JP5013315B2 - Illumination light source device, liquid crystal display device, and projector - Google Patents

Description

  The present invention relates to an illumination light source device, a liquid crystal display device, and a projector, and more particularly to an illumination light source device suitable for an illumination light source of a projector using a backlight of a liquid crystal display device or a MEMS.

  Conventionally, there has been disclosed a liquid crystal display device configured to use a near-infrared reflection filter or a bandpass filter as a backlight for illuminating a liquid crystal display panel so as to reflect an oblique incident component (see Patent Document 1). . Conventionally, a projector using a one-dimensional MEMS (Micro-Electro Mechanical Systems) and a laser light source has been disclosed (see Patent Document 2).

US Patent Publication No. 2007/014127 JP 2004-20590 A

  In the backlight for the liquid crystal display device, the light use efficiency is enhanced, but it is not intended to strictly control the light emission angle. Incidentally, with the recent development of light emitting diodes (LEDs), liquid crystal display devices having improved color characteristics using RGB three-color LEDs as light sources instead of white cold cathode tubes have been developed.

  In the projector, the one-dimensional MEMS is illuminated by condensing light from a laser light source in a line shape with a cylindrical lens. In this case, if the laser beam has no large anisotropy, the illumination light beam is irradiated at a narrow angle in the longitudinal direction of the one-dimensional MEMS and at a wide angle in the short direction. For example, considering a one-dimensional MEMS of about 500 pixels, the aspect ratio of the one-dimensional MEMS is about 1: 500, and the ratio of incident angles of illumination light is also about 500: 1.

  In the one-dimensional MEMS, an image is formed by changing the emission direction of the used light and the unused light and blocking the unused light. Therefore, it is desirable that the incident light beam has a narrow angle in the short direction of the one-dimensional MEMS. On the other hand, in the conventional technique using a cylindrical lens, unless the light emission distribution of the light source is special, illumination is performed at a wide angle in the short direction of the one-dimensional MEMS as described above, which is inefficient. It becomes lighting.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an illumination light source device that can supply illumination light with a limited exit angle from an exit surface having a desired shape.

In order to solve the above problem, in the first embodiment of the present invention, in an illumination light source device that emits light from a predetermined surface,
A light source that supplies quasi-monochromatic light;
A light guide plate for propagating light supplied from the light source,
On the exit surface corresponding to the predetermined surface of the light guide plate, a dielectric multilayer film having a function of limiting the exit angle is formed ,
The dielectric multilayer film has a Fabry-Perot type film configuration, and a transmission wavelength region varies depending on the size of the emission angle.
The spacer in the dielectric multilayer film is made of a low refractive index film material,
The refractive index of the spacer with respect to the used light is a factor that determines the dependence of the change in the transmission wavelength range on the emission angle, and the refractive index is smaller than 1.5. To do.

  According to a second aspect of the present invention, there is provided a liquid crystal display device comprising the illumination light source device according to the first aspect and a liquid crystal display panel illuminated by the illumination light source device.

  According to a third aspect of the present invention, there is provided a projector including the illumination light source device according to the first aspect and a MEMS illuminated by the illumination light source device.

  In the illumination light source device of the present invention, a dielectric multilayer film having a bandpass effect is formed on the exit surface of the light guide plate that propagates the quasi-monochromatic light supplied from the light source. As a result, in the illumination light source device of the present invention, illumination light with a limited emission angle is supplied from the emission surface of a desired shape by the action of wavelength shift of the film characteristics due to the emission angle of the dielectric multilayer film having a bandpass effect. be able to.

  Prior to the description of specific embodiments, the principle of the present invention will be described below. In the illumination light source device of the present invention, a dielectric multilayer film having a bandpass function is formed (coated) on the exit surface of the light guide plate, and quasi-monochromatic light is incident from a region (end surface or back surface) other than the exit surface. A dielectric multilayer film having a bandpass action causes a wavelength shift of film characteristics depending on an emission angle as shown in the following formula (1).

In Equation (1), θ is the emission angle of light from the dielectric multilayer film into the air, λ _θ is the wavelength at the emission angle θ, λ ₀ is the wavelength at normal incidence, and N ^* is This is the effective refractive index of the dielectric multilayer film. The relationship between the emission angle θ into the air and the incident angle θ ′ to the dielectric multilayer film in the light guide plate is expressed by the following equation (2), where n is the refractive index of the light guide plate. Is done.
sinθ = n × sinθ ′ (2)

  Referring to Equation (1), it can be seen that the transmission wavelength region shifts to the short wavelength side as the emission angle θ increases. For this reason, when quasi-monochromatic light is incident on the light guide plate, light having an emission angle greater than a predetermined angle out of the incident light on the dielectric multilayer film is reflected by the dielectric multilayer film and can be emitted from the light guide plate. Can not. In other words, only light having an emission angle smaller than a predetermined angle can be emitted, and the light reflected by the dielectric multilayer film is reflected and scattered inside the light guide plate until the emission angle becomes smaller than the predetermined angle. repeat.

