JPS6168336A - Production of parent material for single polarization optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled parent material having superior dimensional accuracy by assembling graphite rods for forming a side pit together with a core rod and a clad material, melting the materials to form one body and then pulling off the graphite rods. CONSTITUTION:A core rod 12 having 5mm outside dia. is inserted into the central part of a quartz jacket tube 11 having 15mm inside dia.; two graphite rods 13 having 5mm outside dia. are inserted to both sides of the core rod; four quartz spacer rods 14 having 5mm outside dia. are inserted into the remaining space, and thin quartz spacer rods 15 are inserted to the space between each rod. Thus, an end of the tube 11 is sealed, and the tube is collapsed by moving an oxyhydrogen burner from the sealed side to another side while evacuating the gaps in the tube 11 from an end opposite to the sealed end of the tube 11. By this method, a compound rod 16 is obtd. by melting the materials except the graphite rods 13 to form one body. Then, the rod 16 is covered with a quartz jacket tube 17, and both ends of the collapsed compound parent material are cut and the graphite rods are pushed out and removed. Thus, the titled parent material 20 having a core rod 12 and side pits 18 axisymmetric to the core rod 12 formed in the clad material 19 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing a base material used in manufacturing a single polarization optical fiber.

[Prior art and its problems]

Recently, a side-pit type optical fiber shown in FIG. 2 has been prototyped as an optical fiber that provides a larger absolute single polarization region. (IEICE Technical Report Vol. 1.82jlo, 1000
QE82-39) This optical fiber has bits 3 (holes, usually air) with a lower refractive index than the cladding 2 on both sides of the core l, and the two orthogonal HE++ modes have different cutoff frequencies. Under certain conditions, only one polarization mode can be transmitted (I! vs. single polarization mode), so it is expected to be applied to sensors, etc.

This optical fiber is made as follows.

That is, a base material 6 consisting of a core 4 and a cladding 5 as shown in FIG. 3 fa+ is prepared, and as shown in FIG. This rod 8
Insert it into the quartz jacket tube 9 as shown in the same figure (C1), and make the groove 7.
While adjusting the air pressure inside the fiber, melting and drawing are carried out in the usual manner to obtain an optical fiber as shown in FIG. Although the groove 7 is rectangular, it becomes circular due to surface tension during the melting process during wire drawing.

However, such a manufacturing method has the following problems.

(l) MJ in the axial direction so that the U-shaped groove is in contact with the core.
It is extremely difficult to grind well. (2) In the drawing process, square holes are made circular by surface tension, but
It is difficult to control the same circular shape, and the difference in the shape and size of the left 4 focal points tends to lead to characteristic deterioration. (3)
The complicated process increases the cost of the optical fiber.

Another method is to use a diamond drill to drill holes axially symmetrically in contact with the core in the cladding part of the base material consisting of the core and cladding, and then melt and draw the holes. It will be done. However, with this method, the machining accuracy of the +11 diamond drill is not sufficient, (2) the core is prone to cracking, (3) it requires polishing the inner surface of the hole, (
4) There are problems such as limited length, making it impractical.

[Means for solving problems and their effects]

The present invention provides a method for manufacturing a base material for a polarized optical fiber that solves the problems of the prior art as described above.
The method is characterized by assembling graphite condos for forming side pits together with core rods and cladding materials, heating and melting them to integrate them, and then extracting the graphite condos to form side pits. It is.

Graphite has good processing accuracy, so graphite 1+ and C with high dimensional accuracy can be easily obtained, and it does not melt even at the melting temperature of quartz. Therefore, by embedding the graphite condo together with the core rod in the cladding 4A, melting and integrating the graphite condo, and then pulling out the graphite condo, a side pit can be formed in the same shape as the graphite condo.

In order to manufacture a brightly polarized optical fiber from the base material manufactured by the method of the present invention, the base material may be drawn as is (with the sides and throat empty), but the side pits are filled with cladding material and thermal expansion. The wire may be drawn with stress applying materials having different coefficients inserted.

〔Example〕

FIG. 1 (al~(C1 shows an embodiment of the manufacturing method of the present invention. First, as shown in ta+, a quartz jacket tube 11
A core rod 12 is inserted into the center of the core rod 12, two graphite rods 13 are inserted on both sides of the core rod 12, and four quartz spacer rods 14 are inserted into the remaining space.The inner diameter of the quartz jacket tube 11 is 15 m. , the outer diameters of the graphite rod 13 and the quartz spacer rod 14 are each 5 mm. Further, a thin quartz spacer rod 15 is additionally inserted into the space between each rod. This is to minimize deformation of the core rod 12 when melted and integrated. The core rod 12 has a slightly higher refractive index than the quartz spacer rods 14 and 15 and the quartz jacket tube 11 that constitute the cladding material.

Next, after sealing one end of the jacket tube 11, while exhausting the gas inside the jacket tube 11 from the other end with a rotary pump, the oxyhydrogen burner is gradually moved from the sealed side to the exhaust side on a glass lathe. Then, collapse is performed. As a result, each member other than the graphite rod 13 is melted and integrated, creating a composite rod with the graphite condo 13 embedded inside.The outer peripheral surface of this composite condo is ground to remove some unevenness. do.

Next, as shown in (bl), a quartz jacket tube 17 is further placed on the outside of the composite rod 16 so that a single mode core diameter can be obtained when it is made into a fiber, and the size is adjusted by collapsing it. Both ends of the composite base material thus obtained are cut using a cutting machine so that both ends of the graphite rod 13 are exposed.

After that, when the graphite rod 13 is pushed out and removed, (C
), it is possible to obtain a single polarization optical fiber preform 20 in which a sight focus 18 axially symmetrical to the core rod 12 is formed in the cladding material I9.

This base material 20 is held at a pressure of 20 to 3
A wire was drawn according to a normal wire drawing method while applying a slight pressure to achieve QmmAq. As a result, the core diameter is 8
A single polarization optical fiber as shown in FIG. 2 with a side pit diameter of 8 μm and a side pit diameter of 8 μm was obtained. Since the side pits were perfectly circular from the time of the base material, their shape did not change during the melting process during wire drawing and remained perfectly circular. In addition, the core, site focus, and cladding of this single polarization optical fiber have extremely stable dimensions in the longitudinal direction.A rod for the core and a graphite condo for forming a tide bit are used for the cladding and a quartz spacer for forming the tide bit. This is because they are clustered adjacent to each other inside the condo and are collapsing.

In the above example, a quartz tube was used as the tube, but
A synthetic rad layer may be formed in advance on this quartz tube by a CVD method.

Further, in the above embodiments, the site pits were formed on both sides of the core rod, but it is also possible to use only one graphite rod and form the side pits only on one side of the core rod.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to
By embedding lead rhofd into the cladding material and extracting it to form side pits, it is possible to manufacture a base material with side pits with extremely high dimensional accuracy in both the cross-sectional and length directions. - It greatly contributes to improving and stabilizing the characteristics of polarized optical fibers. Furthermore, since there is no troublesome and skill-required process such as groove grinding or hole drilling, the manufacturing method is simpler than conventional methods, and the manufacturing cost of single-polarized optical fibers can be reduced.

[Brief explanation of drawings]

FIGS. 1 ial to FC+ are cross-sectional views showing in order of steps a method for manufacturing a preform for a Chinese-polarized optical fiber according to an embodiment of the present invention;
Figure 2 shows a cross section of an example of a side pit type polarized optical fiber.
11T is a sectional view shown in FIG. 11~Quartz jacket tube, 12~Rondo for core, 13~
Male lead rondo, 14 ~ Quartz baser Ronlov 17 ~ Quartz jacket 1 ~ Tube, 18 ~ Sight focus, 19 ~ Clad (A, 20 ~ Base material for single polarized optical fiber.

Claims (1)

[Claims] A single polarized optical fiber characterized in that a graphite rod for forming a side pit is assembled together with a core rod and a cladding material, and after they are heated and melted to be integrated, the graphite rod is extracted to form a side pit. Method of manufacturing base material for use.