JP3507014B2 - Optical amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier used in an optical fiber communication system, an optical signal processing system and the like.

[0002]

2. Description of the Related Art The basic structure of a conventional optical amplifier is shown in FIG. This optical amplifier has two amplification units (amplification unit-L, amplification unit-S) having different gain bands, a demultiplexer and a multiplexer, and couples the two gain bands in the wavelength region. By doing so, we are aiming for a wider band ("Broadband and gai
n-flattened amplifier composed of a 1.55 μm-band
and a 1.58 μm-band Er ³⁺ -doped fiber amplifier i
na parallel configuration ", M. Yamada et al., IEE
Electronics Letters, Vol.33, No.8, 1997, pp.710-7
11 (Reference 1)).

Several types of demultiplexers and multiplexers are used, such as a dielectric multilayer filter and a set of a circulator and a fiber grating. An example using a dielectric multilayer filter is described in the following document. (Reference 1) "Broadband and gain-flattened amplifier
composed of a 1.55μm-band and a 1.58μm-band Er
³⁺ -doped fiber amplifier in a parallel configurati
on ", M. Yamada et al., IEE Electronics Letters, Vo
l.33, No.8, 1997, pp.710-711 (Reference 2) Japanese Patent Laid-Open No. 10-229238 (Heisei 10)
(August 25, 2013) (Reference 3) Japanese Patent Laid-Open No. 11-204859 (1999)
(July 30, 2013) (Reference 4) International Application Published Unde
r The Patent Cooperation Treaty, PCT / US98 / 16558, "
Optical amplifier apparatus ", International public
ation date April 8, 1999, International Publicatio
n Number WO 99/17410

An example using a set of a circulator and a fiber grating is described in the following document. (Reference 5) European Patent Application, EP 0 883 21
8 A1, "Wide band optical amplifier", Publication d
ate 09.12.1998 (Reference 6) "A gain-flattened ultra wide band EDFA f
or high capacity WDM optical communications system
s ", Y. Sun et al., Technical Digest of ECOC'98, p
p.53-54, 1998

There are also documents in which the type is not specified; (Reference 7) JP-A-4-101124 (April 4, 1992).
(May 2)

[0006] In all the above-mentioned documents, it is stated that the wavelength separation characteristics of the demultiplexer and the multiplexer are complete or not a particular problem. However, as will be concretely shown below, its wavelength separation characteristic is incomplete, which causes a problem depending on the application form and situation of the optical amplifier.

First, the most typical case will be described in which the demultiplexer and the multiplexer are dielectric multilayer filters. FIG. 1 shows the configuration of a conventional optical amplifier.
(A) shows that the demultiplexer and the multiplexer are long wavelength transmission type (L
Type) dielectric multilayer filter (demultiplexer-L
(3), multiplexer-L (4)), and FIG. 1 (b) uses a dielectric multi-layer film filter of the short wavelength range transmission type (S type) as the demultiplexer and the multiplexer. This is the case (demultiplexer-S (5), multiplexer-S (6)).

The amplifying section has a gain medium and a pumping section for pumping the gain medium, and examples thereof include a rare earth-doped fiber amplifier, a fiber Raman amplifier, and a semiconductor laser amplifier. As the rare earth-doped fiber amplifier, there is an erbium-doped fiber amplifier or the like, and in particular, a flat gain band is expanded by a gain equalizer (H. Masud
a et al., IEE Electronics Letters, Vol.34, No.6, 1
998, pp. 567-568 (see Reference 8)) is advantageous because a large total gain bandwidth can be obtained.

In an optical fiber communication system, generally, the wavelength-multiplexed signal light is incident on the optical amplifier.
Further, in an optical signal processing system for measurement or the like, generally wavelength-multiplexed light or light of a single wavelength is incident.

FIG. 2 shows the structure of the demultiplexer. FIG. 2 (a) is a structure using an L type dielectric multilayer film filter (demultiplexer-L), and FIG. 2 (b) is an S type. It is a configuration (demultiplexer-S) using a dielectric multilayer filter. The demultiplexer-L outputs the light of the long wavelength λl from the transmitted light port (1) and the light of the short wavelength λs to the incident light of the short wavelength λs and the long wavelength λl from the common optical port (c). It is emitted from the reflected light port (s). On the other hand, the demultiplexer-S emits the light of the long wavelength λl from the reflected light port (1) for the incident light of the short wavelength λs and the long wavelength λl from the common optical port (c) and outputs the light of the short wavelength λs. Light is emitted from the transmitted light port (s).

