Waveband-tunable optical fiber broadband orbital angular momentum mode converter based on dispersion turning point tuning technique

A wave-band-tunable optical fiber broadband orbital angu-lar momentum (OAM) mode converter based on a helical long-period fiber grating (HLPFG) and dispersion turning point (DTP) tuning technique is demonstrated both theoret-ically and experimentally. The DTP tuning is achieved by thinning the optical fiber during the HLPFG inscription. As a proof of concept, the DTP wavelength of the LP1,5 mode is successfully tuned from the original-2.4 mu m to-2.0 mu m and-1.7 mu m. With the help of the HLPFG, broadband OAM mode conversion (LP0,1 -> LP1,5) is demonstrated near the 2.0 mu m and 1.7 mu m wave bands. This work addresses a long-standing problem that the broadband mode conversion is limited by the intrinsic DTP wavelength of the modes and provides a new, to the best of our knowledge, alternative for broadband OAM mode conversion at the desired wave bands. (c) 2022 Optica Publishing Group