Medium / long wave dynamic regulation and control filter for infrared detector

Abstract

The invention provides a medium / long wave dynamic regulation and control filter for an infrared detector. The upper-layer rotatable superstructure unit layer is composed of a lower-layer fixed superstructure unit layer, and the upper-layer rotatable superstructure unit layer is driven by a micro stepping motor to rotate around a central shaft of the silicon nitride ceramic bearing. And multi-band dynamic regulation and control: through rotation of an upper-layer medium, medium wave and long wave dynamic detection of different bands can be realized. Through the design of the resonant ring units and the optimization of geometric parameters, the broadband high transmission of a target wave band and the high suppression of a non-target wave band are realized, the interference of the non-target wave band is filtered out, and the signal-to-noise ratio is improved. According to the invention, a traditional multi-stage optical filter stack or light splitting assembly is abandoned, and multiband filtering and switching are realized through a single metamaterial device. The light source is bonded to a staring type imaging detector (such as a HgCdTe focal plane array) through epoxy resin, additional light path adjustment is not needed, and integration complexity and cost are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared detection. Background Art

[0002] Infrared detection technology, which captures infrared light signals radiated or reflected by target objects, enables non-contact sensing of temperature distribution, material composition, and motion state, and has become a key enabling technology in the field of modern optoelectronic sensing. Based on the atmospheric transmission window and the characteristics of the detection target, the infrared spectrum is typically divided into three typical bands: shortwave infrared (SWIR, 1-3μm), mediumwave infrared (MWIR, 3-5μm), and longwave infrared (LWIR, 8-14μm). The mediumwave infrared and longwave infrared bands, due to their unique physical properties and application advantages, have become core bands for complex environment detection. 1) Medium-wave infrared (MWIR): This band covers the peak radiation wavelengths of most high-temperature targets (such as engine exhausts and industrial heat sources) and is highly compatible with the characteristic absorption spectra of gas molecules (such as CO2 and CH4), making it irreplaceable in industrial process monitoring, gas leak detection, and high-temperature target identification. 2) Long-wave infrared (LWIR): The radiation peak of objects at normal temperature (20-30°C) is in this band, and it is less affected by atmospheric scattering. It can penetrate environmental interference such as smoke and dust, and is widely used in security monitoring, night imaging, human body temperature measurement and low-contrast scene detection. As infrared detection systems develop towards multi-functional integration and scene adaptation, single fixed-band detectors face severe challenges in multiple scene compatibility and dynamic environment adaptability. Taking mercury cadmium telluride infrared detectors as an example, although mercury cadmium telluride materials can produce photoelectric responses to a wide spectral range of short, medium and long-wave infrared, they cannot detect a specific characteristic band. Therefore, the development of an infrared filtering technology that has both wide spectral coverage and dynamic adjustment of medium / long wave bands is an inevitable requirement for promoting the development of the next generation of intelligent infrared detection systems.

[0003] Introducing an infrared optical filtering structure into an infrared detector chip is a common method for filtering out interference from non-target bands and improving the signal-to-noise ratio. However, existing filtering structures and technologies often only filter static modulation of a single band or multiple bands. For example, the mid-infrared static multispectral imaging filter (CN202111207546.0) disclosed by Jiang Hongyan et al. proposes a mid-infrared (3.5-5μm) spectral imaging filter, in which a bandpass denoising film and a pixel modulation film structure are integrated on both sides of the base. The pixel modulation film adopts a 2×2 mosaic filter unit group, and covers different mid-wave infrared spectral bands (such as 3.5-4.2μm, 4.4-5μm and 3.5-5μm) through the first, second and third interference cutoff films. Staring multispectral imaging is achieved through multi-band static filtering, improving target recognition accuracy and anti-interference ability. However, the spectral transmission range of its filtering unit is pre-solidified by the film structure, and the central wavelength or bandwidth cannot be dynamically adjusted according to detection requirements. It only supports a limited number of fixed band combinations and is difficult to meet multi-scenario applications across the mid- and long-wave infrared.

[0004] In addition, Yin Baoju et al. disclosed a filter for near-infrared dual-band imaging and its design method (CN202111662138.4). This patent designs a near-infrared dual-band (800-875nm transmission, 950-1010nm reflection) filter, which achieves high transmission (≥90%) and high reflection (≥90%) in a specific near-infrared band through a wedge-angle prism and a multilayer film structure (such as a combination of Ti3O5 / SiO2 / MgF2). This solves the problem of excessive energy difference between the transmission and reflection bands in near-infrared imaging and improves the balance of dual-band imaging. However, the filtering range of this structure is narrow and it relies on fixed film layer parameters to achieve dual-band separation, lacking dynamic adjustment capabilities.

