JP2000299522A - Fiber Raman amplifier and optical fiber communication system using the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a Raman amplifier, a Raman gain band △ λ
To enlarge. An optical fiber communication system using the improved Raman amplifier is provided. SOLUTION: In a fiber Raman amplifier for directly amplifying a signal light as it is by an optical fiber, an optical demultiplexer for demultiplexing the signal light according to a wavelength (or frequency), and a multiplexing of the signal light according to the wavelength. An optical multiplexer, a plurality of centralized amplification type fiber Raman amplifiers, the input signal light is divided into a plurality of wavelength regions by the optical demultiplexer, and the signal light in each wavelength region is divided into one centralized amplification type. And amplifies the signal light after passing through the centralized amplification type fiber Raman amplifier by the optical multiplexer to amplify the signal light over a wide wavelength range. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber Raman amplifier and an optical fiber communication system, and more particularly, to a fiber Raman amplifier for directly amplifying signal light as it is through an optical fiber. An optical demultiplexer, which multiplexes the signal light according to the wavelength, and a plurality of centralized amplification type fiber Raman amplifiers. And amplifies the signal light of each wavelength band by passing through one centralized amplification type fiber Raman amplifier, and multiplexes the signal light after passing through the centralized amplification type fiber Raman amplifier by the optical multiplexer. The present invention relates to a fiber Raman amplifier for amplifying signal light over a wide wavelength range and an optical fiber communication system using the same.

[0002]

2. Description of the Related Art FIG. 18 shows a basic structure of a conventional fiber Raman amplifier (hereinafter referred to as a Raman amplifier for simplicity) and an optical fiber communication system using the same. FIG. 18A shows a case of a centralized amplification type, and FIG. 18B shows a case of a distributed amplification type Raman amplifier. In FIG. 18, RS is a signal light, 1A is a first optical transmission fiber, 1B is a second optical transmission fiber, 3 is a Raman fiber, 4 is an excitation light source, and 5 is an optical multiplexer. In the case of the centralized amplification type, it is a Raman fiber gain medium having a large Raman gain coefficient. On the other hand, in the case of the distribution amplification type, the optical transmission fiber itself is used as a gain medium. In FIG. 18B, the Raman fiber and the optical transmission fiber in the case of the distribution amplification type are backward pumped with respect to the signal light using the pumping light source and the optical multiplexer, but are forwardly pumped with respect to the signal light. Alternatively, the excitation may be bidirectional.

In FIG. 18, the wavelengths of the excitation light are λpl and λp2. The wavelength of the pump light is set to a value distant to some extent (for example, 3 in the 1.5 μm band) so that the Raman gain band is maximized.
0 to 70 nm) (Reference 1: K. Rottwi)
tt and HD Kidorf, "A92nm bandwidth Raman amp
lifier ”, Proc of Optical Fiber Communications,
1998, PD6).

[0004] The values of equal Raman gain to the signal light propagation loss of the optical transmission fiber G _0, the wavelength of the Raman gain is equal to G ₀ and λsl and Ramudaesu2. If the Raman gain band at this time is △ λ, then △ λ = λs2−λsl. That is, the wavelength multiplexed signal light having the wavelength of the signal light from λsl to λs2 undergoes net amplification. Generally, when the signal light wavelength is shorter than the pump light wavelength, the dB gain becomes negative (signal light suffers loss). Therefore, as shown in FIG. 19, the Raman gain band △ λ is limited by the Raman amplification band. About 13 THz, for example, 1.
It is 100 nm in the 5 μm band.

[0005]

However, according to the prior art, in the Raman amplifier, the Raman gain band △
There is a problem that λ is limited by the Raman amplification band. An object of the present invention is to provide a technique capable of expanding a Raman gain band Δλ in a Raman amplifier. An object of the present invention is to provide an optical fiber communication system using the improved Raman amplifier. The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0006]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows. (1) In a fiber Raman amplifier that directly amplifies signal light as it is through an optical fiber, an optical demultiplexer that splits the signal light according to the wavelength (or frequency) and multiplexes the signal light according to the wavelength. An optical multiplexer; and a plurality of centralized amplification type fiber Raman amplifiers, wherein the optical demultiplexer divides the input signal light into a plurality of wavelength ranges, and converts the signal light of each wavelength range into one corresponding concentrated light. The optical signal is amplified through an amplification type fiber Raman amplifier, and the signal light after passing through the centralized amplification type fiber Raman amplifier is multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range. ing.

