A perfect absorption device based on dielectric grating with ultra-high quality factor

Abstract

The application discloses a perfect absorption device based on a dielectric grating and having an ultrahigh quality factor. The perfect absorption device comprises a substrate, a dielectric grating and a metal microstructure, wherein the dielectric grating is located on the substrate, and the metal microstructure is periodically arranged on protrusions of the dielectric grating, so that guided modes (GMs) are excited in a non-resonance region of a localized surface plasmon resonance (LSPR), thereby realizing perfect absorption with an ultrahigh quality factor. The device structure of the application realizes double-band near-perfect absorption in a near-infrared region and a high quality factor (Q >= 8115), and obtains the highest quality factor of near-perfect absorption in a currently known plasmonic system, and is a perfect absorption device with excellent performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a perfect absorption device in the near-infrared band, in particular to a perfect absorption device based on high robustness and ultra-high quality factor of guided modes in dielectric gratings. BACKGROUND

[0002] Absorption is an important process of light-matter interaction, supporting a range of applications, including sensing, photothermal devices, photocatalysis, and photodetection. The absorption of metals shows promise in thermal photonic and thermal emission devices, driving the research of absorption enhancement. However, the suboptimal structures often lead to reduced absorption efficiency and limited spectral tuning flexibility. With the advancement of micro-nano fabrication technology, highly tunable artificial microstructures have become a widely used tool in research and practical applications. Perfect absorption is a basic requirement for efficient energy conversion and enhancement of optoelectronic devices. Various structures including metal-insulator-metal (MIM) and Tamm structures are commonly used to achieve perfect absorption. Theoretically, methods such as coupled mode theory (CMT), equivalent circuit, and impedance matching have been developed for perfect absorption design.

[0003] Perfectly absorbing metasurfaces can be divided into two types: broadband and narrowband. The former is widely used in energy collection, while the latter shows potential in thermal emitters, high-resolution sensing, and photodetection. Existing designs have applied strategies such as bound states in the continuum (BIC), surface lattice resonances (SLR), Fano resonances, Fabry-Pérot (FP) resonances, and hybrid coupling to achieve narrowband high-absorption metasurfaces. Absorbing materials can be mainly divided into two categories: dielectric and metal. Due to the low intrinsic loss, all-dielectric designs usually show higher Q factors (10 2 -10 4 ). In contrast, it is elusive to achieve high Q factors in traditional plasmonic systems, as the radiative and non-radiative losses caused by plasmonic damping reduce the spectral quality (Q < 10). Using alkali metals with relatively low in-band damping as absorbers is a potential option, but the main difficulties to overcome include fabrication and structural instability. Therefore, it is still a challenge to achieve narrowband high absorption in high-loss plasmonic systems.

[0004] Recent studies have focused on using optical resonances and hybrid coupling to improve the Q factor. For example, Li et al. (S. B. Zhongyang Li, and Koray Aydin, "Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces," ACS Nano (2014)) proposed a photodetector based on a perfect absorber by depositing a gold film on a pre-patterned silicon substrate, achieving near-perfect absorption and high photoresponsivity (Q ~ 3.5) through the overlap of LSPR and FP resonances. Liu et al. (Z. Liu, G. Liu, G. Fu, et al., "All-metal meta-surfaces for narrowband light absorption and high performance sensing," Journal of Physics D: Applied Physics 49 (2016)) designed an all-metal metasurface that utilized SLR supported by an array of resonators and hybrid coupling with particle plasmons, achieving a Q factor of 591 and up to 89% absorption in a dual-band resonant absorption spectrum. Wang (J. Wang, Z. Zhang, Z. Lin, et al., "Tunable narrowband and broadband coexisting absorber enabled by a simple all-metal grating for sensing applications," Frontiers in Physics 11 (2023)) utilized the interaction between two diffractively coupled surface plasmon polariton (SPP) modes to achieve a tunable narrowband and broadband coexisting absorber based on a simple stepped all-metal grating structure, exhibiting an ultranarrow absorption band of 1.5 nanometers and a relatively wide absorption band of 29.8 nanometers, both with an absorption rate close to 100% in the infrared region.