[0005] 1) Insufficient band fixation and coverage: Existing solutions are mostly single or limited fixed band designs (such as medium wave or near infrared), lack the wide spectrum coverage capability of medium and long wave infrared, and cannot achieve dynamic switching across bands.

[0006] 2) Limitations of static spectroscopic mechanisms: Relying on spatial spectroscopic techniques (such as mosaic filter units) or fixed film parameters results in poor real-time performance and complex optical paths, making it difficult to meet the rapid response requirements in dynamic environments. Summary of the Invention

[0007] This application addresses the technical bottleneck of dynamic filtering for mid- and long-wave infrared and proposes a mid- and long-wave dynamic control filter solution for infrared detectors based on variable structure metamaterials.

[0008] 1. A medium- and long-wave dynamic control filter for infrared detectors, characterized in that it includes: an upper rotatable superstructure unit layer and a lower fixed superstructure unit layer, the upper rotatable superstructure unit layer is driven by a micro stepping motor and rotates around the central axis of a silicon nitride ceramic bearing, and the interlayer gap is ≤100nm.

[0009] 2. The upper rotatable superstructure unit layer and the lower fixed superstructure unit layer are both embedded with periodically arranged resonant rings, which are open ring structures;

[0010] 3. The upper rotatable superstructure unit layer can change the relative position and coupling mode of the upper and lower resonant rings by rotation to dynamically switch the filtering bands of the medium-wave infrared (3-5μm) and the long-wave infrared (8-14μm).

[0011] 4. The line width of the resonant ring is 0.3-0.7 μm, the opening angle is 3-180°, the unit size is 2 μm×2 μm-5 μm×5 μm, the period spacing is 1-4 μm, and the resonant unit size in the upper and lower layers is the same.

[0012] 5. The materials of the upper rotatable superstructure unit layer and the lower fixed superstructure unit layer are zinc sulfide (ZnS), zinc selenide (ZnSe) or germanium (Ge), and the thickness of the upper and lower superstructure units is the same and is 2 to 15 μm.

[0013] 6. Furthermore, the material of the resonant ring unit is copper (Cu), gold (Au), or aluminum (Al), with a thickness of 2 to 50 nm, and the resonant units in the upper and lower layers are made of the same material.

[0014] 7. Furthermore, the rotation angle of the upper rotatable superstructure unit layer can be 90°, 180° or 270°, which is used to switch between medium-wave filtering and long-wave filtering states.

[0015] 8. Furthermore, the filter is bonded to the surface of the focal plane array using epoxy resin, and micron-scale alignment marks are made using a photolithography process with an accuracy of ≤1μm.

[0016] 9. The method for preparing the medium- and long-wavelength dynamic control filter is characterized by comprising the following steps:

[0017] (1) forming periodically arranged resonant ring units on a medium through a photolithography process;

[0018] (2) depositing a metal film on the upper surface of the medium and forming an open ring structure through an etching process;

[0019] (3) Assemble the upper dielectric layer and the lower dielectric layer through a mechanical rotation mechanism to ensure that the rotation axes are aligned.

[0020] The key points are as follows:

[0021] (1) Double-layer variable structure metamaterial design

[0022] The filter consists of an upper rotatable superstructure unit layer and a lower fixed superstructure unit layer. Periodically arranged resonant ring units (such as open rings, cross rings or nested ring structures) are embedded in both layers of dielectrics. The upper rotatable superstructure unit layer is driven by a micro-stepping motor and can rotate around the central axis by 90°, 180° and other angles, further changing the relative position and coupling mode of the upper and lower resonant rings. Figure 1 As shown:

[0023] (2) Dynamic control mechanism

[0024] In the initial state, the upper and lower resonant rings form an equivalent LC resonant circuit through electromagnetic coupling. Its resonant frequency f0 is determined by the equivalent inductance L and equivalent capacitance C of the resonant ring, satisfying:

[0025]

[0026] Among them: the equivalent capacitance C is mainly composed of the resonant ring opening gap d and the dielectric constant ε of the dielectric material r Decide:

[0027]

[0028] Where A gap is the area of ​​the opening, and ε0 is the dielectric constant of vacuum.

[0029] The equivalent inductance L is related to the geometric dimensions of the resonant ring (line width w and perimeter P) and the skin effect of the metal material:

[0030]

[0031] μ0 is the vacuum permeability, μ r is the relative magnetic permeability of the metal (usually μ r ≈1).

