JPS61141630A - Production of preform for constant polarization optical fiber - Google Patents

Abstract

PURPOSE:The parent material with a prescribed structure is heated with a sub-burner which moves in the direction of the axis of the material, as it is allowed to rotate, to effect diameter contraction and fushion, then heated with the main burner to effect colapse whereby a preform with a uniform cross section at the part to which a stress is loaded is obtained. CONSTITUTION:The parent material is composed of the core glass rod 3 containing stress-loading glass rod 2, core 10 and clad 20, the quartz rod 4 and the quartz jacket 7. The parent material is set to the support 11 in the colapser 10 and allowed to rotate in the direction of arrow B, as it is evacuated in the direction of arrow A. The parent material is heated at about 1,600 deg.C with the sub-burner 12, as it is allowed to move at a certain speed in the direction of the material axis C, to effect diameter contraction and fuse the contact points between individual parts 2, 3, 4, 7. Then, the main burner following the sub-burner is allowed to move at the same speed of the sub-burner 12 in the same direction D to heat the material at about 1,900 deg.C for complet colapse. Thus, a preform for constantly polarized optical fiber with highly uniform cross section in the lengthwise direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of manufacturing a preform for a multi-rond type polarization constant optical fiber.

[Prior Art] There are various types of polarization-constant optical fibers depending on how stress birefringence is imparted to the core.

For example, a stress-applying type is a typical example, and there are several methods for applying stress using a stress-applying glass rod, a typical example of which is the multi-rond type. As shown in FIG. 2, this method consists of a core glass rod 3 having a core portion lO and a cladding portion 20 disposed in the center of a jacketed quartz tube 7; A base material having stress applying glass rods 2.2 arranged at symmetrical positions with the glass rod 3 as the center and a quartz rod 4.4.4.4 circumscribing the core glass rod 3 is directly drawn. (hereinafter referred to as direct wire drawing method), or the base material is preheated to melt and integrate the voids in the jacket quartz tube 7 to obtain a preform, and then this is drawn (hereinafter referred to as heating method). (referred to as the melting method).

However, the former direct drawing method has problems in that the symmetry of the stress-applying glass rod 2.2 is likely to be lost, and furthermore, the cross-sectional shape is likely to be non-uniform in the longitudinal direction. Therefore, today, efforts are being focused on the latter heating and melting method, but even with this method, although the symmetry of the stress-applying glass rod 2.2 can be improved to some extent, there are no defects in the longitudinal cross-sectional shape. Uniformity cannot be improved.

By the way, when processing different types of glasses, it is usually easier to process them by combining glasses whose thermal expansion coefficients and softening points are as close as possible. However, in the stress-applying type polarization-constant optical fiber, the larger the thermal expansion coefficient of the stress-applying glass rod 2, in other words, the larger the difference in softening point temperature, the better the characteristics as a polarization-constant optical fiber. In this way, in the production of polarization-controlled optical fiber preforms using the heat-melting method, processability and properties as polarization-controlled optical fibers are in a contradictory relationship, and non-uniformity in the cross-sectional shape in the longitudinal direction occurs. This is thought to be due to the use of different types of glasses with large differences in softening points as mentioned above.

More specifically, when we investigate the cause of the non-uniformity of the cross-sectional shape in the longitudinal direction, we find that the softening point temperature of the stress-applying glass rod 2 is several hundred degrees Celsius lower than that of the core glass rod 3 and the quartz rod 4, and the collapse temperature At around 1900°C, the viscosity decreases significantly and becomes a fluid state. Therefore, the stress applying glass rod 2 in a fluid state flows into the gaps on the upstream side where the collapse has not yet progressed, that is, the gaps between the core glass rod 3, the quartz rod 4, and the jacket quartz tube 7, and the cross-sectional shape It is presumed that this is causing non-uniformity.

As described above, in the conventional multi-loft type heating melting method, the cross-sectional shape in the longitudinal direction becomes non-uniform, and therefore it is not possible to obtain a constant polarization optical fiber preform with good characteristics.

[Purpose of the invention]

In view of the above problems, an object of the present invention is to provide a manufacturing method for obtaining a preform for a constant polarization optical fiber that has excellent symmetry with respect to the core portion of a stress-applying glass rod and uniformity of longitudinal cross-sectional shape. There is a particular thing.

[Structure of the invention]

In order to achieve the above object, the present invention provides a core glass rod having a core portion and a cladding portion disposed in the center of a jacketed quartz tube, and a core glass rod circumscribing the core glass rod and symmetrical about the core glass rod. A preform for a constant polarization optical fiber is manufactured by collapsing a base material having a stress applying glass rod placed at a position and a quartz rod circumscribing the core glass rod. In the manufacturing method, an auxiliary burner that moves in the axial direction of the rotated base material heats the base material to reduce its diameter, and each external contact point of the core glass rod, stress-applying glass rod, and quartz rod; The jacketed quartz tube, the stress-applying glass rod, and each contact point of the quartz rod are fused together, and then moved in the axial direction of the base material and heated completely with a main burner having a higher heating temperature than the auxiliary burner. It is characterized by collapsing.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the method for manufacturing a preform for a polarization-controlled optical fiber according to the present invention. A base material in which the core glass rod 3, the stress-applying glass rod 2.2, and the quartz rod 4.4.4.4 are arranged in the jacket quartz tube 7 is set on the support stand 11 of the collapse device 10. While vacuuming the inside of the base material from one end, for example, in the direction of arrow A, rotate it in the direction of arrow B. In this state, for example, turn on the auxiliary burner 12 at a constant speed from the right side of FIG. The base material is preheated at about 1600° C. while being moved in the axial direction of the base material, for example, in the direction of arrow C, and the diameter of the base material is reduced, and the core glass rod 3 and the stress applying glass rod 2.2 are The outer contact points of the quartz rod 4.4.4.4 and the contact points between the jacketed quartz tube 7 and the stress-applying glass rod 2.2 and the quartz rod 4.4.4.4 are then fused.

Next, while moving the main burner 13 following the auxiliary burner 12 at the same speed and in the same direction as the auxiliary burner 12, the base material is heated to about 1900°C and completely collapsed. Reference numeral 14 is a second auxiliary burner,
This is for supplementary heating to prevent the preform collapsed by the main burner 13 from cooling and cracking.

In the method for manufacturing a preform for a constant polarization optical fiber of the present invention, the base material is prepared in advance by the auxiliary burner 1.
2 at about 1600° C., and while reducing the diameter of the base material, each external contact point of the core glass rod 3, the stress-applying glass rod 2.2, and the quartz rod 4.4.4.4, and the jacket quartz tube 7
and stress-applying glass rod 2.2 and quartz rod 4.4.4.
The stress applying glass rod 2.2 is completely molten near the main bar 13 following this auxiliary burner 12 and is in a fluid state, but has not yet been heated. Prevents it from flowing into the upstream void. That is, each of the fused outer contacts and each contact serves as a leakage prevention stopper that prevents the stress-applying glass rod 2.2 in the flowing state from flowing out to the unheated upstream side. , the volume of the stress-applying glass rod 2.2 per unit volume does not become uneven due to bending in the longitudinal direction of the fiber, and the cross-sectional shape of the stress-applying portion becomes uneven in the longitudinal direction. There is no.

Here, two specific examples will be shown.

Specific Example-1 A core glass rod 3, a stress-applying glass rod 2.2, and a quartz rod 4.4, 4.4 each having an outer diameter of 5.5 mm are used as shown in Fig. 2 (outer diameter 26 cm, inner diameter It was housed in a jacketed quartz tube 7 of No. 18 Tsuru, and heated and collapsed using an auxiliary burner 12 and a main burner 13 installed 50 m behind the auxiliary burner 12. Firepower is H1
-50j/sin, 0x-171/sin, the thermal power of the main burner 13 is H*-901/ale, Ox-301/
win, and both moving speeds are 1 m/win.

