Optical system and display device

Abstract

To provide an optical system having a diffraction surface and capable of displaying an excellent image.SOLUTION: An optical system for guiding light from a display surface ID to an observation side includes a first lens L1, a second lens L2 disposed closer to the display surface side than the first lens, and a third lens L3 having positive refractive power and disposed closer to the observation side than the first lens or closer to the display surface side than the second lens. The display-surface-side surface of the first lens and the observation-side surface of the second lens are adjacent to each other, and a diffractive surface is formed on each of these surfaces. The first transmissive-reflective surface HM1 is provided on one of two surfaces different from the diffractive surface in the optical system, and the second transmissive-reflective surface HM2 is provided on the other surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for a head-mounted display or the like that guides light from a display surface to a viewing side to allow a viewer to view an image. [Background technology]

[0002] As such an optical system, a so-called folded optical system has been proposed. Patent Document 1 discloses a folded optical system that can improve the definition of a displayed image by using a diffractive surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7103566 Summary of the Invention [Problem to be solved by the invention]

[0004] When a diffractive surface is used to correct chromatic aberration, it is necessary to reduce flare caused by unwanted diffracted light. [Means for solving the problem]

[0005] One aspect of the present invention is an optical system that guides light from a display surface to an observation side. The optical system includes a first lens, a second lens arranged closer to the display surface than the first lens, and a third lens with positive refractive power that is arranged closer to the observation side than the first lens or closer to the display surface than the second lens. The display surface side surface of the first lens and the observation side surface of the second lens are adjacent to each other, and a diffractive surface is formed on each of these surfaces. The optical system is characterized in that one of two surfaces other than the diffractive surface is provided with a first transmissive-reflective surface, and the other surface is provided with a second transmissive-reflective surface. Note that a display device using the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an optical system that has a diffractive surface and is capable of displaying a good image. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment. [Figure 2] 4A to 4C are aberration diagrams of the optical system of Example 1. [Figure 3] FIG. 2 is a partial cross-sectional view of the diffractive optical element according to the first embodiment. [Figure 4] 4A and 4B are diagrams showing the diffraction efficiency of the diffractive optical element in the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view of the optical system of the second embodiment. [Figure 6] 10A to 10C are aberration diagrams of the optical system of Example 2. [Figure 7] 10A and 10B are diagrams showing the diffraction efficiency of the diffractive optical element in Example 2. [Figure 8] FIG. 10 is a cross-sectional view of the optical system of the third embodiment. [Figure 9] 10A to 10C are aberration diagrams of the optical system of Example 3. [Figure 10] 10A and 10B are diagrams showing the diffraction efficiency of a diffractive optical element according to the third embodiment. [Figure 11] FIG. 10 is a cross-sectional view of the optical system of Example 4. [Figure 12] 10A to 10C are aberration diagrams of the optical system of Example 4. [Figure 13] FIG. 10 is a partial cross-sectional view of a diffractive optical element according to a fourth embodiment. [Figure 14] 10A and 10B are diagrams showing the diffraction efficiency of a diffractive optical element according to the fourth embodiment. [Figure 15] FIG. 10 is a cross-sectional view of an optical system according to a fifth embodiment. [Figure 16] 10A to 10C are aberration diagrams of the optical system of Example 5. [Figure 17] 13 is a diagram showing the diffraction efficiency of a diffractive optical element according to the fifth embodiment. [Figure 18] FIG. 10 is a cross-sectional view of an optical system according to a sixth embodiment. [Figure 19] 10A to 10C are aberration diagrams of the optical system of Example 6. [Figure 20] FIG. 13 is a partial cross-sectional view of a diffractive optical element according to a seventh embodiment. [Figure 21] A diagram of the optical path of an optical system that uses polarized light. [Figure 22] Another optical path diagram of an optical system using polarized light. [Figure 23] FIG. 1 is a diagram showing an HMD using the optical systems of Examples 1 to 7. [Figure 24] FIG. 13 is a partial cross-sectional view of a diffractive optical element according to an eighth embodiment. [Figure 25] 13 is a diagram showing the diffraction efficiency of the diffractive optical element in Example 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] 1, 5, 8, 11, 15 and 18 respectively show cross sections of the optical systems of Examples 1 to 6. First, matters common to the optical systems of the examples will be described.

[0010] The optical system in each embodiment is an optical system that guides light from a display surface ID to a pupil surface SP on the observation side. The display surface ID is a surface on which an original image is displayed on a display element such as an LCD. The observer's eye (pupil) is placed on the pupil surface SP as the observation surface. An aperture stop may be placed on the pupil surface SP.

[0011] The optical system of each embodiment has a first lens L1, a second lens L2 arranged closer to the display surface than the first lens L1, and a third lens L3 with positive refractive power arranged closer to the observation side than the first lens L1 or closer to the display surface than the second lens L2.

[0012] The display-side surface of the first lens L1 and the observation-side surface of the second lens L2 are adjacent to each other (side by side), and each of these surfaces includes a diffractive surface (first diffractive surface and second diffractive surface) with a diffraction grating. The two diffractive surfaces work together to create a predetermined phase difference, forming a diffractive optical element that converts incident light into diffracted light of a specific diffraction order. To achieve good optical performance with a small number of lenses, it is desirable that the surfaces of the first and second lenses L1 and L2 on which the diffractive surfaces are formed are both curved, but at least one of them may be flat if necessary.

[0013] Furthermore, one of the two surfaces in the optical system other than the surface on which the diffractive surface is formed is provided with a first transmission-reflection surface HM1, and the other surface is provided with a second transmission-reflection surface HM2. In order to construct the optical system using as few lenses as possible, it is preferable that each transmission-reflection surface be provided on one of the first to third lenses L1 to L3, and it is more preferable that a transmission-reflection surface be provided on each of the second lens L2 and the third lens L3. The ratio of transmittance to reflectance of each transmission-reflection surface is preferably 50:50, but is not limited to this ratio.

[0014] In the optical system of each embodiment, the distance on the optical axis between the pupil plane (eye point) SP and the lens surface closest to the observation side is the eye relief.

[0015] 2, 6, 8, 12, 16, and 19 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Examples 1 to 6, respectively. In the spherical aberration diagrams, EPD indicates pupil diameter (mm), the solid line indicates spherical aberration at the d-line (wavelength 587.6 nm), the dashed-dotted line indicates spherical aberration at the C-line (wavelength 656.3 nm), and the dashed-two-dot line indicates spherical aberration at the F-line (wavelength 486.1 nm). In the astigmatism diagrams, the solid line ΔS indicates astigmatism at the sagittal image plane, and the dashed line ΔM indicates astigmatism at the meridional image plane. The distortion diagrams show distortion at the d-line. The chromatic aberration diagrams show chromatic aberration of magnification at the C-line and F-line. ω is the half angle of view (°).

[0016] Note that there is a one-to-one correspondence between the aberration of a ray of light that reaches the pupil plane SP when a light emitting point is provided on the display surface ID and the aberration of a ray of light that reaches the display surface ID when a light emitting point is provided on the pupil plane SP. For this reason, each aberration diagram shows the aberration at the display surface ID. Furthermore, since the diameter of the human pupil is about Φ4 mm, longitudinal aberration is shown with an EPD of Φ4 to 6 mm.

[0017] The optical systems of each embodiment will be described in detail below. In each embodiment, when simply referring to the refractive index and Abbe number, they refer to the refractive index at the wavelength of light incident on the optical system (incident wavelength) and the Abbe number based on the incident wavelength. The refractive index Nd indicates the refractive index at the d-line, which is a portion of the incident wavelength, and the Abbe number vd indicates the Abbe number based on the d-line. The partial dispersion ratio θgF indicates the partial dispersion ratio at the g-line and the F-line. The Abbe number vd based on the d-line and the partial dispersion ratio θgF at the g-line and the F-line are defined by the following equations (a) and (b), respectively. The refractive indices at the g-line (wavelength 435.8 nm), F-line, d-line, and C-line of the Fraunhofer lines are defined as Ng, NF, Nd, and NC, respectively.

[0018] νd=(Nd-1) / (NF-NC) (a) θgF=(Ng-NF) / (NF-NC) (b) [Example]

[0019] An explanation will be given of the optical system of Example 1 shown in Fig. 1. After the explanation of Example 7, Numerical Example 1 corresponding to Example 1 will be shown.

[0020] The optical system of Example 1 includes, in order from the observation (pupil plane SP) side, a first lens L1, a second lens L2, and a third lens L3. The curved surface of the first lens L1 facing the display surface and the curved surface of the second lens L2 facing the observation surface are adjacent to each other with an air gap between them, and diffractive surfaces (first and second diffractive surfaces) are formed on each of these curved surfaces. A first transmission-reflection surface HM1 is provided on the surface of the second lens L2 facing the display surface, and a second transmission-reflection surface HM2 is provided on the surface of the third lens L3 facing the display surface. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0021] Light emitted from display surface ID passes through second transmission-reflection surface HM2 and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the viewing side. After this, the light passes through third lens L3 again, passes through first transmission-reflection surface HM1, second lens L2, two diffractive surfaces, and first lens L1 in that order, and reaches pupil plane SP.

[0022] In this way, by providing transmissive-reflective surfaces on multiple surfaces different from the diffractive surface, i.e., by not locating the diffractive surface on the reflective surface (between the first and second transmissive-reflective surfaces HM1 and HM2), it is possible to narrow the angular range of light beams incident on the diffractive surface. This makes it possible to reduce flare that occurs at the wall surface of the diffraction grating provided on the diffractive surface. In other words, it is preferable to locate the first and second transmissive-reflective surfaces HM1 and HM2 closer to the viewing surface or the display surface than the diffractive surface.

[0023] Figure 3(a) shows a cross section of the first lens L1 and the second lens L2 on which a diffractive surface is formed in the optical system of Example 1. Figure 3(b) shows an enlarged view of the area surrounded by the dashed line in Figure 3(a). As shown in Figures 3(a) and 3(b), the display-side surface of the first lens L1 and the observation-side surface of the second lens L2 are curved surfaces with approximately the same curvature, and diffraction gratings DG1 and DG2 are formed on the respective curved surfaces.

[0024] The diffraction grating DG1 is made of the same material as the first lens L1 and is injection molded integrally with the lens surface of the first lens L1. The peripheral portion of the surface of the first lens L1 facing the display surface has a convex shape toward the display surface. The diffraction grating DG1 is composed of multiple sloped surfaces 13 and wall surfaces 14 between adjacent light-emitting surface portions 13. The sloped surfaces 13 of the diffraction grating DG1 act as a diffractive surface with positive power with respect to an envelope 12 connecting the grating vertices of the diffraction grating DG1.

