System based on brillouin scattering with multiple fbg

FIELD: measuring equipment.

SUBSTANCE: invention belongs to area of instrumentation and can be used for creation of distributive systems of measurement of temperature and deformation. The Brillouin system for tracking of temperature and deformation contains one - or bilateral fibre with a set of fibre Bragg gratings (FBG) on different lengths of waves and a laser system with the setting excitation, adjusted in a range essentially bigger, than Brillouin shift. FBG are distributed along the length of the placed fibre and serve as chosen reflectors of length of the wave, allowing to support operation of the device even in case of a rupture of fibre.

EFFECT: increase of accuracy and reliability of these measurements.

7 cl, 4 dwg

 

Cross references to related applications

This application claims the priority of provisional patent application U.S. No. 61/279,632, filed October 23, 2009.

The scope of the invention

The description relates to distributed measurement systems for measuring temperature and strain, and more specifically methods and systems to improve system reliability on the basis of stimulated scattering of Mandel'shtam-Brillouin by adding redundancy.

Background of the invention

The effects of Raman scattering and Mandel'shtam-Brillouin used for distributed temperature monitoring for many years. The Raman effect was first proposed for use in measuring programs in the 80s, whereas the effect of the Mandel'shtam-Brillouin was introduced later as a way to increase the outside dimensions of the optical time domain reflectometry (OTDR), and then for use in monitoring temperature and/or strain.

Fiber-optic sensors based on the effect of scattering Mandel'shtam-Brillouin, was used extensively in the measurement of distributed temperature and/or voltage. As the frequency shift and the power of the Brillouin signal backscatter depends on temperature and voltage. Scattering Mandel'shtam-Brillouin can be used for distributed sensors in venued nom, and in the spontaneous mode.

Spontaneous scattering uses a single beam of laser light at a stable wavelength (optical frequency) and measures the spectrum of light backscattering. The advantage of this is the lack of the necessary modulation to sweep the light in the unilateral fiber. This simplicity is a great advantage.

However, it has the disadvantage of a small dynamic range. In order to perform the spectral analysis, the detection scheme can become confusing. In addition, since the signal back-scattering is very weak, the ratio of signal to noise ratio will be small and will require a long integration time, a large number of measurements for averaging, or both.

Systems based on stimulated scattering of Mandel'shtam-Brillouin are, or bilateral, or use a reflecting mirror at the end of the fiber connected to the device backward propagation. Stimulated scattering requires two incoming light signals (probe pulse) and at least one of them must be modulated and deployed on the optical band (10-14 GHz). In addition, two input light signal must be reciprocal in order to create a population inversion, so most of the work in this area was based on the DFCS is gonna scheme. This gives a much greater dynamic range. The main disadvantage of such an emergency system is that, if a fiber break occurs, the system fails.

An emerging area is the use of fiber Bragg gratings (FBG). The physical principle underlying the FBG sensor, is that the change in strain, voltage, or temperature will change the center wavelength of light reflected from the FBG. The refractive index of the fiber depends on the density of the contained impurities. UBD are made through the redistribution of impurities to create a region containing larger or smaller amounts, using a method called laser recording. The FBG filter for wavelength consists of a series of perturbations in the refractive index along the length of an optical fiber containing impurities. This lattice refractive index reflects a narrow range, is directly proportional to the period of modulation of the refractive index (L) and the effective refractive index (n).

Because the status of the temperature and strain FBG directly affect their reflection spectrum, they can also be used for a variety of measuring devices. As fiber-optical analogue of the traditional electronic sensors, FBG can serve as strain sensors, DL is providing design engineers with previously unavailable data measurements. Emerging devices account for detecting changes in the voltage of buildings, bridges and buildings aircraft; measure the depth of streams, rivers and reservoirs for flood protection; and measuring the temperature and pressure in deep oil wells. The advantages of FBG sensors include improved accuracy, sensitivity and resistance to electromagnetic interference, radio frequency interference and radiation; the ability to transform into a compact, lightweight, durable device that is small enough to be embedded or attached to structures or substances, to create a "smart" materials that can operate in adverse conditions - for example under water - where traditional sensors can not work; the ability to multiplexable; ease of installation and use; and potential low cost as a result of mass production in the field of telecommunications.