  As a result, the light amount distribution on the exit surface becomes relatively uniform, and only light having an exit angle equal to or less than a predetermined angle is emitted from the exit surface. Since the shape of the exit surface depends on the shape of the light guide plate, for example, an elongated shape corresponding to one-dimensional MEMS is possible. As described above, in the illumination light source device of the present invention, the illumination light whose emission angle is limited is supplied from the emission surface of a desired shape by the action of the wavelength shift of the film characteristic due to the emission angle of the dielectric multilayer film having the bandpass effect. can do.

Referring to Equation (1), it can be seen that the angle dependency of the wavelength shift increases as the effective refractive index N ^* decreases. Therefore, in order to control the exit angle θ with high accuracy, it is preferable that the effective refractive index N ^* is small. In general, the film configuration of a dielectric multilayer film having a bandpass action is (HL) ⁿ HLLH (LH) ⁿ or (HL) ⁿ HH (LH) ⁿ . Here, H represents a film material having a high refractive index, and L represents a film material having a low refractive index. When the wavelength of light is λ, the refractive index of the film material is n, and the physical thickness of the film is h, the optical thickness n × h of the film is λ / 4.

In (HL) ⁿ HLLH (LH) ⁿ , (HL) ⁿ H and H (LH) ⁿ are reflective films, and LL is a spacer. In (HL) ⁿ HH (LH) ⁿ , (HL) ⁿ and (LH) ⁿ are reflective films, and HH is a spacer. That is, a Fabry-Perot dielectric multilayer film having a reflective film-spacer-reflective film structure can be used as the dielectric multilayer film having a bandpass function. The spacer is not limited to LL and HH, and may be any spacer having an optical thickness that is an integral multiple of λ / 2, such as LLLL and HHHH.

The effective refractive index N ^* in the formula (1) depends on the configuration of the film material, but in the Fabry-Perot type dielectric multilayer film having the reflective film-spacer-reflective film structure, the effective refractive index N ^* is In particular, it is greatly influenced by the refractive index of the spacer. Therefore, the use of the film material L having a low refractive index as the spacer can increase the angle dependency of the wavelength shift, which is advantageous for highly accurate control of the emission angle θ. Specifically, the refractive index of the spacer with respect to the light used is preferably less than 1.5. Incidentally, the refractive index of MgF _{2 that} can be used as a spacer is about 1.38, and the refractive index of SiO ₂ is about 1.46.

The film configuration of the dielectric multilayer film having the bandpass action is not limited to, for example, (HL) ⁿ HLLH (LH) ⁿ , and (HL) ⁿ HLLH (LH) ⁿ and (HL) ⁿ HLLH (LH) ⁿ If the multi-stack is repeated with the low refractive index film material L interposed therebetween, the transmission characteristics of the dielectric multilayer film can be made rectangular. It is also possible to optimize the transmission characteristics by devising the film thickness of the dielectric multilayer film and the outermost film. Also in this case, the influence of the refractive index of the spacer on the angle dependency of the wavelength shift is great. Furthermore, by devising the film thickness of the spacer, a transmission band can be obtained for a plurality of wavelengths.

  Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a configuration of an illumination light source apparatus according to the first embodiment of the present invention. In the first embodiment, the present invention is applied to an illumination light source of a projector using MEMS. The illumination light source device of the first embodiment includes a light source 1 that supplies quasi-monochromatic light, and a light guide plate (for example, a plate-shaped light propagation member) 2 that propagates light supplied from the light source 1.

As the light source 1, for example, a laser light source that emits light having a wavelength of 532 nm can be used. Although there are cases where a plurality of light sources are provided depending on the required light quantity, a case where a single light source is provided will be considered below for the sake of simplicity. The light source 1 is disposed close to the end surface 2 a of the light guide plate 2 so that light from the light source 1 enters the end surface (side surface) 2 a of the light guide plate 2. A dielectric multilayer film 3 having a band-pass function with wavelength characteristics as shown in FIG. 2 is formed on the exit surface (surface from which light is emitted) 2 b of the light guide plate 2. The effective refractive index N ^* of the dielectric multilayer film 3 is, for example, 1.6.

