JPH06180404A - Silica-based optical fiber with expanded core end and method for manufacturing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide an optical fiber that can be coupled with an optical element or an optical circuit having a substantially rectangular light emitting surface with extremely high efficiency. [Structure] Central circular core 2 and clad layer 3 around the core
And the low-refractive-index portions 4 and 4 arranged symmetrically on both sides of the core 2
The optical fiber 1 is formed by enlarging the core end surface 21 at one end into a substantially rectangular shape having different dimensions in the direction perpendicular to the cross section, and the core end surface 22 at the other end is formed by the dimension of the circular core 2 that is not enlarged. The refractive index of each part of the optical fiber 1 is in the order of the core 2, the clad layer 3, and the low refractive index part 4. [Effect] Since the mode field pattern of the expanded core end face 21 of the optical fiber 1 is formed similar to or congruent with the mode field pattern of the light emitting surface of the optical element or the optical circuit, the coupling efficiency is high and the optical module is highly functionalized. Contributes to miniaturization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an expanded core end suitable for highly efficiently coupling an optical element or optical circuit having a non-circular light emitting surface with an end of a silica-based optical fiber having a circular core. The present invention relates to a quartz optical fiber and a method for manufacturing the same.

[0002]

2. Description of the Related Art A silica-based single-mode optical fiber widely used for optical communication has a core portion doped with an additive to raise the refractive index of the core or a lower refractive index of the cladding layer. It is common to dope an additive to make the relative refractive index difference Δ between the core and the clad about 0.3%. The mode field diameter, which is a light propagation field of such a single mode optical fiber, is very small, for example, about 6 μm at a wavelength of 0.85 μm and about 10 μm at a wavelength of 1.3 μm. Also, when it is necessary to increase the energy density of light in the optical fiber, a single mode optical fiber in which the relative refractive index difference Δ is made larger than the above value and the mode field diameter is thin is used. The mode field diameter of is smaller and smaller because the relative refractive index difference Δ is increased.

When a single mode optical fiber having such a small mode field diameter and a light emitting element are coupled,
Generally, for example, as shown in FIG. 5, a plurality of spherical optical lenses 9, rod lenses (not shown), and the like are arranged between the light emitting element 8 and the single mode optical fiber 101 so that the light from the light emitting element 8 is in single mode. The light is focused on the mode field portion 102 of the optical fiber 101. However, since the mode field 81 of the light emitting element 8 has a substantially rectangular pattern instead of a circular shape, and the emission angle of light from the mode field 81 of the light emitting element 8 differs in the horizontal direction and the vertical direction, When the emitted light of (1) was incident on the mode field portion 102 of the optical fiber 101 having a circular mode field pattern, the light incident efficiency was extremely low. Further, the light emitted from the light emitting element 8 is narrowed down by the spherical optical lens 9 or the like and the single mode optical fiber 1 of several μm is used.
In order to align the optical axis with the 01 mode field section 102, highly accurate adjustment work was required.

Recently, direct coupling between a single mode optical fiber and a light emitting element has also been studied. For example, FIG. 6 shows a mode field 71 on the light emitting surface of the optical waveguide 7 of the optical circuit element 6 and the single mode optical fiber 1.
This is a case where the mode field 102 of the core 01 is directly connected. However, also in this case, the mode field 71 of the optical waveguide 7 has a substantially rectangular pattern, whereas the mode field 10 of the optical fiber 101 has a substantially rectangular shape.
Since the pattern 2 is circular and the mode field pattern on the connection surface between the optical waveguide 7 and the optical fiber 101 is asymmetric in the direction perpendicular to the connection surface, the optical connection becomes discontinuous at the connection surface and the optical connection is established. There was the inconvenience of causing losses.

Therefore, in order to solve the above-mentioned problems, the quartz single mode optical fiber is locally heated to expand the core diameter of the heated local area into a circular shape, and the quartz having the expanded core diameter portion as the connection end is used. System single-mode optical fiber has been studied. FIG. 7 is a cross-sectional view of a silica single mode optical fiber 201 in which the core diameter at one end is enlarged in a circular shape. 202 is a core, 204 is a circularly enlarged core end surface, and 203 is a clad. It is a layer.

