JP2005258028A - Optical component and projection type display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide optical components of high cooling ability and high reliability, where magnesium oxide is used as glass material. <P>SOLUTION: The whole surface of a plano-convex lens 200 where the monocristal magnesium oxide is used as the glass material is covered with a protection film constituted of silicon nitride, and a polarizing plate 202 is stuck on the planar surface 201 of the plano-convex lens 200 covered with the protection film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical component and a projection display device using the optical component.

  First, an optical system of a projection display apparatus using a liquid crystal panel will be described with reference to FIG. In a projection display device that projects a color image on a projection screen, the light beam emitted from the light source 1 is reflected by the reflector 2, and the luminance distribution is made uniform by the integrators 31 and 32 and the field lens 5. Before entering the field lens 5, the polarization conversion element 4 performs polarization separation and polarization conversion to obtain an S-polarized light beam. The white light that has passed through the field lens 5 is incident on the dichroic mirror 61 to separate the red light (R), and the dichroic mirror 62 separates the green light (G) and the blue light (B). Of each color light, red light (R) is incident on the red liquid crystal panel 11R through the reflection mirror 71 and the condenser lens 9R. The green light (G) enters the green liquid crystal panel 11G through the condenser lens. The blue light (B) enters the blue liquid crystal panel 11B through a relay optical system constituted by the relay lenses 81 and 82 and the reflection mirrors 72 and 73. Here, incident-side polarizing plates 10R, 10G, and 10B are arranged on the incident side of the respective color liquid crystal panels 11R, 11G, and 11B. These incident side polarizing plates 10R, 10G, and 10B are for aligning the polarization planes of polarized light incident on the color liquid crystal panels 11R, 11G, and 11B. In addition, output side polarizing plates 12R, 12G, and 12B are also arranged on the output side of the respective color liquid crystal panels 11R, 11G, and 11B. These exit side polarizing plates 12R, 12G, and 12B are for aligning the polarization planes of polarized light modulated by the respective color liquid crystal panels 11R, 11G, and 11B. The transmission axes of the incident side polarizing plates 10R, 10G, and 10B and the output side polarizing plates 12R, 12G, and 12B are set so as to be orthogonal to each other (crossed Nicols). Only light in the same direction is transmitted, and light having other polarization directions is absorbed by the output-side polarizing plates 12R, 12G, and 12B. The color lights incident on the liquid crystal panels 11R, 11G, and 11B are subjected to light modulation by the liquid crystal panels 11R, 11G, and 11B. Projected onto the projection screen.

  Here, organic materials such as liquid crystal and polyvinyl alcohol are usually used for the liquid crystal panel, the incident side polarizing plate, and the outgoing side polarizing plate as described above. However, the performance of organic materials is degraded by ultraviolet rays and heat. Therefore, it is common to arrange a UV cut filter or the like in front of the liquid crystal panel or polarizing plate. It is also common to provide a means for cooling the liquid crystal panel and the polarizing plate to suppress the temperature rise.

Patent Document 1 discloses a method of cooling a liquid crystal panel or a polarizing plate by air cooling, and the technique disclosed in Patent Document 1 is established as a standard technique today. However, only the technique described in Patent Document 1 has made it difficult to sufficiently suppress the temperature rise of the liquid crystal panel and the polarizing plate accompanying the increase in the light amount of the light source. Therefore, cooling is performed by increasing the thermal conductivity of a translucent substrate (a general polarizing plate has a structure in which an organic material is attached to a translucent substrate such as a glass substrate) that is a main member of the polarizing plate. Technology to improve efficiency has been developed. For example, Patent Document 2 discloses a technique using a single crystal sapphire substrate as a light-transmitting substrate, Patent Document 3 discloses a technique using a quartz substrate, and Patent Document 4 discloses a technique using a magnesia ceramic substrate. Yes. These techniques aim to improve the cooling efficiency by using a light-transmitting substrate having a larger thermal conductivity than that of a conventional glass substrate.
Japanese Patent Laid-Open No. 1-289912 Japanese Patent Laid-Open No. 11-337919 Japanese Patent Laid-Open No. 2002-14419 JP 2003-294949 A JP 2002-214706 A

  Among the above-described conventional techniques, those described in Patent Document 2 and Patent Document 3 are techniques that use a translucent substrate made of a uniaxial crystal, and as described in each document, polarization It is necessary to make the polarization axis of the plate coincide with the crystal axis of the uniaxial crystal within a specified angle. This is an unavoidable problem as long as a translucent substrate made of a uniaxial crystal is used. Therefore, in the process of attaching the light-transmitting substrate and the organic material, there are problems such as quality assurance such as management of angle deviation and high cost of the manufacturing process. The technique described in Patent Document 4 uses an optically isotropic magnesia ceramic substrate as the translucent substrate, and therefore management of angular deviation is not necessary. However, since it is a polycrystal and has grain boundaries, and magnesium oxide, which is a material thereof, has hygroscopicity, the transmittance of the magnesia ceramic substrate changes with time, and there is a problem in reliability.

