JP2012234717A - Light source unit and image display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source unit with high directivity capable of enhancing emission intensity.SOLUTION: The light source unit is provided with a surface light-emitting device 1 emitting light, an angle control part 3 fitted to an emission side of the surface light-emitting device 1, and an angle conversion part 2 fitted between the surface light-emitting device 1 and the angle control part 3. The angle control part 3 transmits light incident at angles within a first incident angle range out of light incident from a surface light-emitting device 1 side, and reflects light incident at angles other than the first incident angle range. The angle conversion part 2 has light incident from the surface light-emitting device 1 side as well as an angle control part 3 side, transmits light incident at angles within a second incident angle range, diffracts or scatters part of light incident at angles other than the second incident angle range, and transmits the rest.

Description

  The present invention relates to a light source unit including a surface light emitting device typified by a light emitting diode (LED).

  In an image display device represented by a projector or a flat panel display, a light source unit with high directivity is required.

  For example, a projector irradiates light from a light source onto a display element and projects an image formed by the display element by a projection optical system. When a light source having a large divergence angle of emitted light is used, In some cases, a part of the light is not used as the projection light, and the light use efficiency is lowered. For this reason, a light source with a small divergence angle of emitted light, that is, a light source with high directivity is required.

  Patent Document 1 describes a surface light source device with high directivity. This surface light source device includes a backlight and an optical element on which light from an exit surface of the backlight is incident.

  The optical element includes a diffusion plate and a bandpass filter. The bandpass filter transmits light incident at an angle within a predetermined incident angle range with respect to light having a specific peak wavelength, and reflects light incident at other angles.

  In the optical element, light from the backlight is diffused by the diffusion plate and then enters the bandpass filter. In the band-pass filter, only the light incident at an angle within a predetermined incident angle range among the diffused light from the diffusion plate is transmitted, and the light incident at other angles is reflected in the direction of the backlight side. .

  The reflected light from the bandpass filter is diffused by the diffusion plate and then enters the backlight. The backlight reflects diffused light from the diffuser plate in the direction toward the optical element side, and at the time of reflection, part of the diffused light is absorbed by the backlight. The reflected light from the backlight is diffused by the diffuser and then enters the bandpass filter.

  According to the surface light source device described above, the emitted light can be obtained within the emission angle range corresponding to the predetermined incident angle range of the bandpass filter.

  Further, the light reflected by the band pass filter is repeatedly reflected between the band pass filter and the backlight. In this reflection process, the reflected light is diffused by the diffusion plate, and a part of the diffused light is transmitted through the band pass filter. As described above, since a part of the light reflected by the band pass filter can be extracted as the outgoing light, the utilization efficiency of the light emitted from the backlight is improved, and the outgoing light intensity of the surface light source device is increased. Can do.

JP 2003-337337 A

  In the surface light source device described in Patent Document 1, the light reflected by the bandpass filter enters the backlight through the diffusion plate, and a part of the incident light is absorbed by the backlight. Due to the light absorption by the backlight, the intensity of the light emitted from the optical element is lowered.

  In order to increase the emitted light intensity of the optical element, it is necessary to suppress light absorption in the backlight. For example, out of light emitted from the backlight, light that can be incident on the bandpass filter at an angle within a predetermined incident angle range is emitted from the optical element without reflection by the bandpass filter. Light absorption in the backlight is suppressed, and the intensity of emitted light from the optical element increases.

  However, in the surface light source device described in Patent Document 1, all the light emitted from the backlight is diffused by the diffusion plate, and a part of the diffused light is reflected by the bandpass filter. It is difficult to suppress light absorption by the light.

  By removing the diffuser plate, the light that can be incident on the bandpass filter at an angle within a predetermined incident angle range out of the light emitted from the backlight, without reflection by the bandpass filter, The light can be emitted from the optical element. However, in this case, the light reflected by the bandpass filter is not diffused and is repeatedly reflected between the bandpass filter and the backlight, so that the reflected light can be used as outgoing light. Can not.

  An object of the present invention is to provide a light source unit with high directivity that can increase the intensity of emitted light, and an image display device using the same.

In order to achieve the above object, the light source unit of the present invention comprises:
A light emitting unit for emitting light;
Provided on the emission side of the light-emitting unit, out of the light incident from the light-emitting unit side, transmits light incident at an angle within the first incident angle range, and enters at an angle other than the first incident angle range An angle control unit that reflects the emitted light toward the light emitting unit side;
Provided between the light emitting unit and the angle control unit, light is incident from each side of the light emitting unit side and the angle control unit side, and the incident light within a second incident angle range An angle conversion unit that transmits light incident at an angle and diffracts or scatters part of the light incident at an angle outside the second incident angle range and transmits the remaining light.

