Slim Optical System

Abstract

The present invention provides a slim optical system comprising a first lens and a second lens from the object side, wherein the first lens is a plano-convex lens having a positive refractive power, and the second lens is an aspherical lens having a refractive power (C8) on the upper side such that |C8| < 0.01, and the exit pupil diameter (EPD) is 8 mm or less and the eye relief is 12 mm or less.

Description

Technology Field

[0001] The present invention relates to an optical system comprising two lenses, and more specifically, to a slim optical system that maintains a wide field of view while minimizing the distance between the user's eyes and the display (Eye Relief). Background Technology

[0002] Recently, Extended Reality (XR) devices such as Virtual Reality (VR) and Augmented Reality (AR) are increasingly advancing, leading to the growing importance of Head-Mounted Displays (HMDs).

[0003] HMD devices require high resolution and a wide field of view (FOV) to provide users with an immersive virtual reality experience, while simultaneously requiring a lightweight and compact structure to ensure comfort even when worn for extended periods.

[0004] Various approaches have been attempted in existing optical system designs to meet these requirements. In particular, pancake optics play an important role in reducing the overall length of the system (OAL) and improving image quality in VR-HMDs.

[0005] Pancake optics uses a complex optical path composed of a polarizing beam splitter (PBS), a quarter-wave plate (QWP), and a half mirror to reduce the thickness of VR-HMDs and enhance visual performance. This design is an important technology that improves the usability of VR-HMDs and helps users have a more vivid and immersive visual experience.

[0006] However, in existing VR-HMD optical systems, stray light can degrade the quality of the image viewed by the user. Stray light is light that is unnecessarily reflected or scattered within the optical system, causing image distortion or reducing contrast, thereby lowering screen clarity.

[0007] This phenomenon is a particular issue in VR-HMD environments where high-resolution image rendering is critical. Although existing designs control light paths in various ways to reduce stray light, problems remain that have not been completely eliminated.

[0008] In addition, eye relief is defined as the minimum distance that must be maintained between the eyes and the lenses when a user wears an HMD; if adequate eye relief is not secured, the user may experience discomfort or image distortion during wear.

[0009] However, increasing eye-relief leads to a problem where the FOV decreases. FOV refers to the field of view a user can see on the screen, and a wide FOV is essential for an immersive VR experience.

[0010] In existing VR-HMD designs, it is difficult to balance these two factors, resulting in a trade-off between eye relief and FOV.

[0011] In addition, advanced optical designs such as pancake optics increase the complexity of the system, which exacerbates the difficulty of the manufacturing process and increases costs. Since precise alignment between optical components is required, this leads to higher product prices and an increased possibility of defects. Prior art literature

[0012] US Public Patent US2023 / 0143390 The problem to be solved

[0013] The present invention requires the design of a new optical system to solve the above problems, and aims to provide a slim optical system that includes a first lens and a second lens from the object side, thereby minimizing the distance between the user's eye and the display (Eye Relief) while maintaining a wide field of view. means of solving the problem

[0014] To achieve the above objective, the present invention provides a slim optical system comprising a first lens and a second lens from the object side, wherein the first lens is a plano-convex lens having a positive refractive power, and the second lens is an aspherical lens having a refractive power (C8) on the upper side such that |C8| < 0.01, and the exit pupil diameter (EPD) is 8 mm or less and the eye relief is 12 mm or less.

[0015] In addition, the slim optical system comprises a display, an aperture, a quarter wave plate (QWP), a polarizing beam splitter (PBS), and a half mirror, and it is preferable that a first lens is positioned between the aperture and the quarter wave plate (QWP), and a second lens is positioned between the first lens and the top surface.

[0016] Here, in the slim optical system, it is preferable that a polarizing beam splitter (PBS) is implemented on the upper side of the first lens, a quarter wave plate (QWP) is implemented on the object side of the second lens, and a half mirror is implemented on the upper side.

