Optical combiner

Abstract

An optical multiplexer comprising: a plurality of light sources for emitting a plurality of laser beams having different wavelengths; a collimator that makes the laser beams emitted from the light sources parallel to each other; and a diffraction grating in which the laser beams made parallel by the collimator are diffracted and emitted in an identical optical path, wherein the light sources are linearly arranged on the beam-entering-side focal plane of the collimator, the grating plane of the diffraction grating is disposed on the beam-exiting-side focal plane of the collimator, and a distance D between two of the light sources is set to D=f×(λ1-λ2) / p, where λ1 and λ2 (λ1>λ2) represent the wavelengths of laser beams emitted from the two adjacent light sources, f represents the focal distance of the collimator, and p represents the pitch of the diffraction grating.

Description

[Technical Field]

[0001] The present disclosure relates to an optical multiplexer that multiplexes a plurality of lights with different wavelengths. [Background technology]

[0002] Patent Document 1 discloses an optical multiplexer that uses a diffraction grating. As shown in Fig. 21, the optical multiplexer disclosed in Patent Document 1 is formed by integrating a diffraction grating 100 and collimator lenses 110, 120, and 130. Light beams L1, L2, and L3 with different wavelengths are collimated by the collimator lenses 110, 120, and 130, respectively, and are diffracted and reflected by the diffraction grating 100. The light beams L1, L2, and L3 are incident on the same position on the diffraction grating 100, and the angles of incidence on the diffraction grating 100 are set so that the reflected light of each light beam follows the same optical path L4. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-243987 Summary of the Invention

[0004] An optical multiplexer according to one aspect of the present disclosure is an optical multiplexer that multiplexes and emits multiple laser beams of different wavelengths, and includes multiple light sources that emit laser beams of different wavelengths, a collimator that collimates the multiple laser beams emitted from the multiple light sources, and a transmission diffraction grating that diffracts the multiple laser beams collimated by the collimator and emits them along the same optical path, wherein the multiple light sources are arranged in a straight line on an incident focal plane of the collimator, and the grating surface of the diffraction grating is arranged on an exit focal plane of the collimator, and the arrangement direction of the multiple light sources and the groove direction of the diffraction grating are mutually perpendicular, and when the wavelengths of the laser beams emitted from two adjacent light sources in the multiple light sources are λ1 and λ2 (λ1 > λ2), the focal length of the collimator is f, and the pitch of the diffraction grating is p, the distance D between two adjacent light sources is set to D = f × (λ1 - λ2) / p. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration of an optical multiplexer according to a first embodiment of the present disclosure. [Figure 2] FIG. 1 is a diagram schematically illustrating a configuration of an optical multiplexer according to a first embodiment of the present disclosure. [Figure 3] FIG. [Figure 4] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a modified example of the first embodiment. [Figure 5] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a modified example of the first embodiment. [Figure 6] FIG. 2 is a diagram showing light emitted from a light source. [Figure 7] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second modification of the first embodiment. [Figure 8] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second modification of the first embodiment. [Figure 9] FIG. 2 is a diagram showing the arrangement of a photodetector. [Figure 10] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second embodiment. [Figure 11] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second embodiment. [Figure 12] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second embodiment. [Figure 13] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a second embodiment. [Figure 14] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a first modification of the second embodiment. [Figure 15] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a first modification of the second embodiment. [Figure 16] FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a first modification of the second embodiment. [Figure 17]FIG. 10 is a diagram schematically illustrating the configuration of an optical multiplexer according to a first modification of the second embodiment. [Figure 18] FIG. 10 is a diagram schematically illustrating a configuration of an optical multiplexer according to a second modification of the second embodiment. [Figure 19] FIG. 10 is a diagram schematically illustrating a configuration of an optical multiplexer according to a second modification of the second embodiment. [Figure 20] FIG. 10 is a diagram schematically illustrating a configuration of an optical multiplexer according to a second modification of the second embodiment. [Figure 21] FIG. 1 is a diagram showing an optical multiplexer disclosed in Patent Document 1. DETAILED DESCRIPTION OF THE INVENTION

[0006] In the optical multiplexer disclosed in Patent Document 1, light sources with different wavelengths are placed apart, so if the diffraction angle at the diffraction grating is increased, the diffraction efficiency of the diffraction grating drops significantly. This is because, while high diffraction efficiency can be optimized for light of one wavelength, the diffraction efficiency drops for light of wavelengths other than the optimized wavelength.

