JPH0930824A - Polarization maintaining optical fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber retaining polarized waves hardly forming bubbles even if the integration and drawing of stressing members and a perforated preform are simultaneously carried out. SOLUTION: A perforated preform 111 having a columnar core 10 and a clad 20, surrounding the core and having the first thermal expansion coefficient and the first softening temperature in the surface layer part of through-holes 50 and 51 provided at a prescribed interval kept from the central axis and columnar stressing members 40 and 41 having the second thermal expansion coefficient and the second softening temperature in the surface layer thereof are initially prepared. Tubular members 30 and 31 having the same softening temperature as that of the stressing members 40 and 41 are then formed on the surfaces of the through-holes in the perforated preform 111. The stressing members 40 and 41 are subsequently inserted into hollow parts 52 and 53 of the tubular members 30 and 31 and the resultant composite comprising the perforated preform 111, tubular members 30 and 31 and stressing members 40 and 41 is then heated to carry out the drawing while integrating the resultant perforated preform 112 having the tubular members formed therein with the stressing members 40 and 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a polarization maintaining optical fiber and a polarization maintaining optical fiber.

[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.

Of these, the method of simultaneously performing heating integration and wire drawing can reduce the number of manufacturing steps as compared with the method of separately performing heating integration and wire drawing, so that polarization can be maintained with good productivity. Optical fibers can be manufactured. In addition, in the method of drawing after the integration, if the base material is cooled after heat integration, cracks may occur due to the difference in thermal expansion coefficient, so the base material is not cooled after integration. However, the method of simultaneously performing heating integration and wire drawing is advantageous in that such consideration is unnecessary.

[0004]

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.

Particularly, in the method of simultaneously performing the integration and the drawing, the optimum conditions for the integration (optimal heating temperature, heating time, etc.) and the optimum conditions for the drawing do not coincide with each other. Since the integration is carried out under the conditions, bubbles are apt to occur. If drawing is performed while bubbles are generated at the interface between the clad and the stress applying member, the optical fiber is likely to break during drawing. Even if the optical fiber is manufactured without breaking, the optical fiber does not have sufficient transmission characteristics and strength because it contains bubbles.

The present invention has been made in view of the above problems, and it is possible to suitably manufacture a polarization-maintaining optical fiber by preventing bubbles from being generated even if heating and unifying are performed simultaneously with drawing, and An object of the present invention is to provide a polarization-maintaining optical fiber having a structure that is easy to manufacture while preventing bubbles from being generated.

[0007]

In order to solve the above-mentioned problems, the first aspect of the method of manufacturing a polarization maintaining optical fiber according to the present invention is (a) a columnar core and surrounding this core. A tubular clad having through holes along the axial direction provided in the tube wall at a predetermined distance from the central axis and having a first thermal expansion coefficient and a first softening temperature in the surface layer portion of the through holes. And a columnar stress applying member having 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. A second step of (b) forming a tubular member having a second softening temperature on the surface of the through hole of the apertured base material, and (c) the stress applying member of the tubular member. The third step of inserting into the hollow part, and (d) the perforated base material, tubular member and Heating the optical fiber preform comprising a stress applying member, and a fourth step of performing drawing while integrating the base material and the stress applying member aperture where the tubular member is formed.

The integration of the perforated base material and the stress imparting member means, for example, when these members are made of glass,
It means joining glass pieces together.

A second aspect of the method for manufacturing a polarization-maintaining optical fiber according to the present invention is (a) a columnar core and a tubular clad surrounding the core, the axial wall extending along the axial direction. A through hole having a first thermal expansion coefficient and a first softening temperature at a surface layer portion of the through hole, the through hole having a predetermined distance from the central axis; A first step of preparing a columnar stress-applying member having a second thermal expansion coefficient different from the coefficient and a second softening temperature different from the first softening temperature in its surface layer portion;
(B) a second step of forming on the surface of the stress-applying member a tubular member that surrounds the surface of the stress-applying member and has a softening temperature substantially the same as the first softening temperature; and (c)
A third step of inserting a columnar body composed of a stress applying member and a tubular member into the through hole of the perforated base material, and (d) the perforated base material,
A fourth step of heating the composite body including the tubular member and the stress applying member to draw the wire while integrating the columnar body and the perforated base material.

