JP2018124494A - Color combining prism and projector including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both a reduction in angle dependence and extension of the width of a reflection band to improve the efficiency in use of light in an actual use form of a projector.SOLUTION: A color combining prism used for a projector comprises a prism base, and a dichroic film that is formed on the prism base and has a reflection band and a transmission band. The dichroic film has a characteristic in which the average reflectance of the reflection band for light made incident on the dichroic film from the prism base side is higher than the average reflectance of the reflection band for light made incident on the dichroic film from the opposite side of the prism base.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a color composition prism that performs color separation of illumination light and color composition of projection light, and a projector including the color composition prism.

  In recent years, projectors that project an image on a screen using a plurality of image display elements such as DMD (Digital Micromirror Device; registered trademark) have become widespread. In this projector, light (white light) emitted from the light source enters the color synthesis prism via the illumination optical system, and red (R), green (G), and blue (B) are emitted by the color synthesis prism. Each color light is separated and guided to each image display element. In each image display element, incident illumination light of each color is modulated according to image data and emitted as projection light. The projection light of each color is synthesized by the color synthesis prism and guided to the screen via the projection lens. Thereby, the image displayed on each image display element is enlarged and projected on the screen.

  Here, the conventional color synthesis prism will be described in more detail. FIG. 14 is a cross-sectional view showing a detailed configuration of a conventional color synthesis prism 100. In FIG. 14, the regular optical paths of illumination light and projection light in the color synthesis prism 100 are indicated by two-dot chain lines, and the optical paths of light L1 and L2 that become stray light described later are indicated by broken lines. The color combining prism 100 includes a first prism 101, a second prism 102, and a third prism 103. A dichroic film 104B is formed on the surface of the first prism 101 on the second prism 102 side, and an air layer is provided between the dichroic film 104B and the second prism 102. A dichroic film 104 </ b> R is formed on the surface of the second prism 102 on the third prism 103 side, and an air layer is provided between the dichroic film 104 </ b> B and the third prism 103. The dichroic film 104B is a B reflection (blue reflection) dichroic film that reflects B light and transmits R light and G light. The dichroic film 104R is an R reflection (red reflection) dichroic film that reflects R light and transmits B light and G light.

  An optical path of regular light in the color combining prism 100 having the above configuration will be described. Illumination light (white light) incident on the color combining prism 100 enters the dichroic film 104B via the first prism 101. Among these, the B light is reflected by the dichroic film 104B, totally reflected inside the first prism 101, and then guided to the DMD 105B. The light (projection light) reflected by the DMD 105B and corresponding to the image data ON is totally reflected inside the first prism 101 and then enters the dichroic film 104B where it is reflected in the direction toward the projection lens.

  Of the illumination light, R light and G light are transmitted through the dichroic film 104 </ b> B and enter the dichroic film 104 </ b> R via the second prism 102. Among these, the R light is reflected by the dichroic film 104R, totally reflected inside the second prism 102, and then guided to the DMD 105R. The light (projection light) corresponding to the image data ON reflected by the DMD 105R is totally reflected inside the second prism 102 and then enters the dichroic film 104R where it is reflected in the direction toward the projection lens.

  On the other hand, the G light passes through the dichroic film 104 </ b> R and is guided to the DMD 105 </ b> G via the third prism 103. Light (projection light) reflected by the DMD 105G and corresponding to the image data ON is incident on the dichroic film 104B via the third prism 103, the dichroic film 104R, and the second prism 102, where B light and R light Synthesized. Then, the combined projection lights of the respective colors are guided in the direction toward the projection lens via the first prism 101.

FIG. 15 shows the optical characteristics (relationship between incident light wavelength and transmittance) of the dichroic film 104B, and FIG. 16 shows the optical characteristics (relationship between incident light wavelength and transmittance) of the dichroic film 104R. Show. In any of the drawings, a broken line indicates an optical characteristic for illumination light, and a solid line indicates an optical characteristic for projection light. Table 1 shows the film configuration of the dichroic film 104B, and Table 2 shows the film configuration of the dichroic film 104R. In addition, Substance M2 (made by Merck) in Table 1 is a mixture of aluminum oxide (Al ₂ O ₃ ) and lanthanum oxide (La ₂ O ₃ ).

  In the configuration using the color synthesizing prism 100, the incident angle with respect to the dichroic film 104B or the dichroic film 104R differs between the illumination light and the projection light. For example, when the glass materials of the first prism 101, the second prism 102, and the third prism 103 all correspond to Schott BK7 (refractive index 1.52), the incident angle of the illumination light with respect to the dichroic film 104B is 32.1. The incident angle of the projection light is 28.5 °. The incident angle of the illumination light with respect to the dichroic film 104R is 19.1 °, and the incident angle of the projection light is 11.3 °. Thus, with respect to the same dichroic film, the incident angle of illumination light is larger than the incident angle of projection light.

  When the incident angle increases with respect to the dichroic films 104B and 104R formed of the dielectric multilayer film, so-called dichroic shift occurs in which the optical characteristics shift to the short wavelength side. That is, as shown in FIGS. 15 and 16, the optical characteristics of illumination light having a relatively large incident angle shift to the shorter wavelength side than the optical characteristics of projection light having a relatively small incident angle. As described above, since the dichroic films 104B and 104R have an angle dependency in which the optical characteristics differ depending on the incident angle, the light in the wavelength region sandwiched between the solid line and the broken line (the transition band between the reflection band and the transmission band). (Light) utilization efficiency is reduced, and the light becomes stray light that travels in a direction different from that of regular light, leading to problems such as deterioration in image quality of the projected image.

  For example, in FIG. 14, when the illumination light includes light L1 having a wavelength of 490 nm, the light L1 is incident on the dichroic film 104B at the incident angle of the illumination light, and is reflected by the dichroic film 104B according to the characteristics of the broken line in FIG. Without passing through, it goes in the direction of DMD 105G. The light L1 reflected by the DMD 105G is incident on the dichroic film 104B at the incident angle of the projection light, and is reflected by the dichroic film 104B in accordance with the characteristics indicated by the solid line in FIG. As a result, the light L1 becomes stray light (non-regular light) that travels in a direction different from the optical path of the regular B light.

