Optical element, optical system, and optical device

Abstract

The present invention provides an optical element using a glass substrate and a resin, which has reduced warping due to temperature changes. The optical element (10) of one embodiment of the present invention has a glass substrate (11), an optical function part (12) made of resin, and a bonding part (13) that bonds the glass substrate (11) and the optical function part (12), and the glass transition point of the bonding part (13) is 85°C or less, or the Young's modulus of the bonding part (13) is less than 100 MPa.

Description

[Technical field]

[0001] The present invention relates to an optical element using a glass substrate and a resin, an optical system having the optical element, and an optical device having the optical element. [Background technology]

[0002] A wafer lens technology is known in which a lens is formed on a glass substrate by molding an ultraviolet curable resin or a thermosetting resin on the glass substrate by an imprint method (see, for example, Patent Document 1). Wafer lenses contribute to making lens systems more compact.

[0003] Patent Document 2 describes an optical system in which a lens (focus lens) and an optical filter are integrated. When a wafer lens is used in such an optical system, the thickness is reduced, and the wafer lens contributes to making the optical system compact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2010 / 050304 [Patent Document 2] Japanese Patent Publication No. 2005-234038 [Patent Document 3] Japanese Patent Application Publication No. 2008-250285 [Non-patent literature]

[0005] [Non-Patent Document 1] Naotoshi Yamashina, "Special 5: Mechanism of Warpage in Copper-Clad Laminates," Abstracts of a Discussion Meeting, Japan Plastics Industry Association, 1985, Vol. 35, pp. 125-128 Summary of the Invention [Problem to be solved by the invention]

[0006] When a laminate of a glass substrate and a resin lens is produced, warping occurs due to temperature changes due to the difference between the linear expansion coefficients of glass and resin. The warping deteriorates the optical properties of the lens system. In particular, when the resin is present only on one side of the glass substrate, the warping is significant. Furthermore, when the glass substrate is thin and the resin is thick, the warping is particularly significant.

[0007] Patent Document 3 describes a laminate in which a resin lens and a glass optical filter (specifically, an infrared filter) are laminated. When laminating the lens and the optical filter, if the optical filter is attached over the entire surface of the lens, the optical filter is highly likely to peel off due to the difference between the volume expansion coefficient of the resin and the volume expansion coefficient of the glass. Therefore, in the laminate described in Patent Document 3, the lens and the optical filter are bonded outside the effective areas of the lens and the optical filter in order to suppress peeling.

[0008] However, even if the adhesive is limited to a certain area, the glass and resin are constrained by the adhesive, and warping or sagging may occur when the temperature changes.

[0009] One aspect of the present invention aims to provide an optical element using a glass substrate and a resin, in which warping due to temperature changes is reduced, an optical system having the optical element, and an optical device having the optical element. [Means for solving the problem]

[0010] An optical element according to one embodiment of the present invention has a glass substrate, an optical functional part made of resin, and a bonding part that bonds the glass substrate and the optical functional part, and the glass transition point of the bonding part is 85°C or lower.

[0011] Another embodiment of the optical element of the present invention is an optical element having a glass substrate, an optical functional part made of resin, and a bonding part bonding the glass substrate and the optical functional part, wherein the Young's modulus of the bonding part is less than 100 MPa.

[0012] An optical system according to one aspect of the present invention includes the optical element according to the above aspect.

[0013] An optical device according to one aspect of the present invention includes the optical element according to the above aspect. Effect of the Invention

[0014] According to an aspect of the present invention, warping due to temperature changes is reduced in an optical element using a glass substrate and a resin. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an embodiment of an optical element. [Diagram 2] 2(a) and 2(b) are cross-sectional views showing examples of other embodiments of the optical element. [Diagram 3] 3(c) and 3(d) are cross-sectional views showing examples of other embodiments of the optical element. [Figure 4] 4(a) and 4(b) are diagrams illustrating the reduction of warpage in an optical element. [Diagram 5] FIG. 5 is a graph showing the results of calculations, using the finite element method, of the amount of warping when the temperature difference between the temperature at which the optical element functions and room temperature is 25° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described below.

[0017] [Optical elements] The optical element according to one embodiment of the present invention includes a glass substrate, an optical function portion, and a bonding portion that bonds the glass substrate and the optical function portion together.

