JP2008153270A - Optical amplifier and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a matter that constant gain control of respective GBs cannot be carried out individually, and an EDFA becomes expensive because GBs doubling the number of gain equalizers are required and the EDFA has a large number of components. <P>SOLUTION: A first optical amplifier includes a GB, branches provided, respectively, at the signal light input and output stages of the GB, a monitor gain equalizer having a loss spectrum for correcting the gain spectrum deviation of the GB and equalizing the signal light spectrum of output light from the GB branched by a branch arranged at the output stage, a light receiving unit receiving the output from the monitor gain equalizer, and a gain control circuit performing constant gain control of the GB based on the light reception level depending on the output from the monitor gain equalizer of the light receiving unit. Further, a second optical amplifier having gain equalizers arranged between the plurality of first optical amplifiers is constituted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical fiber amplifier and an optical fiber communication system for optically amplifying signal light.

  A configuration relating to constant gain control of an erbium-doped fiber amplifier (EDFA) as an optical amplifier used in a conventional optical fiber communication system is shown in FIGS. 1 and 2 (see, for example, Non-Patent Document 1 or 2).

  FIG. 1 shows a configuration using two erbium-doped fiber (EDF) gain blocks (hereinafter referred to as GB) and one gain equalizer (GEQ) in the middle of them, that is, one GB unit. FIG. 2 shows a configuration using two GB units. However, the GB unit is composed of two GBs and a gain equalizer installed at an intermediate stage between them. Therefore, for convenience, the configuration in FIG. 1 is referred to as a 1GEQ configuration, and the configuration in FIG. 2 is referred to as a 2GEQ configuration. 1 and 2 are dispersion compensating fibers, variable attenuators, optical switches, and the like.

  The gain equalizers 3, 12, and 21 are used for flattening the gain spectrum of the EDFA and expanding the flat gain band. By using a gain equalizer with a larger peak loss, a wider gain is obtained. It is known that bandwidth can be obtained. However, it has been found that in the 1GEQ configuration, the noise figure (NF) of the EDFA deteriorates when the peak loss of the gain equalizers 3, 12, and 21 becomes too large.

  Therefore, it is known that a wider gain band can be obtained by using the 2GEQ configuration instead of the 1GEQ configuration. Also, the reason why GBs 2, 5, 11, 13, 20, and 22 are installed before and after the gain equalizers 3, 12, and 21 in each GB unit is to operate the GB unit with low NF and high output. is there.

  Here, an example of the gain spectrum of GB is shown in FIG. In FIG. 8, the horizontal axis represents wavelength and the vertical axis represents gain. However, this spectrum shape is simplified for easy understanding. When the gain at 1550 nm and 1600 nm is 10 dB, the gain at 1560 nm is 15 dB. Therefore, for example, the gain spectrum of this GB can be flattened using a gain equalizer having a peak loss of 5 dB at 1560 nm.

  1 and 2 is generally performed by comparing the input signal light power and the output signal light power between the GB units. That is, with reference to FIG. 1, the input light and the output light to the EDFA are branched at the front stage and the rear stage branch (the front stage branch 1 and the rear stage branch 6 respectively), and the front stage and the rear stage light receivers (the front stage light receiver 7 respectively Then, the light is received by the rear light receiver 9) to obtain the input and output signal light power.

  Thereafter, the gain control circuit 8 calculates the gain from these powers, and controls the front-stage and rear-stage GB (first GB2 and second GB5, respectively) so that a desired gain can be obtained. In the wavelength division multiplexing optical network system using the constant gain control (AGC), the gain is controlled to be constant at each WDM wavelength particularly when the number of channels and the channel arrangement of the input signal light are changed.

  The above-described constant gain control operation is obviously the same as in FIG. At this time, each GB unit is designed so that the gain spectrum is flat in the optimum operation between the front-stage branches 10 and 19 and the rear-stage branches 14 and 23. Therefore, each GB unit can perform an AGC operation with respect to an arbitrary number and channel arrangement of input signal light.

Masuda et al. Electron. Lett. , Vol. 33, no. 12, pp. 1070-1071, 1997 Masuda et al. Electron. Lett. , Vol. 34, no. 6, pp. 567-568, 1998

  In the above prior art, each GB cannot be individually controlled with a constant gain. Further, GB twice as many as the number of gain equalizers is required, and there are disadvantages that the number of parts of the EDFA is large and the EDFA is expensive.

  That is, in the constant gain control operation of the prior art, in order to perform feedback control for calculating the control gain in the gain control circuit, for example, GB-1 is excited at a constant pumping light power level, and the gain of GB-2 is increased. The EDFA gain is controlled to be constant. Therefore, there is a drawback that the gain of GB-1 changes according to the input signal light power level to the EDFA.

  The present invention has been performed under such a background, and has been a problem in the prior art. Each GB cannot be controlled individually with a constant gain, and the number of gain equalizers is twice the number of gain equalizers. Therefore, an object of the present invention is to provide an optical amplifier and an optical communication system that can solve the disadvantages that the number of parts of the EDFA is large and the EDFA is expensive.

  The present invention has a GB for optically amplifying signal light of a single wavelength or a plurality of wavelengths, a branch installed at each of the signal light input stage and output stage of the GB, and a loss spectrum for correcting the gain spectrum deviation of the GB. And a monitor gain equalizer for equalizing the signal light spectrum of the output light from the GB branched by the branch installed in the output stage, and a photoreceiver receiving the output of the monitor gain equalizer as inputs And a gain control circuit that controls the gain of the GB to be constant based on the light reception level corresponding to the output of the monitor gain equalizer of the light receiver.

  Alternatively, instead of the monitor gain equalizer, an input to the GB having a loss spectrum shape obtained by inverting a loss spectrum for correcting the gain spectrum deviation of the GB and branched by a branch installed in the input stage An inversion monitor gain equalizer for equalizing the signal light level of light may be provided. These are called first optical amplifiers.

  Further, an optical amplifier in which a gain equalizer is installed between each of the plurality of first optical amplifiers can be configured. The gain equalizer can equalize the spectral deviation of the total gain of the plurality of first optical amplifiers. This is called a second optical amplifier.

  According to the present invention, it is not necessary to compare the input signal light power and the output signal light power between the plurality of GB units as in the prior art, so that each GB can be individually controlled with a constant gain. In addition, the number of gain equalizers is halved compared to the prior art, and the disadvantage that the number of EDFA parts is large and the EDFA is expensive can be solved.

  Alternatively, the optical amplifier of the present invention includes a first and second GB that optically amplifies signal light having a single wavelength or a plurality of wavelengths, and a gain equalizer disposed between the first and second GBs, A branch installed in each of the signal light input stage and output stage of the optical circuit comprising the first and second GB and the gain equalizer, and a loss spectrum for correcting the gain spectrum deviation of the optical circuit; A monitor gain equalizer that equalizes the signal light spectrum of the output light from the optical circuit branched by the branch installed in the output stage; and a light receiver that receives the output of the monitor gain equalizer as input A gain control circuit that controls the gain of the optical circuit at a constant level based on the received light level corresponding to the output of the monitor gain equalizer of the light receiver may be provided.

  Further, instead of the monitor gain equalizer, the optical circuit has a loss spectrum shape obtained by inverting the loss spectrum for correcting the gain spectrum deviation of the optical circuit, and is branched by a branch installed in the input stage. An inverting type monitor gain equalizer for equalizing the signal light level of the input light may be provided. These are called third optical amplifiers.

  An optical amplifier in which a gain equalizer is installed between the first optical amplifier and the third optical amplifier can also be configured. At this time, the gain equalizer can equalize the spectral deviation of the total gain of the first optical amplifier and the third optical amplifier.