[0025] The diffraction grating DG2 is made of the same material as the second lens L2 and is injection molded integrally with the lens surface of the second lens L2. The peripheral portion of the observation-side surface of the second lens L2 has a concave shape toward the display surface. The diffraction grating DG2 is composed of multiple inclined surfaces 23 and wall surfaces 24 between adjacent light-emitting surface portions 23. The inclined surfaces 23 of the diffraction grating DG2 act as a diffractive surface having negative power with respect to the envelope 21 connecting the grating vertices of the diffraction grating DG2.

[0026] Diffraction gratings DG1 and DG2 are arranged close to each other with an air layer 30 in between. Diffraction grating DG1, air layer 30, and diffraction grating DG2 work together to form a diffractive optical element that obtains a predetermined phase difference. Diffraction gratings DG1 and DG2 have concentric grating shapes, and the grating pitch changes in the radial direction, resulting in a lens effect.

[0027] One method for arranging the diffraction gratings DG1 and DG2 closely together is to bond the outer periphery of the lens L1 on which the diffraction grating DG1 is formed to the outer periphery of the lens L2 on which the diffraction grating DG2 is formed. In this case, it is desirable to improve the accuracy of the shape of the outer periphery outside the effective area of ​​each lens (described later). This allows the outer periphery of the first lens L1 and the outer periphery of the second lens L2 to abut against each other, thereby accurately controlling the distance da between the envelope 12 connecting the grating vertices of the diffraction grating DG1 and the envelope 21 connecting the grating vertices of the diffraction grating DG2.

[0028] It is also important to position and bond the diffraction gratings DG1 and DG2 with high radial precision. For example, it is possible to improve radial positioning precision by providing a minute alignment feature near the center of the diffraction grating DG1 or DG2 and observing that feature during bonding. Alternatively, tapered surfaces may be provided on the outer peripheries of the first lens L1 and the second lens L2. By abutting these tapered surfaces against each other, the coaxiality of the first lens L1 and the second lens L2 is improved, allowing the diffraction gratings DG1 and DG2 to be positioned with high radial precision.

[0029] The tilt angle of the wall surface portions 14 of the diffraction grating DG1 and the wall surface portions 24 of the diffraction grating DG2 is preferably set to be close to the angle of the light beam 31 incident on the diffractive surface. This reduces flare that occurs at the wall surface portions 14, 24. In this case, as shown in FIG. 3(b), it is preferable that the power generated at the diffractive surface including the diffraction grating DG1 is positive and the power generated at the diffractive surface including the diffraction grating DG2 is negative. This allows the angle of the wall surface portions 14 of the diffraction grating DG1 and the wall surface portions 24 of the diffraction grating DG2 to be aligned with the direction of the incident light beam 31, while improving the mold releasability during molding of each diffraction grating.

[0030] In this embodiment, the wavelength range of light incident on each diffractive surface, i.e., the wavelength range used, is the visible range, and the materials and grating heights of the diffraction gratings DG1 and DG2 are selected to increase the diffraction efficiency of first-order diffracted light across the entire visible range.

[0031] Next, the specific configuration of the diffraction gratings DG1 and DG2 will be described. In Numerical Example 1, a cycloolefin-based thermoplastic resin material (Nd=1.544, vd=56.0) is used as the first material forming the diffraction grating DG1 (first lens L1). A polycarbonate-based thermoplastic resin material (Nd=1.671, vd=19.2) is used as the second material forming the diffraction grating DG2 (second lens L2). The refractive index of the air layer 30 between the diffraction gratings DG1 and DG2 is Nd=1.0.

[0032] The grating height d1 of diffraction grating DG1 is 8.00 μm, and the grating height d2 of diffraction grating DG2 is 5.62 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 27.3 μm. The distance da between envelope curve 12 connecting the grating vertices of diffraction grating DG1 and envelope curve 21 connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0033] Next, the relationship between the phase difference and the diffraction efficiency of the diffractive optical element of this embodiment will be described. In the diffractive optical element of this embodiment, the condition under which the diffraction efficiency of the diffraction order m with respect to the wavelength λ is maximized is when the optical path length difference Φ(λ) is: Φ(λ)=(n03-n01)×d1+(n02-n03)×d2=mλ (c) In formula (c), n01 is the refractive index of the material forming diffraction grating DG1 for light of wavelength λ (d-line in this embodiment), and n02 is the refractive index of the material forming diffraction grating DG2 for light of wavelength λ. n03 is the refractive index of the layer between diffraction gratings DG1 and DG2 (air layer 30 in this embodiment) for light of wavelength λ. d1 and d2 are the grating heights of diffraction gratings DG1 and DG2, respectively.

[0034] For the incident light beam 31 in Fig. 3(b), the diffraction orders of light diffracted downward from the zeroth-order diffracted light are defined as positive diffraction orders, and the diffraction orders of light diffracted upward from the zeroth-order diffracted light are defined as negative diffraction orders. As shown in Fig. 3(b), if the diffraction grating DG1 on the incident side has a grating shape in which the grating height decreases from bottom to top within one period, the sign of the grating height d1 in equation (c) will be negative.

[0035] Moreover, the diffraction efficiency η(λ) at wavelength λ is η(λ)=sinc 2 {π[m-Φ(λ) / λ]} (d) In equation (d), m is the diffraction order of the diffracted light to be evaluated, and Φ(λ) is the optical path difference in one unit cell of the diffraction grating for light of wavelength λ. sinc(x) is a function expressed as sin(x) / x.

[0036] In this example, high diffraction efficiency is achieved in the visible wavelength range when the grating height d1 of diffraction grating DG1 is 8.00 μm and the grating height d2 of diffraction grating DG2 is 5.62 μm. The grating heights d1 and d2 indicate the grating heights when the angle of the wall surface of the diffraction grating is perpendicular to the envelope curve connecting the grating vertices. The angle of the wall surface can be changed appropriately depending on the incident light.

[0037] In this embodiment, the diffraction gratings DG1 and DG2 are made of different materials. Specifically, the diffraction grating DG1 is made of a material with a low refractive index and low dispersion, and the diffraction grating DG2 is made of a material with a higher refractive index and higher dispersion.

[0038] Next, we will explain the selection of materials for the diffraction grating DG1 (first lens L1) and the diffraction grating DG2 (second lens L2). Since a folded optical system like that of this embodiment is required to be compact, it is necessary to correct aberrations with a small number of lenses. It is preferable that it is composed of two to three lenses.

[0039] To effectively correct various aberrations, especially chromatic aberration, with as few as two or three lenses, it is desirable to combine a low-dispersion positive lens with a high-dispersion negative lens. Furthermore, to correct chromatic aberration that remains and cannot be fully corrected by the refractive power of the lens, it is possible to correct the chromatic aberration using a diffractive surface. To achieve high diffraction efficiency in a diffractive optical element, which has one diffractive surface sandwiched between two materials, it is necessary to select a material with a high refractive index and low dispersion and a material with a low refractive index and high dispersion, while maintaining the necessary refractive index difference between the two materials.

[0040] However, among general optical lens materials, many high-refractive index materials have high dispersion, while many low-refractive index materials have low dispersion. Furthermore, plastic lenses are often used in folded optical systems to reduce weight and achieve the aberration correction effect of aspherical surfaces. There are few high-refractive index, low-dispersion resin materials for plastic lenses, and many high-refractive index, low-dispersion resins are designed for replica molding, such as ultraviolet-curable resins. However, ultraviolet-curable resins have large thickness variations, and creating a lens shape with high power can easily compromise manufacturing stability. For this reason, using materials that can be injection-molded, such as thermoplastic resins, allows for the stable production of high-power lenses.

[0041] In this embodiment, the materials for the diffraction gratings DG1 and DG2 are selected from moldable thermoplastic resins, one with a high refractive index and high dispersion, and the other with a low refractive index and low dispersion. Furthermore, by arranging the two diffractive surfaces facing each other with a low refractive index layer between them, the grating heights of the diffraction gratings DG1 and DG2 can be set independently. As a result, high diffraction efficiency is achieved by combining a diffraction grating made of a high refractive index and high dispersion material with a low refractive index and low dispersion material.

[0042] Fig. 4 shows the diffraction efficiency of the annular zones in the center (pitch 852 µm) of the diffractive optical element of Numerical Example 1. As shown in Fig. 4, high diffraction efficiency is obtained over a wide range of the visible wavelength region.

[0043] 2 shows longitudinal aberrations when the pupil diameter is Φ6 mm, the eye relief is 17 mm, and the diopter is 0 diopter in Numerical Example 1. As shown in FIG. 2, various aberrations such as axial chromatic aberration, lateral chromatic aberration, and astigmatism are well corrected.

[0044] In order to achieve both good chromatic aberration correction effect due to the refractive power of the first lens L1 and the second lens L2 and high diffraction efficiency on the diffractive surface, it is preferable to appropriately set the refractive power of each of the first lens L1 and the second lens L2 and the power of the diffractive surface.

[0045] Specifically, the radius of curvature of the effective area (hereinafter referred to as the effective diameter area) of the curved surface on the observation side of the first lens L1 is R11, and the radius of curvature of the effective diameter area of ​​the curved surface on the display surface side is R12. The effective area (effective diameter area) is the area through which light rays that contribute to image formation on each surface pass, and the diameter of this area (twice the distance between the optical axis and the position farthest from the optical axis in the area) is the effective diameter. When light rays are incident on the same surface two or more times due to reflection, etc., the largest effective diameter is defined as the effective diameter of that surface. The radius of curvature of the effective diameter area on a surface on which a diffractive surface is formed refers to the radius of curvature of the envelope connecting the tips of the diffraction grating (grating vertices). Furthermore, if the curved surface on the observation side of the first lens L1 and the curved surface on the display surface side of the second lens L2 (the surface on which no diffractive surface is provided) are aspherical, the radius of curvature may be used as the radius of curvature of the reference spherical surface of the aspherical surface.

