JPH0346637A - Optical amplifier and optical amplifying method - Google Patents

Abstract

PURPOSE:To multiplex and demultiplex both signal light and exciting light with high efficiency without reference to their wavelengths by employing polarization multiplexing and demultiplexing for the multiplexing of the signal light and exciting light in optical amplification which uses a fiber type optical amplifier. CONSTITUTION:The signal light 1 and exciting light 2 are inputted to input ports 4 and 5 of a polarization multiplexer 3 and multiplexed light beams 8 and 9 are outputted from output ports 6 and 7 of the polarization multiplexer 3, so that the signal light 1 and exciting light 2 are polarized and multiplexed. Then multiplexed light beams 8 and 9 outputted from ports 6 and 7 of a polarization multiplexer 3 are inputted to fiber type amplifiers 14 and 15 respectively. The multiplexed light beams 8 and 9 after passing through the fiber type optical amplifiers 14 and 15 are inputted to input ports 17 and 18 of a polarization demultiplexer 16. The polarization demultiplexer 16 performs polarization demultiplexing, the horizontal polarized component 10 of the signal light of the multiplexed light 8 is outputted from a 7th port 19 of the polarization demultiplexer 16, and the vertical polarized component of the exciting light is outputted from an 8th port 20 of the polarization demultiplexer 16. Consequently, the signal light 1 and exciting light 2 are both multiplexed and demultiplexed with high efficiency without reference to their wavelengths.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical amplification method in the fields of optical communication, optical measurement, optical information, etc.

(Prior art) Optical amplifiers that directly amplify signal light without photoelectric conversion are extremely effective for increasing the distance and capacity of optical communications, increasing the scale of optical switching systems, and increasing the sophistication of optical information processing. be. °Fiber-type optical amplifiers, which are a type of optical amplifier, are used as optical amplifiers in optical fiber transmission systems because they have almost no connection loss with the optical fiber transmission line, have little polarization dependence, and have low noise. very suitable. Fiber-type optical amplifiers include rare-earth-doped optical fiber amplifiers in which optical fibers are doped with rare earth elements, and optical fiber Raman optical fibers that perform optical amplification by utilizing the reduction of nonlinearity in optical fibers. amplifier and fiber optic Brilliant amplifier. Among rare earth doped optical fiber amplifiers, erbium doped has a gain in the 1,511 m band, which is the low loss wavelength band of quartz optical fiber, can use a 1.5 pm band semiconductor laser as a pumping light source, and is highly efficient.・Optical fiber amplifiers have attracted particular attention in recent years. Regarding this erbium-doped optical fiber amplifier, HAGIMOTO et al.
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A detailed explanation is given in the literature such as PAPER8PDP15.1989.

(Problem to be solved by the invention) When performing optical amplification using the above-mentioned fiber type optical amplifier,
In order to excite a fiber-type optical amplifier, it is necessary to multiplex signal light and pump light and introduce them into the fiber-type optical amplifier. The pumping light after passing through the fiber-type optical amplifier needs to be separated from the signal light so as not to affect the light source or receiver.

Conventionally, wavelength multiplexing and wavelength demultiplexing techniques have been used to multiplex and demultiplex pump light and signal light without loss.

However, some fiber-type optical amplifiers have signal light and pump light in wavelengths very close to each other.

For example, in the case of erbium-doped optical fibers and amplifiers,
The peak wavelength of gain is around 1.536 pm, and the most efficient pumping light wavelength is around 1.485 pm.

When the wavelengths of the signal light and the pumping light are very close to each other in this way, multiplexing and separating them using wavelength multiplexing and demultiplexing is difficult because the wavelength characteristics are steep and it is difficult to obtain a wavelength filter with low loss. It is very difficult for this reason. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical amplification method that can multiplex and demultiplex signal light and pump light with high efficiency, regardless of their wavelengths, in optical amplification using a fiber-type optical amplifier.

