阅读说明：本技术 一种基于准周期光子多层与石墨烯的复合结构 (Composite structure based on quasi-periodic photon multilayer and graphene ) 是由 章普 于 2021-07-27 设计创作，主要内容包括：本发明公开了一种基于准周期光子多层与石墨烯的复合结构,将两种折射率不同的电介质薄片层和石墨烯层依次逐层堆叠,所述电介质薄片满足Octonacci序列规则；Octonacci序列的迭代规则为：S-(N)=S-(N-1)S-(N-2)S-(N-1),复合结构为S-(N-1)GS-(N-)-(2)GS-(N-1),其中G表示石墨烯层；N>2时,而S-(1)=A,S-(2)=B,其中N为序列的序数,A、B是两种折射率不同的均匀电介质；则：S-(3)=BAB,S-(4)=BABBBAB,S-(5)=BABBBABBABBABBBAB,S-(6)=S-(5)S-(4)S-(5),S-(7)=S-(6)S-(5)S-(6),S-(8)=S-(7)S-(6)S-(7),……。本发明Octonacci序列光子多层也具有光学分形的特性,且这些光学分形态对电场具有很强的局域性；特别地,Octonacci序列光子多层的共振透射模彼此之间可以独立,且间隔距离适当。这可以被用于实现多个彼此独立的光学双稳态,从而得到多值全光开关。(The invention discloses a composite structure based on quasi-periodic photon multilayer and graphene, wherein two dielectric thin sheet layers and graphene layers with different refractive indexes are sequentially stacked layer by layer, and the dielectric thin sheets meet the Octonacci sequence rule; the iteration rule for the Octonacci sequence is: s N =S N‑1 S N‑2 S N‑1 The composite structure is S N‑1 GS N‑ 2 GS N‑1 Wherein G represents a graphene layer; n is a radical of>2 is, and S 1 =A，S 2 = B, where N is the ordinal number of the sequence, A, B being two homogeneous dielectrics with different refractive indices; then: s 3 =BAB，S 4 =BABBBAB，S 5 =BABBBABBABBABBBAB，S 6 =S 5 S 4 S 5 ，S 7 =S 6 S 5 S 6 ，S 8 =S 7 S 6 S 7 … …. The Octonacci sequence photon multilayer of the inventionThe optical fractal characteristics are also provided, and the optical fractal characteristics have strong locality to an electric field; in particular, the resonant transmission modes of the Octonacci-sequence photonic multilayer can be independent of each other and spaced at an appropriate distance. This can be used to implement a plurality of optical bistability independent of each other, resulting in a multi-valued all-optical switch.)

1. A composite structure based on quasi-periodic photon multilayer and graphene is characterized in that two dielectric thin sheet layers and graphene layers with different refractive indexes are sequentially stacked layer by layer, and the dielectric thin sheets meet Octonacci sequence rules;

it is characterized in that the preparation method is characterized in that,

the iteration rule of the Octonacci sequence is as follows: s_N=S_N-1S_N-2S_N-1When N ≧ 3, and N =1 and 2, S₁=A，S₂= B, wherein N is the ordinal number of the sequence;

the composite structure is S_N-1GS_N-2GS_N-1Wherein G represents a graphene layer;

A. b is two homogeneous dielectrics with different refractive indices;

then: s₃=BAB，S₄=BABBBAB，S₅=BABBBABBABBABBBAB，S₆=S₅S₄S₅，S₇=S₆S₅S₆，S₈=S₇S₆S₇，……。

2. The composite structure of claim 1, wherein the Octonacci-sequence photonic multilayer of ordinal number N =5 is a composite structure of graphene, which can also be expressed as BABBBABGBABGBABBBAB.

3. The composite structure of claim 1, wherein the first dielectric layer (a) is silicon and the second dielectric layer (B) is silicon dioxide.

4. The composite structure of claim 1 wherein dielectric a is silicon dioxide and has a refractive index n_a=3.53, thickness 1/4 optical wavelength, i.e. d_a=λ₀/4n_a=0.1098 μm, where λ₀=1.55 μm as center wavelength; b is silicon and has a refractive index n_b1.46, thickness d_b=λ₀/4n_b=0.2654 μm; the thickness of the single layer graphene is 0.33 nm.

5. A four-value all-optical switch comprising a composite structure based on quasi-periodic photonic multilayers and graphene according to any one of claims 1 to 4.

6. An optical storage device comprising a composite structure based on a quasiperiodic photonic multilayer and graphene according to any one of claims 1 to 4.