[0005] However, the above mechanisms are largely dependent on spectral overlap and mode coupling. Recent theoretical work uses quasi-bound state Q-BIC excitation of narrowband modes with high absorption, such as the device proposed by Wang et al. (W. Wang, L. V. Besteiro, P. Yu, et al., "Plasmonic hot-electron photodetection with quasi-bound states in the continuum and guided resonances," Nanophotonics 10, 1911-1921 (2021)) based on silver grating / TiO2, which achieves near-perfect absorption in multi-band narrowband devices with a theoretical Q factor of 475. Yang et al. (S. Yang, M. He, C. Hong, et al., "Single-peak and narrow-band mid-infrared thermal emitters driven by mirror-coupled plasmonic quasi-BIC metasurfaces," Optica 11 (2024)) introduced a mirror-coupled system based on plasmonic Q-BIC, which theoretically shows super-narrow single-peak and near-perfect absorption with a Q factor of about 64. Although the BIC method shows the potential of high narrowband absorption, its manufacture usually relies on the symmetry breaking in the precise structure, which leads to high requirements for manufacturing.

[0006] Therefore, although several mechanisms have been introduced to continuously improve the mode Q factor, its numerical value still needs to be further improved, and most device structures use a gold or silver layer about 100 nanometers thick as a complete mirror to achieve zero transmission, which brings difficulties in preparation and application. SUMMARY

[0007] In view of the deficiencies in the prior art, the present application provides a perfect absorption device based on dielectric grating to realize near-perfect optical absorption with ultra-high quality factor.

[0008] The technical scheme adopted by the present application is:

[0009] An ultra-high quality factor perfect absorption device based on dielectric grating, the device comprising a substrate, a dielectric grating and a metal microstructure, wherein the dielectric grating is located on the substrate, and the metal microstructure is periodically arranged on the protrusions of the dielectric grating, so that guided modes are excited in the non-resonance region of localized surface plasmon resonance to realize perfect absorption with ultra-high quality factor.

[0010] Further, the dielectric grating is made of silicon material, the thickness of the grating is 460-490nm, the width of the single grating protrusion is 330-550nm, and the period is 660-710nm.

[0011] Further, the refractive index of the silicon material is 3-4, and the substrate is made of silicon dioxide material with a refractive index of 1.4-1.6.

[0012] Further, on the protrusion of each dielectric grating, there are at least one column of metal microstructures arranged periodically along the grating axis.

[0013] Further, the center of the metal microstructure coincides with the grating axis or deviates by a certain distance.

[0014] Further, on the protrusion of each dielectric grating, there are two columns of metal microstructures arranged periodically along the grating axis.

[0015] Preferably, the size of the metal microstructure is: radius 50-75nm, height 20nm-40nm, and period 500-600nm.

[0016] Further, the size error of the metal microstructure is within 10%.

[0017] The present application provides a new optical structure device based on hybrid plasmonic of dielectric grating, compared with the prior art, has the following beneficial effects:

[0018] (1) Using a high-reflectivity planar waveguide layer to replace the traditional metal reflector, exciting guided modes (GMs) in the non-resonant region of localized surface plasmon resonance (LSPR), thereby realizing a tunable dual-band, high-Q (≥8115) perfect light absorber.

[0019] (2) By adjusting the size and position of the metal microstructure, the radiation and non-radiation loss of the device structure can be adjusted, and a double-section narrow-band perfect absorption peak can be realized in a wide wavelength range of 1500nm-1600nm.

[0020] (3) By designing the structural symmetry to introduce destructive interference mechanism, the quasi-bound state (Q-BIC) in the continuum or guided mode resonance (GMRs) can be selectively suppressed, thereby realizing a single-peak high-Q perfect absorption, and the spectral selectivity of the device is also enhanced.

[0021] (4) The present application is the highest quality factor of near-perfect absorption in the known plasma system, higher than the quality factor based on the principle of LSPR resonance work in the past.

[0022] (5) The device of the present application shows excellent structural parameter robustness, which belongs to a perfect absorber with excellent performance in the light absorption system.

