CN117289374A - high-Q-value plasmon resonance super-surface device with high robustness - Google Patents

Abstract

The invention relates to a highly robust high-Q plasmon resonance metasurface device, which from bottom to top includes a substrate layer, a periodic array arrangement and "supramolecular" units on the substrate, and an arrangement The surface metal layer on the substrate and the "supramolecular"unit; the "supramolecular" unit includes two uprights arranged at a certain distance apart and a crossbar arranged between the two uprights; the length direction of the crossbar and the arrangement of the uprights The direction is the same, and the length is equal to the distance between the two columns; the radii of the two columns are different, showing an asymmetric configuration; the metasurface device of the present invention has a higher Q value and a higher Q value than the metasurface device that regulates the height of one side It is relatively insensitive to structural changes, which can effectively suppress the shortcomings of a sharp drop in the Q value of the device caused by errors introduced during device processing, greatly improving the practicality of the device.

Description

A robust high-Q plasmon resonance metasurface device

Technical field

The invention relates to the field of new micro-nano photonic devices, and in particular to a robust high-Q plasmon resonance metasurface device.

Background technique

Optical frequency electromagnetic metasurface is a new type of artificial two-dimensional microstructure thin-layer electromagnetic metamaterial that can control parameters such as amplitude, phase, polarization and angular momentum of the incident light field. Compared with traditional three-dimensional metamaterials, it has sub-wavelength thickness. , multifunctional integration, simple preparation process and other characteristics, it has become a research hotspot in the field of international micro-nanoscale electromagnetic wave regulation in recent years. Surface plasmon resonance metasurface devices with high quality factor (Q value) have longer photon lifetime and higher spectral resolution, which can greatly enhance the interaction between light and matter. In nonlinear optics, surface-enhanced pulling It has important applications in Mann microscopy and optical sensing. However, due to the large absorption loss and radiation loss of metal micro-nanostructures in the optical band, the Q value of plasmonic metasurfaces is generally low. The low Q value of the optical resonance system means that the intensity of the interaction between light and matter is weak, limiting the application of surface plasmon resonance metasurfaces. Therefore, how to improve the Q value of plasmonic metasurfaces has become a challenge in the international nanooptics research field. In recent years, in order to overcome the shortcomings of low Q value of plasmonic metasurface devices, scientists have introduced the principle of bound states in the continuum (BICs) to design high Q value plasmon resonance metasurfaces. The continuum bound state is a non-radiative localized state that exists in a radiative continuum and is a method that can be used to design ultra-high Q quality factor plasmonic metasurfaces.

Continuum bound states can be divided into continuum bound states based on symmetry protection (Symmetry protected BICs) and accidental continuum bound states (Accidental BICs). Since devices designed based on symmetry-protected continuum bound states are easier to implement in experiments than accidental continuum bound states, research on plasmonic metasurface devices based on this principle is more extensive and in-depth. Plasmon resonance metasurface devices designed based on the principle of parametric space symmetry protection allow designers to destroy structural symmetry in plane (In plane) and out of plane (Out plane), realizing the transition from BICs to quasi-BICs, extremely The earth enriches and improves the regulatory freedom and flexibility of plasmonic metasurfaces.

Although metasurfaces based on the principle of symmetry protection theoretically have infinitely high Q values and infinitely long photon lifetimes, they are also easily affected by non-ideal structural parameters of the metasurface resonance unit, especially the errors introduced by the processing process. Reduce the Q value of the device, thus affecting the practical application of high Q plasmon metasurfaces. Therefore, how to stabilize the Q value of surface plasmon metasurface devices is an important topic. However, the discussion on this issue is very limited. Although the impact of processing errors can be reduced by using high-precision processing equipment, the high price, high maintenance costs and some limiting factors make high-precision processing equipment difficult to obtain, thus affecting the practical application of high-Q plasmonic metasurface devices. . Therefore, for the manufacture of high-Q plasmon metasurface devices, it is necessary to study robust high-Q metasurface design solutions to improve the processing tolerance of the device itself and achieve high Q under the accuracy of existing processing equipment. The fabrication of high-Q plasmon metasurfaces is of great significance in promoting the research and application of high-Q plasmon metasurfaces.

