Optical system and optical apparatus including the same

Abstract

The utility model discloses an optical system and optical equipment comprising the optical system, and the optical system sequentially comprises a first lens with positive focal power from a first side to a second side along an optical axis, a second lens with negative focal power, a third lens with positive focal power, a fourth lens with positive focal power, a fifth lens with negative focal power and a sixth lens with negative focal power, a reflective polarizing element; a first quarter-wave plate; the second lens has negative focal power, and the second side surface of the second lens is a concave surface; the first side surface of the third lens is a convex surface, and the second side surface of the third lens is a convex surface; a partially reflective element; the first side surface of the fourth lens is a concave surface, and the second side surface of the fourth lens is a plane; a second quarter-wave plate; and a polarizer; the optical system further includes a third spacer element; the optical system satisfies: 2.0 lt; f3 / d3slt; 2.9 and-2.2 lt, 2.9 and-2.2 lt; fz2 / d3mlt, fz2 / d3mlt F3 is the effective focal length of the third lens, d3s is the inner diameter of the first side face of the third spacing element, fz2 is the combined focal length of the fourth lens, the second quarter-wave plate and the polarizing film, and d3m is the inner diameter of the second side face of the third spacing element.

Description

Technical Field

[0001] This application relates to the field of optical elements, and more specifically, to an optical system and an optical device including the optical system. Background Art

[0002] In recent years, with the concept of "metaverse" being proposed, the ways people entertain have become increasingly rich, and AR / VR and other devices for human-computer interaction are becoming more and more popular among people. However, the biggest disadvantages of current VR lenses are large size, heavy weight, and dizziness. Therefore, the miniaturization, light weight, and imaging quality of the lens have become the most important factors in improving the consumer experience. In order to eliminate these defects and achieve a better user experience, making the lens structure more compact and lightweight, while optimizing the structural design to eliminate chromatic aberration, phase difference, and various stray light problems and improving the molding quality, has become one of the current research hotspots. Summary of the Utility Model

[0003] A first aspect of this application provides an optical system, which sequentially includes, along the optical axis from the first side to the second side: a first lens with positive optical power, whose first side is convex and the second side is flat; a reflective polarizing element; a first quarter-wave plate; a second lens with negative optical power, whose second side is concave; a third lens with positive optical power, whose first side is convex and the second side is convex; a partial reflection element; a fourth lens with negative optical power, whose first side is concave and the second side is flat; a second quarter-wave plate; and a polarizer; wherein, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens; the first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element; the second quarter-wave plate is placed on the second side of the fourth lens and at least partially adheres to the second side of the fourth lens; the polarizer is placed on the second side of the second quarter-wave plate and at least partially adheres to the second side of the second quarter-wave plate; the optical system further includes: a third spacer element placed between the third lens and the fourth lens and abutted against the second side of the third lens; the optical system satisfies: 2.0 < f3 / d3s < 2.9 and -2.2 < fz2 / d3m < -1.7, where f3 is the effective focal length of the third lens, d3s is the inner diameter of the first side of the third spacer element, fz2 is the combined focal length of the fourth lens, the second quarter-wave plate, and the polarizer, and d3m is the inner diameter of the second side of the third spacer element.

[0004] In one embodiment, the optical system further includes: a lens barrel and a first spacer element; the first spacer element is disposed between the first lens and the second lens and abuts against the second side surface of the first lens; the optical system satisfies: 2.6 < (CT1 + CTR + CTQ1) / EP01 < 3.25, where CT1 is the central thickness of the first lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, CTQ1 is the central thickness of the first quarter-wave plate on the optical axis, and EP01 is the distance along the optical axis from the first side end surface of the lens barrel to the first side surface of the first spacer element.

[0005] In one embodiment, the optical system further includes: a first spacer element disposed between the first lens and the second lens and abutting against the second side surface of the first lens; the optical system satisfies: 0.8 < T12 / CP1 < 1.5, where T12 is the on-axis distance from the second side surface of the first lens to the first side surface of the second lens, and CP1 is the maximum thickness of the first spacer element along the optical axis.

[0006] In one embodiment, the optical system further includes a lens barrel and satisfies: 1.6 < D0s / R1 < 1.8, where D0s is the outer diameter of the first side end surface of the lens barrel, and R1 is the radius of curvature of the first side surface of the first lens.

[0007] In one embodiment, the optical system further includes: a second spacer element disposed between the second lens and the third lens and abutting against the second side surface of the second lens; the optical system satisfies: 1.4 < (d2s + D2s) / R4 < 1.7, where d2s is the inner diameter of the first side surface of the second spacer element, D2s is the outer diameter of the first side surface of the second spacer element, and R4 is the radius of curvature of the second side surface of the second lens.

[0008] In one embodiment, the optical system further includes: a first spacer element and a second spacer element, the first spacer element is disposed between the first lens and the second lens and abuts against the second side surface of the first lens, and the second spacer element is disposed between the second lens and the third lens and abuts against the second side surface of the second lens; the optical system satisfies: 2.7 < TD / EP12 < 3.55, where TD is the distance on the optical axis from the first side surface of the first lens to the second side surface of the fourth lens, and EP12 is the distance along the optical axis from the second side surface of the first spacer element to the first side surface of the second spacer element.

[0009] In one embodiment, the optical system further includes: a second spacer element disposed between the second lens and the third lens and abutted against the second side surface of the second lens; the optical system satisfies 1.4 < (CT3 + T34) / EP23 < 1.85, where CT3 is the central thickness of the third lens on the optical axis, T34 is the on-axis distance from the second side surface of the third lens to the first side surface of the fourth lens, and EP23 is the distance along the optical axis from the second side surface of the second spacer element to the first side surface of the third spacer element.

[0010] In one embodiment, the optical system further includes a lens barrel and satisfies 2.1 < (d0m + D0m) / L < 2.3, where d0m is the inner diameter of the second side end surface of the lens barrel, D0m is the outer diameter of the second side end surface of the lens barrel, and L is the distance along the optical axis from the first side end surface of the lens barrel to the second side end surface.

[0011] In one embodiment, the optical system further includes: a first spacer element disposed between the first lens and the second lens and abutted against the second side surface of the first lens; the optical system satisfies 1.2 < (d1s + d1m) / fz1 < 1.4, where d1s is the inner diameter of the first side surface of the first spacer element, d1m is the inner diameter of the second side surface of the first spacer element, and fz1 is the combined focal length of the first lens, the reflective polarizing element, and the first quarter-wave plate.

[0012] In one embodiment, the optical system further includes: a second spacer element disposed between the second lens and the third lens and abutted against the second side surface of the second lens; the optical system satisfies 1.1 < (D2m - d2m) / CT2 < 2.2, where D2m is the outer diameter of the second side surface of the second spacer element, d2m is the inner diameter of the second side surface of the second spacer element, and CT2 is the central thickness of the second lens on the optical axis.

[0013] In one embodiment, the optical system further includes: a first spacer element disposed between the first lens and the second lens and abutted against the second side surface of the first lens; the optical system satisfies 1.3 < f1 / D1s < 1.5, where f1 is the effective focal length of the first lens and D1s is the outer diameter of the first side surface of the first spacer element.

[0014] In one embodiment, the optical system further includes: a first spacer element disposed between the first lens and the second lens and abutted against the second side surface of the first lens; the optical system satisfies 1.9 < (D3s + D3m) / D1m < 2.1, where D3s is the outer diameter of the first side surface of the third spacer element, D3m is the outer diameter of the second side surface of the third spacer element, and D1m is the outer diameter of the second side surface of the first spacer element.

[0015] In one embodiment, the optical system further includes a lens barrel and satisfies: 1.4 < d0s / ∑CT < 1.8, where d0s is the inner diameter of the first side end face of the lens barrel, and ∑CT is the sum of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis.

[0016] In one embodiment, the optical system further includes: a first spacer element and a second spacer element. The first spacer element is disposed between the first lens and the second lens and abuts against the second side face of the first lens. The second spacer element is disposed between the second lens and the third lens and abuts against the second side face of the second lens. The optical system satisfies: -5.9 < f2 / (EP12 + CP2) < -4.5, where f2 is the effective focal length of the second lens, EP12 is the distance along the optical axis from the second side face of the first spacer element to the first side face of the second spacer element, and CP2 is the maximum thickness of the second spacer element along the optical axis.

[0017] In one embodiment, the optical system further includes: a first spacer element and a second spacer element. The first spacer element is disposed between the first lens and the second lens and abuts against the second side face of the first lens. The second spacer element is disposed between the second lens and the third lens and abuts against the second side face of the second lens. The optical system satisfies: -7.4 < f4 / (EP23 + CP3) < -4.7, where f4 is the effective focal length of the fourth lens, EP23 is the distance along the optical axis from the second side face of the second spacer element to the first side face of the third spacer element, and CP3 is the maximum thickness of the third spacer element along the optical axis.

