Orbital angular momentum modes by twisting of a hollow core antiresonant fiber

Generation and use of orbital angular momentum (OAM) of light is finding more and more interest in a wide variety of fields of photonics: communications, optical trapping, quantum optics, and many more [1]. In the investigation of such behavior, twisting of photonic crystal fibers shows interesting physical phenomena [2]. We previously reported the ability to create helical hollow fibers by mechanically twisting a tube lattice fiber made of polyurethane, the twist of which can be adjusted and reversed [3]. In this work we report how such deformation induces a mode transformation to an OAM mode, allowing a simple and tunable way to generate OAM modes. We take advantage of THz time domain spectroscopy to obtain information on both intensity and field components, and to be able to investigate how they change both in time and with frequency.