JPH03229223A - Quartz system optical fiber - Google Patents

Abstract

PURPOSE:To make a mode field diameter large by providing >=1 outer core which has a lower refractive index than a center core and a clad which has a lower refractive index than the outer core, and incorporating erbium in the center core. CONSTITUTION:More than one outer core 12 which has the lower refractive index than the center core 11 and the clad 13 which has the lower refractive index than the outer core 12 are provided and erbium is incorporated in the center core 11. Thus, not only the center core, but the outer core are provided. Consequently, the mode field having the large diameter is secured to decrease the center core diameter and the erbium is doped in the small-diameter center core to improve light emission efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to a silica-based optical fiber suitable for use in optical amplification.

rPrior Art J A quartz-based optical fiber for optical amplification whose core is doped with erbium (Er) is known, and an example of this optical fiber has the refractive index profile shown in Fig. 5. be.

In the silica-based optical fiber shown in Fig. 5, the diameter of the core 1 is approximately 3 mm, the mode field diameter is approximately 5 mm, and the outer diameter of the cladding 2 (outer diameter of the optical fiber) is 125 mm. .

In the case of such a silica-based optical fiber, the distribution of optical power passing through the waveguide approximates a Gaussian distribution, and the light is excited at the top of the optical power distribution (the area where the optical intensity is maximum). , an erbium atom doped in the core,
It is possible to effectively utilize light emission around a wavelength of 1.53 Bm to amplify light.

However, in the case of a silica-based optical fiber having the refractive index profile shown in Fig. 5, not only is the core diameter as small as approximately 39Lφ, but the mode field diameter is also approximately 5Lφ. Because of its small size, for example, when this is interconnected with a dispersion shifted fiber having a mode field diameter of about 8 strands φ, the connection loss will be as high as 0.3 to 0.5 dB, and this large connection loss becomes a problem.

In view of these technical problems, the present invention aims to provide a silica-based optical fiber that can increase the mode field diameter without reducing the optical amplification function.

1 Means for Solving the Problems j In order to achieve the intended purpose, the silica-based optical fiber according to the present invention has a center core,
It is characterized by comprising one or more 7-outa cores having a refractive index lower than the center core and a cladding having a refractive index lower than the 27-outa cores, and that the center core contains erbium.

[Function j] The silica-based optical fiber according to the present invention has a plurality of refractive index profiles formed by a center core and one or more outer cores.

In the case of such a silica-based optical fiber, since it has not only a center core but also an outer core, it is possible to secure a mode field with a large diameter and reduce the center core diameter. ), the erbium can be effectively used to emit light at a wavelength of around 1.53 g.

In particular, when the mode field diameter is large, doping the center core with erbium can increase the luminous efficiency without reducing the optical power within the mode field.

Embodiment Embodiments of the silica-based optical fiber according to the present invention will be described based on the drawings.

In the silica-based optical fiber illustrated in FIG.

11 indicates the center core, 12 indicates the outer core, 1
3 indicates a cladding, and 14 indicates a covering layer.

The center core 1 is made of, for example, doped quartz containing germanium (Ge) and erbium (Er), and has an outer diameter of about 3 pmφ.

Note that the content of erbium (Er) in the center core 11 is less than toopp fat.

The outer core 12 is made of doped quartz containing fluorine (F), for example, and has an outer diameter of about 8 wells and 1 φ.

The cladding 13 is also made of, for example, doped quartz containing fluorine (F), and the outer diameter of the cladding (=outer diameter of the optical fiber) is 125 mm.

The coating layer 14 has an outer diameter of, for example, 250 mm. Made of gmφ ultraviolet curing resin.

In the silica optical fiber shown in FIG. 1, if the refractive index of the center core 11 is nl, the refractive index of the outer core 12 is 12, and the refractive index of the cladding 13 is n3, then these refractions are nl
> n2 > n3, and the core portion has multiple refractive index profiles.

As a refractive index profile in this case, the center core 11
There are a step type (single mode) shown in FIGS. 2(A) and 2(B), a square distribution type, and a triangular type (not shown in FIG. 1).

The silica-based optical fiber illustrated in FIG. 3 has a center core 11
, multiple 7 Uta cores 121.122, and clad 1
3, and a coating Jij 14 is provided on the outer periphery of the cladding 13.

The silica-based optical fiber in this illustrated example has a plurality of 7 outer cores 1
21.122, but other than that, the first
It is substantially the same as that shown.

In the silica-based optical fiber shown in FIG. 3, the refractive index of the center core 11 is 11, the refractive index of the outer core 12+ is 121,
Is the refractive index of the outer core 122 n2? , when the refractive index of the cladding 13 is n3, these refractions are nl>nH>n
22>n3, and has a refractive index profile as shown in FIG.

