JP5173295B2 - Optical scanning device and scanning image display device - Google Patents

Description

  The present invention relates to an optical scanning device that scans a light beam from a light source on a surface to be scanned, and further relates to a scanning image display device that forms an image on the surface to be scanned by the light beam scanning.

  Patent Documents 1 to 4 disclose an optical scanning device that displays (forms) an image on a surface to be scanned by scanning modulated light from a light source with a scanning device, or an image projection device such as a scanning image display device or a liquid crystal projector. Are disclosed.

  The apparatus disclosed in Patent Document 1 includes a light source that emits light having coherence, a scanning device that scans the light, a first optical system that forms an intermediate image on the light from the scanning device, And a second optical system that forms light on the surface to be scanned from the intermediate image. In this apparatus, a diffusion angle conversion element is disposed at the position of the intermediate image or a position close thereto, and the spread angle of the light beam emitted from the diffusion angle conversion element is expanded. A microlens array or the like is used as the diffusion angle conversion element, and speckle noise is reduced by condensing diffracted light generated by the diffraction action on the surface to be scanned.

  In the apparatus disclosed in Patent Document 2, an imaging lens and a condenser lens that constitute a projection lens are supported so as to be movable in the optical axis direction relative to a transmissive image panel. Then, when changing the projection distance from the imaging lens to the screen, both of these lenses are moved relative to the transmissive image panel to adjust the focus on the screen.

In the apparatus disclosed in Patent Document 3, some of the coaxial optical systems whose optical axes do not coincide with each other are moved in the optical axis direction as a focus lens group. Thus, an oblique projection optical system is configured that performs focusing so that the image plane moves parallel to the object plane with a constant inclination angle, that is, without causing trapezoidal distortion in the projected image.

In the apparatus disclosed in Patent Document 4, an image is presented by scanning a light beam on the retina of an observer. The pupil enlargement element is used to enlarge the exit pupil while suppressing multiplexing of the display image due to the modulation of the wavefront curvature of the light flux.
JP 2006-053495 A JP-A-8-106065 Japanese Patent No. 312396 JP 2006-251125 A

  However, Patent Document 1 does not mention focus adjustment when the distance from the apparatus to the scanning surface (projection distance) changes. As a general focus adjustment method when the projection distance is changed, it is conceivable to move the second optical system that forms light from the intermediate image on the surface to be scanned in the optical axis direction.

  Further, in the apparatus of Patent Document 2, since the entire projection lens is moved in the optical axis direction, it is necessary to secure a space corresponding to the stroke necessary for focus adjustment, and the apparatus becomes large.

  Moreover, in the apparatus of Patent Document 3, a part of a plurality of lens groups constituting the projection optical system is moved as a focus lens group. However, since the focus lens group has a function of projecting an image from the intermediate image plane to the image plane, many lenses are required. Since the lens group arranged closest to the image plane is the focus lens group, it is necessary to secure a space corresponding to the focus adjustment stroke. That is, the apparatus becomes large.

  Furthermore, in the apparatus of Patent Document 4, an optical system that projects a light beam onto the retina of the eye is configured by the relay optical system and the eye optical system of the apparatus. In this apparatus, when the position of the intermediate image plane moves in the optical axis direction along with wavefront modulation, the focus is adjusted by changing the focal length of the optical system of the eye. That is, the optical system of the eye is a variable focus lens. Further, when the pupil enlarging element is shifted from the focus position, the images projected on the retina are multiplexed. Therefore, it is necessary to adjust the pupil enlarging element so as to coincide with the intermediate image plane.

  The optical system of the retinal scanning image display device of Patent Document 4 may be applied to a scanning image display device that displays an image on a screen by replacing the retina with a screen. In this case, since the variable focus lens is included in the optical system that projects the light beam on the screen, the focus adjustment may be performed using the variable focus lens when the projection distance changes. Therefore, it is not necessary to adjust the pupil enlarging element in the optical axis direction.

  However, it is difficult to insert a variable focus lens into an optical system that projects a light beam onto a screen, and focus adjustment cannot be performed as easily as an optical system of an eye. Therefore, in general, focus adjustment is performed by moving the projection optical system and a lens group constituting a part thereof in the optical axis direction. For this reason, it is necessary to ensure a stroke necessary for focus adjustment, and the apparatus becomes large.

  Further, the projection lens of Patent Document 2, the focus lens group of Patent Document 3, and the relay optical system and eye optical system of Patent Document 4 all use a coaxial lens system. For this reason, focus adjustment is possible by moving these in the direction of the optical axis.

  On the other hand, when a decentering optical system such as a decentering lens or an imaging mirror is used, the following problems occur.

  The decentered optical system is configured to bend the optical path of the incident light beam, and the central light beam incident on the decentered optical system and the central light beam emitted from the decentered optical system are non-parallel. In particular, when an imaging mirror is used, the degree of non-parallelism increases.

