PRISM UNIT AND PROJECTOR

CROSS-REFERENCE TO RELATED APPLICATION(S)

The entire disclosure of Japanese Patent Application No. 2014-191149 filed on Sep. 19, 2014 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to prism units and projectors, and more particularly, to a prism unit that combines light in the three colors of R (red), G (green), and B (blue) on the same optical axis, for example, and a three-plate projector including the prism unit.

2. Description of the Related Art

Digital micromirror devices are known as reflective display devices mounted on projectors. A digital micromirror device has an image display surface formed with minute micromirrors, and controls the tilt of each mirror surface on the image display surface, to modulate the intensity of illumination light and thus form an image. Switching on and off of each pixel of the digital micromirror device is expressed by ±12-degree rotation of the mirror surfaces about a rotational axis at an angle of 45 degrees with respect to each side of the image display surface (or micromirror drive about one axis), for example. As for micromirror movement, a digital micromirror device of a new operation type (Tilt & Roll Pixel DMD) that drives micromirrors with respect to two axes perpendicular to each other is suggested in DLP Tilt & Roll Pixel Architecture and DLP IntelliBright™, <URL:http://www.dlp.com/pico-projector/pico-product-developers/2trp-chip.aspx>.

In a projector that uses a reflective display device such as a digital micromirror device and a color separating/combining prism, the angles of incidence with respect to the dichroic coatings in the color separating/combining prism differ between illumination light and projection light (on-state light). Therefore, light loss is caused due to a difference in angular characteristics between the dichroic coatings. So as to reduce such light loss, JP 10-104763 A, JP 10-319344 A, and JP 11-142992 A suggest projectors in which the angles of light incidence with respect to dichroic coatings are adjusted.

In each of the projectors suggested in JP 10-104763 A, JP 10-319344 A, and JP 11-142992 A, a prism unit that first separates G from the three colors of R, G, and B is provided, and the separation cutoff between B and R is set almost at the center of the reflection band of G. A prism unit that first separates G is known as a prism unit for video optical systems, LCOS (reflective crystal liquid) projectors, and the like. In that color combination, only projection light should be taken into consideration, and therefore, the separation wavelength between B and R does not affect performance at any part of the G wavelength band.

For example, in a projector optical system compatible with digital micromirror devices of the above described new operation type, the angle of incidence at the time of separation/combination of B and R differs between the illumination light path and the projection light path. The cutoff wavelength varies with the angle of incidence in a dichroic coating. Therefore, if the rising wavelength position is set by using a BR dichroic coating having a film structure that takes into account only the projection light path, there is a possibility that efficiency will rapidly drop in the illumination light path. Therefore, with the angular characteristics of the dichroic coatings disclosed in JP 10-104763 A, JP 10-319344 A, and JP 11-142992 A, it is difficult to sufficiently reduce light loss in illumination light.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a prism unit that has light loss reduced in both projection light and illumination light in the dichroic coatings, and has a high light use efficiency, and a projector that includes the prism unit.

A prism unit that combines light in the three primary colors of R, G, and B on the same optical axis, reflecting one aspect of the present invention, comprises: a G-reflecting dichroic coating that reflects G light and passes R and B light; and an RB dichroic coating that reflects one of R and B, and passes the other one of R and B, the prism unit satisfying the following conditional expression (1):

λrg≧λrb≧0.67×λrg+0.33×λgb (1)

where λgb represents the wavelength at which the transmittance is 50% when the colors of G and B on the composite optical axis are combined in the G-reflecting dichroic coating, λrg represents the wavelength at which the transmittance is 50% when the colors of R and G on the composite optical axis are combined in the G-reflecting dichroic coating, and λrb represents the wavelength at which the transmittance is 50% when the colors of R and B on the composite optical axis are combined in the RB dichroic coating.

According to one or more embodiments, the G-reflecting dichroic coating and the RB dichroic coating are formed from at least two vapor-deposited materials of a high-refractive-index material, an intermediate-refractive-index material, and a low-refractive-index material, the high-refractive-index material is TiO₂, or Nb₂O₅, or Ta₂O₅, the intermediate-refractive-index material is Al₂O₃or a mixed oxide of Al₂O₃and La₂O₃, and the low-refractive-index material is SiO₂.

A projector in accordance with one or more embodiments includes: the prism unit in accordance with one or more embodiments described above; three image display devices that display an R image, a G image, and a B image on respective image display surfaces; an illumination optical system that illuminates the respective image display surfaces; and a projection optical system that projects the images displayed on the respective image display surfaces onto a screen, wherein the prism unit is a color separating/combining prism that separates colors in illumination light and combines colors for projection light, the angle of incidence of principal illumination light with respect to the image display surfaces differs from the angle of emission of principal projection light with respect to the image display surfaces, and the angles of incidence of the principal projection light and the principal illumination light with respect to the G-reflecting dichroic coating are substantially the same.

According to one or more embodiments, the following conditional expressions (2A) and (2B) are satisfied:

λirg≧λprb≧0.67×λprg+0.33×λpgb (2A)

0.5×λprg+0.5×λpgb>λirb≧λpgb (2B)

where λirg represents the wavelength at which the transmittance is 50% when the colors of R and G in the principal illumination light are separated from each other in the G-reflecting dichroic coating, λprg represents the wavelength at which the transmittance is 50% when the colors of R and G in the principal projection light are combined in the G-reflecting dichroic coating, λirb represents the wavelength at which the transmittance is 50% when the colors of R and B in the principal illumination light are separated from each other in the RB dichroic coating, λprb represents the wavelength at which the transmittance is 50% when the colors of R and B in the principal projection light are combined in the RB dichroic coating, and λpgb represents the wavelength at which the transmittance is 50% when the colors of G and B in the principal projection light are combined in the G-reflecting dichroic coating.

According to one or more embodiments, the composite optical axis of the prism unit and the principal projection light coincide with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

Various advantages and features of embodiments of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:

FIG. 1 is a perspective view of a prism unit in accordance with one or more embodiments;

FIG. 2 is a top view of the prism unit shown in FIG. 1;

FIG. 3 is a side view of the prism unit shown in FIG. 1;

FIG. 4 is a front view of the prism unit shown in FIG. 1;

FIG. 5 is a schematic diagram showing an example structure of a projector on which the prism unit shown in FIG. 1 is mounted;

FIG. 6 is a perspective view for explaining the operation of a digital micromirror device that performs micromirror drive with respect to two axes perpendicular to each other, in accordance with one or more embodiments;

FIG. 7 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Example 1;

FIG. 8 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Example 2;

FIG. 9 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Example 3;

FIG. 10 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Example 4;

FIG. 11 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Example 5;

FIG. 12 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Comparative Example 1;

FIG. 13 is a graph showing the spectral transmission characteristics of first and second dichroic coatings in a prism unit of Comparative Example 2;

FIG. 14 is a graph showing the light use efficiencies in the prism units of Example 1 and Comparative Example 1; and

FIG. 15 is a graph showing the light use efficiencies in the prism units of Example 4 and Comparative Example 2.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of prism units and projectors of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

FIGS. 1 to 4 show an optical system PU1 that includes a color separating/combining prism PB as a prism unit in accordance with one or more embodiments. FIG. 1 shows the optical system PU1 as viewed from obliquely above, FIG. 2 shows the optical system PU1 as viewed from above, FIG. 3 shows the optical system PU1 as viewed from a side, and FIG. 4 shows the optical system PU1 as viewed from front. FIG. 5 shows a schematic example structure of a projector PJ on which the optical system PU1 is mounted. As shown in FIG. 5, the projector PJ includes a projection optical system LN, the optical system PU1, a light source 11, an illumination optical system 12, a control unit 13, and an actuator 14, and the optical system PU1 includes a TIR (Total Internal Reflection) prism PA, a color separating/combining prism PB, and a digital micromirror device DP. The entire projector PJ is controlled by the control unit 13.

