JP2003218439A - Optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To flatten the gain-wavelength characteristic of an optical amplifier using a rare-earth-doped optical fiber without lowering the gain efficiency of the amplifier and, in addition, to widen the amplification bands of the amplifier. <P>SOLUTION: The plurality of low-gain bands of this EDFA 2 is used as the amplification bands of this EDFA 2 by installing distributed Raman amplifiers 3-5 which respectively amplify signal light rays with pumping light rays respectively having corresponding wavelengths to the low-gain bands. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplification device for amplifying an optical signal used for communication.

[0002]

2. Description of the Related Art As an optical amplifier used in an optical communication system or the like, pumping light and signal light are combined, incident on an optical fiber doped with a rare earth element such as erbium or neodymium, and excited by the pumping light. There is a rare earth-doped optical fiber amplifier that amplifies signal light in an optical fiber by using a rare earth element.

In particular, in the optical fiber using Erbium-doped optical fiber, the amplification wavelength range matches the minimum loss wavelength of 1.55 μm which is often used in optical communication.
Erbium-doped optical fiber amplifier (EDFA: erbium-doped fiber) with high amplification performance
Amplifier).

FIG. 5 and FIG. 6 show the 153 of this EDFA.
0 nm to 1565 nm C band and 1565 nm to
It shows an example of a gain wavelength characteristic in the L band of 1625 nm, and in both the C band and the L band, as shown by the solid line, the gain wavelength characteristic has two peaks and one valley. There is.

Since the gain varies with the wavelength as described above, in order to reduce the variation of the gain, conventionally, a gain equalizer is used as shown by broken lines in FIGS. 5 and 6. A gain is equalized by giving a loss to a high gain band.

[0006]

As described above, in an optical amplifying apparatus using a rare earth-doped optical fiber represented by EDFA, the gain is different with respect to the wavelength. Therefore, the power in the high gain band is reduced. Since gain equalization is performed, there is a drawback in that gain efficiency is reduced.

The present invention has been made in view of the above points, and in an optical amplifier using a rare earth-doped optical fiber, it is possible to flatten the gain wavelength characteristic without lowering the gain efficiency. The present invention further aims to widen the amplification band.

[0008]

In order to achieve the above object, the present invention is configured as follows.

That is, the optical amplifying device of the present invention is an optical amplifying device including a rare earth-doped optical fiber that amplifies signal light by pumping light and outputs the amplified signal light, in a wavelength range corresponding to a low gain band of the rare earth-doped optical fiber. A Raman amplifier that amplifies the signal light by pumping light is provided, and the Raman amplifier uses the band with the low gain as an amplification band.

Here, the low gain band means a band having a lower gain than at least the peak of the gain.

The Raman amplifier is an optical amplifier utilizing stimulated Raman scattering.

The Raman amplifier used in the present invention includes a distributed type and a concentrated type.

As the distributed type, for example, a silica type single mode fiber for normal signal transmission or the like is used as a Raman amplification medium. Such a distributed Raman amplifier has the advantages of low noise and relatively low non-linear deterioration.

On the other hand, as the concentrated type, a high refractive index designed to increase the energy density in the core by making the refractive index of the core larger than usual or making the core diameter smaller than usual. An example is one in which a nonlinear optical fiber is used as a Raman amplification medium. Such a concentrated Raman amplifier has an advantage that a fiber having a short fiber length can be used.

According to the invention, the Raman amplifier
Since the low gain band of the rare earth-doped optical fiber is amplified as the amplification band, the gain wavelength characteristics can be flattened, and the low gain bands of the rare earth-doped optical fiber are amplified as multiple amplification bands. By doing so, it is possible to widen the amplification band.

Further, in the optical amplifying apparatus of the present invention, the amplified signal power is not wasted unlike the conventional gain equalization using the gain equalizer. Furthermore, the gain of the Raman amplifier is a few d that the rare earth-doped optical fiber amplifying device has.
Since it is only necessary to compensate the gain deviation of B, the power of the Raman pumping light may be small and efficient, as compared with the case where the signal loss in the transmission line is entirely compensated by Raman amplification.

In one embodiment of the present invention, the Raman amplifier is a Raman amplification pumping light source that outputs pumping light of a wavelength corresponding to a band in which the gain of the rare earth-doped optical fiber is low, and this Raman amplification pumping light source. And an optical multiplexer for making the pumping light from the laser light incident in a direction opposite to the propagation direction of the signal light.

According to the present invention, pumping light from the pumping light source for Raman amplification can be incident in the direction opposite to the propagation direction of the signal light for Raman amplification.

In a preferred aspect of the present invention, the Raman amplification pumping light source outputs pumping light having a plurality of wavelengths corresponding to a plurality of low-gain bands of the rare earth-doped optical fiber.

According to the present invention, the pumping light source for Raman amplification outputs pumping light of a plurality of wavelengths respectively corresponding to a plurality of bands having a low gain. With the optical multiplexer, the signal light can be incident on the transmission path, and the number of optical multiplexers can be reduced.

[0021] In another embodiment of the present invention, a plurality of Raman amplifiers are provided in correspondence with a plurality of bands of the rare earth-doped optical fiber having a low gain.

According to the present invention, a plurality of low-gain bands of a rare earth-doped optical fiber can be amplified by a plurality of Raman amplifiers, respectively, to flatten the gain wavelength characteristic and widen the amplification band.

In still another embodiment of the present invention, the Raman amplifier is a distributed amplifier that amplifies the signal light in an optical fiber transmission line that transmits the signal light.

According to the present invention, since it is a distributed amplifier that amplifies the signal light in the optical fiber transmission line, it is possible to suppress the noise to be lower than that of the centralized amplifier. In addition, compared to the case where the loss in the transmission line is compensated by only distributed Raman amplification, the power of the Raman pumping light can be small as described above, and since there is no large optical power in the transmission line, deterioration of the signal pulse It is easy to handle when installing and maintaining the transmission line.

In another embodiment of the present invention, the Raman amplifier is a lumped amplifier.

According to the present invention, the fiber length of the Raman amplification fiber for propagating high optical power can be shortened, and the fiber is housed in the housing. Therefore, in the case of disconnection or the like, high power optical fiber can be obtained. Will be trapped inside the housing and will not leak out of the housing.

[0027] In still another embodiment of the present invention, the pumping light having a wavelength corresponding to a low gain band is incident on the rare earth-doped optical fiber, and the rare earth-doped optical fiber is also used as a Raman amplification medium. is doing.

According to the present invention, since the rare earth-doped optical fiber is also used as the Raman amplification medium, it is not necessary to separately provide the Raman amplification fiber, and the size can be reduced accordingly.

In a preferred embodiment of the present invention, the rare-earth-doped optical fiber has a lower concentration of the rare-earth element to be added and a longer fiber length than that of an ordinary rare-earth-doped optical fiber to increase the gain by Raman amplification. Is getting bigger.

Here, the rare earth-doped optical fiber has a rare earth doping concentration of, for example, about 500 ppm or more, and its fiber length is, for example, several meters for the C band and several tens of meters for the L band. It is a degree.

According to the present invention, the Raman amplification gain is increased by adjusting the doping concentration of the rare earth element and the fiber length of the rare earth-doped optical fiber. Therefore, even if a large gain deviation occurs in the rare earth-doped optical fiber amplifier, it can be increased. Can be compensated.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing the overall configuration of an optical amplifier according to one embodiment of the present invention.

The optical amplifying device 1 of this embodiment is an optical amplifying device for C band, and is an erbium.
EDFA2 for C-band using optical fiber doped with
Is equipped with.

This C-band EDFA 2 is similar to the conventional example and has the gain wavelength characteristics shown in FIG. 5 described above, and the low gain bands are around 1520 nm, 1540 nm and 1570 nm, respectively. Has become.

In the optical amplifying device 1 of this embodiment, the gain wavelength characteristic is flattened without lowering the gain efficiency,
Further, in order to broaden the amplification band, the following is done.

That is, in this embodiment, the EDFA
The first to third Raman amplifiers 3 to 5, which respectively set the above-mentioned respective bands having a low gain of 2 as amplification bands, are provided, and the isolator 6 is provided on the output side of the signal light. Each of the Raman amplifiers 3 to 5 is a distributed amplifier that uses an ordinary optical fiber, which is a transmission path for signal light, as an amplification medium.

Each of the Raman amplifiers 3 to 5 outputs a Raman amplification pumping light source 7 to 9 which outputs a pumping light having a wavelength corresponding to each band where the gain of the EDFA 2 is low, and the Raman amplification pumping light sources 7 to 9 respectively. The optical multiplexers 10 to 12 respectively make the pumping light enter in a direction opposite to the propagation direction of the signal light.

