Anti-reflection shading cylinder for medium-wave infrared detector

Abstract

The inner wall of the shading cylinder is of a multi-layer structure, the bottom layer of the multi-layer structure is made of a blackening material, the bottom layer is coated with an Al2O3 thin film to serve as a dielectric material, bracelet-shaped or doughnut-shaped metal rings are inlaid in the surface of the Al2O3 thin film, and the metal rings are periodically arranged on the inner wall of the shading cylinder up and down. The circle center of the section of each metal ring is located on the surface of the Al2O3 thin film, under the condition that incident light is infrared light with the wavelength of 4200 nm, the diameter of each metal ring is 0.5 micrometer, and the distance between the upper metal ring and the lower metal ring is 5 micrometers. According to the invention, the reflectivity of 4200nm infrared light on the inner wall of the shading cylinder can be effectively reduced, the total reflectivity of TE waves is not more than 40% and the total reflectivity of TM waves is not more than 15% when the incident angle is less than 70 degrees, and the reflectivity is further reduced after the shading cylinder is combined with a blackening material, so that the reflection loss of the inner wall of the shading cylinder to effective light is reduced, and the service life of the shading cylinder is prolonged. And the lighting effect of the medium-wave infrared detector is improved.

Description

Technical Field

[0001] The present invention belongs to the field of mid-wave infrared detectors, and particularly relates to an anti-reflection light-shielding cylinder for a mid-wave infrared detector. Background Art

[0002] A mid-wave infrared detector is a photoelectric sensor operating in the wavelength range of 3 - 5 microns, belonging to the "atmospheric window" band (high atmospheric transmittance). It can convert infrared radiation into an electrical signal through the photoelectric effect or the pyroelectric effect. Its core function is to detect the thermal radiation of the target object or reflect infrared light, so as to realize the recognition, monitoring, and tracking of the target, and is widely used in fields such as atmospheric monitoring, infrared imaging, and meteorological remote sensing.

[0003] The light-shielding cylinder in an infrared imaging detector mainly plays the roles of focusing infrared radiation, suppressing the interference of stray light, defining the detection field of view angle, and protecting the sensor element. The existing light-shielding cylinders often eliminate stray light by blackening the inner wall. In some designs, the edges of the light-blocking rings are sharpened at an angle (such as 45°) and further suppress edge scattering by blackening. This light-shielding cylinder design has the following disadvantages:

[0004] 1) Although the blackening treatment of the inner wall component of the light-shielding cylinder can suppress stray light, it will absorb 5% - 8% of the effective light. Experimental data shows that after the 45° sharp-angle light-blocking ring is blackened, the overall light efficiency of the system drops by about 3.2 lumens per watt, and it is more likely to form dark areas especially in low-illumination environments.

[0005] 2) Under the working conditions of thermal expansion and contraction (such as a temperature difference of -20°C to 60°C), metal fatigue cracks are likely to occur at the edges of the 45° sharp-angle light-blocking ring. A certain actual engineering case shows that such a structure has a 12% edge cracking rate after being used in the northern region for 3 years. Summary of the Invention

[0006] The purpose of the present invention is to provide an anti-reflection light-shielding cylinder for a mid-wave infrared detector, which can reduce the reflection loss of the inner wall of the light-shielding cylinder to effective light, improve the light efficiency of the mid-wave infrared detector, and avoid the problem of metal fatigue cracks.

[0007] One aspect of the present invention provides an anti-reflection light-shielding cylinder for a mid-wave infrared detector. The inner wall of the light-shielding cylinder is a multi-layer structure. The bottom layer of the multi-layer structure is a blackening material, and an Al2O3 film is coated on the bottom layer as a dielectric material. Bracelet-shaped or donut-shaped metal rings are inlaid on the surface of the Al2O3 film, and the metal rings are arranged periodically up and down on the inner wall of the light-shielding cylinder. The center of the cross-section of the metal ring is located at the surface of the Al2O3 film.

[0008] Preferably, the thickness of the Al2O3 film is 10 μm.

[0009] Preferably, the material of the metal ring is gold.

[0010] Preferably, when the incident light is infrared light with a wavelength of 4200 nm, the diameter of the metal ring is 0.5 μm, and the distance between adjacent upper and lower metal rings is 5 μm.

