JP3924265B2 - Optical fiber connector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber connector, and more particularly to an optical fiber connector having a plurality of holes around a core.
[0002]
[Prior art]
Examples of the optical fiber having holes around the core include a holey optical fiber and a photonic crystal optical fiber.
[0003]
Since the holey optical fiber is an optical fiber having a plurality of holes around the core, the optical fiber has high resistance to bending and twisting of the optical fiber, and can suppress an increase in transmission loss due to bending. This optical fiber has low-loss transmission characteristics even when a curl with a small diameter that cannot be achieved with a single mode fiber is formed.
[0004]
The photonic crystal optical fiber is an optical fiber having a photonic crystal structure, that is, a refractive index periodic structure, in a clad. By reducing the wavelength of the periodic structure to the wavelength of light or several times that, and introducing defects and local inhomogeneities in the crystal, light can be localized. Can confine light.
[0005]
Here, taking a holey optical fiber as an example, the cross-sectional structure will be described with reference to FIG.
[0006]
As shown in FIG. 4, the holey optical fiber 31 has six holes 32, and around the core 33, holes 32 having an inner diameter of 10 μm are formed at equal intervals in the circumferential direction over the entire length of the optical fiber. . The diameter of the clad 34 is 125 μm, and the central core 33 is doped with germanium in the same manner as an ordinary single mode fiber (SMF), the diameter of the core 33 is about 9 μm, and the diameter relative to the surrounding pure quartz clad 34 is The relative refractive index difference is 0.35%.
[0007]
The holey optical fiber 31 is characterized in that the refractive index of the air holes 32 around the core 33 is about 1, and the effective relative refractive index difference is much larger than that of a normal single mode fiber. Since the light confinement effect is high, the loss generated when the holey optical fiber 31 is bent is extremely small.
[0008]
Regarding the connector peripheral technology of the holey optical fiber 31, since this fiber itself is a newly developed optical fiber, there is no particularly established technology and structure, but the following three examples are shown as main techniques.
[0009]
(1) Hole-untreated In the same way as ordinary SMF, it can be processed so that it can be connected to a standard connector that is generally used, and the insertion loss is equivalent to about 0.1 to 0.2 dB. It is.
[0010]
(2) Crushing the hole by heating In the state where the hole is exposed on the end face of the connector, there is concern about long-term reliability due to the contamination of the hole by polishing. Therefore, a process of crushing the holes at the tip of the connector by heating is necessary. The following two examples are shown as the processing method.
[0011]
i) A method using an arc discharge fusion machine for connecting a heating fiber by arc discharge. The arc discharge fusion will be described in detail later, but the discharge power was about the same as that of ordinary optical fiber fusion splicing, and the vacancies were sufficiently melted and integrated in a discharge time of about 1 second. In the crushed portion, the cross-sectional area of six 10 μm holes decreased, and the cladding diameter decreased by 2.5 μm to 122.5 μm.
[0012]
ii) Heating method using a microtorch for heating fiber type couplers using a microtorch. Since the fusion temperature does not rise as much as during arc discharge, the burner is moved by about 5 mm over about 15 seconds, and the holes are formed. I crushed it. The portion where the voids were crushed was 121.5 μm, which was even smaller than that caused by arc discharge. Since the heating time is longer than the arc discharge in addition to the decrease in the number of holes, the quartz glass on the cladding surface is volatilized by flame etching.
[0013]
i), ii) After the air holes 32 are crushed by the respective heating methods, the holey optical fiber 31 is mounted on the ferrule.
[0014]
Here, FIG. 5A shows a cross-sectional view in which the air holes 32 are crushed by heating with a micro torch and attached to the FC connector ferrule 35, and a cross-sectional view seen from the end face 36 of the ferrule 35 is shown in FIG. 5B. .
[0015]
The holey optical fiber 31 is used in the state of a fiber core wire 38 in which the periphery of the clad 34 is covered with a UV resin coating 37, and the connection portion with an optical connector or the like is used as a bare fiber 39 by peeling the UV resin coating 37. To do.
[0016]
The FC connector ferrule 35 is an element component constituting an optical connector, and includes a fixing portion 40 for fixing the bare fiber 39 and a fiber holding portion 41 for mounting the fiber core wire 38. When used in a single optical connector, the ferrule 35 has a cylindrical shape. The holey optical fiber 31 is fixed to the ferrule 35 with an adhesive, and the ferrule 35 to which the holey fiber 31 is fixed is connected to an optical connector. In the case of the FC optical connector, the ferrule 35 is fixed to the optical connector by the fastening portion 42 with a screw or a pressing spring.
