JP4391062B2 - Optical transmission line - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber and an optical transmission line used for optical fiber communication.
In particular, the present invention relates to an optical transmission line using a distributed Raman amplification type optical transmission line.
[0002]
[Prior art]
In optical fiber communication, a distributed Raman amplification type optical transmission line has been intensively studied as a communication system capable of extending a signal transmission distance and reducing noise.
[0003]
The Raman amplification will be described.
In general, when light is incident on a substance such as glass, light having a wavelength slightly longer than the original wavelength is generated due to molecular vibration and lattice vibration of the substance. This light is called Raman scattered light. Furthermore, when the incident excitation light is strengthened, strong Raman scattered light having the same phase is generated. This is called stimulated Raman scattered light. If the wavelengths of the incident signal light and the stimulated Raman scattered light match, the stimulated Raman scattered light undergoes the same change in intensity as the signal light, and amplifies the signal light. In this way, Raman amplification means that when strong excitation light is irradiated onto an optical fiber, the light scattered by the atoms that make up the material quartz glass (stimulated Raman scattered light) is converted to a wavelength different from that at the time of incidence. This is a technique for amplifying optical signal intensity utilizing the fact that it is scattered.
The optical fiber type amplifier utilizes the amplification action resulting from the nonlinear optical phenomenon generated in the optical fiber.
[0004]
Since Raman amplification is amplification that occurs in an optical transmission line (optical transmission optical fiber) as described above, it can be said to be a system in which amplified light other than transmission light enters the optical transmission line. As devices using such Raman amplification, distributed constant Raman amplifiers and lumped constant Raman amplifiers are known.
[0005]
The distributed constant Raman amplifier is an amplifier that uses an optical fiber in a so-called cable as an optical transmission line. As illustrated in FIG. 1, a pumping light source (pump) 1, an optical multiplexing means 2, an optical fiber (optical fiber) (Transmission path) 3.
[0006]
The lumped-constant Raman amplifier is an amplifier having a device configuration in which amplified light is incident on an optical fiber (equipped in a coil and installed in a relay station or the like) such as a dispersion compensation module. It is.
[0007]
The Raman amplifier, which is the subject of the present invention, is a distributed constant Raman amplifier and is called a distributed Raman amplification optical transmission line.
[0008]
In the distributed Raman amplification type optical transmission line using the distributed constant type Raman amplifier, pumping light having a frequency about 13 T (tera) Hz higher than the wavelength band of the signal light is input to the optical transmission line, and the optical transmission line itself is connected to the Raman transmission line. Treat as an amplification medium. As a result, all or part of the transmission loss occurring in the optical transmission path can be canceled, and the transmission loss can be reduced, the signal transmission distance can be extended, and noise can be reduced.
[0009]
[Problems to be solved by the invention]
However, the pumping power used for Raman amplification is large, and in some cases, 1 W class power may be input to the optical fiber 3 from the pumping light source 1 via the optical multiplexing means 2. Such an input of large excitation power is naturally processed as unnecessary power because the excitation power reaches the emission end.
For this reason, an appropriate termination process is required at the emission end, and high power is output to the emission end several km away via the optical transmission line is considered as a problem in terms of safety.
[0010]
An object of the present invention is to achieve a safe termination process of pumping light incident on a distributed Raman amplification type optical transmission line and a reduction of termination parts in an optical transmission line using the distributed Raman amplification type optical transmission line. Is to provide.
[0011]
[Means for Solving the Problems]
The inventor of the present application sets a section where the transmission loss of the pumping light wavelength is large in a part of the optical transmission path used for the distributed Raman amplification, and sufficiently attenuates the pumping light in the section, thereby terminating the end part of the optical transmission path. I found a concept to prevent high-power excitation light from being emitted from.
[0012]
Therefore, according to the present invention, in a pumping light source, optical multiplexing means, a distributed Raman amplification type optical transmission line having an optical transmission line optical fiber, and an optical transmission line using an amplifier ,
A section with a large transmission loss of the pumping light wavelength is set in a part of the optical transmission line, an attenuation optical fiber is inserted into the section, and unnecessary components of the pumping light are attenuated or extinguished by the attenuation optical fiber. ,
Examples attenuating optical fiber, the optical fiber has been introduced impurities, have rows said attenuated by absorption by the introduced impurity,
The length of the optical transmission line optical fiber is not less than the effective length Leff of the optical transmission line ,
The product of the transmission loss difference at a specific wavelength in the excitation light band of the attenuation optical fiber and the optical transmission line optical fiber and the length of the attenuation optical fiber is the exit end from which the excitation light is emitted from the optical transmission line An optical transmission line is provided, characterized in that the optical transmission line is greater than
However, the effective length Le ff of the optical transmission line is
Leff = 1 / β · (1-exp (−β × L) )
Is defined as
Here, beta is the optical fiber of the optical transmission path (i.e., the optical transmission line optical fiber, and the attenuating optical fiber) and loss factor, L is the optical fiber of the optical transmission path (i.e., It is the length of the optical transmission line optical fiber and the attenuation optical fiber) .
