CN111708111B - Multifunctional Bragg grating structure with dynamically controllable mid-infrared band - Google Patents

Multifunctional Bragg grating structure with dynamically controllable mid-infrared band Download PDF

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CN111708111B
CN111708111B CN202010573612.5A CN202010573612A CN111708111B CN 111708111 B CN111708111 B CN 111708111B CN 202010573612 A CN202010573612 A CN 202010573612A CN 111708111 B CN111708111 B CN 111708111B
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bragg grating
graphene
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CN111708111A (en
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李先平
安刚
晁晓宏
魏康
李鹏江
苟永植
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China Information Consulting and Designing Institute Co Ltd
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    • G—PHYSICS
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    • G02B5/18—Diffraction gratings
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    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
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    • G—PHYSICS
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    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G—PHYSICS
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    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
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Abstract

The invention provides a multifunctional Bragg grating structure with a dynamically controllable intermediate infrared band, which specifically comprises a silicon-based Bragg grating and a single-layer graphene material covered on the silicon-based Bragg grating. The graphene Bragg grating provided by the invention can be dynamically adjusted in a middle infrared band, and can realize the functions of optical filtering and optical switching. Compared with the traditional Bragg grating, the optical grating has good optical filtering and optical switching effects, the optical characteristics of the grating can be controlled only by changing the bias voltage loaded on the graphene, various defects that the optical characteristics of the grating are controlled by changing structural parameters, external environments and the like of the traditional Bragg grating are overcome, and the optical grating has important significance in environmental monitoring and spectrum analysis.

Description

Multifunctional Bragg grating structure with dynamically controllable mid-infrared band
Technical Field
The invention relates to the field of micro-nano photonics, in particular to a multifunctional Bragg grating structure with a dynamically controllable mid-infrared band.
Background
Bragg gratings are a very important optical device with a wide range of applications in spectroscopy and information processing. The silicon-based bragg grating is expected to realize ultra-high-speed data transmission communication due to small damping coefficient, low radiation loss and mature integration process, and is widely applied to the fields of optical filtering, optical switches, wavelength division multiplexing, sensing and the like. However, silicon-based bragg gratings face a number of problems, and one of the important problems is how to realize the modulation of the silicon-based bragg grating. The optical characteristics of the grating as a precision instrument are closely related to the material and the structural parameters of the grating, but once the traditional silicon-based grating is manufactured, the material and the structural parameters cannot be changed, so that the fixed grating can only act on light in a fixed wavelength range, and much inconvenience and waste are caused.
At present, the method for regulating and controlling the fixed structure grating on the micro-nano size mainly comprises the following steps: the first method is to use the photosensitive characteristic of some materials to manufacture a composite photosensitive grating, which needs high-power laser to excite, so that the miniaturization and integration of devices are not easy to realize, and the generated strong light can form extremely strong scattered light to completely eliminate the incident light for exciting the plasma; the second method is to change the refractive index of the material by changing the temperature of the external environment, thereby achieving the purpose of regulation. However, this method not only easily causes material deformation, but also changes temperature, and changes in refractive index of the material are relatively small, and usually, the bragg resonance wavelength changes only by tens of pm/deg.c, and the adjustment range is very limited. The third method is to introduce liquid crystal and other fluid into the grating, and to regulate the optical characteristic of the grating via micro flow control technology based on the great refractive index and shape varying characteristic of the fluid. Although the method is generally large in adjusting range and can reach hundreds of nanometers, the adjusting and controlling method is complex to operate, fluid with specific refractive index needs to be adjusted for specific adjusting and controlling wavelength, response speed is low, and filling the fluid into the micro-nano device is a complex project. Although the three methods can achieve the purpose of regulating and controlling the grating characteristics, the three methods have the defects of complex regulation, slow response speed and the like, and have a lot of inconvenience in practical application, so that it is very necessary to find a method for regulating and controlling the grating simply and conveniently at a high speed.
Disclosure of Invention
The invention provides a multifunctional Bragg grating structure with a dynamically controllable intermediate infrared band, which aims to solve the problems of complex adjustment, low response speed and the like of the conventional grating regulation and control and is inconvenient in practical application.
