Generation Of Vector Vortex Beams In An Optical Fiber

Vector vortex beams with spiral phase structure, can be focused to form annular optical trap. For carrying photons orbital angular momentum, momentum and angular momentum coupling can happen with particles, that can be used in manipulation of particles, especially low refractive index particle in translation and rotation, controlling the biological specimen has important applications. In recent years it has been widely used in waveguide laser optics, particles, biological medicine, atom optics, optical micro manipulation, nonlinear optics, optical information transmission, optical computing and other fields research and application.The mainly methods to get vector vortex beams are mode conversion, spatial light modulation and computer holograph, in which the devices are often complex,costly. This paper tries to use ordinary optical fiber, by controlling the Gaussian beam incidence, directly produces vector vortex beams. Then the theory and experiment have been carried out to verify this method.First of all, from the wave equation, the optical fiber mode field distribution was analyzed by using the optical fiber mode theory and classification of vector model is given as well as the corresponding relationship with scalar models. Then the cut-off conditions, propagation constant and effective refractive index, excitation efficiency of each fiber model are calculated by the Mathematica software, as well given the relationship between each order mode excitation efficiency and incident light Angle and offset. Secondly using Comsol software we simulate the distribution of optical fiber mode field, calculate the effective refractive index of the model. The calculation results are in good agreement with Mathematica software calculation.According to the theoretical model above, we design experiment system setup.The laser of 0.6328?m wavelength is coupled into the SMF-28 e optical fiber at a certain incident angle and offset, by controlling the incident angle, offset and polarization of incident light. the output light waves vortex characteristic of eachorder model is verified by the coherent detection and polarization vector characteristic of each order model is verified by the polarization detection, that proves the feasibility of vector vortex beams obtaining through the optical fiber incidence method. This study provides a simple, low-cost way to product vector vortex beam and provides the support for promotion and application of vector vortex beam.