Optical system and image projection apparatus

Abstract

To improve the light utilization efficiency of an optical system.SOLUTION: The optical system 20 projects light from the display element 18. The optical system includes a first transmissive-reflective surface 2002, a first wave plate 2003, and a second transmissive-reflective surface 2004, disposed in that order from the display element side to the projection side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical system used in an image projection device. [Background technology]

[0002] Projectors, AR (Argumented Reality) glasses, etc. are known as image projection devices that image-modulate light from a light source using a display element and project the modulated light onto a screen or guide it to the observer's eyes via an optical system. Patent Document 1 discloses a small optical system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-21309 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical system described above, it is desirable to improve the light utilization efficiency. [Means for solving the problem]

[0005] An optical system according to one aspect of the present invention projects light from a display element. The optical system is characterized by having, in order from the display element side to the projection side, a first transmissive-reflective surface, a first wave plate, and a second transmissive-reflective surface. Note that an image projection device using the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0006] According to the present invention, an optical system with improved light utilization efficiency can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing the configuration of an image projection device. [Figure 2] FIG. 2 is a diagram showing a projection optical system having a first optical configuration. [Figure 3] FIG. 10 is a diagram showing a projection optical system having a second optical configuration. [Figure 4] FIG. 1 is a cross-sectional view of a projection optical system according to a first embodiment. [Figure 5] 4A to 4C are aberration diagrams of the projection optical system of Example 1. [Figure 6] FIG. 10 is a cross-sectional view of a projection optical system according to a second embodiment. [Figure 7] 10A to 10C are aberration diagrams of the projection optical system of Example 2. [Figure 8] FIG. 10 is a diagram showing the configuration of a PBS array according to a second embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a projection optical system according to a third embodiment. [Figure 10] 10A to 10C are aberration diagrams of the projection optical system of Example 3. [Figure 11] FIG. 10 is a cross-sectional view of a projection optical system according to a fourth embodiment. [Figure 12] 10A to 10C are aberration diagrams of the projection optical system of Example 4. [Figure 13] FIG. 10 is a cross-sectional view of a projection optical system according to a fifth embodiment. [Figure 14] 10A to 10C are aberration diagrams of the projection optical system of Example 5. [Figure 15] FIG. 13 is a cross-sectional view of a projection optical system according to a sixth embodiment. [Figure 16] 13A to 13C are aberration diagrams of the projection optical system of Example 6. [Figure 17] 10A and 10B are diagrams showing application examples of an image projection device using the projection optical system of the embodiment. [Figure 18] 10A and 10B are diagrams showing another application example of an image projection device using the projection optical system of the embodiment. [Figure 19] FIG. 10 is a diagram showing yet another application example of the image projection device using the projection optical system of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] 1 shows the configuration of an image projection device 10 having a projection optical system according to Example 1. The image projection device 10 comprises a light source 11, a collimator lens 12, a first fly-eye lens 13, a second fly-eye lens 14, a PS conversion element 15, a condenser lens 16, a display element 17, a polarizing plate 18 as a polarizing means, and a projection optical system 20. The polarizing plate 18 may be included in the projection optical system 20. The components from the light source 11 to the condenser lens 16 constitute an illumination optical system.

[0010] In this embodiment, the light source 11 is configured with a white LED. However, the light source 11 may be configured to combine three colors of light from a red LED, a green LED, and a blue LED using a combining element such as a dichroic mirror to generate white light. Alternatively, the light source 11 may be a laser light source, a mercury lamp, or the like.

[0011] A light beam emitted from light source 11 is collimated by collimator lens 12 and split into multiple light beams by first fly-eye lens 13. The multiple split light beams are condensed near second fly-eye lens 14, converted by PS conversion element 15 into polarized light (linearly polarized light) with the x direction as the polarization direction in the figure, and superimposed on the display surface of display element 17 via condenser lens 16 to illuminate the display surface. Display element 17 generates image light by image-modulating the incident light beam. The image light is polarized light with the y direction as the polarization direction in the figure. The image light passes through polarizing plate 18 and is projected onto the projection surface via projection optical system 20. If image projection device 10 is a projector, the irradiated surface is a screen, a wall surface, or the like. If it is AR glasses, the irradiated surface is the entrance part of a light guide plate or the like that guides the image light to the viewer's eyes.

[0012] In this embodiment, the display element 17 is a transmissive liquid crystal panel. However, a reflective liquid crystal panel, a digital micromirror device in which pixels are composed of micromirrors, or a MEMS (Micro Electro Mechanical Systems) may also be used. Furthermore, if the light source 11 and the illumination optical system emit red, green, and blue light, a display element may be provided for each color light.

[0013] FIG. 2 shows a projection optical system 20 having a first optical configuration. The projection optical system 20 of the first optical configuration has, arranged in this order from the display element side (left side of the figure) to the projection side, a first lens group 21, a first transmission-reflection system 2000, and a second lens group 22. The first transmission-reflection system 2000 has, arranged in this order from the display element side, a first lens 2001, a polarizing beam splitter (PBS) 2002 as a reflective polarizer constituting the first transmission-reflection surface, and a first λ / 4 phase plate 2003 as a first wave plate. It also has a half mirror 2004 constituting the second transmission-reflection surface, a second λ / 4 phase plate 2005 as a second wave plate, and a polarizing plate 2006. In FIG. 2, the optical axis of the projection optical system 20 is indicated by a dashed line.

[0014] Image light (y-direction polarized light) L21 from the display element 17 passes through the first lens group 21 and enters the PBS 2002. The PBS 2002 has the property of transmitting y-direction polarized light and reflecting x-direction polarized light. The image light L21 that passed through the PBS 2002 is converted into circularly polarized light by the first λ / 4 phase plate 2003 and enters the half mirror 2004. The half mirror 2004 has the property of having a transmittance and reflectance of approximately 50% at the dominant wavelength of the image light (e.g., 470 nm, 550 nm, and 620 nm). The image light that passed through the half mirror 2004 is converted into x-direction polarized light by the second phase plate 2005 and enters the polarizing plate 2006. The polarizing plate 2006 has the property of transmitting y-direction polarized light and absorbing x-direction polarized light. Therefore, the image light transmitted through the half mirror 2004 is absorbed by the polarizing plate 2006 as unnecessary light.

[0015] On the other hand, the image light L22 reflected by the half mirror 2004 is converted into x-direction polarized light by the first λ / 4 phase plate 2003, enters the PBS 2002, and is reflected by the PBS 2002. The image light (x-direction polarized light) L23 reflected by the PBS 2002 is converted into circularly polarized light by the first λ / 4 phase plate 2003, a part of which passes through the half mirror 2004, is converted into y-direction polarized light by the second λ / 4 phase plate 2005, and passes through the polarizing plate 2006. The image light L23 then passes through the second lens group 22 and is projected onto the projection surface.

