JP3317321B2 - Optical fiber amplifier and method of using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier used in optical communication and the like, and a method of using the same.

[0002]

2. Description of the Related Art An optical fiber amplifier for amplifying 1.5 μm light using Er as active ions is a key device of an optical communication system. FIG. 1 shows an energy level diagram of Er. For 1.5 μm band amplification, ⁴ I _13/2 → ⁴ I
Stimulated emission of _15/2 is used, and light of 1.48 μm and 0.98 μm is often used for excitation.
It has been found that an optical fiber amplifier with lower noise is realized when the light of μm is used as the pumping light than in the case of pumping of 1.48 μm. The mainstream of this amplifier generally uses an optical fiber based on quartz glass. On the other hand, an optical fiber amplifier using an optical fiber based on a fluoride glass has recently been receiving attention.
This is because the amplification band is wide and 1.5
This is because the gain becomes constant in the range of 5 to 1.56 μm.

[0003]

In an Er-doped optical fiber amplifier using a quartz fiber, the fluorescence lifetime of the ⁴ I _11/2 level is short and 0.98 μm due to the high polyphonon emission rate.
High-efficiency excitation by band excitation becomes possible. However, when 0.98 μm pumping is performed in a fiber amplifier using a glass having a low polyphonon emission rate, such as fluoride glass, ions excited with a long lifetime of the ⁴ I _11/2 level, which is the pumping level, are excited. , The absorption of the excited level to a higher level is increased. For this reason, the efficiency of the optical fiber amplifier is poor, and a low-noise optical fiber amplifier cannot be realized. At present, only a 1.48 μm-pumped, broadband, but high-noise optical fiber amplifier has been realized.

SUMMARY OF THE INVENTION An object of the present invention is to provide an Er-doped 1.5 μm band optical fiber amplifier using glass having a low polyphonon emission rate, such as a fluoride fiber, to enable 0.98 μm pumping, thereby achieving a wide band low noise. Optical fiber amplifier and
It is to provide a method of using the same.

[0005]

In order to achieve the above object, the present invention comprises at least an excitation light source, an optical multiplexing / demultiplexing element, an optical fiber for optical amplification using Er as active ions , and an optical isolator. 1.5 μm band optical signal
An optical fiber amplifier for amplifying said excitation light
The source _converts Er ions from the ⁴ I _15/2 level to the ⁴ I _{11/2 level.}
The optical fiber for optical amplification is a light source for exciting to a level. In addition to Er ions, at least a core of one or more of terbium, europium and dysprosium from Er ions is cross-relaxed with ⁴ I _{11 / two} levels
The optical fiber is characterized by being doped with ions that cause transition from the level to the ⁴ I _13/2 level . Claim 2
The invention according to claim 1 is the invention according to claim 1,
It is noted that the optical fiber for optical amplification is a fluoride fiber.
Sign. In addition, the invention according to claim 3 has at least
Excitation light source, optical multiplexer / demultiplexer, optical isolator, and core
From terbium, europium and dysprosium
One or more ions and erbium ions are co-added
To use an optical fiber amplifier with an amplified optical fiber
Removing Er ions from the excitation light source by ⁴ I
Excitation light to be excited from the _15/2 level to the ⁴ I _11/2 level
Generate the 1.5 μm band signal light with the optical multiplexer / demultiplexer.
The excitation light is multiplexed and incident on the amplification optical fiber.
It is characterized by the following. The invention according to claim 4 is a contractor.
The optical fiber for optical amplification according to claim 3, wherein
Is a fluoride fiber.

