JP2011186175A - Laser optical element and image projector using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small laser optical element that performs synthesis in colors of a plurality of laser beams of different wavelengths to emit the synthesized laser beams, and to provide a laser scanning type image projector equipped with the laser optical element. <P>SOLUTION: The laser optical element P1 includes: first and second laser light sources 11 and 12 for emitting laser beams of mutually different wavelengths; a collimating lens 2 that all parallelizes or nearly parallelizes the laser beams L1 and L2 emitted from the laser light sources 11 and 12; and a diffraction grating DG that, in the laser beams L1 and L2 emitted from the laser light sources 11 and 12, works on the laser beam L1 of the first wavelength and does not work on the laser beam L2 of the second wavelength, and thereby emits, in the same direction, the laser beam L1 of the first wavelength and the laser beam L2 of the second wavelength. The diffraction grating DG is installed on the emission face of the collimating lens 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser optical element and an image projection apparatus using the laser optical element. For example, an ultra-compact laser optical element that synthesizes and emits laser light of a plurality of wavelengths and a laser beam obtained by using the laser optical element. The present invention relates to an image projection apparatus (for example, a laser projector) of a laser scanning type that projects an image on a screen surface by two-dimensionally deflecting and scanning with a mirror.

  As a small-sized image projection apparatus, a projector using a light modulation element such as a digital micromirror device or a liquid crystal element has been conventionally known. However, the method of enlarging and projecting the image displayed by the light modulation element (so-called micro display method) has a limit in downsizing the device. This is because if it is intended to project a two-dimensional image, it is difficult to avoid an increase in the size of the illumination optical system and the projection optical system.

  Laser scanning image projection apparatuses such as laser projectors are also conventionally known as compact image projection apparatuses. For example, in the case of a laser scanning method adopted in a laser projector, two-dimensional scanning is performed by deflecting laser light in first and second scanning directions orthogonal to each other and scanning the screen surface two-dimensionally with a beam spot. Image formation is performed. A small deflection reflection mirror such as a MEMS (Micro Electro Mechanical Systems) mirror is used for the deflection of the laser beam, and the luminance modulation of the laser beam is performed following the deflection scan.

  The laser scanning image projection apparatus has various features. For example, the deflection reflecting mirror is small compared to a light modulation element such as a digital micromirror device, the light source is a laser light source, and only the laser beam is irradiated to the deflecting reflecting mirror. The scanning lens system can be made smaller or unnecessary compared with a projection optical system that projects a two-dimensional image of the light modulation element, since the screen surface is simply scanned with a beam spot. And so on. Therefore, if this laser scanning method is adopted, the apparatus can be miniaturized.

  In an image projection apparatus that employs the laser scanning method described above, in order to make a plurality of wavelengths of laser light enter one deflecting / reflecting mirror, it is necessary to synthesize optical paths of the laser beams of a plurality of wavelengths (that is, color synthesis). As optical elements for color synthesis, diffraction gratings, dichroic prisms, dichroic mirrors, and the like have been conventionally known (see, for example, Patent Documents 1 to 3).

JP 2005-294279 A JP 2002-15448 A Special table 2009-533715

  The color composition described in Patent Document 1 uses a diffractive action, the color composition described in Patent Document 2 uses switching of the diffractive action by polarized light, and the color composition described in Patent Document 3 uses the wavelength selectivity of the dichroic mirror. Is used. However, both configurations require a large space for color synthesis, which is disadvantageous for downsizing the image projection apparatus.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a compact laser optical element that synthesizes and emits a plurality of laser beams having different wavelengths, and a laser scanning system including the same. An object is to provide an image projection apparatus.

