Light source device

Abstract

Provided is a light source device with which, despite the small size thereof, light having good color rendering properties can be obtained with high light extraction efficiency.　This light source device is provided with: an excitation light source that includes a semiconductor laser element; a wavelength conversion member that converts at least some wavelengths of incident light and emits fluorescence; a condensing optical system that is disposed between the excitation light source and the wavelength conversion member and guides the excitation light to the wavelength conversion member while reducing the angle of divergence of the excitation light; and a concave reflector that is disposed, relative to the wavelength conversion member, on the side away from the excitation light source and includes a reflecting surface that exhibits reflection properties with respect to emitted light from the wavelength conversion member. The concave reflector comprises an opening section for extracting the emitted light into a region that includes a region through which the optical axis of the excitation light passes, and the wavelength conversion member, when viewed in the direction of the optical axis of the excitation light, is disposed in a region that includes the center of the concave reflector.

Description

light source device

[0001] The present invention relates to a light source device, and more particularly to a light source device in which light emitted from a semiconductor laser element is wavelength-converted by a wavelength conversion member and then emitted.

[0002] 2. Description of the Related Art Conventionally, in order to increase the amount of extracted light, a technique of arranging a hemispherical reflector around the periphery of a light source has been known (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses a configuration in which a hemispherical reflector having an opening at a certain location is disposed outside the LED light source for the purpose of increasing the amount of light from the LED light source.

[0004] Patent Document 2 discloses a configuration in which a hemispherical reflector having an opening in one location is disposed outside a phosphor as a secondary light source in order to increase the amount of light from the phosphor. An excitation light source is disposed outside the reflector, and excitation light from the excitation light source is reflected by a dichroic mirror and then guided to the phosphor through the opening in the reflector.

[0005] Patent No. 5642385 Publication Special Publication No. 2015-528988

[0006] Depending on the application, it is expected that the light emitted from the light source device will be propagated through an optical fiber for use. As a method for guiding white light from an LED into an optical fiber, for example, a method can be used in which light from each of the R, G, and B LEDs is combined into white light using a combining optical system such as a cross prism, and then the combined light is input into an optical fiber.

[0007] However, because the etendue of an optical fiber is small, the light emitted from the LED cannot be efficiently guided into the optical fiber, resulting in the problem of difficulty in ensuring a sufficient amount of light irradiation from the optical fiber.

[0008] One solution to the above problem would be to provide a hemispherical reflector with an opening around the periphery of the LED, as disclosed in Patent Document 1. Among the light beams emitted from the LED, those with a small divergence angle are directly extracted through the opening. On the other hand, those with a large divergence angle are reflected by the reflector and returned to the LED.

[0009] Here, with regard to light emitted from near the center of the LED, there is a possibility that the light is reflected by the reflector and returned to the LED, and then extracted from the opening by being diffused and reflected on the light extraction surface of the LED, for example.

[0010] In reality, the surface of the light extraction surface is roughened to prevent light generated in the light-emitting layer inside the LED from being reflected by the light extraction surface and returned to the light-emitting layer. Furthermore, since an electrode is provided on a portion of the light extraction surface, regular irregularities are inevitably formed. From this perspective, the proportion of light reflected from the reflector that is diffusely reflected by the light extraction surface of the LED is inherently limited. In other words, a high proportion of the light returned from the reflector to the light extraction surface of the LED is re-reflected at an angle substantially the same as the angle at which it was incident on the light extraction surface of the LED. This light is repeatedly reflected between the reflector and the light extraction surface of the LED, and cannot be extracted to the outside through the opening.

[0011] Furthermore, an LED is a surface-emitting light source and has a certain size. As a typical example, the light extraction surface (light-emitting surface) of an LED has a size of about 2 mm square to 4 mm square. In the case of an LED, light is also emitted from a location away from the center position of the light extraction surface within this light extraction surface having a size of about 2 mm square to 4 mm square. In this way, when light emitted from a location away from the center of the light extraction surface is reflected by the reflector, it is also returned to a location away from the center of the LED. As a result, it is expected that light emitted from a location away from the center position of the LED will only be repeatedly reflected between the LED and the reflector and will not be extracted through the opening.

[0012] In other words, from the viewpoint of increasing the amount of light emitted from an LED while reducing the etendue, it is understood that the effect of providing a reflector on the outside of the LED as in Patent Document 1 is extremely limited. In addition, since the amount of light emitted from an LED per unit size is small, in order to increase the amount of light emitted, it is necessary to increase the size of the LED. However, due to the above-mentioned circumstances, this supports the fact that the effect of increasing the amount of extracted light by reflecting light with a reflector cannot be fully expected.

[0013] In view of the above circumstances, it is conceivable to use a light source device that uses a hemispherical reflector and a fluorescent light source, as disclosed in Patent Document 2.

[0014] 18 is a diagram schematically showing the configuration of a light source device disclosed in Patent Document 2. The light source device 100 includes a phosphor layer 101, a hemispherical reflector 104, and an excitation light source 105. An opening 104a is formed in a portion of the hemispherical reflector 104. The phosphor layer 101 is disposed inside the hemispherical reflector 104.

[0015] The excitation light L105 emitted from the excitation light source 105 is reflected by the dichroic mirror 106 and its traveling direction is changed. The excitation light L105 passes through the opening 104a and is incident on the phosphor layer 101. The phosphor layer 101 is fixed to the heat sink 103 via the reflecting mirror 102.

[0016] The phosphor layer 101 is excited by the incident excitation light L105 and emits fluorescence L101. Because the excitation light L105 is a bundle of rays with a narrow line width, the light-emitting region 101c within the phosphor layer 101 is limited, and the phosphor layer 101 essentially serves as a point light source.

[0017] Of the fluorescence L101 generated in the light-emitting region 101c, the light beam with a small divergence angle is directly guided to the dichroic mirror 106 via the opening 104a. On the other hand, the light beam with a large divergence angle is reflected by the hemispherical reflector 104 and returned to the phosphor layer 101.

