JPWO2012120738A1 - Light source and projection display device using the light source - Google Patents

Abstract

Provided is a light source capable of increasing light extraction efficiency while increasing directivity. The optical unit (3) has an incident surface (31) on which light generated from the light emitting unit is incident, and an output surface (32) that emits the light. On the incident surface (31), a structure group (31A) is formed in which the refractive index changes at intervals equal to or less than the first interval shorter than the wavelength of light. On the emission surface 32, a periodic structure (32A) whose refractive index changes at a second interval longer than the first interval is formed.

Description

  The present invention relates to a light source having directivity.

  In recent years, a projector using an LED (Light Emitting Diode) as a light source has attracted attention. Such a projector includes an LED, an illumination optical system into which light from the LED is incident, a modulation element that modulates and emits light from the illumination optical system in accordance with a video signal, and light from the modulation element on a screen. And a projection optical system for projecting onto the screen.

  In the projector described above, in order to increase the brightness of a projected image, it is required to efficiently use light from a light source as projection light. How much light from the light source can be used as projection light varies depending on the etendue, which is the product of the light emitting area and the radiation angle of the light source. More specifically, if the etendue of the light source is made equal to or less than the product of the light receiving area of the modulation element and the capture angle determined by the F number of the illumination optical system, the light from the light source can be efficiently used as projection light. it can. For this reason, as a light source of a projector, a light source with high directivity is desired in order to reduce etendue.

  On the other hand, Patent Document 1 describes a light-emitting element that efficiently emits light in a predetermined direction. In this light emitting element, an optical part that propagates and emits light from the light emitting part is laminated on a light emitting part that generates light. A light emitting surface in the optical unit is formed with a periodic structure in which the refractive index periodically changes in a two-dimensional direction parallel to the light emitting surface. Since light is diffracted and emitted in a predetermined direction by this periodic structure, light can be emitted efficiently in the predetermined direction.

JP 2006-310737 A

  In the light emitting element described in Patent Document 1, Fresnel reflection occurs when light enters the optical unit, and the reflected light returns to the light emitting unit. Since the light returned to the light emitting portion is a loss that is not emitted from the light emitting element, there is a problem that the light extraction efficiency is low. Note that the loss of light can be reduced by providing the light emitting portion with a reflective film and allowing the light returning to the light emitting portion to reenter the optical portion. However, the light extraction efficiency is not sufficient because the light attenuates during reflection.

  An object of the present invention is to provide a light source capable of increasing light extraction efficiency while increasing directivity, and a projection display device using the light source.

  A light source according to the present invention includes a light-emitting unit that generates light, an optical unit that includes an incident surface on which light generated from the light-emitting unit is incident, and an output surface that emits the light. A structure group is formed in which the refractive index changes at an interval equal to or less than the first interval shorter than the wavelength of the light, and the refractive index changes at the second interval longer than the first interval on the emission surface. A periodic structure is formed.

  The projection display device according to the present invention uses the light source described above.

  According to the present invention, it is possible to increase light extraction efficiency while increasing directivity.

It is a perspective view which shows the light source of the 1st Embodiment of this invention. It is a perspective view which shows an example of an optical part. It is a longitudinal cross-sectional view which shows an example of an optical part. It is a cross-sectional view of the first periodic structure. It is a cross-sectional view of the second periodic structure. It is a figure for demonstrating the refractive index of a 1st periodic structure. It is a perspective view which shows the other example of an optical part. It is a figure for demonstrating propagation of the light in an optical part. It is a figure for demonstrating the simulation for evaluating the directivity of a light source. It is a figure for demonstrating an example of the simulation result on specific conditions. It is a figure which shows a simulation result. It is a figure which shows an example of a structure of the projector using the light source of the 1st Embodiment of this invention. It is a figure which shows the other example of a structure of the projector using the light source of the 1st Embodiment of this invention. It is a perspective view which shows the light source of the 2nd Embodiment of this invention. It is a longitudinal cross-sectional view which shows the light source of the 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having the same function may be denoted by the same reference numerals and description thereof may be omitted.

  FIG. 1 is a perspective view showing a light source according to the first embodiment of the present invention. As shown in FIG. 1, the light source 10 is laminated in the order of the light emitting unit 1, the bonding unit 2, and the optical unit 3.

