JP2508846B2 - Optical amplifier and optical amplification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical amplification method in the fields of optical communication, optical measurement, optical information, and the like.

(Prior Art) An optical amplifier that directly amplifies signal light without photoelectric conversion is extremely effective for long-distance, large-capacity optical communication, large-scale optical switching system, and advanced optical information processing. is there. A fiber-type optical amplifier, which is a type of this optical amplifier, is extremely useful as an optical amplifier in an optical fiber transmission system because it has almost no connection loss with the optical fiber transmission line, has small polarization dependence, and has low noise. Suitable for The fiber-type optical amplifier includes a rare earth element-doped optical fiber amplifier in which an optical fiber is doped with a rare earth element and an optical fiber Raman There are amplifiers and fiber optic Brilliant amplifiers. Among the rare earth-doped optical fiber amplifiers, erbium-doped optical amplifiers that have a high gain in the low-loss wavelength band of the quartz optical fiber, 1.5 μm band, can use a 1.5 μm band semiconductor laser as the excitation light source, and are highly efficient. Fiber amplifiers have received particular attention in recent years. Regarding this erbium-doped optical fiber amplifier, K.HAGIMOTO et al.'A212km NON-REPEATED TRA
NSMISSION EXPERIMENT AT1.8Gb / s USING LD PUMPED FIBE
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It is explained in detail in the literature such as YSTEM ', OFC'89 POSTDEADLINE PAPERS PDP15, 1989.

(Problems to be Solved by the Invention) When optical amplification is performed using the above fiber-type optical amplifier, it is necessary to multiplex signal light and pumping light and introduce them into the fiber-type optical amplifier in order to pump the fiber-type optical amplifier. is there.
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 and the receiver. In order to perform the multiplexing and demultiplexing of the pumping light and the signal light without loss, wavelength multiplexing / wavelength demultiplexing technology has been used.

However, in some fiber type optical amplifiers, the wavelengths of the signal light and the pumping light are very close to each other. For example, in the case of an erbium-doped optical fiber amplifier, the peak wavelength of gain is around 1.536 μm, and the most efficient pumping light wavelength is around 1.485 μm. In this way, when the wavelengths of the signal light and the pumping light are very close to each other, it is difficult to obtain a wavelength filter with steep wavelength characteristics and low loss, etc., by multiplexing and demultiplexing the two. Is very difficult because of. Therefore, it is an object of the present invention to provide an optical amplification method capable of highly efficiently multiplexing and demultiplexing both signal light and pumping light in optical amplification using a fiber-type optical amplifier.

(Means for Solving the Problems) An optical amplifier according to 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 each of two output ports of the polarization multiplexer, and two input ports for receiving output light of the two fiber type optical amplifiers, and a polarization direction obtained by separating the output light by the polarization multiplexer. It is characterized in that it comprises a polarization separator which separates in the same or orthogonal polarization directions and multiplexes the orthogonal polarization components of the lights inputted from different input ports.

Further, the signal light and the pumping light are separated into two orthogonal polarization directions, the orthogonal polarization components of the separated signal light and the pumping light are multiplexed, and the two multiplexed lights are combined into two fiber type optical amplifiers. Each of them is input to excite the two fiber type optical amplifiers, the two multiplexed lights after passing through the fiber type optical amplifiers are polarized and separated, and the polarization components of the signal lights are orthogonal to each other and the excitation lights are orthogonal to each other. In the optical amplification method, the polarized light components are combined to separate the signal light and the excitation light.

Further, polarization separation of the signal light is performed, and the signal light separated by the polarization is input to two fiber type optical amplifiers,
The polarization splitting of the pumping light is performed, and the pumping splitting light is input to the two fiber type optical amplifiers on the side orthogonal to the polarization direction of the signal light from the opposite direction to the signal light, and the two fiber type An optical amplifier characterized in that the polarization-separated signal light after passing through the two fiber-type optical amplifiers for pumping the optical amplifier is multiplexed, and the polarization-separated pumping light after passing through the fiber-type optical amplifier is multiplexed. Is the way.

The signal light and the pumping light are split into two orthogonal polarization directions, and the orthogonal polarization components of the separated signal light and the first pumping light are polarization-multiplexed, and the two multiplexed lights are two fiber type lights. The two multiplexed lights that have been input to the amplifiers and have been transmitted through the fiber-type optical amplifier are polarized and separated, and the orthogonal components of the signal light and the orthogonal components of the pump light are multiplexed to obtain the signal light and the first component. 1 excitation light is separated,
Of the pumping light of (1) is split into two orthogonal polarization directions, and the second pumping light is input to the two fiber type optical amplifiers on the side orthogonal to the polarization direction of the signal light from the opposite direction to the multiplex light,
The optical amplification method is characterized in that the two fiber-type optical amplifiers are pumped together with the first pumping light, and the second pumping light that has passed through the fiber-type optical amplifier is separated from the signal light optical path. .

(Operation) According to the present invention, the multiplexing and demultiplexing of the signal light and the pumping light is performed by polarization multiplexing and demultiplexing. Figure 2 shows this polarization multiplexing
It is a figure for demonstrating the method of separation. First, the signal light 1 and the pump light 2 are first and second input ports of the polarization multiplexer 3.
Input to the ports 4 and 5, and output the multiplexed lights 8 and 9 from the 3rd and 4th ports 6 and 7, which are the output ports of the polarization multiplexer 3, to polarize the signal light 1 and the pump light 2. I do.
At this time, the horizontal polarization component 10 of the signal light and the vertical polarization component 11 of the excitation light are multiplexed in the multiplexed light 8, and the vertical polarization component 12 of the signal light and the horizontal polarization component 13 of the excitation light are multiplexed in the multiplexed light 9. Has been done.

The multiplexed lights 8 and 9 output from the third and fourth ports 6 and 7 of the polarization multiplexer 3 are input to fiber type optical amplifiers 14 and 15, respectively. 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. The fiber type optical amplifiers 14 and 15 amplify the signal light components in the multiplexed lights 8 and 9.

The multiplexed lights 8 and 9 after passing through the fiber type optical amplifiers 14 and 15 are the fifth and sixth ports 17 and 18 which are the input ports of the polarization separator 16.
Is input to Polarization separation is performed in the polarization splitter 16, and the horizontal polarization component 10 of the signal light of the multiplexed light 8 is output from the seventh port 19 of the polarization splitter 16 and the vertical polarization component 11 of the excitation light is input to the first of the polarization splitter 16. Output from 8 port 20. The vertical polarization component 12 of the signal light of the multiplexed light 9 is output from the seventh port 19 of the polarization separator 16, and the horizontal polarization component 13 of the excitation light is output from the eighth port 20 of the polarization separator 16. Thus, the amplified signal light 21 is output from the seventh port 19 which is the output port of the polarization splitter, and the pump light 22 after pumping is output from the eighth port 20. Or separation is done.

The intensity and phase of the horizontal polarization component 10 of the signal light and the vertical polarization component 12 of the signal light change depending on the polarization state of the signal light 1. However, both signal light components are fiber type optical amplifier 1
Polarization separator 16 after being amplified by 4, 15 with equal gain
, The intensity of the signal light 21 after amplification is constant regardless of the polarization state of the signal light 1. Further, when the horizontal polarization component 10 of the signal light and the vertical polarization component 12 of the signal light in the polarization separator 16 are combined, the polarization states of the two are orthogonal to each other. They do not cancel each other out. Therefore, according to the present invention, optical amplification can be performed regardless of the polarization state of the signal light 1.

Further, according to the present invention, the pumping light can be multiplexed in the opposite direction to the signal light. That is, in FIG. 2, the pumping light 2 is not input to the second port 5 of the polarization multiplexer 3 but is a polarization splitter.
It is also possible to input to the 16th eighth port 20. In this case, the traveling directions of the pumping light 2 are simply reversed, and the polarization multiplexing / separation of the pumping light 1 and the signal light 2 can be performed without loss as in the case where the pumping light and the signal light are input from the same direction. it can. In this case, even if the separation between the signal light 1 and the pumping light 2 is insufficient, there is an advantage that the pumping light 2 does not leak in the signal direction of the signal light 1, that is, the direction in which the optical receiver is present.

Further, according to the present invention, it is also possible to multiplex two pump lights in the same direction as the signal light and in the opposite direction. That is, it is possible to simultaneously input two pumping lights to the second port 5 and the eighth port 20 in FIG. Also in this case, the polarization multiplexing and demultiplexing of the pumping light and the signal light can be performed without loss, and the amount of pumping light input into the fiber type optical amplifier increases, so that the gain can be increased.

