JP3482348B2 - Remote pump light transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote pumping optical transmission system used in a repeaterless transmission system that does not include an optical repeater (regenerative optical repeater or linear optical repeater).

[0002]

2. Description of the Related Art An optical transmission system is provided in the middle of an optical transmission line.
It is roughly classified into a repeaterless transmission system that does not include an optical repeater (regenerative optical repeater or linear optical repeater) and a repeater transmission system that includes an optical repeater. For example, in a submarine optical transmission system, a non-relay transmission system is used for short-distance shallow seas, and a relay transmission system is used for long-distance deep seas.

The relay transmission system requires a power feeding device and a power feeding cable for feeding power from the transmitting station or the receiving station to the optical repeater, whereas the non-repeating transmission system does not require a power feeding device or the like and is therefore an inexpensive system. become. However, in the repeaterless transmission system, the transmission distance is limited due to loss and waveform deterioration in the optical transmission line. When the transmission light power is increased for long distance transmission, the transmission quality is deteriorated due to the non-linear optical effect of the optical fiber and the transmission distance is also limited.

Therefore, in order to increase the transmission distance in the repeaterless transmission system, an optical amplification fiber (hereinafter referred to as "EDF") doped with a rare earth element such as erbium is inserted in the middle of the transmission optical fiber. Is proposed. This is because pumping light is input to the EDF from a pumping light source provided in a transmitting station or a receiving station via an optical fiber for pumping light different from the optical fiber for transmission, and the attenuated signal light is amplified to transmit the transmission distance. This is a configuration for increasing the distance. The linear optical repeater has an EDF and a pumping light source inside, and it is necessary to supply power from a transmitting station or a receiving station. The EDF that inputs pumping light from the outside in the present specification is distinguished from a linear optical repeater.

FIG. 6 shows an example of the configuration of a conventional relayless transmission system in which the transmission distance is increased. (a) is a configuration example in which the EDF is inserted at a position several tens of kilometers away from the receiving station, and (b) is several tens of kilometers from the transmitting station and the receiving station.
This is a configuration example in which the EDF is inserted at the positions separated as described above.

In FIG. 6A, the transmitting station 61 and the receiving station 6
Reference numeral 2 denotes an optical fiber 63 for transmission that transmits a signal light in the 1.55 μm band and EDFs 64-1, 64 inserted in the receiving station side.
-2 is connected. The pumping light transmitted from the pumping light source 65 provided in the receiving station 62 via the pumping light optical fibers 66-1 and 66-2, respectively, is input to the EDFs 64-1 and 64-2, and the signal light is transmitted. Amplify. 67-
Reference numerals 1 and 67-2 are optical couplers for inputting pumping light.

In FIG. 6B, the transmitting station 61 and the receiving station 6
2 is a transmission optical fiber 63 for transmitting a signal light in the 1.55 μm band, and an EDF 6 inserted in the transmitting station side and the receiving station side.
It is connected via 4-1 to 64-4. EDF64-
1, 64-2, the pumping light source 6 provided in the transmitting station 61
5-1 to pump optical fibers 66-1 and 6 respectively
The pumping light transmitted via 6-2 is input and amplifies the signal light. The EDF 64-3 and 64-4 include a receiving station 62.
The pumping light transmitted from the pumping light source 65-2 provided in the pump light source via the pumping light optical fibers 66-3 and 66-4 is input to amplify the signal light. 67-1 to 67-4
Is an optical coupler for inputting excitation light.

The pumping light may be input from either the front side or the rear side of the EDF. The excitation light has a wavelength of 1.
48 μm is used. Actually, in the configuration of FIG. 6 (a), non-relay transmission of 350 km at 2.5 Gbit / s is realized,
In the configuration of FIG. 6 (b), 511km, 16 at 2.5Gbit / s
× 427km non-relay transmission is realized at 2.5Gbit / s (Reference: OFC'95 San Diego CApostdeadline p
aper PD26, ECOC'95 Brussel Beligium paper Th.
A.3.3).

[0009]

By the way, the pumping light power to be sent to each is determined according to the distance to the EDF (the length of the pumping light optical fiber), but since the EDF and the pumping light source are separated from each other. It is necessary to make the excitation light source have a large output. Furthermore, in order to extend the transmission distance without relay, E
When the number of DFs is increased, the conventional configuration requires as many pumping optical fibers as the number of EDFs. In this case, if the optical fiber for pumping light is housed in the same cable as the optical fiber for transmitting signal light, the cable becomes thick, and if a separate cable for housing the optical fiber for pumping light is provided, the configuration becomes complicated.

The present invention does not use an optical fiber for pumping light,
Another object of the present invention is to provide a remote pumping light transmission system capable of efficiently transmitting pumping light to a plurality of optical amplification fibers (for example, EDF) inserted in a transmission optical fiber.

