Analysis of a distributed fiber-optic temperature sensor using single-photon detectors

We demonstrate a high-accuracy distributed fiber-optic temperature sensor using superconducting nanowire single-photon detectors and single-photon counting techniques. Our demonstration uses inexpensive single-mode fiber at standard telecommunications wavelengths as the sensing fiber, which enables extremely low-loss experiments and compatibility with existing fiber networks. We show that the uncertainty of the temperature measurement decreases with longer integration periods, but is ultimately limited by the calibration uncertainty. Temperature uncertainty on the order of 3 K is possible with spatial resolution of the order of 1 cm and integration period as small as 60 seconds. Also, we show that the measurement is subject to systematic uncertainties, such as polarization fading, which can be reduced with a polarization diversity receiver

A fiber-optic current sensor for aerospace applications

A robust, accurate, broad-band, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low and high voltage 60 Hz terrestrial power systems and in 400 Hz aircraft systems. It is intrinsically electromagnetic interference (EMI) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a novel fiber-optic temperature sensor embedded in the sensing head. The technology contained in the sensor is examined and the results of precision tests conducted at various temperatures within the wide operating range are given. The results of early EMI tests are also given

Strain Sensor Based on a Pair of Single-Mode-Multimode-Single-Mode Fiber Structures in a Ratiometric Power Measurement Scheme

The strain and temperature dependencies of a step-index single-mode–multimode–single-mode (SMS) fiber structure are investigated numerically and experimentally. For intensity-based strain measurement using a single SMS fiber structure, at a selected wavelength, it is found that there is a high strain dependence, but also a temperature dependence that will induce strain measurement error. To minimize the temperature-induced strain measurement error, two SMS fiber structures are proposed and demonstrated in a ratiometric power measurement scheme; one SMS structure acts as the strain sensor, and the other SMS structure acts as the temperature monitor. The extracted temperature information is used to determine a strain value based on a suitable calibration of strain responses with temperature variations. It is demonstrated that for strain measurement from 0 to 1000 με within the temperature range from 10°C to 40°C, the proposed configuration can provide a strain and temperature resolution of 0:34 με and 0:14°C, respectively, with a temperature-induced strain measurement error as low as 0:39 με

Fiber Loop Ringdown — a Time-Domain Sensing Technique for Multi-Function Fiber Optic Sensor Platforms: Current Status and Design Perspectives

Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and small volume of fluids. In FLRD, optical losses of a light pulse in a fiber loop induced by changes in a quantity are measured by the light decay time constants. FLRD measures time to detect a quantity; thus, FLRD is referred to as a time-domain sensing technique. FLRD sensors have near real-time response, multi-pass enhanced high-sensitivity, and relatively low cost (i.e., without using an optical spectral analyzer). During the last eight years since the introduction of the original form of fiber ringdown spectroscopy, there has been increasing interest in the FLRD technique in fiber optic sensor developments, and new application potential is being explored. This paper first discusses the challenging issues in development of multi-function, fiber optic sensors or sensor networks using current fiber optic sensor sensing schemes, and then gives a review on current fiber optic sensor development using FLRD technique. Finally, design perspectives on new generation, multi-function, fiber optic sensor platforms using FLRD technique are particularly presented

Refractive-index-modified-dot Fabry-Perot fiber probe fabricated by femtosecond laser for high-temperature sensing

An optical fiber Fabry-Perot probe sensor for high-temperature measurement is proposed and demonstrated, which is fabricated by inducing a refractive-index-modified-dot (RIMD) in the fiber core near the end of a standard single mode fiber (SMF) using a femtosecond laser. The RIMD and the SMF end faces form a Fabry-Perot interferometer (FPI) with a high-quality interference fringe visibility (<20dB). As a high-temperature sensor, such an FPI exhibits a sensitivity of 13.9 pm/°C and 18.6 pm/°C in the range of 100-500 °C and 500-1000 °C, respectively. The fabrication process of this device is quite straightforward, simple, time saving, and the sensor features small size, ease of fabrication, low cost, assembly-free, good mechanical strength, and high linear sensitivity