As shown in FIG. 5, illumination light L1 emitted from the light source 11 is guided to the digital micromirror device DP by the illumination optical system 12, the TIR prism PA, and the color separating/combining prism PB. The digital micromirror device DP is a reflective display device that generates an image by modulating light, and has a cover glass CG on the image display surface DS that displays an image. On the image display surface DS of the digital micromirror device DP, a two-dimensional image is formed through illumination light intensity modulation.

The pixels of the conventionally-known digital micromirror device DP have a rotational axis at an angle of 45 degrees with respect to each side of the rectangular image display area formed by the image display surface DS, and rotationally move ±12 degrees about the axis, to express switching on and off. Only light reflected by micromirrors (pixel surfaces) in an on-state passes through the optical system PU1 and the projection optical system LN, as will be described later. In the case of a digital micromirror device of the new operation type (see DLP Tilt & Roll Pixel Architecture and DLP IntelliBright™, <URL:http://www.dlp.com/pico-projector/pico-product-developers/2trp-chip.aspx>), on the other hand, mirror surfaces do not rotate about one rotational axis, but rotate about two rotational axes perpendicular to each other.

FIG. 6 shows the feature of a digital micromirror device DP of the new operation type, or an on-state and an off-state of a pixel formed with the rectangular pixel reflecting surface (micromirror surface) MS of a micromirror MR. On the image display surface DS formed with pixel reflecting surfaces MS in the digital micromirror device DP (FIG. 6), switching on and off of each pixel reflecting surface MS is controlled, and the micromirrors MR switch between two angles: an image display state (on-state) and an image non-display state (off-state). In this manner, the intensity of illumination light L1 is modulated, and a desired image can be formed.

As described above, micromirror drive is performed with respect to two axes perpendicular to each other. Therefore, as can be seen from FIG. 6, the pixel reflecting surface MS of a micromirror MR is in an on-state when tilted to one side, and is in an off-state when tilted to a side perpendicular to the one side. In generally-conceivable on/off control, when the pixel reflecting surface MS is in an on-state, the illumination light L1 that has entered the micromirror MR is reflected in the normal direction of the image display surface DS, and turns into on-state light (projection light) L2. When the pixel reflecting surface MS is in an off-state, the illumination light L1 that has entered the micromirror MR is reflected in a direction at a large angle with respect to the normal direction of the image display surface DS, and turns into off-state light (unnecessary light) L3.

The optical system PU1 is a three-plate image projection optical system as shown in FIGS. 1 to 4. That is, the optical system PU1 is a prism system that includes a prism optical system formed with the TIR prism PA and the color separating/combining prism PB, and first to third digital micromirror devices D1 to D3 (equivalent to the digital micromirror device DP in FIG. 5), and separates the illumination light L1 and the projection light L2 from each other, and the projection light (on-state light) L2 and unnecessary light (off-state light) (not shown) from each other. An image displayed on the digital micromirror device DP is enlarged and projected on a screen SC by the projection optical system LN. Movement (such as zooming or focusing) of the projection optical system LN or part of the projection optical system LN is conducted by the actuator 14 (FIG. 5).

In the optical system PU1 (FIGS. 1 to 5), the TIR prism PA is formed with fourth and fifth prisms P4 and P5 each having the shape of a triangular prism, and an air gap layer is provided between the tilted surfaces of the prisms. With this TIR prism PA, the illumination light (input light) L1 for and the projection light (output light) L2 from the first to third digital micromirror devices D1 to D3 are separated from each other. Illumination light L1 emitted from the illumination optical system 12 enters the fifth prism P5 of the TIR prism PA, enters the tilted surface forming the air gap layer between the fourth and fifth prisms P4 and P5 at an angle that satisfies the total reflection conditions, is totally reflected, and enters the color separating/combining prism PB.

In the optical system PU1, the color separating/combining prism PB is formed with three prisms P1, P2, and P3, to be compatible with the three primary colors: R (red), G (green), and B (blue). As the digital micromirror device DP (FIG. 5), the first, second, and third digital micromirror devices D1, D2, and D3 that are used for light in the respective colors of red, green, and blue, and the illumination light L1 is separated into the respective colors of red, green, and blue by the color separating/combining prism PB.

The three prisms P1, P2, and P3 constituting the color separating/combining prism PB are two triangular prisms and one block-like prism. A first dichroic coating C1 (FIG. 2) that reflects first-color light, and an air gap layer adjacent to the first dichroic coating C1 are provided between the first prism P1 and the second prism P2. A second dichroic coating C2 (FIG. 2) that reflects second-color light, and an air gap layer adjacent to the second dichroic coating C2 are provided between the second prism P2 and the third prism P3. In FIG. 2, β1 and β2 represents the angles between the surface normals of the first and second dichroic coatings C1 and C2, and the normal line of the image display surface DS of the third digital micromirror device D3 (this normal line is located parallel to the projection optical axis AX2).

Of the illumination light L1 (FIG. 5) that has entered the first prism P1 of the color separating/combining prism PB, the first-color light is reflected by the first dichroic coating C1 (FIG. 2), and the second-color light and third-color light pass through the first dichroic coating C1. The first-color light reflected by the first dichroic coating C1 is totally reflected, is then emitted from the color separating/combining prism PB, and illuminates the first digital micromirror device D1. Of the second- and third-color light that has passed through the first dichroic coating C1, the second-color light is reflected by the second dichroic coating C2 (FIG. 2), and the third-color light passes through the second dichroic coating C2.

The second-color light reflected by the second dichroic coating C2 is totally reflected, is then emitted from the color separating/combining prism PB, and illuminates the second digital micromirror device D2. The third-color light that has passed through the second dichroic coating C2 is emitted from the color separating/combining prism PB, and illuminates the third digital micromirror device D3. In FIG. 3, a represents the angle of incidence of the illumination light L1 with respect to the third digital micromirror device D3.

The projection light L2 (FIG. 5) formed with the first-color light reflected by the first digital micromirror device D1 enters the color separating/combining prism PB, is totally reflected, and is then reflected by the first dichroic coating C1. The projection light L2 formed with the second-color light reflected by the second digital micromirror device D2 enters the color separating/combining prism PB, is totally reflected, is then reflected by the second dichroic coating C2, and further passes through the first dichroic coating C1. The projection light L2 formed with the third-color light reflected by the third digital micromirror device D3 enters the color separating/combining prism PB, and passes through the second dichroic coating C2 and the first dichroic coating C1. In this manner, of the light emitted from the three digital micromirror devices D1 to D3 that have received the illumination light L1, the projection light L2 to be used in image projection is formed through color combination performed in the first and second dichroic coatings C1 and C2.

In the optical system PU1, the projection light L2 formed with light in the respective colors of red, green, and blue is formed on the same optical axis (equivalent to the projection optical axis AX2 in FIGS. 1 to 3, and the optical axis AX in FIG. 5), and is emitted from the color separating/combining prism PB, to enter the TIR prism PA. The projection light L2 that has entered the TIR prism PA does not satisfy the total reflection conditions at this point, and therefore, passes through the air gap layer, to be projected onto the screen SC by the projection optical system LN. The prism optical system including the color separating/combining prism PB that separates and combines the three colors of R, G, and B can be used not only in an image display apparatus (such as a projector) but also in an image recording apparatus (such as a video camera).

As shown in FIGS. 2 to 4, the plane including the illumination optical axis AX1 and the projection optical axis AX2 on the image display surface DS of the third digital micromirror device D3 is a first plane H1, and the plane including the surface normals of the first and second dichroic coatings C1 and C2 and the surface normal extending through the center of the third digital micromirror device D3 is a second plane H2. In the optical system PU1, the first plane H1 and the second plane H2 are located not to be perpendicular to each other, as shown in FIG. 4. Specifically, the first plane H1 and the second plane H2 perpendicular to each other have rotated in a relative manner in such a direction that the angle of incidence of the illumination optical axis AX1 with respect to the first dichroic coating C1 or the second dichroic coating C2 becomes smaller. In FIG. 4, θ (=20.8°) indicates the angle of rotation from the state where the first plane H1 and the second plane H2 are perpendicular to each other.

