Optical devices and methods for manufacturing optical devices

Abstract

The optical device comprises: a metal reflective layer, which is essentially formed of a metal material; a first light-transmitting layer disposed on the metal reflective layer; an optical multilayer reflective film disposed on the first light-transmitting layer, which is formed by stacking multiple layers with different refractive indices; and a wavelength conversion layer disposed on the optical multilayer reflective film, which contains a fluorescent material capable of absorbing incident excitation light and generating lower-energy fluorescence, and capable of generating a mixed light of excitation light and fluorescence based on the irradiation of excitation light.

Description

Technical Field

[0001] This invention relates to optical devices, and more particularly to optical devices comprising a phosphor component that emits fluorescence upon excitation light. Background Technology

[0002] Japanese Patent Application Publication No. 2014-082401 discloses a light source device that irradiates excitation light from a laser diode onto a wavelength conversion component having a phosphor. The excitation light receiving surface of the wavelength conversion component has a periodic structure, which can suppress backscattering of the excitation light.

[0003] Japanese Patent Application Publication No. 2019-006967 discloses a phosphor layer (wavelength conversion component) with high thermal conductivity, which is made by high-density sintering of inorganic phosphor particles such as YAG:Ce (yttrium aluminum garnet with added cerium) and inorganic transparent microparticles such as alumina.

[0004] International Publication No. 2011 / 126000 discloses a method for directly bonding a light-emitting element and a wavelength conversion component by activating the bonding surface by sputtering etching with an ion beam or plasma. Summary of the Invention

[0005] According to the main idea of ​​the present invention, an optical device is provided, comprising: a metal reflective layer comprising a metal material; a first light-transmitting layer disposed on the metal reflective layer; an optical multilayer reflective film disposed on the first light-transmitting layer, which is formed by stacking multiple layers with different refractive indices; and a wavelength conversion layer disposed on the optical multilayer reflective film, comprising a fluorescent material. Attached Figure Description

[0006] Figure 1 This is a side view showing the structure of an illumination device that uses a laser source.

[0007] Figure 2 (2a) is a cross-sectional view showing the wavelength conversion element of the reference example. Figure 2 (2b) is a graph showing the wavelength dispersion (spectrum) of the light reflectance of the laminate containing the metal reflective layer and the optical multilayer reflective film that constitutes the wavelength conversion element.

[0008] Figure 3 (3a) is a cross-sectional view showing the wavelength conversion element of the first embodiment. Figure 3 (3b) is a graph showing the wavelength dispersion (spectrum) of the light reflectance of the laminate containing the metal reflective layer, the first light-transmitting layer and the optical multilayer reflective film constituting the wavelength conversion element.

[0009] Figure 4This is a graph showing the emitted light flux (light extraction efficiency) of the wavelength conversion element relative to the excitation light intensity of the reference example and the first embodiment.

[0010] Figure 5 (5a)~ Figure 5 (5c) is a cross-sectional view showing the manufacturing process of the wavelength conversion element of the first embodiment.

[0011] Figure 6 This is a cross-sectional view showing the wavelength conversion element of the second embodiment. Detailed Implementation

[0012] Figure 1 The diagram schematically illustrates an example of a lighting device using a laser source. Such lighting devices include, for example, headlights for vehicles, projectors, and floodlights.

[0013] The lighting device 100 includes: a laser source 93 that emits a laser 93L; a wavelength conversion element 10 that reflects the laser 93L, absorbs the laser 93L, and emits a fluorescent 93C with a wavelength different from that of the laser; and an optical system 95 that includes a projection lens that amplifies and projects a composite light 93R, which is obtained by combining the laser 93L and the fluorescent 93C, onto an imaginary surface.

[0014] As the laser source 93, a semiconductor laser diode such as GaN or InGaN that emits blue light with an intensity of 1W or more can be used. It should be noted that the laser source is not limited to one; there may be two or more sources.

[0015] Wavelength conversion element 10 includes, for example, a fluorescent component that absorbs blue light and emits yellow light. Wavelength conversion element 10 reflects blue light 93L and emits yellow light 93C, and emits white light 93R as a composite light of the two. Wavelength conversion element 10 absorbs blue light (light energy hν1) and releases heat by dissipating the difference in energy (hν1-hν2) when emitting yellow light (light energy hν2), and is therefore usually fixed to a heat dissipation plate 97 such as a heat sink.

