Light source apparatus

Abstract

To realize a light source apparatus which can provide light of high color rendering even when light extraction is high efficient, in spite of its small size.SOLUTION: A light source apparatus comprises: an excitation light source including a semiconductor laser device; a wavelength converting member for emitting fluorescent light by converting at least a part of wavelengths of incident light; a light collecting optical system disposed between the excitation light source and the wavelength converting member for guiding light to the wavelength converting member while reducing a divergence angle of the excitation light; and a concave surface reflector disposed on the side away from the excitation light source with reference to the wavelength converting member and including a reflection surface indicating reflectivity to emitted light from the wavelength converting member. The concave surface reflector has an opening portion for taking out the emitted light to a region including a region through which an optical axis of the excitation light passes. The wavelength converting member is disposed at a region including a center of the concave surface reflector when viewed in an optical axis direction of the excitation light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[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. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in order to increase the amount of extracted light, a technique of arranging a hemispherical reflector on the outer periphery of a light source is 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 one location is disposed outside an 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 at one location is disposed outside the 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 of the reflector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5642385 [Patent Document 2] Special Publication No. 2015-528988 Summary of the Invention [Problem to be solved by the invention]

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

[0007] However, because optical fibers have a small etendue, the light emitted from the LED cannot be efficiently guided to the optical fiber, making it difficult to ensure a sufficient amount of light irradiation from the optical fiber.

[0008] As a countermeasure to the above problem, it seems that a method of providing a hemispherical reflector with an opening on the periphery of the LED can be used, as disclosed in Patent Document 1. Among the light emitted from the LED, the light beam with a small divergence angle is directly extracted through the opening, while the light beam with a large divergence angle is reflected by the reflector and returned to the LED side.

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

[0010] In reality, the surface of the light extraction surface is roughened in order to prevent the 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 side. In addition, since an electrode is provided on a part of the light extraction surface, regular unevenness is inevitably formed. From this perspective, the proportion of the reflected light from the reflector that is diffusely reflected by the light extraction surface of the LED is originally limited. In other words, of the light returned from the reflector to the light extraction surface of the LED, the proportion of the light that 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 is high. 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] Moreover, an LED is a surface-emitting light source and has a certain degree of 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 position away from the center position of the light extraction surface within the light extraction surface having a size of about 2 mm square to 4 mm square. In this way, when the light emitted from a position away from the center of the light extraction surface is reflected by the reflector, it is also returned to a position away from the center of the LED. As a result, it is assumed that the light emitted from a position away from the center position of the LED is merely reflected repeatedly between the LED and the reflector and is not extracted from 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 by an LED per unit size is small, it is necessary to increase the size of the LED in order to increase the amount of light emitted. However, this supports the fact that, due to the above-mentioned circumstances, the effect of increasing the amount of extracted light by reflecting it with a reflector cannot be fully expected.

[0013] In view of the above circumstances, as disclosed in Patent Document 2, use of a light source device using a hemispherical reflector and a fluorescent light source is considered.

[0014] 18 is a diagram illustrating a schematic configuration of a light source device disclosed in Patent Document 2. Light source device 100 includes phosphor layer 101, hemispherical reflector 104, and excitation light source 105. Hemispherical reflector 104 has opening 104a formed in a portion thereof. Phosphor layer 101 is disposed inside hemispherical reflector 104.

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

[0016] The phosphor layer 101 is excited by the incident excitation light L105 and emits fluorescence L101. Since the excitation light L105 is a light beam with a narrow line width, a light emitting region 101c in the phosphor layer 101 is limited and essentially serves as a point light source.

[0017] Of the fluorescence L101 generated in the light-emitting region 101c, a light beam with a small divergence angle is directly guided to the dichroic mirror 106 via the opening 104a. Meanwhile, a 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, the light traveling in the opposite direction to 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 that uses an LED as a light source, and 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 stage of the dichroic mirror 106 originates from the fluorescence L101. In this case, the color rendering of the light guided to the rear stage 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 long wavelength (yellow band, green band, etc.) when it receives the blue light. In this case, the spectrum of the light guided to the rear stage of the dichroic mirror 106 has an extremely small blue component, resulting in light with low color rendering properties.

