JP3169138B2 - Optical repeater amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical repeater used mainly in an optical communication network, and more particularly to an optical repeater using an optical amplifier having a large insertion loss, such as a semiconductor laser amplifier.

[0002]

2. Description of the Related Art In an optical communication network, when an optical signal path becomes long, it is necessary to arrange an optical amplifier in the optical signal path to compensate for attenuation of the optical signal. FIG.
Shows a configuration example of a general optical communication network using an optical amplifier. A plurality of terminal devices 11a, 11b, 1 are connected to an optical transmission line 10 such as an optical fiber for transmitting an optical signal.
1c are connected via couplers 12a, 12b, and 12c, respectively. An optical repeater amplifier 13 for compensating for the attenuation of the optical signal is provided at a predetermined position in the optical transmission line 10.
a and 13b are inserted.

As typical optical amplifiers used as optical repeater amplifiers, there are a semiconductor laser optical amplifier and a rare earth doped optical fiber amplifier.

A semiconductor laser optical amplifier uses an ordinary semiconductor laser as it is as an optical amplifier, or operates as a traveling-wave optical amplifier by applying antireflection films to both end faces of the semiconductor laser (for example, ,
Mochizuki: "Semiconductor Laser Optical Amplifier", Optics, Vol. 18,
No. 6 (June 1989), P297 (17) -302
(See (22)). In addition, a rare-earth-doped optical fiber amplifier amplifies input light by irradiating a rare-earth-doped optical fiber with excitation light from an excitation light source such as a laser to bring the optical fiber into an excited state (for example, Horiguchi). : "Optical fiber amplifier", Optics, 19th
Vol.5, May 1990, P276 (2) -28
2 (8)).

[0005]

The former semiconductor laser optical amplifier generally has a larger coupling loss with an optical fiber than the latter rare earth-doped optical fiber amplifier, and a larger loss when current injection is stopped. There is. That is, in the latter rare-earth-doped optical fiber, even if the pumping light source serving as a source of amplification is cut off, the signal light can be transmitted to some extent.
In contrast, the former semiconductor laser amplifier has a large coupling loss with the fiber, and the insertion loss including the internal loss of the amplifier is about 10 dB on average. This insertion loss is further increased by 5 to 10 dB when the operation of the amplifier is stopped, and becomes about 15 to 20 dB in total.

For example, if the internal gain is 23 dB, the effective gain is 13 (= 23-10) dB in a normal state.
(20 times), but at the time of failure, the effective gain is -15 dB
(1 / 31.6), and the output at the time of failure is attenuated by 38 dB compared to the normal state (to 1/6300).

Therefore, a semiconductor laser amplifier is smaller than a rare earth-doped optical fiber amplifier in that the entire device is small, the wavelength range that can be amplified is changed in a considerably wide range, and the wavelength band at that time is wide. However, it was inferior to the rare-earth-doped optical fiber amplifier in securing a communication path when a trouble occurred, that is, in fail-safe function.

Now, in the optical communication network shown in FIG. 2, considering an optical signal transmitted in the direction of arrow A, for example, if the optical repeater amplifier 13b fails, the output from the optical repeater amplifier 13b becomes 1 / 6300. For this reason, it becomes impossible for a terminal device subsequent to the optical repeater amplifier 13b, for example, the terminal device 11c, to receive an optical signal of a sufficient level, and serious trouble occurs in the optical communication network.

Although it is conceivable to increase the input gain on the terminal device side, excessively increasing the gain not only causes deterioration of the signal-to-noise ratio but also causes saturation of the signal in a normal state. There is a limit to the increase in gain because it causes inconvenience such as waveform deterioration.

According to the present invention, even when a failure occurs in an optical amplifier, the amount of attenuation of the optical signal passing through the optical repeater amplifier is reduced, so that even when a failure occurs, a communication path for the optical signal can be secured and the ferrule can be obtained. The purpose is to obtain a safe function.

[0011]

In order to achieve the above object, an optical repeater according to the present invention splits an input signal light into a plurality of signals by an optical demultiplexer, and outputs one input signal from the split input signal lights. While amplifying the light with an optical amplifier, passing other input signal light through a bypass optical waveguide, the output light from the optical amplifier and the passing light from the bypass optical waveguide are multiplexed by an optical multiplexer. Optical repeater amplifier
The light increase compared to the amount of branching to the bypass optical waveguide.
It is characterized in that the amount of branching to the breadth is reduced .

