In 1977 McDonnell Douglas Astronautics Company began a project to investigate the usage of optical gyros to support the Delta Launch vehicle. This resulted in the invention of the closed loop fiber optic gyro and several derivative inventions that allowed entry into acoustics for undersea applications, launched the field of fiber optic smart structures, and resulted in some strange detours into secure fiber optic communication. Health monitoring activities with Blue Road Research, Inc. and later Columbia Gorge Research, LLC continuing to develop fiber sensors for an ever wider range of use including civil structures, oil and gas, environmental sensing, high speed machining, composite manufacturing, energetic materials, robotic surgery and electric power. This paper primarily follow the path to the moon, Mars and beyond with the objective of showing how fiber sensors are helping us to get there and ultimately will help us stay there.

Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. We examine aerospace applications that benefit from HD-FOS, such as for defect detection, FEA model verification, and structural health monitoring. We describe how HD-FOS is used in applications spanning the full design chain, review progress with sensor response calibration and certification, and examine the challenges of data management through the use of event triggering, synchronizing data acquisition with control signals, and integrating the data output with established industry protocols and acquisition systems.

Today, it is commonly agreed that mid-range rangefinders (typical range: 10 km) based on fiber laser technology, constitute the best trade-off between performance and reliability. But to intend to compete with long-range devices and propose an alternative to bulk solid state laser systems, it is essential to increase significantly their extinction ratio (ER) compared to the state of the art. In this paper, we report on successive real-time statistical algorithms performed on 2 different fiber laser rangefinders and the feasability to achieve an extinction ratio up to 45dB in an eye-safety burst mode. Based on a bi-static architecture and equipped with a 38 μJ and 125 μJ, 10 ns pulse fiber laser, their intrinsic ER in single-pulse emission has been measured respectively at 28 and 33 dB. A 45 mm optical aperture receiver and a specially designed compact electronics complete the device. This alternative to solid-states systems dedicated to long range application, represents then a cost-effective solution.

Thermally induced bias error is one of the main performance limits for the fiber optic gyroscopes (FOGs). We reviewed the thermal sensitivity of FOG in detail and created a simulation environment by the Finite Element Method (FEM). Thermal sensitivity analysis is based on Shupe and elastooptic effects. Elastooptical interactions are modeled by using the two different FEM simulations and homogenization-dehomogenization processes. FEM simulations are validated by comparing the results with a laboratory FOG setup. We report the changes in the error characteristics for practical quadruple winding patterns.

The need for precision guidance of systems in tactical theaters is becoming increasingly more important. This need has renewed interest in Interferometric Fiber Optic Gyroscopes (IFOG) that are capable of delivering navigation grade performance. The challenges however, include satisfactory performance over a large and severe operating temperature range (-60°C to +90°C), low unit cost and relatively small footprint. Performance of the IFOG depends critically on the quality of the sensing element, optical fiber coil, and many of the performance limiting issues of the IFOG can be traced back to coil quality. Although significant progress has been made in the fabrication of temperature insensitive coils with high optical reciprocity, more needs to be done. In this paper, data is presented on the performance of similar size (inside diameter, outside diameter, height) freestanding coils that were wound in quadrupole winding pattern at low tension using different polarization maintaining fibers. Performance characteristics of the coils were measured under variables including (i) fiber geometry, (ii) fiber coating, (iii) winding epoxy, and (iv) epoxy curing profile. Although each coil had the same footprint, they contained different lengths of fiber based on the fiber coating size. Coils were characterized as a function of temperature with respect to: (i) optical loss, (ii) polarization extinction ratio (PER), and (iii) coherence. The data suggests that high performance navigation grade coils can be realized over a large and severe temperature range with careful choice of fiber, winding epoxy and cure cycle.