  In order to achieve the above object, a laser optical element according to a first aspect of the present invention includes a plurality of laser light sources that emit laser beams having different wavelengths and a laser beam emitted from the plurality of laser light sources, all of which are parallel light or substantially A collimating lens for collimating light and a laser beam having a first wavelength by acting on a laser beam having a first wavelength and not a laser beam having a second wavelength among laser beams emitted from the plurality of laser light sources, And a diffraction grating that emits laser light of the second wavelength in the same direction, and the diffraction grating is provided on an exit surface of the collimator lens.

According to a second aspect of the present invention, there is provided a laser optical element according to the first aspect, wherein the first laser light source is a laser light source that emits laser light having a first wavelength, and the second laser is a laser light source that emits laser light having a second wavelength. As a light source, the following conditional expression (1) is satisfied.
0.8 <(d · ΔT) / (M · λ · f) <1.2 (1)
However,
d: grating pitch on the optical axis of the collimating lens,
ΔT: shift amount from the second laser light source to the first laser light source,
M: diffraction order,
λ: first wavelength,
f: focal length of collimating lens,
It is.

  According to a third aspect of the present invention, in the first or second aspect, the laser optical element is a semiconductor laser chip in which the plurality of laser light sources are formed on the same substrate.

  According to a fourth aspect of the present invention, there is provided a laser optical element according to any one of the first to third aspects, wherein the laser light source that emits the laser beam having the first wavelength is the first laser light source, and the laser beam having the second wavelength is emitted. If the laser light source to be used is the second laser light source, the diffraction grating has a finer grating pitch toward the periphery in the arrangement direction of the first laser light source and the second laser light source.

  According to a fifth aspect of the present invention, there is provided a laser optical element according to any one of the first to fourth aspects, wherein the laser light source that emits the first wavelength laser light is the first laser light source, and the second wavelength laser light is emitted. If the laser light source to be used is a second laser light source, the first laser light source is a blue light emitting laser light source, and the second laser light source is a green light emitting laser light source.

  According to a sixth aspect of the present invention, there is provided a laser scanning type image projection apparatus comprising: the laser optical element according to any one of the first to fifth aspects of the present invention; and a deflection device that deflects the laser light in two directions orthogonal to each other. And projecting an image onto a screen surface with a laser beam emitted from the laser optical element and two-dimensionally deflected and scanned by the deflecting device.

  According to the present invention, since the diffraction grating is provided on the exit surface of the collimating lens, it is possible to perform color synthesis of a plurality of laser beams having different wavelengths while achieving downsizing of the laser optical element. . By using the laser optical element according to the present invention, it is possible to realize a small-sized image projection apparatus that can obtain a high-quality image.

  By satisfying conditional expression (1), it is possible to perform color synthesis well and project a high-quality image without color misregistration. By using a plurality of semiconductor laser chips formed on the same substrate as the laser light source, it is possible to effectively reduce the size of the laser optical element, and any laser light source that emits blue light and green light can be used. This makes it possible to fabricate with the same material substrate. When the grating pitch of the diffraction grating is made finer toward the periphery in the arrangement direction of the first laser light source and the second laser light source, the coma aberration can be corrected effectively.

1 is a schematic diagram showing an embodiment of an image projection apparatus. The schematic diagram for demonstrating the color synthesis | combination in embodiment of a laser optical element. The optical path figure of the laser optical element which does not have a diffraction grating. The schematic diagram for demonstrating the influence of arrangement | positioning of the diffraction grating in embodiment of a laser optical element. The schematic diagram for demonstrating the coma aberration correction in embodiment of a laser optical element. The schematic diagram which shows the diffraction grating before and behind giving a coma aberration correction function. The optical path figure of the Example of a laser optical element. The phase distribution diagram of the diffraction grating used for the Example and comparative example of a laser optical element. The graph which shows the pitch of the lens up-down direction of an Example and a comparative example. The spot diagram of the Example and comparative example of a laser optical element. FIG. 2 is a schematic diagram illustrating a schematic configuration example of a general laser projector.

