JPH0930823A - Optical fiber preform, optical fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber preform having a structure resistant to bubbles generated when a clad and a stress-imparting member are integrated with heat. SOLUTION: An optical fiber preform 100 has a columnar core 10 and a tubular clad 20 surrounding the core 10 and is composed of a preform in which the surface layer has the first thermal expansion coefficient and the first melting point, stress-imparting members 40, 41 of a columnar form each of which has the second thermal expansion coefficient different from the first one and the second softening point different from the first one on its surface layer, and the tubular members 30, 31 surrounding the side faces of the stress-imparting members 40, 41 where the softening temperature distributes radially in the diameter direction between the first and the second softening temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber preform for producing a polarization maintaining optical fiber, a method for producing the same, a polarization maintaining optical fiber and a method for producing the same.

[0002]

2. Description of the Related Art As a method of manufacturing a polarization maintaining optical fiber, a method disclosed in Japanese Patent Publication No. 3-7613 has been known. This is to form at least one set of through-holes at symmetrical positions with respect to the core center of the ordinary optical fiber preform, and insert a stress-applying member having a different thermal expansion coefficient from the clad into the through-holes, In this method, a stress-type polarization-maintaining optical fiber is manufactured by integrally drawing the cladding and the stress-applying member by heat treatment, and then performing drawing, or drawing simultaneously with integration by heating.

[0003]

However, usually,
The stress-applying member and the clad have greatly different physical property values, particularly the softening temperature. Therefore, during heating and integration, air bubbles often remain at the bonding interface between the two. This is because if there is a difference in softening temperature, only one of them will soften and the other surface will be integrated before being sufficiently smoothed by heating, resulting in easy occurrence of bubbles at the bonding interface. Because.

Therefore, when the clad and the stress applying member are heated and integrated by the above method, an optical fiber preform having bubbles generated at the interface between the clad and the stress applying member is produced. If air bubbles are generated inside the optical fiber preform, this alone causes cracking and deteriorates the characteristics of the optical fiber obtained by drawing the preform, which is not preferable.

Further, when the drawing is performed while heating and integrating the clad and the stress applying member by the above method, the drawing is performed while bubbles are generated at the interface between the clad and the stress applying member. The optical fiber is easy to break on the way. Moreover, even if the optical fiber is manufactured without breaking,
Since the optical fiber contains bubbles inside, it does not have sufficient transmission characteristics or strength.

The present invention has been made in order to solve the above-mentioned problems, and has a structure that can be manufactured while preventing the generation of bubbles, and an optical fiber that can satisfactorily manufacture a polarization-maintaining optical fiber. It is an object of the present invention to provide a base material and a method for manufacturing the same, a method for manufacturing an optical fiber in which bubbles are less likely to occur, and an optical fiber having a structure that can be manufactured while preventing the generation of bubbles.

[0007]

In order to solve the above problems, the optical fiber preform according to the present invention comprises (a) a columnar core and (b) a tubular clad surrounding the core. A through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis, and has a first thermal expansion coefficient and a first softening temperature in the surface layer portion of the through hole;
(C) A second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature inserted into the through hole.
A columnar stress-applying member having a softening temperature of 1. in the surface layer portion, and (d) a tubular member which is inserted into the through hole and surrounds the stress-applying member, between the first and second softening temperatures. Having a set radial softening temperature distribution.

The tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, this constant softening temperature is different from both the first and second softening temperatures, and is preferably a softening temperature obtained by averaging the first and second softening temperatures.

The tubular member may have a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side.

Further, the refractive index of the stress applying member and the tubular member is preferably less than or equal to the refractive index of the clad.

Next, a first aspect of the method for producing an optical fiber preform according to the present invention is (a) a columnar core and a tubular clad that surrounds the core, the axial wall extending along the axial direction. And a through hole having a first thermal expansion coefficient and a first softening temperature in the surface layer portion of the through hole, the through hole having a predetermined distance from the central axis, and the through hole. A columnar stress applying member to be inserted,
A first step of preparing a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in its surface layer portion; and (b) applying stress A tubular member which should surround the member and has a radial softening temperature distribution set between the first and second, i) on the surface of the through hole, ii) on the surface of the stress applying member Between the surface of the through hole and iii) or on the surface of the stress applying member at one or more positions, and a second step of integrating the hole forming base material, the stress applying member and the tubular member. I have it.

In the second step, the tubular member is formed on the surface of the through hole, the stress applying member is then inserted into the hollow portion of the tubular member, and then the stress applying member and the tubular member are integrated. It may be a step of performing.

In the second step, a tubular member is formed on the surface of the stress-applying member, and then a columnar body composed of the stress-applying member and the tubular member is inserted into the through hole of the perforated base material. After that, a step of integrating the columnar body with the perforated base material may be performed.

In the second step, the tubular member is inserted into the through hole, the stress applying member is inserted into the hollow portion of the tubular member, and then the perforated base material, the stress applying member and the tubular member. It may be a step of integrating members.

If the perforated base material, the stress-applying member and the tubular member are made of glass, they can be achieved by joining the glasses together by, for example, heat treatment.

A second aspect of the method for producing an optical fiber preform according to the present invention is (a) a columnar core and a tubular clad surrounding the core, and a through hole extending along the axial direction in the tube wall. Different from the first thermal expansion coefficient, and a perforated base material having a first thermal expansion coefficient and a first softening temperature in the surface layer portion of the through hole provided at a predetermined distance from the central axis. A columnar stress-applying member having a central portion having a second thermal expansion coefficient and a second softening temperature different from the first softening temperature in its surface layer portion and set between the first and second softening temperatures. First step of preparing a tubular member having the specified radial softening temperature distribution on its surface layer portion (surface layer portion of the stress applying member), and (b) perforating the stress applying member with a base material. Second step of inserting into hole, (c) stress applying member and hole opening mother And a third step of integrating.

If the perforated base material and the stress applying member are made of glass, they can be integrated by joining the glasses together by, for example, heat treatment.

In the base material manufacturing methods according to the first and second aspects, the tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, this constant softening temperature is different from both the first and second softening temperatures, and is preferably a softening temperature obtained by averaging the first and second softening temperatures.

Further, in the above-mentioned first and second aspects,
The tubular member may have a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side.

Next, a first aspect of the method for producing an optical fiber according to the present invention is (a) a columnar core and a tubular clad surrounding the core, which penetrates the tube wall in the axial direction. A perforated base material having holes having a predetermined distance from the central axis and having a first coefficient of thermal expansion and a first softening temperature in the surface layer portion of the through hole, and the hole is inserted into the through hole. A columnar stress applying member to be
A second step of preparing a second layer having a second coefficient of thermal expansion different from the coefficient of thermal expansion and a second softening temperature different from the first softening temperature in its surface layer portion, and (b) surrounding the stress applying member. A tubular member having a radial softening temperature distribution set between the first and second softening temperatures, i)
A second step provided at one or more positions on the surface of the through-hole, ii) intermediate between the surface of the stress-applying member and the surface of the through-hole, or iii) on the surface of the stress-applying member; )
A third step of heating the composite body composed of the perforated base material, the stress applying member and the tubular member to draw the composite body while integrating the perforated base material, the stress applying member and the tubular member There is.

In the case where these members are made of glass, the perforated base material, the stress applying member and the tubular member can be integrated by, for example, joining the glasses by a heat treatment.

The above-mentioned second step may be a step of forming a tubular member on the surface of the through hole of the perforated base material and then inserting the stress applying member into the hollow portion of the tubular member.

