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In-line reflected fiber sensor for simultaneous measurement of temperature and liquid level based on tapered few-mode fiber

Yichun Li, Zhuo Song, Jiao Pan, Hanglin Lu, and Junhui Hu

Open Access Open Access

Abstract

An in-line reflective dual-parameters fiber-optic sensor is proposed in this work, whereas it is experimentally verified by measuring both the liquid level and the local temperature distribution simultaneously. The proposed sensor configuration comprises a single-mode fiber (SMF), a tapered few-mode fiber (TFMF), as well as a silver-coated capillary tube. The extracted experimental results indicate that the liquid level only affects the power of the resonant dips, while having little impact on the wavelength. On the other hand, both the wavelength and the power of the resonant dips vary with the temperature change. Therefore, the simultaneous measurement of the liquid level and temperature can be realized according to the different responses of the resonant dips to the liquid level and temperature. The obtained liquid level and temperature sensitivities can reach the values of 0.106 dB/mm and 0.029 dB/°C, 35 pm/°C, respectively. The sensor exhibits the advantages of high stability and low cost, the demodulation relates on only one wavelength which can shorten the scanning wavelength range during measurement. The proposed sensor can be potentially applied where accurate and simultaneous measurements of both temperature and liquid level are required.

© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

1. Introduction

The execution of both liquid level and temperature real-time measurements is quite important since these are the most fundamental parameters that need to be constantly monitored in various scientific and industrial fields, such as water management, ocean observation, the fuel storage systems, the bio-chemical progressing, the pharmaceutical industries and the environment monitoring. The conventional electrical sensors [1–3] that are currently utilized for liquid level sensing suffer from severe electromagnetic interference (EMI), which limits their wide exploitation. On the contrary, optical fiber sensor (OFS) offers excellent merits such as robust electromagnetic immunity, chemical erosion resistance, high sensitivity, and compact size which can be integrated on flexible substrates [4]. As a result, they are regarded suitable for utilization in harsh conditions sensing applications, such as in downholes for oil recovery [5], as well as in nuclear power plants [6].

As far as the liquid level sensing based on the employment of OFSs is concerned, they have achieved fruitful results. More specifically, various potential configurations have been developed including the fiber Bragg grating (FBG) [7–9], the chirped fiber Bragg grating [10], the tilted fiber Bragg grating (TFBG) [11], and the long fiber Bragg grating (LFBG) etc. [12,13]. However, the fabrication of grating-based optical fiber sensors requires the utilization of special instruments and high precision control of the respective manufacturing processing. As a result, the relative cost will be inevitably high, where the involved procedures are time-consuming. On the other hand, the fabrication of novel fiber in-line sensing configurations based on Mach-Zehnder interferometers (MZI), Michelson interferometers (MI), Fabry-Perot have displayed several comparative advantages. More specifically, they can be easily manufactured at a low cost, which renders them a suitable candidate in the liquid-level sensing field. Joana et al. [14]. and Jauregui-Vazquez et al. [15]. proposed different types of Fabry-Pérot interferometers (FPI), which are embedded into a polyurethane resin diaphragm and Mylar polymer, respectively, and applied to liquid level measurement. By considering that the refractive index (RI) has an important impact on the level measurement, Liang et al. [16]. Feng et al. [17]. and Cui et al. [18]. investigated the liquid level sensitivity of the sensors under enforcing different RI, respectively. Moreover, Roldán et al. [19]. and Fan et al. [20]. proposed and demonstrated two different novel optical fiber sensors structures capable of measuring both the liquid level and its refractive index.

However, in several practical applications, the liquid level and the temperature require the execution of frequent and simultaneous measurements. Yet, the majority of the aforementioned sensors do not meet such requirements. Under this perspective, numerous structures assisted by FBG can achieve the simultaneous measurement of dual parameters [21–23]. For instance, Choi et al. [24]. proposed an optical fiber sensor by utilizing cascaded long-period fiber gratings (LPFGs) that were inscribed on high-birefringence fiber (HBF) and a Faraday rotator mirror (FRM). As a result, the authors demonstrated the simultaneous measurement of both the liquid level and temperature. Additionally, Zhang et al. [25]. proposed a compact OFS structure based on an inline MZI for concurrent measurement of the liquid level and the temperature, whereas the reported optimal liquid level and temperature sensitivities were −231.67 pm/mm and 77.86 pm/°C, respectively. On top of that, in the same year, a thin-core fiber-based in-line MZI was proposed and experimentally fabricated through the application of a symmetric core-offset splicing technique [26]. The outcomes of the liquid level measurement reached the values of 101 pm/mm (short-range) and 41.8 pm/cm (long-range), respectively. The temperature crosstalk was eliminated in terms of self-differential compensation. Therefore, the measured error was compressed within the range of 0.68%.

