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US-12619081-B2 - Optical system and display apparatus

US12619081B2US 12619081 B2US12619081 B2US 12619081B2US-12619081-B2

Abstract

An optical system guides a light beam from an image display element to an exit pupil and includes, in order from an exit pupil side to an image display element side, a first transmissive reflective surface, a second transmissive reflective surface, and an optical element disposed closer to the exit pupil than the first transmissive reflective surface. The optical element includes, in order from the exit pupil side to the image display element side, a first optical element made of a first optical material and a second optical element made of a second optical material different from the first optical material. The first and second optical elements are cemented together, and a diffraction grating is formed on a cemented surface. The diffraction grating includes a grating surface and a grating wall surface, the grating surface having a convex shape facing the image display element side. A predetermined inequality is satisfied.

Inventors

  • Yu MIYAJIMA
  • Yuma Kobayashi

Assignees

  • CANON KABUSHIKI KAISHA

Dates

Publication Date
20260505
Application Date
20231128
Priority Date
20221227

Claims (14)

  1. 1 . An optical system configured to guide a light beam from an image display element to an exit pupil, the optical system comprising, in order from an exit pupil side to an image display element side: a first transmissive reflective surface; a second transmissive reflective surface; and an optical element disposed closer to the exit pupil than the first transmissive reflective surface, wherein the optical element includes, in order from the exit pupil side to the image display element side, a first optical element made of a first optical material and a second optical element made of a second optical material different from the first optical material, wherein the first optical element and the second optical element are cemented together, and a diffraction grating is formed on a cemented surface of the first optical element and the second optical element, wherein the diffraction grating includes a grating surface contributing to diffraction and a grating wall surface adjacent to the grating surface in a radial direction, the grating surface having a convex shape facing the image display element side, and wherein the following inequalities are satisfied: 0.5 ≤ d ⁢ 1 ≤ 2 ⁢ 0 . 0 0.02 ≤ d ⁢ 2 ≤ 0 . 4 ⁢ 0 where d1 [mm] is a thickness of the first optical material in an optical axis direction, and d2 [mm] is a thickness of the second optical material in the optical axis direction.
  2. 2 . The optical system according to claim 1 , wherein the first optical material is a thermoplastic resin.
  3. 3 . The optical system according to claim 1 , wherein the second optical material is a UV curable resin.
  4. 4 . The optical system according to claim 1 , wherein the following inequality is satisfied: 0 . 0 ⁢ 2 ≤ ❘ "\[LeftBracketingBar]" n ⁢ 1 - n ⁢ 2 ❘ "\[RightBracketingBar]" ≤ 0.2 where n1 is a refractive index of the first optical material for d-line, and n2 is a refractive index of the second optical material for the d-line.
  5. 5 . The optical system according to claim 1 , wherein the following inequality is satisfied: 5 ≤ ❘ "\[LeftBracketingBar]" v ⁢ 1 - v ⁢ 2 ❘ "\[RightBracketingBar]" where ν1 is an Abbe number based on d-line of the first optical material, and ν2 is an Abbe number based on the d-line of the second optical material.
  6. 6 . The optical system according to claim 1 , wherein the following inequalities are satisfied: n ⁢ 1 > n ⁢ 2 v ⁢ 1 > v ⁢ 2 where n1 is a refractive index of the first optical material for d-line, n2 is a refractive index of the second optical material for the d-line, ν1 is an Abbe number based on the d-line of the first optical material, and ν2 is an Abbe number based on the d-line of the second optical material.
  7. 7 . The optical system according to claim 1 , wherein the following inequalities are satisfied: 25 ≤ v ⁢ 1 ≤ 6 ⁢ 0 18 ≤ v ⁢ 2 ≤ 4 ⁢ 0 where ν1 is an Abbe number based on d-line of the first optical material, and ν2 is an Abbe number based on the d-line of the second optical material.
  8. 8 . The optical system according to claim 1 , wherein the following inequality is satisfied: 0 . 0 ⁢ 0 ⁢ 1 ≤ h ≤ 0 . 0 ⁢ 2 ⁢ 0 where h [mm] is a grating height of the diffraction grating.
  9. 9 . The optical system according to claim 1 , wherein the following inequality is satisfied: 0 . 0 ⁢ 1 ≤ ⁢ P ⁢ min where Pmin [mm] is a minimum grating pitch of the diffraction grating.
  10. 10 . The optical system according to claim 1 , wherein the following inequality is satisfied: N ≤ 1 ⁢ 0 ⁢ 0 ⁢ 0 where N is the number of annuli of the diffraction grating.
  11. 11 . The optical system according to claim 1 , wherein the first optical material has pencil hardness higher than 3H, and the second optical material has a pencil hardness lower than 3H.
  12. 12 . The optical system according to claim 1 , wherein an optical surface facing the exit pupil is made of acrylic resin.
  13. 13 . The optical system according to claim 1 , wherein a surface of the second optical material that faces the cemented surface is the first transmissive reflective surface.
  14. 14 . A display apparatus comprising: the optical system according to claim 1 ; and an image display element configured to display an image.