The second step is a step of forming a tubular member on the surface of the stress-applying member, and then inserting a columnar body composed of the stress-applying member and the tubular member into the through hole of the base material. Is also good.

The second step may be a step of inserting the tubular member into the through hole and inserting the stress applying member into the hollow portion of the tubular member.

Second Method of Manufacturing Optical Fiber According to the Present Invention
(A) is a columnar core and a tubular clad that surrounds the core, and a through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis, and the surface layer of the through hole is A base material having a first coefficient of thermal expansion and a first softening temperature in a portion, and a second coefficient of thermal expansion different from the first coefficient of thermal expansion and a second coefficient different from the first temperature of softening. A columnar stress-applying member having a central portion having a softening temperature in its surface layer portion, wherein a tubular member having a radial softening temperature distribution set between the first and second softening temperatures is formed in the surface portion ( A first step of preparing a stress-applying member for the surface layer portion), (b) a second step of inserting the stress-applying member into a through hole of a perforated base material, and (c) a perforated mother Heating a composite of material and stress-applying member to give a perforated base material and stress While integrated wood and a third step of drawing the complex.

In the optical fiber manufacturing methods according to the first and second aspects, the tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, this constant softening temperature is different from both the first and second softening temperatures, and is preferably a softening temperature obtained by averaging the first and second softening temperatures.

Further, in the above first and second aspects,
The tubular member may have a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side to the center side.

Next, the optical fiber of the present invention comprises (a) a columnar core and (b) a tubular clad surrounding the core, and a through hole along the axial direction is formed in the tube wall along the central axis. And having a first coefficient of thermal expansion and a first softening temperature at the surface layer portion of the through hole, and (c) the first thermal expansion inserted into the through hole. A columnar stress-applying member having a second coefficient of thermal expansion different from the coefficient and a second softening temperature different from the first softening temperature in its surface layer portion; and (d) the stress-applying member inserted into the through hole, An enclosing tubular member having a radial softening temperature distribution set between the first and second softening temperatures.

The above-mentioned tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, this constant softening temperature is different from both the first and second softening temperatures, and is preferably a softening temperature obtained by averaging the first and second softening temperatures.

The above-mentioned tubular member may have a radial softening temperature distribution which continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side.

The refractive index of the stress applying member and the tubular member is preferably less than or equal to that of the clad.

[0032]

[Action]

(1) In the optical fiber preform of the present invention, the tubular member having the radial softening temperature distribution set between the first and second softening temperatures is present between the clad and the stress applying member. The softening temperature change between the surface layer of the clad and the tubular member, or between the surface layer of the tubular member and the stress imparting member, between the surface layer of the clad and the surface layer of the stress imparting member in the absence of the tubular member, It is more relaxed than the change in the softening temperature.
Therefore, the optical fiber preform of the present invention has a joint interface between the clad and the tubular member or a joint interface between the tubular member and the stress imparting member even when the clad and the stress imparting member are integrated by a heat treatment during manufacturing. It has a structure that does not easily generate bubbles.

When the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, the difference in softening temperature between the cladding and the tubular member or the tubular member Since the difference in softening temperature between the stress applying member and the cladding is smaller than the difference in softening temperature between the clad and the stress applying member, it becomes a structure in which bubbles are less likely to be generated.

When the tubular member has a radial softening temperature distribution which continuously changes from the surface side to the center side of the cladding, the softening temperature being the lower limit of the cladding to the softening temperature being the upper limit of the stress applying member, Since the softening temperature distribution is formed so as to change almost continuously from the surface layer portion of the clad to the surface layer portion of the stress applying member, it becomes a structure in which bubbles are less likely to be generated. In particular, if the softening temperature is the same at the joint interface between the clad and the stress applying member, it becomes a structure in which bubbles are extremely unlikely to be generated at the joint interface.

If the stress-applying member or tubular member has a refractive index lower than that of the cladding, light is propagated in the polarization-maintaining optical fiber obtained by drawing the optical fiber preform of the present invention. Even in the case, the movement of the optical power from the core to the stress applying member or the tubular member is less likely to occur.

(2) Next, in the first aspect of the method for producing an optical fiber preform according to the present invention, in the second step, the surface of the through hole of the perforated preform and the surface of the stress applying member are penetrated. The optical fiber mother of the present invention is provided by providing the tubular member at an intermediate position with the surface of the hole or at one or more positions on the surface of the stress applying member, and integrating the hole preform, the stress applying member and the tubular member. The material is manufactured.

In this method, by providing the tubular member, the change in the softening temperature between the surface layer portion of the clad and the tubular member, or the change in the softening temperature between the tubular member and the surface layer portion of the stress applying member, It is more relaxed than the change in the softening temperature between the surface layer portion of the clad and the surface layer portion of the stress-applying member in the absence of the stress. Therefore, bubbles are generated at the joint interface between the clad and the tubular member or at the joint interface between the tubular member and the stress applying member even when the perforated base material, the stress applying member and the tubular member are integrated to complete the base material. Hard to do.

Next, in a second aspect of the method for producing an optical fiber preform according to the present invention, the surface layer portion is provided with a tubular member having a radial softening temperature distribution between the first and second softening temperatures. The optical fiber preform of the present invention is manufactured by inserting the stress applying member into the through hole of the perforated preform and then integrating the stress applying member and the perforated preform.

In this method, since the above-mentioned tubular member is present in the surface layer portion of the stress applying member, the surface layer portion of the clad and the central surface layer portion of the stress applying member (stress application in the absence of the tubular member) The change in the softening temperature between the surface layer of the member and the change in the softening temperature between the surface layer of the clad and the surface layer of the stress-applying member in the absence of the tubular member is more moderate.
For this reason, even when the base material with holes and the stress applying member are integrated to complete the base material, bubbles are less likely to be generated at the bonding interface between the clad and the stress applying member.

In the base material manufacturing methods according to the first and second aspects, when the clad has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, Since the difference in softening temperature between the tubular member and the stress applying member or the difference in softening temperature between the tubular member and the stress applying member is smaller than the difference in softening temperature between the clad and the stress applying member, bubbles are less likely to be generated.

When the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side to the center side, stress from the clad is applied. Since the softening temperature distribution is formed so as to change almost continuously up to the applying member, bubbles are less likely to be generated.

(3) Next, in the first aspect of the optical fiber manufacturing method according to the present invention, the tubular member having the radial softening temperature distribution set between the first and second softening temperatures is used as the cladding. An optical fiber is manufactured by interposing the perforated base material, the stress-applying member and the tubular member after the interposing between the stress-applying member and the stress-applying member. The obtained optical fiber becomes a polarization-maintaining optical fiber by the action of the stress applied to the core by the stress applying member.

In this method, the softening temperature change between the surface layer of the clad and the tubular member is caused by interposing the tubular member,
Alternatively, the softening temperature change between the tubular member and the surface layer portion of the stress applying member is more moderate than the softening temperature change between the surface layer portion of the clad and the surface layer portion of the stress applying member in the absence of the tubular member. Therefore, bubbles are generated at the joint interface between the clad and the tubular member or the joint interface between the tubular member and the stress applying member even when the wire drawing is performed while integrating the perforated base material, the stress applying member and the tubular member. Hateful.

Next, in the second aspect of the method for producing an optical fiber according to the present invention, the stress imparting is provided with the tubular member having the radial softening temperature distribution between the first and second softening temperatures in the surface layer portion. After inserting the member into the through hole of the perforated base material, by performing drawing while integrating the stress applying member and the perforated base material,
Optical fibers are manufactured. The obtained optical fiber becomes a polarization-maintaining optical fiber by the action of the stress applied to the core by the stress applying member.

