JP2009140916A - Surface light-emitting device and polarized light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light-emitting device capable of suppressing disturbance of polarization characteristics of polarized light outputted and a polarized light source. <P>SOLUTION: The surface light-emitting device includes: a polarized light source 1 for emitting polarized light 20; and a light guide plate 11 which has a light incident face 11a in which the polarized light 20 emitted from the polarized light source 1 enters and a light outgoing face 11b for emitting light, and which is made of a light-transmitting resin having a low double refraction in which retardation is one fourth or less of wavelength of the polarized light 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light emitting device, and more particularly to a surface light emitting device that emits polarized light and a polarized light source.

  In recent years, light-emitting elements that emit polarized light have been developed (see, for example, Non-Patent Document 1). By using a polarized light source including such a light emitting element as a light source for a liquid crystal display device or a front projector, the light use efficiency of the liquid crystal display device or the front projector can be improved. That is, since these liquid crystal display devices are equipped with polarizing plates so as to sandwich the liquid crystal cell, if polarized light is emitted from the light emitting device, the light component that can pass through the polarizing plate located in front of the liquid crystal cell increases, Therefore, the amount of light that can pass through the liquid crystal cell is increased.

Hereinafter, a description will be given with reference to FIG. As shown in FIG. 12, as the surface light emitting device 110 of the liquid crystal display device 100, a polarized light source 111 that emits polarized light and polarized light 150 emitted from the polarized light source 111 are incident, and the incident polarized light 150 is dispersed inside. A backlight including a resin light guide plate 112 that uniformly emits light 160 from the emission surface 112a has been proposed. In FIG. 12, reference numerals 120 and 140 denote polarizing plates provided so as to sandwich the liquid crystal cell 130 therebetween.
T. Takeuti et al., “Japanese Journal of Applied Physics vol.39”, 2000, pages 413-416.

  Normally, the resinous light guide plate 112 shown in FIG. 12 is manufactured by molding a resin such as acrylic into a predetermined shape by a technique such as injection molding. During such molding, molecular orientation occurs in the resin. In addition, when the resin is thermoset after molding, the resin molecules are oriented or residual stress is generated. The orientation of the resin molecules and the generation of residual stress cause birefringence to appear inside the light guide plate. When birefringence develops in the resin constituting the light guide plate, the polarized light generated by the polarized light source passes through the light guide plate and the polarization characteristics are disturbed to approach random polarization. Therefore, the light 160 emitted from the light guide plate 112 as schematically shown in FIG. 12 cannot actually maintain the polarization characteristics, and cannot fully utilize the advantage of using the polarized light source 111 that emits the polarized light 150. . Incidentally, when random polarized light is passed through the polarizing plate, the intensity of light passing through the polarizing plate is attenuated to about 35%.

  In addition to the above problems in the light guide plate 112, the polarized light source 111 as a package has the same problems. That is, similar to the manufacture of the light guide plate 112, in the manufacture of the polarized light source 111, the resin molecules are oriented during the thermosetting of the sealing resin such as epoxy resin or silicone resin that seals the light emitting element (not shown). Residual stress may occur. The orientation of the resin molecules and the generation of residual stress cause birefringence to develop inside the sealing resin. Thus, when birefringence develops in the sealing resin, the polarization characteristics are disturbed by the polarized light generated in the light emitting element passing through the sealing resin. Therefore, the polarization characteristics of polarized light emitted from the polarized light source 111 as a package cannot be maintained, and the advantages of using a light emitting element that emits polarized light cannot be fully utilized.

  Accordingly, as shown in FIG. 12, the light 160 emitted from the light guide plate 112 has more light components that cannot pass through the polarizing plate 120, and the light 170 having a small light quantity passes through the liquid crystal cell 130. And the light component which can pass through the polarizing plate 140 as an analyzer further decreases. For this reason, the display brightness in the liquid crystal display device 100 is low, and the contrast is also lowered.

  In view of the above problems, an object of the present invention is to provide a surface light-emitting device and a polarized light source that can suppress disturbance of polarization characteristics of output polarized light.

  According to one aspect of the present invention, (b) a polarized light source that emits polarized light, (b) a light incident surface on which polarized light emitted from the polarized light source is incident, and a light emitting surface that emits light. A surface light emitting device comprising a light guide plate made of a light-transmitting resin having a low birefringence with retardation equal to or less than ¼ of the wavelength of polarized light can be provided.

  According to another aspect of the present invention, (b) a light emitting element that emits polarized light, (b) a mounting base on which the light emitting element is mounted, and (c) a retardation that is a quarter of the wavelength of the polarized light emitted by the light emitting element. A polarized light source comprising a light-transmitting resin having a low birefringence of 1 or less and a sealing portion that covers the light-emitting element can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the surface light-emitting device and polarized light source which can suppress disorder of the polarization characteristic of the polarized light to output can be provided.

  Hereinafter, details of a surface light emitting device and a polarized light source according to embodiments of the present invention will be described with reference to the drawings.

