JP2000338340A - Method for expanding core diameter of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible expand the core diameter of an optical fiber without the occurrence of bending and flexing at an optical fiber at the time of a heat treatment of the optical fiber in a method for expanding the core diameter described above by a heat treatment method. SOLUTION: This method for expanding the core diameter consists in arranging a bed 2 of an optical fiber heater 1 in a direction perpendicular to a horizontal floor surface 10, disposing an optical fiber holding part 3A and an optical fiber holding part 3B respectively in the upper part and lower part of the bed 2, stretching and fixing the optical fiber F rectilinearly between a groove 7A disposed in the optical fiber holding part 3A and a groove 7B disposed in the optical fiber holding part 3B in a direction approximately perpendicular to the horizontal floor surface 10 and bringing a heat source 4 to the middle point A of the optical fiber F in this state while controlling the heat source with a heat source movement control part 6 and a heat source control part 5 to heat the point, thereby expanding the core outside diameter of the heat treated point of the optical fiber F.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for enlarging a core diameter of an optical fiber which is useful for connecting optical fibers having different mode fields or optical fibers and optical components such as optical semiconductors. In particular, the present invention relates to a method for enlarging the core diameter of an optical fiber that can accurately increase the core outer diameter without causing bending or bending of the optical fiber.

[0002]

2. Description of the Related Art When two optical fibers having different core diameters or two optical fibers having different mode fields such as optical semiconductor elements are connected to each other, the spot size of the light on the connection surface may be discontinuous. Therefore, transmission loss increases. In order to reduce such transmission loss, it is desirable that the mode fields at the connection surfaces between the optical fibers or between the optical fibers and the optical semiconductor element or the like have the same size. As this measure, a technology for reducing the transmission loss by enlarging the core diameter of the connection end of the optical fiber according to the mode field size of the optical fiber or the optical semiconductor element to be connected has been widely put to practical use. I have.

As a method for enlarging the core diameter of the optical fiber, a dopant for increasing the refractive index of light is added to the core of the optical fiber, or a dopant for lowering the refractive index of light is added to the cladding of the optical fiber. Is added, and the outer peripheral portion of the optical fiber to which the dopant is added is heated by a heat source such as a micro burner, and the dopant in the core or the clad is thermally diffused to enlarge the core diameter. In the case of such a heat treatment method, the portion of the optical fiber to be subjected to the heat treatment needs to be stretched and held straight. FIG. 4 is a side view of an optical fiber heating apparatus used in the conventional method for expanding the core diameter of an optical fiber. The base 26 of the heating device 21 is placed parallel to the floor surface 27 so that the device can be easily arranged, and the optical fiber F is connected to the optical fiber fixing portion 22A provided on the base 26. It is stretched and held between the fixing portions 22B in a straight state parallel to the floor surface 27. The extension of the optical fiber strand F is performed by the optical fiber strand fixing portion 22A.
And V-shaped grooves 2 respectively provided in the fixing portion 22B
3A and 23B, the optical fiber F is stretched in a straightened state, and the pressing plates 24A and 24
B is put on and fixed. In the state where the optical fiber F is stretched in this way, a heat source 25 such as a micro burner is brought close to the outer peripheral portion A of the optical fiber F to perform a heat treatment. The core diameter of the portion A where the heat treatment is performed is enlarged and formed in a mountain shape. Thereafter, the optical fiber F is cut at the position where the core diameter is enlarged at the maximum, the optical fiber ferrule is inserted into the optical fiber ferrule with the position at the maximum enlarged core diameter as the end face, and the end face is polished to be used as an optical fiber connector. Can be done.

[0004]

In the case of a method for enlarging the core diameter of an optical fiber by a heat treatment method, an optical fiber strand F
Is heated at a temperature near the glass transition temperature of about 1500 ° C. to 2000 ° C. for about 1 to 2 minutes. However, in the above-described conventional method for enlarging the core diameter of an optical fiber, the optical fiber F is subjected to a heating treatment in a state of being stretched in parallel with the floor surface.
As a result of the self-weight of the optical fiber F being applied as a stress to the heated portion A in a state where the optical fiber F is exposed to a high temperature near the glass transition temperature, a phenomenon in which the optical fiber F is slightly bent downward or bent or bent at the heated portion A. Had occurred. Since the optical axis of the optical fiber is also bent at such a bent or bent portion of the optical fiber F, when a bent or bent portion is used as the connection end face, the other end of the optical fiber or the optical fiber to be connected at the connection surface is connected. An optical axis shift occurs with a semiconductor element or the like, which causes a connection loss of light and increases transmission loss of an optical fiber. In addition, when the optical fiber F is inserted into and fixed to the ferrule, the clearance between the insertion hole hole diameter of the ferrule and the outer diameter of the optical fiber F is set at most to prevent eccentricity of the optical axis of the optical fiber in the ferrule. It is about 1-2 μm. Therefore, if there is a bent or bent portion in the optical fiber F, it becomes difficult to insert the optical fiber F into the ferrule insertion hole, and the diameter of the insertion hole of the force ferrule has to be increased. As a result, in the ferrule insertion hole whose diameter has been increased, the optical axis of the optical fiber F is shifted from the central axis of the ferrule, causing eccentricity of the ferrule optical axis, and this also causes an eccentricity in the connection surface when the optical fiber is connected. An optical axis deviation from the optical fiber or the optical semiconductor element of the other party occurs, which causes transmission loss.

