A low threshold optical bistable switch based on hybrid metasurface

Abstract

The application discloses a low-threshold optical bistable switch based on a hybrid superstructure surface and relates to an optical bistable switch device. From bottom to top, the device is sequentially provided with a supporting substrate, a uniform surface plasmon film, a low-refractive Kerr nonlinear medium film and a high-refractive medium disc periodic array. Under the configuration of the hybrid superstructure surface, mirror surface effect of electric dipole resonance and coupling effect of surface plasmon resonance can be simultaneously generated, electric field energy of incident light is localized in the low-refractive Kerr nonlinear medium film, and thus the Kerr effect of the low-refractive Kerr nonlinear medium film is effectively excited. When the intensity of the incident light continuously increases, the low-threshold optical bistable switch can jump from an 'on' state to an 'off' state. Conversely, when the intensity of the incident light continuously decreases, the low-threshold optical bistable switch can jump from the 'off' state to the 'on' state. The low-threshold optical bistable switch has a large switch ratio, is not related to polarization, is simple to prepare and compatible with a complementary metal oxide semiconductor process, and can become a potential all-off switch device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical bistable switching devices, and in particular to low threshold optical bistable switching based on hybrid super surface. BACKGROUND

[0002] Optical bistability refers to the phenomenon that an optical system has multiple values. In a nonlinear optical system, there is a hysteresis phenomenon similar to a magnetic hysteresis loop between the output light intensity and the input light intensity. Optical bistable switching can switch light from one state to another state by using light itself. Because it can obtain unique all-optical devices such as switches, transistors, logic gates and storage elements, this phenomenon has been studied for decades. Today, it attracts the attention of a large number of researchers in important application fields such as high-speed optical communication, optical information processing, optical computing and optical logic processing. In particular, bistable devices using some semiconductor materials such as GaAs, InSb, etc. have the advantages of small structure size, low input power, short switching time, etc. and have great development prospects in the logic elements of future photonic computers.

[0003] Small size and low threshold are the keys to the application of optical bistable switching. Enhanced bistability has been demonstrated and studied in many micro-nano structures, such as super materials and super surfaces, photonic crystals, Fabry-Perot cavities and nano structures, etc. These studies mainly focus on enhancing the local electromagnetic field and improving the resonance quality factor to reduce the bistable switching threshold and improve its performance. However, due to the low field enhancement factor of the local electromagnetic field, the optical bistability is usually weak, which limits its switching efficiency and practical application. Therefore, it is necessary to design high enhancement and high efficiency resonance to achieve excellent performance of the bistable switching device.

[0004] In the past few decades, the scientific and engineering communities have made various efforts, mainly as follows: 1. Based on photonic crystal technology, for example, in 2022, Jiao Xu et al. designed a graphene photonic crystal structure to make an optical bistable switch. By using the strong nonlinear conductivity of graphene to achieve strong nonlinear response, the device obtained the lowest threshold of 2.65 KW / cm 2 Although the switching threshold is low, the structure is complex and difficult to prepare. 2. Based on the traditional Fabry-Perot cavity technology, for example, in 2022, ZeQiang Wang et al. used a classic metal-dielectric-metal Fabry-Perot cavity as an asymmetric nanocavity. When 6 layers of graphene oxide (GO) were integrated in the nanocavity to excite nonlinear response, the optical bistable threshold of the device was as low as 150 kW / cm 2However, this tunable optical bistable switch can only work at visible light frequency, and the application scene is limited. 2 Based on the superstructure surface technology, for example, the metal-dielectric-metal superstructure surface structure generates coupling enhanced magnetic resonance, which can effectively enhance the electromagnetic field intensity in the Kerr medium, realize a low switching threshold of about 0.19 MW / cm 2 , but has the disadvantages of low switching ratio and the like. SUMMARY

[0005] The purpose of the present application is to solve the problems of the prior art optical bistable switch device, and provide a low threshold optical bistable switch device based on a hybrid superstructure surface, which has a precisely designed reflection spectrum, a low threshold, a large switching ratio, no polarization dependence, and simple preparation.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A low threshold optical bistable switch based on a hybrid superstructure surface, which is sequentially provided with a supporting substrate, a uniform surface plasmon thin film, a low refractive index Kerr nonlinear medium thin film and a high refractive index medium disc periodic array from bottom to top; under the configuration of the hybrid superstructure surface, mirror effect of electric dipole resonance and coupling effect of surface plasmon resonance can be generated at the same time, the electric field energy of the incident light is localized in the low refractive index Kerr nonlinear medium thin film, and the Kerr effect is effectively excited, so as to obtain the bistable switching function.