[0007] On the other hand, if the diffraction angle of the diffraction grating is reduced, the diffraction efficiency increases, but the diffraction angles of the light of each wavelength become closer to each other. Therefore, in order to separate the light sources of each wavelength from each other, it is necessary to lengthen the optical path length from the light source of each wavelength to the diffraction grating. As a result, the light sources of each wavelength must be located at a considerable distance from the diffraction grating, which poses the problem of increasing the size of the optical system including the light sources.

[0008] Furthermore, when a collimator lens is provided for each light source, there is a problem that a color shift occurs in the combined light due to a positional error between the light source and the collimator lens.

[0009] The present disclosure has been made in consideration of these points, and its main purpose is to provide an optical multiplexer that has high diffraction efficiency, little color shift, and a compact optical system including a light source.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following embodiments. Furthermore, appropriate modifications are possible within the scope of the effects of the present disclosure.

[0011] (First embodiment) 1 and 2 are diagrams schematically illustrating the configuration of an optical multiplexer according to a first embodiment of the present disclosure. Here, the left-right direction on the paper is the X-axis, the up-down direction on the paper is the Y-axis, and the depth direction on the paper is the Z-axis. Fig. 1 is a diagram of the optical multiplexer as viewed from the Z-axis direction, and Fig. 2 is a diagram of the optical multiplexer as viewed from the Y-axis direction.

[0012] As shown in Figures 1 and 2, the optical multiplexer in this embodiment includes a plurality of light sources 10, 11, and 12 that emit laser beams of different wavelengths, a collimator lens (collimator) 20 that collimates the laser beams L1, L2, and L3 emitted from the light sources 10, 11, and 12, and a transmission diffraction grating 30 that diffracts the laser beams L1', L2', and L3' that have been collimated by the collimator lens 20 and emits them along the same optical path.

[0013] Light sources 10, 11, and 12 are, for example, semiconductor lasers, each having a small light emitting point that can be considered as a point light source, and emitting elliptically spreading light forward (positive direction of the X axis) and backward (negative direction of the X axis).

[0014] The light sources 10, 11, and 12 are arranged in a straight line on the incident-side focal plane of the collimator lens 20. The light sources 10, 11, and 12 are arranged so that the ellipse minor axis direction (fast axis direction) of the laser light is aligned with the Z axis direction, and the ellipse major axis direction (slow axis direction) is aligned with the Y axis direction (first direction).

[0015] The light sources 10, 11, and 12 emit laser beams L1, L2, and L3, each representing one of the three primary colors (green, red, and blue), respectively. The light sources 10, 11, and 12 are arranged in a line in the positive direction of the Y axis in the order of the wavelengths of the emitted laser beams (blue, green, and red).

[0016] Photodetectors 40, 41, 42 that receive laser light emitted from the light sources 10, 11, 12 are disposed behind the light sources 10, 11, 12 (in the negative direction of the X-axis) and at positions corresponding to the positions where the light sources 10, 11, 12 are disposed. The outputs of the photodetectors 40, 41, 42 are used by a control circuit (not shown) to stabilize the optical output of the light sources 10, 11, 12. The light sources 10, 11, 12 and the photodetectors 40, 41, 42 constitute a light receiving / emitting unit.

[0017] The collimator lens 20 is a rotationally symmetrical lens with corrected chromatic aberration, and is made up of, for example, lenses made of materials with different refractive indices cemented together.

[0018] 3, the diffraction grating 30 is configured as a blazed diffraction grating in which sawtooth-shaped grating grooves with a pitch p are formed parallel to the Z axis. The grating surface of the diffraction grating 30 is placed on the exit-side focal plane of the collimator lens 20. The arrangement direction of the light sources 10, 11, and 12 (Y-axis direction) and the groove direction of the diffraction grating 30 (Z-axis direction) are perpendicular to each other.

[0019] Laser light L1 emitted from green light source 10 is collimated by collimator lens 20 and enters diffraction grating 30 as parallel light L1' parallel to the X axis, and is emitted in the first-order diffraction direction. If the wavelength of green is λg and the emission direction of diffraction grating 30 is φ, then sin(φ)=λg / p holds.

