JPH09312433A - Broadband Er-doped optical fiber amplifier - Google Patents

Abstract

(57) Abstract: Gain is flattened over a wide band of wavelengths 1530 to 1570 nm. SOLUTION: The pumping light 7 is merged with the signal light S ₁ , and the merged signal light is propagated to the Er-doped optical fiber 1 to perform optical amplification. Of the wavelength band of the signal light after the optical amplification, the signal light of the wavelength 1530 nm band is demultiplexed by the optical multiplexer / demultiplexer 8 and guided to the Er-doped optical fiber 10, and only the signal light near 1530 nm of other wavelength bands is The signal light S ₆ is attenuated to a gain level, and the signal light S ₆ after this attenuation is made by the optical multiplexer / demultiplexer 9
To the signal light S ₄ from. As a result, the signal light S ₂ having a flat gain over the entire area can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband Er-doped optical fiber amplifier having a flat gain wavelength characteristic over a wide band.

[0002]

2. Description of the Related Art In recent years, optical fiber amplifiers in which a rare earth element such as Er (erbium), Pr (praseodymium), or Nd (neodymium) is added to the core of an optical fiber have reached a practical level. In particular, an Er-doped optical fiber amplifier has a high gain and a high saturation output in the 1.55 μm band, and is therefore expected to be applied to various systems. Among them, 1.53μm to 1.56μ
High-speed, large-capacity, long-distance transmission and optical CATV (Cable Televis) by wavelength multiplex transmission using several or more wavelengths of signal light in m wavelength band
Ion) application to the system is attracting attention. When the Er-doped optical fiber amplifier is applied to such a system, the gain of the Er-doped optical fiber amplifier in the above-mentioned wavelength band is flat in order to suppress the deterioration of the optical S / N characteristic and the crosstalk characteristic. This is very important.

In order to achieve such high gain and flattening, the present inventors have shown the Er-doped multicore optical fiber as shown in FIG. 6 and FIG. 7 using this Er-doped multicore optical fiber. Such an optical amplifier is proposed. First, the Er-doped multi-core optical fiber 1 used
00 indicates the primary cladding layer 1 as shown in FIG.
No. 02 is coated, and the glass rods 103 having a plurality of cores 101a to 101g to which a rare earth element (for example, Er) and Al are co-added are assembled, and the glass rods 10 are further assembled.
3 has a structure in which the periphery of 3 is thickly covered with the secondary cladding 104. By using such an Er-doped multi-core optical fiber 100, it is possible to achieve a high gain and a flat gain wavelength characteristic.

There are two reasons for this achievement. First, the first reason is that the Er-doped multi-core optical fiber has a conventional Al core concentration of 1
It is possible to sufficiently increase the amount for one Er-doped optical fiber. The second reason is that when the power of the pumping light in the core is lowered with the conventional optical fiber, the wavelength of 1.535μ
The gain peak near m decreases and the gain-wavelength characteristic gradually becomes flat. As the power is further lowered, the wavelength 1.
Since the gain in the short wavelength region on the 53 μm side is decreased and the gain in the long wavelength region on the 1.56 μm side is increased, that is, a so-called gain-wavelength characteristic that increases to the right from the short wavelength to the long wavelength, the pumping light is lowered. It was known that the gain became extremely low and could not be used as an optical amplifier, but this Er-doped multi-core optical fiber, on the contrary, made active use of this principle. That is, as shown in the drawing, if the core diameter D and the core interval d are optimized so that the excitation light and the signal light propagate almost uniformly in the Er-added cores 101a to 101g, respectively, the core 101a Although the amplification gain of the signal light propagating inside each of the cores 101 to 101g becomes low, its wavelength characteristic becomes almost flat, and after propagating a desired length, each of the cores 101a to 101g. The fact that the internally amplified signal is superposed and the wavelength characteristic of the gain becomes almost flat is used.

