A robust high-Q plasmon resonant metasurface device

Abstract

The present invention relates to a highly robust high-Q plasmon resonant metasurface device, which comprises, from bottom to top, a substrate layer, "supramolecular" units arranged in a periodic array on the substrate, and a surface metal layer arranged on the substrate and the "supramolecular" units; the "supramolecular" units comprise two pillars arranged at a certain interval and a crossbar arranged between the two pillars; the length direction of the crossbar is the same as the arrangement direction of the pillars, and the length is equal to the distance between the two pillars; the two pillars have different radii, presenting an asymmetric configuration; compared with a metasurface device with unilateral height control, the metasurface device of the present invention has a higher Q value and is relatively insensitive to structural changes. It can effectively suppress the disadvantage of a sharp drop in the Q value of the device caused by errors introduced during device processing, thereby greatly improving the practicality of the device.

Description

Technical Field

[0001] The present invention relates to the field of novel micro-nano photonic devices, and in particular to a high-Q-value plasmon resonance metasurface device with strong robustness. Background Art

[0002] Optical frequency electromagnetic metasurfaces are a new type of artificial two-dimensional, microstructured, thin-layer electromagnetic metamaterial that can manipulate parameters such as the amplitude, phase, polarization, and angular momentum of the incident light field. Compared to traditional three-dimensional metamaterials, they offer subwavelength thickness, multifunctional integration, and simple fabrication processes. They have become a research hotspot in the field of micro- and nanoscale electromagnetic wave manipulation in recent years. Surface plasmon resonant metasurface devices with high quality factors (Q) exhibit longer photon lifetimes and higher spectral resolution, significantly enhancing light-matter interactions and holding important applications in nonlinear optics, surface-enhanced Raman microscopy, and optical sensing. However, due to the significant absorption and radiation losses of metallic micro- and nanostructures in the optical wavelength range, the Q values ​​of plasmon metasurfaces are generally low. The low Q value of optical resonant systems implies weak light-matter interactions, limiting the application of surface plasmon resonant metasurfaces. Therefore, improving the Q value of plasmon metasurfaces has become a major challenge in the field of nano-optics research. In recent years, to overcome the low Q factor of plasmonic metasurface devices, scientists have introduced the principle of bound states in the continuum (BICs) to design high-Q plasmonic resonant metasurfaces. BICs are non-radiative localized states that exist within a radiative continuum and are a method that can be used to design plasmonic metasurfaces with ultra-high Q factors.

[0003] Continuum bound states can be divided into symmetry-protected continuum bound states (BICs) and accidental BICs. Because devices designed based on symmetry-protected BICs are easier to implement experimentally than accidental BICs, research on plasmonic metasurface devices based on this principle has been more extensive and in-depth. Plasmonic resonant metasurface devices designed based on the principle of parameter-space symmetry protection allow designers to break structural symmetries both in-plane and out-of-plane, achieving a transition from BICs to quasi-BICs, greatly enriching and enhancing the controllable freedom and flexibility of plasmonic metasurfaces.

[0004] Although metasurfaces based on the principle of symmetry protection theoretically possess infinitely high Q values ​​and infinitely long photon lifetimes, they are also susceptible to the non-ideal effects of the structural parameters of the metasurface's resonant units. In particular, errors introduced during the machining process can dramatically reduce the device's Q value, thereby affecting the practical application of high-Q plasmonic metasurfaces. Therefore, how to stabilize the Q value of surface plasmonic metasurface devices is an important topic, but discussion of this issue is very limited. Although the impact of machining errors can be reduced by using high-precision machining equipment, the high price, high maintenance costs, and other limitations make high-precision machining equipment difficult to obtain, thus hindering the practical application of high-Q plasmonic metasurface devices. Therefore, for the fabrication of high-Q plasmonic metasurface devices, it is of great significance to develop robust high-Q metasurface design schemes, improve the machining tolerance of the device itself, and achieve high-Q plasmonic metasurface fabrication within the precision of existing machining equipment. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a high-Q plasmon resonant metasurface device with strong robustness. In-plane and out-of-plane regulation are two basic ways to design high-Q plasmon metasurface devices based on the principle of parameter space symmetry protection. The present invention deeply studies the high and low Q values ​​of the device and the strength of the Q value robustness under the in-plane regulation and out-of-plane regulation of the parameter space, and finally determines the device structure of the present invention. In the embodiment of the present invention, the two methods are compared to show the Q value of the two types of plasmon metasurface devices and their robustness laws as the structural parameters change. Among them, the regulation method with higher Q value and smoother change (stronger robustness) will help people design more practical high-Q plasmon metasurface devices. Compared with out-of-plane modulation, the all-metal plasmon resonant metasurface device designed based on the in-plane modulation continuum bound state principle has a higher Q value and stronger Q value robustness, which will bring convenience to the practical application of the device.