The integration of the columnar body and the perforated base material means
For example, when these members are glass, it means joining the glasses.

In the manufacturing methods according to the first and second aspects, it is preferable that the tubular member having a refractive index lower than that of the clad is formed in the second step.

Next, the polarization maintaining optical fiber of the present invention is
(A) a columnar core, and (b) a tubular clad that surrounds the core, in which through holes are provided in the tube wall along the axial direction with a predetermined distance from the central axis. Having a first coefficient of thermal expansion and a first softening temperature in the surface layer part of, and (c) a second coefficient of thermal expansion and a first softening temperature which are different from the first coefficient of thermal expansion inserted into the through hole. A columnar stress-applying member having a second softening temperature different from that in the surface layer portion, and (d) a tubular member that is formed on the surface of the through hole and surrounds the stress-applying member. And a tubular member having a softening temperature substantially equal to any of the softening temperatures.

In the above polarization-maintaining optical fiber, the stress-applying member and the tubular member preferably have a refractive index equal to or lower than that of the cladding.

[0014]

In the first aspect of the method of manufacturing a polarization maintaining optical fiber according to the present invention, a tubular member having the same softening temperature as the surface layer of the stress applying member is formed on the surface of the through hole of the perforated base material. Then, the stress applying member is inserted, and the perforated base material on which the tubular member is formed and the stress applying member are integrated simultaneously with the drawing. Since it is not necessary to consider the drawing conditions when forming the tubular member on the surface of the through hole, it is possible to form the tubular member under conditions where bubbles are unlikely to occur, and bubbles are generated from this point. It is difficult to do. Further, by forming the tubular member as a sufficiently thin layer, it is possible to suppress the generation of bubbles at the interface between the tubular member and the clad. Furthermore, it is the surface layers of the tubular member and the stress-applying member that are directly integrated during drawing, and since these have the same softening temperature, the optimum drawing process does not take into account the integration conditions. Generation of bubbles is sufficiently suppressed even when the integration is performed under the conditions. As described above, according to the first aspect of the present invention, it is possible to suppress the generation of bubbles and perform the integration without taking the integration condition into consideration, and at the same time, perform the drawing.

Next, in the second aspect of the method for manufacturing a polarization-maintaining optical fiber according to the present invention, a tube having the same softening temperature as the cladding softening temperature on the surface of the through hole on the surface of the stress applying member. After forming the member, a columnar body including the stress applying member and the tubular member is inserted into the through hole of the perforated base material, and the columnar body and the perforated base material are integrated simultaneously with drawing. Since it is not necessary to consider the drawing conditions when forming the tubular member on the surface of the stress applying member, it is possible to form the tubular member under conditions where bubbles are unlikely to occur as much as possible. It is less likely to occur. Also,
By forming the tubular member as a sufficiently thin layer, it is possible to suppress the generation of bubbles at the interface between the tubular member and the stress applying member. Furthermore, it is the tubular member and the surface layer of the through-hole that are directly integrated during drawing, and since these have the same softening temperature, the optimum conditions for drawing are taken into consideration without considering the integration conditions. The generation of bubbles is sufficiently suppressed even when the integration is performed below. As described above, according to the second aspect of the present invention as well, it is possible to suppress the generation of bubbles and perform the integration without considering the integration conditions, and at the same time, perform the drawing.

Further, when the refractive index of the tubular member formed in the present invention is equal to or lower than the refractive index of the clad, even when light is propagated in the polarization-maintaining optical fiber obtained by the present invention, the core member changes to the tubular member. Light power transfer is less likely to occur.

Next, in the polarization-maintaining optical fiber of the present invention, the softening temperature between the through hole and the stress applying member is approximately the same as the softening temperature of either the surface layer of the through hole or the surface layer of the stress applying member. Since the tubular member has the present structure, it has a structure in which bubbles are less likely to be generated even when the stress applying member and the perforated base material are integrated at the same time as drawing in manufacturing the tubular member.
Specifically, when the tubular member has the softening temperature of the surface layer of the stress-applying member, the tubular member is provided on the surface of the through-hole and then integrated and drawn. When the surface layer of the hole has a softening temperature, bubbles can be prevented by forming a tubular member on the surface of the stress applying member and then performing integration and drawing.

