CN113156740A

CN113156740A - Composite structure of tuer-morse sequence multilayer dielectric and graphene

Info

Publication number: CN113156740A
Application number: CN202110518851.5A
Authority: CN
Inventors: 张亚平
Original assignee: Hubei University of Science and Technology
Current assignee: Hubei University of Science and Technology
Priority date: 2021-06-17
Filing date: 2021-06-17
Publication date: 2021-07-23
Anticipated expiration: 2041-06-17
Also published as: CN113156740B

Abstract

The invention provides a composite structure of a tuer-morse sequence multilayer dielectric medium and graphene, and belongs to the technical field of all-optical communication systems. Including two symmetric distribution's composite component, composite component includes a graphite alkene layer, a plurality of first dielectric layer and a plurality of second dielectric layer, and graphite alkene layer, first dielectric layer and the second dielectric layer three in the composite component's the law of arranging does: the graphene comprises a first dielectric layer, a second dielectric layer, a graphene layer, a second dielectric layer, a first dielectric layer and a second dielectric layer from outside to inside in sequence. The invention can realize optical tristable state and multistable state.

Description

Composite structure of tuer-morse sequence multilayer dielectric and graphene

Technical Field

The invention belongs to the technical field of all-optical communication systems, and relates to a composite structure of a Here-Mohs sequence multilayer dielectric medium and graphene.

Background

All-optical switches and optical logic are important devices in all-optical communications. The optical bistable effect is one of the hot topics in the research of all-optical switches and optical logics. In optical bistability, one input value may correspond to two resonance states, i.e. two stable output values.

Changing the input quantity, along the positive stroke, generating an upward jump in the output quantity, and inducing the upward jump of the input light intensity to be called an upper threshold value of the optical bistable state; along the negative stroke, the output will have a downward jump, and the input light intensity induced downward jump is called the lower threshold of the optical bistable state.

The on and off thresholds of the all-optical switch based on the optical bistable state correspond to the upper threshold and the lower threshold of the optical bistable state respectively. Similarly, based on the optical logic device with optical bistable state, the

optical logic

1 and 0 also correspond to the upper and lower threshold values of the optical bistable state, respectively. Obviously, for multi-value switches or multi-state logic devices, optical bistability cannot meet such requirements, and thus, research on optical tristable and multistable effects is required.

Generally, to form an optical bistable state, the structure and wavelength of the device need to satisfy resonance conditions. The simplest resonant structure is a fabry-perot resonator. A nonlinear medium is embedded in the resonant cavity, and the refractive index of the nonlinear medium is proportional to the intensity of the local electric field. When the input light (the wavelength is slightly red detuned with respect to the linear resonance condition) is reflected back and forth, the nonlinear effect just cancels the wavelength detuning amount, reaching the resonance condition, and thus forming a stable resonance output.

The fabry-perot resonator is not yet sufficiently local to the electric field and therefore the threshold of the optical bistability formed is not low enough. And their resonance peaks are independent of each other and cannot form an optical tristable or multistable state. A great deal of research shows that the photonic crystal with defects has strong locality to an electric field, but a single defect mode appears at the center of a photonic band gap of the photonic crystal, so that optical tristable and multistable states cannot be realized.

Ture-Mohs (Thue-Morse: TM) sequence multilayer dielectrics belong to a type of aperiodic photonic crystal, and their properties are intermediate between quasi-periodic and disordered crystals. Compared with a photonic crystal with defects, the transmission spectrum has a plurality of resonance peaks which are overlapped with each other. This provides a resonance condition for the formation of optical tristable and multistable states.

Graphene is used as an ultrathin two-dimensional material, and has the characteristics of ultrafast optical response, adjustable conductivity and the like. In particular, graphene has a large third-order nonlinear coefficient. In near infrared and terahertz wave bands, the third-order nonlinear coefficient of graphene is one order of magnitude larger than that of silicon and silicon dioxide, so that the graphene is a high-quality material for realizing low-threshold optical tristable and multistable devices. The multi-layer dielectric medium of the TM sequence is compounded with graphene, and the optical tristable state and the multistable state of the low threshold can be realized by utilizing the overlapping property of the multi-layer dielectric medium multi-resonance state of the TM sequence and the nonlinearity of the graphene.

