JP2005101516A - Optical fiber communication system, exciting light source device, and optical communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber communication system for remote communication and an optical signal amplification device, which extends a transmission distance of an optical signal. <P>SOLUTION: An optical fiber communication system 1 comprises: a primary exciting light source 31 provided at least one of terminal stations A, B installed at both ends of an optical fiber 50 for transmission of an optical signal S for outputting primary excitation light R<SB>1</SB>; an EDF amplifier 40 for amplifying the optical signal S when the primary exciting light R<SB>1</SB>and the optical signal S are superimposed and inputted; and a secondary Raman light source 32 for outputting secondary Raman exciting light R<SB>2</SB>to amplify the primary exciting light R<SB>1</SB>when an optical fiber 50b is superimposed on the primary exciting light R<SB>1</SB>and outputted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical fiber communication system that performs remote communication, and more particularly, to an optical fiber communication system including a remote pumping optical amplification system that amplifies an optical signal.

  As an optical fiber communication system for amplifying an attenuated optical signal without relying on an optical-electrical conversion element for long-distance repeater transmission of an optical signal from a transmitter unit to a receiver unit which are separated from each other, the following remote control has been conventionally performed. Excitation light amplification systems are known. FIG. 9 is a block diagram showing a basic configuration of a conventional remote excitation light amplification system.

  The remote pumping optical amplification system 8 includes a transmission unit 110 that transmits an optical signal S, a reception unit 120 that receives the optical signal S, an optical fiber 150 that is a transmission path of the optical signal S, and an intermediate path of the optical fiber 150. And an EDF amplifier 140 that amplifies the power of the optical signal S that passes through.

A transmitter (OS: Optical Sender) 112 serving as a light source of the optical signal S and an amplifier 111 that amplifies the light emitted from the transmitter 112 to obtain the optical signal S are disposed inside the transmission unit 110.
Inside the receiving unit 120, a receiver (OR: Optical Receiver) 123 that receives the optical signal S through the coupler 121, a pumping light source 131 that outputs the pumping light R, and the pumping light R that is output as light A coupler 121 for transmitting the fiber 150 in the direction of the EDF amplifier 140 is disposed.

  The EDF amplifier 140 is constituted by a silica-based fiber having a length of several tens to 100 m doped with erbium. When the pumping light R is input to the EDF amplifier 140, the power of the optical signal S passing through the EDF amplifier 140 is amplified. By this amplification action, the power of the optical signal S whose power has been attenuated due to transmission loss can be recovered greatly.

Even if the optical signal S transmitted through the optical fiber 150 is lost due to the configuration of the remote excitation light amplification system 8 described above, the power of the optical signal S is amplified by the EDF amplifier 140 provided in the intermediate path, Long-distance optical communication between remote terminal stations becomes possible. (For example, refer to Patent Document 1).
Japanese Patent No. 2714611 (page 5-9, FIG. 9 etc.)

  However, the method for amplifying the power of the optical signal S by inputting the pumping light R to the EDF amplifier 140 interposed during the transmission of the optical signal S described above has the following problems. That is, when it is assumed that long-distance optical communication is performed between end stations that are further apart, the output of the pumping light R output from the pumping light source 131 must be improved. In short, in consideration of transmission loss of the pumping light R as well, it is necessary that the power of the pumping light R necessary for the optical signal S to obtain a desired amplification gain is ensured at the time of input to the EDF amplifier 140. Because there is.

  On the other hand, when the output power of the excitation light R in the excitation light source 131 is improved, another problem occurs. This problem is that when the power of the pumping light R transmitted through the optical fiber 150 exceeds a predetermined threshold, laser oscillation occurs in the transmission band of the optical signal S, and improvement in the gain of the optical signal S cannot be expected. Therefore, there is an upper limit to the power of the pumping light R that can be output from the pumping light source 131 in order to avoid this laser oscillation, and this upper limit also limits the distance that the optical signal S can be transmitted.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical fiber communication system that increases the transmission distance of the optical signal S.

The present invention was created to achieve the above-described object,
The optical fiber communication system according to claim 1 is an optical fiber communication system that performs communication between two terminal stations installed at both ends of an optical fiber that transmits an optical signal, and at least one of the two terminal stations. A primary pumping light output means for outputting primary pumping light to the optical fiber; and an optical signal amplified when the primary pumping light and the optical signal are superimposed and input. One or two or more amplifying means and the primary pumping light output means arranged in the terminal station, and secondary pumping light that amplifies the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light Secondary pumping light output means for outputting.

  According to such a configuration, the primary pumping light output unit and the secondary pumping light output unit are arranged at one or both of the two terminal stations. The primary pumping light output from the primary pumping light output unit is transmitted through the optical fiber and input to the amplifying unit. The power of the optical signal passing through the amplification means is amplified using the first excitation light.

  On the other hand, the secondary pumping light output from the secondary pumping light output means is also transmitted to the same optical fiber together with the primary pumping light. At this time, since the transmission distance is long, even if the primary pumping light loses power due to transmission loss, energy is absorbed and amplified from the secondary pumping light, and this power loss is compensated. Due to the amplification effect of the primary pumping light by the secondary pumping light, it is possible to secure the input power of the primary pumping light necessary for securing the amplification gain of the amplifying means without increasing the output of the primary pumping light output means. it can.

