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This paper will discuss the development and applications of Bragg grating-based array temperature sensing (ATS) that is used for SAGD heavy oil applications. A Bragg grating-based pressure and temperature gauge has also been developed and successfully implemented for SAGD monitoring applications. The sensing systems have demonstrated long lifetimes and reliable operation for many years in very hostile, hydrogen-rich environments. These wells typically have temperatures exceeding 250°C and pressures nearing 1,000 psi. The applications are ideally suited for the capabilities of fiber optic sensing and harsh environments.

This study attempted to investigate the self-sensing capability of Portland cement composites in sensing temperature and detecting damages through the measurements of materials’ thermoelectric properties. Specimens were made of Ordinary Portland Cement (OPC) with the water to cement ratio of 0.4. Temperature sensing property was characterized at various ages of the specimens from 28 to 49 days and at dried/moisturized conditions. It was found there exists an approximately linear relationship between temperature differences (ΔT) and the measured thermoelectric potentials, which is known as the Seebeck effect. This linearity was observed to be varied but able to be characterized for cement pastes at different ages and water saturation conditions. Mechanical loading that introduced different types and degrees of damages also translated into the variations of thermoelectric properties. Specifically, different types of compressive loads were tested for comparison. The study results have shown that Seebeck coefficient dropped with introduced damages, and restored with the subsequent re-curing as well as the continued cement hydration. Mild and moderate damages can be partially or fully restored, while severe damages that have resulted in significant drop of the Seebeck coefficients would restrain the self-restoration. Determination of the damage threshold was not yet revealed in this study, while it was shown obviously there existed one. Our investigation results indicated that characterizing the self-sensing capability of Portland cement composites is achievable through the measurements of thermoelectric properties. This study, in particular, has showcased the temperature sensing and damage detection capability.

The BGS broadening caused by short pump pulse would degrade the SNR enhancement provided by the optical pulse coding and strongly reduce the measurement accuracy of coded BOTDA sensors, especially at long sensing ranges with sub-meter spatial resolution. In this work, to overcome this trade-off between spatial resolution and measurement accuracy, we implement a BOTDA sensor employing pre-pumped Golay coding with optimized pre-pumped pulse power. The proposed scheme fully exploits the SNR enhancement provided by the coding and the benefits from the pre-activated acoustic field established by the pre-pumped pulse, achieving distributed temperature measurements with 70 cm spatial resolution and temperature resolution better than 1.5 °C throughout the 50 km sensing fiber.

This work introduces the experimental results of a temperature sensor device, with doped fiber and LPGs. The device is introduced in a temperature controlled oven, observing a 1 nm shift in wavelength toward longer wavelengths when the temperature increases 3 °C. It is possible to observe the average rate of change in the power related to increased temperature for two and three fiber gratings temperature sensors, and finally it is noted that the channels generated by the interference pattern are dispersed as temperature increases. The experiment was performed for 2 and 3 LPFGs in series where the wavelength displacement, output power and the number of channels were analyzed when the temperature was increased.

European Workshop on Optical Fibre Sensors (EWOFS2016), 31/05/2016-03/06/2016, Limerick, Irlanda., A method to evaluate distributed temperature gradients along an optical fiber using phase-sensitive optical time domain reflectometry (PhiOTDR) with direct detection is proposed and experimentally validated. The measurement principle derives from the perturbation response of a single-wavelength PhiOTDR signal, which is analyzed as a unidimensional speckle pattern. Our method can be implemented in real-time, relies solely on a low-cost post-processing of the standard PhiOTDR traces and requires no scanning of the laser frequency. This post-processing method can be implemented over a conventional PhiOTDR system used for distributed intrusion detection, without affecting its operation or requiring any additional hardware., Ministerio de Economía y Competitividad, Comunidad de Madrid, Universidad de Alcalá, European Commission

The linear matrix approach is the common method for multi-parameter FBG-based strain and temperature sensing. As it does not include non-linear temperature responses and hence lacks accuracy, the application of an iterative matrix inversion technique can be used to remedy this deficiency. Employing this method in a set-up using a multi-parameter sensor system that consists of two FBGs in fibers, which differ in cladding diameters, significantly reduced temperature uncertainties of ± 1°C could be achieved within a temperature range between -20°C and 150°C.