  It should be noted that the thickness of each layer in an actual light source is very thin, and the difference in thickness between the layers is large, so that it is difficult to illustrate each layer in an accurate ratio. For this reason, in FIG. 1, each layer is not drawn as an actual ratio but is shown typically. Further, as shown in FIG. 1, a plane parallel to the lower surface of the light emitting unit 1 is defined as an XY plane, and a direction orthogonal to the XY plane is defined as a Z direction.

  The light emitting unit 1 generates light. More specifically, the light emitting unit 1 is stacked in the order of a p-type layer 11 formed of a p-type semiconductor, an active layer 12, and an n-type layer 13 formed of an n-type semiconductor. When a voltage is applied to the mold layer 13 by an external power source (not shown) and a current flows between them, light is generated in the active layer 12.

  The joint portion 2 is formed of a transparent dielectric or the like, and guides the light generated from the light emitting portion 1 to the optical portion 3 by propagating inside. It is assumed that the refractive index of the joint portion 2 is smaller than the refractive index of the optical portion 3. The light source 10 may be a light source provided with a gap between the light emitting part 1 and the optical part 3 instead of providing the joint part 2.

  FIG. 2 is a perspective view showing the optical unit 3, and FIG. 3 is a longitudinal sectional view of the optical unit 3 cut along an XZ plane.

  As shown in FIGS. 2 and 3, the optical unit 3 includes an incident surface 31 on which light generated from the light emitting unit 1 is incident, and an output surface 32 that emits light incident on the incident surface 31.

  The incident surface 31 has a first periodic structure 31A that is a group of structures whose refractive index changes in a first period in a two-dimensional direction (XY direction) parallel to the incident surface 31, and the output surface 32 is an output surface. 32 has a second periodic structure 32 </ b> A that is a periodic structure whose refractive index changes in a second period in a two-dimensional direction (XY direction) parallel to 32. The first period is shorter than the wavelength of the light generated from the light emitting unit 1, and the second period is longer than the first period. The second period may be shorter than the wavelength of the light generated from the light emitting unit 1, may be the same, or may be longer. More preferably, if the wavelength of light generated from the light emitting unit 1 is λ, the first period Γ1 is about λ / 4, and the second period Γ2 is about 5λ.

  The first periodic structure 31 </ b> A may be formed so as to be in contact with the incident surface 31, or may be formed so as not to be in contact with the incident surface 31. The first periodic structure 31 </ b> A may have a refractive index that changes in a first period in a one-dimensional direction parallel to the incident surface 31.

  The second periodic structure 32 </ b> A may be formed so as to be in contact with the emission surface 32, or may be formed so as not to be in contact with the emission surface 32. The first periodic structure 32 </ b> A may have a refractive index that changes in a first period in a one-dimensional direction parallel to the emission surface 32.

  Further, instead of the first periodic structure 31 </ b> A, the refractive index changes in a one-dimensional direction or a two-dimensional direction parallel to the incident surface 31 at an interval equal to or shorter than the first interval shorter than the wavelength of the light generated from the light emitting unit 1. A structure group that does not have a periodic structure may be provided.

  2 and 3, the first periodic structure 31A is a moth-eye structure in which irregularities are formed in a first period in the XY direction, and the second periodic structure 32A is formed in irregularities in a second period in the XY direction. It is assumed that it has a periodic structure like a photonic crystal. In addition, it is assumed that the convex portion 31B of the first periodic structure 31A and the convex portion 32B of the first periodic structure 32A have a conical shape.

  4A is a cross-sectional view in which a part of the first periodic structure 31A is cut by the incident surface 31, and FIG. 4B is a cross-sectional view in which a part of the second periodic structure 32A is cut by the emission surface 32.

  As shown in FIGS. 4A and 4B, each of the convex portions 31B and 32B is arranged in a triangular lattice shape, and adjacent convex portions are arranged on the incident surface 31 and the outgoing surface 32 without a gap. Here, as shown in FIG. 4A, the period of the first periodic structure 31A coincides with the distance from the center of the bottom surface of the convex part 31B to the center of the bottom surface of the adjacent convex part 31B, and the period of the first periodic structure 32A is As shown in FIG. 4B, the distance is the same as the distance from the center of the bottom surface of the convex portion 32B to the center of the bottom surface of the adjacent convex portion 32B.

  Each of the convex portions 31B and 32B may be arranged in another arrangement structure such as a square lattice shape or in another arrangement structure having anisotropy in the XY plane. Further, on the incident surface 31 and the emission surface 32, there may be a gap between adjacent convex portions.

