2-D Gyro-magnetic Photonic Crystal Isolator In The Microwave Region

Generally speaking,isolator is a two-port passive device.It only admits signals to pass through in one-way direction.The important widely used application of isolator is to maintain the stability of the signal source and reduce the noise interference during transmission.The isolation of the traditional isolators working in the microwave band is generally between 20 and 30 dB.When microwaves transmit in the waveguide,there exists the edge mode of the Quantum Hall.In this dissertation,the software COMSOL is used to simulate the one-way transmission characteristic of waveguide with edges constructed by magnetic photonic crystals.Using that one-way transmission characteristics,the isolation of the isolator will be increased.Based on the structure of literature,the structure of the isolator is optimized.When the external magnetic bias is reformed,better isolation effect will be observed.At the same time,the chiral edge state one-way transmission behaves,just as what simulating the microwave transmitting in the waveguide.This phenomena of propagation over the obstacle is also demonstrated by simulating the transmission process.This inherent characteristic is important for the design,manufacture and application of the isolator.The band structure of the magnetic photonic crystals is calculated and analyzed by the plane wave expansion method,the finite difference time-domain method,the multiple scattering method and the finite element method.Without the external bias magnetic,there are degenerate points within the neighbor bands of magnetic photonic crystals.With the external bias magnetic applied,the degenerate points are broken.It is a phenomena that the degenerate bands split into two or more,which is caused by external magnetic field.On the edge of these split bands,nonreciprocal transmission mode occurs.This is the basic reason why chiral edge state exists.Previously setting the lattice constant of the photonic crystals as 1.33 cm,the related parameters of the isolator structure are determined by scanning both of the radius of the dielectric rods and the width of the waveguide.Three kinds of isolators with different structures are designed working in frequencies of microwave band finally.One of them is a two-cascaded isolator whose working frequency is between 14.2 GHz and 14.8 GHz;the highest isolator can be as high as 30 d B.Another isolator is a three-cascaded isolator;its working frequency is between 13.7 GHz and 14.7 GHz,and in the whole working frequency the isolation is high enough to about 150 d B.To meet the need of the integrated photonic crystal systems,an initial photonic crystal isolator with multi-ports is also designed.The isolator may play an important role in redistributing the signal sources in the home network without signals interfering with each other.