  A second aspect of the present invention is the optical fiber communication system according to the first aspect, wherein the optical signal has a predetermined bandwidth by multiplexing a plurality of signals having different wavelengths, and the primary pumping light has a wavelength of A plurality of different first single wavelength components are multiplexed to have a predetermined bandwidth, and the secondary pumping light is multiplexed with a plurality of second single wavelength components having different wavelengths to have a predetermined bandwidth, Amplifying effective bands of a plurality of first single wavelength components cover the band of the optical signal, and amplifying effective bands of the plurality of second single wavelength components cover the band of the primary pumping light. .

  According to such a configuration, since the primary pumping light is composed of a plurality of first single wavelength components, the amplification effective bandwidth capable of amplifying the optical signal in the amplifying unit is widened. As a result, the optical signal can be further broadened. Further, since the plurality of first single wavelength components are included in the effective amplification band of the secondary pumping light, the optical power is supplied from the secondary pumping light and Raman amplification is performed in the process of transmitting the optical fiber. Then, the amplified primary pump light can further amplify the optical signal having a broad band using the received optical power.

  According to a third aspect of the present invention, in the optical fiber communication system according to the first or second aspect, the second pumping light output unit and the second pumping light output unit are disposed in the terminal station, and the second pumping light is superimposed on the second pumping light. It is characterized by comprising tertiary pumping light output means for outputting tertiary pumping light that amplifies the secondary pumping light when transmitted through an optical fiber.

  According to such a configuration, the tertiary pumping light output from the tertiary pumping light output means is transmitted through the optical fiber together with the secondary pumping light. At this time, since the transmission distance is long, even if a transmission loss occurs in the secondary pumping light, the transmission loss is compensated by absorbing the energy of the tertiary pumping light. Thus, since the power loss of the secondary pumping light is suppressed, the amplification effect of the primary pumping light by the secondary pumping light is not reduced.

  According to a fourth aspect of the present invention, in the optical fiber communication system according to the third aspect, the tertiary pumping light has a predetermined bandwidth by multiplexing a plurality of third single wavelength components having different wavelengths. The amplification effective band of a plurality of third single wavelength components covers the band of the secondary pumping light.

  According to such a configuration, the plurality of second single wavelength components constituting the secondary pumping light are included in the effective amplification band of the tertiary pumping light. Therefore, in the process of transmitting the optical fiber, the optical power from the tertiary pumping light is increased. It is donated and Raman amplified. The amplified secondary pump light can amplify the primary pump light having a bandwidth using the received optical power.

  According to a fifth aspect of the present invention, in the optical fiber communication system according to any one of the second to fourth aspects, the primary pumping light, the secondary pumping light, or the tertiary pumping light having a bandwidth. Any one of the plurality of first single-wavelength components, the plurality of second single-wavelength components, or the plurality of third-wavelength components constituting each of them, the power on the low wavelength component side is higher than the power on the high wavelength component side Is also set large.

  According to such a configuration, taking the primary pumping light as an example, in the process of transmitting the optical fiber, the optical power of the low wavelength component among the plurality of first single wavelength components is provided to the high wavelength component, and this high wavelength The component is Raman amplified. Thereby, in the process of transmitting the optical fiber, the optical power of the plurality of first wavelength components of the primary pumping light is equalized. The same action can be obtained with respect to the second single wavelength component constituting the secondary excitation light and the third single wavelength component constituting the tertiary excitation light.

  According to a sixth aspect of the present invention, in the optical fiber communication system according to any one of the first to fifth aspects, the optical fiber that connects at least one of the two terminal stations to the nearest amplifying means. The core diameter in a certain section from the terminal station is thicker than other portions.

  According to such a configuration, the nonlinear effect in the high-power primary pumping light immediately after being output from the primary pumping light output means to the optical fiber can be suppressed. Moreover, the nonlinear effect in the high-power optical signal immediately after being output from the transmitter to the optical fiber can also be suppressed. Thereby, favorable communication quality can be ensured.

  The optical fiber communication system according to claim 7 is the optical fiber communication system according to any one of claims 1 to 6, wherein the amplification means is an optical fiber doped with erbium. And

According to such a configuration, the amplifying means is composed of an optical fiber in which erbium (Er), which is one of rare earth elements, is doped in the core. Thereby, when primary excitation light having a wavelength of 980 nm or 1480 nm is absorbed by Er ³⁺ ions, electrons are excited to a high energy level. When an optical signal having a wavelength of 1550 nm band (C band) and 1590 band (L band) is incident on the Er ³⁺ ions in the excited state, stimulated emission occurs and the power of the optical signal is amplified.

  The optical fiber communication system according to any one of claims 1 to 7, wherein the secondary pumping light is preferably secondary Raman pumping light.

  According to such a configuration, the secondary excitation light is composed of secondary Raman excitation light having a wavelength band of about 1380 nm. Thereby, if the primary pumping light is light having a wavelength of 1480 nm, for example, the primary pumping light is Raman-amplified and transmitted to the amplifying means by being superimposed on the secondary Raman pumping light in the optical fiber. Will be.