In the Raman amplifier, the gain depends on the pumping light wavelength, and a predetermined wavelength from the pumping light wavelength, about 110 nm.
It has a characteristic that a gain peak occurs at a wavelength shifted to the long wavelength side, and the gain gradually decreases as it becomes longer or shorter.

Therefore, in the low gain band of the EDFA 2, the above-mentioned 1520 nm, 1540 nm and 1 are set.
In order to cause a gain peak near 570 nm,
In this embodiment, the first to third Raman amplifiers 3 to 5 are used.
The wavelengths of the Raman amplification pumping light sources 7 to 9 are, for example,
The pump wavelengths of 1410 nm, 1430 nm, and 1460 nm are output, and therefore, the gain wavelength characteristics of the Raman amplifiers 3 to 5 are, as shown in FIG. 2, near the gains of 1520 nm, 1540 nm, and 1570 nm. Will have a peak.

Therefore, according to the optical amplifying apparatus 1 of this embodiment, the EDFA 2 having the gain wavelength characteristic shown in FIG.
Of the low gain band of the first to third Raman amplifiers 3 to 5
As a result, the gain wavelength characteristic is flat over a wide band as shown in FIG.
Moreover, since the gain by Raman amplification may be about several decibels, the power of the Raman amplification pumping light sources 7 to 9 may be relatively small.

In this embodiment, the pumping light wavelengths of the Raman amplification pumping light sources 7 to 9 are 1410 nm, 14
Although the thickness is set to 30 nm and 1460 nm, the present invention is not limited to this, and may be selected so that at least one of the low-gain bands of the EDFA 2 can be amplified.

For example, one Raman amplification pumping light source may be provided, and gain equalization may be performed by compensating only the gain near 1540 nm in the C band.

(Embodiment 2) FIG. 7 is a diagram showing an overall configuration of an optical amplifying device according to another embodiment of the present invention.

The optical amplifying device of this embodiment is provided with an optical fiber (EDF) 2 doped with erbium.
An EDFA for C band using 0 is provided. This E
The DFA includes a front pumping light source 21 and a front optical multiplexer 22 for making pumping light for pumping erbium from the same direction as the signal light enter the EDF 20, and pumping erbium from the opposite direction to the signal light. Is a bidirectional pumping type including a backward pumping light source 23 and a backward optical multiplexer 24 for inputting pumping light for driving the first and second isolators on the input side and the output side of the signal light, respectively. 25 and 26 are provided.

In this embodiment, in order to flatten the gain wavelength characteristic, a Raman amplification pumping light source 27 that outputs pumping light of a wavelength corresponding to a band where the gain of the EDFA is low, and this Raman amplification pumping light source 27. The Raman amplifier is provided with an optical multiplexer 28 that multiplexes the pumping light from the optical signal with the signal light and makes it enter the EDF 20. The EDF 20 also serves as a Raman amplification medium to form a Raman amplifier.

The wavelength of the pumping light from the pumping light source 27 for Raman amplification may be set to around 1430 nm when compensating for a low gain band near 1540 nm of the EDFA, for example.

According to this embodiment, the EDF 20 is
Since it also serves as a Raman amplification medium, it is not necessary to separately provide a Raman amplification fiber, and the size can be reduced accordingly.

Here, the Raman-amplified signal power Ps (z) in the fiber length Z can be expressed by the following equation.

Ps (z) = Ps (0) · exp [γ ·
(g _R・ Pp (0) / Aeff) ・ (1 / αp) ・ {1-ex
p (−αp · Z)} − αs · Z] where Ps (z): signal power at fiber length Z Ps (0): signal power at incident point γ: overlap of polarizations of pumping light and signal light Parameter g _R : Raman gain coefficient Pp (0): Pumping power at the point of incidence Aeff: Effective core area of the fiber αp: Loss of pumping light αs: Loss of signal light As shown in the above equation, desired signal power There is an optimum fiber length to obtain
The addition concentration of erbium may be adjusted so that the fiber length of the DF 20 becomes the optimum fiber length.

When the EDF 20 is also used as a Raman amplifying medium, the gain of Raman amplification can be increased by lowering the concentration of erbium to be added and increasing the fiber length, as compared with a normal EDF. it can.

