JP2007057697A - Method for connecting optical fibers, mechanical splice, and optical connector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for connecting optical fibers with each other with a small connection loss, and also to provide mechanical splice and an optical connector. <P>SOLUTION: A refractive index matching agent is designed to be one composed of a refractive index c of 0.99b≤c≤1.00b (measuring wavelength: 1.55 μm). As a result, since the refractive index of the matching agent is smaller than that of a clad, even when the matching agent enters vacant holes, the index difference from the core refractive index is fully secured to enable the connection loss to be satisfied. In addition, the refractive index is larger than a prescribed value, which can satisfy reflection at the connecting part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to connection of optical fibers that mutually connect holey optical fibers or mutually connect holey optical fibers with a refractive index matching agent (matching liquid).

  The optical fiber has a structure in which a cladding having a smaller refractive index is coated around the core. These refractive indexes vary depending on the measurement wavelength, but in general silica-based optical fibers used in the communication field, the refractive index of the core is about 1.45 and the refractive index of the cladding is about 1.444 in the wavelength 1.55um band. ing. By providing such a refractive index difference, light can be transmitted while confining light in the core.

  In recent years, holey optical fibers have been proposed as one of optical fibers resistant to bending. As shown in FIG. 3, the holey optical fiber 1 has a structure in which a plurality of holes 4 are arranged so as to surround the core 2 in the cladding 3 along the longitudinal direction of the core 2. As an example, the core 2 has a diameter of 9 μmφ, the cladding 3 has a diameter of 125 μmφ, and the air holes 4 have a diameter of about 15 μmφ. This value is an example, and the value is not necessarily as described above. Also, the number of holes 4 is not necessarily shown.

  Since air is contained in the air holes 4, the refractive index in the air holes 4 is equivalent to that of air, so that the refractive index of the clad 3 around the core 2 becomes smaller on average. If the refractive index of the clad 3 is reduced, the effect of confining light in the core 2 is enhanced, and the loss can be extremely reduced even if the optical fiber is bent.

  Conventionally, various mechanical splice connections have been proposed for connecting optical fibers to each other. (For example, Patent Documents 1 to 5)

  FIG. 5 shows a mechanical holding type optical connector described in Patent Document 1. In FIG. 5, 10 is a base material having a semicircular groove 11 formed on the surface, 20 is a lid covering the surface of the groove 11, 30 is covering the base material 10 and the lid 20 from the outer periphery thereof, and these opposing surfaces A pressing device having a notch 31 on the outer periphery that presses them against each other, 40 is a ferrule attached to one end of the substrate 10, 50 is a built-in optical fiber built in the ferrule 40, and 60 is a groove 11 It is an optical fiber that is arranged between the lid 20 and the built-in optical fiber 50.

  The optical connector having such a configuration is then covered with a slider 80 or the like as shown in FIG. 4 to complete the mechanical connection type optical connector. As shown in FIG. 4, this optical connector is formed with a wedge 70 inserted through a notch 81 formed on the outer periphery of the slider 80 and further formed on the outer periphery of the pressing device 30 as shown in FIG. By inserting the wedge 70 between the base material 10 and the lid 20 via the notch 31, a space formed by the groove 11 and the lid 20 against the pressing force provided by the pressing device 30 is formed. The optical fiber 60 that is spread and disposed in the groove 11 can be moved along the longitudinal direction of the groove 11. In this state, the end face of the optical fiber 60 is brought into contact with the end face of the built-in optical fiber. Thereafter, the wedge 70 is removed from between the base material 10 and the lid 20, whereby the optical fiber 60 is fixed and held in the groove 11, and the optical connector in which the optical fiber 60 and the built-in optical fiber 50 are optically connected is obtained. can get.

  6 shows the mechanical splice described in Patent Document 2 and Patent Document 3. FIG. In FIG. 6, 10 is a base material having a V-shaped groove 11 formed on the surface, 20 is a cover that covers the groove 11, and 30 is a cover that covers the base material 10 and the cover 20 from the outer periphery so that they are pressed against each other. A pressure applying tool 60 to be pressed, an optical fiber 60 is disposed between the groove 11 and the lid 20, and a space 70 is inserted between the base material 10 and the lid 20 and formed by the groove 11 and the lid 20. It is a wedge that allows the optical fiber 60 to move in the longitudinal direction in the groove 11.

