High-uniformity and high-transmittance fiber optic image inverter, and manufacturing method therefor and use thereof

Abstract

The present application relates to a high-uniformity and high-transmittance fiber optic image inverter, comprising an input end portion, an output end portion, and an optical fiber portion provided between the input end portion and the output end portion. The surface of the input end portion and / or the surface of the output end portion is provided with a film having a thickness gradually decreasing from the center to the edge; and the thickness of the film and the position satisfy: x=-2x10-7y6+8x10-9y5-1x10-4y4-2x10-6y3-0.0315y2-1x10-11y+4.2165, wherein x is the absolute thickness of the film, and y is the distance from the center to the edge. The technical problem to be solved is to improve the drawn contour of a fiber optic image inverter and simultaneously coat a homogenization film to obtain a high-uniformity and high-transmittance fiber optic image inverter.

Description

High-uniformity, high-transmittance optical fiber image invertor and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 30, 2023, with application number 202311624354.9 and invention name “Fiber optic image inverter with high uniformity and high transmittance, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to an optical fiber image transmission element, and in particular to an optical fiber image inverter with high uniformity and high transmittance, and a preparation method and application thereof. Background Art

[0004] Low-light-level night vision technology studies the physical processes and implementation methods for the conversion, enhancement, processing, and display of optical and electronic image information under low-light conditions or in poor visibility. It is a crucial component of modern optoelectronic imaging technology and one of the two key technologies supporting military night vision equipment. The various low-light-level devices, instruments, and systems developed using this advanced technology have broad application prospects in a wide range of fields, including military, public security, astronomy, aerospace, navigation, biology, medicine, nuclear physics, satellite monitoring, and high-speed photography. They play a particularly significant role in military applications, including nighttime combat, reconnaissance, command, fire control, artillery aiming, precision guidance, long-range early warning, and optoelectronic countermeasures. Low-light-level night vision devices feature small size, light weight, clear and rich image quality, easy operation, and a high cost-effectiveness. The key to miniaturizing and lightweighting low-light-level night vision devices lies in a fiber-optic image transmission element with an image inversion function—an image invertor. This fiber-optic image invertor flips the image 180°, creating an inverted image, as shown in Figure 1. It has the characteristics of high resolution, clear transmission, small size and light weight. It is mainly used to replace the relay lens system in low-light-level night vision devices, and is also widely used in devices that require inverted images.

[0005] The problem of non-uniform transmittance of the image inverter in the existing technology is quite serious. The poor edge resolution leads to poor imaging clarity, which is closely related to the preparation process of the image inverter. The image inverter is obtained by melting and pressing tens of millions or even hundreds of millions of micron-sized fibers and then twisting and deforming them at high temperature (as shown in Figure 1). During the twisting process, only the optical fiber at the axis is not twisted and stretched, and the remaining optical fibers are twisted and stretched to coil 180° with different helix angles. The farther away from the axis, the smaller the helix angle; the greater the curvature, the longer the coiling distance; the greater the degree of stretching, the larger the taper formed, and the weaker the light transmission effect, resulting in a phenomenon of high transmittance in the center and low transmittance at the edges. This non-uniform transmittance will directly affect the imaging effect.

[0006] Summary of the Invention

[0007] In view of this, the main purpose of this application is to provide a fiber optic image inverter with high uniformity and high transmittance, as well as its preparation method and application. The technical problem to be solved is to obtain a fiber optic image inverter with high uniformity and high transmittance by improving the drawing profile of the fiber optic image inverter and coating it with a homogenizing film.

[0008] The purpose of this application and the technical problem it solves are achieved by adopting the following technical solutions. This application proposes a high uniformity and high transmittance optical fiber image invertor, comprising an input end, an output end, and an optical fiber portion disposed between the input and output ends; the surface of the input end and / or the output end has a thin film with a thickness gradually decreasing from the center to the edge; the thickness and position of the thin film satisfy: x = -2×10 -7 y 6 +8×10 -9 y 5 -1×10 -4 y 4 -2×10 -6 y 3 -0.0315y 2 -1×10 -11 y+4.2165, where x is the absolute thickness of the film and y is the distance from the center to the edge.

[0009] Furthermore, in the aforementioned high-uniformity, high-transmittance optical fiber image inverter, the value of x is greater than 0, and the value of y is between 0 and 11.5.

[0010] Furthermore, in the aforementioned optical fiber image inverter with high uniformity and high transmittance, the optical fiber image inverter is a biquadratic function type image inverter or a bicubic function type image inverter.

[0011] Furthermore, in the aforementioned optical fiber image inverter with high uniformity and high transmittance, the thin film includes a homogenizing film layer and / or an anti-reflection film layer, and a film layer center is provided at the center thereof.

[0012] The purpose of this application and the solution to its technical problems can also be achieved by adopting the following technical solutions. This application proposes a method for preparing a fiber optic image inverter with high uniformity and high transmittance, comprising the following steps:

[0013] Preparation of the torsion structure of the image invertor;

[0014] Preparation of homogenizing film on the surface of image invertor.

[0015] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the preparation of the torsion structure of the image inverter comprises the following steps:

[0016] According to the optical fiber track in the torsion zone of the image inverter, a double quadratic function type image inverter or a double cubic function type image inverter is prepared respectively.

[0017] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the preparation of the homogenizing film on the surface of the fiber optic image inverter comprises the following steps:

[0018] The surface of the optical fiber image inverter is coated with a thin film whose thickness gradually decreases from the center to the edge.

[0019] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the thin film includes a homogenizing film layer and / or an anti-reflection film layer, and a film layer center is provided at the center thereof.

[0020] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the rotation speed of the film with a thickness gradually decreasing from the center to the edge is 10 rpm-20 rpm.

[0021] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the pressure of the film with a thickness gradually decreasing from the center to the edge is 1.0-2.0 Pa.

[0022] Furthermore, in the above-mentioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the vacuum degree of the film whose thickness gradually decreases from the center to the edge is less than or equal to 3×10 -4 .