Optical fiber sensors for in-situ detection of solid-liquid phase change for n-octadecane

In the past few decades solid-liquid phase change materials (PCMs) have gained an increasingly important role in thermal energy storage applications due to their ability to absorb or release large amounts of energy during melting or solidification. The precise phase change temperature varies with different conditions, such as external pressure, small variations in the PCM composition in the case of multi-component mixtures and/or material purity. In order to achieve better energy efficiency for the energy storage process, it is necessary to be able to accurately detect the solid-liquid phase changes in the bulk of a PCM. Optical fiber sensors allow for direct detection of the phase changes in PCMs while also offering the advantages of a passive nature and small size. The focus of the research presented in this thesis is on the development of a novel approach to detecting the solid-liquid phase changes in selected PCMs using optical fiber sensors. To achieve this goal, initially the correlation between the temperature, changes in the refractive index (RI) and internal pressure acting upon the optical fiber during the phase transitions was studied for the selected PCM, n-octadecane. Based on the results of these studies, several optical fiber sensing structures have been proposed and demonstrated for the detection of phase changes as follows: An optical fiber Fresnel reflection sensor for detection of phase changes. An fiber Fresnel reflection sensor for detection of solid-liquid phase change in n-octadecane is proposed and experimentally demonstrated. The sensor probe consists of a single-mode fiber with a cleaved end immersed in the n-octadecane sample under test. The detection relies on measuring the slope of the output power ratio change which is caused by the RI change during the phase transition. The results of this work suggest that such a simple optical fiber sensor can be used for detection of liquid-solid phase changes in other materials with similar thermo-optic properties to n-octadecane. This sensor realized in-situ detection for a solid liquid phase change, which is a significant advantage compared to the traditional phase change detection methods. A fiber heterostructure based optical fiber sensor for detection of phase changes. A single-mode-no-core-single-mode fiber optical sensor for the detection of solid-liquid and liquid-solid phase changes in n-octadecane is proposed and demonstrated. The transmission-type sensor probe consists of a short section of no-core fiber sandwiched between two sections of a single-mode fiber. The detection relies on measuring the level of the output power ratio which is caused by the large step-like variations in the RI of n-octadecane’s. Importantly, compared to the Fresnel reflection sensor, the proposed fiber heterostructure is resistant to bending and strain disturbances during the measurements. The results of this work suggest that the proposed sensor is potentially capable of detecting liquid-solid phase changes in other materials whose thermo-optic properties are similar to those of n-octadecane. Moreover, this sensor not only has the advantage of achieving in-situ phase change detection, but also has the ability of working in an environment subjected to mechanical disturbance, which makes it has great potential of industry applications. Optical fiber Fabry-Perot sensor based on a singlemode-hollow core-singlemode fiber. An optical fiber Fabry-Perot sensor to monitor the solid-liquid and liquid-solid phase changes in n-octadecane is also proposed and investigated. The sensor probe is fabricated by splicing a short section of a hollow core fiber between two single-mode fibers. By analyzing the changes in the output spectrum of the probe, such as spectral shift of a selected interference dip, the phase change within a material sample in the vicinity of the fiber probe can be accurately detected. The proposed sensor can deal with PCM types whose RI values make it difficult for the other two sensor types to work, and also can be used for detection of the material’s phase state at a particular point of its volume. This work has the potential to better understanding phase change mechanism and its application in energy engineering. Compared to the other sensors developed in the research presented in this thesis, this sensor has the advantage that the application is not limited by the RI of the PCMs

Optical fiber ring resonator as a high-resolution spectrometer: characterization and applications with single line diode lasers