In this method, since the above-mentioned tubular member is present in the surface layer portion of the stress imparting member, the surface layer portion of the clad and the central surface layer portion of the stress imparting member (stress imparting when there is no tubular member) The change in the softening temperature between the surface layer of the member and the change in the softening temperature between the surface layer of the clad and the surface layer of the stress-applying member in the absence of the tubular member is more moderate.
Therefore, even when the wire drawing is performed while the perforated base material and the stress applying member are integrated, bubbles are less likely to be generated at the bonding interface between the clad and the stress applying member.

In the optical fiber manufacturing methods according to the first and second aspects, when the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures. Is less likely to generate bubbles because the difference in softening temperature between the clad and the tubular member or the difference in softening temperature between the tubular member and the stress applying member is smaller than the difference in softening temperature between the clad and the stress applying member.

When the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side to the center side, By forming a softening temperature distribution that changes almost continuously from the clad to the stress applying member inside,
Bubbles are less likely to occur.

(4) Next, the optical fiber of the present invention comprises the first
And a tubular member having a radial softening temperature distribution set between the second softening temperature and the second softening temperature is present between the clad and the stress applying member, the softening temperature between the surface layer portion of the clad and the tubular member. The change, or the softening temperature change between the tubular member and the surface layer portion of the stress applying member, is softer than the softening temperature change between the surface layer portion of the cladding and the surface layer portion of the stress applying member in the absence of the tubular member. There is. Therefore, when the optical fiber of the present invention is integrated with the clad and the stress-applying member by the heat treatment at the time of its production, bubbles are not formed in the joint interface between the clad and the tubular member or the joint interface between the tubular member and the stress-applying member. Has a structure that does not easily generate

When the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, the difference in softening temperature between the cladding and the tubular member or the tubular member Since the difference in softening temperature between the stress-applying member and the clad and the stress-applying member is smaller,
The structure prevents bubbles from being generated.

When the tubular member has a radial softening temperature distribution that continuously changes from the surface side to the center side of the cladding, the softening temperature being the lower limit of the cladding to the softening temperature being the upper limit of the stress applying member, By forming a softening temperature distribution that changes almost continuously from the clad to the stress-applying member inside the base material, it becomes a structure in which bubbles are less likely to be generated. In particular, if the softening temperature is the same at the joint interface between the clad and the stress applying member, bubbles will be extremely unlikely to be generated at the joint interface between the clad and the stress applying member.

When the refractive index of the stress applying member or the tubular member is equal to or lower than the refractive index of the clad, the optical power from the core to the stress applying member or the tubular member is increased even when light is propagated in the optical fiber. Movement is unlikely to occur.

[0052]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.
Also, the dimensional ratios in the drawings do not always match those described.

Example 1 FIG. 1 is a perspective view showing the structure of an optical fiber preform 100 of this example. The optical fiber preform 100 is used for manufacturing a polarization maintaining optical fiber, and includes a core 10 and a clad 2.
0, tubular members 30 and 31, and stress applying members 40 and 41.

The core 10 is a cylindrical glass rod,
The clad 20 is a circular glass tube that surrounds the side surface of the core 10. The central axes of the core 10 and the clad 20 coincide with each other.

Both the core 10 and the clad 20 are made of quartz (SiO ₂ ) glass. Cladding 2
0 is composed of almost pure silica glass, but the silica glass forming the core 10 contains germanium oxide (GeO ₂ ) which is a refractive index increasing material, so that the core has a refractive index higher than that of the cladding. Is also getting higher.

The tubular members 30 and 31 are circular tubes made of quartz glass, and are embedded in the clad 20 while making their axial directions coincide with the axial direction of the clad 20. The tubular members 30 and 31 are arranged at positions symmetrical to each other with respect to the central axis of the core 10.

The stress applying members 40 and 41 are cylinders made of silica glass and are inserted in the hollow portions of the tubular members 30 and 31, respectively. The stress applying members 40 and 4
1 has a larger coefficient of thermal expansion than the clad 20. As is well known, the stress applying members 40 and 41 are strongly contracted during the process of cooling the optical fiber after drawing the optical fiber preform 100, so that a large stress is applied to the core. As a result, the optical fiber obtained by drawing becomes a polarization maintaining optical fiber.

2 to 6 are process drawings showing a method of manufacturing the optical fiber preform 100. Hereinafter, a method of manufacturing the optical fiber preform 100 will be described with reference to these drawings.

First, a glass cylinder 110 composed of a core 10 and a clad 20 which closely covers the core 10 is prepared (FIG. 2). The outer diameter of this glass cylinder 110 is 25 mm
And the outer diameter of the core 10 is 1.35 mm. The glass cylinder 110 is formed by using a method similar to that of a normal optical fiber preform, that is, a known VAD (vapor phase axis attachment) method, OVD (external attachment) method, MCVD (internal attachment) method, rod-in-tube method, or the like. It can be manufactured. In this embodiment, M
This is manufactured using the CVD method.

Then, using an ultrasonic perforator (not shown), through holes 50 and 51 having a diameter of 8 mm extending in the clad 20 of the glass cylinder 110 along the axial direction of the glass cylinder 110.
Are formed (FIG. 3). The through holes 50 and 51 are parallel to the core 10 and are formed at positions symmetrical with respect to the central axis of the core 10. The distance between the central axis of the through holes 50 and 51 and the central axis of the core 10 is 11.6 mm. Hereinafter, the glass cylinder 110 provided with the through holes 50 and 51 will be referred to as a perforated base material 111.

Next, a glass layer having a thickness of 0.5 mm, that is, the above-mentioned tubular members 30 and 31 are formed on the surfaces of the through holes 50 and 51 (FIG. 4). The tubular members 30 and 31
Is 150 ml / min of BCl ₃ (boron trichloride), Si
400 ml / min of Cl ₄ (silicon tetrachloride), O ₂ (oxygen)
Is introduced into the through holes 50 and 51 at a flow rate of 1 l / min, and the flame of an oxyhydrogen flame burner is applied to the outer surface of the perforated base material 111 to heat the inside of the through holes 50 and 51. be able to. The flame of the oxyhydrogen flame burner uses H ₂ (hydrogen) as a fuel gas in the burner at 70 l / min, O ₂
It is formed by introducing 30 l of (oxygen) per minute. After forming the tubular members 30 and 31, the through holes 52 and 53 remain inside the tubular members 30 and 31. In FIG. 4, the perforated base material after the tubular members 30 and 31 are formed is indicated by reference numeral 112.

Next, the stress applying member 4 prepared in advance
Insert 0 and 41 into the through holes 52 and 53 and fix them (FIGS. 5 and 6). The stress applying members 40 and 41 are
It can be produced by a known VAD method. Specifically, first, H ₂ is supplied as fuel gas in the burner at a rate of 50 per minute.
l and O ₂ are introduced at a rate of 12 l / min to form an oxyhydrogen flame,
400 ml / min of SiCl ₄ and BCl ₄ in this oxyhydrogen flame
300 ml / min of ₃ was introduced to the glass particles (SiO 2
₂ + B ₂ O ₃ ). Next, when the rod-shaped starting material is rotated and the glass particles are blown from the burner, the glass particles are deposited on the surface of the starting material in a substantially uniform thickness. By blowing the glass particles while pulling up the starting material, the glass particles can be grown in the axial direction. As a result, the glass particles are uniformly deposited on the entire surface of the starting material, so that a columnar glass particle body is obtained. Next, the glass fine particles are put into a sintering furnace, and BF ₃ is introduced into the helium atmosphere in the sintering furnace for about 120 minutes.
Heat at a temperature of 0 ° C. for 60 minutes, then at a temperature of about 1400 ° C. for 60 minutes, followed by slow cooling. As a result, the glass fine particles become transparent glass, and the columnar glass body (Si
O ₂ -B ₂ O ₃₎ is obtained. When this glass body is heated and stretched to have an outer diameter of about 6.8 mm, the stress applying members 40 and 41 of this embodiment are obtained. The compositions of the two stress applying members are almost the same. The stress applying member 40
And 41 are shorter than the through holes 52 and 53.