[0023] Furthermore, in the aforementioned method for preparing a fiber optic image inverter with high uniformity and high transmittance, the gas flow rate of argon gas is 15-30 sccm when coating a thin film with a thickness gradually decreasing from the center to the edge.

[0024] Furthermore, in the aforementioned method for preparing a high-uniformity, high-transmittance optical fiber image inverter, the film whose coating thickness gradually decreases from the center to the edge is achieved by sputtering; pre-sputtering is started at 30-50W, and after sputtering for 3-5 minutes, the power is adjusted to 60-80W to start formal sputtering, and the sputtering time is 0.5-3 minutes.

[0025] The purpose of the present application and the solution to its technical problems can also be achieved by adopting the following technical solutions: The present application proposes a low-light-level night vision device, which includes the above-mentioned high-uniformity, high-transmittance optical fiber image inverter.

[0026] By means of the above technical solution, the high uniformity and high transmittance optical fiber image inverter described in this application and its preparation method and application have at least the following advantages:

[0027] Based on the non-uniform transmittance of the image inverter, this application designs a homogenizing film on the surface of the image inverter that effectively improves the non-uniform transmittance within the effective area. The homogenizing film has a thickness gradient that gradually decreases from the center to the edge. Furthermore, based on the torsional structure curve and the changes in transmittance of the image inverter, the torsional method of the image inverter is optimized, and a bicubic torsional structure curve is designed, which can greatly improve the vignetting defect. The resulting image inverter can effectively improve the resolution of the image inverter.

[0028] This application addresses the problem of uneven light transmittance at the output end face of the image inverter. By designing the torsional structural curve of the image inverter and the surface microstructure of the image inverter, the non-uniformity of transmittance can be greatly improved, making the output light of the image inverter uniform and reducing the brightness difference between the peripheral and central areas of the image inverter.

[0029] The image invertor prepared in the present application has a non-uniform transmittance of 0.98%-2.10% at a wavelength of 550nm, a transmittance uniformity of 97.9%-99.02%, and a central transmittance of 39.87%-41.08%.

[0030] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application and to implement it in accordance with the contents of the specification, the following is a detailed description of the preferred embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic diagram of a torsion device of the prior art;

[0032] FIG2 is a schematic diagram of the overall structure of the mechanical spin coating device of the present application;

[0033] FIG3 is a schematic diagram of the structure of the mechanical rotary coating device without a protective shell of the present application;

[0034] FIG4 is a partial cross-sectional perspective view of the mechanical spin coating device of the present application;

[0035] FIG4A is a schematic diagram of the structure of a rotating base of the mechanical rotary coating device of the present application;

[0036] FIG5 is a diagram of a snail-shaped mask of the mechanical spin coating device of the present application;

[0037] FIG6 is a schematic diagram of a torsion curve and expansion of a biquadratic function of the present application;

[0038] FIG7 is a schematic diagram of a bicubic function torsion curve and its expansion according to the present application;

[0039] FIG8A is a schematic structural diagram of a biquadratic function type image inverter with a homogenizing film deposited on the output end of the present application;

[0040] FIG8B is a schematic structural diagram of a bicubic function type image invertor with a homogenizing film deposited on the output end of the present application;

[0041] FIG9A is a schematic structural diagram of a biquadratic image inverter with a leveling film deposited on the output end and an antireflection film deposited on the input end according to the present invention;

[0042] FIG9B is a schematic structural diagram of a bicubic image inverter with a leveling film deposited on the output end and an antireflection film deposited on the input end according to the present invention;

[0043] FIG10A is a schematic structural diagram of a biquadratic function type image inverter with a uniform film deposited on the input end of the present application;

[0044] FIG10B is a schematic structural diagram of a bicubic function type image inverter with a uniform film deposited on the input end of the present application;

[0045] FIG11A is a schematic structural diagram of a biquadratic function type image inverter with an antireflection film deposited on the input end and a leveling film deposited on the output end according to the present invention;

[0046] FIG11B is a schematic structural diagram of a bicubic image inverter with an antireflection film deposited on the input end and a leveling film deposited on the output end according to the present invention;

[0047] FIG12A is a schematic structural diagram of a biquadratic function type image inverter with a homogenizing film deposited on both the output end and the input end of the present invention;

[0048] FIG12B is a schematic structural diagram of a bicubic function type image invertor with a homogenizing film deposited on both the output end and the input end of the present application;

[0049] FIG13A is a schematic structural diagram of a double quadratic function type image inverter in which a leveling film is deposited on the output end and a leveling film + an antireflection film is deposited on the input end of the present application;

[0050] FIG13B is a schematic structural diagram of a bicubic image inverter in which a leveling film is deposited on the output end and a leveling film + an antireflection film is deposited on the input end;

[0051] FIG14A is a schematic structural diagram of a biquadratic image inverter of the present invention, in which a leveling film + an antireflection film is deposited on the output end and a leveling film is deposited on the input end;

[0052] FIG14B is a schematic structural diagram of a bicubic image inverter in which a leveling film + an antireflection film is deposited on the output end and a leveling film is deposited on the input end;

[0053] FIG15A is a schematic structural diagram of a biquadratic image inverter in which a leveling film + an antireflection film is deposited on the output end and a leveling film + an antireflection film is deposited on the input end of the present invention;

[0054] FIG15B is a schematic structural diagram of a bicubic image inverter with a leveling film + an antireflection film deposited on the output end and a leveling film + an antireflection film deposited on the input end of the present application;

[0055] FIG16 is a graph showing the transmittance test results before and after coating of Example 1 of the present application;

[0056] FIG17 is a graph showing the transmittance test results before and after coating of Example 2 of the present application;

[0057] FIG18 is a graph showing the transmittance test results before and after coating of Example 3 of the present application;

[0058] FIG19 is a graph showing the transmittance test results of Comparative Example 1 before and after coating;

[0059] Among them: 1-protective shell; 2-motor; 3-small gear; 4-large gear; 5-rotating base; 6-mask plate; 7-sample chamber; 8-platform; 91-output end, 92-output end, 10-input end, 20-input end, 11-averaging film, 21-averaging film, 12-anti-reflection film, 22-anti-reflection film, 13-film layer center, 23-film layer center, 33-film layer center, 43-film layer center, 14-double quadratic function type image inverter, 15-double cubic function type image inverter. DETAILED DESCRIPTION

