JP5488803B2 - OPTICAL DEVICE, PROJECTION IMAGE DISPLAY DEVICE HAVING THE OPTICAL DEVICE, AND OPTICAL DEVICE MANUFACTURING METHOD - Google Patents

Description

The present invention relates to an optical device comprising a collimating lens, a manufacturing method of projection type image display device and an optical device having the optical device. More specifically, the present invention relates to a collimating lens having a diffractive structure that collimates a plurality of laser light sources, and a laser scanning projection image display apparatus having the collimating lens.

  2. Description of the Related Art In recent years, for the purpose of reducing the size and weight, a projection type image display device (projector or the like) using an LED or a laser has been actively developed. The projection-type image display device can be easily carried and improved in portability by reducing the size and weight. Further, by reducing the weight, it is possible to directly attach to a wall or the like that has been difficult to attach.

  Among projection-type image display devices using lasers, the combination of lasers of three primary colors (R (red), G (green), and B (blue)) and MEMS (Micro Electro Mechanical Systems) mirrors In addition, since the scanning type small projector can reduce the number of components and can be miniaturized, research and development have been advanced (see, for example, Patent Document 1).

  FIG. 7 shows a schematic configuration diagram of a scanning type small projector in which these three primary color lasers and MEMS mirrors are combined. A projector 100 shown in FIG. 7 includes laser light sources 101R, 101G, and 101B that respectively emit R, G, and B laser light, and lenses 102R, 102G, and 102B that collimate the laser light from the laser light sources 101R, 101G, and 101B. And dichroic mirrors 103R, 103G, and 103B that reflect only red light, green light, and blue light respectively, and transmit other light, a MEMS mirror device 104 that includes a mirror having a variable tilt angle, and a MEMS mirror device 104. The control circuit 105 is configured to rotate the mirror in the horizontal direction and the vertical direction and emit laser light whose light intensity is modulated from the laser light sources 101R, 101G, and 101B in accordance with the input video signal. The control circuit 105 includes a mirror control unit and a modulation unit, and forms an image on the screen 106 by modulating the laser light intensity in synchronization with the mirror control unit and the modulation unit.

  An optical element such as a collimating lens mounted on such a projector needs to form an optical curved surface in various shapes, and since it is desirable that it can be mass-produced at low cost, it can form various optical curved surfaces. In many cases, it is manufactured by an injection molding method using a resin material that is excellent in cost.

  However, an optical element manufactured using a resin material has a problem that optical characteristics such as a refractive index of the resin material and a focal length greatly change due to a temperature rise due to heat generated by a light source or the like.

  To prevent such problems, optical characteristics are prevented from deteriorating by providing a diffractive structure to an optical element such as a collimating lens, a cylindrical lens, or an optical disk objective lens used in a writing device in an electrophotographic image forming apparatus or the like. Attempts have been made.

  However, the conventionally proposed technique corrects with a diffraction structure optimized for a single wavelength. Therefore, there is a problem that correction is not possible with respect to wavelengths other than the optimized wavelength, or even if correction is performed, the diffraction efficiency is greatly lowered, so that it is not suitable for use in many cases. For this reason, a diffraction collimating lens or the like has to be designed and manufactured individually for each wavelength, resulting in an increase in cost.

With respect to the above problem, the invention described in Patent Document 2 discloses a method for designing a diffractive optical element optimized for two or more wavelengths. In Patent Document 2, λ ₁ and λ ₂ are the wavelengths of the light source, and the refractive index of the material constituting the diffraction lens at λ ₁ and λ ₂ is n (λ ₁ ) and n (λ ₂ ). Is set to a value approximately equal to the least common multiple of λ ₁ / {n (λ ₁ ) -1} and λ ₂ / {n (λ ₂ ) -1}, so that two wavelengths of light can be obtained. In contrast, an invention that can perform the same optical function is disclosed.

  However, the object to be corrected by the diffractive optical element is not limited to the refractive index and thermal expansion of the material constituting the optical element, as described in Patent Document 2, but the thermal expansion of the casing that fixes the optical element. Further, it is desired that the wavelength variation of the laser light source due to heat is also corrected.