(2) In a fiber Raman amplifier for directly amplifying signal light as it is by an optical fiber, an optical demultiplexer for demultiplexing the signal light according to the wavelength (or frequency);
An optical multiplexer for multiplexing the signal light according to the wavelength, and a centralized amplification type fiber Raman amplifier, wherein the input signal light is divided into a plurality of wavelength ranges by the optical demultiplexer, and the signal light in a predetermined wavelength range is provided. Is amplified through a fiber Raman amplifier, the amplified signal light is input to the optical multiplexer, and the divided signal light of the other wavelength range is directly amplified by an optical fiber and input to the optical multiplexer. The input signal light and the signal light having passed through the fiber Raman amplifier are multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range.

(3) In the fiber Raman amplifier according to the means (1) or (2), the lumped amplification type fiber Raman amplifier includes a Raman fiber comprising an optical fiber as an amplification medium, a pump light source, and a signal light. An optical multiplexer for multiplexing the excitation light is provided, and the excitation light from the excitation light source is guided to the Raman fiber to optically excite the Raman fiber for amplification.

(4) In the fiber Raman amplifier according to any one of the means (1) to (3), the wavelength band in which the amplification is performed in the optical transmission fiber is set to a signal light more than the other wavelength bands. Is arranged in a wavelength region where the transmission loss is large, thereby reducing the wavelength non-uniformity of the signal to noise ratio.

(5) In an optical fiber communication system using a fiber Raman amplifier for directly amplifying signal light as light by the optical fiber, the optical transmission fiber and the signal light are demultiplexed according to the wavelength (or frequency). An optical demultiplexer, an optical demultiplexer for multiplexing the signal light according to the wavelength, and one or more centralized amplification type fiber Raman amplifiers, wherein the signal light incident on the optical transmission fiber is transmitted to the optical demultiplexer. Divides the input signal light into a plurality of wavelength ranges, amplifies the signal light in each wavelength range by passing through the corresponding one centralized amplification type fiber Raman amplifier, and after passing through the centralized amplification type fiber Raman amplifier. The signal light is multiplexed by the optical multiplexer, the signal light is amplified over a wide wavelength range, and the amplified signal light is output to an optical transmission fiber.

(6) In an optical fiber communication system using a fiber Raman amplifier for directly amplifying a signal light as it is by an optical fiber, an optical transmission fiber, and an optical multiplexer connected to and adjacent to the optical transmission fiber. An excitation light source connected adjacent to the optical multiplexer, an optical demultiplexer for demultiplexing the signal light according to the wavelength (or frequency), and an optical multiplexer for demultiplexing the signal light according to the wavelength. Comprising at least one lumped amplification type fiber Raman amplifier, guiding pumping light from the pumping light source to the optical transmission fiber through the optical multiplexer, and converting the input signal light into a plurality of wavelength ranges by the optical demultiplexer. Split,
A signal light in a predetermined wavelength band is amplified by passing through a fiber Raman amplifier, and the amplified signal light is input to the optical multiplexer, and the divided signal light in the other wavelength band is directly amplified by an optical transmission fiber. Input to the optical multiplexer, and the input signal light and the signal light after passing through the fiber Raman amplifier are multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range. Is output to the optical transmission fiber.

(7) In the optical fiber communication system according to the means (5) or (6), the centralized amplification type fiber Raman amplifier comprises a Raman fiber comprising an optical fiber as an amplification medium, an excitation light source, and a signal light. An optical multiplexer for multiplexing the excitation light is provided, and the excitation light from the excitation light source is guided to the Raman fiber to optically excite the Raman fiber for amplification.

(8) In the optical fiber communication system according to any one of the means (5) to (7), the wavelength range in which the amplification is performed in the optical transmission fiber is set to be smaller than the other wavelength ranges. It is arranged in a wavelength region where light transmission loss is large, thereby reducing the wavelength non-uniformity of the signal to noise ratio.

Here, a basic configuration in which the present invention is applied to an optical fiber communication system will be described with reference to FIG. FIG. 1 shows a case where the Raman amplifier is a centralized amplification type, where RS is a signal light, 1A is a first optical transmission fiber, 1B is a second optical transmission fiber, 2 is an optical demultiplexer, 3 is a Raman fiber,
A and 4B are pump light sources, 5 is a first optical multiplexer, and 6 is a second optical multiplexer.

