Optical system comprising adhesive layer having stiffness gradient

Abstract

An optical system has a first optical element, a second optical element, and a first adhesive layer. The first adhesive layer is disposed between the first optical element and the second optical element, and is configured to connect the first optical element and the second optical element. The first adhesive layer also has a first stiffness gradient directed from an edge of the optical system toward a center of thermal expansion of the optical system.

Description

Technical Field

[0001] This application relates to optical systems comprising multiple optical elements, and more specifically to multiple optical elements bonded together by an adhesive layer. Background Technology

[0002] In optical systems, the adhesive layer that bonds optical elements together can have low stiffness, especially in systems with a high diameter-to-thickness ratio. If the optical system is subjected to thermal vibrations, such as when used in a head-mounted display (HMD) for virtual reality (VR) systems, these vibrations, combined with low stiffness, can cause changes in the position and shape of the optical elements. Furthermore, the low stiffness of the adhesive layer can induce oscillations between the optical elements, leading to undesirable optical effects. However, increasing the stiffness of the adhesive layer to avoid these problems can compromise the optical performance of the system.

[0003] In this context, the purpose of this disclosure is to reduce changes in the position and shape of optical elements and oscillations in an optical system without compromising the optical performance of the system. Summary of the Invention

[0004] To achieve this objective, the present invention provides an optical system. The optical system includes a first optical element, a second optical element, and a first adhesive layer. The first adhesive layer is disposed between the first optical element and the second optical element and configured to connect the first optical element and the second optical element. The first adhesive layer also has a first stiffness gradient from one edge of the optical system towards the center of thermal expansion of the optical system. Attached Figure Description

[0005] Examples of this disclosure are described below with reference to the accompanying drawings, wherein the same reference numerals refer to the same elements.

[0006] Figure 1A and Figure 1B The general concept of this disclosure is illustrated by examples of this disclosure.

[0007] Figure 2A and Figure 2B An optical system according to an example of this disclosure is shown.

[0008] Figure 3 Examples shown according to this disclosure Figure 2A and Figure 2B A top view of the adhesive layer of the optical system.

[0009] Figures 4A to 4C An illustrative stiffness curve is shown within the adhesive layer of an optical system according to an example of this disclosure.

[0010] Figure 5A and Figure 5BFurther illustrative stiffness curves within the adhesive layer of an optical system according to an example of this disclosure are shown.

[0011] It should be understood that these figures are provided not to limit this disclosure to the aspects shown in the figures. Rather, these figures are provided to aid in understanding the invention. Those skilled in the art will readily appreciate that aspects of the invention shown in one figure may be combined with aspects of another figure, or aspects shown in one figure may be omitted, without departing from the subject matter of this disclosure. Detailed Implementation

[0012] An optical system is described below, comprising at least a first optical element and a second optical element, and an adhesive layer disposed therebetween. The adhesive layer has a stiffness gradient from the edge of the optical system toward the center of thermal expansion. In other words, the stiffness within the first adhesive layer increases from the edge toward the center of thermal expansion. The effect of this increased stiffness is that the adhesive layer has low stiffness at the edge and high stiffness at the center of thermal expansion. The high stiffness at the center of thermal expansion means that the position and / or shape of the optical element will not change with increasing temperature. The stiffness gradient from the edge of the optical system toward the center of thermal expansion, or the decrease in stiffness from the center of thermal expansion toward the edge of the optical system, simultaneously ensures that the high stiffness at the center of thermal expansion does not impair the optical performance of the optical system.

[0013] Figure 1B Through with Figure 1A The comparison illustrates the effect of the stiffness gradient. In Figure 1A In the process, due to the low stiffness k of the adhesive layer, the optical system deforms as the temperature increases, which is caused by... Figure 1A The low linear trend is represented in the curve graph. Figure 1B In this case, the optical system exhibits minimal deformation with increasing temperature. In other words, the effect of the stiffness gradient is that the optical system undergoes only very slight deformation as temperature rises. This is because the stiffness gradient extends towards the center of thermal expansion, which is caused by… Figure 1B The increase in stiffness k towards the center of thermal expansion is represented in the curve diagram. Figure 1A and Figure 1B In the example, the center of thermal expansion is in the middle of the optical system. This is merely illustrative. The center of thermal expansion can be at any other point within the optical system.