  In the embodiment of the present invention, an LED (light emitting diode) is used as a light emitting element, and the present invention is applied to a surface light emitting device having a polarized light source having a surface mounting structure and a resin light guide plate.

[Configuration of surface light emitting device]
As shown in FIG. 1, the surface light emitting device 10 includes a polarized light source 1 and a light guide plate 11 and is roughly configured. As shown in FIG. 1, the surface light emitting device 10 can be incorporated as a backlight of the liquid crystal display device 40. The liquid crystal display device 40 includes a surface light emitting device 10, a polarizing plate 41 as a polarizer, a liquid crystal cell 42 in which liquid crystal is sealed between a pair of glass substrates, and a polarizing plate 43 as an analyzer. . The liquid crystal cell 42 may be either an active matrix LCD (liquid crystal display) or a passive matrix LCD. Further, as another component of the liquid crystal cell 42, a configuration including a color filter and a phase difference plate may be used.

  The light guide plate 11 is a resin plate formed of a low birefringence light-transmitting material having a birefringence of retardation equal to or less than a quarter of the light source wavelength. As shown in FIG. 1, in the light guide plate 11, one side surface is a light incident surface 11 a that faces the polarized light source 1. Polarized light 20 is incident on the light incident surface 11a. Further, the front side surface of the light guide plate 11 is a light emitting surface 11 b that uniformly emits the polarized light 60. L shown in FIG. 1 is a light guide length.

Note that “retardation” refers to a phase shift between two polarization components generated when light travels through a substance, and is generally represented by the following formula (1) or formula (2):
Retardation = 2πdΔn / λ (1)
Retardation = dΔn (2)
Δn is the orientation birefringence of the material (not the intrinsic refractive index), d is the thickness of the material through which light passes, and λ is the wavelength of the light in vacuum. As described above, the retardation increases as the thickness d, which is the distance through which light passes, is increased. Details of the low birefringence light-transmitting material will be described later.

  The surface light emitting device 10 includes a lamp reflector (not shown) or a light guide plate 11 that surrounds the light incident surface 11a of the light guide plate 11 and the polarized light source 1 to prevent light leakage, as in a known backlight system. You may provide the reflective sheet (illustration omitted) etc. which are arrange | positioned at the back side surface. Further, an optical film may be provided between the light guide plate 11 and the polarizing plate 41.

[Configuration of polarized light source]
As shown in FIG. 2, the polarized light source 1 includes a light emitting element 2 that emits polarized light, a mounting base 3 on which the light emitting element 2 is mounted, and a sealing portion 4 that covers the light emitting element 2. In addition, it is preferable that the sealing part 4 is the sealing resin of the low birefringence light transmissive material whose retardation is 1/4 or less of the wavelength of the polarized light 20 emitted from the light emitting element 2.

  The mounting base 3 is a package substrate having a surface mounting structure, and includes a mounting surface 30 having a concave cross-sectional shape that also serves as a reflector 30R. The light emitting element 2 is mounted on the bottom surface of the mounting surface 30 of the mounting base 3. In addition, a reflector 30 </ b> R including an inner peripheral side surface of the recess is formed around the side surface of the light emitting element 2 in the mounting base 3.

[Configuration of Light Emitting Element]
The light emitting element 2 is an LED that emits polarized light 20. Here, “polarized light” means that the linearly polarized light component is not uniform (random) but biased, but in this embodiment, it is not necessary to be 100% linearly polarized light. Therefore, the polarization direction of the polarized light 20 is the direction having the largest linearly polarized light component.

  For example, as illustrated in FIG. 3, the light emitting element 2 includes a light emitting unit 220 that generates polarized light 20 and an output unit 210 that is a substrate on which the light emitting unit 220 is mounted.

The light emitting unit 220 uses a non-polar plane or semi-polar plane of a GaN crystal as a crystal growth surface, and includes a first semiconductor layer 221 of a first conductivity type, an active layer 222, and Each of the second conductivity type second semiconductor layers 223 is sequentially stacked in the normal direction of the crystal growth surface. For example, if the crystal growth surface is an m-plane that is a nonpolar plane, the light-emitting element 2 is composed of a group III nitride semiconductor having the m-plane as a main surface. Examples of the group III nitride semiconductor include aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN). A typical group III nitride semiconductor is represented by Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). The GaN semiconductor is a III-V group compound semiconductor that is well known among hexagonal compound semiconductors containing nitrogen.

  The light emission wavelength of the light emitting element 2 (the wavelength at which the light emission intensity reaches a peak) can be adjusted by changing the In composition of the active layer 222. The light emitting element 2 of the present embodiment emits blue light and has an emission wavelength of 400 nm. However, the present invention is not limited to this. For example, the emission wavelength may be about 530 nm with green light emission, or another wavelength may be used.

