Research On High Dimensional Optical Fiber System And Its Nonlinearity

Since the advent of the optical fiber technology,it has been widely applied in many fields such as fiber laser,communication and sensor.In order to enhance the information capacity of fiber,the arising of different multiplexing technologies,such as wavelength-division multiplexing(WDM),time-division multiplexing(TDM)and spatial-division multiplexing(SDM),has expanded the fiber based optical system to high dimensional.The high dimensional fiber system is a very promising platform for optical communication and high power fiber laser due to its higher information capacity,more varied mode construction and more complicated interactions of modes.WDM and TDM have been widely applied in classical optical communication system.They parallel handle the large amounts of information in multiple time or wavelength channels.Combining the multiplexing technology with the quantum information,a new high dimensional quantum state can be obtained.The high dimensional quantum state play an important role in quantum information,which can be used in high dimensional quantum computation and communication to enhance the quantum information capacity.SDM multiplexing space freedom of light has been used for the next generation of optical communication system.The huge potential value of SDM prompted the recurrence of multimode fiber.The single mode fiber was a priority transmission media for the optical communication.However,with the advent of SDM,multimode fiber has become one of the hot research topics.Especially the report of the vortex fiber which can transfer the orbital angular momentum(OAM)light i.e.a high dimensional structure filed stable,pave a new road for the next generation system.The physical phenomenond in the high dimensional fiber system are different to those in the single mode fiber.The nonlinear process in the multimode fiber was a hot research topics due to its more complicated interactions of different modes.Moreover,owing to the high mode area of multimode fiber,the high dimensional fiber system is suitable to build high power fiber laser.Hence,the research of the nonlinear phenomenon,the fiber laser and the quantum information based on the high dimensional fiber system have great significance.The main contents are as follows:1.By using femtosecond pump laser at 1560nm with mixure of fundamenta]mode and the orbital angular momentum mode,a broadband supercontinuum spanning in 960nm and 2300nm based on the self-designed vortex fiber was demonstrated.The intermodal four-wave mixing(FWM)between fundamental mode and OAM mode was observed in the generation process of supercontinuum.The cascade of intermodal and intra-modal FWM process was demonstrated by theoretical calculation.The results of theoretical calculation is agree well with the experimental results.2.Here we show that by engineering the relative group velocity within spatial dimension,we can tailor the phase-matching condition of orbital angular momentum(OAM)modes.In this article,we demonstrate efficient and low-crosstalk intra-modal four-wave mixing processes between OAM modes in a self-designed and fabricated vortex fiber.The fiber was designed using genetic algorithm such that it can both support stable OAM mode transmission and meet phase matched condition of intra-modal FWM during multi-modes.We experimentally characterize the gain spectral bandwidth of different modes and find that they depend on multimode dispersion properties of the designed fiber,which agree well with our theoretical calculation.3.We propose and experimentally demonstrate an ytterbium-doped fiber laser emitting the single high-order cylindrical vector beams with a high efficiency and a high modal purity based on adaptive modal gain control.By the combination of a high-order pump with a self-designed ytterbium-ring doped fiber,modal dependent gain was tailored and specific transverse mode can be selected in the laser cavity.A model based on multimode propagation-rate equations is built up to demonstrate the behaviors of transverse mode competition in the fiber laser.Modal dependent gain of high-order mode pump are simulated numerically which agree well with our experiment results.The slope efficiency of the fiber laser reaches 79.61%with a low threshold of 47.73mw.The purity of the generated high-order CVBs are in excess of 95%.Such a strategy enables the controllability of modal gain in a fiber laser,reveals the potential to offer a new and promising way to achieve a high power fiber laser with an arbitrary single high-order transverse modes output.4.In this work,by combining the wavelength-and time-division multiplexing technologies,we prepare a multi-frequency-mode time-bin entangled photon pair source at different time slots by using four-wave mixing in a silicon nanowire waveguide,and distribute entangled photons into 3(time)×14(wavelength)channels independently,which can significantly increase the bit rate compared with the single channel systems in quantum communication.Our work paves a new and promising way to achieve a high capacity quantum communication and to generate a multiple-photon non-classical state.The innovations in this dissertation are as follows:1.We demonstrated a broadband superconinuum generation from 960nm to 2300nm by coupling the mixed pump laser into a self-designed vortex fiber.A cascade intra and inter modal FWM was observed in the super continuum.The generated parametric sideband wavelengths from the experiment are agree well with the calculations from phase-matching conditions from FWM.2.The self-designed vortex fiber can transmit the OAM light stable and shift the zero dispersion wavelength for all modes to around 1550nm.Owing to the properties of the vortex fiber,multiple intra-modal FWM occurred with low crosstalk.3.The self-designed active vortex fiber and the high-order pump laser was used to tailor the modal dependent gain.A high-efficiency cylindrical fiber laser is achieved by the competition of the mode in the laser cavity.Numerical calculation results based on the multimode rate equation demonstrated the feasibility of modal gain controller.4.A high-dimensional quantum entanglement is obtained by using the time-wavelength division multiplexing technology.The entanglement can distribute 42 channels for communication and keep the independence of each time slots.