[0014] The following will refer to Figures 2A to 3 Explanatory optical system and Figures 4A to 5B The illustrative stiffness curve is used to illustrate the general concept of this disclosure presented at the outset.

[0015] Figure 2A An optical system 100 is shown. The optical system 100 includes a first optical element 110, a first adhesive layer 120, a second optical element 130, a second adhesive layer 140, and a third optical element 150.

[0016] The first optical element 110, the second optical element 130, and the third optical element 150 are configured to provide their respective optical functions. These optical functions can be, for example, an increase or decrease in the size of the individual optical elements. In the context of an HMD, the optical function can be, for example, field-of-view magnification relative to a short distance in front of the user's eyes. The optical function can also be light transmission, for example, in a waveguide. Depending on their respective optical functions, the first optical element 110, the second optical element 130, and the third optical element 150 have a first refractive index, a second refractive index, and a third refractive index, respectively. Therefore, the first optical element 110, the second optical element 130, and the third optical element 150 can be, for example, a lens, a Fresnel lens, or a waveguide. To illustrate this, Figure 2A A first optical element 110 as a convex lens and a third optical element as a concave lens are shown. It should be understood that these examples are not exhaustive. The first optical element 110, the second optical element 130, and the third optical element 150 can be any type of optical element configured to provide optical functions. Furthermore, the first optical element 110, the second optical element 130, and the third optical element 150 can be, for example... Figure 2A The single-piece optical element shown can also be a multi-piece optical element, that is, an optical element composed of a single segment.

[0017] Since each of the first optical element 110, the second optical element 130, and the third optical element 150 can provide different optical functions, the optical system 100 can provide optical functions resulting from the combination of these optical functions.

[0018] It should be understood that the optical system 100 can have more than Figure 2A The optical system 100 may have more or fewer optical elements. Since the optical system 100 is an optical system with multiple optical elements, it has at least two optical elements. However, this disclosure allows for any number of optical elements, such as an optical system 100 with three optical elements.

[0019] As temperature fluctuates, the first optical element 110, the second optical element 130, and the third optical element 150 can deform, for example, by changing their length or deforming in some other way. For instance, the first optical element 110, the second optical element 130, and the third optical element 150 may each have different first, second, and third coefficients of thermal expansion. The different longitudinal expansion coefficients of the individual optical elements will cause changes in the position and deformation of the optical elements relative to each other, resulting in changes in the optical system 100. This can affect the structural integrity of the optical system 100, particularly its optical function. As described below, the first adhesive layer 120 and the second adhesive layer 140 are configured to substantially prevent or compensate for these deformations.

[0020] A first adhesive layer 120 is disposed between the first optical element 110 and the second optical element 130, and configured to bond the first optical element 110 and the second optical element 130. Similarly, a second adhesive layer 140 is disposed between the second optical element 130 and the third optical element 150, and configured to bond the second optical element 130 and the third optical element 150. As previously described, the optical system 100 has at least two optical elements, and may have any number of optical elements, each of which is incorporated into the optical system 100 by an additional adhesive layer. Thus, the optical system has at least one adhesive layer, and may include more than one adhesive layer depending on the number of optical elements.

[0021] The first adhesive layer 120 has a first stiffness gradient from one edge of the optical system 100 toward the center of thermal expansion of the optical system 100. Alternatively, the first adhesive layer 120 or the entire optical system 100 may be a disk with a radius R, for example... Figure 3 As shown.

