JP2017111173A - Fiber fuse suppression fiber and optical connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber fuse suppression fiber capable of reliably blocking propagation of fiber fuse, and an optical connector.SOLUTION: The fiber fuse suppression fiber is a fiber fuse suppression fiber which has a core 12 and a plurality of vacancies 13 arranged in an annular shape in a clad 11, which has a structure that, in a use wavelength of the fiber fuse suppression fiber, the ratio (c/MFD) between the mode field diameter MFD and a diameter of the inscribed circle of the annular shape is 2.3 or less; and the area occupation rate S1 of the vacancies relative to the area of the annular shape in a circumscribed circle is 0.11 (11%) or more.SELECTED DRAWING: Figure 4

Description

  The present invention provides a fiber fuse stopper that stops or suppresses a fiber fuse phenomenon that may occur when high-power light of several W (watts) order is input to and transmitted to an optical fiber, and protects a transmission device and an optical fiber transmission line, The present invention relates to an optical connector, an optical transmission system, and a fiber fuse stopping method.

  Currently, the demand for expansion of the transmission capacity of optical fiber communication is increasing day by day due to the progress of the Internet, and the total power of light input to the optical fiber already laid in the core optical network is approaching 1W. In the future, further increase is expected. On the other hand, when light of the order of several watts is input to the optical fiber according to the related art, if some kind of trigger such as bending, cutting or heating is given, the glass core portion of the fiber will melt due to heating. It is known that a phenomenon (fiber fuse phenomenon) occurs in which this becomes a high-temperature plasma state and propagates toward the light source side.

  FIG. 1 is a conceptual diagram of the fiber fuse phenomenon. The optical fiber shown in FIG. 1 includes a clad 11 and a core 12 having different relative refractive index differences. The occurrence of the fiber fuse phenomenon itself occurs stochastically and does not necessarily occur even under specific conditions. However, once it has occurred, the propagation can be stopped by “1. A method of making the input light power from the light source relatively smaller than a certain threshold (fuse propagation threshold)” and “2. And a method of disconnecting the transmission line itself before starting.

  However, no other effective method is known. If the generated fiber fuse is not stopped, not only the optical fiber transmission path from the generation point to the light source but also the light source (transmission device) is destroyed. For this reason, a method for preventing the fiber fuse phenomenon or stopping the generated fuse has been strongly demanded.

  In the optical fiber according to the related art, the propagation threshold of the fuse in the method 1 has a slight width depending on the type of the optical fiber, but in SMF (1.3 μm band zero dispersion fiber, ITU-T, G.652). The propagation threshold is reported to be about 1.5 W, and DSF (dispersion shifted fiber, ITU-T, G.653) is about 1.2 W. In the optical fiber according to the related art, it is known that this propagation threshold value has a strong correlation with a mode field diameter (MFD), and both are in a substantially proportional relationship (for example, Non-Patent Document 1). See).

  Accordingly, as countermeasures in the transmission path, various optical fiber type fuse stoppers have been proposed in the related art. When using a fuse stopper, if the power of the input light is set below the propagation threshold of the stopper part, even if a fuse is generated in a part other than the stopper, the fuse stops at the stopper part and the remaining transmission line And the light source can be protected. As a fuse stopper, one in which a fiber having a particularly high propagation threshold is inserted as a small optical component (fuse stopper) in a part of an optical transmission line has been proposed.

  For example, in the first related technology, a multimode fiber (GIF: Grated index fiber) having a large MFD is fusion-spliced to an SMF, and the fiber fuse that has propagated under an input power condition of about 2 to 3 W is used. The stop is realized (for example, see Non-Patent Document 1).

  In the second related technique, a method of heating a part of the DSF, expanding the core diameter and the MFD, and forming a TEC (Thermally-diffused Expanded Core) fiber has been proposed (for example, see Non-Patent Document 2). ). In the third related technique, a method is proposed in which a 125 μmφ clad portion of SMF is thinned to an outer diameter of about 10 to 30 μmφ by etching to improve the fuse propagation threshold (see Non-Patent Document 3, for example). .

