Multi-channel THz Wave Routing Switch Based On Magnetic Photonic Crystal

With the rapid development of communication technology and computer technology,people’s requirements for information transmission and processing are also increasing.The rapid development of wireless communication leads to the lack of spectrum resources and the development of new frequency bands has become a consensus to solve the lack of spectrum resources.Many frequency bands of the terahertz(THz)band have not been developed and used and has attracted people’s attention.The terahertz wave switch has also attracted the attention of scholars as an importmant part of THz technologies in recent years.High performance equipment and easy integrated products are required in terahertz wave communication systems.There are single-channel switches and multi-channel switches with routing function in communication systems,Routing switch is one of the important components of the communication system because of its routing function.The performance of the switch has an important influence on the transmission quality of the communication.Magneto-optical crystal is a kind of photonic crystal whose properties can change with external excitation.In this paper,a garnet-type ferrite material is used as a point defect introduced in the structure.The properties that magnetic permeability of the ferrite material changing with external magnetic field and the coupling characteristics between line defect and point defect are used.A multi-channel THz wave routing switch based on magnetic crystal switch is proposed and theoretically analyzed and numerically investigated by using plane wave method(PWE)and finite-difference time-domain(FDTD).The results show that the four-channel routing switch can be realized by applying different intensity of magnetic fields.This thesis focuses on the study of the multi-channel THz wave routing switch based on magnetic photonic crystal,and the main achievements and conclusions are listed as follows:Based on the forbidden band characteristics of photonic crystals,the defect mode theory and the characteristics of magneto-optical crystals,multi-channel terahertz wave routing switches are proposed.In the third chapter,a three-channel,a four-channel and a six-channel terahertz routing switches are designed.The schemes are realized based on a square lattice 2-D silicon photonic crystal.Line defects and point defects are introduced in the structure,and the size of point defects are the same.The permeability of the ferrite can vary with the magnetic field.So when a external magnetic field is applied to the point defects,the incident terahertz wave can be coupled to the corresponding channels due to the couping between line and point defects.Routing function can be realized by applying a magnetic field of the same magnitude to a particular one or several ferrite point defects.The proposed device is theoretically analyzed and numerically investigated by using PWE and finite-difference time-domain FDTD in Rsoft software.The results show that the designed routing switches work at the wavelength of 84μm,The transmittance of TE mode of the THz wave is above 92%,the extinction ratio is higher than 14 dB,the proposed THz routing switch has a good performance.On the basis of the scheme above,the controlling way of magnetic field in the three-channel and four-channel routing switch is optimized.In the former scheme,the magnetic field is added to the single dielectric column,which is difficult to realize in reality for the ultra small size of the point defects.In the optimized scheme,the external magnetic fields are added to the entire routing switch.Ferrite point defect with different radii are introduced in different channels.When applying a magnetic field to the entire routing switch structure,all the magnetic permeability of the ferrite point defects can be changed.Which channel the wave is output from depends on the extensity of the applied magnetic field.The optimized multi-channel routing switches are simulated using Rsoft software.The results show that the designed routing switches work at 85.33μm,the transmittance of TE mode of THz wave is above 93%,and the extinction ratio is higher than 12 dB,which effectively realizes the multi-channel routing switch function.The multi-channel THz wave routing switch based on magneto-optical crystal proposed in this thesis is simple in structure and easy to integrate,and has a good application prospect in future THz wave communication.