LCOS continuous zoom projection lens

Abstract

The application provides a LCOS continuous zoom projection lens, and belongs to the technical field of vehicle-mounted head-up displays, and specifically comprises a first lens group with negative focal power, a second lens group with positive focal power, an aperture stop, a third lens group with negative focal power, and a fourth lens group with positive focal power, wherein the first lens group, the second lens group, the aperture stop, the third lens group and the fourth lens group are arranged in the order from a projection end to a chip display end along an optical axis; the first lens group and the fourth lens group are fixed relative to a lens barrel; the second lens group, the aperture stop and the third lens group are arranged in a sliding mode along the length direction of the lens barrel; the third lens group and the aperture stop move synchronously, and the movement direction of the third lens group is opposite to that of the second lens group. Through the processing scheme, the imaging quality of the vehicle-mounted head-up display is improved.

Description

Technical Field

[0001] This application relates to the field of vehicle head-up displays, and more particularly to an LCOS continuously zoomable projection lens. Background Technology

[0002] As a key human-machine interface for improving driving safety, the head-up display (HUD) system in vehicles requires its core imaging component—a projection optical engine based on an LCOS microdisplay—to meet stringent automotive-grade environmental adaptability requirements.

[0003] Traditional LCOS projection lenses face challenges in automotive applications, including thermal drift failure, insufficient zoom stability, and polarization compatibility issues. Existing solutions all have significant limitations. Furthermore, automotive space constraints require a total lens length of <80mm and a rear working distance >15mm, making it difficult for existing zoom lenses to maintain high-resolution imaging performance while achieving a compact design. Therefore, there is an urgent need to develop an LCOS projection lens that integrates thermally stable performance, continuous zoom accuracy, polarization compatibility, and miniaturization to meet the core requirements of high-reliability HUDs in smart cockpits. Summary of the Invention

[0004] In view of this, this application provides an LCOS continuously zoomable projection lens, which solves the problems in the prior art and improves the imaging quality of vehicle head-up displays.

[0005] The LCOS continuously zoomable projection lens provided in this application adopts the following technical solution: An LCOS continuously zoomable projection lens includes a first lens group with negative optical power, a second lens group with positive optical power, an aperture stop, a third lens group with negative optical power, and a fourth lens group with positive optical power. The first lens group, the second lens group, the aperture stop, the third lens group, and the fourth lens group are arranged along the optical axis in order from the projection end to the chip display end. The fourth lens group is a rear fixed lens group used to converge light; the third lens group is a compensating lens group; the second lens group is a zoom lens group; and the first lens group is a front fixed lens group used to expand the field of view; the first lens group and the fourth lens group are fixed relative to the lens barrel, while the second lens group, the aperture stop, and the third lens group are slidably arranged along the length of the lens barrel. The third lens group and the aperture stop move synchronously, and the third lens group moves in the opposite direction to the second lens group; The differential expressions for the motion of the second and third lens groups are: ; in, This is the distance between the principal surfaces of the third and fourth lens groups. This represents the amount of movement change of the second lens group. This represents the change in movement of the third lens group. The focal length of the third lens group. This is the focal length of the fourth lens group. Optionally, the effective focal length of the first lens group is The focal length of the second lens group is , and The signs are opposite, and the inequality is satisfied: .

[0006] Optionally, the first lens group includes a first negative lens, a second negative lens, and a first positive lens sequentially distributed from the projection end to the chip display end. The first negative lens is an aspherical lens, the surface of the first negative lens near the projection end is an even-order aspherical surface, and the first negative lens has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic.

[0007] Optionally, the second lens group is a cemented doublet lens, and the cemented doublet lens consists of a third negative lens and a second positive lens sequentially from the projection end to the chip display end.

[0008] Optionally, the third lens group includes a third positive lens, a fourth negative lens, and a fifth negative lens, which are sequentially distributed from the projection end to the chip display end.