WO2010 / 023881

Fujita et al., “Fibre Fuse Breaking with GI Fiber”, 2004 IEICE Communication Society Conference, B-10-5, 2004 Yanagi et al., "Development of fiber fuse breaker parts", IEICE Technical Report, OPE 2004-178, 2004 E. M.M. Dianov et. al. , “Description of silica fiber cladding by the fuse effect”, OPTICS LETTERS, 29, 16, 1852-1854, 2004

  However, the related technology has problems as specifically described below. The first related technology uses a fiber fuse stopper with a GIF with a large MFD fused to the SMF to stop the fiber fuse under an input power condition of about 2 to 3 W. In order to reduce the GIF, it is necessary to adjust the GIF to an optimum length on the order of several hundreds of μm, which makes it difficult to manufacture.

  Specifically, an extra loss of about 5 dB occurs when the optimum length is shifted by about 500 μm. In addition, since SMF and GIF with greatly different core diameters are connected, it also becomes a factor that a high-order mode is generated in the GIF portion, and it is necessary to avoid transmission errors when transmitting high-speed signals. There is also a problem that it remains at a relatively low level of about 3 W.

  Further, according to the second related technique, a method of heating a part of an optical fiber to form a TEC (Thermally-diffused Expanded Core) fiber can make a stopper small in size, while maintaining a single mode condition. Therefore, there is an upper limit value for enlarging the MFD (about 20 to 30 μm), and therefore there is a problem that there is a limit in improving the fuse propagation threshold.

  For example, in the second related technology, the effectiveness is confirmed only when the input optical power is 2 W. Further, the second related technology also shows the result of examination of a fuse stopper using a TEC fiber, but the effectiveness is only confirmed under a condition where the input optical power is about 4 W. In addition, since TEC conversion is performed by heating and diffusing the dopant contained in the core portion, it is necessary to control and set the fine conditions at the time of manufacturing, and it is difficult to manufacture the MFD characteristics, that is, the fuse propagation threshold with good reproducibility. There is a disadvantage in terms of cost.

  In addition, in the method according to the third related technique, in which the fiber cladding is thinned to an outer diameter of about 10 to 30 μm by etching, it is possible to reduce the insertion loss while maintaining the MFD at a constant value in the initial state. However, it takes a long time to sufficiently reduce the diameter of hard quartz glass by etching, which is disadvantageous in terms of cost. In addition, since the resin coating of the fiber is also removed at the reduced diameter portion, in addition to the effect of reducing the diameter of the glass portion, the glass surface is likely to be scratched, so the mechanical strength is reduced. It becomes. Also in the third related technology, the effectiveness is only confirmed under the condition that the input optical power is 3 W at the maximum.

  As described above, in the method according to the related art, it is extremely difficult to realize a fuse stopper that is effective even at a large input power in the vicinity of 4 W or even significantly exceeding 4 W. Furthermore, it is extremely difficult to realize a fiber fuse stopper that satisfies all the conditions that the insertion loss is sufficiently low, the occurrence of higher-order modes and the mechanical strength is low, and that it is possible to manufacture with good performance at low cost. Although difficult, a fiber fuse stopper has been proposed as a fourth related technique by HAF (Hole Assisted Fiber) that has a sufficiently low insertion loss and a small concern about a decrease in mechanical strength (for example, Patent Document 1). reference).

  However, although the structure in which the fiber fuse stops in the HAF according to the fourth related technology is shown, the definition regarding the hole diameter used in the hole structure in the cross section of the HAF is not common. Specifically, the ratio of W to MFD, W / MFD (corresponding to d / MFD of the present invention), and the hole when the width in the radial direction of the region where the hole exists in the clad 11 is W The structure is defined by 2Rmin / MFD (corresponding to c / MFD of the present invention) where Rmin is the shortest distance between the core and the core, and does not include general parameters such as the number of holes and hole diameter. It is not a general definition.

  Further, as will be described later, in the fourth related technology, HAF in the range of the structure in which the propagation of the fiber fuse is stopped, that is, W / MFD is 0.3 or more and 2Rmin / MFD is 1. Experiments were also conducted on HAF under the condition of 2 to 2.1, and it was confirmed that the fiber fuse actually propagated with three types of HAF. Therefore, at present, the structural conditions of the HAF holes for stopping the propagation of the fiber fuse are unclear.