  Further, for example, when the illumination light includes light L2 having a wavelength of 580 nm, the light L2 is incident on the dichroic film 104R at the incident angle of the illumination light, and is reflected by the dichroic film 104R according to the characteristics of the broken line in FIG. Is incident on. The light L2 reflected by the DMD 105R is incident on the dichroic film 104R at the incident angle of the projection light. Therefore, the light L2 is transmitted through the dichroic film 104R and incident on the third prism 103 in accordance with the solid line characteristics of FIG. As a result, the light L2 also becomes stray light (non-regular light) that travels in a direction different from the optical path of the regular R light.

  In order to reduce the angle dependency of the dichroic films 104B and 104R in order to avoid the above-described decrease in light use efficiency and deterioration in the image quality of the projected image due to stray light, it is more advantageous to use a material having a higher refractive index as the constituent material of the film. It is. For example, Patent Document 1 shows that an alternating layer of a high-refractive index material and an intermediate refractive index material can reduce the angle dependency compared to an alternating layer of a high-refractive index material and a low-refractive index material.

Japanese Patent No. 3679746 (see paragraphs [0036], [0038], etc.)

  However, when the refractive index of the constituent material of the dichroic film is increased as described above, the angle dependency is improved, but the reflection band is narrowed, and a new problem arises that the utilization efficiency of light used for reflection is lowered. From various studies, it was found out. For example, in the dichroic film 104B having the characteristics shown in FIG. 15, it is found that when the refractive index of the constituent material of the film is increased, the short wavelength side of the reflection band approaches the long wavelength side and the reflection band becomes narrow. Therefore, in order to improve the light utilization efficiency in the actual usage form of the projector, it is necessary to reduce the angle dependency of the dichroic film and to secure a necessary (wide) reflection band. However, a dichroic film that can achieve both reduction of the angle dependency and widening of the reflection band has not been proposed yet.

  The present invention has been made in order to solve the above-described problems, and its purpose is to reduce the angle dependency and widen the reflection band in an actual use form of the projector, thereby improving the light use efficiency. The object is to provide a color synthesizing prism having a dichroic film that can be raised, and a projector using the same.

  A color combining prism according to one aspect of the present invention is a color combining prism used in a projector, and includes a prism base and a dichroic film formed on the prism base and having a reflection band and a transmission band. The dichroic film has an average reflectance of the reflection band for light incident on the dichroic film from the prism base side, and an average of the reflection band for light incident on the dichroic film from the side opposite to the prism base. It has characteristics higher than reflectance.

  The dichroic film is formed by alternately laminating a high refractive index material and a low refractive index material, and alternately laminating a first alternating layer having an average refractive index of n1, and a high refractive index material and a low refractive index material. A second alternating layer having an average refractive index n2 larger than n1, and the first alternating layer and the second alternating layer may be laminated in this order from the prism base side.

The refractive index of the high refractive index material of the first alternating layer is nH1, the refractive index of the low refractive material is nL1, the refractive index of the high refractive index material of the second alternating layer is nH2, and the refractive index of the low refractive material. Is nL2,
(NH1-nL1) / nH1> (nH2-nL2) / nH2
It may be.

In the above color synthesis prism,
nH1 = nH2
It may be.

  The dichroic film has a blue light reflection band, and the high refractive index material of the first alternating layer and the second alternating layer constituting the dichroic film may be titanium oxide.

  The dichroic film has a red light reflection band, and the high refractive index material of the first alternating layer and the second alternating layer constituting the dichroic film may be niobium oxide.

  The low refractive index material of the first alternating layer may be aluminum oxide.

  The low refractive index material of the second alternating layer may be a mixed material of aluminum oxide and lanthanum oxide.

  A projector according to another aspect of the present invention includes the color combining prism described above.

  The projector further includes a light source and a digital micromirror device corresponding to a plurality of colors, and the color synthesis prism separates the illumination light emitted from the light source into each color and guides it to each digital micromirror device. On the other hand, the structure which synthesize | combines and radiate | emits the projection light radiate | emitted from each digital micromirror device may be sufficient.

  According to the configuration of the dichroic film, it is possible to increase the utilization efficiency of light that is incident from the prism substrate side and reflected by the dichroic film in the actual use state of the projector. In particular, in the dichroic film, since the reflection characteristics are different between the front side (side in contact with the prism base) and the back side (side opposite to the prism base), for example, the front side has a layer configuration that ensures a wide reflection band, and on the back side, A layer configuration that reduces the angle dependency can be employed. By reducing the angle dependence, the wavelength band of the transition band between the reflection band and the transmission band is narrowed, so that the utilization efficiency of light near the cutoff wavelength where the transmittance is 50% increases. Further, by ensuring a wide reflection band, the utilization efficiency of light used for reflection can be increased. That is, according to the above configuration, in the actual use state of the projector, it is possible to reduce the angle dependency and widen the reflection band and increase the light use efficiency.

It is explanatory drawing which shows the schematic structure of the projector which concerns on one Embodiment of this invention. It is explanatory drawing which expands and shows the prism unit of the said projector. It is sectional drawing which shows the detailed structure of the color synthesis prism of the said prism unit. 3 is a graph showing optical characteristics of a blue reflective dichroic film of Example 1. It is a graph which shows the transmittance | permeability and reflectance about the light which injects into the optical path of projection light with respect to the said blue reflective dichroic film | membrane. It is a graph which shows the reflectance about the light which injects from the air side with respect to the said blue reflective dichroic film | membrane. It is a graph which shows the transmittance | permeability and reflectance about the light which injects into the optical path of projection light with respect to the blue reflection dichroic film | membrane of the comparative example 1. It is a graph which shows the reflectance about the light which injects into the blue reflective dichroic film | membrane of the comparative example 1 from the air side. 6 is a graph showing optical characteristics of a red reflective dichroic film of Example 2. It is a graph which shows the transmittance | permeability and reflectance about the light which injects into the optical path of projection light with respect to the said red reflection dichroic film | membrane. It is a graph which shows the reflectance about the light which injects from the air side with respect to the said red reflection dichroic film | membrane. It is a graph which shows the transmittance | permeability and reflectance about the light which injects with the optical path of projection light with respect to the red reflection dichroic film | membrane of the comparative example 2. It is a graph which shows the reflectance about the light which injects into the red reflection dichroic film | membrane of the comparative example 2 from the air side. It is sectional drawing which shows the detailed structure of the conventional color synthesis prism. It is a graph which shows the optical characteristic of the blue reflective dichroic film | membrane of the said color synthesis prism. It is a graph which shows the optical characteristic of the red reflection dichroic film | membrane of the said color synthesis prism.

