JP5487834B2 - Color prism unit and image projection apparatus - Google Patents

Description

  The present invention relates to a color prism unit and an image projection apparatus.

  In a color image projector (projector) including a reflective image display element such as a digital micromirror device (DMD), a color prism unit is used for color separation of illumination light and color synthesis of projection light. The color prism unit includes a plurality of prisms combined so that a minute interval (air gap) is interposed. These air gaps are inclined with respect to the optical axis of the projection light. In addition, a dichroic coat layer for color separation is provided on one of the two surfaces of the prism forming each air gap. In general, the two surfaces of the prism forming the air gap are both flat and parallel to each other.

  Since the air gap is inclined with respect to the optical axis of the projection light, an astigmatism difference that is a difference in condensing position depending on the imaging direction occurs. For example, the projection light passing through the air gap has a different light collection position in a plane including the optical axis of the projection light and the normal direction of the air gap and in a plane perpendicular to the plane. This astigmatic difference degrades the imaging performance and also causes flare in the image projected on the screen.

  The astigmatic difference in the color prism unit differs for each color light (red, green, and blue), and becomes larger as the thickness of the air gap is thicker (the wider the distance between the two surfaces forming the air gap). Therefore, the thickness of the air gap is preferably as thin as possible in order to suppress the astigmatic difference. However, if the thickness of the air gap is set too thin, the thermal expansion of the prism due to the absorption of light energy causes the space between the two surfaces forming the air gap to narrow and contact each other, causing the air gap to collapse and function. Disappear.

  As described above, since the dichroic coat layer is provided on one of the two surfaces forming the air gap, absorption of light energy is particularly remarkable, and the air gap is easily crushed due to thermal expansion. Therefore, in order to prevent the air gap from collapsing due to thermal expansion, it is necessary to set the thickness of the air gap to a certain extent. Further, the intensity of illumination light tends to increase in order to meet the demand for higher definition of projected images. When high-intensity illumination light is used, the thermal expansion of the prism becomes significant, so that it is necessary to take sufficient measures against the collapse of the air gap.

  Patent Document 1 discloses a color prism unit in which an air gap formed by two surfaces (planar surfaces) of a prism has a wedge shape. This wedge-shaped air gap is intended to suppress the astigmatic difference while ensuring the thickness of the air gap effective for preventing the air gap from being crushed by the thermal expansion of the prism. However, if the air gap is wedge-shaped, the astigmatic difference cannot be effectively suppressed in a region where the air gap is thick (a region where the distance between the two surfaces forming the air gap is wide).

  Patent Document 2 discloses an air gapless color prism unit in which an interval between two surfaces forming a prism is filled with an adhesive for joining the prisms. This air gapless is intended to avoid astigmatism. However, particularly when the color prism unit is used in a high-luminance projector for cinema or the like, the heat resistance and light resistance of the adhesive against high-intensity illumination light are not reliable. Also, in the case of air gapless, since the joint area between the prisms, that is, the application area of the adhesive is large, it is difficult to discharge and prevent the bubbles in the adhesive. In this respect, the productivity of the air gapless color prism unit is extremely inferior.

JP-A-4-180010 US Pat. No. 5,644,432

  An object of this invention is to provide the color prism unit which implement | achieves prevention of the collapse of the air gap resulting from a thermal expansion, and effective suppression of an astigmatic difference.

The present invention is composed of a plurality of prisms, decomposes illumination light into a plurality of color lights and makes them incident on a plurality of reflective image display elements, and synthesizes projection light from the plurality of reflective image display elements to project projection optics. A color prism unit that emits light to the system and emits non-projection light from the plurality of reflective image display elements in a direction different from the projection light,
A first surface of one of the plurality of prisms and a second surface of the other one of the plurality of prisms face each other with a spacer interposed therebetween, so that the first surface and the first surface An air gap inclined with respect to the optical axis of the projection light is formed between the two surfaces,
A dichroic coat layer that reflects specific color light and transmits other specific color light is formed on one of the first and second surfaces,
The spacer includes the dichroic coat layer in the non-effective area in which neither the illumination light, the projection light, nor the non-projection light passes or reflects on any of the first and second surfaces. A projection light effective area that reflects the projection light of the specific color light and transmits the projection light of the other specific color light; and the dichroic coat layer reflects the non-projection light of the specific color light and the other light disposed at a location between the non-projection light effective area for transmitting the non-projection light of a specific color light Rutotomoni, the direction and the projection optical effective region and the non-projection light effective area are arranged within the non-active area Provided is a color prism unit disposed at both ends .

  Of the non-effective area, the point between the effective area of the projection light and the effective area of the non-projection light is located away from both ends of the first and second surfaces of the two prisms. Crushing easily occurs. By disposing a spacer in the vicinity of a portion where the air gap due to thermal expansion of the prism is likely to be crushed, the air gap can be effectively prevented from being crushed. Since the collapse of the air gap due to thermal expansion can be prevented, the thickness of the air gap can be set thin, the astigmatic difference due to the inclined air gap can be effectively suppressed, and a good projection image can be obtained.

The spacers arranged at both ends in the direction in which the projection light effective area and the non-projection light effective area are arranged are spacers arranged at the end part on the non-projection light effective area side of the non-effective area, The dichroic coat layer of the ineffective area includes a spacer disposed at an end of the illumination light effective area side that reflects the illumination light of the specific color light and transmits the illumination light of the other color light. It is preferable.

  By disposing spacers at both ends of the first and second surfaces of the two prisms, it is possible to more reliably prevent the air gap from being crushed due to the thermal expansion of the prisms.

  The region where the dichroic coat layer is formed preferably includes a portion where the spacer is disposed.

  With this configuration, the thickness of the air gap can be set with high accuracy without being affected by the thickness of the dichroic coat layer.

The dichroic coat layer preferably contains Al ₂ O ₃ or a mixture thereof.

By including Al ₂ O ₃ with high thermal conductivity in the dichroic coat layer, the absorbed heat can be quickly transferred to the entire surface of the prism, and local thermal expansion can be suppressed. Can be prevented.

  Of the first and second surfaces, the surface on which the dichroic coat layer is formed is preferably concave with respect to the air gap.

  By making the surface on which the dichroic coat layer is formed concave, an effect of canceling the convex surface due to thermal expansion due to heat absorption of the dichroic coat layer can be obtained, and the collapse of the air gap can be more effectively prevented.

  The present invention also provides an image projection apparatus comprising the aforementioned color prism unit.

  The air gap of the color prism unit due to thermal expansion can be reliably prevented to ensure high reliability, and the thickness of the air gap can be set thin, effectively reducing astigmatic difference and minimizing flare. An image projection apparatus that realizes a good projection image can be obtained.

  In the color prism unit of the present invention, the spacer interposed between the first and second surfaces forming the air gap is disposed at a position between the projection light effective region and the non-projection light effective region in the non-effective region. Therefore, the collapse of the air gap due to the thermal expansion of the prism can be effectively prevented. Moreover, since the crushing resulting from thermal expansion can be prevented, the thickness of the air gap can be reduced, so that the astigmatic difference can be effectively suppressed.