  FIG. 4C is a diagram in which a part of the first periodic structure 31A is cut out along the XY plane between the apex and the bottom surface of the convex portion 31A. As shown in FIG. 4C, the convex portion 31 </ b> B and the joint portion 2 are arranged in the first cycle in the XY plane. Therefore, since the refractive index of the convex part 31B and the junction part 2 differs from each other, the first periodic structure 31A has a refractive index changing in the first period in the XY plane. That is, by forming the moth-eye structure on the incident surface 31, the refractive index can be changed in the first period with respect to the two-dimensional direction parallel to the incident surface 31. Similarly, by forming the periodic structure on the emission surface 32, the refractive index can be changed in the second period with respect to a two-dimensional direction parallel to the emission surface 32.

  Further, since the convex portion 31B has a conical shape, the volume occupied by the joint portion 2 is larger at the tip of the convex portion 31B than the convex portion 31B, and the bottom surface of the convex portion 31B is larger than the joint portion 2. Thus, the volume occupied by the convex portion 31B increases. For this reason, the effective refractive index that is an average refractive index in the XY plane of the first periodic structure 31A continuously changes from the tip of the convex portion 31B toward the bottom. Here, Fresnel reflection that occurs at the interface between substances having different refractive indexes is less likely to occur as the difference in refractive index between the substances is smaller. Therefore, as described above, the effective refractive index is the tip of the convex portion 31B. Fresnel reflection can be prevented when it continuously changes from the bottom to the bottom.

  Further, since the second periodic structure 32A functions as a diffraction grating that diffracts light and guides it in a predetermined direction, the directivity of the light source 10 can be increased.

  The convex portions 31B and 32B are preferably tapered such as a conical shape, but may be other shapes such as a cylindrical shape or a prism shape. For example, as shown in FIG. 5, in the optical part 3, the convex part 31A may have a conical shape and the convex part 32B may have a cylindrical shape.

  In the optical unit 3 having the above-described configuration, the light generated from the light emitting unit 1 is incident on the incident surface 31 of the optical unit 3 through the bonding unit 2. The light incident on the incident surface 31 passes through the optical unit 3 with almost no reflection by the first periodic structure 31A. Since the refractive index n1 of the junction part 2 is smaller than the refractive index n2 of the optical part 3, as shown in FIG. 6, when the light passes through the incident surface 31, the exit angle becomes small according to Snell's law, and the exit surface 32 Propagate until. The light propagated to the emission surface 32 is emitted after the radiation angle is converted by the second periodic structure 32A.

  The optical unit 3 having the above-described configuration can be manufactured by processing using a glass substrate, PET (Polyethylene terephthalate), an ultraviolet curable resin, or the like by interference exposure, electron beam lithography, nanoimprinting, or the like.

  Further, the fine structure is not processed on both the entrance surface and the exit surface of one optical unit 3, the fine structure is provided on each side of the two optical units 3, and the fine structure of the two optical units 3 is not provided. A configuration in which the surfaces are bonded together may be used.

  Next, the directivity of the light source 10 is evaluated.

  FIG. 7 is a diagram for explaining a simulation based on the FDTD method (Finite Difference Time Domain method) for evaluating the directivity of the light source 10. Moreover, since the difference of the size of each structure is large and it is difficult to represent each structure by an exact ratio, it has shown typically. As shown in FIG. 7, the present simulation performs a Fourier transform on the intensity distribution of the TE-polarized light and the TM-polarized light emitted concentrically from the point light source 41 and reaches the calculation region end 42, thereby far field (Far field). The average of the TE-polarized component and the TM-polarized component in the angular distribution of the light intensity is evaluated. The point light source 41 emits light having a wavelength of 532 nm.

  Further, the diameter of the bottom surface of the convex portion 31B is fixed to 0.1 μm, and the height of the convex portion 31B is fixed to 0.5 μm. The light intensity of light was calculated while changing the diameter v of the bottom surface of the convex portion 32B, assuming that the diameter of the bottom surface of the convex portion 32B was v [μm], the height of the convex portion 32B was 5 v, and the diameter v of the bottom surface of the convex portion 32B was changed.

  FIG. 8 is a diagram illustrating a calculation result when v = 4 [μm] as an example. The horizontal axis represents the radiation angle in the far field, and the vertical axis represents the light intensity in the far field that has not been normalized. The dotted line indicates the light intensity in the far field when TE polarized light is emitted from the light source, and the straight line indicates the light intensity in the far field when TM polarized light is emitted from the light source. Here, for reference, there is no optical unit 3 in the calculation area, that is, the far-field light intensity of TE polarized light in the case of free space is indicated by a chain line. Further, in free space, the result of TM polarization is the same as the result of TE polarization, and is omitted.