In this work, an in-line reflective dual-parameter fiber-optic sensor for the measurement of both the liquid level and the temperature simultaneously is proposed. The sensor consists of a tapered few-mode fiber (TFMF) and a silver-plated capillary. The TFMF is fabricated by enforcing a fusion splicing technique in conjunction with a lead-in SMF, and then is sealed in a silver-plated capillary with UV glue in order to form the sensing element. Furthermore, the liquid level and temperature characteristics of the sensor have been experimentally investigated. The acquired results signify that the resonant dips have different responses to the liquid level and temperature, which indicates that the sensor could be able to measure both the liquid level and the local temperature distribution simultaneously by monitoring the wavelength and power responses. The demodulation only relates on one dip which can shorten the wavelength range of measurement. A liquid level sensitivity of 0.106 dB/mm was obtained, while the respective temperature sensitivities of wavelength and power are 35 pm/°C and 0.029 dB/°C, respectively.

2. Operation principle and fabrication

A schematic illustration of the proposed sensing structure is divulged in Fig. 1. The sensor consists of an SMF, a TFMF and a glass capillary with silver-plated which has the ability to measure the variation of both the temperature and the liquid level. Figure 2 reveals the fabrication process of the proposed sensor. Initially, a section of the FMF is subjected to fusion spliced with a piece of lead-in SMF in order to form the SMF-FMF structure. During the splicing, the discharge intensity is 100 bit, and the discharge time lasted 3000 ms. Then, the FMF end of the SMF-FMF structure is pulled into the taper by employing a commercial fusion splicer (Furukawa, Fitel S183PM II) in order to make up the SMF-TFMF structure. This process is achieved by shifting the SMF-FMF and discharging by S183PM. The discharge intensity is 100bit with the duration of 4900 ms. And the translation distance is set to 32767µm, which is the maximum translation distance of internal motor. The microscopic image of the structure is disclosed in Fig. 3(a). It is interesting to notice that the FMF structure is a step-index type two-mode fiber with a cladding and core diameter of 125 µm and 14 µm, respectively. And it is better controlled involving the number of modes compared with SMF and MMF. The taper made of few-mode fiber transmit a small amount of modes mainly, so the interference in the taper is more stable than that of the single mode fiber or multimode fiber which is depends on the fundamental mode and high-order modes. The used SMF is conventional SMF-28 with the cladding and core diameter of 125 µm and 9 µm, respectively. In addition, a total displacement of 32767 µm (the maximum displacement of the splicer) and a discharge-intensity of 100 bits was selected in the taper fabrication. During the process of translation and taper, the FMF will gradually taper until break, whereas the fiber tapers with a diameter of 35.59 µm (D = 35.59 µm) and a length of 560.76 µm (LT = 560.76 µm) were fabricated.

 figure: Fig. 1.

Fig. 1. Schematic diagram and operating mechanism of the proposed sensing structure.

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 figure: Fig. 2.

Fig. 2. The fabrication process of the sensor. (a) SMF and FMF are fused by discharge in order to form the (b) SMF-FMF structure, then by translating the SMF-FMF and discharge the fiber tip to form (c) SMF-TFMF structure. (d) The glass capillary is plated with silver and (e) the SMF structure is slowly inserted into the interior of the capillary. (f) Finally, glue is used in order to seal the structure.

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 figure: Fig. 3.

Fig. 3. (a) Microscope image of the SMF-TFMF structure. (b) Pictures of the silvering process and (c) silver-plated capillary. (d) Physical display of the sensor and (e) the larger version of the sealing part.

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Subsequently, the tail of a capillary is plated with silver by a silver-mirror reaction. The capillary is sensitized by immersing it in stannous chloride. Then the solvent, Tollens’ reagent, is produced by mixing the silver chloride and ammonia in alkaline solution. The capillary is suspended on a bracket with the end of the capillary just touching the liquid surface. The glucose solution with concentration of 0.75% is gradually added and stood for forming silver film. The preparation device is shown in Fig. 3(b). Significantly, the silver film requires being baked at 100°C for 30 minutes to enhance the robustness. Image of the silver-plated capillary is displayed in Fig. 3(c), the silver film can clearly be seen successfully attached to the capillary and the slide used to hold it.

Finally, the fiber taper tip and the cleaved capillary were fixed on the micro displacement platform, and the structure was manually controlled for reaching the bottom of the capillary closely. The demonstration of material object of sensor is displayed in Fig. 3(d). A sealing process with UV glue was also employed in order to enhance the strength of the structure, and at the same time avoid the RI effects (see in Fig. 3(e)).