  In particular, the influence of fluctuations in the wavelength of the laser light source due to heat has a great influence on the design of the diffractive lens in a semiconductor laser used in a small projector. Further, the magnitude of the wavelength variation varies depending on the emission wavelength of the laser light source. For example, an InGaN semiconductor laser that oscillates near 445 nm has a fluctuation amount of about 0.6 nm per 10 ° C., whereas an AlGaInP semiconductor laser that oscillates near 640 nm has a fluctuation amount of about 2.0 nm per 10 ° C.

  FIG. 8 is a graph showing the focal length variation in the conventional collimating lens. In this example, the amount of change in the focal length of the temperature-corrected diffraction collimating lens with the diffraction surface optimized for a wavelength of 445 nm is shown. Note that the example shown in FIG. 8 does not take into account the thermal expansion of the housing that fixes the optical element.

  In FIG. 8A, the wavelength variation with respect to the temperature of the light source with a wavelength of 445 nm is 0.06 nm / ° C., and the wavelength variation with respect to the temperature of the light source with a wavelength of 640 nm is 0.2 nm / ° C. For comparison, the focal length fluctuation amount of a collimating lens having the same focal length, effective diameter, lens thickness, and the same resin material and having no diffraction structure is also shown.

  As is clear from FIG. 8A, the focal length variation is suppressed for both the light source having a wavelength of 445 nm and the light source having a wavelength of 640 nm as compared with a collimating lens having no diffraction structure. However, there is a difference in the effect, and there is a correction effect of 95% or more for a light source with a wavelength of 445 nm, whereas there is only a correction effect of about 30% for a light source with a wavelength of 640 nm.

  FIG. 8B shows the focal length fluctuation amount when the wavelength fluctuation amount of the light source having a wavelength of 640 nm is set to 0.06 nm / ° C. and the same wavelength fluctuation amount as that of the light source having a wavelength of 445 nm is set. In the example shown in FIG. 8B, a correction effect substantially equivalent to the optimized wavelength of 445 nm is obtained.

FIG. 9 shows the surface shape factor ((a) shows the exit surface and (b) shows the entrance surface) of the collimating lens (hereinafter also referred to as temperature correction diffraction collimating lens), and FIG. 10 shows the temperature correction of this collimating lens. The diffraction structure provided to the diffraction surface is shown. Here, the surface shape formula is expressed by the following formula (1).
Z = {R ² × C} / [1 + √ {1- (1 + K) (R × C) ² }] + A4 × R ⁴ + A6 × R ⁶ + A8 × R ⁸ +.
However,
Z: lens height in the optical axis direction R: distance from the optical axis K: conic coefficient C: curvature Ai: aspherical coefficient (i = 4, 6, 8,...). ... (1)
This temperature-corrected diffraction collimating lens is designed with a focal length of about 3 mm, an effective diameter of 1.4 mm, and a lens thickness of 2 mm.

  As described above, since a wavelength band in which the focal length correction amount is not appropriate is generated, a collimating performance necessary as a collimating lens cannot be obtained, and when this is used for a small projection type image display device or the like, there is a certain specification. There remains a problem that image quality may be deteriorated only at the wavelength of.

Therefore, the present invention provides a collimating lens that changes with temperature by means of a diffractive collimating lens having the same diffractive structure and a spherical surface or an aspherical surface even when the semiconductor material constituting the laser light source is different and the wavelength variation with respect to temperature is different. to make a focal length variation of, by allowing for different plurality of laser light sources wavelengths, projection having an optical device and the optical device can be shared by different laser light sources wavelengths An object of the present invention is to provide a method for manufacturing an image display device and an optical device .

To achieve the above object, an optical device according to claim 1, 2 or more wavelengths _{λ i (i = 1,2,3, ...} ) and a plurality of laser light sources of different, emitted from the plurality of laser light sources a plurality of collimator lenses to perform collimation of the plurality of laser light is, an optical device comprising a has a diffractive structure on at least one surface of the collimating lens, the diffractive structure is diffracted to each wavelength lambda _i The correction amount of the focal length caused by the temperature change with the maximum efficiency is set to the focal length change (change amount is assumed to be ΔfA) with respect to the laser light source A having the minimum wavelength change amount with respect to the temperature change among the plurality of laser light sources. undercorrection Te, corrected for the change in focal length relative to a laser light source B to wavelength variation is maximized with respect to the temperature variation among the plurality of laser light sources (the variation to .DELTA.FB) Next over - and one in which the absolute value of the change amount ΔfA and the change amount ΔfB is the same or the like.

