JP2013246907A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device capable of obtaining images of high light utilization efficiency, low cost and high luminance, by controlling polarizing components of illumination light without widening orientation distribution of retroreflection light.SOLUTION: In a lighting device provided with a light-emitting element, a rod-type integrator with an incident face for receiving light emitted by the light-emitting element and an emission face opposed to the incident face for emitting light, and a reflective polarizer arranged on the emission face of the rod-type integrator, the rod-type integrator is so structured to have its refraction index diminished from the center part toward an outer periphery part.

Description

  The present invention relates to an illuminating device, and more particularly, to an illuminating device that is suitably used for a small projector and has high efficiency, high luminance, and high added value.

Conventionally, there is an illumination device corresponding to a small projection type video display device (pico projector).
In recent years, in such illuminating devices, a light source, a rod-type optical integrator (hereinafter referred to as a rod-type integrator) as an optical element for condensing light from the light source efficiently and with a uniform illuminance distribution, and a reflective type Some have a liquid crystal panel and a projection optical system.

Moreover, the said illuminating device WHEREIN: What provided the reflection type polarizer in the output surface side of a rod type integrator is disclosed (patent documents 1-3).
Further, as in the illumination device shown in FIG. 7, there is disclosed a light source module 1 having a structure in which a rod type integrator 4 is assembled to a light source 3 (LED) having a high reflectance film formed on a reflection surface of a package 2. (Patent Document 4).
In such an illuminating device, the light emitted from the light source 3 passes through the rod integrator 4, and the polarized light is adjusted and emitted by the reflective polarizer 5 disposed on the exit surface side of the rod integrator 4. In FIG. 7, the behavior of typical components (one polarized component, the other polarized component, and the retroreflective component) of the light emitted from the light source 3 is schematically shown by three types of arrows. (See FIG. 1).

JP 2003-241193 A JP 2003-98483 A JP2011-138627A JP 2010-171164 A

Thereby, the polarization component of the illumination light emitted from the light source 3 is adjusted by the reflective polarizer 5, and the light emitted from the rod integrator 4 can be efficiently incident on the light valve (reflective liquid crystal panel). It has become possible. However, the reflection type polarizer 5 tends to deteriorate the efficiency (transmittance and contrast) when the incident angle is large, and depending on the orientation distribution (light intensity distribution with respect to the emission angle) of the light emitted from the rod-type integrator 4, There was a problem that the final light utilization efficiency as a lighting device did not change.
The present invention has been made in view of the problems as described above, and by controlling the polarization component of illumination light without widening the orientation distribution of retroreflected light, the light use efficiency is high, and it is inexpensive and has high brightness. An object of the present invention is to provide an illumination device that can obtain the image of

  A first feature of the present invention is a light-emitting element, a rod-type integrator having an incident surface that receives light emitted from the light-emitting element, an emission surface that faces the incident surface and emits light, and the emission of the rod-type integrator A gist of a lighting device including a reflective polarizer disposed on a surface is that a rod-type integrator is configured such that a refractive index decreases from a central portion toward an outer peripheral portion.

  The second feature of the present invention is summarized in that the refractive index of the rod integrator changes in a parabolic shape.

  Furthermore, the third feature of the present invention is summarized in that the reflective polarizer is a wire grid polarizer.

  By adopting a rod type integrator having a parabolic refractive index distribution characteristic, the amount of light emitted from the reflective polarizer can be increased.

  According to the present invention, a rod integrator used in combination with a reflective polarizer is one that has a refractive index distribution characteristic such that the refractive index decreases from the central part toward the outer peripheral part. The amount of light emitted from the type polarizer can be increased, thereby achieving high brightness and low power consumption of the pico projector.

