JP2610134B2 - Multipoint optical amplification repeater using unidirectional optical amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a repeater in an optical transmission system.

(Prior art and its problems) In an optical fiber communication system currently in practical use, an optical signal is temporarily converted into an electric signal as a relay method.
Amplifying and shaping the waveform in the state of the electric signal, and driving the semiconductor laser again with the amplified electric signal.
Light, electricity, light, and conversion are being performed.

On the other hand, as a new relaying method, an optical amplifier that directly amplifies an optical signal as it is has been proposed. The relay system using optical amplification simplifies the relay circuit compared to the conventional optical / electrical / optical / conversion relay system, and also allows one wavelength multiplexed signal or frequency multiplexed signal at any transmission rate to be combined into one. There are advantages such as being able to be amplified collectively by an optical amplifier. Further, since the amplification degree is constant irrespective of the incident direction of light, bidirectional signal light can be amplified together using one optical amplifier.

As a method of optical amplification, there are a method mainly using a semiconductor laser and an optical fiber Raman amplification using a stimulated Raman scattering phenomenon generated in an optical fiber. Many research results have been reported on the amplification characteristics and noise characteristics of these optical amplifications.

The amplification degree can be 30dB to 40dB, and it is theoretically predicted that it can be transmitted as light for 10,000 km or more without being affected by background light noise due to natural scattered light. The practicality as a relay system is increasing (IEEE.J. Lightwave Tech., Vol. LT-4, pp. 1328-133)
3, IEEE J.Qautum Electron.Vol.QE-17, pp.919-93
Five). When this optical repeater system was put into practical use, an optical cable with a repeater could be considered as a mere optical transmission line, just like a non-repeater optical cable. Multipoint communication to which a frequency (or wavelength) is assigned becomes possible. In this case, in order to enable communication with any point, it is necessary to return a signal coming from each point to each point at a branch point.

FIG. 1 shows an optical branching device using optical amplification. In the figure, an optical signal 1-1 from a point A is coupled to an optical signal 1-2 from a point B by an optical coupler 1-3 such as a fiber coupler, for example, and guided to an optical amplifier 1-4. Amplified. The amplified optical signal 1-5 propagates toward the point C. Conversely, the optical signal 1-6 from the point C is amplified by the optical amplifier 1-7, and then the optical coupler 1-8
, And head to point A and point B, respectively. In this case, communication between AC and between BC is possible, but communication between AB is not possible.

(Object of the Invention) The present invention is directed to a multipoint optical communication system having an optical amplification repeater, which uses a bidirectional optical amplifier that can easily perform multipoint communication by assigning a frequency (or wavelength). A point-to-point optical amplification repeater is provided.

(Constitution of the Invention) A multipoint optical amplification repeater using a one-way optical amplifier according to the present invention converts a plurality of pairs of optical signals of a first optical transmission line into a pair of second optical signals.
A pair of optical multiplexer / demultiplexers connected to transmit the optical signals of the pair of second optical transmission lines to the plurality of first optical transmission lines; and A pair of unidirectional optical amplifiers respectively inserted into the two optical transmission lines and amplifying unidirectional optical signals in opposite directions to each other, and one input light or output light of the pair of unidirectional optical amplifiers is used for the other. A pair of optical couplers inserted for coupling to an input or an output of the plurality of pairs of the first optical transmission line and the multipoint connected to the pair of second optical transmission lines Is configured to enable two-way optical communication.

 Next, the present invention will be described in detail with reference to the drawings.

The present invention enables communication between any points via optical branching. FIG. 2 shows the main configuration of the device of the present invention. The optical signal 2-1 from the point A is combined with the optical signal 2-2 from the point B by the optical coupler 2-3. Next, the combined optical signal is supplied to the unidirectional optical amplifier 2-.
4 and amplified. The amplified optical signal is supplied to the splitter 2-
9, and one signal 2-5 propagates toward the point C. On the other hand, the other is combined with the optical signal 2-6 from the point C by the optical coupler 2-10 and enters the one-way optical amplifier 2-7. The amplified optical signal 2-11 is demultiplexed by the optical demultiplexer 2-8, and propagates to the points A and B. At each of the points A, B, and C, the frequency (or wavelength) assigned to each point is converted to an optical filter or an optical frequency tuning technology (a coherent optical communication method that uses the property of an optical wave is similar to radio communication. , It is possible to receive the signal without interference. That is, by using the present invention,
Communication between AC, between BC, and between AB becomes possible.

Another embodiment of the present invention is shown in FIGS. In FIG. 3, the optical signal branched by the demultiplexer 3-9 is multiplexed with another optical signal 3-6 by the optical multiplexer 3-10 after the unidirectional optical amplifier 3-7, and the optical signal 3 The other points are the same as in FIG. 2 except that −11 is obtained.

