Low-cost Optical Fiber Sensor Research Articles

Prospects for Developing Low-Cost Optical Fiber Sensors for Liquid-Liquid Interface Detection

This work examines the prospects of a low-cost retroreflection optical sensor system for detection of the interface between two immiscible liquids, for applications in oil separation tanks. The sensor in its simplest configuration comprises a bare fiber optic tip, cleaved at an angle of 90º relative to the longitudinal fiber axis. The device tested experimentally is based on a 2x2 bidirectional coupler, which connects the sensor tip to a laser and two photodetectors, one used to measure the signal and the other as a reference. From experiments conducted in a laboratory wateroil system, the measured retro-reflected signal was very small, and of the same order as the differential signal due to low optical contrast liquids. To overcome this difficulty, the detection system was designed with an amplification stage, followed by filtering of the digitally converted signal. With this strategy, an accuracy of 99.7% was reached. On the light of the performance measured by the bare fiber tip configuration, an analysis on the potential improvement in performance obtained, by applying a thin layer of gold to the tip of the sensor, was made. Simulated results indicated that, for an optimized gold film, 13 nm thick, a 13fold improvement in the sensor detection limit is obtained.

Refractive index and temperature measurement by cascading macrobending fiber and a sealed alternated SMF-MMF structure

A simple and low-cost optical fiber sensor is proposed for simultaneous measurement of refractive index (RI) and temperature. The sensor is constructed by cascading a sealed long period fiber grating (LPFG) structure and a macrobending fiber with a certain bending radius. The LPFG structure is fabricated by fusing the single-mode and multimode fiber sections in series and sealed in a thermal shrinkable tube to increase its temperature sensitivity. Two obvious resonance dips in the transmission spectrum are observed for the sensor, which could realize the simultaneous measurement of RI and temperature. Experimental results show that the proposed sensor has a high RI sensitivity of 165.04 nm/RIU in the RI range of 1.335–1.38, and a high temperature sensitivity of −255.52 pm/∘C for the temperature range of 35–80 °C.

High-sensitivity temperature sensor based on single-mode fiber for temperature-measurement application in the ocean

A high-sensitivity and low-cost optical fiber sensor for seawater temperature sensing is designed and fabricated. The large core-offset splicing sensing structure was made of single-mode fiber only. To fabricate the sensing structure precisely with a length deviation <10 μm, the relative fabrication equipment was designed and assembled. Temperature measurement experiment of the sensor was performed in a seawater bath. Also, the experimental results show that redshift of the wavelength occurs with the increase of external temperature. Its temperature response curve conforms to the quadratic curve. The temperature sensitivity can reach up to 2.293 nm/°C, and the fitting degree is up to 0.9998. Moreover, the excellent repeatability of our sensor has been verified. The sensor has great potential to measure the temperature in the ocean.

Dual-Parameters Optical Fiber Sensor With Enhanced Resolution Using Twisted MMF Based on SMS Structure

A compact and low cost optical fiber sensor by introducing higher order modes interference with fiber twisting based on single-mode-multimode-single-mode structure is proposed and demonstrated for simultaneous measurement of strain and temperature. The sensor is fabricated by heating and twisting a section of multimode fiber (MMF), which is spliced between two single-mode fibers. By adjusting the heating temperature and rotate speed during fabrication, the twisted region is introduced in MMF, which is able to couple more power of light into the cladding and introduce higher order modes in modal interferences. With this method, strain sensitivity of -7 and -2.19 pm/με as well as temperature sensitivity of 17.33 and 13 pm/°C are obtained. By spatial frequency demodulation method, measurement resolution reaches ±2.14 με and ±0.89 °C, which has great potential in dual-parameters measurement of temperature and strain with high resolution.

Carotid distension waves acquired with a fiber sensor as an alternative to tonometry for central arterial systolic pressure assessment in young subjects

Abstract In this work it is evaluated the possibility of central blood pressure assessment using distension waves, obtained with a low cost optical fiber sensor, instead of regular arterial tonometry. Carotid distension and pressure waveforms were acquired in 15 young subjects. Form factors, root-mean-square error (RMSE), harmonic decomposition and central systolic pressures for both techniques were analysed. The pressure waves assessed by the piezoelectric probe had lower form factors than the ones assessed by the optical fiber sensor, due to the different nature of the waves (51.05 ± 5.15% versus 40.53 ± 5.70%), translating in a RMSE of 14 ± 2%. Regarding the harmonic analysis, paired t -tests shown that the first four harmonics are not significant different (p ⩽ 0.05), and Pearson correlation studies retrieve that the 2nd–7th harmonics are correlated (p ⩽ 0.03). Central systolic pressures were also obtained with both techniques displaying a very strong Pearson correlation (0.99) and a small difference of 0.63 ± 2.40 mmHg. These pre-clinical results support a future clinical validation study in larger and broader cohorts.

Optrode Based Polymer for the Estimation of Free Chlorine

This paper describes the construction of low cost optical fiber sensor for the measurement of free chlorine and also residuals. The granules of poly (norborene) s bound with Cyanuric acid are synthesized as polymer film and applied on glass surface, which is used as sensing membrane. The prepared sensor membrane has a good photochemical stability and it would not leach out by continuous exposure to sample solution. The film is used to measure the changes in the absorbance intensity as a result of reaction between Cyanuric acid and free chlorine. The chlorine is used for the destruction of microbiological pathogens to protect the public health from water-borne diseases. This experiment was conducted for various chlorine samples. The sensor possess good repeatability with the range from 1.0 mg/l to 9.0 mg/l with minimal response time and also shows the characteristics such as reproducibility and stable results for more than 70 samples with a period of 5 days.

Design and development of low-cost optical-fiber sensors for temperature metrology: Process monitoring of an epoxy resin system

This article reports the design and deployment of two optical-fiber temperature sensors based on the fiber Fabry–Perot etalon. The first involved the use of an extrinsic fiber Fabry–Perot sensor, but in this instance, the coefficient of thermal expansion of the reflector and/or capillary was chosen to offer a mismatch. Hence, the cavity length could increase or decrease according to the coefficient of thermal expansion of the fiber and/or capillary. For comparison, single-mode and multimode optical-fiber Bragg gratings were also used as temperature sensors. The Fabry–Perot sensors operated from −50 to 410°C. The accuracy of the measurements was up to ±0.5°C with a low-cost charged-coupling-device spectrometer. The sensors also worked effectively in a microwave oven and in a composite panel in an autoclave. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 83–95, 2004

Detection of volatile organic compound vapors by using a vapochromic material on a tapered optical fiber

A low-cost optical fiber sensor to detect volatile organic compounds has been developed. Changes of up to 13.5 dB in the transmitted optical power have been detected with different concentrations of acetone and dichloromethane vapors. The device uses a standard single-mode fiber. The sensing mechanism relies on a vapor-induced refractive index change in a film of a vapochromic material deposited on the thinner region of a tapered fiber.