Perfect absorption device of ultra-high quality factor based on dielectric grating

Abstract

The invention discloses an ultra-high quality factor perfect absorption device based on a dielectric grating. The perfect absorption device comprises a substrate, a dielectric grating and metal microstructures, the dielectric grating is located on the substrate, and the metal microstructures are periodically arranged on protrusions of the dielectric grating, so that a guided mode (GMs) is excited in a non-resonance area of localized surface plasmon resonance (LSPR), and perfect absorption of an ultra-high quality factor is achieved. According to the device structure, double-band near-perfect absorption and a high-quality factor (Q is greater than or equal to 8115) in a near-infrared region are realized, the highest quality factor of near-perfect absorption in a currently known plasma system is obtained, and the device is a perfect absorption device with excellent performance.

Description

Technical Field

[0001] The present invention relates to a perfect absorption device in a near-infrared band, and in particular to a perfect absorption device with high robustness and ultra-high quality factor based on a guided mode in a dielectric grating. Background Art

[0002] Absorption is an important process in the interaction between light and matter, supporting a range of applications including sensing, photothermal devices, photocatalysis, and photodetection. Absorption in metals shows promise in thermophotonic and thermoemissive devices, driving absorption enhancement research. However, poorly optimized structures often result in reduced absorption efficiency and limited flexibility in spectral tuning. With the advancement of micro-nanofabrication 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. A variety of structures including metal-insulator-metal (MIM) and Tamm structures are usually used to obtain perfect absorption. In theory, methods such as coupled mode theory (CMT), equivalent circuits, 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 are widely used in energy harvesting, while the latter show potential in thermal radiators, high-resolution sensing, and photodetection. Existing designs apply strategies such as bound states in the continuum (BIC), surface lattice resonance (SLR), Fano resonance, Fabry-Pérot (FP) resonance, and hybrid coupling to achieve narrowband highly absorbing metasurfaces. Absorbing materials can be mainly divided into two categories: dielectrics and metals. Due to low intrinsic losses, all-dielectric designs usually show higher Q factors (10 2 -10 4 ). In contrast, achieving high Q factors in conventional plasmonic systems is elusive because radiative and non-radiative losses due to plasmonic damping degrade the spectral quality (Q < 10). Using alkali metals with relatively low in-band damping as absorbers is a potential option, but the main difficulties that need to be overcome include fabrication and structural instability. Therefore, achieving narrowband high absorption in high-loss plasmonic systems remains a challenge.

[0004] Recent studies have focused on using optical resonances and hybrid coupling to improve the Q factor. For example, Li et al. (SB Zhongyang Li, and Koray Aydin, "Ultra-narrow 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-complete 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 achieved a Q factor of 591 and up to 89% absorption in a dual-band resonant absorption spectrum using SLRs supported by a resonator array and hybrid coupling with particle plasmons. 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)) used the interaction between two diffraction-coupled surface plasmon polariton (SPP) modes to realize a tunable narrowband and broadband coexisting absorber based on a simple stepped all-metal grating structure, showing an ultra-narrow absorption band of 1.5 nanometers and a relatively wide absorption band of 29.8 nanometers, with the absorption rate of both in the infrared region approaching 100%.

[0005] However, the above mechanism relies heavily on spectral overlap and mode coupling. Recent theoretical work uses quasi-bound state Q-BIC to excite narrowband modes with high absorption. For example, Wang et al. (W. Wang, LV Besteiro, P. Yu, et al., "Plasmonic hot-electron photodetection with quasi-bound states in the continuum and guided resonances," Nanophotonics 10, 1911-1921 (2021)) proposed a device based on silver grating / TiO2, achieving 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 thermalemitters driven by mirror-coupled plasmonic quasi-BIC metasurfaces," Optica 11 (2024)) introduced a mirror-coupled system based on plasma Q-BIC, theoretically showing an ultra-narrow single peak with a Q factor of about 64 and near-complete absorption. Although the BIC approach shows the potential for high narrowband absorption, its fabrication usually relies on symmetry breaking in delicate structures, which leads to high demands on manufacturing.

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

[0007] In view of the above deficiencies in the prior art, the present invention provides a perfect absorption device based on a dielectric grating to achieve near-perfect light absorption with an ultra-high quality factor.

[0008] The technical solution adopted by the present invention is:

[0009] A perfect absorption device with an ultra-high quality factor based on a 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 a guided mode is excited in a non-resonant region of a localized surface plasmon resonance to achieve perfect absorption with an ultra-high quality factor.

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

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

[0012] Furthermore, on the protrusion of each dielectric grating, at least one row of metal microstructures is periodically arranged along the grating axis direction. Preferably, the structural parameters and arrangement period of all metal microstructures are the same.