[0018] The fluorescence L101 returned to the phosphor layer 101 has its reflection angle changed by being diffusely reflected on the surface of the phosphor layer 101, and is extracted through the opening 104a. Of the fluorescence L101 generated in the phosphor layer 101 and the fluorescence L101 reflected by the hemispherical reflector 104, light traveling in the opposite direction from the opening 104a is returned by the reflecting mirror 102 to the opening 104a side.

[0019] The fluorescence L101 extracted through the opening 104a passes through the dichroic mirror 106. This allows the fluorescence L101 to be extracted. In other words, the dichroic mirror 106 is designed to reflect light with the same wavelength as the excitation light L105 and to transmit light with the same wavelength as the fluorescence L101.

[0020] According to the light source device 100 shown in FIG. 18, the light-emitting area can be limited compared to the configuration disclosed in Patent Document 1, which uses an LED as the light source, and therefore it appears that the light returned by the hemispherical reflector 104 can be efficiently extracted to the outside.

[0021] However, as described above, the dichroic mirror 106 is designed to reflect light with the same wavelength as the excitation light L105. Therefore, even if the excitation light L105 is reflected on the surface of the phosphor layer 101 and extracted from the opening 104a side, it is reflected by the dichroic mirror 106 and guided to the excitation light source 105 side. In other words, almost all of the light guided to the rear of the dichroic mirror 106 is derived from the fluorescence L101. In this case, the color rendering of the light guided to the rear of the dichroic mirror 106 is low.

[0022] Typically, the excitation light source 105 is a semiconductor laser element that emits excitation light L105 in the blue region, and the phosphor layer 101 contains a phosphor that converts blue light into light of a longer wavelength (yellow band, green band, etc.) upon receiving it. In this case, the spectrum of the light guided to the rear stage of the dichroic mirror 106 contains an extremely small amount of blue components, resulting in light with low color rendering properties.

[0023] 19 , one possible method for dealing with this situation is to arrange a separate blue light source 107 downstream of the dichroic mirror 106 and superimpose the blue light L107 emitted from the blue light source 107 on the fluorescence L101. Specifically, a dichroic mirror 108 designed to substantially reflect blue light, similar to the dichroic mirror 106, and to substantially transmit light of the same wavelength as the fluorescence L101, is arranged downstream of the dichroic mirror 106. As a result, the blue light L107 emitted from the blue light source 107 is reflected by the dichroic mirror 108, and the fluorescence L101 transmits through the dichroic mirror 108. Therefore, the light guided downstream of the dichroic mirror 108 is a superimposed light of the fluorescence L101, which has a low intensity of blue component, and the blue light L107, thereby improving color rendering properties.

[0024] However, with the light source device 100 shown in FIG. 19 , the fluorescence L101 is extracted via multiple dichroic mirrors (106, 108). The fluorescence L101 has a larger half-width than the excitation light L105 and exhibits a relatively broad spectrum. For this reason, it is difficult to transmit all of the wavelength components of the fluorescence L101 without loss. In other words, the intensity of the fluorescence L101 is attenuated to some extent by passing through the multiple dichroic mirrors (106, 108). In other words, with the light source device 100 shown in FIG. 19 , there is a limit to how much the light extraction efficiency can be improved.

[0025] Furthermore, with the light source device 100 shown in FIG. 19, it is necessary to provide a separate blue light source 107 in order to improve color rendering properties, which increases the size of the device.

[0026] 19 has, as heat sources, excitation light sources 105 and blue light sources 107 in addition to phosphor layer 101. However, due to their positioning, it is difficult to cool excitation light sources 105 and blue light sources 107 using heat sink 103 for cooling phosphor layer 101. For this reason, it is necessary to provide a cooling mechanism separate from heat sink 103 for cooling phosphor layer 101, which leads to a further increase in the size of the device.

[0027] In view of the above-mentioned problems, an object of the present invention is to provide a light source device that is compact yet capable of obtaining light with high color rendering properties and high light extraction efficiency.

[0028] a wavelength conversion member that converts the wavelength of at least a portion of incident light to emit fluorescence; a focusing optical system that is arranged between the excitation light source and the wavelength conversion member in the direction of the optical axis of the excitation light emitted from the excitation light source and that guides the excitation light to the wavelength conversion member while reducing the divergence angle of the excitation light; and a concave reflector that is arranged on a side away from the excitation light source when the wavelength conversion member is used as a reference in the direction of the optical axis of the excitation light and that includes a reflective surface that exhibits reflectivity for the light emitted from the wavelength conversion member, wherein the concave reflector has an opening for extracting the emitted light in a region that includes a region through which the optical axis of the excitation light passes, and the wavelength conversion member is arranged in a region that includes the center of the concave reflector when viewed in the direction of the optical axis of the excitation light.

[0029] According to the light source device, the excitation light is guided in a condensed state to the wavelength conversion member, which converts the wavelength of the excitation light when it is incident on the wavelength conversion member and emits fluorescence.

[0030] The concave reflector is disposed on the side farther from the excitation light source when the wavelength converting member is used as a reference in the optical axis direction of the excitation light. That is, the excitation light source, the wavelength converting member, and the concave reflector are arranged in this order in the optical axis direction of the excitation light.

[0031] A portion of the excitation light incident on the wavelength conversion member passes through the wavelength conversion member and exits. Because the concave reflector has an opening in a region including a region through which the optical axis of the excitation light passes, a portion of the excitation light that passes through the wavelength conversion member is extracted to the outside through the opening. Furthermore, among the fluorescence generated by the wavelength conversion member, fluorescence that travels with a relatively small divergence angle is also extracted to the outside through the opening.

[0032] Of the fluorescence generated by the wavelength conversion member, fluorescence traveling with a relatively large divergence angle is reflected by the reflective surface of the concave reflector and returned to the wavelength conversion member. The excitation light source includes a semiconductor laser element, and the excitation light is guided to the wavelength conversion member with a reduced divergence angle via a focusing optical system. As a result, the area where the excitation light is incident on the wavelength conversion member is limited, and the secondary light source formed by the wavelength conversion member becomes closer to a substantial point light source. In other words, the fluorescence emitted from the wavelength conversion member, traveling toward the concave reflector with a relatively large divergence angle, and then reflected by the reflective surface of the concave reflector is returned to the area of ​​the wavelength conversion member where the excitation light was incident, i.e., the location where the substantial point light source is formed.