In the polarization-maintaining optical fiber of the present invention, if the stress-applying member or tubular member has a refractive index equal to or lower than that of the cladding, stress is applied from the core even when light is propagated in the optical fiber. Transfer of optical power to the member or tubular member is unlikely to occur.

[0019]

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 FIGS. 1 to 5 are process drawings showing a method of manufacturing a polarization maintaining optical fiber of this example. The manufacturing method will be described with reference to these drawings.

First, a glass cylinder 110 composed of the core 10 and the clad 20 is prepared (FIG. 1). Core 10
Is a cylindrical glass rod, and the clad 20 is the core 1
It is a circular glass tube that tightly covers the side surface of No. 0. The central axes of the core 10 and the clad 20 coincide with each other.
The glass cylinder 110 has an outer diameter of 25 mm, and the core 10 has an outer diameter of 1.35 mm. Core 10 and clad 20
Are both made of quartz (SiO ₂ ) glass. The clad 20 is composed of substantially pure silica glass, but the silica glass forming the core 10 contains germanium oxide (GeO ₂ ) as a refractive index increasing material, so that the core's refractive index is increased. Is higher than.

The glass cylinder 110 is formed by the same method as that for a normal optical fiber preform, that is, a known VAD (vapor phase axis attachment) method, OVD (external attachment) method, MCVD (internal attachment) method,
It can be manufactured using a rod-in-tube method or the like. In this embodiment, this is manufactured using the MCVD method.

Then, the glass column 110 is attached to the cladding 20 of the glass column 110 using an ultrasonic perforator (not shown).
Through holes 50 and 5 having a diameter of 9 mm extending along the axial direction of
1 (FIG. 2). The through holes 50 and 51 are the core 1
It is formed parallel to the core 10 at a position symmetrical with respect to the central axis of 0. The distance between the central axis of the through holes 50 and 51 and the central axis of the core 10 is 6.3 mm, respectively. Hereinafter, the glass cylinder 110 provided with the through holes 50 and 51 will be referred to as a perforated base material 111.

Next, the through holes 50, 5 of the perforated base material 111.
A 0.5-mm thick boron-doped quartz glass (SiO ₂ + B ₂ O ₃ ) layer 30 or 31 is formed on the surface of 1 (FIG. 3). Since the glass layer has a circular tubular shape, the glass layer is hereinafter referred to as tubular members 30 and 31.

The tubular members 30 and 31 are made of BCl.
₃ (boron trichloride) 200 ml / min, SiCl ₄ (silicon tetrachloride) 400 ml / min, O ₂ (oxygen) 1 l / min
It can be formed by applying a flame of an oxyhydrogen flame burner to the outer surface of the perforated base material 111 while heating the inside of the through holes 50 and 51 while introducing it into the through holes 50 and 51 at a flow rate of. The flame of the oxyhydrogen flame burner is formed by introducing 70 liters of H ₂ (hydrogen) per minute and 30 liters of O ₂ (oxygen) per minute as fuel gas into the burner. After forming the tubular members 30 and 31, the tubular members 30 and 31
Through holes 52 and 53 remain inside. In FIG. 3,
The perforated preform after the tubular members 30 and 31 have been formed is shown at 112.