[0018] 1 is a cross-sectional view showing an embodiment of an optical element 10. The optical element 10 of this embodiment is composed of a glass substrate 11, an optical function part 12 made of resin, and a bonding part (bonding layer) 13 formed of, for example, an adhesive or an OCA (Optical Clear Adhesive) double-sided tape.

[0019] At least a part of the optical function part 12 has a shape having an optical function, such as a lens shape. The optical function part 12 and the glass substrate 11 are bonded via a bonding part 13. A coating such as an anti-reflection film may be provided on the surface of the optical function part 12 or on the interface between the optical function part 12 and the bonding part 13. The width of the bonding part 13 is represented by W.

[0020] The shape of the glass substrate 11 is not limited, and may be, for example, a flat plate. In a plan view, the shape of the glass substrate 11 may be rectangular, circular, or elliptical. The glass substrate 11 may be transparent in at least a part of the wavelength band used in the optical system. The glass substrate 11 may have an anti-reflection layer at the interface between the glass substrate 11 and air or at the interface between the glass substrate 11 and the bonding portion 13.

[0021] The glass substrate 11 may also have an optical filter function. In order to impart an optical filter function, an optical functional layer having a reflecting function or an absorbing function for any one or more of infrared light, visible light, and ultraviolet light may be laminated on the glass substrate 11. As the optical functional layer, an optical multilayer film having a metal, a semiconductor, a dielectric, or an organic film containing an organic dye, a pigment, or the like may be used. Instead of laminating an optical functional layer on the glass substrate 11, a material having a reflecting function or an absorbing function for any one or more of infrared light, visible light, and ultraviolet light may be used as the glass material used for the glass substrate 11.

[0022] The shape of the optical element 10 is not limited to the shape exemplified in Fig. 1. For example, as shown in Fig. 2(a), the glass substrate 11 may have a width greater than that of the optical functional section 12. As shown in Fig. 2(b), the glass substrate 11 may have a width smaller than that of the optical functional section 12. As shown in Fig. 3(c), a bonding section 13 may be provided on the outer periphery side of the optical functional section 12. In this case, the space 14 between the glass substrate 11 and the optical functional section 12 is an air layer.

[0023] The surface shape of the optical function part 12 is not limited to a convex shape. For example, it may be a concave shape as shown in Fig. 3(d). It may also be a substantially planar shape having minute concaves and convexes like a diffraction grating.

[0024] As one example, the optical element 10 is produced by first forming the optical function part 12, and then bonding the optical function part 12 to the glass substrate 11 via the bonding part 13. As another example, the bonding part 13 may be provided on the glass substrate 11, and the optical function part 12 may be formed thereon by an imprint method.

[0025] Next, warping of the optical element 10 due to temperature changes will be considered. Here, the consideration will be made using the general formula for warping of a k-layer laminate described in Non-Patent Document 1.

[0026] In the following formula (1), E k represents the elastic modulus of each layer. k represents the linear expansion coefficient of each layer. Z k represents the position of the interface of each layer in the thickness direction from the reference coordinate that can be set at any position. t represents the temperature difference from the reference temperature. K represents the curvature K of the deformation of the laminate caused by the temperature difference t.

[0027] K = (A × FB × D) / (A × CB 2 ) A = Σ{E k ×(Z k -Z k-1 )} B = (1 / 2) × Σ{E k ×(Z k2 -Z k-1 2 )} C = (1 / 3) × Σ{E k ×(Z k 3 -Z k-1 3 )} D = t × Σ{E k ×α k ×(Z k -Z k-1 )} F = (t / 2) × Σ{E k ×α k ×(Z k 2 -Z k-1 2 )} (1)

[0028] If the amount of displacement (warping) in the thickness direction caused by the arc of curvature K is taken as the amount of displacement ΔH, then ΔH is defined by the following formula (2): W represents the width of the joint.

[0029] ΔH=(1 / |K|)-√{(1 / K) 2 -(W / 2) 2} ···(2)

[0030] Therefore, the warpage of the laminate due to temperature change can be estimated using equations (1) and (2). k The unit is [MPa]. Z k The unit is [mm]. α k The unit of is [ / ℃]. The unit of ΔH is [mm]. The unit of t is [℃].

