Micro-nano infrared polarizer and infrared detector

Abstract

The application discloses a micro-nano infrared polarizer and an infrared detector, and adopts a differential design of each orientation polarization unit, wherein the micro-nano infrared polarizer is composed of periodically arranged composite polarization pixels, and each composite polarization pixel contains polarization units with two or more different polarization orientations. According to application requirements, the size of a region for polarization selection of each polarization unit and / or the material, geometric shape and characteristic size of a micro-nano polarization structure in the polarization selection region are differentially designed to compensate for extinction ratio dispersion caused by polarization orientation-related structural differences and process errors. The application realizes performance balance of each orientation polarization unit in the micro-nano infrared polarizer, effectively reduces a non-uniformity source of polarization imaging, alleviates difficulty in non-uniformity correction in later image processing, and improves polarization imaging quality.

Description

Technical Field

[0001] This invention belongs to the field of infrared detection, specifically relating to a micro / nano infrared polarizer and infrared detector with differentially designed polarization units of various orientations. Technical Background

[0002] Traditional thermal imagers acquire two-dimensional spatial temperature distribution by measuring the intensity of infrared radiation, using temperature differences to distinguish targets from backgrounds. However, this approach is limited by complex backgrounds such as smoke, fire, dust, clouds, and tree shade, as well as by artificial interference such as infrared stealth and countermeasures. The key to solving this problem lies in overcoming the limitations of irradiance intensity detection, which only acquires optical information from a single dimension. This involves enhancing the detection and fusion capabilities of multi-dimensional optical information, more accurately, realistically, and effectively reflecting the intrinsic properties of objects, highlighting the differences between targets and backgrounds, and thus improving the infrared system's comprehensive information processing and identification capabilities.

[0003] As one of the fundamental properties of light, polarization provides information distinct from radiation intensity. Compared to traditional infrared detectors, which can only measure the radiation intensity of objects and struggle to identify weak targets in complex environments, infrared polarization detectors add polarization information to the two-dimensional irradiance information. This effectively distinguishes targets with similar radiation intensities but different polarization characteristics from the background, highlighting the target's outline and details. This enables effective detection of stealth, camouflage, and weak targets, significantly improving the system's anti-interference capabilities. Therefore, infrared polarization detection, as an emerging detection technology that integrates multi-dimensional optical information, has broad application prospects.

[0004] In the development of polarization detection technology, advancements in polarization modulation methods are closely related to improvements in the overall performance of components and systems. Early external time-division rotating polarizers suffered from poor real-time performance, making it difficult to track moving targets. Subsequent amplitude-division and aperture-division polarization detection technologies, while achieving real-time performance, suffered from complex optical paths and large size. With the development of micro-nano technology, focal plane-type micro-nano infrared polarizers are attracting increasing attention. This element utilizes micro-nano polarization selection structures with different polarization orientations to form composite polarization units. The periodic arrangement of these composite polarization units creates a polarization unit array with the same number of polarization units as the target detector chip. This approach offers advantages such as lightweight design, high integration, and real-time detection, aligning perfectly with the current trend of infrared system integration and miniaturization.