The distributed temperature sensor system based in the spontaneous Raman backscattering is demonstrated for the first time to our knowledge, using a commercial OTDR (Optical Time Domain Reflectometer) and a standard erbium doped fiber amplifier (EDFA) with controlled gain. We evaluated this approach in a 30 km of single mode fiber using an OTDR pulse width of 100 ns and an EDFA with 17 dBm of output power.

We demonstrate that BOTDA is the equipment of choice for Distributed Temperature Sensing (DTS) when challenging components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ) are inserted in the sensing line. The parameter of Temperature Measurement Dead Zone (TMDZ) is introduced to support the discussion and quantify possible impairments. A laboratory qualification test with real FORJ and WMC is conducted confirming the theoretical expectations. The system is then implemented offshore demonstrating that FORJ and WMC do not affect the sensing operation in field environment.

In this work we present a comparison between simplex coded and optical amplified simplex coded Raman based Distributed Temperature Sensing (DTS). An increase in performance is demonstrated using erbium doped fiber amplifier (EDFA) with proper gain control scheme that allows a DTS operates with simplex code. Using 63-bit simplex code and gain controlled EDFA we demonstrated the temperature resolution and dynamic range improvement in 16 °C @ 10 km and 4 dB, respectively.

Fiber Bragg gratings (FBGs) in gold-coated SMF have been successfully inscribed with NIR femtosecond laser and a phase mask for high temperature sensing application. The spectrums of FBGs inscribed by femtosecond laser are broader and asymmetrical with flat-toped profile which degrades the accuracy of FBGs interrogation with common peak detection techniques. A smart interrogation algorithm based on pattern matching (PMSIA) is reported in this paper. In this algorithm, an adjustable fitting spectrum template was proposed which enables the ability to suit for various spectrum patterns was proposed. The results of simulation and experiment demonstrate the noise immunity and threshold reliability of PMSIA. Less than 7pm interrogation error PMSIA was obtained even if the spectrum changes greatly in the very large sensing temperature range (up to 700°C).

© 2015 Copyright SPIE. The successful regeneration of fibre Bragg gratings (FBGs) inscribed in an inline fibre etalon is demonstrated. The etalon is formed by UV-micromaching of the fibre end-face to form a cylindrical hole, the fibre is then fusion spliced to seal the cavity. Such a fibre device has excellent potential for the simultaneous measurement of ultra-high temperatures and strain.

We demonstrated an ultrasensitive temperature sensor based on a unique fiber Fabry-Perot interferometer (FPI). The FPI was created by means of splicing a mercury-filled silica tube with a single-mode fiber (SMF). The FPI had an air cavity, which was formed by the end face of the SMF and that of the mercury column. Experimental results showed that the FPI had an ultrahigh temperature-sensitivity of up to -41 nm/°C, which was about one order of magnitude higher than those of the reported FPI-based fiber tip sensors. Such a FPI temperature sensor is expected to have potential applications for highly-sensitive ambient temperature sensing.

High temperature detection of micro structure area with high sensitivity has aroused more and more interest recently. A high temperature sensor based on ultra-abrupt tapered fiber Mach-Zehnder interferometer (MZI) is proposed and fabricated by using a fusion-splicing method.The two normal cleaved ends are separated by a distance and become ellipsoidal by one time discharge using a fiber fusion splicer. Then the two ellipsoidal fiber heads contacted between the splicer electrodes are fused together to form the taper. And the other is formed through the same process separated by a distance of L. The thermal characteristic is investigated in 25–1100 °C, which temperature limit is highest of tapered fiber MZIs. It is observed that sensitivity varies with temperature ranges, which are 25 pm/°C in low-temperature range(25-300°C) and 105 pm/°C in high-temperature range(300-1100°C) respectively. The sensor demonstrates good thermal stability after annealing at 400 °C and 800 °C for 8 h respectively. The simple ultra-taper based MZI sensor has potential application prospect in the field of high temperature detection, such as the temperature of aeroengine.