[0046] In this case, it is preferable that the sign (positive or negative) of the focal length f1e (mm) of the first lens L1 calculated from R11 and R12 is the same as the sign of the diffraction power PD1 generated at the diffractive surface of the first lens L1. Similarly, the radius of curvature of the curved surface on the observation side of the second lens L2 in the effective diameter region is R21, and the radius of curvature of the curved surface on the display surface side in the effective diameter region is R22. In this case, it is preferable that the sign of the focal length f2e (mm) of the second lens L2 calculated from R21 and R22 is the same as the sign of the diffraction power PD2 generated at the diffractive surface of the second lens L2. This makes it possible to select materials with high refractive index and high dispersion and materials with low refractive index and low dispersion for forming the diffraction grating and lenses, thereby achieving both good chromatic aberration correction and high diffraction efficiency.

[0047] The sign of the diffraction power is positive when the curvature of the sloped surfaces 13 of the diffraction grating is convex toward the display surface side with respect to the envelope, when the refractive index of the material on the observation side of the diffraction grating is higher than the refractive index of the material on the display surface side, as in diffraction grating DG1. On the other hand, when the refractive index of the material on the observation side of the diffraction grating is lower than the refractive index of the material on the display surface side, as in diffraction grating DG2, the sign of the diffraction power is negative when the curvature of the sloped surfaces 23 of the diffraction grating is convex toward the display surface side with respect to the envelope.

[0048] The focal length f1e of the first lens L1 is calculated from the radii of curvature R11 and R12 of the effective diameter area of ​​the first lens L1, the refractive index of the first lens L1, and the thickness of the first lens L1 on the optical axis, and does not include diffractive power. The same applies to the focal length f2e of the effective diameter area of ​​the second lens L2.

[0049] The aspherical shape of each surface in this embodiment is expressed by the following equation (e), where X is the amount of 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 Ai (i=4, 6, 8, . . .) is the aspherical coefficient of each order.

[0050]

number

[0051] When the amount of displacement in the optical axis direction at height h from the optical axis in the effective diameter area of ​​the aspherical surface, calculated from equation (e), is xh, the radius of curvature Re of the effective diameter area can be calculated from the following equation (f). This radius of curvature Re may be used instead of the radius of curvature of the reference spherical surface described above. In this embodiment (and other embodiments described later), the radius of curvature Re is used.

[0052]

number

[0053] Furthermore, it is preferable to provide a layer having a refractive index lower than that of the first and second lenses L1 and L2 between the diffractive surface of the first lens L1 and the diffractive surface of the second lens L2. By providing the air layer 30 as in this embodiment, high diffraction efficiency can be obtained even when a diffraction grating made of a material with a high refractive index and high dispersion is combined with a material with a low refractive index and low dispersion. However, the layer does not have to be an air layer, as long as it is made of a low refractive index material (low dispersion material). Specifically, it may be a layer made of an aerosol containing an air layer in SiO2 fine particles.

[0054] Furthermore, it is preferable that the optical system of this embodiment satisfies at least one of the conditions shown in the following expressions (1) to (8): This also applies to the optical systems of other embodiments described later.

[0055] First, let f1e (mm) be the focal length of the first lens L1 in its effective diameter region, f2e (mm) be the focal length of the second lens L2 in its effective diameter region, v1 be the Abbe number of the diffraction grating of the first lens L1, and v2 be the Abbe number of the diffraction grating of the second lens L2. In this case, it is preferable to satisfy the condition of the following formula (1):

[0056] 0<1000×(1 / f1e-1 / f2e) / (ν1-ν2) (1) The condition of formula (1) means that a low-dispersion material is used for the diffraction grating provided on a lens with a positive refractive power in the effective diameter region, and a high-dispersion material is used for the diffraction grating provided on a lens with a negative refractive power in the effective diameter region. By satisfying the condition of formula (1), it is possible to achieve both high diffraction efficiency and high chromatic aberration correction effect.

[0057] It is more preferable to set the numerical range of the formula (1) as follows:

[0058] 0.10≦1000×(1 / f1e-1 / f2e) / (ν1-ν2)≦1.00 (1a) Furthermore, it is more preferable to set the numerical range of formula (1) as follows:

[0059] 0.15≦1000×(1 / f1e-1 / f2e) / (ν1-ν2)≦0.90 (1b) Furthermore, when the Abbe number of the diffraction grating of the lens LH, which has the larger Abbe number out of the first lens L1 and the second lens L2, is νH, it is preferable that the condition of the following formula (2) be satisfied.

[0060] 35≦νH≦70 (2) If vH is below the lower limit of formula (2), the difference between the Abbe number of the diffraction grating of lens LH, which is paired with lens LH and has a smaller Abbe number, becomes too small, making it difficult to obtain high diffraction efficiency, which is undesirable.If vH is above the upper limit of formula (2), it becomes difficult to select the material for the diffraction grating, which is undesirable.

[0061] It is more preferable to set the numerical range of the formula (2) as follows:

[0062] 45≦νH≦65 (2a) Furthermore, it is more preferable to set the numerical range of the formula (2) as follows.

[0063] 50≦νH≦60 (2b) Furthermore, when the Abbe number of the diffraction grating of the lens LL, which has the smaller Abbe number out of the first lens L1 and the second lens L2, is taken as νL, it is preferable that the condition of the following formula (3) be satisfied.

[0064] 10≦νL≦50 (3) If vL is below the lower limit of formula (3), it becomes difficult to select the material for the diffraction grating formed by injection molding, which is undesirable.If vL is above the upper limit of formula (3), the difference between the Abbe number of the diffraction grating of the lens LH with the larger Abbe number becomes too small, making it difficult to obtain high diffraction efficiency, which is undesirable.

[0065] It is more preferable to set the numerical range of the formula (3) as follows:

[0066] 13≦νL≦40 (3a) Furthermore, it is more preferable to set the numerical range of the formula (3) as follows.

[0067] 14≦νL≦30 (3b) It is also preferable that the Abbe numbers of the materials forming the diffraction gratings DG1 and DG2 be set to values ​​that are appropriately different from each other. Specifically, it is preferable that the condition of the following formula (4) be satisfied.

[0068] 0.010≦|1 / νH-1 / νL|≦0.060 (4) By satisfying the condition of formula (4), high diffraction efficiency can be obtained in diffraction gratings DG1 and DG2. Note that formula (4) can be rewritten as formula (4') below, where v1 is the Abbe number of first lens L1 and v2 is the Abbe number of second lens L2.

[0069] 0.010≦|1 / ν1-1 / ν2|≦0.060 (4′) Satisfying the condition of formula (4') can improve the chromatic aberration correction effect due to the refractive power of the first and second lenses L1 and L2. Using the same material for the first lens L1 and the diffraction grating DG1, and the same material for the second lens L2 and the diffraction grating DG2, is preferable because it satisfies the conditions of formula (4) and formula (4') simultaneously.

[0070] It is more preferable to set the numerical range of the formula (4) as follows:

[0071] 0.015≦|1 / νH-1 / νL|≦0.050 (4a) Furthermore, it is more preferable to set the numerical range of the formula (4) as follows.

[0072] 0.020≦|1 / νH-1 / νL|≦0.045 (4b) Similarly, it is more preferable to set the numerical range of formula (4') as follows:

[0073] 0.015≦|1 / ν1-1 / ν2|≦0.050 (4c) Furthermore, it is more preferable to set the numerical range of formula (4') as follows:

[0074] 0.020≦|1 / ν1-1 / ν2|≦0.045 (4d) Furthermore, when the grating height of the diffraction grating of the lens LH, which has the larger Abbe number out of the first lens L1 and the second lens L2, is dH (μm), and the grating height of the diffraction grating of the lens LL, which has the smaller Abbe number, is dL (μm), it is preferable that the condition of the following equation (5) be satisfied.

[0075] dL <dH (5) When a diffraction grating made of a material with a high refractive index and high dispersion is combined with a diffraction grating made of a material with a low refractive index and low dispersion, high diffraction efficiency can be obtained by satisfying the condition of formula (5).

[0076] The refractive index of the diffraction grating of lens LH, which has the larger Abbe number between first lens L1 and second lens L2, is defined as NH, and the refractive index of the diffraction grating of lens LL, which has the smaller Abbe number, is defined as NL. Furthermore, the refractive index difference between the diffraction grating on the diffractive surface formed on lens LH and the material layer in contact with the diffractive surface is defined as ΔNH, and the refractive index difference between the diffraction grating on the diffractive surface formed on lens LL and the material layer in contact with the diffractive surface is defined as ΔNL. In this case, it is preferable to satisfy the following formula (6). By satisfying the formula (6), high diffraction efficiency can be obtained.

[0077] 0.6≦(ΔNH×dH) / (ΔNL×dL)≦1.7 (6) It is more preferable to set the numerical range of the formula (6) as follows:

[0078] 0.8≦(ΔNH×dH) / (ΔNL×dL)≦1.5 (6a) Furthermore, it is more preferable to set the numerical range of the formula (6) as follows.

[0079] 1.0≦(ΔNH×dH) / (ΔNL×dL)≦1.3 (6b) Furthermore, by satisfying the following formula (6-1), good diffraction efficiency can be obtained over the entire visible range.

[0080] 0.45≦ΔNH×dH-ΔNL×dL≦0.75 (6-1) It is more preferable to set the numerical range of the formula (6-1) as follows:

[0081] 0.50≦ΔNH×dH-ΔNL×dL≦0.70 (6-1a) Furthermore, it is more preferable to set the numerical range of the formula (6-1) as follows.

[0082] 0.53≦ΔNH×dH-ΔNL×dL≦0.65 (6-1b) Furthermore, when the diffractive power generated by each diffractive surface is Pdo, it is preferable to satisfy the condition of the following equation (7): The diffractive power generated by a diffractive surface is given by the reciprocal of the focal length due to diffraction.

[0083] 4.0≦|(1 / f1e-1 / f2e) / Pdo|≦40.0 (7) The phase shape P of each diffractive surface is expressed by the following equation (g): where h is the height in the direction perpendicular to the optical axis, m is the diffraction order, λ0 is the design wavelength, and Ci (i=2, 4, 6, ...) is the phase coefficient.

[0084] P(h)=(2π / mλ0)(C2h 2 +C4h 4 +C6h 6 +…) (g) The optical path difference function Ψ of the diffractive surface is expressed by the following equation (h):

[0085] Ψ(h)=C2h 2 +C4h 4 +C6h 6 +… (h) The diffraction power Pdo generated at the diffraction surface for the wavelength λ and the diffraction order m can be expressed as the following equation (i) using the lowest-order phase coefficient C2.

[0086] Pdo=-2C2mλ / λ0(i) In the diffractive optical element of this embodiment, the design order m is the first order, and the design wavelength is the d-line. The diffraction power Pdo used in equation (7) is the value calculated using equation (i) with λ = λ0. These are the same as in the other embodiments described below.