[0009] Optionally, the fourth lens group includes a sixth negative lens, a fourth positive lens, and a fifth positive lens arranged sequentially from the projection end to the chip display end. The fifth positive lens is an aspherical lens, and the side of the fifth positive lens facing away from the chip display end is an even-order aspherical surface. The fifth positive lens has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic.

[0010] Optionally, the telecentricity of the fourth lens group is less than or equal to 0.3°.

[0011] In summary, this application includes the following beneficial technical effects: In this application, the aperture stop and the compensation lens group move synchronously, the optical system always follows a telecentric optical path, the total lens length remains constant, and the image plane illumination uniformity is excellent. The mechanical compensation zoom technology enables high-definition, high-brightness image projection even with rapid and continuous changes in lens focal length, adaptable to the optical-mechanical display needs of various vehicle head-up displays.

[0012] The fixed lens group of this application uses low-heat glass material with good thermal stability to ensure that the lens image is clear and does not have a blurring phenomenon in an ambient temperature range of -40℃ to +85℃.

[0013] The projection lens of this application has a compact structure and good image quality, making it suitable for in-vehicle head-up displays where space is limited. Most of the lenses used in the lens are spherical lenses, which are easy to process and suitable for mass production. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the optical system in the shortest focal length state of the projection lens in an embodiment of this application. Figure 2 This is a schematic diagram of the optical system for designing the focal length of the projection lens in an embodiment of this application. Figure 3 This is a schematic diagram of the optical system in the longest focal length state of the projection lens in an embodiment of this application.

[0016] Explanation of reference numerals in the attached figures: 10, First lens group; 11, First negative lens; 12, Second negative lens; 13, First positive lens; 20, Second lens group; 21, Third negative lens; 22, Second positive lens; 30, Aperture stop; 40, Third lens group; 41, Third positive lens; 42, Fourth negative lens; 43, Fifth negative lens; 50, Fourth lens group; 51, Sixth negative lens; 52, Fourth positive lens; 53, Fifth positive lens; 60, Prism; 70, Protective glass; 80, LCOS chip. Detailed Implementation

[0017] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0018] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0020] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0021] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0022] This application provides an LCOS continuously zoomable projection lens.

[0023] like Figures 1 to 3As shown, an LCOS continuously zoomable projection lens includes a first lens group 10 with negative optical power, a second lens group 20 with positive optical power, an aperture stop 30, a third lens group 40 with negative optical power, and a fourth lens group 50 with positive optical power. The first lens group 10, the second lens group 20, the aperture stop 30, the third lens group 40, and the fourth lens group 50 are arranged along the optical axis in order from the projection end to the chip display end, wherein the chip display end is the image plane and the projection end is the object plane.

[0024] The fourth lens group 50 is a rear fixed lens group used to converge light; the third lens group 40 is a compensation lens group, the second lens group 20 is a zoom lens group, and the first lens group 10 is a front fixed lens group used to expand the field of view; the first lens group 10 and the fourth lens group 50 are fixed relative to the lens barrel, while the second lens group 20, the aperture stop 30, and the third lens group 40 are slidably arranged along the length of the lens barrel.

[0025] The third lens group 40 and the aperture stop 30 move synchronously. The third lens group 40 compensates for the image plane shift caused by the second lens group 20 during zooming. The movement direction of the third lens group 40 is opposite to that of the second lens group 20.

[0026] The differential motion expressions for the second lens group 20 and the third lens group 40 are: .

[0027] in, The distance between the principal surfaces of the third lens group 40 and the fourth lens group 50 is [missing information]. This represents the amount of movement change of the second lens group 20. This represents the amount of movement change of the third lens group 40. The focal length of the third lens group is 40. This is the focal length of the fourth lens group, 50. In this application, the fourth lens group 50 and the third lens group 40 converge the collimated light emitted from the chip display terminal to the system aperture stop 30. The light converged to the system aperture stop 30 is magnified and imaged on the projection screen by the second lens group 20 and the first lens group 10. The movement of the second lens group 20 and the third lens group 40 can realize continuous zoom at different magnifications. During the zooming process, the total length of the lens remains unchanged. In this application, the total length of the lens is less than 55mm.