[0031] The above formula (1) is a formula for a model in which flat plates are stacked, but in the case of a lens in which the surface thickness varies depending on the location, the thickness can be calculated as the thickest part from the joint 13. In addition, if the joint 13 is sufficiently thin (for example, if the thickness of the joint 13 is 1 / 5 or less of the thickness of the optical function part 12), the calculation can be performed for two layers, the glass substrate 11 and the optical function part 12. In this case, K is derived by the following formula (3).

[0032] K = (A × FB × D) / (A × CB 2 ) A = Es × Hs + Em × Hm B = (1 / 2) × [Es × Hs 2 +Em×{(Hs+Hm) 2 -Hs 2}] C = (1 / 3) × [Es × Hs 3 +Em×{(Hs+Hm) 3 -Hs 3}] D=ΔT×{Es×αs×Hs+Em×αm×Hm} F = (ΔT / 2) × [Es × αs × Hs 2 +Em×αm×{(Hs+Hm) 2 -Hs 2}] ···(3)

[0033] In the above formula (3), Hm indicates the thickness (unit: [mm]) of the thickest part of the optical function part 12. Em indicates the Young's modulus (unit: [MPa]) of the optical function part 12. αm indicates the linear expansion coefficient (unit: [ / °C]) of the optical function part 12. Hs indicates the thickness (unit: [mm]) of the glass substrate 11. Es indicates the Young's modulus (unit: [MPa]) of the glass substrate 11. αs indicates the linear expansion coefficient (unit: [ / °C]) of the glass substrate 11. ΔT indicates the difference (unit: [°C]) between room temperature and the upper limit temperature of the temperature range in which the optical element 10 should function. Various ranges are assumed as the temperature range in which the optical element 10 should function, but hereinafter, as an example, ΔT=25°C.

[0034] ΔH is preferably 0.005 mm or more, and ΔH is preferably 0.01 mm or more when ΔT=25° C. In the optical element of one embodiment of the present invention, even though ΔH is in the above range, warping can be reduced by setting the glass transition point and Young's modulus of the bonding portion to specific ranges, as described later.

[0035] The thickness of the optically functional portion 12, the thickness of the glass substrate 11, the thickness of the bonding portion 13, and the width W of the bonding portion 13 can be measured by cross-sectional observation using a scanning electron microscope (SEM) or an optical microscope.

[0036] The Young's modulus can be measured by a tensile test, a compression test, a torsion test, a resonance method, an ultrasonic pulse method, a pendulum method, etc. The measurement method is described in, for example, the following standards. JIS R1602:1995 "Test method for elastic modulus of fine ceramics" JIS R1605:1995 "Test method for high temperature elastic modulus of fine ceramics" JIS Z2201:1998 "Tensile test pieces for metal materials" JIS Z2241:2011 "Method of tensile testing of metallic materials" JIS G0567J:2012 "High temperature tensile test method for steel materials and heat-resistant alloys" JIS Z2280:1993 "Test method for high temperature Young's modulus of metallic materials"

[0037] In addition, when the optical functional part, the glass substrate, and the joint are thin, it may be difficult to measure the Young's modulus using the above method. In such cases, the nanoindenter method may be used. The measurement method of the nanoindenter method is described in, for example, ISO14577.

[0038] The linear expansion coefficient can be measured using a thermomechanical analyzer (TMA). Alternatively, the following JIS standard method may be used. JIS Z2285:2003 Measurement method for linear expansion coefficient of metallic materials JIS R1618:2002 Measurement method for thermal expansion of fine ceramics by thermomechanical analysis JIS R3251:1995 Measurement method for linear expansion coefficient of low expansion glass by laser interferometry JIS R3102:1995 Test method for average linear expansion coefficient of glass It can be measured using

[0039] When measuring the Young's modulus and linear expansion coefficient of the optical function part, the glass substrate, and the joint, they may be measured in a joined state or may be measured separately in a non-jointed state. The measurement methods for the optical function part, the glass substrate, and the joint may be different from each other. Although the values ​​of the Young's modulus and linear expansion coefficient may vary depending on the process that each material undergoes, the Young's modulus and linear expansion coefficient may be measured by molding materials with similar chemical compositions, and the values ​​may be used as the Young's modulus and linear expansion coefficient of each member. The Young's modulus and linear expansion coefficient may be measured using methods other than those described above.

