A novel interrogation scheme for multiplexing the sensors based on long-period grating (LPG) Mach-Zehnder interferometers (MZIs) is proposed. Each LPG-MZI is formed by a pair of cascaded identical LPGs and induces an additional optical path difference (OPD) proportional to the centre-to-centre interval between the two LPGs. A sub-reflectogram including sensing information can be achieved when the OPD induced in one LPG-MZI is compensated by scanning one arm of a Michelson interferometer to a certain range. For multiple sensors, the grating intervals of different LPG-MZIs are set to different values to ensure that their sub-reflectograms can be well separated in time domain. The spectral response of the LPG-MZI is reconstructed from the corresponding sub-reflectogram with a fast Fourier transformation. Applications of the bending and temperature monitoring are demonstrated by measuring the signals in time domain and wavelength domain, respectively.

Date Published: 5 October 2006
PDF: 9 pages
Proc. SPIE 6351, Passive Components and Fiber-based Devices III, 635124 (5 October 2006);

Published in SPIE Proceedings Vol. 6351:
Passive Components and Fiber-based Devices III
Sang Bae Lee; Yan Sun; Kun Qiu; Simon C. Fleming; Ian H. White, Editor(s)