JP3893963B2 - Optical amplifier and optical communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical amplifier that optically amplifies signal light in an optical waveguide supplied with pumping light, and an optical communication system including the optical amplifier.
[0002]
[Prior art]
An optical communication system can transmit a large amount of information at high speed by propagating signal light through an optical fiber transmission line. As the wavelength band of signal light in this optical communication system, the C band (1530 nm to 1565 nm) has already been used, and the use of the L band (1565 nm to 1625 nm) is also being studied. In order to further increase the capacity, the use of the S band (1460 nm to 1530 nm) as the signal light wavelength band is also being studied.
[0003]
In an optical communication system, an optical amplifier is used to optically amplify signal light. As an optical amplifier capable of optically amplifying C-band or L-band signal light, an EDFA using an optical amplification fiber (EDF: Erbium Doped Fiber) in which an Er (erbium) element is added to an optical waveguide region as an optical amplification medium (Erbium Doped Fiber Amplifier) is used. The EDFA can amplify the C-band or L-band signal light propagating through the EDF by supplying excitation light (wavelength 0.98 μm band or 1.48 μm band) to the EDF.
[0004]
On the other hand, as an optical amplifier capable of optically 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 is used as an optical amplification medium. Thulium Doped Fiber Amplifier) is being studied. This TDFA optically amplifies S-band signal light propagating through this TDF by supplying pump light (wavelength 1.05 μm band, 1.4 μm band or 1.55-1.65 μm band) to the TDF. Can do.
[0005]
EDFA uses the transition of the three-level system of Er ions, whereas TDFA uses the transition of the four-level system of Tm ions. From this, in TDFA, even if the length of TDF is constant, the magnitude of the gain can be changed without causing deterioration of the gain flatness (for example, reference 1 “T. Sakamoto, et al. , "Gain-equalized thulium-doped fiber amplifiers for 1460nm-based WDM signals", OAA'99, Technical Digest, WD2 (1999)).
[0006]
[Problems to be solved by the invention]
However, the present inventors have found that TDFA has the following problems.
[0007]
FIG. 17 is a diagram for explaining the operation of each of EDFA and TDFA in comparison. FIG. 5A shows a non-saturated gain spectrum, a non-saturated absorption spectrum, a gain spectrum when the inversion distribution is 60%, and a gain spectrum when the inversion distribution is 50% in the EDFA. FIG. 5B shows a non-saturated gain spectrum, a non-saturated absorption spectrum, a gain spectrum when the inversion distribution is 60%, and a gain spectrum when the inversion distribution is 50% in TDFA. Each gain spectrum can be calculated based on the unsaturated gain spectrum and the unsaturated absorption spectrum. As shown in this figure, in the case of TDFA as compared with the case of EDFA, the number of ions applied to the optical amplification varies depending on the pumping light power, so that the gain spectrum can be obtained without causing the gain tilt variation. It is possible to change to a constant multiple. Thus, in TDFA, even if the length of TDF is constant, the magnitude of the gain can be changed without causing deterioration of gain flatness. In TDFA, when the population inversion becomes large, the gain spectrum shifts to the long wavelength side.
[0008]
However, in the description of TDFA in Document 1 above, an actual operation state in a wavelength division multiplexing (WDM) optical communication system that multiplexes and transmits multi-wavelength signal light is not considered. That is, in this document 1, the wave number of the signal light input to the TDFA is 4 channels, the power of the signal light of each channel is −19 dBm, and these are constant and only the gain is changed. In addition, the power of pumping light supplied to the TDF is 630 mW or more, whereas the power of all signal light output after optical amplification is 11 dBm, and the ratio of both is 2% or less. The efficiency is very low.
[0009]
An optical amplifier used in a WDM optical communication system is designed so that output signal light power is maintained at a constant design value when input signal light power varies due to variations in transmission loss (span loss) of an optical fiber transmission line. It is necessary to change the magnitude of the gain. This control is referred to as automatic output level control (ALC). Therefore, the content described in Document 1 in which only the gain is changed while the input signal light level is constant is different from the actual operation state of the optical amplifier. Even if the wave number of the signal light is 32 channels, the output signal light power is −4 dBm / ch according to the contents described in Document 1. This output signal light power is very small as an optical amplifier used in a terrestrial trunk WDM optical communication system.
[0010]
FIG. 18 is a diagram showing a gain spectrum of TDFA when conventional ALC is performed. FIG. 19 is a diagram showing the output signal light power spectrum of TDFA when conventional ALC is performed. Here, the power P of all signal lights input to the TDFA_inIs -4.2 dBm, -2.2 dBm, -0.2 dBm, and +0.8 dBm, respectively, the power P of the total signal light to be output_outThe excitation light power was controlled so as to be +18 dBm. In addition, for TDF having a Tm element addition concentration of 2000 wt. Ppm and a length of 20 m, pumping light having a wavelength of 1.05 μm is supplied from the same forward direction as the signal light propagation direction, and from the reverse direction. The pumping lights having the same wavelength were supplied, and the powers of the pumping lights supplied to the TDF from the forward direction and the reverse direction were made equal to each other. As shown in these figures, the input signal light power P_inIs larger, the gain slope (wavelength dependence of gain) increases from a negative value to a positive value, and the wavelength dependence of output signal light power also increases from a negative value to a positive value. This can also be said to be a phenomenon in which the gain spectrum of TDFA shifts to the longer wavelength side (that is, gain shift).
[0011]
By the way, Reference 2 “T. Kasamatsu, et al.,“ Novel 1.50-μm Band Gain-Shifted Thulium-Doped Fiber Amplifier by using Dual Wavelength Pumping of 1.05 μm and 1.56 μm ”, OAA'99, Technical Digest, PDP1 (1999 According to the description in Japanese Patent Application Laid-Open No. 2001-203413, when TDF is supplied not only with excitation light having a wavelength of 1.05 μm but also with excitation light having a wavelength of 1.55 to 1.65 μm, It is said that a gain shift in TDFA occurs when the Tm element addition concentration in TDFA is 3000 wt.ppm or more. However, as described above, in TDFA, even when the input signal light power is increased, a gain shift occurs.
[0012]
An optical amplifier used in a WDM optical communication system not only performs ALC when the input signal light power fluctuates due to fluctuations in span loss or the like, but also performs automatic gain control when the wave number of input signal light fluctuates ( AGC (Automatic Gain Control) must also be performed. When AGC is performed in the case of EDFA, the shape of the gain spectrum is maintained regardless of the excitation method. On the other hand, when AGC is performed in the case of TDFA, the shape of the gain spectrum changes and the gain flatness changes.
[0013]
FIG. 20 is a diagram illustrating a gain spectrum of TDFA when conventional AGC is performed. Here, the power P of all signal lights input to the TDFA_inWas -4.2 dBm, -1.2 dBm, and +0.8 dBm, the pump light power was controlled so that the gain peak was 18 dB. In addition, for TDF having a Tm element addition concentration of 2000 wt. Ppm and a length of 20 m, pumping light having a wavelength of 1.05 μm is supplied from the same forward direction as the signal light propagation direction, and from the reverse direction. The pumping lights having the same wavelength were supplied, and the powers of the pumping lights supplied to the TDF from the forward direction and the reverse direction were made equal to each other. As shown in this figure, the input signal light power P_inThe larger the is, the larger the gain slope (gain wavelength dependency) becomes from a negative value to a positive value. That is, a gain shift also occurs when the wave number of the input signal light varies.
[0014]
The present invention has been made on the basis of the above-mentioned knowledge of the present inventor, and the power and gain flatness of the output signal light are kept constant even when the power or wave number of the input signal light fluctuates. An object is to provide an optical amplifier (TDFA) that can be maintained, and an optical communication system including the optical amplifier.
[0015]
[Means for Solving the Problems]
  The optical amplifier according to the present invention includes (1) an optical waveguide in which a Tm element is added to an optical waveguide region, and (2) an optical waveguide having a different wavelength orThe direction of pumping light supply to the optical waveguide is differentExcitation light supply means for supplying a plurality of excitation lights, and (3) monitor means for monitoring at any one of two wavelengths of power of light output from the optical waveguide and power of spontaneous emission light generated in the optical waveguide And (4) adjusting the power of the plurality of pumping lights supplied to the optical waveguide by the pumping light supply means based on the result of monitoring by the monitoring means, so that the two wavelengths of the signal light output from the optical waveguide And a control means for performing ALC control so that the gain flatness of the signal is constant and the power of the signal light output from the optical waveguide is constant.