[0018] The second aspect of the present application provides an optical system. The optical system sequentially includes, from the first side to the second side along the optical axis: a first lens with positive optical power, whose first side is convex and the second side is flat; a reflective polarizing element; a first quarter-wave plate; a second lens with negative optical power, whose second side is concave; a third lens with positive optical power, whose first side is convex and the second side is convex; a partial reflection element; a fourth lens with negative optical power, whose first side is concave and the second side is flat; a second quarter-wave plate; and a polarizer. Wherein, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens; the first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element; the second quarter-wave plate is placed on the second side of the fourth lens and at least partially adheres to the second side of the fourth lens; the polarizer is placed on the second side of the second quarter-wave plate and at least partially adheres to the second side of the second quarter-wave plate. The optical system further includes: a second spacer element and a third spacer element. The second spacer element is placed between the second lens and the third lens and abuts against the second side of the second lens. The third spacer element is placed between the third lens and the fourth lens and abuts against the second side of the third lens. The optical system satisfies: 2.0 < f3 / d3s < 2.9 and 1.1 < (D2m - d2m) / CT2 < 2.2, where f3 is the effective focal length of the third lens, d3s is the inner diameter of the first side of the third spacer element, D2m is the outer diameter of the second side of the second spacer element, d2m is the inner diameter of the second side of the second spacer element, and CT2 is the central thickness of the second lens on the optical axis.

[0019] The third aspect of the present application further provides an optical device, which includes the optical system provided by any one of the above various embodiments.

[0020] The optical system provided by the present application adopts a polarization folding optical path design, arranging the optical powers of 4 lenses alternately positive and negative, and satisfying 2.0 < f3 / d3s < 2.9 and -2.2 < fz2 / d3m < -1.7. It can limit the inner diameters of the first side and the second side of the third spacer element, avoiding the risk of stray light ghost images due to the inability to block excess light when it is too large, and also avoiding an excessive difference between the inner and outer diameters of the third spacer element, which affects its processability. That is, by controlling f3 / d3s and fz2 / d3m within a reasonable range, the present application ensures the processability of the third spacer element, improves the assembly stability, can also block the reflection path of excess light at the edge of the third lens, reduce the generation of stray light, and improve the imaging clarity of the optical system. Description of the Drawings

[0021] In conjunction with the accompanying drawings, through the following detailed description of non-limiting embodiments, other features, objectives, and advantages of the present application will become more apparent. In the drawings:

[0022] Figure 1A shows a schematic structural diagram of an optical system according to Embodiment 1 of the present application;

[0023] Figure 1B shows a schematic structural diagram of an optical system according to Embodiment 2 of the present application;

[0024] Figure 1C shows a schematic structural diagram of an optical system according to Embodiment 3 of the present application;

[0025] FIG. 2A to FIG. 2D respectively show the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical systems according to Embodiments 1 to 3 of the present application;

[0026] Figure 3A shows a schematic structural diagram of an optical system according to Embodiment 4 of the present application;

[0027] Figure 3B shows a schematic structural diagram of an optical system according to Embodiment 5 of the present application;

[0028] Figure 3C shows a schematic structural diagram of an optical system according to Embodiment 6 of the present application;

[0029] 4A to 4D respectively show the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical systems according to Embodiments 4 to 6 of the present application;

[0030] Figure 5A shows a schematic structural diagram of an optical system according to Embodiment 7 of the present application;

[0031] Figure 5B shows a schematic structural diagram of an optical system according to Embodiment 8 of the present application;

[0032] Figure 5C shows a schematic structural diagram of an optical system according to Embodiment 9 of the present application;

[0033] FIG. 6A to FIG. 6D respectively show the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical systems according to Embodiments 7 to 9 of the present application; and

[0034] Figure 7 shows a schematic structural diagram of the optical system according to the present application and a schematic diagram of some parameters. Detailed implementation manners

[0035] To better understand the present application, various aspects of the present application will be described in more detail with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of exemplary embodiments of the present application and do not limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] It should be noted that in this specification, the expressions such as first, second, etc. are only used to distinguish one feature from another feature and do not represent any limitation on the feature. Therefore, without departing from the teachings of the present application, the first lens discussed below may also be referred to as the second lens, and the second lens may also be referred to as the first lens.

[0037] In the drawings, for the sake of clarity, the thickness, dimensions, and shape of the lens have been slightly exaggerated. Specifically, the spherical or aspherical shapes shown in the drawings are shown by way of example. That is, the spherical or aspherical shapes are not limited to the spherical or aspherical shapes shown in the drawings. The drawings are for illustrative purposes only and are not drawn to an exact scale.

[0038] In this document, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the position of the convex surface is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the position of the concave surface is not defined, it means that the lens surface is concave at least in the paraxial region.

[0039] It should also be understood that the terms "comprise", "comprising", "have", "include" and / or "including", when used in this specification, indicate the presence of the stated features, elements and / or components, but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof. In addition, when an expression such as "at least one of..." appears after the list of listed features, it modifies the entire list of listed features, rather than modifying a single element in the list. In addition, when describing the embodiments of the present application, the use of "may" means "one or more embodiments of the present application". And the term "exemplary" is intended to refer to an example or illustration.

[0040] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms (such as those defined in a common dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formalized sense unless expressly so defined herein.

[0041] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] The features, principles, and other aspects of the present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] An optical system according to an exemplary embodiment of the present application sequentially includes, along the optical axis from a first side to a second side: a first lens, a reflective polarizing element, a first quarter-wave plate, a second lens, a third lens, a partially reflective element, a fourth lens, a second quarter-wave plate, and a polarizer.

[0044] In the exemplary embodiment, the first lens has a positive optical power, the second lens has a negative optical power, the third lens has a positive optical power, and the fourth lens has a negative optical power. Alternating the positive and negative optical powers of the four lenses is beneficial to reducing the sensitivity of the optical system to environmental conditions and improving the stability and reliability of the system.

[0045] In the exemplary embodiment, the first side of the first lens is a convex surface and the second side is a flat surface.

[0046] In the exemplary embodiment, the second side of the second lens is a concave surface.

[0047] In the exemplary embodiment, the first side of the third lens is a convex surface and the second side is a convex surface.

[0048] In the exemplary embodiment, the first side of the fourth lens is a concave surface and the second side is a flat surface.

[0049] Those skilled in the art should understand that the reflective polarizing element can reflect polarized light in a certain direction and can also transmit polarized light orthogonal to the polarization direction. The quarter-wave plate can change the state of polarized light. By using the combination of light reflection and refraction of the reflective polarizing element and the quarter-wave plate, the required optical path can be folded, effectively shortening the length of the optical system.

[0050] In the exemplary embodiment, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens. The first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element. Exemplarily, the reflective polarizing element and the first quarter-wave plate can be compounded and adhered to the second side of the first lens through a single attachment process instead of two separate attachment processes, reducing the angular position error caused by the attachment and improving the imaging quality.

[0051] In an exemplary embodiment, the second quarter-wave plate is disposed on the second side surface of the fourth lens and at least partially adheres to the second side surface of the fourth lens; the polarizer is disposed on the second side surface of the second quarter-wave plate and at least partially adheres to the second side surface of the second quarter-wave plate. Exemplarily, the second quarter-wave plate and the polarizer can be compounded and adhered to the second side surface of the fourth lens through a single attachment process, rather than being attached in two separate steps, reducing the angular position error caused by the attachment and improving the imaging quality.

[0052] In an exemplary embodiment, the optical system according to the present application can be applied to, for example, a VR device. The first side can be, for example, the human eye side, and the second side can be, for example, the screen side. As Figure 1A shown, the optical system sequentially includes, along the optical axis from the human eye side to the screen side: a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS (not shown), a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP. Among them, the reflective polarizing element RP is attached to the near-screen side surface of the first lens E1, and the first quarter-wave plate QWP1 is attached to the near-screen side surface of the reflective polarizing element RP; the second quarter-wave plate QWP2 is attached to the near-screen side surface of the fourth lens E4, and the polarizer LP is attached to the near-screen side surface of the second quarter-wave plate QWP2. The partial reflection element BS can have a semi-transmissive and semi-reflective function and is attached to the near-screen side surface of the third lens E3.

[0053] Figure 1A The optical system shown further includes an image plane IMG disposed on the screen side and a protective glass GL for protecting the light-emitting element located on the image plane IMA. The optical system may further include a diaphragm STO (not shown) disposed on the human eye side. The user's eye can view the image projected from the image plane IMG at the position of the aperture STO, that is, the image light on the image plane IMG passes through the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, and the first lens E1, etc., and is finally projected onto the user's eye after multiple refractions and reflections. More specifically, Figure 1AThe path of the light rays of the optical system in [it] is as follows: The light emitted from the image plane IMG sequentially passes through the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1 and reaches the reflective polarizing element RP. It is reflected at the reflective polarizing element RP and passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 again. The light beam is reflected again at the partial reflection element BS on the near-screen side of the third lens E3 and sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP and the first lens E1, then passes through the aperture STO and finally exits toward the human eye side.