  The active layer 222 is supplied with a first conductivity type carrier from the first semiconductor layer 221, and is supplied with a second conductivity type carrier from the second semiconductor layer 223. When the first conductivity type is n-type and the second conductivity type is p-type, electrons supplied from the first semiconductor layer 221 and holes supplied from the second semiconductor layer 223 in the active layer 222 Recombination is performed and polarized light 20 is emitted from the active layer 222. The active layer 222 may employ, for example, a quantum well structure in which a well layer (well layer) is sandwiched between barrier layers (layer barrier layers) having a larger band gap than the well layer. it can. The quantum well structure includes not only one well layer but also a multiplexed quantum well structure, and further includes a quantum well structure in which the active layer 222 has a multiple quantum well (MQW) structure.

  Usually, the light extracted from the active layer made of a group III nitride semiconductor having the c-plane which is the polar plane of the GaN crystal as the crystal growth surface is in a randomly polarized (non-polarized) state. On the other hand, in the active layer 222 formed using a group III nitride semiconductor whose crystal growth surface is a non-polar or semipolar plane such as an a-plane (see FIG. 4) other than the c-plane, m-plane, etc., a strong polarization state Light is generated. For example, when the active layer 222 is configured with the m-plane as the main surface, polarized light 20 that includes a large amount of polarized light components parallel to the m-plane, more specifically, a polarized light component in the a-axis direction, is generated from the active layer 222. Detailed descriptions of the nonpolar plane and the semipolar plane will be described later.

  The light emitting part 220 is formed by growing on the crystal growth surface of the output part 210 by crystal growth. That is, as shown in FIG. 3, the light emitting element 2 includes an output unit 210, the output unit 210, the first semiconductor layer 221 on the output unit 210, and the active layer 222 on the first semiconductor layer 221. And a second semiconductor layer 223 on the active layer 222.

  In the present embodiment, the output unit 210 is composed of, for example, a GaN single crystal substrate. In the case where the main surface that is a non-polar surface is the main surface serving as the crystal growth surface of the output unit 210, the light emitting unit 220 can be formed on the main surface by crystal growth. That is, the light emitting section 220 is made of GaN having the m-plane as the crystal growth main surface, and the light-emitting element 2 is made of a group III nitride semiconductor grown with the m-plane as the crystal growth main surface. The main surface of the output unit 210 is the same as the crystal growth surface of the light emitting unit 220.

  The light emitting element 2 further includes a first electrode 211 that supplies an operating voltage to the first semiconductor layer 221 and a second electrode 212 that supplies an operating voltage to the second semiconductor layer 223. As shown in FIG. 3, the first electrode is formed on the surface of the second semiconductor layer 223, the active layer 222, and a part of the first semiconductor layer 221 that is removed by mesa etching to expose the first semiconductor layer 221. 211 is arranged. The first semiconductor layer 221 and the first electrode 211 are electrically connected. The second semiconductor layer 223 and the second electrode 212 are electrically connected.

  For example, aluminum (Al) is used for the first electrode 211, and palladium (Pd) -gold (Au) alloy is used for the second electrode 212, for example. The first electrode 211 is ohmically connected to the first semiconductor layer 221, and the second electrode 212 is ohmically connected to the second semiconductor layer 223. Note that a first conductivity type contact layer may be interposed between the first semiconductor layer 221 and the first electrode 211. In addition, a second conductivity type contact layer may be interposed between the second semiconductor layer 223 and the second electrode 212.

  In the light emitting element 2, the surface (back surface) facing the crystal growth surface (main surface) in contact with the first semiconductor layer 221 of the output unit 210 is an output surface 210A. The polarized light 20 emitted from the active layer 222 is output as output light from the output surface 210 </ b> A to the outside of the light emitting element 2. Note that the light-emitting element 2 can extract light from the second semiconductor layer 223 side. In the present embodiment, the light emitting element 2 is mounted on the mounting base 3 by a flip chip method, electrically connected to the mounting surface 30 of the mounting base 3 via bump electrodes (not shown).

[Crystal structure of light-emitting element]
The crystal structure of the group cell of III nitride semiconductor constituting the light emitting element 2 is close to a hexagonal crystal structure as shown in FIGS. In the hexagonal crystal structure, the c-axis is a crystal axis along the axial direction of the hexagonal column. The surface (the top surface of the hexagonal column) having the c-axis as a normal line is a c-plane {0001}. When a group III nitride semiconductor crystal is cleaved in two planes parallel to the c-plane, the + c-axis side plane (+ c plane) becomes a crystal plane in which group III atoms are arranged. The plane on the −c axis side (−c plane) is a crystal plane in which nitrogen atoms are arranged. For this reason, the c-plane is called a polar plane because it exhibits different properties on the + c-axis side and the −c-axis side.

  As shown in FIG. 5, four nitrogen atoms are bonded to one group III atom. The four nitrogen atoms are located at the four vertices of a regular tetrahedron with a group III atom arranged in the center. Of these four nitrogen atoms, one nitrogen atom is located in the + c axis direction with respect to the group III atom, and the other three nitrogen atoms are located on the −c axis side with respect to the group III atom. Since it has such a crystal structure, the polarization direction is along the c-axis in the group III nitride semiconductor.

