Optical component with high surface accuracy and sealing method thereof

Abstract

A high-surface-precision optical component and a sealing method thereof, wherein the high-surface-precision optical component comprises an optical lens with high-surface-precision, and is adapted to a metal frame with a through hole in the middle made of different materials according to the geometric dimensions and material properties of the optical lens. The welding method adopts a low-melting-point metal solder to form a soft metal solder buffer layer between the lens and the frame after welding, which greatly alleviates the thermal stress caused by uneven temperature between the lens and the frame, so that the lens after welding can still maintain a high surface-precision. The prepared optical component has the characteristics of high lens surface-precision and good thermal conductivity between the frame and the optical lens. At the same time, the welding part has high-reliability performance indicators such as good vacuum sealing and radiation resistance, and is suitable for precision optical systems such as space optical remote sensors and optical resonant cavities.

Description

Technical Field

[0001] The invention relates to a method for connecting an optical component, in particular to an optical component with high surface shape accuracy and a sealing method thereof. Background Art

[0002] At present, there are three ways to connect optical lenses with high surface accuracy to frames: the first is the more traditional connection method that relies on mechanical force to fix, such as the threaded clamping method, that is, a pressure ring with internal threads is screwed into a frame with external threads that match the pressure ring to fix the lens in the pressure ring and the lens barrel; the second is the adhesive method, that is, the edge area of ​​the lens's light-transmitting surface or the area corresponding to the lens's side circumference is glued together with the frame using optical assembly glue to fix the optical lens. Patent CN 114114607 A describes a method for fixing a plane optical reflector by glueing, but this method is only applicable to plane reflectors and has certain limitations for fixing transmissive optical elements or dichroic mirrors; the third is the planar welding method.

[0003] Optical lenses fixed by mechanical force may produce certain stress and strain due to the mechanical force, resulting in changes in the lens surface shape, which will affect the beam quality to a certain extent; in addition, due to mechanical vibrations that may occur during use, long-term exposure to mechanical vibrations will cause the threads to loosen, and the long-term reliability of the optical components cannot be guaranteed. For optical components prepared by gluing, although the flexible optical assembly adhesive can effectively reduce the impact of temperature changes on the surface shape when the temperature changes, and the reliability is also high, the anti-aging ability is insufficient. During the operation of the optical component, a certain amount of heat will be generated. It is difficult for the adhesive layer to effectively and quickly transfer the heat accumulated in the lens, and the thermal conductivity is poor. Therefore, during long-term use, a large amount of heat will accumulate in the lens, posing challenges to the surface shape of the optical lens and the reliability of the optical component, thereby affecting the beam quality. Patent 100364707C and CN 109116504 A introduce a method for connecting an optical window and a window frame by plane sealing. This method uses low-temperature solder to seal the edge of one light-transmitting surface of the window to the window frame. The stress on the two light-transmitting surfaces of the window in the prepared sealing device is unbalanced, which is bound to affect the surface accuracy of the two light-transmitting surfaces of the optical window.

[0004] Patent CN 109926748 B discloses a vacuum observation window sealed with metal solder and a method for making the same. The vacuum observation window uses a jacket seal to seal a non-metallic lens and a metal thin-walled transition piece with medium-temperature metal solder to obtain an airtight, high-strength sealed window. A thin-walled structure is used to reduce the residual stress of the sealing between the non-metallic lens and the metal transition piece, and a layer of metal solder is filled between the thin-walled structure and the lens as a stress buffer area. The prepared vacuum observation window is used in vacuum equipment such as vacuum brazing furnaces and coating machines, and has extremely high requirements for the airtightness and strength of the sealing device. However, due to the purpose of the vacuum observation window and its use environment, its sealing temperature is generally above 300°C, and the strength of the metal solder used is relatively high, which is very unfavorable for lenses with high surface accuracy or optical films coated on the surface. Therefore, this method is not suitable for welding optical components with surface accuracy requirements. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an optical component with high surface shape accuracy and a sealing method thereof, which has the following technical advantages: First, by metallizing the circumferential surface of the side of the optical lens, a low-temperature metal solder is used to directly and effectively connect the frame and the optical lens. This connection method can form a flexible transition layer between the optical lens and the frame, and does not require patent CN 109926748 The thin-wall transition structure in B can effectively reduce the residual stress generated by the lens due to the external constraints of the frame during the connection and fixation of the optical lens and the frame, thereby ensuring that the lens still has high surface accuracy after welding; secondly, under the condition that the geometric dimensions of the optical lens are certain, the side sealing method can maximize the effective light-transmitting aperture of the optical lens, or under the condition that the required light-transmitting aperture is certain, minimize the size of the lens and the frame to achieve the purpose of weight reduction, thereby contributing to the lightweighting of the entire optical-mechanical system; secondly, the side sealing method can maximize the sealing area between the lens and the frame under the condition that the geometric dimensions of the lens are certain, thereby improving the shear strength of the sealing part and increasing the pressure resistance of the optical component; thirdly, the increase in the sealing area helps to improve the vacuum airtightness of the optical component.