[0006] The Q value of the device of the present invention is as high as 182 when the reflection spectrum is perfectly absorbed, which is nearly 3 times higher than the Q value of the existing patent application "A plasmonic near-infrared polarized light narrow-band perfect absorption metasurface device" when it is perfectly absorbed, which is only 64. This is mainly due to the different physical principles supporting the resonant absorption of each device. In previous patent applications, when the device resonates and absorbs, the light energy of the incident light is mainly localized within the nanoscale of the tips of the two pillars, which is conducive to electric field enhancement, but the Q value of the device is not high enough. When the device of the present invention resonates and absorbs, the light 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 inevitably leads to large differences in the Q value of the device. Therefore, compared with the strong local situation, the non-local design can significantly increase the Q value of the device. At the same time, in the non-local case, we compared the in-plane modulation and out-of-plane modulation schemes and found that the in-plane modulation scheme of the present invention not only has a high Q value, but also has a stronger robustness in following the structural evolution of the Q value, that is, the Q value follows the change of asymmetric parameters more smoothly, and has a better immunity to errors introduced by device processing, which is very beneficial to the actual processing and application of the device.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A robust high-Q plasmon resonant metasurface device, characterized by comprising a substrate, "supramolecular" units periodically arrayed on the substrate, and a surface metal layer arranged on the substrate and the "supramolecular" units;

[0009] The "supramolecular" unit comprises two pillars arranged at a certain distance from each other and a crossbar connecting the two pillars. The two pillars are of the same height; the base radii of the two pillars are different, presenting an asymmetric configuration; the length direction of the crossbar is the same as the arrangement direction of the pillars; the cross-section radius of the pillars is a cone-like shape with a gradually decreasing radius from the base to the top, the height of the crossbar is less than the height of the pillars, and the longitudinal section of the crossbar is a semi-elliptical surface of uniform size;

[0010] When the polarization direction of the incident linearly polarized light 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, a high Q value perfect absorption peak appears in the reflection spectrum.

[0011] The incident normal polarized light is near-infrared polarized light, and its wavelength ranges from 1.5 microns to 2.0 microns.

[0012] The thickness of the surface metal layer is greater than the skin depth of the near-infrared polarized light.

[0013] The surface metal layer is a gold layer, and the thickness of the gold layer is 0.1 micron.

[0014] The number of periodic arrangements of the "supramolecular" units in the transverse and longitudinal directions is greater than or equal to 10; preferably, the number of periodic arrangements of the "supramolecular" units in the transverse and longitudinal directions is equal to 10.

[0015] The "supramolecular" unit is formed by a photoresist layer spin-coated on a substrate through a femtosecond laser direct writing process.

[0016] The radii of the pillars are R=0.25 microns and r=0.15 microns respectively; the height of the pillars is H=1.6 microns; the bottom width of the crossbar is W=0.4 microns, and the height is h=0.6 microns.

[0017] The center distance between the two pillars is 0.8 microns, and the periodic size of the "supramolecular" unit is 1.6 microns×1.6 microns.

[0018] When the wavelength of the incident linearly polarized light is 1.734 μm and a narrow-band perfect absorption peak appears, the quality factor is as high as Q=182.

[0019] The substrate is a silicon dioxide substrate.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects:

[0021] The metasurface device disclosed in the present invention has a simple structure and a simple processing technology. The device can be prepared using existing laser direct writing technology and atomic layer deposition technology. Under the condition of normal incidence of specified linearly polarized light, the reflected light of the metasurface device presents a narrow linewidth perfect absorption peak with a high quality factor Q = 182. Compared with the previously designed strong localization solution (Q = 64), the Q value is increased by about 3 times. In addition, the Q value of the resonant system is more robust, which can effectively reduce the impact of processing errors on the attenuation of the device's Q value and promote the practical application of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 In the figure, (a) is a schematic diagram of the structure of the in-plane metasurface device of one embodiment of the present invention; (b) is a schematic diagram of the structure of the "supramolecular" unit; (c) is a top view of the "supramolecular" unit; (d) is a reflection spectrum curve of the metasurface device.

[0023] Figure 2In the figure, (a) is a schematic structural diagram of an in-plane regulation device according to an embodiment of the present invention; (b) is a schematic structural diagram of a "supramolecular" unit of the in-plane regulation device; (c) is a top view of the "supramolecular" unit of the in-plane regulation device; (d) is a schematic structural diagram of an out-of-plane regulation device for comparison; (e) is a schematic structural diagram of a "supramolecular" unit of the out-of-plane regulation device; (f) is a top view of the "supramolecular" unit of the out-of-plane regulation device.

