| With the continuous development of the fifth generation of mobile communication technology(5G),ultra-fast data processing speed and data transmission speed are needed.When the electronic devices face the demand of high speed and large capacity,the information processing of each node needs to complete the optical/electric/optical conversion.There will be problems such as bandwidth limitation and high energy consumption,which is the so-called "electronic bottleneck" phenomenon.The all-optical network can effectively avoid the problem of electronic bottlenecks.In the all-optical network,the all-optical modulator is used to control the intensity,phase,wavelength and other parameters of light,which is a key component of optical communication and is one of the most important integrated devices.Due to the characteristics of broad-band modulation and ultra-fast response of two-dimensional materials,the combination of two-dimensional materials and all-optical technology will promote the development of the all-optical modulator.At present,researchers have used the saturated absorption characteristics of graphene to achieve an all-optical modulator with a response time of 2.2 ps,corresponding to a bandwidth of 200 GHz.Compared with the bandwidth of current electronic devices,the modulation speed of the all-optical modulator based on two-dimensional materials has been greatly improved.However,the modulation depth and device loss of the modulator are difficult to meet the realistic need.Therefore,exploring new optical materials and all-optical technologies has become an urgent problem to be solved.The phase modulation method can effectively balance the relationship between modulation depth and device loss of the all-optical modulator.When the modulation depth is large,the loss of the device is also reduced.In addition,the two-dimensional material MXene absorbs ultraviolet,visible,near-infrared and mid-infrared bands,has strong nonlinear effects,high photothermal conversion rate and good thermal conductivity.Therefore,the saturated absorption and photothermal characteristics of MXene were studied to achieve pulsed laser output and all-optical modulation,respectively.The main contents are as follows:1.MXene-based 1 μm and 1.3 μm short pulse laser outputs are implemented.Firstly,MXene two-dimensional nanomaterials were obtained by acid etching method.Basic material characterization of MXene ensure high quality materials.Nonlinear optical tests were carried out by Z-scan and dual-arm detection techniques.Experimental results illustrate that the MXene shows the excellent nonlinear optical characteristics and broadband absorption characteristics.The optical cavity is simulated and designed by the ABCD matrix,the continuous light output is realized after the cavity is built,and MXene is used as a passive device to effectively realize the pulse laser output of 1 μm and 1.3 μm region.2.All-optical modulation based on MXene and Michelson interferometer was carried out.Based on the interference theory of Michelson interferometer,it is found through simulation that the smaller the power difference between the two arms of the interferometer is,the larger the modulation depth of the output spectrum is;and the smaller the bandwidth of the signal light is,the easier it is to achieve all-optical intensity modulation.Compared with the Mach-Zehnder interferometer used by the predecessors,the Michelson interferometer can effectively increase the length of light-material interaction and increase the energy conversion efficiency.MXene has excellent photothermal conversion characteristics and heat conduction characteristics.Based on the MXene and Michelson interferometer’s all-optical modulator,the modulation depth and response time are improved.An all-optical phase modulation and total light intensity modulation are effectively realized.After systematically studying the influence of the power,frequency and duty ratio of the pump light on the modulation of the signal light,the all-optical signal loading is also realized.3.Research on all-optical modulation based on MXene and polarization interference.In the operation of Michelson interferometer based all-optical modulator,the conventional interference structure uses a single-mode fiber,which is susceptible to fiber fluctuations,so it leads to modulator instability.And the micro-fiber structure deposited with MXene material absorbs the signal light,resulting in additional device loss.Therefore,in the all-optical modulator using polarization interference,a polarization-maintaining fiber is used to replace the conventional single-mode fiber,an all-optical phase modulator and a full-light intensity modulator are respectively realized with high stability and low loss.4.All-optical modulation based on MXene and polarization rotating was carried out.For the all-optical modulator based on the interferometer structure,the response time is on the order of sub-milliseconds,it is difficult to meet the realistic demand,and the bandwidth of the signal light is limited by the free spectral region of the modulator,and the broadband modulation cannot be realized.To solve the above problems,a broadband all-optical modulator based on light polarization rotation has been developed.Firstly,the basic theoretical knowledge of the polarization characteristics of light is studied,and the relationship between the polarization state of light and the phase difference under linear coordinates and polar coordinates is simulated by matlab software.It is found that the all-optical switching can be realized by the polarization rotation of light.When the angle between the light and the axis is 45°,the modulation depth is maximum.Therefore,using the photothermal characteristics of MXene cause the change of the phase difference and the polarization state,a broadband all-optical modulation with a bandwidth of 40 nm and the response time on the order of microseconds is realized,which indicates that the polarization characteristic of light is an effective way to increase the modulation speed and the modulation bandwidth,which provides a new idea for the development of a new all-optical modulator based on two-dimensional material.Finally,we summarize the work of this paper,expounds the inadequacies of the article,and forecasts the all-optical modulation technology based on two-dimensional materials.The details are as follows: MXene two-dimensional nanosheets are fabricated by acid etching method.A pulsed laser output and all-optical modulators are realized by utilizing nonlinear effects and photothermal effects of materials.Broadband all-optical modulation is achieved by using the polarization rotation of light.The problem of limited bandwidth of signal light caused by the structure of the interferometer is avoided.But when the all-optical modulator based on the thermo-optic effect is operated under a long time,which is easy to cause thermal damage of materials.Therefore,further work is to explore new two-dimensional materials in the future to make full use of the ultra-fast response characteristics of two-dimensional materials.We believe that a high-speed,broadband,integrated all-optical modulator will be achieved. |