We propose and demonstrate an interferometric sensor based on visibility modulation. In the interferometric sensor, a section of polarization maintain (PM) fiber is spliced into one arm as the sensing head. Due to the interference between the two beams in the two arms, respectively, an interferometric fringe can be obtained. The birefringence of the PM fiber splits the beam in the sensing arm, yielding a visibility envelop in the interferometric fringe. Strain applied on the PM fiber can be demodulated by measuring the visibility change in a given wavelength. Experimental result shows that the sensor can achieve resolution of up to 28 nano-strain. This demodulation scheme is immunity to the wavelength shift and power fluctuation of OSA, thus improving the accuracy of the sensor. This type of sensor can be improved by using a wavelength-swept laser or a mode-locked fiber laser.

An improvement in light confinement in sapphire fiber is obtained by employing nanoporous alumina as a cladding. The fabrication strategy entails freeze-coating metal Al on sapphire fiber and its subsequent anodization to form alumina cladding with highly organized nanopore channels vertically aligned to the fiber axis with dimensions of ~20 nm. We investigated the confinement dependence on the porosity of the cladding, showing an improvement in comparison to unclad sapphire fibers. The versatility of anodized alumina cladding with tunable structural and optical characteristics has the potential to enable a new class of specialty sapphire optical fibers by engineering the light propagation for new sensor development.

Single crystal sapphire fiber is an excellent candidate for fiber-optic sensing in harsh environments owing to its superior optical, mechanical and thermal properties at elevated temperatures up to 1500ºC. We have carried out an experimental and theoretical investigation on the mechanical properties of nanostructured sapphire optical fiber (NSOF) cladded with nanoporous anodized aluminum oxide (AAO). The threshold thickness beyond which the integrity of AAO cladding will be compromised due to tensile stress as growth of AAO extends radially outward is determined. Bending tests are conducted to explore relationship of NSOF mechanical properties with AAO porosity and thickness as parameters. Bending simulations using Finite Element Method will be compared with our experimental results. Parallel bending tests are conducted using AAO-clad silica fiber for comparison. Numerical and analytical simulations are also conducted to reveal the stress development during aluminum conversion to AAO on fiber geometry. The knowledge established on mechanical properties of NSOF will be of critical importance in its design, production, and utilization for a variety of demanding applications such as sensing for energy generation and energy production systems.

Single crystal fibers like those made from sapphire are capable of operating at higher temperatures than conventional silica-glass-based fibers. This work aims to construct single-crystal optical fiber sensors capable of providing environmental data in combustion, high-temperature chemical processing, or power generation applications where temperatures exceed 1000 °C and standard silica fibers cease to provide useful information. Here, we explore the functionalization of single crystal fibers using methodologies intrinsic to the crystal growth process or with methods which do not severely reduce their operating temperature range. While operating a laser-heated pedestal growth system to produce single-crystal optical fibers from rod feedstock, we continuously vary parameters such as fiber diameter to produce novel single-crystal linear distributed-sensing devices. The spectral characteristics of those modified devices, along with sensing performance in a high-temperature harsh-environment are reported. Finally, a technique for increasing the intrinsic Rayleigh backscattering using femtosecond laser irradiation is discussed for temperature sensing applications.

Currently, fibre networks are only way how to satisfy the ever growing needs for more bandwidth. Thanks to that the optical fibre can be found almost anywhere and new applications and services can be transmitted through the networks. Accurate time transfer, ultra-stable frequency transfer and fibre-optic sensors networks have been rather common. High speed data transmission, time and frequency transmission, and fibre-optic sensors must share the common fibre-optic infrastructure because it would not be economically feasible to build separate fibre networks for long distances. Each system has individual transmission requirements and is prone to another type of interference. Data transmission systems based on DP-QPSK or DP-xQAM use digital signal processing for signal recovering but it cannot fully compensate signal degradation due to polarization dependent loss and nonlinear effects which are the most dominant sources of signal degradation. Accurate time signals are slow and often OOK modulated, therefore may experience the degrading effect of chromatic dispersion. Ultra-stable frequency signals are not modulated at all information transmitted is the frequency of photons and such signals are continuous wave, but they suffer from phase noise also environmentally introduced, e.g. by vibrations. For phase sensitive OTDR sensor systems the high power pulses are necessary to use which may cause interference with other signals. For this reason, parallel and simultaneous transmission in DWDM spectral grids of standard data, time, frequency, and sensing signals is rather new and unexplored area of research.