[0020] As shown in FIG. 1, light sources 10, 11, and 12 are disposed on the incident focal plane of collimator lens 20, and thus are emitted as parallel light from collimator lens 20. Since light source 10 is disposed on the X-axis, laser light L1' collimated by collimator lens 20 is parallel to the X-axis. Furthermore, if the distance between light source 10 and light source 11 is D1 and the focal length of collimator lens 20 is f, laser light L2', which is obtained by collimating laser light L2 emitted from light source 11 by collimator lens 20, becomes parallel light at an angle atan(D1 / f) with respect to the X-axis. Furthermore, if the distance between light source 10 and light source 12 is D2, laser light L3', which is obtained by collimating laser light L3 emitted from light source 12 by collimator lens 20, becomes parallel light at an angle atan(D2 / f) with respect to the X-axis. Here, atan represents an arctangent function.

[0021] Since the grating surface of the diffraction grating 30 is positioned on the exit focal plane of the collimator lens 20, the laser beams L1', L2', and L3' collimated by the collimator lens 20 overlap at the same position on the diffraction grating 30, as shown in Figure 3.

[0022] If the angle of incidence on the diffraction grating is α, the angle of emergence is β, the wavelength of light is λ, and the grating pitch of the diffraction grating is p, the first-order diffracted light can be expressed as -sin(α)+sin(β)=λ / p. When α and β are small, it can be approximated as -α+β=λ / p (Equation 1).

[0023] If the wavelength of the laser light L1 emitted from the light source 10 is λg, the incident angle αg of the laser light L1′ is 0, and therefore the exit angle βg is given by βg=φ=λg / p (Equation 2).

[0024] Furthermore, if the wavelength of the laser light L2 emitted from the light source 11 is λr, the incident angle αr of the laser light L2' is -atan(D1 / f), and if approximated as D1<<f, then αr=-D1 / f. Therefore, from the above formula 1, the exit angle βr is βr=λr / p-D1 / f (formula 3).

[0025] Here, if the emission angle βg of laser light L1' and the emission angle βr of laser light L2' are the same angle, then λg / p=λr / p-D1 / f is obtained from the above equations 2 and 3. Therefore, by setting the distance D1 between light source 10 and light source 11 to D1=f×(λr-λg) / p (equation 4), it is possible to align the emission angles of the first-order diffracted light of laser light L1, L2 emitted from light source 10 and light source 11 at diffraction grating 30.

[0026] Similarly, if the wavelength of the laser light L3 emitted from the light source 13 is λb, the incident angle αb of the laser light L3' is atan(D2 / f), and if approximated as D2<<f, then αb=D2 / f. Therefore, from the above formula 1, the exit angle βb is βb=λb / p+D2 / f (formula 5).

[0027] Here, if the emission angle βg of laser light L1' and the emission angle βb of laser light L3' are the same angle, then λg / p = λb / p + D2 / f is obtained from the above equations 2 and 5. Therefore, by setting the distance D2 between light source 10 and light source 12 to D2 = f × (λg - λb) / p (equation 6), it is possible to align the emission angles of the first-order diffracted light of laser light L1, L3 emitted from light source 10 and light source 12 at diffraction grating 30.

[0028] As described above, by setting the distance D1 between light source 10 and light source 11 and the distance D2 between light source 10 and light source 12 to the values ​​calculated by the above formulas 4 and 6, the first-order diffracted light of laser beams L1, L2, and L3 emitted from light sources 10, 11, and 12 at diffraction grating 30 follows the same optical path. As a result, when laser beams L1, L2, and L3 emitted from light sources 10, 11, and 12 are the three primary colors of light (green, red, and blue), they are combined at diffraction grating 30, and white light can be emitted.

[0029] According to this embodiment, light sources 10, 11, and 12 are collimated by a common collimator lens 20, and therefore even if the collimator lens 20 is decentered relative to the light sources 10, 11, and 12, i.e., shifted in the Y-axis direction, the orientation change of the light sources 10, 11, and 12 is the same, and color shift of the light combined by the diffraction grating 30 is unlikely to occur. Similarly, even if the collimator lens 20 is defocused, i.e., shifted in the X-axis direction, the expansion of the beams due to the defocus of the light sources 10, 11, and 12 is the same for all three, and color shift of the light combined by the diffraction grating 30 is unlikely to occur.

