JP2003332660A - Optical amplification module, optical amplifier, optical communication system, and white light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier or the like wherein the amplification gain of signal light around a wavelength range of 1,490-1,520 nm is flatter than heretofore. <P>SOLUTION: In the optical amplifier (100), excited light from exciting light sources (171, 172) is supplied to EDFs (141-145). Excited light from exciting light sources (173-175) is supplied to a TDF (146). Signal light inputted from an input terminal (101) passes through an optical isolator (121) and an optical coupler (131) in sequence and amplified by the EDFs (141-145), and its gain is equalized by optical filters (151-154). The amplified signal light passes through an optical coupler (132),an optical isolator (122), and optical couplers (133, 134), and amplified by the TDF (146). Then, it passes through an optical coupler (135), an optical isolator (123) and an optical branch (112) and outputted from an output terminal (102). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplification module including an optical waveguide in which a rare earth element is added to an optical waveguide region, an optical amplifier including the optical amplification module, a white light source, and an optical communication system including the optical amplifier. It is about.

[0002]

2. Description of the Related Art An optical communication system can transmit a large amount of information at high speed by propagating signal light in an optical fiber transmission line. As a wavelength band of signal light in this optical communication system, C band (1530 nm to 1565)
nm) has already been used and the L band (1565 nm-16
25 nm) is also being considered. In order to further increase the capacity, the S band (146
The use of 0 nm to 1530 nm) is also under consideration.

Further, in the optical communication system, an optical amplifier is used to amplify the signal light. As an optical amplifier capable of optically amplifying signal light of C band or L band,
An EDFA (Erbium-Doped FiberAm) in which an optical amplification fiber (EDF: Erbium-Doped Fiber) in which an Er (erbium) element is added to an optical waveguide region is applied as an optical amplification medium.
plifier) is used. The EDFA can amplify the C-band or L-band signal light propagating through the EDF by supplying pump light (wavelength 0.98 μm band or 1.48 μm band) to the EDF.

On the other hand, as an optical amplifier capable of amplifying S-band signal light, an optical amplification fiber (TDF: Thulium-doped fiber) in which a Tm (thulium) element is added to an optical waveguide region.
TDFA (Thu) using Doped Fiber as an optical amplification medium
lium-Doped Fiber Amplifier) is under consideration. This TDFA is a pumping light (wavelength 1.05 μm band,
1.2μm band, 1.4μm band or 1.55 to 1.65μ
By supplying (m band), the signal light of S band propagating in this TDF can be amplified.

[0005]

As a result of examining conventional optical amplifiers, the inventors have found the following problems. That is, the upper limit of the signal wavelength range that can be actually amplified by TDFA is about 1510 nm (see, for example, Document 1 “T.
Kasamatsu, et al., "Laser-diode-pumped highly-eff
icient gain-shifted thulium-doped fiber amplifier
operating in the1480-1510-nm band ", OFC2001, Techn
ical Digest, TuQ4 (2001) ”). On the other hand, EDFA
The lower limit of the signal wavelength range that can be amplified is generally about 1530 nm. Therefore, the wavelength range 1510 nm to 1530
The signal light of nm cannot be amplified only by using these EDFA and TDFA. For this reason, the silica-based optical fiber used as the optical fiber transmission line has poor use efficiency in the low-loss wavelength range.

Therefore, the wavelength range 1490 nm to 1520 n
An EDFA capable of amplifying a signal light near m has been proposed (for example, see Reference 2 “E. Ishikawa, et al.,“ Novel 1500
nm-band EDFA with discrete Raman amplifier ", ECOC2
001, Postdeadline papers, pp.48-49 (2001) "and JP 2001-313433 A). The EDFAs disclosed therein amplify the signal light in the above wavelength range by increasing the population inversion.

However, this EDFA has a very large positive gain slope in the above wavelength range and cannot achieve gain flattening by itself. Therefore, it is inevitable to use a Raman amplifier together for flattening the gain. However, Raman amplifiers use EDFA and T
Compared to DFA, the pumping efficiency is low and the length of the optical fiber is several kilometers, so it is large, and the signal light transmission quality deteriorates due to the nonlinear optical phenomenon in the optical fiber and double Rayleigh scattering. There are challenges.

The present invention has been made to solve the above problems, and has a wavelength range of 1490 nm to 15 nm.
An optical amplifier in which the amplification gain of signal light in the vicinity of 20 nm is flatter than in the past, an optical amplifier module including an optical waveguide in which a rare earth element is added to an optical waveguide region, which can be suitably used in the optical amplifier, and light including the optical amplifier An object of the present invention is to provide a communication system and a white light source including the optical amplification module.

[0009]

An optical amplification module according to the present invention is an optical amplification module for amplifying signal light of a plurality of channels in a signal wavelength range including at least a part of a wavelength range of 1490 nm to 1520 nm. This optical amplification module is a Tm-doped optical waveguide in which a Tm element is added to an optical waveguide region, and is optically connected to the Tm-doped optical waveguide.
An Er-doped optical waveguide in which an r element is added to the optical waveguide region. The optical amplifier according to the present invention is an optical amplifier that amplifies the signal light input from the input end. This optical amplifier includes the above optical amplification module including a Tm-doped optical waveguide and an Er-doped optical waveguide, first pumping light supply means for supplying pumping light having a wavelength capable of exciting Er ions to the Er-doped optical waveguide, and Tm ions. A second pumping light supply means for supplying pumping light having a wavelength capable of pumping to the Tm-doped optical waveguide.

According to the present invention, the excitation light having a wavelength capable of exciting Er ions is supplied to the Er-doped optical waveguide by the first excitation light supply means, and the excitation light having a wavelength capable of exciting Tm ions is second excitation light. It is supplied to the Tm-doped optical waveguide by the supply means. Then, in the optical amplification module including the Er-doped optical waveguide and the Tm-doped optical waveguide, the signal light is amplified in both the Er-doped optical waveguide and the Tm-doped optical waveguide.
Therefore, the overall gain spectrum is the sum of the gain spectra of the Er-doped optical waveguide and the Tm-doped optical waveguide. As a result, the wavelength range from 1490 nm
The amplification gain of the signal light near 1520 nm becomes flatter than before.