[0054] Figure 1A The optical system shown also includes a first spacer element P1, a second spacer element P2 and a third spacer element P3. The first spacer element P1 is disposed between the first lens E1 and the second lens E2 and abuts against the second side surface of the first lens E1. The second spacer element P2 is disposed between the second lens E2 and the third lens E3 and abuts against the second side surface of the second lens E2. The third spacer element P3 is disposed between the third lens E3 and the fourth lens E4 and abuts against the second side surface of the third lens E3.

[0055] Figure 1A The optical system shown also includes a lens barrel P0, which is used to accommodate the first lens, the reflective polarizing element, the first quarter-wave plate, the second lens, the third lens, the partial reflection element, the fourth lens, the second quarter-wave plate, the polarizer and the spacer element, etc.

[0056] In an exemplary embodiment, the optical system may include at least one of the first spacer element, the second spacer element and the third spacer element. The first spacer element is disposed between the first lens and the second lens and abuts against the second side surface of the first lens. The second spacer element is disposed between the second lens and the third lens and abuts against the second side surface of the second lens. The third spacer element is disposed between the third lens and the fourth lens and abuts against the second side surface of the third lens.

[0057] It should be understood that the present application does not specifically limit the number of spacer elements. Any number of spacer elements may be included between any two lenses, and any number of spacer elements may also be included in the entire imaging system. The spacer elements help the imaging system intercept redundant catadioptric light paths, reduce the generation of stray light and ghost images. The spacer elements also help to increase the auxiliary support between the lens and the lens barrel, which is beneficial to improving problems such as poor assembly stability and low performance yield caused by large step differences between lenses.

[0058] Figure 7 The structural schematic diagram of the optical system according to the present application and the schematic diagram of some parameters are shown. As Figure 7As shown, CP1 is the maximum thickness of the first spacing element along the optical axis, CP2 is the maximum thickness of the second spacing element along the optical axis, CP3 is the maximum thickness of the third spacing element along the optical axis, EP01 is the distance from the first side end face of the lens barrel to the first side face of the first spacing element along the optical axis, EP12 is the distance from the second side face of the first spacing element to the first side face of the second spacing element along the optical axis, EP23 is the distance from the second side face of the second spacing element to the first side face of the third spacing element along the optical axis, L is the distance from the first side end face of the lens barrel to the second side end face along the optical axis, d3s is the inner diameter of the first side face of the third spacing element, d2s is the inner diameter of the first side face of the second spacing element, and d1s is the distance from the first side end face of the lens barrel to the second side end face. element, D1s is the outer diameter of the first side of the first spacing element, D3s is the outer diameter of the first side of the third spacing element, D2s is the outer diameter of the first side of the second spacing element, d0s is the inner diameter of the first side end surface of the barrel, D0s is the outer diameter of the first side end surface of the barrel, d3m is the inner diameter of the second side of the third spacing element, d0m is the inner diameter of the second side end surface of the barrel, d2m is the inner diameter of the second side of the second spacing element, d1m is the inner diameter of the second side of the first spacing element, D1m is the outer diameter of the second side of the first spacing element, D3m is the outer diameter of the second side of the third spacing element, D2m is the outer diameter of the second side of the second spacing element, and D0m is the outer diameter of the second side end surface of the barrel.

[0059] Those skilled in the art should understand that some parameters of lenses commonly used in the art (such as the center thickness CT1 of the first lens on the optical axis) are not included in the description. Figure 7 It is shown in Figure 7 Only partial parameters of the lens barrel and the spacer element of an imaging system of the present application are exemplified to facilitate a better understanding of the present invention.

[0060] In an exemplary embodiment, the optical system meets 2.0 <f3 / d3s<2.9,其中,f3为第三透镜的有效焦距,d3s为第三间隔元件的第一侧面的内径。

[0061] In an exemplary embodiment, the optical system satisfies -2.2 <fz2 / d3m<-1.7,其中,fz2为第四透镜、第二四分之一波片和偏振片的组合焦距,d3m为第三间隔元件的第二侧面的内径。

[0062] On the one hand, the present application provides an optical system, which sequentially includes, along the optical axis, from the first side to the second side: a first lens with positive optical power, whose first side is convex and the second side is flat; a reflective polarizing element; a first quarter-wave plate; a second lens with negative optical power, whose second side is concave; a third lens with positive optical power, whose first side is convex and the second side is convex; a partial reflection element; a fourth lens with negative optical power, whose first side is concave and the second side is flat; a second quarter-wave plate; and a polarizer; wherein, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens; the first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element; the second quarter-wave plate is placed on the second side of the fourth lens and at least partially adheres to the second side of the fourth lens; the polarizer is placed on the second side of the second quarter-wave plate and at least partially adheres to the second side of the second quarter-wave plate; the optical system further includes: a third spacer element placed between the third lens and the fourth lens and abutted against the second side of the third lens; the optical system satisfies: 2.0 < f3 / d3s < 2.9 and -2.2 < fz2 / d3m < -1.7, where f3 is the effective focal length of the third lens, d3s is the inner diameter of the first side of the third spacer element, fz2 is the combined focal length of the fourth lens, the second quarter-wave plate and the polarizer, and d3m is the inner diameter of the second side of the third spacer element. Arranging the optical powers of the 4 lenses alternately positive and negative is beneficial to reducing the sensitivity of the optical system to environmental conditions, improving the stability and reliability of the system, and by controlling f3 / d3s and fz2 / d3m within a reasonable range, the inner diameters of the first side and the second side of the third spacer element can be restricted. That is, when it is too large, there is a risk of stray light ghosts due to the inability to block excess light, and when it is too small, the difference between the inner and outer diameters of the third spacer element is too large, affecting its processability. That is, the present application ensures the processability of the third spacer element, improves the assembly stability, and can also block the reflection path of the excess light at the edge of the third lens, reduce the generation of stray light, and improve the imaging clarity of the optical system.

[0063] In an exemplary embodiment, the optical system satisfies 2.6 < (CT1 + CTR + CTQ1) / EP01 < 3.25, where CT1 is the central thickness of the first lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, CTQ1 is the central thickness of the first quarter-wave plate on the optical axis, and EP01 is the distance along the optical axis from the first side end face of the lens barrel to the first side face of the first spacer element. Reasonably setting the distance along the optical axis from the first side end face of the lens barrel to the first side face of the first spacer element indirectly ensures the edge thickness of the first lens, satisfies 2.6 < (CT1 + CTR + CTQ1) / EP01 < 3.25, is beneficial to controlling the thickness ratio of the first lens, is beneficial to the molding of the first lens, and also ensures the dispensing space of the first lens, indirectly ensuring reliability.

[0064] In an exemplary embodiment, the optical system satisfies: 0.8 < T12 / CP1 < 1.5, where T12 is the on-axis distance from the second side face of the first lens to the first side face of the second lens, and CP1 is the maximum thickness of the first spacer element along the optical axis. Controlling the maximum thickness of the first spacer element within a reasonable range can not only avoid the increase in the overall thickness of the whole machine caused by the excessive thickness of the first spacer element, affecting the experience effect, but also prevent the thickness of the first spacer element from being too small to ensure its processability and structural strength.

[0065] In an exemplary embodiment, the optical system satisfies: 1.6 < D0s / R1 < 1.8, where D0s is the outer diameter of the first side end face of the lens barrel, and R1 is the radius of curvature of the first side face of the first lens. Controlling the ratio of the outer diameter of the first side end face of the lens barrel to the radius of curvature of the first side face of the first lens helps to quickly converge light through the first lens and converge the light passing aperture; at the same time, it is beneficial to restricting the light beam, obtaining a large field of view angle, and is beneficial to improving the user experience.

[0066] In an exemplary embodiment, the optical system satisfies: 1.4 < (d2s + D2s) / R4 < 1.7, where d2s is the inner diameter of the first side face of the second spacer element, D2s is the outer diameter of the first side face of the second spacer element, and R4 is the radius of curvature of the second side face of the second lens. Satisfying 1.4 < (d2s + D2s) / R4 < 1.7 helps to control the overall shape of the second lens and improve the processability of the second lens. Controlling the inner diameter size of the first side face of the second spacer element can better change the reflection route of the redundant light, reduce the generation of stray light, and improve the imaging clarity.

[0067] In an exemplary embodiment, the optical system satisfies: 2.7 < TD / EP12 < 3.55, where TD is the distance on the optical axis from the first side surface of the first lens to the second side surface of the fourth lens, and EP12 is the distance along the optical axis from the second side surface of the first spacer element to the first side surface of the second spacer element. Controlling the distance on the optical axis from the first side surface of the first lens to the second side surface of the fourth lens limits the overall length of the optical system, which is of great significance for reducing the size of the whole machine. At the same time, reasonably setting the ratio of TD and EP12 is beneficial to the molding of the first spacer element, the second spacer element and the first lens.

[0068] In an exemplary embodiment, the optical system satisfies: 1.4 < (CT3 + T34) / EP23 < 1.85, where CT3 is the central thickness of the third lens on the optical axis, T34 is the axial distance from the second side surface of the third lens to the first side surface of the fourth lens, and EP23 is the distance along the optical axis from the second side surface of the second spacer element to the first side surface of the third spacer element. Satisfying 1.4 < (CT3 + T34) / EP23 < 1.85 can control the air gap between the third lens and the fourth lens within a reasonable range, which is beneficial to controlling the field curvature of the whole optical system and ensuring its optical performance. At the same time, it also helps to restrict the edge thicknesses of the second lens and the third lens, ensuring the processability of the second lens and the third lens.

[0069] In an exemplary embodiment, the optical system satisfies: 2.1 < (d0m + D0m) / L < 2.3, where d0m is the inner diameter of the second end face of the lens barrel, D0m is the outer diameter of the second end face of the lens barrel, and L is the distance along the optical axis from the first end face of the lens barrel to the second end face. Satisfying 2.1 < (d0m + D0m) / L < 2.3 can prevent the lens barrel from being too long and control the opening sizes of the first end face and the second end face of the lens barrel, ensuring the miniaturization of the volume of the whole machine. At the same time, it can reasonably distribute the thicknesses of the components inside the lens barrel, avoiding them being too small, and ensuring the processability of each component on the premise of ensuring the system assembly.

[0070] In an exemplary embodiment, the optical system satisfies: 1.2 < (d1s + d1m) / fz1 < 1.4, where d1s is the inner diameter of the first side surface of the first spacer element, d1m is the inner diameter of the second side surface of the first spacer element, and fz1 is the combined focal length of the first lens, the reflective polarizing element and the first quarter-wave plate. Satisfying 1.2 < (d1s + d1m) / fz1 < 1.4 can ensure the bearing relationship between the first spacer element and the first lens and the lens barrel, improving its stability. At the same time, restricting the inner diameters of the first side surface and the second side surface of the first spacer element can effectively control the light input amount of the optical system, better change the reflection route of the redundant light, reduce the generation of stray light, and improve the imaging clarity.

[0071] In an exemplary embodiment, the optical system satisfies: 1.1 < (D2m - d2m) / CT2 < 2.2, where D2m is the outer diameter of the second side surface of the second spacer element, d2m is the inner diameter of the second side surface of the second spacer element, and CT2 is the central thickness of the second lens on the optical axis. Satisfying 1.1 < (D2m - d2m) / CT2 < 2.2 helps to eliminate the assembly step difference between the second lens and the third lens and improve the assembly stability. At the same time, it also helps to control the central thickness of the second lens and improve the processability of the second lens.

[0072] In an exemplary embodiment, the optical system satisfies: 1.3 < f1 / D1s < 1.5, where f1 is the effective focal length of the first lens and D1s is the outer diameter of the first side surface of the first spacer element. Satisfying 1.3 < f1 / D1s < 1.5 is beneficial to ensure the processability of the first lens and the first spacer element.

[0073] In an exemplary embodiment, the optical system satisfies: 1.9 < (D3s + D3m) / D1m < 2.1, where D3s is the outer diameter of the first side surface of the third spacer element, D3m is the outer diameter of the second side surface of the third spacer element, and D1m is the outer diameter of the second side surface of the first spacer element. By controlling the outer diameters of the first spacer element and the third spacer element, it is beneficial to control the inner wall size and trend of the lens barrel, avoid too large a trend drop between the first spacer element and the third spacer element in contact with the lens barrel, which affects the processability of the lens barrel, and at the same time avoid too small a trend drop between the first spacer element and the third spacer element, which limits the inner diameter of the lens barrel and thus affects the outer diameter of the lens, increasing the difficulty of lens design and processing.

[0074] In an exemplary embodiment, the optical system satisfies: 1.4 < d0s / ∑CT < 1.8, where d0s is the inner diameter of the first side end face of the lens barrel and ∑CT is the sum of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis. Satisfying 1.4 < d0s / ∑CT < 1.8 helps to control the overall shape of the lens barrel to meet the requirements of the module end and achieve the miniaturized design of the lens.

[0075] In an exemplary embodiment, the optical system satisfies: -5.9 < f2 / (EP12 + CP2) < -4.5, where f2 is the effective focal length of the second lens, EP12 is the distance along the optical axis from the second side surface of the first spacer element to the first side surface of the second spacer element, and CP2 is the maximum thickness of the second spacer element along the optical axis. Controlling the value of f2 / (EP12 + CP2) to satisfy the conditional expression -5.9 < f2 / (EP12 + CP2) < -4.5 can avoid the value of f2 / (EP12 + CP2) exceeding the upper limit of -4.5, which may cause EP12 and CP2 to be too large and affect the processability of the first spacer element and the second spacer element. It can also avoid the value of f2 / (EP12 + CP2) exceeding the lower limit of -5.9 of the conditional expression -5.9 < f2 / (EP12 + CP2) < -4.5, which may cause EP12 and CP2 to be too small and result in insufficient supporting force of the spacer element, thus unable to ensure its supporting performance.

[0076] In an exemplary embodiment, the optical system satisfies: -7.4 < f4 / (EP23 + CP3) < -4.7, where f4 is the effective focal length of the fourth lens, EP23 is the distance along the optical axis from the second side surface of the second spacer element to the first side surface of the third spacer element, and CP3 is the maximum thickness of the third spacer element along the optical axis. Satisfying -7.4 < f4 / (EP23 + CP3) < -4.7 can control spherical aberration, make the imaging quality of the system on the axis good, and at the same time, on the basis of ensuring the bearing effect, it is beneficial to improve the processability of the third spacer element.

[0077] Another aspect of the present application also provides an optical system, which sequentially includes, from the first side to the second side along the optical axis: a first lens with a positive optical power, whose first side is convex and the second side is flat; a reflective polarizing element; a first quarter-wave plate; a second lens with a negative optical power, whose second side is concave; a third lens with a positive optical power, whose first side is convex and the second side is convex; a partial reflection element; a fourth lens with a negative optical power, whose first side is concave and the second side is flat; a second quarter-wave plate; and a polarizer; wherein, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens; the first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element; the second quarter-wave plate is placed on the second side of the fourth lens and at least partially adheres to the second side of the fourth lens; the polarizer is placed on the second side of the second quarter-wave plate and at least partially adheres to the second side of the second quarter-wave plate; the optical system further includes: a second spacer element and a third spacer element, the second spacer element is placed between the second lens and the third lens and abuts against the second side of the second lens, and the third spacer element is placed between the third lens and the fourth lens and abuts against the second side of the third lens; the optical system satisfies: 2.0 < f3 / d3s < 2.9 and 1.1 < (D2m - d2m) / CT2 < 2.2, where f3 is the effective focal length of the third lens, d3s is the inner diameter of the first side of the third spacer element, D2m is the outer diameter of the second side of the second spacer element, d2m is the inner diameter of the second side of the second spacer element, and CT2 is the central thickness of the second lens on the optical axis. By satisfying 2.0 < f3 / d3s < 2.9 and 1.1 < (D2m - d2m) / CT2 < 2.2, by restricting the inner diameter of the first side of the third spacer element, the light input amount of the optical system can be effectively controlled, and the light can be more efficiently utilized to participate in imaging. It can also better change the reflection route of the redundant light, reduce the generation of stray light, and improve the imaging clarity. By controlling the ratio of the inner diameter, outer diameter of the second side of the second spacer element and the central thickness of the second lens, it helps to eliminate the assembly step difference between the second lens and the third lens, improve the assembly stability. At the same time, it also helps to control the central thickness of the second lens and improve the processability of the second lens.

[0078] In an exemplary embodiment, the optical system of the present application may include at least one aperture stop. The aperture stop can restrict the optical path and control the light intensity. The aperture stop can be set at an appropriate position of the optical system. For example, the aperture stop can be located on the first side of the first lens.

[0079] In an embodiment of the present application, at least one of the surfaces of each of the first lens to the fourth lens is an aspherical surface. The characteristic of an aspherical lens is that the curvature continuously changes from the center of the lens to the periphery of the lens. Different from a spherical lens with a constant curvature from the center of the lens to the periphery, an aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and improving astigmatism aberration. After using an aspherical lens, it is possible to eliminate the aberration that appears during imaging as much as possible, thereby improving the imaging quality. Optionally, the first side and the second side of the third lens, and the first side of the fourth lens may be aspherical surfaces. Optionally, the first side and the second side of the first lens, the second side of the second lens, the first side and the second side of the third lens, and the first side of the fourth lens may be aspherical surfaces.

[0080] The optical system provided by the present application can use four lenses. A reflective polarizing element and a quarter-wave plate are attached to the second side of the first lens, and a reflective polarizing element and a polarizer are attached to the second side of the fourth lens. Such a design can convert the natural light emitted from the image plane into polarized light and realize the refolding of the optical path. In addition to reasonably arranging the lenses and reflective elements, the optical system provided by the present application can also reasonably design the size of the spacer element, improve the assembly stability of the optical system, reduce the stray light interference, and improve the imaging quality of the system.