[0006] The technical solution of the present invention is as follows:

[0007] A high surface shape precision optical component, comprising an optical lens and a frame, wherein the optical lens is a circular or elliptical optical element with a certain thickness and high surface shape precision, and the reflection surface shape precision (or transmission wavefront error precision) PV of the light-transmitting surface S1 or S2 is 0 Better than 1 / 10λ@632.8nm, RMS 0Better than 1 / 20λ; the outer circumferential surface or elliptical circumferential surface S3 of the optical lens is the optical lens welding area;

[0008] The middle part of the frame is provided with a through hole, the aperture of which matches the outer diameter of the optical lens, for the optical lens to be embedded; one end of the through hole is a solder drainage chamfer, and the other end is provided with a solder drainage groove and a lens limiting step; the large circumference of the through hole is the frame welding area;

[0009] The frame is nested in the outer circumference of the optical lens, so that a certain welding gap is formed between the welding area of ​​the optical lens and the welding area of ​​the frame, and they are fixed by welding with low-temperature metal solder.

[0010] The optical lens is made of glass-ceramic, quartz glass, K9 glass, sapphire, calcium fluoride or zinc selenide.

[0011] The frame is made of titanium alloy, 4J32, 4J36 and other low expansion precision alloys, aluminum alloy and aluminum-based composite materials or other metal materials that are more compatible with the expansion coefficient of the lens.

[0012] Preferably, the structure of the frame includes a through hole in the middle portion which is adapted to the geometric shape and size of the lens, one end of the through hole is a solder drainage chamfer to ensure that the solder is in full contact with the frame and wets the frame, and flows into the weld along the chamfered surface; the other end of the through hole is a solder diversion groove which can be used to store excess solder to avoid excessive accumulation of solder in the weld area and generate stress; the edge of the solder diversion groove at the other end of the through hole is a lens positioning step, which serves as a supporting edge when the lens and the frame are welded, and is used to ensure the parallelism of the lens and the frame.

[0013] On the other hand, the present invention also provides a sealing method for a high-surface-precision optical component, which is characterized in that it comprises the following steps:

[0014] ①Prepare optical lenses and frames:

[0015] The middle part of the frame is provided with a through hole, the aperture of which matches the outer diameter of the optical lens, for the optical lens to be embedded;

[0016] A solder drainage chamfer is provided at one end of the through hole, and the solder drainage chamfer is used to make the solder flow into the weld along the chamfer surface, ensuring that the solder fully contacts the frame and wets the frame;

[0017] The other end of the through hole is provided with a solder guide groove and a lens limiting step. The solder guide groove is used to store excess solder and serves as a welding end when the lens and the frame are welded to avoid excessive accumulation of solder to generate stress; the step is used to limit the optical lens and serves as a supporting edge when the lens and the frame are welded to ensure the parallelism of the lens and the frame;

[0018] ② Optimizing the optical lenses and frames:

[0019] The light-transmitting surface of the optical lens is shielded and protected, and the outer circumferential surface of the optical lens is metallized to form a metallized layer as a welding area of ​​the optical lens;

[0020] Performing surface modification treatment on the circumferential surface of the through hole welding end, the solder drainage chamfer surface and the solder drainage groove surface of the mirror frame;

[0021] ③ Prepare low melting point metal solder and clean it before welding;

[0022] ④ Embed the metallized optical lens into the surface-modified frame, place the solder at the chamfer of the frame, and perform welding so that the welding area of ​​the frame is welded to the metallized film layer of the welding area of ​​the optical lens through the metal solder, and an optical component with high surface accuracy is completed.