In the case of the centralized amplification type, as shown in FIG. 1, a signal light RS having a wavelength of λsl to λs4 (λsl <λs2 <λs3 <λs4) first receives a loss through an optical transmission fiber and passes through. Then, a short wavelength band (λsl to λs2) is obtained by the optical demultiplexer 2,
The light is separated into long wavelength bands (λs3 to λs4), and is amplified by passing through Raman amplifiers # 1 and # 2, respectively. Raman amplifier #
1 and # 2 are pumped by pumping lights of wavelengths λpl and λp2 and λp3 and λp4, respectively.

Here, the case where the number of pumping light wavelengths is 2 is shown, but the same applies to the case where the number of pumping light wavelengths is 3 or more. The difference is in the magnitude of the ripple of the gain spectrum and the like, and the conclusion in the following description is different. There is no. Raman amplifier # 1, # 2
Are amplified by the optical multiplexer 5, and then transmitted to the second optical transmission fiber 1B. The gain spectrum at this time is shown in FIG. In FIG. 2A, the frequency band is twice as large as the Raman gain band in the related art (approximately twice the wavelength band).

In the case of the distributed amplification and the centralized amplification mixed type, as shown in FIG. 3, the wavelength is changed from λsl to λs4 (λsl <λs2 <λs3 <
The signal light of λs4) first enters the optical transmission fiber 1A, and the signal light having a wavelength of λsl to λs2 obtains the Raman gain together with the loss of the optical transmission fiber. On the other hand, if the wavelength is λs3 to λ
The signal light of s4 experiences an optical transmission fiber loss. afterwards,
The short wavelength band (λsl to λs2) and the long wavelength band (λ
s3 to λs4) by the optical demultiplexer 2, and the signal light in the short wavelength band directly reaches the second optical multiplexer 6. On the other hand, the signal light in the long wavelength band is amplified by the Raman amplifier #,
To the optical multiplexer 6.

The Raman amplifier # is pumped by pumping light of wavelengths λp3 and λp4 from the pumping light source 4B. The signal light of the short wavelength band and the long wave and the band multiplexed by the second optical multiplexer 6 are transmitted to the optical transmission fiber 1B. As shown in FIG. 2B, the gain spectrum at this time has a frequency band twice as large as the Raman gain band in the related art (about twice as large as the wavelength band).

As described above, according to the present invention, the Raman gain band is doubled in the frequency band (approximately twice in the wave ≧ band) as compared with the prior art. Next, features of the signal-to-noise ratio in the present invention and a configuration using the features will be described. Generally, the loss spectrum of a silica-based optical transmission fiber is as shown in FIG. The minimum loss wavelength is around 1.6 μm. Therefore, in the present invention,
The signal-to-noise ratio when the long wavelength band of the Raman gain is set near the 1.5 μm band and the short wavelength band is set near the 1.4 μm band is as shown in FIG. FIG. 5A shows a case of the centralized amplification type, and FIG. 5B shows a case of the distributed amplification and the centralized amplification mixed type.

In the centralized amplification type, since the optical transmission fiber loss becomes larger as the wavelength becomes shorter, the signal-to-noise ratio becomes smaller in the short wavelength band than in the long wavelength band. In general, the transmission distance in the short wavelength band increases in the long wavelength band. It becomes shorter than the transmission distance, which causes restrictions and disadvantages in the system configuration.

On the other hand, in the distributed amplification and the centralized amplification mixed type, since the distributed amplification is used in the short wavelength band, the signal-to-noise ratio is improved (Reference 2: H. Masuda, S. Kawai, K.-I. Suzu
ki, and K. Aida, "75nm 3-dB gain-band optical
amplification with erbium-doped fluoride fiber am
plfiers and distributed Raman amplifiers in 9 ×
2.5Gb / s WDM transmission experiment "Pro
c. of European Conference on Optical Communica
tions, 1997, Vol. 3, see pages 73 to 76) to cancel the above-mentioned decrease in the signal-to-noise ratio due to transmission fiber loss. As a result, there is an advantage that the difference between the long wavelength band and the short wavelength band of the signal-to-noise ratio is reduced, and the transmission distance restriction in the short wavelength band can be removed.

Hereinafter, the present invention will be described in detail together with embodiments (examples) with reference to the drawings. In all the drawings for describing the embodiments, components having the same function are denoted by the same reference numerals, and their repeated description will be omitted.

[0023]

(Embodiment 1) FIG. 6 is a schematic configuration diagram showing a schematic configuration of an optical communication system using a lumped amplification type Raman amplifier according to Embodiment 1 of the present invention. In FIG. 6, RS is an input signal light, # 1 and # 2 are lumped amplification type Raman amplifiers, 1A is a first optical transmission fiber, 1B
Is a second optical transmission fiber, 2 is an optical demultiplexer, 3 is a Raman fiber, 4A, 4B, 4C and 4D are pump light sources, 5A and 5
B is a first optical multiplexer, 6 is a second optical multiplexer, and 7 is an isolator.