[0011] Preferably, when the incident angle of the incident light is less than 70°, the total reflectivity of the TE wave is not greater than 40%, and the total reflectivity of the TM wave is not greater than 15%.

[0012] Preferably, the condition for the absence of second-order or higher-order reflected diffraction beams on the inner wall of the light-shielding cylinder is:

[0013] 2λ0>dn a (1 + |sinα|),

[0014] where λ0 is the vacuum wavelength, d is the distance between the metal rings, and the incident light is incident on the inner wall of the light-shielding cylinder at an incident angle α after passing through a medium with a refractive index of n α of the medium.

[0015] According to the anti-reflection light-shielding cylinder for a mid-wave infrared detector in the above aspect of the present invention, it is possible to reduce the reflection loss of the effective light by the inner wall of the light-shielding cylinder, improve the light efficiency of the mid-wave infrared detector, and avoid the problem of metal fatigue cracks. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts:

[0017] Figure 1 is a schematic cross-sectional structure diagram of an anti-reflection light-shielding cylinder for a mid-wave infrared detector according to an embodiment of the present invention;

[0018] Figure 2 is a schematic diagram of the structural parameters for 4200 nm infrared light according to an embodiment of the present invention;

[0019] Figure 3 is a schematic diagram of a metal wire grating model according to an embodiment of the present invention;

[0020] Figure 4 is a diffraction schematic diagram of a metal wire grating model according to an embodiment of the present invention;

[0021] Figure 5 is a reflection schematic diagram of a metal wire grating model according to an embodiment of the present invention;

[0022] Figure 6Schematic diagram of the relationship between the reflectivity and the incident angle of the TE wave of incident light with a wavelength of 4200nm in an embodiment of the present invention;

[0023] Figure 7 Schematic diagram of the relationship between the reflectivity and the incident angle of the TM wave of incident light with a wavelength of 4200nm in an embodiment of the present invention. Detailed implementation manners

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative efforts belong to the scope of protection of the present invention.

[0025] An embodiment of the present invention provides an anti-reflection light-shielding cylinder for a mid-wave infrared detector, which is mainly used to reduce the reflectivity of light with a wavelength of 4200nm on the inner wall of the light-shielding cylinder, and is also applicable to the design of anti-reflection light-shielding cylinders for light in other bands. The inner wall structure of the light-shielding cylinder in the embodiment of the present invention can be combined with traditional blackened light-absorbing materials to further reduce the reflectivity on the inner wall of the light-shielding cylinder. Compared with traditional methods, there is no need for the sharp-edge design of the light-shielding ring, which can more effectively avoid problems such as the formation of dark areas more easily in low-light environments and the generation of metal fatigue cracks at the edges and corners caused by the sharp-edge light-shielding ring.

[0026] As Figure 1 shown, the anti-reflection light-shielding cylinder in the embodiment of the present invention is located between the imaging lens and the focal plane detector of the mid-wave infrared detector. The anti-reflection light-shielding cylinder in the embodiment of the present invention has a cylindrical structure. The inner wall of the light-shielding cylinder is a multi-layer structure. The inner wall of the light-shielding cylinder uses a blackened material as the bottom layer, and an Al2O3 film with a thickness of up to 10μm is coated thereon as a dielectric material. Bracelet-shaped or donut-shaped metal rings are inlaid on the surface of the Al2O3 film, and the material is gold. The metal rings are arranged periodically up and down inside the light-shielding cylinder, and the center of the cross-section is located on the surface of the Al2O3 film. The design of this multi-layer structure comprehensively considers the optical properties of the materials and the influence of the geometric shape of the metal rings on light reflection.

[0027] In one embodiment, as Figure 2As shown, for the common medium-wave infrared light with a wavelength of 4200 nm, the diameter of the metal ring is designed to be 0.5 μm, and the spacing between adjacent upper and lower metal rings is 5 μm. These precise geometric parameters are the key factors for effectively reducing the reflectivity of 4200 nm infrared light. By optimizing the size and spacing of the metal rings, the propagation and reflection characteristics of light in the inner wall structure of the light-shielding cylinder can be regulated, thereby achieving the purpose of anti-reflection. The anti-reflection light-shielding cylinder of the embodiment of the present invention can effectively reduce the reflectivity of 4200 nm infrared light on the inner wall of the light-shielding cylinder without relying on a blackened material. The precise configuration of each layer of materials and structural parameters works together to achieve the purpose of reducing the reflectivity.