[0016] It should be noted that optical systems such as condenser lenses and collimators are sometimes also configured between the laser source 93 and the wavelength conversion element 10. In addition, optical fibers are sometimes used to irradiate the wavelength conversion element 10 with the laser 93L emitted from the laser source 93.

[0017] Figure 2 (2a) shows a conventional wavelength conversion element 12. The conventional wavelength conversion element 12 is a structure formed by depositing a metal reflective layer 20 made of metal components such as silver, an optical multilayer reflective film 30 such as a distributed Bragg reflector (DBR), and a wavelength conversion layer 40 on a heat dissipation plate 97.

[0018] The optical multilayer reflective film 30 uses a DBR layer that reflects light of specific wavelengths, such as blue or yellow light. The DBR layer is a structure formed by periodically alternating layers of a low-refractive-index layer with a relatively low refractive index and a high-refractive-index layer with a relatively high refractive index. Examples of materials used in the low-refractive-index layers are SiO2, MgF2, LiF, and LaF3, while examples of materials used in the high-refractive-index layers are Nb2O5, TiO2, Ta2O3, Al2O3, HfO2, and Y2O3. It should be noted that, in addition to the DBR layer, sometimes dichroic mirrors and short-pass filters (SPFs) with multiple layers of different refractive indices are also used.

[0019] The wavelength conversion layer 40 includes, for example, a substrate 42 containing inorganic transparent microparticles such as alumina, and inorganic phosphor particles (light-emitting components) 44 dispersed in the substrate 42 such as YAG:Ce. The phosphor particles 44, for example, absorb blue light 93L and emit yellow light 93C. By covering the phosphor particles 44 with an inorganic material 42 with high thermal conductivity such as alumina, the heat generated by the light absorption of the phosphor particles 44 can be effectively diffused and transferred to other components such as the heat dissipation plate 97.

[0020] Figure 2 Figure (2b) shows the wavelength dependence of reflectivity exhibited by the laminate of the metallic reflective layer 20 and the optical multilayer reflective film 30. In the figure, the horizontal axis represents wavelength and the vertical axis represents reflectivity. In the figure, the reflectance spectrum when light is incident perpendicularly to the surface of the laminate (i.e., at an incident angle of 0°) is represented by a solid line, the reflectance spectrum when light is incident at 30° (an incident angle of 30°) relative to the normal of the surface is represented by a dotted line, and the reflectance spectrum when light is incident at 60° (an incident angle of 60°) relative to the normal of the surface is represented by a dashed line.

[0021] The wavelength dependence of the reflectivity of light incident from the wavelength conversion layer 40 containing the YAG:Ce phosphor onto the metal reflective layer 20 and the optical multilayer reflective film laminate 30 was calculated using an optical thin film property calculation program (Essential Matrix). SiO2, a low-refractive-index material, was layered on the YAG:Ce phosphor, followed by Nb2O5, a high-refractive-index material, alternatingly for a total of 47 layers, resulting in a final layer of SiO2. The optical film thickness of each layer was 1 / 4 of the center wavelength, with 4 pairs (8 layers) sharing the same center wavelength. The design aimed to achieve high reflectivity in the visible light region by varying the center wavelength from 805 nm to 380 nm at 85 nm intervals (the final layer was less than one layer). Aluminum was then layered on top at 200 nm. The refractive index of the YAG:Ce phosphor was 1.83. Regarding the refractive index and extinction coefficient of SiO2 and Nb2O5, the reflectance of thin films deposited on silicon wafers at approximately 100 nm was measured using an ion-assisted deposition apparatus. The results were then calculated using the Forouhi-Bloomer model based on these measurements. For example, at 805 nm, the refractive indices of SiO2 and Nb2O5 were 1.47 and 2.31, respectively, and the extinction coefficients of both were 0.

[0022] According to the figure, when light is incident at an angle of 0°, although reflectivity decreases in some wavelength regions, high reflectivity is maintained throughout the entire visible light region. On the other hand, when light is incident at angles of 30° and 60°, reflectivity decreases significantly in multiple wavelength regions.