  A reflection film (not shown) is formed in a region other than the light incident region in the end surface 2 a of the light guide plate 2. In addition, a reflection film (not shown) is also formed on the other end face other than the end face 2a (in FIG. 2, only one end face facing the end face 2a is shown among the other three end faces) 2c. Yes. The back surface 2d facing the light exit surface 2b of the light guide plate 2 is a scattering surface, and a reflective film (not shown) is formed on the scattering surface. Thereby, the back surface 2d of the light guide plate 2 has a reflecting action and a scattering action. It should be noted that the region other than the incident region of the end surface 2a and the end surface 2c can have a reflecting action and a scattering action. As will be described later, the higher the reflectivity of the reflective film and the smaller the light transmission region, the higher the light utilization efficiency.

In FIG. 2 showing the wavelength characteristic of the transmittance of the dielectric multilayer film 3, the vertical axis represents the light transmittance, and the horizontal axis represents the light wavelength. Further, the solid line 21 indicates 532 nm which is the wavelength of the light from the light source 1, the broken line 22 indicates 535.2 nm which is the falling wavelength of the vertical emission (emission angle 0 degree), and the reference numeral 23 indicates the transmission characteristic of the vertical emission. Reference numeral 24 indicates a transmittance characteristic for 10 ° emission (output angle 10 °). According to equation (1), when the effective refractive index N ^* is 1.6 and the falling wavelength of vertical emission is 535.2 nm, the falling wavelength of 10 ° emission shifts to 532 nm.

  Therefore, the light incident on the end surface 2a of the light guide plate 2 from the light source 1 propagates through the light guide plate 2, is reflected and scattered by, for example, the back surface 2d, and enters the output surface 2b. At this time, the transmittance characteristic of the dielectric multilayer film 3 depends on the incident angle θ ′ of the light to the emission surface 2b, and consequently the emission angle θ of the light emitted from the dielectric multilayer film 3. Different. Specifically, as shown in FIG. 2, in the case of vertical emission, the transmittance of the dielectric multilayer film 3 with respect to light having a wavelength of 532 nm is sufficiently high. Therefore, the light perpendicularly incident on the emission surface 2 b passes through the dielectric multilayer film 3 and is emitted from the light guide plate 2 at an emission angle θ = 0 degrees.

  On the other hand, in the case of 10 degree emission, the transmittance of the dielectric multilayer film 3 with respect to light having a wavelength of 532 nm is significantly reduced as compared with the case of vertical emission. Therefore, the light incident on the emission surface 2b at an incident angle θ ′ such that the emission angle θ from the dielectric multilayer film 3 exceeds 10 degrees is reflected without passing through the dielectric multilayer film 3 and is again reflected on the back surface 2d. Incident and reflected and scattered. The light reflected and scattered by the back surface 2d is directly incident on the emission surface 2b, or incident on the emission surface 2b after being reflected by a region other than the incidence region of the end surface 2a or the end surface 2c.

  At this time, light having an emission angle θ of 10 degrees or less is transmitted through the dielectric multilayer film 3 and emitted from the light guide plate 2, but light having an emission angle θ exceeding 10 degrees is emitted from the dielectric multilayer film. 3 is reflected back to the back surface 2d. In this way, only light having an emission angle θ of 10 degrees or less is transmitted through the dielectric multilayer film 3 and emitted from the light guide plate 2 while repeating reflection scattering on the back surface 2d and incidence on the emission surface 2b. As described above, the dielectric multilayer film 3 has an emission angle-dependent transmittance characteristic as shown in FIG. 3, that is, an emission angle characteristic of the transmittance.

  As described above, in the illumination light source device according to the first embodiment, only the light having an emission angle of, for example, 10 degrees or less is generated by the action of the dielectric multilayer film 3 coated on the emission surface 2 b of the light guide plate 2. The light emitted from the light exit surface 2b is repeatedly reflected and scattered inside the light guide plate 2 until the other light has an exit angle of 10 degrees or less. As a result, the light amount distribution on the exit surface 2b of the light guide plate 2 becomes relatively uniform, and only light having an exit angle of 10 degrees or less is emitted from the light guide plate 2 in a limited manner.