1 is a side view of an image projection apparatus according to a first embodiment of the present invention. The partial top view of FIG. FIG. 2 is a schematic perspective view of an internal total reflection (TIR) prism unit included in the image projection apparatus of FIG. 1. The typical side view of the TIR prism unit with which the image projector of FIG. 1 is provided. The typical partial enlarged view of the part V of FIG. The front view which shows the gap formation surface of a 1st prism. The front view which shows the gap formation surface of a 2nd prism. The schematic diagram for demonstrating the astigmatic difference suppression effect by making the gap formation surface of a 2nd prism concave. The schematic diagram for demonstrating the count of Newton fringe. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical side view which shows the other example of a TIR prism unit. The typical perspective view which shows the other example of a TIR prism unit. The typical perspective view which shows the other example of a TIR prism unit. The typical perspective view which shows the other example of the coupling | bonding of two prisms of a TIR prism unit. The typical perspective view which shows the other example of the coupling | bonding of two prisms of a TIR prism unit. The figure which looked at the color prism unit from the arrow A1 direction of FIG. The figure which looked at the color prism unit from the arrow A2 direction of FIG. The side view of the image projector of 2nd Embodiment of this invention. FIG. 16 is a partial plan view of FIG. 15.

(First embodiment)
1 and 2, an image projection apparatus (projector) 1 according to a first embodiment is an example of an illumination optical system 2, an internal total reflection (TIR) prism unit 3, a color prism unit 4, and a reflective image display element. And digital micromirror devices (DMD) 5B, 5R, and 5G that perform light modulation, and a projection optical system 6. The illumination light from the illumination optical system 2 is totally reflected by the TIR prism unit 3 and enters the color prism unit 4. The illumination light incident on the color prism unit 4 is decomposed into blue, red, and green color light and then incident on the corresponding DMDs 5B to 5G. Illumination light (color light) irradiated to each DMD 5B to 5G is reflected as projection light or non-projection light according to the angle of a micromirror described later included in the DMDs 5B to 5G. The projection lights from the DMDs 5B to 5G are combined by the color prism unit 4 and then transmitted through the TIR prism unit 3 and projected onto a screen (not shown) by the projection optical system 6 including a plurality of lenses and the like. On the other hand, the non-projection light passes through the color prism unit 4 and is emitted in a direction away from the TIR prism 3.

  Referring to FIG. 1, the illumination optical system 2 includes a light source 11, a reflector 12, a rod integrator 13, a condenser lens 14, a relay optical system 15, and an entrance lens 16. The light source 11 is an ultra high pressure mercury lamp and generates white light. The reflector 12 is disposed so as to surround the light source 11 and has a reflection surface that is a spheroidal surface. A rod integrator 13 is disposed behind the light source 11 so that its longitudinal direction is along the optical axis. The light source 11 is disposed at one focal position of the spheroid, and the light emitted from the light source 11 is condensed at the other focal position and is incident from one incident surface of the rod integrator 13. The light incident on the rod integrator 13 repeats internal reflection here, and is emitted from the exit surface at the other end in a uniform light quantity distribution. A condenser lens 14 is disposed immediately after the exit surface of the rod integrator 13, and a relay optical system 15 is disposed further rearward. The light emitted from the rod integrator 13 is efficiently guided to the relay optical system 15 by the condenser lens 14 and enters the TIR prism unit 3 through the entrance lens 16 disposed on the incident side of the TIR prism unit 3, The DMDs 5B to 5G are illuminated almost uniformly through the prism unit 4 in a substantially telecentric manner.

  Referring to FIGS. 1 and 3 to 7, the TIR prism unit 3 includes a first prism 21 and a second prism 22 made of optical glass each having a substantially triangular prism shape and three surfaces (side surfaces).

  The first prism 21 includes an incident / exit surface 21a and a gap forming surface 21b that form an acute angle with each other. The first prism 21 includes an incident surface 21c that connects the incident / exit surface 21a and the gap formation 21b. The entrance / exit surface 21a is arranged in a substantially vertical posture with respect to the optical axis of the projection light directed from the DMDs 5B to 5G through the color prism unit 4 to the projection optical system 6. The gap forming surface 21b is arranged in a posture inclined with respect to the optical axis of the projection light directed toward the projection optical system 6. The second prism 22 includes an exit surface 22a and a gap forming surface 22b that form an acute angle with each other. The second prism 22 includes a surface 22c that connects the exit surface 22a and the gap forming surface 22b.

  The first prism 21 and the second prism 22 are combined so that the gap forming surfaces 21b and 22b face each other with a minute interval. Therefore, an air gap 23 that is inclined with respect to the optical axis of the projection light directed from the DMDs 5B to 5G to the projection optical system 6 through the color prism unit 4 is formed between the gap forming surfaces 21b and 22b. In the present embodiment, the air gap 23 is inclined by 33 ° with respect to the projection optical axis. As described above, since the incident / exit surface 21a of the first prism 21 is substantially perpendicular to the optical axis of the projection light directed toward the projection optical system 6, the air gap 23 is inclined with respect to the normal line of the incident / exit surface 21a. ing.

  The TIR prism unit 3 separates illumination light and projection light.

  First, the illumination light emitted from the illumination optical system 2 and incident from the incident surface 21c is totally reflected by the gap forming surface 21b of the first prism 21 (the gap forming surface 21b functions as a total reflecting surface). At this time, the incident angle of the illumination light with respect to the gap forming surface 21b is 48.5 °. In this embodiment, the F number of the illumination light is 2.7, and has an angular distribution of about 10.7 ° on one side in the air and about 7.0 ° on one side in the prism with respect to the principal ray. On the other hand, since the refractive index of the optical glass constituting the first and second prisms 22 is n = 1.52, the total reflection condition on the gap forming surface 21b is the incident angle with respect to the interface with the air satisfying the air gap 23. It is about 41.1 ° or more. Therefore, the illumination light satisfies the total reflection condition and is totally reflected by the gap forming surface 21b. The illumination light totally reflected by the gap forming surface 21 b is emitted from the incident / exit surface 21 a and enters the color prism unit 4.

  On the other hand, the projection light synthesized by the color prism unit 4 enters the first prism 21 of the TIR prism unit 3 from the incident / exit surface 21a, and enters the air gap 23 at an incident angle of 33 °. At this time, similarly to the illumination light, the F number of the projection light is 2.7 and has an angular distribution of about 10.7 ° on one side in the air and about 7.0 ° on one side in the prism with respect to the principal ray. Here, the total reflection condition is not satisfied. Accordingly, the projection light passes through the air gap 23 and is emitted from the exit surface 22 a of the second prism 22, and is projected onto a screen (not shown) by the projection optical system 6.

