The Research Of Three Mode(De)Multiplexer Based On Fiber And SOI

MDM(Mode-division multiplexing)transmission system deals with shannon limit of SMF(single mode fiber)using orthogonal modes in FMF(few mode fiber)as channles to transmit data.This technolgy can multiply the transmission capacity of optical communication network.Mode(de)multiplexer is the key component for MDM system which can realize mode conversation and couple several modes in one or several waveguides.After investigating the research status of mode(de)multiplexer at home and abroad,this paper studies on mode(de)multiplexer based on fiber and SOI(Silicon on Insulator)by means of theoretical analyses and simulations.This paper mainly focuses on the following aspects:(1)Based on fiber and rectangular waveguide,the mode feature of light transmission in the two different waveguides were investigated and simulated.Mode orthogonality demonstrated that mode can be used as transmission channle.Mode coupling and conversation were derived in detail by using the mode theory at the same time.(2)This Chapter introduced a tapered fiber three mode(de)multiplexer,which can realize mode conversion and(de)multiplexing simultaneously.Light fields of the device at inputs and outputs realizing mode(de)multiplexing are simulated with COMSOL.The Overlap integral of electric field of mode multiplexer's output with standard mode field and the light intensity ratio of mode demultiplexer's 3 outputs is further calculated for the efficiency of the device.Finally,the multiplexer's tolerance is calculated with different parameters.Simulation results show that:the tapered structure's lengths of the multiplexer for best effct of mode converting and demultiplexing are 3.88cm and 3.8931cm.The similarities of light fields at outputs of mode multiplexer to standard mode field are 0.8991,0.6834,0.5080 respectively and the the output light intensity at corresponding port of mode demultiplexer is the maximum.It can be also seen that the changes of parameters have not too much influence on the coupling efficiency of LP01?LP11a mode,but the coupling efficiency of LP11b mode is much lower.(3)FDTD(Finite Difference Time Domain)is then used to design and simulate the structure of mode(de)multiplexer based on rib waveguide and ridge waveguide.The light propagating in the designed ADCs(asymmetrical directional couplers)and the light field at the output ends of mode(de)multiplexer are calculated to obtained the crosstalk of each mode.Here we mainly discuss crosstalk of each output as wgap and wavelength change.Simulation results have shown that the hybrid multiplexer has relatively low loss about ldB and low crosstalk about-20dB.The crosstalk is lowest at 1550nm due to the phase-matching condition,and the efficiency of mode conversation is highest.The working wavelength with lowest crosstalk shifts towards long wavelength as the increase of wgap.Combining with the simulation results,the rib mode(de)multiplexer was fabricated based on SOI micromachining and tested.After a thorough comparative analysis,we come to a conclusion that the coupling length of ridge mode(de)multiplexer is shorter but the crosstalk is higher than rib mode(de)multiplexer.