B added to the stress applying members 40 and 41
_{Since 2} O ₃ has a function of increasing the thermal expansion coefficient of SiO ₂ glass, the stress-applying members 40 and 41 are used as the cladding 2
It has a coefficient of thermal expansion greater than zero.

Stress-applying member 4 obtained as described above
0 and 41 are through holes 52 and 53 of the perforated base material 112.
And is fixed inside the hole. Hereinafter, this fixing method will be described with reference to FIGS. 5 and 6. This fixing method is also disclosed in Japanese Patent Application Laid-Open No. 4-97920.

In order to carry out this fixing method, first, quartz glass rods 60a, 60b, 61a having an outer diameter of about 6.8 mm are used.
, 61b and the quartz glass tube 70 are prepared. As shown in FIG. 5, the glass tube 70 is formed by attaching glass tubes 70a and 70c having a larger inner diameter to both ends of a glass ring 70b having a smaller inner diameter.

In order to fix the stress applying members 40 and 41, first, the glass tube 70 is welded to one end surface of the base material 112 having a hole. Next, the glass rod 60a, the stress applying member 40, and the glass rod 60b are inserted in this order from the other end side of the perforated base material 112 into the through hole 52. Similarly for the through hole 53, the glass rod 61a, the stress applying member 41, the glass rod 6
Insert in order of 1b. The tips of the glass rods 60a and 61a respectively project from the end surface of the perforated base material 112, and the end surfaces are pressed against the bottom surface of the glass ring 70b. Thereby, the glass rods 60a and 61a are fixed. The glass rods 60b and 61b and the clad 20 are integrated by heating and drawing the end portion of the perforated base material 112.
As a result, one end of the perforated base material 112 is sealed (FIG. 6).

Since a vacuum connector (not shown) can be connected to the glass tube 70, the inside of the through holes 52 and 53 is depressurized by utilizing this. After this, the tip of the glass tube 70 is collapsed (solidified) by heat treatment and sealed. As a result, the stress applying members 40 and 41 are fixed to the perforated base material 112. The stress applying member 4
It goes without saying that the fixing method of 0 and 41 is not limited to the above method.

Next, the stress applying member 40 is processed as described above.
And 41 are fixed to the perforated base material 112, a heating temperature of 1900 ° C. and a heating time of 120 minutes are applied,
After that, it is gradually cooled. As a result, the glass forming the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41 is melted and integrated. Thus, the optical fiber preform is completed.

Of the optical fiber preforms obtained as described above, it is the portion including the stress applying members 40 and 41 that can actually be used for producing the optical fiber, and therefore the above method is substantially the same as that shown in FIG. The optical fiber preform 100 is manufactured.

FIG. 7 is a diagram showing the refractive index distribution and the softening temperature distribution of the optical fiber preform 100 in the radial direction. In this figure, only the distribution on the right half of the optical fiber preform 100 is shown, but the distribution on the left half is similar to that on the right half. As shown in this figure, tubular members 30 and 31
Is the softening temperature of the clad 20 and the stress applying members 40 and 4
The softening temperature of 1 is averaged. In order to have such a softening temperature, the above-mentioned tubular member 30
In the step of forming Nos. 31 and 31, it is advisable to adjust the addition amount of B ₂ O ₃ which is a softening temperature lowering agent for SiO ₂ .

In order to manufacture the optical fiber preform including the stress applying member, it is necessary to perform heat treatment to integrate the stress applying member and the clad. When integrating two objects,
Generally, it is desirable that the physical properties of the joints between the two are close to each other. In particular, when they are integrated by heat treatment, it is desirable that the softening temperatures of both are close to each other. If there is a difference in the softening temperature between the two joints, only one of them softens first,
Since the other surface is integrated by the effect of heating before being sufficiently smoothed, bubbles are likely to be generated at the bonding interface.

In the optical fiber preform 100 of this embodiment, since the tubular members 30 and 31 having the average softening temperature of both are present between the clad 20 and the stress applying members 40 and 41, Softening temperature difference between the tubular members 30, 31 and the tubular members 30, 31 and the stress applying members 40, 4
The difference in softening temperature between the clad 20 and the stress applying member 4 is
It is smaller than the difference in softening temperature between 0 and 41. Therefore, the surface smoothing effect is sufficiently exerted even when the cladding 20 and the stress applying members 40 and 41 are integrated with each other by the heat treatment during manufacturing. As a result, the generation of bubbles is prevented or reduced at the joint interface between the clad 20 and the tubular members 30 and 31, and at the joint interface between the tubular members 30 and 31 and the stress applying members 40 and 41. Therefore, even when the optical fiber preform 100 is drawn to manufacture an optical fiber,
The optical fiber is unlikely to break, and the obtained optical fiber has good transmission characteristics and polarization characteristics.

In addition, since light propagates in a portion having a high refractive index in the optical fiber, generally, when a portion having a refractive index higher than that of the clad exists near the core, the optical power moves from the core to that portion. As a result, the transmission loss increases. In view of this point, in this embodiment, the tubular members 30 and 3 are
1 and the stress-applying members 40 and 41 are set to have a lower refractive index than the clad (FIG. 7). Since the optical fiber has the same refractive index distribution as the base material, setting the refractive index in this way prevents the movement of optical power in the optical fiber obtained by drawing the optical fiber base material. Can
It is possible to suppress an increase in transmission loss of the optical fiber.

In this embodiment, the optical fiber preform 100 manufactured as described above is drawn by using a normal drawing device to manufacture a polarization maintaining optical fiber. Specifically, first, the optical fiber preform 100 is heated to about 2000 ° C. in a heating furnace, and drawn to have an outer diameter of 125 μm at a linear velocity of 100 m / min. The drawn optical fiber is coated with UV resin twice. The outer diameter of the coated optical fiber is about 250 μm. In this way, a polarization maintaining optical fiber having a length of 10 km is manufactured.

When the crosstalk characteristic which is one of the polarization characteristics of the polarization-maintaining optical fiber manufactured as described above was measured at a wavelength of 1.3 μm, a very good result of −24 dB was obtained. .

For comparison with this example, the present inventors
An optical fiber preform in which a stress applying member was inserted without forming the tubular members 30 and 31 was drawn to manufacture a polarization-maintaining optical fiber of 10 km. The manufacturing method of the optical fiber preform is the same as that of this embodiment except that the tubular members 30 and 31 are not formed. When the crosstalk characteristic of this polarization maintaining optical fiber was measured, it was -8 dB, which was inferior to that of this example. As a result of detailed examination of this polarization-maintaining optical fiber, bubbles were found in the glass at three locations along the entire length of the optical fiber. These bubbles were generated at the interface between the stress applying member and the clad.