[0028] The anti-reflection light-shielding cylinder of the embodiment of the present invention can optimize the size and spacing of the metal rings for 4200 nm infrared light. However, the grating diffraction principle and the multi-layer structure design method adopted are universal and can also be applied to light of other bands. Only the corresponding structural parameters need to be adjusted according to the specific wavelength.

[0029] Specifically, by using the grating diffraction principle, the structural parameters of the inner wall of the light-shielding cylinder, such as the grating constant, the width and height of the metal wire, are precisely calculated and designed to achieve the regulation of the reflection and transmission of light with a specific wavelength. This design method can effectively reduce the reflectivity of the inner wall of the light-shielding cylinder without relying on the traditional design of the sharp angle at the edge of the light-blocking ring, and at the same time avoid problems such as metal fatigue cracks caused by the sharp angle light-blocking ring.

[0030] The following explains the basic theory involved in the design of the anti-reflection light-shielding cylinder of the embodiment of the present invention.

[0031] For a traditional metal wire grating, the structure is as Figure 3 shown.

[0032] On a dielectric material with a refractive index of n β , a gold wire is arranged (in the embodiment of the present invention, metal rings are inlaid on the surface of the Al2O3 film). The grating constant or the distance between the gold wires is d. Plane-polarized light is incident on the grating after passing through a medium with a refractive index of n α , and the incident direction forms an angle α with the vertical plane of the grating.

[0033] If the wavelength involved in the model is short enough compared to the grating constant, there may be one or more diffraction orders, as Figure 4 shown.

[0034] The two transmission paths of light when it is incident on two adjacent units of the grating have a spacing exactly equal to one grating constant. The criterion for constructive interference is whether the optical path length difference along the two paths is an integer multiple of the vacuum wavelength, that is:

[0035] mλ0 = d(n β sinβ m -na sinα)

[0036] where m = 0, ±1, ±2, ..., λ0 is the vacuum wavelength, and β m is the m-th order transmission diffraction angle of the light beam. When m = 0, it is refraction, as described by Snell's law:

[0037]

[0038] Since the sine function can only vary between -1 and 1, there are only higher diffraction orders that satisfy the following condition:

[0039]

[0040] The operating instructions of this model only cover first-order diffraction and are therefore only valid under the following conditions:

[0041] 2λ0 > d(n a |sinα| + n β )

[0042] Note that for special cases such as normal incidence and critical incidence, the right side of the inequality is calculated as dn β and d(n α + n β ), respectively.

[0043] The corresponding reflected light path Figure 5 is shown. For constructive interference, the following expression is obtained:

[0044] mλ0 = dn a (sinα m - sinα)

[0045] where α m is the reflection angle of the light beam with diffraction order m. Setting m = 0 in the equation gives:

[0046] sinα0 = sinα

[0047] That is, specular reflection. The condition for the absence of second-order or higher-order reflected diffraction light beams is:

[0048] 2λ0 > dn a (1 + |sinα|)

[0049] In the embodiment of the present invention, the condition for the absence of second-order or higher-order reflected diffraction light beams on the inner wall of the light-shielding cylinder is:

[0050] 2λ0 > dn a (1 + |sinα|),

[0051] Among them, λ0 is the vacuum wavelength, d is the spacing between the metal rings, and the incident light passes through a medium with a refractive index of n α and then enters the inner wall of the light-shielding cylinder at an incident angle of α.

[0052] To verify the effectiveness of the structure of the embodiment of the present invention, a situation was assumed for verification, and the assumed conditions are as follows:

[0053] 1) The wavelength of the incident light is 4200 nm;

[0054] 2) Calculate without considering the effect of the blackening material on the inner wall of the light-shielding cylinder. Since the actual structure includes the blackening material, the actual reflectivity of the inner wall of the light-shielding cylinder is lower than that obtained from this verification calculation;

[0055] 3) Calculate the reflectivities of the TE wave (Transverse Electric Wave) and the TM wave (Transverse Magnetic Wave) of the incident light with a wavelength of 4200 nm respectively.