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

[0014] Furthermore, on each protrusion of the dielectric grating, two rows of metal microstructures are periodically arranged symmetrically along the grating axis. Preferably, all metal microstructures have the same structural parameters and arrangement period, and the positions of the two rows of metal microstructures along the grating axis are the same or staggered by half a period.

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

[0016] Furthermore, the dimensional error of the metal microstructure is within ten percent.

[0017] The present invention proposes a new optical structure device based on a hybrid plasma of a dielectric grating, which has the following beneficial effects compared with the prior art:

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

[0019] (2) By adjusting the size and position of the metal microstructure, the radiation and non-radiation losses of the device structure can be adjusted, and a dual-band narrowband perfect absorption peak can be achieved in a wider band of 1500nm-1600nm.

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

[0021] (4) The present invention has the highest quality factor for near-perfect absorption in currently known plasma systems, which is higher than the quality factor of previous works based on the LSPR resonance principle.

[0022] (5) The device of the present invention shows excellent structural parameter robustness and is a perfect absorber with excellent performance in the light absorption system.

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

[0024] Figure 1 Schematic diagram of the structure of the high-Q perfect absorption device based on guided mode in the present invention. (a) Schematic diagram of the hybrid structure supporting high-Q perfect absorption of guided mode, (b) top view of a single periodic structure, (c) spectrum diagram under TM polarization.

[0025] Figure 2 Mode analysis of the hybrid structure of the present invention. (a) The dispersion curve shows the low-order mode of the hybrid waveguide structure, (b) The distribution of the x-component of the electric (magnetic) field of different modes, where the black arrows represent the electric (magnetic) field lines. y The changes of Q value (c) and absorption spectrum (d) of the two modes.

[0026] Figure 3 The high absorption spectra of the present invention at different gold disk positions and radii. (a) Absorption spectra of TM-a mode at different Δx, (b) Absorption spectra of TE-s mode at different radii, (c) Q of TM-a mode at different Δx r and Q nr , (d) Q of TE-s mode with different Δx r and Q nr .

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

[0028] Figure 5 The effects of three typical manufacturing deviations on the performance of the hybrid structure of the present invention. (a) Three periods p y Below, Type I: manufacturing deviation of radius, Type II: manufacturing deviation of position in the x-direction, Type III: manufacturing deviation of position in the y-direction; absorption spectra of three groups of radius deviation parameters (b), x-direction position deviation parameters (c) and y-direction position deviation parameters (d), where the inset is an enlarged view of the resonance peak. DETAILED DESCRIPTION

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

[0030] like Figure 1 As shown, the perfect absorption device of this embodiment is a hybrid structure, including a substrate, a dielectric grating and a metal microstructure. Among them, the substrate is made of silicon dioxide material with a refractive index of 1.4-1.6; the dielectric grating is located on the substrate, and a high-reflectivity silicon material is used. Silicon exhibits near-zero absorption in the near-infrared region and has a refractive index of 3-4; the metal microstructure can be in the shape of a disk, a cylinder, a square, etc., and is periodically arranged on the protrusions of the silicon grating; the material of the metal is not limited, and can be gold, silver, aluminum, tungsten, etc. High absorption with ultra-high quality factor can be achieved by adjusting the structural parameters. The operating band of the perfect absorption device 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 a vacuum (λ0).

[0031] Example 1

[0032] In order to better demonstrate the technical solution, in this embodiment, a gold disk microstructure is used, the refractive index of silicon dioxide is 1.48, the refractive index of silicon is 3.48, the dielectric silicon grating is a rectangular parallelepiped, and the structural parameters are: the protrusion thickness h = 461nm, the width of a single grating protrusion w = 525nm, and the 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 transform from a bound state to a leaky state and thus be observed in the far field. Figure 1 Figure (c) shows the period p in the y direction of the gold disk. y=525nm and the disk radius r=60nm, height t=20nm, and when the gold disk is located at the edge of the grating protrusion, the resonance of the asymmetric TM mode and the symmetric TE mode (respectively represented as TM-a and TE-s) at 1525nm and 1534nm is excited, and the absorption rate is 99% and 98%, wherein R-pure grating represents the reflectivity of the pure dielectric grating, R-hybird grating represents the reflectivity of the structure of this embodiment, T represents the transmittance, and A represents the absorptivity. The full width at half maximum (FWHM) obtained by the absorption spectrum is 0.18nm and 0.056nm respectively, and the Q factor of the structure of this embodiment at 1525nm and 1534nm is calculated to be 8115 and 26951 respectively. Compared with previous studies on high-Q, high-absorption metals, this design shows nearly perfect absorption and higher Q value, with the lowest value reaching more than 8115.

