Optical device capable of actively adjusting focal plane position and preparation method and application thereof

Abstract

The invention discloses an optical device capable of actively adjusting the position of a focal plane and a preparation method and application of the optical device, and the optical device comprises a thermal optical element which is a variable-refractive-index transparent sheet with the refractive index changing along with the temperature; the heating element is provided with a heating part and an electric wire connected with the heating part, the heating part is arranged on one surface of the thermal optical element, the refractive index of the thermal optical element is regulated and controlled through the temperature change of the heating part so as to adjust the focal plane position, and the heating part is provided with a light through hole for exposing the thermal optical element; the electric wire is suitable for being connected with an adjustable voltage source. The optical device is arranged between a sample and an objective lens, the density of the thermal optical element is changed and the refractive index of the thermal optical element is changed by controlling the working voltage of the heating element and adjusting the temperature of the thermal optical element, so that the zoom function is realized, the purpose of dynamically regulating and controlling a focal plane is realized, the regulation and control that the single step length is less than 10nm can be realized, and the optical device is suitable for a dynamic optical scene.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and in particular to an optical device for actively adjusting the position of the focal plane, its fabrication method, and its application. Background Technology

[0002] With advancements in technology, the resolution of optical imaging is constantly improving. For example, microspheres, as lenses for nano-imaging, are an effective method to enhance the resolution of optical microscopes. Due to their super-resolution capabilities, label-free nature, good compatibility with traditional microscopes, real-time imaging, and low cost, microsphere nanoimaging has attracted widespread attention from researchers and has broad application prospects in fields such as chip inspection and biomedicine.

[0003] However, high-resolution imaging systems generally face the technical bottleneck of limited depth of field. Taking microsphere nanoimaging as an example, due to the size and surface curvature characteristics of the microspheres, the depth of field of its magnified imaging is usually only a few hundred nanometers. This requires high-precision and dynamic control of the focal plane position during the imaging process to meet the needs of fine observation and detection.

[0004] Currently, the mainstream focal plane array control method in the industry is mechanical control. This method mainly relies on a transmission system composed of a stepper motor and a synchronous belt to achieve position adjustment. However, it has several insurmountable drawbacks: First, the control precision is insufficient, with the minimum single control step size typically only reaching 10 nm, which cannot meet the requirements of higher precision imaging. Second, the operational stability is poor, and vibrations are easily generated during the control process, affecting image quality. Third, there is a significant hysteresis error. Due to the non-ideal characteristics of the mechanical structure and materials, the transmission system will exhibit micron-level positioning deviations when switching between forward and reverse directions, resulting in the inability to accurately reproduce the focal plane position. Fourth, the dynamic control capability is lacking, making it difficult to achieve continuous and smooth adjustment of the focal plane position, and thus unable to adapt to the usage requirements of dynamic optical scenarios. These problems collectively limit the application of mechanical control methods in diverse, refined, and high-precision imaging scenarios.

[0005] To address the shortcomings of mechanical control, non-mechanical control technologies have been explored in related fields. For example, patent CN112068228A discloses a planar focusing lens device based on phonon polarization waves, which adjusts the focal length by changing the size of the metal antenna or the wavenumber of the incident infrared light to control the wave vector of phonon excitons. Although it avoids the inherent defects of mechanical transmission, it still has obvious limitations: its focusing control relies on a specific phonon polarization wave excitation mechanism, which is only applicable to the infrared light band and cannot meet the high-precision imaging requirements of the visible light band; moreover, the control process requires a complex excitation and detection system for excitons, resulting in low device integration and difficulty in conveniently adapting to traditional optical microscopes and other equipment. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in the aforementioned technologies. Therefore, the objective of this invention is to propose an optical device for actively adjusting the position of the focal plane, its fabrication method, and its application, achieving high-precision dynamic adjustment of the focal plane by controlling the refractive index of the material through temperature regulation.

