JP2002261360A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier for simple and fast control of wavelength dependence of amplification gain, when a signal light is input-changed. SOLUTION: In a device for optically amplifying by use of an erbium-doped optical fiber(EDF) 1, WDM signal light are made incident from an input side transmission optical fiber 2, and are emitted to an output side transmission optical fiber 3. Excitation light are emitted from an excitation light source 8 and are made incident on the EDF 1, from the same direction as that of the signal light. Further, in auxiliary light for which the difference in peak wavelengths between the signal light and the excitation light is 0.07 to 1.5% of the length of the excited light peak wavelength, and optical energy is 0.1 to 30% of the excitation light, and auxiliary light is emitted from an auxiliary light excitation light source 9 and are incident to the EDF 1 from the direction opposite to the signal light. When the input of the signal light is changed, the amplification gain of each signal changes according to the wavelength, but the wavelength dependence of the amplification gain can be controlled at high speed by only changing the energy of the auxiliary light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical amplifier using a rare earth element-doped optical fiber.

[0002]

2. Description of the Related Art In an optical communication system, an optical amplifier for directly amplifying an optical signal is used for amplifying an optical signal attenuated by long-distance transmission. As an optical amplifier, an optical fiber doped (doped) with a rare earth element such as erbium (Er), praseodymium (Pr), or neodymium (Nd) is widely used. Among them, an erbium-doped optical fiber (hereinafter, EDF) is used. Is often used.

The mechanism of optical amplification by a rare earth element-doped optical fiber is that when signal light and pump light are simultaneously input to the optical fiber, the rare earth element is excited by the pump light, and stimulated emission occurs when the signal light passes therethrough. Occurs, thereby amplifying the signal light.

[0004] In this optical amplification, forward pumping in which pumping light is input in the same direction as signal light has a feature that the noise figure is small, and backward pumping in which pumping light is input in the opposite direction to signal light is performed by: It has the characteristic that a high output can be obtained. The dual pumping, in which pumping light having substantially the same power is input from both front and rear sides, has characteristics of both forward pumping and backward pumping.

In recent years, in order to simultaneously exchange a large amount of information, a wavelength division multiplexing (WDM) type optical communication system for simultaneously transmitting and receiving a plurality of signal lights having different wavelengths through one optical fiber has been put to practical use. When the WDM signal light is amplified by a rare-earth element-doped optical fiber, if the whole signal input changes due to taking out one wavelength signal during transmission or adding the signal in reverse, for example, the gain of the amplification depends on the wavelength. Is changed, and a reading error may occur at a wavelength having a low gain. For this reason, hitherto, it has been attempted to control the pump input or to connect an optical fiber having an attenuation characteristic opposite to a change in gain.

[0006]

However, in the method of controlling the pumping input, the power of the pumping input needs to be largely changed. However, in the conventional three types of pumping methods, the pumping input power is too high, and Control cannot be performed quickly, causing a control delay. Also,
In the latter method of connecting a special optical fiber, it is difficult to connect an optical fiber having a special structure, so that practical use is difficult.

The present invention has been made in view of such circumstances, and an object of the present invention is to easily and quickly control the wavelength dependence of the amplification gain when the input of signal light changes. It is to provide an optical amplifier.

[0008]

In order to achieve the above object, an optical amplifying device is provided which inputs a small power secondary pump light which can be controlled at high speed from a direction opposite to the main pump light.

Specifically, the invention according to claim 1 is an optical amplifying device using a rare earth element-doped optical fiber,
An excitation light introducing means and an auxiliary light introducing means are provided, the excitation light introducing means introduces an excitation light from any one of the optical fibers, and the auxiliary light introducing means has a peak wavelength with the excitation light. Is 0.0% of the peak wavelength length of the excitation light.
Auxiliary light whose light energy is 7 to 1.5% and whose light energy is 0.1 to 30% of the light energy of the excitation light is introduced from the side opposite to the excitation light introduction side of the optical fiber. This is an optical amplifying device.

According to the structure of the present invention, the auxiliary light can be controlled at a high speed in response to a change in the input of the signal light because the light energy of the auxiliary light is small.