These properties allow the use of many sensors on a single optical fiber, located at an arbitrary distance from each other. Using a custom laser can be independently read each sensor and to receive the distributed measurement of large structures. Since the lattice of multiplexed on a single fiber, it is possible to have access to many of the sensors using a single connection to optical is who is the source and the detector. Traditional strain gauges require that each sensor had its own wire output-connected and connected to the reader sensor. In the device, which will be discussed, the use of spaced UBD is used in a novel way to achieve a significant improvement in system reliability in the system based on the scattering Mandel'shtam-Brillouin.

There is a need for a system that has advantages such as unilateral spontaneous system, and improved dynamic range systems based on stimulated scattering of Mandel'shtam-Brillouin.

The essence of the invention

This need is met by the invention of this specification.

The proposed system based on the scattering Mandel'shtam-Brillouin contains one-way fiber with lots of fiber Bragg gratings (FBG) at different wavelengths and laser system with master pump, adjustable significantly larger than the Brillouin shift. UBD distributed throughout the length of the posted fibers and serve as selective reflectors wavelengths. Fiber Bragg grating (FBG) is a type of distributed Bragg reflector, created in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. It has reached what is by adding a periodic variation to the refractive index of the core fiber, what gives rise to the dielectric mirror that is dependent on wavelength. Fiber Bragg grating, thus, can be used as a reflector, depending on the wavelength.

When you first start the system uses the farthest posted by UBD and laser system tuned to the frequency of this UBD. If this fiber is no problem, then this configuration is saved. If later during operation there is a rupture of the fiber, then the laser system is returned to the remainder of the farthest UBD, providing continuous forced to work for the remainder of the fiber.

In one aspect of the need is met by a method for improving the reliability of systems based on stimulated scattering of Mandel'shtam-Brillouin by adding redundancy, which includes at least the steps of: creating a first optical signal, the first optical signal is adjusted in a predetermined wavelength range; the connection of the first optical signal from a fiber optic cable located in the study area, located fiber optic cable contains multiple distributed fiber Bragg gratings, each fiber Bragg grating has a distinctive and well-known characteristic wavelength reflection; configuring the first optical signal at the characteristic wavelength of the first reflection you the early spaced fiber Bragg gratings; create a second optical signal at a fixed predetermined wavelength, the predetermined wavelength lies outside of the reflectance spectrum of any of spaced fiber Bragg gratings; connection of the second optical signal from the fiber optic cable; and receiving the first reflected signal of the first optical signal, the reflected signal is reflected from the first selected spaced fiber Bragg gratings placed in the optical cable; receiving the second reflected signal of the second optical signal, the second reflected signal is obtained from Brillouin backscattering placed in the optical fiber; measuring shifts in the characteristics between the second optical signal and the second reflected signal that indicates the environmental conditions placed along the optical fiber; where when placed in the fiber optic cable is determined by the gap, the first optical signal is reconfigured at the characteristic wavelength of the second selected spaced fiber Bragg gratings.

In another aspect, the need is satisfied by the system to improve system reliability on the basis of stimulated scattering of Mandel'shtam-Brillouin by adding redundancy, which contains at least: a custom probe laser; laser pumping with fixed h is depends; acousto-optic modulator to shift the optical frequency of the pump laser with a fixed frequency to apply a fixed predetermined wavelength; a connector that combines the signals with a custom probe laser and the pump laser with a fixed frequency and connects to fiber-optic sensor placed in the study area being measured; a detector for collecting light backscatter from the fiber-optic sensor; a module collection/processing for analysis of light backscattering and measurement in the characteristics between the second optical signal and the second reflected signal that indicates the environmental conditions placed along the fiber, where the fiber-optic sensor contains multiple distributed fiber Bragg gratings, each fiber Bragg grating has a separate and well-known different wavelength reflection; and where a fixed predetermined wavelength of the pump laser with a fixed frequency and acousto-optic modulator lies outside of the reflectance spectrum of any of spaced fiber Bragg gratings.

A brief description of graphic materials

For a more complete understanding of the present invention will now appeal to the following graphic materials, in which:

figure 1 p establet an image of the spectrum of scattered light in the optical fiber;

figure 2 is a representation of a configuration of a pulse pump for the implementation of the system based on the scattering Mandel'shtam-Brillouin tracking;

figure 3 is an image of single and bilateral Brillouin configurations prototypes;

figure 4 is an image of single and bilateral Brillouin system of the present invention.