Next, the configuration of the optical amplifier of FIG. 7 based on the above-mentioned principle and the result of evaluation of the wavelength characteristic of the gain for this will be described. Er-doped multi-core optical fiber 1
In No. 00, the core spacing d is 1.3 μm, each core diameter is about 2 μm, the cladding diameter is 125 μm, the relative refractive index difference Δ between the core and the cladding is 1.45%, and the mode field diameter is about 8.8 μm ( (Value at wavelength 1.55 μm), the addition amount of Er and Al in each core is 400 ppm and 8500 p
pm, fiber length of about 45 m, relative refractive index difference Δ of 2.19%, mode field diameter of about 5.2 μm (value at wavelength 1.55 μm), Er and Al in each core
Two kinds of fibers having a doping amount of 400 ppm and 17000 ppm and a fiber length of about 20 m were used.

Isolators 105a and 105b for preventing light from propagating in opposite directions are connected to both ends of the Er-doped multi-core optical fiber 100, and WDM (Wavelength Division Mult) is provided inside each of them.
iplexing) couplers 106a and 106b are provided. The signal light S ₁ is input to the isolator 105a,
The amplified signal light S ₂ is output from the isolator 105b.

Optical fibers 108a and 108b connected to pump semiconductor lasers 107a and 107b are coupled to the WDM couplers 106a and 106b, respectively, and pump lights 109a and 109b generated by the pump semiconductor lasers 107a and 107b are coupled. Is an Er-doped multi-core optical fiber 1
It is configured to be able to propagate to 00. When the signal light S ₁ is incident through the isolator 105a,
A laser beam 10 having a short wavelength is emitted from the exciting semiconductor laser 107a.
9a is generated and the laser beam 109a is generated by the WDM coupler 1
When it is incident on the Er-doped multicore optical fiber 100 via 06a, a certain energy level of ions is excited, and an amplification effect by stimulated emission occurs. The amplified optical signal S ₂ is output from the Er-doped multicore optical fiber 100 to the outside through the isolator 105b. Similarly,
Laser light 10 generated by the pumping semiconductor laser 107b
9b is incident on the Er-doped multi-core optical fiber 100 from the rear direction and performs optical amplification on the principle described above. Here, the excitation light is applied from the front and back, but it may be applied either before or after.

Here, the wavelengths of the pumping lights 109a and 109b are set to 0.98 μm, the pumping light power of the pumping light 109a is set to 70 mW, and the pumping light power of the pumping light 109b is set to 80 mW. These values are values determined from the fact that the gain wavelength characteristic is suitable for flattening. Wavelength characteristics of gain (Al concentration dependence) in the optical amplifier configured as shown in FIG.
Are measured in FIGS. 8 and 9. FIG. 8 shows the measurement when the added amount of Al was set to 8,500 ppm.
Fig. 9 shows the measurement when the addition amount of 17,000ppm.
It is. Here, the wavelength characteristics of the respective gains were measured with the signal light power Sp as a parameter in the above two examples. As is clear from FIGS. 8 and 9, 1,540n
It can be seen that the gain is flattened from m to 1,560 nm.

However, as seen in FIGS. 8 and 9,
A large gain is raised near the wavelength of 1,530 nm, and further flattening is desired. JP-A-6-77561 discloses a method for improving this. The configuration of the optical fiber amplifier shown in this publication is shown in FIG.
0. Optical isolator 20 to which signal light S ₁ is applied
1, Er ⁺³ ion-doped optical fiber 202, WDM
A coupler 203, an optical isolator 204, a bandpass filter (BPF) 205, and a non-pumped Er ⁺³ ion-doped optical fiber 206 that outputs the signal light S ₂ are cascade-connected. Further, the WDM coupler 203 has a fiber 208.
A pumping light source 207 is coupled via.