  The optical fiber communication system according to any one of claims 3 to 7, wherein the tertiary pumping light is preferably tertiary Raman pumping light.

  According to such a configuration, the tertiary excitation light is composed of tertiary Raman excitation light having a wavelength band of about 1280 nm. As a result, when the third-order Raman pump light and the second-order pump light having a wavelength of about 1380 nm are transmitted while being superimposed in the optical fiber, the second-order pump light is Raman-amplified.

  The pumping light source device according to claim 8 is a pumping light source device that amplifies an optical signal by transmitting primary pumping light to an amplifying means interposed in the middle of an optical fiber connecting two terminal stations. A primary pumping light output means for outputting the primary pumping light to the optical fiber; and a secondary pumping light for amplifying the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light. And a next excitation light output means.

  According to this configuration, the primary pumping light output from the primary pumping light output unit and the secondary pumping light output from the secondary pumping light output unit are superimposed and transmitted to the optical fiber. The primary pumping light that amplifies the optical signal in the amplifying means loses power due to transmission loss when transmitted over a long distance, but is amplified by the secondary pumping light and recovers power. Thereby, the power required for the primary pumping light at the time of input to the amplifying unit can be secured without increasing the output of the primary pumping light output unit.

  According to a ninth aspect of the present invention, in the pumping light source device according to the eighth aspect, when the optical fiber is transmitted superimposed on the secondary pumping light, the tertiary pumping light that amplifies the secondary pumping light is output. A tertiary pumping light output means is provided.

  According to such a configuration, the tertiary pumping light output from the tertiary pumping light output means is also superimposed on the primary pumping light and the secondary pumping light and transmitted through the same optical fiber. At this time, since the transmission distance is long, even if the secondary pump light loses power due to transmission loss, energy is absorbed and amplified from the tertiary pump light, so that this power is recovered. Thus, since the power loss of the secondary pumping light is suppressed, the amplification effect of the primary pumping light by the secondary pumping light is not reduced.

  The optical communication method according to claim 10, wherein the optical signal is amplified and received by transmitting the primary pumping light to the amplifying means interposed in the middle of the optical fiber connecting the two terminal stations. A primary pumping light output step for outputting the primary pumping light to the optical fiber; and a secondary pumping light for amplifying the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light. A secondary pumping light output step and an optical signal receiving step of receiving the amplified optical signal are included.

  According to this method, the primary pumping light output in the primary pumping light output step is input to the amplifying unit, and the optical signal is amplified. Then, the secondary pumping light output in the secondary pumping light output step is superimposed on the primary pumping light and transmitted through the optical fiber to amplify the primary pumping light. For this reason, even if the primary pumping light is lost during transmission of the optical fiber, the power loss can be suppressed by the amplification effect of the secondary pumping light. Therefore, even if the primary excitation light is transmitted over a long distance, the power necessary for the operation can be supplied to the amplification means. Thus, when receiving an optical signal received in long-distance communication, it is not necessary to increase the power of the primary pumping light when it is output to the optical fiber.

  The invention according to claim 11 is the optical communication method according to claim 10, wherein the tertiary pumping light that amplifies the secondary pumping light is transmitted when the optical fiber is transmitted superimposed on the secondary pumping light. An excitation light output step is included.

  According to this method, even if the secondary pumping light is lost due to long-distance transmission, this power loss is suppressed by the amplification effect of the tertiary pumping light. Thereby, even when an optical signal is transmitted over a long distance, the power level of the primary pumping light for properly operating the amplification means can be ensured.

The remote excitation light amplification system, excitation light source device, and optical communication method according to the present invention have the following excellent effects.
That is, by performing Raman amplification of the primary pumping light by the secondary pumping light, power loss due to transmission loss of the primary pumping light can be suppressed, and the transmission distance of the optical fiber communication system can be increased. Furthermore, the power loss due to the transmission loss of the secondary pumping light is suppressed by the action of the tertiary pumping light, and the transmission distance can be further increased.
Further, in the optical fiber communication system, if the primary pumping light, the secondary pumping light, and the tertiary pumping light are multiplexed to have a bandwidth, it is possible to increase the bandwidth of long-distance transmission.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
The embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a basic configuration of an optical fiber communication system in the present embodiment.

  The optical fiber communication system 1 is configured such that a terminal station A and a terminal station B existing at two separated points are connected to both ends of two optical fibers 50 and 50 having different transmission directions of the optical signal S, respectively. . In the terminal station A, the WDM transmission unit 10a and the WDM reception unit 20a are arranged, and in the terminal station B, the WDM reception unit 20b and the WDM transmission unit 10b are arranged. The WDM transmission unit 10a and the WDM reception unit 20b are connected to one of the optical fibers 50, and the WDM reception unit 20a and the WDM transmission unit 10b are connected to the other optical fiber 50. Two-way communication between the stations B is possible. Here, the WDM transmission unit 10a and the WDM transmission unit 10b, and the WDM reception unit 20a and the WDM reception unit 20b respectively have the same structure and interaction. Therefore, hereinafter, the configuration and operation of the WDM transmission unit 10a and the WDM reception unit 20b will be mainly described, and the WDM reception unit 20a and the WDM transmission unit 10b will be omitted.

