Fiber Inline Core–Cladding-Mode Mach–Zehnder Interferometer Fabricated by Two-Point CO$_{2}$ Laser Irradiations

Abstract

We report a fiber inline Mach-Zehnder-type core-cladding-mode interferometer fabricated by two-point CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser irradiations on a single-mode fiber. The laser irradiations caused efficient light coupling from the core mode to the lower order cladding modes and vise versa. High-quality interference spectra with a fringe visibility of about 20 dB were observed for four different interferometer lengths (5, 10, 20, and 40 mm). The temperature sensitivity of the device with a length of 5 mm was measured to be 0.0817 nm/degC. The sensitivity for refractive index measurement of the device was comparable with a long-period fiber grating of LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">04</sub> cladding mode.