  An embodiment of the present invention will be described below with reference to the drawings. In addition, in this specification, when a numerical range is described as ab, the value of the lower limit a and the upper limit b shall be included in the numerical range. The present invention is not limited to the following contents.

(About the projector)
FIG. 1 is an explanatory diagram illustrating a schematic configuration of a projector 10 according to the present embodiment. The projector 10 includes a light source 1, an illumination optical system 2, a prism unit 3, a DMD (digital micromirror device) 4, and a projection lens 5. The DMD 4 is composed of DMD 4R, DMD 4G, and DMD 4B (see FIG. 3) corresponding to each color of red (R), green (G), and blue (B).

  The light source 1 emits light (illumination light) that illuminates each DMD 4, and includes a light emitting unit 11 and a reflector 12. The light emitting unit 11 is constituted by, for example, a discharge lamp that emits white light. The reflector 12 is a reflecting plate that reflects light emitted from the light emitting unit 11 and guides it to the illumination optical system 2 and has a spheroidal reflecting surface. The light emitting unit 11 is disposed at one focal position of the reflector 12.

  The illumination optical system 2 is an optical system for guiding light from the light source 1 to each DMD 4, and includes a rod integrator 21, an illumination relay system 22, and a mirror 23. The rod integrator 21 emits light with a uniform light quantity distribution from the light source 1. The illumination relay system 22 uniformly illuminates each DMD 4 by relaying and projecting the image of the light exit surface of the rod integrator 21 onto each DMD 4. The illumination relay system 22 is composed of a plurality of lenses. The light utilization efficiency can be improved by condensing the light from the rod integrator 21 with a plurality of lenses. The mirror 23 reflects the light emitted from the illumination relay system 22 and guides it to the prism unit 3.

  FIG. 2 is an explanatory view showing the prism unit 3 in an enlarged manner. The prism unit 3 includes a TIR prism 31 and a color synthesis prism 32. The TIR prism 31 is a total reflection prism (critical angle prism) that totally reflects the illumination light incident from the illumination optical system 2 and transmits the image light (projection light) from each DMD 4, and includes two prisms 31 a and 31 b. Are bonded together via an air layer. By bending the optical path of the illumination light by the TIR prism 31, the projector 10 can be configured compactly. In FIG. 2, only the optical paths of illumination light incident on DMD 4G and projection light emitted from DMD 4G are shown as an example.

  The color synthesis prism 32 separates the light from the TIR prism 31 into RGB color lights and guides them to each DMD 4 and synthesizes the reflected light (projection light) from each DMD 4 into the same optical path. Details of the color synthesis prism 32 will be described later. The TIR prism 31 and the color combining prism 32 are fixed to a fixing member (not shown) via an adhesive and are held integrally.

  The DMD 4 corresponding to each color is an image display element that displays an image by modulating incident light. More specifically, the DMD 4 has a plurality of micromirrors corresponding to each pixel in a matrix, and projects projection light corresponding to the image data ON by rotating each micromirror according to the image data. The light corresponding to the image data OFF is reflected so as to deviate from the direction toward the projection lens 5.

  In the above configuration, the light emitted from the light source 1 enters the TIR prism 31 of the prism unit 3 via the illumination optical system 2, is totally reflected inside the prism 31a of the TIR prism 31, and then is a color synthesis prism. 32, where it is decomposed into RGB color lights. Each color light enters the corresponding DMD 4 where it is modulated according to the image data. Projection light (light corresponding to the image data ON) emitted from each DMD 4 is incident on the color synthesis prism 32, synthesized there, and then transmitted through the TIR prism 31 (prisms 31 a and 31 b), through the projection lens 5. Through the projection surface (for example, a screen). As a result, the images of the respective colors displayed on the DMDs 4 are combined and enlarged and projected onto the projection surface. Note that the projection surface may be a wall.

(Details of color composition prism)
Next, details of the color combining prism 32 will be described. FIG. 3 is a cross-sectional view showing a detailed configuration of the color synthesis prism 32. The color combining prism 32 is a so-called Philips type color combining prism, and includes a first prism 61, a second prism 62, and a third prism 63. The first prism 61, the second prism 62, and the third prism 63 are all prism bases made of glass, and are made of, for example, BK7 (refractive index 1.52) manufactured by Schott.

  A dichroic film 64 </ b> B is formed on the surface of the first prism 61 on the second prism 62 side, and an air layer is provided between the dichroic film 64 </ b> B and the second prism 62. A dichroic film 64R is formed on the surface of the second prism 62 on the third prism 63 side, and an air layer is provided between the dichroic film 64B and the third prism 63. The dichroic film 64B has characteristics of reflecting B light and transmitting R light and G light, and the dichroic film 64R has characteristics of reflecting R light and transmitting B light and G light. That is, both dichroic films 64B and 64R have a reflection band and a transmission band. Hereinafter, a dichroic film that reflects B light is also referred to as a B reflection (blue reflection) dichroic film, and a dichroic film that reflects R light is also referred to as an R reflection (red reflection) dichroic film.

  The optical path of regular light in the color combining prism 32 having the above configuration will be described. The illumination light (white light) incident on the color combining prism 32 enters the dichroic film 64B via the first prism 61. Among these, the B light is reflected by the dichroic film 64B, totally reflected inside the first prism 61, and then guided to the DMD 4B. The light (projection light) corresponding to the image data ON reflected by the DMD 4B is totally reflected inside the first prism 61 and then enters the dichroic film 64B where it is reflected in the direction toward the projection lens 5. .

  Of the illumination light, R light and G light are transmitted through the dichroic film 64 </ b> B and enter the dichroic film 64 </ b> R via the second prism 62. Among these, the R light is reflected by the dichroic film 64R, totally reflected inside the second prism 62, and then guided to the DMD 4R. The light (projection light) corresponding to the image data ON reflected by the DMD 4R is totally reflected inside the second prism 62 and then enters the dichroic film 64R where it is reflected in the direction toward the projection lens 5. .