The WDM transmission unit 10a includes an amplifier 11, a wavelength multiplexing unit 12, and transmitters (OS) 13, 13.
The amplifier 11 transmits an optical signal S obtained by amplifying the multiplexed signal λ output from the wavelength multiplexing unit 12 to the optical fiber 50.

Wavelength multiplexing unit 12, it is output from the transmitter 13, 13, different signals lambda ₁ wavelengths, respectively, lambda ₂ ... multiplexes enter the lambda _n one multiplexed signal _{λ (λ 1, λ 2 ...} λ n ) Is output. Wavelength division multiplexing (WDM) is a technique for increasing communication capacity by transmitting signal light of different wavelengths to one optical fiber and multiplexing channels.

The signals λ ₁ , λ _2, ... Output from the transmitters 13, 13... Are different in wavelength in a band around 1550 nm. Therefore, the optical signal S obtained by multiplexing and amplifying these signals λ ₁ , λ ₂ ... Is also composed of a wavelength 1550 nm band (C band).

  The optical fiber 50 is provided with an EDF amplifier (amplifying means) 40, which will be described later, in the middle of the path. The optical fiber 50b from the EDF amplifier 40 to the WDM receiver 20 has a larger core diameter for transmitting the optical signal S than the optical fiber 50a to the WDM transmitter 10. With the optical fiber 50b having an enlarged core diameter, when high power light is input from the terminal station to the optical fiber 50, an effect of suppressing the generation of nonlinear effects can be obtained. Applying the optical fiber 50b having an enlarged core as an optical fiber that transmits later-described pumping light R, which is a high-power laser, contributes to a longer transmission distance of the optical signal S.

  By the way, the effect of the optical fiber 50b having an enlarged core is maximized immediately after the terminal station B from which high power light is emitted. For this reason, the optical fiber 50b is applied with a certain length from the terminal station B.

The EDF amplifier (amplifying means) 40 is installed in the middle path of the optical fiber 50, and is composed of a silica-based fiber having a length of several tens to 100 m doped with erbium (Er) which is one of rare earth elements. . When primary excitation light R _{1 of} 1480 nm output from a primary excitation light source 31 described later is input to Er ³⁺ ions doped in this silica-based fiber, electrons are excited to a high energy level. When the optical signal S having a wavelength of 1550 nm (C band) is incident on the Er ³⁺ ions in the excited state, stimulated emission occurs, and the power of the optical signal S is greatly amplified.

  The WDM reception unit 20 includes a coupler 21, a wavelength division unit 22, receivers (OR) 23, 23..., And an excitation light source unit 30 (excitation light source device). The excitation light source unit 30 includes a primary excitation light source (primary excitation light output means) 31, a secondary Raman light source (secondary excitation light output means) 32, and a tertiary Raman light source (tertiary excitation light output means) 33.

The coupler 21 inputs the primary pumping light R ₁ , the secondary Raman pumping light R _2, and the tertiary Raman pumping light R ₃ output from the pumping light source unit 30, outputs them to the optical fiber 50 b, and the direction of the EDF amplifier 40. To be transmitted. On the other hand, the coupler 21 also has an effect of inputting the optical signal S transmitted from the optical fiber 50 and outputting it to the wavelength division unit 22.

The wavelength division unit 22 receives the optical signal S, divides it into the original signals λ ₁ , λ ₂ ... And outputs them to the corresponding receivers (OR) 23, 23.
The receivers 23, 23... Convert the received signals λ ₁ , λ ₂ .

The primary excitation light source (primary excitation light output means) 31 outputs primary excitation light R ₁ having a wavelength of 1480 ± 30 nm. The primary pumping light R ₁ has a function of greatly amplifying the passing optical signal S in the EDF amplifier 40 after being transmitted through the optical fiber 50b. This amplification action is enhanced as the power of the primary pumping light R ₁ input to the EDF amplifier 40 increases. However, if the power of the primary pumping light R ₁ output from the pumping light source unit 30 is equal to or higher than a predetermined threshold, oscillation based on the synergistic effect of Raman amplification and Rayleigh scattered light occurs inside the transmitting optical fiber 50. As a result, the quality of the optical signal S deteriorates. For this reason, the power of the primary pumping light R ₁ output from the primary pumping light source 31 needs to be lower than the level at which this oscillation occurs.

The secondary Raman light source (secondary excitation light output means) 32 outputs secondary Raman excitation light R ₂ having a wavelength of about 1380 ± 30 nm. The secondary Raman pumping light R ₂ has a function of Raman amplification of the primary pumping light R ₁ in the transmission process of the optical fiber 50b. Also in the secondary Raman light source 32, in order to avoid the oscillation of the secondary Raman pump light R ₂ to be output, that there is an upper limit to the acceptable range of power levels the same as for the primary excitation light R ₁ described above It is.

The tertiary Raman light source (tertiary excitation light output means) 33 outputs a wavelength of about 1280 ± 30 nm. The third-order Raman pumping light R ₃ has a function of Raman-amplifying the second-order Raman pumping light R ₂ in the transmission process of the optical fiber 50b.
Then, the primary pumping light R ₁ , the secondary Raman pumping light R _2, and the tertiary Raman pumping light R ₃ are superposed on each other to form the pumping light R and pass through the coupler 21 in the direction of the EDF amplifier 40. 50b is transmitted.