  Since the shape of the emission surface 2b depends on the shape of the light guide plate 2, for example, when a one-dimensional MEMS is arranged facing the emission surface 2b, an elongated emission surface 2b corresponding to the one-dimensional MEMS is realized. It is also possible. As described above, in the illumination light source device according to the first embodiment, the emission angle is limited from the emission surface 2b having a desired shape by the action of wavelength shift of the film characteristic due to the emission angle of the dielectric multilayer film 3 having the bandpass function. Illumination light can be supplied. In particular, when illuminating a one-dimensional MEMS, since the illumination is performed at a narrow angle in the short direction, it is possible to realize illumination that is more efficient than in the related art.

  In the first embodiment described above, the light source 1 is disposed close to the end surface 2 a of the light guide plate 2, and the light from the light source 1 is directly incident on the end surface 2 a of the light guide plate 2. However, the present invention is not limited to this. For example, as shown in FIG. 4, a modification in which the condenser lens 4 is disposed in the optical path between the light source 1 and the end surface 2 a of the light guide plate 2 is also possible. In the modification of FIG. 4, the light from the light source 1 is condensed by the condenser lens 4 and the incident area on the end surface 2a of the light guide plate 2 can be reduced, so that the light utilization efficiency can be improved. .

  Further, in the first embodiment described above, an edge light system is adopted in which light from the light source 1 is incident on the end surface (side surface adjacent to the exit surface 2b) 2a of the light guide plate 2. However, the present invention is not limited to this, and a modification in which light from the light source 1 is incident from the back surface 2d of the light guide plate 2 as shown in FIG. 5 is also possible. In the modification of FIG. 5, for example, a reflection film is formed on the four end surfaces 2 a and 2 c, and the reflection film is formed using a region other than the incident region on the back surface 2 d as a scattering surface. In the modification of FIG. 5, a condensing lens can be disposed in the optical path between the light source 1 and the back surface 2 d of the light guide plate 2. The end faces 2a and 2c can also have a reflecting action and a scattering action.

  FIG. 6 is a diagram schematically showing a configuration of an illumination light source apparatus according to the second embodiment of the present invention. In the second embodiment, the present invention is applied to the backlight of the liquid crystal display device. The illumination light source device of the second embodiment includes a light source 11 that supplies quasi-monochromatic light and a light guide plate 12 that propagates light supplied from the light source 11. As the light source 11, for example, RGB three-color LEDs having a wavelength width of about 20 nm with a full width at half maximum can be used.

  There may be a case where a plurality of light sources are provided according to a necessary light quantity, or a case where each of R, G, and B is provided with individual light sources. The light source 11 is disposed close to the end surface 12 a of the light guide plate 12 so that light from the light source 11 enters the end surface 12 a of the light guide plate 12. If necessary, a condensing lens can be provided in the optical path between the light source 11 and the light guide plate 12. A dielectric multilayer film 13 having a triple band pass function with wavelength characteristics as shown in FIG. 7 is formed on the emission surface 12 b of the light guide plate 12.

The effective refractive index N ^* of the dielectric multilayer film 13 is, for example, 1.6. A reflection film (not shown) is formed in a region other than the light incident region in the end surface 12 a of the light guide plate 12. A reflective film (not shown) is also formed on the end face 12c other than the end face 12a. The back surface 12d facing the light exit surface 12b of the light guide plate 12 is a scattering surface, and a reflective film (not shown) is formed on the scattering surface. It should be noted that the region other than the incident region of the end surface 12a and the end surface 12c can have a reflecting action and a scattering action.

  In FIG. 7, the vertical axis represents light transmittance or light intensity, and the horizontal axis represents light wavelength. Reference numeral 71 is a transmittance characteristic for light of B (Blue), reference numeral 72 is a transmittance characteristic for light of G (Green), and reference numeral 73 is a transmission characteristic for light of R (Red). The rate characteristic is shown. Reference numeral 81 is a wavelength distribution of B light emitted from the LED 11, reference numeral 82 is a wavelength distribution of G light emitted from the LED 11, and reference numeral 83 is a wavelength of R light emitted from the LED 11. Distribution is shown.

As shown in FIG. 7, the transmission wavelength band for each wavelength B, G, R of the dielectric multilayer film 13 is set to about 20 nm which is the full width at half maximum of the wavelength width of each wavelength light emitted from the LED 11. . According to the equation (1), when the effective refractive index N ^* of the dielectric multilayer film 13 is 1.6, the wavelength shift of 20 nm occurs when the emission angle θ is about 25 degrees. Therefore, the light incident on the output surface 12b at an incident angle θ ′ such that the output angle θ from the dielectric multilayer film 13 exceeds 25 degrees, for example, is reflected without passing through the dielectric multilayer film 13 and reflected on the back surface 12d. It is incident again and reflected and scattered.