[0006]

The above-mentioned optical fiber in which the diameter of the end core is enlarged in a circular shape is obtained by passing the light through the light emitting element having a substantially rectangular mode field pattern on the light emitting surface and a spherical optical lens. If they are coupled with each other, or if they are directly coupled with an optical waveguide having a substantially rectangular mode field pattern, it has the effect of facilitating optical axis alignment between the mode field portion of the optical fiber and the light emitting element or the mode field portion of the optical waveguide. , The binding efficiency was not yet improved. The reason for this is that when light is incident from the light emitting element through the lens to the end face of the circular expansion core of the optical fiber, the mode field pattern of the incident light has a substantially rectangular shape which is asymmetrical in the right-angle direction. Since the mode field pattern on the end face of the expanded core has a circular shape symmetrical with respect to the perpendicular direction, discontinuity occurs in the optical connection at the coupling surface, resulting in a decrease in coupling efficiency. Similarly, when the optical waveguide and the end face of the expanded core of the optical fiber are directly connected,
Since there is a difference in the mode field pattern in the direction perpendicular to the connection surface between the optical waveguide with the substantially rectangular mode field pattern and the expanded core end surface of the optical fiber with the circular mode field pattern, there is a discontinuity in the optical connection at the connection surface. As a result, the connection loss was increased.

The present invention is intended to solve the above problems, and facilitates the optical axis alignment at the coupling surface between the mode field of the light emitting element or the optical circuit element and the mode field of the optical fiber, and The present invention provides a silica-based optical fiber with an expanded core end capable of significantly improving the coupling efficiency of the above, and a method for manufacturing the silica-based optical fiber with an expanded core end. It is a thing.

[0008]

The first aspect of the present invention is as follows.
In a silica-based optical fiber in which the core size of one end of a silica-based optical fiber with a circular core is expanded, the size of the expanded end of the core of the silica-based optical fiber is two directions orthogonal to the cross-section of the silica-based optical fiber core. It is an object of the present invention to provide a silica-based optical fiber having an expanded core end characterized by having different lengths.

A second aspect of the present invention is to add a dopant to the core portion so that the refractive index of the core portion is higher than the refractive index of the cladding layer around the core portion, or the dopant is added to the cladding layer. The refractive index of the clad portion is made lower than that of the core portion, and a dopant is added to the clad layers at symmetrical positions on both sides of the core portion to form a low refractive index portion having a lower refractive index than the clad layer. By constituting a quartz optical fiber, by heating the local portion of the silica optical fiber and diffusing the dopant added to the core portion or the clad layer and the low refractive index portion, the dimension of the core portion of the heating local portion is A method for manufacturing a silica-based optical fiber having an enlarged core end, wherein the core cross-section is expanded to different lengths in two directions orthogonal to each other, and the expanded core portion is used as a core end. In the door.

[0010]

The silica-based optical fiber in which the end face of the core at one end of the present invention is enlarged has a substantially rectangular shape in which the mode field pattern of the enlarged end core has different lengths in two directions orthogonal to the cross section of the core. When coupled with a light emitting element or optical circuit element having a similar substantially rectangular mode field pattern, the mode field pattern on the end face of the expanded core of the optical fiber is set to the mode of the light emitting element or optical circuit element. If formed in a pattern similar to the field pattern, the connection loss at the connection portion is greatly reduced and the coupling efficiency is improved. Therefore, it contributes to the sophistication and miniaturization of the functions of the optical module and the like. Further, if the mode field pattern on the end face of the expanded core of the optical fiber is formed in a pattern congruent with the mode field pattern of the light emitting element or the optical circuit element, the coupling efficiency is further improved. on the other hand,
Since the core end surface of the optical fiber opposite to the expanded core end portion remains in the unexpanded circular shape, it has excellent connectivity with other optical fibers of the same shape.

In the method for producing an optical fiber according to the present invention, a dopant is added to the core or the clad of the optical fiber to increase the refractive index of the core above the refractive index of the clad, and
An optical fiber is formed by adding a dopant to the clad layers at symmetrical positions on both sides of the core to provide a low refractive index portion lower than the refractive index of the clad, and locally heating the optical fiber at a predetermined temperature and time. Thus, the dopant added to the core or the clad and the low refractive index portion is diffused in the direction perpendicular to the low refractive index portions arranged on both sides of the core, and an optical fiber having a mode field pattern of different lengths in two directions perpendicular to the core cross section is obtained. It is manufactured. Therefore,
The diffusion of the dopant is adjusted by changing the settings of the optical fiber structure parameters, heating local heating temperature, and heating time, and the length of the mode field pattern in the direction perpendicular to the low refractive index portions arranged on both sides of the core is set appropriately. can do.