[0023] (6) The device designed in the present application not only overcomes the manufacturing and application limitations of the existing structure, but also provides new opportunities for realizing high-performance optoelectronic devices, showing great potential in the fields of narrow-band plasma filtering, hyperspectral imaging and thermal emission, and providing a new method and platform for future optoelectronic device design. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the high-Q perfect absorption device of the present application based on guided mode. (a) Schematic diagram of a mixed structure supporting high-Q perfect absorption of guided mode, (b) top view of a single period structure, (c) spectral diagram under TM polarization.

[0025] Figure 2 It is a mode analysis of the mixed structure of the present application. (a) Low-order mode of the mixed waveguide structure shown by the dispersion curve, (b) x-component distribution of the electric (magnetic) field of different modes, wherein the black arrow indicates the electric (magnetic) field line, and the Q value (c) and the absorption spectrum (d) of the two modes change with p y .

[0026] Figure 3 It is a high absorption spectrum diagram of the present application under different gold disc positions and radii. (a) Absorption spectrum of TM-a mode under different Δx, (b) absorption spectrum of TE-s mode under different radii, (c) Q r and Q nr of TM-a mode under different Δx, (d) Q r and Q nr of TE-s mode under different Δx.

[0027] Figure 4 It is two schemes for realizing single-peak operation of the present application. (a) Absorption diagram of TE-s mode of double-symmetric circular grating structure, the upper inset shows the fitting of Fano line shape and resonance peak, and the lower inset shows the normalized electric field x-component; (b) absorption diagram of TM-s mode of asymmetric double circular grating structure, the upper inset shows the fitting of Fano line shape and resonance peak, and the lower inset shows the normalized magnetic field x-component; (c) absorption spectrum diagram of double-symmetric circular grating structure with different periods (p y = 510nm, 520nm, 530nm, 540nm and 550nm); (d) absorption spectrum diagram of double-symmetric circular grating structure with different periods (p yAbsorption spectra of a double asymmetric disk grating structure (520nm, 530nm, 540nm, 550nm, and 560nm).

[0028] Figure 5 This invention illustrates the impact of three typical manufacturing deviations on the performance of the hybrid structure. (a) Three periods p y Below are the absorption spectra of three sets of parameters: Type I: manufacturing deviation of radius, Type II: manufacturing deviation of x-direction position, and Type III: manufacturing deviation of y-direction position; and the insets are magnified views of the resonance peaks. Detailed Implementation

[0029] This embodiment provides a high-Q perfect absorber based on a hybrid plasma structure with a high-reflectivity dielectric grating. By exciting guided modes in the non-resonant region of the LSPR, dual-band, high-Q (≥8115), near-perfect light absorption in the near-infrared region is achieved. The analysis of this embodiment is performed using COMSOL Multiphysics numerical simulation.

[0030] like Figure 1 As shown, the perfect absorber in this embodiment is a hybrid structure, including a substrate, a dielectric grating, and a metal microstructure. The substrate is made of silicon dioxide with a refractive index of 1.4-1.6. The dielectric grating, located on the substrate, is made of highly reflective silicon, which exhibits near-zero absorption in the near-infrared region and has a refractive index of 3-4. The metal microstructure can be in the form of a disk, cylinder, or square, and is periodically arranged on the protrusions of the silicon grating. The metal material is not limited and can be gold, silver, aluminum, tungsten, etc. High absorption with an ultra-high quality factor can be achieved by adjusting the structural parameters. The operating wavelength of the perfect absorber in this embodiment is 1500nm-1600nm, the incident light is TM-polarized light, and the Q factor is defined as the full width at half maximum (FWHM) divided by the wavelength in vacuum (λ0).