  It can be seen from the graph shown in FIG. 8 that the light intensity in the far field according to the radiation angle is modulated by diffraction due to the periodic structure of the exit surface of the optical unit 3. Here, for example, the integrated value of the far-field light intensity of TE-polarized light and TM-polarized light with respect to the integral value of the far-field light intensity of TE-polarized light in the case of free space within 45 degrees (−45 degrees to +45 degrees). When the ratio of the average value is calculated, it is 1.16, and the directivity is improved.

  FIG. 9 is a diagram showing the relationship between the diameter v of the bottom surface of the convex portion 32B and the gain of light intensity at the calculation region end 42 (Gain of Far field intensity). Here, the gain of light intensity is the ratio of the light intensity of the far field at the calculation region end 42 when the optical unit 3 is present to the light intensity of the far field at the calculation region end 42 when the optical unit 3 is not present. It is. Further, in FIG. 9, the radiation angle is within 15 degrees (-15 to 15 degrees), within 30 degrees (-30 to 30 degrees), within 45 degrees (-45 to 45 degrees), within 60 degrees (- 60 degrees to 60 degrees), within 75 degrees (-75 degrees to 75 degrees), within 90 degrees (-90 degrees to 90 degrees), and within 180 degrees (-180 degrees to 180 degrees). Show.

  As shown in FIG. 9, when the diameter of the bottom surface of the convex portion 32B is larger than the diameter of the bottom surface of the convex portion 31B, the light intensity in the radiation angle within 15 degrees to 75 degrees is greater than about 1, and the light source 10 It can be seen that the directivity of is high. Therefore, since the refractive index period in the first periodic structure 31A and the second periodic structure 32A is the distance from the center of the bottom surface of the convex portion to the center of the bottom surface of the adjacent convex portion, the refractive index in the second periodic structure 32A. It can be seen that the directivity of the light source 10 is increased if the second period, which is the period of, is longer than the period of the refractive index in the first periodic structure 31A.

  In FIG. 8 and FIG. 9, the aspect ratio (ratio of bottom diameter to height) of the convex portions 31B and 32B was calculated as 5. As the aspect ratio is higher, the effect of reducing the Fresnel reflection of the moth-eye structure and the diffraction effect of the photonic crystal are increased, and the light intensity in the far field of FIG. 8 and the gain of the light intensity of FIG. Since the difficulty level increases, it is necessary to determine the aspect ratio by a trade-off between the two. For example, the aspect ratio may be lowered in order to reduce the manufacturing difficulty level.

  Next, a projection display device (projector) using the light source 10 will be described.

  FIG. 10 is a layout diagram illustrating an example of the configuration of the projector according to the present embodiment. In FIG. 10, a projector 100 includes light sources 101R, 101G, and 101B, optical elements 102R, 102G, and 102B, liquid crystal panels 103R, 103G, and 103B, a cross dichroic prism 104, and a projection optical system 105.

  Each of the light sources 101R, 101G, and 101B has the same structure as the light source 10 shown in FIG. The light emitting units 1 of the light sources 101R, 101G, and 101B generate light having different wavelengths. Hereinafter, it is assumed that red (R) light is emitted from the light source 101R, green (G) light is emitted from the light source 101G, and blue (B) light is emitted from the light source 101B.

  Each of the optical elements 102R, 102G, and 102B guides the respective color lights generated from the light sources 101R, 101G, and 101B to the liquid crystal panels 103R, 103G, and 103B, respectively, and enters them.

  The liquid crystal panels 103R, 103G, and 103B are spatial light modulation elements that modulate incident color light according to a video signal and emit the modulated light.

  The cross dichroic prism 104 combines and outputs the modulated lights emitted from the liquid crystal panels 103R, 103G, and 103B.

  The projection optical system 105 projects the combined light emitted from the cross dichroic prism 104 onto the screen 200 and displays an image corresponding to the video signal on the screen 200.

  FIG. 11 is a layout diagram illustrating another example of the configuration of the projector according to the present embodiment. In FIG. 11, the projector 100 ′ includes light sources 101 </ b> R, 101 </ b> G, and 101 </ b> B, a light guide 106, a liquid crystal panel 107, and a projection optical system 108.

  The light guide 106 combines the color lights generated from the light sources 101R, 101G, and 101B and outputs the combined light to the liquid crystal panel 107.