In Raman-based distributed temperature sensing (DTS) systems, the signal to noise ratio (SNR) is often low due to weak backscattered Raman signals. This can limit both sensing distance and temperature resolution. Common methods of increasing the signal, versus noise floor, exist but most have significant limitations. For example, attempting to improve SNR by increasing the launching power is limited by the stimulated Raman scattering (SRS) threshold of the fiber. To overcome this power limitation, we propose a new SRS filtering method that allows more power to be launched into the fiber, beyond the SRS threshold, without causing additional temperature error. With this SRS filtering method we show that 3 dB more power may be launched into the fiber while improving the SNR of the received signals by 1.6 dB.

This paper presents a distributed acoustic sensing based linear asset protection system along with novel signal processing and threat classification techniques. The sensing system is realized by direct detection phase-OTDR (optical time domain reflectometry). An effective signal preprocessing approach for noise reduction that aims to improve the threat detection capability of the system is proposed. The proposed method is not limited to direct detection based systems and is applicable to any phase-OTDR system. A novel deep learning based threat clas- sification method is presented to identify various types of threats. The method uses a deep convolutional neural network trained with real sensor data. Experiments are conducted with an ITU-T G.652 fiber optic cable buried at one meter depth. The effects of applied preprocessing methods on both threat detection and threat classification performance are analyzed. The proposed preprocessing method is compared with the methods commonly used in the literature such as time differencing and wavelet denoising. The results show that by applying the proposed signal conditioning, event detection and classification methods, threat classification accuracies above 93% can be achieved with six typically observed activities, namely, walking, digging with pickaxe, digging with shovel, digging with harrow, strong wind and facility noise caused by water pipes, generators or air conditioning, at ranges of up to 40 km. The proposed classification strategy can easily be generalized for identifying different types of threats that are of interest in various security applications.

This paper is focused on the development and field deployment of a multi-parameter and distributed fiber optic sensor for monitoring of soil and groundwater during in-situ thermal remediation of contaminated brownfields. In-situ thermal remediation (ISTR) is a process in which the soil and groundwater are heated using localized heat sources to evaporate and extract hazardous substances and pollutants from brownfields. In this research, the unique advantages of fiber optic is leveraged through the development of transducers for distributed sensing of temperature and pressure which are critical performance parameters for assessing the efficiency of any ISTR process.

The oil and gas industry is continually striving to produce more hydrocarbons and reduce waste. Many sensing techniques using optical fiber have been developed over the last three decades for all stages of well development. This paper reviews these optical sensing technologies, with emphasis on new applications and business drivers. Expected performance parameters of these new technologies are discussed, including their accuracy, resolution, stability, and operational lifetime. Environmental conditions, such as high temperatures, shock, vibration, crush, and chemical exposure, are also discussed. These optical technologies are expected to provide safe, reliable, cost-effective, and unprecedented monitoring solutions.

Since its invention in the 1970s, optical fiber has provided a technology-based vehicle to improve the performance of a variety of applications that were traditionally served by older copper conductor based systems. Optical fiber based systems have enabled improvements in capabilities and functionality that are simply not possible with copperonly systems. Typically, optical fiber systems enable higher rates of data transfer over longer transmission distances. Telecommunications applications have demonstrated this benefit through improved capability for voice, data and video transmission. Field deployment of optical fiber is executed through the utilization of a protective cabling structure that allows the optical fiber to be safely installed and be protected over its service life. The design and construction of each cable is based upon the expected mechanical and environmental conditions of the operating environment. Performance requirements, published in detailed specifications or industry standards, must also be considered to provide a system with an appropriate service life for each application. Optical fiber applications have now expanded beyond telecommunications. Sensor applications utilizing optical fiber to measure temperature, pressure, acoustics and seismic parameters are being deployed and evaluated today. Applications in Oil and Gas Exploration, Geothermal and Fire Detection Monitoring are being supported by optical fiber-based systems. The sensing environment typically exposes the optical fibers to much more extreme environments that are not prevalent in telecommunications. This includes high temperatures, high pressures and harsh chemical exposure that must be addressed in the cable design containing the fibers in order to extend the useful life of the fibers as much as practical. While optical cable for sensing applications require some specialization, there are basic cable design tenants that still apply to construct a cable that meets or exceeds the application environment. In many cases, design concepts proven in older copper-based cables may be adapted to incorporate one or more optical fibers. Nevertheless, more extreme environments require the use of nontraditional materials and alternative design concepts not utilized in typical telecommunications applications. Some sensor applications, due to their specialized nature, may drive one or more design aspects in a manner that contradicts established telecommunications cable design practices. The focus of this paper is to compare and contrast the cable construction differences between sensing applications and traditional telecommunications applications, review the significant design considerations for the associated application and outline several current design challenges necessary to enable reliable cable deployments.

