CN108803195B - Electrical regulation and control method for graphene nonlinear optical effect - Google Patents
Electrical regulation and control method for graphene nonlinear optical effect Download PDFInfo
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- CN108803195B CN108803195B CN201710300583.3A CN201710300583A CN108803195B CN 108803195 B CN108803195 B CN 108803195B CN 201710300583 A CN201710300583 A CN 201710300583A CN 108803195 B CN108803195 B CN 108803195B
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- G—PHYSICS
- G02—OPTICS
- 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
- G02F1/35—Non-linear optics
- G02F1/355—Non-linear optics characterised by the materials used
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- G—PHYSICS
- G02—OPTICS
- 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
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Abstract
The invention belongs to the technical field of nonlinear optical photoelectric modulation, and particularly relates to an electrical regulation and control method for a graphene nonlinear optical effect. According to the invention, the graphene is electrically doped by utilizing a field effect, namely, a current carrier is injected into the single-layer graphene by utilizing the field effect of the grid electrode so as to adjust the chemical potential of the graphene, and the current carrier is used for opening or closing a resonance transition channel in a nonlinear optical process in the graphene and influencing the strength of nonlinear optical response, so that the nonlinear optical effect of the graphene is effectively excited and regulated. The method can greatly enhance and effectively regulate and control the second-order, third-order and even higher-order nonlinear optical effects of the graphene, and provides a convenient, reliable and effective electrical regulation and control means for the application of the graphene in the field of nonlinear optics.
Description
Technical Field
The invention belongs to the technical field of nonlinear optical photoelectric modulation, and particularly relates to an electrical regulation and control method for a graphene nonlinear optical effect.
Background
As the first two-dimensional material found by human beings to be stable in nature, graphene has attracted extensive attention by researchers and the business world due to its excellent properties such as extremely high mechanical strength, high carrier mobility, fixed light transmittance (undoped graphene), linear band structure, zero energy gap, and the like since it was found by british scientists k.s.novoseov and a.k.geim in 2004. The properties of graphene in the field of linear optics are well known today and have been used in practical engineering applications, such as infrared detectors, touch screens, electronic paper, etc. In contrast, the potential of graphene in the field of nonlinear optics has not yet been fully studied and developed.
Due to the unique linear energy band structure of the graphene, when carriers in the graphene are driven by an alternating current electric field in exciting light, corresponding photocurrent is not sine or cosine signals with the same frequency as that in a traditional semiconductor but square signals, so that a strong nonlinear optical effect is naturally accompanied; meanwhile, due to the zero energy gap characteristic of the graphene, the nonlinear optical effect in the graphene can realize resonance in a very wide waveband, and various resonance transition channels exist. Based on the above two considerations, since 2007, a number of theoretical physicists have predicted that graphene has a strong third-order nonlinear optical effect in succession. Then, experimental physicists observed third-order nonlinear optical effects from single-layer graphene, for example, in 2010, four-wave mixing signals were observed in single-layer graphene by e.hendry et al, and third-order harmonic signals were observed in 2013, n.kumar et al and s.y. Hong et al, and all experimental data show that single-layer graphene has extremely strong third-order nonlinear optical effects.
However, since single-layer graphene has center-inversion symmetry, it is considered that non-linear optical effects of even order, such as second harmonic, optical parametric conversion, etc., do not exist when only electric dipole approximation is considered. However, recent theory states that graphene should exhibit second order nonlinear optical effects when further considering the contributions of electric and magnetic quadrupole moments; however, in the case of oblique incidence excitation, the graphene may exhibit a strong second-order nonlinear optical effect as viewed along the light wave vector direction. Further, based on the specific properties of graphene, it is also expected that higher order nonlinear optical effects are observed in single layer graphene.
Based on the research results, the graphene has a huge application prospect in nonlinear optical devices and devices. A large number of applications based on the nonlinear optical effect of graphene have been proposed and implemented, such as applying graphene to a mode-locked laser, or using graphene as a saturable absorption medium, for example, cladding single-layer graphene outside an optical fiber, or placing on a photonic crystal structure, and using the third-order nonlinear effect of single-layer graphene to realize frequency conversion for excitation light. However, although a large number of devices related to the nonlinear optical effect of graphene have been proposed or implemented at present, an effective method for controlling the intensity of the nonlinear optical effect of graphene is still lacking; in addition, the report of excitation and corresponding regulation of the single-layer graphene even-order nonlinear optical effect is not realized, and the application prospect of the graphene nonlinear optical effect in the aspects related to nonlinear optical modulation and switching is greatly limited.