A cross-section of a polarization-controlled optical fiber obtained by drawing the polarization-controlled optical fiber preform obtained in this way is shown in FIG.
Incidentally, the cross section of the constant polarization optical fiber was examined over four sections, but no non-uniformity in shape was observed. 4 and 5 are comparative examples, which were obtained by a conventional method without using the auxiliary burner 12. Incidentally, Fig. 4 shows a cross section of a polarization-constant optical fiber obtained by drawing the collapse starting part.
FIG. 5 shows what is obtained from the end section, in particular FIG. 5 shows that the stressing glass rod 2.2 flows out into the unheated upstream cavity.

Specific Example 2 A core glass rod 3 with an outer diameter of 3.6 mm, a stress applying glass rod 2.2 with an outer diameter of 9.1 mm, and a glass rod 2.2 with an outer diameter of 9.1 mm. IM quartz rod 4
a, 4a and quartz rods 4b, 4b with an outer diameter of 3.6
5, housed in a jacketed quartz tube 7 with an inner diameter of 23 cm as shown in FIG. The moving speed of is set to 0.6-/in. Figure 7 shows a cross section of a polarization-controlled optical fiber obtained by drawing the preform obtained in this way. No non-uniformity in cross-sectional shape was found.

〔Effect of the invention〕

As described above, according to the method for manufacturing a preform for a polarization-controlled optical fiber of the present invention, the auxiliary burner is placed before the main burner, and the contact portions of each member constituting the base material are fused in advance. To obtain a preform for a polarization optical fiber having a uniform cross-sectional shape in the longitudinal direction of the fiber by preventing a stress-applying glass rod that is in a molten state and easily flowing from flowing out to an unheated upstream portion. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the method for manufacturing a preform for a constant polarization optical fiber according to the present invention, FIG. 2 is a cross-sectional view of a base material according to the present invention, and FIG. FIGS. 4 and 5 are cross-sectional views of polarization-controlled optical fibers obtained by preforming the base material of FIG. 2 according to the present invention and drawing the preform, respectively. A cross-sectional view of a constant polarization optical fiber obtained by refurbishing and drawing the same, FIG. 6 is a cross-sectional view of a base material of another configuration, and FIG. 7 is a cross-sectional view of the base material of FIG. 6 using the method of the present invention. FIG. 2 is a cross-sectional view of a polarization-constant optical fiber obtained by forming a preform and drawing the preform. 2...Glass rod for applying stress 3...Glass rod for core 4...Quartz rod 7...Jacket quartz tube 12-...Auxiliary burner 13-...
...Main burner No. 10 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6

Claims (2)

[Claims] (1) A core glass rod having a core portion and a cladding portion placed in the center of the jacketed quartz tube, and stresses placed in circumscribed positions around the core glass rod and symmetrically around the core glass rod. In a method for manufacturing a preform for a polarization constant optical fiber, the preform for a polarization constant optical fiber is manufactured by collapsing a base material having a glass rod for imparting and a quartz rod circumscribing the glass rod for the core. The base material is heated by an auxiliary burner that moves in the axial direction of the base material to reduce its diameter, and the outer contact points of the core glass rod, the stress-applying glass rod, and the quartz rod, the jacket quartz tube, and the The stress-applying glass rod and each contact point with the quartz rod are fused and then moved in the axial direction of the base material and heated with a main burner having a higher heating temperature than the auxiliary burner to completely collapse. A method for manufacturing a preform for polarization-constant optical fiber. (2) Manufacturing a preform for a constant polarization optical fiber according to claim 1, wherein the base material is heated while the main burner and the auxiliary burner are moved in the same direction at a constant speed. Method.