JP3801148B2 - Optical connector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical connector used for connecting optical fibers in optical communication of an information communication system.
[0002]
[Prior art]
In recent years, with the expansion of the Internet and the like, the construction of a communication network using optical fibers has been rapidly advanced in response to an increase in the amount of information transmission and an increase in transmission speed. In the construction of this optical fiber communication network, the optical connector makes it possible to switch the connection between optical fibers, and is an important circuit element that facilitates connection work at the assembly site by being attached to the optical fiber in advance. Therefore, there is a demand for a low-loss optical connector.
[0003]
Various types of optical connectors have been developed for single-core connectors to multi-fiber connectors, depending on the type of use. In general, optical fibers using ferrules molded of ceramic or resin are used. Is positioned and fixed. The ferrule has a small-diameter optical fiber hole for positioning by inserting the exposed glass fiber portion after removing the fiber coating, and a large-diameter fiber that partially accommodates the fiber coating and the outer skin portion and is fixed with an adhesive. And an insertion hole. The ferrule is housed in an optical connector housing and is configured to attach / detach and lock the connection.
[0004]
FIG. 7 is a diagram for explaining an example of a conventional optical connector (see, for example, Patent Document 1). FIG. 7A is a diagram showing an example in which a small-diameter optical fiber hole is formed short, and FIG. 7B is a diagram showing an example in which a small-diameter optical fiber hole is formed long. In the figure, 1 is an optical fiber, 2 is a core portion, 2a is a mode field diameter enlarged portion (MFD enlarged portion), 3 is a cladding portion, 4 is a fiber coating, 5 is a ferrule, 5a is a ferrule end face, and 5b is an optical fiber hole. 5c is a fiber insertion hole, 6 is a holding metal fitting, 6a is a through hole, and 7 is an adhesive.
[0005]
The optical fiber 1 includes a core portion 2 and a cladding portion 3, and the outer peripheral surface is protected by a fiber coating 4. The distal end portion of the optical fiber 1 is formed by an enlarged portion 2a in which the mode field diameter (hereinafter referred to as MFD) of the core portion 2 is enlarged by heat treatment, thereby widening the allowable range of the optical axis deviation at the time of connection. By forming the MFD enlarged portion 2a on the connection end side of the optical fiber 1, connection loss due to axial displacement of the connection portion can be reduced. Further, in the connection between optical fibers having different MFDs, the increase in the connection loss due to the difference in MFD can be reduced by expanding the MFD of the optical fiber having the smaller MFD to match the MFD having the larger MFD. it can.
[0006]
The optical connector is configured by mounting the optical fiber 1 in a ferrule 5 to which a holding metal fitting 6 is attached. In the ferrule 5 shown in FIG. 7A, a small-diameter optical fiber hole 5b for mounting the tip of the optical fiber 1 is formed on the end face 5a side, and a large diameter that allows the fiber coating 4 to be inserted behind the hole. The fiber insertion hole 5c is formed. The small-diameter optical fiber hole 5b is slightly larger (several μm or less) than the outer diameter of the optical fiber (ordinary optical fiber is 125 μm), and the length thereof is formed so as to reach the center of the MFD enlarged portion 2a. ing. The fiber insertion hole 5c communicates with the optical fiber hole 5b and is set to have a hole diameter larger by several tens μm or more than the optical fiber hole 5b.
[0007]
The optical fiber 1 is positioned by a small-diameter optical fiber hole 5b, and the fiber insertion hole 5c is filled with an adhesive 7 and bonded and fixed. The adhesive 7 penetrates into the gap between the optical fiber hole 5 b and the optical fiber 1, the gap between the fiber insertion hole 5 c and the fiber coating 4, and the gap between the through hole 6 a of the holder 6 and the fiber coating 4. Thus, the ferrule 5 and the optical fiber 1 are bonded and integrated.
[0008]
In the configuration shown in FIG. 7A, the optical fiber 1 mounted in the ferrule 5 has an adhesive filled in the large-diameter fiber insertion hole 5c from the rear end of the small-diameter optical fiber hole 5b. 7 is enclosed. For this reason, the adhesive 7 expands and contracts due to a change in the environmental temperature, and the optical fiber 1 receives a non-uniform bending stress at the boundary portion between the optical fiber hole 5b and the fiber insertion hole 5c, and causes a loss variation due to irregular bending. May occur.
[0009]
In FIG. 7B, in order to improve this point, the optical fiber hole 5b into which the optical fiber 1 is mounted is formed long beyond the MFD enlarged portion 2a, and the fiber coating 4 is removed. The portion of the fiber 1 is substantially surrounded by an adhesive of 1 μm or less. As a result, there is no portion where the MFD enlarged portion 2a and the core portion 2 are exposed to the thick adhesive layer 7, and loss fluctuation due to temperature change can be eliminated.
[0010]
[Patent Document 1]
JP-A-4-73609
[0011]
[Problems to be solved by the invention]
7A and 7B, the optical fiber 1 is positioned by the thin optical fiber hole 5b of the ferrule 5. For this reason, it is necessary to form the optical fiber hole 5b with as high accuracy as possible, and to form the gap between the optical fiber 1 and the optical fiber 1 as much as possible. In the above-mentioned Patent Document 1, it is described that the optical fiber hole 5b is slightly (several μ or less) larger than the outer diameter of the optical fiber, and when the optical fiber is surrounded by an adhesive of about 1 μm or less in the example of FIG. Although there is a description, it is not specified specifically.
[0012]
FIG. 8 is a diagram showing a formation example of the above-described MFD enlargement unit 2a, and the reference numerals in the figure are the same as those used in FIG. When the MFD enlarged portion 2a is formed at the connection end of the optical fiber 1, the fiber coating 4 at the end or in the middle of the optical fiber 1 is removed as shown in FIG. Expose. Next, as shown in FIG. 8B, the MFD enlarged portion 2a is formed by heat-treating the predetermined region and thermally diffusing the dopant added to the core portion 2 toward the cladding portion 3 side. Thereafter, the optical fiber 1 is cut at the center of the MFD enlarged portion 2a to obtain an optical fiber terminal as shown in FIG. The optical fiber terminal is attached to the ferrule 5 as described with reference to FIG.
[0013]
However, the end portion of the optical fiber 1 is narrowed with respect to the outer diameter of the glass fiber that is not heat-treated as shown in FIG. The amount of thinning differs somewhat depending on the heating conditions, but is about 0.5 μm to 2.0 μm when the MFD is enlarged by several μm. When the diameter of the tip of the optical fiber is reduced, the clearance with the optical fiber hole 5b increases when the ferrule 5 shown in FIG. 7 is attached, and the axial deviation of the optical fiber 1 increases. When the axis deviation of the optical fiber 1 increases, connection loss increases due to the connection of the optical connector, defective products increase, and productivity deteriorates.
[0014]
Further, when the optical fiber hole 5b formed in the ferrule 5 has a small diameter, the hole forming pin becomes thin and is easily bent at the time of forming. In addition, when the hole diameter is formed with high accuracy, it is usually finished by polishing using a wire. However, if the hole to be processed has a small diameter, the wire to be used becomes thin and easily cut. For this reason, it is necessary to reduce the polishing rate, and the productivity is lowered and the processing cost is increased. As shown in FIG. 7B, when the length of the optical fiber hole 5b is increased, it is difficult to form a hole without a bend for the reason described above, and it is considered that the processing cost also increases.
[0015]
  The present invention has been made in view of the above circumstances.,ContactProvided is an optical connector having an optical fiber in which the MFD at the connecting end is expanded by heat treatment, and can accurately position the optical fiber with a ferrule and can increase productivity. Is an issue.