Disclosure of Invention
In order to overcome various defects of the conventional graphene nonlinear optical device, the invention aims to provide a feasible method for exciting and regulating the graphene nonlinear optical effect.
The method for exciting and regulating the nonlinear optical effect of the graphene provided by the invention is to perform electrical doping on the graphene by utilizing a field effect, namely, the field effect of a grid electrode is utilized to inject carriers into single-layer graphene so as to regulate the chemical potential of the graphene, so that a resonance transition channel in a nonlinear optical process in the graphene is opened or closed, the strength of nonlinear optical response is influenced, and the nonlinear optical effect of the graphene is effectively excited and regulated.
The physical principle of the method of the invention is as follows: the linear band and zero-gap properties of graphene lead to a wide variety of resonant transition channels when nonlinear optical processes occur in graphene (e.g., when angular frequencies of interest are used 
And 
Has an excitation angular frequency of 
When adding a four-wave mixing signal, there is a corresponding energy of 
And 
Five resonances in total Transition channels) and the nonlinear optical effects in graphene are dominated by these resonant transition channels; when the chemical potential of graphene is adjusted by using an electrical doping method, if a part of resonant transition channels are turned off by the chemical potential, the intensity of the nonlinear optical effect is significantly changed.
According to the method, the graphene chemical potential is adjusted to be close to the energy corresponding to the resonance transition channel, so that the graphene has a turn-off effect and a resonance effect; the turn-off effect means that the intensity of the graphene nonlinear effect is increased or reduced in a step shape before and after the graphene chemical potential approaches the energy corresponding to the resonance transition channel, and the resonance effect means that the intensity of the graphene nonlinear effect is enhanced when the graphene chemical potential is close to the energy corresponding to the resonance transition channel.
According to the invention, the chemical potential of the graphene is adjusted according to a physical principle and an experimental result, and a third-order nonlinear optical effect and a second-order nonlinear optical effect in the graphene can be regulated and controlled. The second-order nonlinear optical response comprises a second harmonic process, a sum frequency and difference frequency process and the like; and the modulation effect is not limited to the third-order and second-order nonlinear optical effects, but can be popularized to more and wider nonlinear optical effects.
In the invention, the resonance transition channels have different intensities and phases, and the chemical potential energies corresponding to the resonance transition channels with different nonlinear optical effects are different, so that the intensity change trends of different nonlinear optical processes are different when the chemical potential of graphene is adjusted. Taking a third-order nonlinear optical effect as an example, for a third harmonic signal, when the chemical potential of the graphene is adjusted to be far away from the electric neutral point of the graphene, the signal intensity is continuously enhanced within a certain range; and for the subtraction four-wave mixing signal, when the chemical potential of the graphene is adjusted to be far away from the electric neutral point of the graphene, the signal intensity is continuously weakened.
The method disclosed by the invention is realized by using a graphene device, electrical regulation and control equipment, an excitation light path and the like. The graphene device comprises graphene, a substrate material, a dielectric material and a gate electrode, and when the graphene device is used, voltage is applied to the gate electrode, and the chemical potential of the graphene is adjusted by using the field effect of the dielectric material; wherein different kinds of dielectric materials may be used for different applications. The electrical control equipment is used for applying grid voltage to the graphene device. The excitation light path can use normal incidence or oblique incidence excitation light, wherein the third-order nonlinear optical effect for exciting the graphene can use normal incidence or oblique incidence excitation light; and for the second-order nonlinear optical effect of the graphene, the oblique incidence exciting light is preferably used.