[0030] Furthermore, since the length of the optical multiplexer is approximately the sum of the focal length on the entrance side and the focal length on the exit side of the collimator lens 20, the optical multiplexer can be made smaller by shortening the focal length. Normally, shortening the focal length of the collimator lens 20 increases the change in the beam caused by decentering and defocusing of the collimator lens 20 relative to the light sources 10, 11, and 12. Therefore, if a collimator lens 20 is provided for each light source, a large color shift will occur. However, by using a common collimator lens 20 for the three light sources, the color shift can be reduced and the focal length can be shortened, making it easier to make the optical multiplexer smaller.

[0031] Simulations of the first-order average diffraction efficiency of optical multiplexing using a diffraction grating showed that when the wavelengths of light sources L1, L2, and L3 were λg = 532 nm, λr = 635 nm, and λb = 467 nm, the first-order average diffraction efficiency was 67% when the pitch p of diffraction grating 30 was 2.0 μm, 81% when the pitch p was 3.9 μm, and 86% when the pitch p was 7.8 μm, with the diffraction efficiency decreasing as the pitch p becomes smaller. Therefore, it is desirable for the pitch p of diffraction grating 30 to be 4 μm or greater, which will result in a diffraction efficiency of 80% or greater.

[0032] In this embodiment, three light sources 10, 11, and 12 are exemplified, but the present invention is not limited to this and two light sources or four or more light sources may be used. In this case, when the wavelengths of the laser beams emitted from two adjacent light sources are λ1 and λ2 (λ1>λ2), the focal length of the collimator lens 20 is f, and the pitch of the diffraction grating 30 is p, the distance D between the two light sources may be set as D=f×(λ1−λ2) / p.

[0033] When the three light sources 10, 11, and 12 are the three primary colors of light (green, red, and blue), the wavelengths of the semiconductor lasers may be set to 610 to 660 nm for red, 510 to 550 nm for green, and 440 to 480 nm for blue. Furthermore, when there are four or more light sources, a combination of visible light and near-infrared light or a combination of visible light and near-ultraviolet light may be used.

[0034] In this embodiment, the collimator lens 20 is a cemented lens, but it may be a combination of multiple lenses. Although chromatic aberration increases, a single lens having a plano-convex or biconvex shape may also be used as long as it is not a problem.

[0035] (Modification 1 of the first embodiment) Figures 4 and 5 are diagrams schematically showing the configuration of an optical multiplexer in a modified example of the first embodiment. Figure 4 is a diagram of the optical multiplexer viewed from the Z-axis direction, and Figure 5 is a diagram of the optical multiplexer viewed from the Y-axis direction. In Figures 4 and 5, the same components as in Figures 1 and 2 are designated by the same reference numerals, and their description will be omitted.

[0036] This modified example differs from the first embodiment in that the collimator lens 20 is divided into a fast axis direction and a slow axis direction to collimate the light emitted from the light source.

[0037] As shown in Figures 4 and 5, the collimator lens is composed of a first collimator lens 20A and a second collimator lens 20B. The laser beams emitted from the light sources 10, 11, and 12 each contain a fast axis component and a slow axis component. The first collimator lens 20A collimates the fast axis component of each laser beam. The second collimator lens 20B collimates the slow axis component of each laser beam.

[0038] The first collimator lens 20A is, for example, an aspherical cylindrical lens with its cylindrical axis in the Y-axis direction. The second collimator lens 20B is, for example, an aspherical cylindrical lens with its cylindrical axis in the Z-axis direction. Since the first collimator lens 20A and the second collimator lens 20B collimate laser light of multiple wavelengths, it is desirable that they be chromatic aberration correcting lenses, for example, cemented lenses made of materials with different refractive indices.

[0039] In this modification, light sources 10, 11, and 12 are arranged on the incident-side focal planes of first collimator lens 20A and second collimator lens 20B, and the grating surface of diffraction grating 30 is arranged on the exit-side focal plane of second collimator lens 20B.

[0040] The arrangement of the light sources 10, 11, and 12 and the mechanism by which the laser light emitted from the light sources 10, 11, and 12 is collimated by the first and second collimator lenses 20A and 20B, and then diffracted and emitted along the same optical path by the diffraction grating 30 are the same as in the first embodiment, so a description thereof will be omitted.