The image display device of the present invention is
The above light source unit;
A display unit that modulates light emitted from the light source unit according to a video signal and displays an image according to the video signal.

  According to the present invention, among the light emitted from the light emitting unit, the light whose incident angle to the angle converting unit is within the second incident angle range is not diffracted or scattered, and is directly converted into the angle converting unit and the angle. It passes through the control unit. Thus, part of the light emitted from the light emitting unit can be extracted as emitted light as it is, so that light absorption in the light emitting unit can be suppressed, and the intensity of the emitted light can be increased.

It is a schematic diagram which shows the structure of the light source unit of the 1st Embodiment of this invention. It is a schematic diagram which shows the cross-section of the surface light-emitting device of the light source unit shown in FIG. It is a figure for demonstrating an example of a diffraction grating. It is a figure for demonstrating the relationship between the incident angle when a light with a wavelength of 460 nm injects into the diffraction grating shown in FIG. 3, a grating period, and the diffraction angle of + 1st order diffracted light. It is a figure for demonstrating the relationship between the incident angle, grating | lattice period, and diffraction angle of -1st order diffracted light when the light of wavelength 460nm injects into the diffraction grating shown in FIG. It is a figure for demonstrating the change of the diffraction angle with respect to an incident angle in case a grating | lattice period is 300 nm and the wavelength of incident light is 460 nm. It is a schematic diagram which shows the structure of the light source unit which is a comparative example. It is a schematic diagram for demonstrating operation | movement of the light source unit shown in FIG. It is a schematic diagram which shows an example of the angle conversion part of the light source unit shown in FIG. It is a schematic diagram which shows another example of the angle conversion part of the light source unit shown in FIG. It is a schematic diagram which shows the structure of the light source unit of the 2nd Embodiment of this invention. It is a schematic diagram for demonstrating operation | movement of the light source unit shown in FIG. It is a figure for demonstrating the relationship between the emitted light intensity of the light source unit of a comparative example shown to FIG. 6A, and an emitted angle. It is a figure for demonstrating the relationship between the emitted light intensity of a light source unit shown in FIG. 9, and an emitted angle. It is a schematic diagram which shows an example of the angle conversion part of the light source unit shown in FIG. It is a schematic diagram which shows another example of the angle conversion part of the light source unit shown in FIG. It is a schematic diagram which shows another example of the angle conversion part of the light source unit shown in FIG. It is a schematic diagram which shows the structure of the light source unit of the 3rd Embodiment of this invention. It is a schematic diagram which shows an example of an image display apparatus provided with the light source unit of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing a configuration of a light source unit according to the first embodiment of the present invention.

  Referring to FIG. 1, the light source unit is used in an image display device typified by a projector or a flat panel display, and includes a surface light emitting device 1, an angle conversion unit 2, and an angle control unit 3. In FIG. 1, an arrow indicated by a solid line indicates zero-order light, and an arrow indicated by a broken line indicates diffracted light.

  The surface light-emitting device 1 is a surface-emitting solid-state light source such as an LED or a surface-emitting laser or a surface light-emitting device including a light source and a light guide plate, and has a desired wavelength (for example, red, green, blue, etc.) The light in a specific wavelength range having a peak wavelength is emitted. Hereinafter, the peak wavelength is the emission wavelength of the surface light emitting device 1.

  FIG. 2 schematically shows a cross-sectional structure of the surface light emitting device 1 of the light source unit.

  As shown in FIG. 2, the surface light emitting device 1 is mounted on a substrate 10 and includes a reflective layer 11, a light emitting unit 12, and electrode pads 15 and 16.

  The reflective layer 11 is mounted on the substrate 10. The light emitting unit 12 is formed on a partial region of the reflective layer 11, and the electrode pad 15 is formed on another region of the reflective layer 11. The electrode pad 16 is formed on a partial region of the light emitting unit 12. The electrode pads 15 and 16 are electrically connected to an external electrode (not shown).

  The light emitting unit 12 includes a p-type semiconductor layer 12A, an active layer 12B, and an n-type semiconductor layer 12C. The active layer 12B is provided between the p-type semiconductor layer 12A and the n-type semiconductor layer 12C. More specifically, the p-type semiconductor layer 12A, the active layer 12B, and the n-type semiconductor layer 12C are stacked on the reflective layer 11 in this order.

  The reflective layer 11 reflects light traveling from the light emitting unit 12 side to the substrate 1 side to the light emitting unit 12 side.