  On the other hand, the G light passes through the dichroic film 64R and is guided to the DMD 4G via the third prism 63. The light (projection light) reflected by the DMD 4G and corresponding to the image data ON is incident on the dichroic film 64B via the third prism 63, the dichroic film 64R, and the second prism 62, where B light and R light Synthesized. Then, the combined projection light of each color is guided to the projection lens 5 through the first prism 61.

  Here, the incident angles of the illumination light and the projection light with respect to the dichroic films 64B and 64R are the incident angles of the illumination light and the projection light with respect to the dichroic films 104B and 104R in the conventional color synthesis prism 100 shown in the configuration of FIG. The same. Specifically, the incident angle of the illumination light with respect to the dichroic film 64B is 32.1 ° when incident from the prism base (BK7) side (53.8 ° when incident from the air layer side), and the incident light of the projection light is incident The angle is 28.5 ° when incident from the prism base (BK7) side (46.4 ° when incident from the air layer side). The incident angle of the illumination light to the dichroic film 64B is 19.1 ° when incident from the prism base (BK7) side (29.8 ° when incident from the air layer side), and the incident angle of the projection light is 11.3 ° when incident from the prism base (BK7) side (17.2 ° when incident from the air layer side).

  As described above, since the incident angles with respect to the dichroic films 64B and 64R are different between the illumination light and the projection light, the dichroic films 64B and 64R have the angle dependency described above, and as a result, as shown in FIG. Non-regular light is generated as stray light. That is, light L1 that is not reflected at the incident angle of the illumination light but reflected at the incident angle of the projection light, or light L2 that is reflected at the incident angle of the illumination light but not reflected at the incident angle of the projection light is generated. However, in the present embodiment, by adopting the film configuration of the dichroic films 64B and 64R as described below, the angle dependency of the dichroic films 64B and 64R is reduced, thereby reducing non-regular light that becomes stray light. This avoids degradation of the projected image quality.

  Hereinafter, details of the dichroic film 64B will be described as Example 1, and details of the dichroic film 64R will be described as Example 2. For comparison with Examples 1 and 2, a comparative example will also be described.

Example 1
Table 3 shows the layer structure of the dichroic film 64B of Example 1. The dichroic film 64B includes a first alternating layer G1 and a second alternating layer G2. The first alternating layer G1 and the second alternating layer G2 are stacked in this order from the prism base side (first prism 61 side). Note that M3 in Table 3 indicates Substance M3 described later.

The first alternating layer G1 is an alternating layer having an average refractive index of n1 in which high refractive index materials and low refractive index materials are alternately stacked. In Table 3, the first alternating layer G1 corresponds to the first to 26th layer regions. doing. In the first alternating layer G1, titanium oxide (TiO ₂ ) having a refractive index of 2.36 is used as the high refractive index material, and an oxide having a refractive index of 1.63 is used as the low refractive index material. Aluminum (Al ₂ O ₃ ) is used.

The second alternating layer G2 is an alternating layer having an average refractive index of n2 in which high-refractive index materials and low-refractive index materials are alternately stacked. In Table 3, it corresponds to the regions of the 27th to 64th layers. doing. In the second alternating layer G2, titanium oxide (TiO ₂ ) having a refractive index of 2.36 is used as the high refractive index material, and Substance having a refractive index of 1.84 is used as the low refractive index material. M3 (Merck) is used. Substance M3 is a mixed material of aluminum oxide (Al ₂ O ₃ ) and lanthanum oxide (La ₂ O ₃ ).

Table 4 shows the average refractive indexes of the first alternating layer G1 and the second alternating layer G2. In this specification, the “average refractive index” is not a simple average of the refractive indexes of the layers constituting the alternating layers, but an average refractive index in consideration of the film thickness (physical film thickness) of each layer, that is, the refractive index. Is a weighted average of Specifically, the average refractive index is calculated by the following formula. The unit of film thickness is nm.
Average refractive index = {total film thickness of each layer (= physical film thickness × refractive index)} / {total film thickness of each layer (physical film thickness)}

  As shown in Table 4, the average refractive index n1 of the first alternating layer G1 is 1.91, and the average refractive index n2 of the second alternating layer G2 is 2.17. That is, the average refractive index n2 of the second alternating layer G2 is larger than the average refractive index n1 of the first alternating layer G1.

FIG. 4 shows the optical characteristics (relation between the wavelength of incident light and the transmittance) of the dichroic film 64B having the layer structure shown in Table 3. The dichroic film 64B is a _second alternating layer in which a high refractive index material (TiO ₂ ) having a refractive index of 2.36 and a low refractive index material (Substance M3) having a refractive index of 1.84 are slightly higher. Layer G2 is included. For this reason, compared with the optical characteristics of the conventional B reflection dichroic film shown in FIG. 15, the wavelength range between the broken line and the solid line (the transition band between the reflection band and the transmission band) is narrowed and is angle-dependent. It can be seen that the property is reduced.

  In addition to the second alternating layer G2, the dichroic film 64B includes the first alternating layer G1 having an average refractive index lower than that of the second alternating layer G2, and the first alternating layer G1 is the second alternating layer G1. Because it is located on the prism base side (first prism 61) side with respect to the alternating layer G2, the light incident from the prism base side is reflected by the first alternating layer G1 prior to the second alternating layer G2. To the DMD 4B. Thereby, while reducing the influence (demerit) of the second alternating layer G2 that the reflection band is narrowed by the high average refractive index, the necessary (wide) reflection band is required by the first alternating layer G1 having a low average refractive index. Can be secured. This can be easily understood from the fact that the optical characteristics in the wavelength range of 400 to 420 nm in FIG. 4 are improved compared to the optical characteristics in the same band in FIG.

  FIG. 5 shows the transmittance and reflectance of light (light entering from the first prism 61 side) incident on the optical path of the projection light with respect to the dichroic film 64B of the first embodiment. The reflectance with respect to the light incident from the air side (the side opposite to the first prism 61) with respect to the dichroic film 64B of the first embodiment is shown. Table 5 shows the average reflectance of the reflection band (for example, a wavelength of 420 to 480 nm) of the dichroic film 64B of Example 1 having the optical characteristics shown in FIGS.

