Compact modal interferometer built with tapered microstructured optical fiber

A modal interferometer was built with tapered large-mode-area microstructured optical fiber (MOF). The tapering was introduced by slowly stretching the fiber while it was heated with a high temperature flame torch. With this slow-and-hot tapering process, the MOF air holes collapse and the taper waist is transformed into a solid unclad multimode fiber. This allows the coupling between the fundamental HE11 MOF mode and the HE1m modes of the solid fiber. The beating of the HE1m modes makes the transmission spectra of the taper to exhibit an oscillatory pattern. The influence of the taper geometry and wavelength on the interference pattern is discussed. The interferometer can be used for diverse applications.