Contents of the invention

In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a robust high-Q plasmon resonance metasurface device. In-plane and out-of-plane regulation are two basic ways to design high-Q plasmonic metasurface devices based on the principle of parameter space symmetry protection. The present invention conducts in-depth research on the Q value and Q value robustness of the device based on in-plane control and out-of-plane control in parameter space, and finally determines the device structure of the present invention. In the embodiments of the present invention, the control of device structural parameters in these two ways is compared and demonstrated to demonstrate the Q values of these two types of plasmonic metasurface devices and their robustness rules as the structural parameters change. Among them, the control method with higher Q value and smoother change (more robust) will help people design more practical high Q value plasmonic metasurface devices. Compared with out-of-plane modulation, the all-metal plasmon resonance metasurface device designed based on the principle of in-plane modulation continuum bound states has a higher Q value and stronger Q value robustness, which will provide practical applications for the device. Application brings convenience.

The Q value of the device of the present invention is as high as 182 when the reflection spectrum is perfectly absorbed. Compared with the existing patent application "a plasmonic near-infrared polarized light narrow-band perfect absorption metasurface device" when the reflection spectrum is perfectly absorbed, the Q value is only 64 , nearly 3 times higher. This is mainly due to the fact that the physical principles supporting the resonance absorption of the respective devices are different. In the previous patent application, when the device resonates and absorbs, the optical energy of the incident light is mainly localized within the nanoscale of the tips of the two pillars, which is beneficial to the electric field enhancement, but the Q value of the device is not high enough. When resonance absorption occurs in the device of the present invention, the optical energy of the incident light has non-local characteristics or weak local characteristics, and the light field energy is within the micron scale near the structure. This difference between local and non-local is the main reason for the difference in device loss, which will inevitably lead to a large difference in the Q value of the device. Therefore, compared with the case of strong localization, non-local design can significantly increase the Q value of the device. At the same time, in the non-local situation, we compared the in-plane modulation scheme and the out-of-plane modulation scheme and found that the in-plane modulation scheme of the present invention not only has a high Q value, but also has a stronger Q value that follows the evolution of the structure, that is, Q The value follows the change of asymmetric parameters more smoothly, and has better immunity to errors introduced by device processing, which is very conducive to the actual processing and application of devices.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A robust high-Q plasmon resonance metasurface device, characterized by comprising a substrate, "supramolecular" units arranged in a periodic array on the substrate, and a "supramolecular" unit arranged on the substrate and A surface metal layer on the "supramolecular" unit;

The "supramolecular" unit includes two uprights arranged at a certain distance apart and a crossbar connected between the two uprights. The heights of the two uprights are the same; the bottom radii of the two uprights are different. It presents an asymmetric configuration; the length direction of the cross bar is the same as the arrangement direction of the upright column; the upright column has a cone-like cross-sectional radius that gradually shrinks from its base side to its top side; the cross bar's length direction is the same as the arrangement direction of the upright column. The height is smaller than the height of the upright column, and the longitudinal section of the crossbar is a semi-elliptical surface with uniform dimensions;

When the polarization direction of the normal incident ray is parallel to the substrate and perpendicular to the center lines of the two pillars, that is, the electric field E is polarized along the X direction, and a high Q-value perfect absorption peak appears in the reflection spectrum.

The normal incident polarized light is near-infrared polarized light, and its wavelength range is from 1.5 microns to 2.0 microns.

The thickness of the surface metal layer is greater than the skin depth of the near-infrared polarized light.

The surface metal layer is a gold layer, and the thickness of the gold layer is 0.1 micron.

The number of periodic arrangements of the "supramolecular" units in both the transverse direction and the longitudinal direction is greater than or equal to 10; preferably, the number of periodic arrangements of the "supramolecular" units in both the transverse direction and the longitudinal direction is equal to 10.

The "supramolecular" unit is formed by using a photoresist layer spin-coated on the substrate through a femtosecond laser direct writing process.

The radii of the upright posts are R=0.25 microns and r=0.15 microns respectively; the height of the upright posts is H=1.6 microns; the bottom width of the crossbar is W=0.4 microns and the height h=0.6 microns.

The center distance between the two pillars is 0.8 microns, and the period size of the "supramolecular" unit is 1.6 microns × 1.6 microns.