  As shown most clearly in FIGS. 4 and 5, the thickness of the air gap 23 is not constant, and the thickness in the central region is larger than that in the peripheral region. Specifically, of the gap forming surfaces 21b and 22b, the gap forming surface 21b of the first prism 21 is a flat surface, but the region through which the projection light of the gap forming surface 22b of the second prism 22 passes is relative to the air gap 23. The concave surface 24 is depressed. In the present embodiment, the concave surface 24 of the gap forming surface 22b includes the optical axis of projection light that enters the TIR prism unit 3 via the color prism unit 4 from the DMDs 5B to 5G, and the method of the air gap 23. A concave spherical shape having substantially the same curvature in both the first virtual plane P1 including the line N1 and the second virtual plane P2 including the normal line N1 of the air gap 23 and perpendicular to the virtual plane P1. The normal line N1 of the air gap 23 is a normal line when the air gap 23 is approximated to a plane.

  The air gap 23 is thicker in the central region than in the peripheral region. Therefore, even if the thickness of the air gap 23 is set to be thin, the prisms by heat absorption such as the optical glass constituting the first and second prisms 21 and 22 and the antireflection coating provided on the surfaces of the gap forming surfaces 21b and 22b. Due to the thermal expansion of 21 and 22, it is possible to prevent the gap forming surfaces 21b and 22b from contacting each other and the air gap 23 from being crushed. Since the collapse of the air gap 23 due to thermal expansion can be prevented, the thickness of the air gap 23 can be set thin. As a result, an astigmatic difference due to the air gap 23 being inclined with respect to the optical axis of the projection light can be effectively suppressed, and a good projection image can be obtained in which the occurrence of flare is considerably suppressed.

  As described above, the concave surface 24 is provided on the gap forming surface 22b of the second prism 22 so that the air gap 23 is thicker in the central region than in the peripheral region, and the concave surface 24 is formed by the first and second virtual planes P1, P2. Both have curvature. FIG. 8 shows the incident angle θi ′ of the projection light from the air gap 23 to the air gap forming surface 22b when the gap forming surface 22b has no curvature in the first virtual plane P1, and the gap forming surface as in this embodiment. A comparison of the incident angle θi to the air gap 23 or the gap forming surface 22b when 22b has a curvature in the first virtual plane P1 is shown. From FIG. 8, the incident angle θi is smaller than the incident angle θi ′. Therefore, the gap forming surface 22b has a curvature in the first virtual plane P1 as in the present embodiment, rather than the astigmatic difference ε ′ in the virtual plane P1 when the gap forming surface 22b has no curvature in the first virtual plane P1. The astigmatic difference ε is small when Thus, having the curvature in the first virtual plane P1 in the gap forming surface 22b has an effect of canceling the astigmatic difference. Therefore, it is preferable that the gap forming surface 22b has a curvature at the first virtual plane P1 larger than a curvature at the second virtual plane P2. For example, as shown in FIG. 11A, the shape of the concave surface 24 of the gap forming surface 22b of the second prism 22 is a cylindrical surface shape having a curvature only in the first virtual plane P1 and no curvature in the second virtual plane P2. It may be. Further, as shown in FIG. 11B, the entire gap forming surface 22b of the second prism 22 may have a cylindrical surface shape having a curvature only in the first virtual plane P1 and no curvature in the second virtual plane P2.

  As shown in FIGS. 3, 6, and 7, in the present embodiment, spacers 25 are arranged at the four corners of the gap forming surfaces 21 b and 22 b forming the air gap 23, and the gaps sandwiching these spacers 25 are interposed. The first prism 21 and the second prism 22 are assembled to each other by bonding the forming surfaces 21b and 22b with an adhesive 26 applied to four locations. The adhesive 26 is preferably an epoxy type in terms of heat resistance. In the present embodiment, the spacer 25 and the adhesive 26 are arranged in a region outside the concave surface 24, that is, the gap forming surfaces 21b and 22b are both planar regions. Specifically, spacers 25 are arranged at two locations near the upper corner in FIG. 3 of the gap forming surfaces 21b and 22b, respectively, and an adhesive 26 is applied to the lower side of these spacers 25. Further, one spacer 25 is disposed in the vicinity of the lower left corner of the gap forming surfaces 21b and 22b in FIG. 3, and an adhesive 26 is applied to the lower side thereof. Further, in FIG. 3 of the gap forming surfaces 21b and 22b, one spacer 25 is disposed near the lower right corner, and an adhesive 26 is applied on the upper side thereof. The prisms 21 and 22 are bonded so that the adhesive 26 does not reach the spacer 25, and the thickness of the adhesive 26 does not affect the thickness of the air gap 23.

  The spacers 25 are preferably arranged with an interval of about 36 mm to 40 mm. As will be described later, with respect to the thickness of the spacer 25 which is 2.5 μm, the arrangement interval between the spacers 25 is only about 36 mm to 40 mm (the spacer 25 is arranged relatively close). 23 has the effect of preventing crushing.

  In this embodiment, the spacer 25 is obtained by cutting a palladium-based aramid film (trade name: Mikutron, Toray Industries Inc.) having a constant thickness of 2.5 μm into, for example, a square with a side of 5 mm. An extremely thin air gap 23 is formed by bonding the gap forming surfaces 21b and 22b with an adhesive 26 in a state where the spacer 25 is sandwiched.

  Other than palladium-based aramid films, polyphenylene sulfide film (trade name Torelina, Toray Industries, Inc.), polyester film (trade name Lumirror, Toray Industries, Inc.), or polyimide film (trade name, Kapton, DuPont) in suitable shapes and dimensions What was cut may be used as the spacer 25. If a palladium-based aramid film, a polyphenylene sulfide film, or a polyimide film is used, an extremely thin film can be manufactured stably with high dimensional accuracy, and a thin air gap 23 can be realized with low cost and high accuracy. In the image projection apparatus 1 that tends to be relatively high in temperature, a heat-resistant palladium-based aramid film, polyphenylene sulfide film, polyimide film, or the like is suitable as the spacer 25.

  Generally, a bead adhesive mixed with fine particles is used as a spacer, but it is difficult to maintain a constant thickness with a bead adhesive, resulting in variations in thickness and parallelism of the air gap. There is a tendency to get worse. By using the film-like spacer 25 having a constant thickness as in the present embodiment, stability of thickness and stability of parallelism can be obtained.

  The arrangement of the spacer 25 and the adhesive 26 is not limited to FIGS. 3, 6, and 7. For example, as shown in FIG. 12A, spacers 25 may be disposed near the four corners of the air gap 23, and the adhesive 26 may be disposed outside the spacers 25. Further, instead of applying the adhesive 26 to the gap forming surfaces 21b and 22b, as shown in FIG. 12B, for example, glass connecting members 27 are arranged on both end faces of the prisms 21 and 22, and these connecting members 27 are arranged. May be joined to the end faces of the prisms 21 and 22 with an adhesive or the like, respectively.