  In order to solve the above-described problems, the present invention has been made in view of the above problems, and HAF that reliably stops propagation of a fiber fuse, and a fiber fuse stopper, optical connector, optical transmission system, and fiber fuse stopping method using the same. The purpose is to provide.

  In order to achieve the above object, in the present invention, the HAF structure in which the propagation of the fiber fuse can be stopped is expressed by a general definition in consideration of both the number of holes and the diameter of the hole, and the hole is formed from the center of the cross section. The ratio of the distance to the MFD and the area occupancy ratio of the holes to the circumscribed circle of the holes or the area surrounded by the circumscribed circle of the holes and the inscribed circle of the holes By these means, the structural range of the HAF that can stop the fiber fuse when the wavelength to be used, that is, the MFD of the optical fiber is determined, is provided.

Specifically, the fiber fuse suppression fiber according to the present invention is:
A fiber fuse suppression fiber having a core and a plurality of holes arranged in an annular shape in a clad,
A ratio (c / MFD) of a mode field diameter (MFD) at a use wavelength of the fiber fuse suppressing fiber and a diameter c of the inscribed circle of the ring shape is 2.3 or less, and the ring The hole has an area occupation ratio S1 of 0.11 (11%) or more with respect to a region in the circumscribed circle of the shape.

Specifically, the fiber fuse suppression fiber according to the present invention is:
A fiber fuse suppression fiber having a core and a plurality of holes arranged in an annular shape in a clad,
A ratio (c / MFD) of a mode field diameter (MFD) at a use wavelength of the fiber fuse suppressing fiber and a diameter c of the inscribed circle of the ring shape is 2.3 or less, and the ring The area occupancy S2 of the pores with respect to the region surrounded by the circumscribed circumference and the inscribed circumference is 0.29 (29%) or more.

In the fiber fuse suppressing fiber according to the present invention,
When the structure of the holes is defined by coordinates (c / MFD, S1), 1, (1.4, 0.40), 2, (1.44, 0.11), 3, (2.1 , 0.16), 4, (2.3, 0.44), and may be a polygonal structural region surrounded by four points.

In the fiber fuse suppressing fiber according to the present invention,
When the structure of the hole is defined by coordinates (c / MFD, S2), 1, (1.4, 0.52), 2, (1.44, 0.29), 3, (2.1 , 0.29), 4, (2.3, 0.67), and may be a polygonal structure region surrounded by four points.

In the fiber fuse suppressing fiber according to the present invention,
A single mode optical fiber may be connected to at least one end.

In the fiber fuse suppressing fiber according to the present invention,
In the wavelength region of the propagating light, the MFD of the fiber fuse suppressing fiber and the MFD of the single mode optical fiber may be substantially equal.

According to the present invention,
The length of the fiber fuse suppressing fiber may be not less than 0.5 mm and not more than 5 mm.

Specifically, the optical connector according to the present invention is:
The fiber fuse suppression fiber described above is provided.

  The above inventions can be combined as much as possible.

  According to the present invention, it is possible to provide a HAF that reliably stops propagation of a fiber fuse, and a fiber fuse stopper, an optical connector, an optical transmission system, and a fiber fuse stopping method using the same.

  In addition, the insertion loss is sufficiently low, there is little concern about the occurrence of higher-order modes and mechanical strength, and it is possible to manufacture with good performance yield at low cost, and the fiber that stops the fiber fuse generated at high input power. A fuse stopper and an optical connector can be provided.

It is a figure which shows the conceptual diagram of a fiber fuse phenomenon. It is a figure which shows an example of sectional drawing of HAF which concerns on this embodiment. It is a figure which shows an example of the measurement evaluation system of the propagation threshold value of the fiber fuse of HAF which concerns on this embodiment. It is a figure which shows c / MFD of the HAF structure which can stop propagation | transmission of the fiber fuse which concerns on this embodiment, and the area occupation rate of a hole. It is a figure which shows c / MFD of the HAF structure which can stop propagation | transmission of the fiber fuse which concerns on this embodiment, and the area occupation rate of a hole. It is a figure which shows an example of the fuse stopper (a) using the HAF structure which can stop propagation | transmission of the fiber fuse which concerns on this embodiment. It is a figure which shows an example of the fuse stopper (b) using the HAF structure which can stop propagation | transmission of the fiber fuse which concerns on this embodiment. It is a table | surface which shows the specific example of the HAF structure which confirmed the presence or absence of fiber fuse propagation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.
(Embodiment 1)

