JPH0456430A - optical communication system - Google Patents

Abstract

PURPOSE:To attain efficient signal amplification over a long range by accommodating an excitation light source driver and a wave synthesis coupler or the like into a transmission section and constituting an optical cable block with a function optical fiber. CONSTITUTION:A transmitter 14, an excitation light source driver 3 and a signal light/excitation light synthesis coupler 2 are installed in a station 11 as a transmission section 11. A signal light from the transmitter 14 is synthesized with an excited light having a comparatively short wavelength at the synthesis coupler 2 and the resulting light is propagated through a rate-earth group added fiber 1. The signal light is amplified by the energy when rare-earth group ions in the rare-earth group added fiber 1 excited by the excitation light are restored from the exciting state into the steady-state. The excitation light is cut off by an excitation light cut filter 7 installed at the termination of the optical cable block. Thus, the reception section receives only the amplified signal light through the rare-earth group added fiber 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical communication system using optical fibers.

[Conventional technology]

FIG. 6 shows the basic configuration of a conventional optical communication system. As shown in the figure, in this optical communication system, a housing 13 serving as an optical fiber amplifier is provided in an optical cable section connecting a station 11 and a terminal 12. This housing 13 collectively holds the rare earth-doped fiber coil 9, the excitation light cut filter 7, the excitation light source driver 3, the optical fiber coupler 2, and the like. In this optical fiber coupler 2, the excitation light from the excitation light source and the signal light from the transmitter in the station 11 are combined, thereby exciting the rare earth in the rare earth doped fiber coil 9. . Note that the X mark 5 in the figure indicates the optical termination. Further, a power supply line is wired from the station 11 to supply power to the excitation light source driver 3 .

[Problem to be solved by the invention]

In conventional optical communication systems, it is necessary to provide a housing as a fiber amplifier between the station and the terminal, and because the optical fiber amplifier has a rare earth fiber coil, etc.
There was a problem that the casing became larger. Furthermore, when the excitation light source is built into the above-mentioned casing, a transmission line must be installed separately from the outside of the casing for power supply, etc., and furthermore, the deterioration state of the excitation light source inside the casing must be monitored. There was a problem that I had to do it.

On the other hand, if the pump light is fed from outside the case via an optical fiber, etc., without providing a transmission line for feeding power to the case, transmission loss will occur before the pump light reaches the amplification section. Excitation efficiency deteriorates. Therefore, a more powerful excitation light source is required, which poses the problem of increasing restrictions on the excitation light sources that can be used.

The present invention is intended to solve the above-mentioned problems.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned problems, and a part of the optical cable section connecting the transmitting section and the receiving section is provided with rare earth elements at a concentration corresponding to the usage distance of the optical cable. A doped optical fiber is used, and an excitation light source and an excitation driver for exciting a rare earth element;
The device is characterized in that a multiplexing coupler for multiplexing the excitation light and the signal light from the transmitter is housed in the transmitter.

[Effect]

In the present invention, since the excitation light source driver, multiplexing coupler, etc. are housed in the transmitting section, by using an optical fiber doped with a low concentration of rare earth elements in a part of the optical cable section,
Signal amplification can be performed.

Moreover, by installing at least one amplification unit in the above-mentioned optical cable section, signal amplification can be performed according to the communication distance.

〔Example〕

A first embodiment of an optical communication system according to the present invention will be described based on FIG.

In this embodiment, a transmitter 1 is included in the station 11 as a transmitter.
4, an excitation light source driver 3, and a signal light/excitation light multiplexing coupler 2 are installed. A rare earth doped fiber 1 is used in a part of the optical cable section on the station 11 side that connects the station 11 and the terminal 12, and an excitation light cut filter 7 is installed at the end of the optical cable section. , connected to a terminal 12 having a receiver 15.

There are two types of optical fibers that can be used as the above-mentioned rare earth doped fiber 1, as shown in FIG. The same figure (a
) is a fiber in which a rare earth element is uniformly added to the core portion of the optical fiber, and (b) of the same figure is a fiber in which a rare earth element is doped only in a portion of the optical fiber core, particularly in the center of the core where the optical power is high.

Due to the structure of optical fibers, the intensity of the signal light and pumping light is highest at the center of the fiber core, and the pumping efficiency of rare earth elements decreases as the distance from the center increases, resulting in a relative increase in transmission loss. There is. Therefore, when these two types of optical fibers are compared, it is possible to maintain a more effective amplification effect over a longer distance by using the one shown in FIG. 2(b).

In this example, an optical fiber doped with a rare earth element only in the central portion of the optical fiber core was used.

The signal light from the transmitter 14 in FIG.

The signal light is amplified by the energy released by the rare earth ions in the rare earth doped fiber 1 excited by the excitation light when returning from the excited state to the steady state. This excitation light is cut by an excitation light cut filter 7 installed at the end of the optical cable section. Therefore, in the receiving section, only the amplified signal light can be received by passing it through the rare earth doped fiber 1.