  The relationship between the thickness t of the spacer 25 and the thickness difference δ between the peripheral region and the central region of the air gap 23 will be described with reference to FIG. The spacer 25 preferably has a uniform thickness t in the range of 1 μm to 5 μm, and the difference in thickness δ between the central region and the peripheral region of the air gap 23 is preferably 0.3 μm to 6 μm. By setting the thickness t and the difference δ within this range, the maximum thickness Tmax of the air gap 23 becomes 1.3 μm or more and 11 μm or less, and it becomes sufficiently thin while ensuring the thickness of the air gap 23, thereby preventing the air gap from being crushed. However, the astigmatic difference due to the air gap 23 inclined with respect to the optical axis of the projection light can be effectively suppressed. More preferably, the spacer 25 has a uniform thickness t in the range of 1 μm to 3 μm, and the difference in thickness δ between the central region and the peripheral region of the air gap 23 is 3 μm to 6 μm. By setting the thickness t and the difference δ within this range, the thickness of the air gap 23 is 4 μm or more and 9 μm or less, and the thickness of the air gap 23 is further reduced while further ensuring the thickness of the air gap 23. Astigmatism difference caused by the air gap 23 inclined with respect to the optical axis can be further effectively suppressed.

  As described above, in this embodiment, the concave surface 24 is provided on the gap forming surface 22 b of the second prism 22 of the TIR prism unit 3. Referring to FIG. 9, the gap forming surface 22b is polished into a concave surface 24 in which the number of Newton fringes 28 is, for example, -1 or more and -20 or less when using He-Ne laser (having a wavelength of 633 nm). (The number of Newton fringes 28 is counted as a negative number of concave surfaces and a positive number of convex surfaces). By polishing in this way, the thickness difference δ (see also FIG. 5) of the central region of the air gap 23 with respect to the peripheral region becomes 0.3 μm or more and 6 μm or less. The first and second prisms 21 and 22 are fixed to each other so that the air gap forming surfaces 21b and 22b are brought into contact with each other with the spacer 25 interposed after the polishing. By polishing the concave surface 24 using measurement by the Newton fringe 28, the TIR prism unit 3 having the air gap 23 having a thicker thickness in the central region than in the peripheral region can be obtained easily and reliably. As will be described later, when a concave surface is formed on the gap forming surface 21b of the first prism 21, a desired concave surface can be easily and reliably obtained by polishing using measurement by Newton fringe.

  10A to 10J show various alternatives related to the air gap 23 of the TIR prism unit 3.

  10A and 10F, the concave surface 24 is formed on both the gap forming surface 21b of the first prism 21 and the gap forming surface 22b of the second prism 22. In the example of FIG. 10A, the concave surface 24 is formed only in the region where the light of the gap forming surfaces 21b and 22b passes, whereas in the example of FIG. 10F, the entire gap forming surfaces 21b and 22b are the concave surface 24. By forming the concave surface 24 on both of the gap forming surfaces 21b and 22b as in the examples of FIGS. 10A and 10F, the air gap 23 can be more effectively prevented from being crushed and both the gap forming surfaces 21b and 22b can be prevented. An effect of canceling the convexity due to thermal expansion can be obtained.

  10A and 10F, when the air gap forming surfaces 21b and 22b form an air gap (hereinafter referred to as an air gap region), the air gap forming surfaces 21b and 22b When polishing so that the number is from -1 to -10 (concave surface), the sum of the number of Newton fringes of the air gap forming surface 21b and the air gap forming surface 22b is changed from -2 to -20. The thickness difference between the central region 23 and the peripheral region is not less than 0.6 μm and not more than 6 μm. Further, when the air gap forming surfaces 21b and 22b are polished so that the number of Newton's fringes is -5 to -10 (concave) with respect to the plane, Newton's fringes between the air gap forming surface 21b and the air gap forming surface 22b. The sum of the numbers from -10 to -20, and the thickness difference between the central region of the air gap 23 and the peripheral region is 3 μm or more and 6 μm or less.

  10B and 10G, the concave surface 24 is formed on the gap forming surface 22b of the second prism 22, and the convex surface 29 having a smaller curvature than the concave surface 24 is formed on the gap forming surface 21b of the first prism 21. In the example of FIG. 10B, the concave surface 24 and the convex surface 29 are formed only in the region where the light of the gap forming surfaces 21b and 22b passes, whereas in the example of FIG. 10G, the entire gap forming surfaces 21b and 22b are the concave surface 24 and A convex surface 29 is formed.

  10B and 10G, in the air gap region, the air gap forming surface 21b is polished so that the number of Newton's fringes is 4 to 10 (convex) with respect to the plane, and the air gap forming surface 22b is When polishing so that the number of Newton's fringes is -11 to -16 (concave) with respect to the plane, the sum of the number of Newton's fringes between the air gap forming surface 21b and the air gap forming surface 22b is from -1 to- The thickness difference is 20 and the difference in thickness from the central region to the peripheral region of the air gap 23 is 0.3 μm or more and 6 μm or less.

  10C and 10H, the concave surface 24 is formed on the gap forming surface 21b of the first prism 21, and the entire gap forming surface 22b of the second prism 22 is a flat surface. In the example of FIG. 10C, the concave surface 24 is formed only in the region where the light of the gap forming surface 21 b passes, whereas in the example of FIG. 10H, the entire gap forming surface 21 b is the concave surface 24.

  10C and 10H, in the air gap region, the air gap forming surface 21b is polished so that the number of Newton fringes is -3 to -18 (concave) with respect to the plane, and the air gap forming surface When the number of Newton's fringes is polished within a range of ± 2 (substantially flat) with respect to the plane 22b, the sum of the number of Newton's fringes between the air gap forming surface 21b and the air gap forming surface 22b is changed from -1 to -20. The difference in thickness between the central region of the air gap 23 and the peripheral region is not less than 0.3 μm and not more than 6 μm. Further, in the air gap region, the air gap forming surface 21b is polished so that the number of Newton fringes is −12 to −18 (concave) with respect to the plane, and the air gap forming surface 22b is polished with the Newton fringe with respect to the plane. Is polished between ± 2 and the sum of the number of Newton fringes on the air gap forming surface 21b and the air gap forming surface 22b is changed from -10 to -20. The difference in thickness is 3 μm or more and 6 μm or less.

  10D and 10I, the concave surface 24 is formed on the gap forming surface 21b of the first prism 21, and the convex surface 29 having a smaller curvature than the concave surface 24 is formed on the gap forming surface 22b of the second prism 22. In the example of FIG. 10D, the concave surface 24 and the convex surface 29 are formed only in the region where the light of the gap forming surfaces 21b and 22b passes, whereas in the example of FIG. 10I, the entire gap forming surfaces 21b and 22b are the concave surface 24 and A convex surface 29 is formed.

  In the case of FIG. 10D and FIG. 10I, in the air gap region, the air gap forming surface 21b is polished so that the number of Newton fringes is −11 to −16 (concave) with respect to the plane. When 22b is polished so that the number of Newton's fringes is 4 to 10 (convex) with respect to the plane, the sum of the number of Newton's fringes between the air gap forming surface 21b and the air gap forming surface 22b is from -1 to- The thickness difference is 20 and the difference in thickness from the central region to the peripheral region of the air gap 23 is 0.3 μm or more and 6 μm or less.