When light travels from SMF to the TFMF, some high-order core modes are excited within the TFMF due to the core diameter mismatch between the SMF and FMF and the diminution of the FMF. As a result, part of the incident light that propagates in the fiber is reflected by the fiber taper tip-air interface due to the Fresnel reflection [27], whereas the interference fringes can be observed in the reflection spectrum. For the reflected light, by assuming that I1 is the intensity of the fundamental mode and I2 is the higher-order mode intensity, the interference fringe can be modeled by employing the two-beam optical interference equation [28]:

$$I = \left[ {{I_1} + {I_2} + 2\sqrt {{I_1}{I_2}} \cos ({\varphi + {\varphi_0}} )} \right] \cdot R$$
where, ${\varphi _0}$ is the initial phase difference and $\varphi$ is the phase difference between the fundamental mode and the higher-order mode. Moreover, R is the reflectance of the end face. The phase difference can further be written as follows:
$$\varphi = \frac{{2\pi \int {({{n_1}(r )- {n_2}(r )} )dz(r )} }}{\lambda }$$
where n1(r) and n2(r) are the effective indices (RI) of LP01 and LP0m modes, respectively, and $\lambda$ is central wavelength. Additionally, the functions of the local radius r(z) of the microfiber probe at position z can be calculated by a three-layer model of finite cladding step-profile fiber with the microfiber probe profile r(z)[29]. In the temperature measurements, the temperature affects the wavelength and the power variation through variational refractive index of the thermal expansion and thermo-optics effect. According to Eq. (2), the relationship between the wavelength shifts with the temperature variation can be calculated by the following differential equation:
$$\begin{aligned} \frac{{d\lambda }}{{dT}} &= \frac{{2\pi }}{\varphi }\left[ {\frac{{d\left( {\int {({{n_2}(r )- {n_1}(r )} )dz(r )} } \right)}}{{dT}}} \right]\\ &\simeq \frac{{2\pi }}{\varphi }\int {\left[ {\frac{{\partial ({{n_1} - {n_2}} )}}{{\partial n}}{\sigma_T} + \frac{{\partial ({{n_1} - {n_2}} )}}{{\partial r}}{\alpha_T}} \right]} dz \end{aligned}$$
where ${\sigma _T}$= 1.1×10−5 /°C and ${\alpha _T}$= 5.5×10−7 /°C are the thermo-optic and the thermal expansion coefficients of the silica fiber, respectively. By calculation, it is about 30 pm/°C, which indicated that a rising temperature causes a shift in wavelength towards long wavelength (red-shift). Both the thermal-induced taper tips length variation and the thermal-induced index change contribute to the spectrum shift. Thus, the wavelength shift induced by the changes in temperature can be simplified as follows:
$$\Delta {\lambda _T} = {K_{T\lambda }} \cdot \Delta T$$
where ${K_{T\lambda }}$ is the temperature sensitivities of the wavelength, while $\Delta T$ is the temperature variation.

According to the Fresnel reflection, the reflectance is related to the RI of the end [28]. This implies that the reflectance will directly drop down to the value of 0.16% if the sensor is immersed in water, which is not attractive for the measurement of the reflection spectrum. By taking into account the influence of RI, the SMF-TFMF structure is encapsulated within a capillary encapsulation in order to cope with this dilemma. Moreover, the silver-mirror reaction was leveraged in order to produce a silver film coating at the bottom of the capillary and further enhance the reflectivity of the reflected light. The comparisons of reflection spectra of the sensor with and without encapsulation are provided in Fig. 4. More specifically, the normalization reflection spectra sensor with and without the encapsulation is divulged in Fig. 4(a). It can be ascertained that the reflected intensity of the sensor after the encapsulation is stronger than that without one. Additionally, the extinction ratio of the encapsulated sensor is enhanced 4.06 dB and with the maximum extinction ratio of 18.37 dB. The encapsulation has also a certain influence on the free spectrum range (FSR) of the sensor. It is interested to notice that the FSR of the sensor with and without encapsulation are 94.86 nm and 92.78 nm, respectively. In order to further analyze the components of the excited modes in the interference spectrum, Fast Fourier transform (FFT) was implemented to the reflection spectrum, while the spatial frequency spectrum acquired is displayed in Fig. 4(b). As far as the spatial frequency spectrum is concerned, only one dominating peak is observed, which indicates that interference mainly originates from the fundamental modes. Besides, a peak with a higher frequency can be observed, which indicates that a strong higher-order mode is excited and evolved in interference. On top of that, the two spatial frequency spectra almost coincide, which illustrates that the encapsulation does not have a significant impact on the interference components.

 figure: Fig. 4.

Fig. 4. (a) Reflection spectra of the sensor with or without encapsulation. (b) Spatial frequency spectrum with or without encapsulation.

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Based on the Beckmann scattering theory [30,31], the most important contribution of the reflected light is the reflection of the specular light. Assuming that the silver film is set up at a distance d from the fiber tip, the radiated power Pi is expressed as a function of the intensity distribution I(r, 2d) on the plane surface at a distance of 2d from the fiber tip by applying the following equation [32]:

$${P_i} = \int\limits_0^R {\int\limits_0^{2\pi } {I({r,2d} )} } rd\phi dr$$
where r is the distance from the fiber tip axis, ф is the azimuth angle, and R is the radius of the light cone at a 2d distance. With the same numerical aperture (NA) and diameter, the power of the reflected light that can be received is only related to the radiated power Pi, the reflectivity δ, as well as the distance of the silver film d. Hence, the power of the reflected light PR can be written as a function of the following components:
$${P_R} = f({{P_i},\delta ,d} )$$

We perform a numerical simulation to explain this process, and the model is shown in Fig. 5(a). During the liquid level measurements, the water pressure will bring the fiber taper tips closer to the bottom of the capillary owing to the elastic deformation of UV glue (seen in Fig. 5(b)), which implies that the distance between the fiber taper tips and the silver film decreases, and the corresponding power will be increased. Figure 5(c) and Fig. 5(d) discloses the transmission and reflection of light through the silver film, respectively. In particular, from Fig. 5(d), we can observe that when the tip is close to the silver film, and the received light will be stronger. By using the solid-mechanics module for simulation, we obtained the variation of the displacement field at the fiber tip when the liquid level was in a variation of 5 mm-30 mm (corresponding to the water pressure from 50 Pa to 300 Pa). And the obtained relationship is shown in Fig. 6, which confirms that the water pressure was in a function of linear relationship with the micro displacement of the fiber tip.

 figure: Fig. 5.

Fig. 5. Schematic diagram of distance change between fiber tip and silver film caused by water pressure. (a) The numerical simulation model. (b) Diagram of the model variation when water pressure is applied. The transmission(c) and reflection(d) of light through the silver film.

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 figure: Fig. 6.

Fig. 6. Relationship between the water pressure and the distance between the end of the fiber and the bottom of the capillary.

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According to Eq. (6), the changing power can be simplified as follows:

$$\Delta {P_L} = {K_{LP}} \cdot \Delta L$$

Here, $\Delta L$ is the liquid level variation, and ${K_{LP}}$ is the liquid level sensitivity. Similarly, thermal expansion caused by temperature changes will also cause corresponding power changes:

$$\Delta {P_T} = {K_{TP}} \cdot \Delta T$$
where the ${K_{TP}}$ is the temperature sensitivity. Therefore, the liquid level can be measured by monitoring the power variation, whereas the temperature can be estimated by monitoring the fringe shift induced by the phase-difference modification.

3. Experiment results and discussion

The schematic diagram of the experimental setup is represented in Fig. 7. A broadband source (BBS) (YANGTZE SOTON LASER, SC-5-FC) ranging from 1350 nm to 1650 nm is used. The light emitted from the BBS source is directly injected into the sensing structure through port 1 of the circulator and outputting from port 2. Consequently, the light passes through the sensing structure and part of it is reflected back from port 3. An optical spectrum analyzers (OSA) (YOKOGAWA, AQ6370C) is employed in order to measure the reflection spectrum of the sensor. The experimental for measuring both the temperature and the liquid level is depicted in Figs. 7(a) and 7(b), respectively.

 figure: Fig. 7.

Fig. 7. Schematic diagram of the experimental setup for performing (a) temperature and (b) liquid level measurements, respectively.

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A rectangular container with a side hole was designed within the liquid level measurement, which was connected by a hose to a large range syringe (see in Fig. 7(b)). The liquid level response of the sensor was characterized by increasing the water level in the container slowly with levels ranging from 5 mm to 30 mm, whereas an interval of 5 mm was selected. When the level is stable for several minutes, the reflection spectra are recorded. Figure 8 highlights the wavelength shift and the power rising as the increase of the liquid level. It can be ascertained in Fig. 9, the two dips in front of the interference pattern behave as a good linear. It is demonstrated that the liquid level maximum sensitivity of the device is 0.106 dB/mm. Due to the low sensitivity and the linear fit of the Dip3, subsequent experiments focused on the analysis of both the Dip1 and the Dip2.

 figure: Fig. 8.

Fig. 8. (a) Reflection spectra to the liquid level. (b) Dip1, (c) Dip2, and (d) Dip3.

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 figure: Fig. 9.

Fig. 9. Distribution of the (a) wavelength and (b) power responses of Dip1 to Dip3 to the liquid level.

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In the temperature measurement experiments, a water bath (HWS-12, resolution of 0.1 °C) is used and the entire sensing structure is immersed within the bath at least 20 min (seen in Fig. 7(a)). The applied temperature ranges from 28 °C to 56 °C with an interval of 4 °C. Take into account the thermal equilibrium, the transmission spectra are collected when the temperature achieved the target value after 15 minutes. In addition, the reflection spectrum shift with the temperature is divulged in Fig. 10. It is observed that the spectrum presented a red-shift behavior and power rise as the temperature enhanced. The wavelength response characteristics of the dips (Dip1 and Dip2) are displayed in Fig. 11, where it can be observed that the dips disclose good linearity as a function of the temperature. Moreover, the measured wavelength sensitivities of Dip1 and Dip2 are 29 pm/°C, 35 pm/°C, respectively, whereas the corresponding power sensitivity reaches the values of 0.018 dB/°C, 0.029 dB/°C, respectively.

 figure: Fig. 10.