[0017]
After the holey optical fiber 31 is mounted on the ferrule 35, the end face 36 is polished. In the vicinity of the connection end 43 of the bare fiber 39, the holes 32 are crushed by heating, so that polishing powder and other foreign matters are contained in the holey fiber 31. Does not invade.
[0018]
Although the description of the mounting of the holey optical fiber 31 according to FIG. 5 has been described with respect to heating with a microtorch, the holey optical fiber 31 is similarly mounted on the FC connector ferrule 35 after heating by arc discharge.
[0019]
(3) Single-mode fiber fusion splicing FIG. 6 shows an FC connector ferrule proposed by the present inventor as a bare fiber 39 at the tip of a holey optical fiber 31 , and the bare fiber 39 and SMF 45 are fusion spliced. FIG.
[0020]
The structure of the FC connector ferrule 35 is the same as that shown in FIG. As shown in FIG. 6, the holey optical fiber 31 mounted in the ferrule 35 has a predetermined length of SMF 45 fused at its tip 44, and the fused surface 44 is located at the center of the fixing portion 40. The holes 32 do not touch the outside. The connection loss is such that a transmission loss of about 0.1 dB due to fusion is added compared to a normal SMF connector.
[0021]
[Patent Document 1]
JP 2002-323625 A
[Problems to be solved by the invention]
However, the above-described holey optical fiber connection has the following problems.
[0023]
(1) Problems in the case where holes are not treated Polishing powder and other foreign matters remain in the six holes on the end face of the connector after the end face of the holey optical fiber 31 is polished. Even if an attempt is made to remove foreign matter, etc., it is hardly possible to remove because the pore diameter is small. For this reason, in the repeated attachment / detachment test, foreign matter in the holes may come out, and if it adheres to the surface of the core 33, the insertion loss increases. Further, when connecting optical connectors by PC connection excellent in low loss and anti-reflection measures, since the holey optical fiber 31 is in a pressed state, the edge portion of the air holes 32 is missing, and the glass piece is the connector. The surface may be damaged. Furthermore, since the air holes 32 in the fiber 31 are in an open state, moisture permeates from the end face of the fiber, particularly in an environment that is not desirable for quartz glass such as high temperature and high humidity, and the fatigue deterioration of the fiber strength proceeds rapidly. There are problems.
[0024]
(2) Problems in the case of crushing holes due to heating By crushing the holes 32 by heating, the problem of foreign matter and moisture entering the holes 32 of the holey optical fiber 31 is solved. In the portion 43 crushed, the diameter of the clad 34 is 121.5 μm, and the ferrule end face 36 after polishing has a large eccentricity of the bare fiber 39, as shown in FIG. 5 (b). There is a gap between them.
[0025]
When the FC connector ferrule was connected to the master connector (not shown) in this state, the connection loss due to the wavelength band of 1.3 μm was as large as 0.7 to 1.0 dB. A plurality of connectors were prototyped, but all the fibers were eccentric at the ferrule end face 36. Since the holey optical fiber 31 heated by the torch is slightly curved, it is very difficult to be positioned at the center in the ferrule 35 even by the viscous force of the adhesive.
[0026]
In addition, when heated by arc discharge, the reduction rate of the cladding diameter was not as great as that of torch heating, but the connection loss was still as large as 0.4 to 0.7 dB.
[0027]
These connection loss values are those of the holey diameter 10 μm of the 6-hole type holey optical fiber 31. When the hole diameter is large or the number of holes is increased, the connection loss is further deteriorated. There is.
[0028]
(3) Problems in the case of SMF fusion splicing Although the hole 32 of the holey optical fiber 31 is not crushed and the SMF 45 is fused to the fiber tip 44, the problem of increasing the connection loss due to the eccentricity of the fiber is improved. Assembling of the ferrule 35 to be attached to the connector is necessary because the fusion position, the cladding outer diameter of the fusion part, the fiber bending of the fusion part, the fusion loss, the fiber strength of the fusion part, etc. must be set to desired values. Tends to be cumbersome.
[0029]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical fiber connector that solves the above-described problems, has excellent strength reliability, is easy to assemble, and can be connected to an SMF connector with low loss.
[0030]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is a connector for an optical fiber in which an optical fiber having a plurality of holes around a core is inserted into a ferrule and attached thereto , at a position away from the end face of the optical fiber. closing the pores in the melt, the vicinity of the end face is not closed pores by melting, the outer diameter of the end face of the optical fiber is a optical fiber connector which is maintained in the outer diameter before closing the pores .