  Here, when the decentered optical system is moved in the direction along the incident light beam of the decentered optical system, focus adjustment is possible, but the image projection position on the image plane (scanned surface) changes. This is because the central light beam incident on the decentered optical system and the central light beam emitted from the decentered optical system are non-parallel, and when the decentered optical system moves along the incident light beam, the emitted light beam shifts. If the position of the image changes in this way, the image position must be adjusted after the focus adjustment.

  The present invention can perform focus adjustment (correction of deteriorated resolution) associated with a change in projection distance with a simple configuration, and can reduce the space required for focus adjustment to achieve downsizing. I will provide a. The present invention also provides an optical scanning device capable of adjusting the focus according to the change of the projection distance without changing the projection position even when the decentered optical system is used.

An optical scanning device according to one aspect of the present invention includes a scanning unit that scans a light beam from a light source, a first optical system that forms an intermediate image on the light beam from the scanning unit, and a specific range that includes the position of the intermediate image. A light beam component generating means for generating a plurality of light beam components from a light beam from the first optical system, and a second optical system for condensing and projecting the plurality of light beam components toward the scanning surface, And a moving means for moving the light beam component generating means within the specific range in the traveling direction of the plurality of light beam components or in the opposite direction in accordance with the change of the projection distance . Here, the second optical system may be a decentered optical system.

  A scanning image display device that includes the optical scanning device and forms an image on a surface to be scanned also constitutes another aspect of the present invention.

  According to the present invention, the light beam component generating means can be moved within a specific range including the intermediate image position, so that the focus adjustment (correction of deteriorated resolution) associated with the change of the projection distance can be performed with a simple configuration. it can. In addition, since the space required for focus adjustment is small, a small optical scanning device and scanning image display device can be realized. In addition, even when an eccentric optical system is used as the second optical system, it is possible to realize an optical scanning device and a scanning image display device capable of adjusting the focus according to the change in the projection distance without changing the projection position. it can.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a configuration of an optical scanning device that is Embodiment 1 of the present invention and a scanning image display device including the same.

  Reference numeral 101 denotes a laser light source, and reference numeral 150 denotes a drive circuit that drives the laser light source. Image information from an image supply device 160 such as a personal computer, a DVD player, or a TV tuner is input to the drive circuit 150. The drive circuit 150 modulates and drives the laser light source 101 according to the input image information. This also applies to the embodiments described later.

  A laser beam (divergent beam) having coherence emitted from the laser light source 101 is converted into a parallel beam by the collimator lens 102. A light beam emitted from the collimator lens 102 is scanned in a two-dimensional direction by a two-dimensional scanning device (scanning unit) 103 and projected onto a screen 105 as a scanning surface via a scanning optical system 104. Thereby, an image is projected (displayed or formed) on the screen 105.

  In this embodiment, a MEMS (Micro Electro-mechanical system) mirror device capable of scanning a light beam in a two-dimensional direction is used as the two-dimensional scanning device 103. In the MEMS mirror device, the mirror part oscillates (vibrates) at a high resonance frequency of, for example, 18 kHz in the horizontal direction, and oscillates at a low frequency of, for example, 60 Hz in the vertical direction.

  Therefore, the scanning line 106 that reciprocates in the horizontal direction is formed on the screen 105 sequentially downward from the top of the image, and when reaching the bottom of the image, the scanning line 106 returns to the top of the image again. Through this series of operations, 300 scanning lines 106 are formed on the screen 105 in the forward path and the backward path, respectively, and, for example, an SVGA 1-frame image having 800 pixels in the horizontal direction and 600 pixels in the vertical direction is formed. Then, by repeating this operation, a moving image is displayed. Actually, there is only one spot of the light beam on the screen 105 at a certain moment, but the image is recognized by the afterimage effect of the observer by scanning the spot in two dimensions.

  In FIG. 1, the scanning line 106 is schematically shown, but actually, an image having a diagonal size of 12 inches and a resolution of SVGA is displayed. The size of one pixel is about 300 μm.

  In addition, as the two-dimensional scanning device, two MEMS mirror devices that can scan a light beam in different one-dimensional directions are used, or a MEMS mirror device that can scan a light beam in one-dimensional direction and a light beam in another one-dimensional direction. A scanable galvanometer mirror may be used.

  FIG. 2 shows a vertical optical cross section of the optical scanning device of this embodiment.

  The divergent light beam emitted from the laser light source 101 is converted into a parallel light beam by the collimator lens 102 and enters the two-dimensional scanning device 103 via the folding mirror 107. The light beam deflected in the horizontal direction and the vertical direction by the scanning device 103 forms a spot image on the screen 105 via the scanning optical system 104 including the first optical system 104A and the second optical system 104B (that is, Image).

The first optical system 104A condenses the light beam from the scanning device 103 and forms an intermediate image 108 on the scanning device side with respect to the second optical system 104B. The intermediate image (position where the intermediate image is formed) 108 is a position where the intermediate image of the laser light source is formed (position conjugate with the screen). That is, by the first optical system, the laser light source 101 and the intermediate image 108 (the microlens array 109 arranged at that position) are in a substantially conjugate relationship. The final image of the laser light source is, of course, an image formed on the screen 105, and this intermediate image is substantially conjugate with both the laser light source and the screen. In the present embodiment, the first optical system 104A is composed of two free-form surface mirrors.