  Therefore, even if the semiconductor materials that make up the laser light source are different, and the amount of wavelength variation with respect to temperature is different, the collimating lens focal length varies with temperature due to the diffraction structure with the same diffraction structure and spherical or aspherical surface. The variation can be performed for a plurality of laser light sources having different wavelengths.

According to a second aspect of the present invention, in the optical device according to the first aspect , the collimating lens is manufactured by an injection molding method using a resin material.

According to a third aspect of the present invention, there is provided a projection type image display apparatus, wherein the light emitted from the plurality of laser light sources and the optical apparatus according to the first or second aspect are collimated by a plurality of collimating lenses. An optical system for synthesizing a light beam having a wavelength of 1 to the same optical path, a scanning unit capable of two-dimensionally scanning the synthesized light beam on the same optical path, and an output of the laser light source in synchronization with the movement of the scanning unit and control means for controlling, and has a.

  According to a fourth aspect of the present invention, in the projection type image display apparatus according to the third aspect, the laser light source A is a GaN (gallium nitride) semiconductor laser, and the laser light source B is GaInP (indium gallium phosphide). A semiconductor laser or a GaAs (gallium arsenide) semiconductor laser.

A projection type image display device according to a fifth aspect includes the optical device according to the first or second aspect. According to a sixth aspect of the present invention, there is provided a method for manufacturing an optical device , comprising: a plurality of laser light sources having different wavelengths λ _i (i = 1, 2, 3,...); And a plurality of laser light sources emitted from the plurality of laser light sources. a method of manufacturing an optical device comprising a plurality of collimating lenses, a performing collimated laser beam, having a diffractive structure on at least one surface of the collimator lens, the diffraction structure is a diffraction for each wavelength lambda _i The correction amount of the focal length caused by the temperature change with the maximum efficiency is set to the focal length change (change amount is assumed to be ΔfA) with respect to the laser light source A having the minimum wavelength change amount with respect to the temperature change among the plurality of laser light sources. Undercorrection, overcorrection for focal length change (change amount is assumed to be ΔfB) with respect to laser light source B that has the largest wavelength change amount with respect to temperature change among a plurality of laser light sources It becomes, and the absolute value of the change amount ΔfA and the change amount ΔfB is that to include a step of designing a diffractive structure such that the equivalent.

  According to the present invention, it is possible to share a diffractive collimating lens, and it becomes unnecessary to design and manufacture a diffractive collimating lens individually for each wavelength laser. In addition, while maintaining the temperature correction function, it is possible to reduce the number of molds produced and shorten the development period, thereby reducing the manufacturing cost of the collimating lens and the projection type image display apparatus using the collimating lens.

It is a schematic block diagram which shows one Embodiment of the projection type image display apparatus which concerns on this invention. It is a schematic diagram which shows one Embodiment of the collimating lens which concerns on this invention. It is an example of the cross-sectional structure of the diffraction surface of a diffraction collimating lens. It is an example of the graph showing the focal distance variation | change_quantity in each wavelength of a diffraction collimating lens. It is an example of the graph which shows the change of the focal distance variation | change_quantity when the temperature rises from 25 degreeC to 80 degreeC in each wavelength of the diffraction coefficient phase function and diffraction collimating lens. It is a surface shape factor of a diffraction collimating lens. It is an example of the schematic block diagram of the conventional projection type image display apparatus. It is an example of the graph showing the focal distance variation | change_quantity in the conventional collimating lens. It is a surface shape factor of the conventional diffraction collimating lens. It is sectional drawing of the diffraction surface of a diffraction collimating lens.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Projection type image display device)
A projection type image display apparatus according to the present invention has a collimating lens according to the present invention (hereinafter also referred to as a diffraction collimating lens) described below, collimates light emitted from a laser light source with a collimating lens, and the collimating An optical system for synthesizing a plurality of light beams having a plurality of wavelengths on the same optical path, a scanning unit capable of two-dimensionally scanning the light beam synthesized on the same optical path, and a laser in synchronization with the movement of the scanning unit. Control means for controlling the output of the light source. Note that the collimating lens according to the present invention is not limited to the projection type image display apparatus having the configuration shown in FIG. 1, and is preferably applied to projection type image display apparatuses having various other configurations.

