Sensitivity Analysis of HF Etched Uniformly Thinned α-Power Refractive Index Profile Fiber Bragg Grating Sensor

An
$\alpha $
-power refractive index profile circular core fiber Bragg grating (FBG) sensor has been numerically and experimentally analyzed for the first time. In the experiment, 40% concentrated hydrofluoric acid (HF) has been used to fabricate an etched FBG (e-FBG) sensor with variable cladding thickness. The proposed study can also be demonstrating the marginal tuning capability of Bragg wavelength shift by deeply etched cladding process. The target of this article is to analyze the
$\alpha $
-power refractive index profile e-FBG sensor. For this purpose, a transfer matrix method (TMM) has been devised to analyze the complicated double-clad waveguide structure, while grating is taken along the length of fiber core. In this article, three samples have been fabricated and analyzed with various etched cladding thicknesses, i.e., 6, 8, and
$10~\mu \text{m}$
, which give significant change in the refractive index sensitivity. Experimental results of sensitivity analysis have been matched closely with the numerical one. The estimated maximum sensitivity of the developed
$\alpha $
-power e-FBG sensor has been found
$\approx 35$
nm/refractive index unit (RIU). Also, this value is equivalent to the minimum change in the refractive index of
$\leq 10^{-5}$
. It has been found that the Bragg wavelength can be tuned marginally as a result of reducing the cladding diameter. It has been noticed that the tuning range can be substantially improved by the deep etching process along with
$\alpha $
-power refractive index profile FBG and found to be
$4.5 \,\times \, 10^{-3}$
RIU at optimum cladding diameter.