  In this optical fiber connector, in the state in which the wedge 70 is inserted between the base material 10 and the lid 20, the optical fibers 60 are inserted from both ends of the optical fiber connector, and the end portions of both optical fibers 60 are inserted. In the groove 11, and the wedge 70 is removed in this state, thereby fixing and holding the two optical fibers 60 in the groove 11, and optically connecting the two optical fibers 60 in the groove 11. Can be formed.

  FIG. 7 shows a mechanical splice described in Patent Document 4. In FIG. 7, 10 is a base material on which an attachment 12 having a groove 11 formed on the surface is disposed, and 20 is a lid covering the groove 11.

  The lid 20 is configured to be rotatable around a pivot 13 formed on the side of the base material 10. The pivot 13 is provided with a spring 14 that urges the lid 20 to be opened from the base material 10. A spring 15 and a locking lever 16 are arranged on the side opposite to the side portion of the base material 10, and a locking hole 21 is formed in the lid 20 opposite to the spring 15 and the lid 20 is used to bias the spring. When the groove 11 is covered, the locking lever 16 and the locking hole 21 are engaged, and the cover 20 covers the optical fiber so that the optical fiber is fixed and held in the V-groove 11. It has become.

An elastically deformable optical fiber pressing member 22 that presses the groove 11 when the cover 20 covers the groove 11 is disposed on the surface of the cover 20 that faces the groove 11. Further, guide portions 17 are arranged on both sides of the groove 11 so as to guide the optical fiber (not shown) at one end portion of the groove 11 so that the optical fiber can be easily stored in the groove 11 so as not to cause lateral displacement. Yes.
This optical fiber holder can hold various types of optical fiber core wires in the groove 11 by means of an elastically deformable optical fiber pressing member (pressing means) 22 and a replaceable attachment 12.

  FIG. 8 shows the mechanical splice described in Patent Document 5. Although the basic configuration is the same as that described in Patent Document 4 shown in FIG. 7, when the optical fiber is stored in the groove 11, it is guided so that the optical fiber is not displaced from the groove 11. The difference is that a plurality of guide pins 18 are formed on both sides of the groove 11.

  When the optical fibers are connected to each other by mechanical splicing, the tip of the optical fiber is not completely adhered, and a slight gap is generated between the tip of the optical fiber and the tip of the optical fiber. For this reason, in general, a refractive index matching agent having a refractive index close to that of the core of the optical fiber connected to the V-groove substrate is applied, and the optical fibers are connected to each other on the V-groove substrate. As a result, light transmission loss is reduced.

Japanese Patent Laid-Open No. 11-142686 JP 2000-304959 A JP 09-297241 A Japanese Patent Laid-Open No. 11-023879 JP 2004-145196 A

Conventionally, in the mechanical connection of optical fibers as described above, a refractive index matching agent close to the refractive index of the core of the optical fiber to be connected has been used in order to reduce connection loss. For this reason, when this technique is adopted for the holey optical fiber, the refractive index matching agent enters the vacancies, and the refractive index of the clad becomes higher than that of the clad alone on average. As a result, the refractive index difference between the cladding and the core is reduced, and the light confinement effect is weakened. Therefore, in the holey optical fiber, light is diffused in a portion where the refractive index matching agent is filled in the hole, resulting in connection loss.
However, in the optical fiber mechanical connection, since the optical fiber is cut to form the tip of the optical fiber, it is difficult to block the hole in the end face when the holey optical fiber is used. Therefore, it is difficult to prevent the refractive index matching agent from entering the holes.