[0005] Existing micro / nano infrared polarizers, aside from meeting the polarization orientation differences necessary for polarization information analysis, generally maintain consistency in terms of micro / nano polarization structure distribution area and polarization structure parameter settings. However, differences in polarization orientation can affect the extinction ratio of polarization units. Taking common subwavelength metal wire gratings as an example, when oblique wire gratings are arranged within a square pixel area, their extinction ratio is lower than that of horizontal and vertical wire gratings with the same structural parameters (i.e., period, duty cycle, thickness) and the same wire grating distribution area, due to the varying lengths of the wire gratings. Several research institutions at home and abroad have reported focal plane-type micro / nano infrared polarizers based on four-oriented wire gratings of 0°, 45°, 90°, and 135°. Test results show that the extinction ratios of 45° and 135° wire gratings are lower than those of 0° and 90°. For image processing in infrared polarization imaging, non-uniformity correction has always been a challenging problem. This is because non-uniformity in polarization imaging originates from numerous sources, including radiation non-uniformity caused by the optical system, non-uniformity in the response performance of the infrared detector, and extinction ratio non-uniformity introduced by structural differences in polarization orientations and manufacturing errors in micro / nano infrared polarizers. Existing designs employ the same polarization structure distribution area and parameters for polarization units with different orientations, which cannot compensate for differences in extinction ratios. This inherent source of polarization non-uniformity exists at the design level, significantly increasing the difficulty of subsequent correction and affecting the quality of polarization imaging. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a new design method for micro-nano infrared polarizers and a micro-nano infrared polarizer. Its main features are: adjusting the polarization structure distribution area and design parameters of polarization units with different orientations to compensate for the extinction ratio differences caused by their polarization orientation, effectively reducing the sources of polarization non-uniformity, and providing good hardware conditions for improving polarization imaging quality.

[0007] The purpose of this invention is to provide a micro / nano infrared polarizer with differentiated polarization orientation units, which can meet the following technical requirements:

[0008] 1. It can effectively control the extinction ratio of each polarization unit.

[0009] 2. Under the premise of meeting the extinction ratio requirements, the extinction ratio of each orientation polarization unit is basically the same.

[0010] This invention provides a micro / nano infrared polarizer comprising at least two polarization units with different polarization orientations. Each polarization unit is square, with consistent size and center-to-center spacing. Each polarization unit consists of a central polarization selection region and an outer transition region. The central polarization selection region is used to achieve polarization selection, and its overall orientation determines the polarization orientation of the polarization unit. The outer transition region does not exhibit polarization selectivity. The polarization units with at least two different polarization orientations are arranged in an "M×N" mosaic pattern to form a composite polarization pixel, where M and N are the row and column numbers of the composite polarization unit, respectively, and M and N are integers ranging from 2 to 4. The composite polarization pixels are periodically arranged to form a micro / nano polarization unit array. Blank areas exist outside the micro / nano polarization unit array.

[0011] Furthermore, the polarization selection function of the central polarization selection region of the polarization unit is realized by the micro-nano polarization structure within the central polarization selection region. The micro-nano polarization structure includes a periodically arranged wire grid array, a metasurface structure, or a structure formed from a two-dimensional material with polarization selectivity.

[0012] Furthermore, the transition region surrounding the polarization unit is entirely used to block or transmit incident light, or a portion of the region is used to block and a portion of the region is used to transmit light.

[0013] Furthermore, the factors affecting the polarization selectivity of the polarization unit include:

[0014] The higher the area ratio of the central polarization-selective region to the peripheral blank region, the better the polarization selectivity.

[0015] The higher the extinction coefficient of the material in the micro / nano polarization structure within the central polarization selection region, the better the polarization selectivity.

[0016] The more pronounced the asymmetry of the geometry of the micro / nano polarization structure within the central polarization selection region, the better the polarization selectivity.

[0017] The feature size of the micro / nano polarization structure within the central polarization selection region is such that the finer the feature size, the better the polarization selectivity.

[0018] Furthermore, in the composite polarization pixel, the polarization units with different polarization orientations have the following design differences:

[0019] The polarization unit has at least two different polarization orientations, and the area ratio of its central polarization selection region to its peripheral transition region is different.

[0020] And / or, at least two polarization units with different polarization orientations, located in the micro / nano polarization structure within the central polarization selection region, have differences in material, geometry, and feature size;

[0021] And / or, at least two polarization units with different polarization orientations, wherein the peripheral transition regions of the polarization units block and / or transmit incident light in different ways.

[0022] Furthermore, in the composite polarization pixel, the polarization orientation of each polarization unit is selected (e.g., based on four orientations: 0°, 45°, 90°, and 135°) to satisfy:

[0023] By modulating the polarization of the incident light, the light intensity variable required to invert the linear Stokes vector can be obtained simultaneously, and the linear polarization information can be calculated.