[0023] As a method for dealing with such a situation, as shown in Fig. 19, a separate blue light source 107 is arranged behind the dichroic mirror 106, and blue light L107 emitted from the blue light source 107 is superimposed on the fluorescence L101. Specifically, a dichroic mirror 108 designed to substantially reflect blue light and substantially transmit light of the same wavelength as the fluorescence L101, similar to the dichroic mirror 106, is arranged behind 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, so that the light guided to the rear 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 the color rendering.

[0024] However, according to 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 a certain extent by passing through the multiple dichroic mirrors (106, 108). In other words, it can be said that there is a limit to how much the light extraction efficiency can be improved in the light source device 100 shown in FIG. 19.

[0025] Furthermore, according to 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 positions, 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 scale 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. [Means for solving the problem]

[0028] The light source device according to the present invention comprises: an excitation light source including a semiconductor laser element; A wavelength conversion member that converts the wavelength of at least a part of the incident light and emits fluorescence; a focusing optical system that is disposed between the excitation light source and the wavelength conversion member in a direction of an 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 a divergence angle of the excitation light; a concave reflector that is disposed on a side away from the excitation light source when the wavelength conversion member is used as a reference in a direction of an optical axis of the excitation light, the concave reflector including a reflective surface that exhibits reflectivity with respect to light emitted from the wavelength conversion member; the concave reflector has an opening for extracting the emitted light in a region including a region through which an optical axis of the excitation light passes, The wavelength conversion member is disposed in a region including a center of the concave reflector when viewed in the optical axis direction 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, when receiving the excitation light, converts the wavelength and emits fluorescence.

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

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

[0032] Among the fluorescence generated by the wavelength conversion member, the fluorescence traveling with a relatively large divergence angle is reflected by the reflecting 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 is close to a substantial point light source. In other words, among the fluorescence emitted from the wavelength conversion member, the light reflected by the reflecting surface of the concave reflector after traveling toward the concave reflector with a relatively large divergence angle is returned to the area of ​​the wavelength conversion member where the excitation light is 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 side provided in the concave reflector.

[0034] That is, according to the light source device described above, it is possible to extract the emitted light in a state in which both the excitation light and the fluorescent light are superimposed to the outside through the opening. This makes it possible to obtain white light with high color rendering properties without superimposing light containing wavelength components equivalent to the excitation light separately at a later stage, and the device scale can be made smaller than before. In addition, since both the wavelength conversion member and the excitation light source can be arranged inside the concave reflector, it is also possible to share the cooling mechanism for the wavelength conversion member and the cooling mechanism for 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 direction of the optical axis of the excitation light.

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

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

[0039] From this viewpoint, the deviation between the focal point of the light collecting 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 the light is extracted is taken as the positive direction.

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

[0041] By providing the light source device with a light diffusion member, the light beams included in the light beam bundle of the excitation light can be guided to the wavelength conversion member with the divergence angle reduced by the light collection optical system while the traveling directions of the light beams included in the light beam bundle of the excitation light are slightly different from each other. This allows the wavelength conversion member to function as a secondary light source that is substantially close to a point light source, while suppressing the decrease in the fluorescence conversion efficiency due to temperature quenching. Furthermore, it is easy to direct a part of the excitation light traveling after passing through the wavelength conversion member toward the concave reflector. As a result, the light in which 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 emitted from the wavelength conversion member and directly extracted through the opening are superimposed is light in which the variation in wavelength components due to the distance from the optical axis center is sufficiently reduced.

[0042] As a preferred example, the secondary light source formed by the wavelength conversion member may have a light source diameter of 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 conversion 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 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 makes it possible to guide the excitation light 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 fixed with a binder made of an inorganic material, or may be a sintered body in which phosphor particles and the binder are sintered. 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 by a method conforming to JIS R 1634 (Method of measuring density and open porosity of sintered body of fine ceramics). In other words, the phosphor layer preferably contains pores with a content of 0.1% to 60%, more preferably 5% to 50%. Effect of the Invention

