阅读说明：本技术 一种基于石墨烯的触发阈值可调光逻辑器 (Graphene-based trigger threshold adjustable optical logic device ) 是由 李永逵 于 2021-09-22 设计创作，主要内容包括：本发明提供了一种基于石墨烯的触发阈值可调光逻辑器,属于全光通讯技术领域。本光逻辑器包括若干第一电介质层A、若干第二电介质层B和四个石墨烯单层G,表示为ABABBBABABB-(1)GB-(2)BB-(3)GB-(4)BB-(4)GB-(3)BB-(2)GB-(1)BABABBBABA,其中B-(1)GB-(2)、B-(2)GB-(1)、B-(3)GB-(4)和B-(4)GB-(3)均表示石墨烯单层嵌入第二电介质层内形成的三明治结构；所述第一电介质层和第二电介质层为两种折射率不同的均匀电介质薄片,所述光逻辑器存在四个光学分形态,光学分形态对应的电场具有局域作用,四个石墨烯单层分别嵌于其中一个分形态对应的局域电场最强位置,使石墨烯单层的三阶非线性效应得到增强,进而实现低阈值光学双稳态；所述第一电介质层和第二电介质层的厚度均为各自光学波长的1/4。本发明具有光学双稳态阈值低等优点。(The invention provides a graphene-based adjustable optical logic device for a trigger threshold, and belongs to the technical field of all-optical communication. The optical logic device comprises a plurality of first dielectric layers A, a plurality of second dielectric layers B and four graphene monolayers G, denoted ABABBBABABB 1 GB 2 BB 3 GB 4 BB 4 GB 3 BB 2 GB 1 BABABBBABA, wherein B 1 GB 2 、B 2 GB 1 、B 3 GB 4 And B 4 GB 3 Both represent a sandwich structure formed by embedding a graphene monolayer into a second dielectric layer; the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes, the optical logic device has four optical fractal states, an electric field corresponding to each optical fractal state has a local effect, and the four graphene single layers are respectively embedded in the strongest position of the local electric field corresponding to one fractal state, so that the three-order nonlinear effect of the graphene single layers is enhanced, and further the low-threshold optical bistable state is realized; the first dielectric layer andthe thickness of the second dielectric layer is 1/4 of the respective optical wavelength. The invention has the advantages of low optical bistable threshold value and the like.)

1. A graphene-based trigger threshold tunable optical logic device is characterized by comprising a plurality of first dielectric layers A, a plurality of second dielectric layers A and a plurality of first dielectric layers AA dry second dielectric layer B and four graphene monolayers G, the multilayer structure of the all-optical digital encoder being denoted ABABBBABB₁GB₂BB₃GB₄BB₄GB₃BB₂GB₁BABABBBABA, wherein B₁GB₂、B₂GB₁、B₃GB₄And B₄GB₃Both represent a sandwich structure formed by embedding a graphene monolayer into a second dielectric layer; the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes, the optical logic device has four optical fractal states, an electric field corresponding to each optical fractal state has a local effect, and the four graphene single layers are respectively embedded in the strongest position of the local electric field corresponding to one fractal state, so that the three-order nonlinear effect of the graphene single layers is enhanced, and further the low-threshold optical bistable state is realized; the optical bistable state can be applied to a binary optical logic with adjustable trigger threshold; the first dielectric layer and the second dielectric layer each have a thickness of 1/4 at the respective optical wavelength.

2. The graphene-based trigger threshold tunable optical logic device of claim 1, wherein the matrix material of the first dielectric layer is lead telluride, and the matrix material of the second dielectric layer is cryolite.

3. The graphene-based trigger threshold tunable optical logic device according to claim 1 or 2, wherein a logic 1 trigger threshold, a logic 0 trigger threshold and a threshold interval of the optical logic device are tuned by a chemical potential of a graphene monolayer.

4. The graphene-based trigger threshold tunable optical logic device of claim 1 or 2, wherein the optical logic device is tuned by an incident wavelength by a logic 1 trigger threshold, a logic 0 trigger threshold, and a threshold interval.

Technical Field

The invention belongs to the technical field of all-optical communication, and relates to a graphene-based trigger threshold value adjustable optical logic device.

Background

In all-optical communication, optical logics are used for storing, relaying, timing, deciding, amplifying, shaping and the like of signals in an optical domain, and optical logics based on optical bistable state are an important class.

Optical bistability is a nonlinear optical effect based on the optical kerr effect of a material. When the incident light intensity is sufficiently large, one input light intensity value may correspond to two different output light intensity values, i.e. one incident light intensity value may induce two stable resonant output states. When an optical bistable effect is applied to an optical logic device, the upper and lower thresholds of the bistable state correspond to the trigger thresholds of a logic 1 and a logic 0 of the optical logic device, respectively. The larger the trigger threshold, the greater the light intensity required to trigger the optical logic decision. When the power of the device is increased, the stability of the device is deteriorated, which puts high demands on heat dissipation. When the interval between the upper and lower thresholds of the optical bistable state is small, the discrimination between the logic 1 and the logic 0 in the optical logic device becomes weak, and the false rate increases. Therefore, the current research on optical bistability mainly focuses on how to lower the threshold of optical bistability by new materials and new structures, and increase the interval between the upper and lower thresholds.

To achieve low threshold optical bistability, materials with large third-order nonlinear coefficients are sought on the one hand, and on the other hand, local electric fields are enhanced by optimizing the system structure. Because the optical kerr effect is proportional to the local electric field, a strong local electric field can enhance the third-order nonlinear effect of the material.

Graphene is an ultrathin two-dimensional material, has excellent conductivity, and the surface conductivity of the graphene can be flexibly regulated and controlled through the chemical potential of the graphene. Importantly, graphene has a considerable third-order optical nonlinear coefficient. This makes graphene a preferred material for achieving low threshold optical bistability. In addition, in order to further reduce the bistable threshold value, the local electric field of the graphene can be enhanced by utilizing the surface plasmon polariton of the graphene, so that the nonlinear effect of the graphene is improved; the graphene can be embedded into a defect layer of the photonic crystal, and the nonlinear effect of the graphene is improved by utilizing the defect-to-electric field locality. In addition, the third-order nonlinear coefficient of the graphene is a function of the chemical potential of the graphene, so that the bistable threshold based on the graphene can be flexibly regulated and controlled through the chemical potential of the graphene. When optical bistability is used for optical logic, the trigger threshold of the optical logic can also be regulated by the chemical potential of graphene.

Two dielectrics with different refractive indexes are arranged alternately in space, thereby forming a photonic crystal with a periodic structure. In the wave vector space, a photonic crystal has a photonic band structure similar to an electron band in a semiconductor. Light waves within the band gap will be totally reflected without transmission. If defects are introduced into the photonic crystal, a defective mode, i.e., a transmission mode, appears in the transmission spectrum. The transmission mode has a strong local effect on the electric field and is often used to enhance the third-order nonlinearity of the material. In quasi-photonic crystals or aperiodic photonic crystals, natural defects exist, and the number of defect modes increases in a geometric progression along with the increase of sequence numbers, which is an optical fractal effect. The optical fractal is one of the defect modes and has strong local effect on an electric field, so that the electric field locality can be enhanced by using the optical fractal effect in the quasi-photonic crystal or the non-periodic photonic crystal.

The Thue-Morse (T-M) sequence is mathematically a quasi-periodic sequence, and the corresponding T-M photonic crystal is a quasi-periodic photonic crystal. The graphene and the T-M photonic crystal are compounded to obtain a strong local electric field and realize the optical bistable state with a low threshold value, and the threshold value of the optical bistable state is about GW/cm²(gigawatts per square centimeter).

To further reduce the threshold of optical bistability, graphene is composited with an Octonacci photonic crystal. Octonacci photons are also quasi-periodic photonic crystals with the characteristic of optical fractal, and the optical fractal has stronger electric field locality. In the composite structure of the graphene and the Octonacci photonic crystal, the threshold value of the optical bistable state can be as low as 100MW/cm²(MW/cm²Representing megawatts per square centimeter). Whether a composite structure of other quasi-periodic photonic crystals and graphene can be obtained further reduces the threshold value of the optical bistable state, realizes the flexible and adjustable threshold value of the optical bistable state, obtains the optical logic device with the adjustable low trigger threshold value, and becomes the research focus in the field.

Disclosure of Invention

The invention aims to provide a graphene-based trigger threshold dimmable logic device aiming at the problems in the prior art, and the technical problem to be solved by the invention is how to reduce the threshold of optical bistable state and realize flexible and adjustable threshold, so that the graphene-based trigger threshold dimmable logic device can be applied to optical logic devices.

The purpose of the invention can be realized by the following technical scheme: the graphene-based trigger threshold dimmable logic device is characterized by comprising a plurality of first dielectric layers A, a plurality of second dielectric layers B and four graphene single layers G, wherein the multilayer structure of the all-optical digital encoder is represented as ABABBBABABB₁GB₂BB₃GB₄BB₄GB₃BB₂GB₁BABABBBABA, wherein B₁GB₂、B₂GB₁、B₃GB₄And B₄GB₃Both represent a sandwich structure formed by embedding a graphene monolayer into a second dielectric layer; the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes, the optical logic device has four optical fractal states, an electric field corresponding to each optical fractal state has a local effect, and the four graphene single layers are respectively embedded in the strongest position of the local electric field corresponding to one fractal state, so that the three-order nonlinear effect of the graphene single layers is enhanced, and further the low-threshold optical bistable state is realized; the first dielectric layer and the second dielectric layer each have a thickness of 1/4 at the respective optical wavelength.

The composite structure comprises four graphene single layers and a Kantol (Cantor) photonic crystal with a sequence number N ═ 3, wherein the Kantol photonic crystal is ABBBABBBBBBBBBBBABABABABA, and letters A, B respectively represent two uniform dielectric sheets with different refractive indexes; the Comptor photonic crystal has a plurality of independent optical fractal states, an electric field corresponding to each fractal state has locality, 4 graphene single layers are embedded into a position where a local electric field corresponding to one fractal state is strongest, and the composite structure can be expressed as follows on the whole: ABABBBABABB₁GB₂BB₃GB₄BB₄GB₃BB₂GB₁Bababbbbaba, wherein G represents single layer graphene; the local electric field of the position of the graphene is strongest, so that the three-order nonlinear effect of the graphene is greatly enhanced, and further the low-threshold optical bistable state is realized; the dielectric sheet A and the dielectric sheetThe thicknesses of the B are 1/4 of respective optical wavelengths; the threshold value of the optical bistable state in the structure can be as low as MW/cm²This is 2 orders of magnitude lower than the threshold for optical bistability in a composite structure of Octonacci photonic crystals and graphene.

The upper and lower thresholds of the optical bistable state in the composite structure based on the Cantor photonic crystal and the graphene and the interval between the upper and lower thresholds are reduced along with the reduction of the chemical potential and incident wavelength of the graphene. Therefore, when the optical bistable state in the structure is applied to an optical logic device, the logic trigger threshold of the optical logic device and the interval between the trigger thresholds of logic 1 and logic 0 can be flexibly regulated and controlled through the chemical potential and the incident wavelength of graphene.

Furthermore, the matrix material of the first dielectric layer is lead telluride, and the matrix material of the second dielectric layer is cryolite.

Further, the threshold value is triggered by a logic 1, the threshold value is triggered by a logic 0, and the threshold interval of the incident wavelength tuning optical logic.

Further, a logic 1 trigger threshold, a logic 0 trigger threshold, and a threshold interval of the photo-logic device are modulated by the chemical potential of the graphene monolayer.

Drawings

Fig. 1 is a schematic diagram of a composite structure of a Cantor photonic crystal with a sequence number N ═ 3 and graphene.

Fig. 2 is a linear transmission spectrum of light in a Cantor photonic crystal with the number N ═ 3.

Fig. 3 shows a normalized electric field distribution of an optical partial form corresponding to a wavelength λ of 1.7209 μm.

FIG. 4 shows the variation of the intensity of the emitted light with the intensity of the incident light.

FIG. 5(a) is a graph showing the input-output intensity relationship corresponding to different chemical potentials of graphene; the graph (b) in fig. 5 shows the variation of the bistable upper and lower thresholds with the chemical potential of graphene.

FIG. 6 is a graph (a) showing the input-output intensity relationship for different incident wavelengths; the graph (b) in fig. 6 shows the variation of the upper and lower thresholds of the bistable state with the incident wavelength.

Fig. 7 is a schematic diagram of an optically bistable binary optical logic.

In the figure, a first dielectric layer; B. a second dielectric layer; G. a graphene monolayer.

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.

Mathematically, the iterative rule for the kantor (Cantor) sequence is: s₀＝A，S₁＝ABA，S₂＝ABA(BBB)ABA,S₃＝S₂(BBB)²S₂，……，S_N＝S_N-1(BBB)^N-1S_N-1… … where N (0, 1, 2, 3, … …) is the sequence number, S_NThe Nth term representing the sequence; (BBB)^N-1Is represented by 3^N-1And B. The letters A, B in the corresponding Cantor photonic crystal respectively represent two homogeneous dielectric flakes having different refractive indices. The composite structure of the Cantor photonic crystal with the sequence number N-3 and graphene is shown in FIG. 1. Symbol I₁Representing incident light, symbol I₂Representing the outgoing light rays. The dielectric sheets and the single-layer graphene are sequentially arranged along the Z axis, and the central position of the structure is a 0 point. This structure may also be denoted ABABBBABABB₁GB₂BB₃GB₄BB₄GB₃BB₂GB₁BABABBBABA, wherein the letter G denotes single-layer graphene, B₁GB₂And B₂GB₁The sandwich structure formed by embedding the graphene monolayer into the second dielectric layer B is shown; the matrix material of A is lead telluride with refractive index n_a＝4.1；B、B₁、B₂、B₃And B₄The matrix materials of (A) are all cryolite with refractive index n_b1.35. The incident light is transverse magnetic wave and is vertically incident from the left. Dielectric sheets A and B are both 1/4 optical wavelengths thick, i.e. A has a thickness d_a＝λ₀/4/n_a0.0945 μm (μm denotes μm), where λ₀1.55 μm as the center wavelength, and B has a thickness d_b＝λ₀/4/n_b＝0.287μm，B₁Has a thickness of d_b1＝0.0482μm，B₂Has a thickness of d_b20.2388 μm, satisfies the condition d_b1+d_b2＝d_b,，B₃Has a thickness of d_b3＝0.1116μm，B₄Has a thickness of d_b40.1754 μm, satisfies the condition d_b3+d_b4＝d_b。

Single layer graphene has a thickness of about 0.33nm (nm means nanometers), which corresponds to the size of one atom. With respect to the dielectric sheet A, B, B₁、B₂、B₃And B₄The thickness of graphene is negligible. Here, the ambient temperature is set to 300K (K denotes kelvin), and the relaxation time τ of the electrons in the graphene is 0.5ps (ps denotes picosecond).

When the incident light frequency is changed, when the influence of graphene is not considered, a linear transmission spectrum of light in the Cantor photonic crystal with the sequence number N-3 is shown in FIG. 2. The ordinate T represents the transmittance of light waves; abscissa (ω - ω)₀)/ω_gapDenotes a normalized angular frequency, where ω is 2 π c/λ, ω₀＝2πc/λ₀And ω_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 [)]In the interval, 8 transmission formants exist, corresponding to 8 resonance optical partial forms, and all have local effect on the electric field. These 8 transmittance peaks are all 1. Here only the 4 th resonance state (marked with an asterisk) is chosen to achieve optical bistability. The resonance wavelength corresponding to the peak is 1.7209 mu m, the electric field distribution corresponding to the peak is calculated in the next step, and then the graphene is embedded at the position with the strongest local electric field, so that the nonlinear effect of the graphene is enhanced, and the low-threshold optical bistable state is realized; in addition, to achieve low threshold optical bistability, the incident wavelength must be properly red detuned relative to the 4 th resonance state wavelength λ of 1.7209 μm.

The dielectric and the graphene are sequentially arranged from left to right along the horizontal direction according to a rule. Fig. 3 shows the electric field distribution of the 4 th resonant optical fractal in the composite structure. The dotted lines represent the interfaces between two adjacent layers of dielectric, and the 4 graphene monolayers G are respectively embedded at the positions of the structure where the electric field intensity is strongest. The ordinate represents the normalized electric field strength of the Z component. It can be seen that the distribution of the electric field energy in the structure is not uniform and localized. The 4 graphene monolayers are just located at the strongest positions of the local electric field 4 respectively. The third-order nonlinear optical effect of the graphene is in direct proportion to the local electric field intensity, so that the nonlinear effect of the graphite is greatly enhanced.

The chemical potential is set to 0.45eV (eV represents electron volts), the other parameters are kept constant, and fig. 4 shows the variation of output light intensity with input light intensity. The wavelength of the incident light is 1.724 μm, and there is a certain red detuning with respect to the 4 th resonance wavelength λ 1.7209 μm. Abscissa I_iRepresenting input light intensity, ordinate I_oIndicating the output light intensity. Unit MW/cm²Representing megawatts per square centimeter. When the light intensity is increased to a certain value, an S-shaped curve can be formed in the relation curve of the input-output light intensity, and the S-shaped curve represents the bistable relation between input and output. In a composite system of Oconacci photonic crystal and graphene, the optical bistable threshold value is 100MW/cm²The optical bistable state is GW/cm in the compounding of T-M photonic crystal and graphene²Magnitude; whereas in the present described structure the threshold for optical bistability is lowered to MW/cm²Magnitude. It can be seen that in the composite structure of the Cantor photonic crystal of N ═ 3 and graphene, the threshold of optical bistability is greatly reduced.

When the input light intensity is gradually increased from a relatively small value, at the right-hand corner of the S-curve segment, the corresponding input light intensity I_i＝I_uThe output light intensity jumps upwards, so that I_uAn upper threshold called optical bistability; when the input light intensity is gradually decreased from a relatively large value, the corresponding input light intensity I is at the left inflection point of the S curve segment_i＝I_dThe output light intensity makes a downward jump, so that I_dCalled the lower threshold of optical bistability. Difference between upper and lower thresholds_u-I_dCalled the threshold interval.

When the input intensity is between the upper and lower thresholds, i.e. I_u<I_i<I_dOne input intensity value corresponds to two output intensity values, which is called the optical bi-stable effect. In the contour of the input-output intensity relationship, the optical bistable effect appears as a segment of an S-shaped curve, and the effect can be used for a binary optical logic device.

Of course, different incident wavelengths, or different chemical potentials of graphene, will correspond to different bistable curves and thresholds.

The fixed incident wavelength λ is 1.724 μm, and other parameters are kept constant, and fig. 5(a) shows the input-output light intensity relationship corresponding to different graphene chemical potentials μ. It can be seen that: when μ ═ 0.425eV, 0.45eV, and 0.475eV, the input-output light intensity relationships are all hyperbolic; increasing the value of μ, the upper and lower thresholds of bistability, and the threshold interval of bistability increase, as shown in fig. 5 (b). The abscissa μ represents the chemical potential of graphene and the ordinate thresh represents the threshold for bistability. Upper Threshold and Lower Threshold represent bistable Upper and Lower thresholds, respectively. The bistable upper and lower thresholds and the threshold interval are increased along with the increase of the chemical potential of the graphene, so that the bistable upper and lower thresholds and the threshold interval can be flexibly regulated and controlled through the chemical potential of the graphene.

When the chemical potential μ of the fixed graphene is 0.475eV, other parameters are kept unchanged, and fig. 6(a) shows the input-output light intensity relationship corresponding to different incident wavelengths. It can be seen that: given the 3 wavelength values λ 1.724 μm, 1.725 μm and 1.726 μm, the input-output light intensity is all in a bi-stable relationship; the bistable curves corresponding to different incident wavelengths are different, namely the upper threshold value, the lower threshold value and the threshold value interval of the bistable state are different; as the incident wavelength increases, i.e., the amount of detuning increases, the bistable upper and lower thresholds increase, and the bistable threshold interval also increases, as shown in fig. 6 (b). It can be seen that bi-stability occurs throughout a given wavelength interval 1.724 μm ≦ λ ≦ 1.726 μm; the upper and lower thresholds and threshold intervals of the bistable state increase with increasing wavelength. Since the larger the detuning amount of a wavelength, the stronger the incident light energy required to compensate for the detuning amount to achieve resonance. Thus, the upper and lower thresholds and threshold spacing of the bistable states can be tuned by the incident wavelength.