Laser pulse width is the limiting factor for high spatial resolution measurement with Raman distributed temperature sensor (RDTS). Typically a 10 ns laser pulse provides a spatial resolution of 1 m. Path delay multiplexing can be used to overcome this limitation. This paper presents formalism for two path delay multiplexing, taking into account the point response function (PRF) of the RDTS.

A dual side hole fiber (DSHF) with a pair of large air holes is proposed for free transducer temperature sensing in the infrared region (1500–1600 nm). The results of birefringence measurement based on a sagnac interferometer showed the linear group birefringence is from 4.35×10 -5 at 1500 nm, to 1.14×10 -4 at 1600 nm, respectively. The group birefringence of DSHF leads to a group temperature sensitivity from 3.9nm/°c at 1501nm to 1nm/°c at 1595nm, respectively.

Conventional high-spatial-resolution Raman distributed temperature sensing (DTS) systems are based on photoncounting techniques, which result in slow measurements over short sensing fibers. We describe an alternative approach that uses a high-power, short-pulse-width laser and provides fast measurements over fibers longer than 1 km. We demonstrate measurements with 1-s update times over fiber lengths greater than 1 km with better than 0.4-m spatial resolution. We introduce a figure of merit for DTS and we show a substantial improvement (x 100) over earlier results.

We theoretically investigate the properties of the eye-like ring resonator (ERR) configuration as a highly sensitive temperature sensor. We theoretically calculate the temperature sensitivity and the temperature detection precision of the configuration as a temperature sensor. The temperature sensitivity and the temperature detection precision of our configuration can achieve 837.91/ °C and 0.015°C respectively. Furthermore, we optimize the parameters of the proposed ERR configuration to enhance the temperature sensitivity and the temperature detection precision. This proposed structure enables highly sensitive, compact and stable temperature sensors.

Raman-assistance (RA) has become a promising technique to enhance the sensing range of standard Brillouin Optical Time Domain Analysis (BOTDA) fiber sensors due to its ability to amplify in a distributed way all the interacting signals within the fiber. Unfortunately, Raman amplification introduces a great amount of Relative Intensity Noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RABOTDA. In Vector Brillouin Optical Time Domain Analysis (VBOTDA) the detected signal is transferred to a highfrequency carrier where the Raman RIN transfer turns out to be much less harmful. In this work we demonstrate, for the first time to our knowledge, Raman-assistance in a VBOTDA. Our results show significant reduction of the RIN transfer effect in RA-VBOTDA compared to standard RA-BOTDA, making this type of scheme particularly interesting for long range distributed sensing., European Commission, Ministerio de Economía y Competividad, Comunidad de Madrid

We propose and experimentally demonstrate the possibility to use a pump signal based on bipolar pulse sequences using single-sideband suppressed-carrier (SSB-SC) modulation in Brillouin optical time-domain analysis (BOTDA) sensors. The SSB-SC modulated pump makes a sequential use of the Brillouin gain and loss spectra, increasing the intensity contrast of the measurements. The method is demonstrated using bipolar Golay codes along a 50 km sensing fiber and 2 m spatial resolution. Results indicate that the use of bipolar sequences provides a higher SNR enhancement and stronger robustness to pump depletion in comparison to BOTDA systems employing conventional unipolar sequences. Keywords: Stimulated Brillouin scattering, distributed optical fiber sensor, temperature sensing, strain sensing 1. INTRODUCTION Distributed optical fiber sensing based on stimulated Brillouin scattering (SBS) is a widely-used technique to measure distributed temperature and strain along several tens of km with meter-scale spatial resolution. The conventional time-domain approach, so called Brillouin optical time-domain analysis (BOTDA)

