阅读说明：本技术 一种基于鲁丁-夏皮诺光子晶体的光逻辑器 (Optical logic device based on rutin-Xiapino photonic crystal ) 是由 方明 于 2021-09-29 设计创作，主要内容包括：本发明提供了一种基于鲁丁-夏皮诺光子晶体的光逻辑器,属于全光通讯技术领域。包括两个对称分布的二元RS光子晶体和两个石墨烯单层,二元RS光子晶体包括若干第一电介质层和若干第二电介质层,第一电介质层记为H,第二电介质层记为L,石墨烯单层记为G,二元RS光子晶体表示为HHHLHHLH,光逻辑器表示为HHHLHHLH-(1)GH-(2)H-(2)GH-(1)LHHLHHH,其中H-(1)GH-(2)和H-(2)GH-(1)均表示石墨烯单层嵌入第一电介质层内形成的三层结构,第一电介质层和第二电介质层的厚度分别为各自光学波长的1/4,第一电介质层和第二电介质层分别为折射率高、低不同的两种均匀电介质薄片。本发明具有判决阈值低等优点。(The invention provides an optical logic device based on a rutin-Charinuo photonic crystal, and belongs to the technical field of all-optical communication. The optical logic device comprises two binary RS photonic crystals and two graphene single layers which are symmetrically distributed, wherein the binary RS photonic crystals comprise a plurality of first dielectric layers and a plurality of second dielectric layers, the first dielectric layers are marked as H, the second dielectric layers are marked as L, the graphene single layers are marked as G, the binary RS photonic crystals are shown as HHHLHHLH, and the optical logic device is shown as HHHLHHLH 1 GH 2 H 2 GH 1 LHHLHHH, wherein H 1 GH 2 And H 2 GH 1 Both represent a three-layer structure in which a graphene monolayer is embedded in a first dielectric layer, the thicknesses of the first dielectric layer and the second dielectric layer are 1/4 of the respective optical wavelengths, and the first dielectric layer and the second dielectric layer are two kinds of uniform dielectric sheets having different refractive indexes. The method has the advantages of low decision threshold value and the like.)

1. An optical logic device based on a Luding-Charnano photonic crystal is characterized by comprising two symmetrically distributed binary RS photonic crystals and two graphene single layers, wherein the binary RS photonic crystals comprise a plurality of first dielectric layers and a plurality of second dielectric layers, the first dielectric layers are marked as H, the second dielectric layers are marked as L, the graphene single layers are marked as G, the binary RS photonic crystals are marked as HHHLHHLH, and the optical logic device is marked as HHHLHHLH₁GH₂H₂GH₁LHHLHHH, wherein H₁GH₂And H₂GH₁Both represent a three-layer structure formed by embedding a graphene monolayer into a first dielectric layer, the thicknesses of the first dielectric layer and a second dielectric layer are 1/4 of respective optical wavelengths, and the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes; the photonics logic based on the rutin-Charcot-Supino photonic crystal can realize low-threshold optical bistable state, and the upper threshold and the lower threshold of the bistable state respectively correspond to the decision threshold of the optical memory logic 1 and the decision threshold of the optical memory logic 0.

2. The ludin-xiapino photonic crystal-based optical logic device of claim 1, wherein the first dielectric layer is a high refractive index material of lead telluride, and the second dielectric layer is a low refractive index material of cryolite.

3. The optical logic device based on the rutin-Xipino photonic crystal as claimed in claim 1 or 2, wherein the logic 1 decision threshold, the logic 0 decision threshold and the interval between the logic 1 decision threshold and the logic 0 decision threshold of the optical logic device are regulated and controlled by the chemical potential of the graphene monolayer.

4. The optical logic device based on the rutin-Prunella vulgaris photonic crystal as claimed in claim 1 or 2, wherein the logic 1 decision threshold, the logic 0 decision threshold and the interval between the logic 1 decision threshold and the logic 0 decision threshold of the optical logic device are regulated by incident wavelength.

Technical Field

The invention belongs to the technical field of all-optical communication, and relates to an optical logic device based on a rutin-Xiapino photonic crystal.

