Tunable high-Q Fano resonance sensor based on asymmetric SOI metasurface

Abstract

The invention discloses a tunable high-Q Fano resonance sensor based on an asymmetric SOI (Silicon On Insulator) metasurface. The sensor adopts a periodic structure design, one unit structure is composed of a silicon dioxide substrate and a silicon dielectric layer, the silicon dioxide substrate is provided with an arrow-shaped structure composed of two parallelograms, and the arrow-shaped structure forms an asymmetric structure of the unit structure about the y axis by adjusting the angle theta of the two parallelograms. When incident light enters along the y axis, the designed sensor excites sharp Fano resonance in a near-infrared fluctuation section, and the Q value reaches 3407.39 by optimizing geometric parameters of the structure. The research shows that the structure has a relatively high Q value, and the designed structure is simple, easy to manufacture and relatively low in material cost, and has a potential application prospect in promoting an integrated photonic device in the aspect of nano-scale optical sensing.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of nanoscale sensors, in particular to a tunable high-Q Fano resonance sensor based on an asymmetric SOI super surface. BACKGROUND

[0002] A sensor is a detection device capable of converting received information into various output forms, and has a very wide range of applications. With the rapid development of nanophotonic technology, optical sensors have shown unique advantages in chemical analysis, biomedical applications and environmental monitoring.

[0003] A super surface is an artificial composite material composed of subwavelength basic units arranged in a periodic or non-periodic manner. By designing the geometric shape, material properties and arrangement of these basic units, the super surface can be endowed with physical properties that natural materials cannot achieve. In all-dielectric super surfaces, symmetry breaking is an important means to excite specific electromagnetic resonances. Symmetry breaking is achieved by changing the geometric structure (such as unit shape, size or arrangement) or material properties to break the original spatial symmetry, so that the system introduces additional resonance modes or enhances certain optical properties.

[0004] Fano resonance is a kind of asymmetric spectral property caused by the interference between discrete resonance states and continuous states. The key to Fano resonance is to regulate the coherent interference of light waves, so that the system has strong spectral sharpness and high sensitivity. In super surfaces, symmetry breaking or the use of multiple resonance states can form Fano resonance, and Fano resonance has a high quality factor (Q value). High quality factor (Q value) Fano resonance excited by symmetry breaking super surface has important applications in biological sensors, optical filters and modulators, and nonlinear optical devices.

[0005] In terms of the performance of the material constituting the super surface, metal super surfaces usually have high ohmic loss, which often affects the performance of the structure. All-dielectric super surfaces effectively solve this problem, so they have been widely used.

[0006] In order to solve the problems of low Q value and difficult tuning of the current metasurface sensor, the application designs a tunable high-Q Fano resonance sensor based on asymmetric SOI metasurface, which is composed of a substrate and a dielectric layer, the substrate is silicon dioxide, and the dielectric layer is an arrow-shaped structure composed of two parallelograms made of silicon. Under TE polarization, the designed sensor excites an asymmetric sharp Fano resonance peak in the communication band of 1500nm-1650nm, has very high reflectivity, and the Q value reaches 3407.39. By adjusting the polarization structure parameters (the angle, width and height of the parallelogram) and the period, the resonant condition of the sensor is controlled, and the tuning function is achieved. By adjusting the polarization angle from TM polarization to TE polarization, the reflection spectrum of the resonance peak can be adjusted. SUMMARY

[0007] The purpose of the application is to provide a tunable high-Q Fano resonance sensor based on asymmetric SOI metasurface, which has simple structure and is easy to manufacture.

[0008] In order to achieve the above purpose, the application realizes the following design scheme:

[0009] A tunable high-Q Fano resonance sensor based on asymmetric SOI metasurface, the structure is a periodic structure, a single unit structure is composed of a silicon dioxide substrate and a silicon dielectric layer, and there are two parallelograms on the silicon dioxide substrate. The arrow-shaped structure forms a non-symmetric structure about the y-axis by adjusting the angle θ of the two parallelograms. In the application, under TE polarization, the tuning function can be realized by adjusting the angle, width and height of the parallelogram and the period of the unit structure. By adjusting the polarization angle from TM polarization to TE polarization, the modulation depth can be controlled.

[0010] Preferably, the thickness of the silicon dioxide substrate h is 2000nm.

[0011] Preferably, the parallelogram constituting the arrow-shaped structure is made of silicon material, the angle θ is 15°, the width w is 400nm, and the thickness d is 166nm.

