Fabrication and modification of temperature FBG sensor: role of optical fiber type and Cu sputtered thickness

Abstract

This paper presents the effects of optical fiber type and copper coating thickness on fiber Bragg grating (FBG) temperature sensitivity. Three types of FBGs including single-mode, step-index, and graded-index multimode fibers were fabricated via the phase mask writing technique. In the temperature range of 30 °C to 80 °C, the step-index multimode FBG exhibits the highest temperature sensitivity of 11.8 pm °C−1 compared to single-mode and graded-index multimode FBG with the sensitivities of 10.5 pm °C−1 and 11.4 pm °C−1, respectively. The temperature sensitivity of the step-index multimode FBG sensor was further improved through the deposition of copper nanolayer which has a greater thermal expansion coefficient than glass. The FBG probe sputtered with a 759.2 nm-thick copper layer achieves the highest temperature sensitivity of 14.2 pm °C−1 compared to those with 306.5 nm and 562.3 nm-thick copper layers which show the sensitivities of 13.2 pm °C−1 and 13.4 pm °C−1, respectively.