Silicon Photonic Devices With On-chip Mode Manipulation

The world encounter with the COVID-19 in 2020,People from all the world have to facing the lockdown policy.More and more online network courses and virtual conferences are driving the investment in the core and access part of the Internet.In addition,it is also promoting the expansion of data centers.The silicon-based integrated circuits,benefiting from its advantages of high integration density,low energy consumption,large bandwidth,low cost and CMOS compatibility,has attracted more and more attention from the scientific research and industry.In the past few decades,countless researchers have invested in the research of silicon optical integrated devices.But before large-scale application is realized,there are still some challenges need to be solved and overcome:In terms of passive devices,we need to further improve device performance,achieving low-loss waveguides,various multiplexer devices to enlarge system capacity,especially polarization multiplexing and mode multiplexing.In this paper,research work has been done on silicon photonic devices with on-chip mode manipulation.First,based on the multi-mode multiplexing system,we proposed and demonstrated a series of high-performance on-chip devices with multi-channel mode manipulation;Next,based on birefringence characteristics of optical waveguide,we proposed and demonstrated some silicon-based integrated high-performance polarization control devices;finally,we designed an efficient mid-infrared optical frequency comb which provides a potential solution for the realization of an on-chip integrated optical frequency comb light source.First,in terms of multimode mode regulation:we have proposed a dual-core adiabatic tapered structure.Utilizing the super-mode evolution theory,the high order mode which confined in the wide core could be converted into the supermode in the narrow core,and be extracted into the output waveguide as fundamental mode.Using this structure,we first implemented a three-channel mode multiplexing/demultiplexer on a 50nm ultra-thin silicon waveguide.This structure uses supermode evolution theory to effectively reduce crosstalk between channels(20dB),reduce insertion loss<-0.2dB,and achieve broadband 1520nm?1585nm;then,we use the dual-core adiabatic cone structure combined with high-performance polarization beam splitter,the dual-polarized ten-channel mode multiplexer/demultiplexer is realized.Due to the characteristics of the adiabatic structure,crosstalk between channels can be effectively reduced,and finally all TM and TE mode channels have low crosstalk(-15?-25dB)and low excessive loss(0.2?1.8dB)in the wide band of?90nm,which is also the mode multiplexer with the largest number of channels at that time;To further reduce the device size and increase the flexibility of the device layout,we designed a compact multimode curved waveguide that can support ten-channel modes.utilising the gradient curvature of the Euler curve,we realized the multi-mode curved waveguide with a radius of only 40?m,with low insertion loss and inter-mode crosstalk;Finally,in order to further improve the optical interaction on the multi-mode chip for flexibility,we have designed a three-channel arbitrary channel add-drop multiplexer.By manipulating the dispersion utilizing sub-wavelength grating waveguides,we can download/upload the basic mode including the fundamental mode arbitrarily without changing the bus waveguide.The extinction ratio of the three modes in the maximum bandwidth of 60 nm is>15 dB,and in the maximum bandwidth of 100 nm the excess loss is<0.32 dBSecondly,in terms of polarization manipulation:we proposed a series of solutions to the difficulty of designing polarization multiplexing devices due to the relatively weak birefringence effect of single-mode waveguides on thicker SOI platforms.First,we adopted a three-waveguide cascade structure to design a polarization beam splitter.By precisely controlling the spacing between the three waveguides,the TM mode can be fully coupled to the other end of the output while the TE mode is still confined in original waveguide due to total phase mismatch;then,we propose a polarization beam splitter based on a sub-wavelength grating waveguide,which utilizing the polarization selectivity of the sub-wavelength grating waveguide to enhance the effective refractive index difference of the dual polarization of the waveguide,and enhance the birefringence of the waveguide;at the same time,because the sub-wavelength grating can effectively enhance the interaction of the light field,it helps to enhance the compactness of the device;Finally,in order to further enhance the performance and improve the fabrication tolerance,we combine the sub-wavelength grating waveguide with the dual-core adiabatic tapered together to realize an ultra-high bandwidth and low-loss polarization beam splitter.Under a simple process of etching,the device realizes measured extra losses of TM and TE polarization are 0.1?0.6 dB and 0.3?1dB,respectively,while the extinction ratio ER>20 dB and ER>25dB bandwidth is about 240 nm and 220 nm.which is better than the previous results much higher.The 1dB bandwidth is also as high as 230 nm.which is much larger than the previous PBS based on 340 nm SOI waveguide.Finally,using mode hybridization and supermode evolution,a compact polarization beam splitter-rotator is proposed.This device has a large process tolerance and can achieve both TE and TM polarization states in the 1520?1610nm bandwidth range.The extinction ratio is greater than 20dB.Finally,using mode hybridization and supermode evolution,a compact polarization beam splitter-rotator is proposed.This device has a large process tolerance and can achieve both TE and TM polarization mode in the 1520?1610nm bandwidth range.The extinction ratio is greater than 20dB.Third,in terms the analysis of the optical waveguide structure dispersion performance,using the third-order nonlinear effect of the material,we designed a micro-cavity double dispersion wave the mid-infrared optical frequency comb effectively solves the bandwidth limitation problem caused by the high refractive index difference.At the same time,thanks to the ultra-high third-order nonlinear effects of aluminum gallium arsenide and the high mode field limitation caused by the high refractive index difference,the device can be designed to achieve low threshold and high conversion efficiency.It provides a potential solution for the realization of an on-chip integrated optical frequency comb light source.Finally,we summarize the main work of the full text and make a prospect of the follow-up research of work based on on-chip Mode Manipulation.