Research On Broadband And Low Loss Thermo-Optical Switch And Its Key Devices

With the development of modern optical networks,an integrated optical switch with characteristics of large bandwidth,low loss and low crosstalk has very important application value.The 3dB optical splitter is a key component in the optical switch,and its characteristics directly affect the performance of the more complex silicon integrated photonic devices.Based on the relevant design theory of integrated optical devices,two kinds of broadband polarization-insensitive 3dB beam splitters based on silicon nitride waveguide and SOI,respectively.On this basis,two kinds of thermo-optically tuned Mach-Zehnder optical switch based on silicon nitride and SOI platform are designed.The specific research contents and results are as follows:(1)A broadband polarization-insensitive 3dB MMI optical power splitter based on silicon nitride platform was designed.The polarization-insensitivity was achieved by using a 1.2?m×0.3?m cross-section waveguide,and broadband characteristic was obtained by using an optimized tapered waveguide instead of a straight waveguide.The device is characterized with bandwidth of 160nm(1460nm~1620nm).Excess loss is less than 1dB and polarization dependent loss is less than 1.25 dB in the operating wavelength range.(2)A wideband and polarization insensitive 3dB optical beam splitter based on a directional coupler structure is designed,which is based on a silicon-on-insulator platform.In the proposed device,the ridge waveguide was adopted to realize compact device size,and the waveguide cross-section parameters were optimized to achieve polarization insensitivity.At the same time,broadband characteristics are obtained by introducing a curved waveguide instead of a straight waveguide.The proposed 3dB power splitter theoretically achieves polarization-insensitivity from 1480 nm to 1620 nm(~140 nm),while having a coupling region length of only 22 ?m.Within the coupling ratio range of 50%±5%,the excess loss for TE and TM polarizations are estimated to be less than 0.04 dB and 0.06 dB respectively,as well as the polarization dependent loss for both output ports are less than 0.7 dB.The device has good manufacturing tolerances.(3)A large-bandwidth,low-loss,high extinction ratio,polarization-insensitive Mach-Zehnder thermo-optic switch based on silicon nitride is proposed by using a broadband-insensitive 3dB optical beam splitter based on multimode interference coupler.The switching powers of TE mode and TM mode are 230 mW and 240 mW,respectively,and the extinction ratio is 31.5dB and 24.8dB respectively.At the “cross” state,the insertion losses of TE mode and TM mode are less than 1.5dB and 1.8dB respectively in the wavelength range of 1460 nm to 1620 nm,meanwhile the channel crosstalk is less than-23.8dB and-22.2dB,respectively.For the “through” state,the insertion loss is less than 1.2dB and 1.1dB,and the channel crosstalk is less than-31.3dB and-21.4dB,respectively.(4)The designed 3dB optical beam splitter based on directional coupler structure is used to construct the Mach-Zehnder thermo-optic switch,the corresponding switch with large bandwidth,low loss,high extinction ratio and polarization-insensitive characteristics is realized.The switching powers for TE and TM modes are both 63 mW,and the extinction ratios are 39.3dB and 47.1dB,respectively.At the cross state,the insertion loss of TE mode and TM mode are less than 2.2dB and 2dB along with the channel crosstalk less than-18.4dB and-25.2dB,respectively,in the wavelength range of 1480nm~1620nm.For the “through” state,the insertion loss is less than 1.6dB for both TE and TM polarizations,and the channel crosstalk is less than-38.4dB and-46.6dB,respectively.