JP4616668B2 - Hybrid optical amplifier - Google Patents

Description

  The present invention relates to an optical fiber amplifier used in an optical fiber communication system.

  Recently, a communication system capable of transmitting a large amount of information at high speed has been demanded from the advancement of information technology. An optical fiber communication system using an optical fiber as a transmission medium for constructing a high-speed and large-capacity communication network has attracted attention. Yes. In such a system, since information is transmitted using signal light, various measures are taken for attenuation of the signal light in order to realize a large-scale network and a long distance.

  As an example of such a device, in the optical fiber communication system, an optical fiber amplifier is inserted at every appropriate transmission distance, thereby amplifying an optical signal transmitted through the optical fiber and attenuating the long distance transmission. It is possible. Since an optical fiber amplifier using stimulated emission can simultaneously amplify a plurality of signal lights having different wavelengths within an amplification band, a wavelength division multiplexing (WDM) optical transmission system using them is used. In addition, photonic networks based on the WDM optical transmission system have been actively studied.

  In general, when an optical amplifier is applied to WDM transmission, it is desirable that the gain spectrum of the optical amplifier is flat so that a plurality of signals having different wavelengths are amplified and output with substantially uniform power. In general, a flat gain spectrum is realized by using a gain equalizer having an inverse characteristic of the gain spectrum of an optical amplifier.

  However, generally in an optical amplifier, the gain spectrum changes when the signal input state changes. Even if gain flattening is realized under a certain input signal power condition, the input power to the amplifier may change due to the span loss of the optical fiber changing with time or the number of WDM channels. Due to this change, WDM signals with interchannel output variations between channels are output. As a result, the channel with high output power is degraded by the nonlinear optical effect generated in the subsequent optical fiber transmission line. On the other hand, a channel with low output power causes the optical signal-to-noise ratio to deteriorate in the optical amplifier at the next stage. In order to suppress these unnecessary signal degradations, the optical amplifier needs to keep the gain spectrum constant with respect to the input power fluctuation.

As a method for constant control of the gain spectrum, a method of performing constant gain control (AGC) is widely used in optical amplifiers (see Non-Patent Document 1). For example, when considering an erbium-doped fiber amplifier (EDFA), the gain spectrum of the EDFA is that the erbium ion density in the EDFA is N _tot , of which the erbium ion density in the amplified initial state is N _2. Assuming that the erbium ion density in the amplified final state is N ₁ (N _tot = N ₂ + N ₁ ), it is expressed by the following equation.

Here, L is the length of the erbium-doped fiber (EDF), g ^* (λ) is the gain in the completely inverted distribution state per unit length, and α (λ) is the absorption per unit length. g, α, and L are constant regardless of the pumping light power or the input signal power. Only N ₂ is a value that depends on the pumping light power and the signal light input power. As can be seen from Equation (1), the gain spectrum G (λ) of the EDFA is uniquely determined by the value of N ₂ . N ₂ can be controlled to be constant by changing the pumping light power and the like, and if this is AGC controlled, the gain spectrum can be controlled to be constant. For fiber Raman amplifiers, optical fiber parametric amplifiers, semiconductor amplifiers, and the like, the optical spectrum can be controlled to be constant by AGC control as in the case of EDFA.

  Normally, when AGC control is performed by an optical amplifier, the total input and total output of the signal of the amplifier are monitored, and gain = (total output of signal / total input of signal) is calculated using the monitor. In addition, feedback control is generally performed on the excitation means of the amplifier so that it is constant. As a result, the gain spectrum can be controlled to be constant even if the signal wavelength or the number of channels changes with respect to the input signal power of the optical amplifier.

  As an optical amplifier, there is a hybrid optical amplifier in which a plurality of optical amplifiers are connected in series. Specifically, examples of hybrid optical amplifiers reported so far include a fiber Raman amplifier (FRA) and an EDFA (see Non-Patent Document 2), an FRA and a thulium doped fiber amplifier (TDFA). ) (See Non-Patent Document 3), TDFA and EDFA (See Non-Patent Document 4), FRA and optical fiber parametric amplifier (OPA: Optical fiber parametric amplifier) (see Non-Patent Document 5) Although amplifiers have been reported, other combinations of two or more optical amplification units including a semiconductor amplifier (SOA), FRA, TDFA, EDFA, OPA, etc. are conceivable. .

  In these hybrid optical amplifiers, the gain control is difficult because each of the constituting optical amplification units is not equalized in gain. FIG. 1 shows an example of a gain spectrum of hybrid optical amplification in which a TDFA optical amplification unit and an EDFA optical amplification unit are connected in series. By connecting these amplification units in series, a large gain can be obtained with TDFA. In addition to 1520-1560 nm, which provides a large gain with 1460-1490 nm and EDFA, a relatively high gain can also be obtained by multiplying the mutual gains of TDFA and EDFA at 1490-1520 nm, which is the intermediate region. I understand. The optical amplifier needs to perform gain equalization as a whole including this intermediate region, and it is appropriate not to perform gain equalization in each optical amplification unit.

Emmanuel Desurvier, “ERBIUM-DOPED FIBER AMPLIFIERS Principles and Applications” Wiley-Interscience Publication H. Masuda, “Review of wideband hybrid amplifiers”, Proc. OFC2000, Paper TuA1, 2000 H. Masuda, S. Aozawa and M. Shimizu, “Ultra-wide-band hybrid amplifier consisting of two dispersion-compensating fibers for Raman amplification and thulium-doped fiber” Electron Letter. Vol. 38 No.11 pp. 500-502 , 2002 T. Sakmoto, et al, “High-gain hybrid amplifier consisting of cascaded fluoride-based TDFA and silica-based EDFA in 1458-1540 nm wavelength region”, ELECTRONIC LETTERS 3rd 37, No. 7, 2003 Min-Chem Ho et, al, “200-nm-bandwidth fiber optical amplifier combining parametric and Raman gain” J. Lightwave Technol, Vol. 19, No.7, pp977-981, 2001 M. Fukui et al, “1580nm band all-optical ADM node prototype equipped with fast automatic level control” in Proc. 24tg European conference on optical communication (ECOC'98), pp 571-572, 1998 J.F.Massicott et al, “1480nm pumped crbium-doped fiber amplifier with automatic gain control” Electronics Letters, Vol.30, No.12 pp 962-964, 1994

  However, when two or more optical amplification units having completely different gain spectra are connected in series, the gains of these units are independent from each other, and fluctuations in input signal power, input signal wavelength, number of input signal channels, and pump light power On the other hand, the gain spectrum behaves differently.

  Therefore, in order to constantly control the entire gain spectrum, the gain spectrum of each optical amplifier unit (amplifier) must be constant, that is, the gain spectrum must not be changed by the above fluctuation. A widely used control method that monitors the input power and output power of an optical amplifier to calculate an error signal of the overall gain, and makes the overall gain constant based on the error signal is applied to the hybrid optical amplifier. In this case, even if the overall gain is constant, there is a possibility that the gain distribution of the individual optical amplification units is shifted and the gain spectrum is not constant.

  Further, changes in individual gain spectra with respect to changes in pumping means (changes in pumping power, etc.) of the amplification medium of the optical amplifier vary from one optical amplification unit to another. For this reason, in the method of feeding back to the excitation means of each optical amplifying unit using one error signal of the entire gain, it is necessary to deal with the above-mentioned disparate spectral changes with one error signal, and How to move it becomes complicated.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a hybrid optical amplifier in which two or more types of optical amplification units having different gain spectra and not necessarily flat are connected in series. An object of the present invention is to provide a hybrid optical amplifier capable of controlling a gain spectrum with high accuracy.

The invention according to claim 1 includes n (n ≧ 2) units of an optical amplification unit having an optical amplification medium that amplifies input light and an excitation unit that excites the optical amplification medium. There are two or more types of optical amplification media in the amplification unit in total, and the n optical amplification units are hybrid optical amplifiers connected in series, respectively (n− m ) among the n optical amplification units. The gain spectrum of the optical amplification unit of the unit (n> m ≧ 1) is controlled to be constant individually, and the whole of the hybrid optical amplifier is controlled with respect to the remaining m optical amplification units not performing the control. Gain control means for controlling the gain spectrum to be constant is provided.

The invention described in claim 2 is the invention described in claim 1, characterized in that m = 1.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the gain control means may be configured to supply excitation light to the optical amplification medium of at least one of the n optical amplification units. An input power and an output power are detected for each of the at least one optical amplification unit, and an input electrical signal related to the input power and an output electrical signal related to the output power are detected for each of the at least one optical amplification unit. The excitation means for each of the at least one optical amplification unit by means of detection means for outputting for each of the at least one optical amplification unit and an input electrical signal and an output electrical signal output for each of the at least one optical amplification unit The optical loss is calculated, and a loss electric signal related to the loss is output for each of the at least one optical amplification unit. An error signal between the pumping light loss calculation means and the loss electric signal output for each of the at least one optical amplification unit and a target signal related to a preset target value is extracted for each of the at least one optical amplification unit. Extraction means and excitation control means for controlling the excitation means of the corresponding optical amplification unit for each of the error signals extracted for each of the at least one optical amplification unit so that the error signal becomes zero. It is characterized by including.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the optical system further includes a multiplexing unit that multiplexes the input signal light and the control channel, and the gain control unit includes the n units. Detecting an input power and an output power of the control channel with respect to the optical amplifying medium of at least one of the optical amplifying units for each of the at least one optical amplifying unit; Detecting means for outputting an input electrical signal related to input power and an output electrical signal related to output power detected for each of the at least one optical amplification unit, and output for each of the at least one optical amplification unit Further, the gain of the control channel for each of the at least one optical amplification unit is determined by the input electrical signal and the output electrical signal. Gain calculating means for calculating and outputting a gain electric signal related to the gain for each of the at least one optical amplification unit, a gain electric signal output for each of the at least one optical amplification unit, and a preset target value Extracting means for extracting an error signal with respect to the target signal for each of the at least one optical amplification unit, and an optical amplification unit corresponding to each of the error signals extracted for each of the at least one optical amplification unit Each of the excitation means included in each includes excitation control means for controlling the error signal to be zero.

