Optimization of Transverse OAM Transmission through Few-Mode Fiber

Abstract

Spatiotemporal optical vortex (STOV) wavepacket is a new type of vortex optical field carrying transverse orbital angular momentum (OAM). Due to the presence of imbalanced dispersion and diffraction phase, the STOV pulse undergoes fragmentation during free space propagation, leading to the disappearance of the spatiotemporal vortex phase structure. For practical applications, having a stable long-distance propagation of STOV pulse is critical. Recent work demonstrates the transmission of transverse OAM in few-mode fiber. However, the maximum transmission distance is limited to 100 cm due to excessive group velocity dispersion between modes. In this work, we optimize the transmission of transverse OAM by engineering fiber parameters. By tuning the radius of the fiber core and the relative refractive index difference, the group time delay difference values between the LP01 and LP11 modes and their corresponding group velocity dispersion coefficients are minimized. The simulation results show that the optimized fiber allows the first-order STOV pulse to propagate up to 500 cm, and the second-order STOV pulse up to 300 cm without distorting the spatiotemporal vortex phase structure. Long-distance propagation of STOV pulse can create new opportunities and facilitate applications such as developing novel transverse OAM lasers and telecommunication approaches.