JPH04220609A - Method for forming spot size converting portion - Google Patents

Abstract

PURPOSE:To enable local heating for forming a core enlarged portion by subjecting only that portion of the optical waveguide line at which its core is enlarged to laser beam machining. CONSTITUTION:The diameter of a core 9 positioned near the end portion of an optical waveguide line is made larger than the core diameter of the portion of the optical waveguide line positioned in other positions so as to form a core enlarged portion and also the core refractive index at the core enlarged portion is made lower than that at the portion of the optical waveguide line in other positions except those near the end portion and one part of the optical waveguide line is heated by laser 7 at the time of forming a spot size converting portion which enlarges spot size at the core enlarged portion. In this case, the higher the power with which CO2 laser 7 for example is applied, the larger the core diameter of the core enlarged portion is and the lower the refractive index of the core becomes. The spot size of waveguide light at the core enlarged portion is therefore enlarged by raising the power with which the CO2 laser 7 is applied.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention provides a method for forming a spot size converter with good manufacturability and reproducibility.

0002

2. Description of the Related Art Generally, the spot size of a conductor light in a semiconductor optical device such as a semiconductor optical modulator and the spot size of a single mode optical fiber are several times different. Therefore, if the semiconductor optical device and this optical fiber are directly coupled as they are, coupling loss will occur.

In order to reduce this coupling loss, there is an optical fiber in which the spot size of the core near the end of the optical fiber is enlarged. In other words, as shown in FIG. The core diameter near the end portion is wide, and the refractive index of the core near the end portion is lower than that of the core 1 at other portions. Therefore, the spot size of the enlarged core portion 3 near the end is larger than that of a conventional single mode optical fiber.

[0004] Conventionally, as a method for manufacturing this expanded core optical fiber, a method has been used in which an optical fiber 5 is heated using a thermal diffusion furnace 4, as shown in FIG. That is, by putting the optical fiber 5 into the thermal diffusion furnace 4 and keeping it at high temperature with the heater 6, the substance that makes the refractive index of the core 1 higher than the refractive index of the cladding 2 is diffused into the cladding. be done. As a result, the core diameter is enlarged and the refractive index of the core is lowered, making it possible to enlarge the spot size of the guided light. By cutting this optical fiber midway,
It is possible to produce an optical fiber with a core enlargement 3 formed at its end.

However, in this method, the entire optical fiber is placed in a thermal diffusion furnace over a certain length and heated, so it is difficult to heat only a small portion of the optical fiber whose core is to be expanded. Moreover, since the heating area is large and local heating is not possible, it is practically impossible to heat only the light output end or the light input end of the silica-based optical waveguide and enlarge the core of only that end. With this conventional manufacturing method, it was not possible to enlarge the core only at the light input or light output end of the silica optical waveguide.

An object of the present invention is to provide a method for forming an expanded core optical fiber or an expanded core optical waveguide by heating only a small portion of the optical waveguide or optical fiber.

[0007]

[Means for Solving the Problems] The present invention, which achieves the above-mentioned objects, forms a core enlarged portion by enlarging the core diameter near the end of the optical waveguide compared to the core diameter at a portion other than the end. In addition, in the method for forming a spot size converting portion, the core refractive index of the core enlarged portion is made lower than the core refractive index of a portion other than the vicinity of the end portion, and the spot size in the core enlarged portion is increased. In forming the optical waveguide, a part of the optical waveguide is heated by a laser.

[0008]

[Operation] By using a high-power laser such as a carbon dioxide (CO2) laser, only a small portion of the optical waveguide or optical fiber can be heated.

FIG. 1 shows an embodiment in which the present invention is applied to a silica-based optical waveguide. Figure 1 uses a CO2 laser 7,
The waveguide end of the quartz optical waveguide formed on the substrate 8 is heated. Since this embodiment uses a high-power CO2 laser, for example, unlike a conventionally used thermal diffusion furnace, the core 9 or It became possible to heat the cladding 10.

FIG. 2 shows the relationship between the optical output (P) of the CO2 laser and the spot size of the core enlarged portion when the irradiation time is constant. As can be seen from the figure, CO
2. The higher the laser irradiation power, the larger the core diameter of the core enlarged portion and the lower the refractive index of the core. Therefore, Figure 3
If the irradiation power of the CO2 laser 7 is increased as shown in FIG. In addition, these high-power lasers for heating can easily control the optical output, heating time, heating position, etc. accurately using a computer, so they have the advantage of being able to accurately produce large quantities of babies, including the tapered shape of the core expansion part. be. Furthermore, it is also possible to melt the tip of the quartz-based optical waveguide and form a lens at the tip of the expanded core portion of the optical waveguide.

[0011] The above description has been made by taking a quartz-based optical waveguide as an example of the optical waveguide, but it goes without saying that the present invention can also be applied to optical fibers.

0012

Effects of the Invention As explained above, the present invention expands the core and reduces the refractive index by heating the optical waveguide or optical fiber with a high-power laser suitable for microfabrication. It is now possible to process only the end of the fiber.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram of laser irradiation power, core diameter, and core refractive index.

FIG. 3 is a characteristic diagram of laser irradiation power and spot size.

FIG. 4 is a structural diagram of an expanded core optical fiber.

FIG. 5 is an explanatory diagram of a heating state by a thermal diffusion furnace.

[Explanation of symbols]

7 CO2 laser 8 Board 9 core 10 Clad

Claims (1)

[Claims] 1. A core enlarged portion is formed by enlarging the core diameter near the end of the optical waveguide compared to the core diameter at a portion other than the end portion, and the core refractive index of the core enlarged portion is set to be the same as that of the end. In the method for forming a spot size converting section that increases the spot size at the core enlarged section by making the core refractive index lower than the core refractive index of a portion other than the vicinity, in forming the core enlarged section, a part of the optical waveguide is 1. A method for forming a spot size converting section, the method comprising: heating the spot size converting section.