Investigation Of All-fiber High-order Mode Pattern Manipulation Technique

With the rapid development of various Internet driven applications,current wavelength division multiplexing(WDM)fiber optical transmission cannot satisfy the ever-growing demand of bandwidth.To explore new signal multiplexing technique in new dimension and further extend the transmission capacity has attracted worldwide research interests.Mode division multiplexing(MDM)is a promising candidate to be considered.MDM technique,which can load different signals into different modes at the transmitter side and multiplex all modes into single fiber,and finally de-multiplex all the modes at the receiver side with the help of multi-input-multi-output digital signal processing(MIMO DSP),can substantially enhance the transmission capacity of fiber optical transmission.In this thesis,we comprehensively investigate the transmission characteristics of high order mode arising in the circular/elliptical core few-mode fiber(FMF).Meanwhile,based on these two fibers,we successfully demonstrate spatial mode rotation within a range of 360°.The main contributions of thesis are summarized as follows.(1)The model of free-space light transmission is established with the aid of diffraction theory.High-order diffraction field distributions are simulated with this model.Based on silicon-based liquid crystal for the purpose of spatial phase modulation,experiment validation of the high-order diffraction field distribution is accomplished.Using free-space optical devices,high order modes can be successfully excited and transmitted over the FMF.(2)Spatial distribution and transmission characteristic of high-order mode in FMF are investigated,especially for the linearly polarized mode and vector mode.Based on the Jones matrix,we establish the mode transmission model of the vector mode basis and simulate the output mode distribution.Experiment validation of the distribution and transmission characteristics is done,in accordance with the simulation results.Finally we can achieve 360°range mode rotation in the FMF based polarization controller(PC)configuration.(3)We design and fabricate the elliptical core optical fiber,study the mode characteristic with finite element analysis.Comparison with traditional circular core FMF is also presented in term of mode distribution and transmission.Based on coupled mode theory,we establish the transmission model of high order modes under the condition of twist.We also conduct experiment for validation.Finally we design a new kind of mode rotator based on the elliptical few mode fiber and also achieve 360°range rotation.