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This article describes of the actual state of building structures by the example of structures of reinforced concrete and metal bridges. It is shown that a high degree of wear of artificial structures leads to the need for a reliable assessment of their actual condition using modern methods and means of non-destructive testing and diagnostics, as well as strengthening exploited structures with polymer composite materials. The results of researches on fiber-optic monitoring and strengthening of bridge spans with composite materials based on domestic and foreign carbon reinforcing fillers and epoxy polymer matrices are presented. It has been experimentally shown that for reinforced concrete structures it is advisable to use composite strengthening systems using external reinforcement installed directly on the damaged object by contact molding. For metal structures, this approach is not applicable due to a significant difference in the coefficients of linear thermal expansion of composites and metals. In this case, an amplification system based on prefabricated composite truss systems made by autoclave and unautoclave molding can be applied. The obtained research results also indicate the advisability of joint use of monitoring systems and strengthening of damaged bridge structures by composites.

This article describes results of the widespread use of external reinforcement systems for reinforced concrete and metal man-made structures based on domestic and foreign polymer composite materials (PCM), as well as fiber-optic monitoring systems, including a network of fiber-optic sensors (FOS) and a hardware-software complex that track the actual state of the control object throughout the entire life cycle. It is shown that for reinforced concrete structures it is advisable to use composite systems of external reinforcement installed directly on the reinforcement object by contact molding using special cold curing binders. In relation to metal structures, this technology is unacceptable due to a significant difference in the coefficients of linear thermal expansion of the metal and the carbon composite. To solve this problem, reinforcement technology has been proposed, which consists in installing discrete mechanical fasteners of finished composite spigots (similar to metal ones) made by autoclave and autoclave-free molding methods. In the event that deviations from the normative indicators for this type of structures are detected, the necessary set of measures is taken to strengthen, after which the monitoring system carries out a similar control, the results of which characterize the quality of the work performed. Thus, the monitoring system can act both as an effective tool for structural control and carry out local time monitoring before or after the relevant works on strengthening and reconstruction, and in real time work throughout the entire period of operation.

This article describes results of studies on the monitoring of deformations of load-bearing metal structures of a span structure of a bridge using fiber-optic sensors based on fiber Bragg gratings before and after reinforcement by polymer composite materials. It is received, that as a result of strengthening the deflection of the bridge has decreased in 2 times. The results of the experimental studies were compared with the computational justification carried out in PC LIRA 10.8. As a result of experimental and theoretical studies it was confirmed that the installed reinforcement system using composite spigots can be effectively used to restore the bearing capacity of artificial structures.

Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.5–2 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.6–3.8°C and 50–83 μεin temperature and strain range of 30–120°C and 0–400 με, respectively.

The temperature of the elementary conductors of the stator winding of a 225 MW turbogenerator has been measured using miniature fiber-optic sensors, built in to the winding during manufacture. This is the first time that practical bench tests have been made in Russian electrical machine construction practice. The results of the experiment are used as the initial data for determining important parameters of the construction of turbogenerators with air cooling, namely, the thermal conductivity of the body insulation in the slot, and the heat-transfer coefficient in the front parts of the stator winding.

Two types of fiber-optical measurement systems are compared: a line with a large number of point sensors based on fiber Bragg gratings (FBGs) interrogated by a tunable continuous fiber laser and a distributed system based on optical time-domain reflectometry (OTDR) of the Raman scattering of radiation of a pulsed fiber laser. Methods for increasing the measurement accuracy with the use of additional calibration of the Bragg wavelength shift over a fiber interferometer in the FBG system and spectral filtration of the Stokes and anti-Stokes components of the Raman scattering with the use of spectral-selective fiber couplers in the OTDR system are proposed and implemented. Physical effects on system parameters are analyzed, compared, and optimized for applications with monitoring of the temperature distribution in turbogenerators and oil wells.

