阅读说明：本技术 一种基于Period-Doubling光子晶体的全光开关 (All-optical switch 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光子晶体的全光开关,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,全光开关的层状结构表示为：HL-(1)GL-(2)HH-(1)GH-(1)HL-(2)GL-(1)HL,其中L-(1)GL-(2)和L-(2)GL-(1)均表示石墨烯单层嵌入第二电介质层内形成的三层结构,H-(1)GH-(1)表示石墨烯单层嵌入第一电介质层中部形成的三层结构,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。本发明能够应用于全光开关。(The invention provides an all-optical switch based on a Period-double photonic crystal, and belongs to the technical field of all-optical communication. The all-optical switch 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 all-optical switch is as follows: HL (HL) 1 GL 2 HH 1 GH 1 HL 2 GL 1 HL, wherein L 1 GL 2 And L 2 GL 1 All represent a three-layer structure formed by embedding a single layer of graphene into a second dielectric layer, H 1 GH 1 The three-layer structure is formed by embedding a graphene monolayer in the middle of a first dielectric layer, the thicknesses of the first dielectric layer and a second dielectric layer are 1/4 of the optical wavelength of each dielectric layer, and the first dielectric layer and the second dielectric layer are two uniform dielectric sheets with different refractive indexes. The invention can be applied toAn optical switch.)

1. An all-optical switch 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 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 all-optical switch is represented by: HL (HL)₁GL₂HH₁GH₁HL₂GL₁HL, wherein L₁GL₂And L₂GL₁All represent a three-layer structure with a single layer of graphene embedded within a second dielectric layer, the H₁GH₁The graphene-based optical waveguide structure is a three-layer structure formed by embedding a graphene single layer in the middle of 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 all-optical switch of the PD photonic crystal can realize low-threshold optical bistable state, and the upper and lower thresholds of the bistable state respectively correspond to the on and off trigger thresholds of the all-optical switch.

2. The all-optical switch based on Period-double photonic crystals as claimed in 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 all-optical switch based on Period-double photonic crystals according to claim 1 or 2, wherein the on-trigger threshold, the off-trigger threshold and the interval between the on-trigger threshold and the off-trigger threshold of the all-optical switch are controlled by the chemical potential of the graphene monolayer.

4. The all-optical switch based on Period-double photonic crystals according to claim 1 or 2, wherein the on-trigger threshold, the off-trigger threshold and the interval between the on-trigger threshold and the off-trigger threshold of the all-optical switch are regulated and controlled by incident wavelength.

Technical Field

The invention belongs to the technical field of all-optical communication, and relates to an all-optical switch based on a Period-double photonic crystal.

Background

In all-optical communication, information needs to be stored, transmitted, relayed, decided, timed, amplified, shaped, and the like in an optical domain, and an optical device for controlling light is used, and an optical switch based on optical bistable is an important class of the optical switch. 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 state is applied to the all-optical switch, the upper threshold value and the lower threshold value of the bistable state respectively correspond to the on-off trigger threshold value of the all-optical switch; the larger the trigger threshold, the stronger the input light energy required to trigger the all-optical switch to turn on and off. However, as the power of the device increases, the operational stability of the device deteriorates and the requirements for heat dissipation conditions increase. In addition, the smaller the interval between the upper and lower bistable thresholds is, the smaller the distinction degree between on and off of the corresponding all-optical switch is, which may result in the increase of the misoperation 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 electric field locality 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.

Graphene is a new two-dimensional material, and has ultrathin property and excellent conductivity. The graphene surface conductivity can be flexibly regulated and controlled through the chemical potential. Importantly, graphene has a considerable third-order nonlinear optical coefficient, which makes graphene an important 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 enhanced.