The invention aims to: aiming at the defects that the traditional Bragg grating cannot be tuned or has a small adjusting range, a low response speed and the like, the invention designs the mixed plasma waveguide based on the graphene Bragg grating, utilizes the characteristics that the graphene has a high response speed, the chemical potential of the graphene is adjusted, the doping concentration can regulate and control the optical property of the graphene, and creates the multifunctional Bragg grating which can be dynamically controlled in a middle infrared band by regulating and controlling the voltage loaded on the graphene on two sides of the Bragg grating, thereby realizing the functions of optical filtering and optical switching.
In order to achieve the purpose, the scheme adopted by the invention is a multifunctional Bragg grating structure with a dynamically controllable intermediate infrared band, wherein the multifunctional Bragg grating structure consists of a silicon-based Bragg grating and a single-layer graphene covering the surface of the silicon-based Bragg grating. In this embodiment, the electrodes on both sides of the bragg grating are led out through the good conductor.
Further, in an implementation manner, the bragg grating is axially symmetrical with a cuboid silicon substrate as an axis, protruding bodies of silicon material are arranged on two sides of the cuboid silicon substrate, the protruding bodies of the silicon material are periodically arranged to form a convex-concave bragg grating, and a single-layer graphene layer covers the surface of the convex-concave bragg grating.
Further, in one implementation, the surface conductivity σ of the graphene is calculated according to the following formula:
Figure BDA0002550255310000021
where e represents the electron charge, ω represents the angular frequency,
Figure BDA0002550255310000022
denotes the Planck constant, kBDenotes the Boltzmann constant, T denotes the temperature, Γ denotes the scattering power, μcRepresenting the chemical potential.
Further, in an implementation manner, the bragg grating is etched on both sides of the rectangular silicon by using a photolithography technique to form a periodic bragg grating, and then a layer of graphene is laid close to the etched grating surface, so as to selectively reflect or transmit a plasma wave propagating in the graphene bragg grating, where the bragg grating satisfies a formula:
d1Real(neff1)+d2Real(neff2)＝mλb/2
wherein, d1Width of the convex body, d2Representing the width between the convexes, Real (neff)1) Is the equivalent refractive index of the convex body, Real (neff) 2) Is the equivalent refractive index between the convex bodies, m is a constant, λbIs the bragg wavelength.
Further, in one implementation manner, the periodic unit of the bragg grating is a symmetric structure with a convex-concave shape, the height W of the cuboid silicon substrate of the bragg grating is 0.5um, and the length of the bragg grating extends along the period of the bragg grating; the thickness delta W of the convex bodies on the two sides of the cuboid silicon substrate is 2um, and the width d of the convex bodies on the two sides of the Bragg grating11um, width d between adjacent convexes21 um. In this embodiment, the bragg gratings are symmetrically distributed along the rectangular silicon-based waveguide, the offset distance Δ L between the upper and lower bragg gratings is 0, and the number of periods of the bragg gratings is 10.
Further, in one implementation, a bias voltage is applied to the graphene bragg grating to change the chemical potential of the graphene, wherein the graphene bragg grating is a bragg grating with a surface covered with single-layer graphene;
when the chemical potential changes of graphene covering the upper surface and the lower surface of the Bragg grating are the same, the effective refractive index of the Bragg grating mixed plasma on the upper layer and the lower layer is changed, the effective refractive index is the same, and the resonance wavelength of the Bragg grating is changed;
The continuous modulation of the resonant wavelength of the Bragg grating from 4650nm to 4550nm is realized in the process that the chemical potential of the graphene is changed from 0.2eV to 0.8eV, the transmittance of the Bragg grating is less than 3%, and the graphene can be used for performing wide-range band-stop filtering.
Further, in one implementation, a defect is introduced into the graphene bragg grating, the width of any one of the protrusions in the bragg grating is changed to 3um, and the graphene bragg grating has a sharp transmission peak on a very wide transmission forbidden band spectrum;
the resonance wavelength of the transmission peak of the Bragg grating is changed from 4350nm to 4250nm as the chemical potential of graphene on two sides of the Bragg grating is changed from 0.2 to 0.8eV, and the graphene Bragg grating can be used as a dynamically tunable band-pass filter. In this embodiment, the graphene bragg grating may be used as a dynamically tunable bandpass filter for suppressing background noise in infrared detection, and may overcome a single-range transmission window, thereby facilitating economy of multi-component measurement application.