  Within a specific range including the position of the intermediate image 108, a microlens array (diffraction element) 109 is disposed as a light beam component generating means. The microlens array 109 generates a plurality of diffracted light beam components (hereinafter simply referred to as a diffracted light beam) as a plurality of light beam components from the light beam from the first optical system 104A. The term “within the specific range” refers to a range that is considered to exert substantially the same action from an optical viewpoint, and this range is one tenth of the focal length of the first optical system. It is good that it is less than (preferably 1/20).

  Then, the second optical system 104B condenses the plurality of diffracted light beams generated by the microlens array 109 at one point on the screen 105, that is, the plurality of diffracted light beams at the same position (one pixel on the screen 105). ) To form an image as a spot.

  3A shows an example of the shape of the microlens array 109, and FIG. 3B shows an example of the distribution of a plurality of diffracted light beams generated from one light beam by the microlens array 109.

  As shown on the left side of FIG. 3A, in the microlens array 109, minute lenses ML having a regular hexagonal outer shape are arranged adjacent to each other with a pitch of 10 μm. Specifically, the microlens ML is arranged so that six microlenses surround one microlens, in other words, a line connecting the centers of the microlenses surrounding the microlens forms a hexagon. ing. Hereinafter, this arrangement is referred to as a hexagonal arrangement. The microlens array 109 functions as a diffractive element that generates a plurality of diffracted light beams from a single incident light beam by being inserted into the optical path.

  The right side of FIG. 3A shows the shape of the cross section of the microlens array 109 (the cross section taken along the line AA in the left figure). The microlens array 109 is configured by forming a microlens ML having a thickness of several tens of μm on a glass substrate GP having a thickness of 1 mm. High diffraction efficiency is obtained by optimizing the curvature of the microlens ML.

  Since the microlenses ML are arranged in a hexagonal shape in the microlens array 109, as shown in FIG. 3B, the distribution (far field pattern) of the diffracted light beam generated from one light beam by the microlens array 109 is also based on the hexagonal shape. Pattern.

  One zero-order diffracted light beam D0 exists at the center of the diffracted light beam distribution, and six first-order diffracted light beams D1 exist around it. Furthermore, there are six second-order diffracted light beams D2 on the outside thereof. Further, a first-order diffracted light beam first-order diffracted light beam (hereinafter referred to as a diagonal first-order diffracted light beam) T1 exists between adjacent second-order diffracted light beams D2. Each diffracted light beam is separated from each other. A high-order diffracted light beam such as a third-order diffracted light beam exists outside the second-order diffracted light beam D2 and the diagonally-order first-order diffracted light beam T1, but this is not shown in the drawing.

  In this embodiment, the second optical system uses the zeroth-order diffracted light beam D0, the first-order diffracted light beam D1, the second-order diffracted light beam D2, and the diagonally-first-order diffracted light beam T1 generated by the microlens array 109 as a plurality of light beam components. The light is condensed at one point on the screen 105 by 104B.

Here, as shown in FIG. 12, the “plurality of light beam components (diffracted light beam)” has a light amount distribution (intensity distribution) including a peak for each light beam component. Further, the “plurality of light beam components” are separated from each other in a light amount portion equal to or higher than a specific light amount level T (light amount level that is 1 / e ^{2 of the} peak light amount) recognized by the observer. In other words, they may overlap each other in a light quantity portion lower than a specific light quantity level T (light quantity level that is 1 / e ^{2 of the} peak light quantity) that is hardly recognized by the observer. In the present embodiment, a plurality of light beam components in such a state (a plurality of light beam components overlapping in a region showing a light amount distribution less than a specific light amount level) are regarded as being separated from each other. Further, it can be said that the 0th-order diffracted light beam, the second-order diffracted light beam, and the second-order diffracted light beam in FIG.

  However, the “plurality of light beam components” may not be separated from each other and may be adjacent to each other (may be overlapped) as long as they have a light amount distribution including a peak for each light beam component. . In FIG. 12, when a light amount portion T ′ slightly lower than a specific light amount level T is included, it can be said that adjacent light flux components are adjacent to each other.

  The meaning of the above “plurality of light beam components” is the same in other embodiments described later.

  By making these plural diffracted light beams enter the screen 105 from different angles and superimposing them at the same position (one pixel), a plurality of speckle patterns generated in different modes for each diffracted light beam are superimposed. Thereby, speckle noise can be averaged and speckle contrast can be reduced.

  As described above, in this embodiment, the light beam component generating means such as the microlens array 109 is arranged in a specific range including the intermediate image position of the scanning optical system 104 or a position close thereto, thereby generating a plurality of light beam components. The plurality of light beam components are condensed at one point on the screen 105. Thereby, the speckle noise which generate | occur | produces by using a laser light source can be reduced.