  FIG. 1 shows an embodiment of a projection type image display apparatus. The projection-type image display apparatus 10 according to the present embodiment includes laser light sources 1R, 1G, and 1B that emit laser beams of R (red), G (green), and B (blue), and laser light sources 1R, 1G, A diffractive collimating lens lens 2R, 2G, 2B for collimating the laser beam from 1B is provided.

  In this embodiment, as the red laser light source 1R, a semiconductor laser that is mainly composed of a GaInP-based semiconductor and emits light in the vicinity of a wavelength of 640 nm is used. Further, as the blue laser light source 1B, a semiconductor laser that is mainly composed of an InGaN-based semiconductor and emits light in the vicinity of a wavelength of 445 nm is used. Further, as the green laser light source 1G, a semiconductor laser that has been developed in recent years and is mainly composed of an InGaN-based semiconductor and emits light in the vicinity of a wavelength of 500 to 545 nm is used. As the green laser light source 1G, it is also preferable to use a YAG (yttrium, aluminum, garnet) laser that is configured using second harmonic generation (SHG) and transmits at a wavelength of 532 nm.

  The diffractive collimating lenses 2R, 2G, and 2B according to the present embodiment are configured with the same diffractive structure, the same spherical surface, or the aspherical surface, as will be described in detail below, and are not individually designed for each wavelength. Therefore, it can be shared.

  The projection-type image display device 10 includes dichroic mirrors (optical systems) 3R, 3G, and 3B that reflect only red light, green light, and blue light, and transmit other light, and mirrors with variable tilt angles. The MEMS mirror device (scanning means) 4 provided and the mirror of the MEMS mirror device 4 are rotated in the horizontal direction and the vertical direction, and the light intensity is modulated from the laser light sources 1R, 1G, 1B according to the input video signal. It comprises a control circuit (control means) 5 that emits laser light. Further, the control circuit 5 has mirror control means and modulation means, and forms an image on the screen 6 by modulating the laser light intensity in synchronization therewith.

(Diffraction collimating lens)
Optical device according to the present invention is carried out two or more wavelengths _{λ i (i = 1,2,3, ...} ) different from the plurality of laser light sources 1 of the collimation of the plurality of laser beams emitted from the laser light source 1 An optical device including a plurality of collimating lenses (diffraction collimating lens 2), and having a diffractive structure on at least one surface of the collimating lens, and the diffractive structure has a maximum diffraction efficiency for each wavelength λ _i. The correction amount of the focal length caused by the temperature change is insufficiently corrected with respect to the change of the focal length with respect to the laser light source A in which the wavelength change amount with respect to the temperature change is minimum among the plurality of laser light sources 1 (the change amount is ΔfA). , it overcorrected with respect to the focal length change of the relative laser light source B to wavelength variation is maximized with respect to the temperature variation among the plurality of laser source (the variation to .DELTA.FB) And one in which the absolute value of the change amount ΔfA variation ΔfB is the same or the like.

  First, “undercorrection” and “overcorrection” will be described. Here, it is molded from the same resin material as that constituting the collimating lens according to the present invention, has the same effective diameter and the same focal length, but does not have a diffractive structure, and is composed only of a spherical surface or an aspherical surface. Let ΔfO be the focal length change amount with respect to the temperature change of the collimating lens.

  Usually, since the light emitted from the laser light source is divergent light, the collimating lens is designed as a convex lens. In this case, the focal length changes in the direction in which the focal length increases as the temperature rises. > 0.

Therefore, “Uncorrected for focal length change (change amount is assumed to be ΔfA) with respect to laser light source A in which the wavelength change amount with respect to temperature change is minimum among laser light sources”, “wavelength change with temperature change among laser light sources “To be overcorrected with respect to the change in focal length with respect to the laser light source B having the maximum amount (change amount is assumed to be ΔfB)” means that the following equation (2) is satisfied.
ΔfB <0 <ΔfA <ΔfO (2)

  FIG. 2 shows a diffractive collimating lens 2 that is an embodiment of the collimating lens according to the present invention. The light beam emitted from the laser light source 1 passes through the cover glass of the light source, enters from the incident surface 2a of the diffractive collimating lens 2, and exits from the output surface 2b. In addition, although the diffraction collimating lens 2 of this embodiment is provided with the diffractive structure on the output surface 2b, it may be provided on the incident surface 2a side, and is not particularly limited.

