250 into parallel light and outputs it.

  By disposing such a homogenizing optical system 170, the spread of the laser beam 250 can be improved and the intensity distribution of the laser beam 250 can be made uniform.

  For example, when the laser beam 250 spreads in the Y-axis direction, a cylindrical lens that converges transmitted light in the Y-axis direction may be appropriately combined with the incident side lens 171. Alternatively, the incident side lens 171 may be replaced with a plurality of lenses having different focal lengths that converge in the Y-axis direction and the X-axis direction, respectively.

  The rod lens 173 may be replaced with an optical fiber, and the optical fiber output may be used as the output of the laser light source device 100a as it is.

  The homogenizing optical system 170 may omit the rod lens 173. Even in this case, the homogenization performance of the homogenization optical system 170 is slightly lowered, but the spread in the Y-axis direction can be reduced with the number of parts being suppressed.

(Embodiment 3)
FIG. 10 is a plan view showing the configuration of the laser light source apparatus according to Embodiment 3 of the present invention.

  As shown in FIG. 10, the laser light source device 100b according to the third embodiment does not include the first right-angle prism 140 and the second right-angle prism 150 according to the first embodiment, and the polarization beam splitter 130 A right angle prism 180 is arranged on the positive direction side of the Z axis. The reflection surface 181 of the right-angle prism 180 is parallel to the polarization separation surface 131 of the polarization beam splitter 130.

  Also with such a configuration, it is possible to control which part of the cross section of the laser beam 210 is translated to a predetermined position. In addition, the selection of the part to be translated can be changed with time. Further, since the number of right-angle prisms can be reduced as compared with the configuration shown in Embodiment Mode 1, simplification and cost reduction of the apparatus can be achieved.

(Embodiment 4)
FIG. 11 is a plan view showing a configuration of a laser light source apparatus according to Embodiment 4 of the present invention.

  As shown in FIG. 11, the laser light source device 100 c according to the present embodiment includes an inversion optical system 190 between the first right-angle prism 140 and the second right-angle prism 150 in the optical path of the S-polarized light 240. It is arranged.

  The reversal optical system 190 has a pair of convex lenses 191 and 192 and has a function of reversing the beam pattern of the S-polarized light 240. Note that the inverting optical system 190 may be configured to have a pair of cylindrical lenses opposed to each other, a dove prism, or a combination of these. The insertion position of the inverting optical system 190 is not limited to the position between the first right-angle prism 140 and the second right-angle prism 150, and after the S-polarized light 240 branches off from the P-polarized light 230, it is combined with the P-polarized light 230 again. Until then.

  According to such a configuration, although the inverting optical system 190 is required, an effect equivalent to the effect described in the second embodiment can be obtained. Further, compared with the configuration of the second embodiment, it is not necessary to adjust the positions of the first and second right-angle prisms 140 and 150, and the spread of the beam and the unevenness of the intensity can be avoided.

  Each embodiment described above is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited to this. That is, the description of the configuration and operation of the laser light source device is an example, and it is obvious that various modifications and additions to these examples are possible within the scope of the present invention.

  Further, the above embodiments can be combined. Specifically, for example, the liquid crystal modulation element driving method and the magnifying optical system described in the first embodiment can be applied to the laser light source devices according to the second to fourth embodiments. In addition, the uniformizing optical system described in the second embodiment can be applied to the laser light source devices according to the first, third, and fourth embodiments.

  Since the laser light source device according to the present invention can electrically control the ratio of the light component for each divided area, the speckle contrast can be effectively reduced without using a mechanical sliding part. It is useful as a laser light source device that can be used. In an application using a laser light source, speckles due to the coherence characteristics of the laser light may have an adverse effect. By replacing the existing laser light source device with the laser light source device of the present invention, speckle can be greatly reduced without a mechanical sliding portion. Such a laser light source device is particularly suitable as a light source for a display that is required to have reliability, lifetime, and quietness.