In the optical communication system using the centralized amplification type Raman amplifier according to the first embodiment, as shown in FIG. 6, two Raman amplifiers # 1 and # 2 are composed of a first optical transmission fiber 1A and a second optical transmission fiber 1A. Are arranged in parallel with the optical transmission fiber 1B. The length of each of the first optical transmission fiber 1A and the second optical transmission fiber 1B and the signal light transmission loss are 80 km.
And about 20 dB. Each Raman amplifier # 1, # 2
Two Raman fibers 3 and two pumping light sources 4A, 4B
, One isolator 7 and two first multiplexers 5. The length of the Raman fiber 3 is 8 km, and the mode field diameter is 5 μm. By installing the isolator 7 between the two Raman fibers 3, the Raman gain is divided into the two Raman fibers 3, and noise due to multiple Rayleigh scattering generated in the Raman fiber 3 when the Raman gain becomes high. (Reference 3: P.
B. Hansen et al., IEEE Photonics Technology
Letters, Vol. 10, No. 1, pp. 159-161, 1998).

The pump light sources 4A and 4B are, for example, semiconductor lasers, and the input light power to the Raman fiber 3 is 1
It is about 200 mW per excitation light wavelength. The wavelength of the pump light is 1.3 at the pump light sources 4A and 4B of the Raman amplifier # 1.
2 μm and 1.40 μm, and 1.42 μm and 1.50 μm for the pump light sources 4C and 4D of the Raman amplifier # 2.

An optical splitter 2 installed after the first optical transmission fiber 1A splits light having a wavelength of 1.55 μm or less and light having a wavelength of 1.52 μm or more. The optical demultiplexer 2 is, for example, an optical filter using a dielectric multilayer film. The wavelength of the signal light is 1.4
2 μm to 1.50 μm and 1.52 μm to 1.60 μm, and the signal light of 1.42 μm to 1.50 μm enters the Raman amplifier # 1 and the signal light of 1.52 μm to 1.60 μm enters the Raman amplifier # 2 And amplified. The optical multiplexer 6 installed in front of the second optical transmission fiber 1B multiplexes light of 1.55 μm or less and light of 1.52 μm or more.

FIG. 7 shows a gain spectrum obtained by using the above configuration. Here, the gain is a gain between the first and second two optical transmission fibers 1A and 1B. Transmission fiber loss is about 20 dB. According to the first embodiment, FIG.
From 1.42 μm to 1.50 μm and 1.52 μm to 1.
At 60 μm, a net gain (difference between the gain and the transmission loss) is obtained. As described above, according to the first embodiment, a bandwidth twice that of the related art is obtained.

(Embodiment 2) FIG. 8 is a schematic configuration diagram showing a schematic configuration of an optical communication system using a mixed Raman amplifier of a centralized amplification and distributed amplification type according to a second embodiment of the present invention. In the optical communication system according to the second embodiment, as shown in FIG. 8, one Raman amplifier # is connected to the first optical transmission fiber 1A.
And the second optical transmission fiber 1B.
First optical transmission fiber 1A and second optical transmission fiber 1
B length and signal light transmission loss are 50km and about 15dB
It is. The first optical transmission fiber 1A and the second optical transmission fiber 1B are bidirectionally pumped by two pumping light sources 4E and 4F to perform distributed amplification. Generally, Raman gain in an optical transmission fiber is limited to about 20 dB or less in order to avoid noise due to multiple Rayleigh scattering (see Reference 3).

The Raman amplifier # has two Raman fibers 3, two pumping light sources 4A and 4B, one isolator 7, and two optical multiplexers 5. Raman fiber 3
Has a length of 5 km and a mode field diameter of 5 μm.

The pump light sources 4A and 4B are, for example, semiconductor lasers, and the input light power to the Raman fiber 3 is 1
It is about 200 mW per excitation light wavelength. Embodiment 1
The transmission loss is smaller than that of
The economy is being shortened by shortening the length. The wavelengths of the pumping light are 1.32 μm and 1.40 μm for the pumping light sources 4E and 4F of the optical transmission fibers 1A and 1B, respectively, and 1.42 μm and 1.50 μm for the Raman amplifier # pumping light sources 4C and 4D.
m.