If the angles of incidence with respect to the dichroic coating surfaces vary between the illumination light path and the projection light path, a difference appears between the spectral characteristics of the coatings. If the angles of incidence become larger, the spectral characteristics generally shift to the shorter wavelength side, and the cutoff wavelength becomes shorter. If the difference between the spectral characteristics of the illumination light path and the projection light path becomes larger, there are wavelengths with different reflection-transmission conditions between the illumination light path and the projection light path, and light at the wavelengths turn into stray light in the prisms, resulting in an increase in light loss and a decrease in light use efficiency. To counter this, in the optical system PU1 (FIGS. 1 to 4), the first plane H1 and the second plane H2 perpendicular to each other have rotated in a relative manner in such a direction that the angle of incidence of the illumination optical axis AX1 with respect to the first dichroic coating C1 or the second dichroic coating C2 becomes smaller, as described above. With this structure, the angle of incidence of the illumination light L1 with respect to the first or second dichroic coating C1 or C2 varies depending on the relative tilt of each of the first and second planes H1 and H2 with respect to the other. Therefore, the first dichroic coating C1 reflects G light so that the angle of incidence becomes substantially the same between the illumination light path and the projection light path. As a result, the cutoff wavelength can be appropriately set in the second dichroic coating C2, and the light use efficiency can be made higher.

More preferably, in one or more embodiments, the first plane H1 and the second plane H2 perpendicular to each other have rotated in a relative manner in such a direction that the angles of incidence of the illumination light L1 and the projection light L2 with respect to the first dichroic coating C1 become smaller.

There are various conceivable sequences of separation and combination of the three colors of R, G, and B. In a case where the color separating/combining prism PB separates the G light before separating the R light and the B light from each other, the G light is separated from the R light and the B light in the first dichroic coating C1, and the R light and the B light are separated from each other in the second dichroic coating C2. That is, the first-color light (G) in the green wavelength band is reflected by the first dichroic coating C1. The second-color light (B or R) in the blue wavelength band is reflected by the second dichroic coating C2, and the third-color light (R or B) in the red wavelength band passes through the second dichroic coating C2.

As described above, the first dichroic coating C1 may reflect the color light (G) in the green wavelength band. Alternatively, the second dichroic coating C2 reflects the color light (B) in the blue wavelength band and passes the color light (R) in the red wavelength band, or reflects the color light (R) in the red wavelength band and passes the color light (B) in the blue wavelength band. In this structure, the green wavelength band is first separated, and the blue wavelength band and the red wavelength band are then separated from each other in the band. Accordingly, even if the angular characteristics become larger in the second dichroic coating C2, the structure is not affected by that.

With the above described change in the angle of incidence of the illumination light L1, the maximum angle of incidence with respect to the first or second dichroic coating C1 or C2 is reduced, and light loss due to the coat spectral characteristics caused by a difference between the angles of incidence of the illumination light L1 and the projection light L2 with respect to the first or second dichroic coating C1 or C2 (or light loss in the color separating/combining prism PB) can be reduced. Accordingly, with a small and simple structure, light loss in the dichroic coatings C1 and C2 can be reduced, and luminance efficiency can be increased. As this optical system PU1 is included in the projector PJ (FIG. 5), the three-plate projector PJ can be made smaller in size and lower in costs, and a high light use efficiency can be achieved.

Specifically, a prism unit that combines light in the three primary colors of R, G, and B on the same optical axis includes: a G-reflecting dichroic coating that reflects G light and passes R and B light; and an RB dichroic coating that reflects one of R and B, and passes the other one of R and B. According to one or more embodiments, this prism unit satisfies the following conditional expression:

λrg≧λrb≧0.67×λrg+0.33×λgb (1)

Here, λgb represents the wavelength at which the transmittance is 50%; when the colors of G and B on the composite optical axis are combined in the G-reflecting dichroic coating, λrg represents the wavelength at which the transmittance is 50% when the colors of R and G on the composite optical axis are combined in the G-reflecting dichroic coating, and λrb represents the wavelength at which the transmittance is 50% when the colors of R and B on the composite optical axis are combined in the RB dichroic coating.

In the structure that satisfies the conditional expression (1), the cutoff wavelength of the second dichroic coating C2 rises in the G wavelength region at both of the angles of incidence of the projection light path and the illumination light path. Accordingly, light loss can be effectively reduced both in the projection light L2 and the illumination light L1, and luminance can be further increased.

The G-reflecting dichroic coating and the RB dichroic coating are formed from at least two vapor-deposited materials of a high-refractive-index material, an intermediate-refractive-index material, and a low-refractive-index material. The high-refractive-index material may be TiO₂, Nb₂O₅, or Ta₂O₅, the intermediate-refractive-index material may be Al₂O₃or a mixed oxide of Al₂O₃and La₂O₃, and the low-refractive-index material may be SiO₂. As these refractive index materials are used in the G-reflecting dichroic coating and the RB dichroic coating, light loss in the first and second dichroic coatings C1 and C2 can be reduced, and luminance efficiency can be increased.

A projector in accordance with one or more embodiments includes: a prism unit; three image display devices that display an R image, a G image, and a B image on respective image display surfaces; an illumination optical system that illuminates the respective image display surfaces; and a projection optical system that projects the images displayed on the respective image display surfaces onto a screen. This prism unit is a color separating/combining prism that separates the colors in illumination light and combines colors for projection light. The angle of incidence of principal illumination light with respect to the image display surfaces differs from the angle of emission of principal projection light with respect to the image display surfaces. In this projector, the angles of incidence of the principal projection light and the principal illumination light with respect to the G-reflecting dichroic coating are substantially the same. The range of the angles of incidence is a range of a few degrees, such as a range of ±1 degrees. The composite optical axis of the prism unit and the principal projection light coincide with each other.

The above projector satisfies the following conditional expressions (2A) and (2B):

λirg≧λprb≧0.67×λprg+0.33×λpgb (2A)

0.5×λprg+0.5×λpgb>λirb≧λpgb (2B)

Here, λirg represents the wavelength at which the transmittance is 50% when the colors of R and G in the principal illumination light are separated from each other in the G-reflecting dichroic coating, λprg represents the wavelength at which the transmittance is 50% when the colors of R and G in the principal projection light are combined in the G-reflecting dichroic coating, λirb represents the wavelength at which the transmittance is 50% when the colors of R and B in the principal illumination light are separated from each other in the RB dichroic coating, λprb represents the wavelength at which the transmittance is 50% when the colors of R and B in the principal projection light are combined in the RB dichroic coating, and λpgb represents the wavelength at which the transmittance is 50% when the colors of G and B in the principal projection light are combined in the G-reflecting dichroic coating.

In the structure that satisfies the conditional expressions (2A) and (2B), the cutoff wavelength of the second dichroic coating C2 rises in the G wavelength region at both of the angles of incidence of the projection light path and the illumination light path. Accordingly, light loss can be effectively reduced both in the projection light L2 and the illumination light L1, and luminance can be further increased.

EXAMPLES

In the description below, the structures of optical systems according to one or more embodiments of the present invention are described as Examples 1 to 5 and Comparative Examples 1 and 2 in details.

Tables 1 to 20 show the film structures of G-reflecting dichroic coatings G1 to G3, and RB dichroic coatings RB1 to RB7. Each of the film structures shown in Tables 1 to 20 indicates, from the leftmost column, the layer number of each layer, the film forming material of each layer, the physical thickness (nm) of each layer, the refractive index of each layer, and the optical thickness of each layer (the principal design wavelength λ0=550 nm).

Example 1 includes the G-reflecting dichroic coating G1 as the first dichroic coating C1, and the RB dichroic coating RB1 as the second dichroic coating C2. Example 2 includes the G-reflecting dichroic coating G2 as the first dichroic coating C1, and the RB dichroic coating RB2 as the second dichroic coating C2. Example 3 includes the G-reflecting dichroic coating G3 as the first dichroic coating C1, and the RB dichroic coating RB3 as the second dichroic coating C2. Example 4 includes the G-reflecting dichroic coating G3 as the first dichroic coating C1, and the RB dichroic coating RB4 as the second dichroic coating C2. Example 5 includes the G-reflecting dichroic coating G2 as the first dichroic coating C1, and the RB dichroic coating RB5 as the second dichroic coating C2.

Comparative Example 1 includes the G-reflecting dichroic coating G1 as the first dichroic coating C1, and the RB dichroic coating RB6 as the second dichroic coating C2. Comparative Example 2 includes the G-reflecting dichroic coating G3 as the first dichroic coating C1, and the RB dichroic coating RB7 as the second dichroic coating C2.

Table 21 shows the plane angles β1 and β2 (°) of the first and second dichroic coatings C1 and C2, and the angles (°) of incidence of the illumination light L1 and the projection light L2 with respect to the first and second dichroic coatings C1 and C2. In Table 21, each angle (°) is shown as an angle in glass and an angle in the air. Table 22 shows the values according to the respective conditional expressions and related data in Examples 1 to 5 and Comparative Examples 1 and 2. Table 23 shows the states according to the respective conditional expressions (∘ or x). As can be seen from Table 23, Comparative Example 1 satisfies the conditional expression (2B), but Comparative Example 2 does not satisfy the conditional expression (2B).

The graphs in FIGS. 7 to 13 show the spectral transmittances (%) in Examples 1 to 5 and Comparative Examples 1 and 2. In each of the graphs, the solid line (G projection Tave) indicates the transmittance of the projection light L2 (or the mean value of s-polarized light and p-polarized light) in the G-reflecting dichroic coating, and the dotted line (G illumination Tave) indicates the transmittance of the illumination light L1 (or the mean value between s-polarized light and p-polarized light) in the G-reflecting dichroic coating. The dashed line (RB projection Tave) indicates the transmittance of the projection light L2 (or the mean value of s-polarized light and p-polarized light) in the AB dichroic coating, and the dot-and-dash line (RB illumination Tave) indicates the transmittance of the illumination light L1 (or the mean value between s-polarized light and p-polarized light) in the RB dichroic coating.

In each of Examples 1 to 3 and Comparative Example 1, the RB dichroic coating forming the second dichroic coating C2 (FIG. 2) reflects the B light (the second-color light), and passes the R light (the third-color light). In each of Examples 4 and 5, and Comparative Example 2, the RB dichroic coating forming the second dichroic coating C2 (FIG. 2) reflects the R light (the second-color light), and passes the B light (the third-color light).

Example 1 and Comparative Example 1 each include the G-reflecting dichroic coating G1 as the first dichroic coating C1. As can be seen from a comparison between Example 1 and Comparative Example 1, in Comparative Example 1, the dot-and-dash line (RB illumination Tave) extends into the B region, and therefore, light loss occurs on the long-wavelength side of the B region. Meanwhile, a comparison between Example 4 and Comparative Example 2 each including the G-reflecting dichroic coating G3 as the first dichroic coating C1 shows that, in Comparative Example 2, the dashed line (RB projection Tave) extends into the R region, and therefore, light loss occurs on the short-wavelength side of the R region. That is, Comparative Example 1 is an example in which a rise in the RB dichroic coating occurs on short-wavelength side of the G region, and Comparative Example 2 is an example in which a rise in the RB dichroic coating occurs on the long-wavelength side of the G region.

The graphs in FIGS. 14 and 15 show the light use efficiencies in the respective color separating/combining prisms PB (the RGB light use efficiencies depending on the characteristics of the respective dichroic coatings). FIG. 14 shows the light use efficiencies in the color separating/combining prisms PB of Example 1 and Comparative Example 1. FIG. 15 shows the light use efficiencies in the color separating/combining prisms PB of Example 4 and Comparative Example 2. In each of the graphs in FIGS. 14 and 15, the solid line represents the B light, the dashed line represents the G light, the dot-and-dash line represents the R light, the bold line represents Example 1 or 4, and the thin line represents Comparative Example 1 or 2.

As can be seen from the graph in FIG. 14, compared with Comparative Example 1, Example 1 has a light use efficiency improved on the long-wavelength side of the B region. As can be seen from the graph in FIG. 15, compared with Comparative Example 2, Example 4 has a light use efficiency improved on the short-wavelength side of the R region.

TABLE 1

G-reflecting dichroic coating G1 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
La_0.5Al_1.5O₃
196.26
1.74
0.620 λ₀

2
Nb₂O₅
182.43
2.38
0.788 λ₀

3
La_0.5Al_1.5O₃
34.38
1.74
0.109 λ₀

4
Nb₂O₅
88.81
2.38
0.384 λ₀

5
La_0.5Al_1.5O₃
75.14
1.74
0.237 λ₀

6
Nb₂O₅
83.22
2.38
0.360 λ₀

7
La_0.5Al_1.5O₃
36.43
1.74
0.115 λ₀

8
Nb₂O₅
89.13
2.38
0.385 λ₀

9
La_0.5Al_1.5O₃
34.38
1.74
0.109 λ₀

10
Nb₂O₅
69.87
2.38
0.302 λ₀

11
La_0.5Al_1.5O₃
100.57
1.74
0.318 λ₀

12
Nb₂O₅
58.19
2.38
0.251 λ₀

13
La_0.5Al_1.5O₃
74.92
1.74
0.237 λ₀

14
Nb₂O₅
74.22
2.38
0.321 λ₀

15
La_0.5Al_1.5O₃
62.22
1.74
0.197 λ₀

16
Nb₂O₅
81.88
2.38
0.354 λ₀

17
La_0.5Al_1.5O₃
40.10
1.74
0.127 λ₀

18
Nb₂O₅
69.28
2.38
0.299 λ₀

19
La_0.5Al_1.5O₃
89.37
1.74
0.282 λ₀

20
Nb₂O₅
60.22
2.38
0.260 λ₀

21
La_0.5Al_1.5O₃
87.78
1.74
0.277 λ₀

22
Nb₂O₅
59.00
2.38
0.255 λ₀

23
La_0.5Al_1.5O₃
87.95
1.74
0.278 λ₀

24
Nb₂O₅
70.96
2.38
0.307 λ₀

25
La_0.5Al_1.5O₃
37.19
1.74
0.117 λ₀

26
Nb₂O₅
78.14
2.38
0.338 λ₀

27
La_0.5Al_1.5O₃
92.93
1.74
0.293 λ₀

28
Nb₂O₅
42.26
2.38
0.183 λ₀

29
La_0.5Al_1.5O₃
98.59
1.74
0.311 λ₀

30
Nb₂O₅
65.02
2.38
0.281 λ₀

TABLE 2

G-reflecting dichroic coating G1 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
La_0.5Al_1.5O₃
89.81
1.74
0.284 λ₀

32
Nb₂O₅
62.34
2.38
0.269 λ₀

33
La_0.5Al_1.5O₃
42.53
1.74
0.134 λ₀

34
Nb₂O₅
103.28
2.38
0.446 λ₀

35
La_0.5Al_1.5O₃
34.38
1.74
0.109 λ₀

36
Nb₂O₅
53.59
2.38
0.232 λ₀

37
La_0.5Al_1.5O₃
104.60
1.74
0.330 λ₀

38
Nb₂O₅
66.05
2.38
0.285 λ₀

39
La_0.5Al_1.5O₃
110.26
1.74
0.348 λ₀

40
Nb₂O₅
122.14
2.38
0.528 λ₀

41
La_0.5Al_1.5O₃
132.55
1.74
0.419 λ₀

42
Nb₂O₅
70.68
2.38
0.305 λ₀

43
SiO₂
88.82
1.47
0.237 λ₀

Air

1.00

TABLE 3

G-reflecting dichroic coating G2 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
Al₂O₃
159.58
1.63
0.471 λ₀

