JP2004363631A - Optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier which uses an amplification medium, doped with common rare-earth element ions and of which gain profile can be held fixed. <P>SOLUTION: The present invention relates to an optical amplifier which uses an amplification medium, doped with a rare-earth element and of which gain profile can be controlled to be fixed. The optical amplifier includes a rare-earth-doped fiber or a rare-earth-doped optical waveguide as an amplification medium in which rare-earth-element ions are doped in its core and/or clad, an excitation means for exciting the amplification medium, an optical resonator which causes laser oscillation at a specified wavelength of an amplified spontaneously emitted light generated in the amplification medium, and a control unit which monitors light signal in the light amplifier, to control the excitation means. The present invention also relates to a method for controlling the gain profile of the optical amplifier to be fixed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical amplifier. More specifically, the present invention relates to a technique for controlling a gain profile of an optical amplifier including an amplification medium containing rare earth ions.

  Wavelength division multiplexing (WDM) communication is one of the most effective means to cope with the rapid increase in optical communication capacity in recent years. WDM communication is characterized in that the communication capacity is expanded by increasing the number of signal channels. For that purpose, it is essential to expand the signal wavelength range.

  In the current WDM communication, a rare earth ion-doped optical fiber amplifier is used. An amplification band used in WDM communication includes a C band (1530 nm to 1570 nm) which is an amplification band of an erbium-doped optical fiber amplifier (EDFA).

  On the other hand, as a band having the same low loss and low dispersibility as the C band, there is the S band (1460 nm to 1530 nm), which is attracting attention as a next-generation signal wavelength band. The thulium-doped optical fiber amplifier (TDFA) has an amplification band in the S band, and has been vigorously studied.

  In the TDFA for the S band, a power conversion efficiency (40%) equivalent to that of the EDFA in the L band is achieved in the entire optical amplifier, and a WDM transmission experiment has also been successful (for example, OFC2001 PD-1 (Non-Patent Document 1)). Reference 1)). Further, a wide band has been achieved by combining the EDFA using the C band amplification band and the EDFA using the L band amplification band, and thereby a wide band transmission of 10.9 Tbit / s has been reported. (For example, see OFC2001 PD-24 (Non-Patent Document 2)).

  By the way, in WDM communication using a plurality of amplifiers each using a rare earth-doped optical fiber as an amplification medium as a repeater, the output spectrum of the amplifier after the relay changes, and in some cases, the spectrum is greatly distorted.

  This phenomenon occurs because the power of the input signal light to the optical amplifier changes due to the change over time of the transmission line loss and the change in the number of signal channels, and the gain spectrum of the optical amplifier changes. This is because signal distortion is accumulated in the entire transmission path.

  Since the above-mentioned phenomenon that the gain spectrum of the amplifier is greatly distorted becomes a factor for limiting the transmission distance, it is necessary to control the gain spectrum of the amplifier to be constant. As a control method, it is effective to control each optical amplifier so as to keep the gain profile constant (hereinafter, also referred to as “gain profile constant control”).

  For example, as an example of a control method of a silica-based EDFA, there is a method of monitoring the gain of signal light of one channel and controlling the power of pumping light so that the gain of the channel is always constant. A method for controlling the gain profile of a silica-based EDFA to be constant has been almost established by this method. Further, the constant control of the gain profile of the fluoride PDFA can be controlled by the same method. The amplification medium (optical fiber) of these optical amplifiers operates by an amplification mechanism in which the levels involved in amplification are substantially two. The mechanism is such that the initial level involved in amplification (hereinafter also referred to as amplification start level) and the final level involved in amplification (hereinafter also referred to as amplification end level) or ground level can be handled only. This is a rare case.

  These cases will be described with reference to FIG. FIG. 1A is a schematic diagram of an excitation level of a silica-based EDFA, and FIG. 1B is a schematic diagram of an excitation level of a praseodymium-doped optical fiber amplifier (PDFA).

In the quartz-based EDFA, as shown in FIG. 1A, the amplification end level coincides with the ground level, so that the levels involved in the amplification are the amplification start level ( ⁴ I _13/2 ) and the amplification end level. Level ( ⁴ I _15/2 ). Therefore, it is possible to monitor the gain of the signal light of one channel, adjust the light amount of the pump light source so that the gain of the channel is always constant, and control the gain profile to be constant.