Standard telecom fibers are systematically studied using Raman spectroscopy as a function of time with increasing temperature and for repeated thermal cycles between ambient temperature and 1000°C. Raman and transmission results strongly suggest that the coupling between fiber core and cladding causes the losses and variations due to glass structural evolution upon stress relaxation after annealing. This is of particular interest in light of recent proposal to understand regeneration process in fiber Bragg gratings at elevated temperatures.

Fiber Optic Distributed Acoustic Sensing (DAS) and Distributed Strain Sensing (DSS) systems have widespread use for asset and security monitoring. The acoustic signal from such sources as intruders, vehicles, or gunfire must be coupled from the earth to an optical fiber which is then interrogated by DAS system technology. Because the optical fiber is the sensing element, and because the cable is required to mediate the interaction of the fiber and its environment, the selection of the optical fiber, cable design, and deployment conditions are critical to the performance of the system. Cable designs specifically created for sensing are shown to achieve 20 dB higher signal-to-noise than standard telecom designs, which correspond to an enhanced sensing range of more than 30 meters. In addition, directly burying the sensing cable in the ground leads to 15 dB higher sensitivity than installing it in a duct. In many cases, standard cables for telecommunications applications are designed to isolate and protect the fibers from the external environment; therefore a cable designed for sensing applications and deployed specifically with this in mind leads to the highest sensitivity with the largest sensing range.

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.

Ultrafast high speed photonics are shown to provide the necessary temporal and spectral information required for understanding FBG response under impulsive loading from either high explosive detonation or an inert shock wave interaction. Demonstration of both, chirped and uniform, silica based FBGs are presented for sensing under harsh conditions that vary from thermal ignition in high explosives to inert tracking of high pressure shock waves. Ultrafast laser based chirped pulse methods are used to time-stretch and streak the spectral response of the FBG sensor to provide information about material response under loading. Coherent broadband pulses from a femtosecond modelocked fiber laser at 1560 nm are used to illuminate and interrogate the FBG at a repetition rate of 100 MHz. After reflecting off the FBG, chromatic dispersion is applied to time stretch the pulse and separate spectral channels for detection with a 35 GHz photoreceiver and recording with a 25 GHz digitizing oscilloscope. Results include pressure wave tracking in weak inert shocks and pressure measurements in thermal ignition of high explosives detonation. The focus of the presentation is present the method and tools used for this approach to high speed FBG sensing.

Fiber Bragg Gratings (FBGs) are increasingly being employed in a novel range of applications, especially in sensing and measurement field. Some of these novel FBG-based sensing applications, especially those requiring high resolution sensing in harsh environments, impose challenges on Bragg gratings and their performance. Additionally, there is a growing list of Fiber Bragg Grating types and manufacturing techniques, each with its own strengths and disadvantages. With the new generation of fiber optic interrogation technologies reaching femtometer-level resolution in Bragg wavelength tracking, the achievable accuracy and stability of the sensing system is becoming limited by the performance of the employed Bragg grating itself. In many cases, correct selection and definition of the FBG parameters can result in defining the success of the sensing system. Here, we explore the specifications of Bragg gratings that are most relevant to FBG-based sensors, propose their characterization and analysis methodologies and explore their effects for both static and dynamic sensing applications in combination with tunable laser based fiber optic interrogation techniques. Bragg gratings manufactured by several different techniques are compared to demonstrate their suitability for different types of sensing applications. Several application focused examples are also provided to demonstrate the importance of the parameters for detection of strain, pressure, sound, vibration and tilt using fiber optic sensors.