[0056] Figure 6 and Figure 7 where R0 is the 0th-order reflectivity of the reflected light, R1 is the 1st-order reflectivity of the diffracted light, R -1 is the -1st-order reflectivity of the diffracted light, and R tot is the total reflectivity. From Figure 6 and Figure 7 it can be seen that when the incident light is infrared light with a wavelength of 4200 nm and the incident angle is less than 70°, the total reflectivity of the TE wave is not greater than 40%; the total reflectivity of the TM wave is not greater than 15%; when combined with the blackening material, the reflectivity will be further reduced.

[0057] The anti-reflection light-shielding cylinder for a mid-wave infrared detector according to the embodiment of the present invention has the following beneficial effects:

[0058] Effectively reduce the reflectivity: By adopting a special structural design on the inner wall of the light-shielding cylinder, that is, setting an Al2O3 thin film with a thickness of 10 μm on the blackening material, and inlaying bracelet-shaped or donut-shaped gold metal rings with a diameter of 0.5 μm on the surface of the thin film, and arranging them in a periodic manner up and down, with an upper and lower spacing of 5 μm, the reflectivity of the 4200 nm infrared light on the inner wall of the light-shielding cylinder can be effectively reduced. When the incident angle is less than 70°, the total reflectivity of the TE wave is not greater than 40%, the total reflectivity of the TM wave is not greater than 15%, and when combined with the blackening material, the reflectivity will be further reduced, thereby reducing the reflection loss of the effective light on the inner wall of the light-shielding cylinder, improving the light efficiency of the mid-wave infrared detector, avoiding the formation of dark areas in low-light environments, and helping to improve the overall performance and imaging quality of the detector.

[0059] Avoiding the problem of metal fatigue cracks: This design does not rely on the traditional sharp-edge design of the light-shielding ring, thus effectively avoiding the problem that the sharp-edge light-shielding ring is prone to generate metal fatigue cracks under the working conditions of thermal expansion and contraction. It improves the reliability and service life of the light-shielding cylinder, ensures the stable operation of the detector in different temperature environments, and reduces the maintenance cost and failure risk of the equipment.

[0060] Having a wide range of application prospects: The present invention is applicable not only to mid-wave infrared detectors with a central wavelength of 4200 nm, but also to the design of anti-reflection light-shielding cylinders for light in other bands. It has a certain degree of generality and flexibility, can provide new ideas and methods for the optical system design in related fields, promote the development of infrared detection technology, and meet the needs of high-performance light-shielding cylinders in different application scenarios.

[0061] Only some exemplary embodiments of the present invention have been described above by way of illustration. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An anti-reflection light-shielding cylinder for a mid-wave infrared detector, characterized in that, The inner wall of the light-shielding cylinder is a multi-layer structure. The bottom layer of the multi-layer structure is a blackened material, and an Al2O3 thin film is coated on the bottom layer as a dielectric material. Bracelet-shaped or donut-shaped metal rings are inlaid on the surface of the Al2O3 thin film, and the metal rings are arranged periodically up and down on the inner wall of the light-shielding cylinder. The center of the cross-section of the metal ring is located at the surface of the Al2O3 thin film.

2. The anti-reflection light-shielding cylinder for the mid-wave infrared detector according to claim 1, characterized in that, The thickness of the Al2O3 thin film is 10 μm.

3. The anti-reflection light-shielding cylinder for a mid-wave infrared detector according to claim 2, characterized in that, The material of the metal ring is gold.

4. The anti-reflection light-shielding cylinder for a mid-wave infrared detector according to any one of claims 1-3, characterized in that, When the incident light is infrared light with a wavelength of 4200 nm, the diameter of the metal ring is 0.5 μm, and the distance between adjacent metal rings above and below is 5 μm.

5. The anti-reflection light-shielding cylinder for a mid-wave infrared detector according to claim 4, characterized in that, When the incident angle of the incident light is less than 70°, the total reflectivity of the TE wave is not greater than 40%, and the total reflectivity of the TM wave is not greater than 15%.

6. The anti-reflection and light-shielding barrel for the mid-wave infrared detector according to claims 1-3, characterized in that, The condition for the absence of second-order or higher-order reflected diffraction beams on the inner wall of the light-shielding cylinder is: 2λ0 > dn a (1 + |sinα|), where λ0 is the vacuum wavelength, d is the spacing between the metal rings, and the incident light passes through a medium with a refractive index of n α and then enters the inner wall of the light-shielding cylinder at an incident angle of α.

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