(Means for Solving the Problems) The optical amplifier of the present invention includes a polarization multiplexer that separates light input from two input ports into two orthogonal polarization directions, and multiplexes orthogonal polarization components; A fiber-type optical amplifier connected to two output ports of a polarization multiplexer, and a polarization direction in which the output lights of the two fiber-type optical amplifiers are received at two input ports, and the output lights are separated by the polarization multiplexer. separated with the same or orthogonal polarization direction,
It is characterized by comprising a polarization separator that multiplexes orthogonal polarization components of light input from different input ports.

In addition, the signal light and the pump light are separated into two orthogonal polarization directions, the orthogonal polarization components of the separated signal light and the pump light are multiplexed, and the two multiplexed lights are sent to two fiber-type optical amplifiers. The two fiber-type optical amplifiers are pumped by inputting the respective signals, and the two multiplexed lights after passing through the fiber-type optical amplifier are polarized and separated, and the orthogonal polarization components of the signal lights and the orthogonal polarization components of the excitation light are separated. This is an optical amplification method characterized by separating the signal light and the excitation light by combining the polarized light components.

Furthermore, polarization separation of the signal light is performed, and the polarization-separated signal light is input into two fiber-type optical amplifiers, and the polarization separation of the pump light is performed, and the polarization separation of the polarization-separated pump light is applied to the polarization of the signal light. The signal light is input into the two fiber-type optical amplifiers on the side orthogonal to the direction from the direction opposite to the signal light, the two fiber-type optical amplifiers are excited, and the polarized light after passing through the two fiber-type optical amplifiers is separated. This is a special optical amplification method that combines signal light and generates a combination of polarization-separated excitation light after passing through the fiber-type optical amplifier.

The signal light and the excitation light are separated into two orthogonal polarization directions, the orthogonal polarization components of the separated signal light and the first excitation light are polarization multiplexed, and the two multiplexed lights are combined into two fiber-type lights. The two multiplexed lights after passing through the fiber type optical amplifier are polarized and separated, and the orthogonal components of the signal light and the orthogonal components of the excitation light are combined to form the signal light and the multiplexed light. The first pumping light is separated, the second pumping light is separated into two orthogonal polarization directions, and the second pumping light is sent to the two fiber-type optical amplifiers on the side orthogonal to the polarization direction of the signal light. input from the opposite direction to the multiplexed light, pumping the two fiber-type optical amplifiers together with the first pumping light, and dividing the second pumping light transmitted through the fiber-type optical amplifier from the signal light optical path. This is an optical amplification method characterized by the following.

(Function) According to the present invention, multiplexing and demultiplexing of signal light and excitation light are performed by polarization multiplexing and demultiplexing. FIG. 2 is a diagram for explaining this polarization multiplexing and six-separation method. First, the signal light 1 and the pumping light 2 are input into the first and second ports 4 and 5, which are the input ports of the polarization multiplexer 3, respectively, and the third and second ports, which are the output ports of the polarization multiplexer 3, are respectively inputted. Multiplexed light 8,9 from the fourth port 6.7
Polarization multiplexing of signal light 1 and excitation light 2 is performed by outputting . At this time, the horizontal polarization component 1 of the signal light is included in the multiplexed light 8.
0 and the vertically polarized component 11 of the pump light are multiplexed, and the multiplexed light 9 has the vertically polarized component 12 of the signal light and the horizontally polarized component 13 of the pump light multiplexed.

3rd of polarization multiplexing 3. The multiplexed lights 8 and 9 output from the fourth port 6.7 are each fed to a fiber-type optical amplifier 14.15.
is input. The polarization states of the signal light component and the pumping light component in the multiplexed lights 8 and 9 are orthogonal to each other, but the amplification characteristics of the fiber type optical amplifiers 14 and 15 do not exist in the polarization states of the signal light and the pumping light. Fiber type optical amplifier 14.15
The signal light components in the multiplexed lights 8 and 9 are amplified.