[0017] In addition, the optical path of the slim optical system is preferably such that light generated from the display passes through the partial reflector of the second lens, converts circular polarization (LCP) into linear polarization through the quarter wave plate (QWP) of the second lens, is reflected from the polarization beam splitter (PBS) of the first lens, passes through the quarter wave plate (QWP) of the second lens again to be converted into circular polarization (RCP), is reflected from the partial reflector of the second lens, is converted into linear polarization through the quarter wave plate (QWP) of the second lens, passes through the aperture, and is transmitted to the user's pupil.

[0018] In addition, the first lens is a plano-convex lens that is convex toward the side of an object, and it is preferable that the thickness (CT1) of the first lens, the thickness (CT2) of the second lens, and the axial distance (T12) between the first lens and the second lens satisfy 0 < (CT1 + CT2) / T12 < 1.5.

[0019] In addition, it is desirable that the Abbe number (V1) of the first lens and the Abbe number (V2) of the second lens satisfy V1 + V2 > 100.

[0020] In addition, it is preferable that the object side curvature (R7) and the upper side curvature (R8) of the second lens satisfy R7 / R8 < 0.

[0021] In addition, it is preferable that the refractive power (P1) of the first lens and the refractive power (P2) of the second lens satisfy -0.1 < P1 + P2 < 0.1.

[0022] In addition, for the above slim optical system, it is desirable that the size of the entrance pupil (EPD) and the size of the image plane (ImgH) satisfy EPD / ImgH < 0.4.

[0023] In addition, it is desirable that the distortion (Dist) of the above slim optical system satisfies -100% < Dist < 0. Effects of the invention

[0024] The present invention relates to an optical system comprising two lenses, wherein the system is composed of a first lens and a second lens from the object side, and the entrance pupil (EPD) of the system is designed to be 8 mm or less and the eye relief is 12 mm or less, thereby minimizing the distance (Eye Relief) between the user's eye and the display while maintaining a wide field of view.

[0025] In addition, according to an embodiment of the present invention, stray light is effectively suppressed to significantly improve the contrast ratio and clarity of the image viewed by the user, thereby enabling the realization of a high-resolution image and minimizing visual distortion.

[0026] In addition, according to an embodiment of the present invention, it is designed to provide a wide field of view while maintaining appropriate eye relief, so that the user can obtain a highly immersive virtual reality experience and discomfort is minimized even when worn for a long time.

[0027] In addition, according to an embodiment of the present invention, an optical system including two lenses is adopted to realize a thinner and lighter design compared to existing systems, which can improve the wearing comfort of the VR-HMD and increase portability.

[0028] In addition, according to an embodiment of the present invention, by appropriately adjusting the Abbe number and refractive power of the lens to minimize chromatic aberration and distortion, the user can receive a clear image without distortion and have a more natural visual experience. Brief explanation of the drawing

[0029] FIG. 1 - Schematic diagram of the main parts of a slim optical system according to an embodiment of the present invention. FIG. 2 - Aqueous diagram according to an embodiment of the present invention. Specific details for implementing the invention

[0030] The present invention relates to an optical system comprising two lenses, wherein the system is composed of a first lens and a second lens from the object side, and the exit pupil diameter (EPD) of the system is designed to be 8 mm or less and the eye relief is 12 mm or less, thereby minimizing the distance (eye relief) between the user's eye and the display while maintaining a wide field of view.

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0033] FIG. 1 is a schematic diagram of the main parts of a slim optical system according to an embodiment of the present invention, and FIG. 2 is a diagram showing an aberration according to an embodiment of the present invention.

[0034] As described above, the slim optical system according to an embodiment of the present invention is a slim optical system composed of a first lens (L1) and a second lens (L2) from the object side, wherein the first lens (L1) is a plano-convex lens having a positive refractive power and the second lens (L2) is an aspherical lens having a refractive power C8 on the upper side surface |C8| < 0.01, and the entrance pupil (EPD) is 8 mm or less and the eye relief is 12 mm or less.

[0035] This provides a slim optical system by appropriately designing the refractive power and shape of the lens, with an entrance pupil (EPD) of 8mm or less and an eye relief of 12mm or less, thereby providing a slim optical system with a wide field of view while minimizing the distance between the user's eye and the display (Eye Relief).