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

[0049] [Figure 1] 1 is a block diagram illustrating a configuration of an embodiment of a light source device of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view illustrating an example of a configuration of a wavelength conversion member. [Diagram 3] 4 is a schematic enlarged view of a portion of a phosphor layer provided on a wavelength conversion member. [Figure 4] 4 is an example of a spectrum of light emitted from a light source device. [Figure 5A] 1 is a diagram illustrating an example of a positional relationship between a wavelength conversion member and a focusing optical system. [Figure 5B] 13 is a diagram illustrating another example of the positional relationship between the wavelength conversion member and the light collecting optical system. [Figure 6A] FIG. 2 is a schematic plan view of a concave reflector. [Figure 6B] 6B is a schematic cross-sectional view of the concave reflector taken along line Q1-Q1 in FIG. 6A. [Figure 7A]1 is a diagram illustrating a schematic configuration of an evaluation optical system for evaluating the light source device of the present embodiment. [Figure 7B] 7B is a diagram showing a schematic configuration of an evaluation optical system for evaluating a light source device of a comparative example, following FIG. 7A. [Figure 8A] 2 is a diagram showing a schematic configuration of a light source device of Comparative Example 1 following FIG. 1. [Figure 8B] 13 is a diagram illustrating a configuration of a light source device of Comparative Example 2. [Figure 9] 11 is a diagram for illustrating a light source diameter set by a wavelength conversion member. [Figure 10] 1 is a graph showing how the received light flux changes when the opening angle of an opening formed in a reflector is changed, and data is shown for each light source diameter. [Figure 11] 1 is a graph showing the relationship between the light source diameter and the received light flux when the aperture angle is fixed. [Figure 12] 4 is a schematic diagram for explaining the positional relationship between a wavelength conversion member and a concave reflector. [Figure 13] 11 is a graph showing the relationship between the deviation between the wavelength conversion member and the concave reflector and the received light flux when the light source diameter and the aperture angle are fixed. [Figure 14] 11 is a graph showing the relationship between the thickness of the phosphor layer and the received luminous flux when the aperture angle is fixed. [Figure 15] 1 is a graph showing the relationship between the relative density in a phosphor layer and the received luminous flux when the aperture angle is fixed. [Figure 16] FIG. 11 is a block diagram illustrating a configuration of a light source device according to another embodiment of the present invention. [Figure 17] FIG. 11 is a block diagram illustrating a configuration of a light source device according to another embodiment of the present invention. [Figure 18] 1 is a diagram illustrating a schematic configuration of a conventional light source device. [Figure 19] 19 is a diagram illustrating a schematic configuration of an improved version of the light source device illustrated in FIG. 18. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The following description will be given of an embodiment of a light source device according to the present invention with reference to the accompanying drawings. Note that in the following drawings, the dimensional ratios 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. The light source device 1 shown in FIG 1 includes an excitation light source 3, a light collecting optical system 5, a light diffusing member 7, a wavelength conversion member 10, and a concave reflector 21.

[0052] FIG. 2 is a cross-sectional view illustrating a schematic 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 conversion member 10 includes a phosphor layer 12, and a 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 capable of exciting the phosphor contained in the phosphor layer 12. However, when it is assumed that the light source device 1 generates white emission 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 a wavelength range of 420 nm to 500 nm, and violet light refers to light in a wavelength range of 370 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 includes a collimating optical system as necessary.

[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 to 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 light collecting 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 diffuse transmission plate, a microlens array, or the like. The light diffusing member 7 is provided for the purpose of preventing the width of the light beam incident on the wavelength conversion member 10 from becoming too narrow when the excitation light L3 is collected by the light collecting optical system 5 and guided into the wavelength conversion member 10. When the high-luminance excitation light L3 originating from the semiconductor laser element is incident on an extremely narrow region in the wavelength conversion member 10, the power density in the wavelength conversion member 10 becomes too high, and there is a possibility that the temperature of the wavelength conversion member 10 becomes extremely high. The wavelength conversion member 10 exhibits a phenomenon called temperature 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 for the purpose of increasing the efficiency of conversion from the excitation light L3 to the fluorescence L10.

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

[0058] The substrate 11 is provided for the purpose of radiating heat generated by the phosphor layer 12 while stably supporting the phosphor layer 12, and for the purpose of guiding the excitation light L3 to the phosphor layer 12. From this viewpoint, a material having a relatively high thermal conductivity and a high transmittance to the excitation light L3 is adopted as 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. From the viewpoint of heat radiation and the like, the surface area of ​​the substrate 11 is preferably larger than the area of ​​the phosphor layer 12.