The light energy of the auxiliary light is required to be 0.1 to 30% of the light energy of the pump light in order to amplify the signal light at a constant gain regardless of the wavelength. 0.1%
If it is less than this, a wavelength having a low gain cannot be sufficiently amplified. If it exceeds 30%, the gain becomes too large at some wavelengths. Also, the control speed is reduced due to the increase in energy, and it is difficult to cope with a change in signal light input. In order to sufficiently amplify the wavelength whose gain has decreased, it is preferable that the optical energy of the auxiliary light is 0.5% or more of the pump light. In addition, it is preferable that the control speed be higher than 20% because the control speed can be further increased. More preferably, it is in the range of 0.7 to 10%.

The direction of introduction of the pumping light may be the same direction as the signal light or the opposite direction.

If the difference between the peak wavelengths of the excitation light and the auxiliary light is less than 0.07% of the length of the peak wavelength of the excitation light, the excitation light and the auxiliary light may interfere with each other. If it exceeds, it is difficult to perform stable and efficient amplification. In order to perform stable and efficient amplification more reliably, it is preferable that the difference between the peak wavelengths is 0.08 to 1.2% of the length of the peak wavelength of the excitation light. More preferably, 0.1-1.
0%.

The light energy of the pumping light is 30 to 95 of the energy required for amplifying the signal light having a plurality of channels having different wavelengths by the pumping light alone so that the gains of all the channels become 10 dB or more. %. The light energy of the excitation light may be set to an optimum energy amount within the above range by the light energy of the auxiliary light.

Next, according to a second aspect of the present invention, in the first aspect, the excitation light and the auxiliary light are obtained by dividing the light supplied from one light source using a WDM coupler. Optical amplifier.

Here, the WDM coupler is a device that splits incident light into a plurality of lights having different wavelength ranges and emits the light, or conversely adds and combines a plurality of incident lights having different wavelength regions and emits the combined light. is there.

According to the configuration of the present invention, the number of light sources for amplification can be reduced to one, so that the configuration of the apparatus is simplified and the cost is reduced.

Next, according to a third aspect of the present invention, in the first aspect, the excitation light source and the auxiliary light source are different semiconductor lasers having the same material and the same structure. An optical amplifier characterized in that a peak wavelength of light to be output is changed by changing an operating environment temperature of a semiconductor laser.

According to the structure of the present invention, two lights having slightly different peak wavelengths can be generated by a simple operation of changing the temperature of the operating environment.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic diagram of an optical amplifying device according to the present embodiment. The optical amplifying device is inserted in the middle from the input side optical fiber for signal light transmission 2 to the optical fiber for output side signal light transmission 3. The main components of the optical amplifying device are, in addition to the EDF 1, the excitation light source 8 and the auxiliary light source 9 and the power supply circuits 10 and 11 for driving them, and the EDF 1
1. Optical multiplexers / demultiplexers 12 and 13 for entering the optical signal 1, optical isolator 4, 5, 6, 7 for removing reflected light of excitation light, auxiliary light and signal light, and optical attenuator 15. Also, 1
Reference numerals 6 and 17 denote temperature control means for controlling the operating environment temperatures of the light sources 8 and 9. Known components may be used for these components, such as using a magnetic garnet single crystal as an optical isolator. Any components may be used as long as they exhibit the function of each component.

The pumping light introducing means comprises a driving power supply circuit 10, a light source 8, an optical isolator 6, and an optical multiplexer / demultiplexer 12. The auxiliary light introducing means includes a drive power supply circuit 11, a light source 9, an optical isolator 7, and an optical multiplexer / demultiplexer 13. In this embodiment,
Semiconductor lasers are used for the light sources 8 and 9.

The optical attenuator 15 adjusts the drive current and the like so that the optical energy of the auxiliary light becomes an appropriate value within the range of 0.1 to 30% of the excitation light. The adjustment method may be manual control or automatic control by computer control or the like, and is not particularly limited. Further, the output of the driving power supply circuit 11 for the auxiliary light may be adjusted without using the optical attenuator 15.