FIG. 3 shows the structure of the multiplexer. FIG. 3 (a) is a structure using an L-type dielectric multilayer filter (combiner-L), and FIG. 3 (b) is an S-type. It is a configuration (multiplexer-S) using a dielectric multilayer filter. The multiplexer-L has a long wavelength λ for the short wavelength λs incident light from the reflected light port (s) and a long wavelength λl incident light from the transmitted light port (1).
The light of 1 and the short wavelength λs is emitted from the common optical port (c). On the other hand, the multiplexer-S has a long wavelength λl and a short wavelength λs for the short wavelength λs incident light from the transmitted light port (s) and the long wavelength λl incident light from the reflected light port (1). Light is emitted from the common optical port (c).

In FIG. 1, the branching filter (branching filter-L,
The demultiplexers-S) 3 and 5 have the long wavelength λ according to the above operation.
1 and the short wavelength λs wavelength-multiplexed signal light is converted into the long wavelength λl.
Signal light having a short wavelength λs and a signal light having a long wavelength λl and a signal light having a short wavelength λs are respectively amplified by amplifiers (amplifier-L, amplifier-S) 1 and 2. , And then output after being multiplexed by the multiplexers 4 and 6.

[0013]

However, the above-mentioned optical amplifier has the following problems.

FIG. 4 shows the gain spectra of the amplifying sections (amplifying section-L and amplifying section-S) 1 and 2, and FIG.
FIG. 4A shows the entire gain band, and FIG.
The boundary wavelength band of the two wavelength bands of the L and the amplification unit -S (wavelength λtr
It shows the vicinity of -s to λtr-1). In FIG. 4B, an arbitrary wavelength in the amplification unit-L is λl *, and the amplification unit-
Let λs * be an arbitrary wavelength in S, and G be the peak gains of the amplification unit-L and the amplification unit-S, and the wavelengths λl * and λs *.
The gain at is G *.

FIG. 5 shows the loss spectrum of the L-type demultiplexer. The transmission loss between the ports c and s and the transmission loss between the ports c and l (Lcs1 and Lcs, respectively) shown in FIG. Lcl1). 5A shows the entire gain band, and FIG. 5B shows the vicinity of the boundary wavelength band. Lcs1 and Lc
In both l1, the signal light wavelengths are the boundary wavelengths (λtr
The loss value increases as the distance from -s and λtr-1) moves outside the gain band.

However, the loss Lcs1 between the port s which is the reflected light port and the common optical port c is near a certain fixed value on the long wavelength side of the wavelength λtr-l because of the residual reflection in the dielectric multilayer filter. Is restricted to.

The typical value of the difference between the wavelengths λtr-s and λtr-1 (referred to as the boundary wavelength band width) is about 5 nanometers (nm) to 10n near 1.5 micrometers (μm).
m, said limit value and typical loss values at wavelength λs * are likewise about 10 dB and about 20 dB. The boundary wavelength band width and the slope of the loss spectrum curve in the vicinity of the boundary wavelength band depend on the parameters (composition and the number of layers of the multilayer film) of the dielectric multilayer filter.

FIG. 6 shows the loss spectrum of the S-type duplexer. The transmission loss between port c and port s and the transmission loss between port c and port 1 (Lcs2 and Lcs, respectively) shown in FIG. Lcl2). 6 (a) shows the entire gain band, and FIG. 6 (b) shows the vicinity of the boundary wavelength band. Lcs2 and Lc
In both l2, the signal light wavelength is the boundary wavelength (λtr
The loss value increases as the distance from -s and λtr-1) moves outside the gain band.

However, the loss Lc12 between the port 1 which is the reflected light port and the common optical port c is near a certain constant value on the short wavelength side of the wavelength λtr-s because of the residual reflection in the dielectric multilayer filter. Is restricted to.

The typical value of the difference between the wavelengths λtr-s and λtr-1 (referred to as the boundary wavelength band width) is about 5 in the vicinity of 1.5 μm.
Typical values of the loss values at nm to 10 nm, said limit value and wavelength λl * are likewise about 10 dB and about 20 dB. The boundary wavelength width and the slope of the loss spectrum curve in the vicinity of the boundary wavelength range depend on the parameters (composition and number of layers of the multilayer film) of the dielectric multilayer filter.

The loss spectra of the L-type multiplexer and the S-type multiplexer are shown in FIGS. 5 and 6 from the reciprocity of optical propagation.
It is the same as the loss spectrum of the L-type demultiplexer and the S-type demultiplexer shown in FIG. That is, the loss value is the same if the transparent ports are the same.

FIG. 7 shows a loss spectrum of a path of a conventional optical amplifier. The paths are a path passing through the amplification section -L and a path passing through the amplification section -S, and the loss of the path is the multiplexer. And the loss of the duplexer (in dB (decibel) unit). 7A shows the case where the L-type demultiplexer and the L-type multiplexer are used (FIG. 1A), and FIG.
(B) shows the case where an S-type demultiplexer and an S-type multiplexer are used (see FIG. 1).
(B)) is shown respectively.

In the case of the L type, the loss value (L1) at the wavelength λl * is limited to about 20 dB which is twice the limit value (about 10 dB) in the path passing through the amplifying section -S. There is. However, if 10 dB and 20 dB are described as a dimensionless quantity, they are 10 and 100, and the latter is 10 times the former. On the other hand, in the case of S type,
In the path that passes through the amplification unit-L, the loss value (Ls) at the wavelength λs * is 2 which is the limit value (about 10 dB).
It is limited to about 20 dB, which is double.

As described above, in the vicinity of the boundary wavelength range,
Since the wavelength demultiplexing characteristics of the demultiplexer and the multiplexer are not perfect, the signal light of a certain wavelength (defined as wavelength λl *) is emitted from the original path (passes through the amplification unit -L). In addition, there is residual light from the other path (passes through the amplification unit -S).

The optical powers of the outgoing light and the residual light of the original path are P and P *, respectively. If P * is not sufficiently small compared to P, coherent interference occurs,
This causes a problem that interference noise is added to the signal light. For example, in an optical fiber communication system, the code error rate increases and system performance deteriorates.

In the configuration using the L-type demultiplexer and the L-type multiplexer (FIG. 1A), P and P * at the wavelength λl * are used.
Is P = Pin + G, P * = Pin + G * -Ll (1) P-P * = G-G * + Ll (2) where Pin (dBm unit) is the input signal light power. However, the wavelength-independent loss of the demultiplexer and the multiplexer is ignored because it is small for the sake of simplicity, and Ll is the path loss described in FIG. Here, for the sake of simplicity, if the difference between G and G * is small compared to Ll and ignored, then P and P *
The difference is L1 from the above equation (2). In the example of FIG. 7, Ll was about 20 dB, but this value is not sufficiently large, so the interference noise occurs.

The same can be said for the configuration using the S-type demultiplexer and the S-type multiplexer (FIG. 1B). That is,
P and P * at the wavelength λs * are input signal light powers P
As in (dBm unit), P = Pin + G, P * = Pin + G * -Ls (3) P-P * = G-G * + Ls (4) However, Ls is the path loss described in FIG. Here, for the sake of simplicity, if the difference between G and G * is small compared to Ls and ignored, the difference between P and P * is Ls from the above equation (4). In the example of FIG. 7, Ls was about 20 dB, but since this value is not sufficiently large, the interference noise occurs.

The optical power difference P- where the interference noise can be ignored
If P * is, for example, 30 dB, the gain difference GG * is 1
In the wavelength range of 0 dB or less, the interference noise cannot be ignored.

In the configuration using the L-type demultiplexer and the L-type multiplexer, the signal light wavelength on the long wavelength side where the gain difference GG * is 10 dB is set to λl ** as shown in FIG. To do. Also,
The gain value at this time is G **. As shown in FIG. 7A, in the vicinity of the signal light wavelength λs ** (the optical power difference P− on the short wavelength side
The optical power difference P-P * is 30 dB or less in the wavelength range between the signal light wavelength λl ** and the wavelength where P * is 30 dB), and the interference noise cannot be ignored in this wavelength range. The same applies to the configuration using the S-type demultiplexer and the S-type multiplexer. Therefore, there arises a problem that the usable signal light wavelength range is limited.

As described above, in the conventional technique using the dielectric multilayer filter, the interference noise is added in the vicinity of the boundary wavelength range, so that there is a problem that the usable signal light wavelength range is limited. Even when a demultiplexer and a multiplexer other than the dielectric multilayer filter are used, the same problem occurs because the wavelength separation characteristics of the demultiplexer and the multiplexer are not perfect.

An object of the present invention is to solve the above-mentioned drawbacks and to provide an optical amplifier having a wide range of usable signal light wavelengths.

