CN106249347B - Bending insensitive photosensitive fiber for on-line preparation of weak grating array and preparation method - Google Patents
Bending insensitive photosensitive fiber for on-line preparation of weak grating array and preparation method Download PDFInfo
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- CN106249347B CN106249347B CN201610695576.3A CN201610695576A CN106249347B CN 106249347 B CN106249347 B CN 106249347B CN 201610695576 A CN201610695576 A CN 201610695576A CN 106249347 B CN106249347 B CN 106249347B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
- G02B6/02152—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating involving moving the fibre or a manufacturing element, stretching of the fibre
Abstract
The invention discloses a bending insensitive photosensitive fiber for on-line preparation of a weak grating array and a preparation method thereof, wherein the type of the fiber is a germanium-doped type, the refractive index distribution type is a step type, the weight percentage content of germanium doped in a core layer of the fiber is 6.5-9%, the refractive index of the core layer is increased by 0.5-0.7% relative to a cladding layer, and the bending loss of the fiber is less than 0.1 dB. The invention can well meet the requirement of writing the weak grating array with the reflectivity of 0.1-2% by single laser pulse, and can be used for large-capacity and long-distance sensing arrays.
Description
Technical Field
The invention relates to the field of optical fiber and optical fiber grating preparation, in particular to a bending insensitive photosensitive optical fiber for preparing a weak grating array on line and a preparation method thereof.
Background
The large-capacity distributed optical fiber sensing system based on the weak-reflectivity optical fiber grating has wide application prospect, and the core preparation technology requires that a large number of optical fiber gratings are written on a long-distance optical fiber and various losses such as welding loss, transmission loss, bending loss and the like are introduced as little as possible. The method for dynamically and continuously preparing the grating array on line effectively avoids access loss caused by preparing the fiber grating array by traditional welding, and is an efficient grating preparation method.
However, the dynamic on-line continuous fiber grating manufacturing process is based on single laser pulse writing of fiber gratings. Due to the limitation of the writing energy and writing time of a single laser pulse, the first condition for obtaining a grating with a certain reflectivity is that the optical fiber has better single-pulse photosensitivity. The conventional approach to increase the photosensitivity of optical fibers is to dope the core with germanium and boron at higher concentrations; at present, the mature photosensitive optical fiber has two types of high germanium-doped type and boron-germanium co-doped type, wherein, due to the introduction of boron element in the fiber core, the photosensitivity of the optical fiber is greatly increased, meanwhile, the refractive index of the fiber core can be reduced, the mode field diameter of the optical fiber is effectively ensured, and the photosensitive optical fiber is a known photosensitive optical fiber suitable for multiple purposes. However, due to the phonon vibration absorption characteristics of the B — O bond, the optical fiber has a large absorption peak in the use C band, increasing the transmission loss of the optical fiber. Obviously, the boron-germanium co-doped optical fiber is not suitable for preparing a large-capacity long-distance weak optical fiber grating sensing array. Germanium and silicon belong to the same group elements, and germanium ions with higher concentration are doped into a silica glass matrix to increase the photosensitive performance of the optical fiber, but the optical fiber does not cause the transmission loss of the optical fiber to be remarkably increased, so that the optical fiber is suitable for the on-line preparation of a large-capacity optical fiber grating array.
The fiber grating sensing array needs 90 in some special use occasions0Turning or small radius bending, such as generator stator vibration monitoring with compact space, partial discharge monitoring of high-voltage transformers, and the like. In addition, the small radius bending of the optical fiber can also happen inadvertently during the wiring process of the fiber grating sensing array. For ordinary optical fibers, these occurrences tend to result in significant attenuation or complete loss of the transmitted signal. Therefore, for a weak fiber grating sensor array, the transmission and detection of weak signals especially need to avoid and overcome the signal attenuation caused by the above situation. For the long-distance weak fiber grating sensing technology, the design and preparation of the bending insensitive optical fiber are necessary. The design of bend insensitive optical fibers is primarily to increase the difference in refractive index between the core and cladding to allow light to propagate more efficiently confined to the core. A bend insensitive optical fiber with depressed inner cladding index profile is a good solution to the above problems. However, for photosensitive fiber, especially for single-pulse written grating, the refractive index depressed trench can absorb and reflect part of the written light to a greater extent, so that it is difficult to prepare fiber grating with relatively large single-pulse reflectivity. Obviously, the bending insensitive photosensitive fiber with the cladding having the depressed-index groove distribution is not suitable for dynamically preparing the weak fiber grating array on line.