[0007] To achieve the above objectives, the present invention provides, in a first aspect, an optical device for actively adjusting the position of the focal plane, comprising: Thermo-optical element, wherein the thermo-optical element is a transparent thin film with a variable refractive index that varies with temperature; A heating element having a heating part and a wire connected to the heating part, the heating part being disposed on one surface of the thermo-optical element, the refractive index of the thermo-optical element being adjusted by the temperature change of the heating part to adjust the position of the focal plane, the heating part having a light-transmitting hole exposing the thermo-optical element; the wire being adapted to be connected to an adjustable voltage source.

[0008] According to the present invention, an optical device for actively adjusting the focal plane position is disclosed. This optical device adopts a minimally integrated structure of a thermo-optical element and a heating element with a light-transmitting aperture, abandoning the traditional mechanical control method. It utilizes temperature-controlled refractive index to achieve active adjustment of the focal plane, fundamentally avoiding defects such as mechanical vibration and backlash error. Moreover, the structure is compact and adaptable to various optical imaging systems, providing a basic solution for high-precision focal plane control. The thermo-optical element adopts a transparent thin film with a variable refractive index. The light-transmitting aperture design of the heating part ensures unobstructed light path. At the same time, it is adapted to an adjustable voltage source through wires. By controlling the voltage applied to the heating part, the heating effect of the current is used to generate heat, thereby transferring heat to the thermo-optical element, changing its refractive index, realizing the zoom function, and achieving the purpose of dynamically controlling the focal plane. It can achieve focal plane position adjustment in a single step of less than 10 nm. The focusing process has high controllability and can accurately adjust the position of the focal plane, making it suitable for dynamic optical scenarios.

[0009] In addition, the optical device for actively adjusting the focal plane position according to the present invention may also have the following additional technical features: Optionally, it also includes heat-insulating tape, which covers the outside of the thermo-optical element and the heating element, and forms a clearance opening corresponding to the light-transmitting hole.

[0010] Optionally, the refractive index of the thermo-optical element changes linearly with temperature.

[0011] Optionally, the visible light transmittance of the thermo-optical element is ≥90%, and the thermo-optical coefficient is 10. -4 Order of magnitude.

[0012] Furthermore, the thermo-optical element is a PC sheet, which is polymerized from bisphenol A and diphenyl carbonate.

[0013] Optionally, the heating element is bonded to the surface of the thermo-optical element with epoxy resin adhesive.

[0014] Optionally, the heating element is made of ceramic.

[0015] Optionally, the heating element is located at the geometric center of the surface of the thermo-optical element.

[0016] To achieve the above objectives, a second aspect of the present invention provides a method for fabricating an optical device that actively adjusts the position of the focal plane, comprising the following steps: Step 1: Provide a thermo-optical element, wherein the thermo-optical element is a transparent thin film with a variable refractive index that varies with temperature; Step 2: Provide a heating element having a heating part with a light-transmitting hole and a wire connected to the heating part; Step 3: Attach the heating element to one surface of the thermo-optical element, and lead the wires out from opposite sides of the heating element; Step 4: Provide heat-insulating tape, wrap the heat-insulating tape around the outside of the thermal optical element and the heating element, and form a clearance opening corresponding to the light-transmitting hole.

[0017] The method for fabricating an optical device that actively adjusts the focal plane position according to the present invention is simple and efficient, with each step being easy to implement and the technology mature. It does not require complex and precise processing equipment, significantly reducing production costs and technical barriers. By using heat-insulating tape for wrapping, the structural stability and heat conduction efficiency are ensured, while effectively reducing heat loss and ensuring the accuracy of refractive index control of the thermo-optical element. The pre-set light-passing aperture and the corresponding design of the avoidance opening ensure unobstructed light path during the fabrication process without additional adjustments, further improving integration efficiency and facilitating large-scale mass production, thus laying a technological foundation for the widespread application of this optical device.

[0018] To achieve the above objectives, a third aspect of the present invention proposes the application of the aforementioned optical device, wherein the optical device is placed between the sample and the objective lens of an optical imaging system, the wire is connected to an adjustable voltage source, and the temperature change of the heating part is controlled by adjusting the output voltage of the adjustable voltage source, thereby regulating the refractive index of the thermo-optical element and adjusting the focal plane position of the optical imaging system.