Background

In all-optical communication, information needs to be stored, transmitted, relayed, decided, timed, amplified, shaped, and the like in the optical domain, which leads to the vigorous development of all-optical devices for optical control of light, and optical logic devices based on optical bistable state are an important class thereof. Optical bistability is a nonlinear optical effect based on the optical kerr effect of a material. When the incident light is sufficiently strong, one input intensity value may correspond to two different output intensity values, i.e. one input intensity value may induce two stable resonant output states.

When the optical bistable is applied to an optical logic device, the upper threshold value and the lower threshold value of the bistable respectively correspond to the decision threshold values of logic 1 and logic 0 of the optical logic device; the larger the decision threshold, the stronger the light intensity required to trigger the optical logic to make a decision. However, as the power of the device increases, the stability of the device during operation may deteriorate and the requirements for heat dissipation conditions may increase. In addition, the smaller the interval between the upper and lower bistable thresholds is, the smaller the discrimination between logic 1 and logic 0 of the corresponding optical logic device is, which may result in an increased false rate. Therefore, current research on optical bistable devices focuses on reducing the threshold of optical bistable states and increasing the interval between upper and lower thresholds by new materials and new structures.

In order to realize the optical bistable effect with low threshold value, on one hand, a material with a large third-order nonlinear optical coefficient is sought; another aspect is to enhance the local electric field by optimizing the system structure. The optical kerr effect is proportional to the local electric field, so a strong local electric field can increase the third-order nonlinear optical effect of the material, thereby reducing the threshold of optical bistability.

Graphene is a new two-dimensional material, and has ultrathin property and excellent conductivity. The surface conductivity of graphene can be flexibly controlled by its chemical potential. Importantly, graphene has a considerable third-order optical nonlinear optical coefficient, which makes graphene a hot material in optical bistable studies. In addition, in order to further reduce the threshold value of bistable state, the local electric field of graphene can be enhanced by using the surface plasmon polariton of the graphene; graphene can also be embedded into a defective photonic crystal to enhance its nonlinear effects. In the defect photonic crystal, the energy of a defect mode is mainly distributed in a defect layer, so that the graphene is embedded in the defect layer, the nonlinear effect of the graphene can be greatly enhanced, and the optical bistable state with a low threshold value is further realized.

Two dielectric sheets with different refractive indexes are arranged alternately in space to form the 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. If defects are introduced into the photonic crystal, a transmission mode can appear in a transmission spectrum, and the transmission mode is a defect mode, has strong local effect on an electric field and is often used for enhancing the third-order nonlinear effect of materials.

Quasi-photonic crystals or aperiodic photonic crystals are often used to enhance the electric field localization because of the natural defect layer and the geometric progression of the number of defect modes with the increasing sequence number.

The Thue-Morse (TM) sequence is mathematically a quasi-periodic sequence, and its corresponding photonic crystal is a quasi-periodic photonic crystal. The graphene is embedded into the TM photonic crystal, so that optical bistable state can be realized, and the threshold value of the optical bistable state is about 100GW/cm²(gigawatts per square centimeter). The TM photonic crystal is provided with a plurality of defect cavities, and a plurality of defect modes, namely resonant transmission modes, exist in the same defect cavity. As the number of serial numbers increases, the number of dielectric layers in the TM photonic crystal correspondingly increases, and the transmission modes in the transmission spectrum split geometrically, so these resonance modes are also called optical modes. The optical molecular morphology has local property to an electric field and is commonly used for enhancing the third-order nonlinear effect of the material, so that the optical bistable state with low threshold value can be realized. Whether a quasi-periodic photonic crystal with stronger electric field locality can be found or not and then a composite structure with graphene is formed, so that the nonlinear effect of the graphene is further enhanced, and the threshold value of optical bistable state is reduced, which is a research focus in the field.

Disclosure of Invention

The invention aims to provide an optical logic device based on a rutin-Charinuo photonic crystal aiming at the problems in the prior art, and the technical problem to be solved by the invention is how to reduce the judgment threshold of the optical logic device.