Disclosure of Invention
The invention aims to solve the technical problems that in the prior art, a boron-germanium co-doped photosensitive fiber has large transmission loss, is not suitable for preparing a long-distance and large-capacity weak fiber grating sensing array, has large bending loss of a fiber with standard refractive index distribution and has small radius, and a bending insensitive fiber with a refractive index with a sunken groove is not suitable for preparing a single pulse grating.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides a bending insensitive photosensitive fiber for preparing a weak grating array on line, which is germanium-doped, has a step index distribution type, 6.5-9 wt% of germanium doped in a core layer of the fiber, 0.5-0.7% of the refractive index of the core layer relative to a cladding layer, and has bending loss less than 0.1 dB.
Further, the mode field diameter of the optical fiber of the present invention at the wavelength of 1550nm is 8 μm, the transmission loss at the wavelength of 1330nm is 0.45dB/km-0.65dB/km, and the transmission loss at the wavelength of 1550nm is less than 0.25 dB/km.
Further, the optical fiber of the present invention has a laser energy density of 100mJ/cm2-600mJ/cm2The weak fiber grating with the reflectivity of 0.1-2% can be formed under the action of single laser pulse in the range.
The invention provides a method for manufacturing a bending insensitive photosensitive fiber for preparing a weak grating array on line, which comprises the following steps:
s1, doping 6.5-9 wt% of germanium element into the core layer of the optical fiber, and controlling the core refractive index increase value of the optical fiber to be 0.5-0.7%;
s2, depositing a core layer through a PECVD process, and fusing and shrinking the core layer and a sleeve rod to obtain a prefabricated rod by combining a sleeve method; introducing oxygen in a certain proportion in the deposition process of the core layer, and controlling the diameter of the fused aperture in the fusing process;
and S3, performing low-temperature optical fiber drawing, and controlling the drawing tension within a set range to obtain the bending insensitive photosensitive optical fiber of the weak grating array.
Further, the conditions of the core layer deposition process in step S2 of the present invention are specifically:
the oxygen-silicon ratio is controlled within the range of 3.5-4.5 when oxygen is introduced, and the diameter of the shrinkage hole is controlled to be 2mm in the process of shrinkage.
Further, the conditions for drawing the optical fiber in step S3 of the present invention are specifically:
the grating wire drawing speed is controlled at 10-30m/min, and the wire drawing tension is 20-100 g.
The inventionThe beneficial effects are that: the invention discloses a bending insensitive photosensitive fiber for on-line preparation of a weak grating array, which is based on a germanium-doped photosensitive fiber, adopts a step-type refractive index distribution design, ensures that the increase value delta of the refractive index of a fiber core is 0.5-0.7% by optimizing the doping concentration of germanium element in a core layer, the diameter of a mode field of the fiber at the wavelength of 1550nm is about 8.0 mu m, the transmission loss at the wavelength of 1550nm is less than 0.25dB/km, and the fiber has better single-pulse photosensitivity at 25mJ (the laser energy density is 100 mJ/cm)2-600mJ/cm2) The weak fiber grating with the reflectivity of 0.1-2% can be formed under the action of 193nm single laser pulse; meanwhile, the bending loss of the optical fiber is less than 0.1dB, the optical fiber can well meet the requirement of writing a weak grating array with the reflectivity of 0.1-2% by a single laser pulse, and can be used for a large-capacity and long-distance sensing array.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a plot of a bend insensitive fiber profile refractive index profile design for an example of a bend insensitive photosensitive fiber for an in-line fabrication of a weak grating array in accordance with an embodiment of the present invention;
FIG. 2 is a design diagram of refractive index profile of a bend-insensitive photosensitive fiber for on-line preparation of bend-insensitive photosensitive fibers for a low-profile grating array according to an embodiment of the present invention;
FIG. 3 is a grating reflection spectrum (a) formed by single laser pulse irradiation of different energy densities of photosensitive fibers of a bending insensitive photosensitive fiber for on-line preparation of a weak grating array according to an embodiment of the present invention;
FIG. 4 shows grating reflection spectra (b) formed by single laser pulse irradiation of different energy densities of photosensitive fibers of a bend-insensitive photosensitive fiber for on-line preparation of a weak grating array according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The bending insensitive photosensitive fiber for the on-line preparation of the weak grating array in the embodiment of the invention is germanium-doped, the refractive index distribution type is a step type, and the weight percentage content of germanium doped in the core layer of the fiber is 6.5-9%.
The refractive index of the core layer is increased by 0.5-0.7% relative to the refractive index of the cladding layer. The mode field diameter of the optical fiber at the wavelength of 1550nm is 8 mu m, the transmission loss at the wavelength of 1330nm is 0.45dB/km-0.65dB/km, and the transmission loss at the wavelength of 1550nm is less than 0.25 dB/km. The fiber bend loss is less than 0.1 dB. The laser energy density of the optical fiber is 100mJ/cm2-600mJ/cm2The weak fiber grating with the reflectivity of 0.1-2% can be formed under the action of single laser pulse in the range.