  FIG. 3 shows a cross-sectional view of the diffractive structure provided on the exit surface 2b of the diffractive collimating lens 2 shown in FIG. 3 assumes that a semiconductor laser with a wavelength of 640 nm is used as a red light source, a semiconductor laser with a wavelength of 530 nm is used as a green light source, and a semiconductor laser with a wavelength of 445 nm is used as a blue light source, as described above. Designed. The diffraction collimating lens 2 is injection-molded with a cycloolefin resin material, and its refractive index is 1.512 with respect to light having a wavelength of 530 nm at 25 ° C. Thus, by manufacturing the diffractive collimating lens 2 by an injection molding method using a resin material, it is possible to reduce the manufacturing cost and to mass-produce.

Here, in order to maximize the diffraction efficiency for each wavelength λ _i, the depth d of the diffraction groove of the diffractive structure formed by the step is set to λ _i / {n (λ _i ) −1} ( The least common multiple of λ _i = 640 nm, 530 nm, or 445 nm may be set. In this embodiment, d = 5.12 μm (refer to Patent Document 2 for this point).

In addition, the diffraction structure shown in FIG. 3 is a blazed diffraction grating having a sawtooth cross section, but is not limited to this, for example, a Fresnel step type diffraction grating having a partially curved cross section, Alternatively, a multi-step diffraction grating having a stepped shape, which is a shape approximating a blazed diffraction grating, may be used. In the case of a multi-step type diffraction grating, if the number of steps is m, the step height h from the first step to the m-th step is expressed by the following equation (3).
h = (m−1) d / m (3)

  Next, FIG. 4 shows a graph showing the focal length fluctuation amount at each wavelength of the diffractive collimator lens 2 when the diffractive lens and the laser light source are heated from 25 ° C. to 80 ° C. FIG. For comparison, the focal length fluctuation amount of a collimating lens having the same focal length, effective diameter, lens thickness, and the same resin material and having no diffraction structure is also shown.

  In the example shown in FIG. 4, the wavelength variation with respect to the temperature of the light source having the wavelength of 445 nm and the wavelength of 530 nm is 0.06 nm / ° C., and the wavelength variation with respect to the temperature of the light source with the wavelength of 640 nm is 0.2 nm / ° C.

  Here, when there are a plurality of wavelengths having the same wavelength variation amount as in the present embodiment, the laser light source A may be selected with the longest wavelength, and the laser light source B candidate may be a wavelength. The one with the shortest may be selected. Therefore, a light source with a wavelength of 530 nm corresponds to the laser light source A, and a light source with a wavelength of 640 nm corresponds to the laser light source B.

  As shown in FIG. 4, when the temperature rises from 25 ° C. to 80 ° C. in a light source with a wavelength of 530 nm, the focal length variation is 0.012 mm, and when the temperature rises from 25 ° C. to 80 ° C. in a light source with a wavelength of 640 nm The focal length variation amount of -0.012 mm is different in sign (variation direction is different), but the magnitudes are almost the same.

  Further, it can be seen that a correction effect of 70% or more appears at any wavelength when compared with the focal length fluctuation amount of the collimating lens having no diffractive structure to be compared.

  Next, FIG. 5 shows a graph showing the change in the focal length variation when the temperature rises from 25 ° C. to 80 ° C. at each wavelength of the diffraction collimator lens 2 and the second order coefficient C2 of the phase function of the diffraction structure.

Here, the phase function φ (R) of the diffractive structure is expressed by the following equation (4). Where C2 is the power of the diffractive structure.
φ (R) = C2 × R ² (4)

  As shown in FIG. 5, for the light source having a wavelength of 445 nm and the light source having a wavelength of 530 nm having the same wavelength variation with respect to the temperature of the light source, the focal length variation gradually changes with respect to the quadratic coefficient C2 of the phase function. On the other hand, in the case of a light source with a wavelength of 640 nm, the focal length fluctuation amount changes abruptly.