[0032] When the upper dielectric rotates by an angle θ, the relative positions of the upper and lower resonant rings change, resulting in a coupling capacitance C couple And dynamic adjustment of mutual inductance M:

[0033]

[0034] Among them, A overloop (θ) is the total area of ​​the resonant ring after rotation, d(θ) is the opening gap of the resonant ring after rotation, D(θ) is the ring spacing after rotation, and r is the radius of the resonant ring. The total inductance L′ and total capacitance C′ are updated as follows:

[0035]

[0036] The resonant frequency f′ after rotation is:

[0037]

[0038] By adjusting θ, the resonant frequency of the device can be dynamically switched between multiple bands such as shortwave, medium wavelength, etc.

[0039] (3) Multi-parameter collaborative design of vibration ring units

[0040] The geometric parameters of the resonant ring need to be optimized based on the electromagnetic characteristics of the target medium-wave (3-5μm) and long-wave (8-14μm) bands. The specific design criteria are as follows:

[0041] The opening angle α affects the equivalent capacitance C and must satisfy the following requirements:

[0042]

[0043] Among them, λ target is the center wavelength of the target band, n eff is the refractive index of the medium, and r is the radius of the resonant ring.

[0044] The line width needs to suppress surface plasma loss and must meet the following requirements:

[0045]

[0046] Among them, Re(n metal ) is the real refractive index of the metal material

[0047] To avoid high-order diffraction and ensure strong coupling, the periodic spacing a must satisfy:

[0048]

[0049] λ min is the shortest wavelength in the target band.

[0050] (4) Material selection

[0051] The dielectric layer uses low-loss, wide-spectrum compatible materials (such as germanium or zinc selenide), covering the medium and long-wave infrared range of 3 to 14 μm; the resonant ring is composed of highly conductive metals (such as gold, aluminum) or infrared transparent conductive oxides (such as ITO, AZO) to balance the resonance efficiency and infrared transmittance.

[0052] (5) Single-device integrated spectral modulation

[0053] A single metamaterial device can achieve multi-band filtering, dynamic switching and background noise suppression without cascade filters or spectrometers; it is compatible with staring imaging detectors (such as cooled HgCdTe focal plane arrays) and can be bonded with epoxy resin to form a compact spectral imaging system, such as Figure 2 shown.

[0054] The medium- and long-wavelength dynamic control filter based on variable structure metamaterials proposed in this application is expected to significantly improve the performance and adaptability of infrared detection systems through innovative structural design and dynamic control mechanism. The specific technical advantages are as follows:

[0055] 1. Dynamic switching capability across bands

[0056] Broad spectrum coverage: Supports dynamic switching between medium-wave (3-5μm) and long-wave (8-14μm) infrared bands, covering multi-scenario detection requirements that traditional single-band filters cannot achieve.

[0057] Multi-band dynamic control: By rotating the upper medium, medium-wave and long-wave dynamic filtering effects can be achieved, and detection of different bands can be realized according to actual needs.

[0058] 2. Highly selective filtering and anti-interference capabilities

[0059] Precise spectral modulation: Through the design of the resonant ring unit and the optimization of its geometric parameters, it achieves broadband high transmission in the target band and high suppression in the non-target band, filtering out interference in the non-target band and improving the signal-to-noise ratio.

[0060] 3. Single device integrated design

[0061] This eliminates the need for traditional multi-stage filter stacks or spectrometers, achieving multi-band filtering and switching through a single metamaterial device. Epoxy bonding to a staring imaging detector (such as a HgCdTe focal plane array) eliminates the need for additional optical path adjustments, reducing integration complexity and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Schematic diagram of the design principle of double-layer variable structure metamaterial

[0063] Figure 2 Schematic diagram of filter and infrared detector chip integration

[0064] Figure 3 Schematic diagram of the structure of the medium / long wave dynamic control filter for infrared detectors based on square resonant ring in two states

[0065] Figure 4 Transmittance curves of the filter in two states DETAILED DESCRIPTION

[0066] This embodiment designs a medium / long wave dynamic control filter for infrared detectors based on a square resonant ring. The dielectric material is composed of ZnSe, and the resonant ring material is Cu with a thickness of 10nm. The unit size is 4μm×4μm, and the thickness of the upper and lower dielectric layers is 4μm. The resonant ring size is 3.2μm×3.2μm, and the line width is 0.5μm. Its initial state (state 1) structure is as follows Figure 3 a) shows an opening width of 0.5 μm. After rotating the upper layer of the medium by 180°, the structure diagram is shown in Figure 3 b) (State 2). The two states show two different filtering characteristics, and their transmittance curves are as follows Figure 4 a) and Figure 4 b).

[0067] Figure 4 In a), it can be found that when it is in state 1, the transmittance of long wave (8-14 μm) is 0.77, and the transmittance of other bands is lower, which plays a long wave filtering effect. Figure 4 In b), it can be found that when it is in state 2, it has a higher transmittance of 0.70 for medium waves (3-5 μm), and the transmittance of other bands is lower, which is 0.21, playing a medium wave filtering effect.