[0016]
[Means for Solving the Problems]
  In the optical connector according to the present invention, the front end side of the optical fiber mounting hole of the ferrule is formed with a small diameter optical fiber hole to position the optical fiber, and the rear side is formed with a large diameter fiber insertion hole. Glue and fix withAttach an optical fiber whose tip mode field diameter has been expanded by heat treatment.It is an optical connector. The small-diameter optical fiber hole and the large-diameter fiber insertion hole communicate with each other through a tapered hole having a taper angle of 90 ° or less, and when the nominal outer diameter of the optical fiber to be mounted is Ea, the hole diameter D of the optical fiber holeaTo Ea + (-1μm or more 0μmAnd the axial length L of the small-diameter optical fiber holea is shorter than the region M in which the mode field diameter of the optical fiber is enlarged.To do.
[0017]
  Further, in another optical connector according to the present invention, the mode field diameter of the tip of the optical fiber to be mounted isBy heat treatmentWhen enlarged,lightWhen the outer diameter of the tip portion where the mode field diameter of the fiber is expanded is Eb, the hole diameter Da of the optical fiber hole is Eb + (over 0 μm to 1 μm or less).AndThe axial length La of the small-diameter optical fiber hole is made shorter than the region M where the mode field diameter of the optical fiber is enlarged.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
  FIG.Is a diagram showing an example of an optical connector using a normal optical fiber, FIG.Of the tip according to the inventionFIG. 3 is a diagram showing an example of an optical connector using an optical fiber with an expanded mode field diameter (hereinafter referred to as MFD), and FIG. 3 is a diagram showing an example of a multi-fiber optical connector. In the figure, 11 and 11 'are optical fibers, 12 is a core part, 12a is a mode field diameter enlarged part (MFD enlarged part), 13 is a cladding part, 14 is a fiber coating, 15 is a ferrule, 15a is a ferrule end face, and 15b is A small-diameter optical fiber hole, 15c is a large-diameter fiber insertion hole, 15d is a tapered hole, 16 is a holder, 16a is a through hole, and 17 is an adhesive.
[0019]
In the example shown in FIG. 1, the optical fiber 11 includes a core portion 12 and a cladding portion 13, and the outer peripheral surface is protected by a fiber coating 14. The optical connector is configured by inserting and fixing the optical fiber 11 into the ferrule 15 and holding and fixing the ferrule 15 by the holder 16 as described in the section of the prior art. The ferrule 15 is formed with a small-diameter optical fiber hole 15b for mounting the tip of the optical fiber 1 on the side of the end face 15a, and a large-diameter fiber insertion hole 15c is formed behind it.
[0020]
The optical fiber 11 is positioned by a small-diameter optical fiber hole 15b, and is bonded and fixed by filling an adhesive 17 into a large-diameter fiber insertion hole 15c. The adhesive 17 penetrates into the gap between the optical fiber hole 15 b and the optical fiber 1, the gap between the fiber insertion hole 15 c and the fiber coating 14, and the gap between the through hole 16 a of the holder 16 and the fiber coating 14. Then, the ferrule 15 and the optical fiber 11 are bonded and integrated.
[0021]
The small-diameter optical fiber hole 15b and the large-diameter fiber insertion hole 15c communicate with each other through a tapered hole 15d. Between the rear end of the small-diameter optical fiber hole 15b and the large-diameter fiber insertion hole 15c, Smooth volume conversion is performed so that the cross-sectional area does not change suddenly. The taper angle θ of the tapered hole 15d is desirably 90 ° or less, more preferably 60 ° or less.
[0022]
By connecting the small-diameter optical fiber hole 15b and the large-diameter fiber insertion hole 15c through the tapered hole 15d, stress concentration does not occur in the optical fiber 11 when the adhesive 17 is cured, and an increase in loss can be suppressed. . In addition, a change in stress applied to the optical fiber 11 due to the expansion and contraction of the adhesive 17 due to a change in the environmental temperature can be reduced. As a result, it is possible to avoid the occurrence of fluctuations in loss due to irregular bending due to uneven bending stress acting on the optical fiber 11.