[0019] According to the application of the present invention, this optical device can be used in various optical imaging systems, can be quickly integrated without major modifications to existing systems, and has strong compatibility and adaptability. By precisely controlling the temperature of the heating element through an adjustable voltage source, the refractive index of the thermal optical element can be dynamically adjusted, thereby achieving high-precision adjustment of the focal plane position, which fully meets the requirements of scenarios with extremely high requirements for image clarity and real-time performance. Since the traditional mechanical focusing method is abandoned, there is no mechanical vibration or backlash error during application, which effectively ensures the stability and consistency of image quality. Its compact structure and rapid response enable the imaging system to flexibly respond to changes in the focal plane in dynamic optical scenarios, providing reliable technical support for high-precision optical imaging. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the optical device according to an embodiment of the present invention; Figure 2 This is a schematic flowchart illustrating the fabrication method of the optical device according to an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the application of the optical device according to an embodiment of the present invention; Figure 4 This is a diagram illustrating the control effect of an embodiment of the present invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] This application is based on the inventor's considerations regarding the following: Existing methods for adjusting the focal plane are mechanical controls, with a minimum single adjustment step size typically of 10 nm. This control method is non-dynamic and cannot allow for continuous changes in the focal plane's position. Another problem is that this control method introduces micrometer-level errors when the direction of motion changes. Essentially, mechanical control devices are transmission systems composed of stepper motors and synchronous belts, which inevitably have backlash errors. Backlash error refers to the angular error that occurs between forward and reverse rotation after the stepper motor completes one rotation. That is, during the mechanism's rotation, due to the non-ideal characteristics of its structure and materials, it cannot accurately return to the initial position when rotating in the reverse direction. This error is commonly seen in servo control systems, especially in equipment with high precision requirements, leading to inaccurate positioning or unstable operation, thus affecting the overall system performance; these factors limit its application at high precision levels. Furthermore, non-mechanical control methods in related technologies are difficult to readily adapt to traditional optical microscopes and other equipment.

[0023] Therefore, this application proposes an optical device for actively adjusting the position of the focal plane, its fabrication method and application, which achieves high-precision dynamic adjustment of the focal plane by controlling the refractive index of the material through temperature regulation.

[0024] Specifically, an optical device for actively adjusting the position of a focal plane according to one or more embodiments includes: The thermo-optical element is a transparent sheet with a variable refractive index whose refractive index changes with temperature. As the adjustable refractive index portion of an actively controlled optical device, the thermo-optical element uses a transparent sheet with a variable refractive index as the optical medium. The transparent sheet with a variable refractive index, such as a polycarbonate (PC) sheet (polymerized from bisphenol A and diphenyl carbonate), is characterized by its superior light transmittance and variable refractive index. The PC sheet has a visible light transmittance of over 90%, ensuring sufficient field-of-view brightness. Meanwhile, its inherent thermo-optical coefficient is around 10. -4 PC is a solid material with a high thermo-optical coefficient, on the order of magnitude. This allows its refractive index to change significantly with temperature, ensuring high-precision focal plane adjustment. Furthermore, PC materials offer advantages such as customizable thermo-optical coefficients, high reliability, ease of miniaturization and lightweight design, low cost, and ease of processing. It's important to understand that the refractive index-changing materials used in thermo-optical components are not limited to PC; they can also be other transparent materials with excellent optical properties and relatively high refractive index tunability, such as other transparent organic materials, phase change materials, and lithium niobate crystals.

[0025] A heating element is provided, comprising a heating section and wires connecting the heating section. The heating section is disposed on one surface of the thermo-optical element, and the refractive index of the thermo-optical element is adjusted by temperature changes in the heating section to regulate the position of the focal plane. The heating section has a light-transmitting aperture exposing the thermo-optical element. The wires are adapted to connect to an adjustable voltage source. The heating element serves as the driving part of an actively controlled optical device, and its heating section has a light-transmitting aperture at its center. The lower surface of the heating element is preferably bonded to the upper surface of the thermo-optical element using epoxy resin. The positive and negative wires of the heating element are attached to the upper surface of the thermo-optical element and extend out from the left and right sides of the thermo-optical element. The heating section can be made of ceramic material, preferably gallium nitride ceramic or silicon carbide ceramic.