[0081] According to some embodiments of the present application, the optical system of the present application has advantages such as small volume, small optical distortion, clear and stable image, etc., and can provide a better virtual reality experience for users. In applications, the optical system according to the exemplary embodiments of the present application can be applied to VR devices. By reasonably setting parameters such as the optical power, entrance pupil diameter, center thickness, refractive index, Abbe number, and curvature radius of the optical system, the purpose of wide angle of the VR device can be achieved, the chromatic aberration of the system can be corrected, the optical distortion can be reduced, and the imaging quality and reliability of the system can be improved.

[0082] Next, taking the optical system applied to, for example, a VR device, with the first side being the human eye side and the second side being the screen side, the specific embodiments of the optical system applicable to the above embodiments will be further described with reference to the accompanying drawings.

[0083] Example 1

[0084] Figure 1A FIG. 16 shows a schematic structural diagram of an optical system 1001 according to Embodiment 1 of the present application.

[0085] As Figure 1AAs shown, the optical system 1001 includes a lens barrel P0 and various components disposed within the lens barrel P0. The optical system 1001, from the human eye side to the screen side in sequence, includes: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG.

[0086] The first lens E1 has a positive optical power. Its side near the human eye is convex, and its side near the screen is flat. The second lens E2 has a negative optical power. Its side near the human eye is concave, and its side near the screen is concave. The third lens E3 has a positive optical power. Its side near the human eye is convex, and its side near the screen is convex. The fourth lens E4 has a negative optical power. Its side near the human eye is concave, and its side near the screen is flat. Among them, the reflective polarizing element RP is attached to the side of the first lens E1 near the screen, and the first quarter-wave plate QWP1 is attached to the side of the reflective polarizing element RP near the screen; the second quarter-wave plate QWP2 is attached to the side of the fourth lens E4 near the screen, and the polarizer LP is attached to the side of the second quarter-wave plate QWP2 near the screen. The partial reflection element BS may have a semi-transmissive and semi-reflective function and is attached to the side of the third lens E3 near the screen.

[0087] In this example, the light emitted from the image plane IMG sequentially passes through the protective glass GL, the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, and the first quarter-wave plate QWP1 to reach the reflective polarizing element RP. At the reflective polarizing element RP, it is reflected and passes through the first quarter-wave plate QWP1, the second lens E2, and the third lens E3 again. The light beam is reflected again at the partial reflection element BS on the side of the third lens E3 near the screen and sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, and the first lens E1, then passes through the diaphragm STO and finally exits toward the human eye side.

[0088] Table 1 shows the basic parameters of the optical system of Example 1, where the units of the radius of curvature and the thickness are both millimeters (mm).

[0089] Table 1

[0090] Serial number Part Name Surface type Radius of curvature thickness Refractive Index Abbe number Refraction / Reflection Cone coefficient 0 Spherical endless -100000.0000 refraction 1 Aperture (STO) Spherical endless 20.0000 refraction 2 First lens (E1) Spherical 21.0000 6.1945 1.472 66.88 refraction 3 Reflective polarizer (RP) Spherical endless 0.1100 1.502 57.00 refraction 4 First Quarter Wave Plate (QWP1) Spherical endless 0.1100 1.502 57.00 refraction 5 Spherical endless 3.5527 refraction 6 Second lens (E2) Aspheric -224.7099 5.7131 1.755 34.95 refraction 0.0000 7 Aspheric 38.0409 0.5575 refraction 0.0000 8 Third lens (E3) Spherical 26.9139 6.0607 1.673 51.76 refraction 9 Partially reflective element (BS) Spherical -5623.1978 -6.0607 1.673 51.76 reflection 10 Spherical 26.9139 -0.5575 refraction 11 Aspheric 38.0409 -5.7131 1.755 34.95 refraction 0.0000 12 Aspheric -224.7099 -3.5527 refraction 0.0000 13 Spherical endless -0.1100 1.502 57.00 refraction 14 Spherical endless -0.1100 1.502 57.00 refraction 15 Reflective polarizer (RP) Spherical endless 0.1100 1.502 57.00 reflection 16 First Quarter Wave Plate (QWP1) Spherical endless 0.1100 1.502 57.00 refraction 17 Spherical endless 3.5527 refraction 18 Second lens (E2) Aspheric -224.7099 5.7131 1.755 34.95 refraction 0.0000 19 Aspheric 38.0409 0.5575 refraction 0.0000 20 Third lens (E3) Spherical 26.9139 6.0607 1.673 51.76 refraction 21 Spherical -5623.1978 1.4915 refraction 22 Fourth lens (E4) Aspheric -17.1036 1.4000 1.546 55.92 refraction 0.0000 23 Second Quarter Wave Plate (QWP2) Spherical endless 0.1100 1.502 57.00 refraction 24 Polarizer(LP) Spherical endless 0.1500 1.502 57.00 refraction 25 Spherical endless 0.5400 refraction 26 Protective glass (GL) Spherical endless 0.7100 1.519 64.17 refraction 27 Spherical endless 0.3000 refraction 28 Image surface (IMG) Spherical endless 0.0000 refraction

[0091] In Example 1, the surfaces of the side near the human eye and the side near the screen of the second lens, and the surface of the side near the human eye of the fourth lens are all aspherical surfaces. The surface profile x of each aspherical lens can be defined by, but not limited to, the following aspherical formula:

[0092]

[0093] Wherein, x is the sagitta, which is the distance from the vertex of the aspherical surface to the position along the optical axis at a height of h; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1 above); k is the conic coefficient; Ai is the correction coefficient of the i-th order of the aspherical surface. Table 2 below gives the higher-order term coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 for each aspherical mirror surface in Example 1.

[0094] Table 2

[0095]

[0096]

[0097] Table 3 shows some basic parameters of the optical system of Example 1. The units of f, f1, f2, f3, f4, fz1, fz2, ∑CT, and TD are all millimeters (mm).

[0098] Table 3

[0099] f f1 f2 f3 f4 fz1 fz2 ∑CT TD 42.00 44.48 -42.72 39.81 -31.31 44.48 -31.31 19.37 25.19

[0100] As Figure 1A shown, the optical system 1001 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the near-screen side surface of the first lens. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the near-screen side surface of the second lens. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the near-screen side surface of the third lens. Table 4 shows the basic parameter table of the spacer elements of the imaging system 1001. The units of the parameters in Table 4 are all millimeters (mm).

[0101] Table 4

[0102] parameter d1s d1m D1s D1m d2s d2m D2s D2m Numeric 26.662 27.382 30.767 30.759 23.322 23.322 31.340 31.340 parameter d3s d3m D3s D3m d0s d0m D0s D0m Numeric 15.974 15.974 30.940 30.940 33.140 17.804 36.140 34.225 parameter EP01 CP1 EP12 CP2 EP23 CP3 L Numeric 2.051 3.376 8.500 0.050 4.200 0.050 23.000

[0103] Example 2

[0104] Figure 1B shows a schematic structural diagram of the optical system 1002 according to Embodiment 2 of the present application. In this embodiment and the following Embodiment 3, for the sake of simplicity, some descriptions similar to those in Embodiment 1 will be omitted.

[0105] As Figure 1BAs shown, the optical system 1002 includes a lens barrel P0 and various components disposed within the lens barrel. The optical system 1002 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These components are exactly the same as those in Embodiment 1 and will not be elaborated further. The basic parameters of the optical system 1002 are shown in Tables 1 to 3 and will not be elaborated further.

[0106] As Figure 1B shown, the optical system 1002 further includes three spacer elements, namely a first spacer element P1, a second spacer element P2, and a third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the near-screen side surface of the first lens. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the near-screen side surface of the second lens. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the near-screen side surface of the third lens. Table 5 shows the basic parameter table of the spacer elements of the imaging system 1002, and the unit of each parameter in Table 5 is millimeter (mm).

[0107] Table 5

[0108]

[0109]

[0110] Example 3

[0111] Figure 1C shows a schematic structural diagram of an imaging system 1003 according to Embodiment 3 of the present application.

[0112] As Figure 1C shown, the optical system 1003 includes a lens barrel P0 and various components disposed within the lens barrel. The optical system 1003 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These components are exactly the same as those in Embodiment 1 and will not be elaborated further. The basic parameters of the optical system 1003 are shown in Tables 1 to 3 and will not be elaborated further.

[0113] As Figure 1CAs shown, the optical system 1003 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the side of the first lens near the screen. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the side of the second lens near the screen. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the side of the third lens near the screen. Table 6 shows the basic parameter table of the spacer elements of the imaging system 1003. The unit of each parameter in Table 5 is millimeter (mm).