7. A four-state optical logic device comprising the composite structure based on quasiperiodic photonic multilayer and graphene according to any one of claims 1 to 4.

Technical Field

The invention belongs to the technical field of all-optical communication systems, and relates to a composite structure based on a quasi-periodic photon multilayer and graphene.

Background

In all-optical communications, processing needs to be performed in the all-optical domain. There is a need to develop a great deal of optically controlled optical devices, which are important types of optical bistable multi-valued all-optical switches or multi-state optical logic devices.

Optical bistability is based on the optical kerr effect of materials, a third-order nonlinear optical effect. 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. Currently, the research based on is mainly focused on how to achieve low threshold optical bistability by new materials and new structures, and to increase the upper and lower threshold separation.

Two dielectric media with different refractive indexes are arranged alternately in space to form a periodic structure, so that the photonic crystal can be formed. In the wave vector space of a photonic crystal, light waves have a photonic band structure similar to the electronic bands in semiconductors. Light waves within the band gap are reflected back all without transmission. The finite length photonic crystal is a photonic multilayer, which also has a bandgap structure. If a defect layer is introduced into the photonic crystal, a resonant transmission mode appears in the transmission spectrum. The transmission mode has strong locality to electric field and is often used for optical bistable devices. Photonic crystals containing a defective layer are known as quasi-photonic crystals or aperiodic photonic crystals.

To realize the optical bistable state with low threshold value, the third-order nonlinear effect of the material is enhanced, on one hand, the optical bistable state with low threshold value can be realized by using the material with larger third-order nonlinear coefficient, on the other hand, the local optical field can be enhanced by optimizing the structure.

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. The mode field energy of the defect mode is mainly distributed in the defect layer, and the nonlinear material is embedded in the defect layer, so that the nonlinear effect of the material can be greatly enhanced.

The optical bistable state with low threshold can be realized by compounding graphene and quasi-photonic crystals, such as embedding the graphene into a Thue-Morse sequence photonic multilayer. The quasi-periodic photonic multilayer can be formed by arranging two dielectric sheets with different refractive indexes according to the Thue-Morse sequence rule. Based on the fact-Morse sequence photon multilayer, a plurality of defect cavities are formed in the same defect cavity, a plurality of defect modes, namely resonance transmission modes, exist in the same defect cavity, the resonance modes are called optical fractal resonance states of the true-Morse sequence photon multilayer, namely, the number of dielectric layers in the multilayer structure is correspondingly increased along with the increase of a serial number, and the transmission modes in the transmission spectrum in the photon multilayer are split in a geometric series manner. However, in these resonance states, either two adjacent resonances are too close to each other and overlap each other, or isolated resonance states exist too far apart, and in the input-output light intensity curve, only one optical bistable or a plurality of optical bistable states which are not independent of each other can be formed, which is difficult to be used for multi-valued all-optical switches.

Disclosure of Invention

The invention aims to provide a composite structure of a plurality of low-threshold optical bistable quasiperiodic photonic multilayer and graphene.

The technical scheme of the invention is as follows:

a composite structure based on quasi-periodic photon multilayer and graphene is characterized in that two dielectric thin sheet layers and graphene layers with different refractive indexes are sequentially stacked layer by layer, and the dielectric thin sheets meet Octonacci sequence rules; the iteration rule for the Octonacci sequence is: s_N=S_N-1S_N-2S_N-1When N ≧ 3, and N =1 and 2, S₁=A，S₂= B, wherein N is the ordinal number of the sequence; the composite structure is S_N-1GS_N-2GS_N-1Wherein G represents a graphene layer;

A. b is two homogeneous dielectrics with different refractive indices;

then: s₃=BAB，S₄=BABBBAB，S₅=BABBBABBABBABBBAB，S₆=S₅S₄S₅，S₇=S₆S₅S₆，S₈=S₇S₆S₇，……。

Preferably, the aforementioned Octonacci sequence photon multilayer with the ordinal number N =5 and graphene composite structure, which can also be expressed as babbbbgbabbbbabbbbab.

Further, the first dielectric layer (a) is silicon, and the second dielectric layer (B) is silicon dioxide.

Further, the dielectric A is silicon dioxide and has a refractive index n_a=3.53, thickness 1/4 optical wavelength, i.e. d_a=λ₀/4n_a=0.1098 μm, where λ₀=1.55 μm as center wavelength; b is silicon and has a refractive index n_b1.46, thickness d_b=λ₀/4n_b=0.2654 μm; the thickness of the single layer graphene is 0.33 nm.

A four-value all-optical switch comprises any one of the above composite structures based on the quasiperiodic photonic multilayer and graphene.

An optical storage device comprising any one of the above composite structures based on the quasiperiodic photonic multilayer and graphene.

A four-state optical logic device comprises any one of the quasi-periodic photonic multilayer and graphene-based composite structures.

The invention has the characteristics and beneficial effects that: the Octonacci-sequence photonic multilayer also has the characteristic of optical fractal, and the optical fractal has strong locality to an electric field.

In particular, the resonant transmission modes of the Octonacci-sequence photonic multilayer can be independent of each other and spaced at an appropriate distance. This can be used to implement a plurality of optical bistability independent of each other, resulting in a multi-valued all-optical switch.

Then compounding the graphene and an Octonacci sequence photon in a multilayer manner, wherein the position of the graphene is just corresponding to the vicinity of the maximum value point of fractal mode field distribution; the method is characterized in that the non-linear effect of graphene is enhanced by utilizing the locality of optical fractal in Octonacci sequence photon multilayer to an electric field, and a plurality of independent low-threshold optical bistable states are realized by utilizing independent optical fractal states at proper distance.

Drawings

FIG. 1 Octonacci sequence S₅A photonic multilayer and graphene composite structure schematic diagram;

FIG. 2 Octonacci sequence S₅A transmission spectrum of light in the photonic multilayer and graphene composite structure;

FIG. 3 is a normalized electric field distribution diagram for a second resonant optical fractal;

FIG. 4 is a graph showing the variation of the intensity of the emitted light with the intensity of the incident light;

FIG. 5(a) input-output light intensity relationships corresponding to different graphene chemical potentials; (b) the input-output light intensity relations corresponding to different incident wavelengths;

FIG. 6(a) transmittance in a Thue-Morse sequence photonic multilayer; (b) an optical multistable state near a transmission mode (I); (c) optical bistability near the transmission mode (iv);

FIG. 7 is a schematic diagram of a four-value all-optical switch based on two optical bistable states;

FIG. 8 is a graph of graphene chemical potential versus switching threshold.

Detailed Description

The principles and features of this invention are described below in conjunction with examples and figures, which are set forth to illustrate the invention and are not intended to limit the scope of the invention.

Referring to fig. 1, the iteration rule of the Octonacci sequence is: s_N=S_N-1S_N-2S_N-1When N ≧ 3, and N =1 and 2, S₁=A，S₂Where N is the ordinal number of the sequence, A, B are two homogeneous dielectrics with different refractive indices. We can thus iterate: s₃=BAB，S₄=BABBBAB，S₅=BABBBABBABBABBBAB，S₆=S₅S₄S₅，S₇=S₆S₅S₆，S₈=S₇S₆S₇… …. Fig. 1 shows a composite structure of an Octonacci sequence photon multilayer with an ordinal number N =5 and graphene G, which can also be denoted as babbbbgbabbbbabbb. The thickness of the single layer graphene is 0.33nm (nm represents nanometers), which is relative to the thickness of dielectrics A and BThe degree is negligible, but here, in order to highlight the existence of graphene, the thickness of graphene is exaggerated when it is shown in the schematic diagram.

Light is incident perpendicularly from the left, symbolI _i Which represents the incident light ray, is,I _o representing the outgoing light rays. The incident light is a Transverse Magnetic (TM) wave. Dielectric A is silicon dioxide with refractive index n_a=3.53, thickness 1/4 optical wavelength, i.e. d_a=λ₀/4n_a=0.1098 μm (μm represents micrometers), where λ₀=1.55 μm as center wavelength; b is silicon and has a refractive index n_b1.46, thickness d_b=λ₀/4n_b=0.2654 μm. Here the ambient temperature is 300 deg.CK（KExpression kelvin), relaxation time of electrons in grapheneτ= 0.5 ps (ps means picosecond).

Referring to FIG. 2, the incident light frequency is varied, and the Octonacci sequence S is shown₅And (3) a transmission spectrum of light in the photonic multilayer and graphene composite structure. Chemical potential isμ=0.2eV (eV representing electron volts), the other parameters being kept constant. The ordinate T represents the transmittance; abscissa (A)ω−ω ₀)/ω _gapRepresents a normalized angular frequency, whereinω=2πc/λ、ω ₀ =2πc/λ₀Andω _gap= 4ω₀arcsin│(n _a −n _b )/(n _a +n _b )｜²and/pi respectively represents incident light angular frequency, incident light central angular frequency and angular frequency band gap, c is light speed in vacuum, and arcsin is an inverse sine function. At a normalized frequency of [ -1, 1 [)]Within the interval, there are four transmission formants corresponding to the four resonance optical partial forms. They are independent of each other and are separated by a suitable distance. The four transmittance peaks are, from left to right: t = [0.6142, 0.5922, 0.5896, 0.5794]The corresponding medium wavelengths are respectively: λ = [2.1962 μm, 1.6785 μm, 1.4425 μm, 1.1982 μm]. The four optical partial forms have a local effect on an electric field, but the position with the strongest local electric field of the second resonance state (marked by a five-star mark) is just right at the inlaid graphene attachmentThus, to achieve multiple low threshold optical bistability, the incident wavelength must be red detuned relative to the second resonant state wavelength.

The dielectric and the graphene are sequentially arranged from left to right along the horizontal rightward direction, namely the positive direction of the Z axis according to the rule. Figure 3 shows the electric field distribution of the second optical fractal in the composite structure. The ordinate represents the normalized electric field strength. It can be seen that the distribution of the electric field energy in the structure is not uniform and localized. The strongest point of the local electric field is right near the two sheets of inlaid graphene. Since the optical third-order nonlinear effect of the graphene is in direct proportion to the local electric field intensity, the nonlinear effect of the graphite is greatly enhanced.

Referring to FIG. 4, the output intensity is plotted against the input intensity. The incident light wavelength is lambda =1.9 μm, a certain red detuning exists relative to the second resonance wavelength, and the chemical potential of the graphene isμ=0.2eV, the other parameters being kept constant. Abscissa of the circleI _i Indicating input light intensity, ordinateI _o Indicating the output light intensity. The unit TW/cm²Representing the terawatts per square centimeter. When the light intensity increases to a certain value, three S-shaped, i.e. three hyperbolic relations appear in the input-output relation curve from bottom to top in sequence. The first S-curve and the third S-curve are independent, and the second S-curve (marked by a dashed box) is included in the first S-curve, so that the threshold jump is ignored here, and only the threshold jump of the inflection points of the first S-curve and the third S-curve is considered.

When the input light intensity is gradually increased from weak to strong, the output light intensity jumps upwards at the right turning point of the first S curve and the third S curve, namely the input-output curves change along the tracks of I and II, and the input-output curves are called as the upper thresholds of the two optical bistable states; when the input light intensity is gradually reduced from strong to weak, the output light intensity jumps downwards at the left turning point of the first S curve and the third S curve, namely the input-output curves change along the trajectories of III and IV, and the input-output curves are called the lower threshold value of the optical bistable state. The difference between the upper and lower thresholds is called the threshold interval. It is clear that these two threshold intervals have no overlap region, so the two optical bistability are independent of each other.

When the input intensity is between the upper and lower thresholds, i.e. or, one input intensity corresponds to two output intensities, this is optically bistable. In the whole input-output light intensity relation, two independent S-shaped curves exist, namely two independent optical bistable states, and the effect can be used for a four-value all-optical switch, an optical memory and an optical logic device.

Of course, different bistable curves are different for different incident wavelengths or different chemical potentials of graphene.

Referring to fig. 5(a), with the incident wavelength λ =1.9 μm fixed, the input-output light intensity relationship is given for different graphene chemical potentials. It can be seen that: the bistable curves corresponding to different chemical potentials are different, and the upper threshold value and the lower threshold value of the bistable state are also different; as the chemical potential of the graphene increases, the upper threshold value and the lower threshold value of the bistable state both increase, and the width between the threshold values of the bistable state increases. Therefore, the upper and lower thresholds and the width between the thresholds of the bistable state can be regulated and controlled by the chemical potential of the graphene. Fixing graphene chemical potentialμFig. 5(b) shows the input-output intensity relationship for different incident wavelengths when =0.2 eV. It can be seen that: the bistable curves corresponding to different incident wavelengths are different, and the upper and lower thresholds of the bistable state are also different; as the incident wavelength decreases, the upper threshold of bistability increases, while the lower threshold decreases, and the inter-threshold width of bistability increases. Therefore, the upper and lower thresholds of the bistable state and the width between the thresholds can also be adjusted by the incident wavelength.