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[Means for Solving the Problems ]
Therefore , the present invention is arranged in parallel with a demultiplexer using a dielectric multilayer filter that demultiplexes the input signal light according to the wavelength, and has different amplification wavelength bands, and outputs from the demultiplexer. The amplified signal lights are respectively emitted from the amplifying units by using two amplifying units for amplifying the signal lights and a dielectric multilayer filter for transmitting a wavelength band different from that of the dielectric multilayer filter provided in the demultiplexer. an optical amplifier signal light and a multiplexer for multiplexing the said demultiplexer, the border
A long-wavelength transmission type dielectric multilayer filter that transmits wavelengths longer than the field wavelength is used .
The gist is an optical amplifier characterized by using a short- wavelength transmission type dielectric multi-layered film filter that transmits a wavelength on the shorter wavelength side .

[0038]

Further, according to the present invention , the wavelength of the input signal light is changed.
Demultiplexer using dielectric multi-layer film filter
Are arranged in parallel and have different amplification wavelength bands.
To amplify the signal light emitted from the demultiplexer.
And two dielectric layers provided in the demultiplexer
Dielectric multilayer film that transmits different wavelength band from membrane filter
The signals output from the amplifiers are filtered using filters.
An optical amplifier comprising: a multiplexer that multiplexes the signal light, wherein the demultiplexer uses a short-wavelength transmission type dielectric multilayer filter that transmits a shorter wavelength side than a boundary wavelength. multiplexer is photosensitizers characterized in that with the aid of a long wavelength transmission type dielectric multi-layer film filter transmitting wavelengths longer than the boundary wavelength
The width is the gist .

[0040]

[0041]

[0042]

[0043]

The present invention also provides an optical amplifier in which the optical amplifier as described above is used as one of the amplifying sections arranged in parallel.

[0045]

[0046]

[0047]

[0048]

FIG. 8 shows the first configuration of the optical amplifier of the present invention. 8A shows a configuration using an L-type demultiplexer and an S-type multiplexer, and FIG. 8B shows a configuration using an S-type demultiplexer and an L-type multiplexer. FIG. 9 shows the loss spectrum of the path in the first configuration of the present invention. The sum of losses (in dB) of the demultiplexer and the multiplexer is shown for the path passing through the amplification unit -L and the path passing through the amplification unit -S. This loss spectrum is obtained from the loss spectra of FIGS. 5 and 6 described in the prior art. The loss value is a typical value as described in the case of the conventional technique.

The power difference PP of the signal light is 30 dB.
The following wavelength range is from near the wavelength λs * to near the wavelength λl * in FIG. This wavelength difference (near λl * and λ
The difference in the vicinity of s *) is considerably smaller than the above-mentioned wavelength difference (difference in the vicinity of λl ** and λs **) in the above-mentioned conventional technique.
That is, according to the first configuration, the signal light wavelength range that suffers the interference noise is narrower than that of the conventional technique, and thus the usable signal light wavelength range can be widened.

A second configuration of the optical amplifier of the present invention is shown in FIG. 10A shows a configuration using an L-type demultiplexer and an L-type multiplexer, and FIG. 10B shows a configuration using an S-type demultiplexer and an S-type multiplexer.

In the second structure, one optical filter is added to the structure of the prior art. The optical filter is shown in FIG.
In the configuration of (a), the short wavelength band transmission type filter 7, FIG.
In the configuration of (b), it is the long-wavelength region transmission type filter 8.
The optical filters 7 and 8 are, for example, 2-port optical filters having the dielectric multilayer film filter, or fiber gratings that selectively reflect signal light in the vicinity of the boundary wavelength range.

However, when the filters 7 and 8 are two-port optical filters having a dielectric multi-layer film filter, the optical filters are low in price, so that an optical amplifier is used as compared with the case of using other filters. Can be at a low price. Also,
When the filters 7 and 8 are fiber gratings, the insertion loss of the fiber grating with respect to the signal light is smaller than that of the other filters, so that it is possible to increase the gain, output, or noise of the optical amplifier. is there.

Although the optical filters 7 and 8 are arranged in series in the latter stage of the amplification section -L or the amplification section -S in FIG. 10, they may be arranged in series in the front stage. However, in consideration of the insertion loss of the optical filter, there is an advantage that the noise figure is lower in the latter stage than in the former stage.

FIG. 11 shows the loss spectrum of the path in the second configuration of the present invention, particularly the configuration using the L-type demultiplexer and the L-type multiplexer (FIG. 10A). The case where the optical filter 7 is a two-port optical filter having the dielectric multilayer filter is shown. The sum of losses (in dB) of the demultiplexer and the multiplexer is shown for the path passing through the amplification unit -L and the path passing through the amplification unit -S. This loss spectrum is obtained from the loss spectra of prior art FIGS. 5 and 6. The loss value is a typical value as in the case of the prior art.