The top view which shows the structure of the laser light source apparatus which concerns on Embodiment 1 of this invention. FIG. 3 is a schematic diagram illustrating an example of a configuration of a TN liquid crystal modulation element according to Embodiment 1; FIG. 3 is a schematic diagram illustrating an example of a configuration of an IPS liquid crystal modulation element according to Embodiment 1; Schematic diagram showing the configuration of a conventional liquid crystal modulation element Schematic diagram showing an example of a state of polarization state control by the liquid crystal modulation element in the first embodiment The schematic diagram which shows the schematic diagram which shows the integral effect of the speckle in Embodiment 1 The top view which shows the expansion optical system in the modification of Embodiment 1, and the structure of the periphery of it FIG. 5 is a plan view showing a configuration of a laser light source device according to Embodiment 2 of the present invention. The top view which shows an example of a structure of the uniformization optical system in the modification of Embodiment 2 The top view which shows the structure of the laser light source apparatus which concerns on Embodiment 3 of this invention. A top view showing composition of a laser light source device concerning Embodiment 4 of the present invention.

100, 100a, 100b, 100c Laser light source device 110 Laser light source 120 Liquid crystal modulation element 130 Polarizing beam splitter 140 First right angle prism 150 Second right angle prism 121, 122 Glass substrate 123, 124 Transparent electrode 125, 126 Alignment film 127 Liquid crystal Layer 160 Magnifying optical system 161 First convex lens 162 Second convex lens 170 Uniform optical system 171 Incident side lens 172 Outgoing side lens 173 Rod lens 180 Right angle prism 181 Reflecting surface 190 Inverting optical system 191, 192 Convex lens

Claims (18)

A light source that emits laser light;
Polarization state control means for controlling the polarization state of the laser light emitted from the light source unit;
Branching means for branching the laser light whose polarization state is controlled by the polarization state control unit into a first polarization component and a second polarization component;
Combining the first polarization component and the second polarization component branched by the branching unit after being propagated with an optical path difference, and
The polarization state control means includes
Polarization of the laser light by electrically controlling at least one of birefringence and optical rotation of the laser light for each of a plurality of areas obtained by dividing the irradiation range of the laser light emitted from the light source unit Control the state,
Laser light source device. The polarization state control means includes
Different polarization state control between at least two of the areas,
The laser light source device according to claim 1. The polarization state control means includes
Controlling the polarization state of the laser beam so that the ratio of the first polarization component and the second polarization component is approximately 1: 1;
The laser light source device according to claim 2. The polarization state control means includes
Controlling the polarization state of the laser beam so that the polarization rotation angle takes a multivalued value between 0 degrees and 90 degrees;
The laser light source device according to claim 2 or claim 3. The polarization state control means includes
Controlling the polarization state of the laser beam so that the polarization rotation angle takes a binary value of 0 degrees and 90 degrees,
The laser light source device according to claim 2 or claim 3. The polarization state control means includes
A liquid crystal modulation element,
The laser light source device according to claim 1. The liquid crystal modulation element is
A glass substrate, a transparent electrode, an alignment film, and a liquid crystal layer,
The laser light source device according to claim 6. The branching means includes
A polarizing beam splitter,
The laser light source device according to claim 1. The synthesis means includes
A light guide optical system for bringing the first polarization component and the second polarization component close to each other;
A combining element that emits the first polarization component and the second polarization component that are close to each other in the same direction;
The laser light source device according to claim 1. The synthetic element is:
Combining at least one optical axis of the first polarization component and the second polarization component with a shift from the optical axis before branching;
The laser light source device according to claim 9. The branching means and the synthesis element are:
One polarization beam splitter,
The laser light source device according to claim 9. The synthetic element is:
A polarization beam splitter different from the branching means,
The laser light source device according to claim 9. The synthetic element is:
A reflecting mirror or prism,
The laser light source device according to claim 9. The light guide optical system is:
Having a reflective mirror or prism,
The laser light source device according to claim 9. The light guide optical system is:
An inversion optical system that inverts the beam pattern of either the first polarization component or the second polarization component;
The laser light source device according to claim 9. The reversal optical system is
Having a pair of convex or cylindrical lenses, or a dove prism,
The laser light source device according to claim 15. The laser beam emitted from the light source unit is incident to enlarge the diameter thereof, and further includes an enlargement optical system that causes the laser beam having an enlarged diameter to enter the polarization state control unit.
The laser light source device according to claim 1. A homogenizing optical system that uniformizes the intensity distribution of the combined light of the first polarized light component and the second polarized light component emitted from the combining means;
The laser light source device according to claim 1.

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