[0022] In the context of this disclosure, stiffness k refers to the resistance to deformation of the adhesive layer 120 relative to the first optical element 110 and the second optical element 130. In short, as shown in Equation (1), the position-dependent elastic modulus E(r) and the position-dependent geometric function F of the adhesive layer 120 can be used. G (r) is used to approximate the stiffness k as the position-dependent stiffness k(r):

[0023] k(r)=E(r)*F G (r) (1)

[0024] In equation (1), the position-related geometric function F G (r) describes the geometry of the adhesive layer 120. Stiffness k(r), elastic modulus E(r), and geometric function F... G The spatial dependence of (r) is found from these values ​​or the radial position dependence of the function within the optical system, for example, as Figure 2A and Figure 2B The lower edge or Figure 3 As shown in the middle. It should be understood that equation (1) constitutes a simplified approximation of the position-dependent stiffness k(r). Depending on the stiffness form considered, such as tensile stiffness or bending stiffness, or a combination of stiffness forms, based on the position-dependent elastic modulus E(r) of the adhesive layer 120 and the position-dependent geometric function F G The location-dependent stiffness k(r) can also be reported in other ways. Based on equation (1), the stiffness gradient... It can be approximated by equation (2):

[0025]

[0026] Therefore, the stiffness gradient depends on the derivative of the location-dependent elastic modulus E(r) and the geometric function F of the adhesive layer 120. G (r) The corresponding derivative. Similar to Equation (1), Equation (2) is intended only as a simplified approximation so that the core of the term “stiffness gradient” is defined as the stiffness derivative based on the position-dependent elastic modulus. Depending on the specific stiffness form or combination of stiffness forms considered, other or different terms may be considered in the actual calculation of the stiffness gradient. Examples of further terms that may be considered in Equation (1) and therefore in Equation (2) are the relative extensibility and compressibility or cross-shrinkage of the adhesive layer 120, and the formation of polymer regions in the adhesive layer 120, such as adhesive areas at the edges or cohesive regions in the middle.

[0027] Exemplary elastic values ​​of the position-dependent elastic modulus E(r) at the edge of the optical system are in the range of 10 kPa to 10 MPa. Exemplary elastic values ​​of the position-dependent elastic modulus E(r) at the thermal expansion center of the optical system are in the range of 1 MPa to 5 GPa.

[0028] In the context of this application, the thermal expansion center refers to a region of the optical system 100 where the optical system 100 has a minimum due to the previously discussed thermal deformation of its optical elements. In other words, the thermal expansion center refers to a region of the optical system from which radial thermal deformation of the optical system 100 emanates, while the system itself is essentially undeformed. Figures 4A to 4C As shown, for example, when all elements of the optical system 100 are axially symmetric, this region can coincide with the axis of symmetry in the optical system 100. However, this region can also be located at a position different from the geometric center of the optical system 100.

[0029] As described above, the stiffness gradient points from one edge of the optical system 100 towards the center of thermal expansion of the optical system 100. The stiffness curve caused by this stiffness gradient substantially prevents deformation of the optical system without impairing its optical function. The stiffness curve substantially reduces or avoids impairment of optical function by minimizing deformation of optical elements 110 and 130. The decrease in stiffness towards the edge of the optical system 100 avoids any impairment of optical function that would otherwise be caused by high stiffness. It should be understood that in some examples of this disclosure, optical function may indeed deteriorate to some extent due to the direction of stiffness in a region of the optical system 100. However, such degradation in a region may be minimal relative to the entire optical system 100. At the same time, the stiffness curve can compensate for or avoid deformation of the optical system 100 and displacement of the first optical element 110 relative to the second optical element 130 due to temperature fluctuations.

[0030] In summary, the stiffness gradient of the adhesive layer 120 has the effect of preventing temperature fluctuations from causing deformation of the optical system 100. Furthermore, due to the stiffness gradient, the adhesive layer 120 does not significantly affect the optical function.

[0031] More specifically, in some examples of this disclosure, the first adhesive layer 120 may have maximum stiffness at the center of thermal expansion. This maximum stiffness can be configured to protect the bond between the first optical element 110 and the second optical element 130. Furthermore, the first stiffness gradient can ensure the optical function of the optical system 100, i.e., ensure that the optical function of the optical system is not impaired by the stiffness of the first adhesive layer 120.

[0032] The following is for reference. Figures 4A to 5B Describe an exemplary stiffness curve caused by the stiffness gradient.

[0033] Figures 4A to 4C Stiffness curves for the stiffness k of the first adhesive layer 120, which has a stiffness gradient, are shown. In the stiffness curves shown, the center of thermal expansion is located at the geometric center of the optical system 100. It should be noted that the representation of the center of thermal expansion at the geometric center of the optical system is merely illustrative. The center of thermal expansion may also be located in other regions of the optical system.

