Novel all-fiber optic temperature sensors based on hollow optical fibers

Abstract

Novel all-fiber optic temperature sensors based on hollow optical fibers (HOFs) are presented. The HOFs with an air hole diameter of 8µm at the center are fabricated through elaborate controls of MCVD and fiber drawing process. Two types of all-fiber temperature sensors are described. One is an all-fiber temperature sensor composed of a short HOF serially concatenated between a pair of long-period fiber gratings using a B/Ge-codoped core single mode fiber (SMF). The broadband pass-band tuning range of 84.3nm, covering both S and C band, is observed in the range from 25 to 215 o C. Transmission peak is linearly shifted showing negative slope of -0.44nm/ o C at 1500nm region. Its design, fabrication arts, and device integration are explained with characteristics of output filter spectrum and temperature tuning. The other is an in-line fiber etalon temperature sensor using a short HOF segment fusion-spliced between standard SMFs. This device is characterized in terms of wavelength shift according to temperature for HOFs with and without Ge-doped ring core. Temperature sensitivity of 3.38×10 -5 / o C and dynamic range of 20dB are observed over the range from 25 to 330 o C at 1550nm. It is confirmed that the experimental results for both fiber optical sensors show a good agreement with theoretical analysis.