[0028] The effective focal length of the first lens group 10 is: The focal length of the second lens group 20 is , and The signs are opposite, and the inequality is satisfied: .

[0029] The first lens group 10 includes a first negative lens 11, a second negative lens 12, and a first positive lens 13, which are sequentially distributed from the projection end to the chip display end. The first negative lens 11 is an aspherical lens, and the surface of the first negative lens 11 near the projection end is an even-order aspherical surface. The first negative lens 11 has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic. This application selects three lenses to optimize the high-resolution imaging performance of the LCOS chip 80, with an optical power structure of "negative-negative-positive" to further correct field curvature and astigmatism. The first negative lens 11 is made of aspherical material to better control off-axis aberration. Considering the potential image shift caused by temperature changes, to reduce the lens's sensitivity to temperature, the aspherical lens material can be low-heat glass or plastic with a high coefficient of thermal expansion (CTE) and temperature coefficient of refractive index (dn / dT).

[0030] The second lens group 20 is a cemented doublet lens, and the cemented doublet lens consists of a third negative lens 21 and a second positive lens 22, arranged sequentially from the projection end to the chip display end. The cemented doublet lens is made of glass, specifically crown glass and flint glass, and is capable of correcting spherical aberration and chromatic aberration.

[0031] The third lens group 40 includes a third positive lens 41, a fourth negative lens 42, and a fifth negative lens 43, which are distributed sequentially from the projection end to the chip display end.

[0032] In this application, the second lens group 20 is a zoom lens group, and the third lens group 40 is a compensation lens group. The optical power signs of the zoom lens group and the compensation lens group are opposite. In engineering, the "negative zoom-positive compensation" architecture is more commonly used, that is, the optical power of the zoom group is negative and the optical power of the compensation group is positive. Considering that the application environment of this application is an in-vehicle head-up display, which has high requirements for compact lens size, this application adopts a "positive zoom-negative compensation" architecture, which can achieve a larger zoom ratio and a more compact structure, and is also beneficial for temperature drift compensation.

[0033] Although the zoom lens group and the compensating lens group are linked, their movement trajectories are different. The zoom lens group changes the system's composite focal length by moving back and forth along the optical axis, while the compensating lens group moves along the optical axis to counteract the image plane drift caused by the zoom lens group. In this application, the zoom lens group has a positive optical power and uses a cemented doublet lens to correct chromatic aberration while sharing the system's optical power, avoiding the spherical aberration out-of-control caused by using only a single positive lens with strong positive optical power. The compensating lens group has a negative optical power. Considering that a single negative lens has too much field curvature and cannot correct chromatic aberration, although two lenses can initially control the field curvature, they are not enough to accurately counteract the image plane shift caused by the zoom lens group. Instead, they amplify positional errors due to their own aberrations. Therefore, the compensating lens group uses three lenses, specifically a "positive-negative-negative" lens combination, with a positive lens added to compensate for field curvature and suppress edge astigmatism.

[0034] The fourth lens group 50 includes a sixth negative lens 51, a fourth positive lens 52, and a fifth positive lens 53, which are sequentially distributed from the projection end to the chip display end. The fifth positive lens 53 is an aspherical lens, and the side of the fifth positive lens 53 facing away from the chip display end is an even-order aspherical surface. The fifth positive lens 53 has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic.

[0035] The fourth lens group 50, used to converge light rays, needs to provide good image-side telecentrism in the lens design. A single positive lens would cause the principal ray to tilt significantly, making it impossible to effectively correct field curvature and chromatic aberration. The rear fixed lens group uses two positive lenses, specifically a "negative-positive-positive" lens structure. The negative lens contributes negative Petzval, and the sum of the positive Petzval contributed by the positive lens approaches zero, correcting off-axis astigmatism and improving telecentrism by less than 0.3°. The fifth positive lens 53 is aspherical, which can maximize the correction of off-axis aberration.