The excitation light and the auxiliary light are light having a wavelength that effectively excites Er, and the 1480 nm band and the 980 nm band are generally used. In each case, a semiconductor laser having the same material and the same structure is used as a light source, and temperature control means 16 and 1 are used.
7, the operating temperatures of the two semiconductor lasers are kept different. By making the operating environment temperature different, the peak wavelengths of the excitation light and the auxiliary light become slightly different. Since the difference between the peak wavelengths depends on the difference between the operating environment temperatures, the operating environment temperature difference is set so that the difference between the peak wavelengths becomes an appropriate value. In addition, even without the above-mentioned temperature control,
It is also possible to use semiconductor lasers having different wavelengths.
Furthermore, even with the same semiconductor laser, the wavelength can be made different by changing the output power of each.

The signal light is supplied to the input side signal transmission optical fiber 2.
The light passes through the optical multiplexer / demultiplexer 12 through the optical isolator 4, enters the EDF 1, and is amplified. Then, the light passes through the optical multiplexer / demultiplexer 13 and the optical isolator 5 in this order, and is emitted to the output-side signal transmission optical fiber 3.

The excitation light is emitted from the excitation light excitation light source 8 to which the drive power supply circuit 10 is connected, passes through the optical isolator 6 and the optical multiplexer / demultiplexer 12, and from the same side as the signal light.
The light enters F1 to excite Er.

Auxiliary light is emitted from the auxiliary light excitation light source 9 to which the driving power supply circuit 11 is connected.
The light passes through the optical isolator 7 and the optical multiplexer / demultiplexer 13 and enters the EDF 1 from the side opposite to the signal light to excite Er.

Note that the present device is one example for explaining the present invention, and the present invention is not limited to the present device. The excitation light and the auxiliary light may be respectively introduced from the side opposite to the present apparatus, or another rare earth element-doped optical fiber may be used instead of the EDF. Further, an optical isolator or the like may not be used, or other components may be added or a substitute may be used.

Embodiment 2 FIG. 4 is a schematic diagram of an optical amplifier of Embodiment 2. In the present embodiment, the excitation light and the auxiliary light are supplied from one light source 21. The light emitted from the light source 21 is transmitted to the optical multiplexer / demultiplexer 2
The light is divided into excitation light and auxiliary light by 2. 20 is a light source 2
1 drive power supply circuit. The pump light passes through the optical isolator 6 and the WDM coupler 24, and is transmitted from the same side as the signal light.
It is incident on DF1 to excite Er. Here, the WDM coupler 24 selectively selects a specific wavelength in the incident pump light by using the EDM.
Pass through DF1.

The auxiliary light passes through the optical attenuator 15 and is attenuated to a predetermined light energy. Then, the light passes through the optical isolator 7 and the WDM coupler 23, enters the EDF 1 from the side opposite to the signal light, and excites Er. In addition, WD
The wavelength of the light to be passed through the M coupler 23 is WD on the excitation light side.
The coupler is different from the passing wavelength of the M coupler 24 by a set length.

In this embodiment, the number of light sources is one, the configuration is simple, and the number of parts is small, so that the manufacturing cost is reduced.

Embodiment 3 FIG. 5 is a schematic diagram of an optical amplifying device according to Embodiment 3. In this embodiment, instead of the optical multiplexer / demultiplexer 22 and the optical attenuator 15 for splitting the pump light and the auxiliary light in the second embodiment of FIG.
You are using As described above, according to the present embodiment, the number of components is reduced, so that the manufacturing cost can be reduced.

[0033]

<Embodiment 1> Signal light having four wavelengths was amplified using the apparatus having the configuration shown in FIG. E in EDF
The r concentration was 70 kppm × m. The signal light is 156
The input was -16 dBm / ch at four wavelengths of 4, 1576, 1588 and 1600 nm.

The excitation light is a semiconductor laser as a light source at 25.0 ° C.
And the wavelength was 1480 nm. The auxiliary light has a wavelength of 1478.5 while keeping the semiconductor laser as a light source at 24.9 ° C.
The gain of the signal light was measured by changing the light energy with a wavelength of nm. FIG. 2 shows the measurement results.

