JP2000151521A - Remote excitation light transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system where optical fiber for excitation light is not employed and the excitation light is efficiently transmitted to a plurality of optical amplification fibers inserted to a transmission optical fiber. SOLUTION: At least a transmission station 11 or a reception station 12 is provided with excitation light sources 15-1-15-2 with a wavelength in response to a distance up to each optical amplification fiber 14 with respect to a plurality of the optical amplification fibers 14-1-14-2 inserted to a transmission optical fiber 13 and the excitation lights with each wavelength are transmission to the transmission optical fiber through wavelength multiplex. Each optical amplification fiber 14 amplifies a signal light by using the excitation light with an assigned wavelength among the excitation lights sent through the transmission optical fiber 13 and transmits the excitation light with other wavelength to a succeeding optical amplification fiber 14. Furthermore, the excitation light with a wavelength λ2 having a large loss is used for the optical amplification fiber 14-2 close to the excitation light source 15 and the excitation light with a wavelength λ1 having a small loss is used for the optical amplification fiber 14-1 remote from the excitation light source 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote pumping light transmission system used in a repeaterless transmission system that does not include an optical repeater (regenerative optical repeater, 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 broadly classified into a non-repeater transmission system that does not include an optical repeater (regenerative light repeater, linear optical repeater), and a repeater transmission system that includes an optical repeater. For example, in a submarine optical transmission system, a relayless transmission system is used for short-distance shallow water, and a relay transmission system is used for long-distance deepwater.

A repeater transmission system requires a power supply device or a power supply cable for supplying power from a transmitting station or a receiving station to an optical repeater, while a non-repeated transmission system does not require a power supply device or the like, so an inexpensive system is required. 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 deteriorates due to the nonlinear optical effect of the optical fiber, and the transmission distance is also limited.

In order to extend the transmission distance in a 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 transmission optical fiber. Has been proposed. This is because the pump light is input to the EDF from the pump light source provided at the transmitting station or the receiving station via the pump light optical fiber different from the transmission optical fiber, and the attenuated signal light is amplified to reduce the transmission distance. This is a configuration for increasing the distance. Note that the linear optical repeater includes an EDF and an excitation light source therein, and needs to be supplied with power from a transmitting station or a receiving station. In this specification, an EDF that inputs pump light from the outside 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 an EDF is inserted at a position more than several tens of kilometers from the receiving station, and (b) is a configuration example of several tens of kilometers from the transmitting station and the receiving station.
This is a configuration example in which an EDF is inserted at a position distant from the above.

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

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

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

[0009]

The power of the pumping light to be transmitted is determined according to the distance to the EDF (the length of the optical fiber for the pumping light). However, since the EDF and the pumping light source are distant from each other. It is necessary to increase the output of the excitation light source. Furthermore, in order to extend the transmission distance without relay, E
When the number of DFs is increased, the conventional configuration requires the same number of optical fibers for excitation light as the number of EDFs. In this case, if the excitation light optical fiber is accommodated in the same cable as the signal light transmission optical fiber, the cable becomes thicker, and if a cable accommodating the excitation light optical fiber is separately provided, the configuration becomes complicated.

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

[0011]

SUMMARY OF THE INVENTION A remote pumping light transmission system according to the present invention provides a pumping light source having a wavelength corresponding to a distance to each optical amplifying fiber for a plurality of optical amplifying fibers inserted into a transmission optical fiber. Is provided in at least one of the transmitting station and the receiving station, and the pump light of each wavelength is wavelength-multiplexed and transmitted to the transmission optical fiber. Each optical amplification fiber amplifies the signal light using the excitation light of the assigned wavelength from the excitation light transmitted using the transmission optical fiber, and the excitation light of the other wavelength is transmitted to the next optical amplification fiber. To send to.

Here, since the loss in the transmission optical fiber varies depending on the wavelength of the pumping light, the pumping light having a large loss is used in the optical amplification fiber close to the pumping light source, and the pumping light having the small loss is used. By using an optical amplification fiber far from the excitation light source, the excitation light can be transmitted efficiently.

[0013]

FIG. 1 shows a first embodiment of a remote pumping light transmission system according to the present invention. In the figure, an optical transmission line connecting a transmitting station 11 and a receiving station 12 is composed of a transmission optical fiber 13 for transmitting signal light in the 1.55 μm band, and optical amplifying fibers 14-1 and 14 inserted into the receiving station. -2.

Here, the optical amplification fiber 1 far from the receiving station
The wavelength of the pump light for pumping 4-1 is λ where the fiber loss is small.
1 (for example, 1.48 μm), the pumping light wavelength for pumping the optical amplification fiber 14-2 close to the receiving station is λ2 (for example, 0.98 μm), which has a large fiber loss, and forms an optical amplification fiber corresponding to each pumping light wavelength. I 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 outputted from each of them is W.
The wavelength is multiplexed on the transmission optical fiber 13 via the DM coupler 16.

An optical filter 17 for inputting signal light of 1.55 μm band and pumping light of wavelength λ2 and bypassing pumping light of wavelength λ1 is provided before and after the optical amplification fiber 14-2.
-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. FIG. 2A shows the transmission characteristics between the ports 1 and 2 of the optical filter 17, and FIG.
FIG. 2 (b) shows the transmission characteristics between the two. The transmission wavelength between ports 1 and 2 is set to 1.55 μm and λ2 (0.98 μm), and the transmission wavelength between ports 1 and 3 is set to λ1 (1.48 μm). Such an optical filter 17 can be realized by a dielectric multilayer filter, a grating filter, or an optical planar circuit (PLC).

With such a configuration, the pumping light of the wavelength λ 2 having a large fiber loss is supplied to the optical amplification fiber 14-
2 and can amplify the signal light in the 1.55 μm band. The pumping light having the wavelength .lambda.1 having a small fiber loss bypasses the optical amplifying fiber 14-2 and is input to the next optical amplifying fiber 14-1 to amplify the 1.55 .mu.m band signal light. That is, the pump 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 the wavelength λ1 (1.
Optical amplification fiber 14 pumped by 48 μm) pump light
Since the sensitivity is higher than -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, a case where two optical amplification fibers are connected (solid line) and a case where no optical amplification fiber is connected (dashed line) are shown. If no optical amplification fiber is connected, the transmission distance is limited to 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 remote pumping light transmission system of the present invention. A feature of the present embodiment is that three or more optical amplifiers 20-1 to 20-n are connected in order from the farthest from the receiving station 12, and the pumping light wavelengths λ1 to λn input to the respective optical amplifiers 20-1 to 20-n. Are set in ascending order of fiber loss. Each optical amplifier 20 includes the optical amplifier fiber 14, the optical filter 17, and the bypass optical fiber 18 described in the first embodiment.

The pumping light sources 15-1 to 15-n having the wavelength λ1 are disposed in the receiving station 12, and the pumping light outputted from each of them is transmitted to the transmission optical fiber 13 via the WDM coupler 16 by the WDM coupler 16. Multiplexed. Optical amplifier 20-n
Optical filters placed before and after the optical amplification fiber of 1.
The signal light in the 55 .mu.m band and the pump light of wavelength .lambda.n are input to the optical amplification fiber, and the pump lights of wavelengths .lambda.1 to .lambda.n-1 are bypassed. Similarly, the pump light used in each optical amplifier is separated, and another pump light is transmitted to the next optical amplifier.

FIG. 5 shows a third embodiment of the remote pumping light transmission system according to the present invention. The feature of the present embodiment lies in that the optical amplifiers 20-1 to 20-n, the pump 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 optical amplifiers 20-1 to 20-n installed on the transmitting station side and the number of optical amplifiers 20-1 to 20-n installed on the receiving station side may not be the same. Further, the wavelengths of the respective pumping lights used for both are arbitrary, and both wavelengths (for example, λ
1) need not be the same.

[0022]

As described above, the remote pumping light transmission system according to the present invention uses the wavelength multiplexing of the pumping light of each wavelength used by the plurality of optical amplification fibers inserted into the transmission optical fiber. Each optical amplification fiber amplifies the signal light using the excitation light of the assigned wavelength, and transmits the excitation light of the other wavelength to the next optical amplification fiber, thereby transmitting the excitation light. Excitation light can be transmitted without using a fiber.

Further, by using pump light having a wavelength with a large loss in an optical amplifying fiber near the pump light source and using pump light with a wavelength with a small loss in an optical amplifier fiber far from the pump light source, the pump light can be efficiently converted. It can transmit and increase the optical amplification efficiency.

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

[Brief description of the drawings]

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

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

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

FIG. 4 is a diagram showing a second embodiment of the remote pumping light transmission system of the present invention.

FIG. 5 is a diagram showing a third embodiment of the remote pumping light transmission system of the present invention.

FIG. 6 is a diagram showing a configuration example of a conventional relayless transmission system in which a transmission distance is increased.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Transmitting station 12 Receiving station 13 Transmission optical fiber 14 Optical amplification fiber 15 Excitation light source 16 WDM coupler 17 Optical filter 18 Bypass optical fiber 20 Optical amplifier (optical amplification fiber, optical filter, bypass optical fiber)

Continuation of front page (72) Inventor Nobuyuki Yoshizawa 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 5F072 AB09 AK06 JJ08 KK30 PP10 RR01 YY17 5K002 AA01 AA03 AA06 BA05 CA10 CA13 DA02 FA01

Claims (4)

[Claims] A transmission optical fiber for transmitting a signal light;
An optical amplification fiber that is inserted into a predetermined position of the transmission optical fiber and amplifies the signal light, wherein at least one of a transmission station and a reception station connected via the transmission optical fiber includes the optical amplification fiber. A pumping light source for generating pumping light for pumping, and a means for wavelength-multiplexing and transmitting the pumping light to the transmission optical fiber and transmitting the pumping light. 2. The remote pumping light transmission system according to claim 1, further comprising a plurality of optical amplifying fibers having different pumping light wavelengths, and a plurality of pumping light sources for generating pumping lights of respective wavelengths, wherein the optical amplification is close to the pumping light source. The pump light wavelengths are set in order from the fiber in the order of larger fiber loss, and the pump light of each wavelength is wavelength-multiplexed and transmitted to the transmission optical fiber.Before and after each optical amplification fiber, signal light and A remote pumping light transmission system comprising means for selecting a pumping light of an assigned wavelength, inputting the selected pumping light to each optical amplification fiber, and transmitting the pumping light of another wavelength to a next stage. 3. The remote pumping light transmission system according to claim 2, wherein a plurality of optical amplifying fibers provided in the receiving station and each performing optical amplification by pumping light of each wavelength input from a plurality of pumping light sources are provided. A remote pumping light transmission system characterized by being installed from the receiving station side in ascending order. 4. The remote pumping light transmission system according to claim 2, wherein when the signal light wavelength is in the 1.55 μm band, the pumping light wavelength having a large fiber loss and a high sensitivity of the optical amplification fiber is 0.98. μ
A remote pumping light transmission system characterized in that the pumping light wavelength is in the m band and the pumping light wavelength is low and the sensitivity of the optical amplification fiber is low in the 1.48 µm band.