In-Fiber Fabry–Perot and Mach–Zehnder interferometers based on hollow optical fiber fabricated by arc fusion splicing with small lateral offsets

Two kinds of in-line all-fiber interferometers, including tip Fabry–Perot interferometer and compact Mach–Zehnder interferometer, are proposed and demonstrated by fusion splicing a short section of hollow optical fiber (HOF) to the end of single-mode fiber (SMF) and sandwiching a section of HOF in between two sections of SMF, respectively. In both interferometers, a small lateral offset is introduced to induce the optical path difference required to form the interferometer. Temperature responses of both types of interferometers are studied experimentally. It is anticipated that such easy making, compact and low-cost fiber-optic interferometers could find important applications in practice.