  In the example of FIG. 10E, the concave surface 24 is provided only in the region where the light passes through the gap forming surface 21b of the first prism 21 and the gap forming surface 22b of the second prism 22, and the surrounding flat portion is abutted without using a spacer. Thus, the first and second prisms 21 and 22 are bonded together.

  In the first prism 21, the illumination light totally reflected by the air gap 23 enters from the illumination optical system 2, so that the thermal load is larger and thermal expansion is likely to occur. 10A, 10C to 10E, 10F, 10H, and 10I, the concave surface 24 is formed on the gap forming surface 21b that is the total reflection surface of the illumination light included in the first prism 21, thereby forming the air gap 23. Crushing can be effectively prevented. Further, by forming the gap forming surface 21b as the concave surface 24, it is possible to prevent the gap forming surface 21b from being deformed into a convex surface due to thermal expansion. Also in this respect, the air gap 23 can be effectively prevented from being crushed and a good projection image can be obtained. Of the various configurations shown in FIG. 4 and FIGS. 10A to 10I, the air gap forming surface 21b and the air gap forming surface 22b are preferably a combination of a substantially flat surface and a concave surface, or a combination of concave surfaces. . In particular, it is most preferable that the air gap forming surface 21b and the air gap forming surface 22b are both concave.

  Referring to FIGS. 1 and 2, the color prism unit 4 is arranged on the right side of the TIR prism unit 3 in the figure, and is a blue prism 31 having a substantially triangular prism shape, a red prism 32 having a generally triangular prism shape, and The block-shaped green prisms 33 are sequentially arranged in this order on the right side in the drawing and combined with each other.

  The blue prism 31 includes an incident / exit surface 31a and a blue dichroic surface 31b (a blue dichroic coat layer 38 is formed) forming an acute angle. Further, the blue prism 31 includes a blue incident / exit surface 31c on which the blue DMD 5B is disposed facing. The red prism 32 has a red gap forming surface 32a disposed opposite to the blue dichroic surface 31b of the blue prism 31, and a red dichroic surface 32b (a red dichroic coat layer 39 is formed at an acute angle with the red gap forming surface 32a. ). The red prism 32 includes a red incident / exit surface 32c arranged so that the red DMD 5R faces the red prism 32R. The green prism 33 includes a green gap forming surface 33a disposed to face the red dichroic surface 32b, and a green incident / exit surface 33c facing the green gap forming surface 33a so as to form an acute angle. A DMD 5G for green is arranged to face the green incident / exit surface 33c.

  An air gap 34 is provided between the blue prism 31 and the red prism 32, specifically, between the blue dichroic surface 31b and the red gap forming surface 32a. The air gap 34 is inclined by 28.5 ° with respect to the optical axis of the projection light, and the surface formed by the normal line of the optical axis of the projection light and the air gap 34 is the normal line N1 of the air gap 23 of the TIR prism unit 3. Are orthogonal to a plane (first virtual plane P1) formed by the optical axis of the projection light. Further, an air gap 35 is provided between the red prism 32 and the green prism 33, specifically, between the red dichroic surface 32b and the green gap forming surface 33a. The air gap 35 is inclined by 11.5 ° with respect to the optical axis of the projection light, and the plane formed by the normal line of the projection optical axis and the air gap 35 is also orthogonal to the first virtual plane P1. .

  FIG. 13 is a view of the red gap forming surface 32a of the red prism 32 (opposing the blue dichroic surface 31b of the blue prism 31) as viewed from the blue prism 31 side as indicated by an arrow A1 in FIG. FIG. 14 is a view of the red dichroic surface 32b of the red prism 32 as viewed from the green prism 33 side as indicated by an arrow A2 in FIG. The air gaps 34 and 35 provided in the color prism unit 4 transmit illumination light and projection light, and also transmit non-projection light in order to prevent generation of stray light, ghost, etc., and are most clearly shown in FIGS. As described above, the regions of the air gaps 34 and 35 have an elongated shape.

  Hereinafter, the optical paths of illumination light, projection light, and non-projection light in the color prism unit 4 will be described with reference to FIGS.

  The optical path of the illumination light is as follows. First, the illumination light from the TIR prism unit 3 enters the blue prism 31 from the entrance / exit surface 31a. Of the illumination light incident on the blue prism 31, blue light is reflected by the blue dichroic surface 31b, and the other green light and red light are transmitted through the blue dichroic surface 31b (illumination light effective region EI in FIG. 13). The blue light reflected by the blue dichroic surface 31b is totally reflected by the entrance / exit surface 31a, and exits from the blue entrance / exit surface 31c of the blue prism 31 to illuminate the blue DMD 5B. Of the illumination light transmitted through the blue dichroic surface 31b, red light is reflected by the red dichroic surface 32b, and green light is transmitted through the red dichroic surface 32b (illumination light effective region EI 'in FIG. 14). The red light reflected by the red dichroic surface 32b is totally reflected by the air gap 34 adjacent to the blue dichroic surface 31b (illumination light total reflection region RI in FIG. 13), and is emitted from the red incident / exit surface 32c of the red prism 32. Illuminate the red DMD5R. The green light transmitted through the red dichroic surface 32b is emitted from the green incident / exit surface 33c of the green prism 33 to illuminate the green DMD 5G.

  Here, the deflection angles of the DMDs 5B to 5G are ± 12 °, and the projection optical axes shown in FIG. 2 are perpendicular to the DMDs 5B to 5G (illustrated as green DMDs), that is, normal directions, and the illumination optical axes are normal lines. Is set to be 24 °. Specifically, the illumination light of each color illuminates the corresponding DMDs 5B to 5G at an incident angle of 24 °. The micro mirrors (corresponding to each pixel of the projection image) provided in the DMDs 5B to 5G emit the projection light in a direction perpendicular to the DMDs 5B to 5G by reflecting the illumination light in a state inclined by 12 ° toward the illumination optical axis side. To do. Further, the micromirror emits non-projection light at an emission angle of 48 ° by reflecting the illumination light in a state inclined by 12 ° in the direction opposite to the illumination optical axis side. Light modulation is performed by switching the tilt direction of the micromirror.

  The optical path of the projection light emitted from each DMD 5B to 5G is as follows. The blue projection light reflected by the blue DMD 5B enters the blue incident / exit surface 31c, is totally reflected by the incident / exit surface 31a, and then is reflected by the blue dichroic surface 31b (projected light effective area EP in FIG. 13). . The red projection light reflected by the red DMD 5R is incident on the red incident / exit surface 32c, and is totally reflected by the air gap 34 adjacent to the blue dichroic surface 31b (projected light total reflection region RP in FIG. 13). Then, it is reflected by the red dichroic surface 32b (projection light effective region EP ′ in FIG. 14) and further passes through the blue dichroic surface 31b (projection light effective region EP in FIG. 13). The green projection light reflected by the green DMD 5G is incident on the green incident / exit surface 33c, and the red dichroic surface 32b (projection light effective region EP ′ in FIG. 14) and the blue dichroic surface 31b (projection light effective region in FIG. 13). EP) is transmitted. The blue, red, and green projection lights are combined on the same optical axis, emitted from the entrance / exit surface 31a, and enter the TIR prism unit 3.

