Background:
Refractive index determination of biological tissues is a challenging
issue. Many biological species also show vibrational signature in infrared domain. The
chalcogenide-based glasses can be used to make the fiber optic evanescent wave sensors for
detection of analyte.
Objectives:
The primary objective is to study the effect of various parameters on the sensitivity
of chalcogenide glass-based evanescent wave sensor for biological tissue detection.
Methods:
An evanescent wave sensor has been proposed with collimated source illumination
and uniform tapering. The chalcogenide materials are chosen such that the weakly guiding
approximation could be followed. Complex refractive indices of liver tissue samples have been
taken for the analysis of sensitivity via method of evanescent absorption coefficient. Equations
for sensitivity have been solved analytically using MATLAB software.
Results:
The simplification of the formula for sensitivity leads to the inference that the
sensitivity is a function of core radius, refractive indices of sample tissues and wavelength
used. Moreover, since the refractive indices of the materials are also a function of temperature,
therefore a change in temperature results into change in the profile of guiding mode. Hence the
effect of temperature must also be observed. The initial simulation parameters are taken; core
radius 100 µm, sensing length 4 cm and wavelength 1.0 µm. In the NIR region we have a better
sensitivity of detection for all the tissues samples and the risk of photodamage of the biosamples is reduced to a good extent. It has been found that sensitivity decreases with
wavelength and core radius whereas increases with temperature. It has also been shown that
sensitivity is found to be better with collimated in comparison with diffused source.
Conclusion:
The comparative study results that one should operate at shorter NIR region of
wavelength for higher sensitivity. The collimated source illumination should be preferred over
diffused one for launching the light within the fiber to have high sensitivity. Further, length of
sensing region should be larger but the fiber core radius should be smaller. The proposed
biosensor is robust and can also be used many times if the probe (sensing region) is cleaned
properly. Moreover, a small amount of analyte is enough for the detection. Thus, the proposed
sensor is very useful for bio-medical applications with its high performance, accuracy and
robustness.
A Novel and Open-Source Illumination Correction for Hyperspectral Digital Outcrop Models