[0114] Table 6

[0115] parameter d1s d1m D1s D1m d2s d2m D2s D2m Numeric 27.115 27.104 30.719 31.128 23.230 23.230 31.340 31.340 parameter d3s d3m D3s D3m d0s d0m D0s D0m Numeric 15.834 15.834 30.940 30.940 33.077 17.961 35.557 34.225 parameter EP01 CP1 EP12 CP2 EP23 CP3 L Numeric 2.167 2.826 9.050 0.050 4.200 0.050 23.433

[0116] Figure 2A Shows the axial chromatic aberration curves of the imaging system 1001 of Example 1, the imaging system 1002 of Example 2, and the imaging system 1003 of Example 3, which represent the deviation of the convergence points of light rays of different wavelengths after passing through the lens. Figure 2B Shows the astigmatism curves of the imaging system 1001 of Example 1, the imaging system 1002 of Example 2, and the imaging system 1003 of Example 3, which represent the curvature of the meridional image plane and the curvature of the sagittal image plane. Figure 2C Shows the distortion curves of the imaging system 1001 of Example 1, the imaging system 1002 of Example 2, and the imaging system 1003 of Example 3, which represent the distortion magnitude values corresponding to different field angles. Figure 2D Shows the modulation transfer function (MTF) curves of the imaging system 1001 of Example 1, the imaging system 1002 of Example 2, and the imaging system 1003 of Example 3. According to FIG. 2A to FIG. 2D It can be seen that the imaging systems 1001 of Example 1, 1002 of Example 2, and 1003 of Example 3 can all achieve good imaging quality.

[0117] Example 4

[0118] Figure 3A Shows a schematic structural diagram of the optical system 2001 according to Embodiment 4 of the present application.

[0119] As Figure 3A shown, the optical system 2001 includes a lens barrel P0 and various elements disposed in the lens barrel. The optical system 2001 includes, in sequence from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG.

[0120] The first lens E1 has a positive optical power, with its side closer to the human eye being convex and its side closer to the screen being flat. The second lens E2 has a negative optical power, with its side closer to the human eye being convex and its side closer to the screen being concave. The third lens E3 has a positive optical power, with its side closer to the human eye being convex and its side closer to the screen being convex. The fourth lens E4 has a negative optical power, with its side closer to the human eye being concave and its side closer to the screen being flat. Among them, the reflective polarizing element RP is attached to the side of the first lens E1 closer to the screen, and the first quarter-wave plate QWP1 is attached to the side of the reflective polarizing element RP closer to the screen; the second quarter-wave plate QWP2 is attached to the side of the fourth lens E4 closer to the screen, and the polarizer LP is attached to the side of the second quarter-wave plate QWP2 closer to the screen. The partial reflection element BS can have a semi-transmissive and semi-reflective function and is attached to the side of the third lens E3 closer to the screen.

[0121] In this example, the light emitted from the image plane IMG sequentially passes through the protective glass GL, the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1 and reaches the reflective polarizing element RP. It is reflected at the reflective polarizing element RP and passes through the first quarter-wave plate QWP1, the second lens E2, and the third lens E3 again. The light beam is reflected again at the partial reflection element BS on the side of the third lens E3 closer to the screen and sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, and the first lens E1, and then passes through the aperture STO and finally exits toward the human eye side.

[0122] Table 7 shows the basic parameters of the optical system of Example 4, where the units of the radius of curvature and the thickness are both millimeters (mm).

[0123] Table 8 shows the higher-order term coefficients of the aspherical mirror surfaces that can be used in Example 4, where each aspherical surface type can be defined by the formula (1) given in the above Example 1.

[0124] Table 7

[0125] Serial number Part Name Surface type Radius of curvature thickness Refractive Index Abbe number Refraction / Reflection Cone coefficient 0 Spherical endless -100000.0000 refraction 1 Aperture (STO) Spherical endless 20.0000 refraction 2 First lens (E1) Spherical 21.0000 6.1300 1.489 70.24 refraction 3 Reflective polarizer (RP) Spherical endless 0.1100 1.502 57.00 refraction 4 First Quarter Wave Plate (QWP1) Spherical endless 0.1100 1.502 57.00 refraction 5 Spherical endless 1.8432 refraction 6 Second lens (E2) Aspheric 530.0845 5.9499 1.787 37.09 refraction 0.0000 7 Aspheric 33.6365 1.3127 refraction 0.0000 8 Third lens (E3) Spherical 25.3681 6.5000 1.546 55.92 refraction 9 Partially reflective element (BS) Spherical -887.9282 -6.5000 1.546 55.92 reflection 10 Spherical 25.3681 -1.3127 refraction 11 Aspheric 33.6365 -5.9499 1.787 37.09 refraction 0.0000 12 Aspheric 530.0845 -1.8432 refraction 0.0000 13 Spherical endless -0.1100 1.502 57.00 refraction 14 Spherical endless -0.1100 1.502 57.00 refraction 15 Reflective polarizer (RP) Spherical endless 0.1100 1.502 57.00 reflection 16 First Quarter Wave Plate (QWP1) Spherical endless 0.1100 1.502 57.00 refraction 17 Spherical endless 1.8432 refraction 18 Second lens (E2) Aspheric 530.0845 5.9499 1.787 37.09 refraction 0.0000 19 Aspheric 33.6365 1.3127 refraction 0.0000 20 Third lens (E3) Spherical 25.3681 6.5000 1.546 55.92 refraction 21 Spherical -887.9282 1.8342 refraction 22 Fourth lens (E4) Aspheric -16.8300 1.4000 1.500 57.28 refraction 0.0000 23 Second Quarter Wave Plate (QWP2) Spherical endless 0.1100 1.502 57.00 refraction 24 Polarizer(LP) Spherical endless 0.1500 1.502 57.00 refraction 25 Spherical endless 0.5400 refraction 26 Protective glass (GL) Spherical endless 0.7100 1.519 64.17 refraction 27 Spherical endless 0.3000 refraction 28 Image surface (IMG) Spherical endless 0.0000 refraction

[0126] Table 8

[0127]

[0128] Table 9 shows some basic parameters of the optical system of Example 4. The units of f, f1, f2, f3, f4, fz1, fz2, ∑CT, and TD are all millimeters (mm).

[0129] Table 9

[0130] f f1 f2 f3 f4 fz1 fz2 ∑CT TD 42.00 42.93 -45.89 45.27 -33.65 42.93 -33.65 19.98 25.19

[0131] As Figure 3A shown, the optical system 2001 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the near-screen side of the first lens. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the near-screen side of the second lens. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the near-screen side of the third lens. Table 10 shows the basic parameter table of the spacer elements of the imaging system 2001. The unit of each parameter in Table 10 is millimeter (mm).

[0132] Table 10

[0133] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.662 27.382 31.348 31.454 23.322 23.322 31.340 31.340 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 15.974 15.974 30.940 30.940 33.140 17.804 36.140 34.225 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 1.987 1.940 9.000 0.050 5.200 0.050 23.000

[0134] Example 5

[0135] Figure 3B shows a schematic structural diagram of the optical system 2002 according to Embodiment 5 of the present application. In this embodiment and the following Embodiment 6, for the sake of simplicity, some descriptions similar to those in Embodiment 4 will be omitted.

[0136] As Figure 3B shown, the optical system 2002 includes a lens barrel P0 and various elements disposed in the lens barrel. The optical system 2002 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These elements are exactly the same as those in Embodiment 4 and will not be described in detail. The basic parameters of the optical system 2002 are shown in Tables 7 to 9 and will not be described in detail.

[0137] As Figure 3B shown, the optical system 2002 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the near-screen side of the first lens. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the near-screen side of the second lens. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the near-screen side of the third lens. Table 11 shows the basic parameter table of the spacer elements of the imaging system 2002. The unit of each parameter in Table 11 is millimeter (mm).

[0138] Table 11

[0139] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.253 27.122 31.354 31.296 23.405 23.405 31.340 31.340 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 16.087 16.087 30.940 30.940 33.341 16.882 36.140 33.833 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 2.225 1.940 9.000 0.050 5.200 0.050 23.238

[0140] Example 6

[0141] Figure 3C The structural schematic diagram of the imaging system 2003 according to Embodiment 6 of the present application is shown.

[0142] As Figure 3C shown, the optical system 2003 includes a lens barrel P0 and various elements disposed within the lens barrel. The optical system 2003 includes, in sequence from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These elements are exactly the same as those in Embodiment 4 and will not be elaborated here. The basic parameters of the optical system 2003 are shown in Tables 7 to 9 and will not be elaborated here.

[0143] As Figure 3C shown, the optical system 2003 further includes three spacer elements, namely a first spacer element P1, a second spacer element P2, and a third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the near-screen side surface of the first lens. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the near-screen side surface of the second lens. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the near-screen side surface of the third lens. Table 12 shows the basic parameter table of the spacer elements of the imaging system 2003. The units of all parameters in Table 12 are millimeters (mm).

[0144] Table 12

[0145] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.740 27.509 30.048 30.214 23.238 23.238 30.040 30.040 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 15.922 15.922 29.640 29.640 31.701 17.963 35.140 33.489 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 1.987 1.940 9.000 0.050 5.200 0.050 23.222

[0146] Figure 4A The axial chromatic aberration curves of the imaging system 2001 of Embodiment 4, the imaging system 2002 of Embodiment 5, and the imaging system 2003 of Embodiment 6 are shown, which represent the deviation of the focusing points of light rays of different wavelengths after passing through the lens. Figure 4B The astigmatism curves of the imaging system 2001 of Embodiment 4, the imaging system 2002 of Embodiment 5, and the imaging system 2003 of Embodiment 6 are shown, which represent the curvature of the meridional image plane and the curvature of the sagittal image plane. Figure 4C The distortion curves of the imaging system 2001 of Embodiment 4, the imaging system 2002 of Embodiment 5, and the imaging system 2003 of Embodiment 6 are shown, which represent the distortion magnitude values corresponding to different field angles. Figure 4DShows the modulation transfer function (MTF) curves of the imaging system 2001 of Embodiment 4, the imaging system 2002 of Embodiment 5, and the imaging system 2003 of Embodiment 6. According to Figures 4A to 4D it can be seen that the imaging system 2001 of Embodiment 4, the imaging system 2002 of Embodiment 5, and the imaging system 2003 of Embodiment 6 can all achieve good imaging quality.

