Silicon Photonics Devices And Transmission Characteristics For Fundamental Mode And High-order Mode

In the recent years,multimode silicon photonics is attracting more and more attention as a new-rising technology in the area of silicon integrated nanophotonics.It is based on introducing higher-order modes and breaking the single-mode condition,so that on the one hand,the number of modes can be expanded to increase the communication capacity,on the other hand,the flexibility and freedom of device design can be increased by introducing the high-order mode.There are two research most attractive:one is to develop photonics devices with multiple mode-channels for Mode Division Multiplexing(MDM)systems,the other is to use multimode waveguides or higher-order modes to design devices with high-performance.In this paper,some research work has been carried out on silicon integrated photonics devices that support the transmission of fundamental and higher-order modes.We proposed and demonstrated the multimode waveguide bend that supports fundamental mode and high-order mode transimitted with low loss and low crosstalk in the wide bandwidth,we proposed ultra-sharp multimode waveguide bend which works for dual polarizations,we also proposed and demonstrated ultra-low-loss silicon strip waveguide assisted with the multimode waveguide structure.Firstly,for multimode waveguide bends,the mode fields are squeezed to the outside sidewall and become very asymmetric when the bend is sharp.This introduces not only the mode-mismatching loss but also the inter-mode crosstalk.Here we proposed and realized an ultra-sharp multimode waveguide bend(MWB)based on a multimode waveguide corner-bend(MWCB).For the MWCB designed for the TEo and TE1 modes,the ELs are less than 0.18 dB and the inter-mode CTs are less than-36 dB in the wavelength range of 1260-1680 nm.The proposed MWCB is promising for multimode silicon photonics because of the simple structure,easy design,easy fabrication as well as excellent performances in an ultra-broad wavelength-band.Secondly,it is often desired to merge MDM and polarization-division multiplexing(PDM)for developing multi-dimensional the hybrid multiplexing technology.Therefore,we proposed a silicon-based on-chip ultra-sharp multimode waveguide bend(MWB)working for dual polarizations by introducing modified Euler-curves and shallowly-etched non-uniform subwavelength-gratings(SWGs).For the designed 90° MWB with an effective bending radius as small as 10 ?m,the excess losses are less than 0.23 dB and the inter-mode crosstalk is lower than<-26.5 dB over a broad band from 1500 nm to 1600 nm for six mode-channels,including three TE-polarization modes and three TM-polarization modes.It shows a great improvement compared to a regular 90° arc-bend(the inter-mode crosstalk is?-8.4 dB).Thirdly,based on the principle that the scattering loss decreases as the width of the strip silicon waveguide increases,we proposed and demonstrated an ultra-compact silicon-based multimode spiral waveguide structure that supports ultra-low-loss transmission for the fundamental mode.In the design process,we optimized the waveguide width,the curvature changes and structure of the multimode spiral waveguide,so that the fundamental mode maintains low-loss transmission in the multimode spiral waveguide while avoid exciting high-order modes,and the entire waveguide structure is also very compact.Experimental results show that for a strip silicon waveguide with a core height of 220 nm,the average waveguide loss in the working wavelength range from 1525 nm to 1585 nm is 0.41 dB/cm,and when the total length of the multimode spiral waveguide is 3.33 cm,The area of corresponding structure covers is only 0.42 mm×0.42 mm.Finally,we summarized the main work of the full text and made an outlook for the future researches.