[0013]
Preferably, in the optical transmission line, a distributed Raman amplification type optical transmission line is disposed at the incident end, and the attenuation optical fiber is disposed at the light emitting end.
Preferably, in the optical transmission line, a distributed Raman amplification type optical transmission line is disposed at the output end, and the attenuation optical fiber is disposed at the incident end.
Preferably, in the optical transmission line, a first distributed Raman amplification type optical transmission line is disposed at an incident end, a second distributed Raman amplification type optical transmission line is disposed at an emission end, and the first distributed Raman line is disposed. The attenuation optical fiber is disposed between the amplification type optical transmission line and the second distributed Raman amplification type optical transmission line.
Preferably, the introduced impurity includes any of Mn, Ni, Cr, V, Co, Fe, and Cu.
Preferably, as the attenuation optical fiber, a hydroxyl group is introduced into the optical fiber, and the attenuation is performed by absorption by the introduced hydroxyl group.
Preferably, a transmission loss difference at a specific wavelength in a pumping light band between the attenuation optical fiber and the optical transmission line optical fiber is at least 0.2 dB / km or more.
Preferably, the fluctuation amount of the wavelength loss characteristic from 1460 nm to 1565 nm is ± 0.1 dB / km over the entire length of the optical transmission line.
Preferably, the fluctuation amount of the wavelength loss characteristic from 1565 nm to 1625 nm is ± 0.1 dB / km over the entire length of the optical transmission line.
[0014]
The pump light incident on the optical fiber in the distributed Raman amplification type optical transmission line goes toward the output end side while amplifying the signal. After that, when entering the loss increasing section, the pump light begins to attenuate greatly, and on the output side, Attenuate to a problem-free level. As a result, it is not necessary to provide special termination means at the emission end, and there is no problem with safety due to high power.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
First embodiment Fig. 2 is a configuration diagram of an optical transmission line according to a first embodiment of the present invention.
The optical transmission path illustrated in FIG. 2 uses a normal single mode optical fiber (SMF), for example, a distributed Raman in the optical transmission path 10 at a distance of 100 km between the transmission optical signal input end and the output end. This is an optical transmission line for performing amplification.
The optical transmission line 10 for optical communication illustrated in FIG. 2 is provided in a first amplifier 11 provided at a transmission optical signal incident end, a first distributed Raman amplification type optical transmission line 12, and an intermediate section. It includes an attenuation optical fiber 13, a second distributed Raman amplification type optical transmission line 14, and a second amplifier 15 provided at the output end.
As described above with reference to FIG. 1, the first distributed Raman amplification type optical transmission line 12 is an amplifier that uses an optical fiber in a so-called cable as the optical transmission line. As illustrated in FIG. (Pump) 121, optical multiplexing means 122, and optical fiber (optical transmission line) 123.
Similarly, the second distributed Raman amplification type optical transmission line 14 includes a pumping light source (pump) 141, an optical multiplexing unit 142, and an optical fiber (optical transmission line) 143.
[0016]
In the present embodiment, the signal light wavelength is C band and L band, and pumping light source (pump) 121 and pumping light source (pump) 141 are used for 1430 nm bidirectional pumping. 1W is input at a time.
The length of sections A and C was 40 km, and the length of section B was 20 km.
In the section B, an attenuation optical fiber 13 having a transmission loss of 2 dB / km larger in the 1390 nm band than the other sections A and C is arranged as the attenuation optical fiber 13.
[0017]
As the attenuation optical fiber 13, for example, a method of introducing an OH group near 1390 nm into the optical fiber in order to absorb an unnecessary amount of excitation power, or an impurity that performs absorption without reflection such as Rayleigh scattering, for example, , Mn, Ni, Cr, V, Co, Fe, Cu and the like are introduced into the optical fiber.
[0018]
In general, the transmission loss of a single mode optical fiber at 1430 nm is about 0.25 dB / km, and about 25 dB in a 100 km optical transmission line.