  As shown in Table 5, the dichroic film 64B of Example 1 has the above-described layer configuration (a configuration in which the first alternating layer G1 and the second alternating layer G2 are stacked in this order on the prism base). The dichroic film 64B has an average reflectance of a reflection band for light incident on the dichroic film 64B from the prism base (first prism 61) side from the side (air side) opposite to the prism base (first prism 61). The characteristic is higher than the average reflectance of the reflection band for the light incident on the dichroic film 64B. This is considered to be due to the following reasons.

  As the average refractive index of the alternating layers increases, the absorption loss of light in the alternating layers also increases as the film thickness increases. Therefore, light incident on the second alternating layer G2 having a large average refractive index prior to the first alternating layer G1 (light incident from the side opposite to the prism base) is generated by the second alternating layer G2. Absorption loss of light increases, and the reflectance decreases according to the wavelength of incident light (see the reflection band in FIG. 6). As a result, the average reflectance of the reflection band decreases (see Table 5). However, since the light incident on the optical path of the projection light is incident on the first alternating layer G1 before the second alternating layer G2, the light absorption loss in the second alternating layer G2 is suppressed, As a result, a decrease in the average reflectance of the reflection band is suppressed (see FIG. 5 and Table 5).

  As shown in FIG. 6, even if the dichroic film 64B of the first embodiment has a characteristic that the average reflectance in the reflection band (B light) decreases with respect to light incident from the air side, the dichroic film from the air side. Light incident on 64B (for example, R light or G light) is transmitted through the dichroic film 64B and guided in the direction toward the projection lens 5, and the reflection band is not used, so there is no problem.

  From the above, it can be said that the dichroic film 64B of Example 1 can be expressed as follows, and thereby has the following effects. That is, the dichroic film 64B of the first embodiment has an average reflectance of a reflection band for light incident on the dichroic film 64B from the prism base, and a reflection band for light incident on the dichroic film 64B from the opposite side of the prism base. It has characteristics higher than the average reflectance (see the broken line graphs in FIGS. 5 and 6). Thus, as described above, in the dichroic film 64B, the front side (prism substrate side) adopts a layer configuration that ensures a wide reflection band, and the back side adopts a layer configuration that reduces the angle dependency. As a result, the light use efficiency can be improved.

  More specifically, the wavelength dependence of the transition band between the reflection band and the transmission band is narrowed by reducing the angle dependency by the layer structure on the back side of the dichroic film 64B, so that the cutoff wavelength at which the transmittance is 50%. The utilization efficiency of light in the vicinity can be improved. That is, by narrowing the transition band, stray light (non-regular light) as shown in FIG. 14, that is, light L1 that is reflected at the incident angle of the projection light but not reflected at the incident angle of the illumination light can be reduced. , Light utilization efficiency can be improved. In addition, image quality degradation of the projected image can be avoided by reducing stray light.

  Further, by ensuring a wide reflection band by the front side layer structure of the dichroic film 64B, it is possible to increase the utilization efficiency of light used for reflection at the dichroic film 64B. Therefore, in the actual use state of the projector 10, it is possible to improve the light use efficiency by reducing both the angle dependency and widening the reflection band. Furthermore, the light absorption loss due to the second alternating layer G2 having a high average refractive index can be suppressed by the characteristics shown by the broken lines in FIGS. 5 and 6, so that the light utilization efficiency can be improved also in this respect. Can do.

(Comparative Example 1)
Next, for comparison with Example 1, the B reflective dichroic film of Comparative Example 1 will be described. In the B reflective dichroic film of Comparative Example 1, the constituent materials (high refractive index material and low refractive index material) of the first alternating layer G1 and the second alternating layer G2 are the same as those of the dichroic film 64B of Example 1. The arrangement of the first alternating layer G1 and the second alternating layer G2 is different from the dichroic film 64B of the first embodiment. That is, the B reflective dichroic film of Comparative Example 1 is configured by laminating the second alternating layer G2 and the first alternating layer G1 in this order from the prism base (first prism 61) side. However, the film thickness of each layer constituting the second alternating layer G2 and the first alternating layer G1 is optimized.

  Table 6 shows the layer structure of the B reflective dichroic film of Comparative Example 1, and Table 7 shows the average refraction of the first alternating layer G1 and the second alternating layer G2 of the B reflective dichroic film of Comparative Example 1. Shows the rate.

  FIG. 7 shows the transmittance and reflectance of light incident on the B reflection dichroic film of Comparative Example 1 through the optical path of the projection light (light incident from the first prism 61 side). These show the reflectance with respect to the light incident from the air side (the side opposite to the first prism 61) with respect to the B reflective dichroic film of Comparative Example 1. Table 8 shows the average reflectance of the reflection band (for example, a wavelength of 420 to 480 nm) of the B reflective dichroic film of Comparative Example 1 having the optical characteristics shown in FIGS.

  In the B reflection dichroic film of Comparative Example 1, the average reflectance of the reflection band for the light incident on the B reflection dichroic film from the first prism 61 side is the reflection band for the light incident on the B reflection dichroic film from the air side. The characteristic is lower than the average reflectance. This is because light incident on the optical path of the projection light (light incident from the first prism 61 side) is incident on the second alternating layer G2 having a high average refractive index prior to the first alternating layer G1. Therefore, due to the absorption loss of light in the second alternating layer G2, the reflectivity decreases according to the wavelength of the incident light (see FIG. 7), and as a result, the average reflectivity of the reflection band decreases. Possible (see Table 8).

  From the results of Example 1 and Comparative Example 1 described above, the following conclusions can be obtained. That is, in adopting two types of alternating layers (the first alternating layer G1 and the second alternating layer G2) in order to reduce the angle dependency and widen the reflection band in the B reflective dichroic film, If the arrangement of the alternating layers is not set appropriately (if the second alternating layer G2 and the first alternating layer G1 are laminated in this order from the prism base side as in Comparative Example 1), the second alternating layer The average reflectance of the reflection band is reduced due to light absorption loss in the layer G2, and the light use efficiency is reduced. Accordingly, in order to improve the light utilization efficiency by configuring the B reflective dichroic film using two types of alternating layers, the first alternating layer G1 and the second alternating layer are formed from the prism base side as in the first embodiment. It is necessary to laminate the alternating layers G2 in this order.