When only the pumping light from the front was used and there was no auxiliary light, at a light energy of 100 mW, the shorter the wavelength, the lower the gain. At 200 mW, conversely, the shorter the wavelength, the higher the gain. At 140 mW, the gain of the four wavelengths was almost constant, and the gain characteristics were excellent. On the other hand, when the pump light was set to 100 mW and the auxiliary light was incident from the rear, the auxiliary light was only 2.7 mW. However, the drop in the gain on the short wavelength side is greatly improved, and good gain characteristics are obtained. When the gain is further reduced to 4.4 mW, the pump light becomes 140 mW.
The gains of the four wavelengths were almost constant, and the gain characteristics were excellent.

That is, in this case, 100 mW only with the excitation light
Although excellent gain characteristics could not be obtained unless 40 mW was added, excellent gain characteristics were obtained only by adding 4.4 mW when auxiliary light was used.

<Embodiment 2> The wavelength of the signal light is 1558,
The gain of the amplified signal light was measured in the same manner as in Example 1 except that the light energy was set to 1572, 1586, and 1600 nm, and the light energy of the excitation light and the auxiliary light was changed. Figure 3 shows the measurement results.
Shown in

When there was no auxiliary light from the rear and only pumping light from the front, 140 mW was the most favorable gain characteristic as in the first embodiment. If the light energy was smaller than 140 mW, the gain on the short wavelength side was reduced, and if the light energy was larger than that, the gain on the short wavelength side was too large. However, the increase in the gain on the short wavelength side when the light energy was large was not so remarkable as in the first embodiment, and within the range of the present embodiment, the gain characteristic was practically usable.

On the other hand, when the pump light is set to 100 mW and the auxiliary light is incident from the rear, the gain characteristics when the light energy of the auxiliary light is 7.0 mW are almost the same as those when only the pump light is 140 mW. Was. When the light energy of the auxiliary light was set to 20 mW, the gain characteristics were almost the same as when the excitation light was only 260 mW.

[0040]

The present invention is embodied in the form described above, and has the following effects.

When the signal light input changes, control is performed by changing the auxiliary light having a small energy so that the amplification gain characteristic does not change. Therefore, high-speed control is possible, and less energy is used for amplification. Further, the device configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical amplification device according to a first embodiment.

FIG. 2 is a diagram illustrating amplification gain characteristics according to the first embodiment.

FIG. 3 is a diagram illustrating amplification gain characteristics according to a second embodiment.

FIG. 4 is a schematic diagram of an optical amplifying device according to a second embodiment.

FIG. 5 is a schematic diagram of an optical amplification device according to a third embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 EDF 2 input-side signal transmission optical fiber 3 output-side signal transmission optical fiber 4 optical isolator 5 optical isolator 6 optical isolator 7 optical isolator 8 excitation light excitation light source 9 auxiliary light excitation light source 10 drive power supply circuit 11 drive power supply circuit DESCRIPTION OF SYMBOLS 12 Optical multiplexer / demultiplexer 13 Optical multiplexer / demultiplexer 15 Optical attenuator 16 Temperature control means 17 Temperature control means 20 Drive power circuit 21 Excitation light source 22 Optical multiplexer / demultiplexer 23 WDM coupler 24 WDM coupler 25 Variable branch coupler

Claims (3)

[Claims] 1. An optical amplifying device using a rare earth element-doped optical fiber, comprising: an excitation light introducing means and an auxiliary light introducing means, wherein the excitation light introducing means is provided from any one of the optical fibers. The pumping light is introduced, wherein the auxiliary light introducing means has a difference in peak wavelength from the pumping light of 0.07 to 1.5% of the length of the peak wavelength of the pumping light, and a light energy of the pumping light. An optical amplifying device for introducing auxiliary light, which is 0.1 to 30% of the light energy of the optical fiber, from the side of the optical fiber opposite to the side where the pumping light is introduced. 2. The optical amplifier according to claim 1, wherein the light supplied from one light source is divided by using a WDM coupler to obtain the pump light and the auxiliary light. 3. The light source according to claim 1, wherein the excitation light source and the auxiliary light source are different semiconductor lasers having the same material and the same structure, wherein the two semiconductor lasers have different operating environment temperatures. An optical amplifier characterized in that the peak wavelength of the light to be output is made different by the following.