Simple and Adjustable LP01-LP11-OAM Mode Conversion Method in One Single-Mode Fiber With Half-Dome Lens

In this study, we propose a novel adjustable rotational half-dome mode conversion for a single-mode fiber (SMF) to generate linearly polarized first-order mode (LP11 mode) and orbital angular momentum (OAM) mode from linearly polarized fundamental mode (LP01 mode). The mode conversion system consists of two modules: the fiber rotation traction (FRT) module, which achieves LP01-LP11 mode conversion by adjusting the rotational angles of theta=45 degrees/135 degrees/225 degrees/270 degrees. Then, elongate it and cut off the optical fiber terminal to form a flat port; and the fiber half-dome lens (FHDL) module, which converts the OAM mode from LP11 mode by fabricating a half-dome lens at the terminal of the FRT module output, introducing two light spots of the LP11 mode with corresponding rotational orthogonal angles. Theoretical and experimental results demonstrate that LP01-LP11 mode conversion can be obtained through our FRT module, and LP11-OAM mode conversion can be generated through our FHDL module. The precise control of the equipment and the model conversion experiment can be made with good robustness and experimental repeatability. Compared with the existing conversion, this mode conversion technique enables the conversion of a single SMF into multiple modes, highlighting its simplicity of operation, which eliminates the necessity for fiber coupling or modulation with optical components. Furthermore, the potential applications of this method extend to optical tweezers particle manipulation experiments. In our future work, we plan to apply this method to enhance the efficiency of particle capture in optical tweezers experiments, leveraging its simplicity and effectiveness.