Design And Research Of Optical Communication Device Based On Defect In Photonic Crystals

Photonic crystals(PCs),which composed of periodic dielectric materials,can create a photonic bandgap due to multiple interference of incident light.Photons cannot propagate through PCs at certain frequency ranges.This provides a new platform to shape and control the flow of light.As the growing demand for high-integration optical communication device in wavelength-division-multiplexing(WDM)system,the PCs-based devices has entered people's horizons.Using plane wave expansion(PWE)and finite difference time domain(FDTD)method,we have analyzed the basic properties of two-dimensional PCs.Then we have designed two photonic devices and their performances are studied.We except that these devices can play an important role in optical communication system.In this paper,we present a simple method that can improve the coupling efficiency between double microcavity and its adjacent waveguide.The defect modes can be introduced by modifying the structure parameters of nanoposts,such as its dielectric constant,size,or position.In general,the localized photonic states located at the center of lattice due to the rotational symmetry of the microcavity.Here,we reduce this symmetry by only optimizing the position of nanoposts which locate at the center of the microcavity,leading to the change of the defect modes.Calculation results show that the coupling efficiency between double microcavity and its adjacent waveguide can be enhanced.Based on this advantage,we design a three-port channel drop filter and its full-width at half-maximum(FWHM)is about 10 nm,which means that the narrowband characteristic of the filter is great.In order to expand the application of the filter in the field of optical-fiber communication,the miniature heterojunction triplexer is designed.We explore the influence of the transmission efficiency as the change of the distance between the coupling cavity and the heterojunction interface.The results show that the transmission efficiencies for the operating wavelengths can almost reach100%at a distance of 2.26?m.The dimension of the device is 14?m×10?m.And it also has the advantages of low crosstalk and high isolation.A magnetic dielectric nanopost is introduced into a 2D-PC to build a magnetic microcavity.The constituent of the nanopost is ferromagnetic metal oxide and its magnetic characteristics is investigated.Then,the migration characteristics of the defect dielectric rod in the micro cavity and the influence of the dielectric column around the microcavity on the transmission performance are analyzed.Besides,the mechanism of migration is revealed from the viewpoint of mode energy.By adjusting the magnetic field intensity,the magnetic permeability of the ferrite defect dielectric rod is changed,and a switch based on magnetic resonance cavity is designed.Also,the permeability distribution scheme corresponding to the switching characteristics is given.Finally,a reconfigurable optical add and drop multiplexer(ROADM)based on the resonant cavity switch is designed which integrates bus waveguide,drop waveguide,add waveguide,reflection microcavity and two switching region.The results show that the designed structure can achieve the function of adding and dropping optical signal at a certain wavelength.The Q-factor of the transmission spectra can reach about 10~3and the transmission efficiencies are both above 90%.The insertion loss is0.1514 and 0.1223,respectively.The isolation of each channel is about 30,which means that the crosstalk between channels is extremely low.This device can satisfy the wavelength dynamic reconfiguration function in WDM system at the wavelength of 1550nm.