Next, the stress applying member 4 prepared in advance
Nos. 0 and 41 are formed through holes 52, 5 of the base material 112, respectively.
3 and fix it (FIGS. 4 and 5). The stress applying members 40 and 41 can be manufactured by a known VAD method. Specifically, H is used as fuel gas in the burner.
₂ liters per minute and O _{2 12} liters per minute were introduced to form an oxyhydrogen flame, and SiCl ₄ was introduced into the oxyhydrogen flame at 400 m / min.
and 300 ml / min of BCl ₃ are introduced to produce glass particles (SiO 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, glass particles are uniformly deposited on the entire surface of the starting material, and columnar glass particle bodies are obtained. Next, the glass fine particles are put into a sintering furnace, and while introducing BF ₃ into the helium atmosphere in the sintering furnace, about 1
Heat at a temperature of 200 ° C. for 60 minutes, then about 1400
After heating at a temperature of 60 ° C. for 60 minutes, it is gradually cooled. As a result, the glass particles become transparent glass, so that a columnar glass body (SiO ₂ —B ₂ O ₃ ) is obtained. When this glass body is heated and drawn to have an outer diameter of about 7.8 mm, the stress applying members 40 and 41 are obtained. The compositions of the two stress applying members are almost the same. The stress applying member 4
The lengths 0 and 41 are shorter than the through holes 52 and 53 into which they are to be inserted.

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. As you know,
Since the stress-applying member strongly contracts in the process of cooling the optical fiber after drawing the optical fiber preform with the stress-applying member embedded therein, a large stress is applied to the core. As a result, the optical fiber obtained by drawing becomes a polarization maintaining optical fiber.

The stress applying member 4 obtained as described above.
0 and 41 are respectively inserted into the through holes 52 and 53 of the perforated base material 112 and fixed inside the holes. Below, FIG.
This fixing method will be described with reference to FIGS. 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 7.8 mm are used.
, 61b and the quartz glass tube 70 are prepared. As shown in FIG. 4, 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 optical fiber preform 112. Next, the glass rod 60a, the stress applying member 40, the stress applying member 40,
The glass rod 60b is inserted in this order. Similarly, for the through hole 53, the glass rod 61a, the stress applying member 41, and the glass rod 61b are inserted in this order. Glass rods 60a and 61a
Of the perforations respectively protrude from the end surface of the perforated base material 112, and the end surface is 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). In this way, the stress applying member 40,
41 is fixed inside the through holes 52 and 53, respectively.

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. Thereby, the optical fiber preform is completed.
Of the optical fiber preform, what can be actually used for manufacturing the optical fiber is a portion including the stress applying members 40 and 41. Needless to say, the method of fixing the stress applying members 40 and 41 is not limited to the above method.

Next, the optical fiber preform produced as described above is drawn by using an ordinary drawing apparatus to manufacture a polarization maintaining optical fiber. Specifically, first, the optical fiber preform is heated to about 2000 degrees in a heating furnace, and the stress applying member 40 is heated.
And 41 and the perforated base material 112 are integrated with each other so that the outer diameter is 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, the length is 10k
m polarization-maintaining optical fiber is obtained.

FIG. 6 is a diagram showing the refractive index distribution and the softening temperature distribution in the radial direction of the optical fiber preform produced in this example. In this figure, only the distribution of the right half of the optical fiber preform is shown, but the distribution of the left half is similar to that of the right half. As shown in this figure, the tubular members 30, 31 have substantially the same softening temperature as the stress applying members 40, 41. In order to make the softening temperature of the tubular member the same as that of the stress applying member, it is necessary to appropriately adjust the addition amount of B ₂ O ₃ which is a softening temperature lowering agent of SiO _{2 in} the forming process of the tubular members 30 and 31 described above. Good.

As described above, in this embodiment, the glass layer (tubular members 30, 31) having the same softening temperature as the stress applying members 40, 41 is formed on the surface of the through holes 50, 51, and then the stress is applied. The members 40 and 41 are inserted, and the stress applying members 40 and 41 and the perforated base material 112 are integrated simultaneously with drawing. Since the tubular members 30 and 31 are sufficiently thin layers, the interface between the tubular members 30 and 31 and the clad 20 is different from that in the conventional case where a stress applying member is inserted into a through hole to heat and integrate both members. Bubbles are less likely to occur. Further, in the method of the present embodiment, it is not necessary to consider the drawing conditions when forming the tubular members 30 and 31 on the surfaces of the through holes 50 and 51. The members 30 and 31 can be formed, and from this point as well, bubbles are unlikely to be generated. Further, in the present embodiment, it is the tubular member 30 and the stress applying member 40, and the tubular member 31 and the stress applying member 41 that are directly integrated at the time of drawing, and they have the same softening temperature. The generation of bubbles can be sufficiently suppressed even when integrated under the optimum drawing conditions. As described above, according to the optical fiber manufacturing method of the present embodiment, it is possible to perform the integration while suppressing the generation of bubbles and to perform the drawing at the same time without considering the integration conditions. Therefore, it is possible to easily manufacture a polarization-maintaining optical fiber that exhibits good transmission characteristics and polarization characteristics.