  An optical communication system including the optical amplifier of the present invention in a transmission apparatus or a relay apparatus can be another aspect of the present invention.

  According to the present invention, each GB can be individually controlled at a constant gain, and the number of parts of the EDFA can be reduced as compared with the conventional case, so that the EDFA can be configured at a low cost.

(First Example)
The configuration of the optical amplifier in the first embodiment of the present invention is shown in FIG. The following points are mainly different from the prior art of FIG. That is, in this embodiment, constant gain control is performed for each GB. When the constant gain control operation is shown for the first GB 31, first, the front branch 30 and the rear branch 32 are installed at the front stage and the rear stage of the first GB 31.

  A monitor gain equalizer 36 is installed between the rear branch 32 and the rear light receiver 35. The loss spectrum of the monitor gain equalizer 36 equalizes the non-flatness of the gain spectrum of the first GB 31. Therefore, the difference between the signal light power received by the rear-stage light receiver 35 and the signal light power received by the front-stage light receiver 33 is equal to the flattening gain of the first GB 31 regardless of the wavelength arrangement of the input signal light.

  That is, the flattening gain of the first GB 31 can be detected and controlled regardless of the wavelength arrangement of the input signal light. The above operation clearly holds for the second GB 40. However, the monitor gain equalizer 45 used in the second GB 40 is referred to as a monitor gain equalizer 45. However, each GB 31 and 40 has a gain medium and an excitation circuit for exciting it. Examples of the optical amplifier include a rare earth doped fiber amplifier, a fiber Raman amplifier, and a semiconductor amplifier.

  On the other hand, in this embodiment, the flat gains after gain equalization of the first GB 31 and the second GB 40 are both 15 dB, the wavelength-independent loss of the optical component 38 is 10 dB, and the flat gain of the entire EDFA is 20 dB.

  FIG. 9 shows gain spectra of the first GB 31 and the second GB 40. In FIG. 9, the horizontal axis represents wavelength and the vertical axis represents gain. Since they are the same spectrum, the graph line appears to be a single line, but the two spectra overlap. FIG. 10 shows a loss spectrum of the gain equalizer 37. In FIG. 10, the horizontal axis indicates the wavelength, and the vertical axis indicates the loss of the gain equalizer 10. However, in order to simplify the explanation, the wavelength-independent loss of the gain equalizer 37 is set to 0 dB. On the other hand, the loss spectra of the monitor gain equalizers 36 and 45 are shown in FIG. In FIG. 11, the horizontal axis indicates the wavelength, and the vertical axis indicates the monitor gain equalizer loss. Since they are the same spectrum, the graph line appears to be a single line, but the two spectra overlap.

  However, if the input signal light power per channel to the first GB 31 and the number of channels are constant, the front branch 30 and the front light receiver 33 for the first GB 31 can be omitted, and the light receiving level of the rear light receiver 35 is made constant. AGC operation is possible.

  As described above, in the present embodiment, the first GB 31 and the second GB 40 can be individually and individually controlled using the monitor gain equalizers 36 and 45, respectively, and the above-described drawbacks of the prior art can be solved.

(Second embodiment)
The configuration of the optical amplifier in the second embodiment of the present invention is shown in FIG. The following points are mainly different from the first embodiment of FIG. That is, in the first embodiment, the monitor gain equalizer 36 or 45 is installed between the rear branch 32, 41 and the rear light receiver 35, 44. However, in this embodiment, the inverting monitor gain is provided. Equalizers 53 and 62 are installed between the pre-stage branches 50 and 59 and the pre-stage light receivers 54 and 63.

  The inverted monitor gain equalizers for the first GB 51 and the second GB 60 are referred to as inverted monitor gain equalizers 53 and 62, respectively. The loss spectra of the inverting type monitor gain equalizers 53 and 62 are shown in FIG. In FIG. 12, the horizontal axis represents the wavelength, and the vertical axis represents the inverting monitor gain equalizer loss. Since they are the same spectrum, the graph line appears to be a single line, but the two spectra overlap. That is, the loss spectrum of the inverting type monitor gain equalizers 53 and 62 is obtained by inverting the loss spectrum of the monitor gain equalizers 36 and 45 up and down to set the minimum loss value to 0 dB.