In this embodiment, the cladding 20, the tubular members 30 and 31, and the stress applying members 40 and 41 are heated and integrated to complete the optical fiber preform 100, and then drawing is performed to manufacture an optical fiber. However, it is also possible to manufacture an optical fiber by simultaneously performing heating integration and drawing.

For example, after the stress applying members 40 and 41 are fixed to the perforated base material 112 by the above method, the composite of the stress applied members 40 and 41 and the perforated base material 112 is heated to about 2000 degrees in a heating furnace. An optical fiber can be manufactured by heating and drawing the stress applying members 40 and 41, the clad 20, and the tubular members 30 and 31 while drawing them so that the outer diameter becomes 125 μm at a linear velocity of 100 m / min. it can. In this case, the optical fiber is manufactured without going through the state of the base material.

In this case as well, the presence of the tubular members 30 and 31 sufficiently exerts the surface smoothing effect at the time of heat integration, so that the joining interface between the clad 20 and the tubular members 30 and 31 and the tubular members 30 and 31. The generation of bubbles at the joint interface between the stress applying members 40 and 41 is prevented or reduced.
Therefore, also by the above method, it is possible to manufacture a polarization-maintaining optical fiber having good characteristics while preventing the optical fiber from breaking.

Example 2 In this example, an optical fiber preform 100 (FIG. 1) is manufactured by a method different from that of Example 1. FIG. 8 is a diagram showing the base material manufacturing method of this embodiment. In this embodiment, first, a glass cylinder 110 (similar to that shown in FIG. 2) is manufactured by the VAD method, and through holes 50 and 51 extending in the axial direction are formed in the clad 20 by an ultrasonic drilling machine. Perforated base material 11
Prepare No. 1. The diameter of the through holes 50 and 51 is 8 mm. The above steps are almost the same as in Example 1, but in this Example, the core composition is SiO ₂ and the clad composition is SiO ₂ —F. F is a refractive index lowering material of SiO ₂ , and by adding this to the clad, the refractive index of the core is higher than that of the clad.

Next, in this embodiment, the same stress imparting members 40 and 41 (outer diameter 18 m as in Embodiment 1 are used by using the VAD method.
After producing m), tubular members 30 and 31 are deposited and formed on the surfaces of the stress applying members 40 and 41. This deposition formation can be performed using a known OVD (external attachment) method. Specifically, SiCl in the oxyhydrogen flame burner
300 ml / min of ₄ (silicon tetrachloride), 50 l / min of H ₂ (hydrogen) and 12 l / min of O ₂ (oxygen) were introduced, and the stress applying members 40 and 41 were rotated about their own axes. While applying the flame of the burner, the burner is moved relative to the stress applying members 40 and 41 along the axial direction. As a result, glass particles of SiO ₂ are deposited on the side surfaces of the stress applying members 40 and 41 with a substantially uniform thickness.

Next, the stress-applying members 40 and 41 in which the glass fine particles are deposited are put into a heating furnace, and BF ₃ and SiF ₄ are introduced into the helium atmosphere in the heating furnace for about 120 times.
It is heated at a temperature of 0 ° C. for 30 minutes, subsequently heated at a temperature of about 1400 ° C. for 30 minutes, and then gradually cooled. By this operation, B and F are added to the glass particles of SiO ₂ , and the glass particles become transparent glass and are integrated with the stress applying members 40 and 41.

In this embodiment, a glass layer (SiO ₂ —B ₂ O ₃ —F) having a thickness of about 2.5 mm is formed on the surfaces of the stress applying members 40 and 41 by the above method. This glass layer is the tubular members 30 and 31 of this embodiment. As a method of forming the tubular members 30 and 31 on the surfaces of the stress applying members 40 and 41, a glass layer to be a stress applying member is formed on the inner surface of a glass pipe previously manufactured using the material of the tubular members 30 and 31. Can be formed by the MCVD method, and then the glass pipe can be collapsed (solidified).

After that, the two columnar bodies composed of the tubular members 30 and 31 and the stress applying members 40 and 41 are heated and stretched so that the outer diameters thereof are about 7.7 mm, respectively. The columnar bodies 80 and 81 thus obtained are perforated as shown in FIG.
Example 1 after inserting into the through holes 50 and 51 of No. 1 respectively.
Fix in the same manner as. Thereafter, heat treatment is performed to integrate the columnar bodies 80 and 81 and the clad 20 with each other, whereby the optical fiber preform 100 (FIG. 1) is completed.

The optical fiber preform manufactured in this example also has the refractive index distribution and the softening temperature distribution shown in FIG. The softening temperature can be adjusted by adjusting the addition amount of B ₂ O ₃ and F, which are the softening temperature changing material of SiO ₂ , in the above-mentioned forming process of the tubular members 30 and 31. Here, B ₂ O ₃ has an effect of lowering the softening temperature of the SiO _2, F has the effect of lowering the softening temperature of the SiO _2.

The optical fiber preform manufactured by the present inventors as described above was drawn in the same manner as in Example 1 to obtain a length of 10 km.
Of the polarization-maintaining optical fiber of FIG.
When measured in μm, a very good result of −26 dB was obtained.

In place of the above method, the heating and integration of the columnar bodies 80 and 81 and the clad 20 are performed simultaneously with the drawing, so that an optical fiber can be manufactured without going through the state of the preform. This is the same as in the first embodiment.

Example 3 In this example also, the optical fiber preform 100 (FIG. 1) is manufactured by a method different from those of Examples 1 and 2. FIG. 9 is a diagram showing the base material manufacturing method of this embodiment. Also in this embodiment,
First, a perforated base material 111 (similar to FIG. 3) is manufactured in the same manner as in Example 2. In this embodiment, the through hole 50
The diameter of 51 and 51 is 9 mm. Then, in the same manner as in Example 1, the stress applying member 40 having an outer diameter of about 7.8 mm.
And 41 are made.

Next, in this embodiment, the tubular members 30 and 3 are
1 is formed independently of the perforated base material 111 and the stress applying members 40 and 41. For this purpose, first, a columnar glass body is manufactured by using the VAD method. Specifically, 50 liters of H ₂ (hydrogen) per minute and 1 of O ₂ (oxygen) per minute are supplied to the oxyhydrogen flame burner.
In the oxyhydrogen flame formed by introducing 2 l each, SiCl
₄ (Silicon tetrachloride) is introduced at a flow rate of 300 ml / min, and SiO ₂ glass particles produced in a flame are deposited and grown on the starting material to form rod-shaped glass particle bodies. The glass fine particles are put into a sintering furnace and heated at a temperature of about 1200 ° C. for 30 minutes while introducing SiF ₄ into a helium atmosphere in the sintering furnace, and then at a temperature of about 1400 ° C. for 60 minutes.
After heating for a minute, cool slowly. As a result, the glass particles of SiO ₂ become transparent glass after F is added. Thus, a SiO ₂ —F glass columnar body is obtained. This glass columnar body was heated and stretched to have an outer diameter of 22 mm, then a through hole having an inner diameter of 20 mm was formed in the center by using an ultrasonic hole punching machine, and again heat-stretched to have an outer diameter of 8.8 mm. A glass tube having an inner diameter of 8 mm is formed. This is the tubular members 30 and 31 of this embodiment.

Next, the tubular member 30 and the stress applying member 40 are inserted in this order from the one end side of the perforated base material 111 into the through hole 50. Similarly for the through hole 51, the tubular member 31,
The stress applying member 41 is inserted in this order. Stress applying member 4
0 and 41 are inserted into the hollow portions of the tubular members 30 and 31, respectively. The tubular members 30 and 31 and the stress applying members 40 and 41 are fixed by the same method as in the first embodiment. Then, heat treatment is performed to integrate the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41, whereby the optical fiber preform 100 (FIG. 1) is completed.