[0033] Therefore, the fluorescence returned to the wavelength conversion member is diffusely reflected on the surface and inside of the wavelength conversion member, and can be guided to the opening provided in the concave reflector.

[0034] In other words, with the light source device described above, it is possible to extract the emitted light in a state in which both excitation light and fluorescent light are superimposed to the outside through the opening. This makes it possible to obtain white light with high color rendering properties without having to superimpose light containing wavelength components equivalent to the excitation light separately in a subsequent stage, and it is possible to make the device smaller than conventional devices. Furthermore, since both the wavelength conversion member and the excitation light source can be arranged inside the concave reflector, it is possible to use a common cooling mechanism for the wavelength conversion member and the excitation light source.

[0035] The concave reflector may typically employ a hemispherical reflector.

[0036] The focal point of the focusing optical system may be located outside the wavelength conversion member in the optical axis direction of the excitation light.

[0037] If the focal point of the focusing optical system is located inside the wavelength conversion member, the density of the excitation light incident on the wavelength conversion member may become too high, resulting in a decrease in the fluorescence conversion efficiency due to thermal quenching. As described above, by adjusting the positional relationship between the focusing optical system and the wavelength conversion member so that the focal point of the focusing optical system is located outside the wavelength conversion member, the decrease in fluorescence conversion efficiency can be suppressed.

[0038] However, if the distance between the focal point of the focusing optical system and the wavelength conversion member is too long, the region of excitation light incident on the wavelength conversion member may become too wide. In this case, the wavelength conversion member as a secondary light source approaches the surface light source, and the fluorescence emitted from near the end of the light-emitting region within the wavelength conversion member and traveling with a large divergence angle is reflected by the concave reflector and returned to near the end of the light-emitting region. At least a portion of this returned light may not be extracted through the opening.

[0039] From this viewpoint, the deviation between the focal point of the focusing optical system and the wavelength conversion member is preferably −1 mm to 1 mm, and more preferably −0.6 mm to 0.4 mm, when the direction in which light is extracted is defined as the positive direction.

[0040] From the same viewpoint, the light source device may include a light diffusing member disposed between the light collecting optical system and the wavelength converting member in the optical axis direction of the excitation light.

[0041] By including a light diffusing member in the light source device, the propagation directions of the individual rays contained in the ray bundle of excitation light can be slightly different from each other, while the divergence angle can be reduced by the focusing optical system and guided to the wavelength conversion member. This allows the wavelength conversion member to function as a secondary light source that is essentially close to a point light source, while suppressing a decrease in fluorescence conversion efficiency due to thermal quenching. Furthermore, it is easy to direct a portion of the excitation light that propagates after passing through the wavelength conversion member toward the concave reflector. As a result, the light that is superimposed between the outgoing light reflected by the concave reflector and then re-reflected by the wavelength conversion member and extracted through the opening, and the outgoing light that is emitted from the wavelength conversion member and extracted directly through the opening, is light in which the variation in wavelength components due to the distance from the center of the optical axis is sufficiently reduced.

[0042] As a preferred example, the light source diameter of the secondary light source formed by the wavelength converting member may be 0.5 mm to 1.4 mm, and the opening angle of the opening may be 14° to 133°. Note that the "light source diameter" will be described later.

[0043] The wavelength converting member may include a substrate, a dichroic layer disposed on the substrate and substantially transmitting the excitation light and substantially reflecting the fluorescence, and a phosphor layer disposed on the dichroic layer and containing a phosphor, whereby the fluorescence generated in the phosphor layer and traveling toward the excitation light source can be reflected by the dichroic layer and directed toward the concave reflector.

[0044] As a preferred example, the thickness of the phosphor layer may be 5 μm to 30 μm.

[0045] The wavelength conversion member may also be arranged on the lower layer of the substrate opposite to the side on which the dichroic layer is arranged, and may have an anti-reflection layer that suppresses reflection of the excitation light.

[0046] This allows the excitation light to be guided into the wavelength conversion member with high efficiency.

[0047] The relative density of the phosphor layer is preferably 40% to 99.9%, more preferably 50% to 95%. The phosphor layer may be a laminate of phosphor particles bonded together with an inorganic binder, or a sintered body formed by sintering phosphor particles and the binder. The relative density of the phosphor layer is the ratio of the apparent density to the theoretical density of the phosphor layer, and can be measured, for example, by a method conforming to JIS R 1634 (Method for measuring the density and open porosity of sintered fine ceramics). In other words, the phosphor layer preferably contains 0.1% to 60% pores, more preferably 5% to 50% pores.

[0048] According to the light source device of the present invention, even though it is small, it is possible to emit light with high color rendering properties and high light extraction efficiency.

[0049] 6A 。 FIG. 6B is a block diagram schematically showing the configuration of an embodiment of a light source device of the present invention. FIG. 6C is a cross-sectional view schematically showing an example of the configuration of a wavelength conversion member. FIG. 6D is a diagram showing a schematic enlargement of a portion of a phosphor layer provided on the wavelength conversion member. FIG. 6E is an example of the spectrum of output light extracted from a light source device. FIG. 6F is a diagram showing an example of the positional relationship between a wavelength conversion member and a focusing optical system. FIG. 6G is a diagram showing another example of the positional relationship between a wavelength conversion member and a focusing optical system. FIG. 6H is a schematic plan view of a concave reflector. FIG. 6I is a schematic cross-sectional view of the concave reflector when cut along the line Q1-Q1 in FIG. 6A. FIG. 6I is a diagram showing an example of the configuration of an evaluation optical system for evaluating the light source device of the present embodiment. FIG. 6I is a diagram showing an example of the configuration of an evaluation optical system for evaluating a light source device of a comparative example, following the example of FIG. 6A. FIG. 6I is a diagram showing an example of the configuration of a light source device of comparative example 1, following the example of FIG. 6A. FIG. 6I is a diagram showing an example of the configuration of a light source device of comparative example 2. FIG. 6I is a diagram for explaining the light source diameter set by the wavelength conversion member. 18 is a graph showing the change in the received luminous flux when the opening angle of the opening formed in the reflector is changed, and data is shown for each light source diameter. 19 is a graph showing the relationship between the light source diameter and the received luminous flux when the opening angle is fixed. 20 is a schematic diagram for explaining the positional relationship between the wavelength conversion member and the concave reflector. 21 is a graph showing the relationship between the deviation between the wavelength conversion member and the concave reflector and the received luminous flux when the light source diameter and opening angle are fixed. 22 is a graph showing the relationship between the thickness of the phosphor layer and the received luminous flux when the opening angle is fixed. 23 is a graph showing the relationship between the relative density in the phosphor layer and the received luminous flux when the opening angle is fixed. 24 is a block diagram schematically showing the configuration of another embodiment of the light source device of the present invention. 25 is a block diagram schematically showing the configuration of another embodiment of the light source device of the present invention. 26 is a diagram schematically showing the configuration of a conventional light source device. 27 is a diagram schematically showing the configuration of an improved version of the light source device shown in FIG. 25.