  Embodiments of a laser optical element and an image projection apparatus according to the present invention will be described below with reference to the drawings. Note that the same or corresponding parts in the embodiment and the like are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  The image projection apparatus according to the present invention is a laser scanning type image projection apparatus that projects an image onto a screen surface by two-dimensional deflection scanning of laser light. The schematic configuration is shown in FIG. The laser projector (image projection apparatus) PJ is a MEMS scanner (deflection) that deflects a laser optical element P1 and laser beams L1 and L2 emitted from the laser optical element P1 in a first scanning direction and a second scanning direction orthogonal to each other. Apparatus) P2, and forms a two-dimensional image on the screen surface (scanned surface) SC by two-dimensional deflection scanning of the laser beam by the MEMS scanner P2.

  The laser optical element P1 includes a light source device 1, a collimating lens 2, and a diffraction grating DG. The light source device 1 includes a first laser light source 11 and a second laser light source 12 that emit laser beams L1 and L2 having different wavelengths, and the collimating lens 2 includes first and second laser light sources 11 and 12, respectively. The emitted laser beams L1 and L2 are both parallel light or substantially parallel light. The diffraction grating DG is provided on the exit surface of the collimating lens 2, and acts on the laser light L 1 having the first wavelength among the laser light L 1 and L 2 emitted from the first and second laser light sources 11 and 12. By not acting on the two-wavelength laser light L2, the first-wavelength laser light L1 and the second-wavelength laser light L2 are emitted in the same direction. As a result, the laser beams L1 and L2 having the first and second wavelengths are optically combined (that is, color combined) in the same direction. The color-synthesized laser beams L1 and L2 are deflected by reflection at a MEMS mirror (deflection / reflection mirror) MR built in the MEMS scanner P2.

  Therefore, even without using a dichroic prism or dichroic mirror for color synthesis, the color synthesis of the two laser beams L1 and L2 having different wavelengths can be performed in a small size by the diffraction grating DG provided on the exit surface of the collimating lens 2. This can be done with the laser optical element P1. By using the laser optical element P1, it is possible to reduce the size of the image projection device PJ that can obtain a high-quality image.

  A third laser light source that emits laser light having a third wavelength different from the first wavelength and the second wavelength may be further provided in the light source device 1. In that case, it does not act on the second wavelength laser beam L2 (for example, green laser beam), and acts on the first wavelength laser beam L1 (for example, red laser beam) by, for example, second-order diffraction. A diffraction grating DG on which a grating structure is superimposed may be provided on the exit surface of the collimator lens 2 so that the laser beam with a wavelength (for example, blue laser light) acts by, for example, third-order diffraction. In this way, by combining the diffraction of different orders M and the wavelength λ, it is possible to combine three or more wavelengths of light by emitting three or more laser beams from the collimating lens 2 in the same direction. In addition, since the height at which the diffraction grating DG does not change varies even with the level number p described later, it is preferable to design in consideration of an optimal combination of the level number p, the diffraction order M, and the wavelength λ.

  The color synthesis function, compactness, aberration performance, etc. of the laser optical element P1 will be described in more detail. FIG. 11 shows a schematic configuration example of a general laser scanning image projection apparatus PJ that has been conventionally known. The image projection apparatus PJ shown in FIG. 11A collimates RGB laser light emitted from the laser light sources 5R, 5G, and 5B by the collimating lenses 6R, 6G, and 6B, and further colors by the dichroic prisms 7R, 7G, and 7B. It is the composition which performs composition. When such a configuration is employed, at least two color synthesis (that is, color synthesis using at least the dichroic prisms 7G and 7B) is required. As shown in FIG. 11B, if the cross dichroic prism 7 is used, two color synthesis can be performed once. However, even in such a case, it is difficult to carry out while keeping the whole small, and on the contrary, it becomes large. For example, an unnecessary space generated between the laser light sources 5R, 5G, and 5B leads to an increase in size of the whole. Therefore, in the configuration as shown in FIG. 11, even if a very small laser light source can be obtained, the volume occupied in the color synthesis portion cannot be greatly reduced, and it is difficult to achieve the ultimate miniaturization.