[0033] Figure 2 As shown, the dispersion curve of the hybrid structure of the present invention in the range of 1500nm-1600nm exhibits four guided modes. According to the different components of the in-plane field, these modes can be divided into TE (transverse electric) and TM (transverse magnetic) types, as shown in Figure (b). TE-a and TE-s, as well as TM-a and TM-s correspond to two groups of degenerate states. The introduction of lossy metal leads to the separation of the characteristic frequencies of these degenerate states, forming four different curves in the dispersion curve. 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 state in the continuous medium mode. In contrast, the symmetric distribution of the TE-s and TM-s modes corresponds to the guided mode resonance mode. When p y The Q value fluctuates slightly when varying in the range of 510nm-560nm, but remains stable on the same order of magnitude, as shown in Figure (c). The spectrum in Figure (d) shows the stability of the high absorption resonance.

[0034] Figure 3 The perfect absorption of the device of the present invention is achieved. (a) shows p y =525nm and the absorption spectra of the TM-a mode with a disk radius of 60nm when the disk is located at different positions on the grating (i.e., the vertical distance Δx from the center of the disk to the axis of the grating protrusion is 190nm, 160nm, and 130nm). As a symmetry-protected BIC mode, the absorption intensity of TM-a is observed to decrease with increasing structural symmetry, accompanied by a slight red shift. The absorption spectrum shows that for the TM-a mode, the closer the gold disk is to the grating edge, the higher the absorption rate, reaching 99.2% at 190nm. This shows that the accurate positioning of the perturbation can promote the balance between radiative and non-radiative losses, thereby 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 decreases with increasing structural symmetry, approaching values ​​closer to 1. When the relative positions of the gold disks along the x-direction are fixed, a smaller radius reduces metal losses and further increases Q. Although Q r and Q nr The theoretical intersection of implies perfect absorption, but this does not mean that the absorption is significantly reduced at non-intersection points. For r = 60 nm, Figure 3 However, in the range of Δx from 150nm to 190nm, Q r / Q nr The ratio of is already less than 1.1, which indicates that high absorption may occur in this wide range. Similarly, for r = 65nm, in the range of Δx from 130nm to 190nm, Q r / Q nr The values ​​ranged from 1.05 to 0.94, indicating a high level of absorption. Figure 3 (b) shows p y =525nm TE-s mode absorption spectrum, gold disk located at Δx = 190nm for different radii (r = 55nm, 60nm, 65nm). As the radius increases, the TE-s mode resonance peak broadens and red-shifts. The absorbance of TE-s exceeds 95% in all three parameters, with a near-perfect absorbance of 99.1% at 60nm. At r = 60nm, Q r / Q nr The ratio is closest to 1. (d) The figure shows the Q of the TE-s mode at different radii r. r and Q nr In contrast to the trend of the TM-a mode, the increase in structural symmetry leads to a Q r and Q nr As increases, these values ​​become closer and closer. This explains why perfect absorption points of two modes can be found at the edge of the grating at the same time, thus achieving dual-band high-Q perfect absorption.

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

[0036] Example 2

[0037] Figure 4The present invention introduces a symmetrically placed gold disk array to achieve a nearly symmetrically protected BIC mode (TM-a). As shown in the inset of (a), the gold disks of r = 40 nm are symmetrically located on both sides of the grating axis at Δx = ±200 nm, the height of the gold disks is t = 20 nm, and the structural parameters of the grating are the same as those of Example 1. Symmetric E x The distribution represents the TE symmetric mode. Due to the symmetrical placement of the gold disks, the symmetry-protected BIC mode (TM-a) is suppressed, leaving only the TE-s mode at 1533.75nm in the range of 1500nm-1600nm. The circles in the inset represent the Fano line shape fit with a half width of 0.06nm and a calculated Q factor of 25566, which matches the 22161 obtained for the bandgap. The design shows excellent tunability, as shown in Figure (c). By varying p between 510nm and 550nm y , which can effectively red-shift the wavelength of the resonance peak, thus being able to dynamically control the resonance absorption peak in the range of 1500nm-1600nm. During the adjustment process, the average absorption remained at 97% and the Q factor increased slightly around 25000.

[0038] In addition, an array of gold disks staggered by half a period along the y-axis was introduced to excite TM-s using only symmetric field distribution. Figure 4 As shown in the inset of (b), the period p of two rows of gold disks with r = 40 nm y The gratings are arranged symmetrically with half a period staggered along the axis y, and the relative positions are within Δx = ±200nm. The illustration shows the magnetic field H of the excitation mode. x Components and Fano linear fitting curve. x The symmetrical magnetic field distribution indicates the TM-s mode. Staggering the gold disk by half a period will introduce an initial phase difference of π, resulting in the suppression of the destructive interference of the magnetic field of the TM-a mode and the excitation of the constructive interference of the magnetic field of the TM-s mode. Obviously, only the TM-s mode is excited in the range of 1500nm-1600nm, and the resonant wavelength only appears at 1525.55nm. Fano fitting of the spectral data obtained a half-width of 0.02nm and a calculated Q factor of 76250. This is exactly consistent with the band calculation of 65705. As Figure 4 As shown in (d), p y Adjusting from 520nm to 560nm effectively red-shifts the wavelength of the resonance peak. The resonance line width and absorption intensity remain stable. The average absorptivity 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 over a relatively wide wavelength range. By adjusting p y , the position of the resonance peak can be flexibly customized, thereby achieving dynamic control of the resonance absorption peak.