[0012]

In the optical repeater amplifier of the present invention, when the optical amplifier is operating normally, the input signal light is sufficiently amplified by the optical amplifier and then output from the optical multiplexer. At this time, the output light from the optical amplifier is sufficiently larger than the signal light that has passed through the bypass optical waveguide, so that the effect of interference between the two lights can be ignored. When a failure occurs in the optical amplifier, the input signal light passes through the bypass optical waveguide and is output from the optical multiplexer. For example, when the branching ratio is 1: 1, even when a failure occurs, half the output of the input signal light can be obtained, so that the minimum necessary signal light can be supplied to subsequent terminal devices. , The function of the optical communication network is maintained. At this time, the output light from the optical amplifier in the inactive state is sufficiently smaller than the signal light passing through the bypass optical waveguide, so that the effect of the interference between the two lights can be ignored.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 shows a schematic configuration example of an optical repeater amplifier according to the present invention. The input signal light is split into two equal parts by an optical splitter / combiner 1a functioning as an optical splitter, one input signal light is supplied to the optical waveguide 2 for bypass, and the other input signal light is coupled. It is supplied to the semiconductor laser amplifier 4 via the lens 3a. The semiconductor laser amplifier 4 itself is described in, for example, Shimada et al .: “Research Status of Semiconductor Laser Amplifier Used in Optical Communication System”, O plus E, 1
August 989, No. 117, pages 106 to 111, etc., and a detailed description thereof will be omitted.

The light amplified by the semiconductor laser amplifier 4 is supplied to one input branch of the optical demultiplexer / combiner 1b via the coupling lens 3b. The passing light from the bypass optical waveguide 2 is supplied to the other input branch of the optical demultiplexing / multiplexing device 1b, and both light beams are transmitted to the optical demultiplexing / multiplexing device 1b.
The signals are synthesized by the multiplexer 1b. The optical demultiplexer / multiplexer 1a and the optical demultiplexer / multiplexer 1b are structurally the same.

In such a configuration, since the signal light is generally a laser light and a coherent light,
The interference caused by the two path differences is expected to be a problem. However, when a semiconductor laser amplifier is used, the problem of the interference hardly occurs because the insertion loss is large as described above. The reason will be described in detail below.

Assuming that the incident power of the signal light is Pin, the signal light is divided into 0.5 Pin by the optical demultiplexer / multiplexer 1a and distributed to the bypass optical waveguide 2 and the semiconductor laser amplifier 4, respectively.

During normal operation, the semiconductor laser amplifier 4
Have an internal gain that exceeds the insertion loss. For example, if the insertion loss is 10 dB and the internal gain is 23 dB, the effective gain is 13 dB. Therefore, the semiconductor laser amplifier 4
Light passing through the P _A is amplified to 20 times with the power of 10Pin. On the other hand, the signal light P passing through the bypass optical waveguide 2
_B has only 0.5 Pin power. The light Pout obtained by combining these two lights is as follows.

P _A −P _B ≦ P out ≦ P _A + P _B (1) ∴9.5 Pin ≦ Pout ≦ 10.5 Pin (2) P _A −P _{B in the} above equation. Is that when the two lights are out of phase,
P _A + P _B corresponds to the case of the same phase.

Next, a case where the current injection to the semiconductor laser amplifier 4 is stopped as an abnormal operation will be considered. At this time, P _A = 0.05 Pin. Therefore, Pout is (1)
It becomes like the following formula from the formula.

0.45Pin ≦ Pout ≦ 0.55Pin (3) As described above, P _A ≫P _B during normal operation, and
At the time of abnormal operation, P _A ≪P _B , so that the effect of interference does not matter.

According to the above embodiment, the optical repeater amplifier
The amplifier has a gain of about 10 db during normal operation, and becomes an attenuator with an insertion loss of about 3 db when a failure occurs.
(1/20) is sent to the next stage. With this level of attenuation, it is within the range of the input dynamic range of the terminal device, so that the subsequent terminal device can normally receive signal light. That is, a fail-safe function in the optical communication network can be realized.

The case where the branching ratio in the optical demultiplexing / combining devices 1a and 1b is 1: 1 has been described above. However, the branching ratio is not limited to 1: 1 and may be another branching ratio. .

FIG. 3 shows an embodiment employing another branching ratio. This embodiment is an example in which the present invention is applied to a multimode fiber.

In the embodiment shown in FIG. 3, the optical demultiplexers / combiners 1a and 1b and the bypass 2 are formed on the polycarbonate substrate 5 by selective polymerization, and the branching ratio is changed according to the width of the optical waveguide. . That is, the width of the optical waveguide 6 branched to the semiconductor laser amplifier 4 is smaller than the width of the bypass path 2.

The thickness D of the polycarbonate substrate 5 is 42 μm.
m, the width W _{1 of the} optical waveguide was 42 μm, and the width W ₂ of the optical waveguide 6 branched to the semiconductor laser amplifier 4 was 4 μm.
This method of forming an optical waveguide is known. For example, Takato and Kurokawa, "Technology for making optical waveguides in polymer materials",
O plus E, November 1984, pp. 78-83
reference. The width W ₂ of the optical waveguide 6 is smaller than the thickness D of the substrate 5, an optical waveguide of such a high aspect ratio, for example, it can be formed by the light selective polymerization of polycarbonate and methyl acrylate. Semiconductor laser amplifier 4
The current is supplied to the electrodes 4a and 4b. The direction of current injection into the semiconductor laser amplifier 4 matches the direction of the minor axis (W ₂ ) of the optical waveguide 6. The coupling between the optical waveguide 6 and the semiconductor laser amplifier 4 is performed via coupling lenses 3a and 3b. The coupling lenses 3a and 3b are cylindrical lenses, and are disposed so as to have a light condensing function in the minor axis direction of the optical waveguide 6.