[0031] Example 1

[0032] To better demonstrate the technical solution, this embodiment employs a gold disk microstructure. The refractive index of silicon dioxide is 1.48, and that of silicon is 3.48. The dielectric silicon grating is cuboid, with the following structural parameters: bump thickness h = 461 nm, width of a single grating bump w = 525 nm, and period p in the x-direction. x =703nm, where the periodic arrangement of gold disks on the grating provides momentum matching for the guided mode, causing the guided mode to change from a bound state to a leaky state, thus being observed in the far field. Figure 1 Figure (c) shows the period p in the y-direction of the gold disk. yWith a gold disk radius r = 60 nm and a height t = 20 nm, and when the gold disk is located at the edge of the grating protrusion, the asymmetric TM mode and the symmetric TE mode (denoted as TM-a and TE-s, respectively) resonate at 1525 nm and 1534 nm, respectively, with absorption rates of 99% and 98%. Here, R-pure grating represents the reflectivity of the pure dielectric grating, R-hybrid grating represents the reflectivity of the structure in this embodiment, T represents the transmittance, and A represents the absorptivity. The full width at half maximum (FWHM) obtained from the absorption spectrum are 0.18 nm and 0.056 nm, respectively. The calculated Q factors of the structure in this embodiment at 1525 nm and 1534 nm are 8115 and 26951, respectively. Compared with previous studies on high-Q, high-absorption metals, this design exhibits near-perfect absorption and a higher Q value, with a minimum value exceeding 8115.

[0033] Figure 2 The dispersion curves of the hybrid structure of this invention in the 1500nm-1600nm range show four guided modes. Based on the different components of the in-plane field, these modes can be classified into TE (transverse electric) and TM (transverse magnetic) types, as shown in Figure (b). TE-a and TE-s, and TM-a and TM-s, correspond to two sets of degenerate states. The introduction of a lossy metal causes the characteristic frequencies of these degenerate states to separate, forming four different curves in the dispersion curves. Figure (b) shows that the field components of the TE-a and TM-a modes exhibit an antisymmetric distribution along the y-direction, which corresponds to the bound states in the continuous medium mode. In contrast, the symmetrical distribution of the TE-s and TM-s modes corresponds to the guided mode resonance mode. When p y When varying within the 510 nm–560 nm range, the Q value fluctuates slightly but remains stable on the same order of magnitude, as shown in Figure (c). The spectrum in Figure (d) demonstrates the stability of the high absorption resonance.

[0034] Figure 3 The diagram illustrates the implementation of perfect absorption in the device of this invention. (a) shows p y Absorption spectra of the TM-a mode at 525 nm and the disk at different positions on the grating (i.e., the vertical distance Δx from the center of the disk to the axis of the grating protrusions is 190 nm, 160 nm, and 130 nm) with a disk radius of 60 nm. As a symmetry-protected BIC mode, the absorption intensity of TM-a decreased with increasing structural symmetry, accompanied by a slight redshift. The absorption spectra show that for the TM-a mode, the closer the gold disk is to the grating edge, the higher the absorptivity, reaching 99.2% at 190 nm. This indicates that accurate perturbation positioning can promote a balance between radiative and non-radiative losses, thus satisfying the prerequisite for perfect absorption. (c) shows the radiative loss Q of TM-a at different radii r. rand non-radiative losses Q nr The results show that for a given radius r, Q r and Q nr decrease with increasing symmetry of the structure, approaching values closer to 1. Smaller radii reduce the metal losses and further increase Q when the relative position of the gold disc along the x-direction is fixed. Although Q r and Q nr the theoretical crossing point implies perfect absorption, it does not mean that the absorption is significantly reduced at non-crossing points. For r = 60 nm, a clear crossing point cannot be distinguished in (c) of Fig. 4. However, in the range of Δx from 150 nm to 190 nm, the ratio of Q Figure 3 r nr has been less than 1.1, which indicates that high absorption can be produced in this wide range. Similarly, for r = 65 nm, in the range of Δx from 130 nm to 190 nm, the Q r nr values range from 1.05 to 0.94, with high levels of absorption. Figure 3 (b) of Fig. 4 shows the absorption spectra of the TE-s mode for p y = 525 nm with the gold disc located at Δx = 190 nm for different radii (r = 55 nm, 60 nm, 65 nm). As the radius increases, the TE-s mode resonance peak broadens and red-shifts. The absorption of the TE-s mode exceeds 95% on all three parameters, with near perfect absorption of 99.1% at 60 nm. At r = 60 nm, the Q r nr ratio is closest to 1. (d) of Fig. 4 shows the Q r and Q nr of the TE-s mode for different radii r. In contrast to the trend of the TM-a mode, increasing the symmetry of the structure results in an increase of Q r and Q nr , with these values increasingly approaching each other. This explains why the perfect absorption points of both modes can be found simultaneously at the edges of the grating, enabling dual-band high-Q perfect absorption.