The present application has been made in view of such a point. In the first invention, a core having a refractive index a is coated on a core having a refractive index a, and a plurality of holes are formed along the core in the cladding in the vicinity of the core. The formed holey optical fiber and the optical fiber interconnecting method in which the end surfaces of the optical fibers are mechanically held with the same or other optical fibers and are opposed to each other. A method for interconnecting optical fibers, comprising disposing a refractive index matching agent having the following refractive index c between end faces of optical fibers.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm)

The second invention of the present application is a mechanical splice in which a groove is formed on the surface of the connection base, a cover is placed on the connection base, and a pressing means for pressing the optical fiber placed on the groove into the groove is formed. A holey optical fiber in which a cladding having a refractive index b is coated on a core having a refractive index a, and a plurality of holes are formed along the core in the cladding in the vicinity of the core; The same or different optical fibers are disposed with their end faces facing each other, and a refractive index matching agent having the following refractive index c is disposed between the end faces of the both facing optical fibers.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm)

In the third invention of the present application, a ferrule incorporating an optical fiber is disposed on one end side, and a mechanical connection portion is provided to mechanically hold the optical fiber to be connected to the other end side and connect to the built-in optical fiber. In the optical connector, a holey optical fiber in which a clad having a refractive index b is coated on a core having a refractive index a and a plurality of holes are formed along the core in the clad near the core is formed by the mechanical connection portion. The built-in optical fiber is disposed with its end face opposed to each other, and a refractive index matching agent having the following refractive index c is disposed between the end faces of both the opposed optical fibers.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm)

In any of the first to third inventions of the present application, a holey optical fiber in which a core having a refractive index a is coated with a clad having a refractive index b and a plurality of holes are formed along the core in the clad near the core. And a refractive index matching agent having the following refractive index c is disposed at the opposing portion where the end faces of the optical fibers that are the same or different from each other are mechanically held and opposed to each other. .
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm)

As a result, if the refractive index of the refractive index matching agent is smaller than the refractive index of the clad, the refractive index of the clad is sufficiently different from the core even if the refractive index matching agent is filled in the hole of the holey optical fiber. And no loss is incurred.
As a result, the first to third inventions can provide a mechanical splice connection method, a mechanical splice, and an optical connector with a small connection loss, respectively.

Hereinafter, embodiments of the present invention will be described based on specific numerical values. As an example, assuming that the refractive index b of the clad at the measurement wavelength of 1.55 μm is 1.444, if the refractive index c of the refractive index matching agent is 1.444 or more, the light confinement effect becomes weak. The refractive index c of the refractive index matching agent may be 1.444 or less. That is, the refractive index c of the refractive index matching agent is c ≦ 1.444 (Formula 1)
That is, c ≦ b.

  Further, the refractive index c of the refractive index matching agent is not necessarily reduced as long as it is smaller than the refractive index of the cladding. As a standard for mechanical connection, a connection loss of 0.5 dB or less and a return loss of 40 dB or more are common. In the mechanical connection, there is a slight gap at the tip of the optical fiber. Therefore, the light emitted from the core of one optical fiber passes through the refractive index matching agent and is transmitted to the core of the other connected optical fiber. The smaller the refractive index c of the refractive index matching agent, the larger the refractive index difference from the core, resulting in connection loss and reflection due to the refractive index difference.

FIG. 2 shows a graph of the relationship between the refractive index c of the refractive index matching agent actually measured and the connection loss. Measurement wavelength: 1.55 μm. It can be seen that the connection loss is large when the refractive index of the refractive index matching agent is 1.450, which is close to the refractive index of the core, and the connection loss decreases as the refractive index of the refractive index matching agent is decreased.
FIG. 1 shows a graph of the relationship between the refractive index c of the refractive index matching agent actually measured and the return loss. FIG. 1 also shows the calculation results.

Calculation conditions in FIG.
Optical fiber tip spacing: 0.2um
NA ratio: Negligible wavelength: 1.55 μm because the distance between optical fiber tips is very small
Points are measured values, lines are calculated values

In FIG. 1, it can be seen that the actually measured value and the calculated value are substantially equal. The calculation results show that the refractive index c of the refractive index matching agent satisfying the return loss of 40 dB or more should be 1.430 or more. That is, c ≧ 1.430 (Formula 2)
That is, c ≧ 0.99b.

