阅读说明：本技术 一种基于Period-Doubling光子晶体的光逻辑器 (Optical logic device based on Period-double 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Period-Doubling光子晶体的光逻辑器,属于全光通讯技术领域。包括若干第一电介质层、若干第二电介质层和两个石墨烯单层,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,光逻辑器的层状结构表示为：HLH-(1)GH-(2)HH-(2)GH-(1)LHL,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。所述基于PD光子晶体的光逻辑器可实现低阈值光学双稳态,双稳态的上、下阈值分别对应着光逻辑器的逻辑1、逻辑0的判决阈值。本发明具有能够用作光逻辑器等优点。(The invention provides an optical logic device based on Period-double photonic crystals, and belongs to the technical field of all-optical communication. The optical logic device comprises a plurality of first dielectric layers, a plurality of second dielectric layers and two graphene single layers, wherein the first dielectric layers are marked as H, the second dielectric layers are marked as L, the graphene single layers are marked as G, and the layered structure of the optical logic device is represented as follows: HLH 1 GH 2 HH 2 GH 1 LHL of which 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 optical logic device based on the PD photonic crystal can realize low-threshold optical bistable state, and the upper and lower thresholds of the bistable state respectively correspond to logic 1 and logic 0 of the optical logic deviceAnd (6) judging a threshold value. The invention has the advantages of being capable of being used as an optical logic device and the like.)

1. An optical logic device based on Period-double photonic crystals, which is characterized by comprising a plurality of first dielectric layers, a plurality of second dielectric layers and two graphene single layers, wherein the first dielectric layers are represented by H, the second dielectric layers are represented by L, the graphene single layers are represented by G, and the layered structure of the optical logic device is represented by: HLH₁GH₂HH₂GH₁LHL of which 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 optical logic device of the Period-double 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 logic 1 and the decision threshold of logic 0 of the optical logic device.

2. The Period-double 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 Period-double photonic crystal as claimed in claim 1 or 2, wherein the logical 1, logical 0 decision value and threshold interval of the optical logic device are controlled by chemical potential of graphene monolayer.

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

Technical Field

The invention belongs to the technical field of all-optical communication, and relates to an optical logic device based on Period-double photonic crystals.

Background

In all-optical communication, information storage, transmission, relaying, decision, timing, amplification, shaping and the like are all carried out and completed in an optical domain, which requires the vigorous development of all-optical devices for optical control of light, and optical logics based on optical bistable states are an important class. Optical bistability is a nonlinear optical effect that exploits the optical kerr effect of materials. 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 output resonance 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 input optical field energy required to trigger the optical logic decision. However, as the power of the device increases, the stability of the device during operation is degraded and the requirements for heat dissipation conditions are increased. 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 the optical bistable device mainly focuses on how to reduce the threshold of the optical bistable device by new materials and new structures, and increase the interval between the upper and lower thresholds.

In order to achieve low threshold optical bistable effects, one aspect is to seek materials with large third-order nonlinear optical coefficients; 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 strength, so that the strong local electric field can improve the third-order nonlinear effect of the material, thereby reducing the bistable threshold value.

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 coefficient, which makes graphene a popular 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. The energy of the defect mode is mainly distributed in the defect layer, so that the graphene is embedded in the defect layer, and the nonlinear effect of the graphene can be greatly improved.

Two dielectric sheets with different refractive indexes are arranged alternately in space to form the photonic crystal with a periodic structure. In wave vector space, a photonic crystal has a photonic band structure similar to an electronic band in a semiconductor, and light waves within a band gap are totally reflected. If defects are introduced into the photonic crystal, a transmission mode appears in the transmission spectrum. The transmission mode is a defect mode, has a local effect on an electric field, and is often used to enhance the third-order nonlinear effect of a material.

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-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. With the increase of the serial number of the photonic crystal sequence, the number of dielectric layers in the TM photonic crystal is correspondingly increased, and the transmission modes in the transmission spectrum are split in a geometric series manner, so that the transmission modes are called fractal resonance states. The optical fractal has strong locality to the electric field and can be used to realize low-threshold optical bistability. Whether quasi-periodic photonic crystals with stronger electric field locality can be found or not can be further compounded with graphene, the nonlinear effect of the graphene is further enhanced, and the threshold value of optical bistable state is reduced; then, the optical bistable state is applied to an optical logic device to obtain the optical logic device with a low decision threshold and an adjustable threshold, which is the research focus in the field.