[0032]
According the invention of claim 2 is a connector for an optical fiber according to claim 1 Symbol placement melted closed pores by arc discharge.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0034]
First, the optical fiber used in this embodiment is the same as the holey optical fiber 31 described in FIG.
[0035]
FIG. 1 shows a cross-sectional view in which a holey optical fiber 12 is connected to an FC connector ferrule 17.
[0036]
A holey optical fiber 12 having a hole 11 around the core is used in the state of a fiber core 15 in which the periphery of a clad 13 is covered with a UV resin coating 14, and the UV is used for connection to an optical connector or the like. A bare fiber 16 from which the resin coating 14 has been peeled off is used.
[0037]
The ferrule 17 is an element part constituting an optical connector, and includes a fixing portion 18 for fixing the bare fiber 16 from which the UV resin coating 14 is peeled off and a fiber holding portion 19 for attaching the fiber core wire 15. When used in a single optical connector, the FC connector ferrule 17 has a cylindrical shape. The holey optical fiber 12 is attached to the ferrule 17 with an adhesive, and the ferrule 17 attached with the holey optical fiber 12 is connected to an optical connector. In the case of the FC connector, it is fixed to the optical connector by the fastening portion 20 with a screw or a pressing spring.
[0038]
The holey optical fiber 12 is attached to the ferrule 17 at a position away from the distal end 21 of the bare fiber 16 and the hole 13 in the closed section 22 is closed.
[0039]
The assembly procedure of the optical connector in which the holey optical fiber 12 is connected to the ferrule 17 will be described.
[0040]
FIG. 2 shows a process chart when the hole of the holey optical fiber is melted and closed by the arc discharge fusion machine 25. FIG. 2 (a) is during arc discharge, and FIG. 2 (b) is after discharge. Show.
[0041]
First, as shown in FIG. 2 (a), the UV resin coating 14 of the holey optical fiber 12 is removed, and an arc discharge fusion machine in a range of about 1.5 mm centering on a position 4 mm away from the coating stripping 23. 25, an arc discharge 26 is performed from the electrodes 27, 27 to the optical fiber 12 for 2 seconds. The discharge power is set to a discharge current of about 15 mA, the temperature is 1800 to 2000 °, and is as strong as the case where the SMF is fusion spliced. During the arc discharge, the glass is in a molten state, surface tension is generated, and the vacancies 11 disappear in about 1 second without applying pressure reduction treatment or pulling in the vacancies. As shown in FIG. 2B, the outer diameter of the cladding becomes smaller in the section 22 where the air holes 11 are closed, as much as the air holes 11 disappear. The minimum outer diameter of the fiber 12 in the hole blocking section 22 varies depending on the diameter and the number of the holes 11 around the core, but the cladding diameter decreased by 2.5 μm to 122.5 μm with 10 μm × 6 holes. On the other hand, it goes without saying that the outer diameter of the holey optical fiber 12 not subjected to the arc discharge 26 is maintained at 125 μm.
[0042]
At the time of arc discharge, attention must be paid to the positional accuracy of the fiber supporting V grooves 28 and 28 that support the holey optical fiber 12 at both ends of the discharge electrode 27. If the accuracy between the supporting V-grooves 28 and 28 is insufficient, the fiber 16 bends in the hole closing section 22, so that it is necessary to suppress axial deviation and angular break as much as possible in the horizontal and vertical directions. The required accuracy is an axis deviation within 1 μm and an angle break within 0.1 °.
[0043]
Next, the holey optical fiber 12 is fixed to the ferrule 17 with an adhesive. In the FC connector ferrule 17 used in this embodiment, the inner diameter of the fixing portion 18 is 125 μm, and the fixing portion length is 8 mm. As a result, the hole closing section 22 is positioned substantially at the center of the fixed portion 18, and the appearance is completely the same as a normal SMF connector.
[0044]
Finally, although not shown, the end face 21 of the holey optical fiber 12 attached to the ferrule 17 is polished, and the ferrule 17 is built into the optical connector to be completed.
[0045]
Next, the operation of the present invention will be described.
[0046]
The optical fiber connector of the present embodiment has a hole 22 closed by arc discharge melting in a predetermined length of a closed section 22 away from the end face 21 of the holey optical fiber 12 having holes 11 around the core of the fiber 12. Therefore, it is possible to prevent intrusion of polishing powder, moisture and other foreign matters when the fiber end face 21 is polished. Thereby, reliability equivalent to that of a normal optical connector can be maintained. In particular, even under severe environments such as high temperature and high humidity, moisture permeates from the holes 11 in the end face 21 and fatigue deterioration of the fiber strength is normal. It is possible to prevent progressing faster than when an optical connector is used.