The optical amplifying module according to the present invention is arranged in the upstream side, the downstream side or in the middle of the Er-doped optical waveguide when viewed from the traveling direction of the signal light, and has a wavelength range of 1490 nm to 1520.
A gain equalizing filter for equalizing the gain of the Er-doped optical waveguide in the region included in nm may be further provided. In this case, the amplification gain of the signal light in the wavelength range of 1490 nm to 1520 nm is further flattened by the gain equalizing filter.

The optical amplification module according to the present invention is provided with a cutoff filter which is arranged upstream, downstream or in the middle of the Er-doped optical waveguide as viewed from the traveling direction of the signal light and which cuts off light in the wavelength range of 1530 nm or more. It may be further provided. In this case, the spontaneous emission light (ASE) in the wavelength range of 1530 nm or more is blocked by the blocking filter and blocked from being output to the subsequent stage.

The optical amplification module according to the present invention has
First supply of excitation light of 98 μm band to Er-doped optical waveguide
An optical coupler may be further provided. In this case, it is preferable to enhance the population inversion of the Er-doped optical waveguide. Further, the optical amplification module according to the present invention is a Tm-doped optical waveguide for pumping light of wavelength 1.05 μm band or wavelength 1.4 μm band and pumping light of wavelength 1.2 μm band or wavelength 1.55 to 1.65 μm band. It may further include a second optical coupler for supplying to. In this case, it is preferable to cause the shift of the gain peak on the long wavelength side.

The optical amplification module according to the present invention is Er
An Er-doped optical waveguide in which an element is added to the optical waveguide region, and E
A temperature adjusting means for maintaining the temperature of the r-doped optical waveguide at room temperature or higher may be provided. This case is preferable for increasing the gain of the Er-doped optical waveguide. Further, it is preferable that the temperature adjusting means maintains the temperature of the Er-doped optical waveguide at 65 ° C. or higher, which is preferable in that an inexpensive heater can be used.

In the optical amplification module according to the present invention, Al ₂ O ₃ and P are contained in the optical waveguide region together with the Er element.
An Er-doped optical waveguide in which ₂ O ₅ is co-doped may be provided.
In this case, the optical amplification module has a wavelength range of 1490n.
Signal light of a plurality of channels in a signal wavelength range including m to 1520 nm in at least a part thereof is amplified. Further, in the S band, the wavelength dependence of the stimulated emission cross section becomes flat,
It becomes easy to flatten the gain.

In the optical amplification module according to the present invention, each of the Tm-doped optical waveguide and the Er-doped optical waveguide preferably includes an optical fiber. This is because in this case, the waveguide length can be easily increased and the gain can be increased.

The optical amplifier according to the present invention comprises an Er-doped optical waveguide in which an Er element is doped in the optical waveguide region, and a wavelength 976.
Excitation light supply means for supplying excitation light in the 0.98 μm band of nm or less to the Er-doped optical waveguide. In this case, the gain in the Er-doped optical waveguide is improved in the wavelength range of 1490 nm to 1520 nm.

In the optical amplifier according to the present invention, the Er-doped optical waveguide is preferably arranged on the upstream side of the Tm-doped optical waveguide as seen from the traveling direction of the signal light. In this case, the power of the signal light input to the Er-doped optical waveguide in the preceding stage becomes small and the population inversion in the Er-doped optical waveguide becomes high, while the power of the signal light input to the Tm-doped optical waveguide in the subsequent stage becomes large. Then, gain saturation occurs in the Tm-doped optical waveguide, which is advantageous for increasing the gain peak wavelength in the Tm-doped optical waveguide.

An optical communication system according to the present invention includes the above optical amplifier (the optical amplifier according to the present invention) and has a wavelength range of 14
The signal light of a plurality of channels in the signal wavelength range including 90 nm to 1520 nm is transmitted, and the signal light in the wavelength range is amplified by the optical amplifier. In this optical communication system, since the signal light in the wavelength range of 1490 nm to 1520 nm is amplified by the optical amplifier, the unused wavelength range becomes smaller than that of the conventional one, and it is possible to transmit / receive a larger amount of information.

In the optical communication system according to the present invention,
The signal wavelength range preferably includes one or more bands separated by an unused wavelength range having a bandwidth of 4 nm to 6 nm.
In this case, from the viewpoint of the fluorescence characteristics of each of the Er element and the Tm element, and the characteristics of each of the optical multiplexer and the optical demultiplexer, the unused wavelength range having such a bandwidth is optimal.

In the optical communication system according to the present invention,
It is preferable to supply pumping light for Raman amplification within the unused wavelength region to the optical transmission line, and Raman-amplify the signal light in the optical transmission line. In this case, the gain spectrum of the entire system can be further flattened, and the adverse effect of Rayleigh scattering of the pumping light for Raman amplification on the signal light can be suppressed.

A white light source according to the present invention comprises the above-mentioned optical amplification module (optical amplification module according to the present invention) including a Tm-doped optical waveguide and an Er-doped optical waveguide, and Er-doped excitation light having a wavelength capable of exciting Er ions. A first excitation light supply means for supplying the optical waveguide and a second excitation light supply means for supplying excitation light having a wavelength capable of exciting Tm ions to the Tm-doped optical waveguide, and the Tm-doped optical waveguide by supplying the excitation light. And the spontaneous emission light generated in each of the Er-doped optical waveguides is output. This white light source has substantially the same configuration as the above optical amplifier, but does not receive signal light and outputs spontaneous emission light generated in each of the Tm-doped optical waveguide and the Er-doped optical waveguide. This white light source can output white light in the wavelength range of 1.45 μm to 1.61 μm.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical amplifier module, an optical amplifier, a white light source and an optical communication system according to the present invention will be described in detail below with reference to FIGS. In addition,
In the description of the drawings, the same elements are designated by the same reference numerals,
A duplicate description will be omitted.