The optical fiber preform manufactured according to this example also has the refractive index distribution and the softening temperature distribution shown in FIG. The softening temperature can be adjusted by adjusting the addition amount of F, which is the softening temperature changing material of SiO ₂ , in the process of forming the tubular members 30 and 31 described above.

The inventors of the present invention draw the optical fiber preform manufactured as described above to manufacture a polarization maintaining optical fiber having a length of 9.7 km, and one of the polarization characteristics of this optical fiber. The crosstalk characteristic was measured at a wavelength of 1.3 μm, and a very good result of −26 dB was obtained.

In the manufacturing process of this embodiment, the inner and outer surfaces of the tubular members 30 and 31 are mechanically smoothed by polishing or heat-smoothed by flame radiation, or these surfaces are washed. By removing the adhering impurities, it is possible to more effectively prevent the generation of bubbles due to heat integration during drawing.

Further, instead of the above method, the cladding 20
By performing the heating integration of the tubular members 30 and 31 and the stress applying members 40 and 41 simultaneously with the drawing, it is possible to manufacture an optical fiber without going through the state of the preform.
This is the same as the above embodiment.

Example 4 In this example, an optical fiber preform different from the optical fiber preform 100 of FIG. 1 is manufactured. First, a method for manufacturing the optical fiber preform of this embodiment will be described in detail. FIG. 10 is a diagram showing a base material manufacturing method of this example.

In this embodiment, first, a glass cylinder 110 (similar to that shown in FIG. 2) is produced by using a known MCVD method, and an ultrasonic perforator is used to penetrate the cladding 20 so as to extend along the axial direction. Forming holes 50 and 51 to form a holed base material 1
11 is produced. The diameter of the through holes 50 and 51 is 8 mm.

Next, the stress applying member 42 is formed by using the VAD method.
And 43 are made. Specifically, H for the oxyhydrogen flame burner
Into the oxyhydrogen flame formed by introducing 50 liter of ₂ per minute and 12 liter of O ₂ per minute, 300 ml of SiCl ₄ per minute,
300 ml / min of ₃ (boron trichloride) is introduced, and glass particles (SiO ₂ —B ₂ O ₃ ) produced in a flame are deposited and grown on the starting material to form columnar glass particle bodies. . B ₂ O ₃ which increases the thermal expansion coefficient of SiO ₂ is added to this glass fine particle body, and as a result, the glass fine particle body has a higher thermal expansion coefficient than the clad 20 of the perforated base material 111. . Also, B ₂ O ₃ is Si
Since it is a softening temperature lowering agent for O ₂ , this glass fine particle has a softening temperature lower than that of the clad 20.

Next, the glass fine particles were put into a sintering furnace and heated at a temperature of about 1100 ° C. for 60 minutes while introducing BF ₃ in a helium atmosphere in the sintering furnace. Approximately 1400 ℃ from the atmosphere of helium only
After heating at the temperature of 60 minutes, it is gradually cooled. This allows
B is added from the surface of the glass particle body, and an oxide of B (B ₂ O ₃ ) is formed inside the glass particle body.

When the atmosphere in the sintering furnace is only helium, B ₂ O added to the glass fine particles in the sintering furnace
₃ diffuses from the outer surface of the glass fine particles into the atmosphere. The amount of diffusion is greater on the surface side of the glass fine particles.
Since transparent vitrification proceeds at the same time as diffusion, B ₂ O ₃ is added to the center of the glass body at a substantially uniform concentration.
In the surface layer portion having a thickness of about ¼ of the outer diameter from the surface toward the center, the addition concentration gradually decreases, and B ₂ O ₃ is hardly added near the surface. When the glass body thus obtained is heated and drawn to have an outer diameter of about 7.7 mm,
The stress applying members 42 and 43 (SiO ₂ -B _{2) of} this embodiment are
O ₃ ) is obtained.

The stress imparting members 42 and 43 have a softening temperature in the surface layer portion from the softening temperature of the clad 20 toward the center side from the surface side of the members to the central portions 42a and 43.
It continuously changes up to the softening temperature of a. That is, the stress imparting members 42 and 43 have a tubular shape having a softening temperature distribution in which the softening temperature continuously changes from the softening temperature of the cladding 20 to the softening temperature of the central portions 42a and 43a from the surface side to the center side. The member is attached to its surface layer portions 42b and 43b.
Prepared for.

Stress-applying members 42 and 4 thus obtained
3, the through hole 50 of the base material 111 with holes, as shown in FIG.
The optical fiber preform of this embodiment is completed by inserting and fixing each in 51 and then subjecting it to heat treatment to integrate the clad 20 and the stress applying members 42 and 43. Although not shown, the stress applying members 42 and 43 are fixed by the same method as in the first embodiment.

The optical fiber preform manufactured according to this example has a refractive index distribution and a softening temperature distribution as shown in FIG. The optical fiber preform of this example is characterized by the softening temperature distribution of the stress applying member inserted into the through holes 50 and 51 of the perforated preform 111. That is, FIG.
As shown in FIG. 7, the surface layer portions 42b and 43b of the stress applying members 42 and 43 are located in the central portions 42a and 43a from the softening temperature of the clad 20 from the surface side to the center side of the members.
It has a softening temperature distribution that continuously changes up to the softening temperature.

In the optical fiber preform of this embodiment, since the stress applying member has such surface layer portions 42b and 43b, the softening temperature difference between the clad 20 and the stress applying members 42 and 43 is relaxed. ing. In particular, since the softening temperature is substantially equal at the joint interface between the clad 20 and the stress applying members 42 and 43, the surface smoothing effect is sufficient even when the clad 20 and the stress applying members 42 and 43 are integrated by heat treatment. This acts to prevent or significantly reduce the generation of bubbles at the joint interface between the clad 20 and the stress applying members 42 and 43.

Also in the optical fiber preform of this example, the refractive index of the stress applying members 42 and 43 is set lower than that of the clad (FIG. 11). This prevents the optical power from moving from the core to the stress applying members 42 and 43, so that it is possible to suppress an increase in transmission loss of the optical fiber obtained by drawing the optical fiber preform of this embodiment. .

The optical fiber preform of this embodiment was heated to about 2000 ° C. in a heating furnace, and the stress applying members 42 and 43 and the perforated preform 111 were integrated and drawn at a linear velocity of 100 m / min. To produce an optical fiber having an outer diameter of 125 μm and further coated with UV resin to produce a polarization maintaining optical fiber having an outer diameter of about 250 μm and a length of 9.5 km. The crosstalk characteristic, which is one of the polarization characteristics of this optical fiber, is calculated as follows.
When measured at 3 μm, a very good result of −25 dB was obtained.

Instead of the above-mentioned method, the stress-applying members 42 and 43 and the clad 20 are heated and integrated with each other at the same time as the drawing, so that the optical fiber can be manufactured without going through the state of the preform. This is the same as in the above embodiment.

