Research On Mode Excitaion Based On Resonant Cavity

Higher-order mode of laser has been widely applied in many fields, such as mode division multiplexing optical fiber communications, optical fiber sensing, quantum information, which made the excitation of the higher-order mode have been extensively researched. Take mode division multiplexing optical fiber communication system as an example. The application of higher-order mode realizes the simultaneous transmission of several spatial modes in fiber, which greatly improves the transmission capacity of a single optical fiber. The mode application is based on the excitation of higher-order mode, and the excitation of higher-order mode provides guarantee of mode application.The key technology of multi-mode simultaneous excitation and the mode excitation of higher-order mode in resonant cavity are studied theoretically, numerically and experimentally in this dissertation. The multi-mode simultaneous excitation based on multi-mode mask is proposed based on the basis of mode conversion in the liglht path. Simulation and experimental verification of multi-mode simultaneous excitation were achieved at the same time. Furthermore, a higher-order mode excitation method based on resonant cavity is presented, and the simulation and experiment system of the laser are built. The output of accurate and pure higher-order modes is achieved. By using the 4-mode few-mode fiber, the Coupling and transmission experiment is realized. The innovations in detail are listed as follows:1. The phase plate based on super-pixel for the simultaneous excitation of multi-modes is proposed.The multi-mode simultaneous excitation by using multi-mode mask is proposed based on the principle of mode conversion in the light path. Firstly,according to the phase transfer function corresponding to the initial mode field and the target mode field in the light path, the phase plate is optimized by super-pixel, so the complex amplitude modulation of the initial mode field is realized and the amplitude damage of the target mode field is avoided.Secondly, the phase of different target modes is superposed in a certain way to form a multi-mode phase setting for the simultaneous and accurate target modes excitation. Lastly, the phase information is loaded on the spatial light modulator to achieved the modulation of the initial mode field. The simultaneous and accurate excitation result of LP01, mode and LP11 mode is obtained through simulation and experiment.2. The on-demand mode laser based on multi-mode mask is proposed.An on-demand mode laser is proposed in the thesis, and the output of on-demand mode in 1550nm band is achieved. Firstly the multi-mode mask for the target modes of LP01 mode and on-demand higher-order mode is set Secondly, the simulation and experiment systems of on-demand laser including gain medium, pump system and ring cavity system are set up Thirdly, the feasibility of higher-order mode output is verified by simulation and experiment. Single-mode erbium-doped fiber used as gain medium provides sufficient gain to realize the population inversion. The excitation of higher-order mode and mode switching control are realized flexibly and in real time by using the spatial light modulator loaded on multi-mode mask.The accuracy of mode excitation is improved by matching the initial mode field radius with the radius of multi-mode mask. The laser power of output mode can been adjustable by using half wave plate and a polarizing plate, the coefficient of multi-mode mask. Through simulation and experiment, the target excitation of on-demand higher-order mode from LP01 mode to LP105 mode is realized.3 the modes outputs from laser are successfully coupled into fiber in experiment, and the transmission of the modes in few-mode fiber is realized.The modes outputs from the laser are coupled into the few-mode fiber,which is achieved by using the fiber collimator. By the use of few-mode fiber which supports 4 modes, the transmission of LP01 mode, LP11 mode, LP21 mode and LP02 mode is achieved, which verify the practicality of the laser.