JPH06188833A - Optical communication system - Google Patents

Abstract

PURPOSE:To immediately attain restoration when a light emitting element breaks down by controlling a polarization beam splitter which selectively allows a laser beam from plural laser elements to pass through or reflect, and switching the light emitting state of the laser elements. CONSTITUTION:A polarization beam splitter 22 of an exciting light source 12 selectively allows the laser beam from each semiconductor laser 16a and 16b to pass through or reflect according to the polarizing direction of the laser beam. Moreover, control circuits 24 and 24b for driving emission are connected to each semiconductor laser 16a and 16b, and when one semiconductor laser 16a breaks down and doesn't emit a light, a detection signal is outputted from the control circuit 24a, and the other control circuit 24b allows the semiconductor laser 16b to emit the light in response to the detection signal. The laser beam is allowed to pass through a lens 20b, reflected by the polarization splitter 22, guided through a lens 20c to an optical fiber 26, and guided through an optical coupler 14 to an optical fiber amplifying element 10. At that time, a time lag can be reduced, and a signal light can be immediately and normally amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system in which an optical amplifier equipped with an optical fiber amplifying element for directly amplifying signal light by utilizing stimulated emission effect is provided in an optical fiber transmission line. .

[0002]

2. Description of the Related Art In some optical communication systems, an optical amplifier is installed at an appropriate position in the middle of an optical fiber transmission line in order to compensate transmission loss of signal light.

In this optical amplifier, conventionally, a signal light from an optical fiber transmission line is converted into an electric signal by a light receiving element, the signal is amplified by an electronic amplifier, and then converted into a signal light by a light emitting element such as a semiconductor laser. It is generally converted and sent out to an optical fiber transmission line.

However, in such a structure, mechanical optical axis alignment with the light emitting element and the light receiving element is required to reduce the connection loss, and since an electronic amplifier is separately provided, it is easily affected by noise. Further, there is a problem that the entire structure of the optical amplifier is complicated and not only increases in size but also becomes expensive.

Therefore, in recent years, it has been considered to use an optical amplifier equipped with an optical fiber amplifier for directly amplifying the signal light by utilizing the stimulated emission effect. FIG. 4 shows a conventional example of an optical communication system using such an optical amplifier.

[0006] optical communication system of this conventional example, a large number of optical fiber transmission line L is arranged, the optical amplifier 1 ₀ in the middle of the optical fiber transmission line L is provided separately.

[0007] Each optical amplifier 1 _0, as shown in FIG. 5, an optical fiber amplifier device 10 which amplifies the signal light by stimulated emission
And a pumping light source 12 'such as a semiconductor laser (LD) that pumps the optical fiber amplifying element 10, and an optical coupler 14 for introducing pumping light from the pumping light source 12' into the optical fiber amplifying element 10. The optical fiber amplification element 10 is
For example, a rare earth element such as Er is doped in the core of the optical fiber or around the core. And the entrance end
The signal light introduced from in is mixed with the pumping light introduced from the pumping light source 12 ′ through the optical coupler 14 inside the optical fiber amplification element 10 and amplified by the stimulated emission effect, and then the output end out. Is emitted from.

By the way, if the semiconductor laser or the like which becomes the pumping light source 12 'fails and does not emit light, the optical fiber amplifier 10 cannot amplify the signal light.

Therefore, in the prior art, the optical switches 2 and 4 are provided before and after the optical amplifier 1'provided on each optical fiber transmission line L, and a spare optical amplifier having the same configuration as these optical amplifiers 1'is provided. 1 '' is installed separately, and further,
The configuration is such that the optical switches 6 and 8 are arranged before and after the spare optical amplifier 1 ″.

Then, for example, when the optical amplifier 1 ₀ in the uppermost optical fiber transmission line L ₀ in FIG. 4 fails, the optical switches 2 and 4 before and after the optical amplifier 10 and a spare optical amplifier 1 ₀ ′ are provided. The optical switches 6 and 8 are switched to connect the uppermost optical fiber transmission line L ₀ to the spare optical amplifier 1 ₀ ′ so as to amplify the signal light.

[0011]

In the configuration of the conventional example shown in FIGS. 4 and 5, a spare optical amplifier 1 '' is separately installed, and the amplifier 1 '' and the optical fiber transmission line L are used. Before and after the amplifier 1 ', optical switches 6, 8 and
It is necessary to deploy 2 and 4. Therefore, the configuration of the entire system becomes complicated.