2
Ta₂O₅
104.79
2.21
0.421 λ₀

3
Al₂O₃
35.00
1.63
0.103 λ₀

4
Ta₂O₅
111.47
2.21
0.448 λ₀

5
Al₂O₃
35.00
1.63
0.103 λ₀

6
Ta₂O₅
39.78
2.21
0.160 λ₀

7
Al₂O₃
142.15
1.63
0.420 λ₀

8
Ta₂O₅
63.91
2.21
0.257 λ₀

9
Al₂O₃
96.53
1.63
0.285 λ₀

10
Ta₂O₅
56.09
2.21
0.225 λ₀

11
Al₂O₃
145.60
1.63
0.430 λ₀

12
Ta₂O₅
35.00
2.21
0.141 λ₀

13
Al₂O₃
63.44
1.63
0.187 λ₀

14
Ta₂O₅
81.78
2.21
0.329 λ₀

15
Al₂O₃
98.72
1.63
0.292 λ₀

16
Ta₂O₅
65.93
2.21
0.265 λ₀

17
Al₂O₃
94.19
1.63
0.278 λ₀

18
Ta₂O₅
64.90
2.21
0.261 λ₀

19
Al₂O₃
98.42
1.63
0.291 λ₀

20
Ta₂O₅
83.34
2.21
0.335 λ₀

21
Al₂O₃
35.00
1.63
0.103 λ₀

22
Ta₂O₅
78.95
2.21
0.317 λ₀

23
Al₂O₃
98.42
1.63
0.291 λ₀

24
Ta₂O₅
66.03
2.21
0.265 λ₀

25
Al₂O₃
96.70
1.63
0.286 λ₀

26
Ta₂O₅
68.99
2.21
0.277 λ₀

27
Al₂O₃
104.71
1.63
0.309 λ₀

28
Ta₂O₅
36.00
2.21
0.145 λ₀

29
Al₂O₃
158.85
1.63
0.469 λ₀

30
Ta₂O₅
35.00
2.21
0.141 λ₀

TABLE 4

G-reflecting dichroic coating G2 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
Al₂O₃
57.96
1.63
0.171 λ₀

32
Ta₂O₅
89.09
2.21
0.358 λ₀

33
Al₂O₃
95.97
1.63
0.284 λ₀

34
Ta₂O₅
96.67
2.21
0.388 λ₀

35
Al₂O₃
67.57
1.63
0.200 λ₀

36
Ta₂O₅
35.00
2.21
0.141 λ₀

37
Al₂O₃
35.00
1.63
0.103 λ₀

38
Ta₂O₅
155.25
2.21
0.624 λ₀

39
Al₂O₃
35.00
1.63
0.103 λ₀

40
Ta₂O₅
139.27
2.21
0.560 λ₀

41
Al₂O₃
211.61
1.63
0.625 λ₀

42
Ta₂O₅
113.07
2.21
0.454 λ₀

43
Al₂O₃
93.19
1.63
0.275 λ₀

44
Ta₂O₅
120.74
2.21
0.485 λ₀

45
Al₂O₃
195.24
1.63
0.577 λ₀

46
Ta₂O₅
38.95
2.21
0.157 λ₀

47
SiO₂
100.67
1.47
0.269 λ₀

Air

1.00

TABLE 5

G-reflecting dichroic coating G3 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
La_0.9Al_1.1O₃
186.78
1.85
0.627 λ₀

2
TiO₂
159.61
2.41
0.698 λ₀

3
La_0.9Al_1.1O₃
101.32
1.85
0.340 λ₀

4
TiO₂
71.76
2.41
0.314 λ₀

5
La_0.9Al_1.1O₃
40.62
1.85
0.136 λ₀

6
TiO₂
93.29
2.41
0.408 λ₀

7
La_0.9Al_1.1O₃
43.13
1.85
0.145 λ₀

8
TiO₂
60.24
2.41
0.264 λ₀

9
La_0.9Al_1.1O₃
99.97
1.85
0.335 λ₀

10
TiO₂
58.76
2.41
0.257 λ₀

11
La_0.9Al_1.1O₃
68.84
1.85
0.231 λ₀

12
TiO₂
65.54
2.41
0.287 λ₀

13
La_0.9Al_1.1O₃
82.50
1.85
0.277 λ₀

14
TiO₂
57.90
2.41
0.253 λ₀

15
La_0.9Al_1.1O₃
81.99
1.85
0.275 λ₀

16
TiO₂
58.30
2.41
0.255 λ₀

17
La_0.9Al_1.1O₃
83.19
1.85
0.279 λ₀

18
TiO₂
58.80
2.41
0.257 λ₀

19
La_0.9Al_1.1O₃
83.07
1.85
0.279 λ₀

20
TiO₂
58.29
2.41
0.255 λ₀

21
La_0.9Al_1.1O₃
82.66
1.85
0.277 λ₀

22
TiO₂
58.44
2.41
0.256 λ₀

23
La_0.9Al_1.1O₃
83.26
1.85
0.279 λ₀

24
TiO₂
58.84
2.41
0.257 λ₀

25
La_0.9Al_1.1O₃
82.59
1.85
0.277 λ₀

26
TiO₂
57.14
2.41
0.250 λ₀

27
La_0.9Al_1.1O₃
79.02
1.85
0.265 λ₀

28
TiO₂
71.62
2.41
0.313 λ₀

29
La_0.9Al_1.1O₃
55.13
1.85
0.185 λ₀

30
TiO₂
73.01
2.41
0.319 λ₀

TABLE 6

G-reflecting dichroic coating G3 (Principal

design wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
La_0.9Al_1.1O₃
63.26
1.85
0.212 λ₀

32
TiO₂
85.10
2.41
0.372 λ₀

33
La_0.9Al_1.1O₃
37.85
1.85
0.127 λ₀

34
TiO₂
92.03
2.41
0.403 λ₀

35
La_0.9Al_1.1O₃
35.00
1.85
0.117 λ₀

36
TiO₂
35.00
2.41
0.153 λ₀

37
La_0.9Al_1.1O₃
147.46
1.85
0.495 λ₀

38
TiO₂
35.00
2.41
0.103 λ₀

39
La_0.9Al_1.1O₃
178.99
1.85
0.600 λ₀

40
TiO₂
85.06
2.41
0.372 λ₀

41
La_0.9Al_1.1O₃
99.08
1.85
0.332 λ₀

42
TiO₂
133.30
2.41
0.583 λ₀

43
La_0.9Al_1.1O₃
113.55
1.85
0.381 λ₀

44
TiO₂
65.68
2.41
0.287 λ₀

45
La_0.9Al_1.1O₃
213.49
1.85
0.716 λ₀

46
TiO₂
88.57
2.41
0.388 λ₀

47
La_0.9Al_1.1O₃
181.69
2.97
0.980 λ₀

48
TiO₂
85.01
3.53
0.546 λ₀

49
La_0.9Al_1.1O₃
113.01
4.09
0.841 λ₀

50
TiO₂
106.75
3.53
0.685 λ₀

51
SiO₂
94.18
1.47
0.252 λ₀

Air

1.00

TABLE 7

RB dichroic coating RB1 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
SiO₂
89.51
1.47
0.239 λ₀

2
Ta₂O₅
25.35
2.21
0.102 λ₀

3
SiO₂
74.66
1.47
0.200 λ₀

4
Ta₂O₅
48.29
2.21
0.194 λ₀

5
SiO₂
80.50
1.47
0.215 λ₀

6
Ta₂O₅
46.72
2.21
0.188 λ₀

7
SiO₂
80.47
1.47
0.215 λ₀

8
Ta₂O₅
44.93
2.21
0.181 λ₀

9
SiO₂
82.01
1.47
0.219 λ₀

10
Ta₂O₅
44.59
2.21
0.179 λ₀

11
SiO₂
73.34
1.47
0.196 λ₀

12
Ta₂O₅
42.43
2.21
0.170 λ₀

13
SiO₂
76.15
1.47
0.204 λ₀

14
Ta₂O₅
45.54
2.21
0.183 λ₀

15
SiO₂
78.86
1.47
0.211 λ₀

16
Ta₂O₅
46.04
2.21
0.185 λ₀

17
SiO₂
83.32
1.47
0.223 λ₀

18
Ta₂O₅
47.03
2.21
0.189 λ₀

19
SiO₂
82.49
1.47
0.220 λ₀

20
Ta₂O₅
73.36
2.21
0.295 λ₀

21
SiO₂
26.70
1.47
0.071 λ₀

22
Ta₂O₅
80.16
2.21
0.322 λ₀

23
SiO₂
121.03
1.47
0.323 λ₀

24
Ta₂O₅
32.33
2.21
0.130 λ₀

25
SiO₂
85.47
1.47
0.228 λ₀

26
Ta₂O₅
57.79
2.21
0.232 λ₀

27
SiO₂
64.83
1.47
0.173 λ₀

28
Ta₂O₅
97.79
2.21
0.393 λ₀

29
SiO₂
57.93
1.47
0.155 λ₀

30
Ta₂O₅
47.39
2.21
0.190 λ₀

TABLE 8

RB dichroic coating RB1 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
SiO₂
83.98
1.47
0.224 λ₀