By the way, since light propagates in a portion having a high refractive index in an optical fiber, generally, when a portion having a refractive index higher than that of a clad exists in the vicinity of 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 the present embodiment, the tubular members 30 and 31, and the stress applying members 40 and 41 are set to have a lower refractive index than the clad (FIG. 6). Since the optical fiber has a refractive index distribution similar to that of the base material, by setting the refractive index in this way, it is possible to prevent movement of the optical power in the optical fiber, and to use a polarization-maintaining optical fiber with low transmission loss. It can be manufactured.

In order to confirm the above effect, the crosstalk characteristic which is one of the polarization characteristics of the polarization-maintaining optical fiber manufactured in this example was measured at a wavelength of 1.3 μm. And got very good results.

For comparison with the present embodiment, the present inventors have drawn the optical fiber preform embedded with the stress applying member without forming the tubular members 30 and 31 to maintain the polarization of 10 km. An optical fiber was manufactured. 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 tubular members 30, 31 made of transparent glass are formed on the surfaces of the through holes 50, 51 of the perforated base material 111, and then the stress applying members 40, 41 are formed.
Was inserted into the tubular members 30 and 31, and then integrated and drawn. However, the following method can be considered in manufacturing the polarization-maintaining optical fiber. That is, the through holes 50, 5
1. A tubular glass fine particle layer is deposited and formed on the surface of 1, and stress imparting members 40 and 41 are inserted into the hollow portion of the glass fine particle layer without making it transparent, and then integrated and drawn by heat treatment. You can go. In this method, the glass fine particle layer is made transparent during the heat treatment during drawing.

Example 2 FIG. 7 is a diagram showing a base material manufacturing method of this example. In this embodiment, first, the glass cylinder 110 is formed by the VAD method.
(Similar to FIG. 1) is produced and through holes 50 and 51 extending in the clad 20 along the axial direction by an ultrasonic perforator.
To form a perforated base material 111 (similar to FIG. 2). 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 formed by using the VAD method.
After producing m), glass tubes 32 and 33 are deposited and formed on the surfaces of the stress applying members 40 and 41, respectively. This deposition formation can be performed using a known OVD (external attachment) method. Specifically, SiCl in the oxyhydrogen flame burner
₄ (Silicon tetrachloride) 300 ml / min, H ₂ (hydrogen) 5 l / min, O ₂ (oxygen) 12 l / min 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 on which the glass particles are deposited are put into a heating furnace, and B is placed in a helium atmosphere in the heating furnace.
While introducing F ₃ and SiF ₄ , heat at a temperature of about 1200 ° C. for 120 minutes, then 60 at a temperature of about 1400 ° C.
After heating for a minute, cool slowly. By this work, SiO ₂
B and F are added to the glass particles of (1) and the glass particles become transparent glass.

In this embodiment, glass layers (SiO ₂ —B ₂ O ₃ —F) 32 and 33 having a thickness of about 2.5 mm are formed on the surfaces of the stress applying members 40 and 41 by the above method.
Since this glass layer also has a circular tubular shape, the glass layers will be referred to as tubular members 32 and 33 below.

As a method of forming the tubular members 32 and 33 on the surfaces of the stress applying members 40 and 41, the tubular member 3 is used.
Adopting a method of forming a glass layer to be the stress applying members 40 and 41 on the inner surface of a glass pipe previously manufactured using the materials 2 and 33 by the MCVD method, and then collapsing the glass pipe. You can also

After this, the tubular member 32 and the stress applying member 40
The columnar body 80 made of and the columnar body 81 made of the tubular member 33 and the stress applying member 41 have an outer diameter of about 7.7.
It is heated and stretched so that the thickness becomes mm.