According to a fifth aspect of the present invention, in the first or second aspect of the invention, the gain control means detects input power and output power of signal light to the hybrid optical amplifier, respectively, and inputs electric power related to the input power. A detection means for outputting a signal and an output electric signal related to the output power, a gain of the signal light is calculated by the input electric signal and the output electric signal, and a gain electric signal related to the gain is output. A gain calculating means; an extracting means for extracting an error signal between the gain electrical signal and a target signal related to a preset target value; and an excitation means included in at least one of the n optical amplifying units. Each of which includes control means having excitation control means for controlling the error signal to be zero.

According to a sixth aspect of the present invention, in the invention according to the fourth or fifth aspect, the gain calculating means is an electric related to a value obtained by subtracting a predetermined constant from the output power of the hybrid optical amplifier actually measured by the detecting means. The gain is calculated from a signal and the input electric signal.

According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the gain control means configures a laser cavity in at least one of the n optical amplification units, and the laser cavity Control that makes the gain spectrum of the at least one optical amplification unit constant is performed by causing laser oscillation.

The invention according to claim 8 is the invention according to any one of claims 1 to 7 , wherein the optical amplification medium of at least one optical amplification unit of the n units of optical amplification units is a rare earth-doped optical fiber, The pumping means of the optical amplification unit pumps pumping light for the rare earth-doped optical fiber.

The invention according to claim 9 is the invention according to any one of claims 1 to 8 , wherein the optical amplification medium of at least one optical amplification unit of the n units of optical amplification units is an erbium-doped optical fiber, The excitation means of the optical amplification unit excites excitation light for the erbium-doped optical fiber.

The invention according to claim 10 is the invention according to any one of claims 1 to 8 , wherein the optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber, The excitation means of the optical amplification unit excites excitation light for the thulium-doped optical fiber.

According to an eleventh aspect of the present invention, in the invention according to any one of the first to seventh aspects, an optical amplification medium of at least one optical amplification unit of the n optical amplification units is an optical fiber, and the optical amplification The excitation means of the unit excites excitation light for the optical fiber and generates stimulated Raman scattering by the excitation light to perform optical amplification.

According to a twelfth aspect of the present invention, in the invention according to any one of the first to seventh aspects, an optical amplification medium of at least one optical amplification unit of the n optical amplification units is an optical fiber, and the optical amplification The excitation means of the unit excites excitation light for the optical fiber and performs parametric amplification with the excitation light.

The invention according to claim 13 is the invention according to any one of claims 1 to 7 , wherein the optical amplification medium of at least one optical amplification unit of the n optical amplification units is a semiconductor amplifier, and the optical amplification unit The excitation means excites excitation light for the semiconductor amplifier or injects current into the semiconductor amplifier.

According to a fourteenth aspect of the present invention, in the tenth aspect of the present invention, the pumping means includes a first pumping light and a second pumping light having different wavelengths with respect to the thulium-doped optical fiber. The first excitation light is incident at a wavelength of 1420 ± 100 nm or 1050 ± 70 nm, and the second excitation light is incident at 1200 nm ± 100 nm or 1650 ± 150 nm.

The invention according to claim 15 is the invention according to any one of claims 3 to 6 , wherein the optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber, The pumping means of the optical amplification unit pumps the first pumping light and the second pumping light having different wavelengths from each other to the thulium-doped optical fiber, and the first pumping light is 1420 ± 100 nm or 1050. The second excitation light having a wavelength of ± 70 nm is incident as the second excitation light of 1200 nm ± 100 nm and 1650 ± 150 nm, and the excitation control means transmits the first excitation light so that the error signal becomes zero. controlled, and controlling the a constant to the second excitation light without depending on the error signal.

The invention according to claim 16 is the invention according to any one of claims 3 to 6 , wherein an optical amplification medium of at least one optical amplification unit of the n units of optical amplification units is a thulium-doped optical fiber, The pumping means of the optical amplification unit pumps the first pumping light and the second pumping light having different wavelengths from each other to the thulium-doped optical fiber, and the first pumping light is 1420 ± 100 nm or 1050. those wavelengths ± 70 nm, incident ones 1200nm ± 100nm, 1650 ± 150nm as the second excitation light, the excitation control means such that said error signal becomes zero, the first excitation light and controlling the contact and the second excitation light.
According to a seventeenth aspect of the present invention, in the invention according to any one of the third to sixth aspects, the gain control means configures a laser cavity in at least one of the n optical amplification units, and the laser cavity By performing laser oscillation, the gain spectrum of the at least one optical amplification unit is controlled to be constant, and the optical amplification medium of at least one optical amplification unit of the n unit optical amplification unit is a thulium-doped optical fiber. And the excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths from each other with respect to the thulium-doped optical fiber, and 1420 ± 100 nm as the first excitation light. Or having a wavelength of 1050 ± 70 nm as the second excitation light, 1200 nm ± 100 nm, Incident light of 50 ± 150 nm is incident, and the excitation control means controls the first excitation light so that the error signal becomes zero, and controls the second excitation light constant regardless of the error signal. It is characterized by doing.
According to an eighteenth aspect of the present invention, in the invention according to any one of the third to sixth aspects, the gain control means configures a laser cavity in at least one of the n optical amplification units, and the laser cavity By performing laser oscillation, the gain spectrum of the at least one optical amplification unit is controlled to be constant, and the optical amplification medium of at least one optical amplification unit of the n unit optical amplification unit is a thulium-doped optical fiber. And the excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths from each other with respect to the thulium-doped optical fiber, and 1420 ± 100 nm as the first excitation light. Or having a wavelength of 1050 ± 70 nm as the second excitation light, 1200 nm ± 100 nm, Enters those 50 ± 150 nm, the excitation controlling means, the error signal is such that the zero, and controlling said first pumping light and said second pumping light.

Invention of claim 1 9, wherein, in the invention described in any one of claims 14 to 1 8, characterized in that inputting the second pumping light to the traveling direction of the signal light in the opposite direction to the amplifying medium And

  As described above, according to the present invention, in the hybrid optical amplifier in which two or more optical amplifying units are connected in series, the gain spectra are different and they are not gain equalized. Even when the wavelength and the number of channels are changed, the gain spectrum can be controlled to be constant with a relatively simple configuration and algorithm.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
One embodiment of the present invention is characterized in that, in a plurality of optical amplification units connected in series, which constitute a hybrid optical amplifier, the gain spectra of all the optical amplification units are individually controlled to be constant. To do. In order to control the overall gain spectrum to be constant, it is necessary to make the gains of the individual optical amplification units constituting the hybrid optical amplifier constant. Therefore, the gain of the entire amplifier is not monitored and controlled so as to be constant as in the prior art, but is controlled so that the gain spectrum of each optical amplification unit is constant.

  In this specification, the “total gain spectrum” refers to the gain spectrum of the hybrid optical amplifier. That is, it indicates a spectrum obtained by adding the gains of the respective optical amplification units constituting the hybrid optical amplifier.

  Also, in this specification, “to make the gain spectrum of each optical amplifier constant individually” means that the gain spectrum of each optical amplifier (optical amplification unit) constituting the hybrid optical amplifier is the power of the input signal to the optical amplifier. It means to make it constant regardless of changes in the wavelength of the input signal and the number of channels.

  Thus, since the feedback control system is independent for each optical amplification unit, there is an advantage that they do not interfere with each other. However, in the above configuration, the gain of the entire hybrid optical amplifier is not controlled.

  Therefore, the overall gain of the hybrid amplifier may be controlled. By this control, a desired overall gain can be obtained even when a large optical loss occurs between the optical amplification units. Here, if the overall gain of the hybrid optical amplifier is not controlled, the desired overall gain cannot be obtained. That is, a desired overall gain can be obtained without controlling the overall gain of the hybrid optical amplifier.

  In one embodiment of the present invention, in order to control the overall gain of the hybrid optical amplifier, among the n (n ≧ 2) optical amplification units connected in series, which constitute the hybrid optical amplifier, the input side The first to (n−1) th optical amplifying units are controlled so that the gain spectrum is individually constant, and the remaining one unit is controlled so that the overall gain spectrum is constant. That's fine. In order to control the entire gain spectrum to be constant, the gain spectrum of each optical amplification unit needs to be constant. In addition to the conventional control for making the calculated gain constant by monitoring the input / output power of the optical amplifier, the (n-1) optical amplification units are controlled so that the gain spectrum becomes constant individually.