On the other hand, the input of 1 W power in the pumps 121 and 141 corresponds to +30 dBm, and by the bidirectional excitation in the pumps 121 and 141, the incident end on the first amplifier 11 side and the output end on the second amplifier 15 side Power of about 5 dBm is emitted from both ends of the. However, the transmission loss at 1390 nm in the attenuation optical fiber 13 disposed in the section B in the optical transmission line 10 is 2 dB / Km larger than the other sections A and C. This corresponds to an increase in transmission loss of about 0.3 dB / km at 1430 nm. When the length of the attenuation optical fiber 13 in this section B is 20 km, a transmission loss of 6 dB occurs. As a result, the power at the output end becomes 0 dBm or less, and safety is improved.
[0019]
From the viewpoint of the effect of excitation by the pump 121 and the pump 141, 100km in length, the effective length Leff of the optical transmission path of the transmission loss 0.25 dB / miles is about 16km, the optical transmission line optical fiber by 40 km 123,14 3 can be said to be long enough for the gain of Raman amplification.
The effective length Le ff of the optical transmission line is defined as Leff = 1 / β · (1−exp (−β × L) ) . However, beta optical fiber (i.e., the optical transmission line optical fiber 123 and 143, and, optical fiber 13 for attenuation) of the optical transmission path is a loss factor, L is the optical fiber of the optical transmission path (i.e., optical It is the length of the transmission line optical fibers 123 and 143 and the attenuation optical fiber 13) . The amount of occurrence of the nonlinear phenomenon in the optical fiber is determined not by the length of the optical fiber but by the effective length Leff of the optical fiber.
[0020]
Further, if the increase factor (attenuation factor) of the transmission loss by the attenuation optical fiber 13 in the section B is, for example, absorption due to impurities or hydroxyl groups (OH groups) introduced into the optical fiber, multiple reflection due to Rayleigh scattering or the like is also caused. Absorption is effective in removing unnecessary power reflected from the sections A and C other than the section B.
[0021]
Furthermore, if the sections A and C are set to 30 km each, even if the transmission loss increase (attenuation amount) at 1390 nm in the section B is 1 dB / km, the transmission loss increase in the section B is 0.16 * 40 = 6.4 dB. The same effect as that obtained when section B has a transmission loss of 2 dB / km and a length of 20 km can be obtained.
[0022]
Further, even if the effective length Leff of the optical fiber is taken into account, the length of the low-loss portion in the sections A and C is 16 km or more, and it can be said that the length is sufficient for obtaining the Raman amplification gain.
[0023]
Note that the lengths of the section A and the section C do not necessarily have to be the same, and it is sufficient if each section has a length of 16 km or more.
[0024]
In the first embodiment of the present invention, if almost the same optical fiber except for transmission loss near 1390 nm is used, the behavior as a signal band is not particularly conscious in communication system design, which is beneficial.
As an example, if optical fibers of the same type are used, naturally there is little variation in the transmission loss of the signal band, and even if the increase in transmission loss at 1390 nm is taken into account, it is sufficient to consider it to be 0.1 dB / km or less. In addition, if the same type of optical fiber is used, dispersion in the longitudinal direction of the optical transmission line is naturally suppressed, and an optical fiber with a dispersion of ± 5 ps / nm / km in the longitudinal direction of the optical transmission line is manufactured. It's easy to do. Therefore, the optical transmission line 10 of the present embodiment can be applied to a communication system using an optical transmission line in which only the effective core area Aeff is changed in the longitudinal direction and the dispersion is kept constant.
[0025]
As another example, the present embodiment is also effective for a communication system using different types of optical fibers. For example, only the effective core cross-sectional area Aeff is changed in the longitudinal direction of the optical transmission line so that the dispersion is constant. It can also be applied to a maintained communication system.
[0026]
In addition, the dispersion management transmission line configured by combining optical fibers with different signs of positive and negative dispersion values, i.e., connecting an optical fiber having a positive dispersion value and an optical fiber having a negative dispersion value, sets the dispersion value. Of course, the optical transmission line of this embodiment can also be applied to an optical transmission line close to zero.
As such a dispersion management transmission line, for example, an optical transmission line in which an optical fiber having a positive chromatic dispersion and an optical fiber having a negative chromatic dispersion are arranged in the section A to the section C is realized. it can.
[0027]
Second embodiment Fig. 3 is a configuration diagram of a second embodiment of an optical transmission line according to the present invention.
The optical transmission line 10 illustrated in FIG. 2 is provided with two distributed Raman amplification optical transmission lines 12 and 14 at the incident end and the emission end, but FIG. 3 shows only one distributed Raman amplification optical transmission line. This is an optical transmission line 20 that constitutes a back-pumped distributed Raman amplification transmission line provided on the output end side, and includes a first amplifier 21 provided at the incident end, and a first optical fiber 22 provided in the section A. , A distributed Raman amplification type optical transmission line 25, and a second amplifier 26 provided at the emission end.