Therefore, in this case, the focal length variation amount ΔfB of the focal length variation ΔfA and wavelength 640nm wavelength 530nm satisfies the following equation (5), in other words, the absolute value of the ΔfA and ΔfB so that the like , C = -0.137 about to (equation (5) comprises the, etc.) that is, the light source of wavelength 445 nm, light of wavelength 530 nm, for any light source of wavelength 640 nm, the focal length variation It is possible to create a diffractive structure having a correction effect.
ΔfA = −ΔfB (5)

FIG. 6 shows the surface shape factor of the diffractive collimating lens 2 ((a) shows the exit surface and (b) shows the entrance surface). The sectional view of the diffractive surface of the diffractive collimating lens 2 is the same as that shown in FIG. Further, the surface shape formula can be expressed by the following formula (6) (the same formula as the formula (1)).
Z = {R ² × C} / [1 + √ {1- (1 + K) (R × C) ² }] + A4 × R ⁴ + A6 × R ⁶ + A8 × R ⁸ +.
However,
Z: lens height in the optical axis direction R: distance from the optical axis K: conic coefficient C: curvature Ai: aspherical coefficient (i = 4, 6, 8,...). (6)

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  For example, in the above embodiment, a collimator lens having a function of emitting a divergent light beam emitted from the laser light source 1 as parallel light has been described as an example. However, the emitted light beam is not limited to a parallel light beam and emits a divergent light beam or a convergent light beam. It is also preferable to apply it to a collimating lens having a function of

  In the above embodiment, the diffractive structure is provided on the collimating lens surface. However, the diffractive optical element is not limited to this, and is separated from the collimating lens and mounted in combination with the collimating lens having no diffractive optical surface. Is also preferably used.

1R, 1G, 1B Laser light sources 2R, 2G, 2B Diffraction collimating lenses 3R, 3G, 3B Dichroic mirror 4 MEMS mirror device 5 Control circuit 6 Screen 10 Projection type image display device

JP 2006-189573 A JP 2008-70797 A

Claims (6)

A plurality of laser light sources having different wavelengths λ _i (i = 1, 2, 3,...) ,
An optical device comprising a plurality of collimating lenses, a performing collimation of a plurality of laser beams emitted from the plurality of laser light sources,
Having a diffractive structure on at least one surface of the collimating lens ;
The diffractive structure has the maximum diffraction efficiency for each wavelength λ _i, and the correction amount of the focal length caused by the temperature change is the same as the laser light source A that has the smallest wavelength change amount with respect to the temperature change among the plurality of laser light sources. Insufficient correction for change in focal length (change amount is set to ΔfA), change in focal length with respect to laser light source B having the maximum wavelength change amount with respect to temperature change among the plurality of laser light sources (change amount is set to ΔfB) ) correction becomes excessive relative and the absolute value of the amount of change ΔfA variation ΔfB optical device characterized by comprising the same or the like. The optical device according to claim 1, wherein the collimating lens is manufactured by an injection molding method using a resin material. An optical device according to claim 1 or 2 ,
An optical system that collimates the light emitted from the plurality of laser light sources by the plurality of collimating lenses and synthesizes the collimated light beams of the plurality of wavelengths onto the same optical path;
Scanning means capable of two-dimensionally scanning a light beam synthesized on the same optical path;
In synchronism with the movement of said scanning means, a projection type image display apparatus characterized by having a control means for controlling the output of the laser light source. The laser light source A is a GaN semiconductor laser,
4. The projection type image display device according to claim 3, wherein the laser light source B is a GaInP semiconductor laser or a GaAs semiconductor laser. A projection-type image display device comprising the optical device according to claim 1. 2 or more wavelengths λ _i A plurality of different laser light sources (i = 1, 2, 3,...);
A plurality of collimating lenses for collimating a plurality of laser beams emitted from the plurality of laser light sources, and a manufacturing method of an optical device comprising:
The collimating lens has a diffractive structure on at least one surface, and the diffractive structure has each wavelength λ _i In contrast, the correction amount of the focal length caused by the change in temperature with the maximum diffraction efficiency is the change in the focal length with respect to the laser light source A in which the wavelength change amount with respect to the temperature change is the minimum among the plurality of laser light sources. Correction is insufficient, correction is overcorrected with respect to a change in focal length with respect to the laser light source B having a maximum wavelength change amount with respect to temperature change among the plurality of laser light sources (a change amount is ΔfB), and A method for manufacturing an optical device, comprising a step of designing the diffractive structure so that the absolute values of the change amount ΔfA and the change amount ΔfB are equal.