[0036] The first lens (L1) has a positive refractive power and is a flat block lens, more specifically, has a shape that is convex toward the side of the object, and plays a role in minimizing distortion while concentrating light through its positive refractive power.

[0037] The second lens (L2) is an aspherical lens that satisfies the condition that the refractive power C8 of the upper surface is |C8| < 0.01. This allows the upper curvature of the lens to be very gentle, thereby reducing light distortion and providing a wide field of view. Additionally, since it is formed as an aspherical lens, it can provide high-resolution images with minimal distortion.

[0038] The optical system according to the present invention is designed to enable a wide field of view, a thin design, and minimized distortion using only two lenses.

[0040] In addition, the slim optical system according to an embodiment of the present invention includes a display, an aperture, a quarter-wave plate (QWP), a polarizing beam splitter (PBS), and a half mirror, wherein a first lens (L1) is positioned between the aperture and the quarter-wave plate (QWP), and a second lens (L2) is positioned between the first lens (L1) and the upper surface.

[0041] According to an embodiment of the present invention, the slim optical system preferably has a polarizing beam splitter (PBS) implemented on the upper side of the first lens (L1), a quarter wave plate (QWP) implemented on the object side of the second lens (L2), and a partial reflector (Half Mirror) implemented on the upper side.

[0042] According to an embodiment of the present invention, a display (top surface) and an aperture (which acts as an eye in front of the first lens (L1)) are respectively located at the front and rear of the slim optical system to form an overall optical path.

[0043] A first lens (L1) is positioned between the aperture and the display, and the upper surface of the first lens (L1) splits the linear polarization of light using a polarization beam splitter (PBS) to affect the reflected polarization according to the angle of incidence and wavelength.

[0044] The object side of the first lens (L1) is formed as a plano-convex lens and serves to collect light and transmit it to the rest of the system. The object side of the second lens (L2) is implemented as a quarter wave plate (QWP) and the upper side as a half mirror, which serves to control the polarization state of the light and minimize distortion.

[0045] The optical path of the slim optical system according to an embodiment of the present invention is characterized in that light generated from a display passes through a partial reflector of the second lens, converts circular polarization (LCP) into linear polarization through a quarter wave plate (QWP) of the second lens, is reflected from a polarization beam splitter (PBS) of the first lens, passes through a quarter wave plate (QWP) of the second lens again to be converted into circular polarization (RCP), is reflected from a partial reflector of the second lens, is converted into linear polarization through a quarter wave plate (QWP) of the second lens, passes through an aperture, and is transmitted to the user's pupil.

[0046] The optical path according to an embodiment of the present invention is the process from the light emitted from the display to reaching the pupil of a person, wherein the lens close to the display is called the second lens (L2) and the lens relatively close to the eye is called the first lens (L1).

[0047] First, the circularly polarized (LCP) beam from the display passes through the half mirror of the second lens (L2). The half mirror is designed to reflect half of the light and transmit the other half, with a reflectivity of 40–50%. The transmitted circularly polarized (LCP) passes through the quarter polarizer of the second lens (L2), and due to the characteristics of the quarter polarizer, the direction of the beam is converted from circularly polarized to linearly polarized (from linearly polarized to circularly polarized) (path ① in Fig. 1).

[0048] Then, the linear S-polarized light passing through the quarter polarizer is reflected by the polarization beam splitter (PBS) of the first lens (L1) and passes through the quarter polarizer of the second lens (L2) again, reaching the half mirror of the second lens (L2) in the form of circular polarized light (LCP) (path ② in FIG. 1).

[0049] Then, the circularly polarized light reflected through the half mirror of the second lens (L2) has its polarization direction changed to the RCP, passes through the quarter polarizer of the second lens (L2), is converted into linear P polarization, passes through the aperture, and reaches the EPD (path ③ in Fig. 1).