Description

BACKGROUND Technical Field One of the aspects of the embodiments relates to an optical system, and is suitable for a display apparatus that enlarges and displays an original image displayed on an image display element such as a head mount display (HMD). Description of Related Art The conventional optical system provided in a display apparatus such as an HMD is demanded to have a reduced overall length. A bending optical system is known as an optical system that can reduce the overall length. Japanese Patent No. 7103566 discloses a bending optical system using a diffractive optical element (DOE) to improve the sense of the definition of an image. However, Japanese Patent No. 7103566 places the DOE between the surface on the side of the image display element of the optical system and the image display surface of the image display element, and cannot sufficiently correct lateral chromatic aberration among senses relating to the definition of an image. SUMMARY An optical system according to one aspect of the embodiment is configured to guide a light beam from an image display element to an exit pupil and includes, in order from an exit pupil side to an image display element side, a first transmissive reflective surface, a second transmissive reflective surface, and an optical element disposed closer to the exit pupil than the first transmissive reflective surface. The optical element includes, in order from the exit pupil side to the image display element side, a first optical element made of a first optical material and a second optical element made of a second optical material different from the first optical material. The first optical element and the second optical element are cemented together, and a diffraction grating is formed on a cemented surface of the first optical element and the second optical element. The diffraction grating includes a grating surface contributing to diffraction and a grating wall surface adjacent to the grating surface in a radial direction, the grating surface having a convex shape facing the image display element side. The following inequalities are satisfied: 0.5≤d⁢1≤20.0.02≤d⁢2≤0.4 where d1 [mm] is a thickness of the first optical material in an optical axis direction, and d2 [mm] is a thickness of the second optical material in the optical axis direction. A display apparatus having the above optical system also constitutes another aspect of the embodiment. Further features of the disclosure will become apparent from the following description of embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an observation apparatus according to this embodiment. FIG. 2 is an aberration diagram of an observation optical system. FIG. 3 is a schematic diagram illustrating an optical path of the observation optical system. FIGS. 4A and 4B explain an optical element. FIGS. 5A and 5B illustrate a grating pitch. DESCRIPTION OF THE EMBODIMENTS Referring now to the accompanying drawings, a detailed description will be given of embodiments according to the disclosure. Corresponding elements in respective figures will be designated by the same reference numerals, and a duplicate description thereof will be omitted. Overview FIG. 1 is a sectional view of an observation apparatus (display apparatus) 1 according to this embodiment. The observation apparatus 1 includes an observation optical system (optical system) 1000 and a panel unit 1400. The observation optical system 1000 is a bending optical system configured to guide a light beam from the panel unit 1400 to the exit pupil. The panel unit 1400 includes, for example, an image display element (light modulation element) such as a liquid crystal display element (LCD) and an organic EL element. The observation optical system 1000 includes, in order from the exit pupil side to the image display element side, a first transmissive reflective surface and a second transmissive reflective surface. The first transmissive reflective surface and the second transmissive reflective surface may be polarization separation (splitting) surfaces. The observation optical system 1000 includes, in order from the exit pupil side to the image display element side, a pupil-side optical system 1100 and a transmissive reflective optical system 1200. The transmissive reflective optical system 1200 includes a first transmissive reflective surface and a second transmissive reflective surface. In this embodiment, each of the pupil-side optical system 1100 and the transmissive reflective optical system 1200 includes optical elements 1101 and 1201. The optical elements 1101 and 1201 refract, reflect, or diffract a light ray. The optical element 1101 includes, in order from the exit pupil side to the image display element side, surfaces R1, R2, and R3. The surfaces R1, R2, and R3 are a plane, a curved surface with a diffraction grating, and a curved surface having the same shape as that of the surface R2 and no diff