The power difference P-P * of the signal light is 30 dB.
The wavelength range below is the wavelength λtr-1 from the vicinity of the wavelength λs ** in FIG. This wavelength difference (difference between λs ** and λtr-1) is considerably smaller than the above-mentioned wavelength difference (difference between λl ** and λs **) in the prior art. That is, according to the second configuration, the signal light wavelength range that suffers the interference noise is narrower than that of the conventional technique, and thus the usable signal light wavelength range can be widened.

Although the case where the demultiplexer and the multiplexer are dielectric multilayer filters has been described above, the following means are used in other cases.

FIG. 23 shows a third configuration of the present invention. When the demultiplexer and the multiplexer are both wavelength-independent fiber couplers (branch ratio = 1: 1), or when either the demultiplexer or the multiplexer is a dielectric multilayer filter. is there.

Since the signal light wavelength λs in the short wavelength band is close to the wavelength in the boundary region between the short wavelength band and the long wavelength band, it is mixed in the amplification unit (amplification unit -L) in the long wavelength band. Therefore, the amplification unit -L An optical filter is installed in the subsequent stage to remove the mixed components. The loss value for the long wavelength band signal light of the optical filter may be 30 dB or more for the same reason as the above example.

However, in the documents 5 and 6, the set of the circulator and the fiber grating is used as the demultiplexer and the multiplexer, but the fiber grating removes the residual reflection component which is a component of the present invention. Clearly different from the optical filter that does.

The above-mentioned three configurations of the present invention (first to third)
Up to 2), the number of amplifiers is two, but when the number of amplifiers is three, two adjacent wavelength bands are bundled into one by using a demultiplexer and a multiplexer. Obviously, if the amplifier of the present invention is regarded as one amplification section, the configuration and operation are the same as in the case of two amplification sections. The same is obviously true when the number of amplifiers is four or more. Therefore, the present invention is applicable when the number of amplifying units is an arbitrary number of 2 or more.

[0062]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[0063]

[First Embodiment] FIG. 12 shows the configuration of a first embodiment of the present invention. This is an example in which an erbium-doped fiber amplifier (EDFA) is used in the amplification section. A normal short wavelength band EDFA (S-type EDFA) 11 is provided on the short wavelength side, and a long wavelength band EDFA (L-type EDFA) 12 is provided on the long wavelength side by the gain equalizer described in the above "Prior Art". Is used.

FIG. 13 shows an amplifier section (S-type ED) of this embodiment.
The outline of the gain spectrum of FA and L type EDFA) is shown. FIG. 13 (a) shows the entire spectrum, and FIG.
(B) is a spectrum near the boundary wavelength range. The boundary wavelength range is 1562-1566 nm. The number of layers of the dielectric multilayer filter is about 100. The peak gain of the amplifier is 20 dB, and the S type EDFA 11 has a peak gain of 157.
Gain at 0 nm and 1558 of L-type EDFA 12
The gains in nm are both 10 dB. FIG. 14 shows the loss spectrum of the path in this embodiment.

The power difference P-P * of the signal light is 30d.
From FIG. 13 and FIG. 14, the wavelength range of B or less is approximately 1560 to 1568 nm. That is, the width of the wavelength range is 8 nm. On the other hand, in the conventional optical amplifier using the L-type demultiplexer and the L-type multiplexer, the wavelength range is about 1
561 to 1574 nm, and the width of the wavelength castle is 13 n
m.

As described above, in this embodiment, the width of the wavelength band (the width of the signal light wavelength band whose use is limited by interference noise) is about ½ (8/3) as compared with the prior art. It has become.

[0067]

[Second Embodiment] FIG. 15 shows the configuration of a second embodiment of the present invention. This is an embodiment in which a semiconductor laser amplifier (SLA) is used for the amplification unit. The gain wavelength range of the SLA changes by changing the semiconductor composition ratio. In the present embodiment, the short wavelength band SLA (S type SLA) 13 and the long wavelength band SLA (L type SLA) 14 are used, but they are mainly different in the semiconductor composition ratio.

FIG. 16 shows the amplifying section (S-type SL of this embodiment).
The gain spectrum of A and L type SLA) is shown schematically. 16 (a) shows the whole spectrum, and FIG. 16 (b) shows
Is a spectrum near the boundary wavelength range. The boundary wavelength range is 1560 to 1570 nm. The number of layers of the dielectric multilayer filter is about 50. The peak gain of the amplifier is 20 dB, the gain of the S-type SLA 13 at 1545 nm and the gain of the L-type SLA 14 at 1585 nm are both 10 dB. FIG. 17 shows the loss spectrum of the path in this embodiment.