Therefore, an object of the present invention is to provide a method for enlarging the core diameter of an optical fiber by a heat treatment method, wherein the core diameter is increased without causing bending or bending of the optical fiber when the optical fiber is heated. An object of the present invention is to provide a method for enlarging an optical fiber core diameter which can be enlarged.

[0006]

According to a first aspect of the present invention, there is provided a method for enlarging an outer diameter of a core of an optical fiber in which the outer diameter of the core is increased by heating the optical fiber. On the other hand, the optical fiber is stretched in a substantially vertical direction, and a heat source is applied to an outer peripheral portion of the optical fiber strand stretched in the substantially vertical direction to perform a heat treatment, thereby increasing a core outer diameter of the heat-treated portion. An object of the present invention is to provide a method for enlarging the core diameter of a fiber.

According to a second aspect, the present invention provides the method for expanding the core diameter of an optical fiber according to the first aspect, wherein the optical fiber and the heat source are brought closer to each other in the optical axis direction of the optical fiber. After the relative movement along the optical fiber, by moving the heat source away from the optical fiber and relatively along the optical axis direction of the optical fiber, the outer peripheral portion of the optical fiber is heated. An object of the present invention is to provide a method for enlarging the core diameter of an optical fiber, characterized by the following.

[0008]

In the method for enlarging the core diameter of an optical fiber according to the present invention, the optical fiber is stretched and held substantially perpendicular to the horizontal plane. Therefore, even if the middle portion of the stretched optical fiber is heated, the own weight of the optical fiber is not applied as a stress to the heated portion of the optical fiber. The phenomenon of bending does not occur. As a result, the optical axis of the mating optical fiber, the optical semiconductor element, or the like at the connection surface due to the bending or bending of the optical fiber is not shifted, and the connection loss is reduced and the transmission characteristics of the optical fiber are improved. In addition, since the optical fiber strand is not bent or bent, the work of inserting the optical fiber strand F into the ferrule insertion hole becomes easy, and it is not necessary to increase the diameter of the ferrule insertion hole. The resulting optical axis deviation of the optical fiber F in the ferrule is also prevented.

In the method for enlarging the core diameter of an optical fiber according to the present invention, the optical fiber and the heat source are relatively moved along the optical axis direction of the optical fiber while approaching each other. By moving relatively along the optical axis direction of the optical fiber while keeping the distance, the heating process can be performed with a temperature gradient over a wide range of the optical fiber. As shown in FIG.
According to such a core diameter enlarging method, the enlarging ratio (H / L) between the maximum core enlarging amount (H) of the enlarging core and the length (L) from the hem to the hem of the core portion enlarged in a mountain shape is determined. It can be formed to 1% or less, and the connection loss is greatly reduced by using such an enlarged core diameter portion as a connection end face.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a method for enlarging the core diameter of an optical fiber according to the present invention. In addition,
This does not limit the present invention.

FIG. 1 is an explanatory side view of an optical fiber heating apparatus used in one embodiment of the method for enlarging the core diameter of an optical fiber according to the present invention. The optical fiber heating apparatus 1 includes an optical fiber that stretches and holds a base 2 disposed in a vertical direction with respect to a horizontal plane 10 and optical fiber wires F provided at an upper portion and a lower portion of the base 2. Wire holding units 3A and 3B, a heat source 4 for heating required portions of the optical fiber F, and a heat source 4
And a heat source movement control unit 6 for moving the heat source 4 up and down and back and forth. The optical fiber holding portions 3A and 3B are made of zirconia (ZrO ₂ ), which is unlikely to cause processing distortion or temporal distortion during use.
And the like. As means for holding the optical fiber strand F in the optical fiber strand holding parts 3A and 3B, V-shaped or semicircular grooves 7A and 7B are provided in the optical fiber strand holding parts 3A and 3B, respectively. The optical fiber F is placed along the grooves 7A, 7B, 7A, 7B, and pressing plates 8A, 8B are respectively placed on the optical fibers F, and fixed by magnets, or as shown in FIG. Fiber holding part 1
The optical fiber strand holding portions 3A and 3A
The fine suction holes 9A and 9B are provided behind the V-shaped or semicircular grooves 7A and 7B of B, respectively, and the optical fiber F laid along the grooves 7A and 7B is supplied with air from the suction holes 9A and 9B. There is a structure to fix by suction, etc., and in any structure, the optical fiber F is securely fixed without damaging the optical fiber F,
The optical fiber F is prevented from being subjected to stress that causes deterioration of transmission characteristics. It is important that the optical fiber F is stretched and held between the optical fiber holders 3A and 3B with high accuracy straightness. Even if the center axis of the groove 7A of the optical fiber strand holding section 3A and the central axis of the groove 7B of the optical fiber strand holding section 3B have a slight deviation of about several μm in the coaxiality, the light is not This is because there is a possibility that the heat-treated portion A of the fiber strand F may be bent or bent. For this reason, it is desirable that the optical fiber holding portions 3A and 3B are integrally formed via the connecting portion 3C.
According to the integral molding process, the central axis of the groove 7A of the optical fiber strand holder 3A and the optical fiber strand holder 3 are formed in the molding stage.
Since the straightness between the central axes of the grooves 7B of B can be formed with extremely high precision, the optical fiber strand F is stretched and held with high precision straightness. There is no variation in the straightness of the stretched F, and the reproducibility of the heat treatment and the ease of the heat treatment work are improved. As the heat source 4, a gas heat system using a micro burner using a mixed gas of oxygen and propane gas or acetylene gas,
Alternatively, an electric heating method using a ceramic heater or the like may be used.