FIG. 1 is a diagram showing the configuration of an embodiment of an optical amplifier 100 according to the present invention. The optical amplifier 100 shown in this drawing has an optical branching device 11 arranged in order on a signal light propagation path from an input end 101 to an output end 102.
1, optical isolator 121, optical coupler 131, EDF1
41, optical filter 151, EDF 142, optical filter 1
52, EDF143, optical filter 153, EDF14
4, optical filter 154, EDF 145, optical coupler 13
2, an optical isolator 122, an optical coupler 133, an optical coupler 134, a TDF 146, an optical coupler 135, an optical isolator 123, and an optical splitter 112.

Further, this optical amplifier 100 has an EDF 14
The temperature adjusting unit 161 for adjusting the temperature of No. 1, the temperature adjusting unit 162 for adjusting the temperature of the EDF 142, the temperature adjusting unit 163 for adjusting the temperature of the EDF 143, the temperature adjusting unit 164 for adjusting the temperature of the EDF 144, and the temperature of the EDF 145 are adjusted. Temperature adjusting unit 165, pumping light source 171 connected to optical coupler 131, pumping light source 17 connected to optical coupler 132
2, pumping light source 173 connected to the optical coupler 133, pumping light source 174 connected to the optical coupler 134, optical coupler 13
5, an excitation light source 175 connected to the optical branching device 5, a signal light detection unit 181 connected to the optical branching device 121, a signal light detection unit 182 connected to the optical branching device 122, and a control unit 190.
The components on the signal light propagation circuit and the temperature adjustment units 161 to 165 form a part of the optical amplification module according to the present invention.

Each of the EDFs 141 to 145 is an optical waveguide in which quartz glass is used as a host glass and Er element is added to at least the core region. These EDF141
Each of ˜145 amplifies the C-band signal light by being supplied with pumping light having a wavelength capable of exciting Er ions. TDF 146 uses fluoride-based glass or tellurite-based glass as a host glass and has Tm in at least the core region.
It is an optical waveguide to which an element is added. These TDF1
The pump light 46 is supplied with pumping light having a wavelength capable of pumping Tm ions, and amplifies the S-band signal light.

The optical couplers 131 and 132 and the excitation light source 17
Reference numerals 1 and 172 function as pumping light supply means for supplying pumping light to the EDFs 141 to 145. The wavelength band of the excitation light is
The band is 0.98 μm or 1.48 μm. Excitation light source 1
A semiconductor laser light source is preferable for 71 and 172. The optical coupler 131 outputs the pumping light output from the pumping light source 171 toward the EDF 141, and also outputs the signal light reaching from the optical isolator 121 toward the EDF 141. The optical coupler 132 outputs the pumping light output from the pumping light source 172 to the EDF 145 and outputs the light reaching from the EDF 145 to the optical isolator 12.
Output to 2.

The optical couplers 133 to 135 and the pumping light source 17
3-175 function as an excitation light supply means for supplying the excitation light to the TDF 146. Wavelength band of excitation light is 1.05
μm band, 1.2 μm band, 1.4 μm band or 1.55
The band is 1.65 μm. The pumping light sources 173 to 175 include a semiconductor laser pumping Nd: YLF laser light source and Nd:
A YAG laser light source, a Yb laser light source, a semiconductor laser light source, etc. are preferable. The optical coupler 133 is a pump light source 173.
The pumping light output from the optical isolator 122 is output to the optical coupler 134, and the signal light reaching from the optical isolator 122 is also output to the optical coupler 134. Optical coupler 134
Pumps the pumping light output from the pumping light source 174 to the TDF 14
6 and outputs the light reaching from the optical coupler 133 to the TDF 146. Optical coupler 1
Reference numeral 35 denotes TDF of the excitation light output from the excitation light source 175.
The light is output toward the optical isolator 123 and the light that has arrived from the TDF 146 is output toward the optical isolator 123.

Each of the optical isolators 121 to 123 passes light only in the forward direction (direction from the input end 101 to the output end 102), but does not pass light in the reverse direction.

Each of the optical filters 151 to 154 is a gain equalizing filter that equalizes the gains of the EDFs 141 to 145 in the wavelength range included in the wavelength range of 1490 nm to 1520 nm, and blocks light in the wavelength range of 1530 nm or more. It is also a cutoff filter.

The optical branching device 111 is arranged on the optical path between the input end 101 and the optical isolator 121, branches a part of the light input from the input end 101, and outputs the branched light. The signal is output to the signal light detector 181. The signal light detection unit 181 inputs the light reaching from the optical branching device 111 and detects the power of the signal light input from the input end 101. In addition, the signal light detector 181 may detect the number of channels of the signal light.

The optical splitter 112 is an optical isolator 123.
It is arranged on the optical path between the output terminal 102 and the output terminal 102, branches a part of the light output from the output terminal 102, and outputs the branched light toward the signal light detection unit 182. The signal light detection unit 182 inputs the light that has arrived from the optical branching device 112 and detects the power of the signal light that is output from the output end 102. Further, the signal light detection unit 182 may detect the number of channels of the signal light.

The temperature adjusting section 161 detects the temperature of the EDF 141 and, based on the detection result, the EDF 1
Maintain the temperature of 41 above room temperature. Temperature adjusting unit 162
Detects the temperature of the EDF 142 and maintains the temperature of the EDF 142 at room temperature or higher based on the detection result. The temperature adjusting unit 163 detects the temperature of the EDF 143 and maintains the temperature of the EDF 143 at room temperature or higher based on the detection result. The temperature adjustment unit 164 uses the EDF.
The temperature of 144 is detected, and the temperature of EDF 144 is maintained at room temperature or higher based on the detection result. Also,
The temperature adjusting unit 165 detects the temperature of the EDF 145 and maintains the temperature of the EDF 145 at room temperature or higher based on the detection result. Particularly, the temperature adjusting units 161-165
Preferably maintains the temperature of the EDFs 141 to 145 at 65 ° C. or higher.

