Distributed fiber temperature alarm system based on thermodynamic phase transition

Abstract

A novel temperature sensing mechanism is proposed for the first time, based on thermodynamic phase transitions of CO2 in hollow-core fibers. A f ast, s ensitive and distributed fiber temperature alarm system is demonstrated using this concept.

New avenues in optical fiber sensing using gas

“…This way, multiple liquid and gaseous sections can be discriminated and localized using a basic OTDR interrogator as fiber sections showing a different linear attenuation, visualized as distinct slopes on the backscattered temporal trace. This has been demonstrated in a side air-holes fiber, where the tiny fraction of the evanescent field propagating in CO2 shows a marked distinct linear attenuation where CO2 is liquid [7].…”

“…A simple alarm system could be devised by a point-to-point measurement of the overall transmitted light. It detects precisely and nearly instantaneously the occurrence of the cold spot, though with no possibility to localize the thermal spot [6]. This coarse binary behavior can be actually improved by converting the radical on-off transmission into a change of linear attenuation.…”

Distributed Temperature Alarm System Based on Incoherent Optical Time-Domain Reflectometry and Side Air-Hole Optical Fibers

“…The method relies on the substantial alteration in optical loss caused by a gas undergoing a phase transition from vapor to liquid at a specific temperature [2]. Through this approach, the proposed system binarily identifies and localizes sections along the fiber where the temperature surpasses or falls below a predefined threshold value, as previously sketched in a rudimentary non-distributed configuration [3]. To achieve this objective, the small evanescent field present in the SAHF proves adequate for detecting alterations in the optical loss when the gas in the air holes undergoes liquefaction [4].…”

“…Through this approach, the proposed system binarily identifies and localizes sections along the fiber where the temperature surpasses or falls below a predefined threshold value, as previously sketched in a rudimentary non-distributed configuration [3]. To achieve this objective, the small evanescent field present in the SAHF proves adequate for detecting alterations in the optical loss when the gas in the air holes undergoes liquefaction [4]. This is performed by introducing carbon dioxide (CO2) into the air holes at a specific pressure, which must be carefully selected to facilitate the gas liquefaction below the designated temperature threshold.…”