Study On Optical Bistability Characteristic Of One Dimensional Photonic Crystal

Photonic crystal is a structure composed of periodic arrangement of dielectric materials with different permittivity.When electromagnetic wave propagates in periodic medium,the density of states of photon will be modulated and distributed,which may form photonic band gap,and the electromagnetic wave corresponding to the frequency and band gap will be forbidden to propagate.Photonic crystal is an important material for the development of new generation optoelectronic information technology.Photonic crystals with periodic structure have been used to fabricate many high-performance photonic devices due to their ability to control electromagnetic waves.If we change the structure and parameters of the photonic crystal and make the perfect impedance match between the photonic crystal and the background material,when the light wave propagates in the medium,we can achieve the purpose of perfect transmission without loss.However,the natural materials in nature do not have this property,so this property of photonic crystal can be applied to some devices with transmission performance requirements.In addition,the use of its photon localization characteristics,such as graphene,which has low optical absorptivity,can enhance the absorption and regulation of light waves.A defect layer is inserted into the photonic crystal with periodic structure.At the defect,the electromagnetic field is superposed and enhanced by the local potential barriers on both sides,resulting in photon localization.Placing the material with low absorptivity here will greatly enhance its interaction with light,thus improving its application in some optoelectronic devices.The periodic potential in photonic crystals is caused by different macroscopic dielectric lattices.However,when the defect layer is introduced into a strictly periodic photonic band gap structure,it can produce donor or acceptor modes in the band gap.The existence of Kerr nonlinearity in PBG structure will change the transmission spectrum including the band edge position.The dynamic movement of the band edge results in optical bistability.As an important material for manipulating photons,photonic crystals have been widely used to fabricate optical bistable devices.Optical bistability is an important research topic in nonlinear optics.It is a good candidate for accelerating optical signal processing and communication.In the second chapter,the transfer matrix method and the mechanism of optical bistability are discussed respectively.The periodic potential in photonic crystal(PC)is caused by different macroscopic dielectric lattices.The reason of using transfer matrix method is introduced,the principle of transfer matrix method is explained,and the necessary formula is deduced.When we discuss that the existence of nonlinearity(the effective refractive index depends on the field strength)in PBG structure will change the transmission spectrum including the position of the band edge,we find that the dynamic shift of the band edge will lead to optical bistability.The reason of optical bistability is explained and its mechanism is deduced.The main task of this chapter is to introduce and deduce the numerical calculation methods used in the research process.In the third chapter,based on the sandwich photonic crystal structure(in which the nonlinear material plate is sandwiched between two magnetized cold plasma layers),the tunable optical bistability at microwave frequency is studied numerically.For example,the hysteresis optical properties such as loop width and switching threshold are affected by the changes of operating frequency,initial incident angle,layer thickness,plasma density and external magnetic field,and the reasonable selection of these parameters can help us to obtain appropriate bistability.In the fourth chapter,the relationship between the frequency of defect mode and the threshold of bistability and the applied magnetic field is studied.The propagation condition of electromagnetic wave is studied by transfer matrix method.The effects of plasma density and magnetic field on the frequency and threshold bistability of defect mode are studied by using the transfer matrix method.The results show that the frequency and bistability threshold of defect mode can be changed without changing the structure of the multilayer.Therefore,the optical bistability of the main structure in magnetized plasma can be used to fabricate devices with wide frequency rangeIn Chapter 5,the traditional positive index medium,nonlinear material with high Kerr effect,advanced negative index material and graphene are organized into quasi periodic photonic multilayer structure.The positive index material and negative index material are stacked according to the Fibonacci sequence rule,and the Kerr type nonlinear dielectric plate and graphene sheet are sandwiched in two identical Fibonacci layers Between the sub multilayers.Here,by changing the layer thickness,incident angle and chemical potential of the graphene sheet,its characteristics(including switch up / down threshold and hysteresis loop width)are adjustable.We can use this hypothetical structure to realize optical bistability and multi bistability.In addition,due to the negative refractive index and special structure of the material,the device can help to reduce the threshold of bistable region and control the hysteresis loop easily.Therefore,through this work,quasi periodic photonic multilayer devices with advanced optical materials will have excellent performance of nonlinear hysteresis.