[0011]

A remote pumping optical transmission system of the present invention is a pumping light source of a wavelength corresponding to a distance to each optical amplifying fiber with respect to a plurality of optical amplifying fibers inserted in a transmission optical fiber. Is provided in at least one of a transmitting station and a receiving station, and pumping light of each wavelength is wavelength-multiplexed with a transmission optical fiber and transmitted. Each optical amplification fiber amplifies the signal light from the pumping light transmitted using the transmission optical fiber by using the pumping light of the respectively assigned wavelength, and the pumping light of the other wavelengths is amplified by the next optical amplification fiber. Send to.

Here, since the loss in the transmission optical fiber differs depending on the wavelength of the pumping light, the pumping light of the wavelength with large loss is used in the optical amplifying fiber close to the pumping light source, and the pumping light of the wavelength with small loss is used. The pumping light can be efficiently transmitted by using the optical amplification fiber far from the pumping light source.

[0013]

FIG. 1 shows a first embodiment of a remote pumping optical transmission system of the present invention. In the figure, an optical transmission line that connects the transmitting station 11 and the receiving station 12 includes an optical fiber 13 for transmission that transmits signal light in the 1.55 μm band, and optical amplifying fibers 14-1 and 14 inserted in the receiving station side. -2.

Here, the optical amplifying fiber 1 far from the receiving station
The wavelength of pumping light for pumping 4-1 is λ with a small fiber loss.
1 (for example, 1.48 μm), the pumping light wavelength for pumping the optical amplifying fiber 14-2 close to the receiving station is set to λ 2 (for example, 0.98 μm) with a large fiber loss, and an optical amplifying fiber corresponding to each pumping light wavelength is formed. To do. The pumping light source 15-1 having the wavelength λ1 and the pumping light source 15-2 having the wavelength λ2 are arranged in the receiving station 12, and the pumping light output from each of them is W.
The wavelength is multiplexed on the transmission optical fiber 13 via the DM coupler 16.

Before and after the optical amplifying fiber 14-2, an optical filter 17 for inputting signal light in the 1.55 μm band and pumping light of wavelength λ2 and bypassing pumping light of wavelength λ1.
-1, 17-2 are arranged, the optical amplification fiber 14-2 is connected between the respective ports 2, and the bypass optical fiber 18 is connected between the ports 3. The transmission characteristics between ports 1 and 2 of this optical filter 17 are shown in Fig. 2 (a).
The transmission characteristics between them are shown in FIG. 2 (b). The transmission wavelength between ports 1 and 2 is set to 1.55 μm and λ 2 (0.98 μm), and the transmission wavelength between ports 1 and 3 is set to λ 1 (1.48 μm). Such an optical filter 17 can be realized by a dielectric multilayer filter, a grating filter, or an optical plane circuit (PLC).

With such a structure, the pumping light of wavelength λ2, which has a large fiber loss, is transmitted to the optical amplification fiber 14-
It is possible to amplify the signal light of the 1.55 μm band that is input to the optical fiber 2. Further, the pumping light of wavelength λ1 having a small fiber loss bypasses the optical amplifying fiber 14-2 and is input to the next optical amplifying fiber 14-1, and the 1.55 μm band signal light can be amplified. That is, the pumping light of each wavelength can be efficiently transmitted to the target optical amplification fiber according to the magnitude of the fiber loss.

The optical amplifying fiber 14-2 pumped by the pumping light having the wavelength λ2 (0.98 μm) has a wavelength λ1 (1.
48 μm) optical amplification fiber 14 excited by excitation light
Since the sensitivity is higher than that of -1, the signal light can be efficiently amplified.

FIG. 3 shows the effect of improving the transmission distance in the first embodiment. When the loss coefficient is 0.2 dB / km and the input signal light is 40 dB, two optical amplifying fibers are connected (solid line) and an optical amplifying fiber is not connected (broken line). If optical amplification fiber is not connected, the maximum transmission distance is 200 km. On the other hand, the gain is 15
When two dB optical amplification fibers are connected, the transmission distance can be extended to 350 km.

FIG. 4 shows a second embodiment of the remotely pumped optical transmission system of the present invention. The feature of the present embodiment is that three or more optical amplification units 20-1 to 20-n are connected in order from the receiving station 12 in the distant order, and pumping light wavelengths λ1 to λn input to the respective optical amplification units 20-1 to 20-n. Is set in the ascending order of fiber loss. Each optical amplification unit 20 includes the optical amplification fiber 14, the optical filter 17, and the bypass optical fiber 18 shown in the first embodiment.

The pumping light source 15-1 having the wavelength λ1 to the pumping light source 15-n having the wavelength λn are arranged in the receiving station 12, and the pumping light output from each of them is transmitted through the WDM coupler 16 to the transmission optical fiber 13 to the wavelength. It is multiplexed. Optical amplifier 20-n
The optical filters placed before and after the optical amplification fiber in 1.
The 55 μm band signal light and pumping light of wavelength λn are input to the optical amplification fiber, and pumping light of wavelengths λ1 to λn-1 is bypassed. Similarly, the pumping light used in each optical amplification unit is separated, and another pumping light is sent to the next optical amplification unit.