Fig. 10. Reflection spectra acquired under enforcing various temperatures. (a) Dip1. (b) Dip2.

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 figure: Fig. 11.

Fig. 11. Wavelength and power responses of (a) Dip1 and (b) Dip2 as a function of the temperature.

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According to the above-mentioned results, the dips exhibit different responses to the liquid level and temperature, which indicates that it is possible to implement simultaneous measurement by using the wavelength and the power responses of one dip. Thus, the sensitivity coefficient matrix [33] based on Eq. (4), Eq. (7) and Eq. (8) can be established as follows:

$$\left[ \begin{array}{c} \Delta \lambda \\ \Delta P \end{array} \right]\textrm{ = }\left[ {\begin{array}{cc} {{K_{L\lambda }}}&{{K_{T\lambda }}}\\ {{K_{L\textrm{P}}}}&{{K_{T\textrm{P}}}} \end{array}} \right]\left[ {\begin{array}{c} {\Delta L}\\ {\Delta T} \end{array}} \right]$$
where, ${K_{L\lambda }}$ and ${K_{LP}}$ are the liquid level sensitivity coefficients, and ${K_{T\lambda }}$ and ${K_{TP}}$ are the temperature sensitivity coefficients, respectively. Thus, the liquid level and temperature can be obtained simultaneously by using the following matrix equation:
$$\left[ {\begin{array}{c} {\Delta L}\\ {\Delta T} \end{array}} \right]\textrm{ = }\frac{\textrm{1}}{D}\left[ {\begin{array}{cc} {{K_{T\textrm{P}}}}&{ - {K_{T\lambda }}}\\ { - {K_{L\textrm{P}}}}&{{K_{L\lambda }}} \end{array}} \right]\left[ \begin{array}{c} \Delta \lambda \\ \Delta P \end{array} \right]$$
where $D = {K_{L\lambda }}{K_{TP}} - {K_{T\lambda }}{K_{LP}}$. According to the above experimental results of the Dip1 and Dip2, Eq. (10) can be rewritten as follows:
$$\begin{aligned} \left[ {\begin{array}{c} {\Delta L}\\ {\Delta T} \end{array}} \right] &= - \frac{\textrm{1}}{{3.045}}\left[ {\begin{array}{cc} {0.018}&{ - 29}\\ { - 0.105}&0 \end{array}} \right]\left[ \begin{array}{l} \Delta \lambda \\ \Delta P \end{array} \right]\\ \left[ {\begin{array}{c} {\Delta L}\\ {\Delta T} \end{array}} \right] &= - \frac{\textrm{1}}{{3.710}}\left[ {\begin{array}{cc} {0.029}&{ - 35}\\ { - 0.106}&0 \end{array}} \right]\left[ \begin{array}{c} \Delta \lambda \\ \Delta P \end{array} \right] \end{aligned}$$

Therefore, the simultaneous liquid level and temperature measurement can be realized based on Eq. (11). By considering the minimum resolution of 0.02 nm of OSA, the resolution of the temperature of the proposed sensor can reach the value of 0.57 °C.

Furthermore, we conducted the stability test and the repeatability test on the sensor. The sensor was placed in the water bath under constant liquid level of 20 mm for a long-time measurement, and temperature was controlled at 26 °C. With an interval of 10 minutes and duration of 90 minutes, the stability of wavelength and power obtained is shown in Figs. 12(a) and 12(b), respectively. Meanwhile, repeated tests on liquid level and temperature with rising and reducing were carried out which is disclosed in Figs. 12(c) and 12(d), respectively. The conclusion is that the sensor has good stability and repeatability.

 figure: Fig. 12.

Fig. 12. (a) The wavelength and the (b) power shift of dips of the sensor as a function of time within 1.5 hours at liquid level of 20 mm and temperature of 26°C. (c) The relationship between the power and the liquid level, and (d) the relationship between the wavelength, power and the temperature.

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Table 1 presents a comparison of the sensing performances with the existing results in liquid level measurements. In striking contrast to the existing outcomes, the proposed SMF-TFMF (silver-gilt capillary) sensing configuration can measure both temperature and liquid level simultaneously, whereas the liquid level and temperature sensitivities can reach the outstanding values of 0.106 dB/mm and 0.029 dB/°C, 35 pm/°C, respectively. On top of that, compared with other reported sensing elements, the measurement of only one resonant dip from the proposed sensor is sufficient in order to achieve the dual-parameter estimation, reducing thus significantly the range of wavelength measurement. In summary, the sensor of proposing illustrated the advantages of enhanced stability, low cost, short-wavelength measurement range, and dual-parameter measurement.