  As described above, the size of one pixel when displaying an SVGA image with a diagonal size of 12 inches is about 300 μm. In a conventional apparatus that scans a single light beam and projects it onto the screen as it is, the F number of the light beam incident on the screen is as large as F = 349 (dark), and a wide depth of focus exceeding ± 100 mm is obtained. For this reason, so-called focus-free projection is possible.

  On the other hand, in the present embodiment in which a plurality of light beam components generated by a light beam component generating means such as a microlens array are collected at one point on the screen, the F number of each light beam is as large as F = 349. Is an F number of 70, which is as small as F = 70.

  Therefore, in this embodiment, when the projection distance is changed, focus adjustment is necessary so as not to degrade the resolution.

  In the conventional optical scanning device, the entire scanning optical system or a part of the optical system constituting the scanning optical system is moved in the optical axis direction to perform focus adjustment. In the optical scanning apparatus of the present embodiment, it is possible to adjust the focus by moving the second optical system 104B in the same manner, but there is a space for a stroke for moving the second optical system 104B in the optical axis direction. This is not preferable because it is necessary and leads to an increase in the size of the apparatus. In particular, miniaturization is strongly desired for optical scanning devices mounted on portable devices.

  In addition, when an eccentric optical system including a reflective optical element such as an imaging mirror is used for the second optical system, the optical path is bent by the reflective optical element, and a central ray incident on the second optical system The central ray emitted from the second optical system is not parallel. Here, the central ray is a principal ray of a light beam reaching the image center of the screen 105, and the direction of the optical path changes in the decentered optical system. When focus adjustment is performed by moving the second optical system using such an eccentric optical system, the projection position of the image on the screen 105 moves up and down or left and right according to the amount of movement of the second optical system. End up. This is not preferable because it requires projection position adjustment for each focus adjustment.

  Furthermore, the reflective optical element has a sensitivity about four times as high as that of the refractive optical element, and the radius of curvature of the reflective optical element decreases with the miniaturization of the optical scanning device. Therefore, the sensitivity of aberration deterioration to the decentration of the reflective optical element becomes very large. For this reason, in order to move the second optical system, it is necessary to accurately suppress movement in a direction orthogonal to the optical axis and tilt with respect to the optical axis, which are not necessary for focus adjustment. This requires a high mechanical accuracy for the mechanism that moves the second optical system, and requires a robustness that does not cause deflection and vibration, which causes an increase in cost.

  Therefore, in this embodiment, the microlens array 109 is moved in a specific range including the intermediate image 108 in the direction in which the light beam component generated in the microlens array 109 travels or in the opposite direction (hereinafter referred to as the light beam direction). Let Thereby, the condensing positions of the plurality of diffracted light beams generated in the microlens array 109 are adjusted, and the focus adjustment can be performed without causing the above-described disadvantages.

  Hereinafter, the focus (resolution) adjustment method accompanying the change of the projection distance in the present embodiment will be described with reference to FIGS. 4A, 4B, and 4C.

  As shown in FIG. 4A, the second optical system 104B is composed of two free-form surface mirrors M1 and M2. FIG. 4A shows a state in which the light beam L from the first optical system 104A forms an intermediate image 108, and the microlens array 109 is disposed at the position of the intermediate image 108. The plurality of diffracted light beams D generated by the microlens array 109 are imaged again on the screen 105 via the free-form surface mirror M1 and the free-form surface mirror M2. The light beams L incident on the intermediate image plane are parallel to each other (including a case where they deviate from parallel to the extent that they can be regarded as parallel).

  FIG. 4B shows a state in which the projection distance is changed by moving the screen 105 from the position 105A to the position 105B. The plurality of diffracted light beams D generated in the microlens array 109 had the best focus position at the original screen position 105A, and the condensing positions of the diffracted light beams D were also coincident. Therefore, at the current screen position 105B, the position where each diffracted light beam D reaches the screen 105 varies, and the resolution deteriorates.

  Therefore, as shown in FIG. 4C, the microlens array 109 is moved in the light ray direction within a specific range A including the position of the intermediate image 108 to move the optical conjugate point of the microlens array 109 from the position 105A to the position 105B. . In other words, the microlens array 109 is moved to a position conjugate with the screen 105.

  Thereby, a plurality of diffracted light beams D generated by the microlens array 109 can be condensed on one point on the screen 105.

  The light direction in FIG. 4C means the direction in which the principal light of the 0th-order diffracted light beam from the light beam reaching the image center Pc of the screen 105 is directed from the microlens array 109 toward the first free-form curved mirror M1. The light beam direction can also be said to be the optical axis direction of the second optical system 104B.

  In this embodiment, the position conjugate with the screen 105 for moving the microlens array 109 is not only strictly a position conjugate with the screen 105, but can be regarded as an optically conjugate position close to the conjugate position. Includes location. This is the same in other embodiments described later.

  Further, in order to move the microlens array 109 in this way, in this embodiment, a moving mechanism 120 as a moving means is provided. The moving mechanism 120 includes, for example, a focus adjustment switch and an actuator that moves according to the operation of the switch and moves the microlens array 109.