[0087] By satisfying the condition of expression (7), the chromatic aberration correction effect and the chromatic aberration correction effect of the diffractive surface can be shared in a balanced manner between the first lens L1 and the second lens L2, and chromatic aberration of the entire optical system can be corrected well.

[0088] It is more preferable to set the numerical range of the formula (7) as follows:

[0089] 5.0≦|(1 / f1e―1 / f2e) / Pdo|≦35.0 (7a) Furthermore, it is more preferable to set the numerical range of the formula (7) as follows.

[0090] 6.0≦|(1 / f1e―1 / f2e) / Pdo|≦30.0 (7b) Furthermore, when a diffractive optical element is used in an optical system, the diffractive power tends to be increased to correct chromatic aberration. As a result, the diffraction pitch of the diffraction grating becomes smaller. However, if the grating height becomes larger relative to the diffraction pitch, the flare generated at the wall surface of the diffraction grating increases, which is undesirable. For this reason, when the minimum pitch of the diffraction gratings DG1 and DG2 is Pmin (μm), it is preferable to satisfy the condition of the following equation (8).

[0091] 0.8≦Pmin / (dH+dL)≦4.0 (8) If Pmin / (dH+dL) exceeds the upper limit of formula (8), the chromatic aberration correction effect of the diffractive surface decreases or it becomes difficult to obtain high diffraction efficiency, which is undesirable.If Pmin / (dH+dL) falls below the lower limit of formula (8), flare occurring at the wall surface of the diffraction grating increases, which is undesirable.

[0092] It is more preferable to set the numerical range of the formula (8) as follows:

[0093] 1.0≦Pmin / (dH+dL)≦3.0 (8a) Furthermore, it is more preferable to set the numerical range of the formula (8) as follows.

[0094] 1.2≦Pmin / (dH+dL)≦2.6 (8b) In addition, by adopting the following polarized light-using configuration 1 or configuration 1, it is possible to suppress a decrease in the amount of effective light that displays an image while reducing ghost light (unwanted light) that passes through the transmissive-reflective surface without ever reflecting.

[0095] [Polarized light configuration 1] Figure 21 shows configuration 1 that uses polarized light. This configuration 1 has two transmissive-reflective surfaces. Here, of the two transmissive-reflective surfaces, the first transmissive-reflective surface HM1, which is located on the observation side, is formed by a polarization-selective semi-transmissive element (PBS) A, and the second transmissive-reflective surface HM2, which is located on the display surface side, is formed by a half mirror (HM) C. A first quarter-wave plate (QWP1) B is disposed between the polarization-selective semi-transmissive element PBS and the half mirror HM. Furthermore, a second quarter-wave plate (QWP2) D and a linear polarizer (POL) E are disposed between the half mirror HM and the display surface ID.

[0096] The polarization-selective semi-transmissive reflector A is an element configured to reflect linearly polarized light polarized in the same direction as when it passed through the linear polarizer E, and to transmit linearly polarized light polarized in a direction perpendicular to the polarized light. The polarization-selective semi-transmissive reflector A is, for example, a wire-grid polarizer or a reflective polarizer having a laminated retardation film structure. In this case, the wire-grid-formed surface or retardation film surface of the polarization-selective semi-transmissive reflector A functions as the transmission-reflection surface.

[0097] Furthermore, the first quarter-wave plate B and the second quarter-wave plate D have slow axes tilted at 45° with respect to the polarization transmission axis of the linear polarizer E. The first quarter-wave plate B and the second quarter-wave plate D are preferably arranged so that their respective slow axes are tilted at 90° with respect to each other. With this arrangement, when light passes through the first quarter-wave plate B and the second quarter-wave plate D, the wavelength dispersion characteristics of the wave plates are canceled out.

[0098] The half mirror C is a half mirror formed by, for example, a dielectric multilayer film or metal deposition, and functions as a transmission / reflection surface. The linear polarizer E is, for example, an absorptive linear polarizer.

[0099] Unpolarized light emitted from display surface ID is converted into linearly polarized light by linear polarizer E. This linearly polarized light is then converted into circularly polarized light by second quarter-wave plate D, and this circularly polarized light is incident on half mirror C. A portion of the light that has entered half mirror C is reflected by this and returns to second quarter-wave plate D as circularly polarized light in the opposite direction to when it entered.

[0100] The reverse circularly polarized light that returns to the second quarter-wave plate D returns to the linear polarizer E as linearly polarized light with a polarization direction perpendicular to that when it first passed through the linear polarizer E, and is absorbed by the linear polarizer E.

[0101] On the other hand, part of the light that reaches the half mirror C is transmitted through it and becomes linearly polarized light in the same polarization direction as when it passed through the linear polarizer E by the first quarter-wave plate B, and then enters the polarization-selective semi-transmissive reflector A. The polarization-selective semi-transmissive reflector A reflects linearly polarized light in the same polarization direction as when it passed through the linear polarizer E due to its polarization selectivity.

[0102] The light reflected by the polarization-selective semi-transmissive reflector A is converted by the first quarter-wave plate B into circularly polarized light with the same rotation as when it was first circularly polarized by the second quarter-wave plate D, and this circularly polarized light is incident on the half mirror C. The light reflected by the half mirror C becomes circularly polarized light with the opposite rotation to when it was incident, and is incident on the first quarter-wave plate B. As a result, the circularly polarized light is converted into linearly polarized light with a polarization direction perpendicular to when it first passed through the linear polarizer E, and is incident on the polarization-selective semi-transmissive reflector A.

[0103] Of the linearly polarized light incident on the polarization selective semi-transmissive reflector A, the linearly polarized light having a polarization direction perpendicular to that of the light passing through the linear polarizer E is transmitted through the polarization selective semi-transmissive reflector A and guided to the pupil plane SP.

[0104] Due to the above optical action, only the light from the display surface ID that passes through the half mirror HM, is reflected by the polarization-selective semi-transmissive reflecting element PBS, is reflected by the half mirror HM, and is transmitted through the polarization-selective semi-transmissive reflecting element PBS is guided to the pupil plane SP.

[0105] [Polarized Configuration 2] FIG. 22 shows Configuration 2, which uses polarized light. Configuration 2 also has two transmissive-reflective surfaces. However, the first transmissive-reflective surface HM1 located on the observation side is a half mirror (HM) C, and the second transmissive-reflective surface HM2 located on the display surface side is a polarization-selective semi-transmissive element (PBS) A. A first quarter-wave plate (QWP1) B is disposed between the polarization-selective semi-transmissive element PBS and the half mirror HM. A linear polarizer (POL) E and a second quarter-wave plate (QWP2) D are disposed between the half mirror HM and the pupil plane SP. The configuration and optical axis orientation of each polarizing element in Configuration 2 are the same as those in Configuration 1.

[0106] Unpolarized light emitted from display surface ID is incident on polarization-selective semi-transmissive reflector A. Of the unpolarized light, linearly polarized light with a polarization direction perpendicular to the transmission axis of linear polarizer E is transmitted through polarization-selective semi-transmissive reflector A. The light transmitted through polarization-selective semi-transmissive reflector A is converted into circularly polarized light by first quarter-wave plate B, and this circularly polarized light is incident on half mirror C.

[0107] A portion of the light incident on half mirror C is transmitted through it and enters second quarter-wave plate D. The circularly polarized light that entered second quarter-wave plate D is converted by second quarter-wave plate D into linearly polarized light with a polarization direction perpendicular to the transmission axis of linear polarizer E, which then enters linear polarizer E and absorbs it.

[0108] On the other hand, part of the circularly polarized light that is incident on the half mirror C is reflected by it, becomes reverse circularly polarized light, and returns to the first quarter-wave plate B. The reverse circularly polarized light that has returned to the first quarter-wave plate B is converted by the first quarter-wave plate B into linearly polarized light whose polarization direction is parallel to the transmission axis of the linear polarizer E, and this linearly polarized light enters the polarization-selective semi-transmissive reflector A. Due to the polarization selectivity of the polarization-selective semi-transmissive reflector A, the linearly polarized light whose polarization direction is parallel to the transmission axis of the linear polarizer E is reflected by the polarization-selective semi-transmissive reflector A.

[0109] The linearly polarized light reflected by the polarization-selective semi-transmissive reflector A is converted into circularly polarized light in the opposite direction to when it was circularly polarized by the first quarter-wave plate B, and then enters the half mirror C. The circularly polarized light that passes through the half mirror C enters the second quarter-wave plate D and is converted into linearly polarized light with a polarization direction parallel to the transmission axis of the linear polarizer E, and this linearly polarized light passes through the linear polarizer E and is guided to the pupil plane SP. Due to the above optical action, of the light from the display surface ID, only the light that passes through the polarization-selective semi-transmissive reflecting element PBS, is reflected by the half mirror HM, is reflected by the polarization-selective semi-transmissive reflecting element PBS, and passes through the half mirror HM is guided to the pupil plane SP. [Example]

[0110] An optical system according to a second embodiment will be described below, as shown in Fig. 5. After the description of the seventh embodiment, a second numerical embodiment corresponding to the second embodiment will be shown.

[0111] The optical system of this embodiment comprises, in order from the observation (pupil plane SP) side, a first lens L1, a second lens L2, and a third lens L3. The curved surface of the first lens L1 on the display surface side and the curved surface of the second lens L2 on the observation side are arranged adjacent to each other with an air gap between them, and a diffractive surface is formed on each curved surface.

[0112] A first transmission-reflection surface HM1 is provided on the observation-side surface of the third lens L3, and a second transmission-reflection surface HM2 is provided on the display-side surface of the third lens L3. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0113] Light emitted from display surface ID passes through second transmission-reflection surface HM2 and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the viewing side. After this, the light passes through third lens L3 again, passes through first transmission-reflection surface HM1, second lens L2, two diffractive surfaces, and first lens L1 in that order, and reaches pupil plane SP.

[0114] In this embodiment, the diffraction grating DG1 formed on the display surface side of the first lens L1 and the diffraction grating DG2 formed on the observation side surface of the second lens L2 have the configuration shown in Figure 3(b), similar to Example 1.

[0115] In Numerical Example 2, a cycloolefin-based thermoplastic resin material (Nd=1.544, vd=56.0) is used as the first material forming the diffraction grating DG1 (first lens L1). A polycarbonate-based thermoplastic resin material (Nd=1.681, vd=18.2) is used as the second material forming the diffraction grating DG2 (second lens L2). An air gap (Nd=1.0) is provided between the diffraction gratings DG1 and DG2.