  In a PDFA, as shown in FIG. 1B, there are three levels involved in amplification: an amplification start level, an amplification end level, and a ground level. However, in the case of the PDFA, the fluorescence lifetime of the amplification end level is much shorter than the amplification start level, so that the amplification end level can be ignored. Therefore, it is possible to control the gain profile to be kept constant in the same manner as the quartz EDFA.

  As described above, when the number of levels involved in amplification is substantially two, it is relatively easy to keep the gain profile constant.

  However, generally, in an optical amplifier using an amplification medium to which rare earth ions are added, there are few cases where the levels involved in amplification can be regarded as substantially two. In addition, a method of monitoring the gain of the wavelength of one signal, adjusting the light amount of the pump light source based on the change in the gain, and controlling the gain profile to be constant cannot be applied. That is, simply controlling the gain of the wavelength of one signal by controlling the amount of light of the excitation light source to control the gain profile to be constant with respect to the fluctuation of the level of the input signal and other conditions (for example, temperature change). I can't.

  For this reason, in such a system, it is basically necessary to monitor the gains at the wavelengths of two different signals, and it is necessary to perform complicated control.

  As described above, in an optical amplifier using an amplification medium (optical fiber or optical waveguide) to which some rare earth ions are added, the gain of one signal is monitored, the pump light is controlled, and the gain is controlled. Although the profile can be controlled to be constant, the gain profile cannot be controlled to be constant in an optical amplifier using an amplification medium to which other rare earth ions are added.

  Apart from the method of monitoring the gain of the wavelength of one signal as described above and adjusting the amount of light of the pump light source based on the change, and keeping the gain profile constant, the gain profile is kept constant using a resonator. A way to keep it has been proposed.

  For example, E. Desurvire et al., "Gain control in erbium-doped fiber amplifiers by all-optical feedback loop"., IEEE, Electronics Letters. Vol. 27, No. 7, pp. 560-561, 28th March 1991 ( Non-Patent Document 3) proposes a technique for controlling a gain spectrum by introducing a configuration of a feedback loop, causing an ASE of one wavelength to oscillate laser, and clamping a gain of the wavelength. In addition, as techniques for clamping the gain, European Patent Application Publication No. 0497491 (Patent Document 1), Japanese Patent Application Laid-Open No. 9-509012 (Patent Document 2), and Japanese Patent Application Laid-Open No. 11-145533 (Patent Document 3) )and so on.

  However, the method using a resonator as described above involves a quartz-based EDFA in which there are only two levels (that is, levels to be considered when determining the state of the gain spectrum) that greatly affect amplification. Can be controlled, but cannot be controlled for TDFA and other rare earth-doped optical fiber amplifiers.

European Patent Application No. 0497491 JP-A-7-521675 JP-A-11-145533 OFC2001 PD-1 OFC2001 PD-24 E. Desurvire et al., "Gain control in erbium-doped fiber amplifiers by all-optical feedback loop"., IEEE, Electronics Letters. Vol. 27, No. 7, pp. 560-561, 28th March 1991. E. Desurvire, "Erbium-Doped Fiber Amplifiers," A. Wiley-Interscience Publication, Chapter 1, 1994 Won Jae Lee et al., "Gain excursion & tilt compensation algorithm for TDFA using 1.4 μm / 1.5 μm dual wavelength control"., OFC2002, ThZ3

  Therefore, there is a demand for an optical amplifier and a control method which can be applied to an optical amplifier using a rare earth-doped amplifying medium by a simple method and which can control a gain profile to be constant.

  The present invention has been made in view of such a problem, and an object of the present invention is to easily control a widely-used optical amplifier using a rare-earth-doped amplification medium so as to keep a constant gain profile. It is to provide an optical amplifier which can be used.

  Another object of the present invention is to provide a control method for controlling a gain profile to be kept constant by using a widely-used optical amplifier using an amplification medium to which rare earth ions are added.

  A first aspect of the present invention relates to an optical amplifier using an amplification medium to which rare earth is added, which can be controlled to keep a gain profile constant. In particular, the optical amplifier of the present invention relates to an optical amplifier using an amplification medium to which one or more general rare earth ions are added.

