Wavelength conversion apparatus and light source apparatus

A wavelength conversion apparatus includes a wavelength conversion member that has an incident surface and an emitting surface and generates a wavelength-converted light by converting the wavelength of incident light that is incident on the incident surface and emits the wavelength-converted light from the emitting surface; and an antenna array including a plurality of antennas that are formed on the wavelength conversion member and arranged at a pitch P, which is equal to the approximate optical wavelength of the wavelength-converted light in the wavelength conversion member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wavelength conversion apparatus and a light source apparatus including the wavelength conversion apparatus.

2. Description of the Related Art

Conventionally, a light source including a light-emitting apparatus and a wavelength conversion apparatus that converts the wavelength of light from the light-emitting apparatus is known as a light source that acquires light with a light-emitting color (or spectrum). For example, the wavelength conversion apparatus includes a fluorescent material as a wavelength conversion member. By mixing the colors from excitation light from the light-emitting apparatus and the fluorescence of the fluorescent material, light with a desired spectrum can be extracted from the light source. For example, Patent Literature 1 (Japanese Patent Application Laid-Open No. 2005-33211) discloses a light source including: a chip with a main light source; and a cap provided with a wavelength conversion material that converts light with a first wavelength from the chip into light with a second wavelength.

SUMMARY OF THE INVENTION

A wavelength conversion apparatus including a wavelength conversion member, such as a fluorescent material, typically has problems in terms of the color and intensity unevenness of light from the wavelength conversion member and light extraction efficiency. For example, light whose wavelength has been converted in a fluorescent material is diffused in all directions. As the refractive index of a fluorescent material is typically high, part of wavelength-converted light is not emitted to the outside due to total reflection and is attenuated or dissipated in the fluorescent material. For example, the refractive index of a YAG:Ce fluorescent material, which is the most commonly used type of white color light source, is approximately 1.82. The total reflection angle is approximately 30° when the external medium is air. Most part of the light are not extracted from inside the fluorescent material. In recent years, by using a light-emitting diode, a semiconductor laser, etc., a wavelength conversion apparatus can readily be irradiated with high-density and high-power light. However, excitation of a wavelength conversion member by high-density and high-power light causes deterioration of the wavelength conversion efficiency of the wavelength conversion member, such as luminance saturation or temperature quenching. Color unevenness (color mixture) or intensity unevenness is thereby generated.

For example, when a lighting device is configured using wavelength-converted light from a wavelength conversion apparatus, an optical system, such as a projection lens, is provided to acquire a desired light distribution. However, the distribution of the wavelength-converted light is lambertian light distribution whereby the light is isotropically diffused from the emitting surface of the wavelength conversion member. To extract a large amount of light, the size of the projection lens need to be increased to increase its weight. This causes an increase in the size of the entire light source apparatus.

The present invention has been made to address the above problems. An object of the present invention is to provide a small-sized wavelength conversion apparatus and light source apparatus that can restrain color unevenness and intensity unevenness and achieve a high level of light extraction efficiency.

A wavelength conversion apparatus according to the present invention includes: a wavelength conversion member having an incident surface and an emitting surface, the wavelength conversion member generating wavelength-converted light by converting a wavelength of incident light that is incident on the incident surface to emit the wavelength-converted light from the emitting surface; and an antenna array including a plurality of antennas that are formed on the wavelength conversion member and arranged at a pitch, which is equal to an approximate optical wavelength of the wavelength-converted light in the wavelength conversion member.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detail.

First Embodiment

FIG. 1is a schematic view illustrating a configuration of a light source apparatus10according to a first embodiment. The light source apparatus10includes a light source12, a wavelength conversion apparatus13, and a projection lens14, all of which are housed in a casing11. In this embodiment, the light source12is a laser light source of, for example, a semiconductor laser. The light source12generates primary light L1. The wavelength conversion apparatus13receives the primary light L1, performs wavelength conversion, and generates secondary light L2containing transmitted light whose wavelength has not been converted and wavelength-converted light. The projection lens14transforms the light distribution of the secondary light L2into a desired form and generates illumination light L3. The illumination light L3is extracted to the outside of the casing11.

The casing11is provided with an opening for fixing the wavelength conversion apparatus13and an opening for fixing the projection lens14. The wavelength conversion apparatus13is disposed between a light-emitting portion of the light source12and the projection lens14. The wavelength conversion apparatus13and the projection lens14are disposed along the optical axis of the primary light L1.

FIG. 2Ais a cross-sectional view of the wavelength conversion apparatus13.FIG. 2Bis a top plan view of the wavelength conversion apparatus13. Also,FIG. 2Ais a cross-sectional view taken along line V-V ofFIG. 2B. As illustrated inFIG. 2A, the wavelength conversion apparatus13includes: a wavelength conversion member20including a fluorescent material plate21and a light reflection film22; and an antenna array30including a plurality of antennas31formed on the wavelength conversion member20.

A description will first be given of the wavelength conversion member20. The wavelength conversion member20includes: an incident surface S1, on which the primary light L1is incident; and an emitting surface S2, from which the secondary light L2is emitted. In this embodiment, the fluorescent material plate21has a flat plate shape. One of the main surfaces is the incident surface S1, and the other main surface is the emitting surface S2. Specifically, the primary light L1is incident on the incident surface S1of the wavelength conversion member20, which is one of the main surfaces of the fluorescent material plate21, and is emitted from the emitting surface S2of the wavelength conversion member20, which is the other main surface of the fluorescent material plate21.

The secondary light L2, which is emitted from the emitting surface S2of the wavelength conversion member20, contains: wavelength-converted light L21, whose wavelength has been converted by the wavelength conversion member20; and transmitted light (i.e. primary light whose wavelength has not been converted) L22that has transmitted through the wavelength conversion member20. Specifically, the wavelength conversion member20converts the wavelength of part of the primary light L1, which has been made incident on the incident surface S1, and generates the wavelength-converted light L21.

In the following description, the primary light L1is sometimes referred to as incident light into the wavelength conversion member20. In other words, the wavelength conversion member20includes the incident surface S1and the emitting surface S2. Also, the wavelength conversion member20is configured to convert the wavelength of the incident light L1, which has been made incident on the incident surface S1, generate the wavelength-converted light L21, and emit the wavelength-converted light L21and the transmitted light L22from the emitting surface S2. In this embodiment, the wavelength conversion member20is disposed so that the incident surface S1thereof is perpendicular to the optical axis of the incident light L1.

In this embodiment, the fluorescent material plate21is a ceramic fluorescent material plate formed from a single phase of yttrium⋅aluminum⋅garnet (YAG:Ce) whose luminescence center is cerium. The light source12is a semiconductor laser whose light-emitting layer is an InGaN-based semiconductor. In this embodiment, the primary light L1is blue light with a wavelength of approximately 450 nm. The wavelength-converted light L21is yellow light with a wavelength of approximately 460 to 750 nm, and the secondary light L2is white light which is a mixture of yellow light and blue light. It is preferable that the fluorescent material plate21have a thickness T of 40 to 200 μm to perform stable whitening of light.

The light reflection film22is disposed on the side surface of the fluorescent material plate21. The light reflection film22is, for example, a white coating material film formed on the side surface of the fluorescent material plate21. The light reflection film22may be replaced with a light absorption film, such as a black coating material.

Hereinbelow, a description will be given of the antenna array30. In this embodiment, the antenna array30includes the plurality of antennas31that are formed on the emitting surface S2of the wavelength conversion member20and are arranged at a pitch P, which is equal to the approximate optical wavelength of the wavelength-converted light L21in the wavelength conversion member20. Each of the plurality of antennas31is a columnar or conical metal protrusion in this embodiment. In this embodiment, each of the plurality of antennas31has a cylindrical shape and includes a material that has a plasma frequency in the visible light region of Au (gold), Ag (silver), Cu (copper), Pt (platinum), Pd (palladium), Al (aluminum), Ni (nickel), or the like, or an alloy or laminate containing these substances.

In this embodiment, the antennas31each have an almost equal antenna height (H) and antenna width (or diameter) W1. When the antenna31has a columnar or conical shape, the antenna width W1 refers to the maximum width of the antenna31. In this embodiment, the plurality of antennas31are arranged at the pitch P in a square lattice shape on the emitting surface S2of the wavelength conversion member20. The antenna array30with an array width of W2 is formed in a square shape at the central portion of the emitting surface S2.

In this embodiment, the antenna width W1 is 150±20 nm, and the array width W2 is 6 mm. The refractive index of the YAG:Ce fluorescent material is approximately 1.82, and the fluorescent material emits light with a wavelength of 460 to 750 nm. Thereby, the optical wavelength is calculated by (light-emitting wavelength/refractive index), and the antenna pitch P ranges preferably from 250 nm to 420 nm. As the light-emitting intensity of the YAG:Ce fluorescent material is high in a wavelength region of 500 nm or greater, the range of the antenna pitch P is set to preferably 300 nm to 420 nm.

When each of the antennas31of the antenna array30is irradiated with light, the electric field intensity increases near the antenna31due to localized surface plasmon resonance on the surface of the antenna31. By setting the arrangement pitch P of the antenna31to the approximate optical wavelength of the wavelength-converted light L21, resonance is induced through optical diffraction due to localized surface plasmon resonance of each of the adjacent antennas31. A further increase in the electric field intensity occurs, and the light extraction efficiency of the wavelength-converted light L21increases. In this description, the approximate optical wavelength of the wavelength-converted light L21in the wavelength conversion member20is, for example, the wavelength bandwidth within 50 nm of the light-emitting wavelength band of the fluorescent material in the fluorescent material plate21.

The wavelength-converted light L21from the wavelength conversion member20is thereby amplified, and the light is distributed in a narrow-angle form (i.e., low etendue) and emitted from the antenna array30. Specifically, the antenna array30intensifies light in the wavelength conversion member20and narrow the direction in which the secondary light L2(wavelength-converted light L21) is emitted.

FIG. 3is a schematic view illustrating the relationship between the light-emitting angle and light-emitting intensity (or luminous intensity) of the wavelength-converted light L21from the wavelength conversion apparatus13.FIG. 3is a view illustrating the intensity distribution of the wavelength-converted light L21when the angle from the center of the antenna array30to the normal direction of the emitting surface S2(front surface direction) of the wavelength conversion member20is set to 0° and the angle of the direction parallel to the emitting surface S2is set to 90°. The wavelength conversion apparatus13was compared with a wavelength conversion apparatus100and a wavelength conversion apparatus200in terms of intensity distribution. The configuration of the wavelength conversion apparatus100is the same as that of the wavelength conversion apparatus13except that the former does not have the antenna array30. The wavelength conversion apparatus200has the same intensity distribution as that of the wavelength conversion apparatus100, the same total luminous flux as that of the wavelength conversion apparatus13, and ordinary lambertian light distribution.

As illustrated inFIG. 3, below approximately 60°, the intensity of the wavelength conversion apparatus13of this embodiment is higher than the intensity of the wavelength conversion apparatus100, which is a comparative example. The total luminous flux, which is calculated from the intensity distribution of the wavelength conversion apparatus13, is approximately twice higher than that of the wavelength conversion apparatus100. Specifically, a large amount of light is extracted from the wavelength conversion member20and travels in a direction near perpendicular to the emitting surface S2. This is caused by the antenna action (i.e., enhanced intensity emission and narrow-angle emission) of the antenna array30using the aforementioned localized surface plasmon resonance and optical diffraction. The total luminous flux of the wavelength conversion apparatus13is the same as that of the wavelength conversion apparatus200. However, the intensity of the former is higher than that of the latter below approximately 45° and twice higher in the front surface direction (0°, i.e. normal direction).

As the wavelength conversion apparatus13has the plurality of antennas31arranged at a nanometer (or submicron) pitch, whereby the wavelength-converted light L21can be distributed in a narrow-angle form (or low etendue) and extracted at a high light extraction efficiency. As in the case of this embodiment, a laser light source is used as the light source13that generates the primary light L1. By taking advantage of the narrow-angle light distribution and high-output characteristics of a laser light source, the primary light L1and secondary light L2(in other words, the wavelength-converted light L21and transmitted light L22, respectively) can be matched in terms of light distribution and intensity distribution. It is thus possible to provide the wavelength conversion apparatus13and light source apparatus10that can suppress color unevenness and intensity unevenness and achieve a high light extraction efficiency.

FIG. 4is a view illustrating the relationship between the light-emitting angle and light intensity of the wavelength conversion apparatus13when the antenna height varies between 50 nm and 250 nm. To create the setting ofFIG. 4, Al is used as a material of the antenna array30, and five wavelength conversion apparatuses13with different antenna heights H are produced so that the height H increases in increments of 50 nm. Between the normal direction (0°) of the emitting surface S2and the direction parallel to the emitting surface S2(90°), optical detectors were disposed at different locations to measure the light intensity at the respective angles. Here, the wavelength of the primary light L1from the light source13was approximately 445 nm, and the antenna array30was produced so that the antenna pitch P was approximately 400 nm, and the antenna width W1 was approximately 150 nm. Although not illustrated in the drawings, the collimate optical system was disposed between the light source12and the wavelength conversion apparatus13. The measured light intensities were plotted on the polar coordinate.

The aspect ratio (H/W1) of the antenna31of each of the wavelength conversion apparatuses13was calculated, and the results are described inFIG. 4. The antenna was produced so that the antenna width W1 was roughly 150 nm, and the actual antenna width W1 was measured using SEM images. The antenna height H was measured using a probe-type step profiler, and it was confirmed that the target antenna heights H (50 nm, 100 nm, 150 nm, 200 nm, and 250 nm) were achieved in the respective antenna arrays30.

As illustrated inFIG. 4, the intensities of all the five wavelength conversion apparatuses13with the antenna array30are greater than that of the wavelength conversion apparatus100without the antenna array30. The three wavelength conversion apparatuses13with the antenna height H ranging from 100 to 200 nm (aspect ratio ranging from approximately 0.6 to 1.4) have intensity distribution greater than those of the wavelength conversion apparatuses with the antenna heights H other than the aforementioned antenna heights H. The aforementioned three wavelength conversion apparatuses13have similar intensity distribution of narrow-angle emission.

A description will next be given of a more preferred configuration of the antenna array30.FIG. 5is a view where the finite element method is used to simulate the electric field intensification (|E|2/|E0|2) near the antenna array30of the wavelength conversion apparatus13. The simulation was conducted for the case where the antenna width W1 was 150 nm and the antenna heights H were 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, and 300 nm (aspect ratio ranging from 0.07 to 2.00). As in the case of the example, a YAG:Ce fluorescent material, Al, and air were used as the fluorescent material plate21, the antenna array30, and the external medium, respectively. Electric field intensification (|E|2/|E0|2) was calculated by setting the electric field intensity of the wavelength conversion apparatus100without the antenna31to E0and the electric field intensity of the wavelength conversion apparatus13with the antenna31to E.

FIG. 5illustrates that the remaining amount of the wavelength-converted light L21increases with an increase in electric field intensification (|E|2/|E0|2) in the fluorescent material plate21(captured by the antenna array30due to localized surface plasmon resonance) and that the wavelength conversion efficiency is enhanced. Electric field intensification in the air is preferably small as it leads to an increase of reflection components that hinders extraction of the wavelength-converted light L21and the transmitted light L22. It is possible to acknowledge that electric field intensification is occurring in the fluorescent material plate21at the antenna height H of 50 nm or higher. When the antenna height H is 100 nm or higher, particularly high electric field intensification was observed near the pole at an end portion of the antenna31on the surface of the fluorescent material plate21. Electric field intensification in the air has been found to be high when the antenna height H is 50 nm and 200 nm or higher.

FIG. 6is a view illustrating the relationship of the aspect ratio (i.e., antenna height H/antenna width W1) of the antenna31and the level of electric field intensification (|E|2/|E0|2) in the fluorescent material plate21calculated in the aforementioned simulation and the reflectance of the antenna array30. The lower horizontal axis ofFIG. 6represents the antenna height H, and the upper horizontal axis represents the aspect ratio.

The right vertical axis ofFIG. 6represents the level of electric field intensification (|E|2/|E0|2), and left vertical axis represents the reflectance of the antenna array30. The level of electric field intensification in the fluorescent material plate21is calculated for the region near the pole of the antenna array30, which particularly substantially affects the wavelength conversion efficiency and light extraction efficiency. Specifically, the level of electric field intensification was surveyed for the region of the fluorescent material plate21from the surface of the fluorescent material plate21to a depth of 50 nm from the surface. The reflectance of the antenna array30is calculated from the integrated value of the level of electric field intensification in the air.

As illustrated inFIG. 6, the level of electric field intensification near the pole of the antenna array30, specifically, the wavelength conversion efficiency and light extraction efficiency of the wavelength conversion apparatus13, also have correlation to the aspect ratio of the antenna31. Specifically, as illustrated inFIG. 6, when the antenna width W1 is 150 nm and the antenna height H ranges from 50 nm to 200 nm, the level of electric field intensification (|E|2/|E0|2) of the antenna31is well above 1.0. Thus, the electric field intensification effect of the antenna array30can be seen.

FIG. 6illustrates that the level of electric field intensification and reflectance at the antenna height of 50 nm, or the aspect ratio (H/W1) of 0.33, are the same as those at the antenna height of 200 nm, or the aspect ratio (H/W1) of 1.33. However, in the example, as can be seen inFIG. 4, the level of electric field intensification or light extraction efficiency achieved by the wavelength conversion apparatus13with the antenna height H of 200 nm is higher than that of the wavelength conversion apparatus13with the antenna height H of 50 nm. This is probably because, as illustrated inFIG. 5, the level of electric field intensification converged near the pole at an end portion of the antenna31is greater when the antenna height H is 200 nm than when the antenna height H is 50 nm. Specifically, (local) convergence of a high level of electric field intensification near the pole of the antenna31is likely to contribute to enhancement of the light extraction efficiency using optical diffraction. On the basis of the foregoing results, the preferable range of the antenna height H is between 100 nm and 200 nm.

As illustrated inFIG. 6, it is preferable that the antenna width W1 and the antenna height H of the antenna31satisfy a relationship of 0.6≤(H/W1)≤1.4. The aspect ratio of 1 is particularly preferable as the level of electric field intensification is maximum and the reflectance is minimum. This may be because, when the aspect ratio of the antenna31is 1, resonance induced by optical diffraction due to localized surface plasmon resonance of each of the adjacent antennas31is maximum, and the level of electric field intensification in the fluorescent material plate21increases and converges near the pole of the antenna31.

In other words, the wavelength conversion efficiency and light extraction efficiency of the wavelength conversion apparatus13depend on the aspect ratio of the antenna31. By optimizing the configuration of the antenna31on the basis of this aspect ratio (H/W1), a high level of wavelength conversion efficiency and light extraction efficiency can be achieved.

When the light source apparatus10is used as a lighting device, it is preferable that a material used in the antenna31have a plasma frequency of localized surface plasmon resonance in the light-emitting wavelength range of a fluorescent material to be used. In view of the foregoing, it is preferable that the antenna31using a YAG:Ce fluorescent material be formed from Ag (silver) or Al (aluminum).