An optical fiber ring resonator (OFRR), a wavelength sensor for testing a single-mode laser system in a wide range of temperature, is presented. We will show that it is possible to calibrate, in relative form, a scale ofwavelength, to determine, accurately enough, a thermally induced laser detuning, using the free spectral range of an OFRR. The optical circuit was constructed using 2 × 2 (50/50) optical fiber coupler obtaining an OFRR of10-cm ring radius. A single-mode diode laser system has been launched into the OFRR, and different experiments have been performed. We tested the OFRR performance, considering fluctuations in the laser wavelengthcaused by small temperature instabilities, measuring the output intensity from the ring resonator. Theoretical simulations and experimental results were in agreement with the expected behavior. Furthermore, OFRR systemscan be used as an excellent control tool to test the wavelength stability for a narrowband laser diode and act as a part of a control system.Centro de Investigaciones Óptica

Optical fiber coated Zinc Oxide (ZnO) nanorods decorated with Palladium (Pd) for hydrogen sensing

A novel hydrogen (H-2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 mu m has been modified as a transducing platform by etching it to 11 mu m diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H-2 detection. The developed sensor operating temperature was found to be 150 degrees C that produces 6.36 dBm increase in response towards the 1% concentration of H-2 in synthetic air. It was then tested with different concentration of H-2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H-2 concentrations at 150 degrees C. The results indicate the optical fiber sensor might improve the performance towards H-2 as oppose to the conventional electrical sensor

Remote temperature sensing with low-threshold-power using erbium-doped fiber laser

Remote temperature sensing is of significant interest nowadays as it can continuously monitor structures located at tens or hundreds of kilometers away from a central location. With remote sensing, any damage of structures can be detected immediately, thus appropriate action can be taken quickly. Optical fiber laser temperature sensor is one of technologies that can be used for the implementation of remote temperature sensing. Few developments have been reported regarding the use of fiber laser for remote temperature sensing. However, in general they use Raman amplifiers which have relatively high threshold power of higher than 1 W to trigger the laser and this consequently increases the total cost for the implementation. Motivated to achieve a lower threshold power, this thesis presents a remote temperature sensor that utilizes erbium-doped fiber laser (EDFL). The configuration of the laser cavity is linear, comprising a fiber mirror reflector at one end, and the other end is formed by a fiber Bragg grating (FBG) with central wavelength of 1560 nm as the sensor head. A 30 km single mode fiber is placed before the FBG to serve as a transmission channel for remote sensing and erbium-doped fiber amplifier (EDFA) as the gain medium. The EDFA is used because it can operate using low pump power owing to the high gain efficiency of the doped-fibers. Based on this proposed design, experimental results indicate that it has a low threshold pump power of only 12 mW. In comparison to the previous study, the obtained threshold power presents an improvement of 98.8%. In addition, the laser has good stability with power fluctuations of less than 1.2 dB over a 30 minute duration, OSNR of 49 dB and power efficiency, up to 0.07%. With this fiber laser, a temperature sensor with a sensitivity of 10.6 pm/°C is realized for a temperature range from 30 °C to 90 °C which has potential to be applied in the oil and gas field. This sensitivity value is comparable with those obtained with Raman-based fiber lasers, albeit with the requirement of lower threshold pump power. The 98.8% reduction of the threshold power requirement presents opportunity for more cost effective operation in the implementation of remote temperature sensing

Analysis and performance of edge filtering interrogation scheme for FBG sensor using SMS fiber and OTDR

Abstract An interrogation technique for fiber Bragg grating (FBG) sensor is devised with customized in-line edge filtering single-multi-single mode fiber (SMS) component and optical time-domain reflectometer (OTDR). The performance of the proposed SMS-OTDR interrogation is established by temperature and strain sensing analysis of a standard FBG. The temperature and strain sensitivity values which are verified by theoretical analysis are estimated as 1.01 × 10−2 dB/℃ and 3.9 × 10−4 dB/µɛ respectively. Furthermore, we have optimized and achieved controlled etching on FBG and tested it for hiking the sensitivity. Using the etched FBG, an enhanced temperature and strain sensitivity of 6.7 × 10−2 dB/℃ and 3.2 × 10−3 dB/µɛ covering the range of 20–200 °C and 100–2015 µɛ respectively are also recorded and analysed by this integration method. Eventually, the efficiency and cost-effectiveness of the proposed method are compared with various reported techniques and presented here