This optical fiber amplifier has a construction in which a non-pumped Er ⁺³ ion-doped optical fiber 206 is connected to the output end of the optical amplification section by the Er ⁺³ ion-doped optical fiber 202. This unexcited Er ⁺³ ion-doped optical fiber 2
If the supersaturated absorption characteristic of 06 is used, the waveform distortion generated in the optical amplification section is flattened, and a large gain rise near the wavelength of 1,530 nm can be eliminated.

[0011]

However, unexcited Er ⁺³
The conventional optical fiber amplifier using the ion-doped optical fiber has the following problems. The loss wavelength characteristic of the unexcited Er ⁺³ ion-doped optical fiber has a maximum loss peak near the wavelength of 1,530 nm as shown in FIG. 11, and the loss gradually decreases toward the longer wavelength side than this wavelength. That is, the wavelength is 1530 nm to 1570 n
It has a loss distribution over m. Therefore, when the non-excited Er ⁺³ ion-doped optical fiber 206 is connected to the output end of the optical amplification section, the amplified 1530 nm to 1570 n is amplified.
As a result, the entire signal light of m is attenuated, and wavelengths other than the signal light of 1530 nm that should be originally attenuated are also attenuated.
It has been found that it is difficult to flatten the gain over a wide band of wavelengths 1530 nm to 1570 nm.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and an object of the present invention is to provide a broadband Er-doped optical fiber amplifier capable of obtaining a sufficient flat characteristic over a wide range even at a high gain. .

[0013]

In order to achieve the above-mentioned object, the present invention provides an optical fiber amplifier for performing optical amplification by merging and propagating signal light and pumping light in a first Er-doped optical fiber, A first optical fiber provided in a subsequent stage of the first Er-doped optical fiber for demultiplexing a signal light in a specific wavelength band in which a gain is partially increased in a wavelength band of the signal light after the optical amplification.
Optical multiplexer / demultiplexer, a second Er-doped optical fiber that attenuates the demultiplexed signal light in a specific wavelength region to a predetermined level, the signal light from the second Er-doped optical fiber, and the first optical fiber. And a second optical multiplexer / demultiplexer that multiplexes the signal light from the optical multiplexer / demultiplexer.

According to this structure, in the wavelength characteristic after amplification, even if there is a part where the gain is projected and the gain is not flat, only the narrow wavelength region where the gain is projected is the first optical demultiplexer. If the optical signal is demultiplexed by the optical demultiplexer and attenuated to gain levels in other wavelength ranges, and the signal light after the attenuation is combined with the other unattenuated signal light by the second optical demultiplexer, a flat gain characteristic is obtained. can get. Therefore, an optical amplifier having a flat gain over a wide range can be obtained.

Further, the above-mentioned object is an optical fiber amplifier for performing optical amplification by merging and propagating a signal light and a pumping light in an Er-doped optical fiber, in which the gain is part of the wavelength band of the signal light after the optical amplification. The optical control means including an Er-adding member that attenuates only the signal light in a specific wavelength range that rises up to a predetermined level and allows other wavelength ranges to pass without being attenuated.
This can also be achieved by an Er-doped optical fiber amplifier arranged in a subsequent stage of the doped optical fiber.

Also in this configuration, even if the gain is not flat because there is a portion where the gain is partially projected in the wavelength characteristic after amplification, when passing through the optical control means, only the narrow wavelength region where the gain is projected is other. Is attenuated to the gain level in the wavelength range of
Other wavelength regions pass without being attenuated. Therefore, the extracted signal light has a wavelength of 1530 nm, for example.
It is possible to obtain an optical fiber amplifier with a flat gain over ˜1570 nm.

As the light control means, a film to which a predetermined concentration of Er is added can be used. According to this,
The light control means can be constructed to be extremely small and lightweight, and the light control means can be easily incorporated into the amplifier and the installation space is not a problem. Further, the optical control means can be manufactured at low cost, and the cost increase of the optical fiber amplifier can be suppressed.