The invention has the following beneficial effects:
1. The electrical regulation and control means for the graphene nonlinear optical effect provided by the invention realizes effective control of the graphene nonlinear optical response. When the chemical potential of graphene is changed by electrical doping, the intensity of the nonlinear optical effect from graphene can be significantly changed;
2. The electrical regulation and control means provided by the invention has different regulation effects on different nonlinear optical effects, so that the relative strength among different effects can be controlled by utilizing the property, or part of nonlinear optical processes can be selectively excited or inhibited;
3. The oblique incidence excitation light path provided by the invention can effectively excite the second-order nonlinear optical response from single-layer graphene. On the basis, the electrical regulation and control means can effectively control the intensity of the second-order nonlinear optical effect from the single-layer graphene;
4. The electrical regulation and control method provided by the invention can be applied to optical parameter conversion, terahertz generation and infrared light generation, and nonlinear optical applications such as optical switches and optical information storage in the field of optical communication, so as to enhance or control the nonlinear optical effect in the application.
Drawings
Fig. 1 is a schematic structural diagram of a single-layer graphene device and electrical control thereof in example 1 and example 2.
Fig. 2 is a light path diagram of the excitation light and nonlinear optical signal collection and analysis for the third-order nonlinear optical effect of graphene in embodiment 1 of the present invention. Wherein the exciting light is normal incidence relative to the graphene device.
Fig. 3 shows the intensity of the three-order nonlinear optical effects of the third harmonic and the subtractive four-wave mixing in graphene according to the variation of the chemical potential of graphene in embodiment 1 of the present invention. Wherein the third harmonic signal is obtained by excitation of excitation light with the wavelength of 1300 nm; the four-wave mixing signal is derived from excitation light with wavelengths of 1040nm and 1300 nm. μ in the figure represents the chemical potential of graphene with the electrical neutral point of graphene as a reference point.
Fig. 4 is a light path diagram for collecting and analyzing the excitation light and the nonlinear optical signal used for the second-order nonlinear optical effect of graphene in embodiment 2 of the present invention. Wherein the exciting light is obliquely incident at 45 degrees relative to the graphene device.
Fig. 5 shows the variation of the intensity of the second harmonic effect in graphene with the chemical potential of graphene in example 2 of the present invention. Wherein, the second harmonic signal is obtained by excitation of excitation light with the wavelength of 1308 nm. μ in the figure represents the chemical potential of graphene with the electrical neutral point of graphene as a reference point.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
Example 1
The embodiment includes a graphene device, an excitation light path, and an electrical control and measurement device, as shown in fig. 1. The graphene device comprises a single-layer graphene sample, a substrate material, a source electrode, a drain electrode, a top gate electrode and a dielectric material. The excitation light path is used for exciting a nonlinear optical effect in single-layer graphene. The electrical regulation and control and measurement device is used for applying grid voltage and simultaneously measuring the transport property of the graphene.
In the graphene device, the source electrode, the drain electrode and the top grid electrode are evaporated on a single-layer graphene sample and a substrate material by using an electron beam evaporation combined mask method. Wherein the substrate material is fused silica.
Among the above-described graphene devices, the graphene device uses an ionic gel as a dielectric material to obtain an optimal tuning capability, because the tuning capability for the chemical potential in single-layer graphene when using the ionic gel as a top gate dielectric material is much greater than that when using other dielectrics.
The preparation and test method of the graphene device capable of regulating and controlling the nonlinear optical effect of the graphene in the embodiment comprises the following steps:
(1) Obtaining a single-layer graphene sample by a chemical vapor deposition method, and transferring the single-layer graphene sample on a fused quartz substrate by a wet transfer method;
(2) Evaporating by electron beams and matching with a mask plate to form a single-layer graphene evaporation electrode, and using a wire dotting machine as an electrode lead;
(3) Preparing ionic gel, wherein the components comprise ionic liquid [ EMIM ] [ TFSI ] and PS-PEO-PS. Afterwards, a small amount of ionic gel was dropped on the graphene sample. Covering the graphene sample and the top grid electrode area with the ionic gel, and then placing the graphene sample and the top grid electrode area in a drying cabinet for standing for a period of time to wait for the ionic gel to be solidified and dried;
(4) According to the connection mode in fig. 1, the graphene device is connected with the electrical regulation and control and measurement device. The electrical regulation and control and measurement device is used for providing a top grid voltage required by the graphene device and detecting the resistance value of the graphene device in real time;
(5) Using the excitation and signal collection optical path in fig. 2, selecting a suitable position in the graphene device to focus the excitation light under the condition that the excitation light is normally incident;
(6) And adjusting the voltage of the top gate while acquiring a corresponding nonlinear optical signal by using a spectrometer or an avalanche photodiode. Different non-linear optical signals can be obtained by using different exciting lights and optical filters along with the intensity change of the top grid voltage.