[0023] Preferably, the soldering process is eutectic reflow soldering.

[0024] Preferably, the welding process is gas shielded welding, and the shielding gas used may be a reducing gas such as formic acid or hydrogen.

[0025] Preferably, the surface modification treatment refers to coating the surface of the frame with a Ni / Au film by electroplating.

[0026] Preferably, the metallization treatment is carried out by using one or a combination of two or more processes selected from vacuum evaporation coating, sputtering coating and ion coating, and the film system is generally Ti / Ni / Au.

[0027] Preferably, the low melting point metal solder is indium solder.

[0028] The thermal expansion coefficient of the optical lens α 1 , the thermal expansion coefficient of the metal frame is α 2 , according to the different materials of the optical lens (1), the metal frames of different materials are matched. The matching principle is α 1 <α 2 On this basis, metal materials with expansion coefficients as close as possible to those of optical lenses are selected as the frames, thereby effectively reducing the residual stress of optical components after welding.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The optical lens and the frame using this welding method have a clearance fit to prevent the lens from being subjected to mechanical force;

[0031] 2. After welding, low-temperature metal solder - indium solder is used to fill the gap between the optical lens and the metal frame to form a flexible transition layer, so that the optical lens can expand and contract freely in different temperature fields without constraints. This can effectively alleviate the residual stress problem caused by the difference in thermal expansion coefficients between the lens and the frame during the welding process and use, thereby avoiding significant changes in the lens surface shape. Finally, the melting point of indium solder is only 157°C, and the required welding temperature is relatively low, which will not cause the lens to experience high temperatures and affect the surface shape. In addition, the lower welding temperature is more friendly to the optical film coated on the surface of the optical lens.

[0032] 3. The optical components prepared by sealing with indium solder have good air tightness and excellent anti-aging performance in the welding area. Compared with the optical components bonded with glue, the welding strength is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of an embodiment of a high surface precision optical component and a metal frame of the present invention.

[0034] Figure 2 Schematic diagram of the high surface precision optical component of the present invention, wherein (1) is an optical lens with high surface precision; and (2) is a metal frame with a circular or elliptical through hole in the middle. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with embodiments and drawings, but the protection scope of the present invention shall not be limited thereto.

[0036] Please refer to Figure 1 and Figure 2 , Figure 1 Schematic diagram of the structure of an embodiment of a high surface precision optical component and a metal frame of the present invention, Figure 2 The figure is a schematic diagram of the high surface shape precision optical component of the present invention. As can be seen from the figure, the structure of the high surface shape precision optical component includes a lens 1 and a frame 2, the S3 circumferential surface of the lens 1, that is, the welding area a, is metallized, the welding area b, the solder drainage chamfer surface and the solder guide groove surface of the frame 2 are surface modified, the welding area a of the lens 1 and the welding area b of the frame 2 are sealed by low-temperature metal solder, the frame 2 and the lens 1 are gap-matched, that is, the inner diameter of the through hole of the frame 2 is larger than the outer diameter of the lens 1, and the solder is liquefied during the reflow soldering process and filled into the gap between the frame 2 and the lens 1 along the solder drainage chamfer of the frame 2, and a soft metal solder layer is formed in the annular gap between the frame 2 and the lens 1, which can alleviate the residual stress generated by the mutual restriction of the two after the thermal expansion and deformation during the welding process, so that the shape change of the lens 1 after welding is maintained at a minimum value, that is, the lens 1 still has high surface shape precision after assembly and welding.

[0037] The specific operation steps of the present invention are as follows:

[0038] First, the lenses and frames are processed according to the design drawings. The surface of the lenses can be coated with a certain optical film or not coated with an optical film;

[0039] Clean the lenses and frames separately before plating;