  According to the first embodiment, an optical amplifier of the present invention provides a rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which rare-earth ions serving as an amplification medium are added to a core and / or a clad, and an excitation for exciting the amplification medium. Means, an optical resonator that oscillates laser light at at least one wavelength in the spectrum of amplified spontaneous emission light generated in the amplification medium, and at least one predetermined wavelength range selected from light input to the optical amplification medium. Monitoring means for monitoring the power of light and at least one light power selected from the power of light in at least one predetermined wavelength range selected from the light output from the optical amplification medium; a value obtained by the monitoring means And a control unit for controlling the excitation means based on the above.

  The control method according to the first embodiment of the present invention includes a rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which rare-earth ions serving as an amplification medium are added to a core and / or a clad, an excitation unit for exciting the amplification medium, and a laser. An optical resonator for oscillating, monitoring means, a method for controlling the gain profile of an optical amplifier including a control unit for controlling the excitation means based on the value obtained from the monitoring means, a method for controlling the gain profile constant, Causing the laser to oscillate in at least one wavelength within the spectrum of the amplified spontaneous emission light of the amplified medium of the amplification medium by the optical resonator in the optical amplifier; Means selected from the power of light in at least one predetermined wavelength range selected from the light input to the optical amplification medium and the light output from the optical amplification medium. At least one optical power selected from the power of light in at least one predetermined wavelength range is monitored, and based on a value obtained by the monitoring means, the control unit controls the excitation means to perform the excitation. Controlling the light amount of the light source.

  In the first optical amplifier of the present invention, at least an optical resonator that oscillates a laser is provided in the optical amplifier to control the gain of an arbitrary signal light, or at least an optical resonator that oscillates a laser is provided in the optical amplifier. And the sum of the laser oscillation light and the signal light power can be controlled to be constant.

  Further, when the optical amplifier of the present invention is applied to a WDM transmission system, it is possible to control the gain spectrum of signal light in response to a change in input level due to a change in the number of signal channels and a change in gain spectrum due to a temperature change. .

  Further, the optical amplifier of the present invention can control the output required for compensating for a change in transmission path loss with time, and can cope with hole burning of the oscillation wavelength.

  INDUSTRIAL APPLICABILITY The control method of the present invention is widely applicable to an optical amplifier using an amplification medium to which rare earth ions are added.

  A first aspect of the present invention relates to an optical amplifier using an amplification medium to which rare earth is added, which can be controlled to keep a gain profile constant.

  A second aspect of the present invention relates to a control method for keeping a gain profile of an optical amplifier using an amplification medium doped with rare earth constant.

  In the present invention, there are the optical amplifiers and control methods of the first and second embodiments as described above. First, the principle of the first and second embodiments will be described.

  First, a description will be given of a method of controlling an optical amplifier and a gain profile to be constant in a case where an amplification medium to which a rare earth is added, in which only two levels of amplification are involved, an amplification level and an amplification level, is used. I do. Some of such amplifiers use a quartz EDFA as an amplification medium.

Optical amplifier for erbium doped optical fiber of silica-based and (EDF) and the amplification medium is level involved in the amplification of the amplifier end凖位⁽⁴ _{I 15/2)} and the amplification start凖位⁽⁴ _{I 13/2)} Two levels, a relatively simple system.

  Such an amplifier is, for example, an optical amplifier (silica-based EDFA) using a silica-based EDF as an amplification medium, a silica-based EDF, an excitation unit for exciting the silica-based EDF, and a monitoring unit for monitoring an input signal light or the like. , And at least a control unit for controlling the excitation means based on information from the monitoring means.

FIG. 2A is a diagram showing the energy levels of Er ³⁺ ions in an optical amplifier using a quartz-based EDF as an amplification medium. In this optical amplifier is performing amplification using a method of exciting the amplification final凖位⁽⁴ _{I 15/2)} to amplify the start凖位⁽⁴ _{I 13/2).} An example of a method of controlling the gain profile of a silica-based EDFA is to monitor the gain of the signal light of one channel (hereinafter also referred to as ch.) And to control the pump light power so that the gain of the channel is always constant. Control.

  Hereinafter, the principle of this control will be described.