The multiplexed light 8°9 after passing through this fiber type optical amplifier 14.15 is input to the input port 5. 6th Pau) entered at 17.18. Polarization separation is performed in the polarization splitter 16 , in which the horizontal polarization component 10 of the signal light of the multiplexed light 8 is sent from the seventh port 19 of the polarization splitter 16 , and the vertical polarization component 11 of the excitation light is sent to the seventh port 19 of the polarization splitter 16 . Output from 8 ports 20. Also, of the multiplexed light 9, the vertically polarized component 12 of the signal light is output from the seventh port 19 of the polarization splitter 16, and the horizontally polarized component 13 of the pump light is outputted from the eighth port 20 of the polarization splitter 16. In this way, the amplified signal light 21 is output from the seventh port 19, which is the output port of the polarization splitter, and the pumping light 22 after pumping is output from the eighth port 20. separation is done.

Note that the intensity and phase of the horizontal polarization component 10 of the signal light and the vertical polarization component 2 of the signal light change depending on the polarization state of the signal light 1. However, both signal light components are
4.15 and then multiplexed in the polarization splitter 16, the intensity of the amplified signal light 21 is constant regardless of the polarization state of the signal light 1. Furthermore, when the horizontally polarized component 10 of the signal light and the vertically polarized component 12 of the signal light are combined in the polarization splitter 16, the polarization states of the two are orthogonal, so no matter what phase relationship they have, interference will occur. They don't cancel each other out.

Therefore, according to the present invention, optical amplification can be performed regardless of the polarization state of the signal light l.

Further, according to the present invention, the pump light can be multiplexed in the opposite direction to the signal light. In other words, instead of inputting the pump light 2 to the second port 5 of the polarization multiplexer 3 in FIG.
It is also possible to input to port 20 of 6@8. In this case, the traveling direction of the excitation light 2 is simply reversed,
Polarization multiplexing and demultiplexing of pump light 1 and signal light 2 can be performed without loss in the same way as when pump light and signal light are input from the same direction. In this case, even if the separation of the signal light 1 and the pumping light 2 is insufficient, there is an advantage that the pumping light 2 will not leak in the signal direction of the signal light 1, that is, in the direction where the optical receiver is located.

Furthermore, according to the present invention, two
It is also possible to multiplex two excitation lights. That is, it is also possible to simultaneously input two pump lights to the second port 1-5 and the eighth port 20 in FIG. In this case as well, lossless polarization multiplexing and separation of pump light and signal light is possible, and since the amount of pump light input into the fiber-type optical amplifier increases, the gain can be increased.

(Example) "11) FIG. 1 shows the constituent countries of the first embodiment of the present invention.

In the first embodiment, a polarization beam splitter is used as the polarization multiplexer 3 and the polarization separator 16, and the fiber-type optical amplifier 14
．． As No. 15, an optical fiber type optical amplifier doped with erbium was used. Signal light 1 and excitation light 2 sent through optical fibers 23 and 24 are collimated by lenses 25 and 26, and then input to first and second ports 4 and 5 of polarization multiplexer 3, respectively. , polarization multiplexed. In this example, the wavelength of the signal light 10 when input to the polarization multiplexer 3 was 1.535 pm and the intensity was -30 dBm, and the wavelength of the pumping light 2 was 1.48 pm and the intensity was +13 dBm. Signal light 1 is output from the third and fourth baud 1-6.7 of polarization multiplexer 3.
Multiplexed lights 8 and 9 obtained by polarization multiplexing the excitation light 2 and the excitation light 2 are output,
The multiplexed lights 8 and 9 are condensed by lenses 27 and 28, and input to a fiber type optical amplifier 14 and 15. However, the polarization state of the excitation light 2 when input to the polarization multiplexer 3 is adjusted by the polarization adjuster 29 so that the intensities of the excitation light components in the multiplexed lights 8 and 9 are equal. This polarization adjuster 29 is 17
It is a combination of a 2-wavelength plate and a 174-wavelength plate, and it is possible to adjust input light to any polarization state and output it.