[0059] As an 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. Also, the phosphor 16 can be one or more phosphors belonging to the group consisting of CASN phosphor, SCASN phosphor, and CASON phosphor as a red phosphor.

[0061] By mixing a plurality of phosphor materials as the phosphor 16 contained in the phosphor layer 12, white light with high color rendering is realized by the emitted light L1 as 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 showing high color rendering 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 plurality of 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 realizes a 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 proceeds 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, for example, by laminating a plurality of dielectric films having different refractive indices.

[0064] 2 has an antireflection layer 13 provided on the surface of the substrate 11 opposite to the phosphor layer 12. The antireflection layer 13 is provided for the purpose of suppressing the reflection of the excitation light L3 incident on the wavelength conversion member 10 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. In addition, 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 in the wavelength conversion member 10 with high luminance, it is expected that the fluorescence conversion efficiency will decrease due to temperature quenching. From this viewpoint, it is preferable to design the focal length of the light-concentrating optical system 5 and the thickness of the wavelength conversion member 10 so that the focal point 5f of the light-concentrating optical system 5 is located outside the wavelength conversion member 10 with respect to the optical axis A3 of the excitation light L3, as shown in Fig. 5A or 5B. Note that, for convenience of explanation, the light diffusion member 7 is omitted in Fig. 5A and Fig. 5B.

[0068] In the example shown in Fig. 5A, the focal point 5f of the focusing optical system 5 is located behind 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 ahead 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. As a result, the excitation light L3 is focused within an extremely narrow region in the wavelength conversion member 10, thereby preventing the wavelength conversion member 10 from becoming hot.

[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, as shown in Fig. 6B, when the concave reflector 21 is cut by an XY plane that passes through the center C21 and is perpendicular to the Z-axis, an angle θ22 defined by lines connecting both ends of the opening 22 with the center C21 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 in the wavelength conversion member 10, the fluorescence L10 having a small divergence angle is directly extracted to the outside of the concave reflector 21 through the opening 22. Moreover, of the fluorescence L10, the fluorescence L10 having 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, the region in the wavelength conversion member 10 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 return light of the fluorescence L10 that is guided into the wavelength conversion member 10 after being reflected by the reflecting surface 21S of the concave reflector 21 is a limited area that is substantially the same as the area into which the excitation light L3 is incident. As a result, the fluorescence L10 as the return light reflected by the reflecting surface 21S can be extracted to the outside through the opening 22 of the concave reflector 21 after being diffusely reflected on the surface or inside of the wavelength conversion member 10.

[0074] The same discussion as for the fluorescent light L10 can 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. The fluorescence L10 with a large divergence angle of the excitation light L3 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, and then 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 as 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 originating from the return light reflected by the reflecting surface 21S of the concave reflector 21, so the light extraction efficiency is improved compared to the case where the concave reflector 21 does not exist. The output light L1 is light emitted through the opening 22, and therefore has a limited etendue.

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

[0077] Furthermore, in the absence of the concave reflector 21, the wavelength components originating from the excitation light L3 contained in the light emitted from the wavelength conversion member 10 tend to be distributed at positions closer to the center of the optical axis, and the wavelength components originating from the fluorescence L10 tend to become more dominant as the distance from the center of the optical axis increases. However, according to the light source device 1, part of the excitation light L3 is also reflected at the reflecting surface 21S of the concave reflector 21, so that it is possible to eliminate the unevenness in wavelength of the emitted light L1 obtained from the light source device 1 according to the distance from the center of the optical axis.

[0078] The concave reflector 21 may be made of any material. The reflective surface 21S of the concave reflector 21 is made of a material capable of substantially reflecting both the excitation light L3 and the fluorescent light L10. Specifically, the reflective surface 21S may be made of a metal material such as aluminum or copper, or a resin material such as PTFE. 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 showing a schematic configuration of the evaluation optical system used in the verification. The evaluation optical system 30 includes a collimator lens 31, a front-stage aperture 32, a condenser lens 33, a rear-stage aperture 34, and an integrating sphere 35. The focal length of the collimator lens 31 was set to 25 mm. The front-stage aperture 32 had an opening of Φ6 mm. The focal length of the condenser lens 33 was set to 60 mm. The rear-stage aperture 34 had an opening of Φ40 μm.