An optical splitter 2 installed after the first optical transmission fiber 1A splits light having a size of 1.55 μm or less and light having a size of 1.52 μm or more. The optical multiplexer 6 installed in front of the second optical transmission fiber 1B has a wavelength of 1.55 μm or less and 1.52 μm.
The above lights are combined.

The wavelength of the signal light is 1.42 μm to 1.50 μm.
m and 1.52 μm to 1.60 μm, and the signal light of 1.42 μm to 1.50 μm is Raman-amplified in the first optical transmission fiber 1A, but the signal light of 1.52 μm to 1.60 μm is Passes without Raman amplification.

1.42 μm split by the optical splitter 2
The signal light of .about.1.50 μm is directly transmitted to the second optical multiplexer 6.
Reach On the other hand, 1.52 demultiplexed by the optical demultiplexer 2
The signal light of μm to 1.60 μm reaches the second optical multiplexer 6 after being amplified by the Raman amplifier #.

FIG. 9 shows a gain spectrum obtained by using the above configuration. Here, the gain is the sum of the Raman distribution gain generated in the first optical transmission fiber 1A and the gain between the two optical transmission fibers. Optical transmission fiber loss is about 15d
B. FIG. 9 shows that a net gain (difference between the gain and the transmission loss) is obtained at 1.42 μm to 1.50 μm and 1.52 μm to 1.60 μm. As described above, according to the second embodiment, a bandwidth twice that of the related art is obtained.

The characteristics of the wavelength dependence of the signal-to-noise ratio obtained in the first and second embodiments are shown in FIGS. 10 and 11, respectively. In the first embodiment, the value of the signal-to-noise ratio in the short wavelength band is about 3 dB smaller than the signal-to-noise ratio in the long wavelength band. In the second embodiment, however, the difference is reduced to near 0 dB. .

This is because distribution amplification is used in the second embodiment as described above. Therefore,
In the second embodiment, since the signal-to-noise ratios of the short wavelength band and the long wavelength band have substantially the same value, the system parameters such as the transmission distance of the signal light in the short wavelength band and the long wavelength band are changed to the two There is an advantage that it can be set without distinction in the band.

(Embodiment 3) FIG. 12 is a schematic configuration diagram showing an outline configuration of an optical communication system using a Raman amplifier of a mixed type of a concentrated amplification and a distribution amplification according to a third embodiment of the present invention. As shown in FIG. 12, in the optical communication system according to the third embodiment, the lengths of the first optical transmission fiber 1A and the second optical transmission fiber 1B and the signal optical transmission loss are 80%.
km and about 20 dB. First optical transmission fiber 1A
Are bidirectionally pumped by two pumping light sources 4E and 4F to perform distributed amplification. The Raman amplifier # 2 has two Raman fibers 3, two pump light sources 4C and 4D, one isolator 7, and two first optical multiplexers 5. On the other hand, the Raman amplifier # 1 has one Raman fiber 3 and one Raman fiber.
It has one pumping light source 4, one isolator 7, and one first optical multiplexer 5B.

The length of each Raman fiber 3 is 8 k
m, the mode field diameter is 5 μm. The pump light sources 4, 4C, 4D, 4E, and 4F are, for example, semiconductor lasers, and the input light power to the Raman fiber 3 is about 200 mW per one pump light wavelength.

The wavelength of the pump light is 1.32 μm and 1.4 at the optical transmission fiber 1A and the pump light source 4 of the Raman amplifier # 1.
0 μm, the pump light sources 4C and 4D of Raman amplifier # 2
42 μm and 1.50 μm.

The optical splitter 2 installed after the first optical transmission fiber 1A splits the light of 1.55 μm or less and the light of 1.52 μm or more. The second optical multiplexer 6 installed in front of the second transmission fiber 1B transmits light of 1.55 μm or less to 1.52 μm.
The light of μm or more is multiplexed.

The wavelength of the signal light is 1.42 μm to 1.50 μm.
m and 1.52 μm to 1.60 μm, and the signal light of 1.42 μm to 1.50 μm is Raman-amplified in the first optical transmission fiber 1A, while the signal light of 1.52 μm to 1.60 μm is Passes without amplification.

1.42 μm demultiplexed by the optical demultiplexer 2
The signal light of １1.50 μm is further amplified by the Raman amplifier # 1 and reaches the second optical multiplexer 6. On the other hand, the 1.52 μm to 1.60 μm signal light split by the optical splitter 2 is amplified by the Raman amplifier # 2 and then reaches the second optical multiplexer 6.