[0026] Thus, this optical device adjusts the focal plane position based on the refractive index change of a variable refractive index transparent sheet. Using a variable refractive index transparent sheet as the optical medium, the temperature of the variable refractive index transparent sheet can be adjusted by controlling the working voltage in the heating element, causing its density to change, thereby altering its refractive index and thickness, and thus achieving high-precision control of the focal plane position. By utilizing the linear change of its refractive index with temperature, not only is the step size of a single adjustment effectively reduced, but also the hysteresis error in the adjustment is eliminated.

[0027] In other words, this optical device improves control precision by precisely controlling the voltage of the heating element to change the temperature of the variable refractive index transparent sheet, thereby altering its refractive index. As the temperature increases, the focal plane moves upward; conversely, as the temperature decreases, the focal plane moves downward. This control of the focal plane position, utilizing the linear change in the material's refractive index with temperature, allows for smaller control steps and eliminates backlash error.

[0028] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0029] Example 1 like Figure 1 and Figure 2 As shown, according to one or more embodiments of the present invention, the optical device for actively adjusting the position of the focal plane includes a thermo-optical element 1, a heating element 2, and an insulating tape 3.

[0030] Thermo-optical element 1, as the refractive index adjustable part of the actively controlled optical device, uses a transparent sheet with a variable refractive index as the optical medium, such as a PC sheet. The length ranges from 10 mm to 20 mm, the width from 8 mm to 10 mm, and the thickness is 1 mm; the specific dimensions can be selected according to actual needs. When using thermo-optical element 1, it can be wiped with an alcohol swab and allowed to air dry naturally to ensure a smooth, scratch-free surface.

[0031] Heating element 2 serves as the driving part of the actively controlled optical device, and its heating section has a light-transmitting hole 21 at its center. The lower surface of heating element 2 is preferably bonded to the upper surface of thermal optical element 1 using epoxy resin adhesive. The positive and negative electrode wires of heating element 2 are attached to the upper surface of thermal optical element 1 and led out from the left and right sides of thermal optical element 2. The material of the heating section is preferably one of gallium nitride ceramic or silicon carbide ceramic. The outer diameter of the heating section is 7 mm, and the inner diameter is 2.8 mm. The left electrode 22 and right electrode 23 are respectively attached to the upper surface of thermal optical element 1 with epoxy resin adhesive and led out to the left and right sides. The epoxy resin adhesive is mixed strictly according to its instructions to ensure optimal mechanical and temperature resistance properties. The prepared epoxy resin adhesive is transferred to the lower surface of heating element 2 using a surgical needle or syringe needle tip for uniform coating and cured at room temperature for 24 hours.

[0032] The heat-insulating tape 3 serves as the outer sheath of the actively controlled optical device. It covers the outer side of the thermo-optical element 1 and the heating element 2, and forms a clearance opening corresponding to the light-transmitting hole 21. Specifically, the heat-insulating tape 3 has good thermal stability and should also be a non-conductive tape.

[0033] More specifically, the fabrication method of this optical device that actively adjusts the position of the focal plane includes the following steps: Step 1: Provide a thermo-optical element 1, which is a transparent sheet with a variable refractive index that changes with temperature. In this embodiment, a PC sheet is selected as the thermo-optical element 1. The PC sheet material has a larger free volume inside, and its thermo-optical coefficient is superior to other solid transparent materials. The PC sheet used in this embodiment has a high thermo-optical coefficient under blue light with a center wavelength of 450 nm, and its maximum temperature resistance is 130°C. During fabrication, cut a PC sheet with a length of 20 mm, a width of 10 mm, and a thickness of 1 mm, wipe its surface with an alcohol swab, and let it stand for 30 seconds to dry.

