JP2001156364A - Wide band optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide band optical amplifier which optically amplifies the signal light in a wider wavelength band. SOLUTION: Related to a wide band optical amplifier 1, optical amplification parts 301-30N are provided in parallel between a split means 10 and a wave synthesizing means 20. Related to the split means 10, a multi-wavelength signal light of multiplex wavelength is inputted and the signal light is split and outputted into split paths P1-PN. The optical amplification part 30n is provided on the slit path Pn, and optically amplifies the signal light transferred on the split path Pn for output. The central wavelength λn+1 of gain of the optical amplification part 30n+1 is longer than a central wavelength λn of gain of the optical amplification part 30n, with parts of the wavelength band wherein the optical amplification part 30n and the optical amplification part 30n+1 have gains overlapped each other (1<=n<=N-1). Related to the wave-synthesizing means 20, the signal lights outputted from the optical amplification parts 301-30N are inputted and the signal lights are wave-synthesized for output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier for collectively optically amplifying multi-wavelength signal light in a wavelength division multiplexing optical communication system.

[0002]

2. Description of the Related Art Wavelength division multiplexing (WDM)
The n Multiplexing) optical communication system generally performs optical communication using signal light of multiple wavelengths in the C band (wavelength 1530 nm to 1560 nm), and can transmit large-capacity information at high speed. In recent years, in order to further increase the capacity, in addition to the C band, the L band (wavelength
(70 nm to 1610 nm) as well. On the other hand, in an optical communication system, an optical amplifier that amplifies and outputs signal light is used to compensate for attenuation of signal light when propagating through an optical transmission line. But,
The wavelength band in which one optical amplifier has gain is limited. That is, generally, an optical amplifier having a gain in the C band does not have a gain in the L band. Similarly, an optical amplifier having a gain in the L band has no gain in the C band. Thus, for example, the literature "T. Naito, et al.," 1
Terabit / s WDM Transmission over 10,000 km ", ECOC '
99, PD2-1 (1999) "proposes a broadband optical amplifier capable of optically amplifying both C-band and L-band signal lights.

FIG. 10 is a schematic configuration diagram of a conventional broadband optical amplifier. This broadband optical amplifier comprises a C-band optical amplifying unit 30 _C and L between a branching unit 10 and a multiplexing unit 20.
Band optical amplifying section 30 _L is provided in parallel. The branching means 10 converts the input multi-wavelength signal light into the C band and the L band.
The signal is split into bands and output. C band optical amplifier 30
_C optically amplifies and outputs the C-band signal light output from the branching means 10. The L-band optical amplifier 30 _L optically amplifies the L-band signal light output from the branching unit 10 and outputs the signal. Then, the multiplexing means 20 multiplexes and outputs the signal lights that have been optically amplified by the C-band optical amplifier _30C and the L-band optical amplifier _30L, respectively.
FIG. 11 is a diagram showing gain characteristics of the conventional wideband optical amplifier. Gain characteristic of the wide band optical amplifier, C gain characteristic of band optical amplifying section 30 _C and L band optical amplifying section 30 _L
And the gain characteristics described above.

[0004]

However, in the above-mentioned conventional broadband optical amplifier, the branching means for splitting the input signal light into the C band and the L band and outputting the divided signal light has wavelengths λ _C1 to λ _C1 in the C band. In the band of λ _C2 and the band of wavelengths λ _{L1 to} λ _L2 in the L band, it is possible to output with sufficient transmittance, but even in the C band, the band of wavelength λ _C2 or more, and L Even within the band, in the band of wavelength λ _L1 or less, no light is transmitted or the transmittance is small. Therefore, as shown in FIG. 11, this conventional broadband optical amplifier cannot optically amplify signal light in the band of wavelengths λ _{C2 to} λ _L1 .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a broadband optical amplifier capable of optically amplifying signal light in a wider wavelength band.