Two types of distributed fiber sensor systems for temperature measurements have been developed: the first one is multi-point Fiber Bragg Grating based system with interrogation by CW tunable laser and nonlinearity compensation by reference interferometer. The second device is Raman scattering system based on optical time domain reflectometry (OTDR) with a pulsed laser providing spatial resolution of several meters and efficient spectral filtering of the Stokes and anti-Sokes signals by means of WDM couplers. Physical effects important for the systems operation are analyzed and their parameters are compared and optimized for applications in oil-gas industry and turbogenerator temperature monitoring.

The instability of the propagation of narrowband 100-ns laser pulses in the transparency window of a single-mode fiber in the presence of continuous broadband noise is demonstrated. The modulation instability developed due to the nonlinearity and anomalous dispersion leads to a rapid decay of the narrowband component after passing through the fiber. The modulation-instability threshold is shown to be sensitive to the noise level in a spectral interval of about 100 GHz near a central wavelength of about 1.55 μm and is inversely proportional to the fiber length (varied from 1.6 to 21.0 km in the experiments). The effect is completely eliminated owing to the application of a dispersion-shifted fiber with normal dispersion.

We demonstrate a Raman-based all-fibre temperature sensor utilising a pulsed erbium fibre laser. The sensor is made of a standard single-mode telecom fibre, SMF-28, and includes a number of directional couplers as band-pass filters. The temperature profile along a 7-km fibreoptic line is measured with an accuracy of 2oC and a spatial resolution of 10 m. In data processing, we take into account the difference in attenuation between the spectral components of the backscatter signal.

We demonstrate that, in the presence of noise, propagation of narrow-band 100-ns pulses through a 6-km long optical fibre sharply reduces their amplitude when a threshold power (~0.2 W) is exceeded. The effect is due to the development of modulation instability and is sensitive to the noise level in the spectral region ~100 GHz in width around the central frequency.

An interrogator of Bragg sensors based on a narrow-band tunable erbium laser is developed. The laser characteristics enable one to interrogate up to 45 temperature sensors in a range of 100°C with an error of no greater than 1°C.

A structural health monitoring system based on optical sensors has been developed and installed on the indoor soccer arena "Zarya" in Novosibirsk. The system integrates 119 fiber optic sensors: 85 strain, 32 temperature and 2 displacement sensors. In addition, total station is used for measuring displacement in 45 control points. All of the constituents of the supporting structure are subjects for monitoring: long-span frames with under floor ties, connections, purlins and foundation.

The rapid development of fiber optics initiated by the increasing demand for the information content and information transmission rate resulted in the development of new technologies in other areas, primarily next-generation lasers and sensors. These achievements are based on the unique properties of optical fibers. These are small optical losses in the propagation of radiation in the fiber ( ~0.2 dB/km in the low-loss transmission window in the region of ~1.55 µ m), the effective heat withdrawal due to the fiber geometry, and low distortions of a light beam. As a result, a high-intensity light can propagate over large distances without decline in beam quality. Furthermore, an important characteristic of fibers is photosensitivity or the ability to locally change the refractive index by the action of UV radiation. This effect makes it possible to construct a light control device directly in the fiber core. The fiber Bragg grating (FBG), a periodic refractive index structure, is an example of such a device. In this study, the properties of FBG are considered as a one-dimensional photonic crystal (PC), and prospects for FBG application as elements of laser and sensor systems are evaluated. The FBG is a piece of a light guide, in the core of which the periodic structure of the refractive index is induced [1]. The FBG possesses the property of narrow-band reflection of radiation at the Bragg wavelength

A tunable ytterbium-doped fibre laser is fabricated. The laser is tuned by using a tunable fibre Bragg grating (FBG) as a selecting intracavity element. The laser is tunable within 45 nm (from 1063 to 1108 nm) and emits ~6 W in the line of width ~0.15 nm, the output power and linewidth being virtually invariable within the tuning range. The method is proposed for synchronous tuning the highly reflecting and output FBGs, and a tunable ytterbium all-fibre laser is built.