  As described above, the F number of each diffracted light beam is very large, and the depth of focus exceeds ± 100 mm when scanning one diffracted light beam. For this reason, sufficient resolution can be obtained on the screen 105 even if the best focus position of each diffracted light beam remains at the position 105A.

  As described above, in this embodiment, the microlens array 109 is moved in the light beam direction within the specific range A including the intermediate image position in the scanning optical system, so that a plurality of diffracted light beams generated by the microlens array 109 are screened. It adjusts so that it may condense to one point on 105. As a result, it is possible to reduce the deterioration of the resolution accompanying the change of the projection distance.

  The specific range A is a range in which the condensing positions of a plurality of diffracted light beams generated by the microlens array 109 can be adjusted according to a change in the projection distance to the screen 105. In other words, it is a range in which the optical conjugate point of the microlens array 109 can be moved according to the change in the projection distance. This is the same in other embodiments described later.

  In this embodiment, the microlens array 109 moves using the space between the first optical system 104A and the second optical system 104B. For this reason, it is not necessary to secure a new space for resolution adjustment, and an increase in the size of the optical scanning device can be avoided.

  Further, in this embodiment, since the microlens array 109 is moved, there is no shift of the image projection position accompanying the resolution adjustment, and adjustment of the image projection position becomes unnecessary.

  In addition, since the free-form curved mirrors M1 and M2 constituting the second optical system 104B can be fixed and installed, highly accurate positioning is possible. As a result, it is possible to suppress aberration deterioration due to shift or tilt in a direction orthogonal to the optical axis that occurs when the assembly error or the optical system is moved, and a good image can be displayed.

  Furthermore, since the plurality of diffracted light beams generated by the microlens array 109 are incident on the screen 105 at different angles even after the projection distance is changed, the speckle reduction effect can be sufficiently exerted, and the speckle noise can be reduced. A quality image can be displayed.

  In this embodiment, the case where the microlens array 109 is moved so that the conjugate point of the microlens array 109 is located on the screen 105 has been described. However, the conjugate point is not necessarily located on the screen 105. .

  In this embodiment, the case of moving only the microlens array 109 has been described. However, the microlens array 109 and the second optical system 104B or a part thereof may be moved. Even in this case, since the moving stroke of the second optical system 104B or a part of the second optical system 104B can be reduced, the increase in size of the apparatus can be suppressed.

  Further, as described above, in this embodiment, since the light beams L incident on the position of the intermediate image 108 are parallel to each other, almost no image distortion occurs when the microlens array 109 is moved in the light beam direction. . Furthermore, even if the microlens array 109 is moved in the light beam direction, the incident angle of the light beam on the microlens array 109 is hardly changed, so that high diffraction efficiency can be maintained.

  The configuration described in the first embodiment (and described in other embodiments described later) can also be applied to the case where a light source that emits three colors of RGB light is used. That is, an optical scanning device and a scanning image display device that project a color image by applying the configuration shown in the first embodiment can be configured.

  FIG. 5 shows an example of a color light source unit used in the apparatus of this embodiment. The color light source unit 501 is configured using, for example, three laser light sources: a red semiconductor laser 501a having an oscillation wavelength of 640 nm, a green laser light source 501b having an oscillation wavelength of 532 nm, and a blue semiconductor laser 501c having an oscillation wavelength of 445 nm. As the green laser light source 501b, an SHG light source that generates a green laser by wavelength conversion from an infrared laser may be used.

  The light beams emitted from these laser light sources 501a, 501b, and 501c are converted into parallel light beams by the corresponding collimator lenses 502a, 502b, and 502c, and then combined into one beam by the dichroic prism 510. And it scans with the two-dimensional scanning device demonstrated in Example 1, and it projects on a screen.

  When such a color light source unit 501 is used, the occurrence of chromatic aberration can be suppressed by using the second optical system 104B configured by the two reflective optical elements (M1, M2) shown in the first embodiment. Can do. As a result, the microlens array 109 can be moved so that any of the conjugate points of the microlens array 109 relating to the three colors is positioned on the screen 105, and a plurality of diffracted light beams of each color are set to one point on the screen 105. It can be condensed.

  As described above, according to the present embodiment, it is possible to prevent the deterioration of the resolution caused by the change in the projection distance even in the optical scanning device and the color scanning image display device using the three color laser light sources.

  FIG. 6 shows a partial vertical section of an optical scanning device (scanning image display device) that is Embodiment 3 of the present invention.

  The present embodiment is different from the first embodiment in that the second optical system is constituted by a prism element.

  Although not shown, the optical scanning apparatus according to the present embodiment also deflects the light beam emitted from the laser light source in the horizontal direction and the vertical direction by the two-dimensional scanning device (MEMS mirror device) as in the first embodiment. Then, the light beam from the scanning device is imaged so as to form an intermediate image 608 by the first optical system constituted by two free-form surface mirrors. At this time, the light beams L incident on the position of the intermediate image 608 are parallel to each other (including cases where they can be regarded as parallel).