The control unit 190 includes signal light detection units 181, 1
The detection results of 82 are received, and the excitation light sources 171 to 17
5 Adjust the power of the pumping light output from each.
The control unit 190 also controls the temperature adjusting units 161 to 165 that adjust the temperatures of the EDFs 141 to 145.

In the optical amplifier 100, the pump light sources 171, 1
The excitation light output from 72 is supplied to the EDFs 141 to 145. Further, the excitation light output from the excitation light sources 173-175 is supplied to the TDF 146. The signal light input from the input end 101 passes through the optical branching device 111, the optical isolator 121, and the optical coupler 131 in order, and then the EDF.
The signals are amplified in 141 to 145 and gain-equalized by the optical filters 151 to 154. The amplified signal light passes through the optical coupler 132, the optical isolator 122, the optical coupler 133, and the optical coupler 134, and then the TDF1.
The signal is amplified at 46 and is output from the output terminal 102 via the optical coupler 135, the optical isolator 123, and the optical branching device 112.

Next, a more specific structure of the optical amplifier 100 will be described. Here, the signal light input from the input end 101 has a wavelength range of 1489.3 nm to 1518.7.
It is assumed that there are 40 channels with a frequency interval of 100 GHz included in nm, the power of each signal channel is -21 dBm, and the total power is -5 dBm.

The specific structure of the EDFA portion is as follows. The total product length of the EDFs 141 to 145 is 1
It is 40 dB, and each EDF is obtained by dividing one EDF into five equal parts. ED from each of the excitation light sources 171 and 172
The wavelength of the excitation light supplied to F141 to 145 is 0.9.
The power is +24 dBm in the 8 μm band.

The optical filters 151 to 154 have the transmission characteristics shown in FIG. Here, the optical filters 151-
Three types of optical filters are assumed as 154. Each of the optical filters A to C used as the optical filters 151 to 154 blocks light having a wavelength of 1525 nm or more with high efficiency. The optical filter A transmits light having a wavelength of 1520 nm or less with almost no loss. The optical filter B has a wavelength range of 1500
The loss is inclined from nm to 1520 nm. The optical filter C has a larger loss slope. The optical filter having such a transmission characteristic can be realized by lengthening the refractive index modulation forming region in the long period grating in which the long period refractive index modulation is formed in the optical fiber. In addition,
In FIG. 2, a graph G210 shows a transmission spectrum of the optical filter A, a graph G220 shows a transmission spectrum of the optical filter B, and a graph G230 shows a transmission spectrum of the optical filter C.

FIG. 3 is a graph showing the gain characteristic and noise figure characteristic of the EDFA portion of the optical amplifier 100. In addition,
In FIG. 3A, the graph G310a is the optical filter A.
, A graph G320a shows the gain spectrum of the optical filter B, and a graph G330a shows the gain spectrum of the optical filter C. Further, in FIG. 3B, a graph G310b is a noise characteristic of the optical filter A, and a graph G32 is shown.
0b shows the noise characteristic of the optical filter B, and the graph G330b shows the noise characteristic of the optical filter C. FIG. 4 shows an optical amplifier 100.
2 is a table summarizing various characteristics of the EDFA portion in FIG. This table shows the wavelength range 14 when the optical filters A to C are applied as the optical filters 151 to 154, respectively.
The relative gain deviation from 90 nm to 1520 nm, the worst noise characteristic, and the pumping efficiency are shown. The relative gain deviation is a value obtained by dividing the gain deviation (dB) by the minimum gain deviation (dB). The worst noise characteristic is the worst value of the noise figure in the signal wavelength range. The pumping efficiency is a value obtained by dividing the signal light power increment by the pumping light power.

As can be seen from these figures, the wavelength range 14
The gain of the EDFA portion from 90 nm to 1520 nm has a very large positive slope. The relative gain deviation of an ordinary EDFA for C band is 20% or less, whereas the relative gain deviation of the EDFA portion in the above wavelength range is 3000%, 270% and 90%, which are very large. Further, the relative gain deviation of the EDFA described in Document 2 is 56%, which is also large. Optical filters 151-1
The gain slope can be improved by increasing the loss in the signal wavelength region of 54, but in that case, the pumping efficiency is significantly deteriorated. The excitation efficiency of an ordinary C-band EDFA is 50.
% To 60%, and the excitation efficiency of an ordinary L-band EDFA is about 40%, so that an excitation efficiency of 10% or less as in this case is unrealistic.

As described above, it is difficult to improve the optical amplification characteristic only with the EDFA section, but the optical amplifier according to the present invention is
By having a TDFA portion in addition to the DFA portion, the optical amplification characteristic is improved.

In the SDF for E-band, since the population inversion must be maintained near 100%, the shape of the gain spectrum (in dB) is almost proportional to the stimulated emission cross section (linear). In the commonly used Al-doped EDF, the wavelength dependence of the stimulated emission cross section around the 1.5 μm wavelength band shows a large slope, as shown in FIG. Note that FIG. 5 is a graph showing the wavelength dependence of the standardized induced cross-sectional area. In FIG. 5, a graph G510 is a standardized stimulated emission sectional area of Al-added EDF, and a graph G520 is P / Al. The normalized stimulated emission cross section of the co-doped EDF is shown respectively.

As a result, wavelength division multiplexing (WDM: Wavelengt
h Division Multiplexing) In order to realize a flat gain spectrum suitable for transmission, the optical filters B and C (see FIG. 2) can be used not only in the C band elimination as shown in FIG. 6 but also in the S band signal wavelength range. Therefore, a gain equalizing filter having a loss slope is required. This results in a wavelength of 1.5
Around 2 μm, a large insertion loss occurs in the optical amplifier, which is disadvantageous from the viewpoint of pumping efficiency and noise characteristics.

