JPH11215069A - Bidirectional optical amplification repeater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent multiplex reflections even if up/down going signals share a single optical amplifier by providing an optical multiplexer/dempultiplexer having four ports multiplexing/demultiplexing the light of a first wavelength area and the light of second wavelength area and an optical isolator, providing an optical amplifier, through which only light in a single direction passes and which amplifies it and specifying a passage characteristic. SOLUTION: A first wavelength area light (upward signal) A and a second wavelength area light (downward signal), which are transmitted through optical fibers 3 and 2, are inputted from a first port 9 and a second port 10 to a multiplexer/demultiplexer 13, are outputted from a third port 11, are amplified in an optical amplifier 14, are inputted from a fourth port 12 to the multiplexer/ demultiplexer 13, are outputted from the second port 10 and the first port 9 and are transmitted through the optical fibers 2 and 3. An upward signal C and a downward signal, which are reflected or scattered, are inputted to the multiplexer/demultiplexer 13, are outputted from the fourth port 12 and an optical isolator 15 interrupts transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying repeater for use in a bidirectional optical transmission technique for transmitting an optical signal in both directions of up and down on a single transmission line.

[0002]

2. Description of the Related Art A bidirectional transmission system for transmitting an optical signal in both directions of up and down on the same transmission line uses an up and down transmission line in comparison with a case of transmitting an optical signal in only one direction. Since they can be shared, the number of necessary optical fibers and optical amplifiers is halved, and the system can be made more economical.

A case where a bidirectional transmission line is formed by simply connecting an optical amplifier and an optical fiber will be described with reference to FIG.
An upstream optical signal (hereinafter, a signal transmitted from left to right in the drawings is referred to as an upstream signal, and a signal transmitted from right to left is referred to as a downstream signal) is transmitted through the optical fiber 2 on the right side of the optical amplifier 1. Some of the light propagates in the opposite direction due to reflection and scattering at the discontinuous point. This backward propagating light is transmitted to the optical amplifier 1
After being amplified by the above, the light propagates through the optical fiber 3 on the left side, but a part of the light propagates from left to right due to reflection and scattering at the discontinuous point, and this part is superimposed on the upstream signal, thereby deteriorating the transmission characteristics of the upstream signal. .

[0004] To avoid such deterioration due to multiple reflection,
A conventional technique for enabling bidirectional transmission will be described with reference to FIG. The upstream optical signal propagating through the optical fiber 3 on the left side of the figure is amplified by the first optical amplifier 5 after passing through the first optical circulator 4, and is amplified by the second optical circulator 6.
And is input to the right optical fiber 2. The downstream optical signal that has propagated through the optical fiber 2 on the right side of the drawing is amplified by the second optical amplifier 7 after passing through the second optical circulator 6, passes through the first optical circulator 4, and passes through the first optical circulator 4. Input to fiber 3.

In the prior art shown in FIG. 2, in order to prevent the multiple reflection phenomenon, the wavelength of the upstream optical signal and the wavelength of the downstream optical signal are set to different wavelengths. And the second optical amplifier 7 is designed to have an amplification characteristic of amplifying only the optical signal having the wavelength of the downstream signal. The reflected light of the upstream signal generated in the right optical fiber 2 is input to the second optical amplifier 7 after passing through the second optical circulator 6, and the second optical amplifier 7 converts the light of the wavelength of the upstream signal into light. On the other hand, since there is no amplification characteristic, the reflected light of the upstream signal is attenuated when passing through the second optical amplifier 7, and the occurrence of multiple reflection is prevented. Similarly, the occurrence of multiple reflection is prevented in the downstream signal.

[0006]

As described above,
The optical amplifying repeater shown in FIG. 2 has an advantage in that multiple reflections can be prevented and both upstream and downstream signals can be amplified. However, the conventional optical amplifier repeater shown in FIG. 2 requires one expensive optical amplifier for each of the upstream and downstream, and has a disadvantage that the economical advantage of the bidirectional transmission system cannot be fully utilized. there were.