[0012]

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

FIG. 1 is a cross-sectional view of a silica-based single mode optical fiber 1 having an enlarged core size at one end according to an embodiment of the present invention. As shown in the figure, the optical fiber 1
Is a circular core 2 at the center and its outer peripheral cladding layer 3 and core 2
Of the optical fiber 1, the core end surface 21 at one end of the core 2 is expanded into a substantially rectangular shape having different dimensions in the direction perpendicular to its cross section. The formed core end surface 22 at the other end has the same size as the unexpanded circular core 2. The refractive index of each part of the optical fiber 1 is the highest in the core 2, the clad 3 and the low refractive index part 4 in that order.

As an example of the structure of the silica type single mode optical fiber 1 of the above embodiment, for example, the circular core 2 has a diameter of 6 μm.
m, the outer diameter of the cladding layer 3 is 125 μm, the low-refractive-index portion 4 has a diameter of 18 μm, and the dimension of the enlarged core end face 21 is 6 μm × 14 μm. The material of the optical fiber 1 respective sections, such as those circular core 2 having a GeO ₂ dopant was added 0.3% to Si0 _2, cladding layer 3 is Si0 _2, the low refractive index portion 4 dopants Si0 ₂ 15 mol of B is added.

FIG. 2 is an explanatory view of a heating process for manufacturing the silica type single mode optical fiber 1 of the present invention in which the core size of one end is enlarged. Fix the fiber 1 between the fixtures 11 and 11,
The central portion of the optical fiber 1 is heated at a temperature of about 1500 ° C. to 2000 ° C. for 1 to 20 minutes by a heating means 10, for example, a gas burner of a mixed gas of propane gas and oxygen, and then cooled, and the central portion of the heating local portion is cooled. The optical fiber 1 having the enlarged core end face 21 is obtained by cutting with a cut surface and polishing the cut surface.

FIG. 3 is an explanatory view showing a state in which the silica single mode optical fiber 1 having an enlarged core size at one end of the present invention and the optical circuit element 6 are directly connected. Optical circuit element 6
Light emitted from the light emitting surface 71 of the optical waveguide 7 is incident on the end face 21 of the expanded core of the optical fiber 1 which is directly joined.

FIG. 4 shows a silica single mode optical fiber 1 and a light emitting element 8 according to the present invention, in which the core size at one end is enlarged.
It is an explanatory view of the state where and are connected through the ball lens 9.
The light emitted from the light emitting surface 81 of the light emitting element 8 is the spherical lens 9
The light is focused on the end face 21 of the expanded core of the optical fiber 1.

Next, a silica-based single-mode optical fiber whose core size at one end is enlarged according to the manufacturing example of the present invention and a silica-based single-mode optical fiber whose core size at the one end is enlarged according to the conventional example are circular. The comparative measurement results of the connection loss when combined with the optical circuit element and the light emitting element will be described.

-Example 1- Core diameter: 6 μm, cladding layer outer diameter: 125 μm, diameter of low refractive index portions provided on both sides of the core: 18 μm, core material: S
Add 0.3% of GeO ₂ to i0 ₂ , clad layer material: S
i0 ₂ , low-refractive-index material: A silica-based single-mode optical fiber in which 15 mol of B was added to SiO ₂ was used, and the local part of this optical fiber was heated at 1800 ° C. for 10 minutes, and the mode field dimension of the end face of the expanded core was 6 μm. An optical fiber of × 14 μm was manufactured.

[0020] - Comparative Example 1 Core diameter: 6 [mu] m, a cladding layer outside diameter: 125 [mu] m, the core material: Si0 ₂ in addition of GeO ₂ 0.3%, cladding layer material: Si0 using ₂ silica based single-mode optical fiber , The mode field size of the end face of the expanded core is 14μ in diameter
m optical fiber was manufactured.

