JP2749686B2 - Silica optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silica-based optical fiber suitable for use in optical amplification.

[Prior Art] As a silica-based optical fiber for optical amplification, an optical fiber in which a core is doped with erbium (Er) is known. As an example of this optical fiber, one having a refractive index profile shown in FIG. is there.

The quartz optical fiber shown in FIG. 5 has a core 1 having a diameter of about 3 μm.
mφ, the mode field diameter is about 5 μmφ, and the outer diameter of the cladding 2 (optical fiber outer diameter) is 125 μmφ.

In the case of such a silica-based optical fiber, the distribution of the optical power passing through the waveguide is similar to a Gaussian distribution, and light is excited at the top part (the part where the light intensity is maximum) of the optical power distribution. The erbium atoms doped in the core can be used for light emission near a wavelength of 1.53 μm to effectively amplify the light.

[Problems to be Solved by the Invention] However, in the case of a silica-based optical fiber having the refractive index profile shown in FIG. 5, not only the core diameter is as small as about 3 μmφ, but also the mode field diameter is as small as about 5 μmφ. This has a mode field diameter of about 8 μmφ
When connected to a dispersion-shifted fiber, the connection loss becomes as large as 0.3 to 0.5 dB, and this large connection loss becomes a problem.

The present invention has been made in view of such technical problems, and has as its object to provide a silica-based optical fiber capable of increasing a mode field diameter without deteriorating an optical amplification function.

[Means for Solving the Problems] The quartz-based optical fiber according to the present invention is characterized by the following means for solving the problems in order to achieve the intended object. That is, the silica-based optical fiber according to the present invention includes a center core, one or more outer cores having a lower refractive index than the center core, and a clad having a lower refractive index than the outer core, from the axial center portion to the outer peripheral portion. It is characterized by containing erbium and having a mode field diameter of about 8 μmΦ.

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

Such a silica-based optical fiber has not only a center core but also an outer core, so that a mode field having a large diameter can be secured and the center core diameter can be reduced. In addition, erbium (Er) is added to the center core having a small diameter. ) Contains erbium at the wavelength
It can be used effectively for light emission near 1.53 μm.

In particular, when the mode field diameter is large, the luminous efficiency can be increased by erbium doping to the center core, and the optical power in the mode field does not decrease.

[Example] An example of a silica-based optical fiber according to the present invention will be described with reference to the drawings.

In the quartz optical fiber illustrated in FIG. 1, 11 indicates a center core, 12 indicates an outer core, 13 indicates a clad, and 14 indicates a coating 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 μmφ.

The content of erbium (Er) in the center core 11 is 1000 ppm or less.

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

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

The coating layer 14 is made of, for example, an ultraviolet curable resin having an outer diameter of 250 μmφ.

In the quartz optical fiber shown in FIG. 1, when the refractive index of the center core 11 is n ₁ , the refractive index of the outer core 12 is n ₂ , and the refractive index of the cladding 13 is n ₃ , these refractions are n ₁ > n ₂ > n ₃ and the core portion has a plurality of refractive index profiles.

As the refractive index profile in this case, the center core 11
May be a step type (single mode) shown in FIGS. 2A and 2B, a square distribution type, or a triangle type not shown.

The quartz optical fiber illustrated in FIG.
And a plurality of outer cores 12 ₁ and 12 ₂ and a clad 13, and a coating layer 14 is provided on the outer periphery of the clad 13.

In the illustrated example, the quartz optical fiber has a plurality of outer cores.
Although it has 12 ₁ and 12 ₂ , the others are substantially the same as those in FIG.

In silica optical fiber of FIG. 3, n ₁ the refractive index of the center core 11, outer core 12 ₁ of refractive index n _21, the outer core
Assuming that the refractive index of 12 ₂ is n ₂₂ and the refractive index of the cladding 13 is n ₃ , these refractions are n ₁ > n ₂₁ > n ₂₂ > n ₃ , and the refractive index is as shown in FIG. Has a profile.

In the quartz 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 Example A specific example of the silica-based optical fiber according to the present invention will be described together with a production example thereof.