An object of the present invention is to provide a bidirectional optical amplifying repeater which eliminates the above-mentioned drawbacks and can prevent multiple reflections even when the upstream and downstream signals share one optical amplifier. And

[0008]

According to the present invention, there is provided a bidirectional optical amplifying repeater for splitting and combining light of a first wavelength band and light of a second wavelength band to achieve the above object. An optical multiplexer / demultiplexer having a plurality of ports, and an optical amplifier having an optical isolator for amplifying and passing only light in a single direction, wherein the pass characteristics of the optical multiplexer / demultiplexer are the first input to the first port. One wavelength band light to the third port, the second wavelength band light input to the first port to the fourth port, the first wavelength band light input to the second port to the fourth port, the second port The input second wavelength band light is configured to be output to the third port, respectively,
The output light of the third port of the optical multiplexer / demultiplexer is amplified by the optical amplifier and then input to the fourth port of the optical multiplexer / demultiplexer.

According to such a bidirectional optical amplifier repeater of the present invention, the distance between the third port and the fourth port of the multiplexer / demultiplexer is
It is connected via a unidirectional optical amplifier that amplifies only the optical signal going from the third port to the fourth port, the first wavelength band light input to the first port and the second light input to the second port. The wavelength band light is output from the third port, amplified by the unidirectional optical amplifier, and output from the second port and the first port through the fourth port of the multiplexer / demultiplexer.
On the other hand, since the first wavelength band light input to the second port and the second wavelength band light input to the first port are both output from the fourth port, the propagation is blocked by the unidirectional optical amplifier. .

Therefore, the first wavelength band light is used as the upstream signal,
When each of the second wavelength band lights is used as the downstream signal, according to the bidirectional optical amplifier repeater of the present invention connected to each transmission line via the first port and the second port of the multiplexer / demultiplexer, By using only one optical amplifier, multiple reflections can be prevented and good bidirectional amplification can be performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing a configuration example of a multiplexer / demultiplexer used in the bidirectional optical amplifier repeater of the present invention. The dielectric multilayer film 8 has a property of transmitting the first wavelength band light A and reflecting the second wavelength band light B. Therefore, as shown in FIG.
The first wavelength band light A and the second wavelength band light B input to the first port 9 of the multiplexer / demultiplexer are sent to the third port 11 and the fourth port 12, respectively, and as shown in FIG. The first wavelength band light A and the second wavelength band light B input to the second port 10 are output to the fourth port 12 and the third port 11, respectively.

FIG. 4 is a diagram showing a configuration example of a bidirectional optical amplifier repeater according to the present invention. The upstream signal (first wavelength band light) A propagated through the left optical fiber 3 is input from the first port 9 to the multiplexer / demultiplexer 13 as shown in FIG.
After being output from 11 and amplified by the optical amplifier 14, the fourth port
The signal 12 is input to the multiplexer / demultiplexer 13, output from the second port 10, and propagates through the right optical fiber 2. On the other hand, a downstream signal (second wavelength band light) B transmitted through the right optical fiber 2
Is input from the second port 10 to the multiplexer / demultiplexer 13, is output from the third port 11, is amplified by the optical amplifier 14, and is input from the fourth port 12 to the multiplexer / demultiplexer 13, and the first port 9 and propagates through the left optical fiber 3.

The upstream signal C that has propagated in the opposite direction through the right optical fiber 2 due to reflection or scattering is input to the multiplexer / demultiplexer 13 from the second port 10, and is output from the fourth port 12 to be output from the optical isolator 15. Block transmission. Also,
A downstream signal (not shown) that has propagated in the opposite direction through the left optical fiber 3 by reflection or scattering is input to the multiplexer / demultiplexer 13 from the first port 9, and is output from the fourth port 12. The transmission is blocked by the optical isolator 15.

FIG. 5 is a diagram showing another configuration example of the multiplexer / demultiplexer used in the bidirectional optical amplifier repeater of the present invention. This multiplexer / demultiplexer has two couplers 16 and 17 and two couplers.
Two waveguides 18 of different optical lengths connecting 16 and 17 and
It has 19 and is generally called a Mach-Zehnder multiplexer / demultiplexer. Assuming that the difference between the optical lengths of the waveguides 18 and 19 is ΔL, this multiplexer / demultiplexer has the following multiplexing / demultiplexing characteristics.
That is, the light A in the first region whose wavelength is represented by ΔL / m (m is a positive integer) is input to the third port 22 when input from the first port 20 and is input from the second port 21. Then, it is output to the fourth port 23. The light B in the second region, whose wavelength is represented by ΔL / m ± 1/2 (m is a positive integer), enters the fourth port 23 when input from the first port 20 and from the second port 21 When input, it is output to the third port 22.

FIG. 6 is a diagram showing a configuration example of a bidirectional optical amplifying repeater of the present invention using the multiplexer / demultiplexer shown in FIG. Uplink signal (first wavelength band light) transmitted through the left optical fiber 3
A is input to the multiplexer / demultiplexer 24 from the first port 20.
After being output from the third port 22 and amplified by the optical amplifier 14,
The light is input to the multiplexer / demultiplexer 24 from the fourth port 23 and output from the second port 21, and propagates through the right optical fiber 2. On the other hand, the downstream signal (second wavelength band light) B propagating through the right optical fiber 2 is input to the multiplexer / demultiplexer 24 from the second port 21 and is output from the third port 22 and amplified by the optical amplifier 14. After that, the signal is input to the multiplexer / demultiplexer 24 from the fourth port 23, output from the first port 20, and propagates through the left optical fiber 3.

The upstream signal C that has propagated in the right optical fiber 2 in the opposite direction due to reflection or scattering is input to the multiplexer / demultiplexer 24 from the second port 21, and is output from the fourth port 23 and is output from the optical isolator 15. Block transmission. Also,
A downstream signal (not shown) that has propagated in the opposite direction through the left optical fiber 3 due to reflection or scattering is input to the multiplexer / demultiplexer 24 from the first port 20, and is output from the fourth port 23. The transmission is blocked by the optical isolator 15.

[0017]

As described above, according to the bidirectional optical amplifying repeater of the present invention, the upstream and downstream signals propagating in the normal direction are both commonly amplified by one amplifier. The upstream and downstream signals propagating in opposite directions are both blocked by the optical isolator. As described above, the bidirectional optical amplifying repeater of the present invention can prevent multiple reflection even if one optical amplifier is commonly used, and achieve economical use of the features of bidirectional transmission. It has the advantage that it can be done.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a conventional bidirectional transmission line in which an optical amplifier and an optical fiber are simply connected.

FIG. 2 is a diagram illustrating a conventional bidirectional transmission line that avoids deterioration due to multiple reflection.

FIG. 3 is a diagram showing a configuration example of a multiplexer / demultiplexer used for a bidirectional optical amplifier repeater of the present invention.

FIG. 4 is a diagram illustrating a configuration example of a bidirectional optical amplification repeater of the present invention.

FIG. 5 is a diagram showing another configuration example of the multiplexer / demultiplexer used for the bidirectional optical amplifier repeater of the present invention.

FIG. 6 is a diagram showing another configuration example of the bidirectional optical amplifier repeater of the present invention.

[Explanation of symbols]

 1, 5, 7 Optical amplifier 2, 3, Optical fiber 4, 6, Optical circulator 8 Dielectric multilayer film 9 First port of multiplexer / demultiplexer 10 Second port of multiplexer / demultiplexer 11 Third port 12 of multiplexer / demultiplexer Fourth port of multiplexer / demultiplexer 13 Multiplexer / demultiplexer 14 Optical amplifier 15 Optical isolator 16, 17 Coupler 18, 19 Waveguide 20 First port of multiplexer / demultiplexer 21 Second port of multiplexer / demultiplexer 22 Third port of the filter 23 Fourth port of the multiplexer / demultiplexer 24 Multiplexer / demultiplexer A First wavelength band light (up signal) B Second wavelength band light (down signal) C Reflected or scattered upstream signal

Claims (2)

[Claims] An optical multiplexer / demultiplexer having four ports for demultiplexing and combining light in a first wavelength band and light in a second wavelength band, and
An optical amplifier having an optical isolator for amplifying and passing light in only one direction is provided, and the transmission characteristics of the optical multiplexer / demultiplexer are such that the first wavelength band light input to the first port is output to the third port, The second wavelength band light input to the port is the fourth port, the first wavelength band light input to the second port is the fourth port, the second wavelength band light input to the second port is the third port Are respectively configured to be output, and after the output light of the third port of the optical multiplexer / demultiplexer is amplified by the optical amplifier, it is configured to be input to the fourth port of the optical multiplexer / demultiplexer. A bidirectional optical amplifying repeater characterized in that: 2. The bidirectional optical amplifying repeater according to claim 1, wherein the optical multiplexer / demultiplexer is a Mach-Zehnder type optical multiplexer / demultiplexer.