  In the hexagonal crystal structure, each side surface of the hexagonal column is an m-plane {1-100}. A plane passing through a pair of ridge lines that are not adjacent to each other is a-plane {11-20}. The m-plane and the a-plane are crystal planes perpendicular to the c-plane and are orthogonal to the polarization direction, and thus are nonpolar planes, that is, nonpolar planes. Furthermore, since the crystal plane that is inclined with respect to the c-plane (not parallel to the c-plane and not perpendicular to it) intersects the polarization direction obliquely, a slightly polar plane, that is, a semipolar plane It is. Specific examples of the semipolar plane include a {01-11} plane shown in FIG. 6A and a {01-13} plane shown in FIG. 6B.

[Constituent materials of light guide plate and sealing part]
The light guide plate 11 and the sealing portion 4 are made of a resin material having light transmittance and having a low birefringence with retardation equal to or less than ¼ of the light source wavelength. The resin material having low birefringence used in the present embodiment has a property that birefringence characteristics are not exhibited even when orientation is exhibited by performing injection molding or extrusion molding of a polymer. In addition, it is preferable that a light scattering fine particle, a void, etc. are not mixed as a polymer.

  In the present embodiment, a light-transmitting substance having a low birefringence having a retardation of ¼ or less of the light source wavelength is a mixture or a co-polymer of a positive birefringent substance and a negative birefringent substance. It is a polymer.

  The positive birefringent material is preferably selected from, for example, polyvinylidene fluoride (PVDF), polyvinylidene fluoride trifluoroethylene (VDF · TrFE-58), polyethylene oxide (PEO) and the like.

  The negative birefringent material is preferably, for example, polymethyl methacrylate (PMMA), but is not limited thereto. Note that each of the positive and negative birefringent substances may be one kind of the above-mentioned substances, or a plurality of substances may be combined.

  As a low birefringence light-transmitting substance having a retardation of ¼ or less of the light source wavelength, a low molecular organic substance having a rod-like molecular shape and anisotropy in polarizability is added to the polymer, resulting in retardation. May have a low birefringence of one quarter or less of the light source wavelength. Alternatively, inorganic birefringent crystal fine particles may be added to the polymer, and as a result, the retardation may have a low birefringence that is ¼ or less of the light source wavelength.

  In general, it is widely known that birefringence exists in polymer resin materials. For almost all of the polymer resin materials usually used as optical materials, the monomers forming the polymer have optical anisotropy with respect to the refractive index. Then, the optical anisotropy of this monomer is manifested by the arrangement or orientation of the polymer in a certain direction, thereby producing birefringence in the polymer resin material.

  When a molding process such as injection molding or extrusion molding is performed, a random polymer bond chain is oriented by an external force applied at that time, and as a result, the polymer exhibits birefringence. For this reason, almost all of the polymer resin materials normally used as optical materials have birefringence. This birefringence is generally called orientation birefringence.

  Furthermore, the polymer resin material may exhibit birefringence even when elastically deformed. This birefringence is generally called photoelastic birefringence.

  Therefore, in this embodiment, even if the orientation is expressed inside by injection molding or extrusion molding, or the elastic deformation occurs, both the orientation and the elastic deformation occur, the retardation is the light source wavelength. A light guide plate 11 made of a low birefringence light-transmitting resin of 1/4 or less is formed. In addition, the light-emitting element 2 is sealed using such a low birefringence light-transmitting resin to form the sealing portion 4.

  Hereinafter, a light transmissive resin that is a light transmissive material constituting the light guide plate 11 and the sealing portion 4 will be described.

○ Light-transparent resin prepared by blending method By mixing a polymer with a positive intrinsic birefringence index and a negative polymer at an appropriate blend ratio, the birefringence cancels each other when orientation occurs, making it macroscopic So that the birefringence does not develop. The combinations of polymers to be blended are, for example, as shown in Table 1 below.

  As shown in Table 1, in this embodiment, a PMMA / PVDF mixture prepared by blending polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVDF) at a weight ratio of 80:20 is used as a light guide plate. 11 and the constituent resin of the sealing portion 4.

  Further, as shown in Table 1, a PMMA / VDF / TrFE-58 mixture prepared by blending PMMA and polyvinylidene fluoride trifluoroethylene (VDF / TrFE-58) at a weight ratio of 90:10 was prepared. You may use as the light-guide plate 11 or the sealing part 4. FIG.

  Further, as shown in Table 1, the light guide plate 11 and the sealing portion 4 are formed of a PMMA / PEO mixture prepared by blending PMMA and polyethylene oxide (PEO) at a weight ratio of 65:35. Also good.