[0116] The grating height d1 of diffraction grating DG1 is 7.50 μm, and the grating height d2 of diffraction grating DG2 is 5.14 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 22.0 μm. The distance da between the envelope curve connecting the grating vertices of diffraction grating DG1 and the envelope curve connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0117] Fig. 6 shows longitudinal aberrations when the pupil diameter is 4 mm, the eye relief is 12 mm, and the diopter is 0 diopter in Numerical Example 2. As shown in Fig. 6, various aberrations such as axial chromatic aberration, lateral chromatic aberration, and astigmatism are well corrected.

[0118] Fig. 7 shows the diffraction efficiency of the annular zones at the center (pitch 1044 µm) of the diffractive optical element of Numerical Example 2. As shown in Fig. 7, high diffraction efficiency is obtained over a wide range of the visible wavelength region. [Example]

[0119] An optical system according to a third embodiment will be described below with reference to Fig. 8. After the description of the seventh embodiment, a third numerical embodiment corresponding to the third embodiment will be shown.

[0120] In Examples 1 and 2, the first and second transmission-reflection surfaces HM1, HM1 were curved surfaces. In contrast, in this example, the first transmission-reflection surface HM1 is made flat, which makes it easier to form the first transmission-reflection surface HM1.

[0121] The optical system of this embodiment comprises, in order from the observation (pupil plane SP) side, a first lens L1, a second lens L2, and a third lens L3. The curved surface of the first lens L1 on the display surface side and the curved surface of the second lens L2 on the observation side are arranged adjacent to each other with an air gap between them, and a diffractive surface is formed on each curved surface.

[0122] A first transmission-reflection surface HM1 is provided on the display surface side of the second lens L2, and a second transmission-reflection surface HM2 is provided on the display surface side of the third lens L3. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0123] Light emitted from display surface ID passes through second transmission-reflection surface HM2 and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the viewing side. After this, the light passes through third lens L3 again, passes through first transmission-reflection surface HM1, second lens L2, two diffractive surfaces, and first lens L1 in that order, and reaches pupil plane SP.

[0124] In this embodiment, the diffraction grating DG1 formed on the display surface side of the first lens L1 and the diffraction grating DG2 formed on the observation side surface of the second lens L2 have the configuration shown in Figure 3(b), similar to Example 1.

[0125] In Numerical Example 3, a cycloolefin-based thermoplastic resin material (Nd=1.494, vd=57.4) is used as the first material forming the diffraction grating DG1 (first lens L1). A polycarbonate-based thermoplastic resin material (Nd=1.681, vd=18.2) is used as the second material forming the diffraction grating DG2 (second lens L2). An air gap (Nd=1.0) is provided between the diffraction gratings DG1 and DG2.

[0126] The grating height d1 of diffraction grating DG1 is 7.50 μm, and the grating height d2 of diffraction grating DG2 is 4.58 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 21.0 μm. The distance da between the envelope curve connecting the grating vertices of diffraction grating DG1 and the envelope curve connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0127] Fig. 9 shows longitudinal aberrations when the pupil diameter Φ is 4 mm, the eye relief is 12 mm, and the diopter is 0 diopter in Numerical Example 3. As shown in Fig. 9, various aberrations such as axial chromatic aberration, lateral chromatic aberration, and astigmatism are well corrected.

[0128] Fig. 10 shows the diffraction efficiency of the annular zones at the center (pitch 1021 µm) of the diffractive optical element of Numerical Example 3. As shown in Fig. 10, high diffraction efficiency is obtained over a wide range of the visible wavelength region. [Example]

[0129] The optical system of Example 4 shown in FIG. 11 will be described. After the description of Example 7, Numerical Example 4, which corresponds to Example 4, is shown. In Examples 1 to 3, the third lens L3 and the first and second transmission-reflection surfaces HM1 and HM2 are arranged closer to the display surface than the two diffractive surfaces. In contrast, this example has a different configuration.

[0130] The optical system of this embodiment has, in order from the observation (pupil plane SP) side, a third lens L3, a first lens L1, and a second lens L2. The curved surface of the first lens L1 on the display surface side and the curved surface of the second lens L2 on the observation side are arranged adjacent to each other with an air gap between them, and a diffractive surface is formed on each curved surface.

[0131] A first transmission-reflection surface HM1 is provided on the observation-side surface of the third lens L3, and a second transmission-reflection surface HM2 is provided on the observation-side surface of the first lens L1. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0132] Light emitted from display surface ID passes through second lens L2 and first lens L1 in that order, passes through second transmission-reflection surface HM2 and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the observation side. After this, the light passes through third lens L3 again, and further passes through first transmission-reflection surface HM1 to reach pupil plane SP.

[0133] Figure 13(a) shows cross sections of the first lens L1 and the second lens L2 in this embodiment. Figure 13(b) shows an enlarged view of the area surrounded by the dashed line in Figure 13(a). As shown in Figures 13(a) and 13(b), the image-side surface of the first lens L1 and the observation-side surface of the second lens L2 are curved surfaces with approximately the same curvature, and diffraction gratings DG1 and DG2 are formed on the respective curved surfaces.

[0134] The diffraction grating DG1 is made of the same material as the first lens L1 and is injection molded integrally with the lens surface of the first lens L1. The peripheral portion of the surface of the first lens L1 facing the display surface has a concave shape toward the display surface. The diffraction grating DG1 is composed of multiple inclined surfaces 13 and wall surfaces 14 between adjacent light-emitting surface portions 13. The inclined surfaces 13 of the diffraction grating DG1 act as a diffractive surface having negative power with respect to an envelope 12 connecting the grating vertices of the diffraction grating DG1.

[0135] The diffraction grating DG2 is made of the same material as the second lens L2 and is injection molded integrally with the lens surface of the second lens L2. The diffraction grating DG2 is composed of a plurality of inclined surfaces 23 and wall surfaces 24 between adjacent light-emitting surfaces 23. The inclined surfaces 23 of the diffraction grating DG2 act as a diffractive surface having positive power with respect to an envelope 21 connecting the grating vertices of the diffraction grating DG2.

[0136] The diffraction gratings DG1 and DG2 are disposed close to each other with an air layer 30 interposed therebetween, and the diffraction gratings DG1, the air layer 30 and the diffraction grating DG2 are configured to work together to obtain the required phase difference.

[0137] In the optical system of this embodiment, as shown by light ray 31 in Figure 13(b), a light beam is incident at an angle going from bottom to top in the figure. In this case, it is preferable to set the diffraction power generated by the diffraction surface of diffraction grating DG1 to negative and the diffraction power generated by the diffraction surface of diffraction grating DG2 to positive. This allows the angle between the wall surface 14 of diffraction grating DG1 and the wall surface 24 of diffraction grating DG2 to be aligned with the direction of incident light beam 31, while improving the mold releasability during molding of each diffraction grating.

[0138] In Numerical Example 4, a polycarbonate-based thermoplastic resin material (Nd=1.681, vd=18.2) is used as the first material forming the diffraction grating DG1 (first lens L1). A cycloolefin-based thermoplastic resin material (Nd=1.544, vd=56.0) is used as the second material forming the diffraction grating DG2 (second lens L2). An air gap (Nd=1.0) is provided between the diffraction gratings DG1 and DG2.

[0139] The grating height d1 of diffraction grating DG1 is 5.37 μm, and the grating height d2 of diffraction grating DG2 is 7.80 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 22.0 μm. The distance da between envelope curve 12 connecting the grating vertices of diffraction grating DG1 and envelope curve 21 connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0140] Fig. 12 shows longitudinal aberrations when the pupil diameter Φ is 4 mm, the eye relief is 12 mm, and the diopter is 0 diopter in Numerical Example 4. As shown in Fig. 12, various aberrations such as axial chromatic aberration, lateral chromatic aberration, and astigmatism are well corrected.

[0141] Fig. 14 shows the diffraction efficiency of the annular zones in the center (pitch 922 µm) of the diffractive optical element of Numerical Example 4. As shown in Fig. 14, high diffraction efficiency is obtained over a wide range of the visible wavelength region. [Example]

[0142] An optical system of Example 5 shown in Fig. 15 will be described. After the description of Example 7, Numerical Example 5 corresponding to Example 5 will be shown.

[0143] The optical system of this embodiment also has, in order from the observation (pupil plane SP) side, a third lens L3, a first lens L1, and a second lens L2, similar to Example 4. The curved surface of the first lens L1 on the display surface side and the curved surface of the second lens L2 on the observation side are arranged adjacent to each other with an air gap between them, and a diffractive surface is formed on each curved surface.

[0144] A first transmission-reflection surface HM1 is provided on the observation-side surface of the third lens L3, and a second transmission-reflection surface HM2 is provided on the observation-side surface of the first lens L1. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0145] Light emitted from display surface ID passes through second lens L2 and first lens L1 in that order, passes through second transmission-reflection surface HM2 and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the observation side. After this, the light passes through third lens L3 again, and further passes through first transmission-reflection surface HM1 to reach pupil plane SP.

[0146] In this embodiment, the diffraction grating DG1 formed on the display surface side of the first lens L1 and the diffraction grating DG2 formed on the observation side surface of the second lens L2 have the configuration shown in Figure 13(b), similar to Example 4.

[0147] In Numerical Example 5, a polyester-based thermoplastic resin material (Nd=1.641, vd=22.3) is used as the first material forming the diffraction grating DG1 (first lens L1). A cycloolefin-based thermoplastic resin material (Nd=1.530, vd=55.5) is used as the second material forming the diffraction grating DG2 (second lens L2). An air gap (Nd=1.0) is provided between the diffraction gratings DG1 and DG2.

[0148] The grating height d1 of diffraction grating DG1 is 6.29 μm, and the grating height d2 of diffraction grating DG2 is 8.70 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 22.0 μm. The distance da between the envelope curve connecting the grating vertices of diffraction grating DG1 and the envelope curve connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0149] Fig. 16 shows longitudinal aberrations when the pupil diameter Φ is 4 mm, the eye relief is 12 mm, and the diopter is 0 diopter in Numerical Example 5. As shown in Fig. 16, various aberrations such as axial chromatic aberration, chromatic aberration of magnification, and astigmatism are well corrected.