32
Ta₂O₅
53.31
2.21
0.214 λ₀

33
SiO₂
133.28
1.47
0.356 λ₀

34
Ta₂O₅
64.55
2.21
0.259 λ₀

35
SiO₂
36.13
1.47
0.097 λ₀

36
Ta₂O₅
54.29
2.21
0.218 λ₀

37
SiO₂
118.20
1.47
0.316 λ₀

38
Ta₂O₅
66.42
2.21
0.267 λ₀

39
SiO₂
114.91
1.47
0.307 λ₀

40
Ta₂O₅
14.62
2.21
0.059 λ₀

41
SiO₂
91.96
1.47
0.246 λ₀

42
Ta₂O₅
80.08
2.21
0.322 λ₀

43
SiO₂
117.32
1.47
0.314 λ₀

44
Ta₂O₅
10.21
2.21
0.041 λ₀

45
SiO₂
201.38
1.47
0.538 λ₀

Air

1.00

TABLE 9

RB dichroic coating RB2 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
TiO₂
33.90
2.41
0.148 λ₀

2
La_0.5Al_1.5O₃
51.68
1.74
0.163 λ₀

3
TiO₂
57.20
2.41
0.250 λ₀

4
La_0.5Al_1.5O₃
78.84
1.74
0.249 λ₀

5
TiO₂
55.83
2.41
0.244 λ₀

6
La_0.5Al_1.5O₃
67.43
1.74
0.213 λ₀

7
TiO₂
43.81
2.41
0.192 λ₀

8
La_0.5Al_1.5O₃
75.25
1.74
0.238 λ₀

9
TiO₂
62.99
2.41
0.276 λ₀

10
La_0.5Al_1.5O₃
74.28
1.74
0.235 λ₀

11
TiO₂
51.42
2.41
0.225 λ₀

12
La_0.5Al_1.5O₃
72.66
1.74
0.229 λ₀

13
TiO₂
51.13
2.41
0.224 λ₀

14
La_0.5Al_1.5O₃
76.35
1.74
0.241 λ₀

15
TiO₂
55.26
2.41
0.242 λ₀

16
La_0.5Al_1.5O₃
78.19
1.74
0.247 λ₀

17
TiO₂
52.54
2.41
0.230 λ₀

18
La_0.5Al_1.5O₃
76.10
1.74
0.240 λ₀

19
TiO₂
51.18
2.41
0.224 λ₀

20
La_0.5Al_1.5O₃
75.67
1.74
0.239 λ₀

21
TiO₂
52.55
2.41
0.230 λ₀

22
La_0.5Al_1.5O₃
78.12
1.74
0.247 λ₀

23
TiO₂
53.89
2.41
0.236 λ₀

24
La_0.5Al_1.5O₃
75.81
1.74
0.239 λ₀

25
TiO₂
50.08
2.41
0.219 λ₀

26
La_0.5Al_1.5O₃
71.62
1.74
0.226 λ₀

27
TiO₂
47.34
2.41
0.207 λ₀

28
La_0.5Al_1.5O₃
66.54
1.74
0.210 λ₀

29
TiO₂
41.36
2.41
0.181 λ₀

30
La_0.5Al_1.5O₃
44.75
1.74
0.141 λ₀

TABLE 10

RB dichroic coating RB2 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
TiO₂
37.79
2.41
0.165 λ₀

32
La_0.5Al_1.5O₃
65.26
1.74
0.206 λ₀

33
TiO₂
46.80
2.41
0.205 λ₀

34
La_0.5Al_1.5O₃
70.63
1.74
0.223 λ₀

35
TiO₂
47.45
2.41
0.208 λ₀

36
La_0.5Al_1.5O₃
70.70
1.74
0.223 λ₀

37
TiO₂
46.88
2.41
0.205 λ₀

38
La_0.5Al_1.5O₃
66.39
1.74
0.210 λ₀

39
TiO₂
39.75
2.41
0.174 λ₀

40
La_0.5Al_1.5O₃
48.28
1.74
0.152 λ₀

41
TiO₂
40.12
2.41
0.176 λ₀

42
La_0.5Al_1.5O₃
64.54
1.74
0.204 λ₀

43
TiO₂
45.08
2.41
0.197 λ₀

44
La_0.5Al_1.5O₃
67.16
1.74
0.212 λ₀

45
TiO₂
46.05
2.41
0.201 λ₀

46
La_0.5Al_1.5O₃
69.87
1.74
0.221 λ₀

47
TiO₂
47.69
2.41
0.209 λ₀

48
La_0.5Al_1.5O₃
67.64
1.74
0.214 λ₀

49
TiO₂
41.02
2.41
0.179 λ₀

50
La_0.5Al_1.5O₃
47.29
1.74
0.149 λ₀

51
TiO₂
40.43
2.41
0.177 λ₀

52
SiO₂
118.21
1.47
0.316 λ₀

Air

1.00

TABLE 11

RB dichroic coating RB3 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
Al₂O₃
176.42
1.63
0.521 λ₀

2
Nb₂O₅
42.46
2.38
0.184 λ₀

3
Al₂O₃
48.23
1.63
0.142 λ₀

4
Nb₂O₅
56.08
2.38
0.242 λ₀

5
Al₂O₃
82.76
1.63
0.245 λ₀

6
Nb₂O₅
61.34
2.38
0.265 λ₀

7
Al₂O₃
56.01
1.63
0.165 λ₀

8
Nb₂O₅
53.72
2.38
0.232 λ₀

9
Al₂O₃
80.16
1.63
0.237 λ₀

10
Nb₂O₅
55.83
2.38
0.241 λ₀

11
Al₂O₃
80.24
1.63
0.237 λ₀

12
Nb₂O₅
52.53
2.38
0.227 λ₀

13
Al₂O₃
75.64
1.63
0.223 λ₀

14
Nb₂O₅
52.02
2.38
0.225 λ₀

15
Al₂O₃
80.25
1.63
0.237 λ₀

16
Nb₂O₅
54.09
2.38
0.234 λ₀

17
Al₂O₃
81.53
1.63
0.241 λ₀

18
Nb₂O₅
52.93
2.38
0.229 λ₀

19
Al₂O₃
79.68
1.63
0.235 λ₀

20
Nb₂O₅
51.76
2.38
0.224 λ₀

21
Al₂O₃
78.37
1.63
0.232 λ₀

22
Nb₂O₅
53.10
2.38
0.229 λ₀

23
Al₂O₃
80.53
1.63
0.238 λ₀

24
Nb₂O₅
53.28
2.38
0.230 λ₀

25
Al₂O₃
77.48
1.63
0.229 λ₀

26
Nb₂O₅
48.93
2.38
0.211 λ₀

27
Al₂O₃
62.02
1.63
0.183 λ₀

28
Nb₂O₅
38.98
2.38
0.168 λ₀

29
Al₂O₃
42.59
1.63
0.126 λ₀

30
Nb₂O₅
36.81
2.38
0.159 λ₀

TABLE 12

RB dichroic coating RB3 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
Al₂O₃
64.73
1.63
0.191 λ₀