[0047]
Further, since the hole 11 is melted and closed by both the heating length and the heating time by arc discharge, deformation such as bending of the fiber in the hole closing section 22 is small. For this reason, when the holey optical fiber 12 is inserted into the ferrule 17, the fiber 12 is hardly caught or broken within the ferrule 17.
[0048]
After hole closing by arc discharge, the mounting of the holey optical fiber 12 to the ferrule 17 and the end surface polishing operation are completely different from the normal optical fiber mounting and end surface polishing operations, so that the ferrule assembly is easy. it can.
[0049]
The hole blocking section 22 is located at the center of the fixed bare fiber 16, and the hole 11 of the holey optical fiber 12 is exposed at the ferrule end face 21, but the cladding diameter is 125 μm. The eccentricity of the bare fiber 16 at the ferrule end face 21 does not occur, and an increase in connection loss due to the eccentricity can be suppressed.
[0050]
Here, a histogram of connection loss in a wavelength band of 1.3 μm when 50 FC connectors manufactured in the present embodiment are connected to the master connector is shown in FIG.
[0051]
The histogram of FIG. 3 shows the connection loss measured with 50 FC connectors, with the horizontal axis representing connection loss (dB) and the vertical axis representing frequency. As shown in FIG. 3, the connection loss of the terminal connected by the optical connector of the present embodiment is 0.32 dB at the maximum and 0.16 dB on the average, which is reduced to the same level as the connection loss of a normal SMF connector. Yes.
[0052]
In the present embodiment, the holey 11 has a diameter of 10 μm and the six-hole type holey optical fiber 12 has been described. However, the hole 11 has a different diameter and number, that is, holey optical fibers having a different porosity and a minute cylindrical void. A photonic crystal fiber in which holes are periodically arranged in a hexagonal lattice pattern from the center can be connected to other SMF connectors.
[0053]
Moreover, although the optical connector using the FC connector ferrule 17 has been described, the present invention is not limited to the FC connector ferrule 17 and can be applied to all other commercially available connectors.
[0054]
Further, the method for closing the holes 11 described in the present embodiment is not limited to melting and closing by discharge. For example, a material such as an adhesive is partially applied without changing the shape of the holes 11. It does not matter if it is filled. Specifically, a very small amount of optical adhesive is injected from the end face of the optical fiber by capillary action and cured at an appropriate position. However, the optical adhesive used in this method has a viscosity that passes through a pore of 10 μm, and is desirably approximately 5 Pas or less.
[0055]
Furthermore, the present invention can also be applied to connection methods other than connectors, such as mechanical splices.
[0056]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0057]
(1) Intrusion of foreign matter, moisture and the like into the hole can be prevented, and reliability equivalent to that of a normal optical connector can be secured.
[0058]
(2) Even a holey optical fiber with a high porosity can be connected to other single mode fiber connectors with low loss.
[0059]
(3) The assembly of the connector becomes easy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of a ferrule for an FC connector equipped with a holey optical fiber according to the present invention.
FIG. 2 is a structural diagram when a holey optical fiber is set in an arc discharge fusion machine in the present invention, (a) shows a state during discharge, and (b) shows a state after discharge. Is shown.
FIG. 3 is a histogram of insertion loss of the FC optical connector of the present embodiment.
FIG. 4 is a cross-sectional view of a 6-hole type holey optical fiber.
5A and 5B are cross-sectional views showing a structure of a ferrule for an FC connector in which holes are crushed by microtorch heating, and FIG. 5B is a cross-sectional view seen from an end surface of the ferrule.
FIG. 6 is a cross-sectional view showing the structure of a previously proposed FC connector ferrule in which SMF is fusion-spliced.
[Explanation of symbols]
11 Hole 12 Holey Optical Fiber 17 Ferrule 21 for FC Connector Fiber End Face 25 Arc Discharge Fusion Machine

Claims (2)

In an optical fiber connector in which an optical fiber having a plurality of holes around a core is inserted into a ferrule and attached, the holes are closed by melting at a position away from the end face of the optical fiber, and the vicinity of the end face is empty by melting. The optical fiber connector is characterized in that the outer diameter of the end face of the optical fiber is maintained at the outer diameter before closing the air hole without closing the hole . Connector for optical fiber according to claim 1 Symbol placement melted closed pores by arc discharge.

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