[0016]
According to the optical amplifier of the present invention, pumping light (wavelength: 1.05 μm band, 1.4 μm band, or 1.55 to 1.5 .mu.m) is applied to the optical waveguide in which the Tm element is added to the optical waveguide region by the pumping light supply means. 65 [mu] m band) is supplied, and signal light of a predetermined wavelength band (1455-1485 nm) is optically amplified and output in this optical waveguide. Either the power of light output from the optical waveguide or the power of spontaneous emission light generated in the optical waveguide is monitored at two or more wavelengths by the monitoring means. Then, based on the result of monitoring by the monitoring unit, the control unit adjusts the power of the pumping light supplied to the optical waveguide by the pumping light supply unit, and the gain flatness of the optical waveguide is feedback-controlled at a constant level. At the same time, the power of the signal light output from the optical waveguide is feedback controlled to be constant.
[0017]
In the optical amplifier according to the present invention, it is preferable that the monitoring means monitors the power of spontaneous emission light emitted to the side of the optical waveguide. In this case, the spontaneous emission light emitted to the side of the optical waveguide is monitored at two or more wavelengths by the monitoring means, and the power of the excitation light is adjusted by the control means based on the monitoring result. Light is not extracted from the signal light main line connected to the optical waveguide, but spontaneous emission light emitted to the side of the optical waveguide is monitored, which is preferable in that there is no increase in insertion loss.
[0018]
In the optical amplifier according to the present invention, the monitoring means includes (1) a first optical branching coupler for branching out a part of the power of the light output from the optical waveguide, and (2) a first optical branching coupler. A second optical branching coupler that splits the extracted light into two, and (3) a first filter that selectively transmits light of a specific first wavelength included in one of the two lights branched by the second optical branching coupler. (4) a second filter that selectively transmits light of a specific second wavelength included in the other light bifurcated by the second optical branching coupler; and (5) a first filter that has passed through the first filter. It is preferable to include a first light receiving unit that detects the power of light having a wavelength and (6) a second light receiving unit that detects the power of light having the second wavelength that has passed through the second filter. In this case, a part of the power of the light output from the optical waveguide is branched out by the first optical branching coupler, and further branched into two by the second optical branching coupler. Light of a specific first wavelength included in one of the lights branched into two by the second optical branching coupler is transmitted through the first filter, and the power is detected by the first light receiving unit. Further, the light of the specific second wavelength included in the other light branched into two by the second optical branching coupler is transmitted through the second filter, and the power is detected by the second light receiving unit. In this way, the power of light output from the optical waveguide is monitored at two or more wavelengths by the monitoring means. This monitoring means is preferable in that it has a simple configuration and is inexpensive.
[0019]
In the optical amplifier according to the present invention, the monitoring means includes (1) an optical branching coupler for branching out a part of the power of the light output from the optical waveguide, and (2) the light extracted by the optical branching coupler. A diffraction grating that diffracts the light, (3) a first light-receiving unit that detects the power of light of a specific first wavelength included in the light diffracted by the diffraction grating, and (4) included in the light diffracted by the diffraction grating It is preferable to include a second light receiving unit that detects the power of the light having a specific second wavelength. In this case, a part of the power of the light output from the optical waveguide is branched out by the optical branching coupler and is diffracted by the diffraction grating. The power of the light of the specific first wavelength included in the light diffracted by the diffraction grating is detected by the first light receiving unit, and the power of the light of the specific second wavelength included in the light diffracted by the diffraction grating is the second. It is detected by the light receiving unit. Furthermore, you may provide many light-receiving parts. In this way, the power of light output from the optical waveguide is monitored at two or more wavelengths by the monitoring means. This monitoring means is suitable in these respects because it can monitor with high accuracy at many wavelengths and can cope with an increase or decrease in the wave number of the input signal light.
[0020]
  In the optical amplifier according to the present invention, (1) the excitation light supply means includes a first excitation light source that outputs excitation light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band, and a wavelength of 1.55 to 1.65 μm. A pumping light output from the first pumping light source and supplying the pumping light output from each of the first pumping light source and the second pumping light source to the optical waveguide, and (2) the control means includes the second pumping light source. By adjusting the power of the pumping light output and supplied to the optical waveguide, the gain flatness of the optical waveguide is controlled, and the power of the pumping light output from the first pumping light source and supplied to the optical waveguide is adjusted. By doing so, it is preferable to control the power of the signal light output from the optical waveguide. In this case, the gain flatness of the optical waveguide is controlled to be constant by adjusting the power of the pumping light in the wavelength range of 1.55 to 1.65 μm output from the second pumping light source and supplied to the optical waveguide. The In addition, the power of the signal light output from the optical waveguide is constant by adjusting the power of the pumping light having a wavelength of 1.05 μm or 1.4 μm that is output from the first pumping light source and supplied to the optical waveguide. Controlled.At this time, the power of the pumping light output from the second pumping light source and supplied to the optical waveguide and the power of the pumping light output from the first pumping light source and supplied to the optical waveguide may be adjusted alternately. Is preferred.
[0021]
  In the optical amplifier according to the present invention, (1) the pumping light supply means supplies pumping light with a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward and reverse directions to the optical waveguide; (2) The control means controls the gain flatness of the optical waveguide by adjusting the power of the pumping light supplied from the forward direction to the optical waveguide, and is supplied from the opposite direction to the optical waveguide. It is preferable to control the power of the signal light output from the optical waveguide by adjusting the power of the excitation light. In this case, the gain flatness of the optical waveguide is controlled to be constant by adjusting the power of the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band supplied from the forward direction to the optical waveguide. The In addition, the power of the signal light output from the optical waveguide is controlled to be constant by adjusting the power of the pumping light having a wavelength of 1.05 μm band or 1.4 μm wavelength supplied to the optical waveguide from the opposite direction. Is done.At this time, it is preferable to alternately adjust the power of the pumping light supplied from the forward direction and the power of the pumping light supplied from the reverse direction.
[0022]
In the optical amplifier according to the present invention, (1) the pumping light supply means supplies pumping light with a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward direction and the reverse direction to the optical waveguide; (2) The control means controls the gain flatness of the optical waveguide by adjusting the ratio of the power of the pumping light supplied from the forward direction and the reverse direction to the optical waveguide. It is preferable to control the power of the signal light output from the optical waveguide by adjusting the sum of the powers of the pumping light supplied from the forward direction and the reverse direction. In this case, the gain of the optical waveguide is flattened by adjusting the ratio of the power of the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band supplied from the forward direction and the reverse direction to the optical waveguide, respectively. The degree is controlled to be constant. Further, the signal light output from the optical waveguide is adjusted by adjusting the sum of the powers of the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band supplied from the forward direction and the reverse direction to the optical waveguide, respectively. Is controlled at a constant power.
[0023]
An optical amplifier according to the present invention includes: (1) an optical waveguide in which a Tm element is added to an optical waveguide region; and (2) a first excitation light source that outputs excitation light having a wavelength of 1.05 μm band or wavelength of 1.4 μm. And a second pumping light source that outputs pumping light in a wavelength range of 1.55 to 1.65 μm, and pumping the pumping light supplied from the first pumping light source and the second pumping light source to the optical waveguide. And (3) the gain of the optical waveguide by adjusting the power of the pumping light output from the second pumping light source and supplied to the optical waveguide based on the wave number or power of the signal light input to the optical waveguide. And a control means for controlling the flatness and the output signal light power. In this case, the excitation light supply means outputs the excitation light of the wavelength 1.05 μm band or the wavelength 1.4 μm band output from the first excitation light source, and the wavelength 1.55 to 1 output from the second excitation light source. The excitation light in the .65 μm band is supplied to the optical waveguide in which the Tm element is added to the optical waveguide region. Then, the control means adjusts the power of the pumping light output from the second pumping light source and supplied to the optical waveguide as a function of the wave number or power of the signal light input to the optical waveguide, so that the gain of the optical waveguide is flattened. The power and output signal light power are feedforward controlled to be constant. Here, the function may be a primary function or a function of second or higher order. Therefore, this optical amplifier is preferable because it does not necessarily have a means for monitoring the power, gain gradient or wave number of the output signal light and performing feedback control, and is small and inexpensive.
[0024]
The optical amplifier according to the present invention includes (1) an optical waveguide in which a Tm element is added to an optical waveguide region, and (2) pumping light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band in the forward direction with respect to the optical waveguide. And pumping light supply means for supplying from both the reverse direction and (3) based on the wave number or power of the signal light input to the optical waveguide, supplied from both the forward and reverse directions to the optical waveguide And a control means for controlling the gain flatness of the optical waveguide and the output signal light power by adjusting the power of the pumping light. In this case, the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band is pumped in both the forward and reverse directions with respect to the optical waveguide in which the Tm element is added to the optical waveguide region. Supplied from Then, the gain flatness of the optical waveguide and the output signal light power are constant by adjusting the power of the pumping light supplied from the forward direction and / or the reverse direction to the optical waveguide by the control means. Feedforward controlled. Therefore, this optical amplifier is not necessarily required to have a means for monitoring the power or wave number of the output signal light for feedback control, and is suitable because it is small in size and inexpensive.