[0006]

SUMMARY OF THE INVENTION A broadband optical amplifier according to the present invention comprises the steps of:
The signal light is branched into N (N ≧ 2) branch paths P ₁ to P ₁ .
A branching means for outputting to P _N, respectively, (2) provided on the N on the branch path P _n of the split path P ₁ to P _N, the signal light propagating through the branch path P _n and the optical amplifier output n pieces of the optical amplifier a _n to (1 ≦ n ≦ n), to input (3) the n optical amplifier _{a n (1 ≦ n ≦ n} ) signal light output from each of these Multiplexing means for multiplexing and outputting the above signal lights. The optical amplifier than the center wavelength of the gain of the optical amplifier A _n A _{n + 1} gain longer towards the center wavelength of the wavelength band optical amplifier A _n and the optical amplifier A _{n + 1} each having a gain Are overlapped with each other (1 ≦
n ≦ N−1).

The overall gain characteristic of this broadband optical amplifier is as follows:
N optical amplifiers A_n(1 ≦ n ≦ N) Each gain characteristic
It is a synthesis of Optical amplifier A_nAnd optical amplifier A
_{n + 1}Some of the wavelength bands that each have gain overlap each other.
(1 ≦ n ≦ N−1), this broadband optical amplification
The unit is each optical amplifier A_nInclude all wavelength bands with gain.
Have sufficient gain over a continuous wide wavelength band.
And multi-wavelength signal light in this wide wavelength band
Light can be amplified. And the optical amplifier A ₁But profit
The lower limit wavelength of the wavelength band having the gain is equal to or less than the lower limit wavelength of the C band.
The lower part, the optical amplifier A_NUpper limit of wavelength band where
If the wavelength is equal to or greater than the upper limit wavelength of the L band, this broadband light
Amplifiers include C-band, L-band and inter-band.
It has sufficient gain over a wide continuous wavelength band.

Further, the broadband optical amplifier according to the present invention is characterized by further comprising a gain equalizing means for equalizing the overall gain. In this case, the gain characteristics of the broadband optical amplifier become sufficiently and flat over a wide wavelength band, and this broadband optical amplifier collectively amplifies the multi-wavelength signal light of the wide wavelength band with uniform gain. can do.

Further, the broadband optical amplifier according to the present invention has N branch paths P ₁ to P ₁ from the branching means to the multiplexing means.
The signal light delay time of each of P _N is substantially equal to each other. In this case, in the band where the wavelength bands where the optical amplification unit _An and the optical amplification unit _{An + 1} each have gain overlap each other, the optical amplification unit _An and the optical amplification unit _{An + 1}
The signal lights that have been respectively optically amplified are output from the multiplexing means at substantially the same timing.

Further, the broadband optical amplifier according to the present invention has N branch paths P ₁ to P ₁ from the branching means to the multiplexing means.
It is characterized by further comprising delay time adjusting means for making the signal light delay times of the respective P _N substantially equal to each other. The delay time adjusting means may have a fixed adjustable delay time, may have a variable delay time, or may have a fixed and a variable delay time. It is preferable that the delay time is roughly adjusted by the fixed delay time adjusting means and the delay time is finely adjusted by the variable delay time adjusting means.

Further, in the broadband optical amplifier according to the present invention,
Preferably, the branching means includes a power splitter and / or a splitter. Also,
Preferably, each of the N optical amplifiers _An (1 ≦ n ≦ N) includes a rare-earth element-doped optical fiber amplifier or a semiconductor optical amplifier.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. In the following, the parameter N is an integer of 2 or more, and the parameter n is any integer of 1 to N unless otherwise specified.

(First Embodiment) First, a first embodiment of a broadband optical amplifier according to the present invention will be described. FIG.
1 is a schematic configuration diagram of a broadband optical amplifier 1 according to a first embodiment. The broadband optical amplifier 1, N pieces of the optical amplifying section 30 ₁ to 30 _N are provided in parallel between the branching means 10 and the combining means 20. The branching means 10 receives the wavelength-multiplexed multi-wavelength signal light, branches the signal light, and outputs the signal light to each of the N branch paths P _{1 to} P _N. This branching means 1
The wavelength band of the multi-wavelength signal light input to 0 includes the C band and the L band, and further includes a band between these two bands (this is referred to as an “inter-band band”).
The n-th optical amplifying section 30 _n, is provided on the branch path P _n, and outputs a signal light propagating through the branch path P _n by optical amplification. Multiplexing means 20, N pieces of the optical amplifying section 30 ₁ to 30 _N
The signal light output from each is input, and these signal lights are combined and output.

