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EP-4325271-B1 - OPTICAL SYSTEM AND HEAD-MOUNTED DEVICE

EP4325271B1EP 4325271 B1EP4325271 B1EP 4325271B1EP-4325271-B1

Inventors

  • HUANG, JIH CHUNG
  • HONG, YU JIE

Dates

Publication Date
20260506
Application Date
20220927

Claims (20)

  1. An optical system (1) comprising: an aperture stop (ST) located at a front side of the optical system (1); an image display surface (IMG) located at a rear side of the optical system (1); a reflective polarizer (RP) located between the aperture stop (ST) and the image display surface (IMG); a partial reflector (BS) located between the reflective polarizer (RP) and the image display surface (IMG); a first quarter-wave plate (QWP1) located between the reflective polarizer (RP) and the partial reflector (BS); a second quarter-wave plate (QWP2) located between the partial reflector (BS) and the image display surface (IMG); a first optical lens element (E1) located between the aperture stop (ST) and the image display surface (IMG); a second optical lens element (E2) located between the first optical lens element (E1) and the image display surface (IMG); and a third optical lens element (E3) located between the second optical lens element (E2) and the image display surface (IMG); wherein the optical system (1) is characterized in that the first optical lens element (E1) has negative refractive power, the third optical lens element (E3) has positive refractive power, and the second optical lens element (E2) has a front-side surface being planar; wherein a curvature radius of a front-side surface of the third optical lens element (E3) is R5, a curvature radius of a rear-side surface of the third optical lens element (E3) is R6, and the following condition is satisfied: 0.13 < R 6 / R 5 .
  2. The optical system (1) of claim 1, wherein the curvature radius of the front-side surface of the third optical lens element (E3) is R5, the curvature radius of the rear-side surface of the third optical lens element (E3) is R6, and the following condition is satisfied: 0.15 < R 6 / R 5 .
  3. The optical system (1) of claim 1, wherein at least one optical lens element of the optical system (1) has an inflection point (P).
  4. The optical system (1) of claim 3, wherein a rear-side surface of the first optical lens element (E1) has at least one inflection point (P).
  5. The optical system (1) of claim 1, wherein an Abbe number of the first optical lens element (E1) is V1, an Abbe number of the second optical lens element (E2) is V2, an Abbe number of the third optical lens element (E3) is V3, an Abbe number of the i-th optical lens element is Vi, a refractive index of the first optical lens element (E1) is N1, a refractive index of the second optical lens element (E2) is N2, a refractive index of the third optical lens element (E3) is N3, a refractive index of the i-th optical lens element is Ni, and at least one optical lens element of the optical system (1) satisfies the following condition: 10 < Vi / Ni < 50 , wherein i = 1, 2 or 3.
  6. The optical system (1) of claim 1, wherein a focal length of the optical system (1) is f, an image height on the image display surface (IMG) is ImgH, and the following condition is satisfied: 1.00 < f / ImgH < 1.50 .
  7. The optical system (1) of claim 1, wherein an axial distance between the aperture stop (ST) and the image display surface (IMG) is SL, an image height on the image display surface (IMG) is ImgH, and the following condition is satisfied: 1.2 < SL / ImgH < 2.0 .
  8. The optical system (1) of claim 1, wherein an axial distance between the aperture stop (ST) and the image display surface (IMG) is SL, a focal length of the optical system (1) is f, and the following condition is satisfied: 1.2 < SL / f < 2.0 .
  9. The optical system (1) of claim 1, wherein an axial distance between the aperture stop (ST) and a front-side surface of the first optical lens element (E1) is ER, an axial distance between the aperture stop (ST) and the image display surface (IMG) is SL, and the following condition is satisfied: 0.30 < ER / SL < 0.50 .
  10. The optical system (1) of claim 1, wherein an axial distance between a front-side surface of the first optical lens element (E1) and the rear-side surface of the third optical lens element (E3) is TD, an axial distance between the aperture stop (ST) and the image display surface (IMG) is SL, and the following condition is satisfied: 0.40 < TD / SL < 0.60 .
  11. The optical system (1) of claim 1, wherein a central thickness of the first optical lens element (E1) is CT1, a central thickness of the second optical lens element (E2) is CT2, a central thickness of the third optical lens element (E3) is CT3, an axial distance between a rear-side surface of the first optical lens element (E1) and the front-side surface of the second optical lens element (E2) is T12, an axial distance between a rear-side surface of the second optical lens element (E2) and the front-side surface of the third optical lens element (E3) is T23, and the following condition is satisfied: 1 < CT 1 + CT 2 + CT 3 / T 12 + T 23 < 20 .
  12. The optical system (1) of claim 1, wherein a central thickness of the first optical lens element (E1) is CT1, a central thickness of the second optical lens element (E2) is CT2, a central thickness of the third optical lens element (E3) is CT3, an axial distance between the aperture stop (ST) and the image display surface (IMG) is SL, and the following condition is satisfied: 0.20 < CT 1 + CT 2 + CT 3 / SL < 1.00 .
  13. The optical system (1) of claim 1, wherein an imaging light is emitted from the image display surface (IMG), and the imaging light sequentially passes through the second quarter-wave plate (QWP2), the partial reflector (BS), the first quarter-wave plate (QWP1) and the reflective polarizer (RP).
  14. A head-mounted device (10) comprising: the optical system (1) of claim 1.
  15. An optical system (1) comprising: an aperture stop (ST) located at a front side of the optical system (1); an image display surface (IMG) located at a rear side of the optical system (1); a reflective polarizer (RP) located between the aperture stop (ST) and the image display surface (IMG); a partial reflector (BS) located between the reflective polarizer (RP) and the image display surface (IMG); a first quarter-wave plate (QWP1) located between the reflective polarizer (RP) and the partial reflector (BS); a second quarter-wave plate (QWP2) located between the partial reflector (BS) and the image display surface (IMG); a first optical lens element (E1) located between the aperture stop (ST) and the image display surface (IMG); a second optical lens element (E2) located between the first optical lens element (E1) and the image display surface (IMG); and a third optical lens element (E3) located between the second optical lens element (E2) and the image display surface (IMG); wherein the optical system (1) is characterized in that the first optical lens element (E1) has negative refractive power, and the second optical lens element (E2) has a front-side surface being planar; wherein a curvature radius of a front-side surface of the first optical lens element (E1) is R1, a curvature radius of a rear-side surface of the first optical lens element (E1) is R2, and the following condition is satisfied: R 2 / R 1 < 1000 .
  16. The optical system (1) of claim 15, wherein the curvature radius of the front-side surface of the first optical lens element (E1) is R1, the curvature radius of the rear-side surface of the first optical lens element (E1) is R2, and the following condition is satisfied: R 2 / R 1 < 500 .
  17. The optical system (1) of claim 15, wherein at least one optical lens element of the optical system (1) has an inflection point (P).
  18. The optical system (1) of claim 17, wherein the rear-side surface of the first optical lens element (E1) has at least one inflection point (P).
  19. The optical system (1) of claim 15, wherein an Abbe number of the first optical lens element (E1) is V1, an Abbe number of the second optical lens element (E2) is V2, an Abbe number of the third optical lens element (E3) is V3, an Abbe number of the i-th optical lens element is Vi, a refractive index of the first optical lens element (E1) is N1, a refractive index of the second optical lens element (E2) is N2, a refractive index of the third optical lens element (E3) is N3, a refractive index of the i-th optical lens element is Ni, and at least one optical lens element of the optical system (1) satisfies the following condition: 10 < Vi / Ni < 50 , wherein i = 1, 2 or 3.
  20. The optical system (1) of claim 15, wherein a focal length of the optical system (1) is f, an image height on the image display surface (IMG) is ImgH, and the following condition is satisfied: 1.00 < f / ImgH < 1.50 .