[0060] To further illustrate the technical means and effectiveness of this application to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the high-uniformity, high-transmittance fiber optic image inverter, its preparation method, and its specific implementation, features, and effectiveness. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features or characteristics of one or more embodiments may be combined in any suitable manner.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0062] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0063] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0064] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0065] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0066] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0067] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0068] 1. Design of the torsional structure curve of the image invertor

[0069] During the twisting process of the image inverter, the optical fiber at the edge and center deforms differently, resulting in differences in light transmission capacity. Changing the twisting method of the image inverter produces different light transmission effects. Based on the thermodynamic and material mechanical properties of the image inverter during twisting (the changes in the optical fiber trajectory during heating and stretching affect light transmission performance), the optical fiber trajectory and light transmission uniformity in the torsion zone of the image inverter are optimized. Structural torsion curves with biquadratic and bicubic distributions in the tapered region are designed. The image inverters corresponding to these two functions are referred to as biquadratic and bicubic, as shown in Figures 6 and 7. As can be seen from Figures 6 and 7, the fiber curve with the bicubic function has a buffer zone compared to the quadratic function, which facilitates optical signal transmission. Theoretical and transmittance test results show that the bicubic distribution has the lowest non-uniform transmittance, reaching 4.13%, effectively alleviating vignetting defects and achieving a high-transmittance image inverter.

[0070] Here, “center” refers to the exact center of the image inverter; and “edge” refers to the edge of the effective area of ​​the image inverter, i.e., the outermost optical fiber of the image inverter.

[0071] Double quadratic function type image invertor:

[0072] The image invertor blank is fixed to the torsion rod using a stretching fixture. The torsion furnace is then controlled through the mechanical operation panel to make the center of the image invertor blank coaxial with the center of the inner torsion furnace. The preparations are now complete. First, heat the outer furnace to the preheating temperature (approximately 500-550℃. Below 500℃, the temperature difference between the inner and outer furnaces is too large, making it impossible to draw the image invertor. Above 550℃, the image invertor will have too many internal defects). After stabilizing the outer furnace temperature for 15-20 minutes (to ensure sufficient preheating), use a heating coil with an inner diameter of 40mm and a width of 2mm (to heat the middle part of the image invertor blank to its softening temperature) to start heating the inner torsion furnace to the softening point of the image invertor (approximately 780-830℃. Below 780℃, the softening temperature is not reached and the image invertor cannot be twisted. Above 830℃, the viscosity of the image invertor blank is too low, and a regular image invertor cannot be twisted). A servo motor and a torque sensor are used to apply two constant but opposite torques (10-15N) to both ends of the image invertor. The center of the image invertor blank in the inner furnace heating area gradually softens, and the torque is slowly applied to both ends until the blank rotates 180 degrees relative to the inner furnace. The inner furnace heating is then stopped, and the outer furnace annealing process is started. Finally, the image invertor blank is removed after the temperature drops to room temperature. At this point, the temperature difference between the inner and outer furnaces is only 280°C. The trend of the stretched image invertor cone surface changes nonlinearly, and the deformation zone of the image invertor exhibits a parabolic shape of a biquadratic function. The corresponding equation type is y=ax 2, where a is greater than or equal to 0.06. If it is less than 0.06, it cannot be twisted into an image invertor. Taking an image invertor blank with a height of 30mm and a diameter of 26mm as an example, when the twisting force is controlled at 14N, a double quadratic function type image invertor can be realized. At this time, a is 0.084, and the corresponding equation is y = 0.084x 2 .

[0073] The external furnace annealing program includes: turning off the heating program on the mechanical control panel, and cooling the temperature at a rate of 5-10 ° C / min. If the cooling program is not set and the temperature is cooled naturally, the cooling rate will be greater than 10 ° C / min, which will have a negative impact on the life of the furnace.

[0074] Bicubic image invertor:

[0075] The twisting method is the same as that of the biquadratic function type image inverter, except that the heating ring of the bicubic function type image inverter is movable. The heating ring is initially located at one-quarter of the image inverter blank. After twisting 90°, the heating ring is moved to three-quarters of the image inverter blank and twisted another 90°. The image inverter prepared using this method will show an image inverter deformation zone in the shape of a cubic function double parabola. The corresponding equation type is y=ax 3 , a is greater than or equal to 0.0038; if a is less than 0.0038, it cannot be twisted into an image invertor. Taking an image invertor blank with a height of 30mm and a diameter of 26mm as an example, when the twisting force is controlled at 14N, a double quadratic function type image invertor can be realized. At this time, a is 0.0048, and the corresponding equation is y = 0.0048x 3 .

[0076] 2. Design and preparation of the homogenizing film on the surface of the image invertor

[0077] Using conventional methods (without using a rotary coating device and without a mask plate) to coat a film of uniform thickness on the surface of the image invertor can only change the overall transmittance of the image invertor, but cannot improve the problem of different brightness between the edge and the center of the image invertor, and cannot achieve a high uniform transmittance effect. Therefore, combining the non-uniform transmittance characteristics of the image invertor (i.e., high transmittance in the center area and low transmittance in the edge area), a spiral mask plate is designed to achieve a film with a thickness gradually decreasing from the center to the edge. The spiral mask plate is shown in Figure 5. The shaded part is the hollow part. The shape is designed according to the non-uniform transmittance of the image invertor. First, a transmittance tester (i.e., a device for detecting the visible light transmittance and uniformity of an optical fiber image transmission element involved in the patent application with publication number CN 111442908A) is used to obtain the transmittance distribution of the image invertor. Next, the functional relationship between the transmittance of the image invertor and the position of the effective area is fitted based on the obtained data. The thickness and position of the required coating film layer are then calculated using this function. The function is: x = -2×10 -7 y 6+8×10 -9 y 5 -1×10 -4 y 4 -2×10 -6 y 3 -0.0315y 2 -1×10 -11 y+4.2165, where x is the absolute thickness of the film layer and y is the distance from the center to the edge (x is greater than 0 and y is between 0 and 11.5). The shape of the snail mask is finally determined according to the formulas θ(x) = θ0d(x) / d0 and ρ = (1-d / H)r. θ(x) is the angle of exposure to the vapor flow, d0 is the thickness at the center of the film layer, θ0 is the aperture angle at the center of the film layer, the distance between the evaporation source and the lower surface of the substrate being coated is H, the distance between the shield and the lower surface of the substrate is d, the polar diameter from the center of the shield to the opening reference point is ρ, and the maximum radius of the glass substrate that the evaporation source can reach is r. As shown in Figure 5, the opening size of the snail mask gradually decreases from the center to the edge. In conjunction with the rotary coating device, the exposure time of the central area is long and the exposure time of the edge area is short during the coating process, thus achieving the target film layer.

[0078] By using a mechanical rotary coating device in conjunction with a snail-shaped mask, a thin film with a thickness gradually decreasing from the center to the edge can be deposited. This, combined with an image inverter with non-uniform transmittance, ultimately results in a highly uniform transmittance image inverter. In actual use, the equalizing film can be deposited on both the input and output ends of the image inverter, or both simultaneously. Alternatively, an antireflection film can be used to achieve both high transmittance and ultra-high light transmission. The equalizing film can reduce vignetting defects, while the antireflection film can increase the overall transmittance of the image inverter. Together, the two can achieve both low vignetting defects within the effective area and high transmittance.

[0079] The above-mentioned mechanical rotary coating device is shown in Figures 2-5, including a protective shell 1, a motor 2, a small gear 3, a large gear 4, a rotating base 5, a mask 6, a sample chamber 7, a platform 8 and a sample 9 fixed by screws. The protective shell 1 is fixedly connected to the platform 8, so that the entire device has a regular shape (it is a rectangular parallelepiped with a length of 173mm, a width of 136mm and a height of 115mm), which is convenient for placement in the chamber. Among them, the platform 8 is a rectangular metal plate with a thickness of 3mm, so that the size can be reduced as much as possible under the premise of ensuring that the motor, sample chamber and other components can bear the load; as shown in Figure 6A, the rotating base 5 is a bearing structure composed of two concentric rings, which includes a non-rotating internal structure and a rotating external structure connected by steel balls. The internal structure is fixed to the sample chamber 7, the upper end face of the external structure is fixed to the large gear 4, and the lower end face of the external structure is fixed to the mask 6, so that the mask can rotate without rotating the sample chamber. Specifically, the rotating base 5 is a high-precision bearing with a very small gap inside the bearing. The distance between the two is filled with steel balls, which makes it very stable and will not shake, thereby ensuring high coaxiality. Since the rotating base 5 is a three-dimensional structure and is located between the sample chamber 7 and the mask plate 6, according to the direction of placing the high-stability, high-coaxiality mechanical rotary coating device in the coating equipment, the sample chamber 7 is fixed above the inside of the rotating base 5, and the mask plate 6 is fixed below the outside of the rotating base 5. The sample 9 is a fiber optic inverter, and there are no requirements for its size and performance. Fiber optic inverters of different sizes can be placed by changing the size of the sample chamber. The rotating base 5 and the mask plate 6 are fixed together, and the motor drives the rotating base 5 to rotate, while the sample chamber 7 remains stationary, so that the mask plate 6 can achieve the effect of self-rotation. By using the mechanical rotary coating device in combination with the snail-shaped mask plate 6, a thin film with a thickness gradually decreasing from the center to the edge can be plated, and with a fiber optic inverter with non-uniform transmittance, a fiber optic inverter with high uniformity can be finally achieved.

[0080] The sample 9 is placed in the sample chamber 7. The sample chamber 7 is 4mm higher than the sample and has a built-in rubber pad to prevent damage to the end face of the sample 9 when the mechanical rotary coating device is inverted and disassembled. Specifically, the rubber pad is located between the large end face of the optical fiber invertor and the sample chamber 7. This arrangement can prevent the large end face of the optical fiber invertor from directly contacting the sample chamber 7. The material of the sample chamber 7 is polytetrafluoroethylene. The reason for choosing polytetrafluoroethylene is firstly because it is light in weight and can reduce the overall weight of the device; secondly, because it can withstand higher temperatures than ordinary plastics. The upper end face of the sample chamber 7 is fixed to the platform 8 by screws, and its lower end face is fixed to the upper end face of the internal structure of the rotating base 5 by screws. The sample chamber 7 is a cylindrical groove with a diameter of 48mm and a depth of 45mm. One end of the platform 8 is fixed to the motor 2 by screws to ensure that the rotation of the mask is not disturbed while ensuring the coating effect.

[0081] A small-diameter pinion 3 is installed at the tail end of the shaft of the motor 2. The rotation of the motor 2 drives the pinion 3 to rotate. This arrangement is to ensure that the rotation of the mask is not disturbed while ensuring the coating effect.

[0082] The pinion 3 meshes with the large, hollow gear 4, which has a larger diameter. Rotation of the pinion 3 drives the large gear 4. In practice, the diameter of the large gear 4 needs to be equal to the outer diameter of the bearing. Considering that the sample chamber 7 needs to be placed in the center of the large gear 4, the large gear 4 is hollow. The diameter of the large gear 4 matches the dimensions of the rotating base. The speed ratio between the pinion 3 and the large gear 4 is 5:1, which achieves good film uniformity. The appropriate diameter of the pinion 3 is selected based on the speed ratio. Too fast or too slow speeds can easily lead to poor film uniformity and surface stains. The speed ratio between the large and small gears is designed to control the rotation speed of the bottom mask and improve the uniformity of the coating thickness. Taking into account the position of the pinion and the speed ratio, the diameter of the pinion 3 is designed to be 3 cm. Furthermore, the mechanical rotary coating device can utilize both large and small gears within a limited space, resulting in high transmission efficiency.

[0083] The motor 2 drives the small gear 3 to rotate, the small gear 3 drives the large gear 4 to rotate, the large gear 4 drives the outer part of the bearing to rotate, and the outer part of the bearing drives the mask to rotate, so that the sample does not rotate but the mask rotates by itself.

[0084] The large gear 4 is fixed to the upper end of the outer portion of the rotating base 5 by screws. The rotation of the large gear 4 drives the rotating base 5 to rotate. There is a 1 mm gap between the large gear 4 and the sample chamber 7 so that the large gear 4 will not be affected by the sample chamber 7 when rotating.

[0085] The outer lower end surface of the rotating base 5 is fixed to the mask 6 by screws. The outer portion of the rotating base 5 drives the mask 6 to rotate. The size of the mask 6 is equal to the outer dimensions of the rotating base 5, and the gap between the two is 2mm. This allows the mask 6 to rotate undisturbed while ensuring the coating effect. Specifically, the mask 6 is a spiral-shaped copper plate with a hollow center, which has a thickness of 0.5mm and a diameter of 120mm. The hollowed-out middle portion of the spiral copper plate has a larger opening, while the edge portions have smaller openings. That is, during coating, the middle exposure time is long and the edge exposure time is short, which can achieve a gradient film with a thick middle film layer and a thin edge film layer. The thinner the copper plate, the better, while ensuring that the mask does not deform. This allows the sputtering material to better adhere to the sample. Tests have found that mask plates with a thickness of less than 0.5mm are prone to deformation. Considering that the mask 6 is fixed to the rotating base by screws, the diameter of the mask 6 is the same as the outer dimensions of the rotating base to facilitate fixation.

[0086] The coating of the thin film optical fiber image invertor with thickness gradually decreasing from the center to the edge comprises the following steps:

[0087] 1) Place the assembled mechanical rotary coating device into the chamber of the magnetron sputtering coating machine; the chamber has good sealing properties and can be used to place samples or devices to be coated; if the mask plate is installed first, the sample cannot be installed, so if the device needs to be used, the sample must be installed first and then the mask plate;

[0088] 2) Turn on the power supply and adjust the speed of the mechanical rotary coating device; since the motor speed of the mechanical rotary coating device is adjustable, turn the button to adjust the motor speed to 10-20 rpm;

[0089] 3) Closing the chamber and starting film coating. Closing the chamber and starting film coating specifically includes the following steps:

[0090] a. After closing the chamber of the coating equipment, turn on the mechanical pump to pre-vacuum. When the vacuum degree is less than or equal to 10Pa, turn off the mechanical pump, open the solenoid valve, and turn on the molecular pump.

[0091] b When the vacuum degree is less than or equal to 3×10 -4 Turn on the gas flow meter and adjust the gas flow of argon and oxygen to 15-30 sccm. Then adjust the pressure in the chamber to 1.0-2.0 Pa through the G valve; the vacuum degree is less than or equal to 3×10 -4 It can meet the coating requirements. The lower the vacuum degree, the fewer impurities in the chamber. The lower the pressure in the chamber, that is, the working pressure, the higher the quality of the film layer, but the speed will be slower. Therefore, 1.0-2.0Pa is selected as the working pressure.

[0092] c. Turn on the sputtering power switch and adjust the power to 30-50W to start pre-sputtering. After sputtering for 3-5 minutes, open the baffle valve and adjust the power to 60-80W to start formal sputtering. The sputtering time is 0.5-3 minutes. The purpose of pre-sputtering is first to preheat the machine. It is not advisable to use high power when starting the machine. Secondly, it sputters away impurities on the surface of the target material.

[0093] d. After sputtering is completed, close the flapper valve, turn off the power switch, turn the gas flow meter knob to 0, close the solenoid valve, turn off the molecular pump, and open the valve connecting the air to balance the internal and external atmospheric pressures of the chamber;

[0094] e. Open the chamber of the coating equipment and remove the mechanical rotary coating device. When the coating is completed, a fiber optic image inverter with high uniformity and high transmittance is obtained, as shown in Figures 8A, 8B, 9A, 9B, 10A, 10B, 11A, 11B, 12A, and 12B. The fiber optic image inverter can be used in electro-low-light-level night vision devices. There are two types of fiber optic image inverters: a biquadratic function type image inverter and a bicubic function type image inverter. As can be seen from Figures 8A, 8B, 9A, 9B, 10A, 10B, 11A, 11B, 12A, and 12B, both input and output end faces of the two different function types of image inverters can be coated with a homogenized film layer, and even both ends can be coated with a homogenized film layer simultaneously. There are a total of 10 coating methods. Specifically, as shown in FIG8A, FIG9A, FIG10A, FIG11A and FIG12A, the biquadratic function type image invertor 14 includes an input end 10, an output end 91 and an optical fiber portion disposed between the input end 10 and the output end 91; the surface of the input end 10 and / or the output end 91 has a thin film whose thickness gradually decreases from the center to the edge; the thickness and position of the thin film satisfy: x = -2×10 -7 y 6 +8×10 -9 y 5 -1×10 -4 y 4 -2×10 -6 y 3 -0.0315y 2 -1×10 -11 y+4.2165, where x is the absolute thickness of the film and y is the distance from the center to the edge. The film includes equalizing film layers 11, 21 and / or anti-reflection film layers 12, 22. The center of the equalizing film layer 11 is provided with a film layer center 13, the center of the equalizing film layer 21 is provided with a film layer center 43, the center of the anti-reflection film layer 12 is provided with a film layer center 23, and the center of the anti-reflection film layer 22 is provided with a film layer center 33. As shown in Figures 8B, 9B, 10B, 11B, and 12B, the bicubic function type image invertor 15 includes an input end 20, an output end 92, and an optical fiber portion disposed between the input end 20 and the output end 92. The surface of the input end 20 and / or the output end 92 comprises a film whose thickness gradually decreases from the center to the edge. The thickness and position of the film satisfy: x=-2×10 -7 y 6 +8×10 -9 y 5 -1×10 -4 y 4 -2×10 -6 y 3 -0.0315y 2 -1×10 -11y+4.2165, where: x is the absolute thickness of the film, y is the distance from the center to the edge; the film includes equalizing film layers 11, 21 and / or anti-reflection film layers 12, 22, the center of the equalizing film layer 11 is provided with a film layer center 13, the center of the equalizing film layer 21 is provided with a film layer center 43, the center of the anti-reflection film layer 12 is provided with a film layer center 23, and the center of the anti-reflection film layer 22 is provided with a film layer center 33.

[0095] In summary, a mechanical rotary coating device combined with a snail-shaped mask can ultimately produce a thin film with a thickness that gradually decreases from the center to the edge. This, combined with an image inverter with non-uniform transmittance, ultimately results in a highly uniform transmittance. Alternatively, an antireflection film can be used to achieve both high transmittance and ultra-high light transmission. The homogenizing film reduces vignetting defects, while the antireflection film increases the overall transmittance of the image inverter. Together, they achieve both low vignetting defects within the effective area and high transmittance.

[0096] The above-mentioned “high uniformity and high transmittance” means that the transmittance uniformity of the image invertor at a wavelength of 550 nm is between 97.9% and 99.02%, and the central transmittance is between 39.87% and 41.08%.

[0097] The present application is described in detail below with reference to specific embodiments.

[0098] The “center” mentioned below refers to the exact center of the image inverter, and the “edge” refers to the edge of the effective area of ​​the image inverter.

[0099] Example 1:

[0100] This embodiment provides a dual quadratic function type image invertor, the production of which specifically includes the following steps:

[0101] S1, use the rod-tube combination method to combine a high-refractive index glass rod and a low-refractive index glass tube together and then draw (temperature is 1850℃) into a single wire (diameter is 3mm); the drawn single wire and the light-absorbing wire (diameter is 3mm) for absorbing stray light are arranged into a hexagonal shape and then drawn (temperature is 1845℃) into a primary multifilament (diameter is 1.3mm); the primary multifilament is once again arranged into a hexagonal shape and drawn (temperature is 1450℃) into a secondary multifilament (diameter is 2mm); the secondary multifilament is placed in a melt-pressed mold and subjected to high temperature and high pressure (temperature is 650℃, pressure is 15 tons) to prepare a blank (height is 40mm, diameter is 26mm). The glass rod has a refractive index of 1.78 at a wavelength of 550 nm, and its composition by weight is: SiO2 54.12%; K2CO3 14.84%; Na2CO3 11.10%; Al(OH)3 5.99%; H2BO3 10.16%; CaCO3 2.88%; BaCO3 0.23%; CeO2 0.07%; MgCO3 0.46%; NiO 0.01%; Nb2O5 0.05%; Y2O3 0.01%; and La2O3 0.08%. The glass tube has a refractive index of 1.49 at a wavelength of 550 nm, and its composition by weight is: SiO2 35.25%; KNO3 0.13%; Na2CO3 0.10%; Al(OH)3 0.84%; H2BO3 24.23%; CaCO3 10.26%; BaCO3 25.50%; MgCO3 0.21%; La2O3 1.68%; Sb2O3 0.06%; and TiO2 1.74%. The composition of the light absorbing filament in weight percentage is: SiO2 55.84%; K2CO3 11.27%; Na2CO3 6.11%; Al(OH)3 9.37%; H2BO3 8.56%; CaCO3 2.67%; BaCO3 0.03%; CeO2 0.19%; MgCO3 0.40%; Fe2O3 0.02%; NiO 0.87%; MnO2 2.87%; CoO 0.42%; La2O3 0.01%; V2O5 1.37%.

[0102] S2: Secure the blank to the torsion rod using a torsion fixture. Then, control the torsion furnace through the mechanical operation panel to align the center of the blank with the center of the inner torsion furnace. This completes the preparations. First, heat the outer furnace to the preheating temperature (approximately 550°C). After stabilizing the outer furnace temperature for 15 minutes (the purpose is to fully preheat, 20 minutes is acceptable), use a heating ring with an inner diameter of 40mm and a width of 2mm (to heat the center of the blank to the softening temperature) to raise the temperature of the inner torsion furnace at a rate of 10°C / min to the softening point of the blank (approximately 820°C). A servo motor and a torsion force sensor apply two constant but opposite torsional forces (150N) to the ends of the blank. The center of the blank in the inner furnace heating area gradually softens. Torsional forces are applied to both ends until the blank rotates 180° relative to the center. Then, heating in the inner furnace is stopped and the outer furnace annealing process is initiated (cooling at a rate of 10°C / min). Finally, the image invertor blank is removed after cooling to room temperature. At this time, the temperature difference between the inner and outer furnaces is only 280°C. The change trend of the twisted image inverter cone is nonlinear, and the deformation zone of the image inverter presents a double quadratic function parabola shape. Taking the image inverter blank with a height of 26mm and a diameter of 22mm as an example, when the torsional force is controlled at 14N, a double quadratic function type image inverter can be realized. The corresponding equation type is y=0.087x 2 .

[0103] S3, polish the image inverter blank for 2 hours to a roughness of 20nm, and then perform performance testing to ensure that the transmittance, resolution and internal defects (such as defects, chicken wire, and grid) of the image inverter meet the national standards (GJB9792-2020 Specification for Fiber Optic Image Transmission Coupling Elements).

[0104] S4. First, a transmittance tester (the device for measuring the visible light transmittance and uniformity of optical fiber image transmission components, as described in patent application publication number CN 111442908A) was used to measure the transmittance distribution at the output of the biquadratic function image invertor. Analysis of the obtained data revealed a non-uniform transmittance of 7.23% and a central transmittance of 45%. A gradient chromium film with a center thickness of 6 nm and an edge thickness of 1 nm was then applied using a rotary coating device. This reduced the non-uniform transmittance to 2.1%, with a central transmittance of 39.87%. The test results are shown in Figure 13.

[0105] Specifically, the assembled rotary coating device was placed in the chamber of the magnetron sputtering coating machine; the power supply was turned on, and the rotation speed of the rotary coating device was adjusted to 10 rpm; the chamber was closed and the coating was started, and the distance between the mask plate and the optical fiber invertor was 1 mm.