The shape of the stimulated emission cross section of EDF can be modified by the glass composition such as host glass and additives. For example, the P / Al co-doped EDF shown in FIG.
2 has a substantially flat stimulated emission cross section in the wavelength band of 1.49 μm to 1.52 μm, and gain flattening can be performed without a special gain equalizer having a transmission characteristic as shown in FIG.
Quantitatively, the ratio of the stimulated emission cross-sections in the 1.49 μm band and the 1.52 μm band was 2.9 in Al-added EDF,
The EDF with P / Al co-addition is 1.6. Optical amplifier 100
As a specific configuration of, the use of an optical filter having the transmission spectrum shown in FIG. 6 can be considered only for the purpose of removing the C band ASE.

Next, the sum of absorption length product peaks is 170d.
The gain spectrum and noise characteristics (Noise Figure) of the optical amplifier in which the silica-based P / Al co-doped EDF that is B is divided into 5 equal parts and the optical filter having the transmission spectrum shown in FIG. It shows in FIG. The operating condition of this optical amplifier is that the input signal light is in the wavelength range 1489.3.
frequency interval 100G included in nm to 1518.7 nm
40 channels of Hz, the signal light power of each channel is -21 dBm, and the total power is -5 dBm.
Suppose The temperature of the silica-based Al-doped EDF is set to 25 ° C., and the excitation light bidirectionally supplied to the silica-based Al-doped EDF has a wavelength of 0.98 μm band and a power of +24 dBm.

Under these operating conditions, the relative gain deviation is 87%, the pumping efficiency is 11.5%, and the noise characteristic is 6.6.
It was dB. As compared with the results of FIGS. 3 and 4 (when the optical filter C of Al-doped EDF is used), the pumping efficiency is 9.0% to 1 even though the gain deviation and noise characteristics are equivalent.
It can be seen that it is improved by 1.5% to about 30%. This is because the insertion loss of the optical filter in the signal wavelength band is suppressed. The above-mentioned P / Al co-added ED
F has a drawback that it has a poor absorption efficiency of 0.98 μm band excitation light. To compensate for this, for example, Yb is added to the P / Al
Co-addition You may co-add to EDF. Yb works well as a Sensitizer when co-added with P.

On the other hand, the specific structure of the TDFA part is as follows. TDF146 has a Tm addition concentration of 20.
It is 00 wt.ppm and the length is 45 m. The pumping light supplied to the TDF 146 from each of the pumping light sources 174 and 175 has a wavelength of 1.05 μm and a power of + 23d.
It is Bm. The pumping light supplied from the pumping light source 173 to the TDF 146 has a wavelength of 1.56 μm and a power of 55.
mW.

FIG. 8 shows the gain characteristic (FIG. 8A) and the noise figure characteristic (FIG. 8) of the TDFA portion of the optical amplifier 100.
It is a graph which shows (b)). As can be seen from these graphs, the TDFA portion has a wavelength range of 1490 nm to 152 nm.
It has a gain even at 0 nm. However, the gain of the TDFA portion in this wavelength range has a negative slope with a large absolute value.

FIG. 9 is a gain spectrum of each part in the optical amplifier 100. In FIG. 9, a graph G61 is shown.
0 shows the gain spectrum of the TDFA portion, graph G620 shows the gain spectrum of the EDFA portion, and graph G630 shows the gain spectrum of the entire optical amplifier. FIG. 10 shows transmission spectra of the optical filters 151 to 154 at this time.
As shown in FIG. 9, the wavelength range is 1490 nm to 1520.
TDFA positive gain slope and TDFA in nm
The negative gain slopes of the parts cancel each other out, and the optical amplifier 10
The relative gain deviation of 0 as a whole is reduced to 25%, and the gain of the entire optical amplifier 100 is flattened.

In order to further flatten the gain of the optical amplifier 100 as a whole, the transmission characteristics of the optical filters 151 to 154 may be further optimized. Further, the optical filters 151 to
The respective 154 may have the same transmission characteristics, but may have different transmission characteristics.

In the optical amplifier 100 having the TDFA part and the EDFA part, as shown in FIG.
It is preferable to provide the EDFA portion in the preceding stage. By doing so, the power of the signal light input to the EDFA in the front stage is reduced, and the population inversion in the EDFs 141 to 145 is increased, while the power of the signal light input to the TDFA in the rear stage is increased to increase the TDF 146. Since gain saturation occurs in, the gain peak wavelength in the TDFA portion is advantageous in increasing the wavelength.

As can be seen from FIG. 9, the wavelength 149
It is desired that the gain of the optical amplifier 100 near 0 nm is even larger. For that purpose, EDF 141 to 14
It is preferable to keep the temperature of 5 high. FIG. 11 shows E
6 is a graph showing the wavelength dependence of the stimulated emission cross section σ _e and the absorption cross section σ _a of DF. In this figure, the solid line is the temperature 7
The case of 5 ° C. is shown, and the broken line shows the case of room temperature of 25 ° C. In the wavelength range of 1490 nm to 1520 nm, the stimulated emission cross section σ _e of EDF has small temperature dependence, but
The absorption cross section σ _a of has a large temperature dependence. The higher the temperature, the smaller the EDF absorption cross section σ _a . From this, as shown in FIG. 11, by maintaining the temperature of the EDFs 141 to 145 high, the gain is improved especially on the short wavelength side. Further, the excitation efficiency was 9.0% when the temperature was 25 ° C., whereas it was 10.6% when the temperature was 75 ° C., which is an improvement of about 0.7 dB. The temperature adjusting units 161 to 165 are the EDFs 141 to 14
This is for maintaining the temperature of 5 at a high temperature, and for example, a Peltier element or a heater is used. The environmental temperature specification of the device generally used in the optical communication system is 0 ° C to 6 ° C.
Since the temperature is 5 ° C, the set temperature of EDFs 141 to 145 should be 6
When the temperature is 5 ° C. or higher, cooling is not required, and an inexpensive heater can be used, resulting in cost reduction.