[0023]
The small-diameter optical fiber hole 15b is formed with high accuracy substantially equal to the outer diameter of the optical fiber 11 to be mounted, and the optical fiber 11 is accurately positioned by making the clearance with the optical fiber 11 as small as possible. Can be done. In the optical fiber 11, when the outer diameter of the clad portion 13 is, for example, a nominal outer diameter of 125 μm, it is preferable that the hole diameter D of the small optical fiber hole 15b is between 125 μm and 126 μm. In recent years, since an optical fiber of 100 μm or less has been developed, assuming that the nominal outer diameter of the optical fiber to be mounted is Ea, the hole diameter D of the thin optical fiber hole 15 b is Ea + (over 0 μm and less than 1 μm) ). The hole diameter of the fiber insertion hole 15c is set to be 100 μm or more larger than the hole diameter D of the thin optical fiber hole 15b. When the nominal outer diameter of the optical fiber is 125 μm, the fiber coating outer diameter is usually around 250 μm, and the hole diameter of the fiber insertion hole 15 c is formed at about 300 μm.
[0024]
When the optical fiber hole 15b is formed with a small diameter hole as described above, the forming pin used for forming the ferrule hole portion has a small diameter and is easily bent. In addition, in order to finish fine holes with high accuracy, it is necessary to polish with thin wires. However, if the holes to be polished are long, the wires are likely to be cut, and it takes time, resulting in lower productivity and higher processing costs. . For this reason, it is preferable that the small-diameter optical fiber hole 15b is formed with the shortest axial length. Since the optical fiber hole 15b is mainly intended for positioning of the connection end of the optical fiber 11, it is only necessary to ensure the axial length necessary for positioning, and the axial length L is formed to be 2.0 mm or less. Is desirable.
[0025]
  According to the inventionIn the example shown in FIG. 2, the optical fiber 11 ′ includes a core portion 12 and a clad portion 13 as in FIG. 1, and the outer peripheral surface is protected by a fiber coating 14.But,The tip portion of the optical fiber is formed by an MFD enlarged portion 12a in which the MFD of the core portion 12 is enlarged by heat treatment. The enlarged portion 12a in which the MFD is enlarged has a wide allowable range of optical axis misalignment at the time of connection, so that the connection loss can be reduced and the yield of the connected portion can be increased.
[0026]
  Also optical connectorThe shape itselfIs substantially the same as the example of FIG. 1, and is configured by mounting an optical fiber 11 'in a ferrule 15 to which a holding metal fitting 16 is attached. The ferrule 15 is formed with a small-diameter optical fiber hole 15b for mounting the tip of the optical fiber 1 on the connection end face 15a side, and a large-diameter fiber insertion hole 15c into which the optical fiber 11 'can be easily inserted behind. Is formed. The optical fiber 11 ′ is positioned by the small-diameter optical fiber hole 15 b, and the adhesive 17 is filled into the large-diameter fiber insertion hole 15 c to be bonded and fixed.
[0027]
The adhesive 17 includes a gap between the small-diameter optical fiber hole 15 b and the optical fiber 1, a gap between the large-diameter fiber insertion hole 15 c and the fiber coating 14, and the through-hole 16 a of the holding bracket 16 and the fiber coating. 14, the ferrule 15 and the optical fiber 11 are bonded and integrated. As in the example of FIG. 1, the small-diameter optical fiber hole 15b and the large-diameter fiber insertion hole 15c communicate with each other via a tapered hole 15d, and a large-diameter fiber is formed from the rear end of the small-diameter optical fiber hole 15b. Smooth volume conversion is performed so that the cross-sectional area of the hole does not change suddenly with the insertion hole 15c. The taper angle θ of the tapered hole 15d is desirably 90 ° or less, more preferably 60 ° or less.
[0028]
Normally, when heat treatment for expanding the MFD is performed, the outer diameter of the optical fiber (cladding outer diameter) is changed from Ea to Eb as shown in the enlarged view of the fiber end portion in FIG. It changes to slightly thin. In the normal case, when the MFD is enlarged by several μm with respect to Ea, the outer diameter Eb is about 0.5 μm to 2 μm thinner than Ea when the heat treatment is not performed. For example, when a single mode optical fiber having a cladding outer diameter Ea of 125 μm and an MFD of 6.5 μm is expanded so that the MFD is 10.5 μm, the cladding outer diameter Eb of the expanded region M is 123.8 μm. That is, the outer diameter is reduced by about 1% by heat treatment. Note that the value of MFD is a value of a wavelength of 1.55 μm.