  The gain Gain (λ, x) per unit length at the position x in the longitudinal direction of the erbium-doped optical fiber amplifier at the wavelength λ is represented by the following equation (for example, E. Desurvire, “Erbium-Doped Fiber Amplifiers, "See A. Wiley-Interscience Publication, Chapter 1, 1994 (Non-Patent Document 4)).

    Gain (λ, x) = (σe (λ) N2 (x) − (σa (λ) N1 (x)) (eq1)

σe: stimulated emission cross section σa: stimulated absorption cross section N2 (x): number of ions at the start level ( ⁴ I _13/2 ) of amplification at position x N1 (x): end level of amplification at position x ( ⁴ I _15/2 ) ion number _N total: total ion number

  Here, the following equation is obtained from the equations (eq1) and (eq2).

    Gain (λ, x) = (σe (λ) N2 (x) − (σa (λ) (Ntotal−N2 (x))) (eq3)

  As can be seen from equation (eq3), the variable is only N2.

  Here, since the stimulated emission cross section and the stimulated absorption cross section are determined by the physical properties of the rare earth ions added to the amplification medium, N2 must be fixed to fix the gain spectrum, that is, the amplification starting level. It is necessary to fix the number of ions at the amplification end level.

In WDM transmission and the like, the power of the signal light input to the optical amplifier changes due to a change with time in the loss of the transmission line and a change in the number of signal channels. Such a change _leads to a change in the stimulated emission rate of Er ³⁺ present in ⁴ I _13/2 in the quartz-based EDFA, resulting in a change in N 2 and a gain spectrum as seen from (eq 3). Change.

  Therefore, when there are two levels involved in amplification, such as an optical amplifier using a silica-based EDF as an amplification medium, an arbitrary signal light wavelength is monitored and the gain at this signal wavelength is kept constant. By controlling the pumping light power in this way, the gain spectrum is kept constant based on (eq3) regardless of the input power to the optical amplifier.

  The specific procedure for controlling the gain to be constant is to split the signal light at the input end and output end of the amplification optical fiber, detect the signal light power at each location, and use the detected value to determine the signal light. Is calculated, and the excitation light amount is adjusted so that the error component between the calculated gain value and the set value becomes zero. This is the principle for controlling the gain profile to be constant in an optical amplifier using a silica-based EDF as an amplification optical fiber.

  By the way, systems in which the amplification mechanism can be described only by ions at the amplification start level and the amplification level are extremely rare. For example, even when the same stimulated emission as described above is used in an erbium-doped optical fiber, even if the host glass constituting the optical fiber is simply changed to a fluoride glass, the level becomes higher than the initial level of amplification to a higher energy excitation level. Transition and the lifetime at the level after the transition cannot be ignored. In such a case, even if the gain at a certain wavelength (for example, one wavelength of the input signal light) is controlled to be constant, the gain profile cannot be uniquely determined. This is because, when describing the amplification operation, it is necessary to consider the amplification start level, the amplification end level, and the number of other ions. That is, in TDFA, for example, the total number of ions is represented by the following (eq2 ′), and it is not sufficient to consider only one parameter (N2) as in the above (eq3). This is because it has to be considered.

  An optical amplifier using a rare earth-doped optical fiber in which three levels greatly contribute to amplification includes an optical amplifier using a thulium-doped optical fiber (TDF). Although this optical amplifier is a four-level optical amplifier as shown in FIG. 2B, there are three levels that greatly contribute to amplification. That is, in TDFA, there are a starting level, an ending level, and a ground level of amplification as energy levels that are greatly involved in amplification. Therefore, since it is necessary to consider all of these levels, it is necessary to monitor the gain of one wavelength and control it to keep it constant, as discussed in the EDFA, and to control the number of ions between the three levels. Cannot be kept constant.

3, when amplifying WDM signal, the power of the wavelength lambda ₁ of the signal beam incident to the optical amplifier in the TDFA, a gain that is calculated from the power of the amplified emitted wavelength lambda ₁ of the signal light from the TDFA FIG. 9 is a diagram illustrating characteristics of the optical amplifier when the excitation light amount of the TDFA is adjusted to be constant.