[0023] As can be seen from the above, in a laminate containing a metallic reflective layer and an optical multilayer reflective film, the decrease in reflectivity can be reduced when the incident angle of the incident light is small, but when the incident angle is large, the decrease in reflectivity may increase depending on the wavelength. This phenomenon is thought to be due to the interference between the light reflected from the surface of the optical multilayer reflective film 30 (at the interface with the wavelength conversion layer 40) or within the film and the light reflected at the interface between the optical multilayer reflective film 30 and the metallic reflective layer 20.

[0024] It is believed that when the incident angle is large, interference occurs beyond 1 / 4 wavelength, which increases the optical path length and reflectivity, resulting in a decrease in reflectivity.

[0025] Refer again Figure 2 (2a)

[0026] A portion of the light 93L incident on the wavelength conversion element 12 is mainly reflected by the optical multilayer reflective film 30 or the metal reflective layer 20 and then emitted to the outside from the surface of the wavelength conversion layer 40. The remaining portion is absorbed by the phosphor particles 44.

[0027] The phosphor particles that absorb light 93L emit light 93C. A portion of the light 93C emitted from the phosphor particles 44 is directly emitted to the outside from the surface of the wavelength conversion layer 40. The other portion is reflected by the optical multilayer reflective film 30 or the metal reflective layer 20 and then emitted to the outside from the surface of the wavelength conversion layer 40.

[0028] according to Figure 2 Regarding the wavelength dependence of reflectivity in (2b), when light 93L and 93C are reflected by the optical multilayer reflective film 30 or the metal reflective layer 20, the component with a small incident angle to the optical multilayer reflective film 30 is effectively reflected, but the component with a large incident angle is not effectively reflected, and the intensity of the reflected light is reduced due to the wavelength. In other words, as a whole, the ratio of the intensity of the extracted (reflected) light to the intensity of the incident light (light extraction efficiency) decreases.

[0029] Silver is often used as an optical reflective layer due to its high reflectivity in the visible light region and low wavelength dependence. However, silver is a material prone to migration. When silver is used in a metallic reflective layer, migration may compromise the long-term reliability of the wavelength conversion element.

[0030] Typically, in wavelength conversion elements, high light extraction efficiency and high long-term reliability are desirable. The inventors have researched a wavelength conversion element that offers both high light extraction efficiency and high long-term reliability (capable of suppressing silver migration used in metallic reflective layers).

[0031] Figure 3 (3a) shows the wavelength conversion element 14 of the first embodiment. The wavelength conversion element 14 is a structure formed by laminating a metal reflective layer 20, a first light-transmitting layer 50, an optical multilayer reflective film 30, and a wavelength conversion layer 40. The metal reflective layer 20, the optical multilayer reflective film 30, and the wavelength conversion layer 40 are the same components as the corresponding components of the wavelength conversion element 12 described above.

[0032] The first light-transmitting layer 50 is formed, for example, from a sapphire substrate with a thickness of 100 μm that has self-holding power. When a sapphire substrate with few grain boundaries and dislocations is used as the first light-transmitting layer 50, the migration of silver constituting the metal reflective layer 20 can be suppressed. This can improve the long-term reliability of the wavelength conversion element 14.

[0033] Figure 3 Figure (3b) shows the wavelength dependence of reflectivity exhibited by the laminate of the metal reflective layer 20, the first light-transmitting layer 50, and the optical multilayer reflective film 30. In the figure, the reflectance spectra of incident light at incident angles of 0°, 30°, and 60° are represented by solid lines, dotted lines, and dashed lines, respectively.

[0034] The wavelength dependence of reflectivity of light incident from a YAG:Ce phosphor onto a metal reflective layer and an optical multilayer reflective film laminate was calculated using an optical thin film property calculation program (Essential Matrix). SiO2, a low-refractive-index material, was layered on the YAG:Ce phosphor, followed by Nb2O5, a high-refractive-index material, alternatingly for a total of 47 layers, resulting in a final layer of SiO2. The optical film thickness (refractive index x physical film thickness) of each layer was set to 1 / 4 of the center wavelength, with 4 pairs (8 layers) sharing the same center wavelength. The design aimed to achieve high reflectivity in the visible light region by varying the center wavelength from 805 nm to 380 nm at 85 nm intervals (the final layer was less than one layer). The reflectivity was calculated using a stacked structure with one side of a sapphire substrate of a thickness of 430 μm (to avoid interference) and the other side of a 200 nm layer of aluminum.