In addition, the optical switches 2, 4, 6 and 8 that are currently in practical use are mechanical ones, and therefore, the optical switches 2, 4 and 4 are provided after the pump light source 12 'has failed. The time lag until switching between 6 and 8 is large, which causes a problem that the transmitted signal light is lost. Further, the optical switches 2, 4, 6, 8 have insertion loss, and reflection is generated to some extent. Therefore, it may cause deterioration of the amplification characteristic of the amplification system and noise.

The present invention has been made in view of the above-mentioned problems, and when the light emitting element of the pumping light source constituting the optical amplifier fails, the signal light is immediately corrected with almost no time lag. It is an object to restore the state where amplification is possible and to realize this with a relatively simple structure.

[0014]

The present invention has been made to solve the above-mentioned problems, and an optical amplifier is provided in the middle of an optical fiber transmission line, and the optical amplifier is provided with a signal by stimulated emission. The following configuration is adopted in an optical communication system including an optical fiber amplification element that amplifies light and a pumping light source that pumps the optical fiber amplification element.

That is, in the present invention, the pumping light source of the optical amplifier includes a plurality of laser elements, a polarization beam splitter for selectively passing or reflecting the laser light from each laser element, and a non-light emitting state of one laser element. And a control circuit for switching one of the remaining laser elements to a light emitting state.

[0016]

In general, since laser light has a polarization characteristic, if the polarization direction of each laser element is adjusted in advance with respect to the polarization beam splitter, the laser light from one laser element will have this polarization. While passing through the beam splitter, the laser light from the other laser element is reflected by this polarization beam splitter.

The present invention utilizes this characteristic, for example, while the laser beam from one laser element is being used as the excitation light by passing through the polarization beam splitter, the laser element fails and does not emit light. Then, the control circuit accordingly makes one of the remaining laser elements emit light, so that the emitted laser light from the laser element is reflected by the polarization beam splitter and emitted as excitation light. Since the switching of the laser elements is performed electrically, the signal light can be immediately and normally amplified with almost no time lag.

[0018]

FIG. 1 is an overall configuration diagram of an optical communication system according to an embodiment of the present invention, and FIG. 2 is a specific configuration diagram of an optical amplifier portion of the optical communication system.

In the optical communication system of this embodiment, as in the conventional example, a large number of optical fiber transmission lines L are arranged in parallel, and the optical amplifier 1 is individually provided in the middle of each optical fiber transmission line L. , Spare optical amplifiers and optical switches are omitted. Therefore, the optical communication system of this embodiment is characterized by the inside of the optical amplifier 1, and specifically has the configuration shown in FIG.

That is, the optical amplifier 1 of this embodiment is the same as the conventional example in that it includes the optical fiber amplifier element 10 and the optical coupler 14, but the structure of the pumping light source 12 is different from the conventional example.

That is, the pumping light source 12 of this example includes two semiconductor lasers 16a and 16b as laser elements, and the semiconductor lasers 16a and 16b are arranged orthogonal to each other and fixed to the inner wall of the case 18. Further, inside the case 18, lenses 20a, 20b, 20c and a polarization beam splitter 22 are provided. The polarization beam splitter 22 selectively passes or reflects the laser light from the semiconductor lasers 16a and 16b depending on the polarization direction of the laser light.
At the intersection of the optical axes of 6b, 45
It is placed at an angle of °. Further, each of the semiconductor lasers 16a and 16b has a control circuit 2 for driving light emission.
4a and 24b are connected to each other, and one light emission drive circuit 24
From a, a detection signal is output when the semiconductor laser 16a fails and goes into a non-light emitting state, while the other light emission drive circuit 24b drives the semiconductor laser 16b to emit light in response to the detection signal input. Is configured.

The pumping light source 12 is connected to the optical coupler 14 via an optical fiber 26 for introducing laser light. Note that in is an incident end of the signal light and out is an exit end of the signal light.

When the pumping light source 12 is assembled, the semiconductor lasers 16a and 16b are rotated about the optical axis to change the polarization direction thereof and one of the semiconductor lasers 16a is rotated.
Laser light from passes through the polarization beam splitter 22,
The laser beam from the other semiconductor laser 16b is adjusted in advance so as to be reflected by the polarization beam splitter 22.
Then, normally, only one control circuit 24a is operated to cause the semiconductor laser 16a to emit light.

