A compact Michelson interferometer (MI) in a single-mode fiber (SMF) is successfully formed by CO<sub>2</sub> laser irradiation
to measure refractive index (RI) values. The fiber inline MI mainly consists of two parts: one is the waist region in fiber
formed by CO<sub>2</sub> laser irradiation and the other one is the fiber tip end facet with pure gold sputter coating. Based on the
MI theory, the interference signal is generate between the core mode and the cladding mode excited by the core mode at
the waist region. Reflective spectra at two different interference lengths of 5mm and 15mm are given and the calculated
lengths based on theory are well verified. After the measurements of matching liquids with seven different refractive
indices, the RI sensitivity of the MI sample is tested of -197.3±19.1nm/RIU (refractive index unit), which suggests well
potential application in RI sensing.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
Reflectivity spectrum of beam propagation method (BPM), for the first time to the best of our knowledge, is realized and utilized to model all-optical fiber interferometric sensor formed by a U-shape microcavity embedded in a single mode optical fiber and illustrate the principle of sensor structures varied by the length and the depth of U-shape microcavity. BPM analysis gives a constructive guideline to get a high interferometric fringe visibility which is most important for sensing application. The simulated results are completely in agreement with the interferometric sensor principle of Fabry-Perot interferometer (FPI) theory. With the conclusion of FPI sensor, refractive index (RI) sensitivity and temperature sensitivity are then simulated and obtained as 1049±5.2nm/RIU (refractive index unit) within RI range of solutions and 1.04±0.03pm/°C respectively.
A fiber inline Michelson interferometer fiber optic sensor was presented for sensing applications, including high
temperature performance and refractive index change. The sensor was fabricated using one-step femtosecond (fs) laser
micromachining technique. A step structure at the tip of a single mode optical fiber was formed during the
micromachining process. The device had a loss of 16 dB and an interference visibility exceeding 18 dB. The capability
of this device for temperature sensing up to 1000 °C and refractive index sensing application in various concentrations of
ethanol solution were all demonstrated.