Intermediate infrared band-stop optical filter based on metal metasurface array structure

Abstract

The invention discloses an intermediate infrared band-stop optical filter based on a metal metasurface array structure, and belongs to the technical field of optical filtering. Comprising a substrate and a metasurface structure. The substrate is made of a mid-infrared high-transmittance substrate material, and the metasurface structure of each array unit is a metal cross structure. Plane wave incident light vertically enters the optical filter from top to bottom; from the perspective of the whole wave band, a spectral transmission curve has an obvious light blocking effect near a target center wavelength, compared with the intrinsic transmittance of a substrate material, the intrinsic transmittance has obvious transmission attenuation, the average bandwidth is small, the average spectral resolution is small, and the average spectral energy utilization rate is larger than 85%. The mid-infrared band-stop optical filter provided by the invention has good band-stop effect, spectral resolution and high spectral energy utilization rate in a working wave band.

Description

Technical Field

[0001] The present invention relates to a mid-infrared band-stop filter based on a metal metasurface, and belongs to the technical field of filters. Background Art

[0002] In order to achieve a filtering function, traditional mid-infrared optical systems often require the use of complex combinations of optical elements or large-scale filtering devices, which increases the volume, weight, and complexity of the system, making the system not in line with the development trend of miniaturization, lightweight, and convenience. Mid-infrared metasurface filters have the characteristics of miniaturization, lightweight, and easy integration. Without reducing the system performance, they can greatly reduce the size and weight of the system, solve the problem that traditional mid-infrared optical systems are difficult to miniaturize and be portable, and enable mid-infrared imaging and spectroscopic analysis systems to be more widely applied in fields such as on-site detection, aerospace, and military detection, which have strict requirements on the volume and weight of equipment. A metasurface is an artificial structured functional material with characteristics such as a compact structure, small volume, and flexible regulation of the spectral and amplitude information of electromagnetic waves. However, existing mid-infrared filters prepared based on metasurface micro-nano structures are all band-pass filters, but the disadvantages of band-pass filters are obvious. They will block the light information outside the target wavelength. If higher resolution is required, it will lead to lower optical flux. Therefore, improving the resolution will sacrifice the light intensity incident on the detector, reduce the signal-to-noise ratio, and extend the integration time, resulting in a resolution-luminance trade-off problem. Summary of the Invention

[0003] In view of the above problems, the present invention proposes a mid-infrared band-stop filter based on an optical metasurface to achieve band-stop filtering in the mid-infrared wavelength band, that is, the target wavelength in the central band is blocked, and the light information outside the target wavelength passes through, improving the resolution.

[0004] A mid-infrared band-stop filter based on an optical metasurface, the structure includes a mid-infrared high-transmittance substrate and a metal metasurface array structure on the upper surface of the substrate; the working wavelength coverage range of the mid-infrared band-stop filter is from 3μm to 5μm.

[0005] In the above structure, the unit structure of the metasurface array is a metal cross structure, and the cross structures in the array are parallel. The parallel includes that the horizontal lines of the crosses are parallel, the vertical lines are parallel, and the lengths of the horizontal lines and the vertical lines are equal; by adjusting one or several of the cross period P (the distance between the centers of two adjacent crosses), the cross length L, and the thickness S, the central wavelength blocked by the band-stop filter is changed, so that the spectral transmittance in a specific stop band including the central wavelength is greatly attenuated relative to the intrinsic transmittance of the substrate material. In particular, the transmittance attenuation of the target central wavelength can reach 50%, and the transmittance outside twice the full width at half maximum exceeds 95%, and the working band covers 3000nm - 5000nm.

[0006] Further, the metal of the metal metasurface array structure includes one or more of gold, silver, copper, and aluminum.

[0007] Further, the material of the mid-infrared transparent substrate includes one or more of aluminum oxide, calcium fluoride, and barium fluoride.

[0008] Further, the thickness d of the metal metasurface structure is 10 nm - 120 nm.

[0009] Further, the period p of the metasurface array is 2000 nm - 3000 nm.

[0010] Further, the length L of the cross-shaped unit structure is 100 nm - 1000 nm.

[0011] Further, the width S of the cross-shaped unit structure is 10 nm - 120 nm.