  An example of the structure in the cross section of the HAF used for the fiber fuse stopper according to the present embodiment and an example of use in the optical transmission line will be described below with reference to FIG. FIG. 2 is a diagram showing an example of a cross-sectional view of the HAF used in the present invention. The optical fiber (HAF) shown in the figure has a clad 11, a core 12, and holes 13, and is constituted by a core 12 and a plurality of holes 13 arranged in an annular shape in the clad 11. In FIG. 2, the hole diameter is d, the inscribed circle diameter of the hole 13 is c, and the circumscribed circle diameter of the hole 13 is c ′. FIG. 3 shows an example of a system for measuring and evaluating the HAF propagation threshold. The HAF 41 and a commercial single mode optical fiber 42 (SMF: Single Mode Fiber) are fusion-spliced, a fiber fuse is generated at the end of the single mode optical fiber 42, passes through the connection point 43, and the fiber fuse is connected to the HAF 41. It was confirmed and evaluated whether or not to propagate.

  In the evaluation, the wavelength of the light source 44 was set to around 1550 nm, which is a typical wavelength used for optical communication. In the HAF 41, it has been reported that when the input power is small, the distance that the fiber fuse enters the HAF 41 is long, that is, it is easy to propagate. Therefore, 2 W, which is close to the propagation threshold of a standard single mode optical fiber. Was evaluated. The HAF in which the fiber fuse stopped under the 2 W condition was also evaluated at 15 W, and it was confirmed that the fiber fuse stopped even under the 15 W condition.

  The table in FIG. 8 shows the results of experiments in which 20 types of HAFs having different structures were checked for the presence or absence of fiber fuse propagation in the experimental system of FIG. In the table, the hole diameter d, the inscribed circle diameter c of the hole 13, the MFD at a wavelength of 1550 nm, d / MFD, c / MFD, the number of holes, the area occupation of the hole 13 with respect to the circumscribed circle of the hole 13 The rate S1, and the area occupancy S2 of the hole 13 with respect to the donut-shaped region surrounded by the inscribed circumference and the circumscribed circumference of the hole 13 are shown. For the eight types of fibers whose propagation of the fuse was confirmed, the propagation threshold of the fuse was also evaluated and all were about 1.5 W.

  On the other hand, in the fourth related technology, the range of the HAF structure suitable for stopping the fiber fuse is defined by one description in the document. Therefore, when HAF in the table in FIG. 8 is within the range described in the document or outside the range, the four types of HAFs No. 4, 12, 17, and 18 are within the range described in the document. Meet. Furthermore, these HAFs also satisfy the other provision of the fourth related technique (because the value of S2 is 0.2, that is, 20% or more). However, fiber fuses are propagated. This indicates that the HAF structure of the fourth related technology is inadequate.

  FIG. 4 is a diagram illustrating the relationship between the propagation or stop of the fiber fuse in the HAF 41 and the area occupancy S1 and c / MFD of the hole 13 with respect to the circumscribed circle of the hole 13. A structural region having a c / MFD value of 2.3 or less and a S1 value of 0.11 (11%) or more is suitable as the fiber fuse stopper of the present invention.

  Further, when the structure of HAF 41 is expressed by coordinates (c / MFD, S1), 1, (1.4, 0.40), 2, (1.44, 0.11), 3, (2.1, 0.16), 4, (2.3, 0.44), the HAF 41 can stop the fiber fuse by selecting the structural region indicated by the polygon surrounded by the above 1-4, Suitable as a fiber fuse stopper.

  FIG. 5 is a diagram showing the relationship between the fiber fuse propagation or stop in the HAF 41 and the area occupancy S2 and c / MFD of the hole 13 with respect to the circumscribed circumference and the inscribed circumference of the hole 13. . A structural region having a c / MFD value of 2.3 or less and an S2 value of 0.29 (29%) or more is suitable as the fiber fuse stopper of the present invention.