[0016] FIG. 3 shows a projection optical system 20 having a second optical configuration. The projection optical system 20 of the second optical configuration includes, in order from the display element side, a first lens group 31, a second transmission-reflection system 3000, and a second lens group 32. The second transmission-reflection system 3000 includes, in order from the display element side, a first lens 3001a, a second lens 3001b, and a first polarizing beam splitter (PBS) 3002a serving as a reflective polarizer constituting the first transmission-reflection surface. The second transmission-reflection system 3000 further includes a second PBS 3002b serving as a reflective polarizer constituting the third transmission-reflection surface, a first λ / 4 phase plate 3003a serving as a first wave plate, a second λ / 4 phase plate 3003b serving as a second wave plate, and a half mirror 3004 constituting the second transmission-reflection surface. The optical axis of the projection optical system 20 is also indicated by a dashed line in FIG. 3 .

[0017] Image light (y-direction polarized light) L31 from the display element 17 passes through the first lens group 21 and enters the first PBS 3002a. The first PBS 3002a has the property of transmitting y-direction polarized light and reflecting x-direction polarized light. The image light L31 that passed through the first PBS 3002a is converted into circularly polarized light by the first λ / 4 phase plate 3003a and enters the half mirror 3004. The half mirror 3004 has the property of having a transmittance and reflectance of approximately 50% at the dominant wavelength. Therefore, the image light L31 is separated by the half mirror 3004 into reflected light L32a and transmitted light L32b.

[0018] The image light as reflected light L32a is converted into x-direction polarized light by the first λ / 4 phase plate 3003a, enters the first PBS 3002a, and is reflected by the first PBS 3002a. The image light (x-direction polarized light) L33a reflected by the first PBS 3002a is converted into circularly polarized light by the first λ / 4 phase plate 3003a and enters the half mirror 3004. The image light L34a transmitted through the half mirror 3004 is converted into y-direction polarized light by the second λ / 4 phase plate 3003b and enters the second PBS 3002b. The second PBS 3002b has the property of transmitting y-direction polarized light and reflecting x-direction polarized light. The image light L34a transmitted through the second PBS 3002b passes through the second lens group 32 and is projected onto the projection surface. The image light L33a reflected by the half mirror 3004 becomes unwanted light.

[0019] On the other hand, the image light as transmitted light L32b from the half mirror 3004 is polarization-converted by the second λ / 4 phase plate 3003b into x-direction polarized light and enters the second PBS 3002b. The image light L33b reflected by the second PBS 3002b is converted into circularly polarized light by the second λ / 4 phase plate 3003b and enters the half mirror 3004. The image light L34b reflected by the half mirror 3004 is converted into y-direction polarized light by the second λ / 4 phase plate 3003b and passes through the second PBS 3002b, passes through the second lens group 32, and is projected onto the projection surface. The image light L33b that passed through the half mirror 3004 becomes unwanted light.

[0020] The second transmission-reflection system 3000 has a first optical path that generates image light L34a using a first PBS 3001a, a first λ / 4 phase plate 3003a, and a half mirror 3004, and a second optical path that generates image light L34b using a second PBS 3001b, a second λ / 4 phase plate 3003b, and a half mirror 3004. The image light L34a and L34b are emitted from the same pixel of the display element 17 and form the same pixel of the projected image (display image). Therefore, the amount of light at the pixel formed by the image light L34a and L34b is approximately twice that of the image light L24 from the first transmission-reflection system 200. The light amount drop that occurs in the projection optical system 20 is two stages (25%) in the first transmission-reflection system 200 and one stage (50%) in the second transmission-reflection system 200.

[0021] Furthermore, by arranging the first PBS 3002a and the second PBS 3002b on the curved surfaces of the lenses, it is possible to appropriately set the refractive power and Petzval sum while suppressing the occurrence of chromatic aberration, thereby realizing a large-diameter projection optical system with a small number of lenses.

[0022] Each λ / 4 phase plate can be, for example, a polymer film having birefringence or a liquid crystal alignment layer. Alternatively, a laminate of polymer films or liquid crystal alignment layers can be used as the λ / 4 phase plate. By appropriately laminating these, a phase difference close to a quarter of the wavelength can be obtained over a wide wavelength range. Furthermore, an inorganic wave plate manufactured by Dexerials Corporation can also be used as the λ / 4 phase plate.

[0023] Furthermore, the λ / 4 phase plate may be disposed separately from the half mirror or PBS, or may be bonded to the half mirror or PBS. When the λ / 4 phase plate is disposed separately from the half mirror or PBS, the λ / 4 phase plate may be inserted directly into the optical path, or a λ / 4 phase plate bonded to a glass plate may be inserted into the optical path. Lenses may be formed on one or both sides of the λ / 4 phase plate. For example, lenses may be formed on one or both sides of the inorganic wave plate using wafer-level optics technology as a substrate. Alternatively, the λ / 4 phase plate and the lens may be bonded together.

[0024] Examples of PBSs that can be used include the "WGF" (registered trademark) PBS manufactured by Asahi Kasei Corporation and the "IQPE" PBS manufactured by 3M Company. Alternatively, the PBS may be an optical element created by forming a grid on the lens reflective surface during lens molding and then depositing, printing, or lithographically depositing a metal or dielectric material on the grid. Furthermore, a half mirror, a cholesteric liquid crystal, a holographic optical element, or the like may also be used.

[0025] The projection optical system 20 equipped with the above-described transmission-reflection systems 2000 and 3000 can significantly reduce the F-number (i.e., make the system brighter) compared to a typical projection optical system. In other words, it is possible to significantly improve the light utilization efficiency. Theoretically, the light utilization efficiency is determined by the etendue between the illumination optical system and the projection optical system. Etendue is defined by the following equations (1) and (2).

[0026] Ea=A×π×NA 2 (1) Eb=B×π / (2×Fnо) 2 (2) In the above formula, A is the light-emitting area of ​​the light source, NA is the numerical aperture of the illumination optical system, B is the effective display area of ​​the display element (the area of ​​the display surface that emits the effective light beam that contributes to image projection), and Fn0 is the F-number of the projection optical system. To theoretically achieve 100% light utilization efficiency, the Etendue of the projection optical system must be greater than the Etendue of the illumination optical system.

