Carbon-nanotube-deposited long period fiber grating for continuous refractive index sensor applications

Abstract

We present a carbon-nanotube-deposited long period fiber grating for refractive index sensing applications in liquid. Carbon nanotubes are deposited around the surface of a long period fiber grating to form the refractive index sensing element. The sensing mechanism relies mainly on the high refractive index properties of the carbon nanotube thin film, which enhances the cladding mode of the long period fiber grating in order to have a significant interaction between the propagating light and the target medium. A sensitivity of 31 dB/ RIU and 47 dB/ RIU are obtained for the refractive index ranges of 1.33 to 1.38 and 1.38 to 1.42, respectively, which have not been demonstrated with normal long period fiber gratings as the sensing element. As the sensing mechanism is based on the change of the transmitted optical power, our proposed scheme can intrinsically solve the limitations of the free spectral range commonly seen in other reported schemes, and continuous and repeatable measurements can be obtained while only acquiring errors mainly from the power fluctuations from the light source. The fiber grating also does not require any further mechanical modification like etching or tapering, which allows the sensing *Manuscript Click here to view linked References Y. C. Tan et. al., "Carbon-Nanotube-Deposited Long Period Fiber Grating ……" p. 2 element to have the advantage of mechanical strength for practical applications. The experimental results are consistent with the modeling of the sensing mechanism.

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“…12 shows a nonlinear response of the resonance band intensity with increasing RI values. These observations are consistent with previously reported studies with GO [18] and carbon nanomaterial [19] based fibre optic RI sensors. Calculations based on the figure showed that in the lower region of RI values (from 1.33 to 1.38), an approximate sensitivity of 17dB/RIU has been achieved, compared to the higher RI region (values from 1.4 to 1.45), where an approximate sensitivity of 55 dB/RIU was achieved.…”

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“…The coupling coefficient between optical modes is a function of the SRI. The increasing SRI reduces the overlap integral between core and cladding modes, hence the decreasing of resonant intensity (Erdogan, 1997;Tan et al, 2014). When the SRI approaches that of cladding, the core mode will be coupled to the broadband radiation mode with no distinct attenuation bands.…”

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“…Accurate multi-parameter detection and mapping with integrated chips show promise for precision applications such as manned spacecraft, intensive care units, and gas reaction chambers. [5,6] The gas refractive index (RI) is a comprehensive parameter [7][8][9] that can be correlated with other essential parameters noted above, under certain conditions. Therefore, monitoring the RI is an effective way to achieve multi-parameter detection.…”