Detailed description of the invention

Although in this document have been described in detail certain embodiments of the present invention and their advantages, it should be understood that various changes, substitutions and modifications can be made without deviating from the essence and scope of the invention as defined by the attached claims. Moreover, it is not implied that the scope of the present invention is limited to particular variants of the implementation processes, mechanisms, products, tools, methods and steps described herein. Specialist average skill in the art will readily understand from this description that other processes, mechanisms, products, tools, methods, or steps, presently existing or to be developed later that perform substantially the same function or resulting in largely the same result as the corresponding embodiments of described in this is the document, can be used in accordance with this invention. Accordingly, it is assumed that the appended claims include within their scope such processes, machines, products, tools, methods, or steps.

Figure 1 is a schematic illustration of the spectrum of scattered light in optical fibers, assuming that a fiber running one wavelength λ0shown as 20. All the components 40 are Stokes components, and all components 30 are anti-Stokes components. Light Romanovka backscatter has two shifted frequency components, Stokes 90 and 50 anti-Stokes asked thermally induced molecular vibrations. Therefore, the light backscatter carries information about the local temperature in the center of the scattering. Different amplitude 60 anti-Stokes components 50 are highly temperature dependent, whereas the amplitudes of Stokes components 90 - no. Therefore, Raman touch method requires some filtering to isolate the relevant frequency components, and consists of writing the ratio between anti-Stokes amplitude and Stokes amplitude, which contains information about the temperature. Since the magnitude of spontaneous Raman backscattering light is low enough, use Magomadov the e fibers with high numerical aperture, to maximize the intensity of the light directed backward scattering. However, the relatively high response attenuation multimode fibers restrict the work of Raman devices a range of approximately 10 km.

Scattering Mandel'shtam-Brillouin shown as 70 in the anti-Stokes mode and 75 in the Stokes regime. It is the result of interaction between the propagating optical signal and thermoacoustic waves in the GHz range, are present in the quartz fiber, causing the rise of the shifted frequency components. It can be seen as the diffraction of light by moving the lattice generated acoustic wave (acoustic wave is actually a pressure wave, which introduces a modulation of the refractive index through elasticoptic effect). Dragirovaniya light experiences a Doppler shift, since the lattice is distributed in the fiber at the speed of sound. The speed of sound is directly related to the density of the medium and depends on both temperature and strain. In the so-called Brillouin frequency shift carries information about the local temperature and deformation of the fiber. In addition, Brillouin methods of tracking are based on measuring the frequency of 80 or 85, in contrast to the Raman modes, which are the basis of yaytsa on the intensity. Brillouin methods, therefore, are inherently more accurate and more stable in the long term, since methods based on intensity, suffer from greater sensitivity to deviations.

Scattering Mandel'shtam-Brillouin has the peculiarity that it can become a forced interaction, provided that the optical signal is called the excitation signal, is used in addition to the original optical signal, commonly called a pump.

The basic configuration of the distributed Brillouin sensor has the following aspects: a strong pulse of light, called pumping, is launched into the fiber. He meets a weak wave of light, called a probe, extending in the opposite direction. Stimulated scattering Mandel'shtam-Brillouin occurs when the pump and probe overlap, leading to amplification of the probe, provided that the difference between the two frequencies lies within the Brillouin spectrum of the extension.

This interaction causes the Association between the optical signals of the pump and probe and acoustic waves when the resonance condition, i.e. when the frequency difference between the light probe and the pump correspond to the Brillouin frequency shift.

It turns out that the resonance condition depends on the strain and those of the temperature, so what is the definition of the resonance frequency directly gives the measurement of temperature or strain. The advantage of measuring the interaction between two optical signals instead of registering spontaneously scattered light of low intensity is the ratio of signal to noise is much more acceptable. As a result, the measurement of the spontaneous light backscattering requires a long integration time, while the method of pump-probe - no, and therefore is very suitable for quick measurements.

Brillouin measurement techniques only work with single-mode optical fibers, and due to the low loss characteristics of single-mode fibers can be obtained measurements over distances of more than several tens of kilometers.

There are a number of hardware configurations that can be used to implement forced Brillouin measurements.

Figure 2 is a picture of one approach - use a custom probe laser 120 (first optical signal) and laser 110 pump with fixed frequency with acousto-optic modulator 130 to move upward optical frequency (second optical signal). Other approaches include the circular design of the optical resonator to repeatedly pass by kr the se signal through the modulator, to continuously climb up to reach the desired frequency. Using any of these approaches for obtaining stimulated scattering of Mandel'shtam-Brillouin considered the concept of this application. The power of the laser radiation passes through the connectors 140, 150 to the elongated fiber-optic sensor 150 placed in the study area to measure, for example, temperature or strain. Light backscatter from the fiber-optic sensor passes through the detector 160 in the module 180 collection/processing for analysis. Module collection/processing can use any Brillouin method of measurement known in the art.

Figure 3 and 4, the rectangle is represented as a system 310, 315, 325, 335 DMS (distributed tracking system), can be any Brillouin system, described previously, which can generate the equivalent pulse and the probing laser radiation at frequencies necessary to obtain forced Brillouin measurements.

Figure 3 is an image of two ordinary prototype implementations of the Brillouin system: two-way system 300, in which the optical fiber 320 is connected on two sides with DMS 310, and a one-way system 330 with the reflecting mirror 350 on the far side.

Figure 4 is a view of embodiment domestic who, providing and superior dynamic range, and protection against losses in the event of breakage. Or unilateral 400, or in bilateral 500 mode, the system has a periodic fiber Bragg gratings 440 or 550 (VBR), acting as mirrors throughout the length of the posted optical cable 420 or 540. Distributed FBG serve as selectable reflectors wavelengths. Each fiber Bragg grating in this embodiment, has a distinctive and well-known characteristic wavelength of reflection. It implements a system based on stimulated scattering of Mandel'shtam-Brillouin at selected points along the system. Custom laser systems DMS can be configured to a specific frequency of each individual FBG using methods known in the art.

These properties allow the use of many sensors at any distance on a single optical fiber. Using custom lasers, it is possible to poll each sensor independently from each other and get distributed measurements on large structures. Since gratings are multiplexed on the same fiber, you can get access to many of the sensors using a single connection to a light source and detector. Traditional electronic strain gauges require that each sensor had its own is revolucni conclusions United and brought to the reader sensor. In the described embodiment, the use of spaced UBD is used in a novel way to achieve a significant improvement in reliability of the device.

Using a one-way system with 4 as an example, the system can be placed, and custom lasers are used to configure the device for the end-VBR 550. If you have a late break in the fiber, the system can be returned immediately to the farthest working VBR away from DMS to provide an emergency Brillouin work for the remainder of the fiber. Now this makes it possible unilateral Brillouin system performance and benefits of the system based on stimulated scattering without the threat of total loss of the system in case of rupture of the fiber.

In the case of a bilateral system with figure 4, applies the same reasoning. The gap in the bilateral system can also be corrected by using any of the remaining UBD as a selectable reflectors wavelength, to continue using the system on the basis of stimulated scattering of Mandel'shtam-Brillouin measurement and temperature profile, and strain.

Described embodiments of provide a system based on stimulated scattering of Mandelstam-Br is Luana, which can be used at a great distance for tracking and deformation, and temperature, while providing a large dynamic range and the ability to cope with the gap fiber without a complete loss of system performance.

1. The way to increase the reliability of sensor systems based on stimulated scattering of Mandel'shtam-Brillouin by adding redundancy, comprising the steps:
a. the creation of the first optical signal, and said first optical signal is adjustable in a predetermined range of wavelengths;
b. supply the specified first optical signal in the fiber optic cable placed in the study area, and specified posted by fiber optic cable contains multiple distributed fiber Bragg gratings, where each fiber Bragg grating has a different well-known and characteristic wavelength of reflection;
c. the configuration of the specified first optical signal at the characteristic wavelength of reflection of the first selected spaced fiber Bragg gratings;
d. create a second optical signal at a fixed predetermined wavelength, and the specified predetermined wavelength is outside of the reflectance spectrum of any of spaced fiber Bragg gratings;
e. feed is shown a second optical signal to the specified fiber optic cable;
f. receiving the first reflected signal of the first optical signal, and specified the reflected signal reflected from the first selected spaced fiber Bragg gratings placed in the optical cable;
g. receiving the second reflected signal of the second optical signal and the second reflected signal received from the inverse scattering Mandel'shtam-Brillouin placed in the optical fiber;
h. measure displacement in the characteristics between the said second optical signal and the specified second reflected signal that indicates the environmental conditions along specified posted optical fiber; where, when placed in the specified cable define a gap, said first optical signal adjusts the characteristic wavelength of the second selected spaced fiber Bragg gratings.