The above-mentioned “intrinsic birefringence” is an index representing the ease of orientation birefringence for each optical resin material, and is defined for optical resin materials based on both homopolymers and copolymers (copolymers). To get. Assuming that the orientation birefringence is Δn and the degree of orientation is f, the intrinsic birefringence Δn0 has a relationship as shown in the following equations (3) and (4):
Δn = f × Δn0 (3)
Δn0 = Δn / f (4)
Here, the degree of orientation f is an index representing the degree of orientation of the polymer main chain, and the state in which the polymer is completely oriented in one direction is represented by f = 1. In the case of non-orientation, f = 0, and the degree of orientation f normally takes a value smaller than 0.3. The magnitude of the orientation birefringence at this time (with a positive or negative sign) corresponds to the intrinsic birefringence Δn0.

On the other hand, the photoelastic birefringence ΔnE is expressed as follows when the principal stress difference σ (difference between the two when the applied stress is decomposed into two orthogonal principal stresses) and the photoelastic coefficient C intrinsic to the substance are: The relationship is as in equation (5):
ΔnE = C · σ (5)
○ Light-transparent resin produced by random copolymerization method Polarization anisotropic in one polymer chain by copolymerizing monomer of positive birefringence and monomer of negative polymer at appropriate ratio Try to counter sex. Since the novel polymer produced by such copolymerization does not have birefringence, birefringence does not appear even if orientation occurs. Examples of combinations of monomers to be copolymerized include those shown in Table 2 below.

  As shown in Table 2, examples of the monomer having a negative birefringence include methyl methacrylate (MMA), styrene, butyl methacrylate (BMA), and cyclohexyl methacrylate (CHMA).

  As shown in Table 2, examples of the monomer having a positive birefringence include trifluoroethyl methacrylate (3FMA), trihydroperfluoropropyl (4FMA), and benzyl methacrylate (BzMA).

  The light guide plate 11 and the sealing portion 4 may be formed using a novel polymer produced by copolymerizing a monomer having a negative birefringence and a monomer having a positive birefringence as described above.

○ Light-transmitting resin produced by anisotropic low molecular dope method Adds low molecular weight organic substance having rod-shaped molecular shape and anisotropy of polarizability to the polymer to offset the birefringence of the polymer. Here, a low molecule having birefringence anisotropy opposite to the birefringence anisotropy of the polymer is used. Specifically, a method of adding several mol% of trans-stilbene, diphenylacetylene, biphenyl, carbazole, etc. to PMMA having a negative orientation birefringence. Taken. You may form the light-guide plate 11 and the sealing part 4 with the light transmissive resin produced | generated by such anisotropic low molecular dope method.

  The light-transmitting resin prepared by each of the above methods is designed so that birefringence characteristics do not appear even when orientation is developed inside by injection molding or extrusion molding. Alternatively, it can be designed so that the birefringence characteristic does not appear even if elastic deformation occurs, or it can be designed so that the birefringence characteristic does not appear even if both orientation and elastic deformation occur. For this reason, when shaping | molding the light-guide plate 11 and the sealing part 4, it becomes possible to employ | adopt various shaping | molding methods.

The intrinsic birefringence of a normal resin such as PMMA is about -4.3 × 10 ⁻³ . On the other hand, the intrinsic birefringence Δn0 of the light transmissive material used in the present embodiment is 3 × 10 ⁻³ or less in absolute value. As shown in Expression (3), the orientation birefringence Δn depends on the orientation degree f, but when the intrinsic birefringence Δn0 is 3 × 10 ⁻³ or less in absolute value, the orientation degree f depends on the manufacturing method. Regardless, the orientation birefringence Δn can be reduced. In the case of the anisotropic low molecular dope method described above, since it is a method of offsetting birefringence by adding a low molecular organic substance having a rod-like molecular shape and anisotropy of polarizability to the polymer, in a strict sense The intrinsic birefringence Δn0 of the polymer molecular chain itself is the same as that before addition. However, since the low molecular organic substance is aligned with the polymer molecular chain, the birefringence of the mixture of the polymer and the low molecular organic substance when the orientation degree f = 1 of the polymer molecular chain corresponds to the intrinsic birefringence Δn0. You can think about it. According to such a definition, even in the polymer by anisotropic low molecular doping method, when the intrinsic birefringence Δn0 is 3 × 10 ⁻³ or less in absolute value, regardless of the orientation degree f depending on the production method, The orientation birefringence Δn can be reduced.

For example, in the MMA / BzMA copolymer and the MMA / 3FMA copolymer, the orientation birefringence Δn is substantially zero within the measurement range of the birefringence measuring apparatus by adjusting the composition ratio, that is, below the measurement limit. . In addition, the measurement lower limit of the retardation by the well-known generally available measuring method is about 0.1 nm. From the relationship of formula (2), the birefringence is obtained by dividing the measured retardation by the thickness of the sample (the distance that light propagates through the sample). Therefore, the lower limit of the required birefringence depends on the thickness of the sample. The lower limit of the birefringence is about 2 × 10 ⁻⁶ when evaluated using a film having a thickness of about 50 μm (thickness d of the substance through which light is transmitted = 50 μm).