An analytical model is presented to describe the behavior of the acoustic wave, probe signal and Brillouin gain in double-pulse Brillouin optical time-domain analysis (DP-BOTDA) sensors. The proposed model is a tool that provides a full physical insight into the Brillouin interaction occurring in this double-pulse configuration, and allows the optimization and complete analysis of the system. The proposed solution is experimentally validated in a long-range system, which is optimized to demonstrate experimentally, for the first time, the capability of DP-BOTDA to achieve a 11 km sensing distance with 20 cm spatial resolution and a frequency resolution of 0.5 MHz. Keywords: Stimulated Brillouin scattering, distributed optical fiber sensor, temperature sensing, strain sensing 1. INTRODUCTION During the last years the sensing capability of distributed optical fiber sensors to measure a physical variable along an optical fiber has attracted the attention of many industrial sectors. In particular, distributed strain and temperature sensing using stimulated Brillouin scattering (SBS) in a pump-probe configuration

The dependence on polarization of the performance of a microfiber coupler based temperature sensor is experimentally investigated. The optical microfiber coupler based temperature sensor has a diameter circa 2µm and can sense temperature in the range from 100°C to 1000°C, with an average sensitivity of 18.9pm/°C. It is shown that different polarization states of the input signal have a significant influence on the proposed temperature sensing accuracy, with a estimated peak error of 63°C at 1000°C.

The combination of Raman amplification and optical pulse coding (OPC) is proposed to reduce the frequency uncertainty in long-distance BOTDA under higher spatial resolution. The experimental characterization of 74.6Km temperature sensing with measurement accuracy ~1oC under ~2.5m spatial resolution over the whole length of sensing fiber is demonstrated. The performance comparisons of BOTDA with purely Raman amplification and combined Raman amplification with OPC are also displayed.

We present 100-μm crack detection and 100-km distributed strain and temperature sensing by fiber-optic distributed strain and temperature sensor (DSTS) based on coherent interaction of probe-pump. The DSTS products have been employed to detect cracks on ceramic by measuring the strain distributions along the surface of the ceramic and a continuing long-term field monitoring of local temperature and stress changes in a 70-km buried fiber-optic cable.

In this paper we demonstrate distributed Raman temperature sensing (RDTS) in a loop scheme employing anti-Stokes light intensity only. Using a single-channel receiver and anti-Stokes traces measured in loop configuration, we implement RDTS with inherent compensation of fiber wavelength-dependent losses, as well as local external perturbations. Experimental results show a signal-to-noise ratio enhancement with respect to a standard RDTS in loop configuration, providing a robust and reliable high-performance sensor for long sensing ranges. Keywords: Raman scattering, fiber optic sensors, temperature sensing.

Heat treatments are important methods to provide safe foods. Conventional heat treatments involve the application of steam and recently microwave treatments have been studied and applied as they are considered as fast, clean and efficient. Optical fiber sensing is an excellent tool to measure the temperature during microwave treatments. This paper shows the application of optical fiber temperature sensing during the heat treatment of different foods such as vegetables (jalapeno pepper and cilantro), cheese and ostrich meat. Reaching the target temperature, important bacteria were inactivated: Salmonella, Listeria and Escherichia coli. Thus, the use of optical fiber sensors has resulted be a useful way to develop protocols to inactivate microorganisms and to propose new methods for food processing.

International audience; In this work it is investigated the strain and temperature sensing characteristics of modal interferometers supported by two Bragg fibers with different cross-section cladding geometries. It is shown that the sensitivity to these measurands is different for the two fibers, which turns feasible the conception of several sensing configurations based on the combination of these two fiber types for simultaneous measurement of strain and temperature.