The purpose of the invention can be realized by the following technical scheme: the optical logic device based on the Luding-Charcinod photonic crystal is characterized by comprising two binary RS photonic crystals and two graphene single layers which are symmetrically distributed, wherein each binary RS photonic crystal comprises a plurality of first dielectric layers and a plurality of second dielectric layers, and each second dielectric layer is provided with a first dielectric layer and a second dielectric layerOne dielectric layer is marked as H, the second dielectric layer is marked as L, the graphene monolayer is marked as G, the binary RS photonic crystal is marked as HHHLHHLH, and the optical logic device is marked as HHHLHHLH₁GH₂H₂GH₁LHHLHHH, wherein H₁GH₂And H₂GH₁Both represent a three-layer structure formed by embedding a graphene monolayer into a first dielectric layer, the thicknesses of the first dielectric layer and a second dielectric layer are 1/4 of respective optical wavelengths, and the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes; the photonics logic based on the rutin-Charcot-Supino photonic crystal can realize low-threshold optical bistable state, and the upper threshold and the lower threshold of the bistable state respectively correspond to the decision threshold of the optical memory logic 1 and the decision threshold of the optical memory logic 0.

Further, the first dielectric layer is made of lead telluride which is a high-refractive-index material, and the second dielectric layer is made of cryolite which is a low-refractive-index material.

Further, the logic 1 decision threshold, the logic 0 decision threshold and the interval between the logic 1 decision threshold and the logic 0 decision threshold of the optical logic device are regulated and controlled by the chemical potential of the graphene monolayer.

Further, the logic 1 decision threshold, the logic 0 decision threshold, and the interval between the logic 1 decision threshold and the logic 0 decision threshold of the optical logic device are regulated and controlled by the incident wavelength.

Two dielectric sheets A and B with different refractive indexes are sequentially arranged according to a Rudin-Shapiro (RS) sequence with the sequence number N being 3 to form an RS photonic crystal pair symmetrical about an origin; embedding the two graphene single layers into the RS photonic crystal pair to form a composite structure; the RS photonic crystal pair has an optical fractal which has a local effect on an electric field; the two graphene single layers are just positioned at the position with the strongest local electric field corresponding to one of the optical fractal states respectively, so that the third-order nonlinear effect of the graphene is greatly enhanced, and further the low-threshold optical bistable state is realized; the threshold value of the optical bistable state in the structure can be as low as 100MW/cm²This ratio is Thue-Morse photonic crystal andthe threshold for optical bistability in a composite structure of graphene is 3 orders of magnitude lower.

The upper and lower thresholds of the optical bistable state in the Luding-Charcinod photonic crystal structure and the interval between the upper and lower thresholds are increased along with the increase of the chemical potential and the incident wavelength of the graphene. Therefore, when the optical bistable effect is applied to an optical logic device, the logic 1 and logic 0 decision thresholds of the optical logic device and the interval between the logic 1 and logic 0 decision thresholds can be flexibly regulated and controlled through the chemical potential and the incident wavelength of the graphene.

Drawings

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

Fig. 2 is a linear transmission spectrum of a light wave in an RS photonic crystal with sequence number N-3.

FIG. 3 shows the wavelength λ₃A normalized electric field distribution corresponding to an optical fractal of 1.4058 μm.

Fig. 4 is a schematic diagram of an optical logic based on optical bistability.

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.

In the figure, H, a first dielectric layer; l, 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 rutin-Charcinod (Rudin-Shapiro: RS) sequence is: s₀＝H，S₁＝HH，S₂＝HHHL，S₃＝HHHLHHLH，……，S_N＝S_N-1(HH → HHHL, HL → HHLH, LH → LLHL, LL → LLLH), … …, wherein N (N ═ 0)1, 2, 3, … …) indicates the sequence number, S_NThe Nth item representing the sequence, HH → HHHL representing S_N-1HH in (1) is replaced by HHHL.

