All Fiber Structure Cylindrical Vector Beam Laser

Compared to traditional solid state lasers, fiber lasers own several advantages such as high efficiency, high beam quality, small volume, compact structure and excellent stability. The fiber lasers are widely used in different fields such as scientific research, industrial processing, fiber communication and sensing. The most output beams from fiber lasers are the fundamental modes with uniform polarization distribution in cross section since such mode is the advantage mode in fiber without cutoff frequency.According to recent researches in vector beam, the demonstration of cylindrical vector beam with singular point in phase distribution has been achieved. The cylindrical vector beam can be classified by orthogonal radial and azimuthal polarization distributions. For applications of the optical controlling and imaging, the CVB can provide more freedom of polarization controlling compared the linear polarized beam. However, the generation of the CVB always needs special optical elements and complex laser cavity design.High order modes for fiber, such as TE and TM modes, own cylindrical polarization distribution property according to basic waveguide theory and there are radially and azimuthally polarized beam respectively. So demonstration of cylindrical vector beam within fiber laser is possible.This work is supported by Chinese Universities Scientific Fund with the aim of generation of the cylindrical vector beam within fiber laser. The demonstration of cylindrical vector beam is achieved through cavity design and wavelength choice with the purpose of generation of portable and concise laser source.The main research works and highlights are as following:1. The laser cavity consist single mode fiber and few-mode fiber and different coupling states between fiber collimators introduce high order mode excitation in few-mode fiber. In the linear cavity, the output through few-mode fiber owns cylindrically polarized property. The CVB has been generated in all-fiber structure laser. In our experiment, the center wavelength is around 1030nm and laser slope efficiency is about 5%. The max output power is lOmW and the threshold pumping power is about 30mW. By introducing stress, the output beam polarization changes have been achieved. Azimuthal and radial polarization beams have been demonstrated.2. By analyzing the relationship between incident light parameters and modes coupling, a spiral phase plate (SPP) has been introduced to improve high order mode coupling efficiency. According to experimental result, the comparison between different mode coupling methods and the SPP has been proved to be suitable for high efficient laser by demonstration of 50% high order mode coupling efficiency.3. Injection locking has been used for single frequency output with cylindrically polarized distribution. Fiber laser performances have been observed according to spectrum, RF spectrum and far field intensity distribution under external and mutual injection methods. A complex cavity has been constructed where a fiber distribution feedback laser acts as a cavity mirror and the DFB output has been used as injection signal to lock the oscillation frequency in linear cavity. The linear cavity with cylindrically polarized beam output is affected by incident signal and single frequency operation has been achieved. Phase-shift Bragg grating in few-mode fiber owning different peaks in transmission spectrum for TE and TM modes has been simulated. Mode purity for transmitted light will be improved by filter effect for narrow line width signal in high order mode.The innovative results in this thesis are as follows:1. An all fiber laser with cylindrically polarized distribution has been demonstrated and the output power exceeds lOmW and the laser oscilates around 1030nm. By introducing shear stress, the polarization change between azimuthal and radial polarization has been achieved.2. A single frequency fiber laser with cylindrically polarized property has been demonstrated experimentally under a fiber DFB laser injection locking. The laser center wavelength is 1053.8nm. The transmission property for high order modes in few-mode phase-shift grating has been analyzied and the vector beam quality will be improved through mode filtering effect.