[0081] Light L1 emitted from light source device 1 was collimated by collimating lens 31, and the width of the light beam was then restricted by front-stage aperture 32. The parallel light that passed through front-stage aperture 32 was then focused by condenser lens 33, and the width of the light beam was further restricted by rear-stage aperture 34. The total light beam received was measured by integrating sphere 35, which was placed behind rear-stage aperture 34.

[0082] Fig. 7B is a diagram showing a schematic configuration of an evaluation optical system for evaluating a light source device 91 of a comparative example, following Fig. 7A. As shown in Fig. 7A, the evaluation optical system 30 used is the same as that of Fig. 7A, except that the light emitted from the light source device 91 of the comparative example is incident on the evaluation optical system 30 instead of the light emitted from the light source device 1, that is, L91.

[0083] 8A is a diagram showing a schematic configuration of a light source device 91 of Comparative Example 1 following 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. As the white LED element 80, a CFT90-WCS-VB600 manufactured by Luminus, Inc., with a light-emitting surface of 3 mm square, was used.

[0084] 8B is a diagram showing a schematic 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. That is, the light source device 92 uses a white LED element 80 similar to that of 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 made incident on the evaluation optical system 30.

[0085] 9 is a diagram for illustrating a 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 output light L1, in which the excitation light L3 and the fluorescence L10 are superimposed, is extracted from the wavelength conversion member 10 to the outside 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 in the wavelength conversion member 10, and a part of the excitation light L3 is converted into the fluorescence L10 in the region. In other words, the excitation light L3 and the fluorescence L10 proceed from substantially the same region of the wavelength conversion member 10 toward the concave reflector 21 side.

[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 while comparing it with the received light flux obtained by the evaluation optical system 30 using a light source device (91, 92) of a comparative example.

[0088] (Verification 1) Fig. 10 is a graph showing the change in the total luminous flux received by integrating sphere 35 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 light beam when the excitation light L3 emitted from the excitation light source 3 is 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] In addition, 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] In the light source device 1, the following conditions were set. Inner diameter of concave reflector 21: 12mm Reflectance of the reflective surface 21S of the concave reflector 21 for the excitation light L3 and the fluorescent light L10: 97% Reflectance of dichroic layer 14 to fluorescence L10: 99% Transmittance of the dichroic layer 14 to 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 manner. 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 is used, with the total luminous flux obtained when the light source device 91 as a comparative example is used as the reference. The same applies to the following graphs.

[0093] 10, it was confirmed that the amount of light emitted from the light source device 1 tends to increase as the light source diameter D10 becomes smaller, and that this tendency becomes stronger 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 emitted light can be increased compared to the light source devices 91 and 92 using the white LED element 80 as comparative examples, regardless of the size of the light source diameter D10.

[0094] 10, regardless of the size of the light source diameter D10, the luminous flux relative value is highest when the opening angle θ22 is 24°, and the luminous flux relative 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°, the light source device 1 can provide a sufficiently higher light output than the light source devices 91 and 92 as comparative examples.

[0095] In contrast, when the opening angle θ22 is decreased from 24°, the reduction in the luminous flux relative value is relatively large compared to when it is increased from 24°. This tendency is particularly noticeable 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 emitted light L1 is extracted through the opening 22, or the amount of light that is not extracted to the outside from the opening 22 increases, resulting 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 because the number of reflections between the reflecting surface 21S of the concave reflector 21 and the wavelength conversion member 10 before being extracted to the outside from the opening 22 remains unchanged, while the width of the ray bundle of the emitted light L1 is increased, resulting in an increase in the amount of light cut by the front-stage 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 luminous flux relative 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 to 0.5 mm to 1.2 mm, particularly preferably to 0.53 mm to 1.0 mm, and particularly more preferably to 0.57 mm to 0.7 mm.