As shown in FIG. 1, the conventional bend insensitive fiber has a profile refractive index profile with cladding with index dip grooves. In order to reduce or eliminate the coupling loss with the standard optical fiber as much as possible, the optical fiber and the standard optical fiber need to be ensured to have consistent mode field diameter, the core layer refractive index increase value delta 1 is generally controlled to be about 0.35%, and r is controlled to be about 0.35% at the same time2/r1About 3.5, the bend insensitive fiber has no difference from the standard communication fiber in terms of the refractive index of the core, however, the relatively small refractive index difference between the core and the cladding body does not strictly bind the optical energy in the core for the optical energy propagating in the fiber, about ten percent of the optical energy propagates through the interface between the core and the cladding into the cladding, and once the fiber is bent to reach the optical energy evanescent condition, the optical energy is easily evanescent in propagation, thereby causing large transmission loss of the fiber. In order to effectively ensure that the light energy in the cladding can not be transmitted and lost in the bent optical fiber, a light transmission constraint condition, namely a cladding refractive index depressed groove, is added into the cladding of the optical fiber again to form an inner cladding reflection interface. In general, the cladding index dip groove increase Δ 2 is typically controlled to be around-0.3%, and r3/r1 is around 5.5. The depressed-index groove of the cladding layer can well ensure that the light energy propagated in the cladding layer is still restrained to propagate in the inner cladding layer when the optical fiber is bent at a smaller radius, and can ensure that the optical fiber has the same value when being coupled with a standard optical fiberMode field diameter.
However, for the side exposure writing grating, especially for the single pulse writing grating, the existence of the cladding layer refractive index depressed groove causes the writing light to be partially reflected when reaching the external surface of the depressed groove, and meanwhile, the depressed layer has strong absorption performance to the writing light by adopting the processes of fluorine doping and the like when designing and preparing the depressed groove, so that only a small amount of writing light reaches the core layer, and the reflectivity of the single pulse writing grating is extremely low.
As shown in FIG. 2, the embodiment of the present invention employs a bend insensitive photosensitive fiber profile refractive index profile design. In order to eliminate the negative influence of the cladding refractive index depression groove on lateral exposure, the bending insensitivity of the optical fiber is realized by directly adopting a high-core refractive index method on the premise of not considering the coupling loss of the optical fiber and a standard optical fiber. The germanium element doped in the fiber core can improve the refractive index of the fiber core, and simultaneously ensure that the transmission loss of the optical fiber is controlled in an ideal range and better single pulse light sensitivity is obtained.
By optimizing the content of germanium element in the core layer, the germanium doping weight percentage in the core layer is controlled to be about 6.5% -9%, the increase value delta of the fiber core refractive index is ensured to be 0.5% -0.7%, and the refractive index distribution of the germanium-doped bending insensitive photosensitive fiber shown in the figure 2 is obtained; and performing core layer deposition by adopting a PECVD (plasma enhanced chemical vapor deposition) process, and fusing and shrinking the core layer and the sleeve by combining a sleeve method to obtain a prefabricated rod. The germanium element is doped by a method of chemical reaction of germanium tetrachloride and oxygen, oxygen with a certain proportion is introduced in the deposition process of the core layer, the oxygen-silicon ratio is controlled within the range of 3.5-4.5, and the melt shrinkage pore diameter is controlled to be 2mm in the melt shrinkage process; considering that the drawing speed of the on-line inscribing grating is usually controlled at 10-30m/min, the drawing temperature is usually controlled at a lower level, and the drawing tension is ensured to be about 20-100 g, the cut-off wavelength of the prepared optical fiber is in the range of 1450 +/-50 nm, the mode field diameter of the optical fiber at 1550nm is about 8.0 mu m, and the transmission loss of the optical fiber at 1550nm is less than 0.25 dB/km.
As shown in fig. 3 and 4, the photosensitive fiber according to the embodiment of the present invention forms a grating reflection spectrum under irradiation of a single laser pulse with different energy densities. The laser energy density can be calculated to be 200mJ/cm2The reflectivity of the prepared grating is about 0.2 percent, and the laser energy density is 400mJ/cm2The reflectivity of the grating prepared below is about 0.65%. The optical fiber has better single-pulse photosensitivity, and can form a weak fiber grating with the reflectivity of 0.1% -2% under the action of 25mJ single laser pulse; meanwhile, the bending loss of the optical fiber is less than 0.1dB (R is 7.5mm 1turn @1550nm), the optical fiber can well meet the requirement of a weak grating array with the single laser pulse writing reflectivity of 0.1% -2%, and the optical fiber is used for a large-capacity long-distance sensing array and is particularly suitable for sensing occasions with compact space and small radius bending.