  The light reflected and scattered by the back surface 12d is directly incident on the exit surface 12b, or is reflected by the region other than the entrance region of the end surface 12a or the end surface 12c and then enters the exit surface 12b. At this time, light having an emission angle θ of 25 degrees or less is transmitted through the dielectric multilayer film 13 and emitted from the light guide plate 12. However, light having an emission angle θ exceeding 25 degrees is emitted from the dielectric multilayer film. 13 is reflected back to the back surface 12d. In this way, only light having an emission angle θ of 25 degrees or less is transmitted through the dielectric multilayer film 13 and emitted from the light guide plate 12 while repeating reflection scattering on the back surface 12d and incidence on the emission surface 12b.

  As described above, in the illumination light source device according to the second embodiment, only the light having an emission angle of, for example, 25 degrees or less is generated by the action of the dielectric multilayer film 13 coated on the emission surface 12 b of the light guide plate 12. Light other than that emitted from the emission surface 12b is repeatedly reflected and scattered inside the light guide plate 12 until the emission angle is 25 degrees or less. As a result, the light quantity distribution on the exit surface 12b of the light guide plate 12 becomes relatively uniform, and only light having an exit angle of 25 degrees or less is emitted from the light guide plate 12 in a limited manner.

  In the second embodiment, as shown in FIG. 7, since the wavelength distribution of the light emitted from the LED 11 has a shape with a tail, the emission angle characteristic of the transmittance of the dielectric multilayer film 13 also has a bottom. However, if it is limited to light in the vicinity of the center wavelength, the angular distribution of emitted light is limited. If the wavelength width of the light emitted from the LED 11 is further narrowed, the emission angle can be limited to a narrower angle range.

It is a figure which shows schematically the structure of the illumination light source device concerning 1st Embodiment of this invention. It is a figure which shows the wavelength characteristic of the transmittance | permeability of the dielectric multilayer film in 1st Embodiment. It is a figure which shows the outgoing angle characteristic of the transmittance | permeability of the dielectric multilayer film in 1st Embodiment. It is a figure which shows schematically the structure of the illumination light source device concerning the 1st modification of 1st Embodiment. It is a figure which shows schematically the structure of the illumination light source device concerning the 2nd modification of 1st Embodiment. It is a figure which shows schematically the structure of the illumination light source device concerning 2nd Embodiment of this invention. It is a figure which shows the wavelength characteristic of the transmittance | permeability of the dielectric multilayer in 2nd Embodiment, and the wavelength distribution of the light from a light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Light source 2,12 Light-guide plate 2a, 12a Incident end surface 2b, 12b Outgoing surface 2d, 12d Back surface 3,13 Dielectric multilayer film 4 which has a band pass action 4 Condensing lens

Claims (8)

In an illumination light source device that emits light from a predetermined surface,
A light source that supplies quasi-monochromatic light;
A light guide plate for propagating light supplied from the light source,
On the exit surface corresponding to the predetermined surface of the light guide plate, a dielectric multilayer film having a function of limiting the exit angle is formed ,
The dielectric multilayer film has a Fabry-Perot type film configuration, and a transmission wavelength region varies depending on the size of the emission angle.
The spacer in the dielectric multilayer film is made of a low refractive index film material,
The refractive index of the spacer with respect to the used light is a factor that determines the dependence of the change of the transmission wavelength range on the emission angle, and the refractive index is smaller than 1.5 . The reflective film is formed in the area | region other than the incident area | region where the light from the said light source injects, and the said output surface among the outer surfaces of the said light-guide plate, The reflective film is formed . Illumination light source device. The illumination light source device according to claim 2, wherein a reflection film is formed on the scattering surface so as to have a reflection action and a scattering action on a back surface of the light guide plate facing the emission surface . 4. The illumination light source device according to claim 1, wherein light from the light source is configured to be incident from an end surface adjacent to the emission surface . 5. 4. The illumination light source device according to claim 1, wherein light from the light source is configured to be incident from a back surface facing the emission surface . 5. The illumination light source device according to claim 1, further comprising a condensing lens disposed in an optical path between the light source and the light guide plate . A liquid crystal display device comprising: the illumination light source device according to claim 1; and a liquid crystal display panel illuminated by the illumination light source device . A projector comprising: the illumination light source device according to any one of claims 1 to 6; and a MEMS illuminated by the illumination light source device .

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