Fig. 1 shows a schematic diagram of a composite structure of a binary RS photonic crystal with sequence number N ═ 3 and graphene. Two binary RS photonic crystals are symmetrically distributed about the origin and can be represented as: HHHLHHLHHLHHLHHH, wherein the letters H, L denote two homogeneous dielectric sheets with different high and low refractive indices, respectively; optical fractal effect exists in the photonic crystal, and then the two graphene single layers are respectively embedded into the position, corresponding to one fractal state, with the strongest local electric field to form a composite structure, wherein the composite structure can be expressed as: HHHLHHLH₁GH₂H₂GH₁LHHLHHH, wherein G represents a graphene monolayer. The whole composite structure is symmetrically distributed about the origin, similar to a distributed feedback bragg grating.

In the composite structure of the RS photonic crystal pair and the graphene, H is a high-refractive-index material lead telluride, and the refractive index of H is n_H＝4.1；L、L₁And L₂Is a low refractive index material cryolite having a refractive index n_L1.35. Both H and L have a thickness of 1/4 optical wavelengths, i.e., H has a thickness d_H＝λ₀/4/n_H0.0945 μm (μm denotes μm), where λ₀1.55 μm as the center wavelength and L as the thickness d_L＝λ₀/4/n_L＝0.287μm。L₁Has a thickness of d_L1＝0.0088μm，L₂Has a thickness of d_L20.0857 μm, satisfies the condition d_L1+d_L2＝d_L. The incident light is transverse magnetic wave and is vertically incident from the left. The horizontal direction to the right is the positive direction of the coordinate axis Z direction.

Single layer graphene has a thickness of about 0.33nm (nm means nanometers), which corresponds to the size of one atom. The thickness of the graphene is negligible relative to the thickness of the dielectric sheets H and L. 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).

Changing the incident light frequency, when the effect of graphene is not considered, FIG. 2 givesThe linear transmission spectrum of light in the RS photonic crystal with the sequence number N-3 is shown. 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_H-n_L)/(n_H+n_L)|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 normalized frequency of [ -0.25,0.25]Within the interval, there are 3 transmission formants corresponding to 3 resonance optical partial forms. They are independent of each other and are separated by a suitable distance. The 3 transmittance peaks are all 1, and the corresponding medium wavelengths are respectively: lambda [ alpha ]₁＝1.7271μm、λ₂1.55 μm and λ₃1.4058 μm. The 3 optical sub-morphologies all have a local effect on the electric field, and only the 3 rd resonance state (marked with a star) is selected here to obtain the corresponding mode field distribution. And then the graphene single layer is embedded at the position with the strongest electric field intensity in the structure, 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 near the 3 rd resonance state, the incident wavelength must be relative to the 3 rd resonance state wavelength λ₃Suitably red detuned at 1.4058 μm.

FIG. 3 shows the electric field distribution of the 3 rd resonant optical fractal in the composite structure of FIG. 2, corresponding to the resonant wavelength λ₃1.4058 μm. The dotted line represents the interface of two adjacent dielectric media, and two graphene monolayers G are respectively embedded at two positions with the strongest local electric field in the structure. The ordinate represents the normalized Z-component electric field strength. It can be seen that the distribution of the electric field energy in the structure is not uniform and localized. The two graphene monolayers are located at two positions with the strongest local electric field. The optical third-order nonlinear 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.