[0025]
In the optical amplifier according to the present invention, the optical waveguide is preferably an optical fiber in which a Tm element is added to a part or all of the core region. This is preferable in that the waveguide length can be easily increased.
[0026]
  An optical communication system according to the present invention includes the optical amplifier according to the present invention described above, and transmits signal light and optically amplifies the signal light by the optical amplifier. According to this optical communication system, signal light in a predetermined wavelength band (1455-1485 nm) is optically amplified by the optical amplifier. Therefore, the transmission quality of the signal light in the predetermined wavelength band is excellent.
  The control method according to the present invention is supplied to an optical waveguide to which a Tm element is added.pluralThe excitation light power is either the power of light output from the optical waveguide or the power of spontaneous emission light generated in the optical waveguide.2 wavelengthsAdjust based on the results monitored byTherebyOptical waveguideBetween two wavelengths of signal light output fromGain flatnessTo be constantcontrolShikatsuPower of signal light output from the optical waveguideALC so that is constantControl. The excitation light includes a first excitation light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band and a second excitation light having a wavelength of 1.55 to 1.65 μm, and the power of the second excitation light. By adjusting the optical waveguideSignal light output fromofBetween two wavelengthsGain flatnessALC so that is constantThe power of the signal light output from the optical waveguide by controlling and adjusting the power of the first pumping lightALC so that is constantIt is preferable to control. The excitation light includes excitation light having a wavelength of 1.05 μm band or wavelength of 1.4 μm, which is supplied to the optical waveguide from both the forward direction and the reverse direction, and the excitation light supplied from the forward direction. Optical waveguide by adjusting powerSignal light output fromofBetween two wavelengthsGain flatnessTo be constantThe power of the signal light output from the optical waveguide by controlling and adjusting the power of the pumping light supplied from the opposite directionALC so that is constantIt is preferable to control.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[0028]
(First Embodiment of Optical Amplifier)
First, a first embodiment of an optical amplifier according to the present invention will be described. FIG. 1 is a configuration diagram of an optical amplifier 100 according to the first embodiment. The optical amplifier 100 shown in this figure includes an optical isolator 111, an optical coupler 121, an optical coupler 122, an optical amplification fiber 140, an optical coupler 123, an optical isolator 112, and an optical branch in order from the input port 101 to the output port 102. A coupler 151 is provided. The optical amplifier 100 includes an excitation light source 131 connected to the optical coupler 121, an excitation light source 132 connected to the optical coupler 122, an excitation light source 133 connected to the optical coupler 123, and an output connected to the optical branching coupler 151. A light monitor unit 152, a side spontaneous emission light monitor unit 160, and a control unit 190 are also provided.
[0029]
The optical amplification fiber 140 is an optical waveguide using fluoride glass or tellurite glass as host glass, and is TDF in which a Tm element is added at least in the core region. The optical amplification fiber 140 optically amplifies signal light having a wavelength within a predetermined wavelength band (1455-1485 nm) when supplied with pumping light.
[0030]
The optical couplers 121 to 123 and the excitation light sources 131 to 133 act as excitation light supply means for supplying excitation light to the optical amplification fiber 140. The excitation light source 131 is an excitation light P having a wavelength band of 1.55 to 1.65 μm.₂Is output. As the excitation light source 131, a semiconductor laser light source or the like is preferably used. On the other hand, each of the excitation light sources 132 and 133 has excitation light P having a wavelength of 1.05 μm band or 1.4 μm band.₁Is output. As the excitation light sources 132 and 133, a semiconductor laser excitation Nd: YLF laser light source, Nd: YAG laser light source, Yb laser light source, or the like is preferably used.
[0031]
The optical coupler 121 outputs the pumping light P output from the pumping light source 131.₂Are output toward the optical coupler 122, and the signal light input from the optical isolator 111 is also output toward the optical coupler 122. The optical coupler 122 outputs the excitation light P output from the excitation light source 132.₁Is supplied to the optical amplification fiber 140 from the forward direction, and the signal light and the pumping light P input from the optical coupler 121 are supplied.₂Is output toward the amplifying fiber 140. Further, the optical coupler 123 outputs the pumping light P output from the pumping light source 133.₁Is supplied to the optical amplification fiber 140 from the opposite direction, and the signal light input from the optical amplification fiber 140 is output to the optical isolator 112.
[0032]
Each of the optical isolators 111 and 112 allows light to pass only in the forward direction (direction from the input port 101 to the output port 102), but does not allow light to pass in the reverse direction.
[0033]
The optical branching coupler 151 is provided on the optical path between the optical isolator 112 and the output port 102, and is part of the power of the light output from the optical amplification fiber 140 and passing through the optical coupler 123 and the optical isolator 112. And the branched light is output to the output light monitor unit 152. The output light monitor unit 152 receives light that has arrived from the optical branching coupler 151 and monitors the power of the light at two or more wavelengths. As a result, the output light monitor unit 152 can monitor the gain flatness of the optical amplifier 100 and can also monitor the power of the signal light output from the optical amplifier 100.
[0034]
The light monitored by the output light monitor unit 152 may be signal light that has been optically amplified and output in the optical amplification fiber 140, or spontaneous emission light that is generated and optically amplified in the optical amplification fiber 140. Alternatively, it may be pilot light output after being optically amplified in the optical amplification fiber 140. The pilot light is input to the optical amplifier 100 for the purpose of monitoring the gain of the optical amplifier 100, and is light having a wavelength different from the signal light wavelength, and preferably within the signal light wavelength band. A wavelength is set for each of the long wavelength side and the short wavelength side. When this pilot light is used, the gain of the optical amplifier 100 can be monitored even when the wave number of the input signal light fluctuates.
[0035]
The side spontaneous emission monitor 160 monitors the power of spontaneous emission emitted to the side of the optical amplification fiber 140 at two or more wavelengths. Thereby, the side spontaneous emission light monitoring unit 160 can monitor the gain flatness of the optical amplifier 100 and can also monitor the power of the signal light output from the optical amplifier 100. In this case, since light is not extracted from the signal light main line connected to the optical amplification fiber 140 but spontaneous emission light emitted to the side of the optical amplification fiber 140 is monitored, an increase in insertion loss is increased. It is preferable in that there is no point. The output light monitoring unit 152 and the side spontaneous emission light monitoring unit 160 may have the same configuration, and will be described later with reference to FIGS.
[0036]
The control unit 190 receives a monitoring result from the output light monitoring unit 152 or the side spontaneous emission light monitoring unit 160. And the control part 190 controls the power of the excitation light output from each of the excitation light sources 131-133 based on this monitor result.
[0037]
The optical amplifier 100 operates under the control of the control unit 190 that receives the monitoring result from the output light monitoring unit 152 or the side spontaneous emission light monitoring unit 160. Excitation light P output from the excitation light source 131₂Is supplied from the forward direction to the optical amplification fiber 140 via the optical coupler 121 and the optical coupler 122. Excitation light P output from the excitation light source 132₁Is supplied to the optical amplification fiber 140 from the forward direction via the optical coupler 122. Further, the excitation light P output from the excitation light source 133₁Is supplied to the optical amplification fiber 140 from the reverse direction via the optical coupler 123. The signal light input to the input port 101 enters the optical amplification fiber 140 through the optical isolator 111, the optical coupler 121, and the optical coupler 122, and is optically amplified in the optical amplification fiber 140. The signal light optically amplified by the optical amplification fiber 140 is output from the output port 102 via the optical coupler 123, the optical isolator 112, and the optical branching coupler 151. A part of the light output from the optical amplification fiber 140 is branched by the optical branching coupler 151, and the power is monitored by the output light monitoring unit 152 at two or more wavelengths. Based on the monitoring result, the control unit 190 adjusts the power of the excitation light output from each of the excitation light sources 131 to 133.
[0038]
FIG. 2 is a diagram illustrating a configuration example of the output light monitoring unit 152 of the optical amplifier 100 according to the first embodiment. The output light monitor unit 152 shown in FIG.₁153₂, Optical filter 154₁, 154₂, And light receiving element 155₁~ 155_Threehave. Optical branching coupler 153₁Divides the light that has arrived from the optical branching coupler 151 into two, and splits one of the lights into the optical branching coupler 153₂To the light receiving element 155_ThreeOutput to. Optical branching coupler 153₂The optical branching coupler 153₁The light that has arrived is branched into two, and one of the branched lights is split into an optical filter 154.₁And output the other light to the optical filter 154₂Output to.