FIG. 13 shows a gain spectrum obtained by using the above configuration. Here, the gain is the sum of the Raman distribution gain generated in the first optical transmission fiber 1A and the gain between the two optical transmission fibers 1A and 1B. Transmission fiber loss is about 20 dB. From FIG. 13, 1.42 μm to 1.5.
At 0 μm and 1.52 μm to 1.60 μm, a net gain (difference between the gain and the transmission loss) is obtained. As described above, according to the third embodiment, a bandwidth twice that of the related art is obtained.

(Embodiment 4) FIG. 14 is a schematic configuration diagram showing a schematic configuration of an optical communication system using a centralized amplification type Raman amplifier according to Embodiment 4 of the present invention. In the optical communication system according to the fourth embodiment, as shown in FIG. 14, the lengths of the optical transmission fibers 1A and 1B and the signal light transmission loss are 80 km and about 20 dB. Raman amplifier #
1, # 2 and # 3 are two Raman fibers 3 and 2
Excitation light sources 4A, 4B (4C, 4D, 4G, 4H)
, One isolator 7 and two optical multiplexers 5. The length of each Raman fiber 3 is 8 km, and the mode field diameter is 5 μm. Excitation light source 4A, 4B
Is a semiconductor laser, for example, and the input light power to the Raman fiber 3 is about 200 mW per pumping light wavelength.

The wavelengths of the pump light are 1.22 μm and 1.30 μm for the pump light sources 4G and 4H of the Raman amplifier # 1, and 1.32 μm and 1.30 μm for the pump light sources 4A and 4B of the Raman amplifier # 2.
40 μm, 1.42 μm and 1.50 μm for the pump light sources 4C and 4D of the Raman amplifier # 3.

The wavelength of the signal light is 1.32 μm to 1.40 μm.
m, 1.42 μm-1.50 μm, and 1.52 μm-1.
The optical splitter 2 having a wavelength of 60 μm and installed after the first optical transmission fiber 1A splits the light of these three wavelength bands. On the other hand, the second optical multiplexer 6 installed in front of the second optical transmission fiber 1B multiplexes the lights of these three wavelength bands. 1.32 μm to 1.40 μm, 1.4 demultiplexed by the optical demultiplexer 2
2 μm to 1.50 μm, and 1.52 μm to 1.60 μm
After being Raman-amplified by the Raman amplifiers # 1, # 2, and # 3, respectively, reach the second optical multiplexer 6.

FIG. 15 shows a gain spectrum obtained by using the above configuration. Here, the gain is a gain between the two optical transmission fibers 1A and 1B. Transmission fiber loss is about 2
0 dB. From FIG. 15, 1.32 μm to 1.40 μm
m, 1.42 μm-1.50 μm, and 1.52 μm-1.
At 60 μm, a net gain (difference between the gain and the transmission loss) is obtained. As described above, according to the fourth embodiment, a band three times that of the related art is obtained.

(Embodiment 5) FIG. 16 is a schematic configuration diagram showing a schematic configuration of an optical communication system using a mixed-type Raman amplifier of centralized amplification and distributed amplification according to Embodiment 5 of the present invention. As shown in FIG. 16, the optical communication system according to the fifth embodiment is an optical communication system using a Raman amplifier of a type that includes both centralized amplification and distributed amplification. Optical transmission fiber 1A, 1B
Are 50 km and about 15 dB, respectively. The optical communication system according to the fifth embodiment includes Raman amplifiers # 1 and # 2 and two Raman fibers 3 each.
And two pump light sources 4A and 4B (4C and 4D), one isolator 7 and two optical multiplexers 5. The length of each Raman fiber 3 is 5 km, and the mode field diameter is 5 μm.

The pumping light sources 4A to 4H are, for example, semiconductor lasers, and the input light power to the Raman fiber 3 is 1
It is about 200 mW per excitation light wavelength. The wavelength of the excitation light is 1.2 at the excitation light sources 4G and 4H of the optical transmission fiber 1A.
2 μm and 1.30 μm, 1.32 μm and 1.40 μm for Raman amplifier # 1 pumping light sources 4A and 4B, 1.42 μm and 1.50 for Raman amplifier # 2 pumping light sources 4C and 4D
μm.

The wavelength of the signal light is 1.32 μm to 1.40 μ.
m, 1.42 μm-1.50 μm, and 1.52 μm-1.
The optical splitter 2 having a wavelength of 60 μm and installed after the first optical transmission fiber 1A splits the light of these three wavelength bands. On the other hand, the optical multiplexer 6 installed in front of the second optical transmission fiber 1B multiplexes the lights of these three wavelength bands.

In the first optical transmission fiber 1A, 1.32
Only the signal light of μm to 1.40 μm is amplified. The 1.32 μm to 1.40 μm signal light split by the optical splitter 2 reaches the second optical multiplexer 6 as it is. On the other hand, 1.42 μm to 1.50 μm demultiplexed by the optical demultiplexer 2,
And the signal light of 1.52 μm to 1.60 μm reach the second optical multiplexer 6 after being Raman-amplified by the Raman amplifiers # 1 and # 2, respectively.

FIG. 17 shows a gain spectrum obtained by using the above configuration. Here, the gain is the sum of the Raman distribution gain generated in the first optical transmission fiber 1A and the gain between the two optical transmission fibers 1A and 1B. Transmission fiber loss is about 15 dB.

From FIG. 17, 1.32 μm to 1.40 μm,
1.42 μm-1.50 μm and 1.52 μm-1.60
A net gain (the difference between the gain and the transmission loss) is obtained at μm. As described above, according to the fifth embodiment, three times the bandwidth of the related art is obtained.

As described above, the present invention has been specifically described based on the above-described embodiment. However, the present invention is not limited to the above-described embodiment, and may be variously modified without departing from the gist thereof. Of course.

[0055]

As described above, according to the present invention,
The gain band can be expanded to twice or more as compared with the prior art. In addition, in the configuration of centralized amplification and mixed distribution width,
By applying distributed amplification to the short wavelength band, the disadvantage that the signal-to-noise ratio of the short wavelength band is lower than that of the long wavelength band can be avoided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a basic configuration in which a lumped amplification type Raman amplifier of the present invention is applied to an optical fiber communication system.

FIG. 2 is a diagram showing gain spectra in the case of centralized amplification of the present invention and in the case of distributed amplification and centralized amplification mixed type.

FIG. 3 is a schematic configuration diagram showing a basic configuration in which a case of a mixed amplification and a centralized amplification of the present invention is applied to an optical fiber communication system in a case of a centralized amplification.

FIG. 4 is a diagram illustrating optical transmission fiber loss.

FIG. 5 is a diagram showing a signal-to-noise spectrum in the case of centralized amplification and in the case of distributed amplification and centralized amplification mixed type according to the present invention.

FIG. 6 is a schematic configuration diagram illustrating a schematic configuration of an optical communication system using a centralized amplification type Raman amplifier according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a gain spectrum obtained by using the configuration of FIG. 6;

FIG. 8 is a schematic configuration diagram showing a schematic configuration of an optical communication system using a mixed-type Raman amplifier of lumped amplification and distributed amplification according to a second embodiment of the present invention.

FIG. 9 is a diagram showing a gain spectrum obtained by using the configuration of FIG. 8;

FIG. 10 is a diagram illustrating a characteristic of a wavelength dependence of a signal-to-noise ratio obtained in the first embodiment.

FIG. 11 is a diagram illustrating a characteristic of a wavelength dependence of a signal-to-noise ratio obtained in the second embodiment.

FIG. 12 is a schematic pictorial diagram showing a schematic configuration of an optical communication system using a mixed-type Raman amplifier of centralized amplification and distributed amplification according to a third embodiment of the present invention.

FIG. 13 is a diagram showing a gain spectrum obtained by using the configuration of FIG.

FIG. 14 is a schematic diagram illustrating a schematic configuration of an optical communication system using a centralized amplification type Raman amplifier according to a fourth embodiment of the present invention.

FIG. 15 is a diagram showing a gain spectrum obtained by using the configuration of FIG. 14;

FIG. 16 is a schematic configuration diagram illustrating a schematic configuration of an optical communication system using a mixed-type Raman amplifier according to a fifth embodiment of the present invention.

FIG. 17 is a diagram showing a gain spectrum obtained by using the configuration of FIG. 16;

FIG. 18 is a schematic configuration diagram showing a basic configuration in which a conventional centralized amplification type Raman amplifier is applied to an optical fiber communication system.

FIG. 19 is a schematic configuration diagram showing a basic configuration in which a conventional distributed amplification and centralized amplification mixed type is applied to an optical fiber communication system in a case of centralized amplification.

[Explanation of symbols]

RS: input signal light, #, # 1, # 2: concentrated amplification type Raman amplifier, 1A: first optical transmission fiber, 1B: second optical transmission fiber, 2: optical demultiplexer, 3: Raman fiber ,
4, 4A to 4H: excitation light source, 5: first optical multiplexer, 6:
Second optical multiplexer, 7... Isolator.

Claims (8)

[Claims] 1. A fiber Raman amplifier for directly amplifying signal light as it is through an optical fiber, comprising: an optical demultiplexer for demultiplexing the signal light according to a wavelength (or frequency); An optical multiplexer that oscillates and a plurality of centralized amplification type fiber Raman amplifiers, the input signal light is divided into a plurality of wavelength regions by the optical demultiplexer, and one signal light corresponding to each wavelength region is correspondingly divided. A configuration in which the signal light is amplified through the centralized amplification type fiber Raman amplifier, and the signal light after passing through the centralized amplification type fiber Raman amplifier is multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range. A fiber Raman amplifier characterized in that: 2. A fiber Raman amplifier for directly amplifying signal light as it is through an optical fiber, comprising: an optical demultiplexer for demultiplexing the signal light according to a wavelength (or frequency); An optical multiplexer that oscillates and a centralized amplification type fiber Raman amplifier, the input signal light is divided into a plurality of wavelength regions by the optical demultiplexer, and the signal light in a predetermined wavelength region is amplified by passing through a fiber Raman amplifier. Then, the amplified signal light is input to the optical multiplexer, and the divided signal light of the other wavelength band is directly amplified by an optical fiber and input to the optical multiplexer, and the input signal light is input. And a signal light that has passed through the fiber Raman amplifier, and is multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range. 3. The lumped amplification type fiber Raman amplifier comprises a Raman fiber comprising an optical fiber as an amplification medium, a pump light source, and an optical multiplexer for multiplexing signal light and pump light. 3. The fiber Raman amplifier according to claim 1, wherein the pumping light is guided to the Raman fiber to optically excite the Raman fiber to perform amplification. 4. 4. A wavelength range in which amplification in the optical transmission fiber is performed is arranged in a wavelength range in which transmission loss of signal light is greater than other wavelength ranges, and a wavelength non-uniformity of a signal-to-noise ratio is reduced. The fiber Raman amplifier according to claim 1, wherein the fiber Raman amplifier is reduced. 5. In an optical fiber communication system using a fiber Raman amplifier for directly amplifying signal light as it is by an optical fiber, an optical transmission fiber and a light component for demultiplexing the signal light according to the wavelength (or frequency). An optical multiplexer that multiplexes the signal light according to the wavelength, and one or more centralized amplification type fiber Raman amplifiers, and the signal light incident on the optical transmission fiber is input by the optical demultiplexer. The signal light is divided into a plurality of wavelength ranges, and the signal light in each wavelength range is amplified by passing through a corresponding one of the centralized amplification type fiber Raman amplifiers, and the signal light after passing through the centralized amplification type fiber Raman amplifier An optical fiber communication system, comprising: amplifying the signal light by the optical multiplexer, amplifying the signal light over a wide wavelength range, and transmitting the amplified signal light to an optical transmission fiber. 6. An optical fiber communication system using a fiber Raman amplifier for directly amplifying signal light as it is by an optical fiber, comprising: an optical transmission fiber; an optical multiplexer connected to and connected to the optical transmission fiber; An excitation light source connected adjacent to the optical multiplexer, an optical demultiplexer for demultiplexing the signal light according to the wavelength (or frequency), and an optical multiplexer for demultiplexing the signal light according to the wavelength; At least one lumped amplification type fiber Raman amplifier is provided, the pump light from the pump light source is guided to the optical transmission fiber through the optical multiplexer, and the input signal light is divided into a plurality of wavelength ranges by the optical demultiplexer. Then, the signal light in a predetermined wavelength range is amplified by passing through a fiber Raman amplifier, and the amplified signal light is input to the optical multiplexer, and the signal light in the other wavelength range is directly divided into an optical transmission fiber. Amplified by The optical signal is input to an optical multiplexer, and the input signal light and the signal light after passing through the fiber Raman amplifier are multiplexed by the optical multiplexer to amplify the signal light over a wide wavelength range and transmit the optical signal. An optical fiber communication system characterized in that the optical fiber is transmitted to a fiber. 7. The lumped amplification type fiber Raman amplifier includes a Raman fiber composed of an optical fiber as an amplification medium, an excitation light source, and a multiplexer for multiplexing signal light and excitation light. 7. The optical fiber communication system according to claim 5, wherein the pumping light is guided to the Raman fiber to optically pump the Raman fiber to perform amplification. 8. A wavelength range in which amplification in the optical transmission fiber is performed is arranged in a wavelength range in which transmission loss of signal light is greater than other wavelength ranges, and a wavelength non-uniformity of a signal-to-noise ratio is reduced. The optical fiber communication system according to claim 5, wherein the number is reduced.