In addition, the Octonacci sequence photon multilayer and the Thue-Morse sequence photon multilayer are respectively compared with the optical bistable state formed by graphene compounding to highlight the characteristics of the invention. FIG. 6(a) shows ordinal numbers S₄Transmission spectrum of the Thue-Morse sequence photon multilayer. Here again, two dielectrics a and B are used as examples for arrangement, S₄=ABBABAABBAABABBA。Three overlapping transmission peaks (c) and two independent transmission peaks (c) and (c) can be seen in the middle of the band gap. The transmission modes have local effect on an electric field, graphene is inserted into the transmission peak (i) and the corresponding mode field strongest position (iii), and the formed composite system structure is ABGBABAABBAABABGBA. When the input wavelength is near the transmission peak (c) and is detuned with respect to the transmission peak (c), fig. 6(b) shows the input-output intensity relationship, and it can be seen that: there are three sigmoid curve segments on the input-output light intensity curve, which means that there are three optical bistable states; however, the three sigmoid curve segments overlap each other, i.e., the three threshold intervals have a common interval with each other. When the incident light intensity increases or decreases, the up-down jump is very complicated and is not easy to control, so that it is difficult to be used as a multi-value switch.

See FIG. 6(a) for transmission in the Thue-Morse sequence photonic multilayer; FIG. 6(b) optical multistability near transmission mode (r); fig. 6(c) optical bistable near the transmission mode (r).

And inserting the graphene into the strongest positions of the mode fields corresponding to the transmission peaks (iv) and (v), wherein the formed composite system structure is ABBAABGBAABABBA. When the input wavelength is near the transmission peak r and is detuned with respect to the transmission peak r, the input-output intensity relationship is given in fig. 6(c), and it can be seen that: for each specific graphene chemical potential, there is one input-output intensity curve, and there is one sigmoid curve segment on each curve, which means that there is one optical bistable state and it can only be used as a binary switch. When the input wavelength is near the transmission peak (c) and is detuned with respect to the transmission peak (c), the resulting input-output intensity relationship is similar to that of fig. 6(c), except that the threshold required to achieve optical bistability is increased.

In conclusion, a plurality of resonance component forms exist in the composite structure of the Octonacci-sequence photon multilayer and the graphene. The fractal has strong local effect on an electric field, and the graphene is just positioned near the position point with the strongest electric field, so that the nonlinear effect of the graphene is greatly enhanced, and two independent low-threshold optical bistable states are realized. The upper and lower thresholds and the threshold interval of the two optical bistable states can be flexibly regulated and controlled by the chemical potential and the incident wavelength of the graphene. The effect can be applied to four-value all-optical switches, optical memories and four-state optical logics.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

As shown in fig. 7, the wavelength of the incident light was set to 1.55μmChemical potential ofμ=0.2eV，Two independent optical bistability exist in the input-output light intensity relationship, which is applied to a four-value all-optical switch.

When the effect is applied to all-optical switches (or optical memories, optical logics). When the input light intensity is gradually increased from a lower value, the upper threshold value corresponds to the on 1 (or writing 1, logic 11) of the optical switch, and when the input light intensity is continuously increased, the upper threshold value corresponds to the on 2 (or writing 2, logic 10) of the optical switch; when the input light intensity is gradually decreased from a higher value, at the lower threshold, corresponding to the off 1 (or read 1, logic 01) of the optical switch, and when the input light intensity is continuously decreased, at the lower threshold, corresponding to the off 2 (or read 2, logic 00) of the optical switch.

Fig. 5(a) shows that the input-output curve of the optical bistable state is regulated by the chemical potential of graphene. The positions of two inflection points of the S curve are changed due to different chemical potentials. Two inflection points of the S curve respectively correspond to an upper threshold and a lower threshold of the optical bistable state, namely an on threshold and an off threshold of the all-optical switch, so that the switching threshold of the all-optical switch can be regulated and controlled through the chemical potential of the graphene.

Referring to fig. 8, a four-value switching threshold based on two independent optical bistability is given as a function of graphene chemical potential. As can be seen, as the chemical potential of graphene increases, the switching threshold of all-optical switches increases, and the threshold interval also becomes larger. The larger the switch threshold interval is, the larger the switch discrimination is, and the smaller the switch misjudgment rate is. To reduce the switch misjudgment rate, the chemical potential of graphene needs to be increased, and the switch threshold value is increased, so that the switch misjudgment rate is reduced at the expense of increasing the switch threshold value.

Similarly, as can be seen from fig. 5(b), the switching threshold of the all-optical switch can be flexibly adjusted by the incident wavelength.

If the bistable effect is applied to optical storage and logic devices, the writing, reading and judgment thresholds of the storage and the logic devices are all regulated and controlled by the chemical potential and incident wavelength of graphene.