Long pass cut-off optical filter based on nanostructure

Abstract

The invention discloses a long pass cut-off optical filter based on a nanostructure in the technical field of optical metamaterials, which comprises a round and square column group cross array growing on a silicon dioxide substrate, and a round and square column group is composed of four side columns uniformly distributed around a central column; the central column is composed of a round-square-square structure from top to bottom, the top-layer column and the bottom-layer square column are both made of gallium arsenide materials, and the middle-layer square column is made of silicon dioxide materials; the side cylinders are divided into three layers from top to bottom, the cylinders on the top layer and the cylinders on the bottom layer are made of gallium arsenide materials, the cylinders on the middle layer are made of aluminum oxide materials, low transmissivity in the wave band of 200-410 nm and high transmissivity in the wave band of 757-20000 nm are achieved, light wavelength distribution can be accurately controlled, ultraviolet interference is reduced, and the performance and reliability of a system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical metamaterials, and particularly relates to a cut-off filter. Background Art

[0002] Traditional optical filtering devices are usually composed of multiple layers of dielectric films, but it is difficult to cope with the scenarios of miniaturization and modularization. In recent years, metasurfaces have received extensive attention due to their excellent performance in micro- and nano-scale structures, and have been widely used in fields such as structural color, photodetectors, and sensors. An optical filter with high transmittance in the transmission region, good cut-off abruptness, low angular sensitivity, easy preparation, low cost, and environmental friendliness is the focus and hotspot of research in the relevant fields in the world today. The metasurface optical filter is based on the Mie resonance principle, and regulates light through material selection, geometric structure, parameter setting, etc. When light waves are incident on the surface of the metasurface optical filtering device, according to the design parameters of the nanocolumns, the light waves will have different optical responses such as reflection, transmission, and absorption, so as to realize the regulation and control of light waves. However, existing metasurface optical filters still face many challenges in specific application scenarios, such as when it is necessary to achieve perfect cut-off and absorption of light.

[0003] In many applications, it is necessary to have an obvious absorption cut-off between the cut-off band and the pass band. The cut-off efficiency can be expressed as extinction ratio ERF = 10 * log(Tpass / Tstop), where Tpass is the minimum transmittance in the pass band, and Tstop is the maximum transmittance in the stop band; extinction difference EDF = Tpass - Tstop; cut-off slope CSP = (Tpass - Tstop) / ( λ pass- λ stop), where λ Pass is the minimum wavelength in the pass band, λ stop is the longest wavelength in the stop band. Ideally, ERF, EDF, and CSP should be as large as possible, which cannot be achieved simultaneously in these proposed filters. The literature Hossain, M.M., Jia, B. and Gu, M. (2015), Metamaterials: A MetamaterialEmitter for Highly Efficient RadiativeCooling (Advanced Optical Materials 8 / 2015). Advanced Optical Materials, 3:980-980 provides a broadband absorber with a conical metamaterial structure, and the ERA, EDA, and CSA of the absorber are -6.04 dB, -0.64, and 0.00013 nm respectively -1; The literature Yu Y, Qian Q, Wang C, et al. An all-dielectric metasurface long-pass cut-off filter based on a multi-nanocircular array perfect cut-off absorber. MicrowOpt Technol Lett . 2022; 64: 300–304 provides a nano-cylindrical array perfect absorber, and the ERA, EDA, and CSA of the absorber are 12.17 dB, 0.88, and 0.0047 nm respectively -1 , these achievements play an important role in the development of the metasurface structure, but there are still problems such as low absorption rate, low cut-off rate, high absorption rate in the non-absorption band, and narrow absorption bandwidth. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a long-pass cut-off filter based on nanostructures, which realizes low transmittance in the 200-410 nm band and high transmittance in the 757-20000 nm band.

[0005] The object of the present invention is achieved in this way: A long-pass cut-off filter based on nanostructures, characterized in that it includes a cross array of circular-square column groups grown on a silica substrate, and the circular-square column group is composed of four side cylinders evenly distributed around the central column; The central column is composed of a circular-square-square structure from top to bottom. The top cylindrical column and the bottom square column are both made of gallium arsenide material, and the middle square column is made of silica material; The side cylinder is divided into three layers from top to bottom. The top and bottom cylindrical columns are both made of gallium arsenide material, and the middle cylindrical column is made of alumina material.