[0050] The following description will discuss embodiments of the light source device of the present invention with reference to the accompanying drawings. Note that in the following drawings, the dimensional ratios shown in the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0051] 1 is a block diagram showing a schematic configuration of an embodiment of a light source device, which includes an excitation light source 3, a focusing optical system 5, a light diffusing member 7, a wavelength converting member 10, and a concave reflector 21.

[0052] FIG. 2 is a cross-sectional view schematically showing an example of the configuration of the wavelength conversion member 10. As shown in FIG.

[0053] The excitation light source 3 includes a semiconductor laser element and emits excitation light L3 toward the light diffusing member 7. The wavelength converting member 10 includes a phosphor layer 12, and the phosphor included in the phosphor layer 12 is excited by the excitation light L3 to emit fluorescence L10 having a wavelength different from that of the excitation light L3.

[0054] The wavelength of the excitation light L3 is not limited as long as it is a wavelength that can excite the phosphor contained in the phosphor layer 12. However, when the light source device 1 is intended to generate white emitted light L1, the wavelength of the excitation light L3 is preferably in the blue or violet region. In this specification, blue light refers to light in the wavelength region of 420 nm to 500 nm, and violet light refers to light in the wavelength region of 370 nm to 420 nm. As a specific example, the excitation light source 3 includes a semiconductor laser element that emits light in the blue region with a wavelength of 445 nm to 465 nm. The excitation light source 3 may include a collimating optical system as needed.

[0055] The focusing optical system 5 is disposed between the excitation light source 3 and the wavelength conversion member 10 in relation to the direction of the optical axis A3 of the excitation light L3. The focusing optical system 5 is an optical system that guides the excitation light L3 toward the wavelength conversion member 10 while reducing the divergence angle. As will be described later with reference to Figures 5A and 5B, in this embodiment, a focal point 5f of the focusing optical system 5 is located outside the wavelength conversion member 10 in relation to the direction of the optical axis A3 of the excitation light L3.

[0056] The light source device 1 of this embodiment includes a light diffusing member 7 disposed between the focusing optical system 5 and the wavelength conversion member 10 with respect to the direction of the optical axis A3 of the excitation light L3. The light diffusing member 7 is composed of, for example, a diffuser-transmitting plate, a microlens array, or the like. The light diffusing member 7 is provided to prevent the width of the ray bundle incident on the wavelength conversion member 10 from becoming too narrow when the focusing optical system 5 focuses the excitation light L3 and guides it into the wavelength conversion member 10. If the high-intensity excitation light L3 from the semiconductor laser element is incident on an extremely narrow region within the wavelength conversion member 10, the power density within the wavelength conversion member 10 may become too high, potentially resulting in an extremely high temperature. The wavelength conversion member 10 exhibits a phenomenon known as thermal quenching, in which the fluorescence conversion efficiency decreases as the temperature increases. The light diffusing member 7 is provided in the wavelength conversion member 10 to increase the efficiency of conversion of the excitation light L3 to fluorescence L10.

[0057] In this way, the excitation light L3 emitted from the excitation light source 3 is incident on the wavelength conversion member 10 via the condensing optical system 5 and the light diffusing member 7. As shown in Fig. 2 , the wavelength conversion member 10 typically includes a substrate 11, a dichroic layer 14, a phosphor layer 12, and an anti-reflection layer 13. Fig. 3 is a schematic enlarged view of a portion of the phosphor layer 12.

[0058] The substrate 11 is provided for the purposes of stably supporting the phosphor layer 12, dissipating heat generated by the phosphor layer 12, and guiding the excitation light L3 to the phosphor layer 12. From these perspectives, a material with relatively high thermal conductivity and high transmittance to the excitation light L3 is used for the substrate 11. Examples of such materials include sapphire and diamond. The thickness of the substrate 11 is, for example, 0.5 mm to 5 mm. Furthermore, from the perspective of heat dissipation, it is preferable that the surface area of ​​the substrate 11 be larger than the area of ​​the phosphor layer 12.

[0059] For example, the phosphor layer 12 has a rectangular plate-like structure when viewed from a direction perpendicular to the surface of the substrate 11. The thickness of the phosphor layer 12 is preferably 5 μm to 30 μm, more preferably 10 μm to 25 μm, and particularly preferably 15 μm to 22 μm. In the example shown in FIG. 3 , the phosphor layer 12 includes a phosphor 16, a binder 17, and pores 18.

[0060] The phosphor 16 is an oxide phosphor activated with Ce or Eu or a nitride phosphor activated with Ce or Eu. As a specific example, one or more phosphors belonging to the group consisting of LSN phosphor, YAG phosphor, and LuAG phosphor can be used as a yellow to green phosphor. Furthermore, one or more phosphors belonging to the group consisting of CASN phosphor, SCASN phosphor, and CASON phosphor can be used as a red phosphor for the phosphor 16.

