The Design Of Photonic Crystal Polarization Beam Splitter And Performance Analysis

In recent years,along with the bringing forth of the concept “the Internet + 5G” and the rapid development of emerging technologies such as big data and cloud computing,people's demand for communication bandwidth has become higher and higher.As the traditional communication fiber optical capacity is approaching the Shannon limit,the most urgent thing is to enlarge the capacity of the optical fiber communication system.The adoption of spatial dimension is a key to solve this contradiction between supply and demand.Polarization multiplexing is just a kind of space division multiplexing(SDM)and can improve the utilization of the high frequency spectrum and the system transmission capacity through the mutually orthogonal polarization state and transmitting two-way independent data information within the same wavelength channel.In the polarization multiplexing system,the signal transmission module is one of critical components and requires the generation of a pair of orthogonal polarized lights.A photonic crystal polarizing beam splitter is designed based on the theory of multimode interference.This beam splitter does not only integrate the photonic crystal's own characteristics and the technical advantages of polarization multiplexing but also contains the strengths of the multimode interference coupled apparatus,which provides a way of thinking for designing an integrated polarization multiplexing device.The multimode interference theory is analyzed firstly,and then,the self-imaging theory analyzed using Mode Propagation Analysis with the case of general self-imaging theory,and the mathematical conditions about the direct and mirror replicas of the input field are obtained in the system.It designs a photonic crystal polarization beam splitter based on the directional coupling according to the multimode interference principle and the total internal reflection effects.The beam splitter is consisted of two single-mode waveguide which can change the coupling length through adjusting the width of two single-mode waveguides.The splitter is simulated and analyzed by using PWM and FDTD to prove,it can realize the function of separating two kinds of polarization states.The simulation results show that the transmittance of the photonic crystal polarizing beam splitter based on directional coupling is 93.8% and 94.6%,and insertion loss are 0.27 dB and 0.27 dB,and the extinction ratios are 22.4dB and 18.2dB respectively.According to the actual needs,a fork-type polarization beam splitter based on photonic crystal is designed.The beam splitter is composed of one coupling waveguide and two output waveguides,and the two output waveguides split into 60 degrees.The function of polarization splitting isachieved according to the principle of coupling between the waveguide and the principle of image.The 60 degrees bent buffer layer is optimized using the method of finite difference time domain(FDTD).The simulation results show that both TE and TM polarization mode can realize splitting filter when the wavelength is 1550 nm,while the transmission rate can reach 88.5% and 93.5%respectively,while the extinction ratio reaches 16.4 dB and 22.5dB;the size of the device is26?m×10?m.It plays an important role in the spatial division multiplexing optical communication system.