In short, a plurality of resonant optical fractal states exist in the composite structure of the Cantor photonic crystal with the sequence number N-3 and the graphene. The optical fractal has a strong local effect on an electric field, and 4 graphene single layers are just positioned at the 4 strongest positions of the electric field corresponding to one fractal respectively, so that the nonlinear effect of the graphene is greatly enhanced, and the low-threshold optical bistable state is realized; threshold of optical bistability down to MW/cm²The optical bistable state is 6 orders of magnitude smaller than that of the optical bistable state in the compounding of the T-M photonic crystal and the graphene, and 2 orders of magnitude smaller than that of the optical bistable state in the compounding of the Octonacci photonic crystal and the graphene. And the upper and lower thresholds and the threshold interval of the optical bistable state can be flexibly regulated and controlled by the chemical potential and the incident wavelength of the graphene. The effect can be applied to a binary optical logic device, and the trigger threshold of the optical logic device can be flexibly regulated and controlled through the chemical potential and the incident wavelength of graphene.

The wavelength of incident light is set to be 1.724 μm, the chemical potential is 0.45eV, and the optical bistable phenomenon appears in the relation of input-output light intensity, and the principle is shown in fig. 7. When the bistable effect is applied to an optical logic. When the input light intensity is gradually increased from a lower value, the output light intensity generates an upward jump at the right turning point, so that the input light intensity I is increased_i＝I_uCalled upper threshold, which corresponds to a logic 1 of the optical logic, and I_i＝I_uA logic 1 trigger threshold called optical logic; when the input light intensity is gradually reduced from a higher value, the output light intensity generates a downward jump at the lower left corner, and the input light intensity I_i＝I_dCalled lower threshold, which corresponds to a logic 0 trigger threshold of the optical logic, so that I_i＝I_dA logic 0 called optical logic triggers a threshold. Upper threshold value I_u＝2.1162MW/cm²Lower threshold value I_d＝0.3424MW/cm²Interval of threshold value I_u-I_d＝1.7738MW/cm²。

FIG. 5(b) shows optical bistabilityThe input-output curve is influenced by the chemical potential of the graphene, the chemical potential is different, and the positions of two inflection points of the corresponding S curve section also change. The two inflection points of the S-curve segment correspond to the upper and lower thresholds of the optical bistable, i.e. the trigger thresholds of logic 1 and logic 0 of the optical logic device, respectively. Keeping the incident wavelength λ 1.724 constant, the chemical potential increases to μ 0.475eV, when the upper threshold I is reached_u＝13.6316MW/cm²Lower threshold value I_d＝0.0367MW/cm^2，Interval of threshold value I_u-I_d＝13.6028MW/cm². It can be seen that as the chemical potential increases, the trigger thresholds of logic 1 and logic 0 of the optical logic, and the threshold interval, increase.

Fig. 6(b) shows the influence of the incident wavelength on the input-output curve of the optical bistable state, and when the chemical potential is 0.45eV and the incident wavelength is decreased to λ 1.723, the corresponding upper threshold I is obtained_u＝1.5487MW/cm²Lower threshold value I_d＝0.0187MW/cm^2,Interval of threshold value I_u-I_d＝1.53MW/cm². It can be seen that as the incident wavelength decreases, the amount of wavelength detuning decreases, the trigger thresholds for logic 1 and logic 0 of the optical logic, and the threshold interval decreases.

The larger the trigger threshold interval is, the larger the logic judgment operation distinction degree of logic 1 and logic 0 is, and the smaller the false judgment rate is. To reduce the false rate of the optical logic device, the chemical potential or wavelength mismatch of the graphene needs to be increased, and at the same time, the trigger threshold is increased, so that the reduction of the false rate of the optical logic device is achieved at the cost of increasing the trigger threshold.

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.