[0150] Fig. 17 shows the diffraction efficiency of the annular zones in the center (pitch 636 µm) of the diffractive optical element of Numerical Example 5. As shown in Fig. 17, high diffraction efficiency is obtained over a wide range of the visible wavelength region. [Example]

[0151] An optical system according to a sixth embodiment will be described below with reference to Fig. 18. After the description of the seventh embodiment, a sixth numerical embodiment corresponding to the sixth embodiment will be shown.

[0152] The optical system of this embodiment has, in order from the observation (pupil plane SP) side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. The curved surface of the first lens L1 on the display surface side and the curved surface of the second lens L2 on the observation side are arranged adjacent to each other with an air gap between them, and a diffractive surface is formed on each curved surface.

[0153] A first transmission-reflection surface HM1 is provided on the observation-side surface of the third lens L3, and a second transmission-reflection surface HM2 is provided on the display-side surface of the third lens L3. A quarter-wave plate is disposed between the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2.

[0154] Light emitted from display surface ID passes through fourth lens L4, second transmission-reflection surface HM2, and third lens L3, is reflected by first transmission-reflection surface HM1 toward the display surface, passes through third lens L3 again, and is reflected by second transmission-reflection surface HM2 toward the viewing side. After this, the light passes through third lens L3 again, passes through first transmission-reflection surface HM1, second lens L2, two diffractive surfaces, and first lens L1 in that order, and reaches pupil plane SP.

[0155] In this embodiment, the diffraction grating DG1 formed on the display surface side of the first lens L1 and the diffraction grating DG2 formed on the observation side surface of the second lens L2 have the configuration shown in Fig. 3(b) as in Example 1. Furthermore, in this embodiment (Numerical Example 6), the same materials as in Example 2 (Numerical Example 2) are used.

[0156] The grating height d1 of diffraction grating DG1 is 7.50 μm, and the grating height d2 of diffraction grating DG2 is 5.14 μm. The minimum pitch between the unit gratings of diffraction gratings DG1 and DG2 is 27.4 μm. The distance da between the envelope curve connecting the grating vertices of diffraction grating DG1 and the envelope curve connecting the grating vertices of diffraction grating DG2 is 1.50 μm.

[0157] Fig. 19 shows longitudinal aberration when the pupil diameter Φ is 4 mm, the eye relief is 12 mm, and the diopter is 0 diopter in Numerical Example 6. As shown in Fig. 19, various aberrations such as axial chromatic aberration, lateral chromatic aberration, and astigmatism are well corrected.

[0158] The diffraction efficiency of the diffractive optical element of Numerical Example 6 is the same as the diffraction efficiency shown in FIG. 7 in Example 2, and high diffraction efficiency is obtained over a wide wavelength range in the visible range.

[0159] Although the optical systems of Examples 1 to 6 described above are configured with three or four lenses, the number of lenses is not limited to these. For example, by adding a thin replica-molded lens on the lens surface made of injection molding material, an optical system with even better aberration correction can be obtained.

[0160] The optical systems of Examples 1 to 6 have two diffractive surfaces, and the combination of these two diffractive surfaces produces the required phase difference. However, an optical system may have a diffractive surface other than the two diffractive surfaces, and by having three or more diffractive surfaces, an optical system in which chromatic aberration can be corrected even better can be obtained. [Example]

[0161] 20 shows an enlarged view of a portion of the diffractive optical element used in the optical system of Example 7, which corresponds to the portion surrounded by the dashed line in FIG. 13(a). The diffractive optical element in this example is a modified version of the diffractive optical element used in Examples 4 and 5.

[0162] In the diffractive optical elements in Examples 1 to 6, the first lens L1 and the diffraction grating DG1 are made of the same material, and the second lens L2 and the diffraction grating DG2 are made of the same material, so that the lens and the diffraction grating are integrally molded. In contrast, in this example, the lens and the diffraction grating are formed separately and then integrated.

[0163] 20, the second lens L2 and the diffraction grating DG2 are formed separately and then integrated by being bonded together. The materials of the second lens L2 and the diffraction grating DG2 may be the same or different.

[0164] By forming the second lens L2 and the diffraction grating DG2 separately in this way, the degree of freedom in selecting the material for the diffraction grating DG2 is increased. As a result, it becomes easier to obtain high diffraction efficiency. In addition, since the total thickness of the diffraction grating DG2 can be reduced, the molding stability of the diffraction grating is improved, making it easier to obtain a highly accurate diffraction grating shape. Specifically, since the resin fills the tips of the grating more easily during injection molding, etc., it becomes easier to obtain high diffraction efficiency.

[0165] The first lens L1 and the diffraction grating DG1 may be molded separately and then integrated. [Example]

[0166] The diffractive optical element in this Example 8 is a modified version of the diffractive optical element used in Example 4. Fig. 24 shows an enlarged view of a portion of the diffractive optical element used in the optical system of Example 8, which corresponds to the portion surrounded by the dashed line in Fig. 13(a).

[0167] In the diffractive optical elements in Examples 1 to 6, an air layer (Nd=1.0) is provided between the diffraction gratings DG1 and DG2. In contrast, in the present examples, the material layer 40 that contacts the diffraction grating DG1 via the diffractive surface 13 is made of a resin material. Diffraction grating DG1 is made of the same material as first lens L1 and is formed integrally with the lens surface of first lens L1 by injection molding, and is composed of a material layer 40 formed by molding a different material layer on the surface of the diffraction grating DG1. Diffraction grating DG1 acts as a diffractive surface having negative power with respect to envelope 12 connecting the grating vertices of diffraction grating DG1.

[0168] The diffraction grating DG2 is made of the same material as the second lens L2 and is injection molded integrally with the lens surface of the second lens L2. The diffraction grating DG2 is composed of a plurality of inclined surfaces 23 and wall surfaces 24 between adjacent light-emitting surfaces 23. The inclined surfaces 23 of the diffraction grating DG2 act as a diffractive surface having positive power with respect to an envelope 21 connecting the grating vertices of the diffraction grating DG2.

[0169] The diffraction gratings DG1 and DG2 are disposed close to each other with an air layer 30 interposed therebetween, and the diffraction gratings DG1, the air layer 30 and the diffraction grating DG2 are configured to work together to obtain the required phase difference.

[0170] In the optical system of this embodiment, as shown by light ray 31 in Figure 24, a light beam is incident at an angle from bottom to top in the figure. In this case, it is preferable to set the diffraction power generated by the diffraction surface of diffraction grating DG1 to negative and the diffraction power generated by the diffraction surface of diffraction grating DG2 to positive. This allows the angle between the wall surface 14 of diffraction grating DG1 and the wall surface 24 of diffraction grating DG2 to be aligned with the direction of incident light beam 31, while improving the mold releasability during molding of each diffraction grating.

[0171] In Numerical Example 8, a polycarbonate-based thermoplastic resin material (Nd=1.681, vd=18.2) is used as the first material forming the diffraction grating DG1 (first lens L1).

[0172] An acrylic ultraviolet curing resin (Nd=1.524, νd=51.6) is used as a material layer that contacts the diffraction grating DG1 via the diffractive surface 13.

[0173] The second material used to form the diffraction grating DG2 (second lens L2) is a cycloolefin-based thermoplastic resin material (Nd=1.544, νd=56.0). An air gap (Nd=1.0) is provided between the diffraction gratings DG1 and DG2.

[0174] The grating height d1 of the diffraction grating DG1 is 5.98 μm, and the grating height d2 of the diffraction grating DG2 is 2.80 μm, and the total height of the grating height d1 and the grating height d2 can be reduced compared to the diffraction grating of the fourth embodiment.

[0175] The minimum pitch between the unit cells of the diffraction gratings DG1 and DG2 is 22.0 μm. The distance between the envelope 12 connecting the grating vertices of the diffraction grating DG1 and the interface 41 of the resin material layer 40 is 4.0 μm.

[0176] The distance da between the interface 41 of the resin material layer 40 and the envelope 21 connecting the grating vertices of the diffraction grating DG2 is 1.50 μm.

[0177] As in this embodiment, by using a diffraction grating consisting of two material layers without using an air layer in either the diffraction grating DG1 or the diffraction grating DG2, the total height of the entire grating can be reduced, which is preferable because it increases the forming stability of the diffraction grating and makes it possible to suppress the generation of unnecessary light generated in the grating wall surface portions 14 and 24.

[0178] Fig. 25 shows the diffraction efficiency of the annular zones in the center (pitch 922 µm) of the diffractive optical element of Numerical Example 8. As shown in Fig. 25, high diffraction efficiency is obtained over a wide range of the visible wavelength region.

[0179] Numerical Examples 1 to 8 are shown below. In each numerical example, the surface number i indicates the order of the surface when counted from the observation side. (Aperture) is the pupil surface SP. r is the radius of curvature (mm) of the ith surface from the observation side, d is the lens thickness or air gap (mm) on the optical axis between the ith and (i+1)th surfaces, and nd is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. νd is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces, and is defined by the above-mentioned formula (a). As mentioned above, the effective diameter is the diameter of the area through which light rays that contribute to image formation at each surface pass.

[0180] The focal length f (mm) is the value when the lens is focused on an object at infinity. BF is the back focus, which is the length on the optical axis from the surface in the optical system closest to the display surface to the display surface. The total lens length is the length on the optical axis from the surface in the optical system closest to the observation side (surface 1) to the display surface. EPD is the pupil diameter (mm).

[0181] The "*" next to the surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the above-mentioned formula (e). The "e±Z" in the conic constant and aspherical coefficient is "×10 ±Z " means.

[0182] The phase shape of each diffractive surface is expressed by the above-mentioned formula (g). Furthermore, the focal length fdo generated by the diffraction grating for the wavelength λ and the diffraction order m can be expressed as the following formula (j) using the lowest-order phase coefficient C2.

[0183] fdo(λ,m)=-1 / (2C2mλ / λ0) (j) In each numerical example, the diffraction order m of each diffraction grating is 1, and the design wavelength λ 0 of the diffraction grating is the same as the design wavelength λ of the optical system.

[0184] Furthermore, after Numerical Example 6, the numerical values ​​relating to the formulas (1) to (8) are summarized in Table 1. The optical systems of each Numerical Example satisfy all of the conditions of the formulas (1) to (8).