Example 5 In this example, an optical fiber preform having the refractive index distribution and softening temperature distribution shown in FIG. 11 is manufactured by a method similar to that of the first embodiment. Specifically, after forming the perforated base material 111 by the same method as in Example 1, the through holes 50 and 5 are formed.
The tubular members 30 and 31 having a thickness of 0.5 mm are formed on the surface of 1. Here, the method of forming the tubular members 30 and 31 is slightly different from that of the first embodiment. That is, the tubular members 30 and 31 of this embodiment contain SiCl ₄ at 400 m / min.
l and O ₂ are introduced into the through holes 50 and 51 at a flow rate of 1 l / min, and a flame of an oxyhydrogen burner is applied to the outer surface of the perforated base material 111 while controlling the flow rate of BCl _3. It is formed by heating the inside of the holes 50 and 51.
BCl ₃ is not introduced at all at the beginning of heating, then the flow rate is gradually increased, and finally BCl ₃ is introduced at a flow rate of 150 ml / min. As a result, the surface layer portions 42b and 43 of the fourth embodiment are formed.
The tubular members 30 and 31 having the same refractive index distribution and softening temperature distribution as b are formed. After that, the same manufacturing process as in Example 1 is performed to manufacture the optical fiber preform having the refractive index distribution and the softening temperature distribution shown in FIG. 11.

Example 6 In this example, an optical fiber preform having the refractive index distribution and softening temperature distribution shown in FIG. 11 is manufactured by a method similar to that of Example 3. Specifically, the perforated base material 111 and the stress applying members 40 and 41 are manufactured in the same manner as in Example 3, and the tubular members 30 and 31 are independent of the perforated base material 111 and the stress applying members 40 and 41. To form. here,
The method of forming the tubular members 30 and 31 is different from that of the third embodiment.

That is, in this example, after forming rod-shaped glass fine particles in the same manner as in Example 3, this was placed in a sintering furnace and SiF ₄ was introduced into the helium atmosphere in the sintering furnace. After heating at a temperature of about 1200 ° C. for 60 minutes, the atmosphere in the sintering furnace is made up of only helium, and then about 1
After heating at a temperature of 400 ° C. for 60 minutes, it is gradually cooled. When the atmosphere in the sintering furnace is only helium, F added to the glass particle body in the sintering furnace diffuses from the outer surface of the glass particle body into the atmosphere. The amount of diffusion is greater on the surface side of the glass fine particles. As vitrification progresses at the same time as diffusion, F from the center side of the glass body toward the surface side.
As a result, a glass columnar body of SiO ₂ having a continuously changing concentration can be obtained.

This glass columnar body was heated and stretched to have an outer diameter of 22 mm, then a through hole having an inner diameter of 20 mm was formed in the center using an ultrasonic perforator, and the outer diameter was 8 A glass tube having a diameter of 0.8 mm and an inner diameter of 8 mm is formed. As a result, the tubular members 30 and 31 having the same refractive index distribution and softening temperature distribution as the surface layer portions 42b and 43b of Example 4 are formed. After that, the same manufacturing process as that of the third embodiment is performed to manufacture the optical fiber preform having the refractive index distribution and the softening temperature distribution of FIG. 11.

Although the embodiments of the present invention have been described above in detail, the present invention is not limited to the above embodiments, and various modifications can be made. For example, for manufacturing a glass cylinder, a glass pipe or a stress applying member composed of a core and a clad, any of generally known manufacturing methods such as VAD method, OVD method and MCVD method may be used. The same applies when the glass layer is formed on the surface of the through hole or the surface of the stress applying member. As the method of forming the through hole for inserting the stress applying member, various methods can be selected from known techniques. Similarly, the cross-sectional shapes of the through hole and the stress applying member can be arbitrarily selected from known techniques regarding polarization-maintaining optical fibers.

Further, after the glass layer is formed on the surface of the through hole or the surface of the stress applying member, the surface of the glass layer is subjected to mechanical smoothing such as polishing or heat smoothing by flame radiation, or the like. By cleaning the surface of (1) and removing the attached impurities, it is possible to more effectively prevent the generation of bubbles during heat integration.

The softening temperature changing material used for adjusting the softening temperature of quartz glass is as follows.

First group (those that lower both the softening temperature and the refractive index)
... B, F Second group (for lowering softening temperature and increasing refractive index) ... Ge, P Third group (for increasing both softening temperature and refractive index)
... Al, Ti, Zr These softening temperature changing materials are selected by adding one or more from the first group, one or more from the first group, and one or more from the second group. Select one or more from the first group, and
Select one or more from the third group and add, first
Select one or more from the group, one or more from the second group, one or more from the third group, and add,
It is good to use by any of the methods.

[0115]

As described above in detail, the optical fiber preform of the present invention has a structure in which bubbles are less likely to be generated at the joint interface between the clad and the tubular member or the joint interface between the tubular member and the stress applying member. As a result, it is possible to manufacture a polarization-maintaining optical fiber exhibiting good transmission characteristics and polarization characteristics by drawing the base material.

According to the optical fiber preform of the present invention in which the stress-applying member or the tubular member has a refractive index not higher than that of the cladding, stress is applied from the core in the optical fiber obtained by drawing the preform. Since it is difficult for the optical power to move to the member or the tubular member, it is possible to obtain a polarization-maintaining optical fiber with less transmission loss.

Next, according to the first aspect of the method for producing an optical fiber preform according to the present invention, even when the stress applying member and the tubular member are integrated to complete the preform, the cladding and the tubular member are Since bubbles are unlikely to be generated at the bonding interface of (1) or at the bonding interface of the tubular member and the stress applying member, it is possible to preferably manufacture the preform for the polarization maintaining optical fiber.

Further, according to the second aspect of the method for manufacturing an optical fiber preform according to the present invention, even when the preform and the stress applying member are integrated to complete the preform, the cladding and the stress applying member are provided. Since bubbles are less likely to be generated at the bonding interface of the members, it is possible to preferably manufacture the preform for the polarization maintaining optical fiber.

Next, according to the first aspect of the method for producing an optical fiber of the present invention, the cladding and the tubular member are also used when the wire drawing is performed while the perforated base material, the stress applying member and the tubular member are integrated. Since bubbles are less likely to be generated at the bonding interface with and the bonding interface between the tubular member and the stress-applying member, it prevents the optical fiber from breaking during drawing, and maintains polarization with good transmission and polarization characteristics. An optical fiber can be obtained.

Further, in the second aspect of the method for producing an optical fiber according to the present invention, even when the wire drawing is performed while the perforated base material and the stress applying member are integrated, the joining interface between the clad and the stress applying member is formed. Since bubbles are less likely to be generated, it is possible to prevent the optical fiber from being broken during drawing and obtain a polarization-maintaining optical fiber having good transmission characteristics and polarization characteristics.

Next, the optical fiber of the present invention has a structure in which bubbles are less likely to be generated at the joint interface between the clad and the tubular member or the joint interface between the tubular member and the stress applying member at the time of manufacture. It can be manufactured without breaking inside, and has excellent transmission characteristics and polarization characteristics.

Among the optical fibers of the present invention, those in which the stress-applying member or the tubular member has a refractive index equal to or lower than the refractive index of the clad are difficult to transfer the optical power from the core to the stress-applying member or the tubular member. It has the advantage of low loss.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an optical fiber preform manufactured in Examples 1 to 3.

FIG. 2 is a first diagram for explaining a base material manufacturing method of Example 1;
FIG.

FIG. 3 is a second diagram for explaining the base material manufacturing method according to the first embodiment.
FIG.

FIG. 4 is a third diagram for explaining the base material manufacturing method according to the first embodiment.
FIG.

FIG. 5 is a fourth diagram for explaining the base material manufacturing method according to the first embodiment.
FIG.

FIG. 6 is a fifth diagram for explaining the base material manufacturing method according to the first embodiment.
FIG.