[0012] Further, the thickness of the mid-infrared high-transmittance substrate material is 1 μm - 1000 μm.

[0013] Beneficial effects: A mid-wave band-stop filter based on a metal metasurface array structure according to the present invention includes a substrate and a metal metasurface micro-nano structure from bottom to top. Plane-wave incident light is vertically incident on the filter from top to bottom. The mid-infrared range from 3000 nm to 5000 nm is set as the working band. It can be seen from the transmittance curves of two different band-stop filters that there is an obvious light-blocking effect near the target center wavelength in the two spectral transmission curves. The transmittance at the target center wavelength is attenuated by nearly 50% compared with the intrinsic transmittance of the substrate material. In the stop band range, the average transmittance is attenuated by 37% and 40% respectively compared with the intrinsic transmittance of the substrate material, and the full width at half maximum is 440 nm and 400 nm respectively, and the spectral resolution is 0.12, and the light outside the two full-width at half maximum regions is highly transmitted, and the average spectral energy utilization rate is greater than 85%. That is, the present mid-wave band-stop filter can work in the 3 μm - 5 μm band, and has good band-stop effect, spectral resolution, and high spectral energy utilization rate. Description of the Drawings

[0010] Figure 1 It is a schematic diagram of the overall structure of the mid-infrared band-stop filter of the present invention.

[0011] Figure 2 It is a schematic diagram of the three-dimensional structure of the array unit.

[0012] Figure 3 It is the front view of the array unit.

[0013] Figure 4 It is the top view of the array unit.

[0014] Figure 5Corresponding diagram of the transmission curve of the mid-infrared band-stop filter processed under the parameters of Preferred Embodiment 1.

[0015] Figure 6 Corresponding diagram of the transmission curve of the mid-infrared band-stop filter processed under the parameters of Preferred Embodiment 2. Detailed implementation manners

[0016] To better understand the technical solution of the present application, the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0017] It should be clear that the embodiments of the present application are only a part of the embodiments of the present application, not all embodiments. To better explain the technical solution, the descriptions of all the following professional terms are for describing specific embodiments and do not limit the present application.

[0018] The present invention provides a mid-infrared band-stop filter based on an optical metasurface, with a working wavelength coverage range from 3 μm to 5 μm. As Figure 1 shown, the structure of the mid-infrared band-stop filter from bottom to top is successively a substrate material with high transmittance in the mid-infrared band and a metal metasurface array structure.

[0019] As Figures 2 to 4 shown, the unit structure of the metasurface array is a metal cross structure. By adjusting the cross array period P and the cross length L, the center wavelength of the band-stop filter is changed, and the wavelength coverage range is from 3000 nm to 5000 nm.

[0020] Furthermore, the thickness d of the metal metasurface structure is 10 nm - 120 nm, and more preferably 70 nm - 120 nm.

[0021] Furthermore, the metasurface array period p is 2000 nm - 3000 nm.

[0022] Furthermore, the length L of the cross unit structure is 100 nm - 1000 nm.

[0023] Furthermore, the width S of the cross unit structure is 10 nm - 120 nm, and more preferably 70 nm - 120 nm.

[0024] Through the above technical solution, the filter can have an obvious transmittance attenuation effect near the target central wavelength within the wavelength range of 3000nm - 5000nm. The transmittance of the target central wavelength is attenuated by nearly 50% compared with the intrinsic transmittance of the substrate material, and it maintains a relatively small full width at half maximum (FWHM) with a spectral resolution of 0.12. Moreover, the light outside twice the FWHM from the target central wavelength is highly transmitted, and the average spectral energy utilization rate is greater than 85%. That is, the design solution enables the filter to operate in the 3000nm - 5000nm band, having good band-stop effect, spectral resolution, and high spectral energy utilization rate.

[0025] In Example 1, the substrate uses a CaF2 substrate material with high mid-infrared transmittance, having a thickness of 500μm. The array structure uses aluminum metal material, with a period P = 2550nm, the long side L of the cross being 1200nm, the thickness d = 100nm, and the short side S = 100nm.