The light control means may be configured to include a film to which a predetermined concentration of Er is added and a WDM filter formed by using an interference film filter and to which the Er-added film is attached. According to this structure, the Er-doped film having the characteristic of attenuating only the signal light in the specific wavelength range can be incorporated in the WDM circuit for injecting the pumping light from the rear direction. Therefore, the amplifier can be downsized, the assembling work can be simplified, and the adjusting work can be eliminated.

The excitation light can be incident on the first Er-doped optical fiber from the front direction, the rear direction, or both directions. According to this configuration, the application range of the broadband Er-doped optical fiber amplifier is expanded, and it can be widely used for preamplifiers, power amplifiers, loss compensation amplifiers of various loss devices, etc., and high-speed, large-capacity, long-distance transmission. It can also be applied to a system, an optical CATV system, an optical subscriber system, and the like.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a broadband Er according to the present invention.
It is a connection diagram showing a first embodiment of a doped optical fiber amplifier. Optical isolators 2 and 3 for advancing signal light in only one direction are connected to both ends of the Er-doped optical fiber 1, and a WDM coupler 4 is provided between the optical isolator 2 and the Er-doped optical fiber 1. . A pumping light source 6 is coupled to the WDM coupler 4 through an optical fiber 5, and pumping light 7 generated by the pumping light source 6 (here,
A wavelength of 0.98 μm or 1.48 μm and an optical power of several tens mW to 200 mW) is sent to the WDM coupler 4 and mixed. That is, an optical fiber amplifier based on the forward pumping method is configured here.

Optical multiplexers / demultiplexers 8 and 9 are cascaded on the output side of the optical isolator 3, and an Er-doped optical fiber 10 is coupled between the optical multiplexers / demultiplexers 8 and 9. Where Er
The doped optical fiber 1 has, for example, a length of 25 meters, and its core material is SiO ₂ —Al ₂ O ₃ -based glass to which Er is added, SiO ₂ —GeO ₂ —Al ₂
The O ₃ based glass material obtained by adding Er, SiO ₂ -P ₂ O
_5- Al ₂ O ₃ glass with Er added, SiO
It is used such as those prepared by adding Er to _{2 -GeO 2 -P 2 O 5 -Al} 2 O 3 based glass. All are Al (aluminum)
The concentration should be at least 5000 ppm. The Al concentration should be as high as possible, and 5 to 6% should be added as a guide. Further, the Er addition amount is 200 ppm to 2000 ppm
Select within the range. In order to make the wavelength characteristics of the gain of the optical amplifier as flat as possible and to obtain a high gain, Al and E
The amount of r added is made as large as possible and the relative refractive index difference Δ between the core and the clad is as high as possible. In addition to the single core structure, a so-called Er-doped multi-core optical fiber having a plurality of cores in the clad may be used.

The Er-doped optical fiber 10 may be the same as the Er-doped optical fiber 1, but
It is more preferable to use an Er-doped optical fiber to which Al is not added so that the loss wavelength characteristic near 1530 nm can be sharpened. Further, the length of the Er-doped optical fiber 10 is such that the gain near 1530 nm is 1540 nm to 1540 in the wavelength characteristics of the gain of the amplified signal light S _3.
It is determined by how high the gain is in the 70 nm band.

Further, the optical multiplexer / demultiplexer 8 is composed of an optical fiber type coupler formed by arranging two optical fibers in parallel, fused and extended, or an interference film filter or the like, and has a wavelength of 1530.
It has a characteristic that only the signal light in the nm band can be demultiplexed. The optical multiplexer / demultiplexer 9 has a similar configuration, and the Er-doped optical fiber 1
Has a characteristic of multiplexing the signal light S ₄ of 1540nm~1570nm band from optical coupler 8 the signal light S6 in attenuated wavelength 1530nm band from 0.