By using the light transmissive resin as described above for the light guide plate 11 or the sealing portion 4, in the present embodiment, the retardation represented by the formula (2) is equal to or less than ¼ of the wavelength. . The light guide plate 11 has a light guide length of 100 mm and a retardation of about 50 nm when light is transmitted in the light guide length direction. In this case, the orientation birefringence Δn is about 5 × 10 ⁻⁷ . In this light guide plate, the orientation birefringence Δn can be allowed to about 1 × 10 ^{−6 with} respect to light having a wavelength of 400 nm. The retardation of the sealing part 4 was about 5 nm. Since the thickness of the sealing portion is 1 mm, the orientation birefringence Δn is about 5 × 10 ⁻⁶ . In this sealing portion, the orientation birefringence Δn can be allowed to about 1 × 10 ^{−4 with} respect to light having a wavelength of 400 nm.

[Polarized light source manufacturing method]
Next, an example of a method for manufacturing the polarized light source 1 according to the embodiment will be described with reference to FIGS.

  As shown in FIG. 7, the light emitting element 2 is mounted on the mounting surface 30 of the mounting base 3 by a die bonding method. Here, although not shown, when the light emitting element 2 is mounted on the mounting base 3, the first electrode 211 and the second electrode 212 of the light emitting element 2 are electrically connected to the electrodes disposed on the mounting surface 30 of the mounting base 3. Connect.

  Next, as shown in FIG. 8, a light transmissive resin 41 </ b> A prepared by the method described above is dropped from the syringe 6. As shown in FIG. 8, the light emitting element 2 is sealed with a light transmissive resin 41A.

  Thereafter, the light-transmitting resin 41A applied dropwise is gradually heated to cure the light-transmitting resin 41A, and the forming process of the sealing portion 4 is completed as shown in FIG.

  The light-transmitting resin 41A prepared by the above method does not exhibit birefringence characteristics even when orientation is expressed inside by injection molding or extrusion molding. For this reason, various shaping | molding methods, such as injection molding and extrusion molding, are applicable besides the method of dripping and applying the light transmissive resin 41A from the syringe 6 mentioned above. Thereby, it is possible to perform sealing in a shape that cannot be achieved with a conventional resin while maintaining the polarization state of the LED. Furthermore, since sealing using an existing molding apparatus is possible, no new equipment investment is required, leading to cost reduction.

  With the manufacturing method as described above, the polarization characteristics can be maintained throughout the package in a state where the light emitting element 2 having the polarization characteristics is sealed.

  According to the present embodiment, the sealing portion 4 is formed of a low birefringence light-transmitting resin whose retardation is equal to or less than ¼ of the wavelength of the polarized light 20. For this reason, the polarized light source 1 which suppressed disorder of the polarization | polarized-light 20 emitted from the light emitting element 2 is realizable. Further, since the light guide plate 11 is formed of the low birefringence light transmissive resin, the disturbance of the polarized light 60 emitted from the light exit surface 11b of the light guide plate 11 can be suppressed.

  Further, according to the present embodiment, by using the surface light emitting device 10 as a light source for backlight of the liquid crystal display device 40, as shown in FIG. 1, the polarized light positioned on the surface light emitting device 10 side in the liquid crystal display device 40. The amount of polarized light 70 transmitted through the plate 41 can be improved. Therefore, the amount of polarized light 80 that can pass through the polarizing plate 43 can be increased, and a liquid crystal display device with high display quality can be realized.

  Furthermore, according to the present embodiment, since the surface light emitting device 10 can maintain the polarization characteristics in the entire package, the polarizing plate 41 of the liquid crystal display device 40 can be omitted. For this reason, the liquid crystal display device 40 can be reduced in thickness and space, and the cost and process can be reduced by omitting the polarizing plate 41. In particular, according to the present embodiment, since the light use efficiency is increased, the power consumption of a mobile device equipped with a liquid crystal display, such as a mobile phone, a PDA, and a laptop computer, is reduced, and the charge can be performed only once. Driving time can be greatly extended.

  Further, according to the present embodiment, since the polarized light 60 emitted from the light guide plate 11 can be made to be nearly completely polarized light, the transmitted light intensity can be reduced to about 70%, and random polarized light is used. Can transmit twice as much light as there is. For this reason, when the luminance of the liquid crystal display device is set to a predetermined value, the luminance of the polarized light source 1 is halved by using the light guide plate 11 having a low birefringence with a retardation of ¼ or less of the light source wavelength. can do. Therefore, according to the present embodiment, there is an effect of reducing power consumption. Conversely, if the liquid crystal display device is driven with the same driving power, it is possible to obtain approximately twice the display brightness. Examples of the use of such an LCD module include a liquid crystal display of a small portable information terminal such as a mobile phone, a PDA, and a notebook personal computer, a front projector, and the like.