In the silica-based optical fiber shown in FIG. 3, the center core 11 may have a refractive index profile such as a square distribution type or a triangular type.

Specific Examples A specific example of the silica-based optical fiber according to the present invention will be described together with an example of its manufacture.

When making the glass rod for the center core.

A quartz-based transparent glass rod uniformly doped with Er: 1100pp and GeO2: 11mo1% was synthesized.
This was heated and stretched to an outer diameter It)s■φ and a length of 200 layers.

When forming the glass for the 7-outa core on the outer periphery of this glass rod, first, soot-like glass particles are deposited on the outer periphery of the glass rod by a flame hydrolysis method using 5iC14 as a raw material.

He: 30Jl/si in an electric furnace with a maximum temperature of 1350℃
n, C12:0.341/s+in, 5iFa:0
．． While supplying 03 sentences/win, a glass rod with a glass fine particle layer was inserted into the electric furnace at a speed of 150 mm/hr to turn the glass fine particle layer into transparent vitrification, and then,
A glass rod with glass for the outer core was heated and stretched to an outer diameter of 71φ.

When forming glass for cladding on the outer periphery of the glass rod with glass for the outer core, first soot-like glass particles are formed on the outer periphery of the glass for the outer core using the flame hydrolysis method described above! IIfJI, then He: 15fL/win, C12: 0.15 in the same electric furnace as above.
While supplying Jl/gin, SiF*: 0.8241/sin, a glass rod with a glass fine particle layer was inserted into the electric furnace at a speed of 150 sn/hr to turn the glass fine particle layer into transparent vitrification, and then these Glass fine particle deposition and transparent vitrification were repeated twice.

The quartz-based optical fiber base material obtained in this way has a center core part:outer core part outer diameter ratio of 1=3 and an outer core part:clad part outer diameter ratio of 1=13.

This optical fiber base material is heated and stretched to an outer diameter of 12 mm.
An optical fiber with a length of 5 elongated diameters is drawn, and a coating layer of an ultraviolet curable resin with an outer diameter of 250μ so φ is formed on the outer periphery of the optical fiber immediately after the drawing, using a well-known coating method.
A coating material 5-right type optical fiber having the cross-sectional structure shown in FIG. 1 and the refractive index profile shown in FIG. 2(A) was obtained.

The thus obtained silica-based optical fiber has an Er-containing center core with a diameter of -3.2 pmφ and Δ゛・1.1z, an outer core with Δ-O, tX, and a cladding with Δ-
It was 0.3m.

A length of 15 layers was sampled from the silica optical fiber of this specific example.
When a laser beam with a wavelength of 1.48 μm was applied to this,
The optical amplification efficiency of 1.5dB/LW can be confirmed.
The mode field diameter was also as large as 7.8μ■φ.

The optical amplification efficiency of the silica-based optical fiber in the above specific example is:
The conventional silica-based optical fiber described in Fig. 5 (core Er content l1-1O0pp, core Δ°-1, 41 core outer diameter -3 pot 1φ, mode field diameter -5, 1w1φ
), but the mode field diameter of the specific example is considerably larger than that of the conventional example.

Note that the silica-based optical fibers (including square distribution type, triangular type, etc. refractive index profiles) shown in Figures 1 to 2 (B) and Figures 3 to 4 also have a mode field diameter of 8.
In the center core 11 having an outer diameter of about 2 gmφ and an outer diameter of 3 to 4 graφ, the Er contained therein can be effectively utilized for optical amplification.

Effects of the Invention J As explained above, the silica-based optical fiber according to the present invention has the following effects:
Since it has high optical amplification efficiency and a large mode field diameter, it can be useful and useful as an optical fiber for optical amplification.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the silica-based optical fiber according to the present invention, and FIGS. 2(A) and 2(B) are explanatory diagrams illustrating the refractive index profile of the silica-based optical fiber of the above-mentioned embodiment. 2. FIG. 3 is a cross-sectional view showing another embodiment of the silica-based optical fiber according to the present invention, FIG. 4 is an explanatory diagram illustrating the refractive index profile of the silica-based optical fiber of the other embodiment described above, and FIG. FIG. 2 is an explanatory diagram showing a refractive index profile in a conventional silica-based optical fiber. 11... Center core 12... Outer core 121... Outer core 122... Outer core 13... Clair 2 14... Coating layer

Claims (1)

[Claims] It is characterized by comprising a center core, one or more outer cores having a lower refractive index than the center core, and a cladding having a lower refractive index than the outer core, extending from the axial center to the outer periphery, and the center core contains erbium. quartz-based optical fiber.