[0027] The Fno required for the projection optical system is Fnо<(B / 4×A) 0.5 / NA (3) When a liquid crystal panel is used as the display element 17, it is necessary to take into account the polarization conversion amount, so Fnо<(B / 8×A) 0.5 / NA (4) This becomes:

[0028] Since polarization separation is equivalent to doubling the light beam, it is necessary to double the Etendue of the illumination optical system. As an example, calculate the Fn0 required for the projection optical system under the following conditions.

[0029] LED light-emitting area A: 2.0mm x 2.0mm LCD panel effective display area B: 5.76mm x 3.24mm Since general LEDs do not have directionality, if the NA is 1, the Fn0 required for the projection optical system is: Fnо<0.76 (5) A typical projection optical system has an Fn0 of around 2, and the light utilization efficiency is quite low, so a large-diameter lens is required. However, since a typical large-diameter lens is quite large, the projection optical system of this embodiment is effective.

[0030] A preferred configuration of the projection optical system of this embodiment will be described below.

[0031] When the ray passing through the center of the aperture stop of the projection optical system is defined as the chief ray, and the absolute value of the angle of the most off-axis chief ray with respect to the optical axis of the projection optical system (i.e., the normal to the display surface of the display element) is defined as θ (°), θ≦10.0° (6) It is preferable that the following condition be satisfied. Since the phase difference generated in the liquid crystal of the display element is highly dependent on the angle of incidence, if θ exceeds the upper limit of formula (6), the contrast of the displayed image decreases, making it impossible to obtain good image quality. It is more preferable that the upper limit of formula (6) be set to 9.0°, 8.0, 7.0, 6.0, 5.0°, or 4.0.

[0032] If the absolute value of distortion occurring in the projection optical system is DST, then DST≦30% (7) It is preferable to satisfy the following condition. If DST exceeds the upper limit of equation (7), the amount of distortion correction that must be performed by the display element to project a rectangular image onto a flat projection surface increases, significantly reducing peripheral resolution and making it impossible to obtain good image quality. It is more preferable to set the upper limit of equation (7) to 28%, 26%, 25%, 24%, 22%, or 20%.

[0033] The F-number of the projection optical system is Fn0, and the effective display area of ​​the LCD panel (mm 2 ) is S, Fnо<(S / 8) 0.5 (8) It is preferable to satisfy the following condition. If Fn0 exceeds the upper limit of formula (8), the Etendue of the projection optical system becomes small, and the light utilization efficiency decreases, making it impossible to obtain the required performance. Note that the upper limit of formula (8) can be set as (S / 10) 0.5 , (S / 12) 0.5 , (S / 14)0.5 , (S / 16) 0.5 , (S / 18) 0.5 or (S / 20) 0.5 It is more preferable to set it to

[0034] When the absolute value of the radius of curvature of the first transmitting-reflecting surface on the optical axis is R1 (mm), and the absolute value of the radius of curvature of the third transmitting-reflecting surface is R3 (mm), 0.80 <R1 / R3<1.25 (9) It is desirable to satisfy the following condition. If R1 / R3 exceeds the upper limit or falls below the lower limit of equation (9), pixel misalignment between image light L34a and image light L34b increases, resulting in a deterioration in image quality. It is more preferable to set the upper limit of equation (9) to 1.24, 1.22, 1.20, 1.08, 1.06, 1.04, or 1.02. It is also more preferable to set the lower limit of equation (14) to 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, or 0.98.

[0035] When the focal length of the projection optical system is f (mm), R1 / f≧1.0 (10) It is preferable to satisfy the following condition. If R1 / f exceeds the upper limit of equation (10), the curvature of field will be over-corrected by the reflecting surface, making it impossible to obtain the required performance. It is more preferable to set the upper limit of equation (10) to 1.2, 1.4, 1.5, 1.6, 1.8, or 2.0.

[0036] When the absolute value of the radius of curvature of the second transmissive-reflective surface is R2 (mm), R2 / f≧1000 (11) It is preferable to satisfy the following condition. If R2 / f exceeds the upper limit of equation (11), pixel shift between image light L34a and image light L34b increases, resulting in a deterioration in image quality. It is more preferable to set the upper limit of equation (11) to 2500, 5000, 7500, 10000, 25000, 50000, 75000, or 100000.

[0037] When the transmittance of the second transmissive-reflective surface for image light is T2 and the reflectance of the second transmissive-reflective surface is R2, 0.70≦T2 / R2≦1.40 (12) It is preferable to satisfy the following condition. If T2 / R2 exceeds the upper limit or falls below the lower limit of formula (12), the light utilization efficiency decreases and the required performance cannot be obtained. It is more preferable to set the upper limit of formula (12) to 1.35, 1.30, 1.25, 1.20, 1.15, or 1.10. It is also more preferable to set the lower limit of formula (12) to 0.75, 0.80, 0.85, or 0.90.

[0038] Let OL (mm) be the total length of the projection optical system (the distance on the optical axis from the lens surface closest to the projection side to the display surface of the display element), and SL (mm) be the distance on the optical axis from the aperture stop (SP) to the display surface. SL / OL≦1.15 (13) It is preferable to satisfy the following condition. If SL / OL exceeds the upper limit of expression (13), aberrations such as field curvature and distortion increase, making it impossible to obtain the required performance. It is more preferable to set the upper limit of expression (13) to 1.14, 1.12, 1.10, 1.08, 1.06, or 1.05.

[0039] It is preferable that the first transmissive-reflective surface has a convex shape facing the display element side, and the third transmissive-reflective surface has a convex shape facing the projection side, which makes it possible to cancel the Petzval sum generated in the refractive lens while providing positive power at the reflective surface, even though the projection optical system as a whole has positive power.

[0040] It is preferable to have a cemented lens, consisting of at least two lenses, on the display element side of the aperture stop. By having a cemented lens, a phase plate or a half mirror can be placed on the cemented surface, which makes it possible to shorten the overall length.

[0041] The first transflective surface is preferably located at the cemented surface of the cemented lens. This is because there is a high risk that the microstructure of a PBS such as a "WGF" will be damaged if it comes into contact with an air surface. For the same reason, it is also preferable that the third transflective surface be located at the cemented surface of the cemented lens.

[0042] The first λ / 4 phase plate and the second λ / 4 phase plate are preferably disposed on the cemented surface of the cemented lens, because a λ / 4 phase plate such as a film is prone to deterioration when in contact with an air surface, and the required durability cannot be obtained.

