阅读说明：本技术 一种基于石墨烯阵列中光学双稳态的全光开关 (All-optical switch based on optical bistable state in graphene array ) 是由 赵东 于 2020-12-02 设计创作，主要内容包括：本发明提供了一种基于石墨烯阵列中光学双稳态的全光开关,属于全光通讯技术领域。包括相间分布的单层石墨烯和电介质薄片层,形成结构式为(gA)~Ng的周期阵列结构,单层石墨烯嵌入相邻电介质薄片层之间,周期阵列结构的两外侧均为单层石墨烯；结构式中的A为电介质薄片层,g为单层石墨烯,N为电介质薄片层的数量；单层石墨烯在不同的化学势下对应的全光开关的开、关阈值和阈值间隔均不同,通过在单层石墨烯上外加电压以改变单层石墨烯的化学势,从而调节光开关的开、关阈值和阈值间隔。本发明具有能够实现低阈值的光学双稳态等优点。(The invention provides an optical bistable all-optical switch based on a graphene array, and belongs to the technical field of all-optical communication. Comprises single-layer graphene and dielectric thin sheet layer which are distributed alternately to form a structure formula (gA) N g, a periodic array structure, wherein single-layer graphene is embedded between adjacent dielectric thin sheet layers, and the two outer sides of the periodic array structure are both the single-layer graphene; a in the structural formula is a dielectric flake layer, g is single-layer graphene, and N is the number of the dielectric flake layers; the on-off threshold and the threshold interval of the corresponding all-optical switch of the single-layer graphene are different under different chemical potentials, and the chemical potential of the single-layer graphene is changed by externally applying voltage on the single-layer graphene, so that the on-off threshold and the threshold interval of the optical switch are adjusted. The invention has the advantages of realizing low-threshold optical bistable state and the like.)

1. Based on optics is two in graphite alkene arrayThe stable all-optical switch is characterized by comprising single-layer graphene (g) and a dielectric flake layer (A) which are distributed at intervals to form a structure formula (gA)^Ng, the single-layer graphene (g) is embedded between adjacent dielectric thin sheet layers (A), and the two outer sides of the periodic array structure are both the single-layer graphene (g); a in the structural formula is a dielectric flake layer, g is single-layer graphene, and N is the number of the dielectric flake layers (A); the on-off threshold values and the threshold intervals of the corresponding all-optical switches of the single-layer graphene (g) are different under different chemical potentials, and the on-off threshold values and the threshold intervals of the optical switches are adjusted by applying a voltage to the single-layer graphene to change the chemical potential of the single-layer graphene (g).

2. The all-optical switch based on optical bistable state in graphene array according to claim 1, wherein the dielectric flake layer (a) is silicon dioxide.

Technical Field

The invention belongs to the technical field of all-optical communication, and relates to an optical bistable switch based on a graphene array.

Background

In conventional optical communication, information processing has an optical-electrical-optical conversion process, which greatly reduces the transmission and processing speed of data. The speed and efficiency of information transmission, analysis and access in fiber optic communication systems can be greatly increased if data can be relayed and stored in the full optical domain.

An all-optical switch is a switching element based on a photo-controlled light that can process information directly within the optical threshold. All-optical switches are widely used as optical switches, optical storage and optical logic devices. All-optical switches are typically implemented using nonlinear effects of materials, which require strong optical fields. The higher the light intensity is, the more the heat generation of the device increases, and the device cannot operate stably.

In all-optical switches, the minimum optical power required to turn on and off is called the switching threshold. In order to reduce the switching threshold, an annular quartz cavity can be coupled with one arm of the Mach-Zehnder interferometer, so that the annular quartz cavity can reach pi phase shift under low power, but the switch has high requirements on the fineness of the annular cavity, the power of the switch is inversely proportional to the square of the fineness, the switching time is proportional to the fineness, so that the power of the switch and the fineness are mutually contradictory, and other optical structures and optical effects have to be considered to realize the all-optical switch.

Optical bistability is based on a third-order nonlinear optical effect in which the refractive index of a material varies with the intensity of an input light. When the incident light reaches a sufficient intensity, one input light intensity value may correspond to two different output light intensity values, i.e. one incident light intensity may correspond to two stable output light intensities. The optical bistable state can be applied to manufacturing all-optical switches and optical memories. The bistable upper and lower thresholds correspond to the on and off thresholds of the all-optical switch, respectively. Current research is mainly focused on how to achieve low threshold optical bistability, and increase the upper and lower threshold separation, by new materials and structures.

The third-order nonlinear optical effect of the material is in direct proportion to the third-order nonlinear coefficient and the square of the local optical field intensity. In order to enhance the third-order nonlinear effect of the material, on one hand, the material with a larger third-order nonlinear coefficient can be used for realizing the low-threshold optical bistable state, and on the other hand, the structure can be optimized to enhance the local optical field at the position of the nonlinear material.

Graphene is an ultrathin two-dimensional material, has excellent conductivity, and the surface conductivity of the graphene can be flexibly adjusted through chemical potential. Importantly, graphene also has a considerable third-order nonlinear coefficient. The local optical field of graphene can be enhanced by utilizing the surface plasmon of graphene, or the nonlinear effect of graphene can be enhanced by embedding the graphene into a defect layer of a photonic crystal.

Graphene can excite surface plasmon, and the surface plasmon can form a strong local optical field. In addition, in the defective photonic crystal, the transmittance of the defective mode is close to 1, and thus it is also called a transmission mode. The mode field energy of the defect mode is mainly distributed in the defect layer, and the nonlinear material, such as graphene, is embedded in the defect layer, so that the nonlinear effect of the material can be greatly enhanced.

In addition, single-layer graphene may be periodically arranged to form a graphene array. The array can be regarded as a one-dimensional photonic crystal, a resonant cavity is formed between two adjacent pieces of graphene, and then the whole array forms a plurality of resonant cavities. Light is transmitted in the graphene array, a resonance state is formed, and mode field distribution of the resonance state has strong locality, so that the third-order nonlinear effect of the graphene can be enhanced.

Disclosure of Invention

The invention aims to provide an all-optical switch based on optical bistability in a graphene array, and the technical problem to be solved by the invention is how to improve the third-order nonlinear effect of graphene so as to realize the optical bistability with a low threshold value, so that the optical bistability can be applied to all-optical switches, optical logic devices and optical memories.

The purpose of the invention can be realized by the following technical scheme: the all-optical switch based on the optical bistable state in the graphene array is characterized by comprising single-layer graphene and dielectric thin sheet layers which are distributed at intervals to form a structure formula (gA)^Ng, the single-layer graphene is embedded between adjacent dielectric thin sheet layers, and the two outer sides of the periodic array structure are both single-layer graphene; a in the structural formula is a dielectric flake layer, g is single-layer graphene, and N is the number of the dielectric flake layers; the on-off threshold and the threshold interval of the corresponding all-optical switch of the single-layer graphene are different under different chemical potentials, and the chemical potential of the single-layer graphene is changed by externally applying voltage on the single-layer graphene, so that the on-off threshold and the threshold interval of the optical switch are adjusted.

Further, the dielectric flake layer is silicon dioxide.

Single-layer graphene is embedded in a silicon dioxide matrix material to form a periodic arrangement structure, so that a graphene array is formed. The graphene array has a local enhancement effect on an optical field in a resonance state, so that a three-order nonlinear effect of graphene is improved, optical bistable state with a low threshold value is realized, and the optical bistable state is applied to all-optical switches, optical logic devices and optical memories.

The bistable threshold is related to the chemical potential of graphene, and the chemical potential of graphene can be regulated and controlled by external voltage, so that the on-off threshold and the threshold interval of an optical bistable all-optical switch in a graphene array can be flexibly adjusted by the chemical potential of graphene.

Drawings

Fig. 1 is a periodic structure of a graphene array.

FIG. 2 is a linear transmission spectrum of light waves in the examples.

Fig. 3 is a non-linear transmission as a function of input light intensity.

FIG. 4 is a graph of output light intensity as a function of input light intensity.

FIG. 5 is a graph of output-input relationships for different chemical potentials.

In the figure, a dielectric foil layer; g. single layer graphene.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.