The manufacturing method of the bending insensitive photosensitive fiber for on-line preparation of the weak grating array comprises the following steps:
s1, doping 6.5-9 wt% of germanium element into the core layer of the optical fiber, and controlling the core refractive index increase value of the optical fiber to be 0.5-0.7%;
s2, depositing a core layer through a PECVD process, and fusing and shrinking the core layer and a sleeve rod to obtain a prefabricated rod by combining a sleeve method; introducing oxygen in a certain proportion in the deposition process of the core layer, and controlling the diameter of the fused aperture in the fusing process; controlling the oxygen-silicon ratio to be 3.5-4.5, and controlling the diameter of a melting shrinkage hole to be 2mm in the melting shrinkage process; considering that the drawing speed of the on-line inscribing grating is usually controlled at 10-30m/min, the drawing temperature is usually controlled at a lower level, and the drawing tension is ensured to be about 20-100 g, the cut-off wavelength of the prepared optical fiber is in the range of 1450 +/-50 nm, the mode field diameter of the optical fiber at 1550nm is about 8.0 mu m, and the transmission loss of the optical fiber at 1550nm is less than 0.25 dB/km.
And S3, performing low-temperature optical fiber drawing, and controlling the drawing tension within a set range to obtain the bending insensitive photosensitive optical fiber of the weak grating array.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (2)
1. The bending insensitive photosensitive optical fiber for preparing the weak grating array on line is characterized in that the type of the optical fiber is a germanium-doped type, the refractive index distribution type is a step type, the weight percentage content of germanium doped in a core layer of the optical fiber is 9 percent, the refractive index of the core layer is increased by 0.5 to 0.7 percent relative to a cladding layer, and the bending loss of the optical fiber is less than 0.1 dB;
the mode field diameter of the optical fiber at the wavelength of 1550nm is 8 mu m, the transmission loss at the wavelength of 1330nm is 0.45dB/km-0.65dB/km, and the transmission loss at the wavelength of 1550nm is less than 0.25 dB/km;
the laser energy density of the optical fiber is 100mJ/cm2-600mJ/cm2The weak fiber grating with the reflectivity of 0.1-2% can be formed under the action of single laser pulse in the range.
2. A method for preparing bending insensitive photosensitive fiber of weak grating array on line, wherein the type of the fiber is germanium-doped type, the refractive index distribution type is step type, the weight percentage content of germanium doped in the core layer of the fiber is 9%, the increase value of the core layer refractive index relative to the cladding is 0.5% -0.7%, and the bending loss of the fiber is less than 0.1 dB;
the mode field diameter of the optical fiber at the wavelength of 1550nm is 8 mu m, the transmission loss at the wavelength of 1330nm is 0.45dB/km-0.65dB/km, and the transmission loss at the wavelength of 1550nm is less than 0.25 dB/km;
the laser energy density of the optical fiber is 100mJ/cm2-600mJ/cm2Weak fiber gratings with reflectivity of 0.1-2% can be formed under the action of single laser pulse within the range;
the method comprises the following steps:
s1, doping 6.5-9 wt% of germanium element into the core layer of the optical fiber, and controlling the core refractive index increase value of the optical fiber to be 0.5-0.7%;
s2, depositing a core layer through a PECVD process, and fusing and shrinking the core layer and a sleeve rod to obtain a prefabricated rod by combining a sleeve method; introducing oxygen in a certain proportion in the deposition process of the core layer, and controlling the diameter of the fused aperture in the fusing process;
the conditions of the core layer deposition process in step S2 are specifically:
controlling the oxygen-silicon ratio to be within the range of 3.5-4.5 when oxygen is introduced, and controlling the diameter of a melting shrinkage hole to be 2mm in the melting shrinkage process;
s3, performing low-temperature optical fiber drawing, and controlling the drawing tension within a set range to obtain a bending insensitive photosensitive optical fiber of a weak grating array;
the conditions for drawing the optical fiber in step S3 are specifically:
the grating wire drawing speed is controlled at 10-30m/min, and the wire drawing tension is 20-100 g.
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| CN101216574B (en) * | 2006-07-13 | 2010-10-20 | 长飞光纤光缆有限公司 | Novel highly germanium-doped -type light-sensitive optical fibre and method for making same |
| US20160109650A1 (en) * | 2014-10-16 | 2016-04-21 | Sumitomo Electric Industries, Ltd. | Optical fiber for fiber bragg grating |
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