[0061] By mixing multiple phosphor materials as the phosphor 16 contained in the phosphor layer 12, white light with high color rendering properties is realized by the emitted light L1, which is a superimposed light of the fluorescence L10 generated in the phosphor layer 12 and the excitation light L3. For example, when LuAG:Ce, YAG:Ce, SCASN:Eu, and CASN:Eu are mixed as the phosphor 16, white light exhibiting high color rendering properties of Ra=93 to 98 is obtained as the emitted light L1, as shown in FIG. 4. FIG. 4 shows an example of the spectrum of the emitted light L1 extracted from the light source device 1 when the wavelength conversion member 10 includes the phosphor 16 containing the multiple phosphor materials.

[0062] The wavelength conversion member 10 shown in Fig. 2 has a dichroic layer 14 provided between the phosphor layer 12 and the substrate 11. The dichroic layer 14 is made of a material that substantially reflects the fluorescence L10 generated in the phosphor layer 12 and substantially transmits the excitation light L3. The dichroic layer 14 has the function of guiding the incident excitation light L3 to the phosphor layer 12, while reflecting the fluorescence L10 generated in the phosphor layer 12 that travels toward the substrate 11 and returning it to the concave reflector 21. Here, "substantially reflect" means that the reflectance is 80% or more, and "substantially transmit" means that the transmittance is 80% or more.

[0063] The dichroic layer 14 is realized by, for example, laminating a plurality of dielectric films having different refractive indices.

[0064] 2 has an anti-reflection layer 13 provided on the surface of the substrate 11 opposite to the phosphor layer 12. The anti-reflection layer 13 is provided for the purpose of suppressing the excitation light L3 incident on the wavelength conversion member 10 from being reflected from the surface of the substrate 11 toward the excitation light source 3. This makes it possible to efficiently guide the excitation light L3 to the phosphor layer 12.

[0065] A general-purpose AR coating layer can be used as the antireflection layer 13. The antireflection layer 13 may have a function of substantially transmitting the excitation light L3 incident on the wavelength conversion member 10.

[0066] The wavelength conversion member 10 may or may not include an antireflection layer 13. The wavelength conversion member 10 may or may not include a dichroic layer 14. However, it is preferable that the wavelength conversion member 10 includes both the antireflection layer 13 and the dichroic layer 14.

[0067] As described above, when the excitation light L3 is concentrated at high brightness within the wavelength conversion member 10, it is expected that the fluorescence conversion efficiency will decrease due to thermal quenching. From this perspective, as shown in Figure 5A or 5B, it is preferable to design the focal length of the focusing optical system 5 and the thickness of the wavelength conversion member 10 so that the focal point 5f of the focusing optical system 5 is located outside the wavelength conversion member 10 with respect to the optical axis A3 of the excitation light L3. Note that for convenience of explanation, the light diffusing member 7 is not shown in Figures 5A and 5B.

[0068] In the example shown in Fig. 5A, the focal point 5f of the focusing optical system 5 is located downstream of the light extraction surface 10S of the wavelength conversion member 10. In the example shown in Fig. 5B, the focal point 5f of the focusing optical system 5 is located upstream of the wavelength conversion member 10 (on the excitation light source 3 side). In either case, the focal point 5f of the focusing optical system 5 is located outside the wavelength conversion member 10 with respect to the optical axis A3 of the excitation light L3, and a separation distance Da is provided between the focal point 5f of the focusing optical system 5 and the wavelength conversion member 10. This prevents the wavelength conversion member 10 from becoming too hot due to the excitation light L3 being focused within an extremely narrow region within the wavelength conversion member 10.

[0069] Fig. 6A is a schematic plan view of the concave reflector 21. Fig. 6B is a schematic cross-sectional view of the concave reflector 21 taken along line Q1-Q1 in Fig. 6A. In Fig. 6A and Fig. 6B, the Z axis corresponds to the optical axis A3 of the excitation light L3.

[0070] The concave reflector 21 has an opening 22 formed in a region facing the center C21 in the Z-axis direction. In this specification, when the concave reflector 21 is cut along an X-Y plane that passes through the center C21 and is perpendicular to the Z-axis, as shown in Fig. 6B, the angle θ22 defined by the lines connecting the center C21 to both ends of the opening 22 is defined as the "opening angle" of the opening 22.

[0071] 6A , when viewed in the Z-axis direction, a part of the wavelength conversion member 10 is located at a position facing the opening 22. More specifically, when viewed in the Z-axis direction, in other words, in the direction of the optical axis A3 of the excitation light L3, the wavelength conversion member 10 is disposed in a region including the center C21 of the concave reflector 21.

[0072] According to the light source device 1 described above, of the fluorescence L10 generated within the wavelength conversion member 10, the fluorescence L10 with a small divergence angle is directly extracted to the outside of the concave reflector 21 through the opening 22. Furthermore, the fluorescence L10 with a large divergence angle is reflected by the reflecting surface 21S of the concave reflector 21 and then returned to the wavelength conversion member 10. Here, within the wavelength conversion member 10, the region where the fluorescence L10 is generated is a limited region where the excitation light L3 is collected by the collecting optical system 5.

[0073] In other words, the incidence area of ​​the returning light of the fluorescence L10 that is reflected by the reflecting surface 21S of the concave reflector 21 and then guided into the wavelength conversion member 10 is a limited area that is substantially the same as the area into which the excitation light L3 is incident. As a result, the returning light of the fluorescence L10 that is reflected by the reflecting surface 21S is diffusely reflected on the surface or inside of the wavelength conversion member 10, and can then be extracted to the outside through the opening 22 of the concave reflector 21.

[0074] The same discussion as for the fluorescent light L10 can also be applied to the excitation light L3 that has passed through the wavelength conversion member 10. That is, the excitation light L3 with a small divergence angle is directly extracted to the outside of the concave reflector 21 through the opening 22. Furthermore, the fluorescence L10 of the excitation light L3 with a large divergence angle is reflected by the reflecting surface 21S of the concave reflector 21, returned to the wavelength conversion member 10 side, and diffusely reflected on the surface or inside of the wavelength conversion member 10 before being extracted to the outside through the opening 22 of the concave reflector 21.

[0075] That is, according to the light source device 1, the output light L1, which is a superimposed light of the excitation light L3 and the fluorescence L10, is extracted to the outside through the opening 22. The excitation light L3 and the fluorescence L10 contained in the extracted output light L1 contain components derived from the returning light reflected by the reflecting surface 21S of the concave reflector 21, and therefore the light extraction efficiency is improved compared to when the concave reflector 21 is not present. The output light L1 is light that is emitted through the opening 22, and therefore has a limited etendue.