[0024] Figure 3 Figure (a) is the reflection spectrum of an in-plane adjustment device according to an embodiment of the present invention, and Figure (b) is the comparison of the reflection spectra of an out-of-plane adjustment comparison device.

[0025] Figure 4 FIG. 1 is a comparison of the Q value evolution of an embodiment of the present invention with in-plane adjustment (In plane) and a comparative device with out-of-plane adjustment (Out plane).

[0026] Figure 5 This is an embodiment of the present invention, in which the electric field distribution of the device is mainly observed when the surface lattice resonance occurs during in-plane regulation. Figure (a) shows the electric field distribution in the yz plane; Figure (b) shows the electric field distribution in the xy plane.

[0027] Figure 6 It is a schematic diagram of the in-plane adjustment (In plane) metasurface device preparation process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present invention. The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can be obtained from public commercial channels.

[0029] Spatially relative terms such as "below," "beneath," "below," "above," "upper," etc. are used in this specification to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures.

[0030] In addition, the use of terms such as "first," "second," and the like to describe various elements, layers, regions, sections, and the like is not intended to be limiting. The use of "having," "containing," "including," and "comprising" are open-ended terms that indicate the presence of stated elements or features, but do not exclude additional elements or features, unless the context clearly indicates otherwise.

[0031] The in-plane adjustment proposed in the present invention refers to adjustment along the xy plane, and the out-of-plane adjustment refers to adjustment beyond the xy plane and along the y-axis direction.

[0032] The present invention proposes a novel non-localized plasmon metasurface device that can achieve a high Q value, narrow line width, perfect absorption peak (Q = 182) for near-infrared polarized light under normal incidence, and the Q value has strong robustness in the evolution of in-plane structural parameters. Figure 1 As shown, 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 the "supramolecular" units. In this embodiment, the substrate is a silicon dioxide substrate, and there is no limit on the thickness of the silicon dioxide substrate. The "supramolecular" units are arranged in a periodic array on the silicon dioxide substrate. The more horizontal and vertical periodicities of the "supramolecular" units, the better. The number of periods is limited in actual processing. When the number of periodic arrangements in the horizontal 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 horizontal and vertical periodicities of the "supramolecular" units is selected to be 10, and they are arranged in 10 rows and 10 columns. Figure 1 A portion of the array arrangement is shown.

[0033] 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 columns and a crossbar, and the crossbar is connected between the two columns. Figure 1 As shown in the figure, in the "supramolecular" unit, along the y-axis, the two pillars are located at the position x = 0.8 microns in the "supramolecular" unit, and the center distance between the two pillars is △y = 0.8 microns. The entire cross-bar structure is symmetrical about the axis where y = 0.8 microns is located. The cross section of the pillars (i.e., the xy plane, as shown in the figure) Figure 1 The radius gradually decreases from the base side to the side away from the base (i.e., the tip side of the column), and the column as a whole is a cone-like shape. Figure 1 (shown as a semi-elliptical surface of uniform size). In this embodiment, the base radii of the two pillars are R = 0.25 microns and r = 0.15 microns respectively, and the height H is 1.6 microns. Figure 1As shown, the width of the bottom of the crossbar (along the x-axis) is W = 0.4 microns, and the height (along the z-axis) is h = 0.6 microns. The size P of the "supramolecular" unit 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 and y planes, with the number of periods in the horizontal and vertical directions being greater than or equal to 10. In the embodiment, as Figure 1 Only a portion of the device array structure (5×5) is schematically shown. The thickness of the metal film layer covering the "supramolecular" unit structure and the substrate surface is greater than the skin depth of the incident light, so that the light cannot be transmitted. In this embodiment, the metal film layer is a gold film layer with a thickness of 0.1 micron. The enlarged side view and top view of the "supramolecular" unit of the metasurface device are shown in Figure 1. Figure 1 (b) and 1(c); when the device is at 1.5-2.0 μm and the polarization direction of the incident linearly polarized light 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, a high Q value, narrow linewidth, perfect absorption peak (Q=182) can be achieved, and the Q value of the resonant system is more robust to changes in the parameters within the structural plane.

[0034] Figure 2 The design methods and structural parameters of devices using in-plane and out-of-plane modulation are compared. For in-plane modulation, the two pillars in the device's "supramolecular" structure have the same height but different base radii, resulting in an asymmetric configuration. For out-of-plane modulation, the two pillars in the device's "supramolecular" structure have different heights, resulting in an asymmetric configuration, but the base radii are the same.