[0040] Use polyimide tape or a special fixture to cover the transparent surface of the lens, exposing only the S3 circumference, i.e. welding area a (see the attached manual). Figure 2 : Welding area a), and then put it into the magnetron sputtering coating machine for magnetron sputtering metallization. There are 3 layers of magnetron sputtering metallized film. The first is the active material Ti that can be tightly bonded to the surface of the lens as a base layer, acting as a link between the non-metallic lens and the subsequently plated metal film layer, with a thickness of about 30 to 50nm; then there is a barrier layer that serves as the interaction between the solder and the film layer. In this embodiment, the material of this layer is Ni or Cr, with a thickness of about 500nm, and finally the Au layer is plated. The Au layer can be well wetted with the low-temperature metal solder indium, and the thickness is about 1μm. The total thickness of the metallized film layer plated by magnetron sputtering is 1 to 2μm;

[0041] The mirror frame is cleaned and electroplated. The film system is generally Ni / Au, and the total thickness of the film layer is not less than 2μm;

[0042] Clean the indium solder before soldering, usually by pickling, and then prepare the solder into a ring shape that matches the circumference of the frame;

[0043] The frame is nested on the outside of the circumferential surface of the lens S3, and a thin aluminum sheet with a size matching the outer diameter of the lens is used to cover the lens as a lens protection device. Then an indium solder ring is placed on the chamfer of the frame. Finally, the assembled product to be welded is placed in a reflow oven and reflow soldering is performed under the protection of a reducing atmosphere.

[0044] Example

[0045] The original surface shape of the sapphire lens was tested by ZYGO interferometer, and the RMS values ​​of the 0° reflection surface shape of the A and B surfaces were 0.078λ and 0.010λ (λ=632.8nm) respectively; then the S1 and S2 light-transmitting surfaces of the sapphire lens were shielded, and the S3 circumferential surface, i.e., the welding area a, was placed in a magnetron sputtering coating machine for magnetron sputtering metallization, firstly the Ti layer was plated for 0.5h, then the Ni layer was plated for 1h, and finally the Au layer was plated for 2h; then the ZYGO interferometer was used to test the reflection surface shape of the metallized sapphire lens, and the RMS values ​​of the 0° reflection surface shape of the A and B surfaces were 0.075λ and 0.011λ (λ=632.8nm) respectively;

[0046] After cleaning the TC4 frame, the surface modification treatment is performed on the welding area b, the solder drainage chamfer surface and the solder guide groove surface, that is, the oxide layer on the surface of the TC4 frame is first removed, and then a Ni / Au layer is plated on the surface by electroplating, and the total thickness of the film layer is not less than 3μm; then the indium solder is cleaned with dilute hydrochloric acid, and then the weld volume is calculated according to the size of the frame and the lens, and an appropriate amount of solder is taken according to the weld volume, and it is prepared into a circular solder ring. The metallized sapphire lens is assembled in the metallized modified TC4 titanium alloy frame, and then the solder ring is placed at the chamfer of the frame. Finally, the assembled sample to be welded is placed in a reflow soldering furnace and welded under the protection of formic acid gas.

[0047] After welding, the welding area a of the sapphire lens and the welding area b of the TC4 frame are connected together by indium solder, and the sapphire-TC4 titanium alloy optical component is completed. The optical component formed by the sapphire lens and the TC4 frame being sealed with indium solder is tested again by ZYGO interferometer. The 0° reflection surface shape RMS values ​​of the A and B surfaces are 0.070λ and 0.012λ respectively, that is, the changes in the 0° reflection surface shape RMS values ​​of the A and B surfaces of the sapphire lens caused by the entire process of the optical component prepared by the welding method of the present invention are 0.008λ and 0.002λ respectively, which are much less than 1 / 50λ. In other words, the optical lens surface shape of the optical component prepared by indium solder sealing has a very small change, and can maintain a high surface shape accuracy that is very close to the original surface shape before welding.

[0048] The present invention discloses an optical component with high surface shape accuracy and a sealing method thereof. The surface shape accuracy of the prepared optical component has an extremely small change compared with the original surface shape. After experiencing changes in welding temperature and changes in the structure after welding, the optical element can still maintain extremely high surface shape accuracy. Therefore, the optical component prepared by the sealing method for optical components with high surface shape accuracy described in this patent can be applied to precision optical systems such as optical remote sensors and optical resonant cavities.