[0012] The technical scheme adopted by the application is more concise than the existing sensor design. In terms of material selection, we choose silicon and silicon dioxide, which not only has low joule loss and low cost, but also has wide application range, good economy and practicability. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The schematic diagram of the three-dimensional array structure of the application (a) and the schematic diagram of the unit structure in the y direction (b) and the schematic diagram in the z direction (c).

[0014] Figure 2 For fixed x and y direction periods p = 920 nm, parallelogram angle θ = 15°, width w = 400 nm, height d = 166 nm, silica substrate height h = 2000 nm, reflectance spectra under TE polarization.

[0015] Figure 3 For fixed x and y direction periods p = 920 nm, width w = 400 nm, height d = 166 nm, silica substrate height h = 2000 nm, reflectance spectra under TE polarization for parallelogram angle θ from 0° - 25° in 5° steps.

[0016] Figure 4 For fixed x and y direction periods p = 920 nm, parallelogram angle θ = 15°, height d = 166 nm, silica substrate height h = 2000 nm, reflectance spectra under TE polarization for width w from 392 nm - 412 nm in 4 nm steps.

[0017] Figure 5 For fixed x and y direction periods p = 920 nm, parallelogram angle θ = 15°, width w = 400 nm, silica substrate height h = 2000 nm, reflectance spectra under TE polarization for height d from 154 nm - 184 nm in 6 nm steps.

[0018] Figure 6 For fixed parallelogram angle θ = 15°, width w = 400 nm, height d = 166 nm, silica substrate height h = 2000 nm, reflectance spectra under TE polarization for period p from 900 nm - 950 nm in 10 nm steps.

[0019] Figure 7 For fixed x and y direction periods p = 920 nm, parallelogram width w = 400 nm, height d = 166 nm, silica substrate height h = 2000 nm, Q value plot under TE polarization for parallelogram angle θ from 5° - 25° in 5° steps.

[0020] Figure 8 For fixed x and y direction periods p = 920 nm, parallelogram angle θ = 15°, width w = 400 nm, height d = 166 nm, silica substrate height h = 2000 nm, reflectance spectra plot under TE polarization for polarization from TM to TE in 10° steps from 0° - 90°. DETAILED DESCRIPTION

[0021] In order to better understand the present application, the following embodiments and drawings will be further explained and described, the following embodiments are only for the purpose of illustrating the present application and not to limit it.

[0022] The application provides a tunable high-Q Fano resonance sensor based on an asymmetric SOI super surface. Figure 1 As shown in the figure, the structure is composed of a silicon dioxide substrate and a silicon dielectric layer, mainly including a silicon dioxide substrate and an arrow-shaped structure composed of two parallelograms.

[0023] The thickness h of the substrate layer silicon dioxide is set to 2000 nm, the dielectric layer is selected from silicon material, the height d is 166 nm, the two parallelograms are closely combined to form an arrow shape, the width w of the parallelogram is 400 nm, and the length of the arrow shape is 2w=800 nm.

[0024] Figure 1 (a) is a schematic diagram of the three-dimensional structure of the sensor, Figure 1 (b) is a schematic diagram of the y direction of a single structure, and Figure 1 (c) is a schematic diagram of the z direction of a single structure.

[0025] The structure is simulated by using a three-dimensional finite difference time domain method (FDTD). The FDTD boundary conditions are set as follows: the x and y directions are set as periodic boundary conditions, the positive and negative directions of the z axis are set as perfect matched layers (PML), light is vertically incident on the structure array from the positive direction of the z axis, the wavelength of the input plane light is 1500-1650 nm, the arrow-shaped structure is covered with a 20 nm grid, a reflector monitor is set above the light source, and a reflection spectrum diagram is obtained after convergence test.

[0026] Figure 2 The reflection spectrum diagram under TE polarization is obtained when the fixed x and y direction periods p are all 920 nm, the parallelogram angle θ is 15°, the width w is 400 nm, the height d is 166 nm, the silicon dioxide substrate height h is 2000 nm. A sharp Fano resonance peak is formed at a wavelength of 1606 nm, and the reflectivity can reach 99.05%.

[0027] Figure 3 The reflection spectrum comparison diagram under TE polarization is obtained when the fixed x and y direction periods p are all 920 nm, the width w is 400 nm, the height d is 166 nm, the silicon dioxide substrate height h is 2000 nm, and the parallelogram angle θ is from 0° to 25° with a step of 5°. Under TE polarization, the symmetry of the structure is not broken when the parallelogram angle θ is 0°, and no Fano resonance peak is generated. When the parallelogram angle θ increases from 5° to 25°, a sharp Fano resonance peak is generated due to the broken symmetry of the structure, and the reflectivity increases continuously with the increase of the angle θ. The resonance peak position moves to the short wave direction, but the sharpness of the resonance peak decreases with the increase of the angle.