[0050] Polarization conversion and reflection along this optical path minimize the generation of stray light, ultimately serving to deliver a high-resolution image to the user.

[0052] In addition, according to an embodiment of the present invention, the first lens (L1) is a plano-convex lens that is convex toward the side of an object, and the thickness (CT1) of the first lens (L1), the thickness (CT2) of the second lens (L2), and the axial distance (T12) between the first lens (L1) and the second lens (L2) satisfy 0 < (CT1 + CT2) / T12 < 1.5.

[0053] This minimizes the thickness of the entire optical system, enabling a slim design for the HMD device. This allows the wearer to put on the HMD more comfortably and reduces fatigue even during prolonged use.

[0054] In addition, according to an embodiment of the present invention, the Abbe number (V1) of the first lens (L1) and the Abbe number (V2) of the second lens (L2) satisfy V1 + V2 > 100.

[0055] This is intended to minimize chromatic aberration of the lenses and provide a clear image by designing the Abbe number values ​​of the first lens (L1) and the second lens (L2) to exceed 100. Chromatic aberration is one of the important factors that degrade image quality in high-resolution display devices, and this condition can effectively suppress chromatic aberration.

[0056] In addition, according to an embodiment of the present invention, the object-side curvature (R7) and the upper-side curvature (R8) of the second lens (L2) satisfy R7 / R8 < 0.

[0057] This serves to minimize optical distortion occurring in the lens by setting the curvature ratio of the second lens (L2). In other words, the curvature on the object side must be smaller than the curvature on the image side; this reduces distortion that may occur during the process of the lens gathering light, ultimately providing the user with a clear and distortion-free image.

[0058] In addition, according to an embodiment of the present invention, the refractive power (P1) of the first lens (L1) and the refractive power (P2) of the second lens (L2) satisfy -0.1 < P1 + P2 < 0.1.

[0059] This is designed so that the sum of the refractive powers of the two lenses falls within a specific range, thereby minimizing optical distortion in the entire optical system and maintaining a constant focal length, which optimizes the performance of the optical system.

[0060] In addition, according to an embodiment of the present invention, the slim optical system satisfies the condition that the size of the entrance pupil (EPD) and the size of the image plane (ImgH) are EPD / ImgH < 0.4.

[0061] This aims to achieve optimal system performance by adjusting the ratio between the light path and the image size in the optical system; the EPD must be designed to be much smaller than the ImgH, thereby enabling the system to provide a wider field of view.

[0062] In addition, according to an embodiment of the present invention, the distortion (Dist) of the slim optical system satisfies -100% < Dist < 0. That is, the distortion is always negative, and as a result, the distortion occurring in the optical system appears as barrel distortion. This suppresses the distortion within a certain range, ensuring that the image viewed by the user is natural and consistent. Although it is barrel distortion, the degree of it is controlled to minimize visual discomfort to the user.

[0063] Thus, the present invention provides a slim optical system comprising two aspherical lenses, and provides a slim optical system with a wide field of view, a slim design, and minimized distortion and chromatic aberration.

[0065] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

[0066] Figure 1 shows an example of a slim optical system according to the present invention.

[0067] As described above, a slim optical system according to an embodiment of the present invention includes a first lens (L1) and a second lens (L2) from the object side, wherein the first lens (L1) is a plano-convex lens having a positive refractive power on the object side, and the second lens (L2) is an aspherical lens having a refractive power (C8) on the upper side such that |C8| < 0.01, the entrance pupil (EPD) is 8 mm or less, and the eye relief is 12 mm or less.

[0068] And, the above slim optical system includes a display, an aperture, a quarter wave plate (QWP), a polarizing beam splitter (PBS), and a half mirror, wherein a first lens (L1) is positioned between the aperture and the quarter wave plate (QWP), and a second lens (L2) is positioned between the first lens (L1) and the upper surface, wherein the polarizing beam splitter (PBS) is implemented on the upper surface of the first lens (L1), the quarter wave plate (QWP) is implemented on the object side of the second lens (L2), and the half mirror is implemented on the upper surface.

[0070] The following Table 1 shows numerical data of lenses constituting an optical system according to a specific embodiment of the present invention.

[0071]

[0072]

[0073] The Qcon polynomial (Qcon polynomial) according to the Qcon aspherical surfaces of the first lens (L1) and the second lens (L2) is given by the following mathematical formula 1.

[0074]

[0075] Here, z is the sag of the plane parallel to the z-axis in the optical system, c is the vertex curvature at the vertex of the lens, k is the conic constant, r is the radial distance from the axis of the lens, r n is the normalization radius, and u is r / r n , a m is the m-th Qcon coefficient, Q m con represents the m-th Qcon polynomial.

[0077] From the above mathematical formula 1, the Qcon coefficient is as shown in the following Table 2.

[0078]

[0079]

[0081] The following Tables 3 and 4 show the design values ​​of an optical system according to an embodiment of the present invention.

[0082]

[0083]

[0084] Here, F is the effective focal length of the entire optical system, f1 (L1_f1) and f2 (L2_f2) are the focal lengths of the first lens (L1) and the second lens (L2), respectively, and P1 and P2 represent the refractive power of the first lens (L1) and the second lens (L2), respectively. ct represents the center thickness of each lens surface (image side and object side), et represents the thickness of the outermost effective diameter of each lens surface (image side and object side), L1 ct represents the center thickness of the first lens (L1), and L2 ct represents the center thickness of the second lens (L2).

[0085] Also, the air gap is the total air gap of the entire optical system, and V1 and V2 represent the Abbe numbers of the first lens (L1) and the second lens (L2), respectively.

[0087]

[0088]

[0089] Effective Focal Length (EFL) is the effective focal length (F) of the entire optical system, Back Focal Length (bfl) is the back focal length (distance from the last plane of the optical system to the focal point), Total Length (TTL) is the length of the entire optical system (distance from the center of the object's side to the image plane), Field of View (FOV) is the angle of view, Half Field of View (HFOV) is the Half Field of View, and Image H (IH) is the image plane height. Chief Ray Angle (cra) max is the magnitude of the maximum chief ray angle, and dist indicates distortion.

[0090] In one embodiment of the present invention, the distortion dist of the optical system satisfies -100% < dist < 0, thereby always providing a barrel-shaped distorted image.

[0091] In one embodiment of the present invention, the fno (f-number) of the optical system is satisfied to be 2.54, thereby enabling clear image quality to be obtained even with a small amount of light. This allows the aperture diameter to be increased, enabling bright image quality to be achieved even in dark places, thus making it possible to provide a compact optical system with high resolution and high image quality. Through this configuration, the angle of view is increased and the f-number is sufficiently reduced to provide an optical system with bright image quality.

[0093] FIG. 2 shows a water aberration diagram according to the first embodiment of the present invention.

[0094] The first data in FIG. 2 represents spherical aberration, where the horizontal axis represents focal length (mm) and the vertical axis represents image height (mm), and each graph represents the wavelength of the incident light. As shown, it is known that the closer the graphs are to the central vertical axis and the closer they are to each other, the better the correction of spherical aberration is, and the spherical aberration of the first embodiment according to the present invention is judged to be good at 0.025 mm (focal length) or less.

[0095] The second data in Figure 2 represents astigmatism, where the horizontal axis represents the focal point (mm) and the vertical axis represents the angle of incidence (deg). Graph S represents the sagittal, which is the ray incident horizontally to the lens, and Graph T represents the tangential, which is the ray incident perpendicularly to the lens. It is known that the closer Graphs S and T are to the center vertical axis, the better the astigmatism correction is.

[0096] The third data in Fig. 2 represents distortion aberration, where the horizontal axis represents the degree of distortion (dist, %) and the vertical axis represents the angle of incidence (deg). The first embodiment of the present invention satisfies -100% < dist < 0, so the first embodiment of the present invention always provides a barrel-shaped distorted image.