  The constant gain control operation of the present embodiment will be described for the first GB 51. As in the case of the first embodiment, the difference between the signal light power received by the rear-stage light receiver 56 and the signal light power received by the front-stage light receiver 54 is a fixed value regardless of the wavelength arrangement of the input signal light. , Equal to the flattening gain of the first GB 51. That is, the flattening gain of the first GB 51 can be detected and controlled regardless of the wavelength arrangement of the input signal light.

  As described above, in this embodiment, the first GB 51 and the second GB 60 can be individually controlled individually by using the inverting type monitor gain equalizers 53 and 62, respectively, and the above-mentioned drawbacks of the prior art can be solved.

(Third embodiment)
The configuration of the optical amplifier in the third embodiment of the present invention is shown in FIG. The following points are mainly different from the prior art of FIG. That is, for the two gain equalizers 77 and 86, the number of GB is 4 in the conventional technique, but the number of GB is 3 in the present embodiment. That is, two gain equalizers 77 and 86 equalize the gain deviation, that is, non-flatness of the three GBs 71, 79, and 88. At this time, the gain of the first GB 71 at 1550 nm and 1600 nm is set to 10 dB. The gain spectrum at this time is the same as in FIG. The gains of the second GB 79 and the third GB 88 are also the same as the gain of the first GB 71.

  In this embodiment, unlike the prior art, the peak loss values of the gain equalizers 77 and 86 can be set to arbitrary values independently of the gains of the GBs 71, 79 and 88. As a first example, the peak loss values of the gain equalizers 77 and 86 are both 7.5 dB. The loss spectrum of the gain equalizers 77 and 86 at this time is shown in FIG. In FIG. 13, the horizontal axis represents wavelength and the vertical axis represents gain equalizer loss. Since they are the same spectrum, the graph line appears to be a single line, but the two spectra overlap. As a second example, the peak loss values of the gain equalizers 77 and 86 may be 5 dB and 10 dB, respectively. That is, there is an advantage that the peak loss values of the gain equalizers 77 and 86 can be optimized according to the configuration and operation of the EDFA.

  On the other hand, in the prior art, two GBs and one gain equalizer are paired, and the total gain deviation of the two GBs is equalized by the loss deviation of the gain equalizer. Therefore, the loss spectrum of the gain equalizer is uniquely determined by the total gain deviation of the two GBs used for the combination.

  Further, the peak losses of the monitor gain equalizers 76, 84, 93 in this embodiment are all 5 dB from the gain deviations of the GBs 71, 79, 88. The peak loss spectrum is shown in FIG. In FIG. 14, the horizontal axis indicates the wavelength, and the vertical axis indicates the monitor gain equalizer loss. Since they are the same spectrum, the graph line appears to be a single line, but the three spectra overlap.

  As described above, in this embodiment, the number of GBs can be reduced, and the above-described drawbacks of the conventional technology can be solved.

  Further, instead of the monitor gain equalizers 76, 84, 93, the inverting type monitor gain equalizer described in FIG. 4 (second embodiment) is replaced with the front stage branches 70, 78, 87 and the front stage light receiver 73, You may provide between 81 and 90, respectively.

(Fourth embodiment)
The configuration of the optical amplifier in the fourth embodiment of the present invention is shown in FIG. The following points are mainly different from the third embodiment. That is, in the third embodiment, the first GB 71 and the second GB 79 are individually controlled with constant gain, but in this embodiment, the first GB 101 and the second GB 103 are collectively controlled with constant gain. In this embodiment, a front branch 100 is installed at the front stage of the first GB 101, and a rear branch 104 is installed at the rear stage of the second GB 103, and the first GB 101 and the second GB 103 are connected by the gain control circuit 106 for the first GB 101 and the second GB 103. I have control.