  As in the image projection apparatus PJ (FIG. 1) described above, if one collimator lens 2 is shared for a plurality of laser beams L1 and L2, the ultimate miniaturization can be achieved. That is, if a plurality of laser light sources are semiconductor laser chips formed on the same substrate, the size can be much smaller than package type laser light sources 5R, 5G, and 5B (FIG. 11). However, as shown in FIG. 2A, one collimating lens 2 (here, a lens that collimates only by refraction) is arranged in front of two laser light sources (that is, red laser light source 1R and green laser light source 1G). Then, the laser light LG from the green laser light source 1G on the optical axis AX is collimated in parallel to the optical axis AX, but the laser light LR from the red laser light source 1R outside the optical axis AX is on the optical axis AX. On the other hand, it is collimated diagonally. Therefore, in order to obtain light without color misregistration, it is necessary to perform color synthesis that aligns the emission direction in the same direction.

  If the collimating lens 2 having a color composition function is used as in the image projection apparatus PJ shown in FIG. 1, the emission directions of the laser beams LR and LG can be made uniform. For example, as shown in FIG. 2B, if a diffraction grating DG that acts only on the red laser beam LR and does not act on the green laser beam LG is disposed on the exit surface of the collimator lens 2, the red laser beam LR and the green color are displayed. The laser beam LG can be emitted in the same direction.

  The diffraction grating DG acts so that the red laser beam LR (the emission angle θ) is parallel to the optical axis AX. In the case of M-order diffracted light, the calculation is performed using the equation: d · sin θ = M · λ. The pitch d is a one-dimensional diffraction grating (λ: wavelength). FIG. 2C schematically shows a one-dimensional diffraction grating DG having a pitch d. In order to obtain high diffraction efficiency, the diffraction grating DG is preferably a phase type diffraction grating, and more preferably a blaze type or a multi-level (4 levels or more) binary type diffraction grating.

  In order to perform color synthesis with the diffraction grating DG, a diffraction grating DG that acts on the red laser light LR without acting on the green laser light LG is required. For this purpose, it is necessary to select the height of the diffraction grating DG (in other words, the groove depth). When the number of levels of the binary structure is p, the height Lt of the diffraction grating DG that maximizes the first-order diffraction efficiency is expressed by the formula: Lt = ((p−1) / p) · (λ / (n−1)) (N: refractive index). For example, when the number of levels is p = 2, the first-order diffraction efficiency is maximum at Lt / λ = 1/2 (n−1), and the first-order diffraction efficiency is minimum at Lt / λ = 1 / (n−1) ( Zero). Therefore, when the refractive index is 1.5, in order to make the red wavelength 640 nm and the green wavelength 530 nm and to act on the red and not on the green, it is necessary to provide a phase step corresponding to two green wavelengths. There is.

  If the refractive index n of the collimating lens 2 is 1.5, the height of the diffraction grating DG that does not act on the green laser beam LG in the first order diffraction is 0.53 / (1.5-1) = 1.06 μm. It becomes. Therefore, the diffraction grating DG does not act on the green laser light LG, but acts on the red laser light LR. That is, since the 1.06 μm step is 1.66 wavelength, the red laser light LR is diffracted. When the color of the laser beam is changed to blue and green, the green laser beam LG is not diffracted because it is the same as above, but the blue laser beam (wavelength 445 nm) is diffracted because the 1.06 μm step has a 2.38 wavelength. Is done. The above setting is for the case where the number of levels p = 2, but other levels p can be set similarly. That is, it is possible to set the diffraction grating DG so as to act on the red laser beam LR or the blue laser beam without acting on the green laser beam LG. Further, the above is an example in the case of the first-order diffraction, but when the height of the diffraction grating DG is doubled to 2.12 μm, there may be a case where the second-order diffracted light does not act on the green laser light LG. it can. In that case, the blue laser light is strongly influenced by the third-order diffracted light, and the red laser light has a lot of second-order diffracted light.