(Example 2)
Next, details of the dichroic film 64R will be described. Table 9 shows the layer configuration of the dichroic film 64R of Example 2. The dichroic film 64R includes a first alternating layer G1 and a second alternating layer G2. The first alternating layer G1 and the second alternating layer G2 are stacked in this order from the prism base side (the second prism 62 side). In Table 9, M3 indicates Substance M3.

The first alternating layer G1 is an alternating layer having an average refractive index of n1 in which high refractive index materials and low refractive index materials are alternately stacked. In Table 9, the first alternating layer G1 corresponds to the regions of the first layer to the 26th layer. doing. In the first alternating layer G1, niobium oxide (Nb ₂ O ₅ ) having a refractive index of 2.34 is used as the high refractive index material, and a refractive index of 1.63 is used as the low refractive index material. Aluminum oxide (Al ₂ O ₃ ) is used.

The second alternating layer G2 is an alternating layer having an average refractive index of n2 in which high-refractive index materials and low-refractive index materials are alternately stacked. In Table 9, corresponding to the 27th to 52nd layer regions. doing. In the second alternating layer G2, niobium oxide (Nb ₂ O ₅ ) having a refractive index of 2.34 is used as the high refractive index material, and the refractive index is 1.84 as the low refractive index material. Substance M3 (Merck) is used.

  Table 10 shows average refractive indexes of the first alternating layer G1 and the second alternating layer G2.

  As shown in Table 10, the average refractive index n1 of the first alternating layer G1 is 1.97, and the average refractive index n2 of the second alternating layer G2 is 2.09. That is, the average refractive index n2 of the second alternating layer G2 is larger than the average refractive index n1 of the first alternating layer G1.

FIG. 9 shows the optical characteristics (relation between the wavelength of incident light and the transmittance) of the dichroic film 64R having the layer structure shown in Table 9. The dichroic film 64R is a second layer in which a high refractive index material (Nb ₂ O ₅ ) having a refractive index of 2.34 and a low refractive index material (Substance M3) having a refractive index of 1.84 are slightly stacked. Of alternating layers G2. For this reason, compared with the optical characteristics of the conventional R reflecting dichroic film shown in FIG. 16, the wavelength range between the broken line and the solid line (the transition band between the reflection band and the transmission band) is narrower, and is angle dependent. It can be seen that the property is reduced.

  In addition to the second alternating layer G2, the dichroic film 64R includes the first alternating layer G1 having an average refractive index lower than that of the second alternating layer G2, and the first alternating layer G1 is the second alternating layer G1. Since the second alternating layer G2 is positioned on the prism base side (second prism 62) side, the light incident from the prism base side is reflected by the first alternating layer G1 before the second alternating layer G2. Can be led to DMD4R. Thereby, while reducing the influence (demerit) of the second alternating layer G2 that the reflection band is narrowed by the high average refractive index, the necessary (wide) reflection band is required by the first alternating layer G1 having a low average refractive index. Can be secured.

  FIG. 10 shows the transmittance and reflectance of light incident on the optical path of the projection light (light incident from the second prism 62 side) with respect to the dichroic film 64R of Example 2, and FIG. The reflectance with respect to the light which injects from the air side (opposite side to the 2nd prism 62) with respect to the dichroic film | membrane 64R of Example 2 is shown. Table 11 shows the average reflectance of the reflection band (for example, a wavelength of 600 to 680 nm) of the dichroic film 64R of Example 2 having the optical characteristics of FIGS.

  As shown in Table 11, the dichroic film 64R of Example 2 has the above-described layer configuration (a configuration in which the first alternating layer G1 and the second alternating layer G2 are stacked in this order on the prism base). The dichroic film 64R has an average reflectance of a reflection band for light incident on the dichroic film 64R from the prism base (second prism 62) side from the side (air side) opposite to the prism base (second prism 62). The characteristic is higher than the average reflectance of the reflection band for the light incident on the dichroic film 64R. The reason why the average reflectance of the reflection band of the light incident on the dichroic film 64R from the air side is relatively low is that the light has a higher average refractive index and a larger film thickness than the first alternating layer G1. This is probably because the light is incident on the second alternating layer G2 having a large light absorption loss. In the second embodiment, the light incident on the optical path of the projection light is incident on the first alternating layer G1 before the second alternating layer G2, so that the light absorption loss by the second alternating layer G2 is suppressed. As a result, it is considered that the decrease in average reflectance in the reflection band is suppressed (see FIGS. 10, 11, and 11).

  As shown in FIG. 11, even if the dichroic film 64R according to the second embodiment has a characteristic that the average reflectance in the reflection band (R light) decreases with respect to light incident from the air side, the dichroic film from the air side. Light incident on 64R (for example, G light) passes through the dichroic film 64R and is guided in the direction toward the projection lens 5, and the reflection band is not used, so that there is no problem.

  From the above, the dichroic film 64R of Example 2 can be expressed as follows, and it can be said that the following effects are obtained. That is, in the dichroic film 64R of the second embodiment, the average reflectance of the reflection band for light incident on the dichroic film 64R from the prism base is such that the reflection band for light incident on the dichroic film 64R from the side opposite to the prism base. It has characteristics higher than the average reflectance. Thereby, as described above, in the dichroic film 64R, the front side (prism substrate side) adopts a layer configuration that ensures a wide reflection band, and the back side adopts a layer configuration that reduces the angle dependency. As a result, the light use efficiency can be improved.

  More specifically, by reducing the angle dependency by the layer configuration on the back side of the dichroic film 64R, the wavelength band of the transition band between the reflection band and the transmission band is narrowed. Can be improved. That is, by narrowing the transition band, stray light (non-regular light) as shown in FIG. 14, that is, light L2 that is reflected at the incident angle of the illumination light but not reflected at the incident angle of the projection light can be reduced. , Light utilization efficiency can be improved. In addition, image quality degradation of the projected image can be avoided by reducing stray light.