  A current is supplied to the light emitting unit 12 from an external power source through the electrode pads 15 and 16, and light is generated from the light emitting unit 12 in accordance with the current. More specifically, when a voltage is applied between the p-type semiconductor layer 12A and the n-type semiconductor layer 12C via the electrode pads 15 and 16 from an external power source, and a current flows between them, the active layer 12B Light is generated at That is, the active layer 12B functions as a light emitting layer that generates light.

  The angle control unit 3 is provided on the emission side (n-type semiconductor layer 12C side) of the surface light emitting device 1, and the first incident angle among the light of a specific wavelength incident from the surface light emitting device 1 side. Light incident within the range is transmitted, and light incident at an angle other than the first incident angle range is reflected in the direction toward the surface light emitting device 1 side.

Specifically, the angle control unit 3 is made of a dielectric multilayer film. The dielectric multilayer film has a structure in which, for example, first and second dielectric layers having different refractive indexes are alternately stacked, and regions having different refractive indexes are periodically arranged in the stacking direction. Have. Examples of the dielectric material include SiO ₂ , Nb ₂ O ₅ , ZnO, TiO ₂ , MgF ₂ , Al ₂ O ₃ , SrO, CaO, BaO, and Bi ₂ O ₃ .

  Such a dielectric multilayer film has characteristics such that light incident at an angle within a predetermined incident angle range is transmitted and light incident at an angle other than the predetermined incident angle range is reflected. The predetermined incident angle range is determined by the refractive index and period (interval) of the dielectric layer.

  The first incident angle range corresponds to the divergence angle of the emitted light of the light source unit of the present embodiment, and can be arbitrarily set by adjusting the refractive index and period (interval) of the dielectric layer.

  For example, when the light source unit according to the present embodiment is applied to a projector, the first incident angle range is set in consideration of a limitation called etendue determined by the light emission cross-sectional area of the light source and the divergence angle of the emitted light. According to etendue, the product of the light emission cross-sectional area of the light source and the divergence angle of the emitted light is less than the product of the display area of the display element and the capture angle (solid angle) determined by the F number of the projection optical system. By doing so, all of the light emitted from the light source can be used as projection light. The first incident angle range is set so as to obtain a divergence angle of the emitted light that satisfies such a condition.

  The angle conversion unit 2 is provided between the surface light emitting device 1 and the angle control unit 3 and is incident within a second incident angle range among light of a specific wavelength incident from the surface light emitting device 1 side. For light that is transmitted and incident at an angle other than the second incident angle range, part of the light is diffracted and the remaining light is transmitted as zero-order light.

  Specifically, the angle conversion unit 2 is composed of a single diffraction grating. For example, the diffraction grating has an uneven structure in which convex portions or concave portions are formed in an array on one surface of a glass plate. The incident angle range in which diffraction occurs is determined by the pitch (grating period) of the unevenness. Examples of the concavo-convex structure include a structure in which grooves (concave portions) extending in one direction are provided at regular intervals, and a convex portion such as a cone, a quadrangular pyramid, a cylinder, or a quadrangular prism is periodically arranged in two dimensions. There is.

As shown in FIG. 3, normally, in the diffraction grating 300 having the grating period P, when light is incident at an incident angle θ1, first-order diffracted light having a diffraction angle θ2 is generated in addition to zero-order light. The incident angle θ1 and the diffraction angle θ2 satisfy the relationship of Equation 1.
Psin θ1-Psin θ2 = mλ (Formula 1)
Here, λ is the wavelength of incident light, and m is a positive or negative integer other than zero. m represents the diffraction order of the diffracted light. For example, diffracted light having a diffraction angle θ2 satisfying Equation 1 when m = + 1 is + 1st order diffracted light, and diffracted light having diffraction angle θ2 satisfying Equation 1 when m = −1. Is called −1st order diffracted light.

  FIG. 4A shows the relationship between the incident angle θ1, the grating period P, and the emission angle (diffraction angle θ2) of the + 1st order diffracted light when light having a wavelength of 460 nm is incident on the diffraction grating 300. FIG. 4B shows the relationship between the incident angle θ1, the grating period P, and the emission angle (diffraction angle θ2) of the −1st order diffracted light when light having a wavelength of 460 nm is incident on the diffraction grating 300. 4A and 4B, the vertical axis represents the incident angle θ1, and the horizontal axis represents the grating period P. Further, the scale shown on the right side in the figure represents the emission angle (diffraction angle θ2) of the first-order diffracted light in terms of concentration.

  As can be seen from FIG. 4A and FIG. 4B, the first incident angle range in which only the 0th order light is generated (the region without the contour line) and the second incident angle in which the + 1st order diffracted light or the −1st order diffracted light and the 0th order light are generated. The threshold value of the incident angle indicated by the boundary with the range (the region having the contour lines) changes according to the grating period P.