Fiber optic sensing, and specifically Distributed Temperature Sensing (DTS), are powerful technologies extremely well suited for monitoring of geothermal wells and geothermal energy production facilities. This paper will discuss fiber optic technologies for high temperature sensing and monitoring applications in geothermal energy plants.

Distributed temperature sensing (DTS) using Raman-OFDR is not limited by non-linear effects or low duty cycles in long single-mode fibres. It shows full spatial and temperature resolution at a range of 30km. The availability of hydrogen resistant fibres favours single-mode DTS in applications with chemical load such as oil and gas production.

Fiber Bragg gratings are reported that are optimized for low wavelength drift, making them suitable for high- accuracy temperature measurements over extended periods of time. Our gratings show drift in the order of a few 10's of pm over 1,300 h at up to 650°C.

We have theoretically investigated the effects of temperature on the superlensing properties of single metal and stacked metal-dielectric films. We find that decreasing the temperature usually has the effect of slightly lowering the optimum operating frequency of the superlens. The imaging performance of various designs are evaluated by analytic calculations and simulations. Accurate modeling of the temperature dependence on the focusing/imaging properties of such structures is important for many potential applications and may in certain suggested cases lead to direct applications as e.g. local temperature sensing.

The fluorescence intensity ratio (FIR) technique for optical fiber-based temperature sensing is discussed in many previous papers. But in the high temperature sensing the FIR technique has been researched a little. In this paper, the temperature dependence of fluorescence in erbium-doped fiber between ∼700 and ∼1300°C is discussed and experimentally demonstrated. 1450nm and 1530nm wavelengths are chosen to calculate the FIR, and the temperature coefficient could achieve - 0.003dB/°C.

The development of new techniques for writing and tailoring the properties of Bragg gratings has generated a suite of distinct grating types that are optimised for performance within different temperature windows. These cover gratings produced by recipes such as hypersensitisation, thermal processing and single and multiphoton writing. In this paper, we review four types of high temperature gratings that offer comprehensive coverage of temperature space for most applications of interest. Up to 1200°C novel processing methods allow standard silica-based optical fibres to be used. However, beyond these temperatures, optical fibres made from other materials, such as sapphire, need consideration.

FBG sensors are more and more accepted in most area of Structure Health Monitoring. However, due to the fact that FBG senses both strain and temperature is monitored simultaneously, temperature compensation for FBG strain sensors of long-term structural monitoring is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, a novel FBG-based sensor for simultaneous dual-measurement of pressure and temperature has been developed. Firstly, in consideration of the requirement of sensors, a novel sensor structure has been designed and its sensing principle is given in details. Secondly, the properties of FBG-based sensor for simultaneous dual-measurement of pressure have been tested by some experiments. Finally, theoretical sensitivity has been compared with that from experiments. The research results show that the FBG-based sensor for simultaneous dual-measurement of pressure has good linearity, repetition, immunity of temperature changes. Such kind of FBG-based sensor for simultaneous dual-measurement ofpressure can be used to practical monitors.

Fiber reinforced polymer (FRP) has gained much attention in civil engineering due to its high strength-to-weight and stiffness-to-weight ratios, corrosion resistance and good fatigue resistance. Optical Fiber Bragg Grating (OFBG) is now widely accepted as smart sensor due to its advantages of electric-magnetic resistance, small size, distributed sensing, durability, and so on. Combined the FRP with OFBG, new kind of smart FRP-OFBG composite laminates was developed. Fabrication method of the smart composite laminates was introduced in this paper. The study presented the basic principle of OFBG sensors. Then the strain and temperature sensing properties of the proposed smart FRP-OFBG composite laminates were experimentally studied on material test system and under hot water, respectively. The experimental results indicate the strain sensing properties of the smart FRP-OFBG composite laminates are nearly the same as that of bare OFBG, however, the temperature sensing abilities of the smart FRP-OFBG composite laminates are improved and the sensitivity coefficient is nearly 3.2 times as much as that of bare OFBG. The strain and temperature sensing precisions of the smart FRP-OFBG composite laminates are 1 mV and 0.03 °C, respectively. The smart FRYOFBG composite laminates are very proper for application in civil engineering.