-Measurement of Connection Loss (A) -In each of the optical fibers of Example 1 and Comparative Example 1 described above, an optical circuit element optical waveguide having a mode field size of 3 μm × 7 μm at the light emitting surface of the end face of the expanded core of the optical fiber Directly emitted from the optical circuit element to emit light having a wavelength of 850 nm,
The splice loss at the joint was measured. The measurement results are shown in Table 1.

Example 2 The same silica-based single mode optical fiber as in Example 1 was used, and the local part of this optical fiber was heated at 1800 ° C. for 15 minutes, and the mode field size of the end face of the expanded core was 6 μm ×.
An 18 μm optical fiber was manufactured.

-Comparative Example 2-Using the same silica-based single mode optical fiber as in Comparative Example 1, the mode field dimension of the end face of the expanding core is 18 μm in diameter.
m optical fiber was manufactured.

-Measurement of Splice Loss (B) -In each of the optical fibers of Example 2 and Comparative Example 2, light having a wavelength of 850 nm was emitted from a light emitting element having a mode field size of 1 μm × 3 μm on the light emitting surface through a spherical lens. The end face of the expanded core of the fiber was made to receive light, and the connection loss at the connection portion at this time was measured. The measurement results are shown in Table 1.

As can be seen from the measurement results of Table 1, when the optical fiber having the enlarged core end face of the present invention is connected to the optical circuit element or the light emitting element, the connection loss at the coupling portion can be greatly reduced.

[0026]

[Table 1]

[0027]

As described above, the optical fiber having the one end face of which the core cross-section is enlarged has the feature that the size of the mode field pattern of the end face core of the light emitting surface of the optical circuit element or the light emitting element to be coupled. Since it is formed similar to or congruent with the mode field pattern, the coupling efficiency is high, and the function of the optical module or the like can be enhanced or downsized.

The optical fiber manufacturing method of the present invention is
Dopants are added to the low refractive index portions at symmetrical positions on both sides of the core or the clad and the core to form an optical fiber, and the local portion of this optical fiber is heated at a predetermined temperature for a very short time. The length of the mode field pattern perpendicular to the arranged low refractive index portion can be appropriately set to a required length.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical fiber having an enlarged core size at one end according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a heating process for manufacturing the optical fiber of the present invention.

FIG. 3 is an explanatory diagram showing a state in which an optical fiber having an enlarged core size at one end of the present invention and an optical circuit element are directly connected.

FIG. 4 is an explanatory diagram showing a state in which an optical fiber having an enlarged core size at one end of the present invention and a light emitting element are connected through a lens.

FIG. 5 is an explanatory diagram showing a state in which a conventional optical fiber and a light emitting element are connected through a lens.

FIG. 6 is an explanatory diagram of a state in which a conventional optical fiber and an optical circuit element are directly connected.

FIG. 7 is a cross-sectional view of a conventional optical fiber in which the core size at one end is enlarged in a circular shape.

[Explanation of symbols]

 1 Optical Fiber 2 Core 3 Clad 4 Low Refractive Index Part 21 Expanded Core End Face 22 Non-Expanded Core End Face 6 Optical Circuit Element 7 Optical Waveguide 71 Optical Waveguide Light Emitting Surface 8 Light Emitting Element 81 Light Emitting Element Light Emitting Surface 9 Lens 10 Heating Means 11 Fixed Ingredient

Claims (2)

[Claims] 1. A core end portion of a silica-based optical fiber having a circular core, wherein the core size on one end side is formed to have different lengths in two directions orthogonal to the cross-section of the silica-based optical fiber core. Expanded silica optical fiber. 2. A dopant is added to the core portion to increase the refractive index of the core portion higher than the refractive index of the cladding layer around the core portion, or a dopant is added to the cladding layer to adjust the refractive index of the cladding layer to the core portion. Lower than the refractive index of
A silica-based optical fiber is formed by adding a dopant to symmetrical positions in the clad layers on both sides of the core part to form a low-refractive-index part having a lower refractive index than the clad layer, and a local part of the silica-based optical fiber is formed. By heating and diffusing the dopant added to the core portion or the clad layer and the low refractive index portion, the dimension of the core portion of the heating local portion is expanded to different lengths in two directions orthogonal to the cross section of the core, A method for manufacturing a silica-based optical fiber having an expanded core end, wherein the expanded core is used as a core end.