FIG. 7 is a diagram showing a refractive index distribution and a softening temperature distribution along the radial direction of the optical fiber preforms manufactured in Examples 1 to 3.

FIG. 8 is a drawing for explaining the base material manufacturing method of the second embodiment.

FIG. 9 is a drawing for explaining the base material manufacturing method according to the third embodiment.

FIG. 10 is a drawing for explaining the base material manufacturing method according to the fourth embodiment.

11 is a diagram showing a refractive index distribution and a softening temperature distribution along the radial direction of the optical fiber preform manufactured in Example 4. FIG.

[Explanation of symbols]

10 ... Core, 20 ... Clad, 30 and 31 ... Tubular member, 40 and 41 ... Stress giving member, 50-53 ... Through hole, 100 ... Optical fiber preform.

Front page continuation (72) Inventor Koichi Uchiyama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (22)

[Claims] 1. A columnar core and a tubular clad surrounding the core, wherein a through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis. A surface layer having a first coefficient of thermal expansion and a first softening temperature, a second coefficient of thermal expansion different from the first coefficient of thermal expansion and the first softening temperature, which is inserted into the through hole, and Different second
A columnar stress-applying member having a softening temperature of its surface layer portion, and a tubular member that is inserted into the through hole and surrounds the stress-applying member, and is set between the first and second softening temperatures. And an optical fiber preform having a radial softening temperature distribution. 2. The optical fiber preform according to claim 1, wherein the tubular member has a substantially constant radial softening temperature distribution. 3. The tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. The optical fiber preform according to claim 1. 4. The optical fiber preform according to claim 1, wherein the refractive index of the stress applying member and the tubular member is less than or equal to the refractive index of the clad. 5. A columnar core and a tubular clad surrounding the core, wherein through holes along the axial direction are provided in the tube wall at a predetermined interval from the central axis, and at the surface layer portion of the through holes. A perforated base material having a first thermal expansion coefficient and a first softening temperature, and a columnar stress applying member to be inserted into the through hole, which is different from the first thermal expansion coefficient. A thermal expansion coefficient and a second softening temperature different from the first softening temperature in a surface layer portion thereof, and a tubular member which should surround the stress applying member, One having a radial softening temperature distribution set between the first and second softening temperatures is provided on the surface of the through hole, between the surface of the stress applying member and the surface of the through hole, or the stress applying. At one or more positions on the surface of the member Kicking with the perforated base material, the second step and the method for manufacturing an optical fiber preform comprising integrating the stress applying member and the tubular member. 6. In the second step, the tubular member is formed on the surface of the through hole, then the stress applying member is inserted into the hollow portion of the tubular member, and then the stress applying member. 6. The method for producing an optical fiber preform according to claim 5, which is a step of integrating the tubular member with the tubular member. 7. In the second step, the tubular member is formed on a surface of the stress applying member, and then a columnar body including the stress applying member and the tubular member is formed into a through hole of the perforated base material. 6. The method for manufacturing an optical fiber preform according to claim 5, wherein the step of inserting the columnar body and the perforated preform into a single body is integrated. 8. In the second step, the tubular member is inserted into the through hole, the stress applying member is inserted into a hollow portion of the tubular member, and thereafter, the perforated base material and the stress applying member are applied. The method for producing an optical fiber preform according to claim 5, which is a step of integrating the member and the tubular member. 9. A columnar core and a tubular clad surrounding the core, wherein through holes along the axial direction are provided in the tube wall at a predetermined distance from the central axis, and in the surface layer portion of the through holes. A perforated matrix comprising a material having a first coefficient of thermal expansion and a first softening temperature, a second coefficient of thermal expansion different from the first coefficient of thermal expansion and a second material different from the first temperature of softening. A columnar stress-applying member having a central portion having a softening temperature in its surface layer portion, wherein a tubular member having a radial softening temperature distribution set between the first and second softening temperatures is provided in the surface layer portion. A second step of inserting the stress applying member into a through hole of the perforated base material; a second step of integrating the stress applied member and the perforated base material; 3. A method of manufacturing an optical fiber preform, comprising: 10. The method for manufacturing an optical fiber preform according to claim 5, wherein the tubular member has a substantially constant radial softening temperature distribution. 11. The tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. The method for manufacturing an optical fiber preform according to claim 5 or 9. 12. A columnar core and a tubular clad that surrounds the core, wherein a through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis, and in the surface layer portion of the through hole. A perforated base material having a first thermal expansion coefficient and a first softening temperature, and a columnar stress applying member to be inserted into the through hole, which is different from the first thermal expansion coefficient. A thermal expansion coefficient and a second softening temperature different from the first softening temperature in a surface layer portion thereof, and a tubular member which should surround the stress applying member, One having a radial softening temperature distribution set between the first and second softening temperatures is provided on the surface of the through hole, between the surface of the stress applying member and the surface of the through hole, or the stress applying. One or more positions on the surface of the member The second step of providing and heating the composite body composed of the perforated base material, the stress applying member and the tubular member to draw the composite body while integrating the perforated base material, the stress applying member and the tubular member. And a third step of manufacturing an optical fiber. 13. The second step is a step of forming the tubular member on the surface of the through hole of the perforated base material, and then inserting the stress applying member into the hollow portion of the tubular member. 13. The method for manufacturing an optical fiber according to claim 12, wherein: 14. In the second step, the tubular member is formed on the surface of the stress applying member, and then a columnar body including the stress applying member and the tubular member is formed into a through hole of the perforated base material. 13. The method for manufacturing an optical fiber according to claim 12, which is a step of inserting into the optical fiber. 15. The method according to claim 12, wherein the second step is a step of inserting the tubular member into the through hole and inserting the stress applying member into a hollow portion of the tubular member. Optical fiber manufacturing method. 16. A columnar core and a tubular clad that surrounds the core, wherein a through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis, and at the surface layer portion of the through hole. A perforated matrix comprising a material having a first coefficient of thermal expansion and a first softening temperature, a second coefficient of thermal expansion different from the first coefficient of thermal expansion and a second material different from the first temperature of softening. A columnar stress-applying member having a central portion having a softening temperature in its surface layer portion, wherein the first and second
A tubular member having a radial softening temperature distribution set between the softening temperatures of
And a second step of inserting the stress-applying member into the through-hole of the perforated base material, and heating a composite of the perforated base material and the stress-applying member to form the perforated base material and A third step of drawing the composite while integrating the stress applying member, and a method for manufacturing an optical fiber. 17. The tubular member has a substantially constant radial softening temperature distribution, according to claim 12 or 16.
The manufacturing method of the optical fiber described in the above. 18. The tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. The method for manufacturing an optical fiber according to claim 12. 19. A columnar core and a tubular clad that surrounds the core, wherein a through hole along the axial direction is provided in the tube wall at a predetermined distance from the central axis, and the through hole A surface layer having a first coefficient of thermal expansion and a first softening temperature, a second coefficient of thermal expansion different from the first coefficient of thermal expansion and the first softening temperature, which is inserted into the through hole, and Different second
A columnar stress-applying member having a softening temperature of its surface layer portion, and a tubular member that is inserted into the through hole and surrounds the stress-applying member, and is set between the first and second softening temperatures. An optical fiber having a radial softening temperature distribution. 20. The optical fiber according to claim 19, wherein the tubular member has a substantially constant radial softening temperature distribution. 21. The tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. The optical fiber according to claim 19. 22. The optical fiber according to claim 19, wherein the stress-applying member and the tubular member have a refractive index equal to or lower than the refractive index of the clad.