C

Fig. (3): The transmission spectra of 125µm diameter for (A): length 20 mm, (B): length 25 mm and (C): length 30 mm.

The transmission spectra response of the designed RI fiber sensor for different sensing length of about 20, 25 and 30 mm is depicted in Fig.3 (A-C). The stimulated evanescent signals will interact with the surrounding RI and initiate the variation in output spectrum. Besides from this Figure, it can be observed that when the RI rises the transmission spectra shifted to longer wavelength. The RI rises from 1.333-1.382, the wavelength was shifted from 1565.5 nm to 1580.4, 1449 nm to 1462.7 and 1562.6 nm to 1578 for lengths 20, 25 and 30 mm respectively. The sensitivities of the fundamental SCS fiber configuration with different CLF lengths (without etching) based RI fiber sensor can be illustrated in table 1, 2 and 3. This is owing to the actuality that, when the light propagates from SMF to CLF, the higher order modes would be agitated and interfered through the CLF length payable to the effect of MMI. Then, as the RI rises, the surrounding medium which function as the cladding layer of the sensing area will be influence by outer solution.

Table 1: The sensitivities of RI sensor with CLF diameter of 125 µm and length of 20 mm.