Fixed incidence wavelength λ 1.423 μm corresponding to the optical fractal resonance wavelength λ₃There is some red detuning at 1.4058 μm. Increasing incidenceThe optical intensity, considering the nonlinear effect of graphene, the chemical potential of graphene is set as 0.4eV, other parameters are kept unchanged, and fig. 4 shows that optical bistable phenomenon occurs in the input-output optical intensity relation, and the optical bistable phenomenon is applied to the optical logic device. Abscissa I_iRepresenting input light intensity, ordinate I_oRepresenting the output light intensity; unit MW/cm²Representing megawatts per square centimeter. The profile of the input-output intensity relationship exhibits an S-shaped curve, which is a typical characteristic of optical bistability. 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 of the S-shaped curve segment, and the input light intensity I_i＝I_uUpper threshold called optical bistable, corresponding to logic 1 of optical logic, and I_i＝I_uCalled the decision threshold of optical logic 1; when the input light intensity is gradually reduced from a higher value, the output light intensity generates a downward jump at the left turning point of the S-shaped curve segment, and the input light intensity I_i＝I_dCalled the lower threshold of the optical bistable, which corresponds to the logic 0 of the optical logic, and I_i＝I_dCalled the decision threshold of optical logic 0. At this time, the decision threshold of logic 1 is I_u＝275.7236MW/cm²The decision threshold of logic 0 is I_d＝232.2537MW/cm²The interval between the logic 1 and logic 0 decision thresholds is I_u-I_d＝43.4699MW/cm²。

Keeping the incident wavelength λ 1.423 μm and other parameters unchanged, fig. 5(a) shows the input-output light intensity relationship corresponding to different graphene chemical potentials μ. It can be seen that: when mu is 0.3eV, 0.4eV and 0.5eV, the input-output luminous intensity relationship curves each have a sigmoid curve, i.e., a bistable relationship.

Increasing the value of mu, different chemical potentials correspond to different bistable curves, and the upper and lower thresholds and the threshold interval of the bistable states are also different. When 0.2eV is less than or equal to mu<0.42eV and 0.44eV ≦ μ, the bistable upper and lower thresholds, and the bistable threshold interval increase with the increase in graphene chemical potential, as shown in FIG. 5 (b). When 0.42eV is less than or equal to mu<0.44eV, bistable upper,The lower threshold, and therefore the threshold separation of the bistable states, decreases with increasing graphene chemical potential. This phenomenon occurs because the internal electrons of graphite undergo a transition from an in-band transition to an inter-band transition at a chemical potential of about 0.43eV at an incident light wavelength λ of 1.423 μm. Ordinate I_thA threshold value indicative of bistability; symbol I_uAnd I_dRepresenting bistable upper and lower thresholds, respectively. Therefore, the upper and lower thresholds and the threshold interval of the bistable state can be regulated by the chemical potential of graphene.

In a Thue-Morse photonic crystal and graphene composite system, the optical bistable threshold is 100GW/cm²In the RS photonic crystal and graphene composite structure, the threshold of optical bistable state is reduced to 100MW/cm²Magnitude.

In addition, the corresponding bistable curves and thresholds are different for different incident wavelengths.

When the chemical potential μ of the fixed graphene is 0.4eV, 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: when λ is 1.746 μm to 1.749 μm, input-output optics are all bistable; the bistable curves corresponding to different incident wavelengths are different, namely the widths of the upper threshold value, the lower threshold value and the threshold value of the bistable state are different; as the incident wavelength increases, i.e., the amount of wavelength detuning increases, the bistable upper and lower thresholds increase, and the bistable threshold interval increases, as shown in fig. 6 (b). The larger the detuning amount of the wavelength, the more the difference needs to be made up by the nonlinear effect to achieve optical resonance, and the stronger the incident light energy needed to satisfy the resonance. Thus, the upper and lower thresholds and threshold spacing of the bistable states can be tuned by the incident wavelength.

In a word, in the process of compounding the RS photonic crystal pair and the graphene, a resonant optical fractal exists, the optical fractal has a strong local effect on an electric field, and the two single-layer graphene are just respectively positioned at the position, corresponding to one optical fractal, of the two optical fractal, where the local electric field is strongest, so that the nonlinear effect of the graphene is greatly enhanced, and the low-threshold optical bistable state is realized, and the threshold value of the optical bistable state is as low as 100MW/cm²Order of magnitude, ratio of Thue-Morse photonic crystalThe optical bistability in the bulk and graphene composite is 3 orders of magnitude smaller. The optical bistable state can be applied to an optical logic device, and the logic 1 and logic 0 judgment thresholds of the optical logic device and the interval between the logic 1 and logic 0 judgment thresholds can be flexibly regulated and controlled through the chemical potential and the incident wavelength of graphene.

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.