Claims

1. A medium / long wave dynamic control filter for an infrared detector, characterized by: It consists of an upper rotatable superstructure unit layer and a lower fixed superstructure unit layer. The upper rotatable superstructure unit layer is driven by a micro stepping motor and rotates around the central axis of the silicon nitride ceramic bearing. The gap between the layers is ≤100nm.

2. The filter according to claim 1, wherein: The upper rotatable superstructure unit layer and the lower fixed superstructure unit layer are both embedded with periodically arranged resonant rings, which are open ring structures.

3. The filter according to claim 1, wherein: The upper rotatable superstructure unit layer changes the relative position and coupling mode of the upper and lower resonant rings by rotation, so as to dynamically switch the filtering bands of medium-wave infrared, i.e. 3-5 μm, and long-wave infrared, i.e. 8-14 μm.

4. The filter according to claim 2, characterized in that: The line width of the resonant ring is 0.3-0.7 μm, the opening angle is 3-180°, the unit size is 2 μm×2 μm-5 μm×5 μm, the period spacing is 1-4 μm, and the resonant unit sizes in the upper and lower layers are the same.

5. The filter according to claim 1, wherein The materials of the upper rotatable superstructure unit layer and the lower fixed superstructure unit layer are zinc sulfide, zinc selenide or germanium, and the thickness of the upper and lower superstructure units is the same and is 2-15 μm.

6. The filter according to claim 1, wherein: The resonant ring unit is made of copper (Cu), gold (Au), or aluminum (Al), with a thickness of 2 to 50 nm, and the resonant ring units in the upper and lower layers are made of the same material.

7. The filter according to claim 1, wherein: The rotation angle of the upper rotatable superstructure unit layer can be 90°, 180° or 270°, which is used to switch between medium-wave filtering and long-wave filtering states.

8. The filter according to claim 1, wherein: The filter is bonded to the focal plane array surface with epoxy resin, and micrometer-scale alignment marks are produced using photolithography.

9. The filter according to claim 1, wherein The design method is as follows: (1) Double-layer variable structure metamaterial design The filter consists of an upper rotatable superstructure unit layer and a lower fixed superstructure unit layer. Both layers of dielectric are embedded with periodically arranged resonant ring units. The upper rotatable superstructure unit layer is driven by a micro-stepping motor and can rotate around the central axis, further changing the relative position and coupling mode of the upper and lower resonant rings. (2) Dynamic control mechanism In the initial state, the upper and lower resonant rings form an equivalent LC resonant circuit through electromagnetic coupling. Its resonant frequency f0 is determined by the equivalent inductance L and equivalent capacitance C of the resonant ring, satisfying: Among them: the equivalent capacitance C is mainly composed of the resonant ring opening gap d and the dielectric constant ε of the dielectric material r Decide: Where A gap is the area of ​​the opening, ε0 is the dielectric constant of vacuum; The equivalent inductance L is related to the geometric dimensions of the resonant ring, the line width w, the perimeter P, and the skin effect of the metal material: μ0 is the vacuum permeability, μ r is the relative magnetic permeability of the metal; When the upper dielectric rotates by an angle θ, the relative positions of the upper and lower resonant rings change, resulting in a coupling capacitance C couple And dynamic adjustment of mutual inductance M: Among them, A overloop (θ) is the total area of ​​the resonant ring after rotation, d(θ) is the opening gap of the resonant ring after rotation, D(θ) is the ring spacing after rotation, and r is the radius of the resonant ring; the total inductance L′ and total capacitance C′ are updated as follows: The resonant frequency f′ after rotation is: By adjusting θ, the resonant frequency of the device can be dynamically switched between shortwave, medium wavelength and other bands; (3) Multi-parameter collaborative design of vibration ring units The geometric parameters of the resonant ring need to be optimized based on the electromagnetic characteristics of the target medium and long wave bands. The specific design criteria are as follows: The opening angle α affects the equivalent capacitance C and must satisfy the following requirements: Among them, λ target is the center wavelength of the target band, n eff is the refractive index of the medium, r is the radius of the resonant ring; The line width needs to suppress surface plasma loss and must meet the following requirements: Among them, Re(n metal ) is the real refractive index of the metal material To avoid high-order diffraction and ensure strong coupling, the periodic spacing a must satisfy: λ min is the shortest wavelength in the target band.

10. A method for preparing a medium- and long-wavelength dynamic control filter according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) forming periodically arranged resonant ring units on a medium through a photolithography process; (2) depositing a metal film on the upper surface of the medium and forming an open ring structure through an etching process; (3) Assemble the upper dielectric layer and the lower dielectric layer through a mechanical rotation mechanism to ensure that the rotation axes are aligned.

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