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 can appear in a transmission spectrum; 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 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, which corresponds to a TM photonic crystal that 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, so these transmission modes are also called optical splitting forms. The optical fractal has the locality to the electric field, and the optical bistable state with low threshold value can be realized. Whether quasi-periodic photonic crystals with stronger electric field locality can be found or not is the quasi-periodic photonic crystals, so that the quasi-periodic photonic crystals are compounded with graphene, the nonlinear effect of the graphene is further enhanced, and the threshold value of optical bistable state is reduced; and then, the optical bistable state is applied to the all-optical switch to obtain the all-optical switch with low trigger threshold and adjustable threshold, which is the research focus in the field.

Disclosure of Invention

The invention aims to provide an all-optical switch based on a Period-double photonic crystal, aiming at the problems in the prior art, and the technical problem to be solved by the invention is how to enhance the nonlinear effect of graphene by utilizing the locality of optical molecular morphology in the Period-double photonic crystal to an electric field, so that the threshold value of optical bistable state is reduced, and the all-optical switch can be applied to a low-threshold value and adjustable threshold value.

The purpose of the invention can be realized by the following technical scheme: an all-optical switch based on Period-double photonic crystals is characterized by comprisingThe all-optical switch 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 all-optical switch is represented as: HL (HL)₁GL₂HH₁GH₁HL₂GL₁HL, wherein L₁GL₂And L₂GL₁All represent a three-layer structure with a single layer of graphene embedded within a second dielectric layer, the H₁GH₁The graphene-based optical waveguide structure is a three-layer structure formed by embedding a graphene single layer in the middle of 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 all-optical switch 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 on-off trigger threshold of the all-optical switch.

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 on-trigger threshold, the off-trigger threshold and the interval between the on-trigger threshold and the off-trigger threshold of the all-optical switch are regulated and controlled by the chemical potential of the graphene monolayer.

Further, the on-trigger threshold, the off-trigger threshold and the interval between the on-trigger threshold and the off-trigger threshold of the all-optical switch are regulated and controlled by 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; embedding the three graphene single layers into the PD photonic crystal to form a composite structure; the PD photonic crystal has an optical fractal which has a strong local effect on an electric field; the three graphene single layers are just positioned at the position with the strongest local electric field corresponding to one of the optical fractal states, so that the third-order nonlinear effect of the graphene is greatly enhanced, and further low-threshold light is realizedLearning bistable state; 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 all-optical switch, the on-off trigger threshold value and the interval between the on-off trigger threshold values of the all-optical switch 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 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 λ₂A normalized electric field distribution corresponding to an optical fractal of 1.2333 μm.

Fig. 4 is a schematic diagram of an optical bistable-based all-optical switch.

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 schematic diagram of a composite structure of a PD photonic crystal with sequence number N ═ 3 and graphene. PD with sequence number N-3 can be expressed 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 three graphene single layers are respectively embedded into the strongest position of electric field intensity distribution corresponding to one fractal state to form a composite structure, wherein the composite structure can be expressed as: HL (HL)₁GL₂HH₁GH₁HL₂GL₁HL, wherein G represents a graphene monolayer.

In the PD photonic crystal pair, H and H₁Is a high refractive index material of lead telluride with refractive index 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＝0.2084μm，L₂Has a thickness of d_L20.0786 μm, satisfies the condition d_L1+d_L2＝d_L。H₁Has a thickness of d_H10.04725 μm, satisfies the condition d_H1＝d_H/2. 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、L、L₁And L₂The thickness of graphene is negligible. Here, the ambient temperature was set to 300K (K denotes kelvin), and the relaxation time τ of electrons in graphene was 0.5ps (ps denotes skin)Seconds).

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)|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, a photonic band gap exists, and 2 transmission formants appear in the middle of the band gap, which correspond to 2 resonance optical fractal. 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 the electric field, and only the 2 nd 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 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 2 nd resonance state, the incident wavelength must be relative to the 2 nd resonance state wavelength λ₂Suitably red detuned at 1.2333 μm.