  In another embodiment, among n optical amplification units that are connected in series and constitute a hybrid optical amplifier, the first to (nm) (n> m ≧ 1) th from the input side The optical amplification unit is controlled so that the gain spectrum is individually constant, and the remaining m units are controlled so that the overall gain is constant. In order to control the entire gain spectrum to be constant, the gain spectrum of each optical amplification unit needs to be constant. In addition to the conventional control of making the calculated gain constant by monitoring the input / output power of the optical amplifier, control is performed so that the gain spectrum of (n−m) optical amplification units becomes individually constant. However, this method is effective when there are m light amplification units of the same type.

  When the gain of such a hybrid optical amplifier is monitored and controlled using it, amplified spontaneous emission (ASE) is output together with the amplified signal to cause a control error. There is a case. In particular, the hybrid optical amplifier often has a wide amplification band, and the control error due to the ASE light is more remarkable than in the case of a normal optical amplifier. When the gain is constant, the ASE optical power often becomes a constant. Therefore, when the ASE power is subtracted from the output and calculated by gain = (amplifier output-constant corresponding to the ASE power) / amplifier input, The control accuracy can be further increased.

  Further, when the overall gain of the hybrid optical amplifier is monitored and controlled, a certain amount of gain deviation may occur, but it is possible to realize a control in which the output does not decrease with an increase in internal loss. However, at this time, since the loop of the feedback control to the excitation means is doubled, it is desirable to change the respective control time constants greatly in order to further stabilize the operation. Or, when one of the loops is operating, it may be devised to stop the control of the other loop.

  Now, in one embodiment of the present invention, the gain of some or all of the optical amplification units constituting the gain is controlled for each unit. At this time, the gain spectrum of the optical amplification unit does not necessarily have to be equalized. That is, there is no need to perform control for equalizing the gain spectrum.

  However, in the conventional hybrid optical amplifier, the gain spectrum of each optical amplification unit must be equalized. That is, the input power and the output power are monitored to calculate the gain, and the excitation means is controlled so that it is constant. In order to apply the conventional single unit to the hybrid optical amplifier, the above-described gain and the like for each unit Must be done. Furthermore, when the single unit described above is applied to a hybrid optical amplifier, it becomes difficult to control the gain spectrum to be constant when fluctuations in the number of channels of WDM signals or fluctuations in signal wavelength occur.

  In one embodiment of the present invention, it is not always necessary to equalize the gain spectrum for each optical amplification unit, so that the above difficulty can be solved and the gain spectrum can be controlled with high accuracy.

  In one embodiment of the present invention, as a method for controlling the gain spectrum for each optical amplification unit constituting the hybrid optical amplifier, (1) a method for controlling the loss of pumping light in the amplification medium of the optical amplification unit to be constant, (2) A method for setting a gain control channel, monitoring the gain in the gain control channel by each optical amplification unit, and controlling the gain so as to be constant, (3) Using an amplification medium in the optical amplification unit For example, a method may be used in which a laser cavity is formed and laser oscillation is caused to make the gain constant.

  Optical amplification media for optical amplification units include erbium-doped fiber (EDF), thulium-doped fiber (TDF), and other rare-earth doped optical fibers, Raman amplification optical fibers, and optical parametric amplification. An optical fiber for semiconductor use, an amplifier for semiconductor amplifier, and the like can be used.

  When a thulium-doped optical fiber is used for the optical amplification unit, control accuracy is improved by using two types of pumping light having different wavelengths. In this case, it is possible to use excitation light having a wavelength of 1420 ± 100 nm, 1050 ± 70 nm, etc. as the first excitation light, and excitation light having 1200 nm ± 100 nm, 1650 ± 150 nm as the wavelength of the second excitation light. is there. The second pumping light is input with a constant power, or the control accuracy is increased by controlling the loss to be constant. Furthermore, when the second excitation light is input from the direction opposite to the signal traveling direction, the control accuracy increases.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following Example, It cannot be overemphasized that it can change variously in the range which does not deviate from the summary.

(First embodiment)
FIG. 2 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the first embodiment of the present invention.
2, the hybrid optical amplifier 20 includes two or more types of n (n ≧ 2) optical amplification units 21-1 to 21-n, which are arranged from the input side (left side in FIG. 2) to the optical amplification unit. 21-1, 21-2... 21 -n are optically connected in series to the output side (the right side in FIG. 2) via optical waveguide means such as an optical fiber (simply “ Also called “optically connected”).

  The optical amplification unit 21-1 includes an amplification medium 22-1, branching units 23 and 24 as means for amplifying input light, a detector 25 as means for monitoring excitation light to the amplification medium, and an amplification medium 21-. 1 includes an excitation light source 26-1 as means for exciting 1, a detector 27 as means for monitoring the output power of excitation light from the amplification medium, and an electric control circuit 28. Note that the branching unit 23 has a function of outputting only the pumping light oscillated from the pumping light source 26-1 from one output end of the input light and outputting the remaining light from the other output end. The electric control circuit 28 includes an error signal extraction unit 29, a storage unit 30, and a loss calculation unit 31.

  In the present embodiment, the branching unit 23 outputs only the pumping light oscillated from the pumping light source 26-1 from the one output terminal among the input light, and outputs the remaining light to the other output. It may have a function of outputting from the end. In this case, a filter that cuts the wavelength of the excitation light of the excitation light source 26-1 may be provided between the branching device 23 and the amplification medium 22-2.

  In the optical amplification unit 21-1, a light source (not shown) that generates signal light is optically connected to the input side of the amplification medium 22-1, and a branching device 23 is optically connected to the output side. It is connected. A detector 27 is optically connected to one output end of the branching device 23, and the excitation light from the excitation light source 26-1 is output from this one output end. In addition, the other output terminal of the branching unit 23 is optically connected to the amplification medium 22-2 of the optical amplification unit 22-2 which is a subsequent stage unit of the optical amplification unit 21-1. An excitation light source 26-1 is optically connected to the input end of the branching device 24, and a detector 25 is optically connected to one output end. The branching device 24 is arranged so that the excitation light incident from the excitation light source 26-1 from the other output end can be appropriately incident on the amplification medium 22-1.

  Loss calculation means 31 as means for calculating and outputting the loss of excitation light is electrically connected to the output ends of the detector 25 and the detector 27 via a conductor or the like (simply referred to as “electrical”). Also called "Connect to"). The loss calculation means 31 is electrically connected to an error signal extraction means 29 that extracts an error between the calculated loss of excitation light and a preset target value and outputs the error signal. The error signal extraction unit 29 is electrically connected to a storage unit 30 that stores target value information related to a preset target value. The target value is set so as to be a pumping light loss amount corresponding to a predetermined gain value. The electrical control circuit 28 having such a configuration is electrically connected to the excitation light source 26-1.

  The optical amplification units 21-2 to 21-n are also provided with the same components as the optical amplification unit 22 described above. However, as for the amplification media 22-1 to 22-n of each unit, two or more types of amplification media are used as a whole. The excitation light source of each optical amplification unit is selected according to the corresponding amplification medium. Further, the branching unit 23 of each optical amplification unit is set so as to selectively branch the excitation light from the excitation light source of the unit.

  In this embodiment, by the above-described configuration, even if the signal input state (total input power, input wavelength, input channel, etc.) to the optical amplifier changes, by controlling the loss of the pumping light to the amplifier to be constant, It is possible to control the gain spectrum. The electric control circuit controls the pumping light power of the amplification medium 22-1 so that the error signal related to the above error becomes zero. That is, with respect to the pumping light power from the pumping light source 26-1, the pumping light power is increased when the pumping light loss increases, and the pumping light power is decreased when the pumping light loss decreases. Do.

  As the amplification medium, rare earth doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, optical excitation semiconductor amplifiers, and the like are used. As the excitation light source, an excitation light source having a wavelength, line width, power and the like corresponding to each is used.

The operation of the hybrid optical amplifier according to the present embodiment will be described below.
When the signal light is input to the optical amplification unit 22-1, the excitation light from the excitation light source 26-1 enters the amplification medium 22-1 through the branching device 24. Therefore, the signal light is amplified when entering the amplification medium 22-1, and is emitted together with the excitation light. At this time, the excitation light is also incident on the detector 25 by the branching means 24. In this way, the power of the excitation light incident on the amplification medium 22-1 is monitored.

  In addition, the signal light and the excitation light emitted from the amplification medium 22-1 are incident on the branching device 23, and the excitation light is emitted to the detector 27 by the branching device 23. In this way, the power of the excitation light emitted from the amplification medium 22-1 is monitored. Each of the detection units 25 and 27 sends an electric signal related to each output value to the loss calculation means 31 based on the monitor result.

  The loss calculation means 31 calculates the loss of the pumping light based on the electrical signals output from the detectors 25 and 27 and outputs a loss signal related to the loss to the error signal extraction means 29. The error signal extraction unit 29 extracts the error signal by comparing the target signal related to the target information stored in the storage unit 30 with the calculated excitation light loss signal, and outputs the error signal. The electric control circuit 28 controls the excitation light source 26-1 so that the output error signal becomes zero. When error signal = loss signal−target signal is defined, control is performed to increase the pumping light power when the error signal is positive, and to decrease the pumping light power when the error signal is negative.