[0035] Figure 3 A comparison of the reflection spectra for in-plane and out-of-plane modulation is shown. The figure shows that both modulation methods achieve perfect absorption, but the reflection spectrum of the in-plane modulation method is narrower than that of the out-of-plane modulation method, indicating a higher Q value. Furthermore, the resonance peak width of the in-plane modulation method varies less drastically than that of the out-of-plane modulation method, indicating that the in-plane modulation method has a more stable Q value, that is, more robust.

[0036] Figure 4 The comparison shows the high and low Q values ​​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 asymmetric parameters. Here, the in-plane asymmetric parameter A1 and the out-of-plane asymmetric parameter A2 are defined as follows:

[0037]

[0038]

[0039] The Q value is defined as the ratio of the resonance center wavelength λ0 to the full width at half maximum of the resonance spectrum Δλ = λ H -λ L The ratio of , that is:

[0040]

[0041] The full width at half maximum is the wavelength difference where the intensity is half of the peak value, λ H ,λ L are the highest and lowest wavelength values ​​at half-maximum full width, respectively.

[0042] Figure 4 It is clearly demonstrated that the Q value of the in-plane adjustment device is significantly higher than that of the out-of-plane adjustment device; and when the Q values ​​of the two methods evolve with the asymmetric parameters, the Q value change behavior of the in-plane adjustment method is more stable, so it is more robust and should have a higher tolerance for errors in the device structure, providing guarantees for the processing and practical application of the device.

[0043] Figure 5 The figure shows the simulation results of the electric field on the main plane of the device's "supramolecular" unit at the resonant absorption peak of 1.734 microns. The figure shows 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 narrowband perfect absorption metasurface device", Q = 64), the device's light attenuation is greatly reduced, which is conducive to improving and stabilizing the Q value.

[0044] Figure 6 This is a schematic diagram of the fabrication process for the metasurface device of the present invention. As shown, a "supramolecular" unit array structure is first fabricated on a glass (silicon dioxide) substrate using femtosecond laser processing technology. Next, a gold film with a thickness of approximately 0.1 microns is deposited on the surface of the "supramolecular" unit array structure using atomic layer deposition technology. This thickness is greater than the skin depth of the incident light operating wavelength, enabling reflection spectrum detection.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A robust high-Q plasmon resonance metasurface device, characterized in that: The invention comprises a substrate, supramolecular units arranged in a periodic array on the substrate, and a surface metal layer arranged on the substrate and the supramolecular units, wherein the surface metal layer is a gold layer having a thickness of 0.1 micrometer; The "supramolecular" unit includes two pillars arranged at a certain distance from each other and a crossbar connected between the two pillars. The two pillars have the same height; the bottom radii of the two pillars are different, presenting an asymmetric configuration; the length direction of the crossbar is the same as the arrangement direction of the pillars; the pillars are cone-shaped with a cross-sectional radius gradually decreasing from their base side to their top side; the height of the crossbar is less than the height of the pillars; the longitudinal section of the crossbar is a semi-elliptical surface of uniform size; the bottom radii of the two pillars are R=0.25 microns and r=0.15 microns respectively; the height of the pillars is H=1.6 microns; the bottom width of the crossbar is W=0.4 microns, and the height is h=0.6 microns. The center distance between the two pillars is 0.8 microns. The periodic size of the "supramolecular" unit is 1.6 microns × 1.6 microns. When the polarization direction of the incident linearly polarized light 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, a high Q value perfect absorption peak appears in the reflection spectrum.

2. The metasurface device according to claim 1, characterized in that The incident normal polarized light is near-infrared polarized light, and its wavelength ranges from 1.5 microns to 2.0 microns.

3. The metasurface device according to claim 2, characterized in that The thickness of the surface metal layer is greater than the skin depth of the near-infrared polarized light.

4. The metasurface device according to claim 1 or 2, characterized in that: The number of periodic arrangements of the "supramolecular" units in the horizontal and vertical directions is greater than or equal to 10.

5. The metasurface device according to claim 1 or 2, characterized in that: The "supramolecular" unit is formed by a photoresist layer spin-coated on a substrate through a femtosecond laser direct writing process.

6. The metasurface device according to claim 1 or 2, characterized in that: When the wavelength of the incident linearly polarized light is 1.734 μm and a narrow-band perfect absorption peak appears, the quality factor is as high as Q=182.

7. The metasurface device according to claim 1 or 2, characterized in that: The substrate is a silicon dioxide substrate.

Images