The distributed Raman amplification type optical transmission line 25 includes a pumping light source (pump) 251, an optical multiplexing unit 252, a second optical fiber 23, and a third optical fiber 24.
[0028]
The first optical fiber 22 is an attenuation optical fiber, similar to the attenuation optical fiber 13 of FIG.
[0029]
The first optical fiber 22, the second optical fiber 23, and the third optical fiber 24 are desirably a mixture of optical fibers having positive and negative chromatic dispersion at 1460 nm to 1625 nm. This is because the first optical fiber 22, the second optical fiber 23, and the third optical fiber 24 cancel out the chromatic dispersion from 1460 nm to 1625 nm, and the dispersion becomes zero or close to zero.
Alternatively, it is desirable that the first optical fiber 22, the second optical fiber 23, and the third optical fiber 24 are a mixture of optical fibers having positive and negative chromatic dispersion at 1530 nm to 1625 nm. This is because the first optical fiber 22, the second optical fiber 23, and the third optical fiber 24 cancel out the chromatic dispersion from 1530 nm to 1625 nm, and the dispersion becomes zero or close to zero.
[0030]
It is clear that the section B immediately after the excitation light incident by the excitation light source (pump) 251 described as the first embodiment has only to have a low transmission loss, and the distance should be 16 km or more.
Others are the same as those described in the first embodiment.
[0031]
Modified embodiment The optical transmission line 20 illustrated in FIG. 3 is backward pumping in which a distributed Raman amplification type optical transmission line 25 is arranged at the output end, but as illustrated in FIG. It is also possible to take the form of forward pumping in which an amplification type optical transmission line is arranged.
The forward pumping type optical transmission line 30 illustrated in FIG. 4 is provided in the first amplifier 31 provided at the incident end, the distributed Raman amplification type optical transmission line 32 provided in the section A, and the section B. It has the 1st optical fiber 33, the 2nd optical fiber 34, and the 2nd amplifier 35 provided in the output end.
The distributed Raman amplification type optical transmission line 32 includes a pumping light source (pump) 321, optical multiplexing means 322, and an optical fiber (optical transmission line) 323.
[0032]
In the case of forward pumping in which the distributed Raman amplification type optical transmission line 32 is arranged on the incident end side illustrated in FIG. 4, it is clear that the section A should have a low loss and the section B should include a transmission loss increasing portion. is there. Accordingly, an attenuation optical fiber similar to the attenuation optical fiber 13 in FIG. 1 is used for the first optical fiber 33 and / or the second optical fiber 34.
[0033]
Third embodiment In the optical transmission line 10 illustrated in FIG. 2, so-called S-band distributed Raman transmission from 1460 nm to 1525 nm is performed. In order to perform amplification effectively in the band of S band, the pump light (pump light) in the pump 121 and the pump 141 is preferably around 1390 nm. The vicinity of 1390 nm coincides with the transmission loss due to the OH group, and the influence of the increase in the transmission loss in the attenuation optical fiber 13 is obvious.
Therefore, there is an increase in transmission loss (increase in attenuation) of 0.2 dB / km in the pumping light band (pump band) in the optical transmission line 10 of the first embodiment illustrated in FIG. The pump light was effective.
[0034]
In addition, in the backward pumping method illustrated in FIG. 3 or the forward pumping method illustrated in FIG. 4, when light in the 1390 nm band is used as the pumping light, the increase in transmission loss is 0.2 dB / km. was there.
[0035]
Fourth embodiment All transmissions in the S, C, and L bands were performed by combining the first embodiment and the third embodiment.
As a result, if the transmission loss increase of 1 dB / km at 1390 nm satisfying the conditions of the C and L bands is satisfied, the effect is sufficiently obtained even in the S band.
[0036]
In each of the above-described embodiments, only the absorption due to the OH group near 1390 nm was mentioned. However, the cause of the increase in loss may be a loss such as absorption without reflection such as Rayleigh scattering. For example, Mn, Ni, Cr, V, Co, Fe, Cu or the like can be used as an impurity introduced into the attenuation optical fiber such as the optical fiber 13.
[0037]
The implementation of the optical transmission line of the present invention is not limited to the above-described exemplary embodiments, and various modifications can be made.
For example, the dispersion management optical transmission line connecting optical fibers having positive and negative wavelength dispersions described with reference to FIG. 3 can be applied to all the above embodiments.