32
Nb₂O₅
49.42
2.38
0.214 λ₀

33
Al₂O₃
77.07
1.63
0.228 λ₀

34
Nb₂O₅
50.84
2.38
0.220 λ₀

35
Al₂O₃
75.26
1.63
0.222 λ₀

36
Nb₂O₅
46.48
2.38
0.201 λ₀

37
Al₂O₃
53.48
1.63
0.158 λ₀

38
Nb₂O₅
36.20
2.38
0.156 λ₀

39
Al₂O₃
46.78
1.63
0.138 λ₀

40
Nb₂O₅
40.24
2.38
0.174 λ₀

41
Al₂O₃
69.02
1.63
0.204 λ₀

42
Nb₂O₅
50.23
2.38
0.217 λ₀

43
Al₂O₃
77.34
1.63
0.229 λ₀

44
Nb₂O₅
50.26
2.38
0.217 λ₀

45
Al₂O₃
66.07
1.63
0.195 λ₀

46
Nb₂O₅
36.82
2.38
0.159 λ₀

47
Al₂O₃
54.45
1.63
0.161 λ₀

48
Nb₂O₅
39.36
2.38
0.170 λ₀

49
Al₂O₃
41.73
1.63
0.123 λ₀

50
Nb₂O₅
46.98
2.38
0.203 λ₀

51
Al₂O₃
78.04
1.63
0.231 λ₀

52
Nb₂O₅
54.67
2.38
0.236 λ₀

53
Al₂O₃
52.43
1.63
0.155 λ₀

54
Nb₂O₅
15.00
2.38
0.065 λ₀

55
SiO₂
70.00
1.47
0.187 λ₀

Air

1.00

TABLE 13

RB dichroic coating RB4 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
Al₂O₃
64.86
1.63
0.192 λ₀

2
Nb₂O₅
86.07
2.38
0.372 λ₀

3
Al₂O₃
100.15
1.63
0.296 λ₀

4
Nb₂O₅
79.40
2.38
0.343 λ₀

5
Al₂O₃
93.45
1.63
0.276 λ₀

6
Nb₂O₅
71.17
2.38
0.308 λ₀

7
Al₂O₃
111.97
1.63
0.331 λ₀

8
Nb₂O₅
59.93
2.38
0.259 λ₀

9
Al₂O₃
127.86
1.63
0.378 λ₀

10
Nb₂O₅
148.37
2.38
0.641 λ₀

11
Al₂O₃
130.10
1.63
0.384 λ₀

12
Nb₂O₅
53.84
2.38
0.233 λ₀

13
Al₂O₃
118.49
1.63
0.350 λ₀

14
Nb₂O₅
61.27
2.38
0.265 λ₀

15
Al₂O₃
105.96
1.63
0.313 λ₀

16
Nb₂O₅
64.57
2.38
0.279 λ₀

17
Al₂O₃
106.03
1.63
0.313 λ₀

18
Nb₂O₅
64.06
2.38
0.277 λ₀

19
Al₂O₃
103.76
1.63
0.307 λ₀

20
Nb₂O₅
68.13
2.38
0.294 λ₀

21
Al₂O₃
98.44
1.63
0.291 λ₀

22
Nb₂O₅
71.08
2.38
0.307 λ₀

23
Al₂O₃
97.95
1.63
0.289 λ₀

24
Nb₂O₅
72.87
2.38
0.315 λ₀

25
Al₂O₃
99.04
1.63
0.293 λ₀

26
Nb₂O₅
76.07
2.38
0.329 λ₀

27
Al₂O₃
103.14
1.63
0.305 λ₀

28
Nb₂O₅
79.16
2.38
0.342 λ₀

29
Al₂O₃
109.29
1.63
0.323 λ₀

30
Nb₂O₅
79.80
2.38
0.345 λ₀

TABLE 14

RB dichroic coating RB4 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
Al₂O₃
109.02
1.63
0.322 λ₀

32
Nb₂O₅
76.31
2.38
0.330 λ₀

33
Al₂O₃
108.03
1.63
0.319 λ₀

34
Nb₂O₅
72.16
2.38
0.312 λ₀

35
Al₂O₃
110.98
1.63
0.328 λ₀

36
Nb₂O₅
69.75
2.38
0.301 λ₀

37
Al₂O₃
116.52
1.63
0.344 λ₀

38
Nb₂O₅
67.47
2.38
0.292 λ₀

39
SiO₂
70.79
1.47
0.189 λ₀

Air

1.00

TABLE 15

RB dichroic coating RB5 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
Nb₂O₅
88.69
2.38
0.383 λ₀

2
SiO₂
118.02
1.47
0.315 λ₀

3
Nb₂O₅
82.90
2.38
0.358 λ₀

4
SiO₂
100.89
1.47
0.270 λ₀

5
Nb₂O₅
83.02
2.38
0.359 λ₀

6
SiO₂
101.24
1.47
0.271 λ₀

7
Nb₂O₅
78.54
2.38
0.339 λ₀

8
SiO₂
111.54
1.47
0.298 λ₀

9
Nb₂O₅
73.29
2.38
0.317 λ₀

10
SiO₂
115.30
1.47
0.308 λ₀

11
Nb₂O₅
73.84
2.38
0.319 λ₀

12
SiO₂
109.73
1.47
0.293 λ₀

13
Nb₂O₅
76.23
2.38
0.329 λ₀

14
SiO₂
108.03
1.47
0.289 λ₀

15
Nb₂O₅
74.74
2.38
0.323 λ₀

16
SiO₂
114.02
1.47
0.305 λ₀

17
Nb₂O₅
71.62
2.38
0.310 λ₀

18
SiO₂
117.29
1.47
0.313 λ₀

19
Nb₂O₅
71.86
2.38
0.311 λ₀

20
SiO₂
114.62
1.47
0.306 λ₀

21
Nb₂O₅
73.42
2.38
0.317 λ₀

22
SiO₂
114.79
1.47
0.307 λ₀

23
Nb₂O₅
72.34
2.38
0.313 λ₀

24
SiO₂
120.99
1.47
0.323 λ₀

25
Nb₂O₅
69.91
2.38
0.302 λ₀

26
SiO₂
127.87
1.47
0.342 λ₀

27
Nb₂O₅
71.44
2.38
0.309 λ₀

28
SiO₂
134.38
1.47
0.359 λ₀

29
Nb₂O₅
78.74
2.38
0.340 λ₀

30
SiO₂
145.15
1.47
0.388 λ₀

TABLE 16

RB dichroic coating RB5 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
Nb₂O₅
80.83
2.38
0.349 λ₀

32
SiO₂
137.58
1.47
0.368 λ₀

33
Nb₂O₅
73.54
2.38
0.318 λ₀

34
SiO₂
132.88
1.47
0.355 λ₀

35
Nb₂O₅
70.17
2.38
0.303 λ₀

36
SiO₂
132.81
1.47
0.355 λ₀

37
Nb₂O₅
72.14
2.38
0.312 λ₀

38
SiO₂
137.02
1.47
0.366 λ₀

39
Nb₂O₅
72.74
2.38
0.314 λ₀

40
SiO₂
69.49
1.47
0.186 λ₀

Air

1.00

TABLE 17

RB dichroic coating RB6 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
SiO₂
97.56
1.47
0.261 λ₀

2
Ta₂O₅
17.06
2.21
0.069 λ₀

3
SiO₂
88.61
1.47
0.237 λ₀

4
Ta₂O₅
32.83
2.21
0.132 λ₀

5
SiO₂
99.96
1.47
0.267 λ₀

6
Ta₂O₅
30.32
2.21
0.122 λ₀

7
SiO₂
96.44
1.47
0.258 λ₀

8
Ta₂O₅
29.85
2.21
0.120 λ₀

9
SiO₂
105.11
1.47
0.281 λ₀

10
Ta₂O₅
15.83
2.21
0.064 λ₀

11
SiO₂
111.45
1.47
0.298 λ₀

12
Ta₂O₅
11.82
2.21
0.047 λ₀

13
SiO₂
106.99
1.47
0.286 λ₀

14
Ta₂O₅
23.56
2.21
0.095 λ₀

15
SiO₂
94.34
1.47
0.252 λ₀

16
Ta₂O₅
36.51
2.21
0.147 λ₀

17
SiO₂
90.65
1.47
0.242 λ₀

18
Ta₂O₅
42.84
2.21
0.172 λ₀

19
SiO₂
87.75
1.47
0.235 λ₀

20
Ta₂O₅
45.34
2.21
0.182 λ₀

21
SiO₂
86.82
1.47
0.232 λ₀

22
Ta₂O₅
47.40
2.21
0.190 λ₀

23
SiO₂
87.05
1.47
0.233 λ₀

24
Ta₂O₅
48.41
2.21
0.195 λ₀

25
SiO₂
87.26
1.47
0.233 λ₀

26
Ta₂O₅
48.25
2.21
0.194 λ₀

27
SiO₂
88.17
1.47
0.236 λ₀

28
Ta₂O₅
47.68
2.21
0.192 λ₀

29
SiO₂
91.23
1.47
0.244 λ₀

30
Ta₂O₅
44.65
2.21
0.179 λ₀

TABLE 18

RB dichroic coating RB6 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
SiO₂
98.73
1.47
0.264 λ₀