[0034] Figure 4A An example of a discrete stiffness curve is shown. Therefore, in Figure 4A In the example, the stiffness gradient is also discrete. Figure 4A In the example, the stiffness is constant throughout the cross section, so the stiffness gradient is zero throughout the cross section, and non-zero only at specific transitions. These transitions are between bonded zones, such as... Figure 2A and Figure 3 As shown. In other words, adhesive layer 120 may include multiple adhesive regions, such as three adhesive regions 1201, 1202, and 1203 that are laterally adjacent to each other. It should be understood that the number of adhesive regions can vary, and the three adhesive regions 1201, 1202, and 1203 are used only as examples. In the context of this disclosure, based on various adhesives with different stiffnesses, the multiple adhesive regions may include any number of adhesive regions required to produce a stiffness curve with a stiffness gradient.

[0035] In addition to generating discrete stiffness curves, adhesive regions adjacent to other adhesive regions on either side can be configured to convert internal tension in the first adhesive layer 120 into compression. Converting internal tension into compression prevents the first adhesive layer 120 itself from significantly affecting the deformation of the optical system 100. For this purpose, the first adhesive layer can have a cross-shrinkage value of less than 0.45.

[0036] Figure 4B An example of a continuous stiffness curve across a cross section is shown. In Figure 4BIn the example, the stiffness increases to varying degrees and in a constant manner across the various portions from the edge of the optical system 100 to the center of thermal expansion. This means that the stiffness gradient is constant across the cross section, non-zero in every case, and jumps to the stiffness gradient value of the next cross section at each transition. Figure 4A As shown, such discrete stiffness curves can be generated by multiple bonding zones, such as three bonding zones 1201, 1202, and 1203. In this case, the adhesive in each bonding zone has a stiffness that increases toward the center of thermal expansion.

[0037] Figure 4C An example of a continuous stiffness curve is shown. Therefore, in Figure 4C In this example, the stiffness gradient is continuous. In other words, the stiffness increases from the edge of the optical element 100 towards the center of thermal expansion without any noticeable discontinuity. Therefore, the stiffness gradient is also stable. In this example, the adhesive layer 120 may not include multiple adhesive regions, for example, as... Figure 2B As shown. It should be noted here that, in addition to multiple adhesive areas, Figure 2B The optical system 100 corresponds to Figure 2A The optical system.

[0038] For example, by adding glass particles to the adhesive in the liquid adhesive layer 120, a continuous stiffness profile can be generated, thus creating a continuous stiffness gradient. The glass particles can be, for example, glass particle powder with an average bead size in the range of a few nanometers to a few micrometers. This addition is made to achieve a non-uniform glass particle density in the adhesive layer 120 upon curing. As a result, as... Figure 4C As shown, the adhesive layer 120 in the cured state has a continuous stiffness curve or a continuous stiffness gradient. The refractive index of the glass particles or glass particle powder approximately corresponds to the refractive index of the first adhesive layer 120. For example, Figure 4B The same method can be used in the example to achieve a continuous increase in the stiffness of the bonded area.

[0039] Figure 5A and Figure 5B Two additional illustrative discrete stiffness curves are shown. In both examples, the center of thermal expansion is located at the geometric center of the optical system 100.

[0040] exist Figure 5A In the middle, viewed from the edge, the stiffness increases segment by segment; that is, for example, for each bonded area, the stiffness decreases again and reaches its maximum value at the center of thermal expansion. Figure 5A The example shows that the stiffness curve does not need to rise continuously from the edge to the center of thermal expansion, but can rise and fall until it reaches the global stiffness maximum. In other words, the stiffness gradient of the first adhesive layer 120 can point from the edge of the optical system 100 to the global stiffness maximum.

[0041] exist Figure 5B In the second bonding region 1202, the optical system 100 exhibits a maximum radial stiffness. Due to the circular shape and orientation of the optical system 100 centered on its geometric center, the maximum stiffness in the second bonding region 1202 is... Figure 5B It appeared twice in the stiffness curve. In other words, Figure 5B The example optical system 100 has a maximum range of annular stiffness around the center of thermal expansion. This maximum range of stiffness can compensate for temperature-dependent deformation of the first optical element 110 and the second optical element 130.

[0042] In some examples of this disclosure, the first adhesive layer 120 can also be configured to compensate for deformations of the first optical element 110 and the second optical element 130, such that the deformations are quasi-isotropic or along a preferred direction, due to the first stiffness gradient. In other words, the first adhesive layer 120 can be configured to substantially prevent or counteract the deformations of the first optical element 110 and the second optical element 130 by controlled radial stiffness difference and thermal expansion, thereby compensating for bending deformations.

[0043] Due to the first stiffness gradient, in some examples of this disclosure, the first adhesive layer 120 can also be configured to generate a bending moment that counteracts the bending moment generated by the thermal expansion of the first optical element 110 and the second optical element 130. Due to the maximum stiffness, the first adhesive layer 120 can be configured to ensure the strength of the adhesive bond. The radially varying bending moment generated by the adhesive layer 120, together with the bending moments of the first optical element 110 and the second optical element 130, results in an effective bending-free deformation state of the optical system 100. Therefore, the first adhesive layer 120 can compensate for or controllably adjust the deformation of the optical system 100.

[0044] The first adhesive layer 120 may also have a first refractive index. The first refractive index may be configured to correspond to the refractive index of at least one of the first optical element 110 and the second optical element 130. This ensures the optical function of either the first optical element 110 or the second optical element 130 because the corresponding refractive index can prevent total internal reflection, for example, at the interface between the first adhesive layer 120 and either the first optical element 110 or the second optical element 130. In the context of this application, the corresponding refractive index implies a variance of up to 2.5%. When the second optical element 130 is a waveguide, the first refractive index may also be lower than the refractive index of the second optical element 130. This ensures total internal reflection, for example, a total internal reflection limiting angle in the first adhesive layer 120 of less than 60°, such as less than 55° or less than 50°.

[0045] The first adhesive layer 120 may have a transmittance configured to substantially not absorb light in the visible spectrum region. This transmittance ensures that the first adhesive layer 120 does not act as an optical damping or color filter element. The first adhesive layer 120 may also be controllably adjustable for color or spectral filtering, such as for color-neutral or color-weighted filtering in sunglasses, or for increasing image contrast in AR systems, to act as a color filter for example, yellow, green, or red, or as a spectral filter that absorbs UV and / or IR radiation.

[0046] In some examples of the optical system 100 according to this disclosure, where the first optical element 110 is a lens and the second optical element 130 is a waveguide, the first adhesive layer 120 can be configured to provide total internal reflection corresponding to total internal reflection of the waveguide. In other words, the first adhesive layer 120 can be configured to provide total internal reflection for light guided in the waveguide, while ensuring that light decoupled from the waveguide is not absorbed or reflected by the first adhesive layer 120. Furthermore, if the first optical element 110 is a lens and the second optical element 130 is a waveguide, the adhesive layer can have a first region and a second region. The first region can have a first region refractive index that provides total internal reflection in the first region of the optical system. The second region can have a second region refractive index greater than or equal to the refractive index of the first region. Through these different refractive indices in the different regions of the first adhesive layer 120, total internal reflection can firstly be provided for light guided in the waveguide. Secondly, undesirable total internal reflection at other interfaces can be avoided.

[0047] The second adhesive layer 140 is disposed between the second optical element 130 and the third optical element 150, and configured to bond the second optical element 130 and the third optical element 150. Furthermore, the second adhesive layer has a second stiffness gradient from one edge of the optical system 100 towards the center of thermal expansion of the optical system 100. In other words, the definition of the second adhesive layer 140 corresponds to the definition of the first adhesive layer. Therefore, the foregoing description relating to the first adhesive layer 120 also applies to the second adhesive layer 140 or any other adhesive layer of the optical system 100.