Single layer graphene is embedded in a silica matrix material to form a periodic array structure, as shown in figure 1. Wherein A is a dielectric flake layer made of silicon dioxide, g is a graphene monolayer, d is a space period between adjacent graphene monolayers, i.e. an interval between adjacent graphene monolayers, and I_iIs an incident light ray, I_oIs the outgoing light. The structure can also be written as (gA)^Ng, where N represents the number of spatial periods of the graphene monolayer, i.e., the number of dielectric flake layers in the periodic array structure. Here, the number N of space periods of graphene monolayers was 40, the space period between adjacent graphene monolayers was 100nm, and the refractive index of silica was N_a1.449. The surface conductivity of graphene is related to temperature, chemical potential and input light wavelength, and the room temperature is T-23 ℃, and the chemical potential of graphene is mu_c＝0.50eV。

When a transverse electric wave is incident on the periodic structure, the nonlinear effect of graphene is not considered, and the transmission spectrum of the obtained optical wave is shown in fig. 2. It can be seen that the transmission spectrum varies with wavelength, with a jump at λ 1.25 μm (μm denotes μm). This is because as the wavelength increases, electrons in graphene are converted from an in-band transition to an inter-band transition, the number density of free electrons increases, loss of incident light by graphene decreases, and thus transmittance increases. In addition, on the transmittance curve, a plurality of resonance peaks exist, each resonance peak corresponds to a resonance state, and the resonance states have a local effect on the light field, namely the light field is locally enhanced. The position of the local optical field enhancement is just at the interface of the medium, and the graphene is also just embedded on the joint surface of two adjacent silicon dioxide dielectric sheets, so that the third-order nonlinear effect of the graphene can be greatly enhanced when the input light intensity is strong.

When the input light is strong, the nonlinear effect of graphene cannot be ignored. Given an input wavelength λ of 1.308 μm, the intensity of incident light was varied, and fig. 3 shows the nonlinear transmittance of a graphene array structure as a function of the input intensity. Abscissa unit TW/cm²Representing the terawatts per square centimeter. It can be seen that as the intensity of light increases, the slope of the transmittance curve appears negative, which is not true physically present, and optical bistability must occur.

Fig. 4 shows the variation of output intensity with input intensity. When the light intensity increases to a certain value, the input-output relationship exhibits a hyperbolic relationship. As the input light intensity increases, the input-output curve varies along the trajectory of path I, at I_i＝I_uThe output light intensity makes an upward jump, and I_uAn upper threshold of optical bistability; when the input light intensity decreases, the input-output curve changes along the trajectory of path II, at I_i＝I_dThe output light intensity makes a downward jump, and I_dCalled the lower threshold of optical bistability. Difference between upper and lower thresholds_u-I_dCalled the threshold interval. When the optical bistable state in the structure is used as an all-optical switch, the upper and lower threshold values of the bistable state correspond to the on and off threshold values of a fully-off switch, namely when the light intensity is I_i＝I_uWhen the optical switch is on, when I_i＝I_dWhen so, the optical switch is turned off. When the input intensity is between the upper and lower thresholds, i.e. I_d＜I_i＜I_uCorresponding to two output intensities, this is called optical bistability. Of course, the incident wavelengths are different, the corresponding nonlinear transmittance curves are different, and the bistable curves are also different.

Fig. 5 shows the input-output relationship corresponding to different chemical potentials of graphene, and it can be seen that different chemical potentials correspond to different bistable curves, and the upper and lower thresholds of the bistable states are also different. When the chemical potential is mu_cAt 0.50eV, the upper threshold of bistability is I_u1The lower threshold is I_d1(ii) a When the chemical potential is mu_cThe upper threshold of the bistable state is I at 0.40eV_u2The lower threshold is I_d2. The input light intensity varies from small to large, and when increased to a certain extent, the input-output relationship varies along the path I, III, respectively; the input light intensity varies from large to small, and when reduced to a certain degree, the input-output relationship varies along paths II, IV, respectively. Therefore, the chemical potential of the graphene can be changed only by applying voltage to the graphene, so that the on-off threshold and the threshold interval of the optical switch can be flexibly adjusted.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.