In this paper, a dual-parameter liquid level and refractive index (R.I.) sensor is fabricated using three pieces of bare polymer optical fibers (POFs), which can independently and simultaneously sense the liquid level and R.I. The proposed sensor design utilizes the twisted coupling technique, in which two optical fibers are twisted and coupled with macro-bending. The liquid level measurement depends on the coupling loss, where the light is transmitted to emission fiber (EF) and twisted with coupled acceptor fiber (AF). The proposed liquid level sensor can measure depths up to 125 mm with a sensitivity of 8.03 nW/mm. Moreover, R.I. sensing depends on the twisted coupled macro-bending (TCMB) technique, where the EF generates bend loss and the AF couples the loss, where the coupled power varies due to the transformation in R.I. of coupling medium. The R.I. sensor revealing a notable sensitivity of -2663%/RIU and an impressive resolution of 3.754 × 10⁻⁴ in the different NaCl-saturated liquids featuring R.I. range extending from 1.333 to 1.361. The experimental findings indicate the sensor exhibits excellent stability and reliability. The sensor’s straightforward, comprehensive, and cost-effective design enables its application in chemical, petroleum, and other industries.

This study introduces a cost-effective solution and sensor arrays for the multipoint liquid-level measuring sensor based on an intensity modulation technique. The sensor structure is based on the twisting of two fibers and creates cascading to achieve a multipoint detection. Three sensors are fabricated on a single illuminated polymer optical fiber. The twisting creates side-coupling between two fibers, and the coupled power is attenuated when liquid emerges in the coupled region. Each sensor has its own output source, which is connected to the power meter. When the liquid-level increases, the coupled power is continuously decreased. The multipoint liquid-level sensor is theoretical and experimentally tested. The experimental results show that sensors have a good response and linearity. The sensors are able to measure the liquid-level up to 12 cm and have a sensitivity of about 0.2726 μW/cm, 0.1715 μW/cm, and 0.1281 μW/cm, respectively. The different flow rate (50 mL/min–300 mL/min) is also analyzed to validate the dynamic response of the sensor. The sensor demonstrates a high sensitivity and resolution in the liquid-level detection. Meanwhile, the liquid-level variation is individually and simultaneously measured. The system does not require any decoupling technique as the system relies on a single LED source, and the coupled power is individually measured from each power meter. The system represents a significant advancement in precise liquid-level sensing technology, as the system has advantages of a flexible, durable, cost-effective, and active response with respect to changes in the liquid-level.

This paper presents a portable optical fiber sensor (OFS) design for continuous liquid level measurement, fabricated using two pieces of bare polymer optical fibers (POFs). The proposed sensor design utilizes the twisted coupling technique, where two optical fibers are twisted and coupled, leading to power coupling from the illumination fiber to the coupled fiber. The casing is fabricated through a 3D printing method. The 3D-printed casing is utilized to mount the sensor onto a smartphone, facilitating the connection of the fibers to both the flashlight and the camera. The flashlight serves as the light source, while the camera records the intensity variations. The liquid level sensing relies on the coupling loss, where the light is transmitted to the illumination fiber, and the twisted coupled fiber couples the power, exhibiting intensity variations with changing liquid levels. The proposed liquid level sensor can measure depths up to 120 mm with a sensitivity of 0.053 ± 0.002 % per mm and an impressive resolution of 0.05 mm. The experimental findings indicate that the proposed sensor has excellent stability and reliability. The sensor’s straightforward, comprehensive, and cost-effective design enables its application in chemical, petroleum, and many other industries.

This paper presents a portable dual-point optical fiber sensor system for continuous liquid level measurement using polymer optical fibers (POFs). The system contains sensor design and integration with smartphone. The sensor design employs a twisted coupling technique, where two bare optical fibers are twisted together, allowing power to transfer from the illumination fiber to the coupled fiber. The 3D-printed casing mounts into smartphone where the sensor system is attached to casing. The light is launched from the smartphone's flashlight and next end of fiber is to the camera. The flashlight serves as the light source, and the camera records intensity variations caused by changes in the liquid level. Experimental results demonstrate a linear response in optical power intensity as liquid levels increase, allowing for precise measurement of levels up to 120 mm simultaneously. Sensor-1 achieved a sensitivity of 0.050%/mm and sensor-2 exhibited a sensitivity of 0.033%/mm, with a resolution of 0.05 mm. Both sensors showed stable and consistent performance during ascent and descent phases of liquid level measurement. This cost-effective, portable sensor system offers high accuracy and reliability, making it suitable for industrial applications such as chemical processing and environmental monitoring.