[0035] The figure shows that high reflectivity is maintained throughout the entire visible light region, regardless of the incident angle. (If compared with...) Figure 2 Compared with the figure shown in (2b), the reduction in reflectivity under large incident angles is improved by inserting the first light-transmitting layer 50 between the metal reflective layer 20 and the optical multilayer reflective film 30.

[0036] A thickness of the first light-transmitting layer 50 that is greater than or equal to the interference distance (coherence length) of light at 93L and 93C is considered preferred. When the thickness of the first light-transmitting layer 50 is 1.5 μm or more, it is considered capable of suppressing light interference throughout the entire visible light region.

[0037] The interference time T of light is expressed by the following formula.

[0038] T = λ^2 / <c·Δλ>

[0039] λ: Center wavelength

[0040] Δλ: Full width at half maximum (FWHM)

[0041] The interferometric distance lc is obtained by multiplying the speed of light C by the interferometric time.

[0042] l_c=c·T=λ^2 / Δλ

[0043] This invention relates to an optical device in the visible light region. Therefore, with a center wavelength of 550 nm and a full width at half maximum (FWHM) of 100 nm, the interference distance is 3 μm. Thus, if the thickness is 1.5 μm or more, which is half of the wavelength, interference can be suppressed.

[0044] If the thickness of the first light-transmitting layer 50 is 100 μm or more, it can effectively suppress interference and also provide mechanical support (self-holding capability) for the wavelength conversion element 14, which is preferred.

[0045] Figure 4 It shows the relationship with Figure 2 The wavelength conversion element 12 of the existing example shown in (2b) is compared with that shown in (2b). Figure 3 The light extraction efficiency of the wavelength conversion element 14 of the first embodiment is shown in (3b). In the figure, the horizontal axis represents the light intensity (excitation intensity) of the incident excitation light 93L incident on the wavelength conversion element, and the vertical axis represents the brightness (luminous flux) of the combined light 93R of the excitation light and fluorescence emitted from the wavelength conversion element. The light intensity obtained by integrating the combined light in the visible light region is expressed in the form of luminous flux. In the figure, the luminous flux of the wavelength conversion element 12 of the conventional example is represented by a dotted line, and the luminous flux of the wavelength conversion element 14 of the first embodiment is represented by a solid line.

[0046] The half-width at half-maximum (FWHM) of light emitted by a laser diode is typically expressed as intensity (W). The luminous flux is calculated by multiplying the intensity wavelength distribution by the visual sensitivity and integrating the result with respect to the wavelength.

[0047] Referring to the figure, especially under conditions of high incident light intensity, compared with the light flux of the wavelength conversion element 12 in the conventional example, the light flux of the wavelength conversion element 14 in the first embodiment has a larger slope relative to the horizontal axis, resulting in higher light extraction efficiency.

[0048] This is believed to be because, by setting the first light-transmitting layer 50, the incident angle of the incident light to the optical multilayer reflective film 30 is changed, and the component with a large incident angle is effectively reflected, thus suppressing the reduction in the light intensity of the synthesized light (reflected light).

[0049] This constitutes the incident light onto the "optical multilayer reflective film," that is, the incident light from the YAG:Ce phosphor onto the laminate.

[0050] Figure 5 (5a)~ Figure 5 (5c) shows the steps for manufacturing the wavelength conversion element of the first embodiment.

[0051] like Figure 5 As shown in (5a), a sapphire substrate is prepared as the first light-transmitting layer 50. Besides sapphire, components with high light transmittance and high thermal conductivity in the visible light region, such as SiO2, SiC, AlN, GaN, or diamond, can also be used. Furthermore, when using a material prone to migration, such as silver, in the metal reflective layer 20, a single-crystal substrate with high coverage (low transfer density), such as SiO2, SiC, AlN, GaN, or diamond, is preferred. Considering physical strength as well, the thickness of the first light-transmitting layer 50 is preferably 100 μm or more.