[0098] As such, the present invention relates to an optical system comprising two lenses, which is composed of a first lens (L1) and a second lens (L2) from the object side, wherein the entrance pupil (EPD) of the system is designed to be 8 mm or less and the eye relief is 12 mm or less, thereby minimizing the distance (Eye Relief) between the user's eye and the display while maintaining a wide field of view.

[0099] In addition, according to an embodiment of the present invention, stray light is effectively suppressed to significantly improve the contrast ratio and clarity of the image viewed by the user, thereby enabling the realization of a high-resolution image and minimizing visual distortion.

[0100] In addition, according to an embodiment of the present invention, it is designed to provide a wide field of view while maintaining appropriate eye relief, so that the user can obtain a highly immersive virtual reality experience and discomfort is minimized even when worn for a long time.

[0101] In addition, according to an embodiment of the present invention, an optical system including two lenses is adopted to realize a thinner and lighter design compared to existing systems, which can improve the wearing comfort of the VR-HMD and increase portability.

[0102] In addition, according to an embodiment of the present invention, by appropriately adjusting the Abbe number and refractive power of the lens to minimize chromatic aberration and distortion, the user can receive a clear image without distortion and have a more natural visual experience.

[0103] Accordingly, the slim optical system according to the embodiment of the present invention enables the lightweighting and slimming of the design of the HMD device, thereby minimizing fatigue and increasing convenience even when the user wears it for a long time. Explanation of the symbols

[0104] L1: First lens L2: Second lens

Claims

Claim 1 A slim optical system comprising a first lens and a second lens from the object side, wherein the first lens is a plano-convex lens having a positive refractive power, and the second lens is an aspherical lens having a refractive power (C8) on the upper side such that |C8| < 0.01, and wherein the exit pupil diameter (EPD) is 8 mm or less and the eye relief is 12 mm or less. Claim 2 The slim optical system according to claim 1 comprises a display, an aperture, a quarter-wave plate (QWP), a polarizing beam splitter (PBS), and a half mirror, wherein a first lens is positioned between the aperture and the quarter-wave plate (QWP), and a second lens is present between the first lens and the image plane. Claim 3 In claim 2, the slim optical system is characterized in that a polarizing beam splitter (PBS) is implemented on the upper side of the first lens, a quarter wave plate (QWP) is implemented on the object side of the second lens, and a partial reflector (Half Mirror) is implemented on the upper side. Claim 4 In claim 3, the optical path of the slim optical system is characterized in that light generated from the display passes through a partial reflector of the second lens, converts circular polarization (LCP) into linear polarization through a quarter wave plate (QWP) of the second lens, is reflected from a polarization beam splitter (PBS) of the first lens, passes through a quarter wave plate (QWP) of the second lens again to be converted into circular polarization (RCP), is reflected from a partial reflector of the second lens, is converted into linear polarization through a quarter wave plate (QWP) of the second lens, passes through the aperture, and is transmitted to the user's pupil. Claim 5 A slim optical system according to claim 1, wherein the first lens is a plano-convex lens that is convex toward the side of an object, and the thickness (CT1) of the first lens, the thickness (CT2) of the second lens, and the axial distance (T12) between the first lens and the second lens satisfy 0 < (CT1 + CT2) / T12 < 1.

5. Claim 6 A slim optical system according to claim 1, characterized in that the Abbe number (V1) of the first lens and the Abbe number (V2) of the second lens satisfy V1 + V2 > 100. Claim 7 A slim optical system according to claim 1, characterized in that the object-side curvature (R7) and the upper-side curvature (R8) of the second lens satisfy R7 / R8 < 0. Claim 8 A slim optical system according to claim 1, characterized in that the refractive power (P1) of the first lens and the refractive power (P2) of the second lens satisfy -0.1 < P1 + P2 < 0.

1. Claim 9 In claim 1, the slim optical system is characterized in that the size of the entrance pupil (EPD) and the size of the image plane (ImgH) satisfy EPD / ImgH < 0.

4. Claim 10 A slim optical system according to claim 1, characterized in that the distortion (Dist) of the slim optical system satisfies -100% < Dist < 0.

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