[0008] The uniform surface plasmon thin film is prepared by using a metal material or a semiconductor material with a negative real part of dielectric constant, and the thickness is greater than or equal to 100 nm.

[0009] The low refractive index Kerr nonlinear medium thin film is prepared by using a low refractive index Kerr nonlinear medium material with a third-order nonlinear optical coefficient, and the refractive index is less than 2, and the thickness is 2-50 nm.

[0010] The high refractive index medium disc periodic array is an array formed by square periodic distribution of high refractive index medium discs, the center distance between adjacent discs is consistent with the period, the period size is 1100-1800 nm, and the array period number is more than 20.

[0011] The high refractive index medium disc is prepared by using a transparent high refractive index medium material, the refractive index is greater than 3, the disc radius is 180-280 nm, and the disc height is 50-150 nm.

[0012] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0013] 1、The low threshold optical bistable switch based on a hybrid superstructure surface provided by the present application has a low switching threshold of 575 kW / cm2 With a switching threshold of 0.5 and a switching ratio of up to 44.5, the all-optical switch and its corresponding field have great potential.

[0014] 2、The low-threshold optical bistable switch based on the hybrid superstructure surface has no polarization dependence and produces the same nonlinear response to electromagnetic waves with different polarization directions.

[0015] 3、The low-threshold optical bistable switch based on the hybrid superstructure surface can be compatible with the complementary metal oxide semiconductor process and can be mass-produced. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structural schematic diagram of the present application;

[0017] Figure 2 is an optical bistable curve of Example 1;

[0018] Figure 3 is an optical bistable curve of Example 2;

[0019] Figure 4 is a reflection spectrum of Example 3;

[0020] Figure 5 is a reflection spectrum of Example 4;

[0021] Figure 6 is a reflection spectrum of Example 5. DETAILED DESCRIPTION

[0022] The present application will be further described in conjunction with the following specific examples and drawings, but the protection scope of the present application is not limited to the following examples. Those skilled in the art can easily modify the following examples and apply the general principles to other examples without creative labor. Therefore, any modification and improvement of the present application made by those skilled in the art according to the hints of the present application are within the protection scope of the present application, and the appended claims are the protection scope.

[0023] As shown in Figure 1 , the low-threshold optical bistable switch based on the hybrid superstructure surface described in the embodiments of the present application is provided with a support substrate (1), a uniform surface plasmonic film (2), a low-refractive Kerr nonlinear medium film (3), and a high-refractive medium disc periodic array (4) in sequence on the superstructure surface. Under the configuration of the hybrid superstructure surface, the mirror effect of electric dipole resonance and the coupling effect of surface plasmon resonance can be produced at the same time, the electric field energy of the incident light is localized in the low-refractive Kerr nonlinear medium film, the Kerr effect is effectively excited, and thus the bistable switch function is obtained.

[0024] Example 1

[0025] Under perpendicular incidence of x-polarized waves, the supporting substrate of the bistable switching device is silicon dioxide with a refractive index of 1.5. The uniform surface plasmon thin film on the substrate is made of metallic silver with a thickness of 200 nm. The low-refractive-index Kerr nonlinear dielectric film covering the silver film is a polybenzoyldiacetylene film with a refractive index of 1.55 and a third-order nonlinear optical coefficient χ. (3) 4.4×10 -17 (m / V) 2 The thickness is 20 nm. The periodic array located above the nonlinear material dielectric film consists of silicon nanodisks of the same radius, unfolded on the surface of the dielectric film in a two-dimensional planar square lattice with a period of 1500 nm. The refractive index of the silicon disk is 3.5, the radius of the silicon disk is 200 nm, and the height of the silicon disk is 100 nm. Since the nonlinear coefficient χ(3) in this invention is positive, the wavelength of the incident light λin = λres + 1.5wFW (λres is the resonant wavelength, wFW is the full width at half maximum) is chosen to ensure that the device has a wide range of bistable states, a high on / off ratio, and a low on / off threshold. The bistable curve between the reflectivity and the input light intensity of the above device is shown in Figure 1. Figure 2 As shown. The study focuses on the bistable state at the point of strongest coupling with a period of 1500 nm. Figure 4 Extract the resonant wavelength.