FIG. 12 is a graph showing the optical amplification characteristic of the S-band EDFA when the EDF temperature is raised. Note that in FIG. 12A, the graph G910a is the EDF.
The gain spectrum of the above EDFA when the temperature is 25 ° C.,
Graph G920a shows the above E when the EDF temperature is 75 ° C.
6 shows a gain spectrum of DFA. Further, in FIG. 12B, a graph G910b is the noise characteristic of the EDFA when the EDF temperature is 25 ° C., and a graph G920b is the EDF.
The noise characteristic of the EDFA when the temperature is 75 ° C. is shown.
As the operating conditions of this EDFA, the signal light input from the input end 101 has a wavelength range of 1489.3 nm to 151.
There are 40 channels with a frequency interval of 100 GHz included in 8.7 nm, and the signal light power of each channel is -21 dB.
m, and the total power is -5 dBm.

The specific structure of the EDFA portion is as follows. Quartz-based A equivalent to EDF 141-145
The total absorption peak product peak of 1-added EDF was 140 dB, and each EDF was divided into 5 equal parts. The pumping light supplied from the pumping light sources 171 and 172 to the EDFs 141 to 145 has a wavelength of 0.98 μm band and a power of +24 dBm. The optical filters 151 to 154 have the transmission characteristics shown by the graph G230 in FIG.

The shape of the gain spectrum of the EDFA portion in the band shorter than the wavelength of 1.53 μm varies depending on the wavelength of the 0.98 μm band pump light. FIG. 13 shows E
It is a gain spectrum of a DFA part. Note that in FIG. 13, a graph G1010 is a gain spectrum when pumping light with a wavelength of 974 nm is supplied, a graph G1020 is a gain spectrum when pumping light with a wavelength of 976 nm is supplied, and a graph G1030 is pumping light with a wavelength of 978 nm. Graph G1040 shows the gain spectrum when the pump light having the wavelength of 980 nm is supplied, and the graph G1040 shows the gain spectrum when the pump light having the wavelength of 980 nm is supplied. As can be seen from these graphs, when the excitation light wavelength is 976 nm or less, the wavelength range is 1490 nm to 1
The gain of the EDFA portion is improved at 520 nm.

Next, an embodiment of the optical communication system according to the present invention will be described. FIG. 14 is a diagram showing a configuration example of the optical communication system 1 according to the present invention. The optical communication system 1 shown in this figure includes an optical transmitter 10, an optical repeater 20, and an optical receiver 30, and an optical fiber transmission line 40 is laid between the optical transmitter 10 and the optical repeater 20. An optical fiber transmission line 50 is laid between the optical repeater 20 and the optical receiver 30.

The optical transmitter 10 includes a light source section 11₁~ 11_Fouras well as
It has an optical multiplexer 12. Light source unit 11 ₁Is the wavelength range 145
5 nm to 1490 nm (hereinafter referred to as "Sb band")
The signal lights of the included multiple channels are multiplexed. Light source unit 11
₂Is in the wavelength range of 1490 nm to 1520 nm (hereinafter referred to as “Sr
(Referred to as “band”) that combines the signal lights of multiple channels.
To wave. Light source unit 11₃Is a plurality of channels included in the C band.
The signal light of the channel is multiplexed. Light source unit 11_FourIs in the L band
The signal lights of the included multiple channels are multiplexed. Also, Hikari
The wave device 12 is a light source unit 11.₁~ 11_FourOutput from each
Signal light from multiple channels is further combined, and this combined light
The (multiplexed signal light) is sent to the optical fiber transmission line 40.
In addition, the optical multiplexer 12 first sets the Sb band and the Sr band.
Demultiplex each signal light, and
After combining the L-band signal lights, after
It may have a configuration of multiplexing the signals.

The optical repeater 20 comprises an optical demultiplexer 21, optical amplifiers 22 _{1 to} 22 ₄ , an optical multiplexer 23, an optical coupler 24 and a pumping light source 25. The optical coupler 24 supplies the pumping light for Raman amplification output from the pumping light source 25 to the optical fiber transmission line 40.
The optical signals are transmitted to the optical demultiplexer 21 while being sent to the optical demultiplexer 21. The optical demultiplexer 21 inputs the signal light of the plurality of channels, demultiplexes the signals for each band, outputs the signal light of the Sb band to the optical amplifier 22 _1, and outputs the signal light of the Sr band to the optical amplifier 22 ₂ . The signal light of C band is output to the optical amplifier 22 ₃ and the signal light of L band is output to the optical amplifier 22 ₄ .
The optical demultiplexer 21 first demultiplexes the Sb band and the Sr band into the C band and the L band, and thereafter,
The demultiplexing may be performed for each band.

The optical amplifier 22 ₁ inputs the signal light of Sb band output from the optical demultiplexer 21, and amplifies the signal light collectively. The optical amplifier 22 ₂ receives the signal light of the Sr band output from the optical demultiplexer 21 and collectively amplifies the signal light. The optical amplifier 22 ₃ inputs the signal light of C band output from the optical demultiplexer 21 and collectively amplifies the signal light. The optical amplifier 22 ₄ outputs the L output from the optical demultiplexer 21.
The band signal light is input and this signal light is collectively amplified.
The optical multiplexer 23 multiplexes the signal light of a plurality of channels output from each of the optical amplifiers 22 _{1 to} 22 ₄ and sends it to the optical fiber transmission line 50.