Next, the effect of the excitation light source unit 30 will be described with reference to FIGS. 1 and 6. FIG. 6 is a schematic diagram showing a power profile when the primary pumping light R ₁ is transmitted through an optical fiber of about 400 km.
A curve (a) is a power attenuation curve of the primary pumping light R ₁ when there is no support of the secondary Raman pumping light R ₂ . A curve (b) is a power attenuation curve of the primary pumping light R ₁ when the secondary Raman pumping light R ₂ is supported. The horizontal axis in FIG. 6 takes the position of the coupler 21 in FIG. 1 as the origin, and the arrow tip is in the direction of the EDF amplifier 40. The vertical axis indicates the relative value of the power of the primary excitation light R _1. In FIG. 6, a broken line y _L shown indicates a region where oscillation occurs in the optical fiber 50 when the power of the primary pumping light R ₁ exceeds the boundary indicated by the broken line.

Here, considering the case of the curve (a), it is assumed that the input power y _I of the primary pumping light R ₁ necessary for the EDF amplifier 40 to operate properly. When the power output from the primary excitation light source 31 is set to y _L which is the upper limit that can avoid oscillation, the maximum distance at which the EDF amplifier 40 can be installed is x _a . On the other hand, in the case of the curve (b), the power output from the primary excitation light source 31 may be determined so that the maximum value does not exceed y _L , so the maximum distance at which the EDF amplifier 40 can be installed is up to x _b. Expand.

That is, the support secondary Raman pump light R _2, and the effect of reducing the output power of the primary excitation light source 31, so that the effect of long-distance communication is achieved at the same time. Here, the reason why the curve (b) has the maximum value is that the Raman amplification effect exceeds the attenuation due to the transmission loss before the maximum value is reached, and the curve is reversed after the maximum value.

  Next, the receiving operation of the optical signal S in the optical fiber communication system 1 will be described with reference to FIG. In the following, the communication operation from the terminal station A to the terminal station B will be described, but the communication from the terminal station B to the terminal station A will be omitted because it is the same.

First, an optical signal S in which a multiplexed signal λ (λ ₁ , λ ₂ ...) Is amplified is transmitted from the WDM transmitter 10a. The optical signal S is transmitted through the optical fiber 50 a while being attenuated in power due to transmission loss, and reaches the EDF amplifier 40. On the other hand, the primary pumping light R ₁ is input from the pumping light source unit 30 to the EDF amplifier 40 via the optical fiber 50 b. Since the input primary pumping light R ₁ is Raman-amplified by the action of the secondary Raman pumping light R ₂ and the third order Raman pumping light R ₃ even after long-distance transmission, there is little power loss due to transmission loss. Therefore, the optical signal S passing through the EDF amplifier 40 is transmitted to the WDM receiver 20 with a sufficient amplification gain. When the wavelength division unit 22 receives the optical signal S, it is divided into the original signals λ ₁ , λ ₂ ... And received by the receivers 23, 23.

In this way, by providing the excitation light source unit 30 having a secondary Raman light source 32 for Raman amplification of the primary excitation light R ₁ to the optical fiber communication system 1, the EDF amplifier 40 to suppress the power loss of the primary excitation light R ₁ Made it possible to reach. Therefore, the optical signal S can obtain a large amplification gain without increasing the output power of the primary pumping light source 31, that is, suppressing the oscillation phenomenon. Furthermore, if the third-order Raman light source 33 is present, the attenuation of the second-order Raman excitation light R ₂ can be suppressed, so that a larger amplification effect of the optical signal S can be obtained.

  As described above, this embodiment is an example for explaining the present invention, and the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the gist of the invention. . For example, in the optical fiber communication system 1 shown in FIG. 1, the pumping light source unit 30 is provided on the WDM receiving unit 20 side, but as shown in FIG. 2, the pumping light source unit 30 is installed on the WDM transmitting unit 10 side. It may be provided. In the case where the excitation light source unit 30 is installed on the WDM transmission unit 10 side, the optical fiber 50a ′ connected to the WDM transmission unit 10 side should have a larger diameter.

  In addition, as shown in FIG. 3, the excitation light source unit 30 may be provided in both the WDM transmission unit 10 and the WDM reception unit 20. In this case, the EDF amplifier 40 is bi-directionally excited by the excitation light source unit 30 provided on the WDM transmission unit 10 and WDM reception unit 20 side. And as shown in FIG. 4, you may provide the light source part 30 for excitation in the path | route of the optical fiber 50 with two or more in a figure. By installing a plurality of pumping light source units 30 in this way, the optical signal S is amplified by the EDF amplifier 40 installed on the WDM transmission unit 10 side, and then the EDF amplifier installed on the WDM reception unit 20 side. 40 is further amplified. Further, the description so far has been related to an optical fiber communication system configured between two terminal stations. However, such an optical fiber communication system is combined, and although not particularly illustrated, it includes a plurality of terminal stations. A network may be formed.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 5A is a block diagram showing a basic configuration of the optical fiber communication system in the present embodiment. 5A is the same as the configuration of the optical fiber communication system 2 shown in FIG. 2, and as will be described later, the excitation light source unit 30 ′ and the transmitter ( OS) 13 ′... Is different from the pumping light W (W ₁ , W ₂ ) and the multiplexed signal Λ (Λ ₁ , Λ ₂ ... Λ _m ) of the optical signal T.

FIG. 5 (B1) is a graph shown as a comparative example, and shows the excitation light R (R ₁ , R ₂ ) and the optical signal S transmitted from the WDM transmitter 10 shown in the first embodiment (FIG. 2). It is a graph showing the optical power with respect to a wavelength.
FIG. 5B2 is a graph showing the optical power with respect to the wavelengths of the pumping light W (W ₁ , W ₂ ) and the optical signal T transmitted from the WDM transmission unit 10 ′ in the second embodiment.
FIG. 5B3 is a graph showing the optical power with respect to the wavelengths of the pumping light W (W ₁ , W ₂ ) and the optical signal T transmitted through the optical fiber 50 or the EDF amplifier 40 in the second embodiment.

In FIG. 5 and the following description, the excitation light corresponding to the _third order Raman excitation light R ₃ (see FIG. 2) is omitted for the sake of simplicity. In addition, in the constituent elements of the optical fiber communication system 2 ′ in FIG. 5A, the same constituent elements as those already described are denoted by the same reference numerals and description thereof is omitted.

5 (A) outputs signals Λ ₁ , Λ ₂ ... Configured by shifting wavelengths in a band (C band) around a wavelength of 1550 nm. . These signals Λ ₁ , Λ ₂ ... Are multiplexed in the wavelength multiplexing unit 12 to become a multiplexed signal Λ, and further amplified by the amplifier 11 to form an optical signal T. It is assumed that the wavelength bandwidth of the signals Λ ₁ , Λ ₂ ... Constituting the optical signal T is wider than that of the optical signal S (see FIG. 2), as shown in FIG.

When the excitation light source unit 30 'transmits the optical fiber 50 superimposed on the optical signal T, the power of the optical signal T is Raman amplified, or the EDF amplifier 40 is transmitted to further amplify the power of the optical signal T. A plurality of single wavelength components (first single wavelength components) are multiplexed to output primary pumping light W ₁ having a predetermined bandwidth.
Here, the primary pumping light W ₁ is obtained by multiplexing a plurality of components (three components in FIG. 5, W _1a , W _1b , W _1c ) among the single wavelength components in the 1480 nm band for amplifying the light in the 1550 nm band. Here, any of these first single-wavelength components (W _1a , W _1b , W _1c ) has a band width in which the optical signal T can be amplified, that is, an amplification effective band width is about 30 nm. .

The wavelength interval of these first single wavelength components (W _1a , W _1b , W _1c ) is desirably set so that both ends of each amplification effective band are in contact with adjacent single wavelength components. Taking the case shown in FIG. 5 (B2) as an example, the wavelength interval of the single wavelength components (W _1a , W _1b , W _1c ) is set so that the wavelength interval is 30 nm within the 1480 nm band. Then, the optical signal T can be amplified with a wide bandwidth of 90 nm.

Further, the excitation light source unit 30 ', the primary excitation light when W superimposed on _one transmitting optical fiber 50 to the power of the primary excitation light W ₁ to Raman amplification, a plurality of single-wavelength components (the second single-wavelength component) Outputs the secondary Raman pumping light W ₂ formed by multiplexing.
Here, the secondary Raman excitation light W ₂ is obtained by multiplexing a plurality of components (three components, W _2a , W _2b , W _{2c in} FIG. 5) among single wavelength components in the 1380 nm band for amplifying light in the 1480 nm band. . The wavelength interval of these second single wavelength components (W _2a , W _2b , W _2c ) is the first single wavelength component (W _1a , W _1b , W _1c ) whose amplification effective band constitutes the primary pumping light W _1. ) Is preferably set so as to cover the entire band.

In addition, the first single wavelength components (W _1a , W _1b , W _1c ) and the second single wavelength components (W _2a , W _2b , W _2c ) constituting the primary pump light W ₁ and the secondary Raman pump light W ₂ here. ) Is set so that the optical power increases as it goes to the lower wavelength component side. This is because the single wavelength component W _1a (W _2a ) on the low wavelength component side _supplies its own power to the single wavelength component W _1c (W _2c ) on the high wavelength component side due to the Raman amplification action between the single wavelength components in the same band. Considering the effect of amplifying by Raman donation.

Next, the operation in the second embodiment will be described.
Immediately after being transmitted from the WDM transmitter 10 ′ shown in FIG. 5A (position L = L ₀ ), the optical power with respect to the wavelength of the pumping light W (W ₁ , W ₂ ) and the optical signal T is shown in FIG. ). Then, as shown in FIG. 5 (B3), the optical signal T ′ is amplified by the primary pumping light W ′ ₁ by the Raman amplification action in the transmission process of the optical fiber 50, and this primary pumping light W ′ ₁ While receiving the optical power from the Raman pumping light W ′ _{2, it} supplies its own optical power to the optical signal T ′. Focusing on the first single wavelength components (W ′ _1a , W ′ _1b , W ′ _1c ) and the second single wavelength components (W ′ _2a , W ′ _2b , W ′ _2c ) in the same band, The effect of equalizing each optical power is obtained by the Raman amplification function.