Further, in one implementation manner, a bias voltage is applied to the graphene bragg grating, and when the bias voltages loaded on the upper layer graphene and the lower layer graphene are different, the coupling coefficient of the bragg grating changes; by adjusting the difference of the voltages loaded on the graphene on the upper surface and the graphene on the lower surface of the Bragg grating, the transmittance of the Bragg grating is changed from 3% to 83% at the resonance wavelength of 4600nm, and the extinction ratio is 14.4 dB. Specifically, as the extinction ratio reaches 14.4dB, the bragg grating structure described in this embodiment has a good optical switching effect in the mid-infrared band.
According to the technical scheme, the embodiment of the invention provides the multifunctional Bragg grating structure with the dynamic control over the intermediate infrared band, and the multifunctional Bragg grating structure consists of a silicon-based Bragg grating and a single-layer graphene covering the surface of the silicon-based Bragg grating. The bragg grating essentially realizes the modulation of periodic refractive index by waveguide, so that the originally orthogonal modes propagated in the bragg grating are mutually influenced due to the periodic modulation of the grating, a specific phase relation is formed, and the phenomena of interference cancellation and interference constructive phenomena occur. The graphene Bragg grating disclosed by the invention has the advantages that the periodic change of the equivalent refractive index of the mixed plasma at the corresponding position is caused by the periodic convex-concave structure distribution, so that the equivalent graphene Bragg grating is formed, and the selective reflection or transmission of the plasma wave transmitted in the graphene Bragg grating is realized.
In the prior art, the defects of complex regulation, slow response speed and the like exist in the regulation of the grating, and the problem of inconvenience exists in practical application. Compared with the prior art, the multifunctional Bragg grating structure with the dynamically controllable mid-infrared band has the following beneficial effects that:
1. The silicon-based Bragg grating is simple in structure, the single-layer graphene covers the silicon-based Bragg grating, the silicon material is convenient to use and compatible with the existing CMOS (complementary metal oxide semiconductor) process, the silicon material is large in refractive index and strong in optical field limiting capacity, and integration of devices is facilitated.
2. Due to the use of the graphene material, the Bragg grating can realize the functions of dynamically adjustable optical filtering and optical switching in the middle infrared band by regulating and controlling the graphene loading voltage on the two sides of the Bragg grating, and the graphene material can be used as a filter and has a good filtering effect; as an optical switch, the extinction ratio reaches 14.4 dB.
3. Compared with other methods for realizing Bragg grating regulation in the prior art, the method has the characteristics of simplicity, convenience, high response speed and wide tunable wavelength range due to the dynamic adjustable graphene and the ultrahigh carrier transfer rate.
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In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a multifunctional bragg grating capable of dynamically controlling a mid-infrared band according to an embodiment of the present invention;
Fig. 2 is a schematic side view of a multifunctional bragg grating with dynamically controllable mid-infrared band according to an embodiment of the present invention;
FIG. 3 is a transmission spectrum of the multifunctional Bragg grating with dynamically controllable infrared band without structural defects, when the scattering rate of graphene is 0.0005ev at normal temperature, in the embodiment of the invention;
fig. 4 is a schematic side view of a multifunctional bragg grating according to an embodiment of the present invention, illustrating the bragg grating with structural defects;
FIG. 5 is a transmission spectrum of a multifunctional Bragg grating with a dynamically controllable infrared band according to the present invention, wherein the scattering ratio of graphene is 0.0005eV at room temperature;
fig. 6 is a transmission spectrum when the multifunctional bragg grating of the present invention with dynamically controllable infrared band is used at normal temperature and the graphene scattering ratio of 0.0005ev in the embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The invention provides a multifunctional Bragg grating capable of being dynamically controlled in a mid-infrared band, and particularly relates to a graphene Bragg grating-based hybrid plasma waveguide. Compared with the traditional Bragg grating, the invention not only has good optical filtering and optical switching effects, but also can control the optical characteristics of the grating only by changing the bias voltage loaded on the graphene, overcomes the defects that the traditional Bragg grating controls the optical characteristics of the grating by changing the structural parameters and the like, has simple and convenient operation and high response speed, and has wide application in the aspects of mid-infrared spectral analysis, filters and modulators.
The embodiment of the invention provides a multifunctional Bragg grating structure with a dynamically controllable intermediate infrared band, which consists of a silicon-based Bragg grating and a single-layer graphene covering the surface of the silicon-based Bragg grating.
In the multifunctional bragg grating structure capable of dynamically controlling the mid-infrared band, the bragg grating takes a cuboid silicon substrate as axial symmetry, convex bodies of silicon material are arranged on two sides of the cuboid silicon substrate, the convex bodies of the silicon material are periodically arranged to form a convex-concave bragg grating, and the surface of the convex-concave bragg grating is covered with a single-layer graphene.
In the multifunctional bragg grating structure capable of dynamically controlling a mid-infrared band in this embodiment, the surface conductivity σ of the graphene is calculated according to the following formula:
Figure BDA0002550255310000051
where e represents the electron charge, ω represents the angular frequency,
Figure BDA0002550255310000052
denotes the Planck constant, kBDenotes Boltzmann constant, T denotes temperature, Γ denotes scattering power, μcRepresenting the chemical potential.
In this embodiment, it can be seen from the above formula that the change in chemical potential causes a change in the conductivity of graphene, thereby causing a change in the refractive index, and a basis is provided for subsequently controlling the change in the bragg grating by adjusting the chemical potential of graphene to change the conductivity of graphene.
In the multifunctional bragg grating structure capable of dynamically controlling a mid-infrared band according to this embodiment, the bragg grating satisfies a formula:
d1Real(neff1)+d2Real(neff2)＝mλb/2
wherein, d1Represents the width of the convexities, d2Representing the width between the convexes, Real (neff)1) Is the equivalent refractive index of the convex body, Real (neff)2) Is the equivalent refractive index between the convex bodies, m is a constant, λbIs the bragg wavelength.
In this embodiment, the above formula indicates that the equivalent refractive indexes of the bragg gratings are different, so that the bragg wavelengths of the bragg gratings are different, which provides a basis for dynamic regulation and control of graphene under different chemical potentials.
In the multifunctional bragg grating structure with a dynamically controllable mid-infrared band, a periodic unit of the bragg grating is a symmetric structure with a convex-concave shape, preferably, a height W of a cuboid silicon substrate of the bragg grating is 0.5um, and a length of the bragg grating extends along a period of the bragg grating; the thickness delta W of the convex bodies on the two sides of the cuboid silicon substrate is 2um, and the width d of the convex bodies on the two sides of the Bragg grating11um, width d between adjacent convexes2＝1um。
In the multifunctional bragg grating structure with dynamically controllable mid-infrared band, bias voltage is applied to a graphene bragg grating to change the chemical potential of graphene, wherein the graphene bragg grating is a bragg grating with a surface covered with single-layer graphene;
When the chemical potential changes of graphene covering the upper surface and the lower surface of the Bragg grating are the same, the effective refractive index of the Bragg grating mixed plasma on the upper layer and the lower layer is changed, the effective refractive index is the same, and the resonance wavelength of the Bragg grating is changed;
the continuous modulation of the resonant wavelength of the Bragg grating from 4650nm to 4550nm is realized in the process that the chemical potential of the graphene is changed from 0.2eV to 0.8eV, the transmittance of the Bragg grating is less than 3%, and the graphene can be used for performing wide-range band-stop filtering. Specifically, the transmittance of the bragg grating may be determined to be less than 3% from the lowest point in the transmittance map of the bragg grating.
In this embodiment, the change of the chemical potential of the graphene may cause the change of the conductivity of the graphene, so that the effective refractive index of the bragg grating mixed plasma changes according to the following formula:
d1Real(neff1)+d2Real(neff2)＝mλb/2
it can be known that the equivalent refraction of the convex bodyRate Real (neff)1) And equivalent refractive index between convex bodies Real (neff)2) The change in (c) will certainly cause a change in the resonant wavelength.