[0026] λres = 1530.2 nm. Based on the above formula, the incident wavelength λin = 1534 nm can be calculated, which is the operating wavelength of the bistable switch. For the branch on the bistable curve, when the input intensity is low, the reflectivity remains relatively stable at a high value, which can be considered as the bistable switch being in the ON state. As the incident light intensity continues to increase, reaching the threshold ION-OFF = 950 kW / cm², the bistable switch continues to operate. 2 At that moment, the reflectivity instantaneously drops from R = 0.80 to a very small R = 0.08, and the bistable switch changes from the "ON" state to the "OFF" state, with an on / off ratio of 10.0. Afterwards, for the lower branch, when the incident intensity changes from... Figure 2 The larger value on the right continues to decrease until the threshold IOFF-ON = 575kW / cm 2 When the reflectivity jumps from near zero (R = 0.02) to a higher value (R = 0.89), the bistable switch changes from the "off" state to the "on" state, with an on / off ratio of 44.5. It can be seen that the optical bistable switch based on the hybrid metasurface described in this invention has a low on / off threshold, a high on / off ratio, and excellent bistable switching performance.

[0027] Example 2

[0028] Based on Example 1, the implementation was carried out by modifying the height of the high-refractive-index dielectric disk to 90 nm. The optical bistable curves of the above-mentioned bistable switching device are as follows: Figure 3 As shown, for the branch on the bistable curve, the incident light intensity continuously increases, reaching the threshold ION-OFF = 302 kW / cm². 2 At this point, the reflectivity will drop instantaneously from R = 0.6 to a very small R = 0.16, and the bistable switch will change from the ON state to the OFF state, with an on / off ratio of 3.75. For the lower branch, when the incident intensity changes from... Figure 3 The larger value on the right decreases to the threshold IOFF-ON = 270kW / cm 2 When the reflectivity jumps from R = 0.2 to a higher value of R = 0.72, the bistable switch will switch from the OFF state to the ON state, and the on / off ratio will be 3.6. It can be seen that compared with Example 1, Example 2 has a lower switching threshold, but sacrifices the on / off ratio performance.

[0029] Example 3

[0030] Based on Example 1, the array period of the high-refractive-index dielectric disk was modified to 1300 nm, 1400 nm, 1500 nm, and 1600 nm, respectively. The reflection spectrum of the above bistable switching device is as follows: Figure 4 As shown, the array period can be adjusted within this range to achieve different coupling states. When the period increases to 1500 nm, the reflection bandwidth at the long wavelength resonance reaches its minimum, and the reflectivity is lowest. Further increasing the period will increase the reflection bandwidth at the long wavelength resonance, thus increasing the reflectivity. However, by varying the array period within a certain range, the device can still maintain a low reflectivity within the operating wavelength band. At a period of 1500 nm, the plasmonic resonance and magnetic dipole resonance coupling on the surface plasmonic film are strongest, resulting in the narrowest resonance bandwidth at long wavelengths in the reflection spectrum, and the strongest local electric field in the nonlinear dielectric film.

[0031] Example 4

[0032] Based on Example 1, the height of the high-refractive-index dielectric disk was modified to 90 nm, 100 nm, 110 nm, and 120 nm, respectively. The spectra of the above bistable switching devices are shown below. Figure 5 As shown, the height of the high-refractive-index dielectric disk has a significant impact on the reflectivity of the optical bistable switch. Within a certain range, the smaller the height, the lower the reflectivity of the device at long-wavelength resonance. When the height of the control dielectric disk is 90 nm, the electric dipole mode resonance is most strongly excited in the high-refractive-index dielectric disk, which helps to form a strong coupling effect with the plasmon resonance on the surface plasmon film, thereby enhancing the local electric field of the nonlinear dielectric film and obtaining a low threshold for the bistable all-optical switch.