Disclosure of Invention

The present invention is directed to provide an optical logic device based on a Period-double photonic crystal, and the technical problem to be solved by the present invention is to design a photonic crystal that can be used in the optical logic device.

The purpose of the invention can be realized by the following technical scheme: an optical logic device based on Period-double photonic crystals is characterized by comprising a plurality of first dielectric layers, a plurality of second dielectric layers and two graphene single layers, wherein the first dielectric layers are made of dielectric materialsThe layer of the optical logic device is represented by H, the second dielectric layer is represented by L, the graphene single layer is represented by G, and the laminated structure of the optical logic device is represented by: HLH₁GH₂HH₂GH₁LHL of which 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 optical logic device based on the Period-double 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 logic 1 and the decision threshold of logic 0 of the optical logic device.

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

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

Sequentially arranging two dielectric sheets H and L with different refractive indexes according to a Period-doubled PD sequence with the sequence number N being 3; then embedding the two graphene single layers into the PD photonic crystal to form a composite structure; the PD 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 strongest position of the electric field corresponding to one optical fractal respectively, so that the three-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 is 3 orders of magnitude lower than the threshold for optical bistability in TM photonic crystals and graphene composite structures.

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

Drawings

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

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

FIG. 3 shows the wavelength λ₁Normalized electric field intensity distribution of the optical fractal state corresponding to 2.0855 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 Period-double (PD) sequence is: s₀＝H，S₁＝HL，S₂＝HLHH，……，S_N＝S_N-1S_N-2S_N-2… … where N (0, 1, 2, 3, … …) denotes the sequence number, S_NThe nth entry of the sequence is represented. In the corresponding PD photonic crystal, the letter H, L indicates two kinds of uniform dielectric sheets having different high and low refractive indices, respectively.

FIG. 1 shows a PD photonic crystal with the sequence number N-3 and graphiteSchematic diagram of alkene complex structure. A PD photonic crystal with sequence number N-3 can be represented as: HLHHHLHL, where the letters H, L denote two uniform dielectric sheets with high and low refractive indices, respectively; optical fractal effect exists in the photonic crystal, and then two graphene single layers are respectively embedded into one of the positions with the strongest fractal local electric field to form a composite structure, wherein the composite structure can be expressed as: HLH₁GH₂HH₂GH₁LHL, wherein G represents a graphene monolayer.

In the PD photonic crystal, H, H₁And H₂Is a high refractive index material of lead telluride with refractive index n_H4.1 as the ratio; l is cryolite of low refractive index material with 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。H₁Has a thickness of d_H1＝0.0145μm，H₂Has a thickness of d_H20.08 μm, satisfies the condition d_H1+d_L2＝d_H. The incident light is transverse magnetic wave and is 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. With respect to the dielectric sheet H, H₁、H₂And L, the 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 PD photonic crystal with the sequence number N being 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_H-n_L)/(n_H+n_L)|²The/pi represents the incident angular frequency and the incidenceThe central angular frequency and the angular frequency band gap of the emitted light, c is the speed of light in vacuum, and arcsin is an inverse sine function. At a normalized frequency of [ -1,1 [)]In the interval, a photonic band gap exists, 2 transmission peaks appear in the middle of the band gap, and the transmission peaks correspond to 2 resonance optical partial forms; they are independent of each other and are separated by a suitable distance; these 2 transmittance peaks are 0.9687, corresponding to medium wavelengths: lambda [ alpha ]₁2.0855 μm and λ₂1.2333 μm. The 2 optical fractal states have a local effect on an electric field, and only the 1 st resonance state (marked with star) is selected to obtain the corresponding mode field distribution; and then the graphene single layer is embedded at the position with the strongest local electric field in the composite structure, so that the nonlinear effect of the graphene is enhanced, and the low-threshold optical bistable state is realized. In addition, the resonance wavelength λ is set at 1 st₁Optical bistable state with low threshold value is realized nearby, and incident wavelength must be opposite to lambda₁Suitably red detuned at 2.0855 μm.