(Embodiment) FIG. 1 shows a block diagram of a first embodiment of the present invention. First
In this embodiment, a polarization beam splitter is used as the polarization multiplexer 3 and the polarization separator 16, and erbium-doped optical fiber type optical amplifiers are used as the fiber type optical amplifiers 14 and 15. The signal light 1 and the pumping light 2 sent by the optical fibers 23 and 24 are collimated by the lenses 25 and 26, and then input to the first and second ports 4 and 5 of the polarization multiplexer 3, respectively. , Polarization multiplexed. In this embodiment, the wavelength of the signal light 1 at the time of inputting the polarization multiplexer 3 is 1.535 μm and the intensity is −3.
The excitation light 2 had a wavelength of 1.48 μm and an intensity of +13 dBm. From the third and fourth ports 6 and 7 of the polarization multiplexer 3, the multiplexed lights 8 and 9 in which the signal light 1 and the pumping light 2 are polarized and multiplexed are output, and these multiplexed lights 8 and 9 are output by the lenses 27 and 28. Collected,
It is input to the fiber type optical amplifiers 14 and 15. However, the polarization state of the excitation light 2 at the time of 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 become equal. The polarization adjuster 29 is a combination of a 1/2 wavelength plate and a 1/4 wavelength plate, and is capable of adjusting the input light into an arbitrary polarization state and outputting the light. The signal light components in the multiplexed lights 8 and 9 are both 15 dB due to the fiber type optical amplifiers 14 and 15.
Amplified.

The multiplexed lights 8 and 9 after passing through the fiber type optical amplifiers 14 and 15 are collimated by the lenses 30 and 31, and then input to the fifth and sixth ports 17 and 18 of the polarization separator 16, respectively.
However, the polarization state of the multiplexed light 8 is adjusted so that only the signal light component in the multiplexed light 8 is output from the seventh port 19
Adjusted by At this time, since the pumping light component in the multiplexed light 8 is in the orthogonal polarization state with the signal light component,
It is output from 20. 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 pumping light component is output from the eighth port 20. . In this way the 7th port
The amplified signal light 21 is output from 19 and the pumped light 22 after pumping is output from the eighth port 20. The signal light 21 after the amplification is condensed by the lens 34 and input to the optical fiber 53 which is a transmission path. At this time, the intensity of the pumping light component output together with the amplified signal light 21 to the seventh port 19 is −40 dBm.
It was suppressed to a very low level below.

FIG. 3 shows a block diagram of the second embodiment of the present invention. In the second embodiment, a fiber coupler type polarization beam splitter is used for the polarization multiplexer 3 and the polarization separator 16, and an erbium-doped optical fiber type optical amplifier is used as the fiber type optical amplifiers 14 and 15. did. The pumping light 2 was multiplexed so that the traveling direction was opposite to that of the signal light 1. In FIG. 3, the signal light 1 transmitted through the optical fiber 23 is input to the first port 4 of the polarization multiplexer 3 of the optical fiber coupler type, and the signal light is output from the third and fourth ports 6 and 7. The horizontal polarization component 10 and the vertical polarization component 12 of the signal light are output. The pumping light 2 transmitted through the optical fiber 36 is input to the eighth port 20 of the fiber coupler type polarization separator 16, and the vertical polarization component 11 of the pumping light 11 is input from the fifth and sixth ports 17 and 18. , And the horizontal polarization component 13 of the excitation light is output. A polarization-maintaining optical fiber is used as the optical fiber 36. The twist angle is adjusted so that the vertical polarization component 11 of the pumping light and the horizontal polarization component 13 of the pumping light are equal in intensity, and then the splice is connected to the eighth port 20. Connected by.
The third and fourth ports 6 and 7 of the polarization multiplexer 3 and the polarization separator 16
The fifth and sixth ports 17 and 18 are connected by a splice via polarization-preserving optical fiber type fiber amplifiers 14 and 15. However, the polarization state of the horizontal polarization component 10 of the signal light in the fiber type optical amplifier 14 and the vertical polarization component 11 of the pumping light, and the horizontal polarization component 13 of the pumping light of the vertical polarization component 12 of the signal light in fiber type optical amplifier 15 So that they are all orthogonal to each other, the fiber type optical amplifiers 14, 15 and the third, fourth, fifth,
The twist angle when connecting to the sixth port 6, 7, 17, 18 is adjusted. By connecting in this way, the horizontal polarization component 10 of the signal light and the vertical polarization component 12 of the signal light are polarization-multiplexed by the polarization splitter 16 and output from the seventh port 19 as the amplified signal light 21. The vertical polarization component 11 of the excitation light and the horizontal polarization component 13 of the excitation light are multiplexed by the polarization multiplexer 3 and output from the second port 5 as the excitation light 22 after the excitation.
In the case of this embodiment, the wavelength is 1.48 μm, as in the first embodiment.
Wavelength 1.535 μm, intensity − using excitation light 2 with intensity +13 dBm
The signal light 1 of 30 dBm could be amplified by 15 dB.