When the wavelength of the incident polarized light is 1.734 microns and a narrow-band perfect absorption peak appears, the quality factor is as high as Q=182.

The substrate is a silicon dioxide substrate.

Compared with the existing technology, the technical solution provided by the present invention has at least the following beneficial effects:

The metasurface device involved in the present invention has a simple structure and a simple processing technology. The device can be prepared by using existing laser direct writing technology and atomic layer deposition technology. When the specified linearly polarized light is normally incident on this metasurface device, its reflected light shows a narrow linewidth and perfect absorption peak, with a high quality factor Q=182. Compared with the previously designed strong local solution (Q = 64), the Q value is increased by approximately 3 times. Moreover, the Q value of the resonance system is more robust, which can effectively reduce the impact of processing errors on the Q value attenuation of the device and promote the practical application of the device.

Description of drawings

In Figure 1, (a) is a schematic structural diagram of a metasurface device for in-plane adjustment (In plane) according to an embodiment of the present invention; (b) is a schematic diagram of a "supramolecular" unit structure; (c) is a "supramolecular" Top view of the unit; (d) is the reflection spectrum curve of the metasurface device.

In Figure 2, (a) is a schematic structural diagram of an in-plane regulating device according to an embodiment of the present invention; (b) is a schematic structural diagram of a "supramolecular" unit of the in-plane regulating device; (c) is a schematic diagram of Top view of the "supramolecular" unit structure of the in-plane adjustment device; (d) is a schematic structural diagram of the out-of-plane adjustment device; (e) is a schematic diagram of the "supramolecular" unit structure of the out-of-plane adjustment device; The picture (f) is a top view of the "supramolecular" unit structure of the out-of-plane adjustment device.

Figure 3 (a) shows the reflection spectrum of an in-plane adjustment device according to an embodiment of the present invention, and (b) shows the reflection spectrum comparison of an out-of-plane adjustment (Out plane) control device.

Figure 4 is a comparison of the evolution of the Q value between in-plane adjustment (In plane) and out-plane adjustment (Out plane) of a comparison device according to an embodiment of the present invention.

Figure 5 shows the electric field distribution on the main observation plane of the device when surface lattice resonance occurs during in-plane adjustment (In plane) according to an embodiment of the present invention, wherein (a) is the electric field distribution on the y-z plane; (b) is the x-y The electric field distribution in the plane.

FIG. 6 is a schematic diagram of the manufacturing process of a metasurface device with in-plane adjustment according to an embodiment of the present invention.

Detailed ways

Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings of the present invention. The described embodiments are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by those of ordinary skill in the art without any creative work shall fall within the scope of protection of the present invention. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described can be obtained from public commercial sources unless otherwise specified.

Spatially relative terms, such as “below”, “below”, “lower”, “above”, “above” and “upper” are used in this specification to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device in addition to those depicted in the figures.

In addition, the use of terms such as "first", "second" and the like to describe various elements, layers, regions, sections, etc. are not intended to be limiting. The use of "having," "containing," "including," "including," etc., are open-ended terms indicating the presence of stated elements or features but not excluding additional elements or features. Unless the context clearly indicates otherwise.

The in-plane adjustment proposed by the present invention refers to the adjustment along the x-y plane, and the out-of-plane adjustment refers to the adjustment along the y-axis direction beyond the x-y plane.

A new type of non-localized plasmon metasurface device proposed by the present invention can realize the near-infrared polarized light to present a high Q value, narrow linewidth and perfect absorption peak (Q=182) under normal incidence, and the Q value It has strong robustness with the evolution of in-plane structural parameters. As shown in Figure 1, the metasurface device includes a substrate, a periodic array of artificial "supramolecular" units arranged on the substrate, and a metal film layer arranged on the substrate and "supramolecular" units. In this embodiment, a silicon dioxide substrate is selected as the substrate, and the thickness of the silicon dioxide substrate is not limited. "Supramolecular" unit periodic arrays are arranged on the silicon dioxide substrate. The more "supramolecular" units have the number of periods in the transverse and vertical directions, the better. In actual processing, the number of periods is limited. The number of periodic arrangements in the transverse and vertical directions is greater than or equal to 10. , the spectral curve is already very close to the ideal value. In this embodiment, the number of transverse and longitudinal periods of the "supramolecular" units is 10, and the units are arranged in 10 rows and 10 columns. Figure 1 shows a part of the array arrangement.

