JPH0364707A - Manufacture of spot size converting optical fiber - Google Patents

Abstract

PURPOSE:To facilitate the formation and to reduce the connection loss by heating a part of an elliptic core type polarization plane maintaining optical fiber which has noncircular spot size and making its elliptic core round. CONSTITUTION:Quartz soot is provided externally on the outer periphery of a glass rod by an external CVD method or VAD method to obtain calcined glass and at this time, the sectional shape of the worked rod is made noncircular according to its viscosity difference to form the elliptic core 1. Then a glass base material is used as an optical fiber base material and drawn in a drawing furnace into a fiber with the drawing tensile force within a range wherein the initial noncircular sectional shape can be maintained. Then the obtained optical fiber which is as long as desired is prepared and a part of it is heated with a burner to make the core 1 which is in an elliptic shape close to a rectangular shape into a circular core 11 gradually. Consequently, the spot size converting optical fiber which can perform conversion from an ellipse to circular spot size without any loss can easily be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical fiber, and in particular to a method for manufacturing an optical fiber that converts spot size.

[Prior Art] When connecting a thin film guiding waveguide and an optical fiber, if they are joined as is, the connection loss will be large at 7° due to the difference in spot size. Therefore, a spot size converter as shown in FIG. 1 is required, in which the shape of the core changes in the longitudinal direction.

Until now, there was no optical fiber like the one shown in Figure 1, and the spot size of the thin film optical waveguide was made to be as close as possible to the spot size of the optical fiber.

[Problems to be Solved by the Invention] However, the conventional subo-7 size modification method has the following problems.

(1) Direct coupling has a large connection loss.

(2) In the method of coupling through a lens, the dimensions of the entire element (module) become large and the configuration becomes complicated.

(3) In order to bring the spot size of the optical waveguide closer to the spot size of the optical fiber, it is necessary to change the refractive index distribution, the dimensions of the leading waveguide, etc., and the configuration of the leading waveguide becomes complicated.

5. Since the optical waveguide 0 slot I size is non-circular, it is completely 11. : It is not possible to match the spot size of the light beam with the spot size of the iba.

An object of the present invention is to provide a method for manufacturing a spot size conversion optical fiber that is easy to manufacture and has low splice loss, which eliminates the drawbacks of the conventional extraction method.

[Means for Solving the Problems 1] The present invention involves preparing a desired length of an elliptical core front wavefront preserving optical fiber obtained by an external method and a mechanical grinding method, and applying stress to a portion of the length. In this method, the spot size conversion optical fiber is manufactured by gradually making the core cross section circular toward the end face.

External attachment is method, vapor phase shaft attachment is method (VAD method) and external CV
Both methods of D are included.

[Function] In an elliptical core type polarization maintaining optical fiber that originally has a non-circular spot size, the elliptical core becomes rounded when heat is applied. Therefore, when heat is applied to a portion of the length, one end of the core becomes elliptical and the other end becomes a core with a circular cross section, thereby providing a spot size conversion optical fiber in which the spot size can be converted without loss.

In addition, by applying heat, the dopant contained in the core (
Gc) is volatilized, thereby making it possible to increase the spot size even if the core diameter is small.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows the outline of the spot size conversion optical fiber. It uses an elliptical core type polarization maintaining optical fiber with a non-circular spot size, and the elliptical core is rounded by applying a radius to a part of it. It is configured.

Here, a thin film optical waveguide with a wavelength of 1.55 μm and a
．． A description will be given by taking as an example a spot size conversion optical fiber that connects a 55 μm SM optical fiber.

The core size of the thin film optical waveguide is approximately 2 x 5 μm.

The relative refractive index difference is 0.3%, and the spot size is an ellipse of approximately 3×6 μm. On the other hand, the core of an SM (single mode) optical fiber is a perfect circle, with a core diameter of about 10 μm, a spot size of about 12 μm, and a relative refractive index difference between the core and the cladding of 0.3%.

First, we designed and produced the structural parameters of an elliptical core type surface wavefront preserving optical fiber so that it becomes a single mode at a wavelength of 1.55 μm and can be matched with an optical waveguide and an 8M optical fiber. FIG. 2 shows its cross-sectional view.

The core 1 is an almost rectangular ellipse with a major axis diameter of 5 μm and a minor axis diameter of 2 μm, the relative refractive index difference of the elliptical core 1 with respect to the cladding 2 is 0.3%, and the spot size is 3.2 × 6.1 μm. Ta. Such an elliptical core type signal wavefront preserving optical fiber can be obtained by external method and mechanical grinding method, for example, as follows.

