CN105301695A - Fiber grating array sensitive optical cable and application method thereof - Google Patents

Abstract

The invention relates to a fiber grating array sensing optical cable and a using method thereof. The optical cable includes an outer sheath and a sensing fiber. The sensing fiber is laid in the outer sheath. It is characterized in that the sensing fiber is an identical grating array fiber that is directly engraved into the grating online during wire drawing. The outer sheath is One-piece extruded integral outer sheath. The sensing optical cable of the present invention has high strength, small transmission loss, good grating consistency, and the prepared fiber grating array can be directly cabled at one time; the sensing optical cable of the present invention has a simple and reasonable structure and strong mechanical properties of compressive and tensile resistance ;Using time-division/wavelength-division hybrid multiplexing signal demodulation technology for sensing signal demodulation, breaking through the limitations of existing sensing optical cables, fast and accurate positioning, good repeatability of measurement results, and easy for long-distance multi-point distribution measurement , which can be multiplexed and form a sensor network.

Description

Fiber Bragg grating array sensing cable and using method thereof

technical field

The invention relates to a fiber grating array sensing optical cable and a using method thereof, belonging to the technical field of optical fiber sensing.

Background technique

At present, temperature sensors are widely used in equipment and facilities such as aerospace, energy base stations, oil and gas pipelines, dams, road bridges, cables, etc., for construction quality monitoring, long-term health monitoring, and fire alarms.

In practical applications, electronic temperature sensors show shortcomings such as susceptibility to electromagnetic interference, poor stability, small measurement range, and short signal transmission distance. Especially in multi-point detection, a large number of signal transmission lines cause great inconvenience to on-site construction. The temperature sensing optical cable has the advantages of high monitoring sensitivity, small size, light weight, safety and explosion-proof.

Although temperature sensing optical cables, such as temperature sensing optical cables based on intensity modulation, have broken through some limitations of traditional electronic temperature sensors, they still have the following defects, such as being greatly affected by the environment, difficult to locate, and repetitive measurement results Poor sex and so on. In terms of structure, the existing optical fiber grating sensing cables need to be fused with fiber gratings, that is, the gratings are prepared individually in the static state of the optical fiber, and then the multiple gratings are welded one by one by a fiber fusion splicer. jacket. This has the disadvantages of low grating preparation efficiency, many fusion points on the optical fiber, large loss, limited number of gratings connected in series, and poor mechanical properties of the final grating array, which cannot fully meet the requirements of practical applications for fiber grating sensing cables.

In addition, the grating is very sensitive to stress and temperature, and the influence of stress must be weakened or eliminated in practical applications. In the process of cabling and cable laying, the optical fiber cable will often be stretched, bent, trampled, etc. If it is not handled properly, it will cause inaccurate temperature measurement and even cause the sensing cable to fail.

To sum up, the optical fiber grating cable used for sensing needs to solve the problems of low grating preparation efficiency in the grating array, small number of gratings, low fiber strength, large loss, poor reliability of optical cables, gratings are easily affected by stress, and complex optical cable structures And other issues.

Contents of the invention

The technical problem to be solved by the present invention is to provide a fiber grating array sensing cable with reasonable structure, high fiber strength, low loss, long measurement and transmission distance, reliable sensing performance and easy fabrication in view of the deficiencies in the prior art above. and how to use it.

The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: an outer sheath and a sensing optical fiber are included, and the sensing optical fiber is laid in the outer sheath. Identical grating array optical fiber, the outer sheath is an integral outer sheath formed by extrusion molding at one time.

According to the above scheme, the sensing fiber is a continuous identical grating array fiber without fusion points; the number of gratings continuously written on the sensing fiber is 5 to 10,000, and the distance between two adjacent gratings is 0.5m ~ 200m.

According to the above solution, the grating on the sensing fiber is a weak reflection Bragg grating with a reflectivity of 1%-0.0001%.

According to the above scheme, the sensing optical fiber is composed of a bare optical fiber engraved into a grating and coated with a resin coating layer, a carbon coating layer or a metal coating layer.

According to the above solution, the static tensile strength of the sensing optical fiber is greater than or equal to 55N, and the entire optical fiber is dynamically screened under a tension of 100 kpsi.

According to the above solution, the sensing fiber is coated with a tight-buffered layer or a loose-buffered layer outside the coating layer to form a tight-buffered sensing fiber and a loose-buffered sensing fiber respectively.

According to the above scheme, a metal armor layer is arranged in the outer sheath, and the sensing optical fiber is loosely laid in the metal armor layer.

According to the above solution, a non-metal strengthening layer is arranged between the outer sheath and the metal armor layer.

According to the above solution, the radial section of the outer sheath is circular or butterfly.

According to the above solution, the outer sheath is provided with reinforcements at intervals in the circumferential direction or on both sides.

