“…Photonic crystal fibers (PCFs) are a special class of optical fibers characterized by a periodical arrangement of microcapillaries that form the fiber’s cladding around a solid or hollow defect core [16,17,18]. Since then, various fiber types such as honeycomb PCF [19], triangular PCF [20], rectangular PCF [21,22,23,24], D-shape PCF [25], side-polished PCF [26], and metal-coated PCF [27] have been demonstrated and applied in the fields of pharmaceutical drug testing, astronomy, communication, and biomedical engineering and sensing [28,29,30,31,32,33,34,35,36,37]. Compared with conventional optical fibers, the unique features of PCFs, such as flexibility of design, endless single-mode wavelength [21], high birefringence [22,23,24], and adjustable dispersion and nonlinearity [38,39], can be obtained by manipulating lattice period, air hole size and shape, refractive index of the materials, and type of lattice.…”