Cover Story:
Magnetic fluid is a kind of nanostructured material which consists of surfactant-coated magnetic nanoparticles dispersed in a suitable base liquid. This “old” nanomaterial has led to renewed interest in optics and photonics since the beginning of the 21st century. It is compatible and easily integrated with optical fibers, opening the door to “seeing” vast prospects for applications in the fiber-optic magnetic field sensing area. This work demonstrates the feasibility of actualizing magnetic field sensors with magnetic-fluid-infiltrated photonic crystal fibers. The whispering gallery mode is effectively excited around the photonic crystal by the tapered microfiber. Reducing the cladding thickness of photonic crystal fibers can increase magnetic field sensitivity, which implies a convenient tunability of sensitivity for pragmatic applications.