Multimodal Interference in Perfluorinated Polymer Optical Fibers: Application to Ultrasensitive Strain and Temperature Sensing

Yosuke MIZUNO  Goki NUMATA  Tomohito KAWA  Heeyoung LEE  Neisei HAYASHI  Kentaro NAKAMURA  

IEICE TRANSACTIONS on Electronics   Vol.E101-C   No.7   pp.602-610
Publication Date: 2018/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E101.C.602
Type of Manuscript: INVITED PAPER (Special Section on Distinguished Papers in Photonics)
polymer optical fibers,  perfluorinated polymer,  modal interference,  strain sensing,  temperature sensing,  

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We review the recent advances on strain and temperature sensing techniques based on multimodal interference in perfluorinated (PF) graded-index (GI) polymer optical fibers (POFs). First, we investigate their fundamental characteristics at 1300nm. When the core diameter is 62.5µm, we obtain strain and temperature sensitivities of -112pm/µε and +49.8nm/°C, the absolute values of which are, by simple calculation, approximately 13 and over 1800 times as large as those in silica GI multimode fibers, respectively. These ultra-high strain and temperature sensitivities probably originate from the unique PF polymer used as core material. Subsequently, we show that the temperature sensitivity (absolute value) is significantly enhanced with increasing temperature toward ∼70°C, which is close to the glass-transition temperature of the core polymer. When the core diameter is 62.5µm, the sensitivity at 72°C at 1300nm is 202nm/°C, which is approximately 26 times the value obtained at room temperature and >7000 times the highest value previously reported using a silica multimode fiber. Then, we develop a single-end-access configuration of this strain and temperature sensing system, which enhances the degree of freedom in embedding the sensors into structures. The light Fresnel-reflected at the distal open end of the POF is exploited. The obtained strain and temperature sensitivities are shown to be comparable to those in two-end-access configurations. Finally, we discuss the future prospects and give concluding remarks.