  On the other hand, the signal light is input to the subsequent optical amplification unit 22-2 by the branching device 23. In the optical amplification units 22-2 to 22-n, an operation similar to that of the optical amplification unit 22-1 described above is performed.

  In this way, the gain spectrum of each of the optical amplification units 21-1 to 21-n constituting the hybrid optical amplifier 20 can be made constant individually.

(Second embodiment)
FIG. 3 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the second embodiment of the present invention.
In FIG. 3, the hybrid optical amplifier 30 includes two or more types of n (n ≧ 2) optical amplification units 33-1 to 33-n, which are arranged from the input side (left side in FIG. 3) to the optical amplification unit. 33-1, 33-2... 33-n are optically connected in series to the output side (right side in FIG. 3).

  The optical amplification unit 33-1 includes an amplification medium 22-1, a detector 25, an excitation light source 26-1, a detector 27, a branching unit 35, and an electric control circuit 37. Note that the branching unit 35 has a function of outputting only the control channel of the input light from one output terminal at a predetermined ratio and outputting the remaining light from the other output terminal. The electrical control circuit 37 includes an error signal extraction unit 38, a storage unit 39, and a gain calculation unit 40.

  In the optical amplifying unit 33-1, a WDM coupler 34 is optically connected to the input side of the branching device 35. A light source (not shown) that generates signal light is connected to one input terminal of the WDM coupler 34. Are optically connected, and a control channel 36 is provided at the other input end. The detector 25 is optically connected to one output end of the branching device 35, and a control channel is output from this one output end. The amplification medium 22-1 is optically connected to the other output terminal of the branching device 35. A branching device 35 is optically connected to the output side of the amplification medium 22-1. A detector 27 is optically connected to one output end of the branching device 35, and a control channel from the excitation light source 26-1 is output from this one output end. In addition, the other output terminal of the branching unit 35 is optically connected to the branching unit 35 of the optical amplification unit 33-2 that is a subsequent stage unit of the optical amplification unit 33-1. The excitation light source 26-1 is arranged so that excitation light can be appropriately incident on the amplification medium 22-1.

  Gain output means 40 as means for calculating and outputting the gain of the control channel is electrically connected to the output ends of the detector 25 and the detector 27. The gain calculation means 40 is electrically connected to an error signal extraction means 38 that extracts an error between the calculated gain of the control channel and a preset target value and outputs the error signal. The error signal extraction unit 38 is electrically connected to a storage unit 39 that stores target value information related to a preset target value. The target value is set to be a predetermined gain value. The electrical control circuit 37 having such a configuration is electrically connected to the excitation light source 26-1.

  The optical amplification units 33-2 to 33-n are also provided with the same components as the optical amplification unit 33-1 described above. However, as for the amplification media 33-1 to 33-n of each unit, two or more types of amplification media are used as a whole. The excitation light source of each optical amplification unit is selected according to the corresponding amplification medium.

  In this embodiment, with the above-described configuration, the pumping light source is controlled so that the gain of the control channel remains constant even if the signal input state (total input power, input wavelength, input channel, etc.) to the optical amplifier changes. By doing so, it is possible to control the gain spectrum (see Non-Patent Document 6). The electrical control circuit 37 controls the pumping light power of the amplification medium 22-1 so that the error signal related to the above error becomes zero. That is, the pumping light power from the pumping light source 26-1 is controlled such that the pumping light power is increased when the gain of the control channel is decreased, and the pumping light power is decreased when the gain is decreased.

  As the amplification medium, rare earth-doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, and the like are used. As the excitation means, excitation light sources having wavelengths, line widths, powers and the like corresponding to the respective excitation means are used. A semiconductor optical amplifier (semiconductor amplifier) can also be used as the amplifying medium. In this case, excitation by current injection, optical excitation, and the like are possible as the excitation means.

The operation of the hybrid optical amplifier according to the present embodiment will be described below.
When the signal light is input to the hybrid optical amplifier 32, the signal light and the control channel are combined by the WDM coupler 34, and the combined light enters the branching unit 35. At this time, the excitation light from the excitation light source 26-1 enters the amplification medium 22-1. In the splitter 35, only the control channel out of the combined light is emitted from the one output end to the detector 25 at a predetermined ratio, and the remaining light (signal light + control channel) is incident on the amplification medium 22-1. To do. In this way, the power of the control channel incident on the amplification medium 22-1 is monitored.

  The combined light incident on the amplifying medium 22-1 is amplified by the amplifying medium 22-1, enters the branching device 35, and the control channel is emitted to the detector 27 by the branching device 35. In this way, the power of the control channel emitted from the amplification medium 22-1 is monitored. Each of the detection units 25 and 27 sends an electric signal related to each output value to the gain calculation means 40 based on the monitor result.

  The gain calculation means 40 calculates the gain of the control channel based on the electrical signals output from the detectors 25 and 27 and outputs a gain signal related to the gain to the error signal extraction means 38. The error signal extraction unit 38 compares the target signal related to the target information stored in the storage unit 39 with the calculated gain signal of the control channel, and extracts and outputs an error signal. The electric control circuit 28 controls the excitation light source 26-1 so that the output error signal becomes zero. When error signal = gain signal−target signal is defined, control is performed to increase the pumping light power when the error signal is positive and to decrease the pumping light power when the error signal is negative.

  On the other hand, the signal light and the control channel branched by the branching unit 35 are input to the subsequent optical amplification unit 33-2. In the optical amplification units 33-2 to 33-n, an operation similar to that of the optical amplification unit 33-1 described above is performed.

  In this way, the gain spectrum of each of the optical amplification units 33-1 to 33-n constituting the hybrid optical amplifier 32 can be made constant individually. In this embodiment, one light source that generates signal light, which is an external light source, can be shared by n light amplification units.

(Third embodiment)
FIG. 4 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the third embodiment of the present invention.
In FIG. 4, the hybrid optical amplifier 41 includes two or more types of n (n ≧ 2) optical amplification units 42-1 to 42-n, which are arranged from the input side (left side in FIG. 4) to the optical amplification unit. 42-1, n are optically connected in series to the output side (the right side in FIG. 4) in the order of 42-1, 42-2,..., 42-n.

  In the optical amplification unit 42-1, a light source (not shown) that generates signal light is optically connected to the input side of the WDM coupler 43 that branches light in a part of the amplification band. At one output end of the WDM coupler 43, a mirror 45 that reflects the cut-out wavelength band is disposed, and the light in the partial band is output from the one output end to the mirror 45. An amplification medium 22-1 is optically connected to the other output terminal of the WDM coupler 43. The WDM coupler 43 has a function of outputting the light of the partial band incident on one side from the output end from the other output end.

  A WDM coupler 44 that optically splits light in a part of the amplification band is optically connected to the output side of the amplification medium 22-1. A mirror 45 is disposed at one output end of the WDM coupler 44, and the light in the partial band is output from the one output end to the mirror 45. Further, the other output terminal of the WDM coupler 44 is optically connected to the WDM coupler 43 of the optical amplification unit 42-2 which is a subsequent stage unit of the optical amplification unit 42-1. The excitation light source 26-1 is arranged so that excitation light can be appropriately incident on the amplification medium 22-1.

  The optical amplification units 42-2 to 42-n are also provided with the same components as those of the optical amplification unit 42-1 described above. However, as for the amplification media 42-1 to 42-n of each unit, two or more types of amplification media are used as a whole. The excitation light source of each optical amplification unit is selected according to the corresponding amplification medium.

  As described above, by installing the WDM couplers 43 and 44 and the mirror 45 at both ends of the amplification medium 21-1, a laser cavity at a wavelength demultiplexed by the WDM couplers 43 and 44 is formed, and laser oscillation occurs at this wavelength. . The gain of the amplification medium 21-1 is fixed by this laser oscillation, and the gain spectrum can be controlled even if the signal input state (total input power, input wavelength, number of input channels, etc.) to the optical amplifier changes. Become.

  In this way, the gain spectrum of each of the optical amplification units 42-1 to 42-n constituting the hybrid optical amplifier 41 can be made constant individually.

  In this embodiment, a WDM coupler and a reflection mirror are used as a method for forming a laser cavity, but the present invention is not limited to this. For example, as shown in FIG. 12A, a method of creating a ring laser cavity by installing WDM couplers 43 and 44 at both ends of the amplification medium 22 and connecting them is also possible. Further, as shown in FIG. 12B, a laser cavity may be configured using a filter 60 (such as a fiber Bragg grating) that reflects a narrow wavelength band at both ends of the amplification medium 22 (Non-patent Document 7). reference).

  As the amplification medium, rare earth-doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, and the like are used. As the excitation medium, excitation light sources having wavelengths, line widths, powers and the like corresponding to the respective excitation media are used. A semiconductor amplifier can also be used as the amplifying medium. In this case, excitation by current injection, optical excitation, or the like can be used as the excitation means.