In the multifunctional bragg grating structure with dynamically controllable mid-infrared band, a defect is introduced into the graphene bragg grating, the width of any one convex body in the bragg grating is changed to 3um, and the graphene bragg grating has a sharp transmission peak on a very wide transmission forbidden band spectrum; in this embodiment, broad and sharp are relative concepts, and specifically, a transmission peak of several tens of nanometers appears on a transmission spectrum of a transmission forbidden band spectrum of about 1000nm, that is, a sharp transmission peak appears on a broad transmission forbidden band spectrum.
The resonance wavelength of the transmission peak of the Bragg grating is changed from 4350nm to 4250nm as the chemical potential of graphene on both sides of the Bragg grating is changed from 0.2ev to 0.8ev, and the graphene Bragg grating can be used as a dynamically tunable band-pass filter. In this embodiment, the graphene bragg grating may be used as a dynamically tunable bandpass filter for suppressing background noise in infrared detection, and may overcome a single-range transmission window, thereby facilitating economy of multi-component measurement application.
In the multifunctional bragg grating structure with dynamically controllable mid-infrared band, a bias voltage is applied to the graphene bragg grating, and when the bias voltages loaded on the upper and lower layers of graphene are different, the coupling coefficient of the bragg grating changes; by adjusting the difference of the voltages loaded on the graphene on the upper surface and the graphene on the lower surface of the Bragg grating, the transmittance of the Bragg grating is changed from 3% to 83% at the resonance wavelength of 4600nm, and the extinction ratio is 14.4 dB. Specifically, as the extinction ratio reaches 14.4dB, the bragg grating structure described in this embodiment has a good optical switching effect in the mid-infrared band.
As shown in fig. 1, a schematic structural diagram of a multifunctional bragg grating capable of being dynamically controlled in the mid-infrared band is shown. It is composed of Bragg grating of silicon material and single-layer graphene tightly adhered to the surface of the grating, and the upper surface of the grating isRespectively applying voltage v to the graphene on the lower surface and the graphene on the lower surface1And v2When light passes through the graphene bragg grating, a plasmon wave is generated to propagate along the grating. As shown in fig. 2, a cross-sectional view of the bragg grating structure and structural parameters are shown. Specifically, in this embodiment, the height W of the rectangular silicon substrate of the bragg grating is 0.5um, the thickness Δ W of the protrusions on both sides of the rectangular silicon substrate is 2um, and the width d of the protrusions on both sides of the bragg grating1Width d between adjacent convex bodies2Equal, d1＝d2The offset distance Δ L between the upper and lower bragg gratings is 0, which is 1 um.
The conductivity of graphene is a major factor affecting its performance and is also key to obtaining dynamically tunable bragg gratings.
For two-dimensional graphene, the plane conductivity of single-layer graphene is represented by the well-known Kubo formula in the absence of static bias magnetic field and spatial dispersion:
Figure BDA0002550255310000071
where e represents the electron charge, the angular frequency of ω,
Figure BDA0002550255310000072
Is Planck constant, kBIs Boltzmann constant, T represents temperature, Γ is scattering power, μcIs a chemical potential.
In order to study the optical characteristics of the proposed graphene bragg grating, time-domain finite difference method software is adopted for simulation, and the basic settings are as follows: the x, z directions are set as perfect absorption boundary conditions and the y direction is set as antisymmetric boundary conditions. The simulated temperature T is 300K, and the graphene scattering ratio is set to 0.0005 ev. In this embodiment, the simulation time can be greatly reduced in this setting.
Example 1
(1) Tunable band-stop filter
The loading voltage on two sides of the Bragg grating is respectively at v1＝v2When the average value is 0.2ev,0.4ev,0.6ev and 0.8ev, the transmission spectrum of the bragg grating is calculated by using a time domain finite difference method, as shown in fig. 3. As can be seen, the transmission rates of the Bragg gratings are all less than 3%, and the 3dB bandwidths are all more than 800nm, so that the band-stop filter has a good band-stop filtering effect. In the process that the chemical potential of the graphene is changed from 0.2ev to 0.8ev, the corresponding Bragg grating resonant wavelength is tuned from 4650nm to 4550nm, the purpose of dynamically adjusting the optical characteristics of the Bragg grating by adjusting the chemical potential of the graphene is realized in a middle infrared band, and the graphene Bragg grating with the structure can be widely applied to a dynamically tunable band-stop filter.