  In this embodiment, the first GB 101 and the second GB 103 are collectively controlled at a constant gain, but the third GB 112 is individually controlled at a constant gain.

  FIG. 15 shows the loss spectrum of the monitor gain equalizer 108 for the first GB 101 and the second GB 103. In FIG. 15, the horizontal axis indicates the wavelength, and the vertical axis indicates the monitor gain equalizer loss. The total loss of the monitor gain equalizer 108 and the gain equalizer 102 equalizes the total gain of the first GB 101 and the second GB 103. Since the spectral deviation of the total gain of the first GB 101 and the second GB 103 is 10 dB and the spectral deviation of the loss of the gain equalizer 102 is 7.5 dB, the spectral deviation of the loss of the monitoring gain equalizer 108 is subtracted by 2 .5 dB.

  This embodiment has an advantage that the number of component parts is smaller than that of the third embodiment. That is, according to the present embodiment, the GB of twice the number of gain equalizers is required, the number of parts of the EDFA is large, and the drawbacks of the above-described conventional technology such that the EDFA is expensive can be solved.

  Further, instead of the monitor gain equalizers 108 and 117, the inverting type monitor gain equalizer described in FIG. 4 (second embodiment) is connected between the front branch 100, 111 and the front light receivers 105, 114. May be provided respectively.

(Fifth embodiment)
The configuration of the optical amplifier in the fifth embodiment of the present invention is shown in FIG. In the present embodiment, the configuration of the constant gain control system of each GB 31 and 40 in the first embodiment is shown more specifically. That is, in this embodiment, an erbium-doped fiber (EDF) 122 is used as the gain medium of the optical amplifier, and signal light and pump light multiplexers (each pre-stage multiplexer 121 respectively) are provided upstream and downstream of the EDF 122. And a post-stage multiplexer 123).

  The pumping light is emitted from pumping light sources (the pre-stage pumping light source 128 and the post-stage pumping light source 129, respectively) connected to the pre-stage multiplexer 121 and the post-stage multiplexer 123, respectively. The front-stage pumping light source 128 and the rear-stage pumping light source 129 are controlled by a gain control circuit 126 adjacent to them.

  The first to fourth embodiments of the present invention are apparent from the operation thereof, but may be an optical amplifier using the EDF, that is, an EDFA, or another rare earth-doped fiber amplifier, a fiber Raman amplifier, and a semiconductor amplifier. .

  According to the present invention, each GB cannot be individually controlled with a constant gain, which is a problem in the prior art, and requires twice as many GB as the number of gain equalizers. Since the disadvantage of being expensive can be solved, an optical amplifier and an optical communication system which are inexpensive and simple in configuration can be realized.

1 is a configuration diagram of a conventional optical amplifier (part 1). 2 is a configuration diagram of a conventional optical amplifier (part 2). FIG. The block diagram of the optical amplifier of a 1st Example. The block diagram of the optical amplifier of a 2nd Example. The block diagram of the optical amplifier of a 3rd Example. The block diagram of the optical amplifier of a 4th Example. The block diagram of the optical amplifier of 5th Example. The figure which shows the example of a gain spectrum of the conventional EDFGB. The figure which shows the gain spectrum of EDFGB in a 1st Example. The figure which shows the gain equalizer loss spectrum in a 1st Example. The figure which shows the gain equalizer loss spectrum for a monitor in a 1st Example. The figure which shows the gain equalizer loss spectrum for inversion type monitors in a 2nd Example. The figure which shows the gain equalizer loss spectrum in a 3rd Example. The figure which shows the gain equalizer loss spectrum for a monitor in a 3rd Example. The figure which shows the gain equalizer loss spectrum for a monitor in a 4th Example.