Fig. 3 shows the intensity of a third harmonic signal when a femtosecond laser having a wavelength of 1300nm was used as the excitation light, and a subtractive four-wave mixing signal (having a wavelength of 867 nm) when femtosecond lasers having wavelengths of 1040 nm and 1300nm were used as the excitation light, as a function of the graphene chemical potential. As shown in fig. 3, the third harmonic signal and the four-wave mixing signal are both significantly controlled by the chemical potential of graphene, and the two signals have different trends of changing with the chemical potential of graphene. Fig. 3 shows that the third harmonic signal is enhanced when the graphene chemical potential turns off part of the resonance transition channel (turn-off effect), and is further enhanced when the graphene chemical potential is further adjusted to be close to other resonance transition channels (resonance effect). Meanwhile, the subtraction four-wave mixing signal is greatly weakened when the graphene chemical potential turns off part of the resonance transition channel.
It should be noted that in this embodiment, since the energy of the excitation light photon used is large, and therefore a large range of adjustment of the graphene chemical potential is required to turn off the corresponding resonance transition channel, an ionic gel is used as the dielectric material, but the selectable dielectric material is not limited to the ionic gel, and for example, when the energy of the excitation light photon used is small, other dielectric materials may be used to achieve the adjustment and control of the graphene nonlinear optical response.
Example 2
The difference is that the second-order nonlinear optical effect of the graphene device is excited by using the 45-degree oblique incidence device shown in fig. 4, as in example 1. Fig. 5 shows the change of the intensity of the second-order nonlinear optical effect in the present embodiment when it is regulated by the chemical potential of graphene. Fig. 5 illustrates that the second harmonic effect in graphene is also significantly controlled by the chemical potential of graphene, and is enhanced when the chemical potential of graphene turns off part of the resonant transition channel.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (2)
1. An electrical regulation and control method for a graphene nonlinear optical effect is characterized in that a field effect is utilized to electrically dope graphene, namely, a field effect of a grid electrode is utilized to inject carriers into single-layer graphene, exciting light is used to directly excite the graphene so as to regulate the chemical potential of the graphene, so that a resonance transition channel in a nonlinear optical process in the graphene is opened or closed, the intensity of nonlinear optical response is influenced, and the nonlinear optical effect of the graphene is effectively excited and regulated;
The method comprises the steps that the chemical potential of graphene is adjusted to be close to the energy corresponding to a resonance transition channel, so that the graphene has a turn-off effect and a resonance effect; the turn-off effect means that the intensity of the graphene nonlinear effect is increased or reduced in a step shape before and after the chemical potential of the graphene approaches the energy corresponding to the resonance transition channel, and the resonance effect means that the intensity of the graphene nonlinear effect is enhanced when the chemical potential of the graphene is near the energy corresponding to the resonance transition channel;
By adjusting the chemical potential of the graphene, the third-order nonlinear optical effect and the second-order nonlinear optical effect in the graphene can be regulated and controlled; the second-order nonlinear optical effect comprises a second harmonic process, a sum frequency process and a difference frequency process;
The device applied to the electrical regulation and control method of the graphene nonlinear optical effect comprises a graphene device, an excitation light path and an electrical regulation and control and measurement device, wherein the graphene device comprises a single-layer graphene sample, a substrate material, a source electrode, a drain electrode, a top gate and a dielectric material, the excitation light path is used for exciting the nonlinear optical effect in the single-layer graphene, and the electrical regulation and control and measurement device is used for applying a gate voltage and measuring the graphene transport property at the same time.
2. The electrical regulation and control method of graphene nonlinear optical effect according to claim 1, characterized in that in an excitation light path, normal incidence or oblique incidence excitation light is used to excite graphene third-order nonlinear optical effect; and exciting a second-order nonlinear optical effect of the graphene by using oblique incidence exciting light.
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