As described above, when the rare earth-doped fiber 1 is used in the communication system of this embodiment, there is a length at which the gain hardly changes even if the fiber length is increased further. Third
The figure shows the relationship between the length of the optical fiber and the gain. Here, the rare earth additive is Er3+. As shown in this figure, when the amount of rare earth added to the optical fiber is constant, the gain stops changing when the input intensity of the pumping light and the length of the optical fiber itself exceed a certain value. That's what I understand.

Next, FIG. 4 shows the relationship between the length of the tip fiber and the amplification degree. In the same figure, fiber #1 has an Er doping concentration of 1.
300 ppm, fiber #2 is E"3 + doping degree is 10
00 ppm. As shown in this figure, Er
When using an optical fiber with a reduced amount of Er3+ doping in a communication system, it is necessary to increase the length of the optical fiber in order to obtain the same gain as when using an optical fiber with a high Er3+ doping concentration. Recognize.

Since there is a constant Lc-constant relationship between the optimum length of the rare earth-doped fiber 1 and the doping concentration C, the above-mentioned Er3+ doped fiber is
When used as an optical cable section of m, the additive concentration is 0.
．． The optimal value is 5 ppm.

From the above-mentioned relationship between the length, gain, and amplification of the rare earth doped fiber, by using the optical fiber doped with a low concentration of rare earth element in the communication system as shown in this example, it is possible to create an optical cable. Signal amplification can be performed without installing a large casing as an optical fiber amplifier in the section.

Next, the basic configuration of a second embodiment according to the present invention will be shown using FIG.

In this embodiment, as shown in the figure, an excitation light source and an excitation light source driver 3b, and a multiplexing coupler 2 are installed in the optical cable section between the station 11, which is a transmitter, and the terminal 12, which is a receiver.
An amplification unit 16 having b is further provided,
In order to supply power to this amplification unit 16, a power supply line 17 is wired from a power supply device 18 within the station 11. Further, a low concentration rare earth doped fiber 1b is used in a part of the optical cable section, that is, in a part of the cable section at the end of the receiving section of the amplification unit 16 described above. Note that, as in the first embodiment, the station 11 includes a multiplexing coupler 2a and an excitation light source driver 3.
a is accommodated, and amplifies the signal light together with the low concentration rare earth doped fiber 1a in the optical cable section. The low concentration rare earth doped fiber 1b has the same structure as the fiber 1a.

With the above configuration, the signal light from the transmitter is amplified via the low concentration rare earth doped fiber 1a, and further amplified again by passing through the amplification unit 16 and the low concentration rare earth doped fiber 1b.

Therefore, even if the distance between the transmitting section and the receiving section is extended, the signal can be efficiently amplified.

〔Effect of the invention〕

In the optical communication system according to the present invention, the excitation light source driver, the multiplexing coupler, etc. can be housed in the transmitter, so that the system can have a simpler configuration. Furthermore, since the optical cable section is made of functional optical fibers, optical signal transmission and amplification can be performed simultaneously, and therefore efficient signal amplification can be achieved over long distances. Furthermore, there is an effect that maintenance and management of this optical communication system becomes easier.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the basic configuration of a first embodiment of the present invention, Fig. 2 is a cross-sectional view of an optical fiber used in the embodiment of the present invention, and Fig. 3 is the relationship between the length of the optical fiber and the gain. Figure 4 is a diagram showing the relationship between the length of the optical fiber and the degree of amplification.
FIG. 5 is a diagram showing the basic configuration of a second embodiment of the present invention, and FIG. 6 is a diagram showing the basic configuration of a conventional optical communication system. 1.1a and 1b...Low concentration rare earth doped fiber, 2
．． 2a and 2b...pumping light/signal light multiplexing coupler, 3.
3a and 3b... excitation light source dry nozzle, 5... optical termination, 7... excitation light cut filter, 9... rare earth doped fiber coil, 11... station, 12... terminal,
14...Transmitter, 15...Receiver, 16...Amplification UniSoto, 17...Feeder line, 18...Feeder.

Claims (1)

[Claims] 1. In an optical communication system in which a transmitting unit including a transmitter and a receiving unit including a receiver are connected by an optical cable, a part of the optical cable section on the transmitting unit side is connected to the optical cable. It is composed of a functional optical fiber doped with a rare earth element at a concentration corresponding to the usage distance, and includes an excitation light source for exciting the rare earth element, excitation light from the excitation light source, and signal light from the transmitter. An optical communication system, characterized in that a multiplexing coupler for multiplexing and inputting the multiplexed signals to the functional optical fiber is housed in the transmitter. 2. A part of the optical cable section on the receiving section side of the optical cable section constituted by the functional optical fiber is further made of another functional optical fiber doped with a rare earth element at a concentration corresponding to the usage distance of the optical cable. An amplification unit having a pumping light source and a multiplexing coupler for introducing pumping light from the pumping light source into the other functional optical fiber is installed on the transmitter side of the other functional optical fiber. The optical communication system according to claim 1, characterized in that: