Research On Manipulation Of Spatially Structured Beams Based On Optical Fibers

In recent years,with the further understanding of characteristics of laser,the application of laser technology has been rapidly expanded.Due to the special spatial phase,intensity and polarization distributions of spatial structured light field,it shows a wide application prospect and important research value in many fields,which has attracted extensive attention from scholars all over the word.At present,it has become one of the forefront research hot topics in the field of optics and related disciplines.The structured light field is usually generated and controlled by spatial light modulators or digital micro-mirror devices.However,due to the large size and difficulty in integration,it is not suitable in some scenarios.Optical fiber has the advantages of small size and low transmission loss,the structured light field can be generated and controlled by adjusting the structure of the optical fiber.In optical fiber,coaxial transmission of structured light field with different wavelength,polarization distribution and intensity also has significant advantages in stimulated emission depletion microscoping and multiplexing.because the optical fiber is more flexible,smaller in size and has higher possibility of integration,it is of special and important significance to the research and application of optical fiber structured light field.In this paper,the optical vortex/LP₁₁ mode beam generating based on optical fiber and the optical field focusing based on multi-mode optical fiber microsphere lens in the first order optical vortex/LP₁₁ mode are studied theoretically and experimentally.The main research contents and achievements include:1.A new scheme of broadband generation of optical vortex/LP₁₁ mode base on optical fiber is proposed and implemented.The device activates the high-order mode by means of end-to-end asymmetric coupling,and controls the phase difference between odd and even modes by adjusting the polarization controller,so as to realize the conversion of fundamental gaussian mode to 1-order optical vortex and LP₁₁ mode,and the output light field can be arbitrarily regulated between 1-order optical vortex and LP₁₁ mode.At the same time,the polarizer controller and polarizer can filter out the non-converted fundamental Gaussian mode and improve the purity of 1-order optical vortex and LP₁₁ mode effectively.The device has high bandwidth,simple fabrication,low cost and high application value.2.Focusing characteristics of microsphere lensed fiber for high-order optical fiber mode were studied theoretically and experimentally.The microsphere lensed fiber is fabricated by fixing the high refractive index microsphere on the end face of the optical fiber.Compared with the traditional optical fiber microlens,this kind of optical fiber microsphere lens has the advantages of low cost,simple fabrication,and can be extended by means of cascade microsphere.This providing the theoretical basis and ideas for generation of high-order optical fiber mode focusing.