(2) Tunable bandpass filter
When other structural parameters are not changed, defects are introduced into the graphene Bragg gratings, namely the sawtooth width d of one Bragg grating3When 3um, as shown in fig. 4. Under the condition that the chemical potentials of the graphene on both sides are the same, respectively at v1＝v2When the measured values are 0.2ev,0.5ev and 0.8ev, the defect bragg grating transmission spectrum obtained by calculation using the time-domain finite difference method is shown in fig. 5. It can be seen that a sharp transmission peak appears on the originally broad transmission forbidden band spectrum. As the chemical potential of graphene on two sides of the Bragg grating changes from 0.2eV to 0.8eV, the resonant wavelength of the transmission peak of the Bragg grating changes from 4350nm to 4250nm, and the graphene Bragg grating can be used as a dynamically tunable band-pass filter.
Example 2
The structural parameters of the Bragg grating are unchanged, when the chemical potentials of the graphene on two sides of the Bragg grating are different, namely v1＝0.2ev,v2When the values are 0.2ev and 0.7ev respectively, the time domain finite difference method is adopted, and the calculated transmission spectrogram of the Bragg grating is shown in FIG. 6. By comparison, it can be seen that when the chemical potentials of the upper graphene layer and the lower graphene layer are the same and are both 0.2ev, the transmittance of the Bragg grating at the resonance wavelength of 4600nm is only 3%, and an almost perfect band-stop filtering effect is obtained; when the voltage applied to the Bragg grating is adjusted to v 1＝0.2ev,v1At 0.7ev, the Bragg grating transmittance is as high as 8 at the same resonance wavelength3 percent. The difference of the loading voltage of the graphene is adjusted, so that the Bragg grating can obtain a larger transmittance difference value at the same resonance wavelength, the extinction ratio reaches 14.4dB, and the Bragg grating can be used as a good optical switch device.
The reason why the above situation occurs is that under the condition that the structural parameters of the grating are not changed, when the chemical potentials of the graphene on the two sides of the bragg grating are different, the equivalent refractive indexes on the two sides of the bragg grating will be changed differently, so that the bragg grating is dislocated, that is, Δ L ≠ 0, and thus 2 π Δ L/(d) of the plasma propagating therein occurs1+d2) The phase of the grating changes, causing the coupling coefficient of the plasma in the grating to change, resulting in destructive attenuation of the interference and an increase in the intensity of the light passing through the bragg grating.
According to the technical scheme, the embodiment of the invention provides the multifunctional Bragg grating structure with the dynamic control over the intermediate infrared band, and the multifunctional Bragg grating structure consists of a silicon-based Bragg grating and a single-layer graphene covering the surface of the silicon-based Bragg grating. The bragg grating is essentially a waveguide that implements periodic refractive index modulation, so that the originally orthogonal modes propagating therein interact due to the periodic modulation of the grating, a specific phase relationship is formed, and destructive and constructive interference phenomena occur. The graphene Bragg grating disclosed by the invention has the advantages that the periodic change of the equivalent refractive index of the mixed plasma at the corresponding position is caused by the periodic convex-concave structure distribution, so that the equivalent graphene Bragg grating is formed, and the selective reflection or transmission of the plasma wave transmitted in the graphene Bragg grating is realized.
In the prior art, the defects of complex regulation, slow response speed and the like exist in the regulation of the grating, and the problem of inconvenience exists in practical application. Compared with the prior art, the multifunctional Bragg grating structure with the dynamically controllable mid-infrared band has the following beneficial effects that:
1. the silicon-based Bragg grating is simple in structure, the single-layer graphene covers the silicon-based Bragg grating, the silicon material is convenient to use and compatible with the existing CMOS (complementary metal oxide semiconductor) process, the silicon material is large in refractive index and strong in optical field limiting capacity, and integration of devices is facilitated.
2. Due to the use of the graphene material, the Bragg grating can realize the functions of dynamically adjustable optical filtering and optical switching in the middle infrared band by regulating and controlling the graphene loading voltage on the two sides of the Bragg grating, and the graphene material can be used as a filter and has a good filtering effect; as an optical switch, the extinction ratio reaches 14.4 dB.
