Theoretical Research On Optical Switch Of Nonlinear 1-D Photonic Crystal

The demand of the high speed to transmit and treat with information ishigher and higher in the modern communication, but there is the choke pointof the electronic devices due to the influence of the electronic response timeand the quantum effect, which restrict the improvement of the speed, andbecause photons have the higher rate than electron and there is no interaction ,so people turn attention to the photons, and set about to research theapplications of the optical devices in the communication.In 1987, Yablonovitch and John put forward the concept of "photoniccrystal" in their researches respectively and independently, which havebrought the dawn to the research of all optical device. For the developmenttime of the optical crystals is less than 20 years till now, many problemsexpect to be resolved and many field 所 expect to be developed fromphotonic theoretical research and design to application of PC device .1-D PC is of simple structure, easy preparation, and it has good bandgap characteristics. This paper carries on the numerical simulation to itthrough the transfer matrix method and the theoretical research and design tothe non-linear 1-D PC optical switch.This paper analyzes the band gap characteristics of 1-D PC firstly. Theexperiments do the numerical simulation and the theoretical analysis tomulti-groups type 1-D PC, such as the different number of layers, thedifferent cyclical optical path, uniform thickness and the non-uniformthickness structure, different refractive index difference multi-groups type1-D PC, and they discovered that 1-D the PC band gap position is decided bythe cyclical optical path mainly, regardless of the dielectric sheet eitheruniform thickness or 1/4 wave length structure;the band center is locatednearby the wavelength that is twice of cyclical optical path all the time;theband gap width is decided by the refractivity, the cyclical optical path andratio of optical path of the higher and lower refractive index layer together,which makes it possible to increase the band gap width through the changecycle optical path or carrying on the rational distribution to the cyclicaloptical path although the refractive index of real material is limited;when therefractive index difference is fixed, the band width and the cyclical opticalpath has the direct ratio;the band gap characteristics are influenced mainlyby the numbers of layers and their refractivity ,and it is not better when thetwo values are bigger by no means , for the random structure photonic crystalhas the good band gap characteristic sufficiently when the two values arefixed, the 1-D PC with uniform thickness and same material structure has theobvious superiority, having the widest band gap , the most perfectcharacteristic, its band center located nearby the wavelength that is twice ofthe cyclical optical path, the band width and the cyclical optical path aredirect ratio.Then, this paper analyzes the band gap characteristic of 1-D PC withdefect. Among the same cycle structure introducing different defects such asdifferent defect layers of refractive index ,different actual thickness ,differentposition and quantity, the experiment discovers that the refractive indexdifference and the actual thickness come down to difference of opticaldistance of defect layers finally, the optical path of defect layer plays thedecisive role to the position and characteristic of the defect mode, and thedefect mode makes "the red shift" along with the defect layer optical pathincreasing;when the optical path of defect layer is equal to the 1-D PC cycleoptical path , the defect mode always appears in the band gap central position;the defect mode characteristic is mainly influenced by the position of defectlayer in the 1-D PC. When the defect located the central position ,defectmode characteristic is to be the best;the position symmetry and the distanceof multi-defect layers influence the band gap and the defect moderemarkably.This paper also carries on the numerical analysis to the transmissioncharacteristic of 1-D NLPC. The experiments select two kind of nonlinearmedium: ZnSe and GaAs, which are all the luminous intensity inductionrefractive index, namely refractive index changing with the incident lightintensity , and design two kind of 1-D NLPC structures, in which one is thatthe high refractive index layer is non-linear medium ZnSe, another is that thecentral defect layer is non-linear medium GaAs. The experiments indicatethey all have the good light restriction and light switch functions. When thedifferent intensity short pulses affect the photonic crystal,1-D NLPC has theobvious light restriction function;When the strong light for the pump lightand the weak light for the signal light act on the 1-D NLPC together , thesignal light penetrates completely if there is no pump light working and thesignal light is zero nearly if there is the pump light working, whichdemonstrates 1-D NLPC has switch characteristic to the signal light.At present, the fast development of entire optical communicationnetwork need the entire light exchange component such as optical switch torealize the network highly effective transmission and the highly transparentrequest urgently, so this paper designs two non-linear photonic crystal opticalswitches operating wavelength of 1. 55μm based on the above--mentionedanalyses and the researches for the photonic crystal transmissioncharacteristic with the transfer matrix method , offers the feasible referenceplans for the practical application of optical switch.The 1st corresponds to the structure one, a 9-layer and uniform thicknessstructure, its cyclical optical path is 9 /24λ 0, each thickness of the higherrefractive index layer is a = 113nm, each thickness of the lower refractiveindex layer is b = 215nm, its total thickness is d = 1.425μm, its effectiverefractive index is n eff=1.916;The 2nd corresponds to the structure two joinsthe defect in the center of 9-layer and uniform thickness PC, each thicknessof the higher refractive index layer is a = 150nm, each thickness of thelower refractive index layer is b = 287nm, GaAs in the central layerconstitution and its optical path is 12 λ 0, its actual thickness to be c = 195nm,its total thickness is d = 1.943μm, its effective refractive index isn eff=3.247.There are two new expounds which have the important value to thephotonic crystal design and the practical application in the manyexperimental conclusions of this paper, which have to be proved by themassive tentative data.1, The 1-D PC band gap position mainly is decided by the cyclicaloptical path and the band center locates nearby the twice of cyclical opticalpath wavelength .2, When the optical path of defect layer is equal to the 1-D PC cycleoptical path, the defect mode always appears in the band gap central position,twice wavelength place of optical path.The two conclusions obtained in this paper provide the sufficient basisfor the photonic crystal design, realize the design of photonic crystal structureaccording to the actual need of operating wavelength and have thesignificance to the photonic crystal component design and preparation.