The optical fiber grating array sensing cable provided by the invention is a quasi-distributed sensor of fiber Bragg gratings, wherein the Bragg gratings can be arranged equidistantly or not equidistantly. The single-pulse ultraviolet laser beam is used for exposure, the phase mask method is used to write the grating, and the weak reflection Bragg grating is prepared, and the bare optical fiber is exposed continuously, and the identical weak grating array is prepared. The grating writing device is an excimer laser combined with a phase mask, which is set under the fiber drawing tower. The single-pulse ultraviolet laser beam output by the excimer laser is shaped by the diaphragm, focused by the lens, and irradiated on the mask. Write the grating on the bare fiber next to the mask. The grating writing process is controlled by the computer, the distance between adjacent gratings and the laser intensity can be set as required, and the whole device continuously and automatically writes gratings on the bare optical fiber pulled down at a constant speed. The optical fiber is coated after writing the grating. Then, the grating array is subjected to mechanical testing and demodulation testing to make a sensing optical cable, and finally the test signal is restored through the fiber grating array signal demodulation technology.

Due to the characteristics of wavelength modulation in grating array wavelength division multiplexing technology, each fiber Bragg grating will occupy a certain bandwidth, and at the same time, it is not allowed to overlap with each other. Therefore, the wavelength division multiplexing technology of fiber gratings is limited by the bandwidth of the light source and the wavelength width of the grating, and the multiplexing of 30 gratings on one fiber has basically reached the limit. The number of gratings in the optical fiber grating array sensing cable provided by the present invention is at least 5, and can be as many as 10,000 or more, which is determined according to needs. However, when the number of multiplexed gratings on an optical fiber exceeds 30, it is difficult to demodulate the signal by using the wavelength division multiplexing technology alone.

The method of using the optical fiber grating sensor of the present invention is: the method of composite use of wavelength division multiplexing technology and time division multiplexing technology, which is a distributed optical fiber grating sensor based on the binary change relationship of sensing pulse signal with time and wavelength Signal demodulation technology, a narrow-band pulse signal output by the light source is coupled into the grating array, the narrow-band pulse signal repeats at a fixed frequency, and the wavelength of the signal is periodically tuned and changed continuously. When incident on the grating consistent with the pulse wavelength, the pulse signal part It is reflected back to the demodulator by the grating, and the remaining part continues to transmit forward; if the wavelength of the incident pulse is inconsistent with the central wavelength of the grating, the pulse signal is transmitted directly until it meets the grating with the same central wavelength; according to the return time of the pulse signal and the wavelength of the grating reflected signal and reflected light intensity, analyze and calculate the spatial position of the grating and the size of the sensing parameter value.

The beneficial effects of the present invention are: 1. There is no welding point on the optical fiber of the identical grating array prepared online, the strength is high, the transmission loss is small, the consistency of the grating is good, and the prepared fiber grating array can be directly cabled at one time; 2. The inventive sensor cable has a simple and reasonable structure and strong mechanical performance against compression and tension. When the cable is under tension, the optical fiber can always be in a relaxed state, ensuring that the grating is not stressed and can measure stably and accurately; Wavelength division hybrid multiplexing signal demodulation technology for sensing breaks through the limitations of existing sensing optical cables, fast and accurate positioning, good repeatability of measurement results, easy to perform long-distance multi-point distribution measurement, and can be multiplexed and formed sensor network.

Description of drawings

Fig. 1 is a radial cross-sectional structure diagram of the first embodiment of the present invention.

Fig. 2 is a radial cross-sectional structure diagram of the second embodiment of the present invention.

Fig. 3 is a radial cross-sectional structure diagram of a third embodiment of the present invention.

Fig. 4 is a radial cross-sectional structure diagram of a fourth embodiment of the present invention.

Fig. 5 is a radial sectional structure diagram of a fifth embodiment of the present invention.

Fig. 6 is a group of demodulation spectra of identical weak grating arrays in one embodiment of the present invention.

Fig. 7 is a spectral diagram of gratings at six consecutive positions in an embodiment of the present invention.

Fig. 8 and Fig. 9 are curves of the central wavelength of two gratings at different positions on the grating array as a function of time in an embodiment of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings.