By setting the diffraction grating DG as described above, wavelength-selective laser light diffraction can be performed. In order to emit the green laser beam LG and the red laser beam LR (or blue laser beam) in the same direction by the diffraction action, it is desirable to use a diffraction grating DG that satisfies a predetermined condition. Laser light (for example, red laser light LR or blue laser light) on which the diffraction grating DG acts is a first wavelength laser light, and laser light (for example, green laser light LG) on which the diffraction grating DG does not act is a second wavelength. The following conditional expression (1) is satisfied when the laser light source that emits the laser light of the first wavelength is the first laser light source and the laser light source that emits the laser light of the second wavelength is the second laser light source. It is desirable to do.
0.8 <(d · ΔT) / (M · λ · f) <1.2 (1)
However,
d: grating pitch on the optical axis of the collimating lens,
ΔT: shift amount from the second laser light source to the first laser light source,
M: diffraction order,
λ: first wavelength,
f: focal length of collimating lens,
It is.

  Considering the diffraction conditional expression: d · sin θ = M · λ, the diffraction angle θ is expressed by the expression: sin θ≈tan θ = ΔT / f. Therefore, the grating pitch d of the diffraction grating DG is preferably in the vicinity of the formula: d≈ (M · λ · f) / ΔT. Specifically, satisfying (0.8M · λ · f) / ΔT <d <(1.2 · M · λ · f) / ΔT, that is, satisfying conditional expression (1) It is preferable for emitting the laser light of one wavelength and the laser light of the second wavelength in the same direction. If the upper limit or lower limit of conditional expression (1) is exceeded, the degree of emission in the same direction by the diffraction gratings will be lost. For example, if the upper limit of conditional expression (1) is exceeded, the influence of diffraction becomes too small, and if the lower limit of conditional expression (1) is exceeded, the influence of diffraction becomes too large. As a result, color composition on the screen is not successful, resulting in color misregistration, making it difficult to obtain a good image. In order to prevent color misregistration, it is preferable that at least one dot misregistration does not occur.

  The laser light that acts on the diffraction grating DG is the first wavelength laser light, the laser light that does not act on the diffraction grating DG is the second wavelength laser light, and the laser light source that emits the first wavelength laser light is the first laser light source. Assuming that the laser light source that emits the laser light having the second wavelength is the second laser light source, it is desirable that the first laser light source is a blue light emitting laser light source and the second laser light source is a green light emitting laser light source. Since the blue laser light source and the green laser light source can be manufactured from a substrate of the same material (for example, gallium nitride), there is an advantage that the blue laser light source and the green laser light source can be simultaneously manufactured on the same chip.

  FIG. 3 is an optical path diagram of the collimating lens 2 not provided with the diffraction grating DG (Z direction: parallel to the optical axis AX, Y direction: perpendicular to the optical axis AX). The green laser light source 1G is on the optical axis AX, and the blue laser light source 1B is at a position deviating from the optical axis AX in the Y direction. Since there is no diffraction grating DG, the blue laser light LB is emitted in an oblique direction on the lower side (the green laser light source 1G side along the Y direction). When the amount of deviation from the optical axis AX of the blue laser light source 1B is ΔT, the emission angle θ of the light (corresponding to the principal ray) at the center of the collimating lens 2 in the blue laser light LB is ΔT = f · tan θ. expressed. For example, when f = 1 mm and ΔT = 0.1 mm, the emission angle θ is 5.7 degrees. Therefore, when the diffraction order M = 1 is used, d · sin θ = M · λ, and M = 1. Therefore, when the wavelength is 0.445 μm, a diffraction grating DG having a pitch of d = 4.47 μm is required. .

