JPS5884137A - Manufacture of optical fiber retaining polarized light - Google Patents

Abstract

PURPOSE:To manufacture an optical fiber retaining polarized light sufficiently and causing no large loss when coupled to laser, etc. by putting a glass rod with a high refractive index in an elliptical glass pipe having a glass layer formed on the inner wall and by making the pipe solid. CONSTITUTION:A high purity quartz glass layer 12 contg. B2O3 or the like is formed on the inner wall of a quartz glass pipe 11 having a circular hollow part by a chemical vapor deposition method, and a glass pipe having an elliptical hollow part is formed by making the internal pressure of the pipe 11 lower than the external pressure and heating the pipe 11. A high-purity quartz glass rod 14 contg. GeO2 or the like and having a refractive index higher than that of the layer 12 is put in the hollow part of the formed glass pipe, and the pipe is shrunk by heating from the outside of fill the gap between the pipe and the rod 14. Thus, a base material for an optical fiber having an elliptical clad and a circular core is obtd. By heating and drawing the rodlike glass as the base material, an optical fiber is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a polarization-maintaining optical fiber used in optical communications, optical sensors, and the like.

There is a strong need for the development of optical fibers that guide light while maintaining polarization, as they are the key to enabling future optical heterodyne communications, along with single-frequency stabilized lasers.

Polarization preserving optical fibers have been developed so far.

Two layers, a glass layer with a low refractive index and a glass layer with a high refractive index, are formed on the inner wall of a glass tube having 9 circular hollow parts by a method commonly called internal CVD method (inner sealing is chemical vapor deposition method). Furthermore, the internal pressure of the glass tube is made lower than the external pressure of the glass tube, and the glass tube is heated to transform it into a glass tube having an elliptical hollow portion.

The product was further heated and solidified to obtain a rod-shaped optical fiber preform, which was then drawn and produced. The optical fiber produced by the above method has an elliptical core and is usually manufactured with a major axis of 10 micrometers and a minor axis of 1.5 micrometers. Optical fibers with such elliptical cores can preserve polarization well, but because of their elliptical shape, there is a problem that large losses are likely to occur when coupling with a laser or when coupling optical fibers together. Zuta.

Therefore, an object of the present invention is to provide a polarization-preserving optical fiber that preserves polarization well and does not cause large losses when coupled with a laser or between optical fibers.

The entire method of manufacturing IPA is provided.

According to the present invention, the first step is to form one layer of glass by chemical vapor deposition on the inner wall of a glass tube having nine circular hollow parts, and the internal pressure of the glass tube formed in the first step is controlled. a second step of heating the glass tube at a temperature lower than the external pressure and transforming it into a glass tube having an elliptical hollow portion; a third step of inserting a glass rod having a refractive index higher than that of the glass layer; and a third step of inserting a glass rod having a refractive index higher than that of the glass layer, and inserting glass so as to fill the gap between the glass tube having the oval hollow part and the inserted glass rod. A fourth step of heating the tube is obtained.

Next, the present invention will be explained using the drawings.

FIG. 1 is a diagram showing the cross-sectional shape of a polarization-maintaining optical fiber manufactured by a conventional method. In the figure, 11 is a quartz glass tube, 12 is a cladding portion formed by chemical vapor deposition, and 13 is a core portion formed by chemical vapor deposition. In the conventional method, as described above, after forming a glass film corresponding to the cladding part 12 and a glass film corresponding to the core part 13 on the inner wall of the starting quartz tube having a circular hollow part, the pressure inside the tube is lowered than the external pressure. As is well known, optical fibers that undergo heating are
The plane of polarization is well preserved. However, in a polarization maintaining optical fiber having an elliptical core, the light intensity distribution is also elliptical.

When coupling with a laser or connecting optical fibers together, losses tend to increase.

FIG. 2 is a diagram showing the cross-sectional shape of a polarization-maintaining optical fiber manufactured by the present invention. In the figure, reference numeral 14 indicates a core portion made of a glass rod inserted as described later. The cross-sectional shape of the polarization-maintaining optical fiber manufactured according to the present invention is such that the core portion 14 is approximately circular, but the cladding portion 12 is elliptical. Such elliptical clad circular core optical fibers enhance the birefringence effect of the core due to strain forces on the core due to the asymmetry of the cladding. Due to the above effect, it has been expected that an elliptical clad circular core optical fiber preserves the plane of polarization, but this has not been realized due to the lack of a manufacturing method. Since the light intensity distribution of such an optical core is approximately circular, the loss does not become so large even when coupled with a laser or when connecting optical fibers together.