[0014] Figure 2 is a diagram showing a gain characteristic and broadband optical amplifier 1 overall gain characteristics of the optical amplifying section 30 _n of the broadband optical amplifier 1 according to the first embodiment. As shown in this figure, from the center wavelength λ _n of the gain of the _n- th optical amplifier 30 _n ,
(n + 1) The central wavelength λ _{n + 1} of the gain of the optical amplifier 30 _{n + 1} is longer (1 ≦ n ≦ N−1). In addition, a part of the wavelength band in which each of the n-th optical amplification unit 30 _n and the (n + 1) -th optical amplification unit 30 _{n + 1} has gain overlaps (1 ≦ n ≦
N-1). Lower wavelength lambda ₁₁ wavelength band first optical amplifying unit 30 ₁ has a gain substantially coincides with the lower limit wavelength in the C-band, or shorter than a lower limit wavelength in the C-band. The upper limit wavelength lambda _N2 wavelength band having the first N optical amplifying section 30 _N gain is approximately coincident with an upper limit wavelength L-band, or longer than the upper wavelength L-band.

The overall gain characteristic of the broadband optical amplifier 1 is N
Optical amplifiers 30₁~ 30_NCompile each gain characteristic
It will be. That is, this broadband optical amplifier 1 has C
Contiguous broadband including band, L-band and interband
Wavelength band λ₁₁~ Λ_N2Have sufficient gain over
And this wide wavelength band λ₁₁~ Λ_N2Multi-wavelength signal light
Can be collectively optically amplified. The wavelength band λ
₁₁~ Λ_N2The gain characteristic of the broadband optical amplifier 1 over a wide range is flat.
Is desirable. Therefore, the n-th optical amplifier 30 _nCenter of
Wavelength λ_nAre substantially equal to each other, and the n-th optical amplifier
30_nCenter wavelength λ_nGain smaller than the gain at
Wavelength λ_n1Band or wavelength λ below_n2Heavy in the above band
Preferably, they match.

In the broadband optical amplifier 1 configured as above, the nth optical amplifier _30n and the (n + 1) th optical amplifier _{30n + 1} have the gains in the overlapping band. It is important that the signal light optically amplified by the _n- th optical amplifying unit 30 _n and the signal light optically amplified by the (n + 1) -th optical amplifying unit 30 _n are output from the multiplexing means 20 at substantially the same timing. It is. If the delay times are different, a signal shift occurs at the time of output from the multiplexing means 30. Therefore, when the bit rate is 2.5 Gbps, the difference between the delay times is set to 40 ps or less (8 mm or less when converted to the difference in the length of the optical fiber). When the bit rate is 10 Gbps, the difference between the delay times is set to 10 ps or less (2 mm or less when converted to the difference in the length of the optical fiber). When the bit rate is 40 Gbps, the difference in delay time is set to 2.5 ps or less (0.5 mm or less in terms of the difference in the length of the optical fiber). Further, it is preferable to provide delay time adjusting means for making the signal light delay times of the respective branch paths _Pn from the branching means 10 to the multiplexing means 20 substantially equal to each other. In particular, a delay time difference of 10 ps is provided. In order to make the delay time or less, it is preferable to provide a delay time adjusting means capable of adjusting the delay time.

As the n-th optical amplifier 30 _n suitably used in such a broadband optical amplifier 1, a rare-earth element-doped optical fiber amplifier or a semiconductor optical amplifier can be used.
A rare earth element doped optical fiber amplifier is a rare earth element (E
(r, Tm, Pr, Nd, etc.) using an optical fiber doped in the optical waveguide region as an optical amplifying medium, supplying excitation light to the optical fiber, and optically amplifying the signal light input to the optical fiber. Output. This optical fiber amplifier adjusts the types and concentrations of elements (including co-doping elements in addition to rare earth elements) added to the optical fiber, and the length of the optical fiber to adjust the C band, L band, and interband. The center wavelength of the gain can be adjusted within a continuous wide wavelength band including the band. The Er element is particularly preferable as the rare earth element to be added. on the other hand,
The semiconductor optical amplifier uses a semiconductor having a multilayer structure including an active layer as an optical amplifying medium, and optically amplifies and outputs signal light input to the active layer. This semiconductor optical amplifier can adjust the center wavelength of the gain in a continuous wide wavelength band including the C band, the L band, and the interband by adjusting the types and the component ratios of the contained elements. Further, by combining a rare earth element-doped optical fiber amplifier and a semiconductor optical amplifier with a filter having a predetermined loss characteristic, the gain characteristic as a whole can be adjusted.

