Influence of different encapsulation types and shapes of polydimethylsiloxane on the temperature sensitivity of the FBG

Fiber Bragg grating (FBG) is formed by the periodic structure in the core of the optical fiber and is one of the widelyused types of fiber optic sensors. FBGs are primarily sensitive to strain and temperature. For sensory application is an important encapsulation of FBG to achieve maximum sensitivity to the desired measurand and ensure of protection against damage. Interesting way to encapsulate FBG is the use of elastomer polydimethylsiloxane (PDMS). Authors of this paper followed on previous research regarding encapsulation of FBG and analyzed the influence of different encapsulation types and shapes of PDMS on the temperature sensitivity and change of the reflected Bragg wavelength of the FBG. Realization of encapsulation is composed of three parts: FBG insertion to a regular form with the liquid PDMS, curing in a temperature box with a constant temperature 100 °C ± 5 % and 24 hours relaxation. Analysis of temperature sensitivity and reflected Bragg wavelength was carried out after curing including relaxation time and it using the broadband source of light LED (Light-Emitting Diode) with central wavelength 1550 nm and the optical spectrum analyzer OSA 203.