  A microlens array 609 serving as a light beam component generation unit is disposed in a specific range (indicated by A in FIG. 7B) including the position of the intermediate image 608 or a position close thereto. The micro lens array 609 generates a plurality of diffracted light beams D from one incident light beam. The configuration of the microlens array 609, the pattern of the generated diffracted light beam, and the plurality of diffracted light beams guided to the screen 605 are the same as in the first embodiment.

  The second optical system 604B includes a prism element 611 having three surfaces. The prism element 611 optically conjugates the microlens array 609 and the screen 605 and condenses a plurality of diffracted light beams D generated by the microlens array 609 at one point on the screen 605. That is, the images are overlapped at the same position (one pixel) on the screen 605.

  In the prism element 611, the first surface S1 is a refracting surface, the second surface S2 is a common surface for total reflection and refraction, the third surface S3 is a reflecting surface, and each surface has a free-form surface shape. In the prism element 611, a region surrounded by the first surface S1 to the third surface S3 is filled with a resin having a refractive index of about 1.5.

  The diffracted light beam generated by the microlens array 609 enters the prism element 611 from the first surface S1, is totally reflected by the second surface S2 and the third surface S3, passes through the second surface S2, and passes through the screen 605. Focused on top.

  Since the prism element 611 can be integrally formed including the three surfaces S1 to S3, the positional relationship between the three surfaces S1 to S3 can be set with high accuracy. Further, since reflection is performed inside the prism element 611, it is not necessary to provide a supporting thickness outside the surface. For this reason, the thickness of the entire second optical system can be kept small. Further, since the surface S2 is a common surface for total reflection and refraction, the area of the surface S2 can be reduced, and as a result, the prism element 611 (second optical system 604B) can be reduced in size.

  Even in the apparatus of the present embodiment, it is required to perform focus adjustment according to the position (projection distance) of the screen 605.

  However, in this embodiment, the prism element 611 constituting the decentered optical system is used as the second optical system 604B, and the light beam incident on the second optical system 604B and the second light beam are bent by the reflecting surface. The light beam emitted from the optical system 604B becomes non-parallel. For this reason, when the prism element 611 is moved for focus adjustment, the image projection position on the screen 605 changes.

  Moreover, since the prism element 611 is a relatively large member filled with resin, the prism element 611 is heavy, and an actuator with a large output is required to move the prism element 611.

  Therefore, in this embodiment, the microlens array 609 is moved in the light beam direction, and the focusing position of the plurality of diffracted light beams generated by the microlens array 609 is adjusted, thereby adjusting the focus without causing the above-described disadvantages. .

  Hereinafter, the focus (resolution) adjustment method accompanying the change of the projection distance in the present embodiment will be described with reference to FIGS. 7A and 7B.

  FIG. 7A shows a state in which the screen 605 is moved from the position 605A to the position 605B. A plurality of diffracted light beams D generated by the microlens array 609 arranged at the position of the intermediate image 608 are condensed at the position 605A by the prism element 611, and the best focus position of each diffracted light beam is also at the position 605A. Therefore, the position where each diffracted light beam D reaches the screen 605 varies with respect to the screen 605 moved to the position 605B, and the resolution deteriorates.

  Therefore, as shown in FIG. 7B, the microlens array 609 is moved in the light beam direction within the specific range A to move the optical conjugate point of the microlens array 609 from the position 605A to the position 605B. Thereby, the plurality of diffracted light beams D generated in the microlens array 609 are collected at one point on the screen 605 at the position 605B.

  The light beam direction in this embodiment means a direction in which the principal light beam of the 0th-order diffracted light from the light beam reaching the center Pc of the screen 605 travels from the microlens array 609 toward the incident surface S1 of the prism element 611.

  Note that the F number of each diffracted light beam is very large, and the depth of focus exceeds ± 100 mm when one diffracted light beam is scanned. For this reason, even if the best focus position of each diffracted light beam remains at the position 605A, sufficient resolution can be obtained on the screen 605 at the position 605B.

  Further, in order to move the microlens array 609 as described above, the moving mechanism 620 similar to that described in the first embodiment is also provided in this embodiment.

  As described above, also in this embodiment, by moving the microlens array 609 in the light beam direction within the specific range A including the intermediate image position in the scanning optical system, a plurality of diffracted light beams generated by the microlens array 609 are screened. Adjust so that the light is focused on one point on 605. As a result, it is possible to reduce the deterioration of the resolution accompanying the change of the projection distance.

  In addition, the microlens array 609 moves using a space between the first optical system and the second optical system 604B. For this reason, it is not necessary to secure a new space for resolution adjustment, and an increase in the size of the optical scanning device can be avoided.

  Further, in this embodiment, since the microlens array 609 is moved, there is no shift of the image projection position accompanying the resolution adjustment, and adjustment of the image projection position becomes unnecessary.

  Furthermore, since the microlens array 609 is lighter than the prism element 611, the load on the actuator of the moving mechanism 620 can be reduced.

  FIG. 8 shows a partial vertical section of an optical scanning device (scanning image display device) that is Embodiment 4 of the present invention.