It is conceivable to use a Raman distributed optical fiber amplifier as the optical amplifier 30 _n . In this case, the length of the optical fiber as the optical amplification medium needs to be several hundred to several km or more. Therefore, the n-th optical amplifier 30
The delay time of the signal light optically amplified by the _n- th optical amplifying unit 30 _n and the (n + 1) _-th and (n + 1) -th optical amplifying units 30 _{n + 1} in a band in which the wavelength bands having gains overlap each other. It is difficult to make the delay times of the signal lights optically amplified by the optical amplifying unit 30 _n substantially equal to each other. Therefore, it is not preferable to use a Raman distributed optical fiber amplifier as the optical amplifier 30 _n .

The branching means 10 preferably used in such a broadband optical amplifier 1 includes the following. The simplest configuration of the branching means 10 is to branch the power of the input signal light of each wavelength into N and output it. In this case, the signal light output from the branching unit 10 to each branch path _Pn includes all the wavelength components of the signal light input to the branching unit 10, but is compared with the power of the signal light input to the branching unit 10. Power of 1 / N.

When the number N of optical amplifiers provided in parallel is two, it is preferable to use a branch coupler as the branching means 10. FIG. 3 is a configuration diagram of the broadband optical amplifier 1 using a branch coupler as the branching unit 10.
In this figure, a branch coupler is also used as the multiplexing means 20. The branch coupler is configured such that two optical waveguides (optical fibers or planar optical waveguides) are arranged close to each other so that optical coupling occurs between the two. The light transmission characteristics are complementary to each other as shown in FIG. The branch coupler used as the branching means 10 in the broadband optical amplifier 1 is such that the peak wavelength of the light output to the branch path P ₁ matches the center wavelength λ ₁ of the gain of the first optical amplifying unit 30 ₁ , and It is designed to the peak wavelength of light output to the path P ₂ and the central wavelength lambda ₂ of the second gain of the optical amplifier 30 ₂ is identical.

When the number N of optical amplifiers provided in parallel is more than 2, it is preferable to use a combination of a power splitter and a duplexer as the splitting means 10. FIG. 5 is a diagram showing a part of the configuration of the broadband optical amplifier 1 using a combination of a power splitter and a duplexer as the splitting means 10. In this figure, the number N of the optical amplifiers is six. The branching means 10 shown in FIG.
Power splitter 11, first duplexer 12, and second duplexer 1
3 The power splitter 11 splits the power of the input signal light of each wavelength into two, outputs one split to the first splitter 12, and outputs the other split to the second splitter 13. Then, as shown in FIG. 6, first duplexer 12, an input signal light is demultiplexed first optical amplifying unit 30 ₁ is light in a wavelength band is output to the branch path P ₁ having a gain the third optical amplifier 30 ₃ outputs a light in a wavelength band having a gain to the branch path P _3, the fifth optical amplifier 30 ₅ outputs the light in a wavelength band having a gain to the branch path P _5. On the other hand, the second duplexer 13
The input signal light is demultiplexed second optical amplifier 30 ₂ is the light of the wavelength band is output to the branch path P ₂ having a gain, a fourth optical amplifier 30 ₄ wavelength band having a gain and outputs the light to the branching path P _4, sixth optical amplifying section 30 ₆ outputs the light in a wavelength band having a gain to the branch path P _5. By branching the power after branching in this way and separating the wavelength bands output to the respective branch paths at the time of branching, the branch loss can be reduced.