[0029]
Therefore, when mounting the optical fiber 11 ′ having the MFD enlarged portion 12 a, it is necessary to make the hole diameter Da of the optical fiber hole 15 b somewhat narrower than in the example of FIG. 1. That is, when the optical fiber 11 ′ having the MFD enlarged portion 12b is mounted, when the nominal outer diameter of the optical fiber is Ea, the hole diameter Da of the thin optical fiber hole 15b is formed by Ea + (−1 μm or more and 0 μm or less). It is desirable to do. Further, the axial length La of the optical fiber hole 15b is shorter than the region M where the MFD of the optical fiber is enlarged.
[0030]
In addition, when the optical fiber 11 ′ having the MFD enlarged portion 12b in which the MFD is enlarged is attached, when the outer diameter of the distal end portion where the MFD of the optical fiber is enlarged is Eb, the hole diameter Da of the small optical fiber hole 15b. Is preferably formed by Eb + (more than 0 μm and 1 μm or less). In this case, the thinning amount of the outer diameter of the optical fiber is several μm. Even in this case, the thin optical fiber hole 15b is formed with high accuracy substantially equal to the outer diameter of the optical fiber 11 to be mounted. By making the clearance with the fiber 11 as small as possible, the optical fiber 11 can be accurately positioned.
[0031]
  Figure 3The figureIt is a figure which shows the example which applied the structure of 2 to the multi-fiber optical connector. In the case of a multi-fiber optical connector, it is necessary that the plurality of small-diameter optical fiber holes 15b be accurately formed with respect to the hole pitch P and the guide holes G formed on both sides of the ferrule 15. It is particularly important to reduce the clearance between the optical fiber hole 15b and the optical fibers 11 and 11 ′. In a multi-fiber optical connector, if the clearance is large, the clearances of both adjacent optical fibers are added, so that the positional deviation is larger than that of a single-fiber optical connector. ThereforeThe figureIt is extremely effective to use the second configuration for a multi-fiber optical connector.
[0032]
FIG. 4 is a diagram illustrating an example in which a gas burner is used as the heat treatment for MFD expansion. In the figure, 18 is a burner body, 19 is a gas supply pipe, and 20 is a gas injection port. The gas burner is configured such that a plurality of gas injection ports 20 are provided in a rectangular shape in a rectangular burner body 18 and combustion gas such as propane gas is supplied from a gas supply pipe 19. The gas injection port 20 is provided with a hole diameter of about 0.3 mmφ and a hole pitch of about 0.7 mm to 1.0 mm. By using such a gas burner and heating the optical fiber 11 'apart by 2.0 mm or more, the amount of thinning of the heating region can be suppressed to some extent.
[0033]
For example, a high-performance optical fiber with a wavelength of 1.55 μm and an MFD of about 5 μm is used, and a gas burner as shown in FIG. 4 is used to expand the MFD to about 10 μm, with a distance of 2.8 mm from the optical fiber. When heat-treated, the amount of thinning (Eb-Ea) was 0.8 μm. If the heating conditions are not so limited, the amount of thinning may be 2 μm or more.
[0034]
FIG. 5 is a diagram showing the connection loss due to the optical axis misalignment. When the MFDs of the single mode optical fibers (SMF) connected to each other are 10.5 μm, the horizontal axis represents the amount of axial misalignment (μm), and The connection loss (dB / 1 place) is shown on the shaft. According to FIG. 5, even when optical fibers having the same MFD are connected to each other, the center axis of the connection end portion is shifted by 0.5 μm to 0.04 dB, 1.0 μm to be shifted to 0.16 dB, 1. By shifting by 5 μm, a connection loss of 0.35 dB occurs.
[0035]
  In order to evaluate the present invention, the following test optical connectors were prepared and the connection loss was measured.