  As shown in FIG. 10, if a direct backlight type in which the polarized light source 1 is installed directly under the diffusion plate 50 on the back of the liquid crystal display device is adopted, the conventional method of installing the polarized light source 1 on the side of the liquid crystal display device and Unlikely, a light guide plate is not required. For this reason, the liquid crystal display device can be further reduced in thickness and cost.

  Moreover, according to this Embodiment, the polarized light source 1 can also be used as a light source of the sensor using polarized light. The semiconductor laser also emits polarized light. However, when used as a light source of a familiar sensor, there is a risk that the irradiated object may be damaged. On the other hand, the polarized light source 1 according to the present embodiment is excellent in versatility and safety. An example of such a sensor is a birefringence measuring device. This birefringence measurement apparatus is an apparatus that measures the refractive index characteristic of a substance by irradiating an object with polarized light and measuring the polarization state of the transmitted light.

[Modified example of polarized light source]
FIG. 11 shows a modification of the polarized light source 1 in the present embodiment. A polarized light source 1A shown in FIG. 11 has a shell-type package structure. As shown in FIG. 11, a polarized light source 1A according to a modification of the present embodiment includes a mounting base 300, a light emitting element 2 that is mounted on the mounting base 300 and emits polarized light 20, and covers the light emitting element 2 to emit light. And a sealing portion 400 made of a light-transmitting resin that transmits the polarized light 20 emitted from the element 2.

  As shown in FIG. 11, the mounting base 300 is disposed at one end of the lead 31 and is configured integrally with the lead 31. In the modification shown in FIG. 11, the lead 31 is used as a cathode electrode. The basic configuration of the mounting base 300 is the same as that of the mounting base 3 of the polarized light source 1 shown in FIG. 2, and includes a mounting surface 30 having a concave cross-sectional shape that also serves as the reflector 30R. The light emitting element 2 is mounted on the bottom surface of the mounting surface 30 of the mounting base 300, and a reflector 30R formed as a tapered surface on the mounting base 300 around the side surface of the mounted light emitting element 2 is configured. A lead 32 is disposed in a region close to the lead 31. The lead 32 is used as an anode electrode, and one end of the lead 32 is electrically connected to the light emitting element 2 through a wire.

  The sealing portion 400 covers the mounting base 300 at one end of the lead 31 and one end of the lead 32, and has a hemispherical lens portion 4 a on the light emitting element 2, that is, a portion that emits the polarized light 20 from the light emitting element 2. The sealing part 400 shown in FIG. 11 is formed of a low birefringence light-transmitting resin having a retardation of ¼ or less of the light source wavelength, like the sealing part 4 of the polarized light source 1 shown in FIG. Has been.

  In addition, the molding method of the sealing part 400 can apply various molding methods, such as the method of dripping from a syringe, the molding method using a dispenser, injection molding, and extrusion molding.

(Other embodiments)
It should not be understood that the descriptions and drawings which form part of the disclosure of the above-described embodiments limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the above embodiment, the surface light emitting device 10 has been described as an example in which one polarization light source 1 is assembled to the light guide plate 11. However, a plurality of surface light emitting devices 10 may be arranged around the light guide plate 11. Moreover, it is good also as a structure which abbreviate | omitted the color filter in the liquid crystal cell 42 using the polarized light source which respectively light-emits red, green, and blue light emission as the polarized light source 1. FIG.

  In each of the above embodiments, the constituent resin of the sealing portion 4 provided in the polarized light source 1 is not only a transparent light-transmitting resin, but also red, green, blue, orange and other pigments are light-transmitting resins. It is good also as a structure mixed in.

  In the said embodiment, although the sealing part 4 of the polarized light source 1 was formed with the low birefringence optically transparent resin whose retardation is 1/4 or less of the light source wavelength, if the polarized light can be emitted, the above A polarized light source that does not have the sealing portion 4 may be used. Thus, even if it is a polarized light source which does not have the sealing part 4, the light quantity of the polarized light which passes to the liquid crystal cell 42 side can be enlarged by providing the light guide plate 11 of the said structure. Therefore, in the present invention, since the disturbance of the polarization can be significantly suppressed in the light guide plate, the light utilization efficiency can be improved even when a polarized light source that emits light with slightly disturbed polarization is used.

  Further, an LED having a nonpolar surface has been used as an example of a light emitting element that emits polarized light, but an LD (laser diode) having a higher polarization ratio can also be used as a light emitting element. Thereby, further improvement in light utilization efficiency can be expected.