[0052] A silver film with a thickness of about 200 nm is formed on one side of the first light-transmitting layer 50 (the lower side in the figure) as a metal reflective layer 20 by electron beam evaporation, sputtering, or other methods. In addition to silver, the metal reflective layer 20 can also use components with high reflectivity throughout the visible light region, such as aluminum.

[0053] It should be noted that an adhesive layer for improving sealing can also be provided between the first light-transmitting layer 50 and the metal reflective layer 20. For example, a Ni layer or Ti layer with a thickness of several angstroms can be used in the adhesive layer.

[0054] like Figure 5 As shown in (5b), a DBR layer is formed on the other side of the first light-transmitting layer 50 (the upper side in the figure) as an optical multilayer reflective film 30. It should be noted that, in addition to the DBR layer, multiple layers with different refractive indices can also be formed and laminated to form dichroic mirrors, short-pass filters, etc.

[0055] A DBR layer is formed by alternately (periodically) depositing low-refractive-index and high-refractive-index layers using methods such as electron beam evaporation, sputtering, and chemical vapor deposition. The number of low-refractive-index and high-refractive-index layers can be between 10 and 100, with each layer having a thickness of between 20 nm and 100 nm.

[0056] If the outermost layer is made of a material with a refractive index lower than that of the YAG:Ce phosphor, the film thickness can be reduced compared to the case with a high refractive index, and therefore it is preferred.

[0057] For example, SiO2 can be used in low refractive index layers. In addition to SiO2, MgF2, LiF, LaF3, etc. can also be used.

[0058] For example, Nb2O5 can be used in high refractive index layers. In addition to Nb2O5, TiO2, Ta2O3, Al2O3, HfO2, Y2O3, etc. can also be used.

[0059] like Figure 5 As shown in (5c), a wavelength conversion layer 40 is formed on the optical multilayer reflective film 30. The wavelength conversion layer 40 is formed, for example, by mixing alumina microparticles, which serve as the base material 42, with YAG:Ce, which serves as the phosphor particles 44, to form a fluid (bulk), molding it into a plate shape, and then firing it. An optically transparent adhesive layer 41, such as a glass bond, is formed on the optical multilayer reflective film 30, and the wavelength conversion layer 40 is adhered thereon.

[0060] The wavelength conversion layer 40 can be any component as long as it is a wavelength conversion layer containing a light-emitting component that emits light with a wavelength different from that of the incident light. The wavelength conversion layer 40 is preferably a component with high heat resistance and thermal conductivity.

[0061] The wavelength conversion element 14 of the first embodiment is completed as described above.

[0062] Figure 6 The wavelength conversion element 16 of the second embodiment is shown. The wavelength conversion element 16 is a structure formed by laminating a metal reflective layer 20, a first light-transmitting layer 50, an optical multilayer reflective film 30, a second light-transmitting layer 60, and a wavelength conversion layer 40. The metal reflective layer 20, the first light-transmitting layer 50, the optical multilayer reflective film 30, and the wavelength conversion layer 40 have the same configuration as the wavelength conversion element 14 of the first embodiment.

[0063] The second light-transmitting layer 60 is composed of a component, such as SiO2, with a refractive index lower than that of the wavelength conversion layer 40, which is a mixture of alumina and phosphor. By making the refractive index of the second light-transmitting layer 60 lower than that of the wavelength conversion layer 40, total internal reflection of light incident on the second light-transmitting layer 60 can be achieved at a large incident angle. As a result, the component of the incident light with a large incident angle can be reflected more effectively, and the reduction in the intensity of the composite light (reflected light) can be further suppressed.

[0064] The second light-transmitting layer 60 can be formed, for example, by the following method: A first light-transmitting layer 50, serving as a transparent substrate, is prepared. A metal reflective layer 20 is formed on the lower side of the first light-transmitting layer 50, and an optical multilayer reflective film 30 is formed on the upper side. A first bonding layer 62 made of SiO2 is formed on the surface of the optical multilayer reflective film 30 by sputtering or the like. A wavelength conversion layer 40 is separately prepared, and a second bonding layer 64 made of SiO2 is formed on one surface of the wavelength conversion layer 40 by sputtering or the like. Since the surface of the second bonding layer inherits the surface roughness and unevenness of the wavelength conversion layer 40, the surface of the second bonding layer is planarized, for example, by CMP polishing. Therefore, the second bonding layer, for example, is a 300 nm thick layer of SiO2, which is then polished to a thickness of 100 nm.