Er: 100pp when making glass rod for center core
A quartz-based transparent glass rod doped with m and GeO ₂ : 11 mol% uniformly was synthesized, and this was heated and stretched to an outer diameter of 10 mmφ and a length of 200 mm.

When forming the outer core glass on the outer periphery of the glass rod, first, soot-like glass particles are deposited on the outer periphery of the glass rod by a flame hydrolysis method using SiCl ₄ as a raw material. ° C. the He in an electric furnace _{of: 30 / min, Cl 2:} 0.3 / min, SiF 4: while supplying 0.03 / min, the glass rod with the glass fine particle layer was inserted at a rate of 150 mm / hr to the electric furnace Then, the glass fine particle layer was turned into a transparent glass, and thereafter, the glass rod with the outer core glass was drawn by heating to an outer diameter of 7 mmφ.

When forming the glass for cladding on the outer periphery of the glass rod with the outer core glass, first, soot-like glass fine particles are deposited on the outer periphery of the outer core glass by the flame hydrolysis method described above. He similarly in the electric _{furnace: 15 / min, Cl 2:} 0.15 / min, SiF 4: while supplying 0.62 / min, the glass rod with the glass fine particle layer was inserted at a rate of 150 mm / hr to the electric furnace Then, the glass fine particle layer was turned into a transparent glass, and thereafter, the deposition of the glass fine particles and the formation of the transparent glass were repeated twice.

In the quartz optical fiber preform thus obtained, the outer diameter ratio of the center core portion to the outer core portion is 1: 3, and the outer diameter ratio of the outer core portion to the clad portion is 1:13.

Such an optical fiber preform is subjected to a known heating and stretching process to have an outer diameter of 12 mm.
A 5 μmφ optical fiber is drawn, and the outer diameter of the optical fiber immediately after the drawing is 250 μmφ with ultraviolet curing resin.
Was formed by known coating means to obtain a coated silica-based optical fiber having a cross-sectional structure shown in FIG. 1 and a refractive index profile shown in FIG. 2 (A).

In the quartz optical fiber thus obtained, the center core containing Er had a diameter of 3.2 μmφ, Δ ⁺ = 1.1%, the outer core had Δ ⁻ = 0.1%, and the clad had Δ ⁻ = 0.3%. .

A 15m length was sampled from the quartz optical fiber of this specific example,
When a laser beam with a wavelength of 1.48 μm was incident on this, 1.5d
The optical amplification efficiency of B / mW was confirmed, and the mode field diameter was as large as 7.8 μmφ.

The optical amplification efficiency of the silica-based optical fiber in the above example is the same as that of the conventional silica-based optical fiber (Er of the core) described in FIG.
Content = 100 ppm, Δ ^{+ of} core = 1.4%, outer diameter of core = 3
μmφ, mode field diameter = 5.1 μmφ), but as for the mode field diameter, the specific example having a diameter of 7.8 μmφ has a diameter of 5.1 μmφ.
Is considerably larger than that of the conventional example.

The quartz-based optical fibers (including the refractive index profiles of the square distribution type, triangular type, etc.) shown in FIGS. 1 and 2 (B) and FIGS. 3 and 4 also have a mode field diameter of 8 μmφ. In the center core 11 having an outer diameter of 3 to 4 μmφ, Er contained therein can be effectively used for optical amplification.

[Effects of the Invention] As described above, the silica-based optical fiber according to the present invention has a good optical amplification efficiency, a large mode field diameter, and a small connection loss, so that it is useful and useful as an optical fiber for optical amplification. Can be useful.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a silica-based optical fiber according to the present invention, and FIGS. 2 (A) and 2 (B) are explanatory views illustrating a refractive index profile in the silica-based optical fiber of the embodiment. 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 view illustrating a refractive index profile in the silica-based optical fiber of the other embodiment,
FIG. 5 is an explanatory view showing a refractive index profile in a conventional silica-based optical fiber. 11… Center core 12… Outer core 12 ₁ … Outer core 12 ₂ …… Outer core 13 …… Clad 14 …… Coating layer

Claims (1)

(57) [Claims] A center core, at least one outer core having a lower refractive index than the center core, and a cladding having a lower refractive index than the outer core, wherein the center core contains erbium; A silica-based optical fiber having a mode field diameter of about 8 μmΦ.