[0034] Step 2: Provide heating element 2, which has a heating part with a light-transmitting hole 21 and wires (22; 23) connecting the heating part. In this embodiment, a ceramic heating element is used as the heating part of heating element 2, with a resistance of 19.1 ohms that does not change with temperature between 20°C and 130°C. The maximum operating temperature is higher than the maximum operating temperature of thermo-optical element 1. The ceramic heating element is made of silicon carbide ceramic, with a diameter of 7 mm and a thickness of 1 mm, and has a light-transmitting hole 21 with a diameter of 2.8 mm in the center. Heating element 2 has two wires, a left wire 22 and a right wire 23, which are led out from the left and right sides of the ceramic heating element, respectively.

[0035] Step 3: The heating element is attached to one surface of the thermal optical element 1, and wires 22 and 23 are led out from the left and right sides of the ceramic heating plate, respectively. The heating element, left wire 22, and right wire 23 are respectively attached to the upper surface of the thermal optical element 1 with epoxy resin adhesive. In this embodiment, the epoxy resin adhesive used is divided into agent A and agent B, which are mixed in a 2:1 ratio and placed on a glass slide. The prepared epoxy resin adhesive is dipped into the tip of a syringe and evenly coated on the lower surface of the ceramic heating plate. The ceramic heating plate is held with tweezers and placed at the geometric center of the upper surface of the thermal optical element 1. It is left to stand at room temperature for 24 hours to ensure that the epoxy resin adhesive is completely cured. After bonding, the left wire 22 and right wire 23 on the ceramic heating plate are then attached to the upper surface of the thermal optical element 1 with epoxy resin adhesive, and led out from the left and right sides of the upper surface, respectively. It is left to stand at room temperature for another 24 hours.

[0036] Step 4: Provide heat-insulating tape 3, and wrap the heat-insulating tape 3 around the outside of the thermo-optical element 1 and the heating element 2, forming a clearance opening corresponding to the light-transmitting hole 21. The heat-insulating tape 3 used in this embodiment is PET green tape with a maximum temperature resistance of 200℃. Figure 1 As shown, two layers of heat-insulating tape 3 are applied to the upper and lower surfaces of the assembly consisting of thermo-optical element 1 and heating element 2. A piece of heat-insulating tape 3 is cut using scissors or a blade, ensuring that the length and width of the heat-insulating tape 3 match the length and width of the thermo-optical element 1. Before application, the material at the geometric center of the heat-insulating tape 3 is removed using a blade or hole punch to create a 3 mm diameter through-hole. Two pieces of heat-insulating tape 3 are first applied to the lower surface of the assembly consisting of thermo-optical element 1 and heating element 2, and then two more are applied to the upper surface to form a strong and reliable heat-insulating layer. Specifically, four pieces of PET green tape, each 20 mm long and 10 mm wide, are prepared, and 3 mm diameter through-holes are punched in the center of each. Two pieces of PET green tape are first applied to the lower surface of the assembly consisting of thermo-optical element 1 and heating element 2, and then the other two pieces are applied to the upper surface of the assembly consisting of thermo-optical element 1 and heating element 2. The lower surface of the PET green tape is mainly used for heat insulation, reducing heat dissipation, increasing the heating rate, and also reducing the impact of the dissipated heat on the sample below. The lower surface of the PET green tape also has corresponding clearance holes to allow light to pass through smoothly without affecting its use.

[0037] Example 2 like Figure 3 As shown, the optical device prepared in Example 1 is used to control the focal plane of a precision optical microscope. A chip is placed at an angle on the stage. The optical device is positioned directly below the 20x objective lens, as far away from the objective lens as possible. The optical device can be supported below the objective lens by a rectangular wooden block with equal height at both ends; the height of the wooden block is 3 to 5 mm; the wooden block is easy to process and has good thermal insulation properties. The wooden blocks at both ends are only in contact with the optical device, without any rigid connection; this is to prevent thermal stress after heating from bending the PC sheet, thereby affecting the overall optical path. Furthermore, the side of the optical device with the heating part attached should face the objective lens (i.e., upward), allowing more heat to dissipate from above and avoiding affecting the morphology of the sample below, such as causing thermal expansion of the sample. The positive wire 22 and the negative wire 23 of the optical device are connected to the positive and negative terminals of an adjustable voltage source, respectively. The temperature of the area near the light-transmitting aperture 21 is measured using a thermocouple. By controlling the voltage of the adjustable voltage source, the temperature of the heating part of the heating element 2 is changed, thus changing the refractive index of the thermo-optical element 1. As the temperature rises, the position of the focal plane changes, and the image appears different. Moving the stage upwards restores the image to its original state. The distance moved, as displayed in the stage control software, represents the change in the focal plane position.