(examined goods1)
  A single-fiber optical connector shown in FIG. 1 was manufactured using an optical fiber having a cladding outer diameter of 80 μm and a fiber coating outer diameter of 165 μm. The length L in the axial direction of the optical fiber hole 15b of the ferrule 15 is 1.0 mm, the hole diameter D of the optical fiber hole 15b is in the range of 80 to 81 μm, the taper angle θ of the taper hole 15d is 60 °, and the fiber insertion hole 15c. The pore diameter was 300 μm. The connection loss at this time was an average of 0.07 dB.
[0036]
  (examined goods2)
  examined goodsAn optical fiber having the same cladding outer diameter of 80 μm as that of No. 1 was used as a 16-core, 180-μm pitch tape core wire to produce a multi-fiber optical connector. The length L in the axial direction of the optical fiber hole 15b of the multi-fiber ferrule is 1.0 mm, the diameter D of the optical fiber hole 15b is in the range of 80 to 81 μm, and the taper angle θ of the tapered hole 15d is 60 °. The connection loss at this time was an average of 0.12 dB.
[0037]
  (examined goods3)
  A single-core optical connector shown in FIG. 2 was manufactured using an optical fiber having a cladding outer diameter Ea of 125 μm and a fiber coating outer diameter of 250 μm, and an MFD at the tip of the optical fiber expanded from 6.5 μm to 10.3 μm. The cladding outer diameter Eb in the MFD enlarged portion 12a was reduced to 123.8 μm, and the range M of the MFD enlarged portion 12a was 1.7 mm. The axial length La of the optical fiber hole 15b of the ferrule 15 is 1.5 mm, the hole diameter Da of the optical fiber hole 15b is formed in the range of 124 to 125 μm, the taper angle θ of the tapered hole 15d is 60 °, and the fiber insertion hole 15c. The pore diameter was 300 μm. The connection loss at this time was 0.08 dB on average.
[0038]
  (examined goods4)
  examined goodsThe optical fiber having the same MFD expansion part as 3 was made into a tape core wire of 8 cores and 250 μm pitch, and a multi-fiber optical connector was manufactured. The axial length La of the optical fiber hole 15b of the multi-fiber ferrule is 1.5 mm, the hole diameter Da of the optical fiber hole 15b is in the range of 124 to 125 μm, and the taper angle θ of the tapered hole 15d is 60 °. . The connection loss at this time was an average of 0.11 dB.
[0039]
  more than,examined goods1 to 4 were produced to confirm the effect of the present invention.BothThere was no bending of the forming pin of the ferrule forming jig, and the finish polishing of the optical fiber hole could be efficiently and accurately performed in a short time because the axial length of the hole was short.That is, in the test products 3 and 4 according to the present invention, the tip end of the optical fiber is thinned by the heat treatment for expanding the MFD, but the loss is equivalent to that of the test products 1 and 2 that are not subjected to the heat treatment. Was able to confirm.In addition, optical fiber was attached to the optical connector and the connection loss was measured.In FIG.Compared with clearance of about 1μ and connection loss of about 0.2dB)EvenIt could be reduced to about 1/2.
[0040]
  (examined goods5)
  Further, in the configuration shown in FIG. 2, the hole diameter Da of the small-diameter optical fiber hole 15b on the optical connector distal end side is changed to the distal end outer diameter E subjected to the heat treatment for MFD expansion.bOn the other hand, it formed accurately in the range of more than 0 μm and 1 μm or less. In this case, the axial deviation of the optical fiber 11 is 0.5 μm at the maximum regardless of the thinning amount, and the connection loss is 0.04 dB at the maximum according to the data in FIG. 5. About this, when 20 samples were produced and measured, the average connection loss was 0.06 dB and the standard deviation was 0.02 dB.