[0039] This embodiment introduces a destructive interference mechanism by designing structural symmetry, which can selectively suppress quasi-bound states (Q-BIC) in the continuum or excite guided mode resonances (GMRs), thereby achieving single-peak high-Q perfect absorption and enhancing the spectral selectivity of the device.

[0040] Example 3

[0041] Figure 5 The structure of the present invention is shown in a comprehensive simulation and discussion of various processing deviations. The present invention sets the structural size deviation range of the gold disk to ±10%, and the relative position deviation range to ±10nm. These design deviations take into account the manufacturing capabilities of electron beam lithography (EBL) and leave enough tolerance. For Type I deviation, there are three different groups of Δr 1-3 The value range is ±(r×10%). These deviation values ​​are assigned to the three gold disks to form a new radius r 1-3 =r+Δr 1-3 . The spectrum is shown in Figure (b), where the numbers 1, 2, and 3 represent three different groups of deviations. The simulation process is calculated as a unit with three cycles, so each group of parameters will have three sub-deviation values. 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 offset in the two absorption peaks, which is less than 0.2nm. The deviation of the absorption performance is negligible. For Type II and Type III deviations, three different groups of Δx are randomly generated. 1-3 and Δy 1-3 Values, ranging from ±10nm. Since the gold disk is initially 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 the three gold disks to form new positions. The spectrum is as follows Figure 5As shown in (c) and (d), the structure with position deviation shows a slight shift in the two absorption peaks compared to the structure without processing deviation, the shift is less than 0.2nm, and the maximum shift does not exceed 0.4nm. The maximum deviation of the absorption peak is less than 0.05. In addition, when the x-direction deviation occurs, the x-direction mode may be weakly excited, resulting in a series of weak disordered resonance peaks. However, these peaks show significant differences in both intensity and Q factor compared to the resonance peaks of interest. Considering their size differences, these redundant resonances are negligible and can be ignored in the experiment. Compared with the ideal structure without deviation, the resonance peaks of the structure with manufacturing deviation show a slight shift, and the maximum shift is controlled within 0.4nm. These findings confirm that the absorption device proposed in the present invention can maintain high performance standards even in the case of unavoidable manufacturing deviations. Therefore, it is reasonable to expect that the design of the present invention will have excellent robustness even in the presence of minor deviations in the experimental manufacturing process, further emphasizing the stability and reliability of the structural characteristics and proving the high robustness of the device.

[0042] The above embodiments are merely illustrative of the principles and functions of the present invention, rather than limiting the present invention. Any insubstantial replacement or modification that does not exceed the essential spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A perfect absorption device with ultra-high quality factor based on dielectric grating, characterized in that: The device includes 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 the guided mode is excited in the non-resonant region of the localized surface plasmon resonance to achieve perfect absorption with an ultra-high quality factor.

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

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

6.

4. The ultra-high quality factor perfect absorption device based on dielectric grating according to claim 1, characterized in that: On the protrusion of each dielectric grating, at least one row of metal microstructures is periodically arranged along the grating axis center line direction.

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

6. The ultra-high quality factor perfect absorption device based on dielectric grating according to claim 4, characterized in that: The center of the metal microstructure coincides with the grating axis, or deviates from it by a certain distance.

7. The ultra-high quality factor perfect absorption device based on dielectric grating according to claim 4, characterized in that: On the protrusion of each dielectric grating, two rows of symmetrical metal microstructures are periodically arranged along the axial center line of the grating.

8. The ultra-high quality factor perfect absorption device based on dielectric grating according to claim 7, characterized in that: The structural parameters and arrangement period of all metal microstructures are the same, and the positions of two rows of metal microstructures along the grating axis are the same or staggered by half a period.

9. A perfect absorption device with ultra-high quality factor based on dielectric grating according to any one of claims 1 to 8, characterized in that: The dimensions of the metal microstructure are: radius of 50-75nm, height of 20nm-40nm, and period of 500-600nm.

10. The ultra-high quality factor perfect absorption device based on dielectric grating according to claim 9, characterized in that: The dimensional error of the metal microstructure is within ten percent.

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