The signal light component in the multiplexed lights 8 and 9 is transmitted through a fiber-type optical amplifier 14.
．． 15, each was amplified by 15 dB.

The multiplexed light beams 8.9 after passing through the fiber-type optical amplifiers 14.15 are collimated by lenses 30.31, and are then collimated by lenses 30.31. It is input to the sixth port 17°18. However, the polarization state of the multiplexed light 8 is
The polarization adjuster 32 adjusts so that only the signal light component in the multiplexed light 8 is output from the port 19 of the multiplexed light 8.

At this time, the pumping light component in the multiplexed light 8 is output from the eighth port 20 because it is in a polarization state orthogonal to the signal light component.

Similarly, the polarization state of the multiplexed light 9 is adjusted by the polarization adjuster 33 so that the signal light component in the multiplexed light 9 is output from the seventh port 19 and the excitation light component is output from the eighth port 20. . In this way, the amplified signal light 21 is output from the seventh port 19, and the pumped light 22 after pumping is output from the eighth port 20.

The amplified signal light 21 is focused by a lens 34 and input into an optical fiber 35 which is a transmission path. At this time, the intensity of the pumping light component outputted together with the amplified signal light 21 to the seventh port 19 was suppressed to a very low level of -40 dBm or less.

FIG. 3 shows the constituent countries of the second embodiment of the present invention.

In the second embodiment, a fiber coupler type polarization beam splitter is used as the polarization multiplexer 3 and the polarization separator 16, and an optical fiber type optical amplifier in which polarization maintaining optical fiber is doped with erbium is used as the fiber type optical amplifier 14,15. did. Further, the excitation light 2 was multiplexed so that the traveling direction was opposite to that of the signal light 1. In FIG. 3, a signal light 1 transmitted through an optical fiber 23 is transmitted to a polarization multiplexer 3 of the optical fiber coupler type.
is input to the first port 4 of the third . 4th bow 1-6
．． 7 outputs a horizontal polarization component 10 of the signal light and a vertical polarization component 12 of the signal light, respectively. Further, the excitation light 2 transmitted through the optical fiber 36 is input to the eighth port 20 of the fiber coupler type polarization splitter 16, and is input to the fifth port 20 of the fiber coupler type polarization splitter 16. A vertically polarized light component 11 of the pumping light and a horizontally polarized light component 13 of the pumping light are outputted from the sixth board 1-17 and 18, respectively. A polarization maintaining optical fiber is used as the optical fiber 36, and after the twist angle is adjusted so that the intensities of the vertically polarized component 11 of the excitation light and the horizontally polarized component 13 of the excitation light are equal, the fiber is connected to the eighth port 20 and spliced. connected by.

(3rd and 4th baud 1-6.7 of polarization multiplexer 3 and 5th and 6th baud of polarization splitter 16) 17.18 refers to the fiber-type optical amplifier 14.15 of polarization-maintaining optical fiber. Connected by splices through. However, the horizontal polarization component 10 of the signal light in the fiber type optical amplifier 14 and the vertical polarization component 11 of the pump light in the fiber type optical amplifier 14, and the horizontal polarization component 13 of the pump light in the vertical polarization component 12 of the signal light in the fiber type optical amplifier 15.
The fiber type optical amplifiers 14, 15 and the third . 4th. Fifth. 6th bow 1
- The twist angle when connecting with 6.7.17.18 has been adjusted. By being connected in this way, the horizontal polarization component 10 of the signal light and the vertical polarization component 12 of the signal light are separated by the polarization splitter 1.
6, and outputted from the seventh port 19 as amplified signal light 21. Further, the vertically polarized component 11 of the pumping light and the horizontally polarized component 13 of the pumping light are multiplexed by the polarization multiplexer 3 and outputted from the second port 5 as the pumped pumping light 22 . In this embodiment, as in the first embodiment,
Using pumping light 2 with a wavelength of 1.48 pm and an intensity of +13 dBm, it was possible to amplify a completed signal by 15 dB with a wavelength of 1.535 pm and an intensity of -30 dBm.