[0076] Furthermore, with the light source device 1, it is possible to superimpose the excitation light L3 itself on the emitted light L1 because there is no need to provide a dichroic mirror outside the concave reflector 21. As a result, the light utilization efficiency is improved and the device size can be made smaller than with the light source device 100 described above with reference to Fig. 19 .

[0077] Furthermore, if the concave reflector 21 were not present, the wavelength components originating from the excitation light L3 contained in the light emitted from the wavelength conversion member 10 would tend to be distributed at positions closer to the center of the optical axis, and the wavelength components originating from the fluorescence L10 would tend to become more dominant as the distance from the center of the optical axis increases. However, with the light source device 1, part of the excitation light L3 is also reflected by the reflecting surface 21S of the concave reflector 21, so it is possible to eliminate the unevenness in wavelength of the emitted light L1 obtained from the light source device 1 depending on the distance from the center of the optical axis.

[0078] The concave reflector 21 can be made of any material. The reflective surface 21S of the concave reflector 21 is made of a material that can substantially reflect both the excitation light L3 and the fluorescent light L10. Specifically, the reflective surface 21S can be made of a metal material such as aluminum or copper, or a resin material such as PTFE. Note that the concave reflector 21 itself may be made of the same material as the reflective surface 21S.

[0079] Next, the performance of the light source device 1 of this embodiment will be described with reference to the results of verification using an evaluation optical system.

[0080] 7A is a diagram schematically illustrating the configuration of the evaluation optical system used in the verification. The evaluation optical system 30 includes a collimating lens 31, a front aperture 32, a condensing lens 33, a rear aperture 34, and an integrating sphere 35. The focal length of the collimating lens 31 was 25 mm. The front aperture 32 had an opening diameter of Φ6 mm. The condensing lens 33 had a focal length of 60 mm. The rear aperture 34 had an opening diameter of Φ40 μm.

[0081] The light L1 emitted from the light source device 1 was collimated by a collimating lens 31, and the width of the ray bundle was then limited by a front-stage aperture 32. The parallel light that passed through the front-stage aperture 32 was then focused by a condenser lens 33, and the width of the ray bundle was then further limited by a rear-stage aperture 34. The total luminous flux received was measured by an integrating sphere 35 arranged after the rear-stage aperture 34.

[0082] Fig. 7B is a diagram that schematically illustrates, following Fig. 7A, the configuration of an evaluation optical system for evaluating a light source device 91 of a comparative example. As shown in Fig. 7A, the evaluation optical system 30 used is the same as that of Fig. 7A, except that, instead of the light emitted from the light source device 1, light emitted from the light source device 91 of the comparative example is incident on the evaluation optical system 30.

[0083] 8A is a diagram schematically illustrating the configuration of a light source device 91 of Comparative Example 1, following the example of FIG. 1. Light source device 91 differs from light source device 1 in that a white LED element 80 is disposed inside a concave reflector 21. The white LED element 80 used was a CFT90-WCS-VB600 manufactured by Luminus, Inc., with a light-emitting surface measuring 3 mm square.

[0084] 8B is a diagram schematically illustrating the configuration of a light source device 92 of Comparative Example 2. The light source device 92 corresponds to a configuration in which the concave reflector 21 is removed from the light source device 91 of Comparative Example 1. In other words, the light source device 92 uses the same white LED element 80 as the light source device 91. When evaluating the light source device 92 of Comparative Example 2, the light source device 92 was installed instead of the light source device 91 shown in FIG. 7B , and the emitted light L92 from the light source device 92 was incident on the evaluation optical system 30.

[0085] 9 is a diagram for schematically explaining the light source diameter set by the wavelength conversion member 10 functioning as a secondary light source, and corresponds to a plan view of the wavelength conversion member 10. As described above, the wavelength conversion member 10 emits output light L1, which is a superimposed mixture of excitation light L3 and fluorescence L10, through the opening 22 of the concave reflector 21. Due to the presence of the focusing optical system 5, the excitation light L3 is incident on a limited region within the wavelength conversion member 10, where a portion of the excitation light L3 is converted into fluorescence L10. In other words, the excitation light L3 and fluorescence L10 travel from substantially the same region of the wavelength conversion member 10 toward the concave reflector 21.

[0086] As shown in Figure 9, the light source diameter D10 in the wavelength conversion member 10 corresponds to the diameter of the ray bundle of the output light L1 emitted from the wavelength conversion member 10 toward the concave reflector 21 on the light extraction surface 10S of the wavelength conversion member 10 (see Figures 2 and 5A).

[0087] [Verification] Next, more preferable conditions for the light source device 1 of this embodiment will be described in comparison with the received light flux obtained by the evaluation optical system 30 using the light source devices (91, 92) of the comparative examples.

[0088] (Verification 1) Fig. 10 is a graph showing how the total luminous flux received by integrating sphere 35 changes when the opening angle θ22 (see Fig. 6B) of opening 22 is changed in light source device 1. Note that the graph in Fig. 10 shows data for each light source diameter D10 in wavelength conversion member 10.

[0089] The light source diameter D10 of the wavelength conversion member 10 was set by adjusting the diameter of the ray bundle when the excitation light L3 emitted from the excitation light source 3 was incident on the wavelength conversion member 10. More specifically, the light source diameter D10 of the wavelength conversion member 10 was adjusted by shifting the position of the focusing optical system 5 in Fig. 1 in the direction of the optical axis A3 of the excitation light L3. Note that the light source diameter D10 can be finely adjusted by adjusting the position of the light diffusing member 7.

[0090] The opening angle θ22 of the opening 22 was adjusted by changing the diameter D22 (see FIG. 6A ) of the opening 22 of the concave reflector 21. The center position of the opening 22 was kept coincident with the center C21 of the concave reflector 21.