The power difference P-P * of the signal light is 30d.
From FIG. 16 and FIG. 17, the wavelength range of B or less is approximately 1554 to 1576 nm. That is, the width of the wavelength range is 22 nm. On the other hand, in the configuration using the L-type demultiplexer and the L-type multiplexer in the conventional optical amplifier, the wavelength range is about 1557 to 1595 nm, and the width of the wavelength range is 38.
nm.

As described above, in the present embodiment, the width of the wavelength band (the width of the signal light wavelength band whose use is limited by interference noise) is about one half (22/38) as compared with the prior art. )It has become.

Reference Example FIG. 18 shows the configuration of a reference example of the present invention. This is a reference example in which a semiconductor laser amplifier (SLA) is used for the amplification unit and an optical filter is used. The gain wavelength range of the SLA changes by changing the semiconductor composition ratio. In this reference example , a short wavelength band SLA (S type SLA) 13 and a long wavelength band SL are used.
Although A (L-type SLA) 14 is used, they mainly differ in the semiconductor composition ratio.

The outline of the gain spectrum of the amplification section (S-type SLA and L-type SLA) of this reference example is the same as that of FIG. The number of layers of the dielectric multilayer filter used in the demultiplexer-L, the multiplexer-L, and the optical filter 15 used in this reference example of FIG. 18 is about 50. FIG. 19
Shows the loss spectrum of the path in this reference example .

The power difference P-P * of the signal light is 30d.
From FIG. 16 and FIG. 19, the wavelength range below B is approximately 1556 to 1570 nm. That is, the width of the wavelength range is 14 nm. On the other hand, in the configuration using the L-type demultiplexer and the L-type multiplexer in the conventional optical amplifier, the wavelength range is about 1557 to 1595 nm, and the width of the wavelength range is 3
It is 8 nm.

As described above, in the present reference example , the width of the wavelength band (the width of the signal light wavelength band whose use is limited by interference noise) is about one-third (14/38) as compared with the prior art. It has become.

[0075]

[Fourth Embodiment] FIG. 20 shows the structure of a fourth embodiment of the present invention. This is an embodiment in which a fiber Raman amplifier (FRA) is used in the enrichment section. The gain wavelength range of the FRA changes by changing the pumping light wavelength. The present embodiment shows a three-wavelength band optical amplifier in which the two-wavelength band optical amplifier of the present invention is regarded as one amplification unit.
Short wavelength band FRA (S type FRA) 16 and long wavelength band FRA
(L-type FRA) 17 is used to construct an optical amplifier for the above two wavelength bands, which is newly added to the long wavelength band FRA (L * type FR).
A), a short wavelength band FRA (S * type FRA) 18 is provided as a third amplifying unit on the short wavelength side of the L * type FRA, and the demultiplexer-L (3 ') and the multiplexer-S ( 6 '). The amplification unit (S-type FRA, L-type FR of this embodiment
Fig. 2 shows the outline of the gain spectra of A and S * type FRA).
Shown in 1.

The demultiplexer used in this embodiment
The number of layers of the dielectric multilayer filters of the L and the multiplexer-S is about 50. Similar to the third embodiment, the width of the wavelength band is 14 nm for the two boundary wavelength bands between the three wavelength bands. On the other hand, in the conventional optical amplifier, the width of the wavelength range is 38 nm.

As described above, in the present embodiment, the width of the wavelength band (the width of the signal light wavelength band whose use is limited by interference noise) is about one-third (14/38) as compared with the prior art. )It has become.

[Reference Example] FIG. 24 shows a configuration of a reference example of the present invention. Although similar to the first embodiment, while the first embodiment is based on the first configuration of the present invention, the present reference
The example is based on the third configuration of the present invention. The amplification unit uses S-type EDFA for the short wavelength band and L-type EDF for the long wavelength band.
A uses a wavelength-independent fiber coupler with a branching ratio of 1: 1 for the demultiplexer and the multiplexer. In addition, S type EDF
Fiber gratings (referred to as fiber gratings -L and -S, respectively) are installed as optical filters for removing the signal light in the long wavelength band and the signal light in the short wavelength band, respectively, after the A and L type EDFAs. S-type and L-type EDFA are 1530 to 1560 nm, respectively
And signal light having a wavelength in the range of 1570 to 1600 nm is amplified.