That is, both sides of the quartz glass rod serving as the core are removed by machining along the axial direction, and quartz glass, which has a softening point higher than that of the processed rod, is placed around the outer periphery of the resulting processed rod, which has a non-circular cross section. This is a method in which a wire is attached externally to a similar cross-sectional shape, and then a wire is drawn with a drawing tension within a range that maintains the initial cross-sectional shape.

The specific steps of the manufacturing method are as follows: First, a glass rod serving as a core is manufactured using the V^0 method or external CVD method, and then the cross-sectional shape of this core rod is made non-circular by grinding, or a porous glass rod is manufactured. At the soot rod stage, the soot rod is cut into a non-circular shape by, for example, using a cutter heated to a high temperature.

Next, quartz soot is externally attached to the outer periphery of the above-mentioned glass rod (processed rod) by an external CVD method or a VAD method, and sintered and vitrified. During this sintering and vitrification, the cross-sectional shape of the processed rod becomes non-circular due to the viscosity difference, and becomes an elliptical core. Then, the obtained glass base material is shaped by grinding both sides of the quartz glass, or stretched, if necessary.

Incidentally, both open faces may be removed and shaped at the quartz soot stage.

Thereafter, the glass base material is used as an optical fiber base material and is drawn in a drawing furnace with a drawing tension within a range that can maintain the initial non-circular cross-sectional shape to form a fiber.

Another method is to form a glass rod consisting of a core glass layer containing germanium oxide and a cladding glass layer containing fluorine surrounding it, and then machine both open faces of this glass rod along the axial direction. to form a processed rod with a non-circular cross section, glass fine particles having a glass composition having a higher viscosity temperature than the glass layer for cladding are deposited on the outer periphery of this processed rod, and this is sintered in step 1. After forming the glass layer No. 4 and 2, a glass base material having a circular cross section is prepared by cutting off the glass layer No. 42, and the above-mentioned glass layer for cladding is formed around the outer periphery of the glasses fE and H. Forming glass layers with the same composition! 7. The obtained glass preform may be drawn as an optical fiber D° material.

Returning to FIG. 2, the sawn optical fiber 3 obtained in 1- as described above is connected to 5. An OcIm was prepared, and heat was applied to a 2.5 cm portion of the core using a burner, so that the core 1 gradually changed from a nearly rectangular ellipse to a perfectly circular core 11. A cross-sectional view of the heated end face is shown in FIG. The core diameter of core 1j is 3.6μ
Although it is small as m, by adding natural gas, G (3 is vaporized l: ?I>, the spot size is 1
The thickness decreased by 1.2 μm.

The optical fiber 4 thus obtained as a sbot size converter is inserted between the above optical waveguide and the 3M optical fiber, and the optical waveguide side is connected by CO21/-, and the 3M optical fiber side is connected by ordinary fusion splicing. As a result, the connection loss is as low as 0.11 dB),'l
As shown in Figure 2, 3M optical fiber and thin film guided waveguide can be connected with low loss, improving overall system performance.
Two. In addition, since the Subop I/Size converter can be obtained by a simple manufacturing method using an elliptical core type surface wavefront preserving optical fiber that is highly mass-producible, the device itself is low cost and highly mass-producible. Therefore, by changing the lens diameter or the structural parameters of the thin film optical waveguide, a significant cost reduction can be expected compared to an element (module) that couples SM optical fiber ε.7 [Effects of the Invention] As described above, the present invention According to the method, it is possible to easily obtain a spot size conversion optical fiber that can perform the conversion from an ellipse to a circular size without loss.

And according to this spot size conversion optical fiber,
i) Since the M optical fiber and the thin film optical waveguide can be connected with low loss, the performance of the entire system is improved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a spot size conversion optical fiber, Figure 2 is a schematic diagram of a spot size conversion optical fiber.
The figure is a sectional view of an elliptical core type polarization maintaining optical fiber used as a spot size conversion optical fiber, and FIG. 3 is a sectional view showing a portion of the spot size conversion optical fiber to which heat is applied and a circular core is formed. In the figure, 1 is the core of an elliptical core type surface wavefront preserving optical fiber, 2
is Clara F, 3 is elliptical core pear wavefront preserving optical fiber, 4
11 indicates a spot size conversion optical fiber, and 11 indicates a circular core.

Claims (1)

[Claims] 1. Prepare a desired length of elliptical core polarization-maintaining optical fiber obtained by external attachment method and mechanical grinding method, and apply heat to a portion of the length direction to gradually make the core cross section circular toward the end face. A method of manufacturing a spot size conversion optical fiber, characterized in that: