Wavelength conversion element, light source apparatus, and projector

A wavelength conversion element according to an aspect of the invention includes a first wavelength conversion layer that has a first light incident surface on which excitation light is incident and a first light exiting surface facing away from the first light incident surface and emits first fluorescence, a second wavelength conversion layer that has a second light incident surface on which at least the first fluorescence is incident and emits second fluorescence, and a substrate that has a first surface and a second surface facing away from the first surface and includes a light transmitting portion that transmits at least the first fluorescence. The first wavelength conversion layer is so provided that the first light exiting surface faces the first surface of the substrate, and the second wavelength conversion layer is so provided that the second light incident surface faces the second surface of the substrate.

BACKGROUND

1. Technical Field

The present invention relates to a wavelength conversion element, a light source apparatus, and a projector.

2. Related Art

As a light source apparatus used in a projector, there has been a proposed light source apparatus using fluorescence emitted from a phosphor irradiated with excitation light outputted from a light emitting device, such as a semiconductor laser. In a light source apparatus of this type, however, the wavelength band to which the fluorescence belongs is determined by the phosphor material to be used. Therefore, fluorescence having a desired color tone is not produced in some cases. To solve the problem, there has been a proposed light source apparatus including a plurality of types of phosphor material that emit light fluxes that belong to wavelength bands different from one another.

For example, JP-A-2016-062012 discloses a light source apparatus including a red light source apparatus, a blue light source apparatus, and a green light source apparatus that includes a phosphor plate having a green phosphor layer and a cyan phosphor layer layered on one surface of a substrate. JP-A-2016-062012 describes that in the light source apparatus, fluorescence that belongs to the cyan wavelength band can adjust the color tone of fluorescence that belongs to the green wavelength band to a color tone shifted toward the shorter wavelength side.

In the light source apparatus described in JP-A-2016-062012, the two phosphor layers that emit light fluxes that belong to wavelength bands different from each other are layered on one surface of the substrate. Therefore, heat dissipation from the two phosphor layers is insufficient, resulting in a decrease in the wavelength conversion efficiency of each of the phosphor layers, and the color gamut of the light outputted from the light source apparatus could therefore change. The light source apparatus cannot therefore undesirably output light having a desired color gamut in a stable manner.

SUMMARY

An advantage of some aspects of the invention is to provide a wavelength conversion element capable of stably outputting light having a desired color gamut. Another advantage of some aspects of the invention is to provide a light source apparatus including the wavelength conversion element described above. Another advantage of some aspects of the invention is to provide a projector including the light source apparatus described above.

A wavelength conversion element according to an aspect of the invention includes a first wavelength conversion layer that has a first light incident surface on which excitation light that belongs to a first wavelength band is incident and a first light exiting surface facing away from the first light incident surface and emits first fluorescence that belongs to a second wavelength band different from the first wavelength band, a second wavelength conversion layer that has a second light incident surface on which at least the first fluorescence is incident and emits second fluorescence that belongs to a third wavelength band different from the first and second wavelength bands, and a substrate that has a first surface and a second surface facing away from the first surface and includes a light transmitting portion that transmits at least the first fluorescence. The first wavelength conversion layer is so provided that the first light exiting surface faces the first surface of the substrate, and the second wavelength conversion layer is so provided that the second light incident surface faces the second surface of the substrate.

In the wavelength conversion element according to the aspect of the invention, a wavelength conversion efficiency of the second wavelength conversion layer may be lower than a wavelength conversion efficiency of the first wavelength conversion layer.

In the wavelength conversion element according to the aspect of the invention, an amount of the second fluorescence emitted from the second wavelength conversion layer may be greater than an amount of the first fluorescence emitted from the first wavelength conversion layer.

In the wavelength conversion element according to the aspect of the invention, a first air layer may be provided between the first light exiting surface of the first wavelength conversion layer, which is the surface opposite the first light incident surface thereof, and the first surface of the substrate.

In the wavelength conversion element according to the aspect of the invention, a second air layer may be provided between the second light incident surface of the second wavelength conversion layer and the second surface of the substrate.

A light source apparatus according to another aspect of the invention includes the wavelength conversion element according to the aspect of the invention described above and a light source that outputs the excitation light toward the wavelength conversion element.

A projector according to another aspect of the invention includes the light source apparatus according to the aspect of the invention described above, a light modulator that modulates light from the light source apparatus in accordance with image information to form image light, and a projection optical apparatus that projects the image light.

In the projector according to the aspect of the invention described above, the first or second surface of the substrate corresponding to the light transmitting portion may have a light diffusing surface that diffuses the excitation light, the first fluorescence, or the second fluorescence.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Embodiment

A first embodiment of the invention will be described below with reference toFIGS. 1 to 4.

In the following drawings, components are drawn at different dimensional scales in some cases for clarity of each of the components.

FIG. 1is a schematic configuration diagram of a projector1000according to the present embodiment.

The projector1000includes an illuminator100, a color separation/light guide system200, a light modulator400R, a light modulator400G, a light modulator400B, a cross dichroic prism500, and a projection optical apparatus600, as shown inFIG. 1.

The illuminator100includes a light source apparatus80, a pickup system60, a first lens array120, a second lens array130, a polarization conversion element140, and a superimposing lens150. The light source apparatus80includes a light source10, a collimation system20, a light collection system70, and a wavelength converter30. The light source apparatus80includes a light source10, a collimation system20, a light collection system70, and a wavelength conversion element30.

The light source10emits blue light B. Although will be described later in detail, the wavelength converter30converts part of the blue light B outputted from the light source10into yellow fluorescence Y and red fluorescence R and outputs the yellow fluorescence Y and red fluorescence R along with the remainder of the blue light B. The light source apparatus80thus outputs white light as a whole.

The light source10includes a plurality of semiconductor lasers15. The semiconductor lasers15each emit blue light B that belongs to a first wavelength band having, for example a peak wavelength of 455 nm at which the intensity of the blue light B peaks. The first wavelength band ranges, for example, from 450 to 480 nm. The semiconductor lasers15may instead each emit blue light B having a peak wavelength other than 455 nm, for example, blue light B having a peak wavelength of 462 nm. The semiconductor lasers15do not necessarily each emit the blue light B and may instead each emit ultraviolet light. The light source10does not necessarily include the semiconductor lasers15and may instead include solid-state light sources, such as light emitting diodes.

The following description uses an orthogonal coordinate system in which the direction of the principal ray of the blue light B is a direction z and the directions perpendicular to each other in a plane perpendicular to the direction z are directions x and y.

The plurality of semiconductor lasers are arranged in a two-dimensional array with the semiconductor lasers separate from each other by a predetermined distance in the directions x and y.

In the present embodiment, the plurality of semiconductor lasers15are arranged in an array formed of four rows and four columns in an xy plane. That is, the array of the plurality of semiconductor lasers15has four semiconductor laser columns15R arranged in the direction x. The semiconductor laser columns15R each have four semiconductor lasers15arranged in the direction y. The number of semiconductor lasers15is, however, not limited to a specific number.

The semiconductor lasers15each have a light exiting surface15a, through which the light is emitted. The light exiting surface15ahas a roughly rectangular shape having a longitudinal direction and a lateral direction in a plan view viewed in the direction z. In the present embodiment, the longitudinal direction of the light exiting surface is parallel to the direction x, and the lateral direction of the light exiting surface is parallel to the direction y.

The blue light B outputted from each of the semiconductor lasers15is formed of linearly polarized light, for example, having a polarization direction parallel to the longitudinal direction of the light exiting surface. The angle of divergence of the blue light B in the lateral direction of the light exiting surface is greater than the angle of divergence of the blue light B in the longitudinal direction of the light exiting surface. The cross-sectional shape of the blue light B in an xy plane is therefore an elliptical shape having a longitudinal direction that coincides with the direction y and a lateral direction that coincides with the direction x.

Although not shown inFIG. 1, the semiconductor lasers15are mounted on a base substrate. The base substrate is desirably made of a metal having high thermal conductivity, such as copper, to effectively dissipate heat generated by the semiconductor lasers15. The semiconductor lasers15may instead be mounted on the base substrate via a sub-mount. Further, a heat sink or any other cooler may be provided on a surface of the base substrate that is the surface opposite the semiconductor laser mounting surface.

The collimation system20includes a plurality of collimator lenses21arranged in a two-dimensional array in correspondence with the arrangement of the plurality of semiconductor lasers15. The collimator lenses21are each formed of a convex lens. The light beam flux emitted from each of the plurality of semiconductor lasers15is parallelized when passing through the corresponding one of the plurality of collimator lenses21, which form the collimation system20.

The light collection system70collects the blue light B having exited out of the collimation system20and causes the collected blue light B to enter a wavelength conversion element45. The light collection system70includes a first lens72and a second lens74. The first lens72and the second lens74are each formed of a convex lens.

FIG. 2is a perspective view of the wavelength converter30in the present embodiment.FIG. 3is a plan view of the wavelength converter30viewed from the light exiting side.FIG. 4is a cross-sectional view of the wavelength conversion element45taken along the line IV-IV inFIG. 3.

The wavelength converter30includes the wavelength conversion element45and a motor50, which rotates the wavelength conversion element45, as shown inFIGS. 2 to 4. The wavelength conversion element45includes a substrate38, a first phosphor layer41, and a second phosphor layer42. The wavelength converter30outputs the white light W toward the side opposite the side on which the blue light B is incident. That is, the wavelength conversion element45provided in the wavelength converter30is a transmissive wavelength conversion element.

The substrate38rotates around a rotary shaft51when the motor50is driven. The substrate38has a circular shape when the wavelength conversion element45is viewed in the direction in which the rotary shaft51extends (direction z). The substrate38is made of a material that transmits the blue light B and first fluorescence Y, which will be described later. The material of the substrate38can, for example, be optical glass, quartz glass, sapphire glass, crystallized quartz, or transparent resin. Reflection suppression layer may be provided on at least one of a first surface38aand a second surface38bof the substrate38.

Since the blue light B formed of laser beams is incident on the wavelength conversion element45, heat is generated in the first phosphor layer41and the second phosphor layer42. In the present embodiment, rotating the wavelength conversion element45with the motor50allows the position where the blue light B is incident on the first phosphor layer41and the second phosphor layer42to change over time. The rotation of the wavelength conversion element45avoids a situation in which the blue light B keeps impinging on the same position on the first phosphor layer41and the second phosphor layer42so that the first phosphor layer41and the second phosphor layer42are locally heated. InFIG. 3, the circle labeled with the reference character T represents the position on which the blue light B is incident.

The first phosphor layer41and the second phosphor layer42each have a circular-ring-like shape having an opening42haround the axis of rotation51, as shown inFIG. 3. That is, the first phosphor layer41is so provided on the first surface38aof the substrate38as to surround the axis of rotation51. The second phosphor layer42is so provided on the second surface38bof the substrate38as to surround the axis of rotation51. The width W1of the first phosphor layer41in the radial direction of the substrate38is roughly equal to the width W2of the second phosphor layer42in the radial direction. Therefore, when the wavelength conversion element45is viewed in the direction in which the axis of rotation51(direction z), the outer shape of the first phosphor layer41roughly coincides with the outer shape of the second phosphor layer42.

The first phosphor layer41has a first light incident surface41a, on which the blue light B (excitation light) is incident, which belongs to the first wavelength band, and a first light exiting surface41b, through which the first fluorescence Y, which belongs to a second wavelength band different from the first wavelength band, and the blue light B that has not been used to excite the first phosphor layer41exit, as shown inFIG. 4. The first phosphor layer41is so provided that the first light exiting surface41bfaces the first surface38aof the substrate38. In the present embodiment, the second wavelength band to which the first fluorescence Y belongs ranges, for example, from about 480 to 700 nm (peak wavelength is about 540 nm), and the first fluorescence Y emitted from the first phosphor layer41is yellow light.

The first phosphor layer41is formed, for example, of a YAG-based phosphor made of (Y1−x, Gdx)3(Al, Ga)5O12(0≤x≤1), in which Ce is dispersed as an activator (Ce:YAG). The yellow phosphor may be formed of the Ce:YAG phosphor in the form of bulk or may be formed of phosphor particles formed of the Ce:YAG phosphor and a binder.

The second phosphor layer42emits second fluorescence R, which belongs to a third wavelength band different from the first and second wavelength bands. The second phosphor layer42has a second light incident surface42a, on which at least the first fluorescence Y is incident. In the present embodiment, the second phosphor layer42has the second light incident surface42a, on which the blue light B and the first fluorescence Y are incident, and a second light exiting surface42b, through which the blue light B, the first fluorescence Y, and the second fluorescence R exit. The second phosphor layer42is so provided that the second light incident surface42afaces the second surface38bof the substrate38. In the present embodiment, the third wavelength band ranges, for example, from about 500 to 800 nm (peak wavelength is about 610 nm), and the second fluorescence R emitted from the second phosphor layer42is red light.

The second phosphor layer42is formed of a YAG-based phosphor made, for example, of (Y1−x, Gdx)3(Al, Ga)5O12in which any of Pr, Eu, and Cr is dispersed as an activator (any of Pr:YAG, Eu:YAG, and Cr:YAG). The activator may be one type selected from Pr, Eu, and Cr or may be a co-activator containing a plurality of types selected from Pr, Eu, and Cr. The red phosphor may be formed of the phosphor described above in the form of bulk or may be formed of phosphor particles made of the phosphor described above and a binder, as in the case of the yellow phosphor.

The first phosphor layer41and the second phosphor layer42are so provided that the first light exiting surface41band the second light incident surface42aface each other with the substrate38interposed therebetween. In the present embodiment, the substrate38is made entirely of a light transmissive material that transmits the blue light B and the first fluorescence Y, such as quartz glass, and the entire area of the substrate38functions as a light transmitting portion that transmits the blue light B and the first fluorescence Y. In place of the configuration in the present embodiment, out of the entire area of the substrate38, only the area where the first phosphor layer41and the second phosphor layer42face each other may be made of a light transmissive material that transmits the blue light B and the first fluorescence Y, and only the area may function as the light transmitting portion.

The wavelength conversion efficiency of the second phosphor layer42, which emits the second fluorescence R, which is red fluorescence, is lower than the wavelength conversion efficiency of the first phosphor layer41, which emits the first fluorescence Y, which is yellow fluorescence.

In the wavelength conversion element45, part of the blue light B having entered the first phosphor layer41as the excitation light is converted in terms of wavelength by the first phosphor layer41into the first fluorescence Y. The remainder of the blue light B passes through the first phosphor layer41. The remainder of the blue light B and the first fluorescence Y thus exit out of the first phosphor layer41. Part of the blue light B having entered the second phosphor layer42as the excitation light is converted in terms of wavelength by the second phosphor layer42into the second fluorescence R. The remainder of the blue light B and the first fluorescence Y pass through the second phosphor layer42. The remainder of the blue light B, the first fluorescence Y, and the second fluorescence R thus exit out of the second phosphor layer42.

The pickup system60includes a first pickup lens62and a second pickup lens64, as shown inFIG. 1. The pickup system60roughly parallelizes the light having exited out of the wavelength conversion element30and outputs the resultant light toward the downstream optical system. The first pickup lens62and the second pickup lens64are each formed of a convex lens.

The first lens array120includes a plurality of first lenses122. The first lens array120divides the light having exited out of the pickup system60into a plurality of sub-light fluxes. The plurality of first lenses122are arranged in a matrix in a plane perpendicular to an illumination optical axis100ax.

The second lens array130includes a plurality of second lenses132corresponding to the plurality of first lenses122of the first lens array120. The second lens array130, along with the superimposing lens150, forms images of the first lenses122of the first lens array120in the vicinity of image formation areas of the light modulators400R,400G, and400B. The plurality of second lenses132are arranged in a matrix in a plane perpendicular to the illumination optical axis100ax.

The polarization conversion element140converts each of the plurality of divided sub-light fluxes from the first lens array120into linearly polarized light. The polarization conversion element140has polarization separation layers that directly transmit one linearly polarized light component of the polarized light components contained in the light having exited out of the wavelength conversion element30and reflects another linearly polarized light component in the direction perpendicular to the illumination optical axis100ax, reflection layers that reflect the other linearly polarized light component reflected off the polarization separation layers in the direction parallel to the illumination optical axis100ax, and retardation films that convert the other linearly polarized light component reflected off the reflection layers into the one linearly polarized light component.

The superimposing lens150superimposes the plurality of sub-light fluxes having exited out of the polarization conversion element140on one another in the vicinity of the image formation areas of the light modulators400R,400G, and400B. The first lens array120, the second lens array130, and the superimposing lens150form an optical integration system that homogenizes the intensity distribution of the light from the wavelength conversion element30in the image formation areas.

The color separation/light guide system200includes dichroic mirrors210and220, reflection mirrors230,240, and250, and relay lenses260and270. The color separation/light guide system200separates the light outputted from the illuminator100into red light LR, green light LG, and blue light LB and guides the red light LR, the green light LG, and the blue light LB to the corresponding light modulators400R,400G, and400B.

Alight collection lens300R is disposed between the color separation/light guide system200and the light modulator400R. A light collection lens300G is disposed between the color separation/light guide system200and the light modulator400G. A light collection lens300B is disposed between the color separation/light guide system200and the light modulator400B.

The dichroic mirror210transmits the red light component and reflects the green light component and the blue light component. The dichroic mirror220reflects the green light component and transmits the blue light component.

The red light LR having passed through the dichroic mirror210is reflected off the reflection mirror230, passes through the light collection lens300R, and is incident on the image formation area of the light modulator400R for red light. The green light LG reflected off the dichroic mirror210is further reflected off the dichroic mirror220, passes through the light collection lens300G, and is incident on the image formation area of the light modulator400G for green light. The blue light LB having passed through the dichroic mirror220travels via the relay lens260, the reflection mirror240, the relay lens270, the reflection mirror250, and the light collection lens300B and is incident on the image formation area of the light modulator400B for blue light.

The light modulators400R,400G, and400B modulate the color light fluxes incident thereon in accordance with image information to form image light fluxes. The light modulators400R,400G, and400are each formed of a transmissive liquid crystal panel. Although not shown, light-incident-side polarizers are disposed between the light collection lens300R and the light modulator400R, between the light collection lens300G and the light modulator400G, and between the light collection lens300B and the light modulator400B. Light-exiting-side polarizers are disposed between the light modulators400R,400G,400B and the cross dichroic prism500.

The cross dichroic prism500combines the image light fluxes outputted from the light modulators400R,400G, and400B with one another. The cross dichroic prism500has a configuration in which four right-angle prisms are bonded to each other. Dielectric multilayer films are formed on the roughly X-letter-shaped interfaces between the bonded right-angle prisms.

The color image having exited out of the cross dichroic prism500is enlarged and projected by the projection optical apparatus600and forms an image on a screen SCR.

To adjust the color tone of emitted fluorescence, a wavelength conversion element made of a plurality of types of phosphor materials that emit light fluxes that belong to different emitted light wavelength bands has been proposed. In the wavelength conversion element of related art, however, two phosphor layers that emit light fluxes that belong to different wavelength bands are layered on one surface of a substrate, and heat generated in the phosphor layer that is not in direct contact with the substrate is transferred to the substrate via the phosphor layer that is indirect contact with the substrate. Therefore, heat dissipation from the phosphor layer that is not in direct contact with the substrate is particularly insufficient, resulting in a decrease in the wavelength conversion efficiency of the phosphor layer, and the color gamut of the light outputted from the light source apparatus could therefore change.

To avoid the problem, in the wavelength conversion element45according to the present embodiment, the two phosphor layers41and42are not layered on one surface of the substrate38, but the first phosphor layer41is so provided as to face the first surface38aof the substrate38, and the second phosphor layer42is so provided as to face the second surface38bof the substrate38. Therefore, in the wavelength conversion element45, the heat generated in each of the phosphor layers41and42is more likely to be transferred to the substrate38than in the wavelength conversion element of related art. The thus configured wavelength conversion element45can suppress a decrease in the wavelength conversion efficiency in each of the phosphor layers41and42and can therefore stably emit light having a desired color gamut.

Further, in the wavelength conversion element45according to the present embodiment, not only are the phosphor layers41and42provided on the surfaces38aand38bof the substrate38, respectively, but the first phosphor layer41is provided on the first surface38aof the substrate38(side on which blue light B is incident) and second phosphor layer42is provided on the second surface38bof the substrate38(side via which blue light B exits), whereby the following actions and effects are provided.

In a phosphor layer, a large amount of heat is generated in the vicinity of the excitation light incident surface. In a case where excitation light fluxes having the same intensity are incident on two phosphor layers having different wavelength conversion efficiencies, heat generated in the phosphor layer having a relatively low wavelength conversion efficiency is greater than heat generated in the phosphor layer having a relatively high wavelength conversion efficiency.

In the wavelength conversion element45according to the present embodiment, in which the wavelength conversion efficiency of the second phosphor layer42is lower than the wavelength conversion efficiency of the first phosphor layer41, the largest amount of heat is generated in the vicinity of the second light incident surface42aof the second phosphor layer42. However, since the second light incident surface42aof the second phosphor layer42is in contact with the second surface38bof the substrate38, the distance from the location where the heat is generated to the substrate38is short, and a large amount of heat generated in the vicinity of the second light incident surface42aof the second phosphor layer42is likely to be transferred to the substrate38. Therefore, the wavelength conversion element45according to the present embodiment can suppress a decrease in the overall wavelength conversion efficiency of the two phosphor layers41and42and stably emit white light having a desired color gamut.

As described above, the wavelength conversion element45according to the present embodiment can add a red tone of the second fluorescence R from the second phosphor layer42to the color tone of the first fluorescence Y from the first phosphor layer41made of a yellow phosphor material typically having an insufficient amount of red light component.

The light source apparatus80according to the present embodiment, which includes the wavelength conversion element45capable of suppressing the wavelength conversion efficiency in each of the phosphor layers41and42, can stably emit white light having a desired color gamut.

The projector1000according to the present embodiment, which includes the light source apparatus80capable of stably emitting white light having a desired color gamut, can display a high-luminance, wide-color-gamut image.

Second Embodiment

A second embodiment of the invention will be described below with reference toFIG. 5.

The configurations of a projector and a light source apparatus according to the second embodiment are the same as those in the first embodiment, and the configuration of the wavelength conversion element differs from that in the first embodiment. No overall description of the projector and the light source apparatus will therefore be made.

FIG. 5is a cross-sectional view of a wavelength conversion element according to the second embodiment. The cross-sectional view corresponds to the cross section taken along the line IV-IV inFIG. 3.

InFIG. 5, components common to those in the drawings used in the first embodiment have the same reference characters and will not be described.

A wavelength conversion element65according to the present embodiment includes the substrate38, a first phosphor layer44, and a second phosphor layer47, as shown inFIG. 5.

The first phosphor layer44has a first light incident surface44a, on which ultraviolet light UV (excitation light), which belongs to a first wavelength band, is incident and a first light exiting surface44b, through which first fluorescence DB, which belongs to a second wavelength band different from the first wavelength band is emitted. The first phosphor layer44is so provided that the first light exiting surface44bfaces the first surface38aof the substrate38. In the present embodiment, the first wavelength band ranges, for example, from about 360 to 400 nm. The second wavelength band ranges, for example, from about 460 to 465 nm and has a peak wavelength of 462 nm, and the first fluorescence DB emitted from the first phosphor layer44is blue light.