Fiber gratings have been used to measure strain fields in pressure vessels made of composite materials and aircraft adhesive joints¹ . Measuring transverse loads have traditionally been performed by inducing a differential strain across the optical core of a fiber. Small changes in load cause the birefringence in the fiber to increase and capturing the spectral shifts using this method necessitates extremely accurate readout systems and careful analysis. This paper suggests a new approach for measuring transverse load by converting it to longitudinal strain and covers a very high-speed system used for measuring velocity, position, and pressure events that are on the order of a few microseconds.

In recent years, many hydro power plants were modified to pump storage operation. This changes the loading conditions and new monitoring concepts are required. We developed a fiber Bragg grating based monitoring system which was installed inside a hydro power dam in 2013. This paper reports on detailed investigations of this network using an optical backscatter reflectometer, which allows distributed strain sensing with a very high spatial resolution up to millimeters. Therefore, an analysis of the strain profile between two anchoring points of a FBG sensor can be performed. In addition to distributed sensing, the different wavelengths of the FBGs are determined in the frequency domain to verify the results of a classical FBG interrogator. These comparisons and further laboratory studies prove the suitability of the fiber optic system and demonstrate that a detailed analysis of FBG networks using optical backscatter reflectometry can provide valuable insights.

Solution pH is one of the most critical parameters for chemical reactions which are important for clinical, environmental or manufacturing applications. The integration of pH-responsive polyelectrolyte via layer-by-layer assembly (LbL) with long period grating (LPG) has enabled the monitoring of the pH in real time with high sensitivity at minimized volume. We show that the pH-responsive profile of the LbL/LPG platform can be tailored to specific needs depending on the deposition parameters during the LbL process. By choosing different deposition pH, weak polyelectrolytes showed either linear responsiveness or responsiveness with a reversal point at pH 4.5 over the pH range of 2-11. The most sensitive area was related to both the pKa of the chosen polyelectrolyte in the coating and the deposition pH during the LbL process. The study provides important guide to optimize and improve the sensitivity in specific pH range by selection of polyelectrolytes and/or deposition parameters. The LbL/LPG platform affords a powerful tool to study the mechanisms of the responsiveness and physiochemical properties of the polyelectrolytes.

The Hybrid Sensor Bus is a space-borne temperature monitoring system for telecommunication satellites combin- ing electrical and fiber-optical Fiber Bragg Grating (FBG) sensors. Currently, there is no alternative method for testing the functionality and robustness of the system without setting up an actual sensor-network implementing numerous FBG sensors in which each must be heated and cooled individually. The HSB system acquires the temperature data over the reflection of the single-ended FBG sensor-network. As a novel verification method for the HSB system, an FBG-emulator is implemented to emulate the necessary FBG sensors. It is capable to emulate any given FBG spectrum, thus any temperature immediately. The concept provides advantages such as emulating different kinds of FBGs with any peak shape, variable Bragg-wavelength λB, maximal-reflectivity rmax, spectral-width, and degradation characteristics. Further, the emulator facilitates an efficient evaluation of different interrogator peak-finding algorithms and the capability of emulating up to 10000 sample points per second. This paper, different concepts for an emulator and material selection regarding the Variable Optical Attenuator (VOA) as the main actuator are discussed. In order to implement a fast opto-ceramic VOA, issues like high temperature dependencies, high control voltages, and capacitive load have to be overcome. These issues are resolved by a custom designed precise temperature controller, and an HV amplifier end-stage providing up to 200 V. Furthermore, a self-calibration procedure mitigates problems like attenuation losses and long-term drifts. A dual-LuT memory handling method enables the emulator to operate at high rates without any interruption. Finally, the emulator’s functionality and its performance are verified over long and short term measurements.