[0036] In this embodiment of the application, the formulas for the even-order aspherical functions of the first negative lens 11 and the fifth positive lens 53 are as follows: .

[0037] in, The sagittal height of the first negative lens 11 or the fifth positive lens 53 along the optical axis. For the conic coefficient of the curved surface, The half-aperture of the first negative lens 11 and the fifth positive lens 53 perpendicular to the optical axis. The curvature of the first negative lens 11 and the fifth positive lens 53, The coefficients of the fourth-order terms of an even-degree aspherical polynomial. The coefficients of the 6th-order term in an even-degree aspherical polynomial. The coefficients of the 8th-order terms of an even-degree aspherical polynomial. The coefficients of the 10th-order term in an even-degree aspherical polynomial. The coefficients of the 12th-order term of an even-degree aspherical polynomial. is the coefficient of the 14th-order term of the even-order aspherical polynomial, and h is the radial distance from the optical axis to the surface.

[0038] In this embodiment, the specific structure of the chip display includes an LCOS chip 80, a protective glass 70, and a prism 60. The prism 60 is located near the fourth lens group 50, and the protective glass 70 is located between the LCOS chip 80 and the prism 60. Specifically, the surface of the LCOS chip 80 has a 0.7mm thick ITO protective glass 70 with a refractive index of approximately 1.5. The prism 60 is the equivalent flat glass after the light propagates through the PBS prism 60. In this embodiment, the LCOS chip 80 is the image plane, and the projection end is the object plane.

[0039] In this application, the prism 60 increases the back cutoff of the optical system. The prism 60 should not obstruct normal light and should prevent stray light from passing through. The principal ray should be parallel to the principal optical axis on the image plane LCOS chip 80. That is, the optical path structure of this application embodiment is an image-side telecentric optical path. The aperture stop 30 and the third lens group 40 of this application move synchronously. The position of the LCOS chip 80 remains fixed during the zoom process.

[0040] The zoom projection lens of this embodiment has high resolution, supports a 1080P LCOS chip 80 with a pixel size of 3.7 micrometers, and can ultimately achieve a projection ratio of 1.14~1.67. When the second lens group 20 moves away from the first lens group 10, that is, moves closer to the fourth lens group 50, and the third lens group 40 moves towards the first lens group 10, the projection distance of the zoom projection lens of this embodiment changes from 80mm to 120mm. The structural parameters of the zoom projection lens of this embodiment are shown in Table 1.

[0041] Table 1 Structural parameters of zoom projection lens

[0042] In Table 1, the radius, or radius of curvature, represents the degree of curvature of the lens surface. A positive radius indicates that the surface bends towards the image plane, a negative radius indicates that the surface bends towards the object plane, and a radius of ∞ indicates that the surface is flat. The thickness represents the central axial distance from the current surface to the next surface. The refractive index represents the ability of the current lens material to deflect light. The Abbe number represents the dispersion characteristics of the current lens material. The surfaces from the projection end to the chip display end are, in order, OBJ, S1 to S9, STO, S11 to S26, and IMA. OBJ is the object plane, STO is the aperture stop 30, and IMA is the surface of the LCOS chip 80. S1 and S2 are the two surfaces of the first negative lens 11, S3 and S4 are the two surfaces of the second negative lens 12, S5 and S6 are the two surfaces of the first positive lens 13, S7, S8 and S9 are the surfaces of the third negative lens 21 facing away from the second positive lens 22, the joint surface of the third negative lens 21 and the second positive lens 22, and the surface of the second positive lens 22 facing away from the third negative lens 21, respectively. S11 and S12 are the two surfaces of the third positive lens 41, S13 and S14 are the two surfaces of the fourth negative lens 42, S15 and S16 are the two surfaces of the fifth negative lens 43, S17 and S18 are the two surfaces of the sixth negative lens 51, S19 and S20 are the two surfaces of the fourth positive lens 52, S21 and S22 are the two surfaces of the fifth positive lens 53, S23 and S24 are the two surfaces of the prism 60, and S25 and S26 are the two surfaces of the protective glass 70.