  The optical path of the non-projection light emitted from each DMD 5B to 5G is as follows. The blue non-projection light reflected by the blue DMD 5B enters the blue incident / exit surface 31c, is totally reflected by the incident / exit surface 31a, and then is reflected by the blue dichroic surface 31b (non-projection light effective region in FIG. 13). ENP). The red non-projection light reflected by the red DMD 5R enters the red incident / exit surface 32c and is totally reflected by the air gap 34 (non-projection light total reflection region RNP in FIG. 13), and then the red dichroic surface 32b. Is reflected (non-projection light effective area ENP ′ in FIG. 14) and further passes through the blue dichroic surface 31b (non-projection light effective area ENP in FIG. 13). The green non-projection light reflected by the green DMD 5G is incident on the green incident / exit surface 33c, and the red dichroic surface 32b (non-projection light effective area ENP ′ in FIG. 14) and the blue dichroic surface 31b (non-projection in FIG. 13). The light effective area ENP) is transmitted. The blue, red, and green projection lights are emitted from the incident / exit surface 31a in directions that do not enter the TIR prism unit 3.

  The air gap 34 is formed by bonding a blue dichroic surface 31 b (blue prism 31) sandwiching the spacer 36 and a red gap forming surface 32 a (red prism 32) with an adhesive 37. Similarly, the air gap 35 is formed by joining a red dichroic surface 32 b (red prism 32) sandwiching the spacer 36 and a green gap forming surface 33 a (green prism 33) with an adhesive 37. In the present embodiment, the spacer 36 uses a polyimide film having a uniform thickness of 7.5 μm cut into a square with a side of 5 mm.

  Referring to FIG. 13, in the air gap 34, the non-effective area NE indicated by a broken line (all of the illumination light, the projection light, and the non-projection light pass through both the blue dichroic surface 31b and the red gap formation surface 32a). Projection light effective area EP (area where blue projection light is reflected by blue dichroic surface 31b as described above, and red and green projection light is transmitted), and non-projection light A pair of spacers 36 is disposed between the effective region ENP (the region in which the blue non-projection light is reflected by the blue dichroic surface 31b and the red and green non-projection light is transmitted as described above). Of the non-effective area NE, the portion between the projection light effective area EP and the non-projection light effective area ENP is from both ends in the longitudinal direction of the blue dichroic surface 31b (blue prism 31) and the red gap forming surface 32a (red prism 32). Since it is in a distant position, the air gap 34 is easily crushed due to thermal expansion of the blue prism 31 and the red prism 32. Therefore, disposing the spacer 36 at this location can prevent the air gap 34 from being crushed due to thermal expansion. Since crushing can be prevented and the thickness of the air gap 34 can be set thin, the astigmatic difference due to the air gap 34 being inclined to the optical axis of the projection light is effectively suppressed, and a good projection image is obtained. It is done. Although a pair of spacers 36 are provided at both ends of the air gap 34 in the short direction, there is an effect of preventing the air gap 34 from being crushed at any one position. However, it is preferable to provide them at two positions on both ends in the short direction because the effect of preventing the air gap 34 from being crushed is higher.

  Further, in the air gap 34, the end of the non-effective area NE on the non-projection light effective area ENP side and the illumination light effective area EI (while blue illumination light is reflected by the blue dichroic surface 31b as described above, A pair of spacers 36 is also arranged at each end on the side where the red and green illumination light passes. Thus, the thermal expansion of the blue prism 31 and the red prism 32 is achieved by arranging the spacers 36 at both ends in the longitudinal direction of the blue dichroic surface 31b (blue prism 31) and the red gap forming surface 32a (red prism 32). The air gap 34 can be prevented from being crushed more reliably. A pair of spacers 36 is provided at each end of the air gap 34 in the longitudinal direction. However, the air gap 34 may be crushed even in a configuration in which the spacer 36 is disposed only at one of the ends in the longitudinal direction. There is an effect to prevent. However, it is preferable to provide a pair of spacers at both ends in the longitudinal direction because the effect of preventing the air gap 34 from being crushed is higher.

  Referring to FIG. 14, in the air gap 35, any of the non-effective area NE ′ (shown with a broken line), which is any of illumination light, projection light, and non-projection light, in any of the red dichroic surface 32 b and the green gap formation surface 33 a Of the projection light effective area EP ′ (the area in which the red projection light is reflected by the red dichroic surface 32b and the green projection light is transmitted) as described above, and the non-projection A pair of spacers 36 is arranged between the light effective area ENP ′ (the area where the red non-projection light is reflected by the red dichroic surface 32b and the green non-projection light is transmitted as described above). Of the non-effective area NE ′, the portion between the projection light effective area EP ′ and the non-projection light effective area ENP ′ is in the longitudinal direction of the red dichroic surface 32b (red prism 32) and the green gap forming surface 33a (green prism 33). Since it is located away from both ends, the air gap 35 is easily crushed by the thermal expansion of the red prism 32 and the green prism 33. Therefore, disposing the spacer 36 at this location can prevent the air gap 35 from being crushed due to thermal expansion. Since the collapse of the air gap 35 can be prevented, the thickness of the air gap 35 can be set thin. Astigmatism difference caused by the inclination of the air gap 35 to the optical axis of the projection light can be effectively suppressed, and a good projection image can be obtained. .

  Further, in the air gap 35, red illumination light is reflected by the end of the non-projection effective region ENP ′ side of the non-effective region NE ′ and the illumination effective region EI ′ (the red dichroic surface 32b as described above. On the other hand, a pair of spacers 36 are also arranged at the end of the green area where the illumination light is transmitted. Thus, the thermal expansion of the red prism 32 and the green prism 33 is achieved by arranging the spacers 36 at both ends in the longitudinal direction of the red dichroic surface 32b (red prism 32) and the green gap forming surface 33a (green prism 33). The air gap 34 can be prevented from being crushed more reliably.

  As shown in FIG. 13, in the air gap 34, the region where the blue dichroic coat layer 38 is formed on the blue dichroic surface 31 b includes a region where the spacer 36 is disposed. Similarly, as shown in FIG. 14, in the air gap 35, the region where the red dichroic coat layer 39 is formed on the red dichroic surface 32 b includes a region where the spacer 36 is disposed. As described above, since the region where the dichroic coat layers 38 and 39 are formed includes the portion where the spacer 36 is disposed, the thickness of the air gaps 34 and 35 can be reduced without being affected by the thickness of the dichroic coat layers 38 and 39. Can be set.

The dichroic coat layers 38 and 39 include Al ₂ O ₃ or a mixture thereof. By containing Al ₂ O ₃ having high thermal conductivity in the dichroic coat layers 38 and 39, the absorbed heat can be quickly transmitted to the entire surface of the color prism unit 4 to suppress local thermal expansion. The crushing of the gaps 34 and 35 can be prevented more effectively.