The columnar bodies 80 and 81 thus obtained are inserted into and fixed to the through holes 50 and 51 of the preform preform 111, respectively, as shown in FIG. Is completed. Although not shown, the columnar bodies 80, 8
1 is fixed by the same method as in the first embodiment.

Next, when the optical fiber preform produced as described above was drawn in the same manner as in Example 1, the length was 10 km.
A polarization maintaining optical fiber is obtained.

FIG. 8 is a diagram showing the refractive index distribution and the softening temperature distribution in the radial direction of the optical fiber preform produced in this example. As shown in this figure, tubular members 32, 33
Has substantially the same softening temperature as the clad 20. The softening temperature is adjusted by the above-mentioned tubular members 32 and 33.
Which is a softening temperature change material of SiO ₂ in the formation process of
It can be performed by adjusting the addition amounts of ₂ O ₃ and F. 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.

As described above, in this embodiment, the glass layers (tubular members 32 and 33) having the same softening temperature as that of the clad 20 are formed on the side surfaces of the stress applying members 40 and 41, and the obtained columnar body 80 is obtained. , 81 through holes 5 of the base material 111
Then, the columnar bodies 80 and 81 and the perforated base material 111 are integrated at the same time as drawing. Since the tubular members 32 and 33 are sufficiently thin layers, the tubular members 32 and 33 and the stress imparting member 40, as compared with the conventional case where a stress imparting member is inserted into a through hole to heat and integrate both members, Bubbles are less likely to be generated at the interface with 41. Further, in the method of the present embodiment, since it is not necessary to consider the drawing conditions when forming the tubular members 32 and 33, it is possible to form the tubular members 32 and 33 under conditions where bubbles are unlikely to occur. This is also possible, and bubbles are less likely to be generated from this point as well. Furthermore, in this embodiment, the tubular member 3 is directly integrated during drawing.
2, 33 and the clad 20, which have the same softening temperature, the generation of bubbles is sufficiently suppressed even when they are integrated under the optimal drawing conditions. As described above, according to the optical fiber manufacturing method of the present embodiment, it is possible to suppress the generation of bubbles and perform the integration without taking the integration condition into consideration, and at the same time, perform the drawing.
Therefore, it is possible to easily manufacture a polarization-maintaining optical fiber that exhibits good transmission characteristics and polarization characteristics.

Also in this embodiment, the tubular members 32 and 3 are
3 and the stress imparting members 40 and 41 are set to have a lower refractive index than that of the clad (FIG. 8). Similar to Example 1,
By setting the refractive index in this way, it is possible to prevent the optical power from moving from the core 10 to the tubular members 32, 33 or the stress applying members 40, 41 in the optical fiber, and the polarization-maintaining optical fiber with less transmission loss. Can be manufactured.

The inventors of the present invention measured the crosstalk characteristic, which is one of the polarization characteristics of the polarization-maintaining optical fiber manufactured in this example, at a wavelength of 1.3 μm.
A very good result of 26 dB was obtained.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and various modifications can be made. For example, the VAD method is used for manufacturing the base material and the stress applying member including the core and the clad.
Any of the generally known manufacturing methods such as the OVD method and the 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.

After forming the glass layer on the surface of the through hole or the surface of the stress-applying member, the surface of the glass layer is mechanically smoothed by polishing or heat-smoothed by flame radiation, or the like. By cleaning the surfaces of (1) and (2) to remove the impurities attached to these surfaces, it is possible to more effectively prevent the generation of bubbles during heat integration.

Further, as the softening temperature changing material used for adjusting the softening temperature of the quartz glass, there are the following materials.

The first group (which lowers 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.

[0054]

As described in detail above, according to the first aspect of the method of manufacturing a polarization maintaining optical fiber of the present invention, it is possible to suppress the generation of bubbles and perform the drawing while simultaneously performing the integration. Therefore, it is possible to easily manufacture a polarization-maintaining optical fiber having good transmission characteristics and polarization characteristics.