[0024] Alternatively, by modulating the polarization of the incident light, the intensity variables required to invert the full Stokes vector can be obtained simultaneously, and the linear polarization information and circular polarization information can be calculated.

[0025] Furthermore, alignment marks are left in the blank areas outside the micro / nano polarization unit array for alignment between the micro / nano infrared polarizer and the infrared detector chip to be integrated therewith.

[0026] Furthermore, the coupling position between the micro / nano infrared polarizer and the infrared detector chip integrated therewith is located in a blank area outside the micro / nano polarization unit array.

[0027] Furthermore, the micro / nano infrared polarizer is fabricated on a discrete substrate or on the surface of an infrared detector chip that will be integrated with the micro / nano infrared polarizer.

[0028] Furthermore, the periodically arranged wire grid array has a period of 700 nm, a linewidth of 350 nm, and a duty cycle of 50%.

[0029] An infrared detector, characterized in that the infrared detector comprises a micro-nano infrared polarizer as described in any one of claims 1-10.

[0030] As can be seen from the technical solution and embodiments, the beneficial effects of the present invention are:

[0031] 1. This invention innovatively adjusts multiple degrees of freedom, such as polarization selection region, peripheral transition region, and micro / nano polarization structure, for polarization units with different orientations. It breaks through the technical limitations of the traditional micro / nano infrared polarizer with undifferentiated design of polarization units of different orientations, makes up for the extinction ratio dispersion caused by polarization orientation, and achieves performance balance of polarization units of different orientations.

[0032] 2. While ensuring that the extinction ratio of each polarization unit meets the application requirements, compared with the original technical solution, the source of polarization non-uniformity is effectively reduced at the hardware level, providing a more solid physical support for reducing the difficulty of back-end correction and improving polarization imaging quality. Attached Figure Description

[0033] Figure 1 The polarizer A provided by the present invention has a different central polarization selection region and an outer transition region between the diagonal polarization unit and the horizontal and vertical polarization units, and the polarization structure parameters of each orientation polarization unit are consistent.

[0034] Figure 2 for Figure 1 Enlarged view of the composite polarization unit of polarizer A shown;

[0035] Figure 3 For use and Figure 2 The composite polarization unit structures for comparison have the same size of central polarization selection region and peripheral transition region in each orientation polarization unit, and the polarization structure parameters of each orientation polarization unit are the same.

[0036] Figure 4 (a) and 4(b) are respectively Figure 2 and Figure 3 The extinction ratio of each oriented polarization unit in the composite polarization unit structure;

[0037] Figure 5 The polarizer B provided by the present invention has a different central polarization selection region and an outer transition region between the diagonal polarization unit and the horizontal and vertical polarization units, and the polarization structure parameters between the diagonal polarization unit and the horizontal and vertical polarization units are different.

[0038] Figure 6 for Figure 5 Enlarged view of the composite polarization unit of micropolarizer B shown;

[0039] Figure 7 For use and Figure 6 The composite polarization unit structure for comparison has the same size of central polarization selection region and peripheral transition region in each oriented polarization unit, and the polarization structure parameters of each oriented polarization unit are the same.

[0040] Figure 8 (a) and 8(b) are respectively Figure 6 and Figure 7 The extinction ratio of each orientation polarization unit in the composite polarization unit structure.