[0106] The process of closing the chamber and starting the film deposition specifically includes the following steps: a. After closing the chamber of the film deposition equipment, first open the mechanical pump to pre-vacuum, and when the vacuum reaches 10 Pa, close the mechanical pump, open the solenoid valve, and open the molecular pump; b. When the vacuum reaches 2×10-4 The process includes: first, turning on the gas flowmeter and adjusting the argon flow rate to 25 sccm; then, adjusting the pressure in the chamber to 0.8 Pa through the G valve; c, turning on the sputtering power switch and adjusting the power to 50 W to start pre-sputtering; after 5 minutes of sputtering, opening the baffle valve and adjusting the power to 60 W to start formal sputtering for 50 seconds; d, after sputtering, closing the baffle valve and the power switch, turning the gas flowmeter knob to 0, closing the solenoid valve and the molecular pump, and opening the valve connected to the air to balance the internal and external atmospheric pressures of the chamber; e, opening the chamber of the coating equipment and removing the rotary coating device. Coating is completed, resulting in a highly uniform and high-transmittance optical fiber image inverter. The optical fiber image inverter can be used in electric low-light-level night vision devices.

[0107] As can be seen from Figure 13, the thickness of the chrome film gradually decreases from the center to the edge, the central transmittance of the image invertor decreases from 45% to 39.87%, and the vignetting defect decreases from 7.23% to 2.1%, proving that this solution can effectively reduce the vignetting defect.

[0108] Example 2:

[0109] This embodiment provides a bicubic function type image invertor, the production of which specifically includes the following steps:

[0110] S1, same as Example 1.

[0111] S2, the twisting method is the same as that of the biquadratic function type image inverter, the difference is that the heating ring of the bicubic function type image inverter is movable. The position of the heating ring is initially located at one-quarter of the image inverter blank. After twisting 90°, the heating ring is moved to three-quarters of the image inverter blank and continues to twist 90°. During the stretching process, the center of the image inverter blank can maintain a straight area of ​​1mm, and then continue to apply a twisting force of 14N. The image inverter prepared using this method will show an image inverter deformation area in the shape of a cubic function double parabola. Taking an image inverter blank with a height of 26mm and a diameter of 22mm as an example, when the twisting force is controlled at 14N, the bicubic function type image inverter can be realized using the above method, and the corresponding equation type is y=0.005x 3 .

[0112] S3, same as Example 1.

[0113] S4. A transmittance tester (the device for measuring visible light transmittance and uniformity of optical fiber image transmission components, as described in patent application publication number CN 111442908A) was used to measure the transmittance distribution at the output of the bicubic image invertor. Analysis of the data revealed a non-uniform transmittance of 4.13% and a central transmittance of 45%. A gradient chromium film with a center thickness of 6 nm and an edge thickness of 1 nm was then applied using a rotary coating device. This reduced the non-uniform transmittance to 0.98%, with a central transmittance of 41.08%. The test results are shown in Figure 14.

[0114] Specifically, the assembled mechanical rotary coating device was placed in the chamber of the magnetron sputtering coating machine; the power supply was turned on, and the rotation speed of the mechanical rotary coating device was adjusted to 10 rpm; the chamber was closed and the coating was started, and the distance between the mask plate and the optical fiber inverter was 1 mm.

[0115] The process of closing the chamber and starting the film deposition specifically includes the following steps: a. After closing the chamber of the film deposition equipment, first open the mechanical pump to pre-vacuum, and when the vacuum reaches 10 Pa, close the mechanical pump, open the solenoid valve, and open the molecular pump; b. When the vacuum reaches 2×10 -4 The process includes: first, turning on the gas flowmeter and adjusting the argon flow rate to 25 sccm; then, adjusting the pressure in the chamber to 0.8 Pa through the G valve; c, turning on the sputtering power switch and adjusting the power to 50 W to start pre-sputtering; after 5 minutes of sputtering, opening the baffle valve and adjusting the power to 60 W to start formal sputtering for 50 seconds; d, after sputtering, closing the baffle valve and the power switch, turning the gas flowmeter knob to 0, closing the solenoid valve and the molecular pump, and opening the valve connected to the air to balance the internal and external atmospheric pressures of the chamber; e, opening the chamber of the coating equipment and removing the rotary coating device. Coating is completed, resulting in a highly uniform and high-transmittance optical fiber image inverter. The optical fiber image inverter can be used in electric low-light-level night vision devices.

[0116] As can be seen from Figure 14, before coating, the vignetting defect of the bicubic function type image inverter is lower than that of the biquadratic function type image inverter, indicating that the structure of the bicubic function type image inverter is optimal. After chrome coating, the central transmittance of the image inverter is reduced from 45% to 41.08%, and the vignetting defect is reduced from 4.13% to 0.98%, and the phenomenon of reducing vignetting defects is more obvious.

[0117] Example 3:

[0118] This embodiment provides a bicubic function type image invertor, the production of which specifically includes the following steps:

[0119] S1, same as Example 2.

[0120] S2, same as Example 2.

[0121] S3, same as Example 2.

[0122] S4. Compared to Example 2, this example differs in that a gradient titanium nitride film with a center thickness of 30 nm and an edge thickness of 5 nm was deposited using a spin coating apparatus. Test results show that the non-uniform transmittance is reduced to 1.08%, while the center transmittance is 40.98%. The test results are shown in Figure 15.

[0123] Specifically, the assembled mechanical rotary coating device was placed in the chamber of the magnetron sputtering coating machine; the power supply was turned on, and the rotation speed of the mechanical rotary coating device was adjusted to 10 rpm; the chamber was closed and the coating was started, and the distance between the mask plate and the image invertor was 1 mm.

[0124] The process of closing the chamber and starting the film deposition specifically includes the following steps: a. After closing the chamber of the film deposition equipment, first open the mechanical pump to pre-vacuum, and when the vacuum reaches 10 Pa, close the mechanical pump, open the solenoid valve, and open the molecular pump; b. When the vacuum reaches 2×10 -4 The process involves: first, turning on the gas flowmeter and adjusting the argon flow rate to 25 sccm; then, adjusting the pressure in the chamber to 0.8 Pa via the G valve; second, turning on the sputtering power switch and adjusting the power to 50 W to begin pre-sputtering; and after 5 minutes of sputtering, opening the flapper valve and adjusting the power to 60 W to begin formal sputtering for 230 seconds; and finally, closing the flapper valve and the power switch after sputtering. The gas flowmeter knob is turned to 0, the solenoid valve and the molecular pump are closed, and the valve connecting to the air is opened to balance the internal and external atmospheric pressures of the chamber. Finally, the chamber of the coating equipment is opened, and the rotary coating device is removed. Coating is completed, resulting in a highly uniform and high-transmittance optical fiber image inverter. The optical fiber image inverter can be used in low-light-level night vision devices.

