Investigation On All-optical MIMO Signal Acquisition Of Mode Division Multiplexing System

The transmission capacity of single mode fiber(SMF)has been greatly enhanced with the development of the fiber technology.The capacity is gradually approaching the limit of Shannon theory,and in the near future there will occur “capacity crunch”.In order to cope with the upcoming bandwidth bottleneck and to satisfy the growing demand for transmission capacity,people start to explore the dimension of space.The mode division multiplexing(MDM)system based on few mode fiber(FMF)is based on the orthogonality among the modes arising in the FMF.Each mode is used as an independent channel for signal transmission.At the receiver side,multi-input-multi-output(MIMO)signal processing is used to eliminate the mode coupling and crosstalk.Traditional signal processing technique relies on the digital signal processing(DSP)after the optical-to-electrical conversion.Recently,there exists a concept of all-optical MIMO signal processing,in order to avoid the use of high speed optoelectronic devices.At the receiver side,the MDM optical signal is processed by using the optical waveguide technique,with obvious advantages of low power consumption and easy integration.The thesis is focused on the all optical MIMO mode division de-multiplexing technology,and introduce the MIMO signal acquisition module.Then,the waveguide design and optimization are presented by matrix method.The main content of the thesis includes:(1)After we introduce the relationship between MIMO signal processing and MDM transmission,the advantages and disadvantages of traditional MIMO digital signal processing method are presented.Then we start the research based on the design and optimization of optical signal acquisition module for all-optical MIMO signal processing.(2)One of the key module for all-optical MIMO signal processing is the optical sampling coupler.After comprehensive optimization,under the condition of three sampling points,mode dependent loss(MDL)can be reduced to 0.03 dB and insertion loss(IL)can be reduced to 1.9 dB.The condition number is used as the optimization parameter.(3)In order to further reduce the IL,a new scheme is proposed to increase the number of sampling points.MDL of 0.04 dB and IL of 1.56 dB can be secured after the optimization.Although IL can be further reduced after we increase the number of sampling points,an optimal number of sampling points do exist under the geometric constraints of FMF and sampling points.