  The liquid crystal panel 107 is a spatial light modulation element that modulates incident combined light according to a video signal and emits the modulated light.

  The projection optical system 108 projects the modulated light emitted from the liquid crystal panel 107 onto the screen 200 and displays an image corresponding to the video signal on the screen 200.

  10 and 11, the liquid crystal panel is used as the spatial light modulation element. However, the modulation element is not limited to the liquid crystal panel and can be changed as appropriate. For example, in the projector shown in FIG. 11, a DMD (Digital Micromirror Device) may be used instead of the liquid crystal panel 107.

  As described above, according to the present embodiment, the optical unit 3 includes the incident surface 31 on which the light generated from the light emitting unit 1 is incident and the emission surface 32 that emits the light incident on the incident surface 31. The incident surface 31 is formed with a first periodic structure 31 </ b> A whose refractive index changes in a first period shorter than the wavelength of light in a two-dimensional direction parallel to the incident surface 31. A second periodic structure 32 </ b> A whose refractive index changes in a second period longer than the first period is formed on the emission surface 32 in a two-dimensional direction parallel to the emission surface 32.

  For this reason, Fresnel reflection occurring on the incident surface 31 can be prevented by the first periodic structure 31A, and the radiation angle of the light emitted from the emission surface 32 can be converted by the second periodic structure 32A. It is possible to increase the light extraction efficiency while increasing.

  In the present embodiment, since the convex portions 31B and 32B are conical, the effective refractive index can be continuously changed in the Z direction perpendicular to the incident surface 31 and the outgoing surface 32, and Fresnel reflection can be performed. The prevention effect can be increased.

  Next, a second embodiment will be described.

  FIG. 12 is a perspective view showing the light source of the present embodiment, and FIG. 13 is a longitudinal sectional view of the light source of the present embodiment cut along an XZ plane.

  The light source 10 ′ shown in FIGS. 12 and 13 is different from the light source 10 shown in FIG. 1 in that the wall surfaces of the joint portion 2 and the optical portion 3 are formed of a reflecting member 51 that reflects light. In addition, the junction part 2 is hollow and is filled with air.

  In the present embodiment, the light incident on the wall surface of the optical unit 3 out of the light generated from the light emitting unit 1 is also reflected by the reflecting member 51 and is incident on the optical unit 3. Since a large amount of light can be guided to the optical unit 3, the light extraction efficiency can be further increased. Further, among the light propagating in the optical unit 3, the light incident on the wall surface of the optical unit 3 can be reflected by the reflecting member 51 and guided to the emission surface 32, so that the light extraction efficiency is further improved. It becomes possible to make it higher.

  In the present embodiment, all of the wall surfaces of the joint portion 2 and the optical portion 3 are formed of the reflecting member 51. However, only a part of the wall surfaces of the joint portion 2 and the optical portion 3 reflects light. If it is the structure provided with, compared with 1st Embodiment, the extraction efficiency of light can be made high.

  In each embodiment described above, the illustrated configuration is merely an example, and the present invention is not limited to the configuration.

  For example, a reflective film that reflects light may be provided on the lower surface or the upper surface of the light emitting unit 1.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2011-05386 for which it applied on March 9, 2011, and takes in those the indications of all here.

Claims (9)

A light emitting section for generating light;
An optical unit having an incident surface on which light generated from the light emitting unit is incident and an output surface that emits the light;
On the incident surface, a group of structures whose refractive index changes at an interval equal to or less than a first interval shorter than the wavelength of the light is formed,
A light source in which a periodic structure whose refractive index changes at a second interval longer than the first interval is formed on the emission surface. The light source according to claim 1,
The structure group is a light source having a moth-eye structure in which irregularities are formed in the first period. The light source according to claim 2,
The convex part of the said structure group is a light source which is a cone shape. The light source according to any one of claims 1 to 3,
The periodic structure is a light source having a moth-eye structure in which irregularities are formed in the second period. The light source according to claim 4.
The convex part of the periodic structure is a light source having a conical shape. The light source according to any one of claims 1 to 5,
The light emitting unit and the optical unit are stacked via a joint that propagates the light,
A light source in which a refractive index of the joint portion is smaller than a refractive index of the optical portion. The light source according to claim 6,
The said junction part is a light source which is hollow. The light source according to claim 6 or 7,
A light source, wherein at least part of the optical part and the wall surface of the joint part includes a reflection part that reflects the light.   A projection display device using the light source according to claim 1.

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