[0043] In this embodiment, the correlation coefficients of the even-order aspherical surfaces of the first negative lens 11 and the fifth positive lens 53 are shown in Table 2.

[0044] Table 2 Surface coefficients of even-order aspherical surfaces of the first negative lens and the fifth positive lens

[0045] Table 3 shows the image quality characteristics of the LCOS continuously zoomable projection lens at different focal lengths in the embodiments of this application.

[0046]

[0047] Furthermore, the MTF values ​​of the LCOS continuously zoom projection lens in this embodiment are >0.35@117lp / mm, >0.41@117lp / mm, and >0.37@117lp / mm at ambient temperatures of -45℃, 25℃, and 85℃, respectively. This demonstrates that the lens exhibits stable performance under varying environmental temperatures, demonstrating good calorific value. MTF represents the modulation transfer function value.

[0048] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An LCOS continuously zoomable projection lens, characterized in that, The LCOS continuously zoomable projection lens is a telecentric lens. The LCOS continuously zoomable projection lens consists of a first lens group (10) with negative optical power, a second lens group (20) with positive optical power, an aperture stop (30), a third lens group (40) with negative optical power, and a fourth lens group (50) with positive optical power. The first lens group (10), the second lens group (20), the aperture stop (30), the third lens group (40), and the fourth lens group (50) are arranged along the optical axis in the order from the projection end to the chip display end. The fourth lens group (50) is a rear fixed lens group used to converge light; the third lens group (40) is a compensation lens group; the second lens group (20) is a zoom lens group; and the first lens group (10) is a front fixed lens group used to expand the field of view; the first lens group (10) and the fourth lens group (50) are fixed relative to the lens barrel, while the second lens group (20), the aperture stop (30), and the third lens group (40) are slidably arranged along the length of the lens barrel; The third lens group (40) and the aperture stop (30) move synchronously, and the third lens group (40) moves in the opposite direction to the second lens group (20); The differential motion expressions for the second lens group (20) and the third lens group (40) are as follows: ; in, The distance between the principal surfaces of the third lens group (40) and the fourth lens group (50) is [missing information]. The amount of movement change of the second lens group (20) The amount of movement change of the third lens group (40) The focal length of the third lens group (40) is... The focal length of the fourth lens group (50); The first lens group (10) consists of a first negative lens (11), a second negative lens (12) and a first positive lens (13) arranged sequentially from the projection end to the chip display end; The second lens group (20) is a cemented doublet lens, and the cemented doublet lens consists of a third negative lens (21) and a second positive lens (22) sequentially from the projection end to the chip display end. The third lens group (40) consists of a third positive lens (41), a fourth negative lens (42) and a fifth negative lens (43) arranged sequentially from the projection end to the chip display end; The fourth lens group (50) consists of a sixth negative lens (51), a fourth positive lens (52), and a fifth positive lens (53) arranged sequentially from the projection end to the chip display end.

2. The LCOS continuously zoomable projection lens according to claim 1, characterized in that, The effective focal length of the first lens group (10) is The focal length of the second lens group (20) is , and The signs are opposite, and the inequality is satisfied: .

3. The LCOS continuously zoomable projection lens according to claim 1, characterized in that, The first negative lens (11) is an aspherical lens. The surface of the first negative lens (11) near the projection end is an even-order aspherical surface. The first negative lens (11) has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic.

4. The LCOS continuously zoomable projection lens according to claim 1, characterized in that, The fifth positive lens (53) is an aspherical lens. The side of the fifth positive lens (53) facing away from the chip display end is an even-order aspherical surface. The fifth positive lens (53) has a thermal expansion coefficient of less than or equal to 50 × 10⁻⁶. -7 / ℃, temperature coefficient of refractive index less than or equal to 5×10 -6 / K is made of glass or transparent plastic.

5. The LCOS continuously zoomable projection lens according to claim 4, characterized in that, The telecentricity of the fourth lens group (50) is less than or equal to 0.3°.

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