Explanation of symbols

1, 10, 19, 30, 39, 50, 59, 70, 78, 87, 100, 111, 120 First branch 2, 11, 31, 51, 71, 101 First GB
3, 12, 21, 37, 57, 77, 86, 102, 110 Gain equalizer 4, 18, 38, 58, 85, 109 Optical component 5, 13, 40, 60, 79, 103 Second GB
6, 14, 23, 32, 41, 52, 61, 72, 80, 89, 104, 113, 124 Rear branch 7, 15, 24, 33, 42, 54, 63, 73, 81, 90, 105, 114 , 125 Pre-stage photoreceiver 8, 16, 25, 34, 43, 55, 64, 74, 82, 91, 106, 115, 126 Gain control circuit 9, 17, 26, 35, 44, 56, 65, 75, 83 , 92, 107, 116, 127 Subsequent optical receivers 20, 88, 112 Third GB
22 4th GB
36, 45, 76, 84, 93, 108, 117, 130 Monitor gain equalizer 53, 62 Inverted monitor gain equalizer 121 Pre-stage multiplexer 122 EDF
123 Back-stage multiplexer 128 Front-stage pumping light source 129 Back-stage pumping light source

Claims (9)

A gain block for optically amplifying single or multiple wavelength signal light;
Branches installed respectively in the signal light input stage and output stage of the gain block;
A gain equalizer for monitoring having a loss spectrum for correcting a gain spectrum deviation of the gain block, and equalizing a signal light spectrum of the output light from the gain block branched by a branch installed in the output stage;
A photoreceiver that receives the output of the monitor gain equalizer;
A first optical amplifier comprising: a gain control circuit that controls the gain of the gain block to be constant based on a light reception level corresponding to an output of the monitor gain equalizer of the light receiver.   Instead of the monitor gain equalizer, the gain block has a loss spectrum shape obtained by inverting the loss spectrum for correcting the gain spectrum deviation of the gain block, and the input to the gain block branched by the branch installed in the input stage 2. The first optical amplifier according to claim 1, further comprising an inverting type monitor gain equalizer for equalizing a signal light level of light.   A second optical amplifier in which a gain equalizer is installed between the first optical amplifiers according to claim 1 or 2.   The second optical amplifier according to claim 3, wherein the gain equalizer equalizes a spectral deviation of a total gain of the first optical amplifier according to claim 1. First and second gain blocks for optically amplifying single or multiple wavelength signal light;
A gain equalizer disposed between the first and second gain blocks;
Branches installed respectively in the signal light input stage and output stage of the optical circuit comprising the first and second gain blocks and the gain equalizer;
A gain equalizer for monitoring, which has a loss spectrum for correcting a gain spectrum deviation of the optical circuit, and equalizes a signal light spectrum of output light from the optical circuit branched by a branch installed in the output stage;
A photoreceiver that receives the output of the monitor gain equalizer;
A third optical amplifier comprising: a gain control circuit that controls the gain of the optical circuit to be constant based on a light reception level corresponding to an output of the monitor gain equalizer of the light receiver.   Instead of the monitoring gain equalizer, an input to the optical circuit having a loss spectrum shape obtained by inverting a loss spectrum for correcting a gain spectrum deviation of the optical circuit and branched by a branch installed in the input stage 6. The third optical amplifier according to claim 5, further comprising an inverting type monitor gain equalizer for equalizing a signal light level of light.   A fourth optical amplifier in which a gain equalizer is installed between the first optical amplifier according to claim 1 or 2 and the third optical amplifier according to claim 5 or 6.   The fourth gain according to claim 7, wherein the gain equalizer equalizes the spectral deviation of the total gain of the first optical amplifier according to claim 1 or 2 and the third optical amplifier according to claim 5 or 6. Optical amplifier.   The first optical amplifier according to claim 1 or 2, the second optical amplifier according to claim 3 or 4, or the third optical amplifier according to claim 5 or 6, or claim 7 or 8. An optical communication system including the fourth optical amplifier described above in a transmission device or a relay device.

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