(Other Embodiments) In the above-described embodiment, the first to third Raman amplifiers 3 to 5 having the low gain bands of the EDFA 2 as the amplification bands are provided. As another embodiment, as shown in FIG. 4, a single Raman amplification pumping light source 13 for outputting pumping light in which the above-mentioned three wavelengths are multiplexed is provided, and pumping from this Raman amplification pumping light source 13 is performed. Light is made incident through the optical multiplexer 14 in the direction opposite to the propagation direction of the signal light, Raman-amplified in the optical fiber transmission line, and similarly to the above-described embodiment,
A flat gain wavelength characteristic may be obtained over a wide band. In this case, the number of optical multiplexers can be reduced, and the loss of signal light can be reduced accordingly.

In the above embodiment, the ED for C band is used.
Although it was explained by applying it to FA2, ED for L band
The same applies to FA. That is, FIG.
EDF for L band having gain wavelength characteristics shown in
A is around 1560 nm, around 1580 nm and 16
A band having a low gain is near 15 nm, and therefore, a wavelength at which a gain peak occurs in the band, for example,
Raman amplification may be performed with excitation light of 1450 nm, 1470 nm, and 1505 nm.

The present invention is not limited to EDFAs, but can be similarly applied to amplifiers using neodymium or other rare earth-doped optical fibers.

In each of the above-mentioned embodiments, the Raman amplifier is a distributed type which amplifies in the optical fiber transmission line, but as another embodiment of the present invention, a lumped constant type Raman amplifier may be used. Good.

[0056]

As described above, according to the present invention, a Raman amplifier having a band in which the gain of a rare earth-doped optical fiber is low is provided as an amplification band. Therefore, the gain efficiency can be reduced without decreasing the gain efficiency as in the conventional case. Wavelength characteristics can be flattened,
Furthermore, it is possible to widen the amplification band.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical amplifier device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a gain wavelength characteristic of the Raman amplifier of FIG.

FIG. 3 is a diagram showing a gain wavelength characteristic of the optical amplifying device of FIG.

FIG. 4 is a configuration diagram of an optical amplifier according to another embodiment of the present invention.

FIG. 5 is a diagram showing a gain wavelength characteristic of an EDFA in a C band.

FIG. 6 is a diagram showing a gain wavelength characteristic of an EDFA in the L band.

FIG. 7 is a configuration diagram of an optical amplifier device according to another embodiment of the present invention.

[Explanation of symbols]

1 Optical amplifier 2 EDFA 3-5 Raman amplifier 7-9,13,27 Raman amplification pumping light source 10-12,14,28 Optical multiplexer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2K002 AA02 AB30 BA01 CA15 DA10                       EA10 GA10 HA24                 5F072 AB09 AK06 JJ20 KK11 PP07                       QQ07 RR01 YY17

Claims (8)

[Claims] 1. An optical amplifier including a rare earth-doped optical fiber that amplifies and outputs signal light by pumping light, wherein the signal light is amplified by pumping light having a wavelength corresponding to a band in which the gain of the rare earth-doped optical fiber is low. And a Raman amplifier, wherein the Raman amplifier uses a band having a low gain as an amplification band. 2. The Raman amplifier includes a Raman amplification pumping light source that outputs pumping light having a wavelength corresponding to a low gain band of the rare earth-doped optical fiber, and pumping light from the Raman amplification pumping light source. The optical amplifier according to claim 1, further comprising: an optical multiplexer that makes the signal light incident in a direction opposite to the propagation direction. 3. The optical amplification apparatus according to claim 2, wherein the Raman amplification pumping light source outputs pumping light having a plurality of wavelengths respectively corresponding to a plurality of bands in which the gain of the rare earth-doped optical fiber is low. 4. The optical amplification device according to claim 1, wherein a plurality of Raman amplifiers are provided in association with a plurality of low-gain optical bands of the rare earth-doped optical fiber. 5. The optical amplification device according to claim 1, wherein the Raman amplifier is a distributed amplifier that amplifies the signal light in an optical fiber transmission line that transmits the signal light. 6. The optical amplification device according to claim 1, wherein the Raman amplifier is a centralized amplifier. 7. The optical amplification device according to claim 1, wherein the pumping light having a wavelength corresponding to a low gain band is incident on the rare earth-doped optical fiber, and the rare earth-doped optical fiber is also used as a Raman amplification medium. . 8. The rare-earth-doped optical fiber has a lower concentration of the rare-earth element to be added and a longer fiber length to increase the gain due to Raman amplification, as compared with a normal rare-earth-doped optical fiber. Optical amplifier.