  The integration of the collimating lens 2 and the diffraction grating DG is preferable for reducing the size of the laser optical element P1, but the selection of the lens surface on which the diffraction grating DG is disposed is also important. This is because the incident angle of the laser beam with respect to the diffraction grating DG varies depending on whether the diffraction grating DG is disposed on the incident surface or the exit surface of the collimator lens 2. 4A shows an optical path when the diffraction grating DG is provided on the incident surface of the collimating lens 2, and FIG. 4B shows an optical path when the diffraction grating DG is provided on the exit surface of the collimating lens 2. Show. 4A and 4B, when the diffraction grating DG is provided on the exit surface of the collimating lens 2, the diffraction angle θ is greater than when the diffraction grating DG is provided on the entrance surface of the collimating lens 2. FIG. Can be reduced, which is advantageous for wavelength fluctuations.

  When the laser light source is located outside the optical axis AX of the collimating lens 2, off-axis aberration occurs. That is, as shown in FIG. 5A, when one collimating lens 2 is arranged in front of two laser light sources (blue laser light source 1B and green laser light source 1G), the off-axis of the collimating lens 2 is used. Therefore, off-axis aberration occurs. In particular, since the influence of coma is large, it is preferable to reduce coma. Since the green laser beam LG is on-axis light, it is emitted as a parallel light beam parallel to the optical axis AX, but coma aberration occurs with respect to the blue laser beam LB from the blue laser light source 1B shifted off-axis. Resulting in. Therefore, as shown in FIG. 5B, even if the principal ray is parallel to the optical axis AX in the diffraction grating DG, the peripheral ray is shifted in the shift direction (upward direction in FIG. 5: green laser light source 1G). Is emitted in the direction opposite to the direction in which the blue laser light source 1B is located (the lower direction in FIG. 5), so that coma with a tail in the direction opposite to the shift direction is generated.

  In order to correct the coma aberration, the peripheral light beam of the blue laser light source 1B may be deflected in the shift direction (upward direction in FIG. 5) as indicated by the white arrow in FIG. For example, the grating pitch d of the diffraction grating DG may be changed slightly with respect to the upper and lower peripheral rays. Then, as shown in FIG. 5C, it is possible to deflect the peripheral rays of the blue laser light source 1B so that the blue laser light LB is emitted as a parallel light beam parallel to the optical axis AX without coma. is there.

  FIG. 6A shows a diffraction grating DG having a pitch of equal intervals, and FIG. 6B shows a diffraction grating DG having a pitch whose interval is changed so as to correspond to coma aberration correction. There is a position dmax where the pitch is maximum on the blue laser light source 1B side in the vertical direction of the lens (arrangement direction of the green laser light source 1G and the blue laser light source 1B), and the pitch becomes finer as it moves away from the position dmax in the vertical direction of the lens. Yes. The upper pitch interval is different from the lower pitch interval, and the pitch d ″ at the lowermost end is finer than the pitch d ′ at the uppermost end.

  As described above, the coma aberration of the blue laser light LB can be corrected by using the diffraction grating DG whose pitch changes asymmetrically with respect to the optical axis AX of the collimating lens 2. Therefore, the laser beam (for example, blue laser beam LB or red laser beam) that acts on the diffraction grating DG is the first wavelength laser beam, and the laser beam (for example, green laser beam LG) that does not act on the diffraction grating DG is the second. Assuming that the first laser light source is a laser light source that emits laser light of a first wavelength and the second laser light source is a laser light source that emits laser light of a second wavelength, Regarding the arrangement direction of the laser light sources, it is preferable that the diffraction grating DG has a finer grating pitch toward the periphery. By adopting the configuration, coma aberration can be easily corrected. In addition, it is preferable to use a diffraction grating DG whose pitch changes asymmetrically with respect to the optical axis AX so that the pitch in the direction in which the tail of coma aberration is drawn (the direction opposite to the shift direction) becomes fine.

  The collimating lens 2 preferably has a biconvex shape. Since the laser beam to which the diffraction grating DG does not work needs to be corrected for aberrations for collimation, a biconvex shape with a higher degree of freedom of aberration correction is preferred compared to the plano-convex shape.

  Hereinafter, the optical configuration and the like of the laser optical element P1 and the image projection apparatus PJ embodying the present invention will be described more specifically with reference to the construction data of the examples. The examples given here are numerical examples corresponding to the above-described embodiment (FIG. 5C, etc.). FIG. 7A shows an optical path diagram of the embodiment, and FIG. 7B shows an enlarged main part thereof. In the construction data of the example, as surface data, in order from the left column, the surface number i, the radius of curvature r (mm), the surface distance d (mm) on the axis, and the refractive index with respect to the d-line (wavelength 587.56 nm). nd is shown.

The exit surface (i = 3) of the collimating lens 2 is an aspherical surface, and the surface shape is defined by the following equation (AS) using an orthogonal coordinate system (X, Y, Z) having the surface vertex as the origin. . A conic constant is shown as aspherical data (the coefficient of a term not described is 0).
Z = (c · h ² ) / [1 + √ {1− (1 + K) · c ² · h ² }] + Σ (Aj · h ^j ) (AS)
However,
h: height in a direction perpendicular to the Z axis (optical axis AX) (h ² = X ² + Y ² ),
z: the amount of sag in the direction of the optical axis AX at the position of the height h (based on the surface vertex),
c: curvature at the surface vertex (the reciprocal of the radius of curvature r),
K: conic constant,
Aj: j-order aspheric coefficient,
It is.

In addition, a diffraction grating DG is provided on the exit surface (i = 3) of the collimating lens 2, and the diffraction grating structure is defined by the following expression (DS) using an orthogonal coordinate system (X, Y, Z). Is done. A diffraction order and a phase coefficient are shown as diffraction surface data.
Φ = M · ΣΣAmn · X ^m · Y ⁿ (DS)
However,
Φ: phase difference (Z-axis direction),
M: diffraction order,
Amn: phase coefficient (radian),
It is.

  As various data, the focal length f (mm) of the entire system, the numerical aperture (NA) on the object side, the wavelength (nm) of the blue laser light LB, the wavelength (nm) of the green laser light LG, and the position of the blue laser light source 1B ( mm; Y direction), the position of the green laser light source 1G (mm; Y direction), the corresponding value of conditional expression (1), and related data.

FIG. 8A shows the phase distribution of the diffraction grating DG (i = 3) of the embodiment, and FIG. 8B shows the phase distribution when the diffraction grating DG is at equal intervals. The interval between the lines is one phase (2π), and as shown in FIG. 8A, the upper interval and the lower interval are different in the phase distribution of the diffraction grating DG of the embodiment. A comparative example in which the diffraction grating DG of the example has an equal pitch as shown in the phase distribution of FIG. 8B (when the coefficient other than the first power of Y in the example is zero to make the grating uniform). Then, the pitches of the diffraction gratings DG of the example and the comparative example are as shown in the graph of FIG. The graph of FIG. 9 is obtained by plotting the differential value of the central section of the phase distribution of FIGS. 8A and 8B and is normalized by the differential value at the center of the phase distribution (En). = × 10 ⁻ⁿ ). As can be seen from the graph of FIG. 9, there is a position where the pitch is maximum on the blue laser light source 1B side in the vertical direction of the lens (Y direction), and the pitch is the finest at the lowest end on the green laser light source 1G side.