(Second Embodiment) Next, a second embodiment of the broadband optical amplifier according to the present invention will be described. FIG.
FIG. 3 is a schematic configuration diagram of a broadband optical amplifier 2 according to a second embodiment. The broadband optical amplifier 2, to the broadband optical amplifier 1 (Fig. 1) according to the first embodiment, in which N filters 40 ₁ to 40 _N is applied. FIG.
Each filter 40 _n loss characteristics of the broadband optical amplifier according to the embodiment, the total gain characteristics of all the filter 40 _1-40 overall loss characteristics of the _N, the total optical amplifying unit 30 ₁ to 30 _N, and the entire broadband optical amplifier 2 FIG. 6 is a diagram showing gain characteristics of the multiplexor.

The n-th filter 40 _n is provided on a branch path P _n between the branching means 10 and the multiplexing means 20.
The loss is large in the wavelength band _where the gain of the n-th optical amplifier 30n is large. N filters 40 ₁ to 40 _N acts as a gain equalization means for equalizing the overall gain of the broadband optical amplifier 2. That is, as shown in FIG. 8, all filters 40 ₁ ~
Overall loss of 40 _N is greater in the total gain is large wavelength range of the total optical amplifying unit 30 ₁ to 30 _N. Therefore, the gain characteristics of the broadband optical amplifier 2 are sufficiently and flat over a continuous wide wavelength band λ _{11 to} λ _N2 including the C band, the L band, and the inter-band, and the broadband optical amplifier 2 has a wide gain characteristic. Signal light of multiple wavelengths in the wavelength bands λ _{11 to} λ _N2 can be collectively amplified with uniform gain.

[0024] Incidentally, as the n filter 40 _n, the long period optical fiber grating insertion loss is small can be preferably used. This long-period optical fiber grating
An optical fiber grating in which a refractive index modulation is formed in an optical waveguide region of an optical fiber, wherein a period of the refractive index modulation is formed so as to be coupled to a cladding mode for propagating light of a specific wavelength, and has a predetermined wavelength. Some of the light propagating in the band is converted into a cladding mode to give a loss, and as a result, the wavelength dependence of the transmittance is caused. Also, a dielectric multilayer filter is preferably used as the n-th filter 40 _n . The n-th filter 40 _n does not necessarily need to be provided on the branch path P _n , and may be provided before the branching unit 10 or after the combining unit 20.

(Third Embodiment) Next, a third embodiment of the broadband optical amplifier according to the present invention will be described. FIG.
FIG. 6 is a schematic configuration diagram of a broadband optical amplifier 3 according to a third embodiment. The broadband optical amplifier 3, to the broadband optical amplifier 1 according to the first embodiment (FIG. 1), the N fixed delay element 50 ₁ to 50 _N and N variable delay elements 60 ₁ -
60 _N is added.

The n-th fixed delay element 50_nAnd nth variable delay
Rolling element 60_nIs between the branching means 10 and the multiplexing means 20
Branch path P_nProvided from the branching means 10
For adjusting the signal light delay time to reach the wave means 20
It is. N-th fixed delay element 50 _nHas a fixed delay time
There is a branch route P_nSignal light delay
Roughly adjust the time. N-th variable delay element 60_nIs delayed
The interval is variable, allowing fine adjustment of the signal light delay time.
Wear. That is, the N fixed delay elements 50₁~ 50_NAnd
And N variable delay elements 60₁~ 60_NIs the branching means 10
From each branch path P to the multiplexing means 20_nSignal light slow
It works as a delay time adjusting means to make the delay times approximately equal to each other.
To use.

As already described in the description of the first embodiment, for example, when the bit rate is 2.5 Gbps, the difference in delay time needs to be 40 ps or less.
The difference in length of the optical fibers must be 8 mm or less.
However, when the n-th optical amplification unit 30 _n is a rare-earth-element-doped optical fiber amplifier, the length of the rare-earth-element-doped optical fiber, which is an optical amplification medium, is not always constant, and is actually about several tens of meters. There may be variations. Therefore, the n-th fixed delay element 50 n is adjusted according to the actual length variation of the rare-earth element-doped optical fiber of the n-th optical amplifier 30 _n.
Insert an optical fiber for transmission as _n . That is, the optical length of the branch path _Pn including the rare earth element-doped optical fiber of the n-th optical amplification unit 30 _n and the n-th fixed delay element (transmission optical fiber) 50 _n is made uniform regardless of the parameter n. To be. By doing so, the branching means 1
The signal light delay time of each branch path _Pn from 0 to the multiplexing means 20 can be made equal to each other.