FIG. 4 shows a block diagram of the third embodiment of the present invention. In the second embodiment, the signal light and the pumping light in the opposite direction are multiplexed, but in the third embodiment, the signal light and the pumping light in the same direction are simultaneously multiplexed. In the third embodiment, as in the second embodiment,
A fiber coupler type polarization beam splitter is used for the polarization multiplexer 3 and the polarization separator 16, and a fiber type optical amplifier 14,
An optical fiber type optical amplifier in which a polarization maintaining optical fiber is doped with erbium is used as 15. The first and second pumping lights 37 and 38 transmitted by the optical fibers 24 and 36 are input to the second and eighth ports 5 and 20, respectively. Here, the optical fibers 24 and 36 are polarization-maintaining optical fibers, and when connecting to the second and eighth ports 5 and 20, the first and second pumping lights 37 and 38 in the fiber type optical amplifiers 14 and 15 are used. The twist angle is adjusted so that the strengths are equal. Further, as in the second embodiment, the fiber type optical amplifiers 14, 15 and the third, fourth, fifth,
The twist angle at the time of connection with the sixth ports 6, 7, 17, 18 is adjusted so that the signal light 1 is output only from the seventh port 19. At this time, the first pumping light 37 input from the second port 3 is used as the pumping light 39 after the first pumping in the eighth port.
It is output from 20. The second pumping light 38 input from the eighth port 20 is used as the second pumping light 40 after the second pumping.
It is output from port 3 of. The optical fibers 24, so that the pumping light 39, 40 after pumping the first and second pumps does not return to the pumping light source.
36 has optical isolators 41 and 42. In the case of this embodiment, the wavelength and intensity of the excitation light 2,37 are both 1.48μ.
m was +13 dBm. As a result of exciting the fiber type optical amplifiers 14 and 15 using these two pumping lights 2 and 37, the wavelength is 1.535 μm.
It was possible to amplify the signal light 1 having m and an intensity of -30 dBm by 25 dB.

Although the 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 various modifications can be made within the scope of the present invention. For example, in the first embodiment, the polarization state of the excitation light 2 is adjusted by the polarization adjuster 29 so that the intensities of the excitation light components in the multiplexed lights 8 and 9 become equal. This is because if there is a difference in gain between the fiber type optical amplifiers 14 and 15, it changes depending on the polarization state of the signal light 1 after amplification. However, if there is a difference in the amplification characteristics of the fiber type optical amplifiers 14 and 15 or if the fiber type optical amplifiers 14 and 15 and the polarization multiplexer 3 and the polarization demultiplexer 16 are coupled differently, excitation is performed by the polarization adjuster 29. By adjusting the polarization state of the light 2 and changing the gains of the fiber type optical amplifiers 14 and 15, it is possible to eliminate the polarization state dependency of the total gain. Further, in the first embodiment, the one using the wave plate is used as the polarization adjusters 29, 32, 33, but it goes without saying that the polarization state can be changed by applying stress or twist to the polarization adjuster of a kind other than the optical fiber, for example. It is also possible to use an optical fiber type polarization adjuster for adjusting. In this case, fiber type optical amplifier 1
The fiber type optical amplifiers 14 and 15 and the polarization adjusters 32 and 33 can be integrated by applying stress or twist to 4 and 15.