In FIG. 4, an optical signal is branched by an optical demultiplexer 4-9 before a unidirectional optical amplifier 4-4, and is combined with an output signal from a unidirectional optical amplifier 4-7 by an optical multiplexer 4-10. The other points are the same as in FIG. 4
Reference numeral -6 denotes a signal before amplification, which arrives from point C, and reference numeral 4-11 denotes an optical signal obtained at the output side of the unidirectional optical amplifier 4-7.

5 is different from FIG. 2 in that an optical signal is branched by an optical demultiplexer 5-9 in a stage preceding a one-way optical amplifier 5-4, and the other points are the same.

Next, FIG. 6 shows an example in which the present invention is applied to a frequency division multiplexing system using a coherent optical communication system. The coherent optical communication system modulates the frequency or phase of light with a signal, and enables a frequency division multiplex communication system. In this system, f _AC is used as a communication optical frequency from point A to point C, and f _CA is used as a communication optical frequency from point C to point A. Similarly, f _BC , f _CB , f _AB , and f _BA are defined as communication optical frequencies between BC and AB.
A signal from point A to point C is modulated by a light source 6-11 having a center frequency f _AC by a modulator 6-13 and transmitted. The signal for the point B is generated by the light source 6-12 having the center frequency f _AB .
Is modulated by the modulator 6-14 and transmitted. These two transmitted signal lights are multiplexed and transmitted by an optical multiplexer 6-15 such as an optical fiber coupler.

On the other hand, a signal from point C to point A reaches point A via the relay device 6-1 of the present invention. In the coherent optical communication system, it is desirable that the polarization states of the signal light and the local light are the same.
The polarization state is adjusted by the polarization compensator 6-16 so as to be the same as the polarization state of 18. By tuning the center frequency of the local light 6-18 to the center frequency f _CA of the signal light from the point C, the signal from the point C can be obtained by the receiver 6-20. In the case of a semiconductor laser, the center frequency of the emitted light can be moved by changing the injection current. Further, a signal from point B to point A is returned by the relay device 6-1 according to the present invention and returned to point A. In point A, by tuning the center frequency of the local light 6-19 to the center frequency f _BA of the signal light from the point B, the receiver 6-21
Thus, a signal from point B can be obtained.

Although the above description has been made focusing on the point A, the transmitting and receiving systems at the points B and C can be similarly considered. In addition, although the present example has been described with respect to communication between three points, the present invention can be similarly applied to multipoint communication at three or more points. In this example, the polarization compensators 6-16 and 6-17 are separately arranged.
It is also possible to perform polarization compensation collectively before the optical demultiplexer 6-22. Further, instead of the polarization compensation, compensation by a polarization diversity system is also possible.

(Effect of the Invention) As described above, bidirectional wavelength (frequency) multiplex communication can be performed between multiple points by using the present invention. In the present invention, three points have been described as an example.
The same applies to multipoints beyond the point.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a conventional unidirectional optical transmission system, and FIGS. 2, 3, 4, 5, and 6 are block diagrams showing an embodiment of the present invention. . 1-1,1-2,1-5,1-6,2-1,2-2,2-5,2-6,2-11,3-
1,3−2,3−5,3−6,3−11,4−11,4−2,4−5,4−6,4−11,
5-1,5-2,5-5,5-6,5-11 ... optical signal, 1-3,1-8,2
-3,2-8,3-3,3-8,4-3,4-8,5-3,5-8,6-3,6-8
...... Optical multiplexer / demultiplexer, 1-4,1-7,2-4,2-7,3-4,3-7,4-
4,4-7,5-4,5-7,6-4,6-7 ... unidirectional optical amplifier, 2
-9,3-9,4-9,5-9,6-9 ... optical demultiplexer, 2-10,3-1
0,4-10,5-10,6-10 ... optical coupler, 6-1 ... optical amplification repeater according to the present invention, 6-11,6-12 ... light source, 6-1
3, 6-14: modulator, 6-15: optical multiplexer, 6-16, 6-1
7 ... Polarization compensator, 6-18, 6-19 ... Local light source, 6-20,
6-21 Receiver.

Claims (1)

(57) [Claims] An optical signal of a plurality of pairs of first optical transmission lines is transmitted to a pair of second optical transmission lines, and an optical signal of the pair of second optical transmission lines is transmitted to the plurality of pairs of first optical transmission lines. A pair of optical multiplexer / demultiplexers connected to be transmitted to the transmission line, and a pair of optical multiplexers / demultiplexers respectively inserted into the pair of second optical transmission lines and amplifying unidirectional optical signals which are opposite to each other. A direction optical amplifier, and a pair of optical couplers inserted to couple one input light or output light of one of the pair of unidirectional optical amplifiers to the other input or output. Multipoint optical amplification repeater using a unidirectional optical amplifier configured to enable bidirectional optical communication between multipoints connected to the pair of optical transmission lines and the pair of second optical transmission lines. .