[0091] The light source device 1 was configured under the following conditions: Inner diameter of the concave reflector 21: 12 mm Reflectance of the reflective surface 21S of the concave reflector 21 for the excitation light L3 and the fluorescence L10: 97% Reflectance of the dichroic layer 14 for the fluorescence L10: 99% Transmittance of the dichroic layer 14 for the excitation light L3: 91%

[0092] For comparison, the total luminous flux received by the evaluation optical system 30 when the light source device 91 described above with reference to Fig. 8A was used, and the total luminous flux received by the evaluation optical system 30 when the light source device 91 described above with reference to Fig. 8B was used were also measured in the same way. In Fig. 10, the "luminous flux relative value" indicated as the value on the vertical axis is the relative value of the total luminous flux received when the light source device 1 was used, with the total luminous flux obtained when the light source device 91 serving as the comparative example was used as the reference. The same applies to the following graphs.

[0093] 10, it was confirmed that the amount of light emitted from light source device 1 tends to increase as the light source diameter D10 becomes smaller, and that this tendency becomes more pronounced when the light source diameter D10 is set to 0.9 mm or less. It is also suggested that by setting the opening angle θ22 in the range of 14° to 133°, the amount of light emitted can be increased compared to light source devices 91 and 92 as comparative examples using white LED elements 80, regardless of the size of the light source diameter D10.

[0094] 10, regardless of the size of the light source diameter D10, the relative luminous flux value is highest when the opening angle θ22 is 24°, and the relative luminous flux value gradually decreases as the opening angle θ22 increases from 24°. However, the amount of decrease is extremely small, suggesting that even when the opening angle θ22 reaches 133°, light source device 1 can obtain a light output that is sufficiently higher than that of light source devices 91 and 92 as comparative examples.

[0095] In contrast, when the opening angle θ22 is decreased from 24°, the decrease in the relative luminous flux value is relatively large compared to when it is increased from 24°. This tendency is particularly evident when the light source diameter D10 is 0.6 mm. However, when the light source diameter D10 is 0.6 mm, even when the opening angle θ22 is set to a small value of 10°, a higher light output is still obtained than in the light source devices 91 and 92 as comparative examples.

[0096] 10 , which shows the relationship between the aperture angle θ22 and the relative luminous flux value, it is presumed that when the aperture angle θ22 is set too small, the fluorescence L10 (and the excitation light L3) is reflected multiple times between the reflecting surface 21S of the concave reflector 21 and the wavelength conversion member 10 before the output light L1 is extracted through the opening 22, or that an increase in the amount of light that is not extracted to the outside through the opening 22 results in a relative decrease in the relative luminous flux value. On the other hand, when the aperture angle θ22 is set to be larger than 24°, the relative luminous flux value is slightly decreased. It is presumed that this is because, while the number of reflections between the reflecting surface 21S of the concave reflector 21 and the wavelength conversion member 10 before the output light L1 is extracted to the outside through the opening 22 remains unchanged, the width of the ray bundle of the output light L1 is widened, resulting in an increase in the amount of light cut by the front aperture 32 (see FIG. 7A ) in the evaluation optical system 30.

[0097] Fig. 11 is a graph showing the relationship between the light source diameter D10 and the relative luminous flux value when the opening angle θ22 is fixed at 24°. Fig. 11 shows that the light source diameter D10 is preferably set to 0.5 mm to 1.4 mm, more preferably 0.5 mm to 1.2 mm, particularly preferably 0.53 mm to 1.0 mm, and particularly preferably 0.57 mm to 0.7 mm.

[0098] (Verification 2) Next, the effect on the received light beam due to changing the positional relationship between the wavelength conversion member 10 and the concave reflector 21 was verified. FIG. 12 is a schematic diagram illustrating the positional relationship between the wavelength conversion member 10 and the concave reflector 21. In this specification, the deviation dz1 between the wavelength conversion member 10 and the concave reflector 21 is defined as the relative position in the Z-axis direction with respect to the center C21 of the concave reflector 21, when the light extraction surface 10S of the wavelength conversion member 10 is used as a reference. As described above, the Z-axis direction here corresponds to the direction of the optical axis A3 of the excitation light L3. The deviation dz1 is considered to be a positive value when the center C21 of the concave reflector 21 is located on the +Z side of the light extraction surface 10S of the wavelength conversion member 10, and a negative value when the opposite is true.

[0099] FIG. 13 is a graph showing the change in the total luminous flux received by integrating sphere 35 when the deviation dz1 is changed with the light source diameter D10 fixed at 0.6 mm and the opening angle θ22 of opening 22 fixed at 24°.

[0100] FIG. 13 suggests that the deviation dz1 is preferably set within the range of −1 mm to +1 mm, and more preferably within the range of −0.2 mm to +0.1 mm.

[0101] As described above, the concave reflector 21 is provided for the purpose of reflecting light (fluorescence L10, excitation light L3) that is emitted from the light extraction surface 10S of the wavelength conversion member 10 and travels at a relatively large divergence angle by the reflecting surface 21S and returning the light to the light extraction surface 10S side of the wavelength conversion member 10. Within the wavelength conversion member 10, the area that functions as a secondary light source is limited. It is preferable that the light reflected by the reflecting surface 21S is also returned to the limited area within the wavelength conversion member 10 that functions as a secondary light source. From this perspective, it is most preferable that the center C21 of the concave reflector 21 is located on the light extraction surface 10S of the wavelength conversion member 10.

[0102] However, there is a possibility that misalignment may occur when mounting the light source device 1. The results in Fig. 13 suggest that even if the light extraction surface 10S of the wavelength conversion member 10 is misaligned in the Z-axis direction from the center C21 of the concave reflector 21, the center C21 of the concave reflector 21 can be considered to be substantially located on the light extraction surface 10S of the wavelength conversion member 10 as long as the amount of misalignment is within the range of -1 mm to +1 mm.

[0103] (Verification 3) The effect on the received luminous flux of changing the thickness of phosphor layer 12 included in wavelength conversion member 10 was verified. Fig. 14 is a graph showing the change in the total luminous flux received by integrating sphere 35 when the thickness of phosphor layer 12 is changed with opening angle θ22 of opening 22 fixed at 24°.

[0104] According to FIG. 14, it is clear that the thickness of the phosphor layer 12 is preferably 5 μm to 30 μm, more preferably 10 μm to 25 μm, and particularly preferably 15 μm to 22 μm.