[0043] Specific examples 1 to 6 will be described below. After example 6, numerical examples 1 to 6 corresponding to examples 1 to 6, respectively, are shown. [Example]

[0044] Figures 4(a) and (b) show the second optical configuration of the projection optical system 100 of Example 1 (Numerical Example 1), where Figure 4(a) shows the first optical path (image light L34a) and Figure 4(b) shows the second optical path (image light L34b).

[0045] The projection optical system 100 has, arranged in order from the projection side (left side in the figure) to the display element side, an aperture stop SP, a first lens 101, a second lens 102, a third lens 103, a fourth lens 104, a fifth lens 105, a sixth lens 106, and a seventh lens 107. It also has an eighth lens 108, a ninth lens 109, and a polarizing plate 110. A transmissive liquid crystal panel is used as the display element 111. A second PBS is provided on surface S11, and a first PBS is provided on surface S13. A second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided on surface S12, arranged in order from the projection side.

[0046] FIG. 5 shows longitudinal aberrations (spherical aberration, astigmatism, and distortion) of the projection optical system 100 of Numerical Example 1 when the projection distance is infinity. The spherical aberration diagram shows the amount of spherical aberration at wavelengths of 470 nm (B), 550 nm (G), and 620 nm (R) at a specific F-number (Fno). In the astigmatism diagram, the solid line S shows astigmatism on the sagittal image plane, and the dashed line M shows astigmatism on the meridional image plane. The distortion diagram shows the amount of distortion for a wavelength of 550 nm. The explanations for these aberration diagrams are the same for the other numerical examples described below.

[0047] The projection optical system 100 can also be used as an imaging optical system for capturing images. In this case, the polarizing plate 110 is not necessary, and the display element 111 serves as the imaging element. The projection side serves as the object side, and the display element side serves as the imaging element side.

[0048] The polarizer 110 is preferably an absorptive polarizer, but may also be a reflective polarizer, and the function of the polarizer may be substituted by the second PBS on the surface S13.

[0049] The aperture stop SP may be substituted by an opening at the entrance portion of the light guide plate in the AR glasses. [Example]

[0050] Figures 6(a) and (b) show the second optical configuration of the projection optical system 200 of Example 2 (Numerical Example 2), where Figure 6(a) shows the first optical path (image light L34a) and Figure 6(b) shows the second optical path (image light L34b).

[0051] The projection optical system 200 includes, arranged in order from the projection side to the display element side, an aperture stop SP, a first lens 201, a second lens 202, a third lens 203, a fourth lens 204, a fifth lens 205, a sixth lens 206, a seventh lens 207, and an eighth lens 208. It also includes a ninth lens 209, a PBS array 210, and a phase compensation plate 211. A reflective liquid crystal panel is used as the display element 212. A second PBS is provided on surface S21, and a first PBS is provided on surface S23. A second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided on surface S22, arranged in order from the projection side.

[0052] FIG. 7 shows longitudinal aberration when the projection distance of the projection optical system 200 in Numerical Example 2 is infinity.

[0053] 8 shows the configuration of a PBS array 210 as a polarization conversion means (polarization means). The PBS array 210 is composed of a first polarization separation surface 210a, a second polarization separation surface 210b, a third polarization separation surface 210c, and a fourth polarization separation surface 210d. The transmittance of P-polarized light and the reflectance of S-polarized light of the first polarization separation surface 210a are 100% and 25%, respectively. The transmittance of P-polarized light and the reflectance of S-polarized light of the second polarization separation surface 210b are 100% and 33%, respectively. The transmittance of P-polarized light and the reflectance of S-polarized light of the third polarization separation surface 210c are 100% and 50%, respectively. The transmittance of P-polarized light and the reflectance of S-polarized light of the fourth polarization separation surface 210d are 100% and 100%, respectively.

[0054] In this embodiment, the light incident from the illumination optical system is S-polarized light, which is linearly polarized light. The S-polarized light from the illumination optical system is split into multiple light beams by the PBS array 210, and illuminates the reflective liquid crystal panel 212. The image light, which is P-polarized light modulated by the reflective liquid crystal panel 212, passes through the PBS array 210 and is projected onto the projection surface.

[0055] The number of polarization separation surfaces of the PBS array needs to be two or more, and a PBS with one polarization separation surface may be used instead of the PBS array. [Example]

[0056] Figures 9(a) and (b) show the second optical configuration of the projection optical system 300 of Example 3 (Numerical Example 3), and Figure 6(a) shows the first optical path (image light L34a) and Figure 6(b) shows the second optical path (image light L34b).

[0057] The projection optical system 300 includes, arranged in order from the projection side to the display element side, a first lens 301, a second lens 302, a third lens 303, an aperture stop SP, a fourth lens 304, a fifth lens 305, a sixth lens 306, a seventh lens 307, and an eighth lens 308. It also includes a ninth lens 309, a tenth lens 310, an eleventh lens 311, and a polarizing plate 312. A transmissive liquid crystal panel is used as the display element 313. A second PBS is provided on surface S31, and a first PBS is provided on surface S33. A second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided on surface S32, arranged in order from the projection side.

[0058] FIG. 10 shows the longitudinal aberration when the projection distance of the projection optical system 300 of Numerical Example 3 is 2.0 mm. [Example]

[0059] Figures 11(a) and (b) show the second optical configuration of the projection optical system 400 of Example 4 (Numerical Example 4), where Figure 11(a) shows the first optical path (image light L34a) and Figure 11(b) shows the second optical path (image light L34b).

[0060] The projection optical system 400 includes, in order from the projection side to the display element side, a first lens 401, a second lens 402, a third lens 403, an aperture stop SP, a fourth lens 404, a fifth lens 405, a sixth lens 406, a seventh lens 407, and an eighth lens 408. It also includes a ninth lens 409, a PBS array 410, and a phase compensation plate 411. A reflective liquid crystal panel is used as the display element 412. A second PBS is provided on surface S41, and a first PBS is provided on surface S43. A second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided on surface S42, in order from the projection side. The configuration of the PBS array 410 is the same as that of the PBS array 210 in the second embodiment.

[0061] FIG. 12 shows the longitudinal aberration when the projection distance of the projection optical system 400 of Numerical Example 4 is 2.0 mm. [Example]

[0062] FIG. 13 shows a second optical configuration of the projection optical system 500 of the fifth embodiment (numerical embodiment 5), and also shows the first optical path (image light L34a) and the second optical path (image light L34b).

[0063] The projection optical system 500 has, arranged in this order from the projection side to the display element side, an aperture stop SP, a first lens 501, a second lens 502, a third lens 503, a fourth lens 504, a fifth lens 505, a sixth lens 506, a seventh lens 507, an eighth lens 508, and a polarizing plate 509. A transmissive liquid crystal panel 510 is used as the display element 510. On surface S51, from the projection side, a polarizing plate, a second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided, and on surface S52, a PBS is provided. FIG. 14 shows longitudinal aberration when the projection distance of the projection optical system 500 of Numerical Example 5 is infinity. [Example]

[0064] FIG. 15 shows a second optical configuration of the projection optical system 600 of the sixth embodiment (Numerical Example 6), and also shows the first optical path (image light L34a) and the second optical path (image light L34b).

[0065] The projection optical system 600 has, arranged in this order from the projection side to the display element side, a first lens 601, a second lens 602, an aperture stop SP, a third lens 603, a fourth lens 604, a fifth lens 605, a sixth lens 606, a seventh lens 607, an eighth lens 608, and a polarizing plate 609. A transmissive liquid crystal panel is used as the display element 610. From the projection side, a polarizing plate, a second λ / 4 phase plate, a half mirror, and a first λ / 4 phase plate are provided on surface S61, and a PBS is provided on surface S62.

[0066] FIG. 16 shows the longitudinal aberration when the projection distance of the projection optical system 300 in Numerical Example 6 is 2.0 mm.

[0067] Numerical Examples 1 to 6 are shown below. In the surface data of each numerical example, the number i indicates the order of the surface counted from the projection side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air gap (mm) on the optical axis between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νd is the Abbe number based on the d-line of the optical material between the i-th and (i+1)-th surfaces. The Abbe number based on the d-line, νd, is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm). The effective diameter is the radius (mm) of the area of ​​the i-th lens surface through which light rays contributing to image projection pass.

[0068] In each numerical example, d, focal length (mm), and F-number are all values ​​when the projection optical system of each numerical example is focused on an object at infinity. The total length is the distance on the optical axis from the front surface of the projection optical system (the lens surface closest to the projection side) to the display surface of the display element.

[0069] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. When X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are the aspherical coefficients of each order, the aspherical shape is expressed as follows: X=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 0.5 ] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 The "E±XX" in the conic constants and aspheric coefficients means "×10±XX." Note that the conic constants K in all numerical examples are 0.

[0070] Furthermore, each numerical example shows the values ​​of the conditions of equations (6), (7), (8), (9), (10), (11), and (13). Each numerical example satisfies the conditions of the above equations.