Surface acoustic wave (SAW) devices are attractive for sensing of the physical, gas, liquid or biological environment because the device has many parameters which can be adjusted for various applications. The temperature coefficient of delay can provide temperature sensing, coupling to liquids, gases or applied films can be controlled by choice of mode, and putting the device under stress or strain can measure pressure or vibration. In addition, there are many substrate choices to attempt to optimize a given measurand. Finally, substrate choices allow sensing from cryogenic to high temperatures (1000°C), which has the potential for use in a wide spectrum of space applications. This paper will describe a novel SAW sensor platform for sensing of various measurands which is passive and wireless, and has several levels of coding available for providing identification. The paper will describe the concept of orthogonal frequency coding used in the device identification and its advantages in communications and sensing, and the mechanism for implementation using reflectors in a SAW sensor. Results of measured SAW device performance versus the coupling of mode (COM) model predictions show excellent correlation for a 250 MHz device on a lithium niobate substrate. The approach presented uses frequency selective reflectors in a differential delay line to measure temperature; measured from cryogenic temperatures to 150°C with the same device. A discussion of substrate materials and device parameters will be presented to exemplify the versatility and practicality of these devices to a wide range of sensor applications.

FBG strain sensors are more and more accepted in the area of structural health monitoring, especially in civil infrastructures. However, due to the fact that FBG senses both strain and temperature simultaneously. And moreover the wavelength shift induced by 1°C is almost equivalent to that induced by 10μe. So temperature compensation for FBG strain sensors of long-term structural monitoring is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, the techniques of dual FBGs temperature compensation and the environmental temperature compensation are brought forward. The experiment of cement paste curing monitroed by dual FBGs was carried out. And the advantage of the technique of dual FBGs temperature compensation are proved, which is proper for long-term structureal monitoring system for civil infrastructures.

The leakage detection system based on the distributed fibre optical temperature measurement method is an analysing method for continuous detection and localization of leakages at pipelines in the steady and unsteady operation states according to the German rules for pipelines TRbF 301/TRFL which is valid in Germany since April 2003. The leakage detection system is useable under the precondition that there is a sufficient large temperature gradient between the leakage area and the unaffected environment. This can be caused by the medium itself or through a physical effect due to the leakage, e.g. gas expansion, evaporation. It's a very sensitive method, so also creeping leakages can be detected.

In this paper, a brief review of recent advances on high-temperature distributed fiber optic sensors is presented, which includes (1) background on fiber gratings, (2) in-fiber grating fabrication methods in single crystal sapphire fiber, (3) reflection-type fiber specklegram generated in single crystal sapphire fiber, and (4) preliminary experimental results on high temperature sensing.

A pressure and temperature sensing system based on fiber-optic Bragg grating sensors for the oil and gas downhole is reported in this paper, the weak pressure sensitivity is enhanced and the cross-sensitivity of temperature and pressure measurands is overcome by an optimally designed mechanical enhancing and compensating structure, the working principle, experimental setup and testing results are also given.

Sensing properties of the bare FBG have theoretically and experimentally been studied in this study, and then a temperature compensation method for FBG strain sensors was proposed. Due to the fragility of bare FBG, a technique of encapsulating bare FBG in a capillary steel tube was developed and the strain and temperature sensing properties of the encapsulated FBG were furthermore studied. With the consideration of the practical application in civil infrastructures, the technique of FBG to adhere or embed on steel and in reinforced concrete structures was studied. With successfully affixing and embedding bare FBGs and encapsulated FBGs sensors on a steel truss and in a reinforced concrete beam, respectively, the experiment of using the above FBG sensors to monitor the structural strain and deformation process. In order to verify the quasi-distribution sensing ability of FBG, the test that 3 bare FBGs were connected one by one and adhered on a steel truss was done and the independently sensing strain ability was found. Finally, FBGs strain sensors were successfully embedded in a reinforced concrete bridge to monitor the strain history and distribution under construction and in service. The measuring signals indicated that the embedded FBGs could precisely and long-term monitor the strain history, therefore, they can be employed to evaluate the fatigue life for the bridge.