  The second incident angle range of the angle conversion unit 2 is determined by the threshold value of the incident angle. By adjusting the grating period P, the threshold value of the incident angle can be set to a desired incident angle. However, the grating period P is in the range of λ / 2 <P <λ. In the example of FIGS. 4A and 4B, λ = 460 nm.

  FIG. 5 shows changes in the diffraction angle with respect to the incident angle when the grating period P is 300 nm and the wavelength of incident light is 460 nm. In FIG. 5, a curve indicated by a black circle indicates a change in the diffraction angle with respect to the incident angle of the + 1st order diffracted light, and a curve indicated by a white circle indicates a change in the diffraction angle with respect to the incident angle of the −1st order diffracted light.

  The threshold value of the incident angle with respect to the + 1st order diffracted light is −30 °, and the threshold value of the incident angle with respect to the −1st order diffracted light is 30 °. In the angle range A1 where the incident angle is 30 ° or less and −30 ° or more, only 0th-order light is generated and diffracted light is not generated. In the angle range A2 where the incident angle exceeds 30 °, 0th-order light and −1st-order diffracted light are generated. In the angle range A3 where the incident angle is less than −30 °, 0th-order light and + 1st-order diffracted light are generated.

  The angle range A1 corresponds to the second incident angle range of the angle conversion unit 2. In the example illustrated in FIG. 5, the diffraction grating transmits light incident at an angle within the angle range A <b> 1 out of incident light having a wavelength of 460 nm. The diffraction grating diffracts a part of the incident light at an angle other than the angle range A1.

  Next, the operation of the light source unit of this embodiment will be described. Here, the angle conversion unit 2 and the angle control unit 3 are arranged substantially in parallel, and the second incident angle range of the angle conversion unit 2 is set to be smaller than the first incident angle range of the angle control unit 3. Has been.

  Light emitted from the surface light emitting device 1 enters the angle conversion unit 2. The angle conversion unit 2 transmits the incident light at an angle within the second incident angle range as it is, and transmits a part of the incident light at an angle other than the second incident angle range. Diffraction.

  The first transmitted light (only the 0th-order light) within the second incident angle range transmitted through the angle conversion unit 2 enters the angle control unit 3. Since the incident angle of the first transmitted light to the angle control unit 3 is within the first incident angle range, the first transmitted light is transmitted through the angle control unit 3 as it is.

  On the other hand, second transmitted light (0th-order light and first-order diffracted light) outside the second incident angle range transmitted through the angle conversion unit 2 also enters the angle control unit 3. Of the light contained in the second transmitted light, the light whose incident angle to the angle control unit 3 is within the first incident angle range is transmitted through the angle control unit 3 and incident to the angle control unit 3. Is outside the first incident angle range, and is incident on the angle control unit 3 and is reflected in the direction of the angle conversion unit 2.

  The second transmitted light includes the first primary diffracted light whose incident angle to the angle control unit 3 is outside the first incident angle range, or the incident angle to the angle control unit 3 is the first incident. Some include second-order first-order diffracted light within an angular range. The first first-order diffracted light is reflected on the incident surface of the angle control unit 3 in the direction of the angle conversion unit 2, but the second first-order diffracted light passes through the angle control unit 3 as it is.

  The reflected light reflected by the incident surface of the angle control unit 3 is repeatedly reflected between the angle control unit 3 and the surface light emitting device 1. In the process of multiple reflection, part of the light incident on the surface light emitting device 1 is absorbed by the surface light emitting device 1.

  In addition, in the process of multiple reflection, part of the reflected light is diffracted by the angle conversion unit 2 and the angle of incidence on the angle control unit 3 changes. Through this diffraction, the incident angle of a part of the reflected light to the angle control unit 3 is within the first incident angle range. The reflected light whose incident angle to the angle control unit 3 is within the first incident angle range is transmitted through the angle control unit 3 as it is. In this way, it is possible to reuse the reflected light by multiple reflection.

  Hereinafter, a comparative example will be described to explain the effect of suppressing the decrease in emitted light intensity by the light source unit of the present embodiment.

  FIG. 6A shows a configuration of a light source unit as a comparative example. The light source unit of the comparative example is provided with a diffusion plate 200 instead of the angle conversion unit 2 of the light source unit shown in FIG. The surface emitting device 1 and the angle control unit 3 are the same as those shown in FIG.