The fiber grating-S is 1550.
Only signal light having a wavelength in the range of ˜1560 nm is removed with a loss value of 20 dB or more. However, the L-type EDFA is 157
20d for signal light in the wavelength range of 0 to 1600 nm
B gain, and at the same time a gain of 10 dB or less for signal light of 1550 to 1560 nm, 1530 to 1550
It shows a loss of 10 dB or more with respect to the signal light of nm. The fiber grating-L is 1570 to 160.
Only signal light with a wavelength in the range of 0 nm is removed with a loss value of 20 dB or more. However, S-type EDFA is 1530-15
A gain of 20 dB is shown for signal light in the wavelength range of 60 nm, and a gain of 10 dB or less is shown for signal light of 1570 to 1600 nm at the same time. The fiber gratings -S and -L having the above characteristics can be manufactured inexpensively and easily.

In the present reference example , the unusable wavelength width as the signal light wavelength is 1560 to 1570 nm of 10 nm. This is clearly smaller than the prior art that does not use the fiber gratings -L and -S, and is less than half.

Further, in this reference example , since the demultiplexer and the multiplexer having the wavelength-independent 1: 1 branching ratio are used for the input part and the output part of the amplifier, it is possible to obtain Excess loss of nearly 3 dB occurs for signal lights of all wavelengths, as compared with the case of using a wavelength demultiplexer and demultiplexer. However, the wavelength-independent fiber coupler with a branching ratio of 1: 1 generally has the advantage of being less expensive than other filters. Further, the above-mentioned excess loss can be compensated by other additional means.

[Reference Example] FIG. 25 shows a configuration of a reference example of the present invention. This ginseng
The example is similar to the above reference example , but a multilayer dielectric filter is used as a demultiplexer and a one-to-one relationship is used as a multiplexer.
A major difference is that a wavelength-independent fiber coupler with a branching ratio of is used. In addition, a fiber grating-S is installed as an optical filter for removing the signal light in the short wavelength band after the L-type EDFA.

This fiber grating-S has 15
Only 10d of signal light with a wavelength in the range of 50 to 1560 nm
Remove with a loss value of B or more. However, the L-type EDFA
A gain of 20 dB is shown for the signal light of 1570 to 1600 nm, a gain of 10 dB or less is shown for the signal light of 1550 to 1560, and a loss of 10 dB or more is shown for the signal light of 1530 to 1550. Also, the duplexer-S
Is a transmission loss between the input port (c) and the port (1) connected to the L-type EDFA of 1530 to 1560 nm.
Shows a loss of 10 dB or more with respect to the signal light.

In the present reference example , the unusable wavelength width as the signal light wavelength is 10 nm of 1560 to 1570 nm. This is clearly smaller than the conventional technique that does not use the fiber grating-S, and is less than half.

The embodiments of the present invention have been described in detail above with reference to the drawings. However, the specific configuration is not limited to these embodiments, and the design etc. within the scope not departing from the gist of the present invention are also possible. included.

[0086]

As described above, according to the present invention,
There is an effect that the wavelength range of the signal light that suffers the interference noise is narrow, and thus the usable wavelength range of the signal light is wide.

Specifically, the optical amplifier according to the present invention has a demultiplexer that demultiplexes the input signal light according to the wavelength and a demultiplexer that is arranged in parallel and has different amplification wavelength bands and is emitted from the demultiplexer. Two amplifying units for respectively amplifying the signal lights, a multiplexer for multiplexing the signal lights respectively emitted from the amplifying units, and a loss in a predetermined wavelength region arranged in series with at least one of the amplifying units. The optical filter causes a loss of the residual wavelength component in the demultiplexing by the demultiplexer, the gain characteristic of the signal path in which the optical filter is arranged becomes good, and the signal noise It is possible to narrow the band to be covered.

Further, the optical amplifier of the present invention has a demultiplexer using a dielectric multi-layer film filter for demultiplexing the input signal light according to the wavelength, and the demultiplexer arranged in parallel and having different amplification wavelength bands, respectively. The amplifying unit includes two amplifying units that respectively amplify the signal light emitted from the wave filter, and a dielectric multilayer film filter that transmits a wavelength band different from that of the dielectric multilayer film filter provided in the demultiplexer. Since each of the signals has a multiplexer that multiplexes the signal light emitted from the multiplexer, the transmission band of the dielectric multilayer filter used in the demultiplexer and the dielectric multilayer filter used in the multiplexer is different, The gain characteristic of the path is improved, and the band that suffers signal noise can be narrowed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an optical amplifier according to a conventional technique.

FIG. 2 is a configuration diagram of a duplexer according to a conventional technique.

