JP2772348B2 - Optical fiber amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 1.3 .mu.m band optical fiber amplifier used in an optical communication system.

[0002]

2. Description of the ^Related Art In recent years, researches on an optical fiber amplifier using a stimulated emission of a transition in a 4f shell by doping a core of an optical fiber with rare earth ions, particularly Er ³⁺ ions, have been actively conducted. This rare earth doped optical fiber amplifier has a high gain and a gain characteristic independent of polarization, and has a low noise figure and a wide band wavelength characteristic.
Application to a μm band optical communication system has become extremely attractive.

On the other hand, the 1.3 μm band where the chromatic dispersion of the silica-based optical fiber becomes zero is an important wavelength band in the field of optical communication along with the 1.5 μm band. Research on the optical fiber amplifier operating in the 1.3 μm band has been conventionally performed using a silica-based optical fiber or a fluoride-based optical fiber doped with Nd ³⁺ ions.

[0004] However, amplification has not been confirmed for both fibers at 1.31 μm used for optical communication because the excited state absorption of Nd ³⁺ ions is large. Regarding this point, for example, W.M. J. Minisculco, L .;
J. Andrews, B .; A. Thompson, R.A.
S. Quinby, L .; J. B. Vacha and
M. G. FIG. Drexhage, "Electron Le
ft ". (vol. 24, 1988, p. 28) or Y. Miyajima, T. Komukai, Y. Su.
gawa and Y. Katsuyama, “Tec
hnicalDigest Optical Five
r Communication Conference
e'90 San Francisco "(1990,
PD16).

[0005] Under such circumstances, it is strongly desired to realize an optical fiber amplifier having an amplifying action at 1.31 µm. Ohshi,
T. Kanamori, T .; Kitagawa, S .; T
Akahashi, E .; Snitzer and G.S.
H. Sigel “Technical DigestO
optical Fiber Communicatio
n Conference '91 San Dieg
o "(1991, PD2), an optical fiber amplifier using an optical fiber obtained by doping Pr ³⁺ into a ZrF ₄ -based fluoride glass as a host material has been proposed.
This optical fiber amplifier is 1.017 μm as shown in FIG.
m light to excite the ¹ G ₄ level of Pr ³⁺ , ¹ G ₄ → ³ H
_It uses the stimulated emission of _five transitions.

However, this type of optical fiber amplifier has an excitation wavelength of 1.017 μm as described above,
Since there is no high-power semiconductor laser that operates as an excitation light source in this wavelength range, there is a problem in that it lacks practicality.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned technical problems, the present invention relates to a method in which the pumping wavelength of an optical fiber as an amplification medium is shifted to the oscillation wavelength band of a high-power semiconductor laser. An object of the present invention is to provide an optical fiber amplifier for a 3 μm band.

[0008]

In order to achieve the above object, the present invention provides an optical fiber as an amplifying medium containing rare earth ions in a core, an excitation light from an excitation light source for exciting the optical fiber, and An optical coupler that mixes a signal light from a signal source to be amplified by an optical fiber and that outputs the mixed light to the optical fiber, wherein the optical fiber has rare-earth ions in its core. comprises Pr ³⁺ ions and Yb ³⁺ ions as, and the excitation light is characterized in that the wavelength range of 1017nm from 900 nm. Here, the core and the clad of the optical fiber may be made of a material selected from the group consisting of fluoride glass, chalcogenide glass, chloride glass, bromide glass and iodide glass.

[0009]

In the present invention, since an optical fiber in which Yb ³⁺ is added to the core together with Pr ³⁺ is used as an amplification medium, the excitation wavelength of the optical fiber is 900 to 980 nm which can be excited by a high-power semiconductor laser. Wavelength range.

[0010]

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

[Embodiment 1] FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes an excitation light source, 2 denotes a lens, 3 denotes a signal source, and 4 denotes an excitation light and a signal source 3 from the excitation light source 1.
Reference numeral 5 denotes an optical fiber for amplifying the output from the optical coupler 4, reference numeral 6 denotes an optical spectrum analyzer for monitoring the signal light, and reference numeral 7 denotes a fiber pigtail.

In the present embodiment, a fluoride fiber co-doped with Pr ³⁺ (0.3 wt%) and Yb ³⁺ (0.2 wt%) is used as an optical fiber for amplification. The core diameter is 4.3 μm, the core / clad refractive index difference is 0.6%, and the glass system of the fiber is ZrF ₄ —BaF ₂ —LaF.
Was _{3 -YF 3 -AlF 3 -LiF-NaF} . 2m
One end of the long amplification optical fiber is connected to the optical coupler 4 using a V-groove.
The other end was connected to one end of the fiber pigtail 7. The other end of the fiber pigtail 7 was connected to the optical spectrum analyzer 6. A Ti-sapphire laser was used as the excitation light source 1, and a semiconductor laser having an oscillation wavelength of 1.309 μm was used as a signal source. FIG. 3 shows the pump wavelength dependence of the gain at 1.309 μm (pump light intensity 900 mW).
As is clear from FIG. 3, the gain was confirmed even when the excitation wavelength was 990 nm or less. That is, although not gain is little obtained when excited with added to 990nm wavelengths below the Pr ³⁺ ions alone became possible following excitation 990nm by the addition of Yb ³⁺ with Pr ³⁺ .

FIG. 3 also shows that the gain is within an experimental error (± 1 dB) with respect to the excitation of 990 nm or less and does not depend on the excitation wavelength. This is because Yb ³⁺ ( ² F _5/2 → ² F _7/2 ) → Pr ³⁺ ( ³
This is because Pr ³⁺ is excited by energy transfer in the process of H ₄ → ¹ G ₄ ).

Incidentally, a high-power semiconductor laser for excitation (for example, an InGaAs-based semiconductor laser) has a drawback that the oscillation wavelength tends to fluctuate due to temperature fluctuation or the like. In the present invention, it has been found that there is a practical advantage that the gain does not largely change even if the oscillation wavelength of the semiconductor laser for excitation fluctuates because the excitation wavelength dependence of the gain is small as described above. In addition, it was confirmed that an excitation wavelength of up to 900 nm can be used to obtain a gain at 1.31 μm. On the shorter wavelength side than 900 nm, as shown in FIG.
Since the absorption efficiency of ² F _7/2 → ² F _5/2 absorption of b ³⁺ is reduced, the excitation efficiency is reduced and is not suitable as an excitation wavelength.

When a semiconductor laser having an InGaAs-based strained quantum well structure capable of lasing at a wavelength of 1020 nm or less is used, a wavelength shorter than 1017 nm, which is the peak wavelength of Pr ³⁺ absorption of ³ H ₄ → ¹ G ₄ , is used. Side and 900n
Excitation is possible in a wavelength band longer than m. When a fiber doped with Pr ³⁺ and Yb ³⁺ is used, the wavelength is 990 nm.
Excitation is possible not only in the shorter wavelength side but also in the wavelength range of 990 to 1017 nm.
It was found that a wide wavelength band from 10 nm to 1017 nm can be adopted.

Example 2 In this example, Pr ³⁺ was used in the same manner as in Example 1 except that the glass material of the optical fiber as the amplification medium was changed from fluoride glass to chalcogenide glass or halide glass other than fluoride. The -Yb3 ⁺ co-doping effect was confirmed.

As a chalcogenide glass, an As-S system,
Ge-S system, As-Ge-S system, Ge-PS system, As
-Ge-PS-based, As-S-Cl-based, Ge-S-Cl
System, As-Ge-S-Cl system, As-S-Br system, Ge
-S-Br system, As-Ge-S-Br system, As-SI
System, Ge-SI system, As-Ge-SI system, As-S
-Cl-Br system, Ge-S-Cl-Br system, As-Ge
-S-Cl-Br system, As-S-Cl-I system, Ge-S
-Cl-I system, As-Ge-S-Cl-I system, As-S
-Br-I system, Ge-S-Br-I system, As-Ge-S
-Br-I system, As-S-Cl-Br-I system, Ge-S
-Cl-Br-I system, As-Ge-S-Cl-Br-I
System, Cd-As-I system, Cd-As-Ge-I system, Sb
-SI system, Cu-Sb-SI system, Pb-S-Br-
When I-based, Zr-Ge-KS-based, or La-Ga-S-based glasses are used, Ag-Cs-Pb-Cl-based, Ag-Cs-Pb-Br are used as halide glasses other than fluoride-based glasses.
System, Ag-Cs-Pb-Br-I system, Ag-Cs-Pb
-Cl-Br-I, Ag-Cs-Pb-Cd-Br
System, Ag-Cu-Cs-Pb-Cl-Br system, Cu-C
s-Pb-Cl-Br, Cu-Cs-Pb-Br-I
System, Cu-Cs-Pb-Cl-Br-I system, Cd-Ba
-Cl system, Cd-Ba-Na-Cl system, Cd-Pb-K
-Cl-I, Cd-Pb-K-Cl-Br-I, Z
nCl ₂ , Zn-K-Cl system, Zn-K-Br-I system,
Zn-K-Cl-Br-I, Zn-K-Tl-Br-
I system, Zn-K-Tl-Cl-Br-I system, Bi-K-
Cl system, Bi-K-Na-Cl system, Bi-Pb-Cl
In the case of using Bi-Pb-Tl-Cl-Br-based glass, it is possible to excite in a wavelength range of 900 nm to 980 nm with Pr ³⁺ and Yb ³⁺ co-doped in the same manner as in Example 1. .

However, Pr ^{3+ on} these glasses
Could be excited at a wavelength of 1.017 μm, but could not be excited at a wavelength of 990 nm or less. FIG.
Shows the pump wavelength dependence of the gain at a wavelength of 1.309 μm (pump light intensity 200 mW). The white circle in the figure is As-G
e-S-Br-I fiber (core diameter: 2.5 μm, refractive index difference between core and clad: 0.5%), black circles indicate Cd-B
This is the characteristic of a-Na-Cl fiber (core diameter: 3 μm, refractive index difference between core and clad: 0.7%), and Pr ³⁺ (0.3 wt%) and Yb ³⁺ (0 .2wt
%) Is co-doped. The measurement conditions were the same as in Example 1 except that the intensity of the excitation light was about 1/5 of that in Example 1. It is apparent from the figure that excitation of 990 nm or less has become possible.

In this embodiment, a gain equivalent to that of Embodiment 1 was obtained at an excitation light intensity of about 1/5, but this was because the phonon energy of the glass system of this embodiment was lower than that of the fluoride glass of Embodiment 1. This is because the excitation efficiency was increased because the excitation efficiency was lower.

[0020]

As described above, according to the present invention,
Since an optical fiber in which Yb ³⁺ is added to the core together with Pr ³⁺ is used as an amplification medium, the excitation wavelength of the optical fiber can be increased from 900 to 980 which can be excited by a high-power semiconductor laser.
It can be moved to the wavelength range of nm. For this reason, a practical semiconductor pump fiber amplifier can be configured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy diagram of Pr ³⁺ and Yb ³⁺ .

FIG. 2 is a schematic configuration diagram showing one embodiment of the optical fiber amplifier of the present invention.

FIG. 3 is a graph showing pump wavelength dependence of gain in the optical fiber amplifier according to the first embodiment of the present invention.

FIG. 4 is a graph showing the pump wavelength dependence of gain in Embodiment 2 of the optical fiber amplifier of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Excitation light source 2 Lens 3 Signal source 4 Optical coupler 5 Amplification optical fiber 6 Optical spectrum analyzer 7 Fiber pigtail

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/10 H01S 3/07 H01S 3/094 H01S 3/17

Claims (2)

(57) [Claims] 1. An optical fiber as an amplification medium containing a rare earth ion in a core, mixing an excitation light from an excitation light source for exciting the optical fiber and a signal light from a signal source to be amplified by the optical fiber. And an optical coupler that outputs the mixed light to the optical fiber, wherein the optical fiber has Pr ³⁺ as a rare earth ion in its core.
Ions and Yb ³⁺ ions, and the excitation light is 900
An optical fiber amplifier having a wavelength range of from 10 nm to 1017 nm. 2. The optical fiber according to claim 1, wherein the core and the clad of the optical fiber are made of a material selected from the group consisting of fluoride glass, chalcogenide glass, chloride glass, bromide glass and iodide glass. 2. The optical fiber amplifier according to 1.