In the configuration of FIG. 1, the optical isolator 2 is used.
Signal light S ₁ (wavelength 1530 nm to 1570 n
Signal light obtained by wavelength-multiplexing several waves to several tens of waves of m, and the power thereof is −40 dBm to ten and several dBm) and the pumping light 7 from the pumping light source 6 is merged and coupled by the WDM coupler 4, and this merged coupling is performed. The generated light is sent to the Er-doped optical fiber 1. The signal light S ₁ is optically amplified in the process of propagating through the Er-doped optical fiber 1 to become the signal light S ₃ and the optical isolator 3
Incident on.

Signal light S emitted from the optical isolator 3
₃ has a high gain of the signal light near the wavelength of 1530 nm as shown in FIGS. 8 and 9, but the wavelengths of 1540 nm to 157
The gain in the 0 nm range is low. In order to flatten the gain from the wavelength of 1530 nm to the wavelength of 1570 nm, it is necessary to suppress the gain near the wavelength of 1530 nm, that is, the signal light power. Therefore, from the signal light S ₃ emitted from the optical isolator 3, only the signal light S ₅ having a very narrow wavelength near 1530 nm is separated by the optical multiplexer / demultiplexer 8.
₅ is incident on the Er-doped optical fiber 10.

The Er-doped optical fiber 10 attenuates the propagating signal light S _5, and the attenuated signal light S ₆ is combined with the signal light S ₄ incident on the optical multiplexer / demultiplexer 8 from the optical multiplexer / demultiplexer 8. Then, the wavelength band of the signal light S ₃ is reproduced. At this time, since the extremely narrow wavelength band near the wavelength of 1530 nm is attenuated to the level of the signal light S ₄ , the wavelength 15
It is possible to obtain a characteristic in which the gain is flattened over the range of 30 nm to 1570 nm.

FIG. 2 is a connection diagram showing a second embodiment of the wide band Er-doped optical fiber amplifier according to the present invention. Note that, in FIG. 2, the same reference numerals are used for the same elements as those shown in FIG. In the Er-doped optical fiber amplifier of FIG. 2, in addition to the configuration of FIG. 1, a WDM coupler 11 is provided between the Er-doped optical fiber 1 and the optical isolator 3.
(With the same structure as WDM coupler 4)
Pumping light source 1 to DM coupler 11 via optical fiber 13
2 (generating the excitation light 14) is combined. That is, it has a configuration capable of exciting the excitation light from both the forward and backward directions. And the excitation light sources 6, 1
2 both generate laser light having a wavelength of 0.98 μm, and the excitation light source 6 outputs 70 mW and the excitation light source 12 outputs 80 mW. Further, as the Er-doped optical fiber 10, an Er-doped multi-core optical fiber having the characteristics shown in FIG. 11 is used,
Its length was about 70 cm.

As a result, the signal light S ₂ output from the optical multiplexer / demultiplexer 9 was able to suppress the gain deviation within 1 dB over the wavelength range of 1530 nm to 1570 nm. Furthermore,
According to the configuration of FIG. 2, since the excitation light can be incident on the Er-doped optical fiber 1 from any direction,
It can be widely used as a preamplifier, a power amplifier, a loss compensation amplifier for various loss devices, and the like. Further, it can be applied to a high speed, large capacity, long distance transmission system, an optical CATV system, an optical subscriber system and the like.

FIG. 3 is a connection diagram showing a modification of the WDM coupler provided in the subsequent stage of the Er-doped optical fiber in the broadband Er-doped optical fiber amplifier according to the present invention. Note that FIG.
In FIG. 1, the same reference numerals are used for the same elements as those shown in FIGS. 1 and 2, and therefore, the description of the overlapping configuration and operation will be omitted below. The WDM coupler 11 may be connected and used as shown in FIG.
3 instead of the WDM coupler 11 of FIG.
May be used.

