Abstract
Temperature-independent Optical Fiber Liquid Level Sensor Based on an In-fiber Mach–Zehnder Interferometer Formed by Cascaded Polarization-maintaining Long-period Fiber Gratings
Highlights
Since the fiber grating technology was first reported in 1978,(1) fiber gratings have received much attention as optical devices for optical fiber sensors and communications owing to their unique characteristics such as high sensitivity, resistance to corrosion, and immunity to electromagnetic interference
Yun et al proposed an optical fiber liquid level sensor (OFLLS) by employing an etched fiber Bragg gratings (FBGs) with a grating length of 24 mm.[9]. Since the clad region of the FBG was etched by hydrofluoric acid, the transmittance of the Bragg resonance dip changed according to the difference in refractive index between air and liquid around the grating element, and the water level sensitivity of the dip transmittance was obtained as ~2.54 dB/mm.[9]. Chang et al reported an OFLLS based on a 7-mm-long chirped FBG (CFBG).(11) Likewise in the case of the OFLLS based on the etched FBG, the CFBG was etched by hydrofluoric acid to measure 12 μm in thickness
We experimentally demonstrated a temperature-independent OFLLS based on a 83.4-mmlong in-fiber Mach−Zehnder interferometer (MZI)
Summary
Since the fiber grating technology was first reported in 1978,(1) fiber gratings have received much attention as optical devices for optical fiber sensors and communications owing to their unique characteristics such as high sensitivity, resistance to corrosion, and immunity to electromagnetic interference. Yun et al proposed an optical fiber liquid level sensor (OFLLS) by employing an etched FBG with a grating length of 24 mm.[9] Since the clad region of the FBG was etched by hydrofluoric acid, the transmittance of the Bragg resonance dip changed according to the difference in refractive index between air and liquid around the grating element, and the water level sensitivity of the dip transmittance was obtained as ~2.54 dB/mm.[9] Chang et al reported an OFLLS based on a 7-mm-long chirped FBG (CFBG).(11) Likewise in the case of the OFLLS based on the etched FBG, the CFBG was etched by hydrofluoric acid to measure 12 μm in thickness.
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