  It should be noted that the method of configuring the laser cavity according to this embodiment can be combined with other embodiments of the present invention. That is, a combination of a method using a laser cavity and a method using a loss of pumping light (for example, the first embodiment), a method using a laser cavity and a method using a gain for a control channel and signal light (for example, a second embodiment) Any combination of the method using the laser cavity and the method using the loss of the pumping light and the gain of the signal light (or control channel) (the fifth embodiment). Combinations can also be used.

(Fourth embodiment)
FIG. 5 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the fourth embodiment of the present invention.
In FIG. 5, the hybrid optical amplifier 46 includes two or more types of n (n ≧ 2) optical amplification units 47-1 to 47-n, which are arranged from the input side (left side in FIG. 5) to the optical amplification unit. 47-n, 47-2,... 47-n are optically connected in series to the output side (right side in FIG. 5). In this embodiment, the optical amplification units 47-1 to 47-n-1 have the same configuration as the optical amplification units 21-1 to 21-n-1 of the first embodiment shown in FIG.

  The optical amplification unit 47-n (nth optical amplification unit) includes an amplification medium 22-n, an excitation light source 26-n, and an electric control circuit 48. The electric control circuit 48 includes an error signal extraction unit 38, a storage unit 39, and a gain calculation unit 40.

  In FIG. 5, a detector 50 is optically connected to one output end of the branching device 49, and the signal light input from this one output end is output. The amplification medium 22-1 of the optical amplification unit 47-1 is optically connected to the other output terminal of the branching device 49. The optical amplification units 47-1 to 47-n-1 are connected as shown in FIG. 2, and one output terminal of the branching unit 23 of the optical amplification unit 47-n-1 is a unit at the subsequent stage of the unit. Is optically connected to the amplification medium 22-n of the optical amplification unit 47-n. The excitation light source 26-n is arranged so that excitation light can be appropriately incident on the amplification medium 22-n.

  A branching device 49 is optically connected to the output end of the amplification medium 22-n, and a detector 51 is optically connected to one output end of the branching device 49. To output signal light from the excitation light source 26-n. The gain calculation means 40 is electrically connected to the output ends of the detector 50 and the detector 51. With this configuration, the gain calculation means 40 is sent with an electrical signal related to the power of the signal light input to the hybrid optical amplifier 46 and a signal related to the power of the signal light output from the hybrid optical amplifier 46.

  In this embodiment, with such a configuration, even if the signal input state (total input power, input wavelength, number of input channels, etc.) to the optical amplifier changes, the loss of pumping light in the optical amplifier is controlled to be constant. Thus, the gain spectrum can be controlled to be constant. Control is performed such that when the loss of pumping light increases, the pumping light power is increased, and when the loss of pumping light decreases, the pumping light power is decreased.

  In addition, the input and output of the entire hybrid amplifier 46 are monitored by the detectors 50 and 51, and the gain is calculated using the same, and an error signal with respect to the target gain is extracted. An electric control circuit 48 for controlling n is provided. The electric control circuit 48 controls the pumping light source 26-n in the remaining one optical amplification unit 47-n so that the overall gain becomes constant. Thereby, the gain of the whole hybrid amplifier can be made constant.

  As the amplification medium, rare earth doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, optical excitation semiconductor amplifiers, and the like are used. As the excitation light source, an excitation light source having a wavelength, line width, power and the like corresponding to each is used.

  In this embodiment, the method for controlling the absorption of pumping light to be constant is used as a method for controlling n-1 optical amplification units from the input side. In addition to this, the control channel described in the second embodiment is used. It is also possible to use a method for providing laser oscillation or a method for causing laser oscillation in the amplifier shown in the third embodiment.

  As described above, in this embodiment, the gain spectrum of each of the optical amplification units 21-1 to 21-n-1 constituting the hybrid optical amplifier 46 can be individually made constant, and the entire hybrid optical amplifier The gain spectrum can be made constant.

  In this embodiment, the optical amplifying unit that controls the gain of the entire hybrid optical amplifier to be constant is provided at the final stage of the series connection, but the present invention is not limited to this. That is, the position of the optical amplifying unit (in this embodiment, the optical amplifying unit 47-n) that performs the above-described control may be any position in series connection.

(Fifth embodiment)
FIG. 6 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the fifth embodiment of the present invention.
In FIG. 6, a hybrid optical amplifier 52 includes two or more types of n (n ≧ 2) optical amplification units 53-1 to 53-n, which are arranged from the input side (left side in FIG. 6) to the optical amplification unit. 53-1, 53-2... 53-i (1 ≦ i <n)... 53-n are optically connected in series to the output side (right side in FIG. 6). In this embodiment, the optical amplification units other than the optical amplification units 53-i and 53-n have the same configuration as the optical amplification unit of the first embodiment shown in FIG.

  The optical amplification unit 53-i includes an amplification medium 22-i and an excitation light source 26-i, and the optical amplification unit 53-n includes an amplification medium 22-n and an excitation light source 26-n. The electric control circuit 54 includes an error signal extraction unit 38, a storage unit 39, and a gain calculation unit 40. The error signal extraction means 38 is electrically connected to the excitation light source 26-i and the excitation light source 26-n, respectively.

  In FIG. 6, a detector 50 is optically connected to one output terminal of the branching device 49, and the signal light input from this one output terminal is output. The other output terminal of the branching device 49 is optically connected to the amplification medium 22-1 of the optical amplification unit 53-1. The optical amplification units 53-1 to 53-i-1 are connected as shown in FIG. 2, and one output terminal of the branching unit 23 of the optical amplification unit 53-i-1 is a unit subsequent to the unit. Is optically connected to the amplification medium 22-i of the optical amplification unit 53-i.

  The output side of the amplification medium 22-i is optically connected to the amplification medium 22-i + 1 of the optical amplification unit 53-i + 1, which is a subsequent unit of the unit. Similarly connected. One output terminal of the branching unit 23 of the optical amplification unit 53-n-1 is optically connected to the amplification medium 22-n of the optical amplification unit 53-n, which is a subsequent unit of the unit. The excitation light sources 26-i and 26-n are arranged so that the excitation light can be appropriately incident on the amplification media 22-i and 22-n, respectively.

  The gain calculation means 40 is electrically connected to the output ends of the detector 50 and the detector 51. With such a configuration, the gain calculation means 40 is sent with an electrical signal related to the power of the signal light input to the hybrid optical amplifier 52 and a signal related to the power of the signal light output from the hybrid optical amplifier 52. An error signal is extracted from the electrical signal sent in this way by the method described in the second embodiment. Based on the extracted error signal, the electric control circuit 54 controls the excitation light source 26-i and the excitation light source 26-n so that the overall gain becomes constant.

  In this way, in the present embodiment, the optical amplification unit 53-i and the optical amplification unit 53-n are controlled to make the overall gain constant, and the remaining optical amplification units have the individual gains made constant. Control to be.

  In the present embodiment, the number of optical amplification units that are controlled so as to keep the overall gain constant is set to two. However, the number is not limited to that, and m (1 ≦ m <n) may be used. good. At this time, the pumping light source of each of the m optical amplification units and the error signal extraction means 38 may be electrically connected. That is, the electric control circuit 54 controls the pumping light sources in the m optical amplification units so that the overall gain is constant. In addition, the arrangement of the m optical amplification units is not particularly limited, and may be arranged in a predetermined pattern in a serial connection or may be arranged randomly.

  In this embodiment, with such a configuration, even if the signal input state (total input power, input wavelength, number of input channels, etc.) to the optical amplifier changes, the loss of pumping light in the optical amplifier is controlled to be constant. Thus, the gain spectrum can be controlled to be constant. Control is performed such that when the loss of pumping light increases, the pumping light power is increased, and when the loss of pumping light decreases, the pumping light power is decreased.

In addition, the input and output of the entire hybrid amplifier 52 are monitored by the detectors 50 and 51, and the gain is calculated using the same, and an error signal with respect to the target gain is extracted. An electric control circuit 54 for controlling i and the excitation light source 26-n is provided. The electric control circuit 54 controls the excitation light sources 26-i and 26-n in the remaining two optical amplification units 53-i and 53-n so that the overall gain is constant. Thereby, the gain of the whole hybrid amplifier can be made constant. This method is particularly effective when m light amplification units are made of the same light amplification body.
With the above method, the gain of the entire hybrid amplifier can be made constant.

  As the amplification medium, rare earth doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, optical excitation semiconductor amplifiers, and the like are used. As the excitation light source, an excitation light source having a wavelength, line width, power and the like corresponding to each is used.

  In this embodiment, the method of controlling the absorption of pumping light to be constant is used as a method for controlling the nm light amplification units. In addition, the control channel described in the second embodiment is provided. It is also possible to use a method or a method of causing laser oscillation in the amplifier described in the fourth embodiment.

(Sixth embodiment)
FIG. 7 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the sixth embodiment of the present invention.
In FIG. 7, the hybrid optical amplifier 55 includes two or more types of n (n ≧ 2) optical amplification units 56-1 to 56-n, which are arranged from the input side (left side in FIG. 7) to the optical amplification unit. Optically connected in series to the output side (right side in FIG. 7) in the order of 56-1, 56-2... 56-n. In this embodiment, the optical amplification units 56-1 to 56-n-1 have the same configuration as the optical amplification units 21-1 to 21-n-1 of the first embodiment shown in FIG.