32
Ta₂O₅
34.27
2.21
0.138 λ₀

33
SiO₂
135.73
1.47
0.363 λ₀

34
Ta₂O₅
15.01
2.21
0.060 λ₀

35
SiO₂
140.40
1.47
0.375 λ₀

36
Ta₂O₅
38.75
2.21
0.156 λ₀

37
SiO₂
107.17
1.47
0.286 λ₀

38
Ta₂O₅
20.54
2.21
0.083 λ₀

39
SiO₂
110.31
1.47
0.295 λ₀

40
Ta₂O₅
48.39
2.21
0.194 λ₀

41
SiO₂
134.70
1.47
0.360 λ₀

Air

1.00

TABLE 19

RB dichroic coating RB7 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

Prism substrate

1.52

1
Al₂O₃
74.91
1.63
0.221 λ₀

2
Nb₂O₅
89.36
2.38
0.386 λ₀

3
Al₂O₃
114.30
1.63
0.338 λ₀

4
Nb₂O₅
82.74
2.38
0.358 λ₀

5
Al₂O₃
98.72
1.63
0.292 λ₀

6
Nb₂O₅
83.65
2.38
0.362 λ₀

7
Al₂O₃
97.96
1.63
0.289 λ₀

8
Nb₂O₅
79.37
2.38
0.343 λ₀

9
Al₂O₃
118.72
1.63
0.351 λ₀

10
Nb₂O₅
176.88
2.38
0.764 λ₀

11
Al₂O₃
117.54
1.63
0.347 λ₀

12
Nb₂O₅
78.43
2.38
0.339 λ₀

13
Al₂O₃
95.62
1.63
0.283 λ₀

14
Nb₂O₅
79.92
2.38
0.345 λ₀

15
Al₂O₃
98.82
1.63
0.292 λ₀

16
Nb₂O₅
74.01
2.38
0.320 λ₀

17
Al₂O₃
108.50
1.63
0.321 λ₀

18
Nb₂O₅
70.38
2.38
0.304 λ₀

19
Al₂O₃
107.72
1.63
0.318 λ₀

20
Nb₂O₅
74.35
2.38
0.321 λ₀

21
Al₂O₃
99.50
1.63
0.294 λ₀

22
Nb₂O₅
78.38
2.38
0.339 λ₀

23
Al₂O₃
98.13
1.63
0.290 λ₀

24
Nb₂O₅
76.09
2.38
0.329 λ₀

25
Al₂O₃
109.58
1.63
0.324 λ₀

26
Nb₂O₅
69.10
2.38
0.299 λ₀

27
Al₂O₃
121.56
1.63
0.359 λ₀

28
Nb₂O₅
65.56
2.38
0.283 λ₀

29
Al₂O₃
125.66
1.63
0.371 λ₀

30
Nb₂O₅
70.09
2.38
0.303 λ₀

TABLE 20

RB dichroic coating RB7 (Principal design

wavelength: λ₀= 550 nm

Physical

Layer

thickness
Refractive
Optical

number
Material
(nm)
index
thickness

31
Al₂O₃
126.35
1.63
0.373 λ₀

32
Nb₂O₅
75.23
2.38
0.325 λ₀

33
Al₂O₃
127.13
1.63
0.376 λ₀

34
Nb₂O₅
76.78
2.38
0.332 λ₀

35
Al₂O₃
126.05
1.63
0.372 λ₀

36
Nb₂O₅
76.49
2.38
0.331 λ₀

37
Al₂O₃
127.19
1.63
0.376 λ₀

38
Nb₂O₅
76.46
2.38
0.330 λ₀

39
SiO₂
75.58
1.47
0.202 λ₀

Air

1.00

TABLE 21

Data of dichroic coatings C1 and C2

(in glass)
(in air)

C1
C2
C1
C2

(G reflection)
(RB)
(G reflection)
(RB)

Surface angle β1, β2 (°)
28.5
11.25
28.5
11.25

Angle (°) of incidence of
28.5
27.60
46.4
44.70

illumination light L1

Angle (°) of incidence of
28.5
11.25
46.4
17.20

projection light L2

TABLE 22

C1
C2
G reflection
RB
Conditional Expression (1)

G reflection
RB
λ gb
λ rg
λ rd
0.67 λ rg + 0.33 λ gb

Example 1
G1
RB1
498
590
571
559.64

Example 2
G2
RB2
507
602
573
570.65

Example 3
G3
RB3
509
598
574
568.63

Example 4
G3
RB4
509
598
569
568.63

Example 5
G2
RB5
507
602
582
570.65

Comparative
G1
RB6
498
590
538
559.64

Example 1

Comparative
G3
RB7
509
598
605
568.63

Example 2

C1
C2
G reflection
RB
Conditional Expression (2A)

G reflection
RB
λ pgb
λ prg
λ irg
λ prd
0.67 λ prg + 0.33 λ pgb

Example 1
G1
RB1
498
590
591
571
559.64

Example 2
G2
RB2
507
602
603
573
570.65

Example 3
G3
RB3
509
598
599
574
568.63

Example 4
G3
RB4
509
598
599
569
568.63

Example 5
G2
RB5
507
602
603
582
570.65

Comparative
G1
RB6
498
590
591
538
559.64

Example 1

Comparative
G3
RB7
509
598
599
605
568.63

Example 2

C1
C2
G reflection
RB
Conditional Expression (2B)

G reflection
RB
λ pgb
λ prg
λ ird
0.5 λ prg + 0.5 λ pgb

Example 1
G1
RB1
498
590
532
544.0

Example 2
G2
RB2
507
602
544
554.5

Example 3
G3
RB3
509
598
545
553.5

Example 4
G3
RB4
509
598
537
553.5

Example 5
G2
RB5
507
602
545
554.5

Comparative
G1
RB6
498
590
500
544.0

Example 1

Comparative
G3
RB7
509
598
573
553.5

Example 2

TABLE 23

Conditional Expression (1)

λ rb ≧ 0.67 λ

λ rg ≧ λ rb
rg + 0.33 λ gb

Example 1
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Example 2
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Example 3
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Example 4
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Example 5
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Comparative
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X

Example 1

Comparative
X
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Example 2

Conditional Expression (2A)

λ prb ≧ 0.67 λ

λ irg ≧ λ prb
prg + 0.33 λ pgb

Example 1
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Example 2
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Example 3
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Example 4
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Example 5
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Comparative
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X

Example 1

Comparative
X
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Example 2

Conditional Expression (2B)

0.5 λ prg + 0.5 λ

pgb ≧ λ irb
λ irb ≧ λ pgb

Example 1
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Example 2
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Example 3
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Example 4
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Example 5
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Comparative
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Example 1

Comparative
X
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Example 2

With a prism unit according to one or more embodiments of the present invention, the cutoff wavelength of the RB dichroic coating is set within a predetermined range, so that the cutoff wavelength falls within the G wavelength band at both angles of incidence of the projection light path and the illumination light path. Accordingly, light loss at the dichroic coatings is reduced in both projection light and illumination light, and light use efficiency can be increased. As this prism unit is included in a projector, a bright and high-performance three-plate projector can be realized.

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.

PRISM UNIT AND PROJECTOR

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Priority Claims (1)