[0185] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 17.000 6.00 2* 444.0262 4.497 1.54400 56.0 37.13 3 (diffraction) -82.0909 3.500 1.67100 19.2 39.12 4* -60.3386 0.300 43.66 5* -71.9328 6.781 1.54400 56.0 45.41 6* -44.6919 -6.781 1.54400 56.0 48.83 7* -71.9328 -0.300 48.89 8* -60.3386 0.300 48.84 9* -71.9328 6.781 1.54400 56.0 48.50 10* -44.6919 9.434 47.22 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4=-1.63018e-06 A6= 1.44922e-08 A8=-4.23843e-11 3rd page K = 0.00000e+00 A4=-1.57483e-06 Surface 3 (diffractive surface) C 2=-8.08446e-04 C 4=-4.87371e-07 C 6= 2.03970e-09 Side 4 K = 0.00000e+00 A4= 1.02974e-05 A6=-3.14829e-09 A8= 2.96426e-12 5th page K = 0.00000e+00 A4= 7.86098e-06 Page 6 K = 0.00000e+00 A4= 2.52551e-06 A6= 3.65413e-09 A8= 1.19748e-12 Side 7 K = 0.00000e+00 A4= 7.86098e-06 Side 8 K = 0.00000e+00 A4= 1.02974e-05 A6=-3.14829e-09 A8= 2.96426e-12 9th page K = 0.00000e+00 A4= 7.86098e-06 Side 10 K = 0.00000e+00 A4= 2.52551e-06 A6= 3.65413e-09 A8= 1.19748e-12 Focal length 21.500 EPD 6.0 Half angle of view (°) 47.000 Lens length 55.674 BF 9.434 (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 12.000 4.00 2* 86.1298 5.000 1.54400 56.0 30.44 3 (diffraction) -43.0539 3.000 1.68100 18.2 32.76 4* -61.1284 0.500 37.80 5* -59.5655 6.382 1.54400 56.0 39.95 6* -34.9728 -6.382 1.54400 56.0 43.01 7* -59.5655 6.382 1.54400 56.0 42.77 8* -34.9728 5.010 41.41 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4=-1.12121e-05 A6= 7.30851e-08 A8=-3.62353e-10 3rd page K = 0.00000e+00 A4= 7.73152e-06 Surface 3 (diffractive surface) C 2=-5.36232e-04 C 4=-2.04774e-06 C 6= 3.81652e-09 Side 4 K = 0.00000e+00 A4= 6.04599e-06 A6= 2.13242e-08 A8=-2.35387e-11 5th page K = 0.00000e+00 A4= 1.13108e-05 A6= 1.78099e-09 Page 6 K = 0.00000e+00 A4= 3.65389e-06 A6= 8.46500e-09 A8= 4.42130e-12 Side 7 K = 0.00000e+00 A4= 1.13108e-05 A6= 1.78099e-09 Side 8 K = 0.00000e+00 A4= 3.65389e-06 A6= 8.46500e-09 A8= 4.42130e-12 Focal length 15.475 EPD 4.00 Half angle of view (°) 50.000 Lens total length 44.657 BF 5.010 (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 11.998 4.00 2 61.5379 4.500 1.49350 57.4 33.67 3 (diffraction) 112.8060 3.000 1.68100 18.2 35.99 4 ∞ 0.500 39.44 5 238.8355 7.938 1.54400 56.0 42.57 6* -66.7708 -7.938 1.54400 56.0 45.45 7 238.8355 -0.500 44.01 8 ∞ 0.500 42.60 9 238.8355 7.938 1.54400 56.0 41.30 10* -66.7708 3.987 38.61 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4=-3.97783e-06 A6=-2.10683e-09 A8=-3.28975e-11 3rd page K = 0.00000e+00 A4=-1.91293e-05 Surface 3 (diffractive surface) C 2=-1.46465e-03 C 4= 1.56113e-06 C 6=-1.02946e-09 Page 6 K = 0.00000e+00 A4=-5.49541e-08 A6=-5.50767e-11 A8= 3.12728e-13 Side 10 K = 0.00000e+00 A4=-5.49541e-08 A6=-5.50767e-11 A8= 3.12728e-13 Focal length 16.815 EPD 4.00 Half angle of view (°) 50.000 Lens total length 48.799 BF 3.987 (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 12.000 4.00 2* 450.8980 4.920 1.54400 54.0 31.31 3* -39.0645 0.453 33.44 4* -78.8757 -0.453 35.57 5* -39.0645 -4.920 1.54400 54.0 36.83 6* 450.8980 4.920 1.54400 54.0 38.06 7* -39.0645 0.453 37.25 8* -78.8757 1.988 1.68100 18.2 36.65 9 (Diffraction) 60.2310 6.243 1.54400 56.0 35.53 10* -77.4925 3.987 34.95 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4= 3.76885e-06 A6= 1.99451e-09 A8= 3.14242e-11 3rd page K = 0.00000e+00 A4= 1.05898e-05 A6=-1.40522e-09 A8= 1.11893e-10 Side 4 K = 0.00000e+00 A4= 9.14291e-07 A6= 1.16943e-08 5th page K = 0.00000e+00 A4= 1.05898e-05 A6=-1.40522e-09 A8= 1.11893e-10 Page 6 K = 0.00000e+00 A4= 3.76885e-06 A6= 1.99451e-09 A8= 3.14242e-11 Side 7 K = 0.00000e+00 A4= 1.05898e-05 A6=-1.40522e-09 A8= 1.11893e-10 Side 8 K = 0.00000e+00 A4= 9.14291e-07 A6= 1.16943e-08 9th page K = 0.00000e+00 A4=-1.68884e-05 Surface 9 (diffractive surface) C 2=-6.90599e-04 C 4=-1.13076e-06 C 6= 2.23600e-09 Side 10 K = 0.00000e+00 A4=-3.05170e-05 A6= 3.81798e-08 Focal length 15.623 EPD 4.00 Angle of view 50,000 Lens total length 40.337 BF 3.987 (Numerical Example 5) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 12.000 4.00 2* 74.8986 5.139 1.54400 54.0 35.80 3* -76.7438 0.442 37.36 4 ∞ -0.442 39.00 5* -76.7438 -5.139 1.54400 54.0 40.28 6* 74.8986 5.139 1.54400 54.0 41.73 7* -76.7438 0.442 40.61 8 ∞ 2.444 1.64100 22.3 39.82 9 (Diffraction) 53.5650 8.008 1.53000 55.5 37.02 10* 123.7150 3.989 34.68 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4= 5.67079e-06 A6=-1.09139e-08 A8= 2.08067e-11 3rd page K = 0.00000e+00 A4= 1.79262e-05 A6=-3.22196e-08 A8= 6.53950e-11 5th page K = 0.00000e+00 A4= 1.79262e-05 A6=-3.22196e-08 A8= 6.53950e-11 Page 6 K = 0.00000e+00 A4= 5.67079e-06 A6=-1.09139e-08 A8= 2.08067e-11 Side 7 K = 0.00000e+00 A4= 1.79262e-05 A6=-3.22196e-08 A8= 6.53950e-11 9th page K = 0.00000e+00 A4=-4.07176e-06 Surface 9 (diffractive surface) C 2=-1.45476e-03 C 4= 1.13133e-06 C 6= 5.37718e-10 Side 10 K = 0.00000e+00 A4=-4.76831e-05 A6= 4.99682e-08 Focal length 16.069 EPD 4.00 Half angle of view (°) 50.000 Lens total length 43.185 BF 3.989 (Numerical Example 6) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 (Aperture) ∞ 12.000 4.00 2* 89.0086 5.000 1.54400 56.0 30.12 3 (diffraction) -36.1351 3.000 1.68100 18.2 32.38 4* -45.4384 0.500 36.40 5* -44.9519 5.156 1.54400 56.0 38.40 6* -30.3984 -5.156 1.54400 56.0 40.48 7* -44.9519 5.156 1.54400 56.0 39.85 8* -30.3984 0.100 39.05 9* -37.5728 2.000 1.68100 18.2 36.08 10* -52.0412 5.007 35.09 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A4=-1.24508e-05 A6= 6.62620e-08 A8=-3.15670e-10 3rd page K = 0.00000e+00 A4= 1.61455e-05 Surface 3 (diffractive surface) C 2=-3.33417e-04 C 4=-2.99473e-06 C 6= 6.45085e-09 Side 4 K = 0.00000e+00 A4= 6.61676e-06 A6= 9.33064e-09 A8= 2.91436e-11 5th page K = 0.00000e+00 A4= 1.33910e-05 A6= 3.96348e-09 Page 6 K = 0.00000e+00 A4= 4.78494e-06 A6= 1.20650e-08 A8= 5.03536e-12 Side 7 K = 0.00000e+00 A4= 1.33910e-05 A6= 3.96348e-09 Side 8 K = 0.00000e+00 A4= 4.78494e-06 A6= 1.20650e-08 A8= 5.03536e-12 9th page K = 0.00000e+00 A4= 4.88072e-06 Side 10 K = 0.00000e+00 A4=-7.80829e-07 Focal length 15.439 EPD 4.00 Half angle of view (°) 50.000 Lens total length 43.076 BF 5.007

[0186] [Table 1]

[0187] [Display device] 23 shows a head-mounted display (HMD) as a display device using the optical systems of Examples 1 to 8. The HMD is worn on the head (in front of the eyes) of the observer by means of a wearing gear (not shown).

[0188] The HMD has display elements RID and LID for the right and left eyes, a right-eye optical system ROS that guides display light from the right-eye display element RID to the observer's right eye, and a left-eye optical system LOS that guides display light from the left-eye display element LID to the observer's left eye.

[0189] By using the optical systems shown in Examples 1 to 8 as the right-eye and left-eye optical systems ROS and LOS, an HMD can be realized that allows bright images to be viewed over the entire field of view. Note that distortion and chromatic aberration of magnification may be partially reduced by electrical correction processing of the original image displayed on the display element.

[0190] The above embodiment includes the following configurations.