The first embodiment of the present invention, as shown in Figure 1, is a circular fiber grating array sensing cable, comprising an outer sheath 3 with a circular cross-section, a metal armor 2 is arranged in the outer sheath, and a metal armor 2 is placed on the metal armor. The sensing optical fiber 1 is loosely laid in the layer; wherein, the outer sheath can be made of polyvinyl chloride sheath material, flame-retardant sheath material or electric tracking-resistant sheath material; the metal armor layer can be made of aluminum-plastic composite Tape, steel-plastic composite tape, spiral steel armor, steel strand or stainless steel pipe, the aperture of the metal armor layer is 0.8-6mm; the sensing optical fiber is an identical grating array optical fiber that is directly engraved into the grating on-line during wire drawing , the number of written gratings is 5 to 10,000, and the distance between two adjacent gratings is 0.5m to 200m, which can be equidistant or unequal, and the grating on the sensing fiber is a weak reflection Bragg grating , and the reflectance is 1% to 0.0001%. The sensing optical fiber is composed of a bare optical fiber engraved into a grating and coated with a resin coating layer, and the coating layer is 1-2 layers. The outer sheath is a one-time extruded integral outer sheath. In this embodiment, the diameter of the optical cable is 2mm, the diameter of the spiral steel armor is 1mm, the length of the optical cable is 1964m, and the distance between the gratings is 2m.

The second embodiment is shown in FIG. 2 . The difference from the first embodiment is that reinforcements 4 are provided on both sides of the outer sheath, and the reinforcements are steel wires. Other structures are the same as the first embodiment.

The third embodiment is shown in FIG. 3 . The difference from the first embodiment is that a reinforcing member 4 is provided in the outer sheath at intervals of 90° in the circumferential direction, and the reinforcing member is a steel wire. Other structures are the same as the first embodiment.

The fourth embodiment is shown in FIG. 4 , which is different from the first embodiment in that a non-metal reinforcing layer 5 is provided between the outer sheath and the metal armor layer, and the non-metal reinforcing layer is aramid yarn. Other structures are the same as the first embodiment.

The fifth embodiment, as shown in Figure 5, is a butterfly fiber grating array sensing cable, including an outer sheath 3 with a butterfly cross section, and a metal armor layer 2 is arranged in the outer sheath, and the metal armor layer is Spiral steel armor, in which the sensing optical fiber 1 is loosely laid in the metal armor layer; reinforcements 4 are arranged on both sides of the outer sheath, and the reinforcements are steel wires. In this embodiment, the cross section of the optical cable is 4.5mm×6.6mm, the diameter of the spiral steel armor is 3mm, and the length of the optical cable is 1099m, wherein the distance between the gratings is 20m.

The cable forming process of the fiber grating array sensing optical cable of the present invention (taking embodiment 3 as an example) is as follows:

During the cabling process, the optical fibers are released in the form of active pay-off with small tension. First, a reinforcement is longitudinally wrapped around the optical fiber, with a diameter of preferably 2-5 mm, and then the steel wire is released. The sheath is made of polyvinyl chloride, and then the sheath is stretched in the cold water tank by selecting the appropriate speed of the traction wheel. At this time, the longitudinal package reinforcement is stretched together, and the optical fiber is in the loose sleeve structure without traction. round effect, accumulating longer fibers in the sheath. Then wait for the sheath to pass through the traction wheel, the longitudinal sheath reinforcement and the sheath recover elastically, and the length is shortened, so that the optical fiber in the loose sheath structure can obtain the required excess length value, and finally it is coiled and the cable is completed.

The weak gratings of the sensing optical fiber of the present invention have the same optical parameters such as reflectivity, central wavelength and bandwidth, and are called identical weak gratings. Using the LG1-100B demodulator to detect, the prepared identical weak grating array can be demodulated, and the demodulated data can be saved as FBG and RAW files, and a certain grating can be observed through the corresponding analysis software (by distance Positioning the grating, that is, the distance between a certain grating and the demodulator is used to calibrate) the central wavelength and its grating spectrum pattern at a certain moment. Fig. 6 shows the demodulation spectrum of a group of identical weak grating arrays, the distance between the gratings in the identical weak grating array is 2m, and the total length of the grating array is 1965m. According to FIG. 6 , it can be known that the central wavelength of the grating at different positions on the grating array at a certain moment, that is, the change of the central wavelength of the grating array with distance at a certain moment. Figure 7 shows the spectrograms of the grating at six consecutive positions. Figures 8 and 9 show the change with time of the central wavelengths of the two gratings at the positions of 20.89m and 50.25m on the grating array under a certain temperature rise regime. Among them, the grating at the position of 20.89m belongs to the temperature experiment group, as shown in Figure 8; the grating at the position of 50.25m belongs to the temperature experiment comparison group, as shown in Figure 9. It can be seen from Figure 8 that the position of the grating can be determined by the demodulator and the change of the center wavelength of the grating with temperature can be measured at this position.

From Figure 6 to Figure 9, it can be seen that the LG1-100B demodulator using time division/wavelength division technology can realize the demodulation of the identical weak grating array, and can collect, save and display the identity of the weak grating array as a whole in a certain The distribution of the central wavelengths of all gratings at each moment, it can be seen that each grating in the grating array has been successfully written, there is no missing engraving, the 2m spacing error between the gratings is very small, the reflection intensity of the gratings is basically the same, and the gratings on the grating array The reflection intensity fluctuation of the grating is small, the symmetry of the grating is good, the extinction ratio is large, and the consistency of the grating spectral shape is good. It can be seen from Figure 6 to Figure 9 that the demodulator can achieve precise addressing and positioning of the grating, and record and save the change of the central wavelength of each grating with time in real time. The central wavelength of the grating is basically unchanged at room temperature. The results show that the grating on the grating array can do temperature sensing very well.