It is a schematic diagram which shows a liquid crystal display device provided with the surface emitting device which concerns on embodiment of this invention. It is sectional drawing of the polarized light source which concerns on embodiment of this invention. It is a section explanatory view of a light emitting element used for a polarization light source concerning an embodiment of the invention. It is a crystal structure figure explaining the nonpolar surface of a group III nitride semiconductor. It is a crystal structure figure explaining the atomic arrangement of a group III nitride semiconductor. (A) And (B) is a crystal structure figure explaining the semipolar surface of a group III nitride semiconductor. It is process sectional drawing for demonstrating the manufacturing method of the polarized light source which concerns on embodiment of this invention (the 1). It is process sectional drawing for demonstrating the manufacturing method of the polarized light source which concerns on embodiment of this invention (the 2). It is process sectional drawing for demonstrating the manufacturing method of the polarized light source which concerns on embodiment of this invention (the 3). It is a schematic diagram which shows the other example of the surface emitting device using the polarized light source which concerns on embodiment of this invention. It is sectional drawing which shows the modification of the polarized light source in the surface emitting device which concerns on embodiment of this invention. It is a schematic diagram which shows the liquid crystal display device using the surface emitting device of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Polarized light source 2 ... Light emitting element 3, 300 ... Mounting base 4, 400 ... Sealing part 4a ... Lens part 10 ... Surface light-emitting device 11 ... Light guide plate 11a ... Light incident surface 11b ... Light-emitting surface 20 ... Polarized light 30 ... Mounting Surface 30R ... Reflectors 31, 32 ... Lead 40 ... Liquid crystal display device 41A ... Light transmissive resin 41 ... Polarizing plate 42 ... Liquid crystal cell 43 ... Polarizing plate 50 ... Diffusion plates 60, 70, 80 ... Polarized light 210 ... Output 210A ... Output Surface 211 ... first electrode 212 ... second electrode 220 ... light emitting portion 221 ... first semiconductor layer 222 ... active layer 223 ... second semiconductor layer

Claims (17)

A polarized light source that emits polarized light;
Light having a light incident surface on which polarized light emitted from the polarized light source is incident and a light emitting surface that emits light, and having a low birefringence of retardation equal to or less than ¼ of the wavelength of the polarized light A light guide plate made of a transparent resin;
A surface light emitting device comprising:   2. The surface emitting device according to claim 1, wherein the light transmissive resin is a mixture of a positive birefringent material and a negative birefringent material.   2. The surface emitting device according to claim 1, wherein the light transmissive resin is a copolymer of the positive birefringent material and the negative birefringent material. The positive birefringent material is selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride trifluoroethylene (VDF · TrFE-58), polyethylene oxide (PEO),
The surface light-emitting device according to claim 2, wherein the negative birefringent substance is polymethyl methacrylate (PMMA).   The surface light-emitting device according to claim 1, wherein the light-transmitting resin is a polymer to which a low molecular organic substance having a rod-like molecular shape and anisotropy in polarizability is added.   2. The surface emitting device according to claim 1, wherein the light transmissive resin is a polymer to which inorganic birefringent crystal fine particles are added. The polarized light source is composed of a group III nitride semiconductor whose main surface is a nonpolar surface or a semipolar surface,
A first conductive type first semiconductor layer, a light emitting layer formed on the first semiconductor layer, and a second conductive type second semiconductor layer formed on the light emitting layer. The surface emitting device according to any one of claims 1 to 6. The polarized light source is
A light emitting element that emits polarized light;
A mounting base on which the light emitting element is mounted;
A sealing portion made of the light transmissive resin and covering the light emitting element;
The surface light-emitting device according to claim 1, comprising: The surface light-emitting device according to claim 1, wherein an intrinsic birefringence of the light-transmitting resin is 3 × 10 ⁻³ or less in absolute value. A light emitting element that emits polarized light;
A mounting base on which the light emitting element is mounted;
A retardation part made of a light-transmitting resin having a low birefringence of ¼ or less of the wavelength of the polarized light, and covering the light emitting element;
A polarized light source comprising:   The polarized light source according to claim 10, wherein the light transmissive resin is a mixture of a positive birefringent material and a negative birefringent material.   The polarized light source according to claim 10, wherein the light transmissive resin is a copolymer of the positive birefringent material and the negative birefringent material. The positive birefringent material is selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride trifluoroethylene (VDF · TrFE-58), polyethylene oxide (PEO),
The polarized light source according to claim 11 or 12, wherein the negative birefringent substance is polymethyl methacrylate (PMMA).   11. The polarized light source according to claim 10, wherein the light-transmitting resin is a polymer to which a low molecular organic substance having a rod-like molecular shape and anisotropy in polarizability is added.   The polarized light source according to claim 10, wherein the light transmissive resin is a polymer to which inorganic birefringent crystal fine particles are added. The light emitting element is composed of a group III nitride semiconductor having a nonpolar surface or a semipolar surface as a main surface,
A first conductive type first semiconductor layer, a light emitting layer formed on the first semiconductor layer, and a second conductive type second semiconductor layer formed on the light emitting layer. The polarized light source according to any one of claims 10 to 15. The polarized light source according to any one of claims 10 to 16, wherein an intrinsic birefringence of the light transmissive resin is 3 x ^10-3 or less in absolute value.

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