[0006] Further, when forming the cross array, the diagonally corresponding side cylinders within each circular-square column group form two axial planes that pass through the axis of the central column and are perpendicular to each other. Among the two axial planes of adjacent circular-square column groups, one axial plane is coplanar and the other axial plane is parallel.

[0007] Further, the heights of the main body of the central column from top to bottom are f3, f1, and f0 respectively, and the heights of the three-layer cylinders of the side cylinder from top to bottom are l, m, and n respectively; the array period is P; where, f 1 = 2-20 nm, f 3 = 30-60 nm, f 0 = 30-60 nm, l = 185-215 nm, m = 55-85 nm, n = 0-30 nm, P = 48-76 nm.

[0008] Further, the height of the main body of the central column from top to bottom is f3, f1, f0 respectively, and the height of the three-layer cylinders of the side cylinder from top to bottom is l, m, n respectively; the array period is P; where, f 1 = 11 nm, f 3 = 45 nm, f 0 = 45 nm, l = 200 nm, m = 70 nm, n = 10 nm, P = 60 nm.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention utilizes the strong coupling resonance between multiple nanoarray structures to achieve efficient absorption in the absorption band. At the same time, since the resonance wavelength is very sensitive to the structural parameters and materials, the absorption wavelength is controlled by reasonably adjusting the parameters, and a rapid cut-off between the absorption band and the non-absorption band is achieved. The low absorption rate in the non-absorption band is realized by using the non-absorbing property of the non-resonant band. In addition, by using the multiple coupling resonances of the multiple structures, the bandwidth of the absorption band is broadened, achieving a low transmittance in the 200 - 410 nm band, a high transmittance in the 757 - 20000 nm band, a transmittance lower than 0.03 in the cut-off band, and a maximum transmittance of about 0.95 in the transmission band, where ERF = 14.918 dB, EDF = 0.873, CSP = 0.0025 nm -1 ; moreover, a sharp cut-off and angle insensitivity are achieved between the cut-off band and the transmission band; this metasurface optical design structure for ultraviolet band cut-off can block ultraviolet rays in optical instruments to avoid interference and damage to samples, improve imaging quality in photography, improve the signal-to-noise ratio in chemical fluorescence analysis, and protect patients and ensure the normal operation of the imaging system in medical applications; it has important functions in many fields, can precisely control the light wavelength distribution, reduce ultraviolet interference, and improve the performance and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0011] Figure 1 It is an axonometric view of the circular and square column group cross-array structure in the present invention.

[0012] Figure 2 It is a top view of the circular and square column group cross-array structure in the present invention.

[0013] Figure 3 It is a schematic diagram of the circular and square column group structure in the present invention.

[0014] Figure 4 This is the theoretical value of the transmission spectrum of the long-pass cutoff filter of the present invention in the wavelength range of 200 - 6000 nm.

[0015] Figure 5 This is a schematic diagram showing the influence of parameter P on the overall transmission in the present invention.

[0016] Figure 6 This is parameter f in the present invention 1 A schematic diagram showing the influence on the overall transmission.

[0017] Figure 7 This is parameter f in the present invention 0 A schematic diagram showing the influence on the overall transmission.

[0018] Figure 8 This is parameter f in the present invention 3 A schematic diagram showing the influence on the overall transmission.

[0019] Figure 9 This is a schematic diagram showing the influence of parameter l on the overall transmission in the present invention.

[0020] Figure 10 This is a schematic diagram showing the influence of parameter m on the overall transmission in the present invention.

[0021] Figure 11 This is a schematic diagram showing the influence of parameter n on the overall transmission in the present invention.

[0022] Figure 12 This is a schematic diagram showing the influence of an incident angle of 30° on the overall transmission in the present invention.

[0023] Figure 13 This is a schematic diagram showing the influence of an incident angle of 80° on the overall transmission in the present invention. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. 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 making creative efforts shall fall within the protection scope of the present invention.