In the process of expanding the core diameter of the optical fiber F, the groove (3A or 3B) of one optical fiber holding portion (3A or 3B) of the optical fiber heating device 1 arranged substantially perpendicular to the horizontal plane 10 is used. 7A or 7B) to the optical fiber F
Is fixed along one end of the optical fiber F, and the optical fiber F is applied to the groove (7B or 7A) of the other optical fiber wire holding portion (3B or 3A) in a state where tension is applied so that the optical fiber F is straightened. The other end of the fiber strand F is fixed along. In this manner, the optical fiber F is stretched and fixed substantially vertically in the substantially vertical direction between the optical fiber holders 3A and 3B so that there is no deviation of the central axis. Next, while controlling the heat source 4 by the heat source movement control unit 6 and the heat source control unit 5, the optical fiber F is brought close to the heat treatment location A of the optical fiber F and heated. For example, core outer diameter 10μ
m, the core diameter of the optical fiber F having a cladding outer diameter of 125 μm is increased by a heating temperature of 1800 ° C. and a heating time of 3
In accordance with a heating condition in which the width of movement of the heat source 4 in the optical axis direction is approximately 4 mm, the core diameter-enlarged optical fiber having a maximum core expansion amount (H) of 20 μm and an expanded core portion length (L) of 2.5 mm was gotten. No problems such as bending or bending were observed in the obtained core diameter enlarged optical fiber, and the insertion into the ferrule hole could be performed without any obstacle.

[0013]

According to the method for enlarging the core diameter of an optical fiber of the present invention, the optical fiber is bent or bent by a very simple means of extending the optical fiber substantially perpendicularly to the horizontal plane. The heat treatment allows the core diameter of the optical fiber to be increased without causing it. As a result, the insertion failure into the ferrule due to the bending or bending of the core diameter enlarged optical fiber is eliminated, and the efficiency of the optical connector assembling process is greatly improved. In addition, when the optical fiber having an enlarged core diameter without bending or bending is connected to another optical fiber or an optical semiconductor element, there is no optical axis shift at the connection end face, so that connection loss is greatly reduced and light having excellent transmission characteristics is obtained. Fiber can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory side view showing one embodiment of an optical fiber wire heating apparatus used in a method for expanding a core diameter of an optical fiber of the present invention.

FIG. 2 is a side sectional view showing another embodiment of the optical fiber strand holding portion used in the optical fiber core diameter enlarging method of the present invention.

FIG. 3 is an explanatory side view showing an enlarged core diameter portion of the optical fiber according to the present invention.

FIG. 4 is an explanatory side view showing an example of an optical fiber heating device used in a conventional method for expanding the core diameter of an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber heating device 2 Base 3A, 3B Optical fiber wire holding part 3C Connecting part 4 Heat source 5 Heat source control part 6 Heat source movement control part 7A, 7B Groove 8A, 8B Holding plate 9A, 9B Suction hole 10 Horizontal plane F Optical fiber strand A Heat treatment location H, L Enlarged core dimensions

Claims (2)

[Claims] 1. A method for expanding a core diameter of an optical fiber, wherein the optical fiber is expanded by heating the optical fiber to increase the outer diameter of the core, wherein the optical fiber is stretched in a direction substantially perpendicular to a horizontal plane. A method for enlarging a core diameter of an optical fiber, wherein a heat source is applied to an outer peripheral portion of the stretched optical fiber to perform heat treatment, and an outer diameter of the core at the heat-treated portion is enlarged. 2. The optical fiber core diameter enlarging method according to claim 1, wherein the optical fiber and the heat source are relatively moved along the optical axis direction of the optical fiber while approaching the heat source. A core diameter of the optical fiber, wherein an outer peripheral portion of the optical fiber is heated by relatively moving the heat source away from the optical fiber along the optical axis direction of the optical fiber. Expansion method.