  The optical amplification unit 56-n (nth optical amplification unit) includes an amplification medium 22-n, an excitation light source 26-n, and an electric control circuit 58. The electric control circuit 58 includes an error signal extraction unit 38, a storage unit 39, a gain calculation unit 40, and a calculation unit 59.

  In FIG. 7, gain calculation means 40 is electrically connected to the output terminal of the detector 50, and calculation as means for subtracting a constant from the output power of the hybrid optical amplifier is connected to the output terminal of the detector 51. It is electrically connected to the means 59. The above constant is set to a value corresponding to the ASE power. The calculation means 59 is electrically connected to the gain calculation means 40.

  Prior to the gain calculation, the calculation means 59 generates an electric signal (also referred to as a subtraction signal) related to a value obtained by subtracting the constant from the output power (output monitor value) of the hybrid optical amplifier 55 monitored by the detector 51. And the subtraction signal is sent to the gain calculation means 40. In the gain calculation means 40, the detection is performed by the electrical signal related to the input power (input monitor value) of the signal light to the hybrid optical amplifier 55 output from the detector 50 and the subtraction signal output from the calculation means 59. The gain of the signal light in the optical amplification unit is calculated, and a gain signal related to the gain is sent to the error signal extraction means. The error signal extraction means compares the target signal with the gain signal and extracts an error signal. The electric control circuit 59 controls the excitation light source 26-n so that the error signal becomes zero.

As can be seen from the above, in this embodiment, in order to obtain the gain signal, the calculation means 59 and the gain calculation means 40
Gain = (Output monitor value-Constant) / Input monitor value
Will be calculated.

  In this embodiment, with such a configuration, even if the signal input state (total input power, input wavelength, number of input channels, etc.) to the optical amplifier changes, the loss of pumping light to the optical amplifier is controlled to be constant. Thus, it is possible to control the gain spectrum of the (n−1) optical amplification units from the output side. Control is performed such that when the loss of pumping light increases, the pumping light power is increased, and when the loss of pumping light decreases, the pumping light power is decreased.

In addition, a detector that monitors the input and output of the entire hybrid amplifier is provided. From the monitored input and output values,
There is provided an electric control circuit 59 for calculating a gain using an equation of gain = (output monitor value−constant) / input monitor value, extracting an error signal from the target gain, and controlling the excitation light source based on the error signal. Yes. The electric control circuit 59 controls the excitation light source 26-n in the remaining one optical amplification unit (optical amplification unit 56-n) so that the overall gain is constant. This constant is a value corresponding to the ASE power included in the output, and using this increases the control accuracy.

With the above method, the gain of the entire hybrid amplifier can be made constant.
As the amplification medium, rare earth doped optical fibers (EDF, TDF), Raman amplification optical fibers, optical parametric amplification fibers, optical excitation semiconductor amplifiers, and the like are used. As the excitation light source, an excitation light source having a wavelength, line width, power and the like corresponding to each is used. In this method, the control loop of each optical amplification unit and the control loop of the overall gain are doubled. Therefore, in order to prevent the overall gain control from becoming unstable, it is sufficient to devise measures such as greatly shifting the time constants of the two loops.

  In the present embodiment, the method of controlling the absorption of pumping light to be constant is used as a method of controlling the n−1 optical amplification units, but in addition, a method of providing the control channel described in the second embodiment. It is also possible to use a method of causing laser oscillation in the amplifier shown in the third embodiment.

  Further, in the above example, the number of the optical amplification units to be controlled independently is set to n−1. However, the number of the optical amplification units to be controlled by the overall gain monitor value is set to nm (1 ≦ m <n) units. Even in the method in which the number of units is m, it is effective to increase the control accuracy to calculate the gain by the equation of gain = (output monitor value−constant) / input monitor value.

(Seventh embodiment)
FIG. 8 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the seventh embodiment of the present invention.
In FIG. 8, the hybrid amplifier according to this embodiment includes a fiber Raman amplification unit (FRA unit) 8-16 and an erbium-doped optical fiber amplification unit (EDFA unit) 8-17, which are connected in series. Yes.

  The FRA unit 8-16 uses a high-power laser diode (LD) 8-8 having a wavelength of 1480 nm as an excitation light source and a highly nonlinear fiber (HNLF) 8-1 as an amplification medium. The excitation light is input from a direction opposite to the traveling direction of the signal light of HNLF8-1. A branch coupler 8-6 is installed on the output side of the pump light source 8-8, and the branch light (pump light) is detected by the photodiode 8-7, thereby monitoring the input of the pump light to the HNLF 8-1. . A WDM coupler 8-3 for branching the pump light and the signal light is installed on the output side of the HNLF 8-1 (with respect to the pump light input), and the pump light is branched and detected by the photodiode 8-4. Thus, the output of the excitation light from the HNLF 8-1 is monitored.

  The electrical control circuit 8-19 calculates the loss of the HNLF8-1 of the pumping light from the monitor value of the input / output of the pumping light to the HNLF8-1, compares them with a preset target value, and outputs an error signal. Extraction is performed, and the excitation light source 8-8 is controlled so that the error signal becomes zero. Thereby, the loss of the excitation light in the HNLF 8-1 can be made constant.

  The EDFA unit 8-17 uses a high output LD8-12 of 980 nm as an excitation light source, and uses an erbium-doped optical fiber (EDF) 8-9 as an amplification medium. A branch coupler 8-11 is installed in the immediate vicinity of the high output LD8-12 of 980 nm, and branch light (excitation light) is introduced into the PD 8-13, thereby monitoring the input of the excitation light to the EDF 8-9. A WDM coupler 8-14 for branching the pumping light and the signal light is installed on the output side (with respect to the signal light) of the EDF8-9, and the pumping light is branched and introduced into the PD8-15 to pump from the EDF8-9 Monitor the light output.

  The electric control circuit 8-20 calculates the loss in the EDF 8-9 of the pumping light from the monitor value of the input / output of the pumping light to the EDF 8-9, compares them with a preset target value, and generates an error signal. And the excitation light source 8-12 is controlled so that the error signal becomes zero. Thereby, the loss of excitation light in the EDF 8-9 can be made constant.

  By controlling as described above, the gain spectrum of the entire hybrid amplifier can be made constant regardless of the total input power of signal light, the input wavelength, the number of input channels, and the like.

(Eighth embodiment)
FIG. 9 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the eighth embodiment of the present invention.
9, the hybrid amplifier according to the present embodiment includes a thulium-doped optical fiber amplification unit (TDFA unit) 9-18 and an erbium-doped optical fiber amplification unit (EDFA unit) 9-20, which are connected in series. Connected.

The TDFA unit 9-18 uses a high output LD 9-5 of 1390 nm and a high output LD 9-10 of 1215 nm as an excitation light source, and a thulium-doped optical fiber (TDF) 9-1 as an amplification medium. The 1390 nm excitation light was input so as to be in the same direction as the traveling direction of the signal light (forward excitation), and the 1215 nm excitation light was input so as to be opposite to the traveling direction of the signal light (backward excitation). As TDF9-1, a product obtained by adding 6000 ppm of thulium (Tm ³⁺ ) to the core is used. A branch coupler 9-4 is installed on the output side of the 1390 nm excitation light source 9-5, and the branched light of the excitation light from the 1390 nm excitation light source 9-5 is detected by the photodiode 9-6, whereby The pumping light input is monitored. A WDM coupler 9-7 for branching the pump light and the signal light is installed at the output end (to the signal light) of the TDF 9-1, and thereby the 1390 nm pump light is branched. The branched 1390 nm excitation light further passes through a WDM coupler 9-8 that separates 1215 nm excitation light and 1390 nm excitation light, and is then detected by a photodiode 9-10.

  The electrical control circuit 9-21 calculates the loss in the TDF9-1 of the 1390nm pump light from the monitor value of the input / output of the 1390nm pump light to the TDF9-1, and compares them with the preset target value. An error signal is extracted, and the excitation light source 9-5 is controlled so that the error signal becomes zero. Thereby, the loss in TDF9-1 of 1390 nm excitation light can be made constant. The 1215 nm excitation light passes through the WDM coupler 9-8 and the WDM coupler 9-7, and is input to the TDF 9-1 from the rear. The excitation light power was constant regardless of the input signal state.

  The FDFA unit 9-20 uses a 980 nm high-power LD 9-14 as an excitation light source and an erbium-doped optical fiber (EDF) 9-11 as an amplification medium. A branch coupler 9-13 is installed in the immediate vicinity of the high output LD 9-14 of 980 nm, and branch light (excitation light) is introduced into the PD 9-15, thereby monitoring the input of the excitation light to the EDF 9-11. On the output side of the EDF 9-11, a WDM coupler 9-16 that branches the pumping light and the signal light is installed, and the pumping light is branched and introduced into the PD 9-17, so that the output of the pumping light from the EDF 9-11 is obtained. Monitor.

  The electrical control circuit 9-22 calculates the loss of the pumping light in the EDF 9-11 from the monitor value of the input / output of the pumping light to the EDF 9-11, compares them with a preset target value, and generates an error signal. And the excitation light source 9-14 is controlled so that the error signal becomes zero. As a result, the loss of the excitation light in the EDF 9-11 can be made constant.