[0071] T2 / R2 in equation (12) is in the range of 0.9 to 1.1. (Numerical Example 1) Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 0.000 2.88 2 ∞ 0.100 2.88 3 6.170 0.380 1.802 42.6 2.97 4 4.309 1.500 1.571 42.4 2.84 5 15.448 0.538 2.82 6* -12.732 0.983 1.773 49.6 2.83 7* -31.025 0.100 3.08 8 ∞ 0.100 3.18 9 23.088 0.380 1.805 25.4 3.62 10 17.248 0.891 1.588 61.0 3.79 11(Reflection) ∞ -0.891 1.588 61.0 4.00 12 (reflection) 17.248 0.891 1.588 61.0 4.16 13 ∞ 0.891 1.588 61.0 4.13 14 -17.248 0.380 1.805 25.4 4.10 15 -23.088 0.100 4.09 16 -578.463 0.380 1.806 25.6 3.99 17 8.916 0.100 3.84 18* 7.269 1.987 1.681 56.2 3.95 19* -9.874 0.300 3.84 20 ∞ 0.500 1.516 64.1 3.63 21 ∞ 0.300 3.52 22 ∞ 0.500 1.516 64.1 3.41 23 ∞ 0.000 1.516 64.1 3.30 Aspheric coefficients Face number 6 7 18 19 A4 1.241E-03 1.906E-03 -3.536E-04 2.776E-03 A6 1.906E-05 1.942E-05 7.254E-05 -1.704E-04 A8 -9.720E-06 -4.373E-06 -3.461E-06 1.348E-05 A10 5.175E-07 1.082E-07 1.957E-07 -2.734E-07 A12 -6.184E-09 Various data Focal length 7.0 Total length 9.9 Image height 3.3 θ 2.75° DST 14.0% Fno 0.80 R1 / R3 1.00 R1 / f 2.46 R2 / f∞ SL / OL 1.01 (Numerical Example 2) Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 0.000 2.74 2 ∞ 0.100 2.74 3 -64.078 0.500 1.834 37.2 2.74 4 3.958 2.327 1.706 29.5 2.87 5 -8.022 0.100 3.04 6* -7.138 0.500 1.834 37.2 3.04 7* -37.159 0.100 3.48 8 ∞ 0.100 3.71 9 19.695 0.522 1.773 49.6 4.30 10 21.929 0.955 1.571 62.1 4.44 11(Reflection) ∞ -0.955 1.571 62.1 4.63 12 (reflection) 21.929 0.955 1.571 62.1 4.78 13 ∞ 0.955 1.571 62.1 4.74 14 -21.929 0.522 1.773 49.6 4.70 15 -19.695 0.100 4.68 16 -38.116 0.500 1.805 25.4 4.56 17 7.689 0.100 4.33 18* 6.549 2.924 1.719 53.5 4.44 19* -8.500 0.300 4.40 20 ∞ 2.000 1.516 64.1 4.04 21 ∞ 0.300 3.66 22 ∞ 0.500 1.516 64.1 3.57 23 ∞ 0.300 3.48 24 ∞ 0.500 1.516 64.1 3.39 25 ∞ 0.000 1.516 64.1 3.30 Aspheric coefficients Face number 6 7 18 19 A4 -3.207E-05 2.068E-05 -8.532E-04 6.100E-04 A6 3.010E-05 1.482E-05 2.047E-05 6.400E-06 A8 -1.347E-06 6.352E-07 -1.347E-06 -1.127E-06 A10 -7.609E-08 -1.539E-07 3.997E-08 5.767E-08 A12 -6.445E-09 Various data Focal length 7.5 Total length 13.7 Image height 3.3 θ 1.44° DST 18.0% Fno 0.90 R1 / R3 1.00 R1 / f 2.92 R2 / f∞ SL / OL 1.01 (Numerical Example 3) Surface number rd nd νd Effective diameter 1 35.487 1.10 1.487 70.2 16.07 2 15.619 9.86 13.31 3 15.000 8.00 1.525 53.1 11.40 4 -198.459 3.39 10.12 5* -17.506 1.10 1.530 51.6 7.44 6* -19.257 0.10 6.87 7 (Aperture) ∞ 1.45 6.76 8 ∞ 1.10 1.516 64.1 6.73 9 ∞ 1.10 1.770 29.0 6.88 10 35.429 1.90 1.488 70.1 7.24 11(Reflection) ∞ -1.90 1.488 70.1 7.65 12 (reflection) 35.429 1.90 1.488 70.1 8.03 13 ∞ 1.90 1.488 70.1 7.95 14 -35.429 1.10 1.770 29.0 7.87 15 ∞ 1.10 1.516 64.1 7.80 16 ∞ 0.10 7.76 17* 16.910 1.80 1.697 55.5 7.62 18* 24.499 0.59 7.27 19 29.063 2.71 1.697 55.5 7.27 20 -36.280 0.10 7.04 21 ∞ 0.50 6.58 22 ∞ 0.50 1.516 64.1 6.29 23 ∞ 0.50 6.11 24 ∞ 0.50 1.544 66.3 5.82 25 ∞ 0.00 1.544 66.3 5.65 Aspheric coefficients Face number 5 6 17 18 A4 1.349E-04 2.294E-04 8.30E-05 1.222E-04 A6 6.338E-06 5.984E-06 5.27E-07 2.659E-07 A8 -1.168E-07 -8.424E-08 4.46E-09 1.175E-08 A10 1.027E-09 5.507E-10 -5.89E-11 -1.558E-10 A12 -4.012E-12 Various data Focal length 15.0 Total length 40.0 Image height 5.65 θ 1.67° DST 7.9% Fno 0.70 R1 / R3 1.00 R1 / f 2.36 R2 / f∞ SL / OL 0.42 (Numerical Example 4) Surface number rd nd νd Effective diameter 1* 377.118 1.50 1.757 50.7 17.65 2* 19.201 8.20 15.10 3 25.945 7.54 1.721 28.9 15.29 4 -358.756 10.37 14.75 5* 93.862 3.00 1.813 27.8 9.63 6* 45.124 0.99 9.05 7 (Aperture) ∞ 2.12 9.05 8 ∞ 1.50 1.805 25.4 9.65 9 60.427 2.37 1.557 63.2 10.22 10 ∞ -2.37 1.557 63.2 10.73 11(Reflection) 60.427 2.37 1.557 63.2 11.23 12(reflection) ∞ 2.37 1.557 63.2 11.23 13 -60.427 1.50 1.805 25.4 11.23 14 ∞ 3.15 1.487 70.2 11.29 15 -40.139 0.10 11.39 16* 25.782 5.28 1.697 55.5 11.21 17* -42.450 0.50 10.96 18 ∞ 8.00 1.516 64.1 9.66 19 ∞ 0.50 6.65 20 ∞ 0.50 1.516 64.1 6.33 21 ∞ 0.50 6.14 22 ∞ 0.50 1.544 66.3 5.83 23 ∞ 0.00 1.544 66.3 5.65 Aspheric coefficients Face number 1 2 5 6 A4 -2.954E-06 -1.222E-05 -3.10E-05 8.483E-06 A6 1.444E-08 -1.912E-08 -9.27E-08 2.662E-08 A8 -4.254E-11 -3.915E-13 -4.35E-10 -3.986E-10 A10 4.869E-14 -3.255E-13 7.51E-13 5.645E-12 Face number 16 17 A4 -1.46E-05 -5.47E-06 A6 -2.09E-08 -1.69E-08 A8 -4.01E-10 -5.85E-12 A10 1.48E-12 2.69E-13 Various data Focal length 15.0 Total length 60.0 Image height 5.65 θ 1.48° DST 10.9% Fno 0.70 R1 / R3 1.00 R1 / f 4.03 R2 / f∞ SL / OL 0.48 (Numerical Example 5) Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 0.100 9.98 2* 27.062 1.489 1.662 57.0 10.01 3* 35.042 7.500 9.83 4* ∞ 2.976 1.692 55.7 10.77 5* -35.137 0.100 10.89 6 ∞ 0.104 10.75 7 -564.695 1.300 1.785 46.4 10.75 8 ∞ 2.160 1.691 55.7 10.72 9 -66.034 0.113 10.68 10* -132.785 1.831 1.508 67.8 10.61 11 -53.624 0.000 10.54 12(reflection) -53.624 0.000 10.54 13 -53.624 -1.831 1.508 67.8 10.54 14* -132.785 -0.113 9.96 15 -66.034 -2.160 1.691 55.7 9.67 16(reflection) ∞ 2.160 1.691 55.7 9.03 17 -66.034 0.113 8.32 18* -132.785 1.831 1.508 67.8 7.86 19 -53.624 1.300 1.805 25.5 7.02 20 12.524 4.208 1.684 56.0 5.86 21 -26.009 0.100 5.11 22* 26.878 1.472 1.774 49.4 4.27 23* 18.656 0.325 3.60 24 ∞ 0.500 1.516 64.1 3.60 25 ∞ 0.500 3.48 26 ∞ 0.000 3.30 Aspheric coefficients Face number 2 3 4 5 10 A4 5.876E-06 3.710E-05 3.05E-06 1.166E-05 2.11E-06 A6 -5.912E-08 1.458E-07 1.83E-08 -4.755E-08 -5.75E-08 A8 1.972E-10 -1.130E-09 8.40E-11 -3.933E-10 -5.48E-10 A10 -5.639E-12 7.152E-12 -7.69E-13 1.049E-12 4.91E-12 A12 -1.78E-14 Aspheric coefficients Face number 14 18 22 23 A4 2.11E-06 2.11E-06 -3.728E-04 6.145E-05 A6 -5.75E-08 -5.75E-08 -3.251E-06 -5.581E-05 A8 -5.48E-10 -5.48E-10 2.490E-07 4.778E-06 A10 4.91E-12 4.91E-12 -5.659E-09 -1.429E-07 A12 -1.78E-14 -1.78E-14 Various data Focal length 12.0 Total length 25.6 Image height 3.30 θ 1.38° DST 2.4% Fno 0.60 R1 / R3 1.00 R1 / f 4.47 R2 / f∞ SL / OL 1.00 (Numerical Example 6) Surface number rd nd νd Effective diameter 1* 164.311 1.600 1.487 70.2 12.94 2* 19.879 1.620 11.28 3 20.543 7.500 1.545 51.3 11.23 4 -73.720 3.496 10.64 5 (Aperture) ∞ 2.375 10.18 6 -60.120 1.600 1.620 35.9 10.04 7 ∞ 1.765 1.737 52.1 10.07 8 -309.236 0.481 10.09 9* -624.424 2.558 1.773 49.6 10.09 10 -45.813 0.000 10.15 11(Reflection) -45.813 0.000 10.15 12 -45.813 -2.558 1.773 49.6 10.15 13* -624.424 -0.481 9.52 14 -309.236 -1.765 1.737 52.1 9.18 15(reflection) ∞ 1.765 1.737 52.1 8.69 16 -309.236 0.481 8.26 17* -624.424 2.558 1.773 49.6 8.02 18 -45.813 1.600 1.768 26.7 7.57 19 12.524 4.011 1.773 49.6 6.86 20 -62.359 0.100 6.74 21* 46.096 2.293 1.697 55.5 6.58 22* -113.989 0.500 6.38 23 ∞ 0.500 1.516 64.1 5.99 24 ∞ 0.500 5.86 25 ∞ 0.000 5.65 Aspheric coefficients Face number 1 2 9 13 A4 -6.242E-06 1.399E-05 -7.76E-06 -7.76E-06 A6 -1.986E-08 1.952E-08 -1.37E-09 -1.37E-09 A8 1.852E-10 3.327E-10 -2.26E-10 -2.26E-10 A10 -5.178E-13 -2.075E-13 2.55E-12 2.55E-12 A12 -1.396E-14 -1.396E-14 Aspheric coefficients Face number 17 21 22 A4 -7.76E-06 -7.22E-05 -1.49E-04 A6 -1.37E-09 -1.93E-06 -2.09E-06 A8 -2.26E-10 3.09E-08 7.38E-08 A10 2.55E-12 -3.66E-10 -8.47E-10 A12 -1.396E-14 Various data Focal length 12.0 Total length 30.0 Image height 5.65 θ 1.34° DST 7.4% Fno 0.60 R1 / R3 1.00 R1 / f 3.82 R2 / f∞ SL / OL 0.56 [Image projection device using a projection optical system] FIG. 17 shows a head-mounted display (HMD) or AR glasses equipped with an image projection device using the projection optical system of each embodiment. A frame 1400 holds eyepiece light guide plates 1200 in front of the eyes of an observer 1000 and holds image projection devices corresponding to each of the eyepiece light guide plates 1200. Image light emitted from each image display device is guided to the eyes of the observer 1000 via the eyepiece light guide plate 1200. This allows the observer 1000 to view a display image 1100. By presenting display images with parallax to the left and right eyes, the observer can also view a stereoscopic image. A control unit 1430 is connected to the frame 1400 and controls the driving of the display elements, the light intensity of the light source, and the like. The control unit 1430 may be located outside the frame 1400 and connected to the image projection device via wired or wireless communication as shown in the figure, or it may be located inside the frame 1400.

