Broadband,Low-loss And High Isolation Circulators Based On Magnetic Photonic Crystals

The artificial material photonic crystal functions optical modulation characteristics.Doing periodic distributing with different dielectric properties leads to the appearance of Photon energy band in the photonic band gap.By introducing defects into the structure,optical waveguide,resonant cavity and magneto-optical effect can be made.It is the main reason why photonic crystals have been widely studied and applied.In this thesis,the above characteristics of photonic crystals and the gyromagnetic properties of magnetic materials are combined in order to designs and analyzes the circulator structure of the optical ring transmission.By optimizing the structure of the photonic crystal and the magnetic material,the performance of circulator functions a wide loop transmission bandwidth,low insertion loss,and high isolation.The design of the structure and the optical characteristic are simulated by the finite element method.In the meantime the optical analysis software is used to analyze the bandgap of the photonic crystal.The circulator performance index standard in this paper: the insertion loss is less than 0.5dB,and the isolation is higher than10 dB.Seven circulator structures are designed and simulated in this paper based on Si substrate and YIG cavity dielectric column material.The three-port Y-type magnetic photonic crystal broadband low loss circulator is studied first,distributing Three-branch waveguide Y-shaped and equipping with a ferromagnetic material ferrite column(YIG)in the Center of Convection.According to the cross-sectional structure of the YIG having the gyromagnetic characteristics,the three-port circulator is divided into a circular,an equilateral triangle and a star.The ring structure with circular section YIG column is studied.The results show that the ring-shaped characteristics are poor,the transmittance is too low,the insertion loss is too high,and the isolation is too low,which does not satisfy the design requirements.The second one is a YIG column structure with a triangular cross section.The transmission spectrum,insertion loss,and isolation are improved compared to the circular section,but the loop bandwidth is too narrow.Further optimizing the YIG structure,a YIG cylinder with a star-shaped cross section was designed.The YIG cylinder Y-type three-port circulator with star-shaped section can realize stable clockwise unidirectional ring transmission in the three frequency bands 4197197 GHz.GHz~,251995198 GHz.GHz~.and 196194GHzGHz~ respectively,and the isolation degrees are respectively greater than 14 dB up to 18 dB and greater than 12 dB.Up to 22 dB and greater than14 dB and up to 24 dB,the insertion loss is less than 0.5dB,0.3dB and 0.18 dB.This result is significantly improved compared to the first two structures,achieving three ports within a certain range,low insertion loss and high isolation,completing and exceeding the design requirements.In order to meet the application requirements of expanding the number of communication channels of the multi-channel communication system,the four-port cross-type circulator is also studied.The lattice constant is 0.56 mm and the radius of the air holes is 0.19 a.The four ring-shaped structures are also designed for the coupling part between the cross-shaped waveguides.The results show that the four-port circulator with the isosceles triangular section of the coupling column reduces the reflection of the structure,improves the coupling efficiency and the loop characteristics between the waveguides,and achieves stable clockwise unidirectional ring transmission in four frequency bands.In the Hz~.2208217 GHzG,the isolation of both isolated ports is higher than10 dB and can reach 14 dB and 32 dB,and the insertion loss is less than 0.45dB;In the Hz~.2002199 GHzG,the isolation of both isolated ports is higher than 10 dB and can reach 12.5dB and 20.5dB,and the insertion loss is less than 0.5dB;In the 220219GHzGHz~,the isolation of both isolated ports is higher than 10 dB and can reach 24 dB and 25 dB,and the insertion loss is less than 0.19dB;In the Hz~.2004197 GHzG,the isolation of both isolated ports is higher than 10 dB and can reach 12.5dB and 16 dB,and the insertion loss is less than 0.5dB as low as 0.2dB.Compared with the other three structures,the four-port circulator has a significant improvement,achieving a low insertion loss and a high isolation in a certain frequency range.The Optical Circulator Based on Two-dimensional Magnetic Photonic Crystal can be widely used in future multi-channel communication system integrated circuits.