  In the light source unit of the comparative example, as shown in FIG. 6A, all the light traveling from the surface light emitting device 1 side to the angle control unit 3 side is diffused by the diffusion plate 200. The diffused light is emitted from both surfaces of the diffusion plate 200 (the surface on the angle control unit 3 side and the surface on the surface light emitting device 1 side).

  Diffused light emitted from the surface of the diffusing plate 200 on the angle control unit 3 side enters the angle control unit 3. The angle control unit 3 transmits light incident at an angle within the first incident angle range out of the diffused light from the diffuser plate 200 and reflects the remaining light in the direction toward the diffuser plate 200. The reflected light from the angle control unit 3 is diffused by the diffusion plate 200.

  Diffused light emitted from the surface of the diffusion plate 200 on the surface light emitting device 1 side enters the surface light emitting device 1. In the surface emitting device 1, a part of the incident light is absorbed.

  As described above, in the light source unit of the comparative example, the light emitted from the surface light emitting device 1 is necessarily diffused by the diffusion plate 200 and part of the light is absorbed by the surface light emitting device 1. Strength decreases.

  On the other hand, according to the light source unit of the present embodiment, as shown in FIG. 6B, the incident angle to the angle conversion unit 2 out of the light emitted from the surface light emitting device 1 is in the second incident angle range. The inner light 1a is transmitted through the angle conversion unit 2 and the angle control unit 3 without being diffracted.

  As described above, since a part of the light emitted from the surface light emitting device 1 can be extracted as emitted light as it is, the light absorption in the surface light emitting device 1 compared with the light source unit shown in FIG. 6A. The fall of the emitted light intensity by can be suppressed.

  Of the light emitted from the surface light emitting device 1, the angle control unit 3 for the first-order diffracted light generated by the angle conversion unit 2 is used for light whose incident angle to the angle conversion unit 2 is outside the second incident angle range. Also included is light 1b having an incident angle within the first incident angle range. As for the light 1 b, a part of the light is diffracted by the angle conversion unit 2, and a part of the first-order diffracted light passes through the angle control unit 3. Also by this, the fall of the emitted light intensity by the light absorption in the surface light-emitting device 1 can be suppressed.

  The light source unit of the present embodiment described above is an example of the present invention, and the configuration is not limited to the illustrated one.

  For example, the grating period P of the angle conversion unit 2 may be constant or random. However, the grating period P needs to satisfy the condition of λ / 2 <P <λ.

  FIG. 7 shows an example of the angle conversion unit 2 in which the grating period P is random.

  Referring to FIG. 7, the angle conversion unit 2 includes a substrate 20 such as glass and a plurality of convex portions 21 formed on the substrate 20. Each convex part 21 is a rectangular parallelepiped shape, and is formed in parallel with one direction at unequal intervals.

  By setting the intervals (grating period P) of the convex portions 21 to be unequal intervals, the diffraction angle of the light diffracted by the angle conversion unit 2 is expanded. That is, the light incident on the angle conversion unit 2 is scattered within an angle corresponding to the variation width (periodic variation width) of the interval between the convex portions 21. Further, when multiple reflection and diffraction are repeated between the light emitting unit 12 and the angle control unit 3, the diffraction angle changes depending on the incident position on the angle conversion unit 2. Thereby, the diffusion effect by the angle conversion part 2 increases, and the reuse efficiency of reflected light improves. However, in this case, the threshold value of the incident angle has a fluctuation width corresponding to the fluctuation width (periodic fluctuation width) of the interval between the convex portions 21.

  FIG. 8 shows another example of the angle conversion unit 2 in which the grating period P is random.

  Referring to FIG. 8, the angle conversion unit 2 includes a substrate 20 such as glass and a plurality of convex portions 22 formed on the substrate 20. The convex portions 22 have a rectangular parallelepiped shape and are two-dimensionally formed at unequal intervals. The intervals between the convex portions 22 arranged in the first direction and the intervals between the convex portions 22 arranged in the second direction orthogonal to the first direction are both unequal intervals.

  The angle conversion unit 2 shown in FIG. 8 also increases the diffusion effect and improves the reuse efficiency of the reflected light.

  In the angle conversion part 2 shown in FIG. 7 and FIG. 8, you may provide several convex part from which height (thickness) and width differ.

  Moreover, in the angle conversion part 2 shown in FIG. 7, the cross-sectional shape of the convex part 21 is not limited to a square shape, Other shapes, such as a triangular shape, may be sufficient. Also in the angle conversion part 2 shown in FIG. 8, the shape of the convex part 22 is not limited to a rectangular parallelepiped, and may be a shape such as a cone, a quadrangular pyramid, or a cylinder.

(Second Embodiment)
FIG. 9 is a schematic diagram showing a configuration of a light source unit according to the second embodiment of the present invention.

