Abstract
A robust optical fiber modal Mach–Zehnder (MZ) interferometer is
proposed, which is embedded in a fiber ring laser system as a tunable
filter to improve the detection limit (DL) due to its narrow full width
half maximum (FWHM) and high signal-to-noise radio (SNR). The sensing
element is composed of two cascaded up-taper joints fabricated by shoving
fusion. After filtering, the laser spectrum possesses the sensing
characteristics that the interferometer possessed. Temperature and
refractive index (RI) are investigated as measurands in experiments and
the response sensitivities are 92.1 pm/°C and 44.8 nm/RIU, respectively.
Accordingly, the DLs for these two measurands are calculated as 0.19 °C
and
$3.86 \times {10^{ - 4}}$
(RIU). Moreover, the axis strain response is
demonstrated to be much lower than many modal interferometers even under
the help of fiber ring laser. Thus, the property contributes to the
resistance of the outer force and disturbance. Compared to the simple
sensing device, the proposed fiber ring laser sensor significantly
improves the DL, which is one of the most crucial parameters. It is the
first time to combine the fiber ring laser device with the up-taper MZ
interferometer as far as we known. It is a feasible balanced way to
improve the sensing capability without the expense of mechanical strength
of sensing element.
© 2016 IEEE
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