Characterization of Brillouin scattering in plastic optical fibers for sensing applications

For health monitoring of civil structures, Brillouin scattering in optical fibers have been fully characterized and exploited. Conventionally, glass optical fibers have been mainly used as the sensor heads, but sometimes suffer from their low strain tolerance. One promising solution to overcome this drawback is the use of highly flexible plastic optical fibers (POFs). In this presentation, we review the unique Brillouin scattering properties in POFs and discuss their applications to distributed large-strain sensing. The first topic is the observation of Brillouin scattering in POFs at the telecom wavelength, leading to the clarification of its basic parameters, such as a Brillouin gain coefficient, Brillouin threshold power, Brillouin frequency shift (BFS), and the BFS dependences on strain and temperature. These results imply that Brillouin scattering in POFs is useful in implementing high-sensitivity temperature sensors and large-strain sensors. The second topic is a newly observed phenomenon referred to as “BFS hopping”, which leads to even higher temperature sensitivity (and lower strain sensitivity). The third topic is the trial experiment of POF-based distributed strain and temperature sensing with Brillouin optical correlation-domain reflectometry (BOCDR). A 10-cm-long heated section of a 1.3-m-long POF is detected. Finally, we present the simplified configuration of the POF-based BOCDR without the reference optical path, which provides higher cost-efficiency. We anticipate that the use of POFs will open up the new field of fiber-optic Brillouin sensing.