From the relationship between the refractive index of the refractive index matching agent and the connection loss described above, and the relationship between the refractive index c of the refractive index matching agent and the return loss, the refractive index matching agent used for the holey optical fiber is in the following range. I know it ’s good.
0.99b ≦ c ≦ b (Formula 3)

  In addition, if the refractive index matching agent according to the present invention is filled in the holes of the holey optical fiber by capillary action, the average refractive index of the cladding increases, and therefore loss occurs when the holey optical fiber is bent. However, the distance by which the refractive index matching agent enters the pores by capillary action is about 1 mm, which is very short compared to the length of the mechanical connection portion. As a result, since bending is not applied to the mechanical connection portion, no loss due to bending occurs even if mechanical splice connection is used in the present invention.

  When a holey optical fiber is mechanically spliced, good optical characteristics can be obtained by using a refractive index matching agent c that satisfies (Equation 3).

The holey optical fibers were connected to each other by the mechanical splice shown in FIG. 6 under the following conditions.
Holy optical fiber core diameter: 9 μmφ, core refractive index a: 1.449, cladding diameter: 125 μmφ, cladding refractive index b: 1.444, hole size: 15 μmφ, number of holes: 6, void Distance between hole center and core center: 20 μm,
Refractive index c of refractive index matching agent: 1.435

  As a result, characteristics were obtained in which the connection loss between holey optical fibers was 0.05 dB or less and the return loss was 44 dB or more. On the other hand, when only the refractive index of the refractive index matching agent is changed to the same as that of the core of the holey optical fiber, the connection loss is 0.95 dB at the maximum and the return loss is 47 dB. It was confirmed that the characteristics were satisfied.

The characteristic view which shows the relationship between the refractive index of a refractive index matching agent, and a return loss. The characteristic view which shows the relationship between a refractive index matching agent and a return loss. The end view which shows an example of a holey optical fiber. Explanatory drawing for demonstrating the operation example of a general optical connector. FIG. 5 shows a main part of FIG. 4, in which A is a cross-sectional view seen from the side surface direction, and B is a cross-sectional view seen the mechanical connection part in the groove direction. It shows an example of a general mechanical splice. A is an explanatory view of operation, and B is a cross-sectional view taken along line AA of A. The perspective view which shows an example of another general mechanical splice. The perspective view which shows one Example of this invention which shows an example of another general mechanical splice.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Base material 11 Groove 12 Attachment 13 Pivot 14 Spring 15 Spring 16 Locking lever 17 Guide part 18 Guide pin 20 Lid 21 Locking hole 22 Member 30 Notch 40 Ferrule 50 Built-in optical fiber 60 Optical fiber 60 Both lights Fiber 70 Wedge 80 Slider 81 Notch

Claims (3)

A holey optical fiber in which a clad having a refractive index b is coated on a core having a refractive index a, and a plurality of holes are formed along the core in the clad in the vicinity of the core; In the method of connecting optical fibers that are mechanically held and faced to each other, the refractive index matching agent having the following refractive index c is placed between the facets of the holey optical fibers placed facing each other. A method for connecting optical fibers to each other.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm) In the mechanical splice in which a groove is formed on the surface of the connection base, a cover is placed on the connection base, and a pressing means for pressing the optical fiber placed on the groove into the groove is formed, the core of the refractive index a A holey optical fiber coated with a clad having a refractive index b and having a plurality of holes formed in the clad near the core along the core is disposed on the groove, and the same or different optical fiber; Are disposed with their end faces facing each other, and a refractive index matching agent having the following refractive index c is disposed between the end faces of the both facing optical fibers.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm) An optical connector in which a ferrule with an optical fiber built in is arranged on one end side, and a mechanical connection part that mechanically holds the optical fiber to be connected to the other end side and is connected to the built-in optical fiber is refracted. A holey optical fiber in which a clad having a refractive index b is coated on a core having a refractive index a and a plurality of holes are formed in the clad near the core along the core is connected to the built-in optical fiber and the end face at the mechanical connection portion. An optical connector characterized in that a refractive index matching agent having the following refractive index c is arranged between the end faces of both of the opposed optical fibers.
0.99b ≦ c ≦ 1.00b (measurement wavelength: 1.55 μm)

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