  The light source unit shown in FIG. 9 is different from that of the first embodiment in that an angle conversion unit 4 is provided instead of the angle conversion unit 2. Since the surface light emitting device 1 and the angle control unit 3 are the same as those described in the first embodiment, detailed description thereof is omitted here.

The angle conversion unit 4 is a multilayer diffraction grating, and includes a dielectric multilayer film in which dielectric layers 4a and 4b having different refractive indexes are alternately stacked. Irregularities are periodically formed on the surface of the dielectric multilayer film on the surface light emitting device 1 side and the interface of the dielectric layers 4a and 4b. Dielectric layer 4a, as the _{4b, SiO 2, Nb 2 O} 5, ZnO, TiO 2, MgF 2, Al 2 O 3, SrO, CaO, BaO, and the like Bi ₂ O _3.

  As with the angle conversion unit 2 described in the first embodiment, each diffraction grating of the angle conversion unit 4 has a specific wavelength within the second incident angle range of light incident from the surface light emitting device 1 side. The incident light is transmitted, and a part of the light is diffracted (or scattered) with respect to the light incident at an angle other than the second incident angle range. Here, the second incident angle range can be defined in the same manner as the second incident angle range of the angle conversion unit 2 described in the first embodiment.

  Further, in the angle conversion unit 4, light incident at an angle other than the second incident angle range is subjected to multiple diffraction (scattering). By utilizing this multilayer diffraction, the light emitted from the surface light emitting device 1 can be efficiently incident on the angle control unit 3 at an angle within the first incident angle range.

  Hereinafter, the operation of the angle conversion unit 4 will be specifically described. Here, the angle control unit 3 and the angle conversion unit 4 are arranged substantially in parallel, and the second incident angle range of the angle conversion unit 4 is set to be smaller than the first incident angle range of the angle control unit 3. Has been.

  As shown in FIG. 10, among the light emitted from the surface light emitting device 1, the light 1 a whose incident angle to the angle conversion unit 4 is within the second incident angle range is not diffracted or scattered, The light passes through the angle conversion unit 4 and the angle control unit 3 as they are.

  Of the light emitted from the surface light emitting device 1, the light 1 b having the incident angle to the angle conversion unit 4 within the second incident angle range is the light incident as the 0th order light in each diffraction grating. Part is diffracted. In FIG. 10, an arrow indicated by a solid line indicates zero-order light, and an arrow indicated by a broken line indicates first-order diffracted light.

  Of the light emitted from the surface light emitting device 1, the incident angle of the light to the angle control unit 3 with respect to the light 1 b transmitted or diffracted with the angle conversion unit 4 as the 0th order light is in the first incident angle range. What is inside passes through the angle control unit 3.

  On the other hand, the light 1b whose incident angle to the angle control unit 3 is outside the first incident angle range is reflected on the incident surface of the angle control unit 3 in the direction of the angle conversion unit 2 side.

  In the first embodiment, since the angle conversion unit 2 includes a single layer diffraction grating, the first incidence of the light 1b emitted from the surface light emitting device 1 out of the 0th-order light transmitted through the diffraction grating. Light outside the angle range is reflected by the angle control unit 3 in the direction of the surface light emitting device 1 side.

  On the other hand, in the present embodiment, the angle conversion unit 4 is composed of a multilayer diffraction grating, and therefore the 0th-order light transmitted through the first diffraction grating of the light 1b emitted from the surface light emitting device 1 is A part of the diffraction grating in the second and subsequent layers is diffracted to generate first-order diffracted light. Part of the first-order diffracted light generated in each diffraction grating passes through the angle control unit 3.

  As described above, since the ratio of the 0th-order light incident on the angle control unit 3 can be reduced with respect to the light 1b, the output by light absorption in the surface light emitting device 1 compared with that in the first embodiment. It is possible to further suppress the decrease in the light intensity. Therefore, it is possible to provide a light source unit with higher emitted light intensity and excellent directivity.

  FIG. 11A shows the relationship between the emission light intensity and the emission angle of the light source unit of the comparative example shown in FIG. 6A, and FIG. 11B shows the relationship between the emission light intensity and the emission angle of the light source unit of this embodiment. In FIG. 11A and FIG. 11B, the curve indicated by the dotted line indicates the emitted light of the surface light emitting device 1, and the curve indicated by the solid line indicates the emitted light of the light source unit. In these examples, the emitted light intensity when the number of reflections between the surface light emitting device 1 and the angle control unit 3 is 1 is obtained by simulation.

