Abstract
In this paper perfluorinated graded-index polymer optical fibers are characterized with respect to the influence of relative humidity changes on spectral transmission absorption and Rayleigh backscattering. The hygroscopic and thermal expansion coefficient of the fiber are determined to be = (7.4 ± 0.1) %r.h.−1 and = (22.7 ± 0.3) K−1, respectively. The influence of humidity on the Brillouin backscattering power and linewidth are presented for the first time to our knowledge. The Brillouin backscattering power at a pump wavelength of 1319 nm is affected by temperature and humidity. The Brillouin linewidth is observed to be a function of temperature but not of humidity. The strain coefficient of the BFS is determined to be (−146.5 ± 0.9) MHz/% for a wavelength of 1319 nm within a strain range from 0.1% to 1.5%. The obtained results demonstrate that the humidity-induced Brillouin frequency shift is predominantly caused by the swelling of the fiber over-cladding that leads to fiber straining.
Highlights
The influence of humidity on numerous polymers has been investigated in the last decades [1,2,3,4].The most commonly used polymer for polymer optical fibers (POFs) is polymethylmethacrylate (PMMA)
The water intake into the core of PMMA-POFs cause fiber attenuation changes [6]
cyclic transparent optical polymer (CYTOP) fibers are characterized by lower water absorption, lower attenuation and higher bandwidth in the near infrared region in comparison to PMMA [12,13]
Summary
The influence of humidity on numerous polymers has been investigated in the last decades [1,2,3,4]. The water intake into the core of PMMA-POFs cause fiber attenuation changes [6]. CYTOP fibers are characterized by lower water absorption, lower attenuation and higher bandwidth in the near infrared region in comparison to PMMA [12,13]. These beneficial characteristics are attractive for sensing applications [14,15,16,17,18] and for high-speed communication systems [19,20,21,22]. (iii) POFBGs inscribed in PFGI-POF without over-cladding did not show humidity-induced wavelength shifts [23]. Combining the obtained measurement results with the humidity-induced BFSs of [24], a humidity-induced strain caused by a swelling of the over-cladding was identified as the dominant origin of the humidity-induced BFS
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