FIG. 3 is a configuration diagram of a multiplexer according to the related art.

FIG. 4 is a graph showing a gain spectrum of an amplification unit according to a conventional technique.

FIG. 5 is a graph showing a loss spectrum of an L-type demultiplexer (and an L-type multiplexer) according to the related art.

FIG. 6 is a graph showing a loss spectrum of an S-type splitter (and an S-type multiplexer) according to a conventional technique.

FIG. 7 is a graph showing a path loss spectrum of a conventional optical amplifier.

FIG. 8 is a first configuration diagram of the optical amplifier of the present invention.

FIG. 9 is a graph showing a loss spectrum of a path in the first configuration of the present invention.

FIG. 10 is a second configuration diagram of the optical amplifier of the present invention.

FIG. 11 is a graph showing a loss spectrum of a path in the second configuration of the present invention.

FIG. 12 is a configuration diagram of a first embodiment of an optical amplifier according to the present invention.

FIG. 13 is a graph showing a gain spectrum of the amplification unit according to the first embodiment of the present invention.

FIG. 14 is a graph showing a loss spectrum of a route according to the first embodiment of the present invention.

FIG. 15 is a configuration diagram of a second embodiment of an optical amplifier according to the present invention.

FIG. 16 is a graph showing a gain spectrum of the amplification section according to the second embodiment of the present invention.

FIG. 17 is a graph showing a path loss spectrum according to the second embodiment of the present invention.

FIG. 18 is a configuration diagram of a third embodiment of an optical amplifier according to the present invention.

FIG. 19 is a graph showing a path loss spectrum according to the third embodiment of the present invention.

FIG. 20 is a configuration diagram of an optical amplifier according to a fourth embodiment of the present invention.

FIG. 21 is a graph showing a gain spectrum of the amplification section according to the fourth embodiment of the present invention.

FIG. 22 is a configuration diagram showing a basic configuration of an optical amplifier according to a conventional technique.

FIG. 23 is a third configuration diagram of the optical amplifier of the present invention.

FIG. 24 is a configuration diagram of an optical amplifier according to a fifth embodiment of the present invention.

FIG. 25 is a configuration diagram of a sixth embodiment of an optical amplifier according to the present invention.

[Explanation of symbols]

1, 2: amplifier, 3, 3 ', 5: duplexer, 4, 6
6 ': multiplexer, 7, 8, 15: optical filter, 11, 1
2: EDFA, 13, 14: SLA, 16, 17, 1
8: FRA.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04J 14/02 (56) References Japanese Patent Laid-Open No. 10-173264 (JP, A) Japanese Patent Laid-Open No. 10-190114 (JP, A) Special Kaihei 4-101124 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00-3/30 H04B 10/02 H04B 10/16 H04B 10/17

Claims (3)

(57) [Claims] 1. A demultiplexer using a dielectric multi-layer film filter for demultiplexing input signal light according to a wavelength, and a demultiplexer arranged in parallel, each having a different amplification wavelength band,
Amplifies each signal light emitted from the demultiplexer 2
A multiplexing unit that multiplexes the signal lights respectively emitted from the amplifying units by using two amplifying units and a dielectric multilayer filter that transmits a wavelength band different from that of the dielectric multilayer filter provided in the demultiplexer. an optical amplifier comprising a vessel, said demultiplexer, than the boundary wavelength uses a long wavelength transmission type dielectric multilayer filter which transmits long wavelength side, the multiplexer is than the boundary wavelength Also , an optical amplifier characterized by using a short-wavelength transmission type dielectric multilayer filter that transmits the short wavelength side . 2. A dielectric for demultiplexing input signal light according to wavelength.
And a demultiplexer using a body multilayer filter , arranged in parallel, each has a different amplification wavelength band,
Amplifies each signal light emitted from the demultiplexer 2
The two amplifying sections and the dielectric multilayer filter provided in the demultiplexer are different from each other.
Using a dielectric multilayer filter that transmits a certain wavelength band
Combined wave that combines the signal lights emitted from the amplifiers
An optical amplifier including a multiplexer, wherein the demultiplexer uses a short wavelength transmissive dielectric multilayer filter that transmits a shorter wavelength side than a boundary wavelength , and the multiplexer is a boundary wavelength the optical amplifier also characterized in that with the aid of a long wavelength transmission type dielectric multilayer filter which transmits long wavelength side. 3. The optical amplifier according to claim 1 , wherein the optical amplifier according to claim 1 or 2 is used as one of the amplifying units arranged in parallel.