[0041] In the picture:

[0042] 1-Polarizer A; 21-90° polarization unit in polarizer A; 22-135° polarization unit in polarizer A; 23-0° polarization unit in polarizer A; 24-45° polarization unit in polarizer A; 2-Combined polarization unit in polarizer A; 3-Array area of ​​polarizer A; 4-Blank area of ​​polarizer A; 5-Alignment mark of polarizer A; 6-Polarization structure distribution area of ​​each polarization unit in polarizer A; 7-Outer transition area of ​​each polarization unit in polarizer A; 8- Polarizer B; 91 - 90° polarization unit in polarizer B; 92 - 135° polarization unit in polarizer B; 93 - 0° polarization unit in polarizer B; 94 - 45° polarization unit in polarizer B; 9 - Composite polarization unit in polarizer B; 10 - Array area of ​​polarizer B; 11 - Blank area of ​​polarizer B; 12 - Alignment mark of polarizer B; 13 - Polarization structure distribution area of ​​each polarization unit in polarizer B; 14 - Peripheral transition area of ​​each polarization unit in polarizer B. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0044] Example 1

[0045] Please refer to the instructions. Figure 1 In this diagram, 1 represents polarizer A, and 2 represents a composite polarization unit 2 within polarizer A. The composite polarization unit 2 is composed of polarization units 21, 22, 23, and 24 arranged in a 2×2 topology, with polarization orientations of 90°, 135°, 0°, and 45°, respectively. In this embodiment, the polarization unit size is 25μm×25μm, and "M×N" composite polarization units 2 are arranged periodically to form array region 3. Clearly, array region 3 contains a total of "2M×2N" polarization units, where the values ​​of M and N depend on the size of the detector chip array coupled to polarizer A. For example, if the detector chip contains 640×512 pixels, then M is 320 and N is 256. Alignment marks 5 are provided in the blank area 4 outside array region 3. These marks are in an equal sign structure and symmetrical about the central axis of array region 3.

[0046] Figure 2The magnified effect of the composite polarization unit 2 in polarizer A is shown. 6 represents the polarization structure distribution region in the center of polarization units 21, 22, 23, and 24, which plays a polarization selection role. 7 represents the transition region surrounding polarization units 21, 22, 23, and 24, both used to block incident light. In this embodiment, a wire grating structure is used. All wire grating materials for all polarization units are aluminum, with parameters designed as follows: period 700 nm, linewidth 350 nm, duty cycle 50%, and thickness 400 nm. Specifically, the polarization structure distribution region of the 45° and 135° polarization units is 23 μm × 23 μm, with an outer region width of 2 μm; the polarization structure distribution region of the 0° and 90° polarization units is 21 μm × 21 μm, with an outer region width of 3.5 μm.

[0047] Figure 3 A magnified view of the composite polarization unit of a polarizer designed using traditional methods is presented. The array size, pixel size, polarization orientation arrangement order, and pixel size of this micro / nano infrared polarizer are the same as those of the traditional polarizer design. Figure 1 In each polarization unit, the central polarization structure distribution region adopts a wire grating structure, and the wire grating material and parameter design are the same as those in the polarization unit. Figure 2 The difference is that... Figure 3 In the model, the polarization structure distribution area of ​​all polarization units is 22μm×22μm; the width of the outer region is 3μm, which is used to block the incident light.

[0048] Figure 4 The polarization performance of micro / nano infrared polarizers under two different design approaches was compared:

[0049] Figure 4 (a) shows the extinction ratios of each oriented polarization unit in the 3.7–5 μm band after adjusting the polarization structure distribution region and the peripheral transition region. The extinction ratios of the 0° and 90° polarization units are in the range of 10.58–11.93, while those of the 45° and 135° polarization units are in the range of 10.41–12.93. It can be seen that the extinction ratios of the horizontal and vertical line gratings are very close to those of the diagonal line gratings.

[0050] Figure 4 (b) shows the extinction ratios of various polarization units in the 3.7–5 μm band when the polarization structure distribution region and the peripheral transition region are consistent, and the polarization structure parameters are consistent. The extinction ratios of the 0° and 90° polarization units range from 12.49 to 14.04, while those of the 45° and 135° polarization units range from 9.08 to 12.36. It can be seen that there is a significant difference in the extinction ratios between the transverse and longitudinal line gratings and the diagonal line gratings, with the difference at each wavelength generally between 2 and 3.