[0041]
  (Test product 6)
  Assume that the optical fiber 11 ′ subjected to the heat treatment for MFD expansion is attached to the optical connector having the configuration shown in FIG. 1. At this time, the hole diameter of the optical fiber hole on the tip side of the optical connector is accurately formed in the range of the nominal outer diameter Ea of the optical fiber (= the outer diameter of the non-heated portion) + (0 μm to 1 μm). To do. If the amount of thinning of the optical fiber by MFD expansion heat treatment at the tip of the optical fiber is 0.8 μm, the axial misalignment of the optical fiber at this time is a maximum of 0.9 μm. The maximum connection loss is 0.13 dB. About this, when 20 samples were produced and measured, the average connection loss was 0.1 dB, and the standard deviation was 0.03 dB. If the amount of thinning of the optical fiber is 2 μm, the axial misalignment of the optical fiber is 1.5 μm at the maximum, and the connection loss is 0.35 dB at the maximum.
[0042]
  examined goods5 andTest product 6From the results, the hole diameter Da of the optical fiber hole 15b having a small diameter of the optical connector is formed with an accuracy of more than 0 μm and within 1 μm with reference to the outer diameter Eb of the distal end portion where the MFD of the optical fiber 11 ′ is enlarged. Is preferred. However, since the heating time and the heating amount vary depending on the MFD value and the enlarged MFD value of the optical fiber 11 'to be mounted, the thinning amount of the optical fiber 11' is not uniform. However, the amount of thinning can be made uniform to some extent if the type of gas burner or optical fiber 11 'used and the MFD enlargement value are set. Therefore, when manufacturing the optical connector, it is possible to realize by forming the hole diameter of the small-sized optical fiber hole 15b slightly smaller than a predetermined value and polishing it to a predetermined value later.
[0043]
In addition, the axial length La of the small-diameter optical fiber hole 15b needs to be shorter than the MFD expansion region M at the tip of the optical fiber. The reason is that the MFD enlarged region M and the narrowed region substantially coincide with each other so that the tip of the optical fiber can be completely inserted into the optical fiber hole 15b. Since the MFD region M is usually 2 to 4 mm or less, the axial length La of the optical fiber hole 15b may be approximately 2 mm or less. With such an axial length, the pore diameter can be polished relatively easily and with high accuracy, and can be manufactured without impairing productivity.
[0044]
FIG. 6 shows the wavelength characteristics according to the curing shrinkage rate of the adhesive that is filled and fixed between the ferrule and the optical fiber. When the optical fibers 11 and 11 ′ are attached to the optical connector, stress remains in the optical connector when the adhesive resin is cured and contracted. The residual stress due to the adhesive resin causes microbending in the optical fibers 11 and 11 'in the optical connector, which contributes to an increase in loss. Therefore, it is desirable that the curing shrinkage rate of the adhesive is small.
[0045]
As shown in FIG. 6, by changing the resin composition of the epoxy adhesive and preparing adhesives with cure shrinkage ratios of 4% and 6%, light that tends to cause a loss with respect to bending using this adhesive. The fibers 11 and 11 ′ were mounted in the optical connector with the configuration shown in FIG. 1 or 2, and the wavelength characteristics were measured. The adhesive having a cure shrinkage of 6% shows an increase in loss on the long wavelength side as compared with the adhesive having a cure shrinkage of 4%. As a result, although not particularly remarkable, it is desirable that the curing shrinkage rate of the adhesive is 5% or less.
[0046]
Further, the optical connector is required to have resistance to the tensile load of the optical fiber 11. For example, when an optical fiber core with an outer diameter of 0.9 mm is attached to the optical connector, a 9.8 N schooling load is applied in the fiber longitudinal direction. When heat treatment for MFD enlargement is applied, the breaking strength at that part has deteriorated, so if the cured adhesive resin is soft, the tensile load reaches the tip of the optical connector and breaks at the MFD enlargement part May occur.