  In the light source unit of the comparative example, the intensity of the emitted light can be increased by diffusing the reflected light with the diffusion plate 200 in the process of reflection between the surface light emitting device 1 and the angle control unit 3. In the example shown in FIG. 11A, the brightness is improved by about 30% with respect to the emitted light intensity of the surface light emitting device 1 at an emission angle of 45 ° or less.

  On the other hand, in the light source unit of the present embodiment, a part of the outgoing light from the surface light emitting device 1 is directly extracted as outgoing light without being reflected by the angle control unit 3, thereby increasing the outgoing light intensity. Can do. In the example shown in FIG. 11B, the brightness is improved by about 70% with respect to the emitted light intensity of the surface light emitting device 1 at an emission angle of 45 ° or less.

  Thus, according to the light source unit of the present embodiment, it is possible to provide a light source unit having high emitted light intensity and excellent directivity.

  The light source unit of the present embodiment described above is an example of the present invention, and the configuration is not limited to the illustrated one. For example, as long as a multilayer diffraction grating can be formed, the number of dielectric layers of the angle conversion unit 4 may be set to any number.

  Further, the angle conversion unit 4 may have a configuration in which three or more kinds of dielectric layers are repeatedly stacked.

  Various shapes such as a rectangular parallelepiped, a cone, a quadrangular pyramid, and a cylinder can be applied to the grating shape (uneven shape) of the diffraction grating of the angle conversion unit 4.

  FIG. 12A shows an example of the angle conversion unit 4.

  12A has a stacked structure in which dielectric layers 4a and 4b are alternately stacked. At the interface between the dielectric layers 4a and 4b, there is formed a diffraction grating in which rectangular parallelepiped convex portions are periodically formed in two dimensions. A similar diffraction grating is also formed on one surface (surface on the dielectric layer b side) of the laminated structure.

  FIG. 12B shows another example of the angle conversion unit 4.

  12B has a stacked structure in which dielectric layers 4a and 4b are alternately stacked. At the interface between the dielectric layers 4a and 4b, there is formed a diffraction grating in which convex portions having a quadrangular cross section extending in the first direction are periodically formed in a second direction orthogonal to the first direction. Yes. A similar diffraction grating is also formed on one surface (surface on the dielectric layer b side) of the laminated structure.

  FIG. 12C shows still another example of the angle conversion unit 4.

  12C has a stacked structure in which dielectric layers 4a and 4b are alternately stacked. At the interface between the dielectric layers 4a and 4b, there is formed a diffraction grating in which convex portions having a triangular cross-sectional shape extending in the first direction are periodically formed in a second direction orthogonal to the first direction. Yes. A similar diffraction grating is also formed on one surface (surface on the dielectric layer b side) of the laminated structure.

(Third embodiment)
FIG. 13 is a schematic diagram showing a configuration of a light source unit according to the third embodiment of the present invention.

  The light source unit shown in FIG. 13 is different from that of the second embodiment in that the grating periods in the in-plane direction of each diffraction grating of the angle conversion unit 4 are set at unequal intervals. Since the surface light emitting device 1 and the angle control unit 3 are the same as those described in the first or second embodiment, detailed description thereof is omitted here.

  As shown in FIG. 13, the light 1 a having an incident angle to the angle conversion unit 4 within the second incident angle range out of the light emitted from the surface light emitting device 1 is not diffracted or scattered. The light passes through the angle conversion unit 4 and the angle control unit 3 as they are.

  Of the light emitted from the surface light emitting device 1, part of the light 1 b incident on the angle conversion unit 4 at an angle outside the second incident angle range is diffracted or scattered by the angle conversion unit 4. The remaining light passes through the angle conversion unit 4 as zero-order light. That is, for the light 1 b, first-order diffracted light and zero-order light are generated in each diffraction grating of the angle conversion unit 4. In FIG. 13, an arrow indicated by a solid line indicates zero-order light, and an arrow indicated by a broken line indicates first-order diffracted light.

  The diffraction angle of the first-order diffracted light depends on the diffraction cycle, and the diffraction angle decreases as the diffraction cycle increases. Since the diffraction period in the in-plane direction of each diffraction grating of the angle conversion unit 4 is unequal, the diffraction angle of the first-order diffracted light varies depending on the position where the light enters in the plane.

  According to the light source unit of the present embodiment, for the light 1b, the first-order diffracted light generated in each diffraction grating is emitted in different directions, so that the angle compared with the light source units of the first and second embodiments The diffusion effect by the conversion part 4 increases, and the reuse efficiency of reflected light improves.

  However, in the case of this embodiment, the threshold value of the incident angle has a variation width corresponding to the periodic variation width of each diffraction grating of the angle conversion unit 4.

