Study On Monolithic Integrated Silicon-based Flexible-grid Mode-and Wavelength-selective Switch

Due to the continuous emergence of bandwidth-consuming applications,such as cloud computing,big data centers,and 5G network,Internet traffic is growing exponentially.In order to accommodate the increasing Internet traffic demand,optical networks have to evolve to improve the spectrum efficiency and increase the transmission capacity.Elastic optical networks(EONs)can effectively utilize spectrum resources by adopting flexible grid channel allocation,while the space division multiplexing(SDM)technology can extend the capacity further by using an additional degree of freedom in the form of the new “space” dimension.Therefore,to meet the increasing bandwidth requirements,the combination of elastic optical networks and space division multiplexing technology would provide an attractive solution.However,how to handle each mode,each wavelength,and a mixture of different channel bandwidths in SDM-EONs is a key issue.To solve this issue,flexible-grid mode-and wavelength-selective switches are required.In this thesis,a monolithic integrated silicon-based flexible-grid mode-and wavelength-selective switch consisting of reconfigurable mode multiplexer/demultiplexers and bandwidth-tunable wavelength-selective optical routers is studied.The main contents are as follows:1.A reconfigurable mode multiplexer/demultiplexer based on symmetric Y-junction is proposed,designed,and analyzed.The proposed reconfigurable mode multiplexer/demultiplexer is composed of a symmetrical Y-junction and two heaters.To avoid the sharp corner and maintain the low insertion loss,a taper is introduced into the symmetrical Y-junction.By controlling the location and heating power of the electrode,the modal switching behavior in the designed symmetric Y-junction can be formed.Within the C-band(1530nm-1565nm),for the designed reconfigurable mode multiplexer/demultiplexer,the insertion loss is less than 0.12 dB and the demultiplexing crosstalk is lower than-15.39 dB.2.A bandwidth-tunable wavelength-selective optical router based on double-series coupled microring with interferometric couplers is proposed,designed,and analyzed.By controlling the resonance and effective coupling coefficients of double-series coupled MRRs with interferometric couplers,and the path phase differences,the proposed bandwidth-tunable wavelength-selective optical router can route individual wavelength from the input port to any one of the output ports.Additionally,individual wavelength from adjacent channels passing optical paths with same length can be coherently combined and the transmission spectrum with an adjustable bandwidth can be formed as desired at the output ports in the horizontal direction.For given field coupling coefficients,the designed bandwidth-tunable wavelength-selective optical router can have different channel spacings.When the channel spacing is selected to be0.8 nm,the extinction ratio is greater than 50.17 dB and the crosstalk is lower than-15.83 dB.Compared with the proposed router using series-coupled double microring resonators,the designed router can support more channel spacings and have larger extinction ratio and wider bandwidth tuning range.3.A design of a monolithic integrated silicon-based flexible-grid mode-and wavelengthselective switch consisting of reconfigurable mode multiplexer/demultiplexers and bandwidthtunable wavelength-selective optical routers is proposed.As an example,a 1 ×(2 × 3)siliconbased flexible-grid mode-and wavelength selective optical switch supporting two mode channels and three wavelength channels is designed and analyzed in detail.For the designed device,each mode and wavelength signal can be independently and flexibly conveyed to any output port with the bandwidth-adjustable properties as desired by thermally controlling the propagation constants of the optical modes in the arm of the symmetric Y-junction,the effective refractive indices of the bus waveguides and rings,and the path phase differences.The wavelength-channel spacing changes from 0.1 nm to 0.8 nm and 3-dB bandwidth varies from0.08 nm to 2 nm.When the wavelength-channel spacing is 0.8nm,the minimum extinction ratio is 50.9dB and the maximum crosstalk is-15.36dB.