[0105] Note that a change in the thickness of the phosphor layer 12 changes the travel distance of the excitation light L3 inside the phosphor layer 12, which may change the light source diameter D10 of the secondary light source inside the wavelength conversion member 10. However, according to Figures 11 and 14, the value of the light source diameter D10 is larger than the thickness of the phosphor layer 12 by one to two orders of magnitude, and therefore changing the thickness of the phosphor layer 12 has little effect on the value of the light source diameter D10.

[0106] (Verification 4) A verification was conducted to examine the effect on the received luminous flux of changing the relative density in the phosphor layer 12 included in the wavelength conversion member 10. For example, as described above with reference to Fig. 3, in a structure in which the phosphor layer 12 includes particulate phosphor 16 and binder 17, the amount of pores 18 present in the phosphor layer 12 can be adjusted by changing the conditions for the heating and sintering process.

[0107] 15, the relative density within the phosphor layer 12 is preferably 40% to 99.9%, and more preferably 50% to 95%. Note that this relative density value is a value measured by a method in accordance with JIS R 1634 (Method for measuring sintered density and open porosity of fine ceramics).

[0108] Another embodiment of the light source device 1 will now be described.

[0109] <1> Fig. 16 is a diagram schematically illustrating the configuration of a light source device 1 according to another embodiment. As shown in Fig. 16, the light source device 1 can employ a structure similar to that of a CAN-type semiconductor laser element.

[0110] Specifically, the light source device 1 includes a housing 41 that houses an excitation light source 3 formed of a semiconductor laser element, a focusing optical system 5, and a light diffusing member 7, and a cap 42 that closes the housing 41. The cap 42 has an opening in a certain location, and the wavelength conversion member 10 is disposed at a position opposite this opening. The excitation light L3 that has passed through the light diffusing member 7 is incident on the wavelength conversion member 10.

[0111] <2> Fig. 17 is a diagram schematically illustrating the configuration of a light source device 1 according to another embodiment, following Fig. 1. As shown in Fig. 17, excitation light L3 emitted from an excitation light source 3 may be guided to the wavelength conversion member 10 via a reflection optical system 45. In the light source device 1 shown in Fig. 17, the reflection optical system 45 is disposed between the condensing optical system 5 and the light diffusing member 7, but it may also be disposed between the excitation light source 3 and the condensing optical system 5, or reflection optical systems 45, 45, ... may be disposed in multiple locations.

[0112] In addition, when the traveling direction of the excitation light L3 is changed by the reflection optical system 45, the optical axis A3 of the excitation light L3 may be set according to the traveling direction of the excitation light L3.

[0113] <3> In the above embodiment, the light source device 1 is described as including the light diffusing member 7, but it is optional whether or not the light source device 1 includes the light diffusing member 7.

[0114] <4> As described above, the focal point 5 f of the focusing optical system 5 is preferably located outside the wavelength conversion member 10 with respect to the direction of the optical axis A3 of the excitation light L3. However, the present invention does not exclude a configuration in which the focal point 5 f of the focusing optical system 5 is located inside the wavelength conversion member 10.

[0115] 1: Light source device 3: Excitation light source 5: Condensing optical system 5f: Focus of condensing optical system 7: Light diffusing member 10: Wavelength conversion member 10S: Light extraction surface of wavelength conversion member 11: Substrate 12: Phosphor layer 13: Anti-reflection layer 14: Dichroic layer 16: Phosphor 17: Binder 18: Pores 21: Concave reflector 21S: Reflecting surface of concave reflector 22: Opening formed in concave reflector 30: Evaluation optical system 31: Collimating lens 32: Front aperture 33: Condenser lens 34: Rear aperture 35: Integrating sphere 41: Housing 42: Cap 45: Reflection optical system 80: White LED element 91, 92: Light source device of comparative example A3: Optical axis of excitation light D10: Light source diameter L1: Emitted light L10: Fluorescent light L3: Excitation light

Claims

1. A light source device comprising: an excitation light source including a semiconductor laser element; a wavelength conversion member that converts the wavelength of at least a portion of incident light to emit fluorescence; a focusing optical system that is arranged between the excitation light source and the wavelength conversion member in the direction of the optical axis of the excitation light emitted from the excitation light source and guides the excitation light to the wavelength conversion member while reducing the divergence angle of the excitation light; and a concave reflector that is arranged on a side away from the excitation light source when the wavelength conversion member is used as a reference in the direction of the optical axis of the excitation light, and includes a reflective surface that exhibits reflectivity with respect to the light emitted from the wavelength conversion member, wherein the concave reflector has an opening for extracting the emitted light in an area including an area through which the optical axis of the excitation light passes, and the wavelength conversion member is arranged in an area including the center of the concave reflector when viewed in the direction of the optical axis of the excitation light.

2. The light source device described in claim 1, characterized in that the emitted light extracted to the outside from the opening is a superimposed light of the excitation light emitted from the excitation light source and the fluorescence obtained by converting the wavelength of the excitation light by the wavelength conversion member.

3. A light source device as described in claim 1 or 2, characterized in that the focal point of the focusing optical system is located outside the wavelength conversion member in the direction of the optical axis of the excitation light.

4. A light source device according to claim 1 or 2, further comprising a light diffusing member disposed between the focusing optical system and the wavelength conversion member in the optical axis direction of the excitation light.

5. A light source device according to claim 1 or 2, characterized in that the secondary light source formed by the wavelength conversion member has a light source diameter of 0.5 mm to 1.4 mm, and the opening angle of the opening is 14° to 133°.

6. The light source device according to claim 1 or 2, wherein the wavelength conversion member comprises: a substrate; a dichroic layer disposed on the substrate, which substantially transmits the excitation light and substantially reflects the fluorescence; and a phosphor layer disposed on the dichroic layer and containing a phosphor, the phosphor layer having a thickness of 5 μm to 30 μm.

7. The light source device described in claim 6, characterized in that the wavelength conversion member is arranged on the lower layer of the substrate opposite the side on which the dichroic layer is arranged, and has an anti-reflection layer that suppresses reflection of the excitation light.

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