[0047]
  Using an adhesive resin with Young's modulus after curing of 490 MPa and 1470 MPa,2The MFD expansion optical fiber 11 ′ was mounted in the optical connector shown in FIG. The number of samples was 20, and a load was applied in the longitudinal direction of the optical fiber, and the tensile load when the optical fiber 11 was peeled from the ferrule 15 was measured. As a result, when an adhesive resin having a Young's modulus of 490 MPa was used, the average value was 17.6 N, the standard deviation was 6.2 N, the maximum value was 27.0 N, and the minimum value was 8.0 N. When an adhesive resin having a Young's modulus of 1470 MPa was used, the average value was 26.1 N, the standard deviation was 3.8 N, the maximum value was 32.9 N, and the minimum value was 21.4 N. As a result, the latter increases by an average value of 8.5 N with respect to the former, and the standard deviation decreases to about 60%, indicating an advantage. It is desirable that the Young's modulus of the adhesive is 980 MPa or more.
[0048]
【The invention's effect】
  As explained above, according to the present invention,,ContactAn optical connector equipped with an optical fiber whose MFD at the end has been expanded by heat treatment, which enables accurate positioning of the optical fiber with a ferrule, low connection loss, and productivityofYou can offer something expensive.
[Brief description of the drawings]
[Figure 1]An example of attaching a normal optical fiber to an optical connector with high accuracyFIG.
FIG. 2The fruitIt is a figure explaining embodiment.
FIG. 3 is a diagram illustrating an example of a multi-fiber optical connector according to the present invention.
FIG. 4 is a diagram showing an example of a gas burner used for heat treatment for MFD expansion according to the present invention.
FIG. 5 is a diagram for explaining a connection loss due to an axial shift of an optical fiber.
FIG. 6 is a diagram illustrating wavelength characteristics of an optical fiber depending on the curing shrinkage rate of an adhesive.
FIG. 7 is a diagram illustrating a conventional technique.
FIG. 8 is a diagram for explaining a part of problems in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Optical fiber, 12 ... Core part, 12a ... Mode field diameter enlarged part (MFD enlarged part), 13 ... Cladding part, 14 ... Fiber coating, 15 ... Ferrule, 15a ... Ferrule end surface, 15b ... Small diameter optical fiber hole , 15c: Large diameter fiber insertion hole, 15d: Tapered hole, 16: Holding metal fitting, 16a: Through hole, 17: Adhesive, 18 ... Burner main body part, 19 ... Gas supply part, 20 ... Gas supply port.

Claims (5)

Performs positioning of the optical fiber to form a front end portion of the ferrule of the optical fiber attachment hole in diameter of the optical fiber holes, the rear side of the distal end portion is bonded and fixed by an adhesive to form at the fiber insertion hole of the large diameter An optical connector for mounting an optical fiber whose mode field diameter is enlarged by heat treatment ,
Wherein A fiber insertion hole of the small-diameter optical fiber hole the large diameter taper angle is communicated by the following tapered hole 90 °, when the nominal outer diameter before Symbol optical fibers mounted to the Ea, the optical fiber An optical connector, wherein a hole diameter Da is Ea + (-1 μm or more and 0 μm or less), and an axial length La of the optical fiber hole is shorter than a region M in which a mode field diameter of the optical fiber is expanded. Performs positioning of the optical fiber to form a front end portion of the ferrule of the optical fiber attachment hole in diameter of the optical fiber holes, the rear side of the distal end portion is bonded and fixed by an adhesive to form at the fiber insertion hole of the large diameter An optical connector for mounting an optical fiber whose mode field diameter is enlarged by heat treatment ,
Wherein the fiber insertion hole of the small-diameter optical fiber hole the large diameter taper angle is communicated by the following tapered hole 90 °, the tip outer diameter of the mode field diameter is enlarged before Symbol optical fiber was Eb The hole diameter Da of the optical fiber hole is Eb + (more than 0 μm and not more than 1 μm), and the axial length La of the optical fiber hole is shorter than the region M in which the mode field diameter of the optical fiber is enlarged. And optical connector. The optical connector according to claim 1 or 2, wherein the diameter of the optical fiber holes are multicore structure in which a plurality formed. The optical connector according to any one of claims 1 to 3 , wherein the thick fiber insertion hole is filled with an adhesive having a curing shrinkage rate of 5% or less. The optical connector according to claim 1-4, characterized in that the Young's modulus after curing the fiber insertion hole of the large diameter is filled with an adhesive is more than 980 MPa.

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