Also, the higher the bit rate, the more
Delay time difference is small, and the
The difference becomes shorter. For example, if the bit rate is 40 Gbps
The delay time difference must be less than 2.5 ps
And the difference in length of the optical fiber is 0.5 mm or less
There is a need. Thus, the optical fiber length is several mm or
When it is necessary to evenly align at the level of mm or less,
N-th fixed delay element 50 _nN-th variable delay element 60_n
Is used. N-th variable delay element 60_nUsing
Each branch from the branching means 10 to the multiplexing means 20
Route P_nThe signal light delay times of
Can be done.

The n-th variable delay element 60_nAs the temperature control
Transmission optical fiber wound on an adjustable bobbin
You. This is to adjust the temperature of this transmission optical fiber.
The effective refractive index is adjusted with
Fine-tune the optical length (ie, delay time). Some
Is effective due to elongation strain by applying stress to the transmission optical fiber.
The optical index of this transmission optical fiber
Fine-tune the length. Using such transmission optical fiber
N-th variable delay element 60_nIs about tens to hundreds of ps
Fine adjustment of the delay time is possible in the range of. Therefore,
N-th fixed delay element 50_nN-th variable delay element 60_n
, The n-th fixed delay element 50 _nAdjusted by
The remaining delay time that cannot be removed is changed to the n-th variable delay element 6.
0_nCan be adjusted.

[0030]

As described in detail above, the broadband optical amplifier according to the present invention has a N-band between the branching means and the multiplexing means.
Comprising a number of optical amplifier A ₁ to A _N in parallel, the optical amplifying section from the center wavelength of the gain of the optical amplifier A _n A _{n + 1} towards longer the center wavelength of the gain, optical amplifier A _n and A part of the wavelength band in which each of the optical amplification units _{An + 1} has a gain overlaps with each other (1).
≤n≤N-1). The overall gain characteristic of this broadband optical amplifier is a sum of the gain characteristics of each of the N optical amplification units _An (1 ≦ n ≦ N). Moreover, the wide-band optical amplifier becomes a have a sufficient gain over a wide wavelength band each optical amplifier A _n are continuously including all wavelength bands having a gain, a multi-wavelength signal light in the wide wavelength band Optical amplification can be performed collectively.

The lower limit wavelength of the wavelength band in which the optical amplifier A ₁ has gain is equal to or less than the lower limit wavelength of the C band, and the optical amplifier A _N
If the upper limit wavelength of the wavelength band having the gain is equal to or larger than the upper limit wavelength of the L band, this broadband optical amplifier can be used for the C band, L band
It has sufficient gain over a continuous wide wavelength band, including bands and interbands. Therefore, the WDM optical communication system using the broadband optical amplifier can use not only the C band and the L band but also the signal light in the inter-band band, and can perform a larger-capacity optical communication.

Specifically, the broadband optical amplifier described in the literature cited in the section of the prior art has a wavelength of 154 as the C band.
A wavelength band of 4.53 nm to 1561.83 nm (bandwidth 17 nm), and a wavelength of 1575.3 as an L band.
7 nm to 160.17 nm wavelength band (bandwidth 25n
m), the signal light can be optically amplified. But,
The broadband optical amplifier of this document has a wavelength of 1561.83 nm.
１５1575.37 nm band between bands (bandwidth 13n
In m), the signal light cannot be optically amplified. On the other hand, the broadband optical amplifier according to the present invention can optically amplify signal light not only in the C band and the L band, but also in the interband. Therefore, in contrast to the broadband optical amplifier described in the literature cited in the section of the prior art, the broadband optical amplifier according to the present invention and the WDM optical communication system using the same have significantly increased the wavenumber of signal light that can be wavelength-multiplexed. Can be increased.

When a gain equalizing means for equalizing the entire gain is further provided, the gain characteristics of the broadband optical amplifier become sufficiently and flat over a wide wavelength band. Signal light of multiple wavelengths in a wide wavelength band can be collectively amplified with uniform gain.