[0125] As can be seen from Figure 15, by changing the coating material from chromium film to titanium nitride film, the central transmittance of the image inverter is reduced from 45% to 40.98%, and the vignetting defect is reduced from 4.13% to 1.08%, indicating that the purpose of equalization can be achieved by changing the coating material.

[0126] Comparative Example 1:

[0127] Compared to Example 2, this comparative example differs in that a conventional method (no spin coating apparatus, no mask, and other operating steps and parameters identical to Example 3) was used to deposit a 5nm thick metal chromium film on the output end of the bicubic image invertor, both at the edge and in the center. Testing revealed that the non-uniform transmittance was reduced to 5.19%, with a central transmittance of 36%. The test results are shown in Figure 16. As can be seen from Figure 16, this conventional method was unable to effectively reduce vignetting defects.

[0128] The non-uniform transmittance and center transmittance of the optical fiber image inverters of Examples 1-3 and Comparative Example 1 before and after coating were tested, and the test results are shown in Table 1. The test principle is: a beam of collimated incident light with a wavelength of 550nm is irradiated to the input end of the optical fiber image inverter, and the light coming out of the output end of the optical fiber image inverter is received by a CCD camera to obtain a light intensity distribution diagram, and the relative transmittance is calculated by the luminous flux of the input and output light. Among them, the luminous flux is equal to the light intensity multiplied by the area, and the light intensity is measured by the transmittance tester. The center transmittance is the transmittance when the position is 0 (the exact center of the optical fiber image inverter). The non-uniform transmittance is the difference between the center transmittance and the transmittance at the edge of the effective area.

[0129] Table 1

[0130] From the data in Table 1, it can be concluded that before coating, when the central transmittance of Examples 1-3 was maintained at 45%, the non-uniform transmittance of the bicubic function type image inverter was 4.13%, the transmittance uniformity was 95.87%, and the structure was optimal. The non-uniform transmittance of the biquadratic function type image inverter was 7.23%, the transmittance uniformity was 92.77%, and the structure was the worst. After coating, while ensuring that the average non-uniform transmittance was around 1%, the central transmittance of the bicubic function type image inverter could reach 41.08%, while the central transmittance of the biquadratic function type image inverter was only 39.87%, which also shows that the bicubic function type image inverter structure is the optimal.

[0131] In the specification of the present application, a large number of specific details are described. However, it is understood that the embodiments of the present application can be practiced without these specific details. In some embodiments, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this specification.

[0132] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0133] In addition, the various implementation methods of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents disclosed in the present application.

[0134] The above is merely a preferred embodiment of the present application and does not constitute any form of limitation to the present application. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present application still fall within the scope of the technical solution of the present application.

Claims

1. A high uniformity and high transmittance optical fiber image invertor, characterized in that: The invention comprises an input end, an output end and an optical fiber part arranged between the input end and the output end; the surface of the input end and / or the output end has a thin film whose thickness gradually decreases from the center to the edge; the thickness and position of the thin film satisfy: x = -2×10 -7 y 6 +8×10 -9 y 5 -1×10 -4 y 4 -2×10 -6 y 3 -0.0315y 2 -1×10 -11 y+4.2165, where: x is the absolute thickness of the film, y is the distance from the center to the edge.

2. The high uniformity and high transmittance optical fiber image invertor according to claim 1, characterized in that: The value of x is greater than 0, and the value of y is between 0 and 11.

5.

3. The high uniformity and high transmittance optical fiber image invertor according to claim 1, characterized in that: The optical fiber image inverter is a biquadratic function type image inverter or a bicubic function type image inverter.

4. The high uniformity and high transmittance optical fiber image invertor according to claim 1, characterized in that: The film comprises a homogenizing film layer and / or an anti-reflection film layer, and a film layer center is arranged at the center thereof.

5. A method for preparing a high-uniformity and high-transmittance optical fiber image invertor, characterized in that: The following steps are involved: Preparation of torsion structure of image invertor; Preparation of homogenizing film on the surface of image invertor.

6. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The preparation of the image invertor torsion structure comprises the following steps: According to the optical fiber trajectory in the torsion zone of the image inverter, a double quadratic function type image inverter or a double cubic function type image inverter is prepared respectively.

7. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The preparation of the homogenizing film on the surface of the optical fiber image invertor comprises the following steps: The surface of the optical fiber image invertor is coated with a thin film whose thickness gradually decreases from the center to the edge.

8. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 7, characterized in that: The film comprises a homogenizing film layer and / or an anti-reflection film layer, and a film layer center is arranged at the center thereof.

9. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The rotation speed of the film whose thickness decreases gradually from the center to the edge is 10rpm-20rpm.

10. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The pressure of the film whose coating thickness gradually decreases from the center to the edge is 1.0-2.0Pa.

11. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The vacuum degree of the film whose thickness decreases gradually from the center to the edge is less than or equal to 3×10 -4 .

12. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: When coating a thin film whose thickness gradually decreases from the center to the edge, the gas flow rate of argon gas is 15-30 sccm.

13. The method for preparing a fiber optic image invertor with high uniformity and high transmittance as claimed in claim 5, characterized in that: The film with a thickness gradually decreasing from the center to the edge is plated by sputtering; pre-sputtering is started at 30-50W, and after sputtering for 3-5 minutes, the power is adjusted to 60-80W to start formal sputtering, and the sputtering time is 0.5-3 minutes.

14. A low-light-level night vision device, characterized in that: The low-light-level night vision device comprises the optical fiber image invertor with high uniformity and high transmittance as described in any one of claims 1 to 4.

Images