Fiber Bragg grating (FBG) is formed by the periodic structure in the core of the optical fiber and is one of the widelyused types of fiber optic sensors. FBGs are primarily sensitive to strain and temperature. For sensory application is an important encapsulation of FBG to achieve maximum sensitivity to the desired measurand and ensure of protection against damage. Interesting way to encapsulate FBG is the use of elastomer polydimethylsiloxane (PDMS). Authors of this paper followed on previous research regarding encapsulation of FBG and analyzed the influence of different encapsulation types and shapes of PDMS on the temperature sensitivity and change of the reflected Bragg wavelength of the FBG. Realization of encapsulation is composed of three parts: FBG insertion to a regular form with the liquid PDMS, curing in a temperature box with a constant temperature 100 °C ± 5 % and 24 hours relaxation. Analysis of temperature sensitivity and reflected Bragg wavelength was carried out after curing including relaxation time and it using the broadband source of light LED (Light-Emitting Diode) with central wavelength 1550 nm and the optical spectrum analyzer OSA 203.

Fiber-optic sensors are one of the dynamically developing areas of photonics, which is today one of the key technologies. Here include even fiber optic interferometers, allowing very sensitive sensing, they are immune to electromagnetic interference and are entirely passive regarding electric power supply. This type of sensor is dependent on the phase shift, the principle of the function based on interference of light. Fiber optic interferometers are used especially in areas that require high sensitivity and measurement accuracy. The fundamental problem of fiber optic interferometry is a proposal storing and fixing the measuring arm of the interferometer and its influence on the frequency range and sensitivity of the interferometer. The authors focused on this issue and analyzed different types of fixing materials. We used a total of 8 different fixation elements with the different composition. We defined the standardized method of fixation and compared it with a reference measurement without fixation. For the analysis of the frequency characteristic of the prototype was used generator harmonic signal with fixed amplitude signal. Sensitivity verified using the size of the amplitude response. The signal processed by the application written in LabView development environment. The results clearly showed that it is necessary to pay attention to fixation materials in the design of the measuring arm of the interferometer for use in practical applications. In the frequency range, thanks to the fixing material increased the value of bandwidth about value 2430Hz against the reference measurements. The sensitivity of the interferometer has increased threefold. The results verified by retesting assembled prototype.

Technology fiber Bragg grating (FBG) belongs to the most widespread fiber optic sensors. It used for measuring a large number of chemical and physical quantities. Immunity to el ectromagnetic interference, small size, high sensitivity and principle information encoding about the measured value to the spectral characteristics cause usability of FBG sensors in medicine for monitoring vital signs such as heart rate, blood pressure, temperature or respiration. An important factor in this area is the use of an inert material for the Bragg gr atings encapsulation. An interesting choice is the elastomer polydimethylsiloxane (PDMS). PDMS is optically clear, general inert, non-toxic and non-flammable. The material commonly used for biomedical and medical applications. Experimental results presented in this paper describe the creation of prototype FBG sensor for the heart rate monitoring of a human body. The sensor is realized by Bragg grating encapsulated into polydimethylsiloxane. The FBG sensor is part of the elastic contact strap which encircles the chest of the patient. This chest expansion leads to a spectral shift of the reflected light from the FB G. The research based on the monitoring of eight different test persons. Heart rate meas urements were compared with a reference signal ECG and analyzed objectively by th e Bland-Altman statistic.

Authors of this article analyzed the influence of the cover layer in combination with the fixation material to measure deformation with the distributed system Brillouin Optical Time Domain Reflectometry (BOTDR). This system is based on the principle of measuring stimulated Brillouin scattering, which is frequency dependent on the measured temperature and the mechanical stress of the optical fiber. Standard telecommunication optical fiber G.652.D was used for experiments to verify whether this widely used type of fibers initially intended for telecommunication transmissions is suitable for measuring the deformation with the distributed system BOTDR. Knowing the impact of encapsulation type optical fiber is important in the use and implementation in practical applications. The results clearly show that it is important to pay attention to the implementation type of optical fiber. Based on post-analysis, it was determined the most appropriate implementation of optical fiber for optimal sensitivity in practical applications.