[0026] Under the condition of meeting the above parameters, the plane-wave incident light is perpendicularly incident on the filter from top to bottom. Figure 5 The transmittance curve of the processed filter under the parameters of the preferred Example 1 is shown. Analyzing this transmittance curve, this structure can well block the light near the wavelength of 3720nm, with a FWHM of 440nm. In the wavelength range of 3000nm - 3720nm, the spectral transmittance attenuates from 85% to 50%. In the wavelength range of 3720nm - 3940nm, the spectral transmittance rapidly rises from 50% to over 80%. In the wavelength range of 3940nm - 5000nm, the spectral transmittance rapidly rises to 90% and finally to over 95%. In the stopband wavelength range of 3440nm - 3880nm, the average spectral transmittance is 62%. Compared with the intrinsic transmittance of the substrate material, there is an average transmittance attenuation of 37%. The transmittance of the target central wavelength of 3720nm is 50%, and the transmittance attenuation is 50%. In the working range of 3000nm - 5000nm, the spectral resolution is 0.12.

[0027] In Example 2, the substrate uses a CaF2 substrate material with high mid-infrared transmittance, having a thickness of 500μm. The array structure uses aluminum metal material, with a period P = 2400nm, the long side L of the cross being 1120nm, the thickness d = 100nm, and the short side S = 100nm.

[0028] Under the condition of meeting the above parameters, the plane-wave incident light is perpendicularly incident on the filter from top to bottom. Figure 6It is the transmittance curve of the processed filter under the parameters of the preferred Embodiment 2. Analyzing this transmittance curve, this structure can well block the light near the wavelength of 3470 nm, with a full width at half maximum of 400 nm. In the wavelength range of 3000 nm - 3470 nm, the spectral transmittance rapidly decays from 80% to 50%. In the wavelength range of 3470 nm - 3870 nm, the spectral transmittance rapidly rises from 50% to 90%. In the wavelength range of 3870 nm - 5000 nm, the spectral transmittance rises from 90% to 100%. In the stopband range of 3270 nm - 3670 nm, compared with the intrinsic transmittance of the substrate material, there is an average transmittance attenuation of 40%. The transmittance at the target center wavelength of 3470 nm is 50%, and the transmittance attenuation is 50%. In the working range of 3000 nm - 5000 nm, the spectral resolution is 0.12.

[0029] The present invention realizes an obvious light blocking effect near the target center wavelength, has an obvious transmittance attenuation compared with the intrinsic transmittance of the substrate material, and the light outside the two full width at half maximum regions away from the center wavelength is highly transmitted.

[0030] It should be understood that the above are only two relatively preferred embodiments of the present application, not limited to two or more embodiments of the present application. For those of ordinary skill in the art, within the spirit and principles of two or more embodiments in this specification, any improvements or changes made according to the above description shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A mid-infrared band-stop filter based on an optical metasurface, characterized in that: The structure includes a mid-infrared high-transmittance substrate and a metal metasurface array structure on the upper surface of the substrate.

2. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: In the above structure, the unit structure of the metasurface array is a metal cross structure, and the cross structures in the array are parallel, and the parallelism includes that the horizontal lines of the cross are parallel, the vertical lines are parallel, and the lengths of the horizontal lines and the vertical lines are equal.

3. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: In the above structure, the thickness d of the metal supersurface structure is 10nm-120nm, the length L of the cross unit structure is 100nm-1000nm; and the width S of the cross unit structure is 10nm-120nm.

4. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: The metasurface array period p is 2000nm-3000nm.

5. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: The mid-infrared high-transmittance substrate material has a thickness of 1 μm-1000 μm.

6. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: The metal of the metal supersurface array structure includes one or more of gold, silver, copper and aluminum.

7. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: The material of the mid-infrared transparent substrate includes one or more of aluminum oxide, calcium fluoride and barium fluoride.

8. A mid-infrared band-stop filter based on an optical metasurface according to claim 1, characterized in that: The central wavelength blocked by the band-stop filter is changed by adjusting one or more of the cross period P, the cross length L, and the thickness S, so that the spectral transmittance in a specific stopband range including the central wavelength is greatly attenuated relative to the intrinsic transmittance of the substrate material. The transmittance of the special target central wavelength can be attenuated to 50%, and the transmittance outside the twice half-width area exceeds 95%. The working band covers 3000nm-5000nm.

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