Flat Spectrum Response And Polarization Independence Of Silicon Based Array Waveguide Gratings

With the rapid development of 5G technology and big data,the demand of transmission rate and communication capacity is increasing explosively.Wavelength Division Multiplexing(WDM)technology can make full use of the bandwidth of optical fiber and reduce the cost of the communication systems.Arrayed Waveguide Grating(AWG)is a key component in the WDM systems because of its compact structure,low insertion loss and low crosstalk.In this dissertation,two key features of the AWG are studied deeply:flat spectrum response and polarization independence.The main works are summarized as follows:Firstly,the research background of optical interconnection and WDM are introduced,and the optical waveguide mode theory and numerical simulation method are analyzed.In addition,the design process and theoretical model of AWG are discussed by taking SOI platform as an example,which lay a foundation for the design of the devices below.Two kinds of ultra thin Si₃N₄ AWGs with flat spectral responses are designed and experimentally validated.Multimode interference(MMI)couplers with a v-shaped groove or a v-shaped subwavelength gratings at the end of the input waveguide are proposed.Compared with the gaussian type AWG,the 1 d B bandwidth of the AWG using the v-shaped groove MMI increased from 0.35 nm to 0.795 nm.In addition,the flat-top AWG designed by SWG-MMI achieves a 1d B bandwidth of 0.74-0.81 nm,which is theoretically about 29%higher than that of the traditional MMI.The experimental results show that the above two devices get 1 d B bandwidth of 0.61 nm and 0.798 nm,respectively,and the crosstalks are both lower than-20 d B.In view of the large birefringence existing in SOI waveguide structure,the polarization diversity method is used to achieve a polarized independent device by cascading a.polarization splitter rotator(PSR)with a bi-directional AWG.Theoretically,the insertion loss of the AWG is about 3.37 d B,the 1d B bandwidth can reach 0.61 nm,and the crosstalk is less than-42 d B.The devices mentioned above are fabricated and measured,the results show that the channel spacing and the central wavelength are well aligned when TE and TM mode incident respectively,the responses of the two polarization states have a high degree of coincidence.The PSR device reaches the loss of 0.3 d B(TE),0.48 d B(TM)and the extinction ratio of 21.1 d B(TE)and 22.6 d B(TM)near 1550 nm.