[0048] Therefore, the second adhesive layer 140 can be configured to generate a second bending moment similar to that of the first adhesive layer 120. Through the first and second bending moments, the first adhesive layer 120 and the second adhesive layer 140 can be configured to provide a combined bending moment that counteracts the bending moment generated by the thermal expansion of the first optical element 110, the second optical element 130, and the third optical element 150.

[0049] Furthermore, the second adhesive layer 140 may have a second refractive index. Starting from this point, the first refractive index of the first adhesive layer and the second refractive index of the second adhesive layer 140 may have a refractive index difference inversely proportional to the opening angle of the transmission cone. Otherwise, the refractive index difference may impair the optical function of the optical system 100.

[0050] In some examples of the invention, the optical system may further include an anti-reflective coating. The anti-reflective coating may be disposed between the first adhesive layer 120 and the first optical element 110, between the first adhesive layer 120 and the second optical element 130, or between the adhesive layer 120 and the first optical element 110 and the first adhesive layer 120 and the second optical element 130. Similarly, the anti-reflective coating may be disposed relative to the second adhesive layer 140, the second optical element 130, and the third optical element 150, or relative to each of the additional adhesive layers.

[0051] The thickness of the optical system 100 can be less than 250 μm, for example, 100 μm or 50 μm. The thickness of a single adhesive layer and optical element can be between 10 μm and 100 μm.

[0052] The following examples further illustrate the present invention.

[0053] In one example, the optical system includes a first optical element, a second optical element, and a first adhesive layer, wherein the first adhesive layer is disposed between the first optical element and the second optical element and configured to connect the first optical element and the second optical element, and the first adhesive layer has a first stiffness gradient from the edge of the optical system to the thermal expansion center of the optical system.

[0054] In one example, the first adhesive layer may have maximum stiffness at the center of thermal expansion, wherein the maximum stiffness may be configured to protect the connection between the first optical element and the second optical element, and wherein the first stiffness gradient may ensure the optical function of the optical system.

[0055] In one example, the first stiffness gradient can be continuous.

[0056] In one example, the first stiffness gradient can be discrete.

[0057] In one example, the first adhesive layer may include multiple adhesive areas that are laterally adjacent to each other.

[0058] In one example, the adhesive areas in a plurality of adhesive strips that are laterally adjacent to other adhesive areas in a plurality of adhesive areas on both sides can be configured to convert internal tension into compression.

[0059] In one example, the first adhesive layer may have a cross-shrinkage value of less than 0.45.

[0060] In one example, the first adhesive layer may have a first refractive index configured to correspond to, or be lower than, the refractive index of, at least one of a first optical element and a second optical element, wherein the second optical element is a waveguide.

[0061] In one example, the first adhesive layer may have a transmittance configured to substantially not absorb light in the visible spectral region.

[0062] In one example, the adhesive layer can be configured for deformation, wherein the deformation of the first adhesive layer can be configured to compensate for the deformation of the first optical element and the second optical element.

[0063] In one example, the first adhesive layer may be configured to generate a bending moment that is configured to counteract the bending moment generated by the thermal expansion of the first and second optical elements.

[0064] In one example, the optical system may further include a third optical element and a second adhesive layer, wherein the second adhesive layer may be disposed between the second optical element and the first optical element and may be configured to connect the second optical unit and the third optical unit, wherein the first adhesive layer may have a second stiffness gradient from one edge of the optical system toward the thermal expansion center of the optical system, and wherein the first adhesive layer and the second adhesive layer may be configured to generate a combined bending moment configured to counteract the bending moment generated by the thermal expansion of the first optical element, the second optical element and the third optical unit.

[0065] In one example, the first adhesive layer and the second adhesive layer may have a refractive index difference that is inversely proportional to the opening angle of the transmitted light cone.

[0066] In one example, the first optical element may have a first longitudinal coefficient of thermal expansion, the second optical element may have a second longitudinal coefficient of thermal expansion, and the first and second longitudinal coefficients of thermal expansion may be different from each other.

[0067] In one example, the first optical element and the second optical element can be either a single-piece optical element or a multi-piece optical element.

[0068] In one example, the first optical element may be a lens, the second optical element may be a waveguide, and the first adhesive layer may be configured to provide total internal reflection corresponding to the total internal reflection of the waveguide.

[0069] In one example, the first adhesive layer may have a first region and a second region, and is further configured to have a first region refractive index in the first region that provides total internal reflection in the first region of the optical system, and a second region refractive index in the second region that is greater than or equal to the first region refractive index.

[0070] The above description is provided to describe an optical system including an adhesive layer with a stiffness gradient. It should be understood that this description is not intended to limit the scope of the invention in any way to the exact embodiments discussed herein. Rather, those skilled in the art will recognize that embodiments can be combined, modified, or simplified without departing from the scope of the invention as defined by the appended claims.

Claims

1. An optical system, comprising: First optical element and second optical element; and First adhesive layer, wherein the first adhesive layer: Arranged between the first optical element and the second optical element and configured to combine the first optical element and the second optical element, and The first adhesive layer has a first stiffness gradient from one edge of the optical system toward the center of thermal expansion of the optical system.

2. The optical system according to claim 1, wherein: The first adhesive layer has maximum stiffness at the thermal expansion center, wherein the maximum stiffness is configured to protect the bond between the first optical element and the second optical element, and The first stiffness gradient ensures the optical function of the optical system.

3. The optical system according to any one of the preceding claims, wherein, The first stiffness gradient is continuous.

4. The optical system according to any one of claims 1 and 2, wherein, The first stiffness gradient is discrete.

5. The optical system according to any one of the preceding claims, wherein, The first adhesive layer includes a plurality of adhesive areas that are laterally adjacent to each other.

6. The optical system according to claim 5, wherein, The adhesive area of ​​the plurality of adhesive areas is configured to convert internal tension into compression on any side of the other adhesive areas of the plurality of adhesive areas.

7. The optical system according to claim 6, wherein, The cross-shrinkage value of the first adhesive layer is less than 0.

45.

8. The optical system according to any one of the preceding claims, wherein, The first adhesive layer has a first refractive index, which is configured as follows: The refractive index corresponding to at least one of the first optical element and the second optical element; or The refractive index is lower than that of the second optical element, which is a waveguide.

9. The optical system according to any one of the preceding claims, wherein, The first adhesive layer has a transmittance configured to substantially not absorb light in the visible spectrum region.

10. The optical system according to any one of the preceding claims, wherein, The adhesive layer is configured for deformation, wherein the deformation of the first adhesive layer is configured to compensate for the deformation of the first optical element and the second optical element.

11. The optical system according to any one of the preceding claims, wherein, The first adhesive layer is configured to generate a bending moment, which is configured to counteract the bending moment generated by the thermal expansion of the first optical element and the second optical element.

12. The optical system according to any one of the preceding claims further comprises a third optical element and a second adhesive layer, wherein: The second adhesive layer is disposed between the second optical element and the third optical element, and is configured to bond the second optical element and the third optical element. The second adhesive layer has a second stiffness gradient from one edge of the optical system toward the center of thermal expansion of the optical system, and The first adhesive layer and the second adhesive layer are configured to generate a combined bending moment, which is configured to counteract the bending moment generated by the thermal expansion of the first optical element, the second optical element and the third optical element.

13. The optical system according to any one of the preceding claims, wherein, The first adhesive layer and the second adhesive layer have a refractive index difference that is inversely proportional to the opening angle of the transmitted light cone.

14. The optical system according to any one of the preceding claims, wherein: The first optical element has a first longitudinal coefficient of thermal expansion. The second optical element has a second longitudinal coefficient of thermal expansion, and The first longitudinal thermal expansion coefficient and the second longitudinal thermal expansion coefficient are different from each other.

15. The optical system according to any one of the preceding claims, wherein, The first optical element and the second optical element are either single-piece optical elements or multi-piece optical elements.

16. The optical system according to any one of the preceding claims, wherein: The first optical element is a lens. The second optical element is a waveguide, and The first adhesive layer is configured to provide total reflection corresponding to the total reflection of the waveguide.

17. The optical system according to claim 16, wherein, The first adhesive layer has a first region and a second region, and is further configured as follows: The first region has a first region refractive index that provides the total internal reflection in the first region of the optical system, and The second region has a refractive index that is greater than or equal to that of the first region.

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