A distributed fibre optical temperature sensing technique for different monitoring tasks, especially for leakage detection in oil and gas facilities, pipelines, underground storage sites, water constructions sites, mining and environmental industries is presented.

In this work, a number of techniques for high temperature sensing and measurement, especially those using a low-cost fluorescence-based approach, are reviewed, results are presented and compared and contrasted. Applications in a number of engineering sectors are considered, and examples are given of trials of such sensors for industrial monitoring.

Linear bolometer arrays are well suited to industrial and space applications, where the object or scene may be convenientlyscanned by a conveyor or in a push-broom mode. The linear format facilitates the introduction of readout features notgenerally available in two-dimensional arrays. Such features include pixel by pixel offset and temperature drift compensation,as well as pixel-level filtering. The latter permits the filtering of detector noise down to a narrow bandwidth while preservinga high output bandwidth to allow oversampling. The former permits superior temperature drift compensation since each pixelmay have a dedicated, matched temperature sensing element.Three types of linear and quasi-linear bolometric detector arrays are being developed at INO within the framework of anR&D program jointly financed by INO and the Centre for Research in Earth and space Technology (CRESTech) of NorthYork (Ontario). The prototypes of these arrays, namely the 1RL256A, 1RL256B and 1RL256C are described in this paper.

In recent years, fibre Bragg gratings (FBG) have shown an enormous potential for strain sensing in smart structures and composite materials [1]. However, temperature sensitivity of FBG can lead to significant limitations in their practical application.

We have demonstrated the principle of distributed temperature sensing using the Brillouin loss mechanism with a single laser source. The technique involves the use of a stimulated Brillouin scattering (SBS) generator to produce down-shifted light.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ski lift tower cable sheaves are a maintenance item in that the sheave bearings must be lubricated periodically. Like most other bearings, wear-out failures can occur. Many times the temperature rise ofthe bearing over ambient is a leading indicator ofa bearing failure. Excessive temperature rise due to increased friction in the bearing often precedes any indication ofvibration or dimensional anomalies. Tests were perfonned using two readily available remote temperature sensing devices, the spot imager and scanning infrared camera. Temperature rise data is presented along with a discussion of temperature measuring techniques. Results show that infrared remote sensing is a cost effective means ofchecking the status oflift tower rotating machinery. Keywords: ski lift towers, ski lift tower sheaves, ski lift tower maintenance, bearing friction, bearing failure, infrared camera, infrared spot imaging, temperature rise data, ski lift tower rotating machinery.

A theoretical analysis of determination and improvement of the resolutions of distributed fiber optic temperature sensing system is discussed. A mathematical expression is derived to reveal the inherent relations between the resolutions. An integral sensing system is set up on the basis of analyzing in theory and the experimental result is also given.

Experimental results show that an all-fiber temperature sensing system, in which the optical heterodyne detection techniques are used, has the advantage of both high resolution and wide unambiguous measurement range. It is successful in greatly weakening the influence of environment unsteadiness. In the experimental system, due to the use of a polarization maintaining fiber coupler as a beamsplitter, the general beamsplitter and reflecting mirror are saved.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Temperature sensing is achieved via the temperature dependance of the absorption of the evanescent field of a polished single mode fiber embedded in an absorptive medium.

We report a method of fabricating a 45° polarization rotating coupler using single polarization maintaining fiber. We demonstrated that the coupler was useful to localize the sensitivity for temperature sensing of the fiber in a one-fiber interferometer.