In addition, the surface conductivity of the graphene is regulated and controlled by the chemical potential (namely the Fermi level) of the graphene, and the chemical potential of the graphene can be regulated and controlled by external bias voltage and chemical doping, so that the surface conductivity of the graphene can be flexibly regulated and controlled by external gate voltage, and further the formation of optical tristable and multistable states and a threshold value can be regulated and controlled.

Disclosure of Invention

The invention aims to provide a composite structure of tuser-morse sequence multilayer dielectric and graphene aiming at the problems in the prior art, and the technical problem to be solved by the invention is how to realize optical tristable and multistable states.

The purpose of the invention can be realized by the following technical scheme: the utility model provides a figure first-mole is compound structure of serial multilayer dielectric medium and graphite alkene, its characterized in that includes two symmetric distribution's composite assembly, composite assembly includes a graphite alkene layer, a plurality of first dielectric layer and a plurality of second dielectric layer, graphite alkene layer, first dielectric layer and the second dielectric layer three among the composite assembly rule of arranging do: the graphene comprises a first dielectric layer, a second dielectric layer, a graphene layer, a second dielectric layer, a first dielectric layer and a second dielectric layer from outside to inside in sequence.

Furthermore, the first dielectric layer is silicon, and the second dielectric layer is silicon dioxide.

The two dielectric thin layers of silicon dioxide and silicon are arranged according to a TM sequence to form a multilayer dielectric, and then graphene is embedded into the TM sequence multilayer dielectric to form a composite structure.

In the frequency spectrum of the TM sequence multilayer dielectric, there is a phenomenon in which a plurality of resonance modes overlap, that is, a plurality of resonance peaks are connected to each other to form a pass band. Although different resonance peaks correspond to different resonance modes, the mode field energy of these overlapped resonance modes is mainly confined in the same resonant cavity, i.e. the position where the graphene is located. The strong local electric field can greatly enhance the third-order nonlinear effect of the graphene. When the wavelength of the input light wave is slightly red detuned relative to the resonance peaks, the intensity of the incident light is increased, and the optical bistable state, the tristable state and the multistable state with low threshold values can be realized, and the threshold values of the bistable state, the tristable state and the multistable state can be flexibly adjusted through the chemical potential of the graphene. These effects can be applied to three-and multi-valued all-optical switches and optical memories.

Drawings

Fig. 1 is a schematic diagram of a composite structure of TM-sequence multilayer dielectric and graphene.

FIG. 2(a) is the transmittance in the composite structure; in FIG. 2, (b), (c), and (d) are the corresponding mode field distributions of the transmission peaks (i), (ii), and (iii) in FIG. (a), respectively.

FIG. 3(a) is a non-linear transmission as a function of incident light intensity; (b) is the variation relation of the output light intensity with the input light intensity; (c) is the threshold of bistability as a function of graphene chemical potential.

FIG. 4(a) is a non-linear transmission as a function of incident light intensity; (b) is the variation of the output light intensity with the input light intensity.

FIG. 5(a) is a schematic diagram of bistable, tristable and tetrastable states; (b) is the case of a jump in output intensity with input intensity.

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

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.

Fig. 1 shows a schematic diagram of a composite structure of a multilayer dielectric and graphene following a TM sequence. Dielectric A is silicon (Si) and dielectric B is silicon dioxide (SiO)₂) And symbol G represents single-layer graphene. Dielectrics a and B alternate in the horizontal direction and follow the TM sequence rules. The TM sequence is an aperiodic sequence that follows a recursive relationship: item 0 of the sequence is S ₀1 st term is S₁{ AB }, the nth term is S_n+1＝{S_n，S_nWhen n is larger than or equal to 2, wherein S is_nIs S_nThe complement of (1) can be obtained byWill S_nWherein the elements A and B are substituted for each other. From this can be obtained S₂＝{ABBA}，S₃＝{ABBABAAB}，S₄＝{ABBABAABBABAABBA}，……。

There are large defect layers in the TM multi-layer dielectric that form the cavity of the defect cavity. The mode field of the defect mode is mainly distributed in these defect layers. Here we use S as₄For example, studies have shown that if graphene is embedded in the middle BB layer while increasing the incident light intensity, a low threshold optical bistability can be achieved. In fact, two consecutive BB's constitute a defect cavity, while in the above composite structure, two BB layers at both sides and the middle BB layer support different defect modes. The defect mode corresponding to the middle BB layer, the electric field of which is locally positioned at the middle BB layer; and the electric fields of the defect modes corresponding to the BB layers on the two sides are localized at the BB layers on the two sides.