Description

BACKGROUND Technical Field The present disclosure relates to an optical system and a head-mounted device, more particularly to an optical system applicable to a head-mounted device. Description of Related Art With the advancement of semiconductor manufacturing technology, electronic components have been miniaturized and the performance of miniature electronic components has been improved, and image sensors for having more pixels has been scaled down. Therefore, featuring high image quality becomes one of the indispensable features of a miniature optical system nowadays. Furthermore, due to the popularization of high-performance microprocessors and microdisplays, the technology related to smart head-mounted devices rapidly develops in recent years. With the rise of artificial intelligence, electronic devices equipped with optical systems are trending towards multi-functionality for various applications, and the functional requirements for computer vision have been increasing. The head-mounted devices have become smaller and more lightweight, and also have various intelligent applications such as virtual reality (VR), augmented reality (AR) and mixed reality (MR) in the rapidly developing technology landscape. VR has been widely applied in medical health areas and engineering, real estate, education, video game and entertainment industries. However, the head-mounted devices are still in the developing stage, and there are still many areas that need to be improved, such as the weight and size of the head-mounted devices and the quality of images. In the early stages, the VR head-mounted devices usually use conventional optical lenses or Fresnel lenses. Conventional optical lenses may provide good image quality, but it is hard to effectively reduce the device size. On the other hand, the use of Fresnel lenses may reduce the device size, but the image quality may be poor. Therefore, researchers and developers are looking for lens combinations that are small in size and provide high image quality. CN 216561229 U relates to a catadioptric optical system for head mounted devices. SUMMARY The invention is set out in the appended set of claims. According to one aspect of the present disclosure, an optical system includes an aperture stop, an image display surface, a reflective polarizer, a partial reflector, a first quarter-wave plate, a second quarter-wave plate, a first optical lens element, a second optical lens element and a third optical lens element. The aperture stop is located at a front side of the optical system. The image display surface is located at a rear side of the optical system. The reflective polarizer is located between the aperture stop and the image display surface. The partial reflector is located between the reflective polarizer and the image display surface. The first quarter-wave plate is located between the reflective polarizer and the partial reflector. The second quarter-wave plate is located between the partial reflector and the image display surface. The first optical lens element is located between the aperture stop and the image display surface. The second optical lens element is located between the first optical lens element and the image display surface. The third optical lens element is located between the second optical lens element and the image display surface. In addition, the first optical lens element has negative refractive power, the third optical lens element has positive refractive power, and the second optical lens element has a front-side surface being planar. When a curvature radius of a front-side surface of the third optical lens element is R5, and a curvature radius of a rear-side surface of the third optical lens element is R6, the following condition is satisfied: 0.13<R6/R5. According to another aspect of the present disclosure, an optical system includes an aperture stop, an image display surface, a reflective polarizer, a partial reflector, a first quarter-wave plate, a second quarter-wave plate, a first optical lens element, a second optical lens element and a third optical lens element. The aperture stop is located at a front side of the optical system. The image display surface is located at a rear side of the optical system. The reflective polarizer is located between the aperture stop and the image display surface. The partial reflector is located between the reflective polarizer and the image display surface. The first quarter-wave plate is located between the reflective polarizer and the partial reflector. The second quarter-wave plate is located between the partial reflector and the image display surface. The first optical lens element is located between the aperture stop and the image display surface. The second optical lens element is located between the first optical lens element and the image display surface. The third optical lens element is located between the second optical lens element and the image display surface. In addition, the first optica