[0035] The device of this embodiment arranges metal microstructures periodically on a dielectric grating, and by adjusting its radius and position on the grating, it can optimize the radiative and non-radiative losses of the structure, thereby achieving narrow-band high-Q perfect absorption in the 1500-1600 nm wavelength band.

[0036] Example 2

[0037] Figure 4 ​​​​The BIC mode (TM-a) with near-symmetry protection is shown by introducing symmetrically placed gold disk arrays. As shown in the inset of (a), two rows of gold disks with r = 40 nm are symmetrically placed at Δx = ±200 nm on both sides of the grating axis. The height of the gold disks is t = 20 nm, and the grating has the same structural parameters as in Example 1. The symmetric E x The distribution represents the TE-symmetric mode. Due to the symmetric placement of the gold disks, the symmetrically protected BIC mode (TM-a) is suppressed, leaving only the TE-s mode at 1533.75 nm in the range of 1500-1600 nm. The circles in the inset represent the Fano line fitting, with a half-width of 0.06 nm and a calculated Q factor of 25566, which matches the band calculation of 22161. This design exhibits excellent tunability, as shown in (c). By changing p y , the wavelength of the resonance peak can be effectively red-shifted, enabling dynamic control of the resonance absorption peak in the range of 1500-1600 nm. During the adjustment, the average absorption remains at 97%, and the Q factor increases slightly to about 25000.

[0038] In addition, a gold disk array is introduced that is staggered by half a period along the y-axis, and only the symmetric field distribution is used to excite TM-s. As shown in the inset of (b) in Figure 4 , two rows of gold disks with r = 40 nm are placed symmetrically on the grating axis y-axis with a period p y is consistent, but is staggered by half a period along the grating axis y-axis, with a relative position at Δx = ±200 nm. The inset illustrates the magnetic field H x component of the excited mode and the Fano line fitting curve. H x The symmetric magnetic field distribution of H y The staggered half-period of the gold disks introduces a π initial phase difference, resulting in the suppression of the destructive interference of the magnetic field of the TM-a mode and the excitation of the TM-s mode. It is clear that only the TM-s mode is excited in the range of 1500-1600 nm, and the resonance wavelength only occurs at 1525.55 nm. Fano fitting of the spectral data gives a half-width of 0.02 nm and a calculated Q factor of 76250. This is completely consistent with the band calculation of 65705. As shown in (d) of Figure 4 , by adjusting p y from 520 nm to 560 nm, the wavelength of the resonance peak can be effectively red-shifted. The resonance linewidth and absorption intensity remain stable. The average absorption is about 94%, and the Q factor increases slightly to about 70,000. Both schemes ensure that there is only one high-Q, high-absorption peak in a relatively wide wavelength range. By adjusting p y , the position of the resonance peak can be flexibly customized, enabling dynamic control of the resonance absorption peak.

[0039] The embodiment can selectively suppress quasi-bound states in continuum (Q-BIC) or excite guided-mode resonances (GMRs) by designing structural symmetry to introduce destructive interference mechanism, so as to realize single-peak high-Q perfect absorption, and further enhance the spectral selectivity of the device.