Claims

1. A high-precision optical component, comprising an optical lens (1) and a lens frame (2), characterized in that: The optical lens (1) is a circular or elliptical optical element with a certain thickness and high surface accuracy, and the reflection surface accuracy PV0 of the light-transmitting surface S1 or S2 is better than 1 / 10λ@632.8nm and RMS0 is better than 1 / 20λ; the outer circumferential surface or elliptical circumferential surface S3 of the optical lens (1) is the optical lens welding area (a); The frame (2) has a through hole in the middle, the aperture of the through hole matches the outer diameter of the optical lens (1) for the optical lens to be embedded; one end of the through hole is a solder drainage chamfer, the other end includes a solder drainage groove and a lens limiting step, and the large circumferential surface of the through hole is a frame welding area (b); The frame (2) is nested in the outer circumference of the optical lens (1), so that a certain welding gap is formed between the optical lens welding area (a) and the frame welding area (b) and the optical lens is fixed by welding with low-temperature metal solder, that is, a soft metal solder buffer layer is formed between the lens and the frame; the low-temperature metal solder is indium solder, the thermal expansion coefficient of the optical lens is α1, and the thermal expansion coefficient of the frame is α2, and α1≤α2.

2. The optical component with high surface accuracy according to claim 1, characterized in that: The optical lens (1) is made of glass-ceramic, quartz glass, K9 glass, sapphire, calcium fluoride or zinc selenide.

3. The optical component with high surface accuracy according to claim 1, characterized in that: The spectacle frame (2) is made of titanium alloy, 4J32, 4J36 precision alloy, aluminum alloy and aluminum-based composite material.

4. The high surface accuracy optical component according to claim 1, characterized in that: The structure of the frame (2) comprises a through hole in the middle portion which is adapted to the geometric shape and size of the lens; one end of the through hole is a solder drainage chamfer to ensure that the solder is in full contact with the frame and wets the frame, and flows into the weld along the chamfered surface; the other end of the through hole is a solder diversion groove which can be used to store excess solder to avoid excessive accumulation of solder in the weld area to generate stress; the edge of the solder diversion groove at the other end of the through hole is a lens positioning step which serves as a supporting edge when the lens and the frame are welded, and is used to ensure the parallelism of the lens and the frame.

5. A sealing method for high surface precision optical components, characterized in that: The steps include: ①Prepare optical lenses and frames: The middle part of the frame is provided with a through hole, the aperture of which matches the outer diameter of the optical lens, for the optical lens to be embedded; One end of the through hole is provided with a solder drainage chamfer, which is used to allow the solder to flow into the weld along the chamfer surface, ensuring that the solder is in full contact with the frame and wets the frame; The other end of the through hole is provided with a lens limiting step and a solder guide groove: the step is used to limit the optical lens and serves as a supporting edge when the lens is welded to the frame to ensure the parallelism of the lens and the frame; the solder guide groove is used to store excess solder to avoid excessive accumulation of solder to generate stress; ② Optimizing the optical lenses and frames: The light-transmitting surface of the optical lens is shielded and protected, and the outer circumferential surface of the optical lens is metallized to form a metallized layer as a welding area of ​​the optical lens; Performing surface modification treatment on the circumferential surface of the through hole, the solder drainage chamfer surface and the solder drainage groove surface of the lens frame; ③ Prepare low melting point metal solder and clean it before welding; The solder is indium solder; ④ Embed the metallized optical lens into the frame with modified surface, place the solder at the chamfer of the frame, and perform welding treatment to weld the frame welding area (b) to the metal film layer of the optical lens welding area (a) through the metal solder, and form a soft metal solder buffer layer between the lens and the frame, and the optical component with high surface accuracy is completed; the thermal expansion coefficient of the optical lens is α1, and the thermal expansion coefficient of the frame is α2, and α1≤α2.

6. The sealing method of a high surface accuracy optical component according to claim 5, characterized in that: The soldering process is eutectic reflow soldering.

7. The sealing method of a high surface accuracy optical component according to claim 5 or 6, characterized in that: The welding process is gas shielded welding, and the shielding gas used is formic acid or hydrogen.

8. The sealing method of a high surface accuracy optical component according to claim 5, characterized in that: The surface modification treatment refers to coating the surface of the frame with a Ni / Au film by electroplating.

9. The sealing method of a high surface accuracy optical component according to claim 5, characterized in that: The metallization treatment is carried out by using one or a combination of two or more processes of vacuum evaporation coating, sputtering coating and ion coating, and the film system is Ti / Ni / Au.

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