Giant Helical Dichroism in Twisted Hollow-Core Photonic Crystal Fibers.

We show that twisted single-ring hollow-core fibers can exhibit strong helical dichroism, i.e., a different transmission depending on the orbital angular momentum of the launched light. Experimentally, we observe loss differences of at least 40 dB/m over a broad spectral range (>60 THz). We investigate the effect via analytical and numerical studies and show that considerably higher differential loss can be achieved over a broader spectral range (>180 THz). Our observation provides new routes for controlling the polarization state, extends previous studies of circularly dichroic waveguides, and has many potential applications, such as the realization of new polarizing elements in previously inaccessible spectral regions, chiral sensing, broadband generation of vortex beams, and optical communication.