Then, the laser light from the semiconductor laser 16a is transmitted to the lens 20a, the polarization beam splitter 22,
Then, the laser light is sequentially passed through the lens 20c and introduced into the optical fiber 26, and further, this laser light is introduced into the optical fiber amplifier 10 through the optical coupler 14 and mixed with the signal light incident from the incident end in. As a result, the signal light is amplified by the stimulated emission effect in the optical fiber amplification element 10, and the amplified signal light is emitted from the emission end out.

Next, when one of the semiconductor lasers 16a stops emitting light due to a failure or the like, the control circuit 24a outputs a detection signal, and the detection signal is output from the other control circuit 24.
Entered in b. The other control circuit 24b is activated in response to this and causes the semiconductor laser 16b to emit light. Then, the laser light from the semiconductor laser 16b passes through the lens 20b and is then reflected by the polarization beam splitter 22, and the reflected light passes through the lens 20c and is introduced into the optical fiber 26. Optical coupler 1
It will be introduced into the optical fiber amplifying element 10 via 4. From the time when one semiconductor laser 16a does not emit light to the time when the other semiconductor laser 16b emits light, electrical switching is performed, so that the time lag is extremely small and the signal light can be immediately amplified normally. ,
Moreover, there is no loss of signal light.

In the above description, one semiconductor laser 16a is normally operated, and the other light-emitting laser 1 is operated when a failure occurs.
Although each of 6b is made to emit light, the opposite case may be possible. However, in this case, it is necessary to activate one control circuit 24a in response to the detection signal from the other control circuit 24b.

Further, in the optical communication system of this embodiment,
Although the optical amplifiers are arranged in the middle of a large number of optical fiber transmission lines L, the present invention can be applied to a case where the optical amplifier 1 is arranged in a single optical fiber transmission line L.

Further, although the semiconductor lasers 16a and 16b are directly fixed to the case 18 in the above-mentioned embodiment, the structure shown in FIG. 3 may be adopted. In this embodiment, one semiconductor laser 16a in FIG. 2 and its control circuit 24a are integrally combined to form one module 3.
0a, the other semiconductor laser 16b and its control circuit 24b are integrally combined, and the other module 3
0b, and each module 30a,
The optical fiber 32a, 32b connects between the case 30b and the case 18. With this configuration, when a failure occurs, the module 30a on the other side can be replaced while the module 30b on the other side is still used, and the repair work for the failure is facilitated.

[0029]

According to the present invention, when the light emitting element of the pumping light source forming the optical amplifier fails, the laser element is electrically switched, so that the signal light can be immediately returned to normal state with almost no time lag. It is possible to return to the state where it can be amplified. Moreover, since the conventional optical switch and the spare optical amplifier are not required, the configuration of the entire system is simple and the cost can be reduced. Further, since the optical switch is not provided in the signal transmission line, there is an excellent effect that no new loss or reflection is generated in the transmission line.

The semiconductor laser used at the time of failure is
Since it is used for a relatively short time until failure recovery, it is a lower grade product than the rated output, and it can be used in an overloaded state to obtain the required light intensity. It may be relatively inexpensive. As a result, the cost of the entire device can be further reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an optical communication system according to an embodiment of the present invention.

FIG. 2 is a specific configuration diagram of an optical amplifier portion of an optical communication system according to an embodiment of the present invention.

FIG. 3 is a specific configuration diagram of a portion of an optical amplifier according to another embodiment of the present invention.

FIG. 4 is an overall configuration diagram of an optical communication system according to a conventional example.

FIG. 5 is a specific configuration diagram of an optical amplifier portion of an optical communication system according to a conventional example.

[Explanation of symbols]

L ... Optical fiber transmission line, 1 ... Optical amplifier, 10 ... Optical fiber amplification element, 12 ... Excitation light source, 16a, 16b ... Laser element (semiconductor laser), 22 ... Polarization beam splitter, 24
a, 24b ... Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Oizumi 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Hisa Sawada 4-chome Ikejiri, Itami City, Hyogo Mitsubishi Cable Industries, Ltd. Itami Seisakusho Co., Ltd. (72) Inventor Masataka Nakazawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Yasuro Kimura 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. An optical amplifier is provided in the middle of an optical fiber transmission line, and the optical amplifier includes an optical fiber amplifier for amplifying signal light by stimulated emission and a pumping light source for pumping the optical fiber amplifier. In the optical communication system, the excitation light source is a plurality of laser elements, a polarization beam splitter that selectively passes or reflects the laser light from each laser element, depending on the non-emission state of one laser element, An optical communication system comprising: a control circuit for switching one of the remaining laser elements to a light emitting state.