3. Compared with other methods for realizing Bragg grating regulation in the prior art, the method has the characteristics of simplicity, convenience, high response speed and wide tunable wavelength range due to the dynamic adjustable graphene and the ultrahigh carrier transfer rate.
The same and similar parts in the various embodiments in this specification may be referred to each other. The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention.

Claims (6)

1. The multifunctional Bragg grating structure is characterized by consisting of a silicon-based Bragg grating and single-layer graphene covering the surface of the silicon-based Bragg grating;
the Bragg grating is axially symmetrical by a cuboid silicon substrate, convex bodies of silicon materials are arranged on two sides of the cuboid silicon substrate, the convex bodies of the silicon materials are periodically arranged to form a convex-concave Bragg grating, and the surface of the convex-concave Bragg grating is covered with a single-layer graphene;
calculating the surface conductivity σ of the graphene according to the following formula:
Figure FDA0003468490360000011
where e represents the electron charge, ω represents the angular frequency,
Figure FDA0003468490360000012
denotes the Planck constant, kBRepresenting boltzmann constant, r representing temperatureDegree, f, denotes the scattering power, μcRepresenting the chemical potential.
2. A mid-infrared band dynamically controllable multifunctional bragg grating structure as claimed in claim 1, wherein said bragg grating satisfies the formula:
d1Real(neff1)+d2Real(neff2)＝mλb/2
wherein d is1Width of the convex body, d2Representing the width between the convexes, Real (neff)1) Is the equivalent refractive index of the convex body, Real (neff)2) Is the equivalent refractive index between the convex bodies, m is a constant, λ bIs the bragg wavelength.
3. The structure of the multifunctional bragg grating capable of dynamically controlling the mid-infrared band according to claim 2, wherein the periodic units of the bragg grating are symmetric structures with a convex-concave shape, the height W of a cuboid silicon substrate of the bragg grating is 0.5um, and the length of the bragg grating extends along the period of the bragg grating; the thickness delta W of the convex bodies on the two sides of the cuboid silicon substrate is 2um, and the width d of the convex bodies on the two sides of the Bragg grating11um, width d between adjacent convexes2＝1um。
4. The multifunctional Bragg grating structure capable of being dynamically controlled in the mid-infrared band as claimed in claim 3, wherein a bias voltage is applied to the graphene Bragg grating to change the chemical potential of the graphene, wherein the graphene Bragg grating is a Bragg grating with a surface covered with a single layer of graphene;
when the chemical potential changes of graphene covering the upper surface and the lower surface of the Bragg grating are the same, the effective refractive index of the Bragg grating mixed plasma on the upper layer and the lower layer is changed, the effective refractive index is the same, and the resonance wavelength of the Bragg grating is changed;
The continuous modulation of the resonant wavelength of the Bragg grating from 4650nm to 4550nm is realized in the process that the chemical potential of the graphene is changed from 0.2ev to 0.8ev, the transmittance of the Bragg grating is less than 3%, and the graphene can be used for large-range band-stop filtering.
5. The structure of the multifunctional Bragg grating capable of being dynamically controlled in the mid-infrared band as claimed in claim 4, wherein a defect is introduced into the graphene Bragg grating, the width of any one of the protrusions in the Bragg grating is changed to 3um, and the graphene Bragg grating has a sharp transmission peak on a transmission forbidden band spectrum;
the resonance wavelength of the transmission peak of the Bragg grating is changed from 4350nm to 4250nm as the chemical potential of graphene on both sides of the Bragg grating is changed from 0.2ev to 0.8ev, and the graphene Bragg grating is used as a dynamically tunable band-pass filter.
6. The multifunctional Bragg grating structure capable of being dynamically controlled in a medium infrared band according to claim 5, wherein a bias voltage is applied to the graphene Bragg grating, and when the bias voltages loaded on the upper graphene layer and the lower graphene layer are different, the coupling coefficient of the Bragg grating is changed; by adjusting the difference of voltages loaded on the graphene on the upper surface and the graphene on the lower surface of the Bragg grating, the transmittance of the Bragg grating is changed from 3% to 83% at the resonance wavelength of 4600nm, and the extinction ratio is 14.4 dB.
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