An Optical Fiber Liquid Level Sensor Based on Side Coupling Induction Technology

Abstract

An optical fiber liquid level sensor based on two twisted polymer optical fibers twining around a racetrack column is demonstrated in this study. The side-coupling power of the passive fiber is modulated by the refractive index (RI) of the environment medium and decreases while the liquid level increases. The variation patterns of the side-coupling power in the bent section and the straight section form a step attenuation, which can improve the measurement range with a superior sensitivity and distinguish liquids with different RIs. Furthermore, the cost-effective sensor also shows good reversibility and low temperature-dependent properties.

A Multipoint Liquid Level Sensor Based on Two Twisted Polymer Optical Fibers in a Race-Track Helical Structure

“…Thus, the decrease in output power for each head is almost the same, forming a step-down output curve with the liquid level rising. For water, the decrease in output power of each sensing head is approximately 112.36 nW, which is 2.45 times more than the one of the sensor without the cement in the [17]. From Figure 3, it is obvious that the variation for liquids of different RI is different.…”

“…The measurement range is 100 cm, and the resolution is 2 cm. For a single sensing head consisting of a bent section and a straight section, the whole attenuation of the output power for water is 112.36 nW, which is higher than the one of the sensor proposed in [17].…”

“…The sidecoupling ratio is very small because the energy of the light source is mainly concentrated in the core of the active fiber. Thus, by measuring the side-coupling power, the influence of the light source perturbation on the passive fiber can be neglected and the SNR is improved [17]. However, the sidecoupling ratio is so small that a power meter with a high resolution is required.…”

“…In our previous work, we proposed a low-cost liquid level sensor based on two twisted POFs twinning around a racetrack column [17]. The side-coupling power is modulated by the RI of the surrounding medium.…”

Fiber-Optic Liquid Level Sensing by Temperature Profiling with an FBG Array

“…In reference [ 13 ], hydrostatic thrust was exploited to design a cantilever with an embedded FBG strain sensor to compute the liquid level. Bending loss or inter-fiber coupling can also be sensitive to the presence of a liquid, making a liquid sensor exploit these effects [ 14 , 15 , 16 ]. Chen and coworkers used an optical power source to actively heat the fiber, measure the thermal response of the fiber using an FBG array and to detect the level [ 17 ].…”