[0025] As Figures 1-3A nanostructure-based long-pass cutoff filter is shown, including a cross-array of circular-square column groups grown on a silica substrate. The circular-square column group consists of four side cylinders evenly distributed around the central column. The central column is composed of a circular-square-square structure from top to bottom. The top circular column and the bottom square column are both made of gallium arsenide material, and the middle square column is made of silica material. The side cylinders are divided into three layers from top to bottom. The top and bottom cylinders are both made of gallium arsenide material, and the middle cylinder is made of alumina material.

[0026] When forming the cross-array, the diagonally corresponding side cylinders within each circular-square column group form two axial planes that pass through the axis of the central column and are perpendicular to each other. For two axial planes within adjacent circular-square column groups, one axial plane is coplanar and the other is parallel. The heights of the main body of the central column from top to bottom are f3, f1, and f0 respectively, and the heights of the three layers of cylinders of the side cylinders from top to bottom are l, m, and n respectively. The array period is P. Among them, f 1 = 2 - 20 nm, f 3 = 30 - 60 nm, f 0 = 30 - 60 nm, l = 185 - 215 nm, m = 55 - 85 nm, n = 0 - 30 nm, P = 48 - 76 nm.

[0027] Figure 4 The theoretical values of the transmission spectrum of the long-pass cutoff filter of the present invention in the wavelength range of 200 - 6000 nm are shown.

[0028] Next, the present invention uses the finite-difference time-domain (FDTD) method to study the physical mechanism of cutoff transmission in the long-pass cutoff filter, explore the allowable range of parameter errors in actual manufacturing, and use the method of controlling variables to sequentially change each geometric parameter to study the influence of different geometric parameters on the working performance of the filter.

[0029] When other simulation parameters remain unchanged, as the array period P changes, the change process of the transmittance of the structure to incident light is as Figure 5 shown. The simulation range set by the present invention is from 48 nm to 72 nm, and the simulation step size is 4 nm. It can be Figure 5 seen that when the period P = 48 nm, the highest transmittance in the passband can reach 0.96, but the average transmittance is 0.918. When the period P = 60 nm, the transmittance peak in the passband slightly decreases, but the average transmittance is 0.929, slightly greater than the former and the curve is more stable. When the P value further increases, the cutoff in the cutoff band decreases significantly. When P = 72 nm, the transmittance in the cutoff band has reached 0.127, which does not meet the expectation and the curve in the passband oscillates significantly. In order to simultaneously maintain low transmittance in the cutoff band and stability in the passband, the present invention sets P = 60 nm in the long-pass cutoff filter.

[0030] When other simulation parameters remain unchanged, as the thickness f1 With the change of Figure 6 as shown. The simulation range set in the present invention is from 2 nm to 20 nm, and the simulation step size is 3 nm. It can be seen from Figure 6 that the influence of thickness h 1 on the average transmittance of the stopband is very small, and the average transmittance is stable between 0.009 and 0.013. When the thickness f 1 = 2 nm, the average transmittance of the stopband is 0.013, and as the thickness f 1 continues to increase, the average transmittance of the stopband is the lowest at the thickness f 1 = 11 nm, which is 0.009. When the thickness f 1 < 11 nm or f 1 > 14 nm, the curve of the passband shows a depression and begins to oscillate. In order to simultaneously maintain low transmittance in the stopband and stability in the passband, the present invention sets the thickness f 1 = 11 nm.

[0031] With other simulation parameters unchanged, with the change of thickness f 0 as shown. The simulation range set in the present invention is from 30 nm to 60 nm, and the simulation step size is 5 nm. It can be seen from Figure 7 that as the thickness f Figure 7 continues to increase, the average transmittance of the passband and the cut-off slope CS of the stopband continuously decrease, and the cut-off ability decreases. Although the average transmittance of the passband is high when the thickness f 0 = 30 nm, the transmittance of the stopband is relatively high at 0.015. When the thickness f 0 = 60 nm, its transmittance of the stopband is 0.006, which is slightly reduced, but the transmittance of the passband and the cut-off slope CS both decrease. Therefore, in order to obtain high cut-off ability, low transmittance in the stopband and high transmittance in the passband, the present invention sets the thickness f 0 = 45 nm. 0 = 45 nm.