Tables Icon

Table 1. Performance comparison of the reported liquid level sensors.

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4. Conclusions

In this work, an in-line reflective dual-parameter fiber-optic sensor is experimentally demonstrated for simultaneous measurement of both the liquid level and the temperature. The sensor is composed of FMF taper tips and capillary tubes with silver-gilt. According to the extracted responses of the power and wavelength modifications of one resonant dip, both liquid level and temperature simultaneous measurement can be realized. The acquired sensitivities of the liquid level and temperature can reach up to the values of 0.106 dB/mm and 35 pm/°C, 0.029 dB/°C, respectively. The sensor possesses also the advantages of improved stability, low cost, short-wavelength measurement range, and dual-parameter measurement, which are of great importance for applications where both temperature and liquid level measurements are required.

Funding

National Natural Science Foundation of China (62165002); Guangxi Key Research and Development Program (AB18221033); Guangxi One Thousand Young and Middle-aged College and University Backbone Teachers Cultivation Program and Innovation Project of Guangxi Graduate Education (YCSW2020098).

Disclosures

The authors declare no conflicts of interest.

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

References

1. B. Jin, Z. Zhang, and H. Zhang, “Structure design and performance analysis of a coaxial cylindrical capacitive sensor for liquid-level measurement,” Sens. Actuators, A 223, 84–90 (2015). [CrossRef]  

2. S. W. Wang, C. C. Chen, C. M. Wu, and C. M. Huang, “A continuous water-level sensor based on load cell and floating pipe//2018,” 2018 IEEE International Conference on Applied System Invention (ICASI). IEEE : 151–154.

3. J. R. Hanni and S. K. Venkata, “A novel helical electrode type capacitance level sensor for liquid level measurement,” Sens. Actuators, A 315, 112283 (2020). [CrossRef]  

4. N. Cennamo, F. Arcadio, L. Noel, L. Zeni, and O. Soppera, “Flexible and Ultrathin Metal-Oxide Films for Multiresonance-Based Sensors in Plastic Optical Fibers,” ACS Appl. Nano Mater. 4(10), 10902–10910 (2021). [CrossRef]  

5. J. Y. Huang, J. Van Roosbroeck, A. Bueno Martinez, T. Geernaert, F. Berghmans, C. Caucheteur, B. Van Hoe, E. Lindner, and J. Vlekken, “Fiber Bragg grating sensors written by femtosecond laser pulses in micro-structured fiber for downhole pressure monitoring//2017,” 2017 25th Optical Fiber Sensors Conference (OFS). IEEE: 1–4.

6. J. Li, K. Liao, X. Kong, S. Li, X. Zhang, X. Zhao, and C. Sun, “Nuclear power plant prestressed concrete containment vessel structure monitoring during integrated leakage rate testing using fiber Bragg grating sensors,” Appl. Sci. 7(4), 419 (2017). [CrossRef]  

7. D. Sengupta, M. Sai Shankar, and P. Saidi Reddy, “Sai Prasad R L N & Srimannarayana K., Sensing of hydrostatic pressure using FBG sensor for liquid level measurement,” Microw. Opt. Technol. Lett. 54(7), 1679–1683 (2012). [CrossRef]  

8. M. Shao, X. Qiao, X. Zhao, Y. Zhang, and H. Fu, “Liquid level sensor using fiber Bragg grating assisted by multimode fiber core,” IEEE Sens. J. 16(8), 2374–2379 (2016). [CrossRef]  

9. W. Xu, J. Wang, J. Zhao, C. Zhang, J. Shi, X. Yang, and J. Yao, “Reflective liquid level sensor based on parallel connection of cascaded FBG and SNCS structure,” IEEE Sens. J. 17(5), 1347–1352 (2017). [CrossRef]  

10. H. Y. Chang, Y. C. Chang, H. J. Sheng, M. Y. Fu, W. F. Liu, and R. Kashyap, “An ultra-sensitive liquid-level indicator based on an etched chirped-fiber Bragg grating,” IEEE Photonics Technol. Lett. 28(3), 268–271 (2016). [CrossRef]  

11. B. Gu, W. Qi, Y. Zhou, Z. Wu, P. P. Shum, and F. Luan, “Reflective liquid level sensor based on modes conversion in thin-core fiber incorporating tilted fiber Bragg grating,” Opt. Express 22(10), 11834–11839 (2014). [CrossRef]  

12. M. Zhang, R. Yu, Y. Du, J. Zou, and L. Wang, “Liquid-level sensor based on reflective mechanically induced long-period grating using double-cladding fiber,” IEEE Sens. J. 18(23), 9568–9575 (2018). [CrossRef]  

13. M. Zhang, Z. Hu, X. Wang, L. Xue, L. Xue, J. Zou, Y. Du, and L. Wang, “Power-type liquid-level sensor for high refractive index liquid based on long-period fiber grating,” Sens. Actuators, A 324, 112652 (2021). [CrossRef]  

14. J. Martins, C. A. R. Diaz, M. F. Domingues, R. A. Ferreira, P. Antunes, and P. S. André, “Low-cost and high-performance optical fiber-based sensor for liquid level monitoring,” IEEE Sens. J. 19(13), 4882–4888 (2019). [CrossRef]  

15. D. Jauregui-Vazquez, M. E. Gutierrez-Rivera, D. F. Garcia-Mina, J. M. Sierra-Hernandez, E. Gallegos-Arellano, J. M. Estudillo-Ayala, J. C. Hernandez-Garcia, and R. Rojas-Laguna, “Low-pressure and liquid level fiber-optic sensor based on polymeric Fabry-Perot cavity,” Opt. Quantum Electron. 53(5), 237 (2021). [CrossRef]  

16. X. Liang, G. Ren, Y. Li, Z. Liu, H. Wei, and S. Jian, “In-fiber liquid-level probe based on Michelson interferometer via dual-mode elliptical multilayer-core fiber,” J. Mod. Opt. 63(13), 1–6 (2016). [CrossRef]  

17. D. Feng, M. Liu, W. Feng, and B. Li, “Michelson liquid-level sensor based on cascaded no-core fiber and single-mode fiber structure,” Optik 206, 163746 (2020). [CrossRef]  

18. Y. Cui, B. Sun, W. Zheng, and Z. Zhang, “Level measurement for high-RI liquids based on the self-imaging effect in no-core fibers,” Opt. Commun. 483, 126615 (2021). [CrossRef]  

19. P. Roldán-Varona, R. A. Pérez-Herrera, L. Rodríguez-Cobo, L. Rodríguez-Cobo, L. Reyes-González, M. López-Amo, and J. M. López-Higuera, “Liquid level sensor based on dynamic Fabry-Perot interferometers in processed capillary fiber,” Sci. Rep. 11(1), 3039 (2021). [CrossRef]  

20. R. Fan, Q. Ma, L. Li, Y. Zhuo, J. Shen, Z. Ren, H. Chen, and B. Peng, “Liquid level and refractive index double-parameter sensor based on tapered photonic crystal fiber,” J. Lightwave Technol. 38(14), 3717–3722 (2020). [CrossRef]  

21. C. Li, T. Ning, C. Zhang, J. Li, X. Wen, L. Pei, X. Gao, and H. Lin, “Liquid level measurement based on a no-core fiber with temperature compensation using a fiber Bragg grating,” Sens. Actuators, A 245, 49–53 (2016). [CrossRef]  

22. O. F. Ameen, M. H. Younus, M. S. Aziz, A. I. Azmi, R. R. Ibrahim, and S. K. Ghoshal, “Graphene diaphragm integrated FBG sensors for simultaneous measurement of water level and temperature,” Sens. Actuators, A 252, 225–232 (2016). [CrossRef]  

23. C. A. R. Díaz, A. G. Leal-Junior, P. S. B. Andre, P. F. Antunes, M. J. Pontes, A. Frizera-Neto, and M. R. N. Ribeiro, “Liquid level measurement based on FBG-embedded diaphragms with temperature compensation,” IEEE Sens. J. 18(1), 193–200 (2018). [CrossRef]  

24. S. Choi, J. Kim, S. L. Lee, M. S. Kim, D. K. Kim, J. Han, and Y. W. Lee, “Simultaneous Measurement of liquid level and temperature using in-fiber grating-based Mach-Zehnder interferometer and faraday rotator mirror,” J. Nanosci. Nanotechnol. 21(3), 2024–2031 (2021). [CrossRef]  

25. W. Zhang, X. Wu, G. Zhang, J. Shi, C. Zuo, S. Fang, L. Gui, and B. Yu, “An inline Mach-Zehnder interferometer for simultaneously measuring liquid level and temperature,” Opt. Fiber Technol. 63, 102501 (2021). [CrossRef]  

26. H. Zhang, H. Zhanga, L. Hou, M. Zhang, and J. Yang, “Self-Temperature compensated fiber-optic liquid level sensor with ultra-long linear range using quasi-single modal interferometer,” 2021, IEEE Sensors Journal. In press.

27. Z. Liu, X. Qiao, and R. Wang, “Miniaturized fiber-taper-based Fabry–Perot interferometer for high-temperature sensing,” Appl. Opt. 56(2), 256–259 (2017). [CrossRef]  

28. J. Zhou, Y. Wang, C. Liao, B. Sun, J. He, G. Yin, S. Liu, Z. Li, G. Wang, X. Zhong, and J. Zhao, “Intensity modulated refractive index sensor based on optical fiber Michelson interferometer,” Sens. Actuators, B 208, 315–319 (2015). [CrossRef]  

29. J. L. Kou, J. Feng, L. Ye, F. Xu, and Y. Q. Lu, “Miniaturized fiber taper reflective interferometer for high temperature measurement,” Opt. Express 18(13), 14245–14250 (2010). [CrossRef]  

30. P. Beckmann and A. Spizzichino, The scattering of electromagnetic waves from rough surfaces. Pergamon, New York, 1963.