[0040] [Table 1]

[0041] Table 1 shows the Young's modulus Es of the glass substrate 11 as 80,000 MPa and the linear expansion coefficient αs of the glass substrate 11 as 1.3×10 -5 / °C, Young's modulus Em of the optical functional part 12 is 2000 MPa, and the linear expansion coefficient αm of the optical functional part 12 is 1×10 -4 The following shows the results of calculating ΔH using equations (2) and (3) when ΔT=25°C, assuming that the thickness Hs of the glass substrate 11 is thin and the thickness Hm of the optical function portion 12 is thick, respectively.

[0042] For example, if the optical function part 12 has a lens shape, the focal length of the lens surface changes with temperature change. When the optical element 10 is incorporated into an optical system, such a change in focal length causes aberration in the optical system. When the optical system is an imaging system, the aberration has adverse effects such as blurring of the image. Although the amount of aberration allowed varies depending on the optical system, for example, the amount of warping of the optical element 10 caused by temperature change is preferably 0.010 mm or less, and more preferably 0.005 mm or less.

[0043] Furthermore, since the optical element 10 is generally bonded inside a package such as a lens barrel, the temperature dependency of the warp of the optical element 10 itself may be reduced by being restricted by the package. In such a case, the amount of warp caused by temperature change of the optical element 10 itself is preferably, for example, 0.020 mm or less.

[0044] In the above study, formulas (1) to (3) were used, but formulas (1) to (3) are formulas that are based on the premise that the laminate is bonded and deforms uniformly. However, as described below, the inventors' study has revealed that when the Young's modulus of the bonding portion 13 is sufficiently small, there is an effect of reducing warpage due to temperature change. Therefore, in an optical element according to one embodiment of the present invention, the Young's modulus of the bonding portion is set to a specific value or less, which will be described below.

[0045] Fig. 4 is an explanatory diagram for explaining the reduction of warpage of the optical element 10. The optical element 10 shown in Fig. 4(a) has a sufficiently small Young's modulus of the bonding portion 13. As shown in Fig. 4(a), when the Young's modulus of the bonding portion 13 is sufficiently small, it is considered that the deformation of the bonding portion 13 in response to the contraction of the optical function portion 12 reduces the warpage of the optical element 10.

[0046] On the other hand, if the Young's modulus of the joint 13 is large, the joint 13 cannot deform sufficiently in response to the contraction of the optical function section 12, and the entire joint 13 warps, as shown in FIG. 4(b).

[0047] The warpage taking such deformation into consideration can be calculated by the finite element method.

[0048] 5 is a graph showing the results of calculating the amount of warpage when the temperature difference between the temperature at which the optical element 10 functions and room temperature is 25° C. using the finite element method. When performing the calculation, the shape of the bonding portion 13 was rectangular in a plan view, and the diagonal length W (width) was 9 mm. The thickness of the glass substrate 11 was 0.2 mm, the thickness of the bonding portion 13 was 0.01 mm, and the thickness of the optical function portion 12 was 0.5 mm. The optical function portion 12 was a concave lens. The calculation method of the finite element method is described in "Finite Element Method" by Jacob Fish, 2008 / 12 / 20, Maruzen, etc. General-purpose finite element method calculation software (Abaqus, ANSYS, Solidworks Simulation, etc.) can be used for the calculation.

[0049] The Young's modulus of the glass substrate 11 is 80000 MPa, and the linear expansion coefficient of the glass substrate 11 is 1.3×10 -5 / °C, the Young's modulus of the optical function part 12 is 2000 MPa, and the linear expansion coefficient of the optical function part 12 is 1×10 -4 At this time, the linear expansion coefficient of the joint 13 was set to 1×10 -4 / °C. Calculations were performed for the Young's modulus of the joint 13 when it was 0.1 MPa, 1 MPa, 10 MPa, and 100 MPa. The amount of warpage was determined as the difference between the center and end positions in the thickness direction of the glass substrate 11. The Young's modulus (MPa) and warpage (mm) in FIG. 5 are shown in Table 2.