It is typical sectional drawing which shows an example of embodiment of the illuminating device concerning this invention. It is explanatory drawing which showed typically the refractive index distribution of the GRIN integrator in the illuminating device concerning this invention. It is explanatory drawing which showed typically the refractive index distribution of the conventional rod type | mold integrator. (A) The figure which showed light intensity distribution with respect to the angle of the emitted light of the GRIN integrator at the time of pitch 1/8, and a conventional rod type integrator, (b) GRIN integrator at the time of pitch 1/4, and a conventional rod type It is the figure which showed light intensity distribution with respect to the angle of the emitted light with an integrator. It is the figure which showed the characteristic depending on the incident angle of a reflection type polarizer. It is a figure which shows the result of having analyzed the orientation distribution of the light radiate | emitted from a half mirror in the structure which has arrange | positioned the half mirror on the output surface of a GRIN integrator. It is typical explanatory drawing which showed an example of the conventional illuminating device.

Hereinafter, an embodiment for carrying out a lighting device according to the present invention will be described and described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of the lighting device 10.
The illuminating device 10 has a reflecting portion 12 arranged on the substrate 11, a light emitting element 13 (hereinafter referred to as an LED 13) provided at the center of the reflecting portion 12, and an axial center (optical axis) in the central direction of the outgoing optical axis of the LED 13. And a reflective polarizer 15 disposed on the light exit surface opposite to the light incident surface of the rod integrator 14 on the LED 13 placement side.

The reflecting portion 12 on the substrate 11 is provided with a recess 12a for installing the LED 13 in the center. In the recess 12a, an inclined surface 12c is formed as a reflection surface of light emitted from the LED 13 so as to surround the LED 13 installed at the center of the bottom 12b.
The light emitted from the LED 13 is reflected by the inclined surface portion 12c and is incident on the lot type integrator 14 described later. In addition, the reflection part 12 has the function to dissipate the heat | fever emitted from LED13 other than a light reflection function.

Next, the rod type integrator 14 will be described.
Here, the rod type integrator 14 is a gradient index type (GRIN: Gradient index).
lens) lenses can be used. Hereinafter, the rod-type integrator 14 is referred to as a GRIN integrator 14.
The GRIN integrator 14 is made of a material (Selfoc (registered trademark): Nippon Sheet Glass Co., Ltd.) having a refractive index gradient in the radial direction so that the refractive index decreases from the center (optical axis) toward the outer periphery. . This material has a refractive index that changes parabolically as a function of radius, and is expressed by the following equation.
n _r = n ₀ [1-A / 2 · r ² ] (1)
Here, n _r : refractive index at a distance r from the optical axis, n ₀ : design refractive index at the optical axis, and A: positive constant.
Due to the parabolic refractive index distribution, incident light from the front surface (incident surface) takes a sinusoidal optical path along the rod lens (see FIG. 2). The period of the sinusoidal optical path is called the “pitch” of the lens, and is one of the important parameters of the imaging function of the gradient index lens. The pitch is given by:
P = 2π / √A ……………………… (2)
The lens length of the GRIN integrator 14 here is set so that, for example, P = 1/2.
For reference, FIG. 3 shows a refractive index distribution corresponding to the distance from the optical axis, with the optical axis in the rod as the center, for a normal rod integrator. The refractive index distribution is substantially constant regardless of the location.

  Next, as the reflective polarizer 15, a known one can be used. Here, a so-called wire grid type polarizer is used. In the wire grid polarizer, a large number of wires are arranged at a narrow pitch (ex. 100 to 150 nm) based on a resin film. Polarized waves parallel to the wire are reflected and polarized waves perpendicular to the wire are transmitted.

In the illuminating device 10 having the above-described configuration, the light emitted from the LED 13 at the center of the reflecting portion 12 disposed on the substrate 11 is directly incident on the incident surface of the GRIN integrator 14 on the side where the LED 13 is disposed and is reflected at the same time. Reflected light from the inclined surface portion 12c of the concave portion 12a of the portion 12 enters.
The light incident on the GRIN integrator 14 travels in the axial direction of the GRIN integrator 14 and enters the reflective polarizer 15 from the exit surface.