In this embodiment, the case where the antennas31are arranged in a square lattice form has been described, but the arrangement of the antennas31is not limited to this form. The antennas31may be arranged at a certain pitch and in the form of, for example, triangular, hexagonal, or rectangular lattice. For example, in a rectangular lattice form, i.e., when the antennas31have different pitches P and Q in a plurality of directions (for example, x and y direction orthogonal to each other) on the emitting surface S2of the wavelength conversion member20, the pitches P and Q are preferably equal to the approximate optical wavelength of the secondary light L2in the wavelength conversion member20.

FIG. 7is a top plan view of a wavelength conversion apparatus13A of a light source apparatus10A according to a modified example of the aforementioned embodiment. As illustrated inFIG. 7, the wavelength conversion apparatus13A has an antenna array30A that includes a plurality of antennas31A arranged in a triangular lattice form at the pitch P. The antennas31A may be arranged in a triangular lattice form as in the case of this modified example. In this modified example, the antennas31A are arranged at the pitch P in all the three directions.

FIGS. 8 to 10illustrate the light distribution of the wavelength conversion apparatus13or13A, in which the antenna pitch P is different in each case.FIG. 8illustrates the light distribution when the wavelength conversion apparatus13A has the antennas31A in a triangular lattice form and the pitch P is 350 nm.FIG. 9illustrates the light distribution when the wavelength conversion apparatus13A has the antennas31A in a triangular lattice form and the pitch P is 400 nm.FIG. 10illustrates the light distribution when the wavelength conversion apparatus13has the antennas31in a square lattice form and the pitch P is 350 nm. In each case, the wavelength conversion apparatus13or13A was produced in the same configuration as that of the aforementioned embodiment or its modified example except for the antenna arrangement and the pitch P. In each case, the form of light distribution was different, but the wavelength conversion efficiency and light extraction efficiency were relatively high in the range of 0.6≤(H/W1)≤1.4 in all the cases. These two types of efficiency have been confirmed to be most preferable when H/W1=1 holds true.

When the antenna width W1 is smaller than 100 nm, it is too small for visible light, and a sufficient increase in the wavelength conversion efficiency cannot be therefore expected. The antenna width W1 is preferably greater than or equal to 100 nm. More preferably, the relationship between the antenna width W1 and the pitch P is represented by 0.3P≤W1≤0.7P. When the antenna width W1 is smaller than the above range, the scattering cross section due to the antenna array30is small, and sufficiently strong localized surface plasmon resonance cannot be acquired. When the antenna width W1 is greater than the above range, the occupation area of the antenna array30on the emitting surface S2increases. A greater percentage of the incident light L1and the wavelength-converted light L2is absorbed by the antenna array30, and the light extraction efficiency decreases.

In this embodiment, the case where the fluorescent material plate21is formed from a single phase yttrium⋅aluminum⋅garnet (YAG:Ce) has been described. However, the fluorescent material plate21may be a plate, for example, whose medium is a glass or resin containing a fluorescent material particle. The aforementioned shape of the fluorescent material plate21is simply one example. The case of disposing the light reflection film22on the side surface of the fluorescent material plate21has been described. However, the light reflection film22does not need to be disposed depending on the required light distribution. For example, in addition to the white color coating material described in this embodiment, an optical multi-layer reflective film, a metal reflective film, or a combination thereof may be used to form a reflective member.

In this embodiment, the incident surface S1of the wavelength conversion apparatus13is configured so that the fluorescent material plate21is exposed. However, the configuration of the incident surface S1is not limited to the aforementioned configuration. For example, to enhance the efficiency of incidence of the primary light L1into the fluorescent material plate21, a reflection prevention film (AR coat) or uneven structure may be formed on the surface of the incident surface S1of the fluorescent material plate21. The antenna array30radiates the wavelength-converted light L21in a narrow angle to the side of the incident surface S1. Specifically, the wavelength-converted light L21, whose light distribution is the same as that illustrated inFIG. 5, is radiated from the emitting surface S2to the incident surface S1with the emitting surface S2being a symmetric surface. An optical multi-layer reflective film (dichroic mirror) that transmits the primary light L1and selectively reflects the wavelength-converted light L21that is directed to the incident surface S1can be formed on the incident surface S1, so that the efficiency of the wavelength conversion apparatus13can be further enhanced.

In this embodiment, the case where the light source12is a laser light source has been described, but the light source12is not limited to a laser light source. For example, the light source12may be a light-emitting diode. Various types of optical systems, such as the collimate and condensing optical systems, may be disposed between the light source12and the wavelength conversion apparatus13. By disposing and combining optical systems, the light distribution of the primary light L1can be formed in a desired shape. The efficiency of incidence of the primary light L1into the fluorescent material plate21can also be enhanced, and the light distribution of the secondary light L2(transmitted light L22) can also be made as identical as possible to that of the wavelength-converted light L21to further reduce color unevenness. The aforementioned configuration of the light source apparatus10is simply one example. The light source apparatus10may not have to have the projection lens14and may have, on the casing11, an opening for extracting the secondary light L2to the outside.

In this embodiment, the antenna array30is formed on the emitting surface S2of the fluorescent material plate21, but the antenna array30may be formed on the side of the incident surface S1. However, it is preferable to form the antenna array30on the emitting surface S2. Specifically, the antenna array30partially reflects and absorbs the primary light L1(transmitted light L22). When the antenna array30is formed on the incident surface S1, the primary light L1is partially reflected and absorbed prior to be incident on the fluorescent material plate21, and the efficiency of the light source apparatus10decreases. As in the case of the embodiment, it is preferable that the antenna array30be formed on the emitting surface S2of the fluorescent material plate21so that the wavelength of the primary light L1is sufficiently converted and the secondary light L2is radiated via the emitting surface S2and the antenna array30.

To protect the antenna array30from damage and enhance the stability of the shape thereof, the antenna array30and the emitting surface S2may be covered with a protective film, such as an oxide film. For example, when Al is used in the antenna array30, by means of heating and being left to stand in an oxygen-containing atmosphere, an oxide film (Al2O3) can be readily formed on the surface of the antenna31. The thickness of the formed oxide film is 1 nm or smaller, and a protective film can be formed without adversely affecting the optical properties of the antenna array30.

In this embodiment, the incident surface S1is a surface opposite to the emitting surface S2of the fluorescent material plate21, but any surface of the fluorescent material plate21may be the incident surface S1. Specifically, the primary light L1may be incident on any surface of the fluorescent material plate21, such as the side surface, incident surface S1, or emitting surface S2, or a plurality of surfaces thereof. In any case, an opening of the light source apparatus10or the projection lens14is disposed on the normal line of the emitting surface S2. A single surface may be used as both the incident surface S1and the emitting surface S2. In such a case, it is preferable to form a reflective film on the surface opposite to the incident surface S1and the emitting surface S2of the fluorescent material plate21.

As described above, in this embodiment, the wavelength conversion apparatus13includes: the wavelength conversion member20that has the incident surface S1and the emitting surface S2and generates the wavelength-converted light L21by converting the wavelength of the incident light L1that is incident on the incident surface S1and emits the wavelength-converted light L21from the emitting surface S2; and the antenna array30including the plurality of antennas31that are formed on the wavelength conversion member20and arranged at the pitch P, which is equal to the approximate optical wavelength of the wavelength-converted light L21in the wavelength conversion member20. It is possible to provide the light source apparatus10and wavelength conversion apparatus13that can restrain color and intensity unevenness and achieve a high level of light extraction efficiency with low etendue.

This application is based on a Japanese Patent Application No. 2016-144215 which is hereby incorporated by reference.