[0006]

In order to enable excitation by light of 0.98 _μm , the fluorescence lifetime of the Er excited level ⁴ I _11/2 is shortened,
It is necessary to suppress the excitation level absorption of the excitation light. T above
The ions b, Eu, and Dy have light absorption of 2.7 to 2.8 μm as shown in FIGS. Energy gap size a (cm ^-1 ) and wavelength of absorbed light λ
Since (μm) has a relationship of λ = (1 / a) × 10 ⁴ , it can be seen that these ions have a level at which the energy gap from the specified level is 3570 to 3700 cm ⁻¹ . ⁴ I of this energy gap is Er _11/2 - ⁴
This corresponds approximately to the energy gap of I _13/2 . Therefore Tb, Eu, by co-addition of ions and Er of Dy, these ions and ⁴ I of Er _11/2 - ⁴ I cross relaxation shown in FIG. 5 (a) ~ (c) between _{13/2 Happens} , ⁴ I _11/2
Er excited to the level _rapidly changes to a state excited to ⁴ I _13/2 (that is, the fluorescence lifetime of ⁴ I _11/2 is shortened), and the efficiency of 1.5 μm band amplification is increased. Will be. In addition, since the ions of Tb, Eu, and Dy do not absorb 1.5 μm band light as shown in FIGS.
It is also important that the efficiency of Er amplification is not reduced.

As described above, by co-doping Er with at least one ion of Tb, Eu, and Dy, even in a host glass having a low polyphonon emission rate such as a fluoride fiber, Er can be removed. The fluorescence lifetime of the ⁴ I _11/2 level is shortened, and excitation with 0.98 μm light with high efficiency becomes possible. As a result, a wideband optical fiber amplifier can be realized.

[0008]

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

Example 1 0.1 wt% of Er was added to the core,
A fluoride fiber doped with 1 wt% of Tb was used. The glass composition has a core of 56ZrF ₄ -14BaF ₂ -3.5.
_{LaF 3 -2YF 3 -7AlF 3 -2.5LiF-} 15
PbF ₂ , with a cladding of 47.5 ZrF ₄ -23.
5BaF ₂ -2.5LaF ₃ -2YF ₃ -4.5AlF
Was ₃ -20NaF. The relative refractive index difference of this fiber was 1.5%, and the cutoff wavelength was 0.95 μm. The fiber length was 10 m.

FIG. 6 shows the configuration of an optical fiber amplifier.
The optical fiber amplifier is the above-mentioned fluoride fiber 1, 0.9.
A semiconductor LD pigtail module 3 (laser output: 100 mW) in which a semiconductor LD (laser diode) in the 8 μm band and an optical fiber are coupled by a lens, and a fiber coupler for combining light in the 0.98 μm band and light in the 1.55 μm band ( For example, wavelength division multiplexing (WDM) fiber coupler)
2 , an optical isolator 4. In order to reduce the connection loss between a general optical fiber and a fluoride fiber, a relative refractive index difference of 1.5% and a cutoff wavelength of 0.95 μm are provided at a multiplexing port of a fiber coupler and an incident side of an optical isolator.
The high relative refractive index difference quartz optical fiber 5 of FIG.
This fusion point is blown with a micro burner to reduce the connection loss. At the connection point between the optical fiber 5 and the fluoride fiber 1, a V-groove block is attached with an ultraviolet-curing adhesive, and the V-groove block is attached with an ultraviolet-curing adhesive for connection.

FIG. 7 shows a small signal gain characteristic, FIG. 8 shows a gain spectrum, and FIG. 9 shows a noise figure characteristic. As can be seen from FIG. 7, when pumped with 100 mW of 0.98 μm light, a gain of 38 dB was achieved at a signal light wavelength of 1.55 μm. In addition, as shown in FIG.
In the case of W, the gain was quite constant in the range of 1.55 to 1.56 μm. As shown in FIG. 9, the noise figure was 3.6 dB in the small signal region.

Comparative Example A fiber having the same composition as that of Example 1 was used in Comparative Example, and its core was made of 0.1 wt% Er.
%, Added alone. The configuration of the optical fiber amplifier was the same as that of the first embodiment. FIG. 10 shows the small signal gain characteristics. The degree of the small signal gain increase rapidly decreases with the increase of the pump light, and only a gain of 12 dB is obtained even with 100 mW pump. From this, the effectiveness of adding Tb to Er was shown.

Embodiment 2 In Embodiment 2, a fiber in which Er was added to the core in an amount of 0.1 w% and Eu was added in an amount of 1.5 w% was used. The fiber composition and the configuration of the amplifier were the same as in the first embodiment.