FIG. 3 shows the electric field distribution of the 1 st resonant optical fractal in FIG. 2 in a composite structure, corresponding to a resonant wavelength λ₁2.0855 μm. The dotted line represents the interface of two adjacent dielectric sheets, 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 non-uniform and localized; the two graphene monolayers are located at two positions with the strongest local electric field. The third-order nonlinear optical effect of graphene is proportional to the local electric field intensity, and therefore, the nonlinear effect of graphite is greatly enhanced.

The fixed incident wavelength λ is 2.23 μm and is relative to the 1 st resonance wavelength λ of the optical fractal₁There is some red detuning at 2.0855 μm. When the input light is strong enough, the chemical potential of graphene is fixed to be 0.4eV, taking into account the nonlinear effect of graphene, and other parameters remain unchanged. Fig. 4 shows the occurrence of optical bistability in the input-output intensity relationship and its application to optical logic. Abscissa I_iRepresenting input light intensity, ordinate I_oIndicating the output light intensity. Unit MW/cm²Representing megawatts per square centimeter. Input-The profile of the output intensity relationship has an S-shaped curve section, which is a typical characteristic of the optical bistable state. 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 inflection 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＝525.2662MW/cm²The decision threshold of logic 0 is I_d＝314.3101MW/cm²The interval between the logic 1 and logic 0 decision thresholds is I_u-I_d＝210.9561MW/cm²。

Keeping the incident wavelength λ 2.23 μm and other parameters constant, fig. 5(a) shows the input-output intensity relationship corresponding to different graphene chemical potentials μ. It can be seen that: when mu is 0.3eV, 0.4eV and 0.5eV, there is a sigmoid curve segment in each input-output luminous intensity relationship curve, namely, a bistable relationship.

Increasing the μ value, different chemical potentials correspond to different bistable curves, and the upper and lower thresholds and threshold intervals of the bistable states are also different, as shown in fig. 5 (b). Ordinate I_thThreshold value, symbol I, representing bistability_uAnd I_dRespectively representing bistable upper and lower thresholds; when 0.2eV is less than or equal to mu<The bistable upper and lower thresholds, and the bistable upper and lower threshold intervals increase with increasing graphene chemical potential at 0.27eV and 0.28eV ≦ μ; when 0.27eV is less than or equal to mu<At 0.28eV, the bistable upper and lower thresholds, and the bistable upper and lower threshold separation, decrease with increasing graphene chemical potential. This is because when the wavelength of incident light is λ 2.23 μm, the internal electrons of graphite transition from in-band to inter-band at a chemical potential μ of 0.275eVAnd (4) converting. Therefore, the upper and lower thresholds and the threshold interval of the bistable state can be regulated by the chemical potential of graphene.

In the composite structure of the TM photonic crystal and the graphene, the optical bistable state threshold is 100GW/cm²In the composite structure of the PD photonic crystal and the graphene, the threshold of the optical bistable state is reduced to 100MW/cm²Magnitude. It can be seen that the threshold for optical bistability is reduced by 3 orders of magnitude.

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

The fixed graphene chemical potential μ 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 lambda is 2.22-2.25 um, the relation of input and output light intensity is bistable; 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 wavelength detuning increases, the bistable upper and lower threshold values increase, and the bistable upper and lower threshold intervals increase, as shown in fig. 6 (b). The larger the detuning of the wavelength, the more the difference needs to be made up by the nonlinear effect to achieve resonance, and the stronger the required incident light field energy. Therefore, the upper and lower thresholds of the bistable state, and the separation between the upper and lower thresholds, can be tuned by the incident wavelength.

In a word, in a composite structure of the PD photonic crystal and the graphene, a resonant optical fractal exists, the optical fractal has a strong local effect on an electric field, and two graphene single layers are just respectively positioned at the strongest position of the local electric field corresponding to one optical fractal, 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 can be as low as 100MW/cm²The magnitude is 3 magnitudes smaller than the optical bistable threshold in the TM photonic crystal and graphene composite structure. The optical bistable state can be applied to an optical logic device, the decision threshold values of logic 1 and logic 0 of the optical logic device respectively correspond to the upper threshold value and the lower threshold value of the optical bistable state, and then the decision threshold values of logic 1 and logic 0 of the optical logic device, and logic 1 and logic 0The interval between the decision thresholds of 0 can be flexibly regulated and controlled by the chemical potential and 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.