  By controlling as described above, the gain spectrum of the entire hybrid amplifier can be made constant regardless of the total input power of signal light, the input wavelength, the number of input channels, and the like. FIG. 10 shows the gain spectrum when the total input power of the signal light of this amplifier is changed. The gain spectrum can be controlled with a substantially constant gain spectrum even when the dynamic range is 20 dB.

  In the above, a high output LD of 1390 nm is used as the excitation light source of the TDFA unit 9-18, but excitation light having a wavelength of 1420 ± 100 nm, 1050 ± 70 nm, or the like can also be used. It is also possible to use excitation light such as 980 nm ± 50 nm and 1480 nm ± 80 nm using a high-power LD of 980 nm as an excitation light source of the EDFA unit 9-20.

(Ninth embodiment)
FIG. 11 is an explanatory diagram of the gain spectrum control method of the hybrid optical amplifier according to the ninth embodiment of the present invention.
11, the hybrid amplifier according to the present embodiment includes a thulium-doped optical fiber amplification unit (TDFA unit) 11-22 and an erbium-doped optical fiber amplification unit (EDFA unit) 11-23, which are connected in series. is doing.

The TDFA unit 11-22 uses a high-power LD 11-6 of 1390 nm and a high-power LD 11-12 of 1215 nm as an excitation light source, and a thulium-doped optical fiber (TDF) 11-1 as an amplification medium. The 1390 nm excitation light was input so as to be in the same direction as the traveling direction of the signal light (forward excitation), and the 1215 nm excitation light was input so as to be opposite to the traveling direction of the signal light (backward excitation). As TDF11-1, a material obtained by adding 6000 ppm of thulium (Tm ³⁺ ) to the core is used. A branch coupler 11-5 is installed on the output side of the 1390 nm excitation light source, and the branch light (1390 nm excitation light) is detected by the photodiode 11-7, thereby monitoring the input of the 1390 nm excitation light to the TDF 11-1. is doing.

  The 1390 nm excitation light further passes through the WDM coupler 11-4 that separates the 1215 nm / 1390 nm excitation light and the excitation light / signal light multiplexing WDM coupler 11-3 and is input to the TDF 11-1. A WDM coupler 11-8 that branches the 1215 nm / 1390 nm pumping light and the signal light is installed at the output end (for the signal light) of the TDF 11-1, thereby branching the 1390 nm pumping light. The branched 1390 nm excitation light further passes through the 1215 nm / 1390 nm WDM coupler 11-9, and is then detected by the photodiode 11-10.

  The electric control circuit 11-24 calculates the loss in the TDF 11-1 of the pumping light from the input / output monitor values of the 1390 nm pumping light to the TDF 11-1, and compares them with a preset target value to obtain an error. The excitation light source 11-6 is controlled so that the signal is extracted and the error signal becomes zero. As a result, the loss of the excitation light in the TDF 11-1 can be made constant.

  On the other hand, a branch coupler 11-11 is installed in the immediate vicinity of the 1215 nm excitation light source 11-12, and the output value is monitored by introducing the branched light (1215 nm excitation light) into the photodiode 11-14. Yes. Thereafter, the 1215 nm pump light passes through the 1215 nm / 1390 nm WDM coupler 11-9 and the pump light / signal light multiplexing WDM coupler 11-8 and is input to the TDF 11-1 from the rear.

  The output light from the TDF 11-1 is branched by passing through the WDM coupler 11-3 for pumping light / signal light multiplexing and the 1215 nm / 1390 nm WDM coupler 11-4, and is detected by the photodiode 11-13. The electric control circuit 11-24 controls the input power of the 1215 nm excitation light source 11-12 so that the loss is constant for the 1215 nm excitation light.

  The EDFA unit 11-23 uses a high output LD11-18 of 980 nm as an excitation light source, and uses an erbium-doped optical fiber (EDF) 11-15 as an amplification medium. The branch coupler 11-17 is installed in the immediate vicinity of the high output LD of 980 nm, and the branch light (excitation light) is introduced into the PD 11-19, thereby monitoring the input of the excitation light to the EDF 11-15. A WDM coupler 11-20 for branching the pumping light and the signal light is installed on the output side (with respect to the signal light) of the EDF 11-15, and the pumping light is branched and introduced into the PD 11-21 to pump the EDF 11-15. Monitor the light output.

  The electric control circuit 11-25 calculates the loss in the EDF 11-15 of the excitation light from the monitor value of the input / output of the excitation light to the EDF 11-15, compares them with a preset target value, and generates an error signal. And the excitation light source 11-18 is controlled so that the error signal becomes zero. Thereby, the loss in excitation light in EDF11-15 can be made constant.

  By controlling as described above, the gain spectrum of the entire hybrid amplifier can be made constant regardless of the total input power of signal light, the input wavelength, the number of input channels, and the like.

  In the above, a high output LD of 1390 nm is used as the excitation light source of the TDFA unit 11-22, but excitation light having a wavelength of 1120 ± 100 nm, 1050 ± 70 nm, etc. can also be used. It is also possible to use excitation light such as 980 nm ± 50 nm and 1480 nm ± 80 nm using a high-power LD of 980 nm as the excitation light source of the EDFA unit 11-23.

(Comparative example)
FIG. 14 is an explanatory diagram of a gain spectrum control method of a conventional hybrid optical amplifier according to a comparative example of the present invention.
In FIG. 14, the hybrid optical amplifier includes an optical amplification unit 61 having an amplification medium 63-1 and an excitation light source 67-1, an amplification unit 62 having an amplification medium 63-2 and an excitation light source 67-2, and an error signal extraction means 69. , A storage means 70, an electric control circuit 68 having a gain calculation means, and detectors 65 and 66.

  In such a configuration, when the signal light is incident on the branching device 64, the signal light is branched into the detector 65 and the amplification medium 63-1. One of the branched signal lights is monitored for its power by the detector 65, and an electric signal related to the input power is sent to the gain calculation means 71. On the other hand, the other of the branched signal light enters the branching device 64 via the amplification media 63-1 and 63-2, and enters the detector 66 by the branching device 64. The detector 66 monitors the power of the signal light (output light of the optical amplifier) incident from the branching unit 64 and sends an electric signal related to the output power to the gain calculation means 71.

  The electric control circuit 68 calculates the gain of the signal light based on the input power and the output power sent to the gain calculation means 71, and extracts an erroneous calculation signal from the gain. Excitation light sources 67-1 and 67-2 are controlled based on this error signal.

  In the hybrid optical amplifier 72 according to the comparative example, when one of the optical amplification units 61 and 62 fails, the unit that does not fail is controlled based on the output power of the entire hybrid optical amplifier. The output light power may exceed an appropriate range.

FIG. 13A is an output spectrum of output light from the hybrid optical amplifier. As can be seen from FIG. 13A, when two optical amplification units are operating normally, the output spectrum obtained is within an appropriate range. However, as shown in FIG. 13C, when one of the optical amplification units fails, the obtained output spectrum exceeds an appropriate range.
However, if the hybrid optical amplifier according to one embodiment of the present invention is used, the gain spectrum is controlled to be constant for each optical amplification unit, so that the output spectrum is expressed as shown in FIG. Although its strength is slightly reduced, it can be within an appropriate output range.

  As described above, in the hybrid optical amplifier according to the embodiment of the present invention, the output spectrum of the hybrid optical amplifier is obtained even if some of the non-amplifying units constituting the hybrid optical amplifier do not operate normally due to a failure or the like. Can fit within the proper range.

It is a figure which shows an example of the gain spectrum of the hybrid amplifier which connected TDFA and EDFA in series. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on 1st Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on 2nd Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 3rd Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 4th Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 5th Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 6th Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 7th Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 8th Example of this invention. It is a figure which shows the gain spectrum of the hybrid optical amplifier which concerns on the 8th Example of this invention. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 9th Example of this invention. (A) And (b) is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the 3rd Example of this invention. (A)-(c) is a figure which shows the output spectrum of a hybrid optical amplifier when two optical amplification units are connected in series. It is explanatory drawing of the gain spectrum control system of the hybrid amplifier which concerns on the comparative example of this invention.