The first phosphor layer44is formed of a blue phosphor material, for example, Sr10(PO4)6Cl2:Eu or (Sr, Ba, Ca)10(PO4)6Cl2:Eu, in which Eu is dispersed as an activator.

The second phosphor layer47emits second fluorescence Y, which belongs to a third wavelength band different from the first and second wavelength bands. The second phosphor layer47has a second light incident surface47a, on which at least the first fluorescence DB is incident. In the present embodiment, the second phosphor layer47has the second light incident surface47a, on which the first fluorescence DB are incident, and a second light exiting surface47b, through which the first fluorescence DB and the second fluorescence Y are emitted. The second phosphor layer47is so provided that the second light incident surface47afaces the second surface38bof the substrate38. In the present embodiment, the third wavelength band ranges, for example, from about 480 to 700 nm, and the second fluorescence Y emitted from the second phosphor layer47is yellow light.

The second phosphor layer47is formed, for example, of a YAG-based phosphor made of (Y1−x, Gdx)3(Al, Ga)5O12(0≤x≤1), in which Ce is dispersed as an activator (Ce:YAG), as the first phosphor layer41in the first embodiment. The second phosphor layer47may instead be made of a phosphor material having a wavelength conversion efficiency higher than the wavelength conversion efficiency of the phosphor material used to form the first phosphor layer41in a case where the second phosphor layer47is excited with the first fluorescence DB having the peak wavelength of 462 nm.

The amount of second fluorescence Y emitted from the second phosphor layer47is greater than the amount of first fluorescence DB emitted from the first phosphor layer44.

In the wavelength conversion element65, part of the ultraviolet light UV having entered the first phosphor layer44as the excitation light is converted in terms of wavelength by the first phosphor layer44into the first fluorescence DB. The first fluorescence DB thus exits out of the first phosphor layer44. The remainder of the ultraviolet light UV may exit along with the first fluorescence DB out of the first phosphor layer44. Part of the first fluorescence DB having entered the second phosphor layer47as the excitation light is converted in terms of wavelength by the second phosphor layer47into the second fluorescence Y. The remainder of the first fluorescence DB and the second fluorescence Y thus exit out of the second phosphor layer47.

Also in the wavelength conversion element65according to the present embodiment, in which the first phosphor layer44is provided on the first surface38aof the substrate38and the second phosphor layer47is provided on the second surface38bof the substrate38, the heat generated in each of the phosphor layers44and47is more likely to be transferred to the substrate38than in the wavelength conversion element of related art. The thus configured wavelength conversion element65can suppress a decrease in the wavelength conversion efficiency in each of the phosphor layers44and47and can therefore stably emit light having a desired color gamut.

Further, in the wavelength conversion element65according to the present embodiment, not only are the phosphor layers44and47provided on the surfaces38aand38bof the substrate38, respectively, but the first phosphor layer44is provided on the first surface38aof the substrate38(side on which first fluorescence DB is incident) and the second phosphor layer47is provided on the second surface38bof the substrate38(side via which first fluorescence DB exits), whereby the following actions and effects are provided.

A phosphor layer that emits a relatively large amount of fluorescence generates a larger amount of heat than the heat generated by a phosphor layer that emits a relatively small amount of fluorescence. In the wavelength conversion element65according to the present embodiment, in which the amount of second fluorescence Y emitted from the second phosphor layer47is greater than the amount of first fluorescence DB emitted from the first phosphor layer44in consideration of the white balance of the white light, a larger amount of heat is generated in the vicinity of the second light incident surface47aof the second phosphor layer47. Since the second light incident surface47aof the second phosphor layer47is so provided as to face the second surface38bof the substrate38, the large amount of heat generated in the vicinity of the second light incident surface47aof the second phosphor layer47is likely to be transferred to the substrate38. Therefore, the wavelength conversion element65according to the present embodiment can suppress a decrease in the overall wavelength conversion efficiency of the two phosphor layers44and47and stably emit light having a desired color gamut.

In the first embodiment, the blue light B outputted from the light source10has the peak wavelength of 455 nm, which is slightly shifted toward the shorter wavelength side in the wavelength region to which the blue light B belongs. As a result, the color gamut provided when the blue light B is used to form white light is undesirably slightly narrow. To avoid the problem, in the wavelength conversion element65according to the present embodiment, the first fluorescence DB (blue light) produced in the first phosphor layer44has the peak wavelength of 462 nm, which is longer than the wavelength of the blue light B used in the first embodiment. As a result, the configuration in which the first fluorescence DB is used to form white light allows generation of wide-color-gamut white light.

Third Embodiment

A third embodiment of the invention will be described below with reference toFIG. 6.

The configurations of a projector and a light source apparatus according to the third embodiment are the same as those in the first embodiment, and the configuration of the wavelength conversion element differs from that in the first embodiment. No overall description of the projector and the light source apparatus will therefore be made.

FIG. 6is a cross-sectional view of a wavelength conversion element according to the third embodiment. The cross-sectional view corresponds to the cross section taken along the line IV-IV inFIG. 3.

InFIG. 6, components common to those in the drawings used in the first embodiment have the same reference characters and will not be described.

A wavelength conversion element75according to the present embodiment includes the substrate38, a first phosphor layer49, the second phosphor layer42, a first dichroic layer53, a second dichroic layer54, a third dichroic layer55, a reflection suppression layer56, bonding layers57, a first air layer58, and a second layer59, as shown inFIG. 6. The second phosphor layer42is so provided that the second light incident surface42afaces the second surface38bof the substrate38.

The first phosphor layer49has a first light incident surface49a, on which the blue light B (excitation light), which belongs to the first wavelength band, is incident and a first light exiting surface49b, through which first fluorescence G, which belongs to a second wavelength band different from the first wavelength band, and the blue light B that has not been used to excite the first phosphor layer49exit. The first phosphor layer49is so provided that the first light exiting surface49bfaces the first surface38aof the substrate38. In the present embodiment, the second wavelength band to which the first fluorescence G belongs ranges, for example, from about 500 to 570 nm (peak wavelength is about 535 nm), and the first fluorescence G emitted from the first phosphor layer49is green light.

The first dichroic layer53is provided on the first light incident surface49aof the first phosphor layer49. The first dichroic layer53has wavelength selectivity of transmitting light that belongs to the blue color gamut and reflects light that belongs to the green color gamut. The first dichroic layer53therefore transmits the blue light B and reflects the first fluorescence G generated in the first phosphor layer49. The first fluorescence G thus does not exit through the first light incident surface49a.

The second dichroic layer54is provided on the first light exiting surface49bof the first phosphor layer49. The second dichroic layer54has wavelength selectivity of transmitting light that belongs to the blue color gamut and light that belongs to the green color gamut. The second dichroic layer54therefore transmits the blue light B and the first fluorescence G generated in the first phosphor layer49.

The third dichroic layer55is provided on the second light incident surface42aof the second phosphor layer42. The third dichroic layer55has wavelength selectivity of transmitting light that belongs to the blue color gamut and the green color gamut, and reflects light that belongs to the red color gamut. The third dichroic layer55therefore transmits the blue light B and reflects the first fluorescence G and reflects the second fluorescence R produced in the second phosphor layer42. The second fluorescence R thus does not exit through the second light incident surface42a.

The reflection suppression layer56is provided on the second light exiting surface42bof the second phosphor layer42. The reflection suppression layer56therefore transmits the entire light incident on the second light exiting surface42bof the second phosphor layer42and causes the light to exit out of the second phosphor layer42toward the pickup system60. In the present embodiment, white light formed of the blue light B that has not been used to excite the first phosphor layer49or the second phosphor layer42, the first fluorescence G (green light) produced in the first phosphor layer49, and the second fluorescence R (red light) produced in the second phosphor layer42exits out of the wavelength conversion element75.

The first phosphor layer49is so attached to the substrate38via the bonding layers57provided along inner and outer circumferential portions of the first phosphor layer49that the first light exiting surface49bfaces the first surface38a. The configuration described above provides the first air layer58between the first light exiting surface49bof the first phosphor layer49and the first surface38aof the substrate38. The thickness of the first air layer58is therefore roughly equal to the thickness of the bonding layers57and is, for example, about 5 μm or smaller.

Similarly, the second phosphor layer42is so attached to the substrate38via the bonding layers57provided along inner and outer circumferential portions of the second phosphor layer42that the second light incident surface42afaces the second surface38b. The configuration described above provides the second air layer59between the second light incident surface42aof the second phosphor layer42and the second surface38bof the substrate38. The thickness of the second air layer59is therefore roughly equal to the thickness of the bonding layers57and is, for example, about 5 μm or smaller.

The other configurations of the wavelength conversion element75are the same as those in the first embodiment.

Therefore, the wavelength conversion element75according to the present embodiment can provide the same effects provided by the first embodiment, that is, can suppress a decrease in the overall wavelength conversion efficiency of the two phosphor layers49and42and stably emit white light having a desired color gamut.

In the present embodiment, the air layers58and59are provided between the phosphor layers49,42and the substrate, respectively, and the phosphor layer49or42is therefore not in direct contact with the substrate38. However, since the air layers58and59each have a very small thickness of, for example, about 5 μm or smaller, the air layer58or59does not prevent the heat transfer, and the heat generated in the phosphor layers49and42is transferred to the substrate38.