The optical fiber accelerometer owns exceptional advantages in various industrial applications due to its high sensitivity, immunity to electromagnetic interference, small size, low cost and easy to form sensor network etc. This study aims to evaluate an optimized interferometric optical fiber accelerometer based on Michelson structure. An integral parameter S was firstly proposed to assess the general performance of the accelerometer including both the sensitivity and resonance frequency, the compliant cylinder of the accelerometer proposed in this study was optimized as the composite structure materials, two typical sensitivity enhanced elastic materials of polycarbonate and silicone rubber were selected. This new type accelerometer was capable to provide higher phase sensitivity and wider flat bandwidth with optimized proportional mixing between two materials. The comparison analysis of Young’s modulus and Poisson ratio on the promotion of integral parameter S was finally discussed.

Distributed optical fiber sensing system (DOFS) has great potential in areas of petroleum exploration and ocean defense. By algorithm optimization in different coding environment, the multi-point and real-time heterodyne demodulation of DOFS is achieved. In experiments, the length of the optical fiber is 500m, the spatial resolution is 5m and the system sampling rate is 200kHz, under which condition the data rate reaches up to 160MB/s and the system can stilled be demodulated timely. Based on this, by plotting the three-dimensional diagram (vibration intensity versus time and space), the whole DOFS can be detected continuously and accurately.

In this study, a numerical model based on finite element method was proposed to evaluate the thermo-mechanical behavior of a composite structure material. The composite structure consisted of substrate, thermal spray coating, and an embedded optical fiber. The stress level of the composite structure especially the embedded fiber at the end of elaboration process was analyzed. The variations of refractive index of the embedded fiber due to the thermo-optic effect and the elasto-optic effect were investigated. The results showed that the the variation of stress and refractive index during the elaboration process had an insignificant effect on the embedding quality of the optical fiber under the presented optimized experimental conditions.

The paper discuss about aging of the optical couplers in their burdened high temperature. The article focuses on applied research and experimental development of resources for safety operation of optical networks in environment with higher temperature. It addresses issues of accelerated aging of optical fiber components in their burdened with high temperature. This article is devoted the impact of temperature loading on the SM optical FBT coupler with 8 branches. Optical passive component were exposed to temperature 95 °C for 433 hours. Measurements are focused on the parameters of geometry of optical beam. The detect changes are useful to understand the phenomenon of accelerated ageing elements of optical networks.

The monitoring of building structures deformations and testing of construction materials resilience are very important processes in the development and production of given materials and structures. This paper deals with the concrete deflection measurement using fiber optic distributed strain system. The own principle of the measurement evaluation is based on stimulated Brillouin scattering. In this paper, we explore the use of different types of optical fibers and the possibilities of their fixing. Above all, we are focusing on the possibility of their attachment to the measured objects. This is the most important step of the whole process that most affects the functionality and accuracy of measurement.

Distributed temperature sensing systems (DTS) are based on the principle of time-domain reflectometry where an optical fiber acts as a temperature sensor. DTS is capable of measuring the temperature along the optical fiber using the nonlinear phenomenon referred as Raman scattering. The biggest advantage of such sensing system is the use of an optical fiber itself as a sensor which gives the benefits of electromagnetic interference immunity, low sensor cost, measurement distances up to 10 kilometers and the safe use in flammable and corrosive environments. Fiber optic DTS can be therefore used in the environments and processes in which the application of conventional sensors is impossible. This article discusses the use of DTS for the moisture measurement in the masonry. In structures with built-in optical fiber, the immediate detection and location of moisture are possible. To perform the measurements an experimental brick wall has been built and between each wall layer the optical fiber was placed. The wall was built in stainless steel tub with a drain valve and was placed on a mobile trolley. The dimensions of the wall were 106 x 100 x 30 cm. The actual measurements were carried out in two stages. In the first, the tub was filled with water and the temperature change associated with the gradual increase of moisture inside the wall was measured. This measurement lasted until the saturation which was the time when the wall has no more moisture to adopt. The second stage then examined the evolution of the temperature inside the wall during gradual desiccation until the time when the temperature inside the wall was uniform between all layers.