[0033] Example 5

[0034] On the basis of example 1, the radius of high refractive index medium disc is modified to 180nm, 190nm, 200nm and 210nm respectively. Figure 6 As shown in the reflection spectrum of the bistable switching device, the radius of the dielectric silicon disc of the bistable switching device can affect the reflectivity, when the radius increases from 180nm to 200nm, the reflection bandwidth at the long wavelength resonance reaches the minimum; when it continues to increase, it will make the reflection bandwidth become large again. When the radius of the silicon disc is 200nm, strong electric dipole resonance can be excited in the high refractive index silicon disc, which helps to form strong coupling effect with the plasmon resonance on the surface plasmon film, and further enhances the local electric field of the nonlinear medium film, so as to obtain low switching threshold and high switching ratio.

[0035] The working principle of the present application is as follows:

[0036] By adjusting the diameter and height of the mixed superstructure surface, the electric dipole mode resonance is excited in the high refractive index medium disc; through the metal mirror effect of the uniform surface plasmon film, the electric dipole mode inside and outside the mirror surface is coupled with each other, and is converted into the magnetic dipole resonance in the low refractive index Kerr nonlinear medium film, so that the electromagnetic field is effectively localized in the Kerr nonlinear medium film; further, by adjusting the period of the high refractive index medium disc, the plasmon resonance on the uniform surface plasmon film is induced, and the resonance can effectively and the magnetic dipole resonance occur mutual coupling, under a certain period, the coupling is the strongest, so as to realize the great enhancement of the local electromagnetic field in the Kerr nonlinear medium film, and the high contrast of the reflection spectrum, and obtain the excellent performance of low threshold and large switching ratio.

Claims

1. A low threshold optical bistable switch based on hybrid metasurface, characterized in that: From bottom to top, successively arranged are a supporting substrate (1), a uniform surface plasmon thin film (2), a low refractive index Kerr nonlinear medium thin film (3) and a high refractive index medium disc periodic array (4); the mirror effect of electric dipole resonance and the coupling effect of surface plasmon resonance can be simultaneously generated, the electric field energy of incident light is localized in the low refractive index Kerr nonlinear medium thin film (3), the Kerr effect is effectively excited, and thus the bistable switching function is obtained; The uniform surface plasmon thin film (2) is prepared by using a metal material or a semiconductor material with a negative real part of dielectric constant; The low refractive index Kerr nonlinear medium thin film (3) is prepared by using a low refractive index Kerr nonlinear medium material with a third-order nonlinear optical coefficient, and the refractive index is less than 2; The high refractive index medium disc periodic array (4) is an array formed by square periodic distribution of high refractive index medium discs, and the center distance between adjacent discs is consistent with the period.

2. The low threshold optical bistable switch based on hybrid metasurface of claim 1, wherein: The thickness of the uniform surface plasmon thin film (2) is not less than 100 nm.

3. The low threshold optical bistable switch based on hybrid metasurface of claim 1, wherein: The thickness of the low refractive index Kerr nonlinear medium thin film (3) is 2-50 nm.

4. The hybrid metasurface-based low-threshold optical bistable switch of claim 1, wherein: The period size of the high refractive index medium disc periodic array (4) is 1100-1800 nm, and the array period number is more than 20.

5. The hybrid metasurface-based low-threshold optical bistable switch of claim 1, wherein: The high refractive index medium disc is prepared by using a transparent high refractive index medium material, and the refractive index is greater than 3.

6. The hybrid metasurface-based low-threshold optical bistable switch of claim 1, wherein: The radius of the high refractive index medium disc is 180-280 nm.

7. The hybrid metasurface-based low-threshold optical bistable switch of claim 1, wherein: The height of the high refractive index medium disc is 50-150 nm.

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