  Further, by ensuring a wide reflection band by the layer structure on the front side of the dichroic film 64R, it is possible to increase the utilization efficiency of light used for reflection by the dichroic film 64R. Therefore, in the actual use state of the projector 10, it is possible to improve the light use efficiency by reducing both the angle dependency and widening the reflection band. Moreover, since the light absorption loss due to the second alternating layer G2 having a high average refractive index can be suppressed by the characteristics shown by the broken lines in FIGS. 10 and 11, the light utilization efficiency can be improved also in this respect. Can do.

(Comparative Example 2)
Next, for comparison with Example 2, the R reflection dichroic film of Comparative Example 2 will be described. In the R reflective dichroic film of Comparative Example 2, the constituent materials (high refractive index material and low refractive index material) of the first alternating layer G1 and the second alternating layer G2 are the same as those of the dichroic film 64R of Example 2. The arrangement of the first alternating layer G1 and the second alternating layer G2 is different from the dichroic film 64R of the second embodiment. That is, the R reflective dichroic film of Comparative Example 2 is configured by laminating the second alternating layer G2 and the first alternating layer G1 in this order from the prism base (second prism 62) side. However, the film thickness of each layer constituting the second alternating layer G2 and the first alternating layer G1 is optimized.

  Table 12 shows the layer configuration of the R reflective dichroic film of Comparative Example 2, and Table 13 shows the average refraction of the first alternating layer G1 and the second alternating layer G2 of the R reflective dichroic film of Comparative Example 2. Shows the rate.

  FIG. 12 shows the transmittance and reflectance of light incident on the R reflection dichroic film of Comparative Example 2 through the optical path of the projection light (light incident from the second prism 62 side). These show the reflectance with respect to the light incident from the air side (the side opposite to the second prism 62) with respect to the R reflecting dichroic film of Comparative Example 2. Table 14 shows the average reflectance of the reflection band (for example, wavelength 600 to 680 nm) of the R reflection dichroic film of Comparative Example 2 having the optical characteristics of FIGS. 12 and 13.

  In the R reflection dichroic film of Comparative Example 2, the average reflectance of the reflection band for the light incident on the R reflection dichroic film from the second prism 62 side is the reflection band for the light incident on the R reflection dichroic film from the air side. The characteristic is lower than the average reflectance. This is because light incident on the optical path of the projection light (light incident from the second prism 62 side) is incident on the second alternating layer G2 having a high average refractive index before the first alternating layer G1. Therefore, it is considered that the average reflectance in the reflection band is reduced due to the absorption loss of light in the second alternating layer G2 (see FIG. 12, Table 14).

  From the results of Example 2 and Comparative Example 2 described above, the following conclusions can be obtained. That is, in adopting two types of alternating layers (the first alternating layer G1 and the second alternating layer G2) in order to reduce the angle dependency and widen the reflection band in the R reflecting dichroic film, If the arrangement of the alternating layers is not set appropriately (if the second alternating layer G2 and the first alternating layer G1 are laminated in this order from the prism base side as in Comparative Example 2), the second alternating layer The light absorption loss in the layer G2 decreases the average reflectance in the reflection band, and the light utilization efficiency decreases. Therefore, in order to improve the light utilization efficiency by constructing the R reflection dichroic film using two kinds of alternating layers, the first alternating layer G1 and the second alternating layer are formed from the prism base side as in the second embodiment. It is necessary to laminate the alternating layers G2 in this order.

(Supplementary information)
In the dichroic films 64B and 64R of Examples 1 and 2, the refractive index of the high refractive index material of the first alternating layer G1 is nH1, the refractive index of the low refractive material is nL1, and the high refractive index of the second alternating layer G2. When the refractive index of the material is nH2 and the refractive index of the low refractive material is nL2, in Example 1, nH1 = nH2 = 2.36, nL1 = 1.63, nL2 = 1.84, and in Example 2, NH1 = nH2 = 2.34, nL1 = 1.63, and nL2 = 1.84. Therefore, in Examples 1 and 2, the following conditional expressions are satisfied.
(NH1-nL1) / nH1> (nH2-nL2) / nH2

  When the above conditional expression is satisfied, the refractive index ratio (nL1 / nH1 or nL2 / nH2) of the low refractive index material to the high refractive index material is higher in the second alternating layer G2 than in the first alternating layer G1. The average refractive index becomes larger in the second alternating layer G2 than in the first alternating layer G1. Accordingly, the first alternate layer G1 having a relatively small average refractive index ensures a wide reflection band, and the angular dependence is reduced by the second alternate layer G2 having a relatively large average refractive index and It becomes possible to reliably realize the configuration of 2.

  In particular, in Example 1, nH1 = nH2, and in Example 2, nH1 = nH2. As described above, the first alternating layer G1 and the second alternating layer G2 have the same refractive index (the same material) as the high refractive index material, so that the first film thickness with a realistic design can be obtained. Each of the alternating layers G1 and the second alternating layers G2 can be formed, and the productivity of the color combining prism 32 can be improved.

Further, the dichroic film 64B of the first embodiment has a B light reflection band (for example, 400 to 480 nm), and the high refraction of the first alternating layer G1 and the second alternating layer G2 constituting the dichroic film 64B. The rate material is TiO ₂ . In a dichroic film for a projector, transition bands in which the cutoff wavelength is shifted between illumination light and projection light are between B light and G light and between G light and R light. TiO ₂ is a material that has the highest refractive index in practical use, particularly a high refractive index on the short wavelength side, and has a high effect of reducing the angle dependence of the transition band between B light and G light. For this reason, TiO ₂ is very effective as a high refractive index material constituting the dichroic film 64B. Although the loss due to absorption and scattering is large in the wavelength region of B light, the loss can be suppressed by making the reflection where the thickness of the portion where the light passes through the material is smaller than that in the case of transmission.

Further, the dichroic film 64R of Example 2 has an R light reflection band (for example, 600 to 680 nm), and the high refraction of the first alternating layer G1 and the second alternating layer G2 constituting the dichroic film 64R. The rate material is Nb ₂ O ₅ . Nb ₂ O ₅ is a high refractive index material similar to TiO ₂ and is effective in that the angle dependency can be reduced in the transition band between the G light and the R light. Further, the loss of absorption and scattering with respect to the transmission of light is less than when TiO ₂ is used, and the light use efficiency is good.

In Examples 1 and 2, the low refractive index material of the first alternating layer G1 is Al ₂ O ₃ . Among low-refractive index materials that can ensure a difference in refractive index from high-refractive index materials in order to ensure the reflection band of dichroic films for projectors, Al ₂ O ₃ has a higher refractive index and loss of absorption and scattering. Less is. For this reason, Al ₂ O ₃ is very effective as a low refractive index material for the first alternating layer G1.

  In Examples 1 and 2, the low refractive index material of the second alternating layer G2 is Substance M3 (a mixed material of aluminum oxide and lanthanum oxide). When the average refractive index is increased in order to reduce the angle dependency, the film becomes considerably thin with aluminum oxide. When a mixed material of aluminum oxide and lanthanum oxide is used, a film having a relatively high average refractive index can be formed with a relatively thick film, so that the manufacturing thickness can be easily controlled and stable productivity can be secured.

  The projector 10 according to this embodiment includes the color combining prism 32 having the dichroic films 64B and 64R described in the first and second embodiments. The dichroic films 64B and 64R of the first and second embodiments reduce the angle dependency and secure a wide reflection band, so that the projector 10 with high light utilization efficiency and capable of projecting a bright image can be obtained. In particular, since the angle dependence is reduced, non-regular light that becomes stray light by light in the vicinity of the cutoff wavelength can be reduced, so that it is possible to avoid a ghost and a decrease in contrast due to stray light and maintain good projection quality. Moreover, the temperature rise of the peripheral components by stray light can also be suppressed. Further, since the absorption of light in the dichroic films 64B and 64R can be reduced, it is possible to reduce the deterioration of the projected image due to the thermal deformation of the prism and the change in the refractive index distribution due to the absorption.

  The projector 10 of the present embodiment further includes a light source 1 and DMDs 4 corresponding to a plurality of colors, and the color synthesis prism 32 separates the illumination light emitted from the light source 1 into each color and guides it to each DMD 4. On the other hand, the projection light emitted from each DMD 4 is synthesized and emitted, and is guided in a direction toward the projection lens 5. In the projector 10 using the color synthesis prism 32 and the plurality of DMDs 4, as described above, the incident angle of the illumination light from the light source 1 and the projection light from the DMD 4 with respect to the dichroic films 64B and 64R of the color synthesis prism 32 The incident angle is different. However, since the angle dependence of the dichroic films 64B and 64R is small, the light use efficiency can be improved in color separation / color synthesis, and a bright image can be projected.

The high refractive index material and the low refractive index material may be the same in the first alternating layer G1 and the second alternating layer G2 of the dichroic film 64B. Similarly, the high refractive index material and the low refractive index material may be the same in the first alternating layer G1 and the second alternating layer G2 of the dichroic film 64R. In this case, the average film thickness of the high refractive index material of the first alternating layer G1 is dH1 (nm), the average film thickness of the low refractive material is dL1 (nm), and the high refractive index material of the second alternating layer G2 When the average film thickness is dH2 (nm) and the average film thickness of the low refractive material is dL2 (nm),
dH1 <dH2, dL1> dL2
Is desirable.

  As described above, the film thickness of the high refractive index material is made relatively thicker in the second alternating layer G2 than the first alternating layer G1, and the film thickness of the low refractive index material is changed to the first alternating layer G1. The average refractive index of the second alternating layer G2 can be made larger than the average refractive index of the first alternating layer G1 by making the second alternating layer G2 relatively thin. Accordingly, even with such a configuration, the angle dependency can be reduced by the second alternating layer G2. Further, when the first alternating layer G1 and the second alternating layer G2 are the same in the high refractive index material and the low refractive index material, since the types of materials constituting the dichroic films 64B and 64R are small, the handling property is improved. There is also an advantage that it is easy to control to make the film thickness uniform in the dome during film formation (vapor deposition).

  The color synthesis prism of the present invention can be used for a projector that projects a color image, for example.

1 Light source 4 DMD (Digital micromirror device)
10 projector 32 color composition prism 61 first prism (prism base)
62 Second prism (prism base)
64B Dichroic film 64R Dichroic film G1 First alternating layer G2 Second alternating layer

Claims (10)

A color combining prism used in a projector,
A prism base and a dichroic film formed on the prism base and having a reflection band and a transmission band;
The dichroic film has an average reflectance of the reflection band for light incident on the dichroic film from the prism base side, and an average of the reflection band for light incident on the dichroic film from the side opposite to the prism base. A color synthesizing prism having characteristics higher than reflectance. The dichroic film is
A first alternating layer having an average refractive index of n1 in which a high refractive index material and a low refractive index material are alternately stacked;
A second alternating layer in which the average refractive index is n2 larger than n1, in which a high refractive index material and a low refractive index material are alternately laminated,
The color synthesizing prism according to claim 1, wherein the first alternating layer and the second alternating layer are laminated in this order from the prism base side. The refractive index of the high refractive index material of the first alternating layer is nH1, the refractive index of the low refractive material is nL1, the refractive index of the high refractive index material of the second alternating layer is nH2, and the refractive index of the low refractive material. Is nL2,
(NH1-nL1) / nH1> (nH2-nL2) / nH2
The color synthesizing prism according to claim 2, wherein: nH1 = nH2
The color synthesizing prism according to claim 2 or 3, wherein The dichroic film has a blue light reflection band,
5. The color synthesizing prism according to claim 4, wherein the high refractive index material of the first alternating layer and the second alternating layer constituting the dichroic film is titanium oxide. The dichroic film has a red light reflection band,
5. The color synthesizing prism according to claim 4, wherein the high refractive index material of the first alternating layer and the second alternating layer constituting the dichroic film is niobium oxide.   The color synthesizing prism according to claim 5 or 6, wherein the low refractive index material of the first alternating layer is aluminum oxide.   8. The color synthesizing prism according to claim 5, wherein the low refractive index material of the second alternating layer is a mixed material of aluminum oxide and lanthanum oxide. 9.   A projector comprising the color synthesizing prism according to claim 1. A light source and a digital micromirror device that supports multiple colors;
The color synthesis prism separates illumination light emitted from the light source into each color and guides it to each digital micromirror device, while synthesizing projection light emitted from each digital micromirror device. The projector according to claim 9.

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