The Fundamental And Applied Research Of Singular Beams In Optical Fiber Communication

At present,the information society has entered the Internet age.The rapid development of the Internet has put forward new requirements for the bandwidth of optical fiber communication technology.On the one hand,the spectrum bandwidth resources of the existing optical fiber communication are close to saturation.On the other hand,with variety of multiplexing technique continues to break through,the capacity of optical fiber communication system is increasing greatly,the single channel communication capacity of existing single-mode fiber is close to Shannon limit.Therefore,in order to meet the future bandwidth requirements of optical fiber communication,it is urgent to find new technique of beam multiplexing and fibers with large capacity multiplexed.The singular beams are the orbital angular momentum(OAM)and cylindrical vector beam(CVB)based on the phase singular and polarization singularity,respectively.They provide a new degree of freedom for beam multiplexing.However,the transmission of singular beams in free-space is susceptible to atmospheric disturbances and turbulence,resulting in a modest crosstalk of the low-density of singular beam.The signal is distorted in the optical communication system.At the end of system,the signal cannot be detected.The fiber provides conditions for the stably transmission of singular beams.The thesis proposes the application of OAM and CVB beam multiplexing and demultiplexing technology in optical fiber communication,and carries on the fundamental and applications research to transmit OAM and CVB beam in optical fiber.It has provided the new technical means and ideas for the development of modern optical fiber communication technology.The main contents and achievements of this thesis are as follows:(1)We demonstrate OAM modes transmission in a grapefruit-type micro-structured optical fiber.Firstly,the eigen vector modes in the fiber are calculated by using the finite element method.These eigen vector modes can form the OAM modes by using the theory of superposition calculation.The effective refractive index difference between the eigen modes in the fiber can reach 10-2 or more.The mutual coupling between the eigen modes can be effectively reduced in theory,and the performance of OAM transmission in fiber is improved greatly.Secondly,we use the fiber with high refractive index difference to transmit OAM modes in experiment and the OAM modes are detected by using the optical vortex Dammann grating with special desigened after transmitting in the fiber.(2)We demonstrate CVBs transmission and singal communications in a few-mode fiber.Firstly,the eigen vector modes in the fiber are calculated by using the finite element method.The effective refractive index distributions of the eigen vector modes in different wavelengths are analyzed,and the effective refractive index difference between the eigen vector modes is compared.Secondly,we use the fiber to transmit CVBs in experiment,and tested the modes purity of different CVBs which are detected.In the experiment of optical fiber communication,we use two high order coaxial CVBs carrying 10Gbit/s on-off keying(OOK)signal for 5km optical fiber communication.We also use the same order CVBs with polarization multiplexing and achieve four coaxial CVBs for 5km optical fiber communication.The bit error rate of communication systems is tested which satisfies the threshold of forward error correction(FEC).They conform to the standard of optical communication system and achieve the CVBs with fiber transmission,multiplexing and communication.In conclusion,the fundamental and applications research of OAM and CVB in optical fiber communication is studied in the thesis.It is possible to enhance the capacity of modern optical fiber communication system by using the multiplexing and demultiplexing technology of singular beam.It will lay the foundation for the development of optical communication technology in the future data center.