[0039]
Optical filter 154₁The optical branching coupler 153₂The light that has arrived more is input, and light having a specific wavelength on the short wavelength side of the wavelength band of the signal light that is optically amplified in the optical amplification fiber 140 is selectively transmitted. Optical filter 154₂The optical branching coupler 153₂The light that has arrived is input, and light having a specific wavelength on the long wavelength side in the signal light wavelength band is selectively transmitted.
[0040]
Light receiving element 155₁The optical filter 154₁Is transmitted to the controller 190 according to the power of the received light. Light receiving element 155₂The optical filter 154₂Is transmitted to the controller 190 according to the power of the received light. In addition, the light receiving element 155_ThreeThe optical branching coupler 153₁The light that has arrived is received, and an electric signal corresponding to the power of the received light is output to the control unit 190.
[0041]
Therefore, the output light monitor unit 152 shown in FIG.₁And 155₂Thus, the power of the light reaching from the optical branching coupler 151 can be monitored with two wavelengths, and the gain tilt can be monitored. The output light monitor unit 152 includes a light receiving element 155._ThreeThus, the total power of the light reaching from the optical branching coupler 151 can be monitored. This output light monitor unit 152 is preferable in that it has a simple configuration and is inexpensive.
[0042]
FIG. 3 is a diagram illustrating another configuration example of the output light monitoring unit 152 of the optical amplifier 100 according to the first embodiment. The output light monitor unit 152 shown in this figure includes an arrayed waveguide grating (AWG) 156 and a light receiving element 157.₁~ 157_Nhave. However, N is an integer of 2 or more.
[0043]
The AWG 156 is a diffraction grating in which a plurality of optical waveguides are formed in an array on a planar substrate, and can input and output input light by being multiplexed or demultiplexed. Here, the AWG 156 is used as an optical demultiplexer. That is, the AWG 156 demultiplexes the light that has arrived from the optical branching coupler 151, and receives the demultiplexed light of each wavelength as the light receiving element 157.₁~ 157_NOutput to. Light receiving element 157₁~ 157_NEach receives light of each wavelength outputted and reached by the AWG 156 and outputs an electric signal corresponding to the power of the received light to the control unit 190.
[0044]
Therefore, the output light monitor unit 152 shown in FIG.₁~ 157_NAs a result, the power of light reaching from the optical branching coupler 151 can be monitored at the N wavelength, and the gain tilt can be monitored. The output light monitor unit 152 includes a light receiving element 157.₁~ 157_NBased on the respective monitoring results, the total power of the light reaching from the optical branching coupler 151 can be monitored. The output light monitor unit 152 is suitable in these respects because it can monitor with many wavelengths with high accuracy and can cope with increase / decrease of the wave number of the input signal light.
[0045]
Next, the control operation of the control unit 190 in the optical amplifier 100 according to the first embodiment will be described. The control by the control unit 190 is feedback control performed based on the monitoring result (gain tilt, output signal light power) by the output light monitor unit 152 or the lateral spontaneous emission light monitor unit 160, and any of the excitation light sources 131 to 133 is controlled. This adjusts the power of the pumping light output from the head. There are three control methods described below.
[0046]
In the first control method, the control unit 190 determines whether the gain tilt obtained by monitoring is positive or negative, and if the gain tilt is positive, the optical amplification fiber from the pump light source 131. Excitation light P supplied to 140₂If the power of the (wavelength 1.55 to 1.65 μm band) is reduced and conversely the gain slope is negative, the pump light P₂Increase the power of. Further, the control unit 190 compares the monitored output signal light power with the design value, and if the output signal light power is smaller than the design value, the control unit 190 supplies the light amplification fiber 140 from the pump light source 132 or the pump light source 133. Excitation light P₁If the power of the (wavelength 1.05 μm band or 1.4 μm band) is increased and, conversely, if the output signal light power is greater than the design value, the excitation light P₁Reduce the power of. The control unit 190 uses the excitation light P₁Power control and pumping light P₂It is preferable to alternately perform power control.
[0047]
FIG. 4 is a diagram illustrating a gain spectrum when ALC is performed by the first control method in the optical amplifier 100 according to the first embodiment, and FIG. 5 illustrates the pumping light P at this time.₂It is a figure which shows the relationship between this power and input signal light power. Here, the power P of the total signal light input to the optical amplifier 100_inAre -4.2 dBm, -3.2 dBm, -2.2 dBm, -1.2 dBm, -0.2 dBm, and +0.8 dBm, respectively, the power P of the total signal light to be output_outThe power of each pumping light was controlled so as to be +18 dBm. Excitation light P supplied from the excitation light source 131 to the optical amplification fiber 140₂The wavelength of was 1557 nm. Excitation light P supplied from the excitation light source 132 or the excitation light source 133 to the optical amplification fiber 140₁The wavelength of was 1.05 μm. As shown in FIG. 4, even when the input signal light power is changed, the gain flatness is maintained and the output signal light power is kept constant. Further, as shown in FIG. 5, the excitation light P at the time of ALC₂Is well approximated by a first order function or a second order function of the input signal light power.
[0048]
FIG. 6 is a diagram showing a gain spectrum when AGC is performed by the first control method in the optical amplifier 100 according to the first embodiment, and FIG. 7 shows the pumping light P at this time.₂It is a figure which shows the relationship between the power of and the wave number of input signal light. Here, the power of each pumping light was controlled so that the gain peak was 18 dB when the wave numbers of the signal light input to the optical amplifier 100 were 10, 12, 16, 20, 26, and 32, respectively. Excitation light P supplied from the excitation light source 131 to the optical amplification fiber 140₂The wavelength of was 1557 nm. Excitation light P supplied from the excitation light source 132 or the excitation light source 133 to the optical amplification fiber 140₁The wavelength of was 1.05 μm. As shown in FIG. 6, even when the wave number of the input signal light changes, the gain flatness is maintained and the output signal light power is maintained constant. Further, as shown in FIG. 7, the excitation light P at the time of AGC₂Is well approximated by a first order function or a second order function of the wave number of the input signal light.
[0049]
In the second control method, the control unit 190 determines whether the gain tilt obtained by monitoring is positive or negative, and if the gain tilt is positive, the optical amplification fiber from the pump light source 132. The power of the pumping light (forward pumping light) supplied from the forward direction to 140 is reduced. Conversely, if the gain slope is negative, the power of the forward pumping light is increased. Further, the control unit 190 compares the monitored output signal light power with the design value, and if the output signal light power is smaller than the design value, the control unit 190 is supplied from the pumping light source 133 to the optical amplification fiber 140 from the reverse direction. If the output signal light power is larger than the design value, the power of the reverse excitation light is decreased. It is preferable that the controller 190 alternately controls the power of the forward pumping light and the power of the backward pumping light. In the second control method, the pumping light source 131 and the optical coupler 121 are unnecessary, and the optical amplifier 100 is small and inexpensive.
[0050]
In this second control method, the power of the pumping light supplied to the optical amplification fiber 140 and the gain are in a substantially proportional relationship, and the gain peak and the degree of saturation of the inversion distribution are in a substantially proportional relationship. This is based on the fact that the gain peak has a correlation with the value of the power ratio between the signal light and the pump light.
[0051]
The degree of saturation of the inversion distribution is determined in the vicinity of the output end of the optical amplification optical fiber 140 where the signal light power approaches the pumping light power. For this reason, in the case of AGC in which the output signal light power decreases as the input signal light power decreases, it is necessary to reduce the backward pumping light power accordingly. On the other hand, since it is necessary to control the gain so as to be constant in AGC, it is necessary to increase the forward pumping light power to reduce the fluctuation of the entire pumping light power.
[0052]
In the case of ALC, since it is necessary to keep the output signal light power constant, the change in the backward pumping light power cannot be increased. On the other hand, it is necessary to increase the gain as the input signal light power decreases. Therefore, in order to increase the overall pumping light power, it is necessary to increase the forward pumping light power.
[0053]
That is, in both cases of ALC and AGC, when the input signal light power decreases, it is necessary to increase the forward pumping light power. The second control method is based on such a concept.