[0051] Example 2

[0052] Please refer to Figure 5In this diagram, 8 represents polarizer B, and 9 represents a composite polarization unit within polarizer B. The composite polarization unit 9 is composed of polarization units 91, 92, 93, and 94 arranged in a 2×2 topology, with polarization orientations of 90°, 135°, 0°, and 45°, respectively. In this embodiment, the polarization unit size is 25μm×25μm, and the composite polarization units 9 are arranged periodically to form an array region 10. Alignment marks 12, in a cross-shaped structure, are provided in the blank area 11 outside the array region 10, symmetrical about the central axis of the array region 9.

[0053] Figure 6 The magnification effect of the composite polarization unit 9 is shown. Unit 13 is the central polarization structure distribution region of polarization units 91, 92, 93, and 94, which plays a polarization selection role; unit 14 is the transition region surrounding polarization units 21, 22, 23, and 24, all used to block incident light. In this embodiment, a wire grating structure is used, with the grating material being aluminum and a thickness of 400 nm. Specifically, the polarization structure distribution region of the 45° and 135° polarization units is 23 μm × 23 μm in size, with an outer transition region width of 2 μm, a grating period of 600 nm, a linewidth of 300 nm, and a duty cycle of 50%; the polarization structure distribution region of the 0° and 90° polarization units is 21 μm × 21 μm in size, with an outer transition region width of 4 μm, a grating period of 750 nm, a linewidth of 375 nm, and a duty cycle of 50%.

[0054] Figure 7 A magnified view of the composite polarization unit of a polarizer designed using traditional methods is presented. The array size, pixel size, polarization orientation arrangement order, and pixel size of this micro / nano infrared polarizer are the same as those of the traditional polarizer design. Figure 6 In each polarization unit, the central polarization structure distribution region employs a wire grating structure, with the wire grating material being aluminum. The difference is... Figure 7 In the design, the polarization structure distribution area of ​​all polarization units is 21μm×21μm in size; the width of the outer region is 4μm, which is used to block the incident light; the grating parameters of each orientation polarization unit are consistent: period 700nm, linewidth 350nm, duty cycle 50%, and thickness 400nm.

[0055] Figure 8 The polarization performance of micro / nano infrared polarizers under two different design approaches was compared:

[0056] like Figure 8 As shown in (a), after adjusting the polarization structure distribution area, the peripheral transition area, and the wire grid design parameters, the extinction ratios of the 0° and 90° polarization units are in the range of 11.70–12.70, and the extinction ratios of the 45° and 135° polarization units are in the range of 11.01–13.76. It can be seen that the extinction ratios of the horizontal and vertical wire grids are very close to those of the diagonal wire grids.

[0057] Figure 8 (b) shows the extinction ratios of each oriented polarization unit when the polarization structure distribution region, peripheral transition region, and grating design parameters are all consistent. The extinction ratios of the 0° and 90° polarization units range from 12.78 to 15.78, while those of the 45° and 135° polarization units range from 9.82 to 13.66. It is evident that there is a significant difference in extinction ratios between the transverse and longitudinal gratings and the diagonal gratings, with the largest difference exceeding 3 at each wavelength.

[0058] It should be noted that in Examples 1 and 2, although the extinction ratio of the transverse and longitudinal gratings is reduced, it still remains above the required value (>10) for accurate polarization information calculation. Therefore, this invention, by combining methods such as increasing the distribution density of the diagonal gratings and appropriately increasing or decreasing the distribution area size of the diagonal and transverse gratings, enables the previously generally poor polarization performance of the oblique polarization unit to achieve an extinction ratio comparable to that of the transverse and longitudinal polarization units. While meeting application requirements, this effectively improves the consistency of polarization performance among the various orientation polarization units and suppresses the sources of non-uniformity in the polarization imaging process.

[0059] Furthermore, the specific embodiments described above are intended to provide a more detailed explanation of the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A micro / nano infrared polarizer, characterized in that: A polarization unit comprising at least two different polarization orientations, wherein the polarization unit is square and has the same size and center-to-center spacing, each polarization unit consists of a central polarization selection region and an outer transition region, wherein the central polarization selection region is used to realize the polarization selection function and its overall orientation determines the polarization orientation of the polarization unit, and the outer transition region has no polarization selectivity. The polarization units with at least two different polarization orientations are arranged in an "M×N" mosaic pattern to form a composite polarization pixel, where M and N are the number of rows and columns of the composite polarization unit, respectively, and M and N are integers from 2 to 4; the composite polarization pixels are arranged periodically to form a micro-nano polarization unit array. There is a blank area outside the micro / nano polarization unit array; In the composite polarization pixel, the polarization units with different polarization orientations have the following design differences: The polarization unit has at least two different polarization orientations, and the area ratio of its central polarization selection region to its peripheral transition region is different. And / or, at least two polarization units with different polarization orientations, located in the micro / nano polarization structure within the central polarization selection region, have differences in material, geometry, and feature size; And / or, at least two polarization units with different polarization orientations, wherein the peripheral transition regions of the polarization units block and / or transmit incident light in different ways; The blank area outside the micro-nano polarization unit array is left with alignment marks for alignment between the micro-nano infrared polarizer and the infrared detector chip to be integrated therewith. The coupling position between the micro / nano infrared polarizer and the integrated infrared detector chip is located in the blank area outside the micro / nano polarization unit array; The micro-nano infrared polarizer can effectively control the extinction ratio of each orientation polarization unit, and achieve a basically consistent extinction ratio for each orientation polarization unit while meeting the extinction ratio requirements.

2. The micro / nano infrared polarizer according to claim 1, characterized in that, The polarization selection function of the central polarization selection region of the polarization unit is realized by the micro-nano polarization structure within the central polarization selection region. The micro-nano polarization structure includes a periodically arranged wire grid array, a metasurface structure, or a structure formed by a two-dimensional material with polarization selectivity.

3. The micro / nano infrared polarizer according to claim 1, characterized in that, The transition region surrounding the polarization unit is used entirely to block or allow incident light to pass through, or a portion of the region is used to block and a portion of the region is used to allow light to pass through.

4. The micro / nano infrared polarizer according to claim 1, characterized in that, The factors affecting the polarization selectivity of the polarization unit include: The higher the area ratio of the central polarization-selective region to the peripheral blank region, the better the polarization selectivity. The higher the extinction coefficient of the material in the micro / nano polarization structure within the central polarization selection region, the better the polarization selectivity. The more pronounced the asymmetry of the geometry of the micro / nano polarization structure within the central polarization selection region, the better the polarization selectivity. The feature size of the micro / nano polarization structure within the central polarization selection region is such that the finer the feature size, the better the polarization selectivity.

5. The micro / nano infrared polarizer according to claim 1, characterized in that, In the composite polarization pixel, the polarization orientation of each polarization unit satisfies: By modulating the polarization of the incident light, the light intensity variable required to invert the linear Stokes vector can be obtained simultaneously, and the linear polarization information can be calculated. Alternatively, by modulating the polarization of the incident light, the intensity variables required to invert the full Stokes vector can be obtained simultaneously, and the linear polarization information and circular polarization information can be calculated.

6. The micro / nano infrared polarizer according to any one of claims 1-5, characterized in that, The alignment marks are used for alignment between the micro / nano infrared polarizer and the infrared detector chip to be integrated therewith.

7. The micro / nano infrared polarizer according to any one of claims 1-5, characterized in that, The micro / nano infrared polarizer is fabricated on a discrete substrate or on the surface of an infrared detector chip that will be integrated with the micro / nano infrared polarizer.

8. The micro / nano infrared polarizer according to claim 2, characterized in that, The periodically arranged wire grid array has a period of 700 nm, a linewidth of 350 nm, and a duty cycle of 50%.

9. An infrared detector, characterized in that, The infrared detector includes a micro-nano infrared polarizer as described in any one of claims 1-8.

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