Here, we embed the graphene in the middle of BB layers on both sides, respectively, and the composite structure can be expressed as { abbabaabaabaabaabaabaabagabbba }. The input light intensity is improved, and low-threshold optical bistable state, tristable state and multistable state phenomena can be realized. The thickness of the dielectric A is d_a＝λ₀/4n_aThe thickness of the dielectric B is d_b＝λ₀/4n_bWherein λ is₀Is a central wavelength, and is set to λ₀1.55 μm (unit μm represents μm). Parameter n_a3.53 is the refractive index of dielectric a, n_b1.46 is the refractive index of dielectric B. Arrow line 1 represents incident light and arrow line 2 represents projected light. A transverse electric wave is perpendicularly incident on the composite structure from the left.

Fig. 2(a) shows the transmittance in a TM-sequence multilayer dielectric and graphene composite structure. The ordinate T represents the transmittance, and the abscissa (ω - ω)₀)/ω_gapDenotes a normalized frequency, where ω is 2 π c/λ, ω₀＝2πc/λ₀And ω_gap＝4ω₀arcsin│(n_a-n_b)/(n_a+n_b)|²The/pi represents the incident light frequency, the incident light center frequency and the forbidden band frequency respectively, c is the light speed in vacuum, lambda is the incident wavelength, arcsin represents the arcsineA function. It can be seen that there are seven transmission peaks in the transmission spectrum, corresponding to 7 defect modes respectively. The peaks are mutually overlapped and connected together to form a pass band. This property is advantageous for achieving optical tristable and multistable states around these three peaks.

The distribution of the three electric fields is shown in FIG. 2(b, c, d), where the abscissa Z-axis is the Z-axis, i.e. the direction of the dielectric stack, and the ordinate | E_Z|²Is the normalized electric field strength. The larger the peak value of the profile, the larger the electric field intensity at that position. Obviously, the electric field is strongest at the central position of the BGB defect cavities at two sides of the structure, namely the electric field is strongest at the position where the graphene is located. Therefore, the structure can enhance the third-order nonlinear effect of graphene. As long as the incident light wavelength is slightly red detuned with respect to these peak wavelengths, optical tristabilites and multistates can form when the incident light intensity increases sufficiently.

When the incident wavelength is detuned with respect to the transmission peak c, for example, when λ is 1.501 μm, the nonlinear transmittance varies with the output light intensity as shown in fig. 3 (a). Abscissa I_iIs the input light intensity, the ordinate T represents the transmittance, and the abscissa unit (GW/cm)²) Representing gigawatts per square centimeter. It can be seen that different graphene chemical potentials correspond to a specific transmittance curve, and each curve has a transmittance peak. When μ is 0.5eV and 0.6eV, the slope of the transmittance curve shows a negative value near the transmittance peak with the change in input light intensity, which indicates that a bistable phenomenon occurs in the input-output light intensity relationship. When μ is 0.3eV and 0.4eV, the slope of the transmittance curve is positive in the vicinity of the transmission peak, which indicates that no bistable phenomenon occurs in the input-output intensity relationship.

FIG. 3(b) shows the variation of output intensity with input intensity. Ordinate I_oIs the output light intensity. It can be seen that when μ is 0.5eV and 0.6eV, a sigmoid curve appears on each curve, which is a bistable phenomenon. The greater the chemical potential, the greater the upper and lower thresholds of bistability. On the other hand, when μ is 0.3eV or 0.4eV, the input-output relationship curve has no sigmoid curve, and therefore, in both casesThere is no bi-stability. It can be seen that the formation of bistability, and the threshold of bistability, can be controlled by the chemical potential of the graphene.

Fig. 3(c) shows the variation of bistable upper and lower thresholds with the chemical potential of graphene. The ordinate, through, represents the bistable Threshold, Upper Threshold represents the Upper Threshold and Lower Threshold represents the Lower Threshold. It can be seen that bi-stability occurs when μ >0.414 eV; the chemical potential of the graphene is continuously increased, and the width between the upper threshold and the lower threshold of the bistable state is continuously increased. When the optical bistable effect is applied to the all-optical switch, the bistable upper and lower thresholds respectively correspond to the on and off thresholds of the all-optical switch, so that the larger the switch threshold interval is, the smaller the false judgment rate of the switch is. The phenomenon also shows that the interval width of the switching threshold of the all-optical switch can be regulated and controlled by the chemical potential of the graphene.

When the incident wavelength is detuned with respect to the transmission peak (r) red, for example, when λ is 1.7 μm, the nonlinear transmittance variation with the output light intensity is as shown in fig. 4 (a). Abscissa unit of input light intensity (TW/cm)²) Representing the terawatts per square centimeter. It can be seen that different graphene chemical potentials correspond to a specific transmittance curve, and each curve has two transmission peaks. As the input intensity changes, the slope of the transmittance curve will exhibit negative values near the transmission peak, which is not present in practice, which is indicative of bi-stability in the input-output intensity relationship.

FIG. 4(b) shows the variation of output intensity with input intensity. It can be seen that by varying the input light intensity, two sigmoid curves, one smaller and one larger, appear on each curve. The two S-shaped curves correspond to two bistable operating ranges. The upper and lower thresholds of the two bistable operating ranges are different in size, and the widths of the upper and lower thresholds are also different. The threshold size and the interval width of the bistable state are regulated and controlled by the chemical potential of the graphene.

When the incident wavelength is detuned with respect to the transmission peak (r) red, for example, when λ is 1.9 μm, one output light intensity may correspond to two, three, or four output light intensities, as shown in fig. 5 (a). Chemical formula of graphene hereinMu is 0.4 eV. It can be seen that a quasistatic state (N) occurs first as the incident light intensity gradually increases from low to high₁，N₂，N₃，N₄) And then tristable (M) occurs₁，M₂，M₃) Finally, bistability (K) appears₁，K₂)。

At different input intensity positions, there will be sudden upward or downward jumps in the output intensity, as shown in fig. 5 (b). When the input light intensity I_iAt I, increasing gradually from zero_i＝T_u1At an output light intensity I_oAn upward transition occurs along the track I; continue to increase I_iTo T_u2Output light intensity I_oAgain, an upward transition occurs along the trajectory II. When the input light intensity I_iSlowly decreasing from a larger value at I_i＝T_d3At an output light intensity I_oA downward jump takes place along the track IV. This case needs to be discussed in two cases: 1. if increase I_iTo T_u3Output light intensity I_oAn upward jump again occurs along the trajectory III; 2. if I is continuously decreased_iTo T_d2Output light intensity I_oA downward jump occurs along track V, which is possible in two ways: a. if increase I_iTo T_u2Output light intensity I_oThen an upward jump occurs along the track II, b, if I is further decreased_iTo T_d1Output light intensity I_oAgain, a downward jump occurs along the trajectory VI. Symbol T_u1，T_u2And T_u3Respectively representing three upper thresholds, denoted by the symbol T_d1，T_d2And T_d3Three lower thresholds are respectively indicated. When the input light intensity is in the interval (T)_d1，T_u2) The output light intensity may be two, three or four stable values when varied, which correspond to the optical bistable state, the tristable state and the tristable state, respectively. All-optical binary, ternary and quaternary switches can be manufactured based on the optical effects, and the on and off thresholds of the switches can be flexibly regulated and controlled through the chemical potential 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.

Claims

1. The utility model provides a figure first-mole is compound structure of serial multilayer dielectric medium and graphite alkene, its characterized in that includes two symmetric distribution's composite assembly, composite assembly includes a graphite alkene layer (G), a plurality of first dielectric layer (A) and a plurality of second dielectric layer (B), graphite alkene layer (G), first dielectric layer (A) and second dielectric layer (B) among the composite assembly rule of arranging of three do: the graphene-based composite material comprises a first dielectric layer (A), a second dielectric layer (B), a graphene layer (G), a second dielectric layer (B), a first dielectric layer (A) and a second dielectric layer (B) from the outside to the inside in sequence.

2. The composite structure of graphene and chaes-morse-sequence multilayer dielectric according to claim 1, wherein the first dielectric layer (a) is silicon and the second dielectric layer (B) is silicon dioxide.