It is also possible to use, as the excitation light, wavelength-multiplexed or polarization-multiplexed output light from a plurality of light sources in order to increase the excitation light intensity.

Further, in two embodiments of the present invention, a fiber type optical amplifier is used.
The optical fiber type optical amplifiers doped with erbium were used as 14, 15 but it is of course possible to use other fiber type optical amplifiers.

(Effects of the Invention) In the present invention, the use light and the excitation light in the optical amplification using the fiber type optical amplifier are multiplexed by polarization multiplexing / demultiplexing. Therefore, according to the present invention, the signal light and the pumping light can be multiplexed and demultiplexed with high efficiency regardless of the wavelengths, and the signal light can be amplified with extremely high efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the present invention, FIG. 3 is a block diagram of the second embodiment of the present invention, and FIG. FIG. 6 is a configuration diagram of a third embodiment of the present invention. In each figure, 1 ... Signal light, 2,37 ... Excitation light, 3 ... Polarization multiplexer, 4,5,6,7
... 1st, 2nd, 3rd, 4th ports, 8, 9 ... Multiplexed light, 10
… Horizontal polarization component of signal light, 11… Vertical polarization component of excitation light,
12 ... Vertical polarization component of signal light, 13 ... Polarization component of excitation light, 1
4,15… Fiber type optical amplifier, 16… Polarization separator, 17,18,1
9,20 ... Fifth, sixth, seventh and eighth ports, 21 ... Amplified signal light, 22 ... Pumped light after pumping, 23, 24, 35, 36 ... Optical fiber, 25, 26, 27 , 28, 30, 31, 34 ... Lens, 29, 32, 33 ... Polarization adjuster, 37, 38 ... First and second excitation light, 39, 40 ... First and second
Pumping light after pumping, 41, 42 ... Optical isolators.

Claims (4)

(57) [Claims] 1. A polarization multiplexer for separating light input from two input ports into two polarization directions orthogonal to each other, and a polarization multiplexer for multiplexing orthogonal polarization components, and connected to two output ports of the polarization multiplexer. Fiber type optical amplifier
The output lights of the two fiber type optical amplifiers are received by two input ports, and the output lights are separated in the same or orthogonal polarization directions as the polarization directions separated by the polarization multiplexer, and the lights input from different input ports are separated. An optical amplifier comprising: a polarization separator that multiplexes orthogonal polarization components. 2. Signal light and pumping light are orthogonal to each other.
The signals are separated into two polarization directions, and the orthogonal polarization components of the separated signal light and excitation light are multiplexed, and the two multiplexed lights are divided into two.
The two fiber-type optical amplifiers are respectively input to excite the two fiber-type optical amplifiers, the two multiplexed lights after passing through the fiber-type optical amplifiers are polarized and separated, and the orthogonal polarization components of the signal lights, And an optical amplification method characterized in that orthogonal polarization components of the excitation light are multiplexed to separate the signal light and the excitation light. 3. The polarization separation of the signal light, the polarization-separated signal light is input to two fiber type optical amplifiers respectively, the polarization separation of the excitation light is performed, and the polarization-separated excitation light is converted into the signal. The signal light is input from the opposite direction to the two fiber type optical amplifiers on the side orthogonal to the polarization direction of the light.
The two fiber-type optical amplifiers are excited, and the polarization separated signal lights after passing through the two fiber-type optical amplifiers are multiplexed,
An optical amplification method, characterized in that the excitation light that has been polarized and separated after passing through the fiber type optical amplifier is multiplexed. 4. Signal light and pumping light are orthogonal to each other.
The polarization signals are separated into two polarization directions, the orthogonal polarization components of the separated signal light and the first pumping light are polarization-multiplexed, and the two multiplexed lights are respectively input to two fiber-type optical amplifiers. The two multiplexed lights after passing through the amplifier are polarized and separated, and the orthogonal components of the signal light and the orthogonal components of the excitation light are multiplexed to separate the signal light and the first excitation light, Of the pumping light is split into two orthogonal polarization directions, and the second pumping light is input to the two fiber type optical amplifiers on the side orthogonal to the polarization direction of the signal light from the direction opposite to the multiplexed light, An optical amplification method, wherein the two fiber-type optical amplifiers are excited together with the first pumping light, and the second pumping light that has passed through the fiber-type optical amplifier is separated from the signal light optical path.