[0038]
Further, the band of the transmission signal is an example, and the embodiment of the present invention is not limited to the illustrated band.
[0039]
【The invention's effect】
According to the present invention, it is possible to attenuate the excitation light that has entered the optical transmission line and is no longer needed, so that it is possible to ensure the safety of system construction and to contribute to the reduction of parts.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a distributed Raman amplification type optical transmission line.
FIG. 2 is a configuration diagram of an optical transmission line according to the first embodiment of this invention.
FIG. 3 is a configuration diagram of an optical transmission line according to a second embodiment of this invention.
FIG. 4 is a configuration diagram of an optical transmission line according to a modification of the second embodiment of this invention.
[Explanation of symbols]
10 .. Optical transmission line 11 .. First amplifier,
12. First distributed Raman amplification type optical transmission line,
121..Pumping light source (pump) 122..Optical multiplexing means 123..Optical fiber (optical transmission line)
13. ・ Attenuating optical fiber 14 ・ ・ Second distributed Raman amplification type optical transmission line 141 ・ ・ Pumping light source (pump), 142 ・ ・ Optical multiplexing means 143 ・ ・ Optical fiber (optical transmission line)
15 .. Second amplifier 20.. Optical transmission line 21.. First amplifier,
22 .. First optical fiber 23.. Second optical fiber 24.. Third optical fiber 25 .. Distributed Raman amplification type optical transmission line 251 .. Pumping light source (pump) 252. ..Optical fiber (optical transmission line)
26 ·· Second amplifier 30 · · Optical transmission line 31 · · First amplifier 32 · · Distributed Raman amplification type optical transmission line 321 · · Pumping light source (pump) 322 · · Optical multiplexing means 323 · · optical fiber (Optical transmission line)
First optical fiber 34 Second optical fiber 35 Second amplifier

Claims (9)

In an optical transmission line using an excitation light source, optical multiplexing means, a distributed Raman amplification type optical transmission line having an optical transmission line optical fiber , and an amplifier ,
A section with a large transmission loss of the pumping light wavelength is set in a part of the optical transmission line, an attenuation optical fiber is inserted into the section, and unnecessary components of the pumping light are attenuated or extinguished by the attenuation optical fiber ,
Examples attenuating optical fiber, the optical fiber has been introduced impurities, have rows said attenuated by absorption by the introduced impurity,
The length of the optical transmission line optical fiber is not less than the effective length Leff of the optical transmission line ,
The product of the transmission loss difference at a specific wavelength in the excitation light band of the attenuation optical fiber and the optical transmission line optical fiber and the length of the attenuation optical fiber is the exit end from which the excitation light is emitted from the optical transmission line An optical transmission line characterized by having a power greater than
However, the effective length Le ff of the optical transmission line is
Leff = 1 / β · (1-exp (−β × L) )
Is defined as
here,
β is the optical fiber of the optical transmission path (i.e., the optical transmission line optical fiber, and the attenuating optical fiber) and loss factor,
L is the length of the optical fiber in the optical transmission line (that is, the optical transmission line optical fiber and the attenuation optical fiber) . A distributed Raman amplification type optical transmission line is arranged at the incident end ,
Wherein placing the attenuating optical fiber emission end of the light,
The optical transmission line according to claim 1. A distributed Raman amplification type optical transmission line is arranged at the output end,
The optical fiber for attenuation is arranged at the incident end ,
The optical transmission line according to claim 1. The first distributed Raman amplification type optical transmission line is disposed at the incident end,
A second distributed Raman amplification type optical transmission line is disposed at the exit end;
The attenuation optical fiber is disposed between the first distributed Raman amplification type optical transmission line and the second distributed Raman amplification type optical transmission line,
The optical transmission line according to claim 1. The introduced impurity includes any one of Mn, Ni, Cr, V, Co, Fe, and Cu.
The optical transmission line according to claim 1. As the attenuation optical fiber, a hydroxyl group is introduced into the optical fiber, and the attenuation is performed by absorption by the introduced hydroxyl group.
The optical transmission line according to claim 1. The transmission loss difference at a specific wavelength of the excitation light band of the attenuation optical fiber and the optical transmission line optical fiber is at least 0.2 dB / km or more,
The optical transmission line according to claim 1. The fluctuation amount of the wavelength loss characteristic from 1460 nm to 1565 nm is ± 0.1 dB / km over the entire length of the optical transmission line.
The optical transmission line according to claim 1. The amount of variation in wavelength loss characteristics from 1565 nm to 1625 nm is ± 0.1 dB / km over the entire length of the optical transmission line.
The optical transmission line according to claim 1.

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