[0147] Example 7

[0148] Figure 5A Shows a schematic structural diagram of the optical system 3001 according to Embodiment 7 of the present application.

[0149] As Figure 5A shown, the optical system 3001 includes a lens barrel P0 and various elements placed inside the lens barrel. The optical system 3001 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG.

[0150] The first lens E1 has a positive optical power. Its side near the human eye is convex, and its side near the screen is flat. The second lens E2 has a negative optical power. Its side near the human eye is concave, and its side near the screen is concave. The third lens E3 has a positive optical power. Its side near the human eye is convex, and its side near the screen is convex. The fourth lens E4 has a negative optical power. Its side near the human eye is concave, and its side near the screen is flat. Among them, the reflective polarizing element RP is attached to the side of the first lens E1 near the screen, and the first quarter-wave plate QWP1 is attached to the side of the reflective polarizing element RP near the screen; the second quarter-wave plate QWP2 is attached to the side of the fourth lens E4 near the screen, and the polarizer LP is attached to the side of the second quarter-wave plate QWP2 near the screen. The partial reflection element BS may have a semi-transmissive and semi-reflective function and is attached to the side of the third lens E3 near the screen.

[0151] In this example, the light emitted from the image plane IMG sequentially passes through the protective glass GL, the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, and the first quarter-wave plate QWP1 to reach the reflective polarizing element RP, where it is reflected and passes through the first quarter-wave plate QWP1, the second lens E2, and the third lens E3 again. The light beam is reflected again at the partial reflection element BS on the side of the third lens E3 near the screen and sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, and the first lens E1, then passes through the diaphragm STO and finally exits towards the human eye side.

[0152] Table 13 shows the basic parameters of the optical system of Example 7, where the units of the radius of curvature and the thickness are both millimeters (mm). Table 14 shows the coefficients of the higher-order terms of the aspherical mirrors that can be used in Example 7, where each aspherical surface type can be defined by the formula (1) given in Example 1 above.

[0153] Table 13

[0154]

[0155]

[0156] Table 14

[0157]

[0158] Table 15 shows some basic parameters of the optical system of Example 7. The units of f, f1, f2, f3, f4, fz1, fz2, ∑CT, and TD are all millimeters (mm).

[0159] Table 15

[0160] f f1 f2 f3 f4 fz1 fz2 ∑CT TD 42.00 41.44 -42.65 45.36 -39.20 41.44 -39.20 22.41 25.19

[0161] As Figure 5A shown, the optical system 3001 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is placed between the first lens and the second lens and abuts against the near-screen side surface of the first lens. The second spacer element P2 is placed between the second lens and the third lens and abuts against the near-screen side surface of the second lens. The third spacer element P3 is placed between the third lens and the fourth lens and abuts against the near-screen side surface of the third lens. Table 16 shows the basic parameter table of the spacer elements of the imaging system 3001, and the units of the parameters in Table 16 are all millimeters (mm).

[0162] Table 16

[0163] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.616 27.382 31.415 31.454 23.322 23.322 31.340 31.340 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 22.460 22.460 30.940 30.940 33.140 16.258 36.140 34.385 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 2.317 0.959 7.200 0.050 8.150 0.050 22.150

[0164] Example 8

[0165] Figure 5B shows a schematic structural diagram of the optical system 3002 according to Embodiment 8 of the present application. In this embodiment and the following Embodiment 9, for the sake of simplicity, some descriptions similar to those in Embodiment 7 will be omitted.

[0166] As Figure 5BAs shown, the optical system 3002 includes a lens barrel P0 and various components placed inside the lens barrel. The optical system 3002 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These components are exactly the same as those in Embodiment 7 and will not be elaborated further. The basic parameters of the optical system 3002 are shown in Tables 13 to 15 and will not be elaborated further.

[0167] As Figure 5B shown, the optical system 3002 further includes three spacer elements, namely a first spacer element P1, a second spacer element P2, and a third spacer element P3. The first spacer element P1 is placed between the first lens and the second lens and abuts against the near-screen side surface of the first lens. The second spacer element P2 is placed between the second lens and the third lens and abuts against the near-screen side surface of the second lens. The third spacer element P3 is placed between the third lens and the fourth lens and abuts against the near-screen side surface of the third lens. Table 17 shows the basic parameter table of the spacer elements of the imaging system 3002. The unit of each parameter in Table 17 is millimeter (mm).

[0168] Table 17

[0169] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.999 27.559 31.208 31.270 23.126 23.126 31.340 31.340 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 22.325 22.325 30.940 30.940 33.297 17.490 36.140 34.012 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 2.531 0.959 7.200 0.050 8.150 0.050 23.214

[0170] Example 9

[0171] Figure 5C shows a schematic structural diagram of an imaging system 3003 according to Embodiment 9 of the present application.

[0172] As Figure 5C shown, the optical system 3003 includes a lens barrel P0 and various components placed inside the lens barrel. The optical system 3003 sequentially includes, from the human eye side to the screen side: a diaphragm STO (not shown), a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, a polarizer LP, a protective glass GL, and an image plane IMG. These components are exactly the same as those in Embodiment 7 and will not be elaborated further. The basic parameters of the optical system 3003 are shown in Tables 13 to 15 and will not be elaborated further.

[0173] As Figure 5CAs shown, the optical system 3003 further includes three spacer elements, namely the first spacer element P1, the second spacer element P2, and the third spacer element P3. The first spacer element P1 is disposed between the first lens and the second lens and abuts against the side of the first lens near the screen. The second spacer element P2 is disposed between the second lens and the third lens and abuts against the side of the second lens near the screen. The third spacer element P3 is disposed between the third lens and the fourth lens and abuts against the side of the third lens near the screen. Table 18 shows the basic parameter table of the spacer elements of the imaging system 3003, and the unit of each parameter in Table 18 is millimeter (mm).

[0174] Table 18

[0175] Parameter d1s d1m D1s D1m d2s d2m D2s D2m Value 26.604 27.235 29.844 30.223 23.414 23.414 30.040 30.040 Parameter d3s d3m D3s D3m d0s d0m D0s D0m Value 22.575 22.575 29.640 29.640 31.589 18.510 33.941 34.225 Parameter EP01 CP1 EP12 CP2 EP23 CP3 L Value 2.317 0.959 7.200 0.050 8.150 0.050 23.000

[0176] Figure 6A Shows the axial chromatic aberration curves of the imaging system 3001 of Example 7, the imaging system 3002 of Example 8, and the imaging system 3003 of Example 9, which represent the deviation of the convergence points of light rays of different wavelengths after passing through the lens. Figure 6B Shows the astigmatism curves of the imaging system 3001 of Example 7, the imaging system 3002 of Example 8, and the imaging system 3003 of Example 9, which represent the curvature of the meridional image plane and the curvature of the sagittal image plane. Figure 6C Shows the distortion curves of the imaging system 3001 of Example 7, the imaging system 3002 of Example 8, and the imaging system 3003 of Example 9, which represent the distortion magnitude values corresponding to different field angles. Figure 6D Shows the modulation transfer function (MTF) curves of the imaging system 3001 of Example 7, the imaging system 3002 of Example 8, and the imaging system 3003 of Example 9. According to Figures 6A to 6D it can be known that the imaging systems 3001 of Example 7, 3002 of Example 8, and 3003 of Example 9 can all achieve good imaging quality.

[0177] In summary, the optical systems of Examples 1 to 9 have the relationships shown in Table 19.

[0178] Table 19

[0179] Conditional / Example 1 2 3 4 5 6 7 8 9 f3 / d3s 2.49 2.47 2.51 2.83 2.81 2.84 2.02 2.03 2.01 fz2 / d3m -1.96 -1.94 -1.98 -2.11 -2.09 -2.11 -1.75 -1.76 -1.74 (CT1 + CTR + CTQ1) / EP01 3.13 2.87 2.96 3.20 2.85 3.20 2.88 2.64 2.88 T12 / CP1 1.12 1.46 1.33 1.06 1.06 1.06 0.86 0.86 0.86 D0s / R1 1.72 1.71 1.69 1.72 1.72 1.67 1.72 1.72 1.62 (d2s + D2s) / R4 1.44 1.44 1.43 1.63 1.63 1.58 1.67 1.67 1.64 TD / EP12 2.96 2.71 2.78 2.80 2.80 2.80 3.50 3.50 3.50 (CT3 + T34) / EP23 1.80 1.80 1.80 1.60 1.60 1.60 1.41 1.41 1.41 (d0m + D0m) / L 2.26 2.19 2.23 2.26 2.18 2.22 2.29 2.22 2.29 (d1s + d1m) / fz1 1.22 1.21 1.22 1.26 1.24 1.26 1.30 1.32 1.30 (D2m - d2m) / CT2 1.40 1.38 1.42 1.35 1.33 1.14 2.09 2.14 1.72 f1 / D1s 1.45 1.46 1.45 1.37 1.37 1.43 1.32 1.33 1.39 (D3s + D3m) / D1m 2.01 2.04 1.99 1.97 1.98 1.96 1.97 1.98 1.96 d0s / ∑CT 1.71 1.73 1.71 1.66 1.67 1.59 1.48 1.49 1.41 f2 / (EP12 + CP2) -5.00 -4.57 -4.69 -5.07 -5.07 -5.07 -5.88 -5.88 -5.88 f4 / (EP23 + CP3) -7.37 -7.37 -7.37 -6.41 -6.41 -6.41 -4.78 -4.78 -4.78

[0180] This application also provides an optical device, which can be an independent projection device such as a projector, or a projection module integrated on a mobile electronic device such as VR. The optical device is equipped with the optical system described above.

[0181] The above description is only a preferred embodiment of the present application and an explanation of the technical principles applied. Those skilled in the art should understand that the scope of protection involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the concept of the present application. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) disclosed in the present application that have similar functions.

Claims

1. An optical system, characterized in that It sequentially includes, from the first side to the second side along the optical axis: A first lens with positive optical power, whose first side is convex and second side is flat; A reflective polarizing element; A first quarter-wave plate; A second lens with negative optical power, whose second side is concave; A third lens with positive optical power, whose first side is convex and second side is convex; A partial reflection element; A fourth lens with negative optical power, whose first side is concave and second side is flat; A second quarter-wave plate; and A polarizer; Wherein, the reflective polarizing element is placed on the second side of the first lens and at least partially adheres to the second side of the first lens; the first quarter-wave plate is placed on the second side of the reflective polarizing element and at least partially adheres to the second side of the reflective polarizing element; the second quarter-wave plate is placed on the second side of the fourth lens and at least partially adheres to the second side of the fourth lens; the polarizer is placed on the second side of the second quarter-wave plate and at least partially adheres to the second side of the second quarter-wave plate; The optical system further includes: a third spacer element placed between the third lens and the fourth lens and abutting against the second side of the third lens; The optical system satisfies: 2.0 < f3 / d3s ≤ 2.84 and -2.11 ≤ fz2 / d3m < -1.7, where f3 is the effective focal length of the third lens, d3s is the inner diameter of the first side of the third spacer element, fz2 is the combined focal length of the fourth lens, the second quarter-wave plate and the polarizer, and d3m is the inner diameter of the second side of the third spacer element; The number of lenses with optical power in the optical system is four.

2. The optical system according to claim 1, wherein The optical system further includes: a lens barrel and a first spacer element; The first spacer element is placed between the first lens and the second lens and abuts against the second side of the first lens; The optical system satisfies: 2.6 < (CT1 + CTR + CTQ1) / EP01 < 3.25, where CT1 is the central thickness of the first lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, CTQ1 is the central thickness of the first quarter-wave plate on the optical axis, and EP01 is the distance along the optical axis from the first side end face of the lens barrel to the first side of the first spacer element.

3. The optical system according to claim 1, wherein The optical system further includes: a first spacer element placed between the first lens and the second lens and abuts against the second side of the first lens; The optical system satisfies: 0.86 ≤ T12 / CP1 < 1.5, where T12 is the on-axis distance from the second side of the first lens to the first side of the second lens, and CP1 is the maximum thickness of the first spacer element along the optical axis direction.

4. The optical system according to claim 1, wherein The optical system further includes a lens barrel and satisfies: 1.6 < D0s / R1 ≤ 1.72, where D0s is the outer diameter of the first side end face of the lens barrel, and R1 is the radius of curvature of the first side face of the first lens.

5. The optical system according to claim 1, characterized in that The optical system further includes: a second spacer element disposed between the second lens and the third lens and abutted against the second side face of the second lens; The optical system satisfies: 1.4 < (d2s + D2s) / R4 < 1.7, where d2s is the inner diameter of the first side face of the second spacer element, D2s is the outer diameter of the first side face of the second spacer element, and R4 is the radius of curvature of the second side face of the second lens.

6. The optical system according to claim 1, wherein The optical system further includes: a first spacer element and a second spacer element. The first spacer element is disposed between the first lens and the second lens and abutted against the second side face of the first lens, and the second spacer element is disposed between the second lens and the third lens and abutted against the second side face of the second lens; The optical system satisfies: 2.7 < TD / EP12 < 3.55, where TD is the distance on the optical axis from the first side face of the first lens to the second side face of the fourth lens, and EP12 is the distance in the optical axis direction from the second side face of the first spacer element to the first side face of the second spacer element.

7. The optical system according to claim 1, wherein The optical system further includes: a second spacer element disposed between the second lens and the third lens and abutted against the second side face of the second lens; The optical system satisfies: 1.4 < (CT3 + T34) / EP23 < 1.85, where CT3 is the central thickness of the third lens on the optical axis, T34 is the axial distance from the second side face of the third lens to the first side face of the fourth lens, and EP23 is the distance in the optical axis direction from the second side face of the second spacer element to the first side face of the third spacer element.

8. The optical system according to claim 1, characterized in that The optical system further includes a lens barrel and satisfies: 2.18 ≤ (d0m + D0m) / L < 2.3, where d0m is the inner diameter of the second side end face of the lens barrel, D0m is the outer diameter of the second side end face of the lens barrel, and L is the distance in the optical axis direction from the first side end face of the lens barrel to the second side end face.

9. The optical system according to any one of claims 1 to 8, wherein The optical system further includes: a first spacer element disposed between the first lens and the second lens and abutted against the second side face of the first lens; The optical system satisfies: 1.2 < (d1s + d1m) / fz1 ≤ 1.32, where d1s is the inner diameter of the first side face of the first spacer element, d1m is the inner diameter of the second side face of the first spacer element, and fz1 is the combined focal length of the first lens, the reflective polarizing element, and the first quarter-wave plate.

10. The optical system according to any one of claims 1 to 8, wherein The optical system further includes: a second spacer element disposed between the second lens and the third lens and abutting against the second side surface of the second lens; The optical system satisfies: 1.1 < (D2m - d2m) / CT2 ≤ 2.14, where D2m is the outer diameter of the second side surface of the second spacer element, d2m is the inner diameter of the second side surface of the second spacer element, and CT2 is the central thickness of the second lens on the optical axis.

11. The optical system according to any one of claims 1 to 8, characterized in that The optical system further includes: a first spacer element disposed between the first lens and the second lens and abutting against the second side surface of the first lens; The optical system satisfies: 1.3 < f1 / D1s < 1.5, where f1 is the effective focal length of the first lens and D1s is the outer diameter of the first side surface of the first spacer element.

12. The optical system according to any one of claims 1 to 8, characterized in that The optical system further includes: a first spacer element disposed between the first lens and the second lens and abutting against the second side surface of the first lens; The optical system satisfies: 1.96 ≤ (D3s + D3m) / D1m ≤ 2.04, where D3s is the outer diameter of the first side surface of the third spacer element, D3m is the outer diameter of the second side surface of the third spacer element, and D1m is the outer diameter of the second side surface of the first spacer element.

13. The optical system according to any one of claims 1 to 8, characterized in that: The optical system further includes a lens barrel and satisfies: 1.4 < d0s / ∑CT ≤ 1.73, where d0s is the inner diameter of the first side end face of the lens barrel and ∑CT is the sum of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis.

14. The optical system according to any one of claims 1 to 8, characterized in that The optical system further includes: a first spacer element and a second spacer element, the first spacer element is disposed between the first lens and the second lens and abuts against the second side surface of the first lens, and the second spacer element is disposed between the second lens and the third lens and abuts against the second side surface of the second lens; The optical system satisfies: -5.9 < f2 / (EP12 + CP2) ≤ -4.57, where f2 is the effective focal length of the second lens, EP12 is the distance along the optical axis from the second side surface of the first spacer element to the first side surface of the second spacer element, and CP2 is the maximum thickness of the second spacer element along the optical axis.

15. The optical system according to any one of claims 1 to 8, characterized in that The optical system further includes: a first spacer element and a second spacer element, the first spacer element is disposed between the first lens and the second lens and abuts against the second side surface of the first lens, and the second spacer element is disposed between the second lens and the third lens and abuts against the second side surface of the second lens; The optical system satisfies: -7.4 < f4 / (EP23 + CP3) ≤ -4.78, where f4 is the effective focal length of the fourth lens, EP23 is the distance along the optical axis from the second side surface of the second spacer element to the first side surface of the third spacer element, and CP3 is the maximum thickness of the third spacer element along the optical axis.

16. An optical device, characterized in that: Comprising the optical system according to any one of claims 1 to 15.

Images