Simultaneous detection of liquid level and refractive index with a long-period fiber grating based sensor device

Abstract

In this study, a long-period fiber grating (LPFG) based optical fiber sensor device is proposed for simultaneous detection of liquid level and refractive index. When part of the grating was submerged in an unknown liquid, the resonant wavelength of each cladding mode of the LPFG sensor varied linearly with the submerged length and nonlinearly with the refractive index of the liquid. By retaining the first-order (sensitivity) and second-order (cross sensitivity) terms of a Taylor expansion of the nonlinear relation, the changes in submerged length (or liquid level) and refractive index can be simultaneously evaluated from the changes in resonant wavelength of two cladding modes. The sensitivity coefficients to liquid level, refractive index, their cross effect, and environmental effects were studied both analytically and experimentally. The maximum prediction error by the proposed evaluation algorithm was found to be 1 mm for liquid level and 0.005 for refractive index.

Continuous Liquid-Level Sensor Based on a Long-Period Grating and Microwave Photonics Filtering Techniques

“…5. This shift represents the same behavior corroborated in other works, such as [14]. When this occurs, the magnitude of the tap related to the LPG, grows causing a gradual imbalance between the amplitudes of the two taps of the MWP filter.…”

Fiber optic sensing system for in-situ simultaneous monitoring of water stage, quality, and temperature

“…1 corresponds to one cladding mode. The resonant wavelength (λ res,m ) of a LPFG sensor can generally be expressed as a function of its grating period ( Λ ) and effective refractive indices of the core ( The operational principle of the LPFG sensor for multiple-parameter sensing of water level, quality (referred as surrounding refractive indexes), and temperature is based on the LPFG sensing capability for simultaneous liquid level, refractive index changes, and temperature, which refers to the previous publication from the author's research group as described in [27]. …”

“…The sensor structure also follows reference [27] as shown in Figure 2. The sensor consists of two parallel LPFGs and one glass tube.…”

“…The two cladding modes of the In-LPFG (illustrated as LP 06, in and LP 07, in in Figure 1b) are used to measure temperature following the published procedure [22,28]. The two cladding modes of the Out-LPFG (illustrated as LP 06, out and LP 07, out in Figure 1b) are used to monitor water level and quality as well as temperature following the published procedure [27]. A MATLAB program is developed with the personal computer to automatically record the wavelength changes and analyze the water stage, quality, and temperature from the device.…”

Liquid level sensor based on CMFTIR effect in polymer optical fiber

“…So these sensors can hardly be applied and popularized in cost-sensitive areas. The refractive index-sensitive sensors mainly include long-period fiber grating (LPFG) sensors [12][13][14] and fiber frustrated total internal reflection (FTIR) sensors. The LPFG sensors are similar to the pressure-sensitive types in complexity and cost.…”