[0191] (Configuration 1) An optical system that guides light from a display surface to an observation side, A first lens; a second lens disposed closer to the display surface than the first lens; a third lens having a positive refractive power, which is disposed closer to the observation side than the first lens or closer to the display surface side than the second lens; a display surface side surface of the first lens includes a first diffractive surface, and an observation side surface of the second lens includes a second diffractive surface; the first diffractive surface and the second diffractive surface are adjacent to each other, An optical system comprising a first transmissive-reflective surface and a second transmissive-reflective surface, which are disposed at positions different from the display surface side surface of the first lens and the observation side surface of the second lens. (Configuration 2) The optical system described in configuration 1, wherein the display surface side surface of the first lens and the observation side surface of the second lens, on which the first and second diffractive surfaces are respectively formed, are curved surfaces. (Configuration 3) 3. The optical system according to configuration 1 or 2, wherein the first transmission-reflection surface and the second transmission-reflection surface are both disposed closer to the observation surface or the display surface than the first and second diffraction surfaces. (Configuration 4) 4. The optical system according to any one of configurations 1 to 3, wherein at least one of the first transmission-reflection surface and the second transmission-reflection surface is a flat surface. (Configuration 5) 5. The optical system according to any one of configurations 1 to 4, wherein the sign of the focal length f1e of the first lens, which is calculated from the radius of curvature R11 of the effective area on the observation-side surface of the first lens and the radius of curvature R12 of the effective area on the display-side surface of the first lens, is the same as the sign of the diffractive power generated by the first diffractive surface. (Configuration 6) The optical system described in any one of configurations 1 to 5, characterized in that the sign of the focal length f2e of the second lens, which is calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens, and the sign of the diffractive power generated by the second diffractive surface are mutually the same. (Configuration 7) 7. The optical system of any one of configurations 1 to 6, further comprising a layer between the first diffractive surface and the second diffractive surface, the layer having a refractive index at the incident wavelength lower than the refractive index of the first and second lenses at the incident wavelength. (Configuration 8) The focal length of the first lens is determined from the radius of curvature R11 of the effective area on the observation side surface of the first lens and the radius of curvature R12 of the effective area on the display surface side surface of the first lens, and is f1e (mm). The focal length of the second lens calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens is f2e (mm), When the Abbe number of the diffraction grating on the first diffractive surface based on the incident wavelength is ν1 and the Abbe number of the diffraction grating on the second diffractive surface based on the incident wavelength is ν2, 0<1000×(1 / f1e-1 / f2e) / (ν1-ν2) 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) When the Abbe number based on the incident wavelength of a diffraction grating on a diffractive surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength is denoted by νH, 35≦νH≦70 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) When the Abbe number based on the incident wavelength of a diffraction grating on a diffractive surface formed on one of the first and second lenses having a smaller Abbe number based on the incident wavelength is νL, 10≦νL≦50 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) Let vH be the Abbe number based on the incident wavelength of a diffraction grating on a diffraction surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength, and vH be the Abbe number based on the incident wavelength of a diffraction grating on a diffraction surface formed on the lens having a smaller Abbe number, 0.010≦|1 / νH-1 / νL|≦0.060 11. The optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) When the grating height of the diffraction grating on the diffraction surface formed on the lens having the larger Abbe number based on the incident wavelength out of the first and second diffraction surfaces is dH (μm), and the grating height of the diffraction grating on the diffraction surface formed on the lens having the smaller Abbe number is dL (μm), dL <dH 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) When a refractive index difference at the incident wavelength between a diffraction grating on a diffraction surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength and a material layer that contacts the diffraction grating via the diffraction surface is defined as ΔNH, and a refractive index difference at the incident wavelength between a diffraction grating on a diffraction surface formed on the lens having a smaller Abbe number and a material layer that contacts the diffraction grating via the diffraction surface is defined as ΔNL, 0.6≦(ΔNH×dH) / (ΔNL×dL)≦1.7 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) 0.45≦ΔNH×dH-ΔNL×dL≦0.75 14. The optical system according to configuration 13, wherein the following condition is satisfied: (Configuration 15) The focal length of the first lens is determined from the radius of curvature R11 of the effective area on the observation side surface of the first lens and the radius of curvature R12 of the effective area on the display surface side surface of the first lens, and is f1e (mm). The focal length of the second lens calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens is f2e (mm), When the diffraction power generated by the first and second diffractive surfaces is Pdo, 4.0≦|(1 / f1e-1 / f2e) / Pdo|≦40.0 15. The optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) When the grating height of the diffraction grating on the first diffraction surface is dH, the grating height of the diffraction grating on the second diffraction surface is dL, and the minimum pitch of the diffraction gratings on the first and second diffraction surfaces is Pmin, 0.8≦Pmin / (dH+dL)≦4.0 16. The optical system according to any one of configurations 1 to 15, wherein the following condition is satisfied: (Configuration 17) 17. The optical system according to any one of configurations 1 to 16, wherein at least one of the first and second diffractive surfaces is made of a material containing a thermoplastic resin. (Configuration 18) 18. The optical system according to any one of configurations 1 to 17, wherein a transmission-reflection element having polarization selectivity is provided on only one of the first transmission-reflection surface and the second transmission-reflection surface. (Configuration 19) 19. The optical system described in any one of configurations 1 to 18, wherein the first transmissive-reflective surface and the second transmissive-reflective surface are provided on any of the first, second, and third lenses. (Configuration 20) 20. The optical system according to configuration 19, wherein the first transmissive-reflective surface and the second transmissive-reflective surface are provided on the second and third lenses. (Configuration 21) a display element including the display surface; A display device comprising the optical system according to any one of configurations 1 to 20.

[0192] 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]

[0193] HM1 1st transmissive reflective surface HM2 2nd transmissive reflective surface L1 First lens L2 Second lens L3 Third lens SP pupil plane ID display surface

Claims

1. An optical system that guides light from a display surface to an observation side, A first lens; a second lens disposed closer to the display surface than the first lens; a third lens having a positive refractive power, which is disposed closer to the observation side than the first lens or closer to the display surface side than the second lens; a display surface side surface of the first lens includes a first diffractive surface, and an observation side surface of the second lens includes a second diffractive surface; the first diffractive surface and the second diffractive surface are adjacent to each other, An optical system comprising: a first transmissive-reflective surface and a second transmissive-reflective surface, the first lens and the second lens being disposed at positions different from each other on a display surface side and an observation surface side of the second lens.

2. 2. The optical system according to claim 1, wherein the display surface side surface of the first lens and the observation side surface of the second lens, on which the first diffractive surface and the second diffractive surface are formed, are curved surfaces.

3. 2. The optical system according to claim 1, wherein both the first transmissive-reflective surface and the second transmissive-reflective surface are disposed closer to the viewing surface or the display surface than the first and second diffractive surfaces.

4. 2. The optical system according to claim 1, wherein at least one of the first transmissive-reflective surface and the second transmissive-reflective surface is a flat surface.

5. 2. The optical system according to claim 1, wherein the sign of the focal length f1e of the first lens, which is calculated from the radius of curvature R11 of the effective area on the observation-side surface of the first lens and the radius of curvature R12 of the effective area on the display-side surface of the first lens, is the same as the sign of the diffractive power generated by the first diffractive surface.

6. The optical system described in claim 1, characterized in that the sign of the focal length f2e of the second lens, which is calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens, and the sign of the diffraction power generated by the second diffraction surface are mutually identical.

7. 2. The optical system according to claim 1, further comprising a layer between the first diffractive surface and the second diffractive surface, the layer having a refractive index at the incident wavelength lower than the refractive indexes of the first and second lenses at the incident wavelength.

8. The focal length of the first lens calculated from the radius of curvature R11 of the effective area on the observation side surface of the first lens and the radius of curvature R12 of the effective area on the display surface side surface of the first lens is f1e (mm), The focal length of the second lens calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens is f2e (mm), When the Abbe number of the diffraction grating on the first diffractive surface based on the incident wavelength is ν1, and the Abbe number of the diffraction grating on the second diffractive surface based on the incident wavelength is ν2, 0<1000×(1 / f1e-1 / f2e) / (ν1-ν2) 2. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the Abbe number based on the incident wavelength of a diffraction grating on a diffractive surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength is denoted by νH, 35≦νH≦70 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the Abbe number based on the incident wavelength of a diffraction grating on a diffractive surface formed on one of the first and second lenses having a smaller Abbe number based on the incident wavelength is νL, 10≦νL≦50 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the Abbe number based on the incident wavelength of a diffraction grating on a diffraction surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength is defined as νH, and the Abbe number based on the incident wavelength of a diffraction grating on a diffraction surface formed on the lens having a smaller Abbe number is defined as νH, 0.010≦|1 / νH-1 / νL|≦0.060 2. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the grating height of the diffraction grating on the diffraction surface formed on the lens having the larger Abbe number based on the incident wavelength out of the first and second diffraction surfaces is dH (μm), and the grating height of the diffraction grating on the diffraction surface formed on the lens having the smaller Abbe number is dL (μm), dL<dH 2. The optical system according to claim 1, wherein the following condition is satisfied:

13. When a refractive index difference at the incident wavelength between a diffraction grating on a diffraction surface formed on one of the first and second lenses having a larger Abbe number based on the incident wavelength and a material layer that contacts the diffraction grating via the diffraction surface is defined as ΔNH, and a refractive index difference at the incident wavelength between a diffraction grating on a diffraction surface formed on the lens having a smaller Abbe number and a material layer that contacts the diffraction grating via the diffraction surface is defined as ΔNL, 0.6≦(ΔNH×dH) / (ΔNL×dL)≦1.7 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied:

14. 0.45≦ΔNH×dH−ΔNL×dL≦0.75 14. The optical system according to claim 13, wherein the following condition is satisfied:

15. The focal length of the first lens calculated from the radius of curvature R11 of the effective area on the observation side surface of the first lens and the radius of curvature R12 of the effective area on the display surface side surface of the first lens is f1e (mm), The focal length of the second lens calculated from the radius of curvature R21 of the effective area on the observation side surface of the second lens and the radius of curvature R22 of the effective area on the display surface side surface of the second lens is f2e (mm), When the diffraction power generated by the first and second diffractive surfaces is Pdo, 4.0≦|(1 / f1e-1 / f2e) / Pdo|≦40.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

16. When the grating height of the diffraction grating on the first diffraction surface is dH, the grating height of the diffraction grating on the second diffraction surface is dL, and the minimum pitch of the diffraction gratings of the first and second lenses is Pmin, 0.8≦Pmin / (dH+dL)≦4.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

17. 2. The optical system according to claim 1, wherein at least one of the first and second diffractive surfaces is made of a material containing a thermoplastic resin.

18. 2. The optical system according to claim 1, wherein a transmission / reflection element having polarization selectivity is provided on only one of the first transmission / reflection surface and the second transmission / reflection surface.

19. 2. The optical system according to claim 1, wherein the first transmission-reflection surface and the second transmission-reflection surface are provided on any one of the first, second and third lenses.

20. 20. The optical system according to claim 19, wherein the first transmissive-reflective surface and the second transmissive-reflective surface are provided on the second and third lenses.

21. a display element including the display surface; A display device comprising the optical system according to any one of claims 1 to 20.

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