Here, the WDM coupler 11 is partially constructed by using an Er-doped optical fiber. That is, the two optical fibers 11a (lengths A to B) and the optical fiber 11b
(Lengths C to D) are arranged in parallel, and the parallel arranged portions are fused and stretched while being heated by a heating source (not shown) to form a desired joint E, and the Er-doped optical fiber 1 The signal light S _{3 in} the wavelength range from 1530 nm to 1570 nm and the excitation light 14 (wavelength 0.98 μm) from the excitation light source 12 can be combined.

An Er-doped optical fiber is used as the optical fiber 11a.
The signal light S optically amplified by using_ThreeIs the joint E
Signal is amplified separately from the Er-doped optical fiber 1 at
Light S ₇And is emitted from the portion of the coupling portion E. Only
Signal light S₇Exits the coupling portion E and B of the optical fiber 11a
Signal light near the wavelength of 1530 nm until reaching the position
Only undergoes strong damping. As a result, the optical isolator 3
The signal light incident on the light has a wavelength of 1530 nm to 1570 n.
It has a flat characteristic over m
Signal light S_TwoWill be output. This
As shown in FIG.
It is possible to eliminate the occurrence of peaks in the vicinity.

According to this structure, the optical control means capable of attenuating only the signal light in the specific wavelength range can be obtained with a simple structure, and the cost can be easily reduced.
FIG. 4 is a connection diagram showing a third embodiment of a broadband Er-doped optical fiber amplifier according to the present invention. Note that, in FIG. 4, the same reference numerals are used for the same components as those shown in FIGS. 1 to 3, and therefore, the description of the duplicated configuration and operation will be omitted below.

In FIG. 4, the optical multiplexers / demultiplexers 8 and 9 and the Er-doped optical fiber 10 are removed from the configuration of FIG. 2 and optical control means is provided at the place where the optical multiplexers / demultiplexers 8 and 9 were provided. The Er-added film 15 is provided.
This Er-added film 15 is a glass (or plastic) film containing an Er ₂ O ₃ film or an SiO ₂ film containing Er.
It is configured by forming a film or the like.

The Er-added film 15 has a wavelength of 1530n.
Acts as a neutral density filter for wavelengths near m,
It acts as an optical component that does not attenuate in other wavelength regions. In this case, the degree of attenuation of the signal light near the wavelength of 1530 nm can be controlled by adjusting the Er addition amount of the Er addition film 15. As described above, in the Er-doped optical fiber amplifier having the configuration of FIG.
Since it is possible to suppress only the signal light power in the vicinity of nm, it is possible to obtain flat characteristics over a wide band.

If the number of films of the Er-added film 15 is increased to form a multilayer, the amount of attenuation can be adjusted according to the number of layers. Further, when Er is added to the film having the band elimination filter structure having an attenuation peak for the light having the wavelength of 1530 nm (or the light having the wavelength shorter than 1530 nm), the attenuation amount in the 1530 nm band can be easily adjusted.

FIG. 5 is a connection diagram showing a fourth embodiment of a wide band Er-doped optical fiber amplifier according to the present invention. Note that, in FIG. 5, the same reference numerals are used for the same elements as those shown in FIGS. 1 to 4, and therefore, in the following, the description of the overlapping configuration and operation will be omitted. In FIG. 5, a WDM filter 16 is provided instead of the WDM coupler 4 having the configuration of FIG. 4, and a WD is used instead of the WDM coupler 11.
An M filter 17 is provided. This WDM filter 1
Reference numerals 6 and 17 are configured using interference film filters. Further, the Er-added film 15 is transferred from the position shown in FIG. 4 to the WDM filter 17, and the Er-added film 15 is attached to the back surface of the WDM filter 17 to form a light control means. A bidirectional pumping type optical amplifier is formed with such a configuration, and the attenuation in the 1530 nm band is Er as in the case of FIG.
The addition film 15 is used.

The Er-added film 15 is applied to the WDM filter 1
With the structure attached to 7, the mounting cost of the optical amplifier can be reduced and the size can be reduced.