[0041] According to this modification, although the number of parts increases, by dividing the collimator lens into a first collimator lens 20A and a second collimator lens 20B, the shape of the combined optical beam emerging from the diffraction grating 30 can be changed.

[0042] 6, the light emitted from light sources 10, 11, and 12 spreads in an elliptical shape, and if the spread angle in the fast axis direction (Z axis direction) is η1 and the spread angle in the slow axis direction (Y axis direction) is η2, then the ratio of the elliptical beam in the fast axis direction to the slow axis direction is tan(η1):tan(η2). If the focal length of first collimator lens 20A in the fast axis direction is f1 and the focal length of second collimator lens 20B in the slow axis direction is f2, then the beam shape can be made circular by setting the focal length ratio to tan(η1):tan(η2)=f2:f1.

[0043] Furthermore, since light sources 10, 11, and 12 are arranged in the slow axis direction (Y axis direction), when collimating light in the slow axis direction, light source 10 is incident on the axis to second collimator lens 20B, making it less likely to produce aberrations, but light sources 11 and 12 are incident off-axis to second collimator lens 20B, making it more likely to produce large aberrations.

[0044] On the other hand, in the fast axis direction (Z axis direction), the light sources 10, 11, and 12 are incident on the axis of the first collimator lens 20A, and therefore aberrations are unlikely to occur.

[0045] Therefore, by making the focal length f2 of the second collimator lens 20B longer than the focal length f1 of the first collimator lens 20A, it is possible to reduce off-axis aberrations in the second collimator lens 20B.

[0046] (Modification 2 of the first embodiment) Figures 7 and 8 are diagrams schematically showing the configuration of an optical multiplexer in Modification 2 of the first embodiment. Figure 7 is a diagram of the optical multiplexer as seen from the Z-axis direction, and Figure 8 is a diagram of the optical multiplexer as seen from the Y-axis direction. In Figures 7 and 8, the same components as in Figures 1 and 2 are designated by the same reference numerals, and their description will be omitted.

[0047] In the first embodiment, the photodetectors 40 to 42 are arranged behind the light sources 10 to 12, i.e., on the side where the laser light is emitted in the negative direction of the X-axis. However, in this modified example, the diffraction grating 30 is arranged at an angle in a plane perpendicular to the direction in which the light sources 10 to 12 are arranged, and the photodetectors 40 to 42 are arranged at a position where the reflected light from the diffraction grating 30 is focused by the collimator lens 20, which is different from the first embodiment.

[0048] 8, the photodetectors 40-42 are arranged on the incident-side focal plane of the collimator lens 20, just like the light sources 10-12. The diffraction grating 30 is arranged tilted at an angle θ in the direction in which the light sources 10-12 are arranged, i.e., in a plane (ZX plane) perpendicular to the slow axis. Therefore, the zero-order reflected light beams L1"-L3" at the diffraction grating 30 return to the light sources 10-12 at an angle of 2θ in the ZX plane.

[0049] 9, by arranging the photodetectors 40-42 at positions spaced a distance W=f×tan(2θ) from the light sources 10-12 in the Z-axis direction, the light beams L1″-L3″ reflected by the diffraction grating 30 are focused on the photodetectors 40-42 by the collimator lens 20. Note that, since the laser light beams L1-L3 emitted from the light sources 10-12 are reflected by the diffraction grating 30 and their Y-axis directions are reversed within the XY plane, the arrangement order of the photodetectors 40-42 in the Y-axis direction is reversed to the arrangement order of the light sources 10-12 in the Y-axis direction.

[0050] It is preferable that the width of the light receivers 40 to 42 in the fast axis direction (Z axis direction) of the light sources 10 to 12 is wider than the width of the light sources 10 to 12 in the slow axis direction (Y axis direction).

[0051] The semiconductor lasers serving as the light sources 10-12 emit laser light not only forward but also backward, and in the first embodiment, photodetectors 40-42 are disposed behind the light sources 10-12 to detect the output of the semiconductor lasers. However, because the light from the semiconductor lasers has a divergence, if the distance between the light sources 10-12 arranged in the Y-axis direction is narrowed, light from adjacent light sources will be incident on the photodetectors 40-42, resulting in incorrect detection of laser output. For this reason, it is necessary to provide a sufficient distance between adjacent light sources 10-12, which places a limit on the size of the optical multiplexer.

[0052] According to this modification, the photoreceivers 40-42 are disposed in positions where the rearward-emitted light from the light sources 10-12 does not enter, i.e., at the same positions in the X-axis direction as the light sources 10-12, and receive the zeroth-order reflected light from the diffraction grating 30, thereby preventing unnecessary light from the adjacent light sources 10-12 from entering the photoreceivers 40-42. This reduces the distance between the light sources 10-12, thereby enabling the optical multiplexer to be made more compact. However, since the amount of zeroth-order reflected light from the diffraction grating 30 is small compared to the rearward-emitted light from the light sources 10-12, the amount of light detected by the photoreceivers 40-42 is small.

[0053] Furthermore, it is preferable that the width of the light receivers 40 to 42 in the fast axis direction (Z axis direction) of the light sources 10 to 12 is wider than the width of the light sources 10 to 12 in the slow axis direction (Y axis direction). This reduces the effect of misalignment of the reflected light from the diffraction grating 30 caused by an error in the tilt angle θ of the diffraction grating 30.

[0054] (Second embodiment) Figures 10 to 13 are diagrams showing the configuration of an optical multiplexer in the second embodiment. Figure 10 is a diagram of the optical multiplexer as seen from the Z-axis direction, Figure 11 is a diagram of the optical multiplexer as seen from the Y-axis direction, Figure 12 is a diagram of the optical multiplexer as seen from the X-axis direction, and Figure 13 is a perspective view of the optical multiplexer. In Figures 10 to 13, the same reference numerals are used for the same components as in Figures 1 and 2, and their explanations will be omitted.

[0055] In the first embodiment, a transmissive collimator lens 20 is used as a collimator for collimating the laser light emitted from the light sources 10 to 12, but in this embodiment, a reflective concave reflecting mirror is used. Also, in the first embodiment, the collimator lens 20 and the diffraction grating 30 are disposed in the air, but in this embodiment, the concave reflecting mirror (collimator) and the diffraction grating 30 are formed on the surface of a transparent member and are integrated into one piece.

[0056] 10 to 13, the optical multiplexer (excluding the light sources 10 to 12) in this embodiment is made up of a transparent member 60. The transparent member 60 can be made of a resin such as PMMA or polycarbonate.

[0057] Of the surface of transparent member 60, the portion designated by reference numeral 21 is cylindrical and its XZ cross section constitutes an aspherical convex lens, with the cylindrical axis parallel to the Y direction. The portion designated by reference numeral 22 is cylindrical and its XZ cross section constitutes a parabolic first concave reflecting mirror, with the cylindrical axis parallel to the Y axis. Lens 21 and first concave reflecting mirror 22 are positioned so that the incident-side focal plane when they are combined is on light sources 10-12.

[0058] The portion designated by the reference numeral 23 constitutes a cylindrical second concave reflecting mirror whose XY cross section is a parabolic surface, and the cylindrical axis is parallel to the Z axis. The second concave reflecting mirror 23 is positioned so that its incident-side focal plane is on the light sources 10-12 and its exit-side focal plane is on the grating surface of the diffraction grating 30.

[0059] The arrangement of the light sources 10, 11, and 12 is the same as in the first embodiment, so a description thereof will be omitted.

[0060] In this embodiment, laser beams L1 to L3 emitted from light sources 10 to 12 are collected by lens 21, and then the collimated laser beam is reflected by first concave reflecting mirror 22. The laser beam reflected by first concave reflecting mirror 22 is reflected by second concave reflecting mirror 23 as collimated laser beams L1' to L3', and the laser beam reflected by second concave reflecting mirror 23 is incident on diffraction grating 30, where it is diffracted and emitted along the same optical path. Note that FIGS. 10 to 13 only show the optical path of laser beam L1 emitted from light source 10.

[0061] According to this embodiment, the laser beams L1 to L3 emitted from the light sources 10 to 12 can be collimated and multiplexed by the lens 21 and the first and second concave reflecting mirrors 22 and 23 formed on the surface of the transparent member 60, so that the first and second concave reflecting mirrors (collimators) 22 and 23 can be integrated with the diffraction grating 30. This makes it possible to provide a more compact optical multiplexer (excluding the light sources 10 to 12) at low cost.

