Ultracompact in-line broadband Mach-Zehnder interferometer using a composite leaky hollow-optical-fiber waveguide

We report on an ultracompact fiber optic Mach-Zehnder interferometer (MZI) using a novel concatenated structure, single-mode-fiber (SMF)-hollow optical fiber (HOF)-SMF. An optimized air-hole size in the HOF provided two unique optical paths; the leaky waveguide modes through the central air hole and the radiation channel into the silica cladding, which enabled a compact MZI configuration with enhanced optical performances, such as high visibility, high temperature sensitivity, and wide dynamic range.