[0050] [Table 2]

[0051] When ΔH is calculated using formulas (1) and (2), ΔH=0.04 mm. When ΔH is calculated using formulas (2) and (3) assuming that the bonding portion 13 is sufficiently thin, ΔH=0.04 mm. It can be seen that the amount of warpage can be reduced by selecting the Young's modulus of the material of the bonding portion 13. That is, referring to the results shown in FIG. 5 and Table 2, it can be seen that if the Young's modulus of the bonding portion 13 is less than 100 MPa, the amount of warpage is 0.033 mm or less. Therefore, in the optical element according to one embodiment of the present invention, the Young's modulus of the material of the bonding portion is less than 100 MPa.

[0052] Furthermore, when the Young's modulus of the material of the joint is 20 MPa or less, the amount of warping is preferably 0.03 mm or less. When the Young's modulus of the material of the joint is 10 MPa or less, the amount of warping is more preferably 0.025 mm or less. When the Young's modulus of the material of the joint is 2 MPa or less, the amount of warping is even more preferably 0.01 mm or less. When the Young's modulus of the material of the joint is 0.6 MPa or less, the amount of warping is particularly preferably 0.005 mm or less.

[0053] In the above calculations, the Young's modulus and the linear expansion coefficient are set to one value. However, in general, the Young's modulus and the linear expansion coefficient change depending on the temperature. Therefore, instead of using the values ​​at room temperature, the average values ​​in a predetermined temperature range may be used as the values ​​of the Young's modulus and the linear expansion coefficient.

[0054] Generally, a resin material softens at a temperature higher than its glass transition point. Therefore, the glass transition point of the material of the bonding portion 13 is preferably below the upper limit of the operating temperature range of the optical element 10 or an optical member incorporating the optical element 10 (for example, below 85°C or below 50°C) or close to the lower limit of the operating temperature range (for example, below 25°C). If the glass transition point is within the above temperature range, the bonding portion 13 softens in at least a part of the operating temperature range, and the Young's modulus decreases, thereby reducing the amount of warping. Therefore, in the optical element according to one embodiment of the present invention, the glass transition point of the bonding portion 13 is 85°C or lower. The glass transition point of the bonding portion 13 is preferably 50°C or lower, more preferably 25°C or lower, and even more preferably 0°C or lower.

[0055] The change in Young's modulus around the glass transition point is described, for example, in "Mechanical and thermal properties of graphite platelet / epoxy composites," Polymer 45 (2004) 8211-8219. This document shows the behavior of the storage modulus around the glass transition point (Tg), but the Young's modulus can be considered to be similar. As shown in this document, the Young's modulus generally shows a change of one order of magnitude or more around Tg. Therefore, when Tg is within the above temperature range, the Young's modulus of the joint below Tg is preferably less than 100 MPa, and more preferably 20 MPa.

[0056] The glass transition temperature of the joint can be measured by differential scanning calorimetry (DSC), differential thermal analysis (DTA), etc. The measurement method is described in, for example, the following standards. JIS K 7121:2012 "Method of measuring transition temperature of plastics" JIS K 6240:2011 "Raw rubber - Determination of glass transition temperature by differential scanning calorimetry (DSC)"

[0057] Furthermore, if the width W of the joint 13 is large, the amount of warping increases. In consideration of this, W is preferably, for example, 20 mm or less, and more preferably 10 mm or less. Furthermore, the thinner the glass substrate 11 is, the greater the amount of warping becomes. Therefore, it is preferable to set the thickness of the glass substrate 11 to, for example, 0.3 mm or less and select the above width W.

[0058] The above-mentioned idea of ​​reducing warpage is also effective when bonding the optical element 10 to other members such as a package or other optical members. For example, when an optical unit is produced by bonding the glass substrate 11 or the optical function part 12 to a package member having a different linear expansion coefficient, warpage of the optical unit due to temperature change is reduced by using a material with a small Young's modulus as an adhesive. The Young's modulus of the adhesive may be, for example, 2 MPa or less, or 0.6 MPa or less.

