Transverse single-mode operation in a passive large pitch fiber with more than 200  mm mode-field diameter

In this Letter, we present, to the best of our knowledge, the largest effective single-mode fiber reported to date. The employed waveguide is a passive large pitch fiber (LPF), which shows the core area scaling potential of such a fiber structure. In particular, we achieved stable single-transverse mode transmission at a wavelength of 1.03 mm through a straight passive LPF with a pitch of 140 mm, resulting in a measured mode-field diameter of 205 mm.