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.