  The present invention has been made in view of the problems of the prior art as described above, and realizes an optical component having high reliability and high cooling efficiency, and a projection display device using the optical component. For the purpose.

  The optical component of the present invention that achieves the above object uses magnesium oxide as a glass material, and the surface is covered with nitride or oxide. For this reason, the nitride and oxide which coat | cover the surface of magnesium oxide function as a protective film (moisture absorption prevention film | membrane), the moisture absorption of magnesium oxide is suppressed, and the transmittance | permeability fall is suppressed. At this time, if single crystal magnesium oxide having no grain boundary is used as a glass material, a decrease in transmittance due to moisture absorption is further suppressed.

  Further, by making the refractive index of the protective film equal to the refractive index of magnesium oxide, there is an advantage that restrictions on various coatings are eased. A method of making the refractive index of the protective film made of nitride equal to the refractive index of magnesium oxide can be realized by bonding an oxide to the nitride at the time of film formation. For example, when the protective film is formed by reactive RF sputtering, the oxide can be bonded to the nitride by increasing the sputtering gas pressure. In addition, when a protective film is formed by a plasma CVD (Chemical Vapor Deposition) method, an oxide can be bonded to a nitride by adding oxygen to a reaction gas.

  The projection display device of the present invention that achieves the above object includes an illumination optical system for irradiating an image forming element with light emitted from a light source, and projection optics for projecting image light formed by the image forming element. The optical component of the present invention is used as an optical component constituting the system.

  The optical component of the present invention uses magnesium oxide as a glass material, and the surface thereof is coated with nitride or oxide. Therefore, a reduction in transmittance due to moisture absorption is suppressed without impairing the excellent cooling performance of magnesium oxide, and an optical component having high reliability and high cooling efficiency is realized.

  In the projection display device of the present invention, all or part of the optical system is constituted by the optical component of the present invention having excellent reliability and cooling efficiency. Therefore, the restriction caused by the temperature rise of the optical component is relaxed, the degree of freedom of design is improved, and various demands such as high luminance by increasing the light quantity of the light source can be met.

(Embodiment 1)
Hereinafter, an example of an embodiment of the optical component of the present invention will be described by taking as an example the case where the optical component is a polarizing element. FIG. 1 is a schematic perspective view of a polarizing element described here. In the polarizing element shown in FIG. 1, a protective film (not shown) is formed on the entire surface of a planoconvex lens 200 made of a single crystal of magnesium oxide (hereinafter referred to as “single crystal magnesium oxide”), and the flat surface 201 of the planoconvex lens 200 is formed. A polarizing plate 202 is pasted on the protective film covering the film. That is, the main part of the polarizing element of this example is a plano-convex lens 200, and the plano-convex lens 200 is formed using single crystal magnesium oxide as a glass material. The polarizing plate 202 is an existing polarizing plate in which a polarizing film is formed on the surface of a light-transmitting plate material.

  Single crystal magnesium oxide, which is a glass material of the plano-convex lens 200, has a face-centered cubic (fcc) crystal structure and is optically isotropic. Accordingly, the refractive index and transmittance are uniform regardless of which surface is cut out. This means that it is not necessary to make the polarization axis of the polarizing plate 202 coincide with the crystal orientation as in the case of using a plano-convex lens made of uniaxial crystal such as single crystal sapphire or crystal. This is one of the advantages of using the plano-convex lens 200 made of crystalline magnesium oxide. In this example, the plano-convex lens 200 is formed so that the (100) plane of the single crystal magnesium oxide becomes the flat surface 201 of the plano-convex lens 200 in consideration of economy.

  In addition, the single crystal magnesium oxide does not have a grain boundary like a polycrystal as a matter of course. If there is a grain boundary, moisture permeates into the inside from the grain boundary, and there is a disadvantage that the transmittance of magnesium oxide tends to decrease due to moisture absorption. However, according to the polarizing element of this example using the plano-convex lens 200 made of single crystal magnesium oxide, there is no such inconvenience as described above. This is also one of the advantages of using the plano-convex lens 200 made of single crystal magnesium oxide. Furthermore, when moisture permeates from the grain boundary, the transmittance starts to decrease from the vicinity of the grain boundary, resulting in a distribution in the transmittance, causing display unevenness and microscopic partial deterioration of the polarizing film, and significant reliability and lifetime. Leading to a decline. The use of the plano-convex lens 200 made of single crystal magnesium oxide is advantageous in that it can avoid such a decrease in reliability and a decrease in life. In addition, when a plano-convex lens made of a magnesium oxide polycrystal is used, “grain boundary noise” is generated due to the grain boundary. This grain boundary noise is not usually a big problem, but cannot be ignored when using a light source with high coherence such as laser light. For example, Patent Document 5 discloses a technique related to a projection display device using a laser as a light source. The use of the polarizing element of this example using the plano-convex lens 200 made of single-crystal magnesium oxide in such a projection display device has few crystal defects and grain boundary noise due to the grain boundary, and the local high temperature. It is effective in that it can withstand. In addition, the single crystal is superior to the polycrystal in that the surface accuracy can be precisely flattened to about λ / 20. Therefore, the polarizing element of this example using the plano-convex lens 200 made of single crystal magnesium oxide is particularly effective in a scene requiring high reliability and high accuracy such as in the optical communication field.

  Next, the protective film covering the plano-convex lens 200 will be described. This protective film covers the entire surface of the plano-convex lens 200 as described above. Since magnesium oxide itself has a hygroscopic property, it is difficult to completely prevent a characteristic change such as a decrease in transmittance due to moisture absorption even if the single crystal is formed to eliminate the grain boundary. Therefore, in this example, moisture absorption of the plano-convex lens 200 is prevented by covering the entire surface of the plano-convex lens 200 made of single crystal magnesium oxide with a protective film. From the viewpoint of preventing moisture absorption, it is desirable to form a protective film with silicon nitride or silicon oxide. Moreover, in order to make the moisture absorption preventing effect more reliable, it is desirable that the thickness of the protective film is 10 nm or more. The reason why the thickness of the protective film is desirably 10 nm will be described in another embodiment.

(Embodiment 2)
Hereinafter, another example of the embodiment of the optical component of the present invention will be described by taking the case where the optical component is a polarizing element as an example. FIG. 2 is a schematic cross-sectional view of the polarizing element described here. The basic configuration of the polarizing element shown in FIG. 2 is the same as that of the polarizing element described in the first embodiment. The difference is that the polarizing plate 202 is not attached to the plano-convex lens 200 as shown in FIG. 1 but to a flat substrate 300 having a thickness of 0.5 mm. That is, the main part of the polarizing element of this example is a substrate 300, and the substrate 300 is formed by using single crystal magnesium oxide as a glass material. Note that reference numeral 301 in the drawing indicates a silicon nitride film as a protective film.

  Next, the results of tests conducted to confirm the cooling efficiency of the polarizing element of this example will be described. In this test, the following three polarizing elements were prepared for comparison with the polarizing element of this example. One is a polarizing element in which a polarizing plate is directly attached to the surface of a 0.5 mm thick substrate (single crystal sapphire substrate) made of single crystal sapphire. The other is a polarizing element in which a polarizing plate is directly attached to the surface of a 0.5 mm thick substrate (quartz substrate) made of quartz. The other is a polarizing element in which a polarizing plate is directly attached to the surface of a 1.5 mm thick substrate (quartz substrate) made of quartz. Furthermore, in this test, the light emitted from the 180 W high-pressure mercury lamp was condensed and irradiated on the polarizing element of this example and the three polarizing elements to be compared with a lens, and from below, by a fan at 4 m / s. Air was blown, and the temperature of each polarizing element at that time was measured by a thermocouple.

  The measurement results of the above test are shown in FIG. The graph shown in FIG. 3 shows that the temperature of the polarizing element using the quartz substrate is the highest, and there is almost no temperature difference between the polarizing element using the single crystal sapphire substrate and the polarizing element of this example. From this, it can be said that the cooling capacity of the polarizing element of this example is higher than that of the polarizing element using the quartz substrate and is comparable to that of the polarizing element using the single crystal sapphire substrate. This result means that the thermal conductivity of the substrate 300 made of single crystal magnesium oxide is comparable to that of the single crystal sapphire substrate, and cooling efficiency is not impaired at all even if the entire surface of the substrate 300 is covered with the protective film 301. To do.

  In the present embodiment, the cooling efficiency of the polarizing element has been mainly described. However, the substrate 300 is covered with the protective film 301 so that moisture absorption of the substrate 300 is prevented as in the first embodiment. It is.

(Embodiment 3)
Hereinafter, still another example of the embodiment of the optical component of the present invention will be described by taking the case where the optical component is a polarizing element as an example. FIG. 4 is a schematic cross-sectional view of the polarizing element described here. The basic configuration of the polarizing element shown in FIG. 4 is the same as that of the polarizing element described in the second embodiment. The difference is that the polarizing film 400 is formed on the protective film 301 covering the upper surface 302 of the substrate 300. That is, the polarizing element of Embodiment 2 is formed by attaching a separate polarizing plate 202 to the substrate 300 covered with the protective film 301, but the polarizing element of this example is covered with the protective film 301. A polarizing film 400 is formed on the substrate 300 thus formed.

  Also in the polarizing element of this example, since the substrate 300 made of single crystal magnesium oxide is covered with the protective film 301, moisture absorption is prevented without impairing the cooling efficiency of the substrate 300 at all. However, when the polarizing film 400 is formed on the substrate 300 as in this example, it is necessary to set the film thickness and refractive index of the protective film 301 in consideration of not only moisture absorption prevention but also optical characteristics. There is. This is because various coatings may be applied to the surface of an optical component such as a polarizing element. The coating here means means for controlling the reflectance and transmittance of light using multiple interference of light, and usually one layer or two layers having various film thicknesses and refractive indexes. This is realized by forming the above film. Furthermore, the multiple interference of light is determined by the number of layers, the film thickness, and the refractive index of the film existing on the substrate 300. Therefore, it is desirable to optimize the film thickness and refractive index of the protective film 301 so that the protective film 301 does not affect the coating characteristics.

  First, the film thickness of the protective film 301 shown in FIG. 4 will be described. The film thickness of the protective film 301 is preferably as thin as possible while ensuring the necessary and sufficient moisture absorption prevention performance, in order to reduce the influence on the coating characteristics and increase the versatility for various coatings. Therefore, an environmental test was conducted on a plurality of samples in which silicon nitride films having different film thicknesses were formed on a substrate made of single crystal magnesium oxide, and the change in transmittance before and after that was measured. More specifically, a sample in which silicon nitride films having different thicknesses from 5 nm to 100 nm are formed on a 0.5 mm thick substrate made of (100) single crystal magnesium oxide by plasma CVD. The samples were exposed to an atmosphere of 80 ° C. and 90% RH for 200 hours, and the change in transmittance was measured before and after that. A helium neon laser (λ = 633 nm) was used as a light source, and measurement was performed at normal incidence.

  The measurement results of the above test are shown in FIG. From FIG. 5, when the silicon nitride film (SiN film) is not formed, the substrate is colored and the transmittance is reduced by 20%, but when the silicon nitride film has a thickness of 10 nm or more, It can be seen that the transmittance has hardly changed. Therefore, if at least a silicon nitride film having a thickness of 10 nm or more is used as the protective film 301, it is possible to minimize the influence on the coating characteristics while ensuring a sufficient moisture absorption preventing effect. In addition, the point which can ensure sufficient moisture absorption prevention effect with the protective film 301 of 10 nm is the same also in the first and second embodiments.