When the signal light delay times of the _N branch paths P _{1 to} P _N from the branching means to the multiplexing means are substantially equal to each other, the optical amplifiers _An and A
_{In the} band in which the wavelength bands each having _{n + 1} gain overlap each other, the signal light optically amplified by each of the optical amplification unit _An and the optical amplification unit _{An + 1} is output from the multiplexing unit at substantially the same timing. .

It is preferable to further comprise delay time adjusting means for making the signal light delay times of the _N branch paths P _{1 to} P _N from the branch means to the multiplexing means substantially equal to each other. The delay time adjusting means may have a fixed adjustable delay time, may have a variable delay time, or may have a fixed and a variable delay time. It is preferable that the delay time is roughly adjusted by the fixed delay time adjusting means and the delay time is finely adjusted by the variable delay time adjusting means.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a broadband optical amplifier according to a first embodiment.

FIG. 2 is a diagram illustrating a gain characteristic of each optical amplification unit of the broadband optical amplifier according to the first embodiment and a gain characteristic of the entire wideband optical amplifier.

FIG. 3 is a configuration diagram of a broadband optical amplifier using a branch coupler as a branching unit.

FIG. 4 is a diagram illustrating transmission characteristics of light from an input port of a branch coupler to each of two output ports.

FIG. 5 is a diagram showing a part of the configuration of a broadband optical amplifier using a combination of a power splitter and a splitter as a splitting means.

FIG. 6 is a diagram showing light transmission characteristics of each demultiplexer of the branching unit shown in FIG. 5;

FIG. 7 is a schematic configuration diagram of a broadband optical amplifier according to a second embodiment.

FIG. 8 is a diagram showing a loss characteristic of each filter of the broadband optical amplifier according to the second embodiment, a total loss characteristic of all the filters, a total gain characteristic of the all-optical amplifier, and a gain characteristic of the entire wide-band optical amplifier. is there.

FIG. 9 is a schematic configuration diagram of a broadband optical amplifier according to a third embodiment.

FIG. 10 is a schematic configuration diagram of a conventional broadband optical amplifier.

FIG. 11 is a diagram illustrating a gain characteristic of a conventional broadband optical amplifier.

[Explanation of symbols]

1-3 broadband optical amplifiers, 10 branching means, 20 multiplexing means, 30 _n n-th optical amplifier, 40 _n n-th filter, 5
0 _n ... n-th fixed delay element, 60 _n ... n-th variable delay element.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04J 14/00 14/02

Claims (6)

[Claims] 1. A multi-wavelength multiplexed signal light is input, and the signal light is branched and divided into N (N ≧ 2) branch paths P.
A branching means for outputting to ₁ to P _N, respectively, provided on the branch path P _n of said N branch path P ₁ to P _N, the signal light propagating through the branch path P _n and the optical amplifier output n pieces of the optical amplifier a _n to (1 ≦ n ≦ n), said n optical amplifier _{a n (1 ≦ n ≦ n} ) to input signal light output from each of these signals and a multiplexing means for outputting the optical multiplexing, the optical amplifying section from the center wavelength of the gain of the optical amplifier a _n a _{n + 1} towards longer the center wavelength of the gain, optical amplifier a _n and light Amplifier A
A wideband optical amplifier, wherein a part of wavelength bands each having a gain of _{n + 1} overlap with each other (1 ≦ n ≦ N−1). 2. The broadband optical amplifier according to claim 1, further comprising a gain equalizing means for equalizing the entire gain. 3. The wide band according to claim 1, wherein the signal light delay times of the _N branch paths P _{1 to} P _N from the branching unit to the multiplexing unit are substantially equal to each other. Optical amplifier. 4. The apparatus according to claim 1, further comprising delay time adjusting means for making the signal light delay times of said N branch paths P _{1 to} P _N from said branch means to said multiplexing means substantially equal to each other. The broadband optical amplifier according to claim 1, wherein 5. The broadband optical amplifier according to claim 1, wherein said branching means includes at least one of a power splitter and a duplexer. 6. The N optical amplifiers A _n (1 ≦ n ≦ N).
2. The broadband optical amplifier according to claim 1, wherein each of the optical amplifiers includes a rare earth element doped optical fiber amplifier or a semiconductor optical amplifier.