[0028] Figure 4 For fixed x and y direction period p is 920 nm, parallelogram angle θ = 15°, height d is 166 nm, silica substrate height h = 200 nm, under TE polarization, the reflection spectrum changes from 392 nm to 412 nm with 4 nm step size of width w. When the parallelogram width w increases from 392 nm to 412 nm, with the increase of width w, the fano resonance peak position gradually moves to the long wave direction, and when w = 400 nm, the reflection spectrum is the highest.

[0029] Figure 5 For fixed x and y direction period p is 920 nm, parallelogram angle θ = 15°, width w is 400 nm, silica substrate height h = 2000 nm, under TE polarization, the reflection spectrum changes from 154 nm to 184 nm with 6 nm step size of height d. When the parallelogram height d increases from 154 nm to 184 nm, with the increase of parallelogram height d, the fano resonance peak position gradually moves to the long wave direction, and when d = 166 nm, the reflection spectrum is the highest.

[0030] Figure 6 For fixed parallelogram angle θ = 15°, width w is 400 nm, height d is 166 nm, silica substrate height h = 2000 nm, under TE polarization, the reflection spectrum changes from 900 nm to 950 nm with 10 nm step size of period p. When the period p of the structure increases from 900 nm to 950 nm, with the increase of period p, the fano resonance peak position gradually moves to the long wave direction, and when p = 920 nm, the reflection spectrum is the highest.

[0031] Figure 7 For fixed x and y direction period p is 920 nm, parallelogram width w is 400 nm, height d is 166 nm, silica substrate height h = 2000 nm, under TE polarization, the Q value is measured from 5° to 25° with 5° step size of parallelogram angle θ. In theory, when the symmetry of the structure is not destroyed, the energy of the field is limited inside the structure, and the Q value of the structure is infinite, but it is difficult to achieve in the process, so the symmetry of the structure is destroyed, and the energy will leak out slightly, but a high Q value can also be achieved, while the reflectivity is compromised, when θ = 15°, the reflection spectrum is the highest, and the Q value reaches 3407.39.

[0032] Figure 8The contrast diagram of the reflection spectrum of the polarization from TM to TE with a step of 10° from 0° to 90° is shown when the period p in x and y directions is fixed as 920 nm, the parallelogram angle θ is 15°, the width w is 400 nm, the height d is 166 nm, the height h of the silica substrate is 2000 nm. Under TM polarization, a resonance peak is generated at 1512 nm, and when the polarization angle increases from 0° to 90°, the resonance peak reflectivity at 1512 nm decreases until it disappears. When the polarization angle is 10°, a resonance peak is generated at 1606 nm, and as the polarization angle increases, the resonance peak reflectivity at 1606 nm increases.

[0033] It should be noted that the above-described embodiments are merely specific descriptions of the present application, but are not limited to the scope of the present application. Without departing from the principles of the present application, any equivalent modifications or improvements made by those skilled in the art to the technical solutions of the present application are considered to be within the scope of protection of the present application.

Claims

1. A tunable high-Q Fano resonance sensor based on an asymmetric SOI metasurface. The sensor consists of an asymmetric periodic structure. The unit structure consists of a silicon dioxide substrate and a silicon dielectric layer, from bottom to top. An arrow-shaped structure consisting of two parallelograms is placed on the silicon dioxide substrate. This arrow-shaped structure is asymmetric about the y-axis by adjusting the angle θ between the two parallelograms.

2. The tunable high-Q Fano resonance sensor based on an asymmetric SOI metasurface according to claim 1, characterized in that: The parallelogram structures that make up the arrow-shaped structure have exactly the same size and are symmetrical about the x-axis.

3. The tunable high-Q Fano resonance sensor based on an asymmetric SOI metasurface according to claim 1, characterized in that: The arrow-shaped structure is made of silicon material with a width of w = 400 nm, a thickness of d = 166 nm, and an angle of θ = 15°.

4. The tunable high-Q Fano resonance sensor based on an asymmetric SOI metasurface according to claim 1, characterized in that: The thickness of the silicon dioxide substrate is fixed at h = 2000 nm.

5. The tunable high-Q Fano resonance sensor based on an asymmetric SOI metasurface according to claim 1, characterized in that: The periods p of the sensor structure in the x-direction and the y-direction are both set to 920 nm.

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