The static tensile strength of the identical grating array optical fiber of the present invention is greater than or equal to 55N, and the whole of the optical fiber with a length of 5000m can remain intact after being dynamically screened with a tension of 100kpsi. The specific embodiment is to guide the optical fiber containing the grating array The pulley is pulled to the pay-off and take-up driving wheels, the driving wheel pressure belt prevents the optical fiber from slipping on the wheel, but there is no additional stress on the optical fiber and does not damage the fiber coating. There is a tension sensor with a sensor between the two driving wheels The seat applies a fixed weight corresponding to the specification of the optical fiber, so that the tension is transmitted to the optical fiber to realize the tension inspection of the optical fiber. In actual operation, the stress is gradually added to the optical fiber linearly, and after stabilization, the entire optical fiber is screened, and after the inspection is completed, it is linearly reduced from full load to zero stress, that is, the loose winding state. However, the existing gratings with welding points above 2m cannot withstand the overall screening of the same strength. It is easy to understand, because the strength is damaged due to optical fiber fusion, and the probability of fracture is high, especially for longer ones. For example, on a 100m long optical fiber, even if there are only 10 fusion points, as long as one breaks, the entire sensing optical cable will fail. . Therefore, the high strength of the integral fiber grating of the present invention is unmatched by all gratings with fusion points. The invention greatly improves the reliability of cabling through the high-strength optical fiber grating screened by the overall loading tension, and is of great significance for prolonging the service life of the sensing optical cable.

Claims (10)

1. A fiber grating array sensing optical cable, comprising an outer sheath and sensing optical fiber, the sensing optical fiber is laid in the outer sheath, and it is characterized in that the sensing optical fiber is directly engraved into the identical fiber grating on-line when drawing. For the grating array optical fiber, the outer sheath is an integral outer sheath formed by extrusion molding at one time. 2. The optical fiber grating array sensing cable according to claim 1, characterized in that the number of continuously written gratings on the sensing fiber is 5 to 10,000, and the distance between two adjacent gratings is 0.5m to 200m . 3. The fiber Bragg grating array sensing cable according to claim 1 or 2, characterized in that the grating on the sensing fiber is a weak reflection Bragg grating with a reflectivity of 1% to 0.0001%. 4. The optical fiber grating array sensing cable according to claim 1 or 2, characterized in that the sensing fiber is coated with a resin coating layer or a carbon coating layer or a metal coating layer on the surface of the bare optical fiber engraved into the grating. layer composition. 5. The optical fiber grating array sensing cable according to claim 4, characterized in that the static tensile strength of the sensing optical fiber is greater than or equal to 55N, and the entirety of the optical fiber is dynamically screened with a tension of 100kpsi. 6. The optical fiber grating array sensing cable according to claim 4, wherein the sensing optical fiber is covered with a tight-buffered layer or a loose-tubed layer outside the coating layer, forming a tight-buffered sensing fiber and a loose-tubed fiber respectively. Sensing fiber. 7. The optical fiber grating array sensing cable according to claim 1 or 2, characterized in that a metal armor layer is arranged in the outer sheath, and the sensing optical fiber is loosely laid in the metal armor layer. 8. The optical fiber grating array sensing cable according to claim 7, characterized in that a non-metal strengthening layer is arranged between the outer sheath and the metal armor layer. 9. The optical fiber grating array sensing cable according to claim 7, characterized in that the radial section of the outer sheath is circular or butterfly-shaped. 10. A method for using the fiber grating array sensing cable according to any one of claims 1 to 9, characterized in that it adopts a method in which wavelength division multiplexing technology and time division multiplexing technology are used in combination, which is a Distributed fiber grating sensing signal demodulation technology based on the binary change relationship of sensing pulse signal with time and wavelength, a narrow-band pulse signal output by the light source is coupled into the grating array, the narrow-band pulse signal repeats at a fixed frequency, and the wavelength of the signal Periodic continuous tuning changes, when it is incident on the grating that is consistent with the pulse wavelength, part of the pulse signal is reflected back to the demodulator by the grating, and the rest continues to transmit forward; if the incident pulse wavelength is inconsistent with the center wavelength of the grating, the pulse signal is directly transmitted In the past until encountering a grating with the same central wavelength; according to the return time of the pulse signal, the wavelength of the reflected signal of the grating and the reflected light intensity, analyze and calculate the spatial position of the grating and the size of the sensing parameter value.