As described above, when light passes through the GRIN integrator 14, the material of the GRIN integrator 14 is incident from the front because of the refractive index distribution in which the refractive index changes parabolically as a function of radius (see FIG. 2). The light ray takes a sinusoidal optical path along the rod lens.
4A and 4B show the light intensity distribution with respect to the angle of the emitted light from the conventional rod integrator and the GRIN integrator 14.
4A shows the case where the pitch is 1/8, and FIG. 4B shows the case where the pitch is 1/4 (note that the rod-type integrator has the same external shape as the GRIN integrator 14). )
When the pitch in FIG. 4A is 1/8, the emission angle is 0 degree, that is, the intensity of light passing through the center of the optical axis of the GRIN integrator 14 is larger than that of the conventional rod integrator, and the emission The intensity is attenuated as the emission direction is inclined (the absolute value of the emission angle is increased) with the light intensity at an angle of 0 degree as a vertex. In the case where the pitch in FIG. 4B is 1/4, the light intensity when the emission angle is 0 degree is larger than that of the conventional rod-type integrator, and the emission angle is within a certain range (−20 degrees). (About +20 degrees), the light intensity is maintained substantially constant.

  When the outgoing light as described above is incident on the reflective polarizer 15, one polarized component b <b> 1 of the incident light is transmitted through the reflective polarizer 15. The other polarization component b2a is reflected in the GRIN integrator 14, and becomes re-reflected light b2b from the incident surface of the GRIN integrator 14, and travels through the GRIN integrator 14. If the retroreflected light b <b> 2 b has the same polarization plane as the one polarization component b <b> 1 transmitted through the reflective polarizer 15, the retroreflected light b <b> 2 b can pass through the reflective polarizer 15.

  Then, it is known that the reflective polarizer 15 on which the outgoing light as described above is incident has characteristics depending on the incident angle, as shown in FIG. Here, the solid line indicates the transmittance, and the broken line indicates the contrast. The transmittance tends to decrease as the incident angle increases from 0 degree (as the absolute value increases). On the other hand, the contrast depends on the incident angle depending on the wavelength, and the maximum incident angle is from 0 °. Although it is not necessarily strict such as deviating, it can be said that the whole tends to decrease as the incident angle becomes larger, similarly to the transmittance.

  It can be easily understood that the amount of linearly polarized light emitted from the reflective polarizer can be increased synergistically when the light having passed through the GRIN integrator 14 is incident on the reflective polarizer 15 exhibiting the above incident angle dependency. Let's be done.

For reference, FIG. 6 shows the result of analyzing the orientation distribution of the light emitted from the half mirror in the configuration in which the half mirror is arranged on the exit surface of the GRIN integrator 14. Replacing the reflective polarizer with a half mirror is an optical element that returns half of the incident light to the integrator regardless of the polarization direction. This is because it is considered that the effect of providing the refraction distribution can be confirmed.
As can be seen from the figure, the light emitted from the half mirror has a narrow orientation distribution (a narrow orientation distribution is maintained) and the amount of emitted light increases by using the GRIN integrator.

DESCRIPTION OF SYMBOLS 10 Illuminating device 11 Board | substrate 12 Reflection part 12a Recessed part 12b Bottom part 12c Slope part 13 LED
14 GRIN Integrator 15 Reflective Polarizer

Claims (3)

A light emitting element;
An incident surface that receives light emitted by the light emitting element, a rod-type integrator that faces the incident surface and emits light, and a reflective polarizer disposed on the output surface of the rod-type integrator; In a lighting device comprising:
The rod-type integrator is configured to have a refractive index that decreases from a central portion toward an outer peripheral portion.   The illumination device according to claim 1, wherein a refractive index of the rod integrator changes in a parabolic shape.   The illumination apparatus according to claim 1, wherein the reflective polarizer is a wire grid polarizer.