In the case of the second aspect of the present invention as well, since it is possible to simultaneously perform drawing while suppressing the generation of bubbles and performing integration, excellent transmission characteristics and polarization characteristics can be obtained. The polarization maintaining optical fiber shown can be easily manufactured.

According to the method for manufacturing a polarization maintaining optical fiber of the present invention, which forms a tubular member having a refractive index equal to or lower than the refractive index of the clad, the obtained polarization maintaining optical fiber is formed from the core to the tubular member. Since the movement of the optical power does not easily occur, it is possible to manufacture a polarization maintaining optical fiber with less transmission loss.

Next, the polarization-maintaining optical fiber of the present invention has a structure in which bubbles are less likely to be generated even when the stress applying member and the perforated base material are integrated at the same time as drawing in manufacturing. Therefore, it can be manufactured without breaking during drawing, and has excellent transmission characteristics and polarization characteristics.

Among the polarization-maintaining 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 less likely to cause the optical power to move from the core to the stress-applying member or the tubular member. Therefore, it has an advantage that the transmission loss is small.

[Brief description of drawings]

FIG. 1 is a first process diagram illustrating a method for manufacturing an optical fiber preform according to a first embodiment.

FIG. 2 is a second process chart showing the method for manufacturing the optical fiber preform of Example 1.

FIG. 3 is a third process chart showing the method for manufacturing the optical fiber preform of Example 1.

FIG. 4 is a fourth process chart showing the method of manufacturing the optical fiber preform of Example 1.

FIG. 5 is a fifth process chart showing the method for manufacturing the optical fiber preform of Example 1.

FIG. 6 is a diagram showing a refractive index distribution and a softening temperature distribution along a radial direction of the optical fiber preform manufactured in Example 1.

FIG. 7 is a drawing for explaining the base material manufacturing method of the second embodiment.

FIG. 8 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 2;

[Explanation of symbols]

10 ... Core, 20 ... Clad, 30-33 ... Tubular member,
40 and 41 ... Stress imparting member, 50 to 53 ... Through hole, 1
10 ... Glass cylinder, 111 ... Perforated base material, 112 ... Perforated base material after the tubular members 30 and 31 are formed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Uchiyama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (5)

[Claims] 1. A columnar core and a tubular clad that surrounds the core, wherein a through hole along the axial direction is provided in the wall of the tube 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 first step of preparing a columnar stress-applying member having a softening temperature in its surface layer portion, and a tube having a softening temperature substantially the same as the second softening temperature on the surface of the through hole of the perforated base material A second step of forming a member, a third step of inserting the stress-applying member into the hollow portion of the tubular member, and heating the composite body including the perforated base material, the tubular member and the stress-applying member. The perforated base material on which the tubular member is formed, A fourth step of performing drawing while integrally forming the force imparting member, and a method for manufacturing a polarization maintaining optical fiber, comprising: 2. A columnar core and a tubular clad surrounding the core, wherein through holes are provided in the tube wall along the axial direction at a predetermined distance from the central axis, and at 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 first step of preparing a columnar stress applying member having a softening temperature in its surface layer portion; and a tubular member surrounding the surface of the stress applying member on the surface of the stress applying member, the first softening A second step of forming one having a softening temperature substantially the same as the temperature; a third step of inserting a columnar body composed of the stress applying member and the tubular member into a through hole of the perforated base material; Perforated base material, tubular member and stress applying part A fourth step of heating a composite body made of a material to draw the columnar body and the perforated preform while integrating them, and a method of manufacturing a polarization-maintaining optical fiber. 3. The method for manufacturing a polarization maintaining optical fiber according to claim 1, wherein in the second step, a tubular member having a refractive index lower than that of the cladding is formed. 4. 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, 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 in its surface layer portion, a tubular member provided between the surface of the through hole and the surface of the stress-applying member, and surrounding the stress-applying member, A polarization-maintaining optical fiber, comprising: a tubular member having a softening temperature substantially equal to any one of the first and second softening temperatures. 5. The polarization-maintaining optical fiber according to claim 4, wherein the stress-applying member and the tubular member have a refractive index equal to or lower than that of the cladding.