  Referring to FIG. 2, the light passing regions of the blue and red dichroic surfaces 31b and 32b are concave with respect to the air gaps 34 and 35, respectively. The blue and red dichroic surfaces 31b and 32b on which the dichroic coat layers 38 and 39 are formed have remarkable heat absorption. By making the blue and red dichroic surfaces 31b and 32b concave, the effect of canceling the convexity caused by the thermal expansion of the dichroic coat layers 38 and 39 can be obtained, and the collapse of the air gaps 34 and 35 can be prevented more effectively. it can. For example, the blue and red dichroic surfaces 31b and 32b are polished into concave surfaces having a number of Newton fringes of, for example, -6 or more and -10 or less when a He-Ne laser (wavelength is 633 nm) is used.

(Second Embodiment)
FIG.15 and FIG.16 shows the image projector 1 of 2nd Embodiment.

  Referring to FIG. 15, in this embodiment, the spacer 25 ′ of the TIR prism unit 3 is different from that in the first embodiment.

The spacer 25 ′ in this embodiment forms a SiO ₂ film having a film thickness of 5 μm on the gap forming surface 22 b of the second prism 22, which is the smaller prism of the two prisms 21 and 22 constituting the TIR prism unit 3. Is formed. Specifically, a mask covering a portion other than the portion where the spacer 25 ′ of the second gap forming surface 22b of the prism 21 is disposed is attached, and an SiO ₂ film is formed by vapor deposition or sputtering. Thereafter, the prisms 21 and 22 are bonded to each other with an adhesive, for example. The formation location of the spacer 25 ′ is the same as that of the spacer 25 of the first embodiment (see, for example, FIGS. 3, 6, and 7). The interval between the spacers 25 ′ is preferably about 27 to 50 mm with respect to the film thickness of 5 μm. As in the first embodiment, the adhesive is applied at a position not on the spacer 25 ′, and the thickness of the adhesive does not affect the thickness of the air gap 23.

  By forming the spacer 25 ′ by film formation as in this embodiment, the thickness accuracy and parallelism accuracy of the air gap 23 are further improved. Further, since the spacer 25 ′ is integrated with the second prism 22, the workability at the time of bonding the prisms 21 and 22 is very good.

In addition to SiO ₂ , a deposition type spacer 25 ′ may be formed using a vapor deposition material such as Al ₂ O ₃ , Nb ₂ O ₅ , TiO ₂ , or a metal material such as Al.

  In the present embodiment, the gap forming surface 22b of the second prism 22 is polished within a range allowing ± 2 Newtons fringes relative to the plane to allow a shape shift to the concave surface or convex surface. On the other hand, the gap forming surface 21b of the first prism 21 has an air gap between −12 and −18 in terms of the number of Newton fringes when He—Ne laser (wavelength is 633 nm) light is used for the plane. When the air gap 23 is formed by being bonded to form a concave shape with respect to 23, the thickness of the air gap 23 is 3 μm or more and 6 μm or less in the central region from the peripheral region. Thus, by setting the thickness of the central region of the air gap 23 to be sufficiently larger than the thickness of the peripheral region, the collapse of the air gap 23 due to thermal expansion can be more effectively prevented.

  Of the TIR prism unit 3, the first prism 21 through which the illumination light passes is more susceptible to heat. However, by forming the gap forming surface 21b of the first prism 21 into a concave shape, deformation of the air gap forming surface 21b into a convex surface due to thermal expansion can be prevented. Also in this respect, the air gap 23 can be effectively prevented from being crushed and a good projection image can be obtained.

  This embodiment is different from the first embodiment in the configuration of the color prism unit 4. Specifically, the color prism unit 4 in the present embodiment is arranged on the right side in the figure of the TIR prism unit 3 and includes a clear prism 41 having a substantially triangular prism shape, and a red prism 32 ′ having a substantially triangular prism shape as well. A blue prism 31 ′ and a block-shaped green prism 33 ′ are sequentially arranged in this order on the right side and combined with each other.

  The clear prism 41 includes an incident / exit surface 41a and a gap forming surface 41b that form an acute angle with each other. The red prism 32 ′ is a red gap forming surface 32 a ′ disposed opposite to the gap forming surface 41 b of the clear prism 41, and a red dichroic surface 32 b ′ (red dichroic coating layer 39) that forms an acute angle with the red gap forming surface 32 a ′. ') Is provided. Further, the red prism 32 'includes a red incident / exit surface 32c' on which the red DMD 5R is disposed so as to face the red prism 32 '. The blue prism 31 ′ has a blue gap formation 31a ′ disposed opposite to the red dichroic surface 32b ′ of the red prism 32 ′, and a blue dichroic surface 31b ′ (blue dichroic coat layer 38 ′) that forms an acute angle with the gap formation 31a ′. Are provided). The blue prism 31 'includes a blue incident / exit surface 31c' disposed so that the blue DMD 5B is opposed to the blue prism 31 '. The green prism 33 'includes a green gap forming surface 33a' disposed to face the blue dichroic surface 31b 'of the blue prism 31', and a green incident / exit surface 33c 'disposed to face the green DMD 5G.

  An air gap 42 is provided between the gap forming surface 41 b of the clear prism 41 and the red gap forming surface 32 a ′ of the red prism 32 ′. The air gap 42 is inclined by 18 ° with respect to the optical axis of the projection light. Further, the surface composed of the optical axis of the projection light and the normal line of the air gap 42 is the surface composed of the normal line N1 of the air gap 23 of the TIR prism unit 3 and the optical axis of the projection (first virtual plane P1 shown in FIG. 3). Is orthogonal.

  An air gap 43 is provided between the red dichroic surface 32b 'of the red prism 32' and the blue gap forming surface 31a 'of the blue prism 31'. The air gap 43 is inclined by 18 ° with respect to the optical axis of the projection light. Further, the surface made up of the optical axis of the projection light and the normal line of the air gap 43 is orthogonal to the surface made of the normal line N1 of the air gap 23 of the TIR prism unit 3 and the optical axis of the projection light (first virtual plane P1). ing. The inclination direction of 18 degrees is opposite to the inclination direction of the air gap 42 by the clear prism 41 and the red prism 32 '.

  An air gap 44 is provided between the blue dichroic surface 31b 'of the blue prism 31' and the green gap forming surface 33a 'of the green prism 33'. The air gap 44 is also inclined by 18 ° with respect to the optical axis of the projection light. Similarly, the surface composed of the optical axis of the projection light and the normal line of the air gap 44 is similar to the surface composed of the normal line N1 of the air gap 23 of the TIR prism unit 3 and the optical axis of the projection light (first virtual plane P1). Orthogonal. The inclination direction of 18 degrees is the same as the inclination direction of the air gap 42 by the clear prism 41 and the red prism 32 '.