FIG. 3 shows the electric field distribution of the 2 nd resonant optical fractal in FIG. 2 in a composite structure with a resonant wavelength λ₂1.2333 μm. The dotted line represents the interface of two adjacent dielectric layers, and three graphene monolayers G are respectively embedded at three positions with the strongest electric field intensity 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, with locality; the three graphene single layers are just positioned at three positions with strongest local electric fields; 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 incidenceWavelength λ is 1.275 μm, corresponding to the resonance wavelength λ of the 2 nd optical partial form₂There is some red detuning at 1.2333 μm. When the incident light is strong enough, the chemical potential of the graphene is fixed when μ ═ 0.4eV, and other parameters are kept unchanged, and fig. 4 shows that the optical bistable phenomenon occurs in the input-output light intensity relationship, and the optical bistable phenomenon is applied to the all-optical switch. Abscissa I_iRepresenting input light intensity, ordinate I_oIndicating the output light intensity. Unit MW/cm²Representing megawatts per square centimeter. The existence of a sigmoid curve segment in the profile of the input-output intensity relationship is a typical characteristic of optical bistability. When the input light intensity is gradually increased from a lower value, an upward jump of the output light intensity occurs at the right-hand corner of the S-shaped curve segment, thereby increasing the input light intensity I_i＝I_uCalled optical bistable upper threshold, which corresponds to the switching-on process of an all-optical switch, and_i＝I_ucalled as the trigger threshold of the on-state of the all-optical switch; when the input light intensity is gradually decreased from a higher value, the output light intensity is in a downward jump at the left-hand corner of the S-shaped curve segment, thereby the input light intensity I is gradually decreased_i＝I_dCalled optical bistable lower threshold, which corresponds to the switching-off process of the all-optical switch, and I_i＝I_dCalled the trigger threshold for all-optical switch turn-off. At this time, the turn-on trigger threshold is I_u＝1023.5MW/cm²The turn-off trigger threshold is I_d＝903.3MW/cm²The interval between the on and off trigger thresholds is I_u-I_d＝120.2MW/cm²。

Keeping the incident wavelength λ 1.275 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 or 0.5eV, each of the input-output luminous intensity relationship curves has a sigmoid curve segment, i.e., a bistable relationship.

Increasing the μ value, different chemical potentials correspond to different bistable curves, and the upper and lower thresholds and the width between the thresholds of the bistable curves are different, as shown in fig. 5 (b). Ordinate I_thIndicating bistabilityThreshold of state, sign I_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 threshold interval, increase with increasing graphene chemical potential at 0.47eV and 0.49eV ≦ μ; when 0.47eV is less than or equal to mu<At 0.49eV, the bistable upper and lower thresholds, and the separation between the bistable upper and lower thresholds, decrease 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 in the vicinity of a chemical potential μ of 0.48eV at an incident light wavelength λ of 1.275 μm. 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 composite system of TM photonic crystal and graphene, the optical bistable state threshold is 100GW/cm²In the composite structure of the PD photonic crystal and graphene, the threshold of optical bistability 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 1.26 μm, the input-output optics are non-bistable; when λ is 1.27 μm and 1.28 μm, both input-output optics are bistable; the bistable curves corresponding to different incident wavelengths are different, namely the upper threshold value and the lower threshold value of the bistable state and the width between the threshold values are different. When λ >1.2675 μm, a bistable phenomenon occurs, and as the incident wavelength increases, that is, the amount of detuning increases, the upper and lower thresholds of the bistability increase, and the threshold interval of the bistability 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 resonance, and the stronger the incident light energy needed to satisfy 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 compounding 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,the three single-layer graphene layers are just positioned at the strongest position of the electric field corresponding to one of the optical fractal states, so that the nonlinear effect of the graphene is greatly enhanced, and the optical bistable state with the low threshold value is realized, and the threshold value of the optical bistable state is as low as 100MW/cm²The order of magnitude is 3 orders of magnitude smaller than the optical bistability in the compounding of the TM photonic crystal and the graphene. The optical bistable state can be applied to all-optical switches, and the on-off trigger threshold values and the intervals between the on-off trigger threshold values of all-optical switches 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.