In the present embodiment, providing the first air layer58provides the following effect.

Out of the first fluorescence G, which is produced in the first phosphor layer49and travels toward the substrate38, the first fluorescence G incident on the first light exiting surface49bat angles of incidence smaller than the critical angle associated with the first light exiting surface49bpasses through the first light exiting surface49b, and the first fluorescence G incident on the first light exiting surface49bat angles of incidence greater than or equal to the critical angle is reflected off the first light exiting surface49b. In the configuration of the present embodiment, in which the first air layer58is provided between the first phosphor layer49and the substrate38, the difference in the refractive index at the interface between the first phosphor layer49and a member located on the light exiting side thereof (first air layer58or substrate38) is greater than the difference in a case where no first air layer58is provided, and the critical angle increases accordingly. As a result, the amount of first fluorescence G passing through the first light exiting surface49bincreases, whereby the amount of first fluorescence G emitted from the first phosphor layer49can be increased.

Similarly, in the present embodiment, providing the second air layer59provides the following effect.

Out of the blue light B and the first fluorescence G, which are incident on the second light incident surface42aof the second phosphor layer42, the blue light B and the first fluorescence G incident on the second light incident surface42aat angles of incidence smaller than the critical angle associated with the second light incident surface42apass through the second light incident surface42aand enter the second phosphor layer42, and the blue light B and the first fluorescence G incident on the second light incident surface42aat angles of incidence greater than or equal to the critical angle are reflected off the second light incident surface42a. In the configuration of the present embodiment, in which the second air layer59is provided between the second phosphor layer42and the substrate38, the difference in the refractive index at the interface between the second phosphor layer42and a member located on the light incident side thereof (second air layer59or substrate38) is greater than the difference in a case where no second air layer59is provided, and the critical angle increases accordingly. As a result, the amount of blue light B and first fluorescence G passing through the second light incident surface42aincreases, whereby the amount of blue light B and first fluorescence G that enter the second phosphor layer42can be increased.

The technical range of the invention is not limited to the embodiments described above, and a variety of changes can be made thereto to the extent that the changes do not depart from the substance of the invention.

For example, the wavelength conversion element according to the first embodiment includes the first phosphor layer that emits yellow first fluorescence and the second phosphor layer that emits red second fluorescence, but the combination of the emitted light colors from the phosphor layers is not limited to yellow and red. For example, the wavelength conversion element may instead include, for example, a first phosphor layer that emits green first fluorescence and a second phosphor layer that emits red second fluorescence.

Further, the light outputted from the wavelength conversion element is not necessarily white light. In this case, for example, the wavelength conversion element may include, for example, a first phosphor layer that emits blue first fluorescence and a second phosphor layer that emits red second fluorescence or a first phosphor layer that emits blue first fluorescence and a second phosphor layer that emits green second fluorescence.

The first and second surfaces of the substrate corresponding to the light transmitting portion may each have a light diffusing surface that diffuses the excitation light, the first fluorescence, or the second fluorescence. According to the configuration described above, in a case where the light emission distribution of the excitation light (blue light, for example) differs from the light emission distribution of the first fluorescence (yellow light, for example) or the second fluorescence (red light, for example), the light diffusing surface can diffuse the excitation light, the first fluorescence, or the second fluorescence in such a way that the light emission distribution of the excitation light approaches the light emission distribution of the first fluorescence or the second fluorescence. A projector capable of displaying a wide-color-gamut image with color unevenness suppressed can thus be provided.

For example, the third embodiment has been described with reference to the case where any of the dichroic layers and the reflection suppression layer is provided on each of the light incident surface and the light exiting surface of each of the first and second phosphor layers. Dichroic layers and a reflection suppression layer of this type may also be used in the wavelength conversion elements according to the first and second embodiments.

In addition to the above, the specific descriptions of the shape, the number, the arrangement, the material, and other factors of the components of the wavelength converter, the illuminator, and the projector are not limited to those in the embodiments described above and can be changed as appropriate. The above embodiments have been described with reference to the case where the illuminator according to each of the embodiments of the invention is incorporated in a projector using liquid crystal light valves, but not necessarily. The illuminator may be incorporated in a projector using a digital micromirror device as each of the light modulators.

The above embodiments have been described with reference to the case where the illuminator according to each of the embodiments of the invention is incorporated in a projector, but not necessarily. The illuminator according to each of the embodiments of the invention may be used as a lighting apparatus, a headlight of an automobile, and other components.

The entire disclosure of Japanese Patent Application No. 2018-059826, filed on Mar. 27, 2018 is expressly incorporated by reference herein.