Study On Selective Mode Excitation In Laser Resonant Cavity

The orbital angular momentum model is similar to the other modes and can be applied to many fields such as free space optical communication,optical fiber communication system,quantum information and optical fiber sensing.In theory,different orbital angular momentum modes are mutually orthogonal and do not merge,and do not interfere with each other in transmission.Therefore,the orbital angular momentum mode has more potential applications.With the more and more applications of the orbital angular momentum model,the generation of orbit angular momentum model has become a hot research topic.At present,there are a variety of methods for generating orbital angular momentum modes.However,these methods are difficult to generate the required orbital angular momentum mode flexibly and efficiently.Therefore,the laser that outputs the orbital angular momentum mode should be born.In this paper,based on the existing laser scheme,the multi-mode phase plate is used to improve the simultaneous excitation of the fundamental mode and any one of the orbital angular momentum modes.An optical fiber with any orbital angular momentum mode laser program,the program can be flexible and efficient output of any orbit angular momentum mode with the advantages of simple,adjustable,high energy conversion efficiency.The innovation and main work of the paper are as follows:1.A multi-mode phase plate is proposed to realize the simultaneous excitation of the fundamental mode and orbital angular momentum mode.According to the mode transformation theory,the blazed grating is introduced after superposing the phases of the initial light field and the target light field,then the multi-mode phase plate is generated.This phase plate can realize the cyclic oscillation of the fundamental mode and the direct output of the higher order mode simultaneously.Loading the multi-mode phase plate on spatial light modulator,the initial field can be modulated to obtain the output of the target mode.2.An arbitrary orbital angular momentum fiber laser based on the single spatial light modulator and multi-mode phase plate is proposed.Based on the equipment,we propose a fiber laser which can produce arbitrary orbital angular momentum mode.The laser could simultaneously realize the cyclic oscillation of fundamental mode and direct output of the higher order mode by using the multi-mode phase plate.First of all,using the soft to confirm the feasibility of the program.Then,an experimental platform of the fiber laser including gain medium,excitation source and ring resonator is constructed.We use a 10-meter-long single-mode erbium-doped fiber as the gain medium to amplify the 980 nm pump light.The multi-mode phase plate loaded on the spatial light modulator is used as the mode controller to realize the higher order mode excitation in real time and efficiently output,and the fundamental mode of the circular oscillation simultaneously.By adjusting the half-wave plate and polarizer and other devices to achieve the laser output power tunable.By changing the different multi-mode phase plates loaded on the spatial light modulator,it is flexible to achieve the output of any orbital angular momentum mode,without changing any experimental devices.