  According to the first to third embodiments described above, in addition to the improvement effect of the emitted light intensity, the problem of the influence of the heat emitted from the surface light emitting device 1 on other members can also be solved.

  For example, in the light source unit described in Patent Document 1 or the comparative light source unit shown in FIG. 6A, when a high output light source is used as the backlight or the surface light emitting device 1, the resin of the diffusion plate is caused by heat from the light source. As a result, problems such as a decrease in light diffusion effect and a decrease in transmittance occur.

  On the other hand, according to the light source unit of the first embodiment, the angle conversion unit 2 is made of an optical material having excellent heat resistance such as glass, so that the surface light emitting device 1 has a high output light source. Even if is used, the angle conversion part 2 is not denatured by heat.

  Further, in the light source units of the second and third embodiments, the angle conversion unit 4 is made of a dielectric material having excellent heat resistance. Therefore, also in this case, the angle conversion unit 4 is not denatured by heat.

  As described above, according to the first to third embodiments, since a high-output light source can be used as the surface light-emitting device 1, a light source unit with high emission light intensity can be provided.

  The light source unit of each embodiment described above is an example of the present invention, and the configuration is not limited to the illustrated one.

  For example, the surface on which the diffraction grating of the angle conversion unit is formed may face either side of the surface light emitting device 1 side and the angle control unit 3 side.

  The angle conversion unit may be formed of a three-dimensional photonic crystal. A photonic crystal is a nanostructure having a periodic refractive index distribution of the order of the wavelength of light, and has a characteristic that entry of light corresponding to the period is prohibited. A three-dimensional photonic crystal is a nanostructure formed in three dimensions.

  Moreover, in each embodiment, although it has a space | gap between a surface light-emitting device and an angle conversion part, and between an angle conversion part and an angle control part, it is not limited to this. The surface light emitting device and the angle conversion unit, and the angle conversion unit and the angle control unit may be formed in close contact with each other.

  The light source unit of the present invention described above can be applied to all image display devices represented by projectors and flat panel displays.

  FIG. 14 shows an example of an image display device to which the light source unit of the present invention is applied.

  In FIG. 14, the image display device is a projector and includes a light source unit 50 and a display unit 51.

  The light source unit 50 is any of the light source units of the first to third embodiments described above.

  The display unit 51 modulates light from the light source unit 50 according to the video signal and displays an image according to the video signal. More specifically, the display unit 2 includes a spatial light modulation unit 52 and a projection optical system 54.

  The spatial light modulator 52 is a spatial modulation element such as a liquid crystal LV (light valve), for example, and modulates light from the light source unit 50 according to the video signal. The projection optical system 53 is, for example, an optical system such as a lens, and projects the emitted light (modulated light) from the spatial light modulator 52 onto the screen 54. As a result, an image corresponding to the video signal is displayed on the screen 54.

DESCRIPTION OF SYMBOLS 1 Surface light-emitting device 2 Angle conversion part 3 Angle control part

Claims (8)

A light emitting unit for emitting light;
Provided on the emission side of the light-emitting unit, out of the light incident from the light-emitting unit side, transmits light incident at an angle within the first incident angle range, and enters at an angle other than the first incident angle range An angle control unit that reflects the emitted light toward the light emitting unit side;
Provided between the light emitting unit and the angle control unit, light is incident from each side of the light emitting unit side and the angle control unit side, and the incident light within a second incident angle range An angle conversion unit that transmits light incident at an angle, diffracts or scatters part of the light incident at an angle other than the second incident angle range, and transmits the remaining light; Light source unit.   The light source unit according to claim 1, wherein the second incident angle range is smaller than the first incident angle range.   The angle conversion unit includes at least one diffraction grating, and a grating period of the diffraction grating is smaller than a light emission wavelength of the light emitting unit and larger than a half wavelength of the light emission wavelength. Light source unit.   The light source unit according to claim 3, wherein a grating period of the diffraction grating is constant.   The light source unit according to claim 3, wherein a grating period of the diffraction grating is indefinite.   The angle conversion unit is formed of a dielectric multilayer film in which first and second dielectric layers having different refractive indexes are alternately stacked, and the diffraction grating is formed at an interface between the first and second dielectric layers. The light source unit according to claim 3, wherein the light source unit is formed.   6. The light source unit according to claim 3, wherein the angle conversion unit is made of a three-dimensional photonic crystal in which nanostructures having a periodic refractive index distribution are three-dimensionally formed. The light source unit according to any one of claims 1 to 7,
An image display device comprising: a display unit that modulates light emitted from the light source unit according to a video signal and displays an image according to the video signal.