[0062] In this embodiment, the first concave reflecting mirror 22 functions as a first collimator that collimates the laser light in the fast axis direction, and the second concave reflecting mirror 23 functions as a second collimator that collimates the laser light in the slow axis direction. The first and second concave reflecting mirrors 22 and 23 are preferably total reflection type reflecting mirrors, but may also be reflecting mirrors coated with a reflecting mirror film.

[0063] Lens 21 may have a flat or concave lens surface. The smaller the curvature of the convex lens and the closer it is to a concave surface, the smaller the wavefront aberration, but the greater the light leakage from first concave reflecting mirror 22. Note that if the laser light emitted from light sources 10 to 12 has good focusing properties, lens 21 may not be provided.

[0064] (Modification 1 of the second embodiment) Figures 14 to 17 are diagrams schematically showing the configuration of an optical multiplexer in Modification 1 of the second embodiment. Figure 14 is a diagram of the optical multiplexer as seen from the Z-axis direction, Figure 15 is a diagram of the optical multiplexer as seen from the Y-axis direction, Figure 16 is a diagram of the optical multiplexer as seen from the X-axis direction, and Figure 17 is a perspective view of the optical multiplexer. In Figures 14 to 17, the same components as in Figures 10 to 13 are designated by the same reference numerals, and their description will be omitted.

[0065] This modified example differs from the second embodiment in that the second concave reflecting mirror (reflecting mirror in the slow axis direction) 23 in the second embodiment is divided into two reflecting mirrors.

[0066] 14 to 17, the portions of the surface of transparent member 60 designated by reference numerals 23 and 24 are cylindrical and constitute second and third concave reflecting mirrors with parabolic XY cross sections, with the cylindrical axis parallel to the Z axis. Second and third concave reflecting mirrors 23 and 24 have the same focal length and are arranged close to each other. When second and third concave reflecting mirrors 23 and 24 are combined, light sources 10 to 12 are arranged at the incident-side focal plane, and the grating surface of diffraction grating 30 is arranged at the exit-side focal plane.

[0067] In this modification, two concave reflecting mirrors 23 and 24 are used to collimate the light in the slow axis direction, which allows the focusing angle of the laser light by each reflecting mirror to be divided in half, and the wavefront aberration of the light generated by the reflecting mirrors can be significantly reduced to 1 / 4. In addition, by using two reflecting mirrors in the slow axis direction, the laser light is folded back one more time, which allows the optical multiplexer (excluding light sources 10 to 12) to be made more compact.

[0068] When the focal lengths of the concave reflecting mirror 23 and the concave reflecting mirror 24 are the same, the wavefront aberration in the slow direction is minimized. However, if it is acceptable for the wavefront aberration to worsen, the concave reflecting mirror 23 and the concave reflecting mirror 24 may have different focal lengths.

[0069] (Modification 2 of the second embodiment) Figures 18 to 20 are diagrams schematically showing the configuration of an optical multiplexer in Modification 2 of the second embodiment. Figure 18 is a diagram of the optical multiplexer as seen from the Z-axis direction, Figure 19 is a diagram of the optical multiplexer as seen from the Y-axis direction, and Figure 20 is a diagram of the optical multiplexer as seen from the X-axis direction. In Figures 18 to 20, the same components as in Figures 10 to 13 are designated by the same reference numerals, and their description will be omitted.

[0070] This modification differs from the first modification of the second embodiment in that a system for folding back the optical path is further added in the XZ plane.

[0071] 19, the portion of the surface of transparent component 60 designated by reference numeral 25 is a first inclined plane, which is a plane inclined at -45° with respect to the X axis in the XZ plane. The portion designated by reference numeral 26 is a second inclined plane, which is a plane inclined at +45° with respect to the X axis in the XZ plane.

[0072] That is, the first inclined plane 25 and the second inclined plane 26 form an angle of 90° with each other in the XZ plane, and the laser light reflected by the first concave reflecting mirror 22 traveling from the positive direction of the X-axis to the negative direction of the X-axis is reflected by the first and second inclined planes 24, 25 and converted into an optical path traveling from the negative direction of the X-axis to the positive direction of the X-axis.