  Further, when the structure of HAF 41 is expressed by coordinates (c / MFD, S2), 1, (1.4, 0.52), 2, (1.44, 0.29), 3, (2.1, 0.29), 4, (2.3, 0.67), the HAF can stop the fiber fuse by selecting the structural region indicated by the polygon surrounded by 1-4, and Suitable as a fiber fuse stopper.

  In the HAF 41 having the structure shown in FIG. 4 and FIG. 5, when the experimental verification was performed in the experimental system of FIG. 3, the penetration depth of the fiber fuse that entered the HAF 41 was mostly 0.5 mm or less, and the maximum length was 5 mm. Never reached. Therefore, when the HAF having the above structure is used as a fuse stopper, the length of the HAF 41 is preferably set to about 0.5 to 5 mm.

  Further, as shown in FIG. 6A, a single mode optical fiber (SMF) 72 having an appropriate length may be fused and connected to the HAF 71 having the length. However, in this case, at the time of fusion splicing, depending on the conditions, the holes 13 may be crushed by the discharge in the vicinity of the connection point 73. Pay attention to the fusing conditions or the length of the hole portion of the HAF 71 after fusing. It is necessary to confirm whether the thickness is 0.5 mm or more.

  In order to suppress fusion splice loss, it is preferable that the MFD of the HAF 71 and the MFD of the single mode optical fiber (SMF) 72 are substantially equal. Further, as shown in FIG. 7B, an optical connector 74 may be attached to both ends to form an optical code. In the figure, the connection point 73 by fusion is formed outside the optical connector 74. However, since the HAF 71 may be as short as 0.5 mm to several mm as described above, the connection point 73 is formed inside the connector. In addition, it may be configured to protect this.

  In the case of such an optically coded configuration, it is easy to insert in the vicinity of the transmission device or in the middle of the transmission path. Even if a fiber fuse is generated in the optical fiber transmission line, the fiber fuse can be stopped by the fuse stopper, so that the transmission device and the optical fiber transmission line can be protected from destruction by the fiber fuse.

  The present invention can be applied to the information communication industry.

11: Clad 12: Core 13: Hole 41, 71: HAF
42, 72: single mode optical fibers 43, 73: connection point 44: light source 74: optical connector

Claims (8)

A fiber fuse suppression fiber having a core and a plurality of holes arranged in an annular shape in a clad,
A ratio (c / MFD) of a mode field diameter (MFD) at a use wavelength of the fiber fuse suppressing fiber and a diameter c of the inscribed circle of the ring shape is 2.3 or less, and the ring A fiber fuse suppression fiber having a structure in which a hole area occupancy S1 with respect to a region in a circumscribed circle of a shape is 0.11 (11%) or more. A fiber fuse suppression fiber having a core and a plurality of holes arranged in an annular shape in a clad,
A ratio (c / MFD) of a mode field diameter (MFD) at a use wavelength of the fiber fuse suppressing fiber and a diameter c of the inscribed circle of the ring shape is 2.3 or less, and the ring A fiber fuse suppression fiber having a structure in which an area occupation ratio S2 of holes is 0.29 (29%) or more with respect to a region surrounded by a circumscribed circumference and an inscribed circumference. When the structure of the holes is defined by coordinates (c / MFD, S1), 1, (1.4, 0.40), 2, (1.44, 0.11), 3, (2.1 , 0.16), 4, (2.3, 0.44), and a polygonal structure region surrounded by four points. When the structure of the hole is defined by coordinates (c / MFD, S2), 1, (1.4, 0.52), 2, (1.44, 0.29), 3, (2.1 , 0.29), 4, (2.3, 0.67), a polygonal structural region surrounded by four points, 3. The fiber fuse suppression fiber according to claim 2, The fiber fuse suppression fiber according to any one of claims 1 to 4, wherein a single mode optical fiber is connected to at least one end. 6. The fiber fuse suppressing fiber according to claim 5, wherein the MFD of the fiber fuse suppressing fiber and the MFD of the single mode optical fiber are substantially equal in a wavelength region of propagating light. The length of the said fiber fuse suppression fiber is 0.5 mm or more and 5 mm or less, The fiber fuse suppression fiber of Claim 5 or 6 characterized by the above-mentioned.   An optical connector comprising the fiber fuse suppressing fiber according to claim 5.

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