[0065] The first bonding layer 62 and the second bonding layer 64 are bonded at the atomic level using a surface activation method or the like to form a second light-transmitting layer 60 composed of bonding layers 62 and 64. In the second light-transmitting layer 60, the first bonding layer 62 and the second bonding layer 64 are bonded at the atomic level without using materials with low thermal conductivity such as resin or glass, thus resulting in low thermal resistance and efficient heat transfer from the wavelength conversion layer 40.

[0066] The present invention has been described above with reference to embodiments, but the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, and combinations can be made.

Claims

1. An optical device comprising: A metallic reflective layer, which is formed of metallic materials; A first light-transmitting layer is disposed on the metal reflective layer, having a first surface on the side of the metal reflective layer and a second surface on the opposite side of the metal reflective layer; An optical multilayer reflective film disposed on the second surface of the first light-transmitting layer; and A wavelength conversion layer, disposed on the optical multilayer reflective film, comprises a fluorescent material capable of absorbing incident excitation light and generating lower-energy fluorescence, based on the ability to generate a hybrid light of excitation light and fluorescence upon irradiation by excitation light. The first light-transmitting layer is composed of a transparent substrate with a thickness of 1.5 μm or more. The optical multilayer reflective film is a laminated structure composed of multiple layers of low-refractive-index layers with relatively low refractive indices and high-refractive-index layers with relatively high refractive indices, and is grounded to the second surface of the first light-transmitting layer. The fluorescence emitted from the fluorescent material contained in the wavelength conversion layer is incident on the metal reflective layer through the optical multilayer reflective film and the first light-transmitting layer, and after being reflected by the optical multilayer reflective film and the metal reflective layer, it is emitted to the outside from the surface of the wavelength conversion layer.

2. The optical device as claimed in claim 1, wherein, The low refractive index layer is formed of SiO2, MgF2, LiF, and LaF3.

3. The optical device as claimed in claim 1, wherein, The optical multilayer reflective film and the wavelength conversion layer are bonded together via an optically transparent adhesive layer.

4. The optical device according to any one of claims 1 to 3, wherein, The transparent substrate is formed of SiO2, SiC, GaN, sapphire, or diamond.

5. The optical device as claimed in claim 4, wherein, The metallic reflective layer is formed of silver.

6. The optical device of claim 4, further comprising a second light-transmitting layer disposed between the optical multilayer reflective film and the wavelength conversion layer, the second light-transmitting layer having a refractive index lower than that of the wavelength conversion layer.

7. The optical device as claimed in claim 4, further comprising: An excitation light source, disposed above the second surface, is capable of irradiating the wavelength conversion layer with excitation light; and An optical system configured on the optical path of the hybrid light generated by the wavelength conversion layer.

8. The optical device as claimed in claim 7, wherein, The excitation source includes a semiconductor laser.

9. A method for manufacturing the optical device according to claim 1, comprising the following steps: In the first step, the metal reflective layer is formed on the back side of the first light-transmitting layer; In the second step, the optical multilayer reflective film is formed on the surface of the first light-transmitting layer; and In the third step, the wavelength conversion layer is bonded to the upper surface of the optical multilayer reflective film using an optically transparent adhesive layer.

10. The method of manufacturing the optical device as claimed in claim 9, wherein, The third step includes: The first sub-step involves forming a first bonding layer on the upper surface of the optical multilayer reflective film; The second sub-process involves forming a second bonding layer on the lower surface of the wavelength conversion layer. The third sub-process involves planarizing the lower surface of the second bonding layer. as well as In the fourth sub-step, the upper surface of the first bonding layer and the lower surface of the second bonding layer are bonded together using a surface activation method, thereby integrating the first bonding layer and the second bonding layer to form the second light-transmitting layer. The refractive index of the second light-transmitting layer is lower than that of the wavelength conversion layer.

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