The optical receiver 30 includes an optical demultiplexer 31 and light receiving parts 31 _{1 to} 32 _N. The optical demultiplexer 31 demultiplexes the signal light of a plurality of channels, which has propagated through the optical fiber transmission line 50, for each signal channel. The light receiving section 31 _n includes the optical demultiplexer 31 _n.
The signal light of the wavelength λ _n output from is input and the signal light is received. However, N is an integer of 4 or more, and n is 1.
It is an arbitrary integer not less than N and not more than N.

Of the four optical amplifiers included in the optical repeater 20, the optical amplifier 22 that amplifies the signal light in the Sb band is used.
Reference numeral ₁ is a TDFA pumped in a 1.05 μm wavelength band. Sr
The optical amplifier 22 ₂ that amplifies the band signal light has the same configuration as the optical amplifier 100. The optical amplifier 22 ₃ for amplifying the C-band signal light is a normal C-band EDFA. The optical amplifier 22 ₄ for amplifying the signal light of L band is L
It is an EDFA for bands. FIG. 15A shows the gain spectrum of the Sb band optical amplifier 22 ₁ . Figure 15 (b)
Is a gain spectrum of the C-band optical amplifier 22 ₃ .
15C shows the gain spectrum of the L-band optical amplifier 22 ₄ .

Next, a more specific structure of the optical communication system 1 will be described. Here, the Sb band multiplexed signal light is 39 channels with a frequency interval of 100 GHz included in the wavelength range of 1456.7 nm to 1486.3 nm. The Sr band multiplexed signal light has a wavelength range of 1490.8.
Frequency interval 100G included in nm to 1522.6 nm
42 channels of Hz. The C-band multiplexed signal light is 45 channels with a frequency interval of 100 GHz included in the wavelength range of 1528.0 nm to 1563.9 nm. Further, the L band multiplexed signal light has a wavelength range of 1568.8n.
Frequency interval 100GH included in m to 1603.2 nm
41 channels of z. In the optical communication system 1 configured as described above, the unused wavelength band is 15 nm or less, and the multiplexed signal light in the wavelength band of 1.45 μm to 1.61 μm can be transmitted with good transmission characteristics.

In the above embodiment, the signal wavelength range includes one or more bands separated by an unused wavelength range having a bandwidth of 4 nm to 6 nm. This is appropriate considering the fluorescence characteristics of the Er element and the Tm element. Also,
When each optical multiplexer and each optical demultiplexer are composed of a dielectric multilayer filter, it is reasonable even considering the current technical level.

Considering Raman amplification of the signal light in the optical fiber transmission line, an unused wavelength band between the Sb band and the Sr band, an unused wavelength band between the Sr band and the C band, or , It is preferable to set the wavelength of the pumping light for Raman amplification to an unused wavelength range between the C band and the L band. At this time, it is desirable that the 30 dB down bandwidth of the pumping light is narrower than the unused wavelength bandwidth so that the Rayleigh scattering of the Raman amplification pumping light does not adversely affect the signal light. The Raman amplification pumping light source that is often used at present is a semiconductor laser light source with a fiber grating, and has an output light spectrum as shown in FIG. 16, and a 30 dB down bandwidth of 4 nm.
It is about 5 nm. From this point as well, it is appropriate that the unused wavelength band width is 4 nm to 6 nm.

The present invention is not limited to the above-described embodiment, but various modifications can be made.
For example, the optical amplification module according to the present invention is an ED as an Er-doped optical waveguide in which an Er element is added to an optical waveguide region.
It was provided with F and TDF as a Tm-doped optical waveguide in which the Tm element was added to the optical waveguide region. But,
The optical amplification module may include an optical waveguide formed on a flat substrate to which Er element or Tm element is added. However, in the case of an optical fiber to which a rare earth element is added, such as EDF and TDF,
The waveguide length can be easily lengthened and the gain can be increased, which is preferable.

Further, the optical amplification module according to the present invention can amplify the input signal light by being supplied with the pumping light having the predetermined wavelength. However, this optical amplifier module is only supplied with pumping light of a wavelength capable of pumping Er and Tm, and if signal light is not input,
The spontaneous emission light generated in each of the Tm-doped optical waveguide Er-doped optical waveguide is output. In this case, the optical amplification module and the pumping light supply means have a wavelength range of 1.45 μm to
A white light source that outputs a white light of 1.61 μm is configured.
This white light source has substantially the same configuration as that shown in FIG.
Since there is no input / output of signal light, the optical splitters 121 and 122 and the signal light detectors 181 and 182 are unnecessary.

[0067]

As described above, according to the present invention, the excitation light having the wavelength capable of exciting Er ions is supplied to the Er-doped optical waveguide by the first excitation light supply means, and the excitation light having the wavelength capable of exciting Tm ions is excited. The light is supplied to the Tm-doped optical waveguide by the second excitation light supply means. Then, in the optical amplification module including the Er-doped optical waveguide and the Tm-doped optical waveguide, the signal light is amplified in both the Er-doped optical waveguide and the Tm-doped optical waveguide. At this time, the gain spectrum of the entire optical amplification module is a spectrum obtained by integrating the gain spectra of the Er-doped optical waveguide and the Tm-doped optical waveguide. As a result, the wavelength range 1490 nm to 1520 nm
The gain of signal light amplification in the vicinity becomes flatter than in the past.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical amplifier according to the present invention.

FIG. 2 is a transmission spectrum of the optical filter in FIG.

FIG. 3 is a graph showing a gain characteristic and a noise figure characteristic of an EDFA portion in the optical amplifier shown in FIG.

FIG. 4 is a table summarizing various characteristics of the EDFA portion in the optical amplifier shown in FIG.

FIG. 5 is a graph showing normalized stimulated emission cross sections of Al-doped EDF and P / Al co-doped EDF.

FIG. 6 is a transmission spectrum of a P / Al co-doped EDF optical filter.

FIG. 7 is a graph showing optical amplification characteristics of P / Al co-doped EDFA for S band amplification.

8 is a graph showing a gain characteristic and a noise figure characteristic of a TDFA portion in the optical amplifier shown in FIG.