  This embodiment differs from the first embodiment in the configuration of the second optical system and the configuration of the microlens array as the light beam component generating means.

  Although not shown, the optical scanning apparatus according to the present embodiment also deflects the light beam emitted from the laser light source in the horizontal direction and the vertical direction by the two-dimensional scanning device (MEMS mirror device) as in the first embodiment. The light beam from the scanning device is imaged so as to form an intermediate image 808 by the first optical system constituted by two free-form surface mirrors. At this time, the light beams L incident on the position of the intermediate image 808 are parallel to each other (including cases where they can be regarded as parallel).

  A diffractive element unit 809 serving as a light beam component generating unit is disposed in a specific range (indicated by A in FIG. 10) including the position of the intermediate image 808 or a position close thereto. The diffraction element unit 809 generates a plurality of diffracted light beams D from one incident light beam. The plurality of diffracted light beams D are collected at one point on the screen 805 by the second optical system 804B, that is, overlapped at the same position (one pixel) on the screen 805.

  In the present embodiment, the second optical system 804B is configured as a decentered optical system having free-form surface mirrors M1 and M2. For this reason, the light beam incident on the second optical system 804B and the light beam emitted from the second optical system 804B become non-parallel, and when the focus adjustment is performed by moving the second optical system 804B, The projected position of the image changes. Therefore, also in this embodiment, the diffraction element unit 809 is moved to adjust the focus.

  FIG. 9 shows a diffraction element unit 809 in the present embodiment. The diffraction element unit 809 includes a first diffraction element 809H and a second diffraction element 809V whose diffraction directions are orthogonal to each other.

  The direction of the grating G of the first diffractive element 809H is aligned with the vertical direction in the second optical system 804B. The first diffraction element 809H diffracts the incident light beam in the horizontal direction (that is, the diffraction direction is the horizontal direction). The orientation of the grating G of the second diffractive element 809V is aligned with the horizontal direction in the second optical system 804B. The second diffraction element 809V diffracts the incident light beam in the vertical direction (that is, the diffraction direction is the vertical direction).

  The first and second diffractive elements 809H and 809V are arranged with the surface where the respective gratings G are provided facing each other and sandwiching the position of the intermediate image 808 or a position close thereto.

  As shown in FIG. 8, when the second optical system 804B is a decentered optical system including reflecting surfaces (free-form surface mirrors) M1 and M2 having optical power (condensing action), the second optical system 804B can There is a tendency that the optical power is increased and the imaging magnification is increased. FIG. 8 shows a case where the second optical system 804B folds the light beam in the vertical direction, and the imaging magnification in the vertical direction parallel to the drawing sheet is higher than the horizontal direction perpendicular to the drawing sheet.

  As described above, when the imaging magnification is different between the horizontal direction and the vertical direction, when the second optical system 804B is moved in the light ray direction, the amount of movement of the conjugate point of the diffraction element unit 809 differs between the horizontal direction and the vertical direction. This is due to the influence of the vertical magnification of the second optical system 804B, and the amount of movement of the conjugate point of the diffraction element unit 809 increases in proportion to the square of the imaging magnification. On the other hand, the same problem occurs even when the diffraction element unit 809 is moved in the direction of the light beam.

  Therefore, in the present embodiment, even when the vertical magnification is different between the horizontal direction and the vertical direction (two directions orthogonal to each other) of the second optical system 804B, in order to satisfactorily correct the deterioration in resolution due to the change in the projection distance, The following method is adopted.

  A focus (resolution) adjustment method that accompanies a change in projection distance in this embodiment will be described with reference to FIGS. 10, 11A, and 11B.

  In this embodiment, the diffractive element unit 809 includes first and second diffractive elements 809H and 809V whose diffracting directions are horizontal and vertical, respectively, and the horizontal and vertical directions of the second optical system 804B. Each diffraction element is arranged in accordance with the vertical magnification of the direction.

  FIG. 11A shows a horizontal section of the first diffractive element 809H and the second optical system 804B, and FIG. 11B shows a vertical section of the second diffractive element 809V and the second optical system 804B. Show.

  The second optical system 804B is composed of two free-form surface mirrors M1 and M2, and is generated by the first and second diffractive elements 809H and 809V arranged at the position of the intermediate image 808 or at a position close thereto. A plurality of diffracted light beams D are condensed on one point on the screen 805. The first and second diffraction elements 809H and 809V can be moved to different positions within the specific range A, respectively. In order to move the first and second diffraction elements 809H and 809V in this manner, a moving mechanism 820 is provided in this embodiment. The moving mechanism 820 includes, for example, a focus adjustment switch and two actuators that operate according to the operation of the switch and move the first and second diffraction elements 809H and 809V to different positions.

  When the screen 805 is moved from the original position 805A shown in FIG. 8 to the position 805B and the projection distance is changed, the first diffraction element 809H is moved greatly in the horizontal direction where the vertical magnification is small, and the vertical direction where the vertical magnification is large. Then, the second diffraction element 809V is moved small. Thereby, the optical conjugate points of the first and second diffraction elements 809H and 809V can be simultaneously adjusted on the screen 805 in the horizontal direction and the vertical direction, respectively. Therefore, a plurality of diffracted light beams generated by both diffractive elements 809H and 809V can be condensed at one point on the screen 805.