FIG. 4 shows a configuration diagram of a third embodiment of the present invention.

In the second embodiment, the signal light and the pump light in the opposite direction were multiplexed, but
The third embodiment further multiplexes the signal light and the pumping light in the same direction at the same time. In the third embodiment, as in the second embodiment, a fiber coupler type polarization beam splitter is used as the polarization multiplexer 3 and the polarization separator 16, and a polarization maintaining optical fiber is doped with erbium as the fiber type optical amplifier 14.15. A fiber optic amplifier was used. The first . The second excitation light beams 37 and 38 are the second excitation lights 37 and 38, respectively. 8th bow 1-5.2
It is input to 0. Here, the optical fiber 24.36 is a polarization maintaining optical fiber, and when connected to the 2nd degree 8th baud) 5, 20, the first
The twist angle is adjusted so that the intensity is equal to that of the second excitation light 37 and the second excitation light 37 and 38, respectively. Further, as in the second embodiment, the fiber type optical amplifiers 14, 15 and the third, fourth, and fifth
, the twist angle at the time of connection with the sixth port 6, 7.17.18 is adjusted so that the signal light 1 is output only from the seventh port (15) 19. At this time, the second
The first pumping light 37 inputted from the port 3 of is outputted from the eighth port 20 as the pumping light 39 after the I-th pumping. Further, the second pumping light 38 inputted from the eighth port 20 is outputted from the second port 3 as pumping light 40 after second pumping. After the first and second pumping, the optical fiber 2 is
4.36 has optical isolators 41.42. In the case of this example, the wavelength and intensity of excitation lights 2 and 37 were both 1.48 pm and +13 dBm. Using these two pumping lights 2 and 37, the fiber type optical amplifier 14
As a result of exciting ゜15, the wavelength is 1.535 pm and the intensity is -3.
Signal light 1 of 0 dBm could be amplified by 25 dB.

Although three embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to these embodiments and that various changes can be made within the scope of the present invention. For example, in the first embodiment, the polarization adjuster 29 adjusts the polarization state of the excitation light 2 so that the intensities of the excitation light components in the multiplexed lights 8 and 9 are equal.
Adjusted with. This is because if there is a difference in the gains of the fiber-type optical amplifiers 14 and 15, it will change depending on the polarization state of the (16) signal light 1 after amplification. However, if there are differences in the amplification characteristics of the fiber type optical amplifiers 14, 15, or if there are variations in the coupling between the fiber type optical amplifiers 14, 15, the polarization multiplexer 3, and the polarization separator 16,
By adjusting the polarization state of the pumping light 2 with the polarization adjuster 29 and changing the gain of the fiber type optical amplifier 14, 15, the dependence of the total gain on the polarization state can be eliminated. In addition, in the first embodiment, the polarization adjuster 29.32.33
Although we used a wavelength plate as the method, it is of course possible to use other types of polarization adjusters, such as optical fiber type polarization adjusters that adjust the polarization state by applying stress or twist to the optical fiber. . In this case, the fiber type optical amplifier 14.15 and the polarization adjuster 32.33 can be integrated by applying stress or twist to the fiber type optical amplifier 14.15.

Furthermore, in order to increase the intensity of the excitation light, output lights from a plurality of light sources may be wavelength-multiplexed or polarization-multiplexed and used as the excitation light.

Further, in two embodiments of the present invention, a fiber type optical amplifier 1
Although an erbium-doped optical fiber type optical amplifier was used as 4.15, it is of course possible to use other fiber type optical amplifiers.

(Effects of the Invention) In the present invention, signal light and pump light are multiplexed by polarization multiplexing and separation in optical amplification using a fiber type optical amplifier. Therefore, according to the present invention, it is possible to multiplex and separate the signal light and the pumping light with high efficiency regardless of their wavelengths, and it is possible to amplify the signal light with extremely high efficiency.

[Brief explanation of drawings]

1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a diagram for explaining the present invention in detail, FIG. 3 is a block diagram of a second embodiment of the present invention, and FIG. 4 is a block diagram of a second embodiment of the present invention. FIG. 2 is a configuration diagram of a third embodiment of the present invention. In each figure, 1...signal light, 2,37...pumping light, 3...polarization multiplexer, 4,5°6.7...first, second, third, fourth
Port of 8.9.1. Multiplexed light, 10... Horizontal polarization component of signal light, 11... Vertical polarization of excitation light (19), 129. - Vertical polarization component of signal light, 13... Polarization fraction of excitation light, 14.15... Fiber type optical amplifier, 16... Polarization splitter, 17.18.19.20...
・5th, 6th, 7th, 8th ports, 21... Signal light after amplification, 22... Pumping light after pumping, 23° 24, 3
5.36...Optical fiber, 25.26.27.28.
30.31.34...Luns, 29.32.33...
Polarization adjuster, 37.38...$1, second excitation light, 3
9.40...Excitation light after first and second excitation, 41°4
2... Optical isolator.

Claims (4)

[Claims] (1) A polarization multiplexer that separates the light input from two input ports into two orthogonal polarization directions and multiplexes the orthogonal polarization components, each connected to the two output ports of the polarization multiplexer. A fiber-type optical amplifier receives output lights from the two fiber-type optical amplifiers at two input ports, separates the output lights in a polarization direction that is the same as or orthogonal to the polarization direction separated by the polarization multiplexer, and separates the output lights into different input ports. An optical amplifier comprising a polarization separator that multiplexes orthogonal polarization components of light input from a port. (2) Separate the signal light and pump light into two orthogonal polarization directions, multiplex the orthogonal polarization components of the separated signal light and pump light, and send the two multiplexed lights to two fiber-type optical amplifiers. to pump the two fiber-type optical amplifiers, polarize and separate the two multiplexed lights after passing through the fiber-type optical amplifier, and separate orthogonal polarization components of the signal lights and the excitation light. An optical amplification method characterized by separating orthogonal polarized light components into signal light and excitation light by combining orthogonal polarized light components. (3) Perform polarization separation of the signal light, input the polarization-separated signal light into two fiber-type optical amplifiers, perform polarization separation of the pump light, and separate the polarization-separated pump light from the signal light. The signal light is input to the two fiber-type optical amplifiers on the side orthogonal to the polarization direction from the direction opposite to the signal light, the two fiber-type optical amplifiers are excited, and the polarized light after passing through the two fiber-type optical amplifiers is separated. This is a special optical amplification method in which the signal light is multiplexed, and the polarization-separated excitation light after passing through the fiber-type optical amplifier is multiplexed. (4) Separate the signal light and excitation light into two orthogonal polarization directions, polarization multiplex the orthogonal polarization components of the separated signal light and the first excitation light, and combine the two multiplexed lights into two
the two multiplexed lights after passing through the fiber-type optical amplifiers are polarized and separated, and the orthogonal components of the signal light and the orthogonal components of the excitation light are combined. Separating the signal light and the first excitation light,
Separates the second excitation light into two orthogonal polarization directions, and
The excitation light of
The multiplexed light is input into two fiber-type optical amplifiers from the opposite direction to the multiplexed light, and the two fiber-type optical amplifiers are excited together with the first pumping light, and the second light that passes through the fiber-type optical amplifier is
An optical amplification method characterized in that the excitation light is separated from the signal light optical path.