FIG. 5 shows a third embodiment of the remotely pumped optical transmission system of the present invention. The feature of this embodiment is that the optical amplifiers 20-1 to 20-n, the pumping light sources 15-1 to 15-n, and the WDM coupler 16 in the second embodiment are also installed on the transmitting station side. . The number of the optical amplification units 20-1 to 20-n installed on the transmission station side and the number of the optical amplification units 20-1 to 20-n installed on the reception station side do not have to be the same. Also, the wavelengths of the pumping light used by both are arbitrary, and both wavelengths of the same notation (for example, λ
1) need not be the same.

[0022]

As described above, the remote pumping light transmission system of the present invention wavelength-multiplexes pumping light of each wavelength used in a plurality of optical amplifying fibers inserted in a transmission optical fiber into the transmission optical fiber. Each optical amplification fiber amplifies the signal light using the pumping light of the assigned wavelength, and pumping light of other wavelengths is sent to the next optical amplification fiber to generate the pumping light. The pumping light can be transmitted without using a fiber.

Further, by using the pumping light of the wavelength with large loss in the optical amplification fiber near the pumping light source and the pumping light of the wavelength with small loss in the optical amplification fiber far from the pumping light source, the pumping light is efficiently supplied. It can be transmitted and the optical amplification efficiency can be improved.

Further, by arranging a plurality of optical amplification fibers to which pumping light is input from the receiving station side from the receiving station side in descending order of sensitivity, the signal light can be efficiently amplified.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a remote pumping optical transmission system of the present invention.

FIG. 2 is a diagram showing a transmission characteristic of an optical filter 17.

FIG. 3 is a diagram showing an effect of improving a transmission distance in the first embodiment.

FIG. 4 is a diagram showing a second embodiment of the remotely pumped optical transmission system of the present invention.

FIG. 5 is a diagram showing a third embodiment of the remotely pumped optical transmission system of the present invention.

FIG. 6 is a diagram showing a configuration example of a conventional non-repeatered transmission system in which the transmission distance is increased.

[Description of Reference Signs] 11 transmitting station 12 receiving station 13 transmission optical fiber 14 optical amplification fiber 15 pumping light source 16 WDM coupler 17 optical filter 18 bypass optical fiber 20 optical amplification unit (optical amplification fiber, optical filter, bypass optical fiber) )

Continuation of the front page (56) References Japanese Patent Laid-Open No. 9-197452 (JP, A) Takayuki Iida et al., Prototype study of high-power pumping light source for remote pumping transmission system, 1996 Institute of Electronics, Information and Communication Engineers Communication Society Conference, Nihon , The Institute of Electronics, Information and Communication Engineers, August 13, 1996, B-1044, p. 529 Haruki Ogoshi et al., Study on Remotely Pumped Optical Amplification System, 1996 IEICE Electronics Society Conference, Japan, The Institute of Electronics, Information and Communication Engineers, August 13, 1996, C-183, p. 183 Norio Okawa et al., Study on large-capacity undersea relay network system by remote excitation, 1997 IEICE General Conference, Japan, Institute of Electronics, Information and Communication Engineers, March 6, 1997, SB-10-7, pp. 829-830 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H01S 3/06 H01S 3/094 H01S 3/10 JISST File (JOIS)

Claims (3)

(57) [Claims] 1. A transmission optical fiber for transmitting signal light,
An optical amplification fiber that is inserted into a predetermined position of the transmission optical fiber and amplifies signal light, and the optical amplification fiber is provided in at least one of a transmission station and a reception station connected via the transmission optical fiber. A pumping light source for generating pumping light for pumping, and means for wavelength-multiplexing and transmitting the pumping light to the transmission optical fiber.
In a remote pumping optical transmission system, a plurality of optical amplification fibers having different pumping light wavelengths and each wavelength
Equipped with multiple excitation light sources that generate excitation light of
From the optical amplification fiber closer to
Set in order of decreasing fiber loss, and pump the pumping light of each wavelength.
It is configured to long-multiplex and transmit to the transmission optical fiber, and the signal light and the
Select the pumping light of the applied wavelength to each optical amplification fiber
Input and bypass the pumping light of other wavelengths and send it to the next stage.
Remotely pumped optical transmission system characterized by having steps . 2. The remote pumping light transmission system according to claim 1, wherein a plurality of optical amplifying fibers each provided with a receiving station and optically amplifying by a pumping light of each wavelength input from a plurality of pumping light sources are provided. A remote-pumped optical transmission system characterized in that it is installed from the receiving station side in descending order. 3. The remote pumping optical transmission system according to claim 1 or 2, wherein the signal light wavelength is 1.55 μm.
In the band, the pumping light wavelength with large fiber loss and high sensitivity of the optical amplifying fiber is set to 0.98 μm band, and the pumping light wavelength with small fiber loss and low sensitivity of the optical amplifying fiber is set to 1.48 μm band. A feature of the remote pumping optical transmission system.