Explanation of symbols

8-1 Highly nonlinear fiber (HNLF)
8-2, 9-2, 11-2 Optical isolators 8-3, 8-5, 8-10, 8-14, 9-3, 9-7, 9-12, 9-16, 11-3, 11 -8, 11-16, 11-20 Excitation light / signal light branching WDM coupler 8-4, 8-15, 9-9, 9-17, 11-21 Excitation light output monitor PD
8-6, 8-11, 9-4, 9-13, 11-5, 11-11, 11-17 Branch coupler 8-7, 8-13, 9-6, 9-15, 11-19 Excitation light Input monitor PD
8-8 1480 nm excitation light source 8-9, 9-1, 11-151 Erbium-doped fiber (EDF)
8-12, 11-18, 9-14 980 nm excitation light source 8-16 FRA light amplification unit 8-17, 9-20, 11-23 EDFA light amplification unit 8-19, 8-20, 9-21, 9- 22, 11-24, 11-25 Electric control circuit 9-1, 11-1 Thulium-doped optical fiber (TDF)
9-5, 11-6 1390 nm excitation light source 9-8, 11-4 1215 nm / 1390 nm multiplexing / demultiplexing WDM coupler 9-10, 11-12 1215 nm excitation light source 9-18, 11-22 TDFA light amplification unit 11-7 1390 nm Excitation light input monitor PD
11-9 1215 nm / 1390 nm multiplexing / demultiplexing WDM coupler 11-10 1390 nm excitation light output monitor PD
11-13 1215 nm excitation light output monitor PD
11-14 1215nm excitation light input monitor PD
20, 32, 41, 46, 52, 55, 72 Hybrid optical amplifiers 21-1 to 21-n, 33-1 to 33-n, 42-1 to 42-n, 47-1 to 47-n, 53- 1-53-n, 56-1 to 56-n, 61, 62 Optical amplification unit 21, 211-1 to 21-n, 63-1, 63-2 Amplification medium 23, 24, 35, 43, 44, 49 Branch device 25, 27, 50, 51, 65, 66 Detector 26, 26-1 to 26-n, 67-1, 67-2 Excitation light source 28, 37, 48, 54, 58, 68 Electrical control circuit 29, 38, 69 Error signal extraction means 30, 39, 70 Storage means 31 Loss calculation means 40, 68 Gain calculation means 45 Mirror 59 Calculation means 60 Narrow band reflection filter

Claims (19)

An optical amplification unit having an optical amplification medium that amplifies input light and an optical amplification unit having excitation means for exciting the optical amplification medium is provided (n ≧ 2) units, and the optical amplification medium of the optical amplification unit of the n units is There are two or more types in total, and the n units of optical amplification units are respectively connected in series in a hybrid optical amplifier,
Of the n optical amplifying units, (n−m) units (n> m ≧ 1) are controlled such that the gain spectrum of each of the optical amplifying units is individually constant, and the remaining m not performing the control A hybrid optical amplifier comprising: gain control means for controlling the optical gain unit of the hybrid optical amplifier so that the overall gain spectrum of the hybrid optical amplifier is constant.   2. The hybrid optical amplifier according to claim 1, wherein m = 1. The gain control means includes
An input power and an output power of pumping light to the optical amplifying medium of at least one optical amplifying unit among the n optical amplifying units are detected for each of the at least one optical amplifying unit, and the at least one optical amplifying unit is detected. Detection means for outputting, for each of the at least one optical amplification unit, an input electric signal related to input power and an output electric signal related to output power detected for each unit;
The loss of the pumping light is calculated for each of the at least one optical amplification unit based on the input electric signal and the output electric signal output for each of the at least one optical amplification unit, and a loss electric signal related to the loss is calculated. Pumping light loss calculating means for outputting each at least one optical amplification unit;
Extraction means for extracting, for each of the at least one optical amplification unit, an error signal between the loss electric signal output for each of the at least one optical amplification unit and a target signal related to a preset target value;
Excitation control means for controlling each of the error signals extracted for each of the at least one optical amplification unit to have a corresponding error signal of zero. The hybrid optical amplifier according to claim 1 or 2. It further comprises a multiplexing means for multiplexing the input signal light and the control channel,
The gain control means includes
The input power and output power of the control channel to the optical amplification medium of at least one optical amplification unit of the n optical amplification units are detected for each of the at least one optical amplification unit, and the at least one light Detection means for outputting, for each of the at least one optical amplification unit, an input electrical signal related to input power and an output electrical signal related to output power detected for each amplification unit;
A gain electrical signal related to the gain is calculated by calculating a gain of the control channel for each of the at least one optical amplification unit based on an input electrical signal and an output electrical signal output for each of the at least one optical amplification unit. A gain calculating means for outputting each at least one optical amplification unit;
Extraction means for extracting, for each of the at least one optical amplification unit, an error signal between the gain electrical signal output for each of the at least one optical amplification unit and a target signal related to a preset target value;
Excitation control means for controlling each of the error signals extracted for each of the at least one optical amplification unit to have a corresponding error signal of zero. The hybrid optical amplifier according to claim 1 or 2. The gain control means includes
Detection means for detecting input power and output power of signal light to the hybrid optical amplifier, respectively, and outputting an input electrical signal related to the input power and an output electrical signal related to the output power;
Gain calculating means for calculating a gain of the signal light based on the input electric signal and the output electric signal, and outputting a gain electric signal related to the gain;
Extraction means for extracting an error signal between the gain electrical signal and a target signal related to a preset target value;
2. A control means comprising: excitation control means for controlling the excitation means of at least one of the n optical amplification units of the n optical amplification units so that the error signal becomes zero, respectively. Or the hybrid optical amplifier of 2.   The gain calculating means calculates the gain from an electric signal related to a value obtained by subtracting a predetermined constant from the output power of the hybrid optical amplifier actually measured by the detecting means and the input electric signal. Item 6. The hybrid optical amplifier according to Item 4 or 5. The gain control means includes
A laser cavity is configured in at least one of the n optical amplification units, and a laser oscillation is generated in the laser cavity, thereby performing control to make a gain spectrum of the at least one optical amplification unit constant. The hybrid optical amplifier according to claim 1. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a rare earth-doped optical fiber,
8. The hybrid optical amplifier according to claim 1, wherein the pumping means of the optical amplification unit pumps pumping light for the rare earth-doped optical fiber. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is an erbium-doped optical fiber,
9. The hybrid optical amplifier according to claim 1, wherein the excitation means of the optical amplification unit excites excitation light for an erbium-doped optical fiber. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber,
9. The hybrid optical amplifier according to claim 1, wherein the pumping means of the optical amplification unit pumps pumping light for the thulium-doped optical fiber. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is an optical fiber,
8. The optical amplification unit according to claim 1, wherein the excitation unit of the optical amplification unit excites excitation light for the optical fiber and generates stimulated Raman scattering by the excitation light to perform optical amplification. Hybrid optical amplifier. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is an optical fiber,
The hybrid optical amplifier according to claim 1, wherein the excitation unit of the optical amplification unit excites excitation light for the optical fiber and performs parametric amplification using the excitation light. The optical amplification medium of at least one of the n optical amplification units is a semiconductor amplifier,
The hybrid optical amplifier according to claim 1, wherein the excitation unit of the optical amplification unit excites excitation light for the semiconductor amplifier or injects current into the semiconductor amplifier.   The excitation means has a wavelength of 1420 ± 100 nm or 1050 ± 70 nm as the first excitation light among the first excitation light and the second excitation light having different wavelengths with respect to the thulium-doped optical fiber. 11. The hybrid optical amplifier according to claim 10, wherein the second pumping light is incident at 1200 nm ± 100 nm and 1650 ± 150 nm. The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber,
The excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths with respect to the thulium-doped optical fiber, and the first excitation light is 1420 ± 100 nm, or The light having a wavelength of 1050 ± 70 nm is incident as the second excitation light at 1200 nm ± 100 nm, 1650 ± 150 nm,
It said excitation control means according to claim wherein said error signal controls the so becomes zero the first excitation light, and controls the second excitation light without depending on the error signal to a constant The hybrid optical amplifier according to any one of 3 to 6 . The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber,
The excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths with respect to the thulium-doped optical fiber, and the first excitation light is 1420 ± 100 nm, or The light having a wavelength of 1050 ± 70 nm is incident as the second excitation light at 1200 nm ± 100 nm, 1650 ± 150 nm,
Said excitation control means, such that the error signal becomes zero, hybrid according to any one of claims 3 to 6, wherein the controller controls the first pumping light Contact and the second excitation light Optical amplifier. The gain control means is configured to configure a laser cavity in at least one of the n units of optical amplification units and cause laser oscillation in the laser cavity, thereby making a gain spectrum of the at least one optical amplification unit constant. And
The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber,
The excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths with respect to the thulium-doped optical fiber, and the first excitation light is 1420 ± 100 nm, or The light having a wavelength of 1050 ± 70 nm is incident as the second excitation light at 1200 nm ± 100 nm, 1650 ± 150 nm,
  4. The excitation control means controls the first excitation light so that the error signal becomes zero, and controls the second excitation light to be constant irrespective of the error signal. The hybrid optical amplifier according to any one of Items 1 to 6. The gain control means is configured to configure a laser cavity in at least one of the n units of optical amplification units and cause laser oscillation in the laser cavity, thereby making a gain spectrum of the at least one optical amplification unit constant. And
  The optical amplification medium of at least one optical amplification unit of the n optical amplification units is a thulium-doped optical fiber,
The excitation means of the optical amplification unit excites the first excitation light and the second excitation light having different wavelengths with respect to the thulium-doped optical fiber, and the first excitation light is 1420 ± 100 nm, or The light having a wavelength of 1050 ± 70 nm is incident as the second excitation light at 1200 nm ± 100 nm, 1650 ± 150 nm,
The hybrid light according to claim 3, wherein the excitation control unit controls the first excitation light and the second excitation light so that the error signal becomes zero. amplifier. Hybrid optical amplifier according to any one of claims 14 to 1 8, characterized in that inputting the second pumping light from the direction opposite to the traveling direction of the signal light to the amplifying medium.

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