Broadband OAM modes excitation within a single-mode fiber

A helical long-period fiber grating (HLPFG) based on a single-mode fiber (SMF) is prepared near the dispersion turning point (DTP) to excite orbital angular momentum (OAM) mode in a broadband wavelength range. By calculating the phase match condition and optimizing the grating period, the mode conversion with a bandwidth of 182.0 nm and a conversion efficiency of 90% is achieved in the proposed HLPFG.