  Next, the refractive index of the protective film 301 shown in FIG. 1 will be described. The refractive index of silicon nitride suitable for the material of the protective film 301 is n = 2.0 (λ = 633 nm). The refractive index of single crystal magnesium oxide is n = 1.74 (λ = 633 nm). Therefore, when the protective film 301 is formed of silicon nitride, the refractive index of the protective film 301 and the substrate 300 are different, and the protective film 301 needs to be taken into account for coating such as an AR (Anti Reflection) coat. There is no problem when the coating condition is satisfied only by changing the film thickness of the protective film 301, but it may be possible to cope with this by changing the refractive index of the protective film 301. Therefore, a method of changing the refractive index of the protective film 301 when the protective film 301 is formed using silicon nitride will be described. The protective film 301 made of silicon nitride can be formed not only by a plasma CVD method but also by a reactive RF sputtering method. FIG. 6 shows the sputtering gas pressure dependence characteristics of the refractive index of silicon nitride (d = 100 nm) at λ = 633 nm when a silicon target is used and a one-to-one mixed gas of Ar and nitrogen is used as the sputtering gas. FIG. 6 shows that the refractive index of silicon nitride can be controlled by changing the sputtering gas pressure. As the sputtering gas pressure is increased, the refractive index of silicon nitride is lowered, so that it can be matched with that of magnesium oxide. When the refractive index of silicon nitride matches the refractive index of magnesium oxide, the presence of the protective film 301 can be ignored optically regardless of the thickness of the protective film 301 made of silicon nitride. That is, the substrate 300 can be handled in the same manner as when the protective film 301 is not provided while increasing the thickness of the protective film 301 to ensure a sufficient moisture absorption preventing effect. This means that there are no restrictions on the coating, and the range of application is wide and is industrially important. Although an example in which the protective film 301 made of silicon nitride is formed by reactive RF sputtering is shown here, when forming the protective film 301 made of silicon nitride by plasma CVD, oxygen is added to the supply gas. The refractive index of silicon nitride can be controlled by controlling the oxygen concentration at that time, so that the refractive indexes of the protective film 400 and the substrate 300 can be matched. The control of the refractive index of silicon nitride shown here is because oxygen and silicon are combined when oxygen is added during the generation of silicon nitride, and approaches the refractive index of silicon oxide (n = 1.45). is there.

  Incidentally, in the type of polarizing element to which a polarizing plate is attached as described in the first and second embodiments, the influence of the protective film on the multiple interference condition of light is very small. Therefore, it is not always necessary to adjust the refractive index of the protective film.

  In the first to third embodiments, the details of the optical component of the present invention have been described using the polarizing element as an example. However, the optical component of the present invention is not limited to the polarizing element, and includes all optical components having the structure described in the claims. For example, prisms and mirrors other than the polarizing element are also included.

  In addition to the polarizing elements described in the first to third embodiments, other optical components of the present invention can be applied to various optical devices. For example, the polarizing elements described in the first to third embodiments are different from the incident-side polarizing plates 10R, 10G, and 10B and the outgoing-side polarizing plates 12R, 12G, and 12B included in the projection display device illustrated in FIG. The polarizing element of the present invention described in 3 to 3 can be employed.

FIG. 2 is a schematic perspective view showing the polarizing element of Embodiment 1. 6 is a schematic cross-sectional view showing a polarizing element according to Embodiment 2. FIG. It is a figure which shows the cooling performance of a board | substrate. 6 is a schematic cross-sectional view showing a polarizing element of Embodiment 3. FIG. It is a figure which shows the moisture absorption prevention performance of a silicon nitride film. It is a figure which shows the sputtering gas pressure dependence of the refractive index of a silicon nitride film. Diagram showing the configuration of the projection display device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Reflector 4 Polarization conversion element 5 Field lens 9R Condenser lens 10 Incident side polarizing plate 11 Liquid crystal panel 12 Outgoing side polarizing plate 13 Cross dichroic prism 14 Projection lens 61, 62, 63 Dichroic mirror 71 Reflecting mirror 72, 73 Reflecting mirror 81 , 82 Relay lens 200 Plano-convex lens 201 Flat surface of plano-convex lens 202 Polarizing plate 300 Substrate 301 Protective film 302 Upper surface 400 of substrate Polarizing film

Claims (10)

  Optical components made of magnesium oxide as a glass material and covered with nitride.   An optical component made of magnesium oxide as a glass material and covered with oxide.   Optical parts made of magnesium oxide as a glass material and covered with a mixture of nitride and oxide   The optical component according to claim 1, wherein the nitride is silicon nitride.   The optical component according to claim 2, wherein the oxide is silicon oxide.   The optical component according to claim 1, wherein the magnesium oxide is a single crystal.   The optical component according to claim 1, which has a refractive action for diverging or converging light.   The optical component according to claim 1, wherein the optical component has a reflection function of reflecting light.   The optical component according to any one of claims 1 to 6, which has a polarization conversion function of converting a polarization state of light.   A light source, an image forming element that modulates light emitted from the light source based on an image signal to form image light, and a projection lens or a projection mirror that projects the image light formed by the image forming element A projection display device in which at least one optical component according to any one of claims 1 to 9 is disposed on an optical path from the light source to the projection lens or projection mirror.

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