As in the first embodiment, the air gaps 42 to 44 included in the color prism unit 4 in the present embodiment also transmit illumination light and projection light, and also transmit non-projection light to prevent stray light and ghosts from occurring. The shape is elongated (see FIGS. 13 and 14). In the air gaps 42 to 44, as in the TIR prism unit 3, a spacer 36 ′ made of a SiO ₂ film having a thickness of 10 μm is formed. In addition to the four locations (four corners) at both ends of the non-effective area of the air gaps 42 to 44 (see symbols NE and NE 'in FIGS. 13 and 14), the spacer 36 ′ has a projection effective area (see FIGS. 13 and 14). They are arranged at two locations (see the symbols EP and EP ′) and the non-projection light effective area (see the symbols ENP and ENP ′ in FIGS. 13 and 14). By disposing the spacer 36 ′ at these locations, the elongated air gaps 42, 43, 44 are reliably prevented from being crushed during thermal expansion.

  The optical path of the illumination light in the color prism unit 4 is as follows. The illumination light from the TIR prism unit 3 enters the clear prism 41 from the incident / exit surface 41a, and further enters the red prism 32 'through the air gap. Red light of the illumination light is reflected by the red dichroic surface 32b ', and the other green light and blue light are transmitted through the red dichroic surface 32b'. The red light reflected by the red dichroic surface 32b 'is totally reflected by the air gap 42 and is emitted from the red incident / exit surface 32c' to illuminate the DMD 5R. On the other hand, of the green light and the blue light transmitted through the red dichroic surface 32b ', the blue light is reflected by the blue dichroic surface 31b', and the green light is transmitted through the blue dichroic surface 31b '. The blue light reflected by the blue dichroic surface 31b 'is totally reflected by the air gap 43 and emitted from the blue incident / exit surface 31c' to illuminate the DMD 5B. The green light transmitted through the blue dichroic surface 31b 'is emitted from the green incident / exit surface 33c' of the green prism 33 'to illuminate the DMD 5G.

  The optical path of the projection light in the color prism unit 4 is as follows. The red projection light reflected by the red DMD 5R enters the red incident / exit surface 32c ', is totally reflected by the air gap 42, and then reflected by the red dichroic surface 32b'. The blue projection light reflected by the blue DMD 5B enters the blue incident / exit surface 31c ′, is totally reflected by the air gap 43, is reflected by the blue dichroic surface 31b ′, and is further reflected by the red dichroic surface 32b. 'Transparent. Further, the green projection light reflected by the green DMD 5G is incident on the green incident / exit surface 33c 'and is transmitted through the blue dichroic surface 31b' and the red dichroic surface 32b '. The red, blue, and green projection lights are combined on the same optical axis, exit from the entrance / exit surface 41 a of the clear prism 41, and enter the TIR prism unit 3. The optical path of the non-projection light in the color prism unit 4 is such that the position where it passes and reflects is upward in the figure, and is emitted from the incident / exit surface 41a of the clear prism 41 in the direction away from the TIR prism PR. Except for the projection light.

  Other configurations and operations of the second embodiment are the same as those of the first embodiment. The configurations of FIGS. 10A to 10I, FIGS. 11A and 11B, and FIGS. 12A and 12B can also be employed in the second embodiment.

DESCRIPTION OF SYMBOLS 1 Image projector 2 Illumination optical system 3 Internal total reflection (TIR) prism unit 4 Color prism unit 5B, 5R, 5G Digital micromirror device (DMD)
6 Projection optical system 11 Light source 12 Reflector 13 Rod integrator 14 Condensing lens 15 Relay optical system 16 Entrance lens 21 First prism 21a Incident exit surface 21b Gap forming surface 21c Incident surface 22 Second prism 22a Ejecting surface 22b Gap forming surface 22c Surface 23 Air gap 24 Concave surface 25, 25 'Spacer 26 Adhesive 27 Connecting member 28 Newton fringe 29 Convex surface 31, 31' Blue prism 31a Incident exit surface 31b Blue dichroic surface 31c Blue incident exit surface 31a 'Blue gap forming surface 31b' Blue dichroic surface 31c ' Blue incident exit surface 32, 32 'Red prism 32a Red gap forming surface 32b Red dichroic surface 32c Red incident exit surface 32'a Red gap forming surface 32b' Red dichroic surface 32c 'Red incident exit surface 33, 3 'Green prism 33a Green gap forming surface 33c Green incident exit surface 33a' Green gap forming surface 33c 'Green incident exit surface 34,35 Air gap 36,36' Spacer 37 Adhesive 38,38 'Blue dichroic coat layer 39,39' Red dichroic Coat layer 41 Clear prism 41a Incident exit surface 41b Gap forming surface 42, 43, 44 Air gap N1 Normal line P1 First virtual plane P2 Second virtual plane t Spacer 25 thickness δ The thickness of the peripheral region and the central region of the air gap 23 Difference Tmax Maximum thickness of air gap θi, θi ′ Incident angle ε, ε ′ Astigmatic difference NE, NE ′ Non-effective area EI, EI ′ Illuminating light effective area EP, EP ′ Projected light effective area ENP, ENP ′ Non-projected light Effective area RI Total illumination area for illumination light RP Total reflection area for projection light RNP Non-projection light total reflection area

Claims (6)

Composed of a plurality of prisms, the illumination light is decomposed into a plurality of color lights and incident on a plurality of reflective image display elements, and the projection lights from the plurality of reflective image display elements are combined and emitted to a projection optical system. And a color prism unit for emitting non-projection light from the plurality of reflective image display elements in a direction different from the projection light,
A first surface of one of the plurality of prisms and a second surface of the other one of the plurality of prisms face each other with a spacer interposed therebetween, so that the first surface and the first surface An air gap inclined with respect to the optical axis of the projection light is formed between the two surfaces,
A dichroic coat layer that reflects specific color light and transmits other specific color light is formed on one of the first and second surfaces,
The spacer includes the dichroic coat layer in the non-effective area in which neither the illumination light, the projection light, nor the non-projection light passes or reflects on any of the first and second surfaces. A projection light effective area that reflects the projection light of the specific color light and transmits the projection light of the other specific color light; and the dichroic coat layer reflects the non-projection light of the specific color light and the other light disposed at a location between the non-projection light effective area for transmitting the non-projection light of a specific color light Rutotomoni, the direction and the projection optical effective region and the non-projection light effective area are arranged within the non-active area Color prism unit arranged at both ends . The spacers arranged at both ends in the direction in which the projection light effective area and the non-projection light effective area are arranged are spacers arranged at the end part on the non-projection light effective area side of the non-effective area, The dichroic coat layer of the ineffective area includes a spacer disposed at an end of the illumination light effective area side that reflects the illumination light of the specific color light and transmits the illumination light of the other color light. , color prism unit according to claim 1.   The color prism unit according to claim 1, wherein the region where the dichroic coat layer is formed includes a portion where the spacer is disposed. 4. The color prism unit according to claim 1, wherein the dichroic coat layer includes Al ₂ O ₃ or a mixture thereof. 5.   5. The color prism unit according to claim 1, wherein a surface of the first and second surfaces on which the dichroic coat layer is formed is a concave surface with respect to the air gap. 6. .   An image projection apparatus provided with the color prism unit of any one of Claims 1-5.

Images