[0038]

As described above, according to the present invention, the predetermined attenuation is performed only on the signal light in the specific wavelength band in which the gain is partially increased in the wavelength band of the signal light after the optical amplification. As a result, even in the wavelength characteristics after amplification, even if there is a part where the gain is partially projected and the gain is not flat, a flat gain characteristic can be obtained, and an optical amplifier with a flat gain and a high gain over a wide range can be obtained. It can be obtained with a simple configuration. It is also suitable for downsizing and cost reduction, and has excellent versatility.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a first embodiment of a broadband Er-doped optical fiber amplifier according to the present invention.

FIG. 2 is a connection diagram showing a second embodiment of a broadband Er-doped optical fiber amplifier according to the present invention.

FIG. 3 is a WDM provided downstream of an Er-doped optical fiber in a broadband Er-doped optical fiber amplifier according to the present invention.
It is a connection diagram which shows the modification of a coupler.

FIG. 4 is a connection diagram showing a third embodiment of a broadband Er-doped optical fiber amplifier according to the present invention.

FIG. 5 is a connection diagram showing a fourth embodiment of a broadband Er-doped optical fiber amplifier according to the present invention.

FIG. 6 is a cross-sectional view showing an example of a conventional Er-doped multicore optical fiber.

7 is a connection diagram showing a configuration of an optical amplifier using the Er-doped multicore optical fiber of FIG.

FIG. 8 is a wavelength characteristic diagram of a gain in the case where the amount of Al added is 8,500 ppm in the optical amplifier having the configuration of FIG.

9 is a wavelength characteristic diagram of gain in the case where the amount of Al added is 17,000 ppm in the optical amplifier having the configuration of FIG. 7.

FIG. 10 is a connection diagram showing a configuration of another conventional optical amplifier for which flattening is achieved.

FIG. 11 is a characteristic diagram showing a loss wavelength characteristic of an Er ⁺³ ion-doped optical fiber.

[Explanation of symbols]

 1 Er-doped optical fiber 2, 3 Optical isolator 4 WDM coupler 6, 12 Pumping light source 8, 9 Optical multiplexer / demultiplexer 10 Er-doped optical fiber 11a, 11b Optical fiber 15 Er-doped film 16, 17 WDM filter

Claims (5)

[Claims] 1. An optical fiber amplifier for performing optical amplification by merging and propagating signal light and pumping light into a first Er-doped optical fiber, wherein the gain is partially included in the wavelength band of the signal light after the optical amplification. A first optical multiplexer / demultiplexer provided at a stage subsequent to the first Er-doped optical fiber to demultiplex the rising signal light in a specific wavelength range, and the demultiplexed signal light in the specific wavelength range at a predetermined level. A second Er-doped optical fiber for attenuating the second Er-doped optical fiber, the signal light from the second Er-doped optical fiber, and the first Er-doped optical fiber
And a second optical multiplexer / demultiplexer that multiplexes the signal light from the optical multiplexer / demultiplexer (1). 2. An optical fiber amplifier for performing optical amplification by merging and propagating signal light and pumping light into an Er-doped optical fiber, wherein the gain partially increases in the wavelength band of the signal light after the optical amplification. An optical control means including an Er-doped member that attenuates only the signal light in the wavelength region to a predetermined level and allows other wavelength regions to pass without being attenuated is disposed in the subsequent stage of the Er-doped optical fiber. Broadband Er-doped optical fiber amplifier. 3. The broadband Er-doped optical fiber amplifier according to claim 2, wherein the light control means is a film doped with a predetermined concentration of Er. 4. The light control means is configured to include a film to which Er having a predetermined concentration is added, and a WDM filter configured by using an interference film filter and having the Er-added film attached thereto. The broadband Er-doped optical fiber amplifier according to claim 2. 5. The broadband Er-doped optical fiber amplifier according to claim 1, wherein the pumping light propagates to the first Er-doped optical fiber from a forward direction, a backward direction, or both directions.