[0098] (Verification 2) Next, the influence on the received light flux due to the change in the positional relationship between the wavelength conversion member 10 and the concave reflector 21 was verified. FIG. 12 is a schematic diagram for explaining 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 a 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. The Z-axis direction here corresponds to the direction of the optical axis A3 of the excitation light L3, as described above. The deviation dz1 is 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 in the opposite case.

[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 the light (fluorescence L10, excitation light L3) emitted from the light extraction surface 10S of the wavelength conversion member 10 and traveling 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. In 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 a limited area in the wavelength conversion member 10 that functions as a secondary light source. From this viewpoint, 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 result in Fig. 13 suggests 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, so long as the amount of misalignment is within the range of -1 mm to +1 mm.

[0103] (Verification 3) An investigation was conducted to examine the effect on the received luminous flux of changing the thickness of phosphor layer 12 included in wavelength conversion member 10. 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 the opening angle θ22 of opening 22 fixed at 24°.

[0104] According to FIG. 14, it is apparent 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 if the thickness of the phosphor layer 12 changes, the travel distance of the excitation light L3 inside the phosphor layer 12 changes, which may result in a change in the light source diameter D10 of the secondary light source inside the wavelength conversion member 10. However, according to Fig. 11 and Fig. 14, the value of the light source diameter D10 is larger than the thickness of the phosphor layer 12 by about one to two orders of magnitude, and therefore the effect of changing the thickness of the phosphor layer 12 on the value of the light source diameter D10 is small.

[0106] (Verification 4) An investigation was conducted into the effect on the received luminous flux of the phosphor layer 12 included in the wavelength conversion member 10 by changing the relative density within the phosphor layer 12. 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 within the phosphor layer 12 is adjusted by changing the conditions for the heating and sintering treatment.

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

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

[0109] <1> Fig. 16 is a diagram showing a schematic 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 configured with 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 at a certain location, and the wavelength conversion member 10 is disposed at a position facing the 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 showing a schematic configuration of a light source device 1 according to another embodiment following Fig. 1. As shown in Fig. 17, the excitation light L3 emitted from the 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 light collecting optical system 5 and the light diffusing member 7, but it may be disposed between the excitation light source 3 and the light collecting optical system 5, or the reflection optical systems 45, 45, ... may be disposed at a plurality of locations.

[0112] 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. However, it is optional whether or not the light source device 1 includes the light diffusing member 7.

[0114] <4> As described above, it is preferable that the focal point 5f of the focusing optical system 5 is 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 5f of the focusing optical system 5 is located inside the wavelength conversion member 10. [Explanation of symbols]

[0115] 1:Light source device 3: Excitation light source 5: Light collecting optical system 5f: Focus of the focusing optical system 7: Light diffusion material 10: Wavelength conversion material 10S: Light extraction surface of wavelength conversion material 11: Substrate 12: Phosphor layer 13: Anti-reflection layer 14: Dichroic layer 16: Phosphor 17: Binder 18: Stoma 21: Concave reflector 21S: Reflective surface of concave reflector 22: Opening formed in the 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: Reflective 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: Output light L10: Fluorescence L3: Excitation light

Claims

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

2. 2. The light source device according to claim 1, wherein 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. 3. The light source device according to claim 1, wherein a focal point of the light collecting optical system is located outside the wavelength conversion member in the direction of an optical axis of the excitation light.

4. 3. The light source device according to claim 1, further comprising a light diffusing member disposed between the light collecting optical system and the wavelength converting member in a direction of an optical axis of the excitation light.

5. The light source diameter of the secondary light source formed by the wavelength conversion member is 0.5 mm to 1.4 mm; 3. The light source device according to claim 1, wherein the opening has an opening angle of 14° to 133°.

6. The wavelength conversion member is A substrate; a dichroic layer disposed on the substrate and configured to substantially transmit the excitation light and substantially reflect the fluorescent light; a phosphor layer disposed on the dichroic layer and containing a phosphor; 3. The light source device according to claim 1, wherein the phosphor layer has a thickness of 5 μm to 30 μm.

7. 7. The light source device according to claim 6, wherein the wavelength conversion member is disposed on a lower layer of the substrate opposite to the side on which the dichroic layer is disposed, and has an anti-reflection layer that suppresses reflection of the excitation light.

Images