The amplification characteristic of this amplifier shows almost the same tendency as that of the first embodiment, that is, 35 dB, 100.
An almost constant gain and a noise figure of 3.7 dB were achieved in the small signal region in the range of 55 to 1.56 μm.

[Embodiment 3] In Embodiment 3, a fiber in which Er was added to the core in an amount of 0.1 w% and Dy was added in an amount of 1.2 w% was used. The fiber composition and the configuration of the amplifier were the same as in the first embodiment.

The amplification characteristic of this amplifier shows almost the same tendency as that of the first embodiment.
The gain and the noise figure were almost constant in the range of 55 to 1.56 μm, and the noise figure achieved 4.0 dB in the small signal region.

Usually, Er alone is 0.05 to 0.5 watts.
It is added in a range of t%, and an addition amount of about 0.1 wt% is particularly preferably used. Tb, Eu and Dy are E
When co-added with r, an effect is obtained by adding 0.01 wt%, but if it exceeds 0.3 wt%, the optical properties of the optical fiber are deteriorated, which is not preferable.

[0018]

As described above, according to the present invention, at least the core of the optical fiber has Er, Tb, and Eb.
By co-doping at least one ion of u and Dy, the fluorescence lifetime of the ⁴ I _11/2 level of Er is shortened even in a host glass having a low polyphonon emission rate such as a fluoride fiber. As a result, highly efficient excitation with light of 0.98 μm becomes possible. As a result, a wideband optical fiber amplifier can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an energy level of Er.

FIG. 2 is a graph showing absorption characteristics of Tb.

FIG. 3 is a diagram showing absorption characteristics of Eu.

FIG. 4 is a diagram showing absorption characteristics of Dy.

FIG. 5 is a diagram showing energy level diagrams of Tb, Eu, and Dy and cross relaxation of Er.

FIG. 6 is a schematic diagram illustrating a configuration of an optical fiber amplifier.

FIG. 7 is a diagram showing a small signal gain characteristic of an Er-Tb-doped optical fiber amplifier.

FIG. 8 is a gain spectrum diagram of the Er-Tb-doped optical fiber amplifier.

FIG. 9 is a diagram illustrating noise characteristics of an Er-Tb-doped optical fiber amplifier.

FIG. 10 is a diagram illustrating a small signal gain characteristic of an Er-doped optical fiber amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fluoride fiber for optical amplification 2 Fiber coupler 3 Semiconductor LD 4 Optical isolator 5 High relative refractive index difference silica fiber

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Teruju Kanamori 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Shoichi Sudo 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-5-145168 (JP, A) JP-A-3-109785 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (4)

(57) [Claims] At least an excitation light source, an optical multiplexer / demultiplexer, and E
Amplifying 1.5 μm band optical signal with optical fiber for optical amplification using r as active ion and optical isolator
An optical fiber amplifier for the excitation light source, the Er ions from ⁴ I _15/2 level ⁴
A light source for pumping to the I _11/2 level, wherein the optical amplification optical fiber has at least a core of at least one of terbium, europium, and dysprosium, in addition to Er ions, which is cross-relaxed with Er ions.
To transition the emissions from the ⁴ I _11/2 level to the ⁴ I _13/2 level
Optical fiber amplifier, characterized in that that ion is an optical fiber that is added. 2. The optical fiber amplifier according to claim 1, wherein said optical fiber for optical amplification is a fluoride fiber. 3. An optical system comprising at least an excitation light source, an optical multiplexer / demultiplexer, an optical isolator, and an amplification optical fiber in which at least one of terbium, europium, and dysprosium ions and erbium ions are co-doped in a core. a method of using a fiber amplifier, the ⁴ I _15/2 level of Er ions from the excitation light source ⁴
A pump light generating pumping light to an I _11/2 level, wherein the 1.5 μm band signal light and the pumping light are multiplexed by the optical multiplexing / demultiplexing device and made to enter the amplification optical fiber. How to use fiber amplifier. 4. The method according to claim 3, wherein the optical fiber for optical amplification is a fluoride fiber.