By the way, in the above description, the pumping light corresponding to the _third order Raman pumping light R ₃ (see FIG. 2) is omitted. However, the pumping light source unit 30 ′ overlaps the secondary pumping light W ₂ with the optical fiber 50. When transmitted, the power of the secondary pumping light W ₂ is Raman-amplified, and third-order Raman pumping light (not shown) formed by multiplexing a plurality of single wavelength components (third single wavelength component) can also be output. .
Further, the optical power of the optical signal T ′ shown in FIG. 5 (B3) is shown to be larger than the optical power of the optical signal T shown in FIG. 5 (B2), which is a transmission loss in the optical fiber 50. This is because the amount contributed by the amplification effect of the excitation light W is added without being expected, and actually has a smaller value.
In the above description, the optical fiber communication system 2 ′ has been described by simulating the optical fiber communication system 2 shown in FIG. 2, but other optical fiber communication systems 1, 3, 4 (FIGS. 1, 3, 4). The same explanation holds when imitating 4).

Next, examples in which the effects of the present invention have been confirmed will be described.
FIG. 7 is a graph showing the power dependence of the primary pumping light R _{1 on} the Q value of the optical signal S received by the WDM receiver 20 in the optical fiber communication system 1 (FIG. 1).
Here, the Q value is an evaluation index used for quality evaluation of signals used for digital communication. A higher Q value means better signal quality.
Here, the vertical axis indicates the Q value of the optical signal S received by the receivers 23 in FIG. The horizontal axis indicates the power of the primary pumping light R ₁ input to the EDF amplifier 40.

In FIG. 7, a curve (a) is a data curve when the power of the secondary Raman pumping light R ₂ input to the EDF amplifier 40 while being superimposed on the primary pumping light R ₁ is 1.3 W. Curve (b) is a data curve when the power is 0.9 W. A curve (c) is a data curve in the conventional method shown in FIG. 9 when the power is 0 W. Here, the optical fiber 50b from the WDM receiver 20 to the EDF amplifier 40 is about 100 km.

It can be seen from the graph of FIG. 7 that each of the data curves (a), (b), and (c) has a convex shape upward, and the Q value has a maximum value. The reason for having such a maximum value is that when the power of the primary pumping light R ₁ transmitted through the optical fiber 50 increases and exceeds a predetermined threshold value (power value at which the maximum value is reached), Raman amplification and Rayleigh scattered light Oscillation due to the synergistic effect occurs, and the waveform of the optical signal S is disturbed. It can be said that the power of the primary pumping light having the maximum value is the optimum input power in the EDF amplifier 40. From FIG. 7, it can be seen that data curve by the action of the secondary Raman pump light R ₂ is shifted to the low power side and peak value can be improved. As a result, the optimum power value of the primary pumping light R ₁ input to the EDF amplifier 40 can be reduced by applying the secondary Raman pumping light R _2, and the quality of the optical signal S can be improved. .

FIG. 8 is a graph showing the correlation between the power when the primary pumping light R ₁ is output from the primary pumping light source 31 (output power) and the power when the primary pumping light R ₁ is input to the EDF amplifier 40 (input power). That is, the vertical axis represents the power after the primary pumping light R ₁ is transmitted through the optical fiber 50b and Raman amplified. Further, the vertical axis is a value obtained by normalizing and plotting other input powers based on the input power at the output power (= 1.3 W) taking the maximum value of the curve (c) in FIG. Here, the power of the secondary Raman pumping light R ₂ is 1.3 W for the curve (a), 0.9 W for the curve (b), and 0 W for the curve (c), as in the case shown in FIG.

In the curve (b), the input power can be increased by about 0.8% with the output power of about 60% compared to the conventional method represented by the curve (c), and about 40% in the curve (a). It can be seen that the input power can be increased by about 1.5% with the output power of. These are due to the Raman amplification effect of the primary excitation light R ₁ by the secondary Raman excitation light R ₂ .

It is a block diagram which shows the basic composition of the optical fiber communication system concerning 1st Embodiment of this invention. FIG. 3 is a block diagram of an optical fiber communication system showing another basic configuration in the first embodiment. FIG. 3 is a block diagram of an optical fiber communication system showing another basic configuration in the first embodiment. FIG. 3 is a block diagram of an optical fiber communication system showing another basic configuration in the first embodiment. (A) It is a block diagram which shows the basic composition of the optical fiber communication system concerning 2nd Embodiment of this invention. (B1) A graph showing optical power with respect to wavelengths of pumping light R and optical signal S transmitted from the WDM transmission unit in the first embodiment. (B2) It is the graph showing the optical power with respect to the wavelength of the excitation light W and the optical signal T transmitted from the WDM transmission part in 2nd Embodiment. (B3) In 2nd Embodiment, it is the graph showing the optical power with respect to the wavelength of the excitation light W and the optical signal T which transmitted the optical fiber or the EDF amplifier. It is the schematic which shows the power profile of this primary pumping light when transmitting primary pumping light to an optical fiber in the optical fiber communication system concerning this invention. It is a graph which shows the correlation with Q value of the optical signal received with the receiver of the optical fiber communication system concerning this invention, and the input power of primary excitation light. In the optical fiber communication system concerning this invention, it is a graph which shows the correlation of the output power of primary excitation light, and the input power when inputting into an EDF amplifier. It is a block diagram which shows the basic composition of the remote excitation light amplification system shown as a prior art example.