Region 4 with gain of semiconductor laser amplifier
G is a considerable width in the direction perpendicular to the current injection direction,
For example, it can have a width of about 100 μm. On the other hand, only a width of about 2 to 3 μm can be taken in the current injection direction. Therefore, for example, even if the width of W ₂ in FIG. 3 is 20 μm, the input light of the semiconductor laser amplifier is not so different from the case where W ₂ is 4 μm, and it is meaningless to increase the width of W ₂ . Thus, in the present embodiment, the coupling efficiency can be increased by setting the cross-sectional shape of the optical waveguide 6 according to the thickness and width of the gain region of the semiconductor laser amplifier.

The gain of the semiconductor laser amplifier 4 is 30 d
B, since the insertion loss (branch ratio) of the optical demultiplexers / combiners 1a and 1b is -10 dB and the coupling loss between the semiconductor laser amplifier 4 and the optical waveguide 6 is about -3 dB, the net gain is 17d.
B. In this embodiment, even if the semiconductor laser amplifier 4 fails, most of the optical signal is bypassed by the bypass path 2, so that the fail-safe property is higher than in the case of a 1: 1 branching ratio.

FIG. 4 shows a modification of the embodiment shown in FIG. FIG.
In the embodiment shown in FIG. 3, the two-branch optical demultiplexer shown in FIG.
3-branch optical demultiplexer / multiplexer 9a instead of multiplexers 1a and 1b
And 9b are provided. Further, a semiconductor laser amplifier 7 is provided in addition to the semiconductor laser amplifier 4. This semiconductor laser amplifier 7 is coupled to the optical waveguide 10 via coupling lenses 8a and 8b as in the embodiment shown in FIG. Electrodes 7a and 7b are drawn out of the semiconductor laser amplifier 7.

In this embodiment, the two semiconductor laser amplifiers 4 and 7 are not operated simultaneously. That is, between the electrodes 4a and 4b or the electrode 7
A voltage is applied to only one between a and 7b. Normally, the semiconductor laser amplifier 4 is operated, and for some reason, the first
When the semiconductor laser amplifier 4 of the
Is operated. That is, the semiconductor laser amplifier 7 is a backup for the semiconductor laser amplifier 4.

In the above embodiment, an optical repeater amplifier using a semiconductor laser amplifier has been described as an example. However, the present invention is not limited to this, and an optical repeater using an optical amplifier having a large insertion loss is used. The present invention can be applied to an amplifier.

Also, in any of the embodiments shown in FIGS. 1, 3 and 4, the optical amplification is not limited to one direction, and it goes without saying that the optical amplifier can be used as a bidirectional optical amplifier.

[0033]

As described above, according to the present invention,
Since an optical waveguide is provided as a bypass in parallel with an optical amplifier having a large insertion loss, such as a semiconductor laser amplifier having a large insertion loss, an optical signal passes to some extent even if a failure occurs in the optical amplifier. Therefore, even when the optical amplifier fails, the influence on the communication network can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration example of an optical repeater amplifier according to the present invention.

FIG. 2 is a schematic diagram illustrating a configuration example of a general optical communication network using an optical repeater amplifier.

FIG. 3 is a perspective view showing a configuration of an embodiment of the optical repeater amplifier of the present invention.

FIG. 4 is a perspective view showing a configuration of a modification of the optical repeater amplifier of the present invention.

[Explanation of symbols]

1a, 1b optical demultiplexer / combiner, 2 optical waveguide for bypass, 3a, 3b coupling lens, 4 semiconductor laser amplifier, 4a, 4b electrode of semiconductor laser amplifier, 4G
Area with gain of semiconductor laser amplifier, 5 polycarbonate substrate, 6 optical waveguide on semiconductor laser amplifier side,
7 Second semiconductor laser amplifier, 7a, 7b Electrode of second semiconductor laser amplifier, 8a, 8b coupling lens, 9a, 9b Three-branch optical demultiplexer / combiner, 10 second
Optical waveguide, 10 optical transmission line, 11a, 11b, 11c terminal device, 12a, 12
b, 12c coupler, 13a, 13b optical repeater amplifier,
The thickness of the D polycarbonate substrate, W ₁ bypass optical waveguide width, W ₂ semiconductor laser amplifier side of the optical waveguide width

Claims (2)

(57) [Claims] An input optical signal is split into a plurality of input optical signals by an optical demultiplexer, one of the input optical signals is amplified by an optical amplifier, and the other input optical signal is transmitted to a bypass optical waveguide. An optical repeater that passes through the optical path and multiplexes the output light from the optical amplifier and the light passing through the bypass optical waveguide by an optical multiplexer.
To the optical amplifier compared to the amount of branch to the optical waveguide for
An optical repeater having a small amount . 2. The optical demultiplexer and the optical waveguide for the bypass.
And the optical amplifier are formed on the same substrate.
A semiconductor laser amplifier
The semiconductor laser amplifier in its junction
Is perpendicular to the substrate and parallel to the optical path.
And a branch to said semiconductor laser amplifier
2. The optical repeater amplifier according to claim 1 , wherein a width of the optical repeater is smaller than a width of the bypass optical waveguide .