[0032] With other simulation parameters unchanged, with the change of thickness f 3 as shown. The simulation range set in the present invention is from 30 nm to 60 nm, and the simulation step size is 5 nm. It can be seen from Figure 8 that with other simulation parameters unchanged, the influence of parameter f Figure 8 and parameter f 3 on the overall transmittance is roughly the same, which will not be elaborated here. The present invention sets the optimal parameter thickness f 0 = 45 nm. 3 = 45 nm.

[0033] With other simulation parameters remaining unchanged, as the thickness l changes, the process of the transmittance of the structure to incident light is as follows Figure 9 shown. The simulation range set in the present invention is from 185 nm to 215 nm, and the simulation step size is 5 nm. As can be seen from Figure 9 it, the thickness l has little influence on the structure within this range. During the process of l increasing continuously from 185 nm to 200 nm, the transmittance of the passband shows an upward trend. However, during the process of increasing from 200 nm to 215 nm, the transmittance of the passband decreases. In order to obtain high efficient cut-off ability and maintain high transmittance in the passband, the present invention sets l = 200 nm.

[0034] With other simulation parameters remaining unchanged, as the thickness m changes, the process of the transmittance of the structure to incident light is as follows Figure 10 shown. The simulation range set in the present invention is from 55 nm to 85 nm, and the simulation step size is 5 nm. During the process of m increasing continuously from 55 nm to 35 nm, the transmittance of the passband increases significantly, but the cut-off slope of the cut-off band decreases continuously, and at the same time, the transmittance in the cut-off band increases. In order to maintain low transmittance in the cut-off band, a relatively high cut-off slope and high transmittance in the passband simultaneously, the present invention sets m = 70 nm.

[0035] With other simulation parameters remaining unchanged, as the thickness n changes, the process of the transmittance of the structure to incident light is as follows Figure 11 shown. The simulation range set in the present invention is from 0 nm to 30 nm, and the simulation step size is 5 nm. During the process of n increasing continuously from 0 nm to 30 nm, although the average transmittance of the passband increases, there is an increasingly expanding depression at the top of the curve, the spectral width of the passband becomes narrower, and the cut-off slope decreases. Therefore, in order to have both a wide passband spectral width, high transmittance and a relatively high cut-off slope, the present invention sets n = 10 nm.

[0036] In addition, the present invention also finds that this structure has good angular insensitivity. As shown in Figures 12-13 it, when the incident angle of light reaches 80°, it can still maintain good short-wave cut-off performance, and has a good cut-off effect. The transmittance is still below 0.06 at 410 nm, and then rapidly reaches above 0.9 at 504 nm, and the transmittance of most wavelengths reaches above 0.9 later.

[0037] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A nanostructured long pass cutoff filter, characterized in that: It comprises a cross array of round square pillars grown on a silicon dioxide substrate, wherein the round square pillar group is composed of four side pillars uniformly distributed around a central pillar; The central column is composed of a circle-square-square structure from top to bottom, the top circle column and the bottom square column are both made of gallium arsenide material, and the middle square column is made of silicon dioxide material; The side cylinders are divided into three layers from top to bottom, the cylinders in the top layer and the bottom layer are both made of gallium arsenide material, and the cylinder in the middle layer is made of aluminum oxide material.

2. The nanostructured long pass cutoff filter according to claim 1, characterized in that: When the array is crossed, the obliquely corresponding side cylinders in each group of circular square cylinders form two axial planes that pass through the axis of the central cylinder and are perpendicular to each other. The two axial planes in two adjacent circular square cylinder groups are coplanar in one and parallel in the other.

3. The nanostructured long pass cutoff filter according to claim 2, characterized in that: The heights of the main body of the central column from top to bottom are f3, f1, and f0, respectively, and the heights of the three layers of side columns from top to bottom are l, m, and n, respectively; the array period is P; wherein, f1=2-20nm, f3=30-60nm, f0=30-60nm, l=185-215nm, m=55-85nm, n=0-30nm, and P=48-76nm.

4. The nanostructured long pass cutoff filter according to claim 3, characterized in that: The heights of the main body of the central column from top to bottom are f3, f1, and f0 respectively, and the heights of the three layers of side cylinders from top to bottom are l, m, and n respectively; the array period is P; among them, f1=11nm, f3=45nm, f0=45nm, l=200nm, m=70nm, n=10nm, and P=60nm.

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