Research On Tunable Or Reconfigurable Optical Filters Based On Silicon Micro-ring Resonators

To meet the flexible and reconfigurable requirements of future optical networks,we focus on the tunable and reconfigurable optical filters based on silicon micro-ring resonators(MRRs)and make extensive research in this paper.Then we find out a dilemma in tunable schemes.When increasing the number of rings for box-like filtering,the difficulty of tuning and the power consumption of the device will increase at the same time.For reconfigurable schemes,there is currently no research to integrate multiple series or parallel topologies in the same device.Thus,we propose a low-order narrow-bandwidth bandpass filter of high shape factor with tunable center wavelength and bandwidth,and a multi-topology reconfigurable filter.The main contents of this article are as follows:(1)With the basic principles of MRRs,the transmission matrices of two basic types,AllPass MRR and Add-Drop MRR,are derived.The models,transmission matrices,and design ideas of each configuration are analyzed to provide a theoretical basis for the design.The expressions of each important performance parameter are given with influencing factors analyzed for further optimization.According to the equipment conditions of the fabrication platform,the process used in the fabrication is introduced with the specific process and parameters of each step.(2)A low-order narrow-bandwidth tunable filter with high shape factor is proposed.This filter is an asymmetric three-microring-assisted Mach-Zehnder interferometer structure.Because one more MRR is loaded on the upper arm than the lower of the MZI,there shows a unique phase response that at the output there is constructive interference within the passband and destructive interference outside,which helps to improve the filtering rectangularity while reducing the order.The initial structure is designed with the pole-zero method,of 3 MRRs,with simulated bandwidth tunable from 4 to 10 GHz,insertion loss less than 2.3d B,and SF of0.39-0.61,which is comparable to the reported 4-order schemes.The device was fabricated and tested,and the results verified the bandwidth tuning capability,which was 8.8-18 GHz,with SF mainly of 0.2-0.3.(3)A reconfigurable microring filter based on optical phase change material with low power consumption is proposed.By switching the working state of each coupling region independently,the reconfiguration of different series or parallel topology filters can be realized.In this paper,we explain the realization of the four topologies in this filter in detail.Since the size of reconfigurable coupling regions is difficult to reduce due to the limited refractive index perturbations of thermo-optic and electro-optic effects,here introduce non-volatile low-loss phase change materials with high refractive index contrast in different states,Ge2Sb2Se4Te1 or Sb2Se3,and design a low-loss compact reconfigurable optical coupler.The insertion loss is less than 0.5d B,the total length is less than 100?m,and power consumption drops significantly due to non-volatile characteristics.Based on this reconfigurable coupler,the performance of the 2-order and 3-order filters under different topologies is obtained by simulation and compared with the ideal structures,which verifies the reconfigurable assumption.Further,the reasons for the cost are analyzed.