FIGS. 6(a) to 6(,) are diagrams showing cross-sectional shapes in each step according to the present invention. In the figure, 11 is the starting quartz tube;
12 is glass corresponding to the cladding portion.

14 is glass corresponding to the core portion. According to the first step of the present invention, a glass tube 1 is prepared as shown in FIGS.
A glass layer 12 is formed inside the glass tube 1, and in the second step, the shape of the glass tube becomes an ellipse as shown in Figure (C). Next, in the third step, the glass rod 14 corresponding to the core is inserted as shown in Figure (d), and then in the fourth step, as shown in Figure (,).
The glass tube is heated and shrunk from the outside to form an elliptical clad circular core optical fiber. The rod-shaped glass produced through the above steps is further heated and stretched to become an optical fiber. The optical core fiber manufactured by the above method has an elliptical cladding and a substantially circular core as described above.Next, the manufacturing conditions of the optical fiber actually manufactured according to the present invention will be explained.Fifth. The starting quartz tube shown in figure (a) has an outer diameter of 14 mm and an inner diameter of 12 mm.

A typical internal fitting of 1 meter in length is mounted on a glass lathe used in chemical vapor deposition. Next, high-purity quartz glass containing about 2% 132o3i is applied internally by chemical vapor deposition to a thickness of about 0.5 layer.
The film is deposited to a thickness of .l, and the first step is performed. Next, lower the internal pressure of the quartz tube by about 10 H20 compared to the external pressure.99
The quartz tube is heated to 1700° C. and the second step is performed. next.

A high-purity quartz glass rod with an outer diameter of 0.5 mm containing about 5% of Gem, f is inserted into the oval tube, and the third step is performed. Next, heat the quartz tube again until it reaches 1800℃.
A fourth step is performed so that the hollow space between the quartz tube and the inserted quartz glass rod disappears. Ge02f used here is about 0
% of high purity quartz glass rods are manufactured by the well-known soot method. The soot method refers to Ge in an oxyhydrogen flame.
Ct.

In this method, a gas containing 44% of 5iC and 5iC is flowed to grow the mixed soot of GeO2 and SiO□ produced by a heated hydrolysis reaction in the axial direction, and then introduced into a high-temperature sintering furnace to obtain a transparent glass rod. The outer diameter of the rod-shaped glass base material produced through the fourth step is approximately 9 mm, and the major axis of the cladding is 6 mm.
Otas + 3 short diameters of the cladding, and a core diameter of about 0.5 mm, and is further heated and stretched to have an outer diameter of 125 μm and a core diameter of 7 μm.
fiber.

In this example, the cladding dopant is B2O3,
Although Ge02f was used as the core dopant, it is clear that the present invention does not limit the type of dopant.

In this embodiment, a glass rod manufactured by the soot method is used as the glass rod used for the core, but it is clear that the present invention does not limit the method of manufacturing the glass rod, although a plasma method may also be used.

As is clear from the above explanation, by using the present invention, polarization can be well preserved and the laser

[Brief explanation of drawings]

FIG. 1 shows the cross-sectional shape of a polarization-maintaining optical fiber manufactured by the conventional method, and FIG. FIGS. 3A to 3E are diagrams showing the cross-sectional shape of a polarization-maintaining optical fiber manufactured according to the present invention, and FIGS. 3A to 3E are diagrams showing the cross-sectional shape of the fiber preform at each step of the present invention. Figure 1 7 Introduction 2

Claims (1)

[Scope of Claims] 1. A first step of forming a glass layer on the inner wall of a glass tube having a circular hollow portion by chemical vapor deposition. a second step of reducing the internal pressure of the glass tube formed in the first step to be lower than the external pressure of the glass tube and heating the glass Wt to transform it into a glass tube having an elliptical hollow portion; a third step of inserting a glass rod having a refractive index higher than the refractive index of the glass layer into the glass tube having the elliptical hollow portion; and a fourth step of heating the glass tube so that the σ gaps between the rods are filled. Below margin