2. The method according to claim 1, further comprising pulse generating specified second optical signal.

3. The method according to claim 1, where the specified first selected spaced fiber Bragg grating is chosen as the farthest posted by fiber Bragg grating in the interested area.

4. The method according to claim 1, where after identifying a gap in the specified posted by fiber optic cable specified second selected spaced fiber Bragg grating wybir the t as the most distant posted by fiber Bragg grating in the remaining unbroken fiber optic cable.

5. System to improve the reliability of sensor systems based on stimulated scattering of Mandel'shtam-Brillouin by adding redundancy, containing:
a. custom probe laser;
b. the pump laser with a fixed frequency;
c. acousto-optic modulator for shifting the optical frequency of the specified pump laser with a fixed frequency to provide a fixed predetermined wavelength;
d. the connector, which combines the signals from the specified custom probe laser and the pump laser with a fixed frequency and connects to fiber-optic sensor placed in the interested area being measured;
e. a detector for collecting light backscatter from the specified fiber optic sensor;
f. module collection/processing for analysis of the specified light backscatter measurements of shifts in the characteristics between the said second optical signal and the specified second reflected signal that indicates the environmental conditions along the specified hosted fiber;
g. where specified fiber-optic sensor contains multiple distributed fiber Bragg gratings, each fiber Bragg grating has a different well-known and characteristic wavelength of reflection, and
h. where this fixed the bathroom predetermined wavelength from the specified pump laser with a fixed frequency and a specified acousto-optic modulator lies outside of the reflectance spectrum of any of spaced apart fiber Bragg arrays.

6. System to improve the reliability of sensor systems based on stimulated scattering of Mandel'shtam-Brillouin according to claim 5, where the optical fiber sensor containing multiple distributed fiber Bragg gratings, is a two-way system.

7. System to improve the reliability of sensor systems based on stimulated scattering of Mandel'shtam-Brillouin according to claim 5, where the optical fiber sensor containing multiple distributed fiber Bragg gratings, is a one-way system.



 

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4 cl, 2 dwg

FIELD: physics, measuring.

SUBSTANCE: invention concerns noncontact examinations of a surface of metals and semiconductors optical methods. Device contains radiant of laser radiation smoothly reconstructed on frequency, the solid-state sample with a flat surface and an explored stratum on it, a device of transformation of volume radiation (VR) in the superficial electromagnetic wave (SEW) and back, a photointake, reformative VR in an electrical signal, and the block of processing of observed datas. The device of VR in SEW transformation also is back executed as a single whole in the form of the transparent plane-parallel plate with an oblique end face. The plate the facet converted to the sample, is located in the SEW field parallelly the surface of the sample apart from it not less than 10λ where λ a radiation wave length in vacuo, and has length along the SEW track not less than length of SEW distribution. Photointake is executed in the form of a ruler of photodetectors and disposed on the upper facet of a plate.

EFFECT: cutting of time of measurings and making of possibility for the coordination of length of SEW distribution with the size of surface of the sample.

1 dwg

FIELD: physics.

SUBSTANCE: system contains monochromatic source of wavelength varying under time law, optical splitter, optical modulator, photodetector and computing unit, as well as gas correlation filter, reference comparison resolver and auxiliary photodetectors.

EFFECT: elimination of environment effect; of supply voltage instability; of interference and destabilising factors.

2 dwg

FIELD: electricity.

SUBSTANCE: invention is referred to electric cable with in-built strain-gage fit specifically to measure static and dynamic deformations, in particular, bending strain. Method of bending strain control for electric cable includes stages of the cable equipment with peripheral and mechanically unsymmetrical bearing element having higher resistance to tensile loads than to compression ones and with fibre-optical sensor.

EFFECT: invention provides for high duty cables, in particular, in mobile units, controllability and traceability of bending strain area.

9 cl, 15 dwg

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