[0054]
FIG. 8 is a diagram illustrating a gain spectrum when ALC is performed by the second control method in the optical amplifier 100 according to the first embodiment. FIG. 9 is a diagram illustrating forward power and backward pumping power at this time. FIG. 10 is a diagram showing the relationship between each optical power and the input signal light power, and FIG. 10 is a diagram showing the relationship between the forward pumping light power and the input signal light power at this time. FIG. 10 also shows an approximate curve represented by a linear function. Here, the power P of the total signal light input to the optical amplifier 100_inAre -4.2 dBm, -3.2 dBm, -2.2 dBm, -1.2 dBm, -0.2 dBm, and +0.8 dBm, respectively, the power P of the total signal light to be output_outThe power of each pumping light was controlled so as to be +18 dBm. As shown in FIG. 8, even when the input signal light power changes, the gain flatness is maintained and the output signal light power is maintained constant. Also, as shown in FIG. 10, the forward pumping light power at the time of ALC is well approximated by the first order function of the input signal light power.
[0055]
FIG. 11 is a diagram showing a gain spectrum when AGC is performed by the second control method in the optical amplifier 100 according to the first embodiment, and FIG. 12 shows the forward pumping light power and the backward pumping at this time. FIG. 13 is a diagram illustrating the relationship between the optical power and the input signal light power. FIG. 13 is a diagram illustrating the relationship between the wave number of the input signal light and the input signal light power at this time. FIG. 13 also shows an approximate curve represented by a quadratic function. Here, the power of each pumping light was controlled so that the gain peak was 18 dB when the wave numbers of the signal light input to the optical amplifier 100 were 10, 12, 16, 20, 26, and 32, respectively. As shown in FIG. 11, even when the wave number of the input signal light changes, the gain flatness is maintained and the output signal light power is kept constant. Further, as shown in FIG. 13, the forward pumping light power at the time of AGC is well approximated by a secondary function of the wave number of the input signal light.
[0056]
In the third control method, the control unit 190 determines whether the gain slope obtained by monitoring is positive or negative, and if the gain slope is positive, the ratio (forward pumping light power / On the contrary, if the gain slope is negative, the ratio is increased. Further, the control unit 190 compares the monitored output signal light power with the design value, and if the output signal light power is smaller than the design value, the control unit 190 calculates the sum of the forward pump light power and the reverse pump light power. Conversely, if the output signal light power is greater than the design value, the sum is reduced. The control unit 190 preferably performs the ratio control and the sum control alternately. Even in the third control method, the pumping light source 131 and the optical coupler 121 are not necessary. Even with the third control method, even when the input signal light power changes during ALC, the gain flatness is maintained and the output signal light power is maintained constant. Further, even when the wave number of the input signal light changes during AGC, the gain flatness is maintained and the output signal light power is kept constant.
[0057]
(Second Embodiment of Optical Amplifier)
Next, a second embodiment of the optical amplifier according to the present invention will be described. FIG. 14 is a configuration diagram of an optical amplifier 200 according to the second embodiment. The optical amplifier 200 shown in this figure includes an optical branching coupler 251, an optical isolator 211, an optical coupler 221, an optical coupler 222, an optical amplifying fiber 240, an optical coupler 223, an optical fiber in order from the input port 201 to the output port 202. An isolator 212 is provided. The optical amplifier 200 also includes an excitation light source 231 connected to the optical coupler 221, an excitation light source 232 connected to the optical coupler 222, an excitation light source 233 connected to the optical coupler 223, and an input connected to the optical branching coupler 251. An optical monitor unit 252 and a control unit 290 are also provided.
[0058]
The optical amplification fiber 240 is an optical waveguide using fluoride glass or tellurite glass as host glass, and is TDF in which a Tm element is added at least in the core region. The optical amplification fiber 240 optically amplifies signal light having a wavelength within a predetermined wavelength band (1455-1485 nm) when supplied with pumping light.
[0059]
The optical couplers 221 to 223 and the excitation light sources 231 to 233 function as excitation light supply means for supplying excitation light to the optical amplification fiber 240. The excitation light source 231 is an excitation light P having a wavelength band of 1.55 to 1.65 μm.₂Is output. A semiconductor laser light source or the like is preferably used as the excitation light source 231. On the other hand, each of the excitation light sources 232 and 233 has excitation light P having a wavelength of 1.05 μm band or 1.4 μm band.₁Is output. As the excitation light sources 232 and 233, a semiconductor laser excitation Nd: YLF laser light source, an Nd: YAG laser light source, a Yb laser light source, or the like is preferably used.
[0060]
The optical coupler 221 outputs the pumping light P output from the pumping light source 231.₂Is output toward the optical coupler 222, and the signal light input from the optical isolator 211 is also output toward the optical coupler 222. The optical coupler 222 outputs the pumping light P output from the pumping light source 232.₁Is supplied to the optical amplification fiber 240 from the forward direction, and the signal light and the excitation light P input from the optical coupler 221 are supplied.₂Is output toward the amplifying fiber 240. Further, the optical coupler 223 outputs the pumping light P output from the pumping light source 233.₁Is supplied to the optical amplifying fiber 240 from the opposite direction, and the signal light input from the optical amplifying fiber 240 is output toward the optical isolator 212.
[0061]
Each of the optical isolators 211 and 212 allows light to pass only in the forward direction (direction from the input port 201 to the output port 202), but does not allow light to pass in the reverse direction.
[0062]
The optical branching coupler 251 is provided on the optical path between the input port 201 and the optical isolator 211. The optical branching coupler 251 branches a part of the power of the light input from the input port 201 and monitors the branched light as an input optical monitor. Output to the unit 252. The input light monitor unit 252 receives the light that has arrived from the optical branching coupler 251 and monitors the power or wave number of the signal light input to the optical amplifier 200. The input light monitoring unit 252 may have the same configuration as that shown in FIG. The control unit 290 receives the monitoring result from the input light monitoring unit 252 and controls the power of the excitation light output from each of the excitation light sources 231 to 233 based on the monitoring result. Note that the optical branching coupler 251 and the input monitor unit 252 are not necessarily provided, and the control unit 290 may receive the power or wave number of the input signal light from other means. In this case, the optical amplifier 200 is small and inexpensive.
[0063]
The optical amplifier 200 operates under the control of the control unit 290. Excitation light P output from the excitation light source 231₂Is supplied from the forward direction to the optical amplifying fiber 240 via the optical coupler 221 and the optical coupler 222. Excitation light P output from the excitation light source 232₁Is supplied from the forward direction to the optical amplification fiber 240 via the optical coupler 222. Also, the excitation light P output from the excitation light source 233₁Is supplied to the optical amplification fiber 240 from the reverse direction via the optical coupler 223. The signal light input to the input port 201 enters the optical amplification fiber 240 through the optical branching coupler 251, the optical isolator 211, the optical coupler 221, and the optical coupler 222, and is optically amplified in the optical amplification fiber 240. The signal light optically amplified by the optical amplification fiber 240 is output from the output port 202 via the optical coupler 223 and the optical isolator 212. Part of the signal light input from the input port 201 is branched by the optical branching coupler 251 and the power is monitored by the output light monitoring unit 252 at two or more wavelengths. Based on the monitoring result, the control unit 290 adjusts the power of the excitation light output from each of the excitation light sources 231 to 233. Note that the power of pumping light output from each of the pumping light sources 231 to 233 may be adjusted by the control unit 290 based on the power or wave number of input signal light received from other means.
[0064]
Next, the control operation of the control unit 290 in the optical amplifier 200 according to the second embodiment will be described. The control by the control unit 290 is feedforward control performed based on the power or wave number of the input signal light, and adjusts the power of the pumping light output from any of the pumping light sources 231 to 233. The control method in the optical amplifier 200 according to the second embodiment is substantially the same as the first to third control methods in the optical amplifier 100 according to the first embodiment. However, the first embodiment is feedback control, but the second embodiment is different in that it is feedforward control.
[0065]
That is, in the first control method, as shown in FIG.₂Is well approximated by a first-order function or a second-order function of the input signal light power, and, as shown in FIG.₂Is well approximated by a first order function or a second order function of the wave number of the input signal light. In the second or third control method, as shown in FIG. 10, the forward pumping light power at the time of ALC is well approximated by the first-order function of the input signal light power, and as shown in FIG. The forward pumping light power during AGC is well approximated by a second order function of the wave number of the input signal light. Therefore, the control unit 290 adjusts the power of the pumping light output from any of the pumping light sources 231 to 233 based on the power or wave number of the input signal light, and any one of the first to third control methods. Execute. By doing so, even when the input signal light power changes during ALC, the gain flatness is maintained and the output signal light power is kept constant. Further, even when the wave number of the input signal light changes during AGC, the gain flatness is maintained and the output signal light power is kept constant.
[0066]
In the present embodiment, means for monitoring the power or wave number of the input signal light may not necessarily be provided, and the control unit 290 may receive the power or wave number of the input signal light from other means. . In this case, the optical amplifier 200 is suitable because it is small and inexpensive. In the present embodiment, since the power of the pumping light output from any of the pumping light sources 231 to 233 is adjusted based on the power or wave number of the input signal light, the control unit 290 performs calculation for that purpose. There is a need. However, since the calculation is simple, it hardly causes a load on the control unit 290.
[0067]
(Third embodiment)
Next, a third embodiment of the optical amplifier according to the present invention will be described. FIG. 15 is a configuration diagram of an optical amplifier 300 according to the third embodiment. The optical amplifier 300 shown in this figure includes an optical coupler 351, an optical isolator 311, an optical coupler 321, an optical coupler 322, an optical amplification fiber 340, an optical coupler 323, and an optical isolator in order from the input port 301 to the output port 302. 312 and an optical coupler 353. The optical amplifier 300 includes a pumping light source 331 connected to the optical coupler 321, a pumping light source 332 connected to the optical coupler 322, a pumping light source 333 connected to the optical coupler 323, and a monitoring light connected to the optical coupler 351. A monitor unit 352, a monitoring light source 354 connected to the optical coupler 353, and a control unit 390 are also provided.
[0068]
The optical amplification fiber 340 is an optical waveguide using fluoride glass or tellurite glass as a host glass, and is TDF in which a Tm element is added at least in the core region. The optical amplification fiber 340 optically amplifies signal light having a wavelength in a predetermined wavelength band (1455-1485 nm) when supplied with pumping light.
[0069]
The optical couplers 321 to 323 and the excitation light sources 331 to 333 function as excitation light supply means for supplying excitation light to the optical amplification fiber 340. The excitation light source 331 is an excitation light P having a wavelength band of 1.55 to 1.65 μm.₂Is output. A semiconductor laser light source or the like is preferably used as the excitation light source 331. On the other hand, each of the excitation light sources 332 and 333 has excitation light P having a wavelength of 1.05 μm band or 1.4 μm band.₁Is output. As the excitation light sources 332 and 333, a semiconductor laser excitation Nd: YLF laser light source, Nd: YAG laser light source, Yb laser light source, or the like is preferably used.
[0070]
The optical coupler 321 outputs the pumping light P output from the pumping light source 331.₂Is output toward the optical coupler 322, and the signal light input from the optical isolator 311 is also output toward the optical coupler 322. The optical coupler 322 outputs the pumping light P output from the pumping light source 332.₁Is supplied to the optical amplification fiber 340 from the forward direction, and the signal light and the excitation light P input from the optical coupler 321 are supplied.₂Is output toward the amplifying fiber 340. In addition, the optical coupler 323 outputs the excitation light P output from the excitation light source 333.₁Is supplied to the optical amplification fiber 340 from the opposite direction, and the signal light input from the optical amplification fiber 340 is output toward the optical isolator 312.
[0071]
Each of the optical isolators 311 and 312 allows light to pass only in the forward direction (direction from the input port 301 to the output port 302), but does not allow light to pass in the reverse direction.
[0072]
The optical coupler 351 is provided on the optical path between the input port 301 and the optical isolator 311. Of the light (including signal light and monitoring light) input from the input port 301, the signal light is transmitted to the optical isolator 311. The monitoring light is output to the monitoring light monitoring unit 352. The monitoring light monitor unit 352 monitors the power or wave number of the signal light input to the optical amplifier 300 based on the monitoring light reaching from the optical coupler 351. The monitoring light source 354 outputs monitoring light having a wavelength different from the signal light wavelength. The optical coupler 353 combines the signal light reaching from the optical isolator 312 and the signal light reaching from the monitoring light source 354 and outputs the combined light toward the output port 302.
[0073]
The control unit 390 receives the monitoring result from the monitoring light monitoring unit 352, controls the power of the excitation light output from each of the excitation light sources 331 to 333 based on the monitoring result, and also monitors the monitoring light from the monitoring light source 354. Control the output.
[0074]
The optical amplifier 300 operates under the control of the control unit 390. Excitation light P output from the excitation light source 331₂Is supplied to the optical amplifying fiber 340 from the forward direction through the optical coupler 321 and the optical coupler 322. Excitation light P output from the excitation light source 332₁Is supplied from the forward direction to the optical amplification fiber 340 via the optical coupler 322. Also, the excitation light P output from the excitation light source 333₁Is supplied to the optical amplification fiber 340 from the reverse direction via the optical coupler 323. The signal light input to the input port 301 enters the optical amplification fiber 340 through the optical coupler 351, the optical isolator 311, the optical coupler 321, and the optical coupler 322, and is optically amplified in the optical amplification fiber 340. The signal light amplified by the optical amplification fiber 340 is output from the output port 302 via the optical coupler 323, the optical isolator 312, and the optical coupler 353. The monitoring light input from the input port 301 is demultiplexed by the optical coupler 351 and input to the monitoring light monitor unit 352. The monitoring light monitor unit 352 monitors the power or wave number of the signal light input to the optical amplifier 300 based on the monitoring light. And based on this monitoring result, the power of the excitation light output from each of the excitation light sources 331 to 333 is adjusted by the control unit 390.
[0075]
Next, the control operation of the control unit 390 in the optical amplifier 300 according to the third embodiment will be described. The control by the control unit 390 is feedforward control based on the power or wave number of the input signal light obtained by monitoring the monitoring light, and the power of the pumping light output from any of the pumping light sources 331 to 333 is controlled. To be adjusted. The control method in the optical amplifier 300 according to the third embodiment is substantially the same feedforward control as the first to third control methods in the optical amplifier 200 according to the second embodiment.
[0076]
That is, in the first control method, as shown in FIG.₂Is well approximated by a first-order function or a second-order function of the input signal light power, and, as shown in FIG.₂Is well approximated by a first order function or a second order function of the wave number of the input signal light. In the second or third control method, as shown in FIG. 10, the forward pumping light power at the time of ALC is well approximated by the first-order function of the input signal light power, and as shown in FIG. The forward pumping light power during AGC is well approximated by a second order function of the wave number of the input signal light. Therefore, the control unit 390 adjusts the power of the pumping light output from any of the pumping light sources 331 to 333 based on the power or wave number of the input signal light, and any one of the first to third control methods. Execute. By doing so, even when the input signal light power changes during ALC, the gain flatness is maintained and the output signal light power is kept constant. Further, even when the wave number of the input signal light changes during AGC, the gain flatness is maintained and the output signal light power is kept constant.
[0077]
(Embodiment of optical communication system)
Next, an embodiment of an optical communication system according to the present invention will be described. FIG. 16 is a configuration diagram of the optical communication system 1 according to the present embodiment. The optical communication system 1 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 receiver 30 and the optical receiver 30.
[0078]
In the optical transmitter 10, a light source unit 11 is provided.₁~ 11_ThreeAnd an optical multiplexer 12 is provided. Light source 11₁Generates multi-wavelength signal light in the S band, combines them, and outputs them. Light source 11₂Generates multi-wavelength signal light in the C band, combines them, and outputs them. Light source 11_ThreeGenerates multi-wavelength signal light in the L band, combines them, and outputs them. The optical multiplexer 12 includes a light source unit 11.₁S-band multi-wavelength signal light output from the light source unit 11₂C-band multi-wavelength signal light output from the light source unit 11 and the light source unit 11_ThreeThe output L-band multi-wavelength signal light is input, combined, and sent to the optical fiber transmission line 40.
[0079]
In the optical repeater 20, an optical demultiplexer 21 and an optical amplifier 22 are provided.₁~ 22_ThreeIn addition, an optical multiplexer 23 is provided. The optical demultiplexer 21 receives the multi-wavelength signal light of each of the S, C, and L bands that has been propagated through the optical fiber transmission line 40, and demultiplexes and outputs the signal light for each band. Optical amplifier 22₁Inputs the S-band multi-wavelength signal light output from the optical demultiplexer 21, and collectively amplifies and outputs these. Optical amplifier 22₂Inputs the C-band multi-wavelength signal light output from the optical demultiplexer 21, and collectively amplifies and outputs these. Optical amplifier 22_ThreeReceives the L-band multi-wavelength signal light output from the optical demultiplexer 21, and amplifies and outputs these signals in a lump. The optical multiplexer 23 includes an optical amplifier 22.₁S-band multi-wavelength signal light optically amplified by the optical amplifier 22₂C-band multi-wavelength signal light optically amplified by the optical amplifier 22 and the optical amplifier 22_ThreeThe L-band multi-wavelength signal light that has been optically amplified is input, combined, and sent to the optical fiber transmission line 50.
[0080]
In the optical receiver 30, a light receiving unit 31 is provided.₁~ 31_N(N is an integer above) and an optical demultiplexer 32 are provided. The optical demultiplexer 32 receives the multi-wavelength signal light of each of the S, C, and L bands that has propagated through the optical fiber transmission line 50 and arrives at it, demultiplexes it for each wavelength, and outputs it. Light receiver 31_nIs the wavelength λ output from the optical demultiplexer 32_nAre received and received (n is an arbitrary integer between 1 and N).
[0081]
Of the three optical amplifiers shown in this figure, the optical amplifier 22 for S band is used.₁Is the same configuration (TDFA) as the optical amplifier 100, 200 or 300 according to this embodiment described above. Also, an optical amplifier 22 for C band₂And L band optical amplifier 22_ThreeEach is an EDFA that optically amplifies signal light by supplying excitation light having a wavelength of 0.98 μm band or 1.48 μm band to the EDF.
[0082]
The optical communication system 1 operates as follows. In the optical transmitter 10, the light source unit 11₁S-band multi-wavelength signal light output from the light source unit 11₂C-band multi-wavelength signal light output from the light source unit 11 and the light source unit 11_ThreeThe output L-band multi-wavelength signal light is combined by the optical multiplexer 12 and transmitted to the optical fiber transmission line 40. In the optical repeater 20, the multi-wavelength signal light in each of the S, C, and L bands that has arrived after propagating through the optical fiber transmission line 40 is demultiplexed for each band by the optical demultiplexer 21. The S-band multi-wavelength signal light demultiplexed and output by the optical demultiplexer 21 is supplied to the optical amplifier 22₁The C-band multi-wavelength signal light that has been optically amplified by the optical amplifier and demultiplexed by the optical demultiplexer 21 is output to the optical amplifier 22.₂The L-band multi-wavelength signal light that is optically amplified by the optical demultiplexer 21 and demultiplexed by the optical demultiplexer 21 is output to the optical amplifier 22._ThreeIs optically amplified. These optically amplified multi-wavelength signal lights of S, C, and L bands are multiplexed by the optical multiplexer 23 and sent to the optical fiber transmission line 50. In the optical receiver 30, the multi-wavelength signal light in each of the S, C, and L bands that has propagated through the optical fiber transmission line 50 and arrived is demultiplexed by wavelength by the optical demultiplexer 32. Then, the wavelength λ output after being demultiplexed by the optical demultiplexer 32_nThe signal light of the light receiving unit 31_nIs received.
[0083]
As described above, the optical communication system 1 multiplexes the multi-wavelength signal lights of the S, C, and L bands and propagates them to the optical fiber transmission lines 40 and 50, so that a large amount of information is transmitted at high speed. be able to. Also, an optical amplifier 22 for S band₁Is the same configuration (TDFA) as the optical amplifier 100, 200 or 300 according to the present embodiment described above, so that the output signal optical power can be kept constant and the gain flatness is kept constant. can do. Therefore, this optical communication system 1 has excellent transmission quality of S-band signal light.
[0084]
(Modification)
The present invention is not limited to the above embodiment, and various modifications can be made. For example, the optical amplification medium included in the optical amplifiers 100, 200, and 300 is an optical fiber (TDF) to which a Tm element is added in the above embodiment, but is not limited to this, and is formed on a planar substrate. A Tm element may be added to the manufactured optical waveguide. However, TDF is preferred in that the waveguide length can be easily increased.
[0085]
【The invention's effect】
As described above in detail, according to the present invention, excitation light (wavelength: 1.05 μm band, 1.4 μm band, or 1.2. 55 to 1.65 μm band) is supplied, and signal light in a predetermined wavelength band (1455 to 1485 nm) is optically amplified and output in this optical waveguide. Either the power of light output from the optical waveguide or the power of spontaneous emission light generated in the optical waveguide is monitored at two or more wavelengths by the monitoring means. Then, based on the result of monitoring by the monitoring unit, the control unit adjusts the power of the pumping light supplied to the optical waveguide by the pumping light supply unit, and the gain flatness of the optical waveguide is feedback-controlled at a constant level. At the same time, the power of the signal light output from the optical waveguide is feedback controlled to be constant.
[0086]
Particularly preferably, the gain flatness of the optical waveguide is controlled to be constant by adjusting the power of the pumping light with a wavelength of 1.55 to 1.65 μm output from the second pumping light source and supplied to the optical waveguide. The Further, the power of the signal light output from the optical waveguide is constant by adjusting the power of the pumping light having a wavelength of 1.05 μm or 1.4 μm that is output from the first pumping light source and supplied to the optical waveguide. Controlled.
[0087]
Preferably, the gain flatness of the optical waveguide is controlled to be constant by adjusting the power of the pumping light having a wavelength of 1.05 μm or 1.4 μm that is supplied from the forward direction to the optical waveguide. Is done. In addition, the power of the signal light output from the optical waveguide is controlled to be constant by adjusting the power of the pumping light having a wavelength of 1.05 μm or 1.4 μm that is supplied to the optical waveguide from the opposite direction. Is done.
[0088]
Preferably, the gain of the optical waveguide is adjusted by adjusting the ratio of the power of the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band supplied from the forward direction and the reverse direction to the optical waveguide, respectively. Flatness is controlled to be constant. Further, the signal light output from the optical waveguide is adjusted by adjusting the sum of the powers of the pumping light of the wavelength 1.05 μm band or the wavelength 1.4 μm band supplied from the forward direction and the reverse direction to the optical waveguide, respectively. Is controlled at a constant power.
[0089]
By the feedback control as described above, the gain flatness of the optical waveguide is controlled to be constant, and the power of the signal light output from the optical waveguide is controlled to be constant, thereby enabling stable operation.
[0090]
Further, according to the present invention, the power of the pumping light output from the second pumping light source and supplied to the optical waveguide is adjusted based on the wave number or power of the signal light input to the optical waveguide. The gain flatness and the output signal light power are feedforward controlled to be constant. Also, by adjusting the power of the pumping light supplied from the forward and / or backward direction to the optical waveguide, the gain flatness of the optical waveguide and the output signal light power are feedforward controlled to be constant. Is done. When such feedforward control is performed, it is preferable because the optical amplifier is small and inexpensive.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical amplifier 100 according to a first embodiment.
FIG. 2 is a diagram illustrating a configuration example of an output light monitoring unit 152 of the optical amplifier 100 according to the first embodiment.
FIG. 3 is a diagram illustrating another configuration example of the output light monitoring unit 152 of the optical amplifier 100 according to the first embodiment.
FIG. 4 is a diagram illustrating a gain spectrum when ALC is performed by the first control method in the optical amplifier 100 according to the first embodiment.
FIG. 5 shows pumping light P when ALC is performed by the first control method in the optical amplifier 100 according to the first embodiment.₂It is a figure which shows the relationship between this power and input signal light power.
FIG. 6 is a diagram showing a gain spectrum when AGC is performed by the first control method in the optical amplifier 100 according to the first embodiment.
FIG. 7 shows pumping light P when AGC is performed by the first control method in the optical amplifier 100 according to the first embodiment.₂It is a figure which shows the relationship between the power of and the wave number of input signal light.
FIG. 8 is a diagram showing a gain spectrum when ALC is performed by the second control method in the optical amplifier 100 according to the first embodiment.
FIG. 9 is a diagram showing a relationship between forward pumping light power and reverse pumping light power and input signal light power when ALC is performed by the second control method in the optical amplifier 100 according to the first embodiment. is there.
FIG. 10 is a diagram showing a relationship between forward pumping light power and input signal light power when ALC is performed by the second control method in the optical amplifier 100 according to the first embodiment.
FIG. 11 is a diagram illustrating a gain spectrum when AGC is performed by the second control method in the optical amplifier 100 according to the first embodiment.
FIG. 12 is a diagram showing a relationship between forward pumping light power and reverse pumping light power and input signal light power when AGC is performed by the second control method in the optical amplifier 100 according to the first embodiment. is there.
FIG. 13 is a diagram showing a relationship between the wave number of input signal light and input signal light power when AGC is performed by the second control method in the optical amplifier 100 according to the first embodiment.
FIG. 14 is a configuration diagram of an optical amplifier 200 according to a second embodiment.
FIG. 15 is a configuration diagram of an optical amplifier 300 according to a third embodiment.
FIG. 16 is a configuration diagram of an optical communication system 1 according to the present embodiment.
FIG. 17 is a diagram for explaining the operation of each of EDFA and TDFA in comparison.
FIG. 18 is a diagram showing a gain spectrum of TDFA when conventional ALC is performed.
FIG. 19 is a diagram showing an output signal light power spectrum of TDFA when conventional ALC is performed.