  Note that the F number of each diffracted light beam is very large, and the depth of focus exceeds ± 100 mm when one diffracted light beam is scanned. Therefore, even if the best focus position of each diffracted light beam remains at the position 805A, a sufficient resolution can be obtained on the screen 805 at the position 805B.

  As described above, in this embodiment, when the first and second diffraction elements 809H and 809V are moved to different positions in the light beam direction within the specific range A, the vertical magnification of the second optical system 804B varies depending on the direction. However, it is possible to correct the deterioration in resolution caused by the change in the projection distance.

  In this embodiment, since the first and second diffraction elements 809H and 809V are moved in the space between the first optical system and the second optical system 804B, a new space is used for adjusting the resolution. Therefore, a compact optical scanning device can be provided.

  In this embodiment, since the first and second diffraction elements 809H and 809V are moved, there is no shift of the image projection position accompanying the adjustment of the resolution, and adjustment of the image projection position is not necessary.

  Furthermore, in this embodiment, the first and second diffractive elements 809H and 809V are arranged so that the diffractive action surfaces provided with the grating G face each other, so that the diffractive action surfaces can be brought close to each other. The resolution adjustment range can be expanded.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  For example, in each of the above-described embodiments, the second optical system is configured to include a reflecting surface having a condensing function. However, such a reflecting surface is not necessarily included.

  In each of the above embodiments, the case where the second optical system is configured as a decentered optical system has been described. However, the second optical system is not necessarily configured as a decentered optical system.

  Further, in each of the above-described embodiments, the case where a diffraction element is used as the light beam component generating means has been described. However, any means for generating a plurality of light beam components from a single light beam, such as a hologram element or a polarizing beam splitter, can be used. Other optical elements may be used.

1 is a schematic diagram illustrating a configuration of an optical scanning device and a scanning image display device that are Embodiment 1 of the present invention. FIG. 1 is a vertical sectional view of an apparatus according to Embodiment 1. FIG. FIG. 3 is a diagram showing a structure of a microlens array used in the apparatus of Example 1. The figure which shows the distribution pattern of the diffracted light beam of a micro lens array. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 1. FIG. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 1. FIG. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 1. FIG. FIG. 5 is a diagram illustrating a configuration of a color light source unit used in an optical scanning device and a scanning image display device that are Embodiment 2 of the present invention. FIG. 6 is a vertical cross-sectional view illustrating a partial configuration of an optical scanning device and a scanning image display device that are Embodiment 3 of the present invention. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 3. FIG. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 3. FIG. FIG. 6 is a vertical cross-sectional view illustrating a partial configuration of an optical scanning device and a scanning image display device that are Embodiment 4 of the present invention. FIG. 6 is a perspective view showing a configuration of a diffraction element unit used in the apparatus of Example 4. Explanatory drawing of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 4. FIG. Explanatory drawing (horizontal sectional drawing) of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 4. FIG. Explanatory drawing (vertical sectional drawing) of the focus adjustment method accompanying the change of the projection distance in the apparatus of Example 4. FIG. The conceptual diagram which shows the light quantity distribution of the several light beam component in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Light source 102 Collimator lens 103 Two-dimensional scanning device 104 Scanning optical system 104A 1st optical system 104B, 604B, 804B 2nd optical system 105,605,805 Screen (scanned surface)
108,608,808 Intermediate image 109,609 Microlens array 809H, 809V Diffraction element 120,620,820 Moving mechanism

Claims (7)

Scanning means for scanning a light beam from a light source;
A first optical system that forms an intermediate image on the light flux from the scanning means;
A light beam component generating means disposed within a specific range including the position of the intermediate image, and generating a plurality of light beam components from the light beam from the first optical system;
A second optical system for condensing and projecting the plurality of light beam components toward the surface to be scanned;
An optical scanning apparatus comprising: a moving unit that moves the light beam component generating unit in a traveling direction of the plurality of light beam components within the specific range or in the opposite direction in accordance with a change in a projection distance .   2. The plurality of light beam components are overlapped at the same position on the scanned surface by moving the light beam component generating means to a position conjugate with the scanned surface by the moving means. Optical scanning device.   3. The optical scanning device according to claim 1, wherein the second optical system includes a reflecting surface having a condensing function.   4. The optical scanning device according to claim 1, wherein the second optical system is a decentered optical system. 5.   5. The optical scanning device according to claim 1, wherein the light beam component generating means is a diffraction element. The second optical system has different vertical magnifications in two directions orthogonal to each other,
The diffraction element has a first diffraction element and a second diffraction element whose diffraction directions are orthogonal to each other,
The optical scanning apparatus according to claim 5, wherein the moving unit moves the first and second diffraction elements to different positions in the specific range.   A scanning image display device comprising the optical scanning device according to claim 1, wherein an image is formed on the surface to be scanned.