[0038] Image at 25°C as follows Figure 4 As shown in (a); the image at 50°C is as follows. Figure 4 As shown in (b); the image at 75°C is as follows. Figure 4 As shown in (c); the image at 105°C is as follows. Figure 4 As shown in (d). In each image, the area containing the black dashed line is the clearest and is considered the location of the focal plane. The image after the stage has been moved 2.1 μm at 105°C is compared with... Figure 4 (a) Consistent. This indicates that an 80°C increase in temperature shifts the focal plane upward by 2.1 μm. That is, for every 0.1°C increase in temperature, the focal plane shifts upward by an average of 2.6 nm. When the temperature near the aperture 21 exceeds 105°C, a clear image is no longer observed. This is because the temperature of the contact surface between the thermal optical element 1 made of PC sheet and the heating element is too high, exceeding the maximum temperature resistance of 130°C for the PC sheet in this embodiment, causing irreversible deformation of the PC sheet. Therefore, 2.1 μm is considered the maximum control range of this active control optical device.

[0039] In the description of this invention, it should be understood that the terms "upper surface", "lower surface", "left and right sides", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0044] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An optical device for actively adjusting the position of the focal plane, characterized in that, include: Thermo-optical element, wherein the thermo-optical element is a transparent thin film with a variable refractive index that varies with temperature; A heating element having a heating part and a wire connected to the heating part, the heating part being disposed on one surface of the thermo-optical element, the refractive index of the thermo-optical element being adjusted by the temperature change of the heating part to adjust the position of the focal plane, the heating part having a light-transmitting hole exposing the thermo-optical element; the wire being adapted to be connected to an adjustable voltage source.

2. The optical device as described in claim 1, characterized in that, It also includes heat-insulating tape, which covers the outside of the thermo-optical element and the heating element, and forms a clearance opening corresponding to the light-transmitting hole.

3. The optical device as described in claim 1, characterized in that, The refractive index of the thermo-optical element changes linearly with temperature.

4. The optical device as described in claim 1, characterized in that, The visible light transmittance of the thermo-optical element is ≥90%, and the thermo-optical coefficient is 10. -4 Order of magnitude.

5. The optical device as described in any one of claims 1-4, characterized in that, The thermo-optical element is a PC sheet, which is polymerized from bisphenol A and diphenyl carbonate.

6. The optical device as claimed in claim 1, characterized in that, The heating element is bonded to the surface of the thermo-optical element with epoxy resin adhesive.

7. The optical device as claimed in claim 1, characterized in that, The heating element is made of ceramic.

8. The optical device as claimed in claim 1, characterized in that, The heating element is located at the geometric center of the surface of the thermo-optical element.

9. A method for fabricating an optical device that actively adjusts the position of the focal plane, characterized in that, Includes the following steps: Step 1: Provide a thermo-optical element, wherein the thermo-optical element is a transparent thin film with a variable refractive index that varies with temperature; Step 2: Provide a heating element having a heating part with a light-transmitting hole and a wire connected to the heating part; Step 3: Attach the heating element to one surface of the thermo-optical element, and lead the wires out from opposite sides of the heating element; Step 4: Provide heat-insulating tape, wrap the heat-insulating tape around the outside of the thermal optical element and the heating element, and form a clearance opening corresponding to the light-transmitting hole.

10. The application of the optical device as described in any one of claims 1-8, characterized in that, The optical device is placed between the sample and the objective lens of the optical imaging system. The wire is connected to an adjustable voltage source. By adjusting the output voltage of the adjustable voltage source, the temperature change of the heating part is controlled, thereby adjusting the refractive index of the thermal optical element and adjusting the focal plane position of the optical imaging system.

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