  FIG. 10A shows the optical performance of the example in a spot diagram, and FIG. 10B shows the optical performance of the comparative example in a spot diagram. The spot diagrams shown in FIGS. 10A and 10B are imaging characteristics (scale: 10 mm) on the screen surface (focal plane) SC of the blue laser light LB and the green laser light LG (in the case of the center of the optical axis AX). Respectively. In the example shown in FIG. 10A, it can be seen that both the laser beams LB and LG are similarly reduced. On the other hand, in the case of the comparative example shown in FIG. 10B, it can be seen that the image quality deteriorates because it becomes a very large point 500 mm ahead (the position of the screen surface SC). Further, since the blue laser light source 1B is shifted upward (Y + direction), the frame has a shape with a tail in the downward direction (Y− direction).

Example unit: mm
Surface data
ird nd
1 (Laser surface) ∞ 0.5
2 (Lens entrance surface) 13.48709 3.963726 1.618728
3 (Lens exit surface) -1.79587 500
4 (focal plane) ∞

Aspheric data of the third surface
K = -0.46487

Diffraction surface data of the third surface
M = 2
A01 = 244.00213
A20 = 14.959611
A02 = 15.970044
A21 = 8.9849254
A03 = 7.7153871
A05 = 0.50185094

Various data Blue laser beam LB Wavelength: 445 (nm)
Wavelength of green laser beam LG: 532 (nm)
Position of blue laser light source 1B: 0.1 (mm)
Position of green laser light source 1G: 0.0 (mm)
f = 2.87 (mm)
NA (object side) = 0.5
Corresponding value of conditional expression (1): (d · ΔT) / (M · λ · f) = 1.00847
d = 0.02576 (mm)
ΔT = 0.1 (mm)
M = 2
λ = 0.00045 (mm)
θ = 1.98
sin θ = 0.03455
tan θ = 0.03484

PJ laser projector (image projector)
P1 Laser optical element 1 Light source device 11 First laser light source 12 Second laser light source L1 First wavelength laser light L2 Second wavelength laser light 1R Red laser light source 1G Green laser light source 1B Blue laser light source LR Red laser light LG Green laser Light LB Blue laser light 2 Collimating lens P2 MEMS scanner (deflection device)
MR MEMS mirror (deflection / reflection mirror)
DG diffraction grating SC screen surface

Claims (6)

  A plurality of laser light sources that emit laser beams having different wavelengths, a collimator lens that makes each of the laser beams emitted from the plurality of laser light sources parallel light or substantially parallel light, and laser light emitted from the plurality of laser light sources A diffraction grating that emits laser light of the first wavelength and laser light of the second wavelength in the same direction by acting on the laser light of the first wavelength and not acting on the laser light of the second wavelength. A laser optical element, wherein the diffraction grating is provided on an exit surface of the collimating lens. The following conditional expression (1) is satisfied, where a laser light source that emits laser light of a first wavelength is a first laser light source and a laser light source that emits laser light of a second wavelength is a second laser light source: The laser optical element according to claim 1;
0.8 <(d · ΔT) / (M · λ · f) <1.2 (1)
However,
d: grating pitch on the optical axis of the collimating lens,
ΔT: shift amount from the second laser light source to the first laser light source,
M: diffraction order,
λ: first wavelength,
f: focal length of collimating lens,
It is.   3. The laser optical element according to claim 1, wherein the plurality of laser light sources are semiconductor laser chips formed on the same substrate.   When the laser light source that emits the first wavelength laser light is the first laser light source and the laser light source that emits the second wavelength laser light is the second laser light source, the arrangement direction of the first laser light source and the second laser light source The laser optical element according to claim 1, wherein the diffraction grating has a finer grating pitch toward the periphery.   When the laser light source that emits the first wavelength laser light is the first laser light source and the laser light source that emits the second wavelength laser light is the second laser light source, the first laser light source is a blue light emitting laser light source, The laser optical element according to any one of claims 1 to 4, wherein the second laser light source is a green light emitting laser light source.   A laser optical element according to any one of claims 1 to 5 and a deflecting device that deflects the laser light in two directions orthogonal to each other. An image projection apparatus using a laser scanning method, wherein an image is projected onto a screen surface with laser light that is dimensionally deflected and scanned.

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