31. J. C. Leader, “Multiple scattering of electromagnetic waves from rough surfaces,” Optical Society of America Annual Meeting, 1970.

32. A. Suhadolnik, A. Babnik, and J. Možina, “Optical fiber reflection refractometer,” Sens. Actuators, B 29(1-3), 428–432 (1995). [CrossRef]  

33. R. M. André, C. R. Biazoli, S. O. Silva, M. B. Marques, C. M. Cordeiro, and O. Frazão, “Strain-temperature discrimination using multimode interference in tapered fiber,” IEEE Photonics Technol. Lett. 25(2), 155–158 (2013). [CrossRef]  

34. J. Ning, “Liquid level measurement based on multi-S-bend plastic optical fiber,” Sens. Rev. 39(4), 522–524 (2019). [CrossRef]  

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (12)
Fig. 1.
Fig. 1. Schematic diagram and operating mechanism of the proposed sensing structure.

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Fig. 2.
Fig. 2. The fabrication process of the sensor. (a) SMF and FMF are fused by discharge in order to form the (b) SMF-FMF structure, then by translating the SMF-FMF and discharge the fiber tip to form (c) SMF-TFMF structure. (d) The glass capillary is plated with silver and (e) the SMF structure is slowly inserted into the interior of the capillary. (f) Finally, glue is used in order to seal the structure.

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Fig. 3.
Fig. 3. (a) Microscope image of the SMF-TFMF structure. (b) Pictures of the silvering process and (c) silver-plated capillary. (d) Physical display of the sensor and (e) the larger version of the sealing part.

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Fig. 4.
Fig. 4. (a) Reflection spectra of the sensor with or without encapsulation. (b) Spatial frequency spectrum with or without encapsulation.

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Fig. 5.
Fig. 5. Schematic diagram of distance change between fiber tip and silver film caused by water pressure. (a) The numerical simulation model. (b) Diagram of the model variation when water pressure is applied. The transmission(c) and reflection(d) of light through the silver film.

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Fig. 6.
Fig. 6. Relationship between the water pressure and the distance between the end of the fiber and the bottom of the capillary.

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Fig. 7.
Fig. 7. Schematic diagram of the experimental setup for performing (a) temperature and (b) liquid level measurements, respectively.

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Fig. 8.
Fig. 8. (a) Reflection spectra to the liquid level. (b) Dip1, (c) Dip2, and (d) Dip3.

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Fig. 9.
Fig. 9. Distribution of the (a) wavelength and (b) power responses of Dip1 to Dip3 to the liquid level.

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Fig. 10.
Fig. 10. Reflection spectra acquired under enforcing various temperatures. (a) Dip1. (b) Dip2.

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Fig. 11.
Fig. 11. Wavelength and power responses of (a) Dip1 and (b) Dip2 as a function of the temperature.

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Fig. 12.
Fig. 12. (a) The wavelength and the (b) power shift of dips of the sensor as a function of time within 1.5 hours at liquid level of 20 mm and temperature of 26°C. (c) The relationship between the power and the liquid level, and (d) the relationship between the wavelength, power and the temperature.

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Tables (1)

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Table 1. Performance comparison of the reported liquid level sensors.

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Equations (11)

Equations on this page are rendered with MathJax. Learn more.

I = [ I 1 + I 2 + 2 I 1 I 2 cos ⁡ ( φ + φ 0 ) ] ⋅ R
φ = 2 π ∫ ( n 1 ( r ) − n 2 ( r ) ) d z ( r ) λ
d λ d T = 2 π φ [ d ( ∫ ( n 2 ( r ) − n 1 ( r ) ) d z ( r ) ) d T ] ≃ 2 π φ ∫ [ ∂ ( n 1 − n 2 ) ∂ n σ T + ∂ ( n 1 − n 2 ) ∂ r α T ] d z
Δ λ T = K T λ ⋅ Δ T
P i = ∫ 0 R ∫ 0 2 π I ( r , 2 d ) r d ϕ d r
P R = f ( P i , δ , d )
Δ P L = K L P ⋅ Δ L
Δ P T = K T P ⋅ Δ T
[ Δ λ Δ P ]  =  [ K L λ K T λ K L P K T P ] [ Δ L Δ T ]
[ Δ L Δ T ]  =  1 D [ K T P − K T λ − K L P K L λ ] [ Δ λ Δ P ]
[ Δ L Δ T ] = − 1 3.045 [ 0.018 − 29 − 0.105 0 ] [ Δ λ Δ P ] [ Δ L Δ T ] = − 1 3.710 [ 0.029 − 35 − 0.106 0 ] [ Δ λ Δ P ]
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