[0040] Embodiment 3

[0041] Figure 5 The structure of the present application is shown to be fully simulated and discussed for various processing deviations. The structural size deviation range of the gold disc of the present application is set to ±10%, and the relative position deviation range is set to ±10nm. These design deviations take into account the manufacturing capability of electron beam lithography (EBL) and leave enough tolerance. For Type I deviation, there are three different Δr 1-3 values, ranging from ±(r×10%). These deviation values are assigned to three gold discs to form new radii r 1-3 = r+Δr 1-3 . The spectrum is shown in (b), and the numbers 1, 2, and 3 in the figure represent three different deviation conditions. The simulation process is operated in three periods per unit, so there are three sub-deviation values for each 1 set of parameters. Among them, Δr1={+3, +2, +4}, Δr2={+3, -3, -2}, and Δr3={+6, +1, -6}. Compared with the structure without processing deviation (Δr=0nm), the structure with radius deviation shows a slight shift of less than 0.2nm on the two absorption peaks. The deviation of the absorption performance can be ignored. For Type II and Type III deviations, three different Δx 1-3 and Δy 1-3 values are randomly generated, ranging from ±10nm. Since the initial setting of the gold disc is arranged at the edge of the grating and cannot be moved outside the grating, Δx<0. Among them, Δx1={-7, -5, -4}, Δx2={-10, -4, -1}, and Δx3={-7, -3, -2}. Δy1={+8, +7, -4}, Δy2={-5, +7, -2}, and Δy3={+6, -4, -2} are assigned to three gold discs to form new positions. The spectrum is shown in Figure 5The structures with position deviations show slight shifts in the two absorption peaks compared to the structure without fabrication deviations, with shifts less than 0.2 nm, and the maximum shift is no more than 0.4 nm, as shown in (c) and (d). The maximum deviation of the absorption peak value is less than 0.05. In addition, when the x-direction deviation occurs, the x-direction mode can be weakly excited, thereby generating a series of weak disordered resonance peaks. However, compared with the resonance peaks of interest, these peaks show significant differences in both intensity and Q factor. Considering their size difference, these redundant resonances can be ignored and can be ignored in experiments. Compared with the ideal structure without deviation, the resonance peaks of the structure with manufacturing deviation show slight shifts, with the maximum shift controlled within 0.4 nm. These findings confirm that the proposed absorption device of the present application can maintain high performance standards even in the case of inevitable manufacturing deviations. Therefore, it can be reasonably expected that even in the presence of slight deviations in the experimental manufacturing process, the design of the present application will have excellent robustness, thereby further emphasizing the stability and reliability of the structural characteristics and proving the high robustness of the device.

[0042] The above examples only illustrate the principles and functions of the present application, and are not intended to limit the present application. Any non-essential replacement or modification of the application within the scope of the essential spirit of the present application falls within the scope of the present application.

Claims

1. A dielectric grating based perfect absorption device with ultra-high quality factor, characterized in that, The device comprises a substrate, a dielectric grating and metal microstructures, wherein the dielectric grating is located on the substrate, and the metal microstructures are periodically arranged on the protrusions of the dielectric grating, so that guided modes are excited in the non-resonance region of the localized surface plasmon resonance to realize perfect absorption with super-high quality factor; on each protrusion of the dielectric grating, at least one column of metal microstructures is periodically arranged along the grating axis, and the center of the metal microstructure is offset from the grating axis by a certain distance.

2. The ultra-high quality factor perfect absorption device based on dielectric metasurfaces according to claim 1, wherein, The dielectric grating is made of silicon material, the thickness of the grating is 460-490 nm, the width of a single grating protrusion is 330-550 nm, and the period is 660-710 nm.

3. The ultra-high quality factor perfect absorption device based on dielectric metasurfaces according to claim 2, characterized in that, The refractive index of the silicon material is 3-4, and the substrate is made of silicon dioxide material with a refractive index of 1.4-1.

6.

4. The ultra-high fineness of a perfect absorption device based on dielectric grating according to claim 1, characterized in that, The structural parameters and arrangement period of all metal microstructures are the same.

5. The ultra-high fineness of a perfect absorption device based on dielectric grating according to claim 1, characterized in that, On each protrusion of the dielectric grating, two symmetrical columns of metal microstructures are periodically arranged along the grating axis.

6. The ultra-high quality factor perfect absorption device based on dielectric metasurfaces according to claim 5, characterized in that, The structural parameters and arrangement period of all metal microstructures are the same, and the positions of the two columns of metal microstructures along the grating axis are the same or staggered by half a period.

7. A dielectric grating based perfect absorption device with ultra-high quality factor according to one of claims 1-6, characterized in that, The size of the metal microstructure is: radius 50-75 nm, height 20 nm-40 nm, and period 500-600 nm.

8. The ultra-high quality factor perfect absorption device based on dielectric metasurfaces according to claim 7, characterized in that, The size error of the metal microstructure is within 10%.

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