Explanation of symbols

1, 2, 3, 4 Optical fiber communication system 10, 10 ', 10a, 10b Transmitter 13, 13' Transmitter 20, 20a, 20b Receiving unit 23 Receiver 30, 30 'Excitation light source unit (excitation light source device) )
31 Primary excitation light source (primary excitation light output means)
32 Secondary Raman light source (secondary excitation light output means)
33 Tertiary Raman light source (tertiary excitation light output means)
40 EDF amplifier (amplification means)
50, 50a, 50b Optical fiber A, B Terminal station S, T Optical signal λ ₁ , λ ₂ ... Λ _n , Λ ₁ , Λ ₂ ... Λ _m signal R ₁ , W ₁ primary pump light R ₂ , W ₂ secondary Raman excitation light (secondary excitation light)
R ₃ , W _{3 3rd} order Raman excitation light (3rd order excitation light)
_{W 1a, W 1b, W 1c} , W'1a, W'1b, W'1c first single wavelength component _{W 2a, W 2b, W 2c} , W'2a, W'2b, W'2c second single wavelength component

Claims (11)

An optical fiber communication system that performs communication between two terminal stations installed at both ends of an optical fiber that transmits an optical signal,
Primary pumping light output means provided in at least one of the two terminal stations and outputting primary pumping light to the optical fiber;
One or more amplifying means that are interposed in the middle of the optical fiber and amplify the optical signal when the primary pumping light and the optical signal are superimposed and input;
Secondary pumping light output means arranged in the terminal station together with the primary pumping light output means, and outputs secondary pumping light that amplifies the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light; An optical fiber communication system comprising: The optical signal has a predetermined bandwidth by multiplexing a plurality of signals having different wavelengths,
The primary excitation light has a predetermined bandwidth by multiplexing a plurality of first single wavelength components having different wavelengths,
The secondary excitation light has a predetermined bandwidth by multiplexing a plurality of second single wavelength components having different wavelengths,
The amplification effective band of the plurality of first single wavelength components covers the band of the optical signal, and the amplification effective band of the plurality of second single wavelength components covers the band of the primary pumping light, The optical fiber communication system according to claim 1.   A tertiary pumping light output unit that is arranged at the terminal station together with the secondary pumping light output unit and outputs a tertiary pumping light that amplifies the secondary pumping light when transmitted through the optical fiber superimposed on the secondary pumping light. The optical fiber communication system according to claim 1, comprising: an optical fiber communication system according to claim 1. The tertiary excitation light has a predetermined bandwidth by multiplexing a plurality of third single wavelength components having different wavelengths,
The optical fiber communication system according to claim 3, wherein an effective amplification band of the plurality of third single wavelength components covers a band of the secondary pumping light.   Any of the primary pumping light, the secondary pumping light, and the tertiary pumping light having a bandwidth includes the plurality of first single wavelength components, the plurality of second single wavelength components, or the plurality of 5. The optical fiber communication system according to claim 2, wherein in the third wavelength component, the power on the low wavelength component side is set larger than the power on the high wavelength component side. .   The core diameter in a certain section from the terminal station in the optical fiber connecting at least one of the two terminal stations to the nearest amplification means is thicker than the other part. 6. The optical fiber communication system according to any one of items 5.   The optical fiber communication system according to any one of claims 1 to 6, wherein the amplification means is an optical fiber doped with erbium. A pumping light source device that amplifies an optical signal by transmitting primary pumping light to an amplifying means interposed in the middle of an optical fiber connecting two terminal stations,
Primary pumping light output means for outputting the primary pumping light to the optical fiber;
A pumping light source device comprising: secondary pumping light output means for outputting secondary pumping light that amplifies the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light.   9. The pumping light source according to claim 8, further comprising tertiary pumping light output means for outputting tertiary pumping light that amplifies the secondary pumping light when transmitted through the optical fiber superimposed on the secondary pumping light. apparatus. An optical communication method for amplifying and receiving an optical signal by transmitting primary pumping light to an amplifying means interposed in the middle of an optical fiber connecting two terminal stations,
A primary pumping light output step for outputting the primary pumping light to the optical fiber;
A secondary pumping light output step of outputting to the optical fiber secondary pumping light that amplifies the primary pumping light when transmitted through the optical fiber superimposed on the primary pumping light;
An optical signal receiving step of receiving the amplified optical signal.   11. The method according to claim 10, further comprising: a tertiary pumping light output step of outputting, to the optical fiber, tertiary pumping light that amplifies the secondary pumping light when transmitted through the optical fiber while being superimposed on the secondary pumping light. Optical communication method.

Images