[0059] [Optical system] The optical element according to one aspect of the present invention has been described above, but the optical element according to the above aspect can be applied (for example, incorporated) into various optical systems.

[0060] Examples of the optical system include, in addition to the optical elements described above, lenses that cooperate with the optical elements, optical filters such as anti-reflection filters and bandpass filters, cover glass, apertures, etc. However, these are merely examples, and the application of the optical elements described above is not limited to these.

[0061] [Optical device] It is also assumed that the optical element or the optical system described above is applied to an imaging device such as a camera, or to a measuring device that projects light to measure distance or shape. That is, the optical element or optical system according to one embodiment of the present invention can be applied to optical devices including imaging devices and measuring devices. However, these are merely examples, and the uses of the optical system to which the optical element is applied are not limited to these. EXAMPLES

[0062] Hereinafter, the embodiment of the present invention will be specifically described with reference to the optical element 10 illustrated in FIG. 3(d). The bonding portion 13 is rectangular in plan view, and the diagonal length (width) W is 9 mm. The thickness of the glass substrate 11 is 0.2 mm, the thickness of the bonding portion 13 is 0.01 mm, and the thickness of the optical function portion 12 is 0.5 mm. As shown in FIG. 3(d), the optical function portion 12 is a concave lens. The Young's modulus of the glass substrate 11 is 80,000 MPa, and the linear expansion coefficient of the glass substrate 11 is 1.3×10 -5 / °C, Young's modulus of the optical functional part 12 is 2000 MPa, and the linear expansion coefficient of the optical functional part 12 is 1×10 -4 / °C, and the linear expansion coefficient of the joint 13 is 1×10 -4 The Young's modulus of the joint 13 is 0.1 MPa. The glass transition point is 0°C.

[0063] When ΔH is calculated using formulas (1) and (2), it is ΔH = 0.04. When ΔH is calculated using formulas (2) and (3), it is ΔH = 0.04. When the amount of warping is calculated using the finite element method when the temperature changes by 25°C, it is 1 μm. In other words, it can be said that the amount of warping is sufficiently small.

[0064] Although the present invention has been described in detail using specific embodiments, it is clear to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2018-153404) filed on August 17, 2018, and is incorporated by reference in its entirety. [Explanation of symbols]

[0065] 10 Optical elements 11 Glass substrate 12 Optical function section 13 Joint 14 Space

Claims

1. A glass substrate; An optical function portion made of resin; a bonding portion that bonds the glass substrate and the optical function portion; An optical element having The Young's modulus of the joint is 0.1 MPa or less, The cross-sectional shape of the optical function part is a convex shape or a concave shape, When the thickness of the thickest part of the optical functional part is represented by Hm, the Young's modulus of the optical functional part is represented by Em, the linear expansion coefficient of the optical functional part is represented by αm, the thickness of the glass substrate is represented by Hs, the Young's modulus of the glass substrate is represented by Es, the linear expansion coefficient of the glass substrate is represented by αs, and the width of the bonding part is represented by W, the displacement amount ΔH is defined by the following formula: ΔH is 0.005 mm or more when ΔT = 25 ° C. Optical elements. ΔH=(1 / |K|)−√{(1 / K) 2 −(W / 2) 2} (In the above formula, K=(A×F-B×D) / (A×C-B 2 ) A=Es×Hs+Em×Hm B=(1 / 2)×[Es×Hs 2 +Em×{(Hs+Hm) 2 −Hs 2}] C=(1 / 3)×[Es×Hs 3 +Em×{(Hs+Hm) 3 −Hs 3}] D=ΔT×{Es×αs×Hs+Em×αm×Hm} F=(ΔT / 2)×[Es×αs×Hs 2 +Em×αm×{(Hs+Hm) 2 −Hs 2}])

2. The optical element according to claim 1 , wherein the glass transition point of the bonding portion is 0° C. or lower.

3. The optical element according to claim 1 , wherein the ΔH is 0.01 mm or more.

4. The cross-sectional shape of the glass substrate is flat, The shape of the glass substrate in a plane is rectangular, circular, or elliptical; The optical element according to claim 1 .

5. An optical system comprising the optical element according to any one of claims 1 to 4.

6. An optical device comprising the optical element according to any one of claims 1 to 4.

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