9 is a gain spectrum of each part in the optical amplifier shown in FIG.

FIG. 10 is a transmission spectrum of the optical filter in FIG.

FIG. 11 is a graph showing the wavelength dependence of the stimulated emission cross section σ _e and the absorption cross section σ _a of EDF.

FIG. 12 is a graph showing a gain characteristic and a noise figure index of an EDFA portion at temperatures of 25 ° C. and 75 ° C., respectively.

FIG. 13 is an ED when excitation lights having wavelengths of 974 nm, 976 nm, 978 nm, and 980 nm are supplied, respectively.
It is a gain spectrum of the FA portion.

FIG. 14 is a diagram showing the configuration of an embodiment of an optical communication system according to the present invention.

15 is a gain spectrum of each of the optical amplifiers included in the optical communication system shown in FIG.

FIG. 16 is an output light spectrum of a semiconductor laser light source with a fiber grating.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical communication system, 10 ... Optical enhancer, 20 ... Optical repeater, 30 ... Optical receiver, 100 ... Optical amplifier, 101 ... Input end, 102 ... Output end, 111, 112 ... Optical branching device, 12
1-123 ... Optical isolator, 131-135 ... Optical coupler, 141-145 ... EDF, 146 ... TDF, 151
... 154 ... Optical filter, 161-165 ... Temperature adjusting unit,
171 to 175 ... Excitation light source, 181, 182 ... Signal light detection unit, 190 ... Control unit.

Claims (16)

[Claims] 1. An optical amplification module for amplifying signal light of a plurality of channels in a signal wavelength range including at least a part of a wavelength range of 1490 nm to 1520 nm, comprising a Tm-doped optical waveguide in which a Tm element is added to an optical waveguide region. An optical amplification module, which is optically connected to the Tm-doped optical waveguide and comprises an Er-doped optical waveguide in which an Er element is added to an optical waveguide region. 2. The Er as seen from the traveling direction of the signal light
A gain equalizing filter which is arranged on the upstream side, the downstream side or in the middle of the doped optical waveguide and which equalizes the gain of the Er doped optical waveguide in a region included in the wavelength range of 1490 nm to 1520 nm. Item 1. The optical amplification module according to item 1. 3. The Er as seen from the traveling direction of the signal light
The optical amplification module according to claim 1, further comprising a cutoff filter arranged upstream, downstream or in the middle of the added optical waveguide to cut off light in a wavelength range of 1530 nm or more. 4. The optical amplification module according to claim 1, further comprising a first optical coupler that supplies the Er-doped optical waveguide with a 0.98 μm band excitation light. 5. A second optical coupler for supplying 1.05 μm band or 1.4 μm band pumping light and 1.2 μm band or 1.55 to 1.65 μm band pumping light to the Tm-doped optical waveguide. The optical amplification module according to claim 1, further comprising: 6. An optical amplification module for amplifying signal light of a plurality of channels in a signal wavelength range including at least a part of a wavelength range of 1490 nm to 1520 nm, comprising an Er-doped optical waveguide in which an Er element is added to an optical waveguide region. An optical amplification module comprising: a temperature adjusting unit that maintains the temperature of the Er-doped optical waveguide at room temperature or higher. 7. The optical amplification module according to claim 6, wherein the temperature adjusting means maintains the temperature of the Er-doped optical waveguide at 65 ° C. or higher. 8. An optical amplification module for amplifying signal light of a plurality of channels in a signal wavelength range including at least a part of a wavelength range of 1490 nm to 1520 nm, wherein Al ₂ O ₃ and P ₂ O ₅ together with an Er element are optical. An optical amplification module comprising an Er-doped optical waveguide co-doped in the wave region. 9. The optical amplification module according to claim 1, wherein each of the Tm-doped optical waveguide and the Er-doped optical waveguide includes an optical fiber. 10. An optical amplifier for amplifying signal light input from an input end, comprising a Tm-doped optical waveguide and an Er-doped optical waveguide.
Optical amplification module, first excitation light supply means for supplying excitation light having a wavelength capable of exciting Er ions to the Er-doped optical waveguide, and excitation light having a wavelength capable of exciting Tm ions, the Tm-doped optical waveguide An optical amplifier comprising: 11. An optical amplifier for amplifying signal light of a plurality of channels in a signal wavelength range including at least a part of a wavelength range of 1490 nm to 1520 nm, wherein an Er-doped optical waveguide in which an Er element is added to an optical waveguide region, The excitation light in the 0.98 μm band with a wavelength of 976 nm or less is added to the E
An optical amplifier having a pumping light supply means for supplying the r-doped optical waveguide. 12. The optical amplifier according to claim 10, wherein the Er-doped optical waveguide is arranged on the upstream side of the Tm-doped optical waveguide when viewed from the traveling direction of the signal light. 13. A light including the optical amplifier according to claim 10, transmitting signal light of a plurality of channels in a signal wavelength range including a wavelength range of 1490 nm to 1520 nm, and amplifying signal light in the wavelength range by the optical amplifier. Communications system. 14. The signal wavelength band has a bandwidth of 4 nm to 6 nm.
14. The optical communication system according to claim 13, comprising one or more bands separated by an unused wavelength region of nm. 15. The optical communication system according to claim 14, wherein the Raman amplification pumping light in the unused wavelength region is supplied to an optical transmission line, and the signal light is Raman-amplified in the optical transmission line. 16. The optical amplification module according to claim 1, comprising a Tm-doped optical waveguide and an Er-doped optical waveguide, and a first pumping light supply for supplying pumping light having a wavelength capable of exciting Er ions to the Er-doped optical waveguide. Means and a second excitation light supply means for supplying excitation light of a wavelength capable of exciting Tm ions to the Tm-doped optical waveguide, wherein the Tm-doped optical waveguide and the Er-doped optical waveguide are respectively supplied by the excitation light. A white light source that outputs the spontaneous emission light generated in.