First, a photoresist layer of a certain thickness is formed on the substrate, and then a femtosecond laser direct writing process is used to process the "supramolecular" unit structure to form a periodic array of "supramolecular" units. Each "supramolecular" unit consists of two identical uprights and a crossbar connected between the two uprights. As shown in Figure 1, in the "supramolecular" unit, along the y-axis direction, the two pillars are located at x = 0.8 microns in the "supramolecular" unit, and the center distance between the two pillars Δy = 0.8 microns. The entire The crossbar structure is symmetrical about the axis at y=0.8 microns. The radius of the cross-section of the column (that is, the xy plane, as shown in Figure 1) gradually decreases from the basal side to the side away from the base (that is, the tip side of the column), and the column as a whole is in the shape of a cone. The longitudinal section of the crossbar (i.e. the xz plane, as shown in Figure 1) is a semi-elliptical surface with consistent dimensions. In this embodiment, the bottom radii of the two columns are R=0.25 microns and r=0.15 microns respectively, and the height H is 1.6 microns. As shown in Figure 1, the width (along the x-axis direction) of the bottom of the crossbar is W=0.4 micron, and the height (along the z-axis direction) h=0.6 micron. The "supramolecular" unit size P is 1.6 microns × 1.6 microns. The device structure of the present invention is composed of "supramolecular" units arranged in a periodic array in the x, y plane, and the number of periods in the transverse and longitudinal directions is greater than or equal to 10. In the embodiment, only a part (5×5) of the device array structure is schematically presented in FIG. 1 . The thickness of the "supramolecular" unit structure and the metal film layer covering the surface of the substrate is greater than the skin depth of the incident light, making it impossible to transmit light. In this embodiment, a gold film layer is selected as the metal film layer, and the thickness of the gold film layer is 0.1 micron. The enlarged side view and top view of the "supramolecular" unit of the metasurface device are shown in Figure 1(b) and 1(c) respectively; the device is 1.5-2.0 microns, and the polarization direction of the normal incident ray polarized light is parallel to the substrate and perpendicular to When the two pillars are at the center line, that is, the electric field E is polarized along the X direction, a high Q value and a narrow linewidth perfect absorption peak can be achieved (Q = 182), and the Q value of the resonance system is more robust in following changes in the structural in-plane parameters.

Figure 2 shows a comparison of the device design and structural parameters of the two control methods of in-plane adjustment (In Plane) and out-of-plane adjustment (Out Plane). When adjusted in-plane, the heights of the two pillars in the device's "supramolecular" structure are the same, but the base radii are different, resulting in an asymmetric configuration. When adjusted out of plane, the heights of the two pillars in the "supramolecular" structure of the device are different, resulting in an asymmetric configuration, but the radius of the bottom surface is the same.

Figure 3 shows the comparison of reflection spectra under two control modes: in-plane adjustment (In Plane) and out-of-plane adjustment (Out Plane). As can be seen from the figure, both control methods can achieve perfect absorption, but the reflection spectrum of the in-plane adjustment method is narrower than the reflection spectrum of the out-of-plane adjustment method, which means it has a higher Q value; and the in-plane adjustment method has a narrower reflection spectrum than the out-of-plane adjustment method. The intensity of the change in the resonance peak width of the in-plane adjustment method is smaller than that of the out-of-plane adjustment method, which means that the stability of the Q value of the in-plane adjustment method is better, that is, it is more robust.

Figure 4 shows the comparison of the Q value under the two adjustment methods of in-plane adjustment (In Plane) and out-of-plane adjustment (Out Plane), and the results of the Q value following the change of the corresponding in-plane structural asymmetry parameters. Here, the in-plane asymmetry parameter A ₁ and the out-of-plane asymmetry parameter A ₂ are defined as:

The Q value is defined as the ratio of the resonance center wavelength λ ₀ to the resonance spectrum line full width at half maximum Δλ = λ _H - λ _L , that is:

Among them, the full width at half maximum refers to the wavelength difference at which the intensity is half of the maximum value of the peak value, and λ _H and λ _L are respectively the highest and lowest wavelength values at the full width at half maximum.