[0072] Furthermore, a first information acquisition unit 1410 including a camera that acquires pupil information indicating the position and movement (viewpoint or line of sight) of the observer 1000's pupil is attached to the frame 1400. A control unit 1430 corrects the position of the display image 1100 (the display position of the image on the display element) based on the pupil information. A second information acquisition unit 1420 including a camera that acquires external world (surroundings) information is also attached to the frame 1400. The control unit 1430 adjusts the brightness of the display image 1100 according to the brightness of the external world obtained from the external world information.

[0073] 18 shows a head-up display (HUD) 4450 as an in-vehicle image projection device using the projection optical system of each embodiment. The HUD 4450 has an image projection device 4100, a reflection optical system 4050, a first information acquisition unit 4410, a second information acquisition unit 4420, and a control unit 4430. The HUD 4450 is mounted on an automobile 4500 as a mobile device, and projects and displays an image (virtual image) 4600 to support a user (driver or passenger) 4000 of the automobile 4500. Note that the mobile device may be a train, a ship, an airplane, or the like, in addition to an automobile.

[0074] The first information acquisition unit 4410 includes a camera that acquires pupil information indicating the position and movement (point of view or line of sight) of the pupil E of the user 4000. The control unit 4430a corrects the position of the display image 4600 (the display position of the image on the display element) based on the pupil information. The second information acquisition unit 4420 includes a camera that acquires external world (surroundings) information. The control unit 4430 adjusts the brightness of the display image 4600 according to the brightness of the external world obtained from the external world information, or superimposes the display image 4600 on the external world image obtained from the external world information. The second information acquisition unit 4420 may acquire external world information not only of the front, but also of the rear, sides, etc. Furthermore, the control unit 4430 determines the possibility of collision of the automobile 4500 with an obstacle (object) obtained from the external world information, and if there is a possibility of collision, issues a warning or controls any of the drive unit (engine, motor, etc.), brakes, and steering of the automobile 4500. The warning method may include emitting a warning sound, displaying warning information on the display screen of the car navigation system, and vibrating the seat belt or steering wheel.

[0075] 19 shows the configuration of a real image projection system (projector) as an image projection device using the projection optical system of each embodiment. Image light emitted from a display element 5100 is projected onto a projection surface 5300 such as a screen via a projection optical system 5200. The projection surface 5300 may be flat or curved. A control unit 5400 drives the display element in response to an image signal input from outside, adjusts the light intensity of a light source (not shown), and adjusts the zoom and focus of the projection optical system 5200.

[0076] The above embodiment shows the following configuration.

