Investigation of Fiber Optic-Based-Refractometer for Biogas Sensing

In this study, a fiber-based refractometer (FOR) applied for biogas sensing has been investigated. Two types of fiber, single-mode (SMF) and multimode fiber (MMF) have been proposed as sensing elements. The research aims to investigate the spot and power attenuation of both fiber types in 4 main conditions; fiber cladding, de-cladding, compound coating, and biogas feeding. The experimental results showed that the spot diameters from both fiber types are constantly at 4 and 26 mm in any conditions. This causes the difference in core diameters and also the dispersion of light characteristics within the fibers. Moreover, when the sensing element has been modified by the following conditions, the results indicated that the output intensity has proportionally changed, according to the fiber modification and the concentration of biogas absorbed into the sensing element. Besides, the power attenuation from MMF is larger than SMF. This causes the length of fiber de-cladding and dispersion of light within the MMF can easily be induced by biogas feeding. Therefore, it can be concluded that the MMF is more suitable than SMF for employment as a sensing element of the fiber refractometer.