Figure 4 clearly shows that the Q value of the in-plane adjustment device is significantly higher than the Q value of the out-of-plane adjustment device; and when the Q value of the two methods evolves with the asymmetric parameters, the Q value change behavior of the in-plane adjustment method is more stable. Therefore, it is more robust and should have a higher tolerance for errors in the device structure, providing guarantee for device processing and practical applications.

Figure 5 shows the simulation results of the electric field on the main plane of the "supramolecular" unit of the device at the resonance absorption peak of 1.734 microns. It can be seen from the figure that the device has a weak binding effect on the electric field. Compared with the strong binding effect previously applied for ("a plasmonic near-infrared polarized light narrow-band perfect absorption metasurface device", Q=64), the device The attenuation of light is greatly reduced, which is beneficial to the improvement of Q value and the stability of Q value.

Figure 6 is a schematic diagram of the preparation process of the metasurface device of the present invention. As shown in the figure, first, femtosecond laser processing technology is used to process the "supramolecular" unit array structure on a glass (silicon dioxide) substrate. Then, atomic layer deposition technology is used to deposit the surface of the "supramolecular" unit array structure to a thickness of approximately The 0.1 micron gold film layer, which is thicker than the skin depth of the incident light working wavelength, is used to detect the reflection spectrum.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, etc. may be made without departing from the spirit and principles of the present invention. All simplifications should be equivalent substitutions, and are all included in the protection scope of the present invention.

Claims (10)

1. The high-Q-value plasmon resonance super-surface device with high robustness is characterized by comprising a substrate, a 'supermolecule' unit periodically arranged on the substrate in an array manner and a surface metal layer arranged on the substrate and the 'supermolecule' unit;

the supermolecule unit comprises two stand columns which are arranged at a certain interval and a cross rod connected between the two stand columns, and the heights of the two stand columns are consistent; the bottom surface radius of the two upright posts is different, and the two upright posts are in asymmetric configuration; the length direction of the transverse rod is the same as the arrangement direction of the upright posts; the vertical column is a cone-like body with the cross section radius gradually shrinking from the base side to the top end side, the height of the cross rod is smaller than that of the vertical column, and the longitudinal section of the cross rod is a semi-elliptical surface with consistent size;

when the polarization direction of normal incidence linearly polarized light is parallel to the substrate and perpendicular to the central lines of the two upright posts, namely the electric field E is polarized along the X direction, a perfect absorption peak with high Q value appears in the reflection spectrum.

2. The device of claim 1, wherein the normally incident linearly polarized light is near infrared polarized light having a wavelength in the range of 1.5 microns to 2.0 microns.

3. The super surface device according to claim 1 or 2, wherein the thickness of the surface metal layer is larger than the skin depth of the near infrared polarized light.

4. The device of claim 3, wherein the surface metal layer is a gold layer, and the thickness of the gold layer is 0.1 microns.

5. The device according to claim 1, 2 or 4, wherein the number of periodic arrangements of the "supermolecule" units in the lateral direction and the longitudinal direction is 10 or more; preferably, the number of periodic arrangements of the "supermolecule" units in the transverse and longitudinal directions is equal to 10.

6. The device of claim 1, 2 or 4, wherein the "supermolecule" unit is formed by a femtosecond laser direct writing process using a photoresist layer spin-coated on a substrate.

7. The device of claim 1, 2 or 4, wherein the pillars each have a radius R = 0.25 microns, R = 0.15 microns; the height of the pillars h=1.6 microns; the bottom surface of the rail has a width w=0.4 micrometers and a height h=0.6 micrometers.

8. The device of claim 7, wherein the two posts have a center-to-center distance of 0.8 microns, and wherein the "supermolecule" cell cycle size is selected to be 1.6 microns by 1.6 microns.

9. The device of claim 1, 2 or 4, wherein the incident polarized light wavelength is 1.734 microns at which a narrow band perfect absorption peak occurs, the quality factor being up to q=182.

10. The device of claim 1, 2 or 4, wherein the substrate is a silicon dioxide substrate.