[0077] (Configuration 1) An optical system that projects light from a display element, An optical system comprising a first transmission-reflection surface, a first wave plate, and a second transmission-reflection surface, arranged in this order from the display element side to the projection side. (Configuration 2) 2. The optical system according to configuration 1, wherein polarized light from a polarizing means is incident on the first transmitting-reflecting surface. (Configuration 3) 3. The optical system according to configuration 1 or 2, wherein the light is transmitted through the first transmission-reflection surface, reflected by the second transmission-reflection surface, reflected by the first transmission-reflection surface, transmitted through the second transmission-reflection surface, and projected. (Configuration 4) When the absolute value of the angle of the most off-axis chief ray of the light with respect to the optical axis of the optical system is θ (°), θ≦10.0° 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the absolute value of the distortion occurring in the optical system is DST, DST≦30% (7) 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) The F-number of the optical system is Fn0, the effective display area of ​​the display element is 2 ) is S, Fnо<(S / 8) 0.5 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) 7. The optical system according to any one of configurations 1 to 6, comprising the first transmission-reflection surface, the first wave plate, the second transmission-reflection surface, the second wave plate, and a third transmission-reflection surface, which are arranged in this order from the display element side to the projection side. (Configuration 8) The light is projected along a first optical path in which the light is transmitted through the first transmission-reflection surface, reflected by the second transmission-reflection surface, reflected by the first transmission-reflection surface, and transmitted through the second and third transmission-reflection surfaces; The optical system described in Configuration 7, wherein the light is projected via a second optical path in which the light is transmitted through the first and second transmission-reflection surfaces, reflected by the third transmission-reflection surface, reflected by the second transmission-reflection surface, and transmitted through the third transmission-reflection surface. (Configuration 9) When the absolute value of the radius of curvature of the first transmission-reflection surface on the optical axis of the optical system is R1 and the absolute value of the radius of curvature of the third transmission-reflection surface on the optical axis is R3, 0.80 <R1 / R3<1.25 9. The optical system according to configuration 7 or 8, wherein the following condition is satisfied: (Configuration 10) 10. The optical system described in any one of configurations 7 to 9, wherein the first transmissive-reflective surface and the third transmissive-reflective surface are each configured as a reflective polarizer that transmits polarized light in a specific polarization direction and reflects polarized light in a polarization direction orthogonal to the specific polarization direction. (Configuration 11) 11. The optical system according to any one of configurations 7 to 10, wherein the first transmissive-reflective surface has a convex shape facing the display element side, and the third transmissive-reflective surface has a convex shape facing the projection side. (Configuration 12) When the transmittance of the second transmissive-reflective surface for the light is T2 and the reflectance of the second transmissive-reflective surface for the light is R2, 0.70≦T2 / R2≦1.40 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) When the absolute value of the radius of curvature of the first transmitting-reflecting surface on the optical axis of the optical system is R1 (mm) and the focal length of the optical system is f (mm), R1 / f≧1.0 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) When the absolute value of the radius of curvature of the second transmitting-reflecting surface on the optical axis of the optical system is R2 (mm), and the focal length of the optical system is f (mm), R2 / f≧1000 14. The optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) including the aperture stop, When the distance on the optical axis of the optical system from the surface of the optical system closest to the projection side to the display surface of the display element is OL (mm), and the distance from the aperture stop to the display surface is SL (mm), SL / OL≦1.15 15. The optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) including the aperture stop, 16. The optical system according to any one of configurations 1 to 15, further comprising a cemented lens, in which at least two lenses are cemented together, on the display element side of the aperture stop. (Configuration 17) 17. The optical system according to any one of configurations 1 to 16, further comprising a polarization conversion means for converting light from a light source toward the display element into linearly polarized light. (Configuration 18) The optical system according to any one of configurations 1 to 17; and an image projection device comprising the display element.

[0078] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0079] 20 Projection optical system (first and second optical configurations) 100,200,300,400,500,600 Projection optical system (second optical configuration) 2002 Polarizing beam splitter (first transmission / reflection surface) 2003 1st λ / 4 phase plate (1st wavelength plate) 2004 Half mirror (second transmissive / reflective surface) 3002a First polarizing beam splitter (first transmission / reflection surface) 3002b Second polarizing beam splitter (second transmission / reflection surface) 3003a 1st λ / 4 phase plate (1st wavelength plate) 3003b 2nd λ / 4 phase plate (second wave plate) 3004 Half mirror (second transmission / reflection surface)

Claims

1. An optical system that projects light from a display element, An optical system comprising a first transmission-reflection surface, a first wave plate, and a second transmission-reflection surface, which are arranged in this order from the display element side to the projection side.

2. 2. The optical system according to claim 1, wherein polarized light from a polarizing means is incident on said first transmitting / reflecting surface.

3. 2. The optical system according to claim 1, wherein the light is transmitted through the first transmission-reflection surface, reflected by the second transmission-reflection surface, reflected by the first transmission-reflection surface, transmitted through the second transmission-reflection surface, and projected.

4. When the absolute value of the angle of the most off-axis chief ray of the light with respect to the optical axis of the optical system is θ (°), θ≦10.0° 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the absolute value of the distortion occurring in the optical system is DST, DST≦30% 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. The F-number of the optical system is Fno, the effective display area of ​​the display element (mm ２ ) is S, Fnо<(S / 8) ０．５ 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. 2. The optical system according to claim 1, further comprising: the first transmission-reflection surface, the first wave plate, the second transmission-reflection surface, the second wave plate, and a third transmission-reflection surface, which are arranged in this order from the display element side to the projection side.

8. the light is projected along a first optical path in which the light is transmitted through the first transmission-reflection surface, reflected by the second transmission-reflection surface, reflected by the first transmission-reflection surface, and transmitted through the second and third transmission-reflection surfaces; 8. The optical system according to claim 7, wherein the light is projected via a second optical path in which the light is transmitted through the first and second transmission-reflection surfaces, reflected by the third transmission-reflection surface, reflected by the second transmission-reflection surface, and transmitted through the third transmission-reflection surface.

9. When the absolute value of the radius of curvature of the first transmission-reflection surface on the optical axis of the optical system is R1 and the absolute value of the radius of curvature of the third transmission-reflection surface on the optical axis is R3, 0.80<R1 / R3<1.25 8. The optical system according to claim 7, wherein the following condition is satisfied:

10. 8. The optical system according to claim 7, wherein the first transmissive-reflective surface and the third transmissive-reflective surface are each configured as a reflective polarizer that transmits polarized light in a specific polarization direction and reflects polarized light in a polarization direction orthogonal to the specific polarization direction.

11. 8. The optical system according to claim 7, wherein the first transmission-reflection surface has a convex shape facing the display element side, and the third transmission-reflection surface has a convex shape facing the projection side.

12. When the transmittance of the second transmissive-reflective surface for the light is T2 and the reflectance of the second transmissive-reflective surface for the light is R2, 0.70≦T2 / R2≦1.40 2. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the absolute value of the radius of curvature of the first transmitting-reflecting surface on the optical axis of the optical system is R1 (mm) and the focal length of the optical system is f (mm), R1 / f≧1.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

14. When the absolute value of the radius of curvature of the second transmitting-reflecting surface on the optical axis of the optical system is R2 (mm), and the focal length of the optical system is f (mm), R2 / f≧1000 2. The optical system according to claim 1, wherein the following condition is satisfied:

15. including the aperture stop, When the distance on the optical axis of the optical system from the surface of the optical system closest to the projection side to the display surface of the display element is OL (mm), and the distance from the aperture stop to the display surface is SL (mm), SL / OL≦1.15 2. The optical system according to claim 1, wherein the following condition is satisfied:

16. including the aperture stop, 2. The optical system according to claim 1, further comprising a cemented lens, in which at least two lenses are cemented together, on the display element side of the aperture stop.

17. 2. The optical system according to claim 1, further comprising a polarization conversion means for converting light from a light source toward said display element into linearly polarized light.

18. An optical system according to any one of claims 1 to 17; and an image projection device comprising the display element.

Images