[0073] The laser light reflected by the first and second inclined planes 24, 25 is collimated by the second and third concave reflecting mirrors 23, 24, and the collimated laser light enters the diffraction grating 30, where it is diffracted and emitted along the same optical path.

[0074] In this modified example, the laser light reflected by the first concave reflecting mirror 22 is reflected by the first and second inclined planes 24 and 25, thereby making it possible to shorten the length of the optical multiplexer (excluding the light sources 10 to 12) in the X-axis direction without changing the optical characteristics.

[0075] The inclination angles of the first and second inclined planes 24, 25 with respect to the X axis are -45° and +45°, respectively, but the angle may be set to 45° or more, although this increases the length of the optical multiplexer in the Z axis direction. However, an inclination angle of 45° or less is not preferable because total reflection does not occur and light leakage occurs.

[0076] While the present disclosure has been described above using preferred embodiments, these descriptions are not limiting and various modifications are possible. For example, in the second embodiment and its modifications 1 and 2, the diffraction grating 30 may be arranged tilted in a plane perpendicular to the linear arrangement of the light sources 10 to 12, as described in the modification 2 of the first embodiment. In this case, the photodetectors 40 to 42 are arranged at positions where the light reflected from the diffraction grating 30 is collected by the first concave reflecting mirror (collimator) 22.

[0077] According to the present disclosure, it is possible to provide an optical multiplexer that has high diffraction efficiency, little color shift, and allows for miniaturization of an optical system including a light source. [Explanation of symbols]

[0078] 10~12 light source 20 Collimator lens (collimator) 20A First collimator lens 20B Second collimator lens 21 Lens 22 First concave reflector (collimator) 23 Second concave reflector (collimator) 24 Third concave reflector (collimator) 25 First inclined plane 26 Second Inclined Plane 30 Diffraction Grating 40, 41, 42 Receiver 60 Transparent parts

Claims

1. An optical multiplexer that multiplexes and emits a plurality of laser beams having different wavelengths, a plurality of light sources that emit a plurality of laser beams having different wavelengths; a collimator that collimates the plurality of laser beams emitted from the plurality of light sources; a transmission type diffraction grating that diffracts the plurality of laser beams that have been collimated by the collimator and emits them along the same optical path; Equipped with the plurality of light sources are arranged in a straight line on an incident-side focal plane of the collimator, a grating surface of the diffraction grating is disposed on an exit-side focal plane of the collimator, an arrangement direction of the plurality of light sources and a groove direction of the diffraction grating are perpendicular to each other; Among the plurality of light sources, the wavelengths of the laser beams emitted from two adjacent light sources are defined as λ １ , λ ２ (λ １ >λ ２ ), the focal length of the collimator is f, and the pitch of the diffraction grating is p, the distance D between the two adjacent light sources is D=f×(λ １ -λ ２ ) / p, the diffraction grating is disposed at an angle in a plane perpendicular to the direction in which the plurality of light sources are linearly arranged, an optical multiplexer, wherein a plurality of photodetectors for receiving the laser beams emitted from the respective light sources are disposed at positions where the reflected light from the diffraction grating is focused by the collimator;

2. 2. The optical multiplexer according to claim 1, wherein the plurality of light sources are three or more light sources and are arranged in a straight line on the incident-side focal plane of the collimator in order of wavelength length of the three or more laser light beams emitted from the three or more light sources.

3. 3. The optical multiplexer according to claim 1, wherein said collimator is composed of a lens or a concave reflecting mirror.

4. each of the plurality of laser beams includes a fast axis component and a slow axis component; a slow axis component of each of the plurality of laser beams is parallel to a first direction; 4. The optical multiplexer according to claim 1, wherein the plurality of light sources are arranged in a straight line in a direction parallel to the first direction.

5. each of the plurality of laser beams includes a fast axis component and a slow axis component; the collimator is composed of a first collimator that collimates a fast axis component of each of the plurality of laser beams, and a second collimator that collimates a slow axis component of each of the plurality of laser beams, the plurality of light sources are disposed on incident-side focal planes of the first collimator and the second collimator, 5. The optical multiplexer according to claim 1, wherein a grating surface of said diffraction grating is disposed on an exit-side focal plane of said second collimator.

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