FIG. 20 is a diagram illustrating a gain spectrum of TDFA when conventional AGC is performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical communication system, 10 ... Optical transmitter, 11 ... Light source part, 12 ... Optical multiplexer, 20 ... Optical repeater, 21 ... Optical demultiplexer, 22 ... Optical amplifier, 23 ... Optical multiplexer, 30 ... Light Receiver 31, light receiver 32, optical demultiplexer 40, 50 optical fiber transmission line 100 optical amplifier 101 input port 102 output port 111, 112 optical isolator 121 to 123 Optical couplers 131 to 133... Pumping light source, 140 optical fiber for amplification, 151 optical branching coupler, 152 output light monitoring unit, 160 side spontaneous emission light monitoring unit, 190 control unit, 200 optical amplifier, DESCRIPTION OF SYMBOLS 201 ... Input port, 202 ... Output port, 211, 212 ... Optical isolator, 221-223 ... Optical coupler, 231-233 ... Excitation light source, 240 ... Optical amplification fiber, 251 ... Optical branching coupler, 252 ... Forced light monitoring unit, 290 ... control unit, 300 ... optical amplifier, 301 ... input port, 302 ... output port, 311, 312 ... optical isolator, 321-323 ... optical coupler, 331-333 ... excitation light source, 340 ... optical amplification Optical fiber, 351... Optical coupler, 352... Monitoring light monitoring unit, 353... Optical coupler, 354.

Claims (18)

An optical waveguide in which a Tm element is added to the optical waveguide region;
A pumping light supply means for supplying a plurality of pumping light supply direction is different to the optical waveguide of the wavelength to the optical waveguide is different or excitation light,
Monitoring means for monitoring the power of light output from the optical waveguide and the power of spontaneous emission light generated in the optical waveguide at two wavelengths;
Based on the result of monitoring by the monitoring unit, the power of the plurality of pumping lights supplied to the optical waveguide by the pumping light supply unit is adjusted, and the signal light output from the optical waveguide is between the two wavelengths. An optical amplifier comprising: control means for controlling the gain flatness of the optical signal to be constant and performing ALC control so that the power of the signal light output from the optical waveguide is constant.   2. The optical amplifier according to claim 1, wherein the monitoring means monitors the power of spontaneous emission light emitted to the side of the optical waveguide. The monitoring means includes
A first optical branching coupler for branching out a part of the power of the light output from the optical waveguide;
A second optical branching coupler for bifurcating the light extracted by the first optical branching coupler;
A first filter that selectively transmits light of a specific first wavelength included in one of the lights branched into two by the second optical branching coupler;
A second filter that selectively transmits light of a specific second wavelength included in the other light branched into two by the second optical branching coupler;
A first light receiving unit that detects the power of the light having the first wavelength that has passed through the first filter;
The optical amplifier according to claim 1, further comprising: a second light receiving unit that detects power of the light having the second wavelength that has passed through the second filter. The monitoring means includes
An optical branching coupler for branching out a part of the power of the light output from the optical waveguide;
A diffraction grating for diffracting the light extracted by the optical branching coupler;
A first light receiving unit for detecting the power of light of a specific first wavelength included in the light diffracted by the diffraction grating;
The optical amplifier according to claim 1, further comprising: a second light receiving unit that detects power of light having a specific second wavelength included in the light diffracted by the diffraction grating. The excitation light supply means includes a first excitation light source that outputs excitation light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band, and a second excitation light source that outputs excitation light having a wavelength of 1.55 to 1.65 μm. And supplying excitation light output from each of the first excitation light source and the second excitation light source to the optical waveguide,
The control means includes
By adjusting the power of the pumping light output from the second pumping light source and supplied to the optical waveguide, the gain flatness of the optical waveguide is controlled,
2. The light according to claim 1, wherein the power of the signal light output from the optical waveguide is controlled by adjusting the power of the excitation light output from the first pumping light source and supplied to the optical waveguide. amplifier.   The power of the pumping light output from the second pumping light source and supplied to the optical waveguide and the power of the pumping light output from the first pumping light source and supplied to the optical waveguide are adjusted alternately. The optical amplifier according to claim 5. The excitation light supply means supplies excitation light of a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward direction and the reverse direction to the optical waveguide,
The control means includes
By adjusting the power of the pumping light supplied from the forward direction to the optical waveguide, the gain flatness of the optical waveguide is controlled,
The optical amplifier according to claim 1, wherein the power of the signal light output from the optical waveguide is controlled by adjusting the power of the pumping light supplied from the opposite direction to the optical waveguide.   8. The optical amplifier according to claim 7, wherein the power of the pumping light supplied from the forward direction and the power of the pumping light supplied from the reverse direction are adjusted alternately. The excitation light supply means supplies excitation light of a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward direction and the reverse direction to the optical waveguide,
The control means includes
By adjusting the ratio of the power of the pumping light supplied from the forward direction and the reverse direction to the optical waveguide, the gain flatness of the optical waveguide is controlled,
The power of the signal light output from the optical waveguide is controlled by adjusting the sum of the powers of pumping light supplied from the forward direction and the reverse direction to the optical waveguide, respectively. The optical amplifier described. An optical waveguide in which a Tm element is added to the optical waveguide region;
A first pumping light source that outputs pumping light in a wavelength band of 1.05 μm or a wavelength of 1.4 μm; and a second pumping light source that outputs pumping light in a wavelength band of 1.55 to 1.65 μm. Excitation light supply means for supplying excitation light output from each of the excitation light source and the second excitation light source to the optical waveguide;
The gain flatness of the optical waveguide and the output signal light are adjusted by adjusting the power of the excitation light output from the second excitation light source and supplied to the optical waveguide based on the wave number of the signal light input to the optical waveguide. An optical amplifier comprising: control means for controlling power. An optical waveguide in which a Tm element is added to the optical waveguide region;
A first pumping light source that outputs pumping light in a wavelength band of 1.05 μm or a wavelength of 1.4 μm; and a second pumping light source that outputs pumping light in a wavelength band of 1.55 to 1.65 μm. Excitation light supply means for supplying excitation light output from each of the excitation light source and the second excitation light source to the optical waveguide;
The gain flatness of the optical waveguide and the output signal light are adjusted by adjusting the power of the pumping light output from the second pumping light source and supplied to the optical waveguide based on the power of the signal light input to the optical waveguide. An optical amplifier comprising: control means for controlling power. An optical waveguide in which a Tm element is added to the optical waveguide region;
Excitation light supply means for supplying excitation light of a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward direction and the reverse direction to the optical waveguide;
The gain of the optical waveguide is adjusted by adjusting the power of the pumping light supplied from the forward direction and / or the reverse direction to the optical waveguide based on the wave number of the signal light input to the optical waveguide. An optical amplifier comprising: control means for controlling flatness and output signal light power. An optical waveguide in which a Tm element is added to the optical waveguide region;
Excitation light supply means for supplying excitation light of a wavelength of 1.05 μm band or a wavelength of 1.4 μm band from both the forward direction and the reverse direction to the optical waveguide;
Based on the power of the signal light input to the optical waveguide, the power of the optical waveguide is adjusted by adjusting the power of the excitation light supplied from the forward direction and / or the reverse direction to the optical waveguide. An optical amplifier comprising: control means for controlling flatness and output signal light power.   The optical amplifier according to any one of claims 1 to 13, wherein the optical waveguide is an optical fiber in which a Tm element is added to a core region.   14. An optical communication system comprising the optical amplifier according to claim 1, wherein the optical amplifier transmits signal light and optically amplifies the signal light by the optical amplifier. A plurality of excitation light power Tm element is supplied to the optical waveguide that is added, the power of light output from the optical waveguide, and one of the spontaneous emission light power generated in the optical waveguide, two wavelengths in based on the monitored results, adjusted, whereby the optical waveguide wherein the output signal light from the gain flatness between 2 wavelengths outputted from the control vital the optical waveguide so as to be constant signal light A control method that performs ALC control so that the power is constant . The excitation light includes a first excitation light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band and a second excitation light having a wavelength of 1.55 to 1.65 μm,
The second power of the excitation light is adjusted, the gain flatness of between 2 wavelengths of the signal light output from the optical waveguide to ALC controlled to be constant,
The first by adjusting the power of the pump light, the signal light power output from the optical waveguide is ALC controlled to be constant, the control method according to claim 16, wherein. The excitation light includes excitation light having a wavelength of 1.05 μm band or a wavelength of 1.4 μm band, which is supplied to the optical waveguide from both the forward direction and the reverse direction,
By adjusting the power of the pumping light supplied from the forward direction , the gain flatness between the two wavelengths of the signal light output from the optical waveguide is controlled to be constant ,
The control method according to claim 16, wherein ALC control is performed so that the power of the signal light output from the optical waveguide is constant by adjusting the power of the pumping light supplied from the reverse direction.

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