3A to 3C show the characteristics of the optical amplifier, where a is when the total input signal power to the TDFA is low, b is an intermediate value, and c is a high value. The conditions for evaluating this characteristic were as follows: the Tm ³⁺ addition concentration of TDFA was 6000 ppm, and the excitation wavelength was 1400 nm. The pumping of the Tm-doped fluoride optical fiber for amplification is bidirectional pumping in which the optical fiber is pumped forward and backward. The ratio between the forward pumping light power and the backward pumping power was always constant. As is clear from FIG. 3, simply keeping the gain of one wavelength constant changes the gain profile with respect to a change in input signal light power.
Such a phenomenon also occurs when a gain clamp using a resonator is used. That is, the gain at the oscillation wavelength is always constant, but the other gains are not uniquely determined, and the gain profile is not constant.

  The following control method has been proposed as a method for controlling an optical amplifier including an amplifying medium having three levels largely involved in such amplification. This control method relates to a TDFA optical amplifier, and there are two methods. One such control method is used in a bidirectionally pumped TDFA optical amplifier. In this control method, the gains of two types of signal light are monitored. Based on the monitor information, the gain band is adjusted by controlling the ratio of the power of the pump light in front of and behind the amplifying optical fiber, and the overall gain is adjusted by controlling the total power of the pump light. Is the way. In the TDFA, a phenomenon occurs that the gain spectrum shifts in wavelength when the power ratio between the front and rear pump lights is changed.

  Further, as a second control method of TDFA, there is a method of controlling a light amount of an excitation light source having two wavelengths (1.4 μm, 1.56 μm) and adjusting a gain spectrum (Won Jae Lee et al., “Gain excursion”). & tilt compensation algorithm for TDFA using 1.4 μm / 1.5 μm dual wavelength control "., OFC2002, ThZ3 (see Non-Patent Document 5).

  Except for the optical amplifier including an amplification medium having substantially two levels involved in amplification as described above, in the case of an optical amplifier using an amplification medium to which rare earth ions are added, one is adjusted by adjusting the amount of light of the pump light source. By simply controlling the wavelength gain to a constant value, it is not possible to control the gain profile to be constant with respect to fluctuations in the level of the input signal or changes in other conditions (for example, temperature changes). Therefore, in such a system, it is basically necessary to monitor gains at two kinds of signal wavelengths, and it is necessary to perform complicated control.

  In the optical amplifier and the control method of the present invention, it is possible to use an amplification medium to which a rare earth is added to which the amplification start level, the amplification end level, and other levels need to be considered. Hereinafter, a case where the other level is only the third level will be described, but the present invention is not limited to this and includes a case where more levels are involved.

In the optical amplifier of the present invention, an amplification medium in which the third level is involved in stimulated emission transition and the final level or the third level is the ground level can be used. The control method of the present invention controls the number of ions at these three levels by the following methods (1) to (4), thereby realizing simple gain profile constant control.
(1) First method In this method, a laser is generated in an optical path including the optical amplifier by a transition between any two levels of the amplifying medium causing stimulated emission among the three levels described above. Oscillation is performed, and at the same time, for example, an arbitrary signal light of the wavelength-multiplexed signal light or an arbitrary input signal light separately input within the amplification band is monitored, and the gain is controlled to be constant for the wavelength.
(2) Second method In this method, a transition between any two levels of the amplifying medium causing stimulated emission among the three levels described above causes a laser in the optical path including the optical amplifier. Oscillation is performed, and at the same time, the incident power of the signal light and the power of the laser oscillation light incident on the optical amplifier are monitored, and the gain profile is controlled to be constant based on the value obtained from the power.
(3) Third Method In this method, a transition between any two levels of the amplifying medium causing stimulated emission among the three levels described above causes a change in the optical path including the optical amplifier. The laser oscillation is performed, and at the same time, the output power of the signal light and the power of the laser oscillation light are monitored, and the gain profile is controlled to be constant based on the value obtained from the power.
(4) Fourth Method This method does not monitor the signal light. In this method, two types of laser oscillation are performed at two different types of transitions, each of which is composed of two levels selected from the three levels described above. That is, of the three levels described above, the first transition between any two levels of the amplification medium causing stimulated emission causes the first laser oscillation in the optical path including the optical amplifier. . At the same time, the second laser oscillation is performed in the optical path including the optical amplifier in a combination different from the level related to the first transition among the three levels.

  According to the above-described first to third methods (first embodiment), laser oscillation is performed in an optical path including an optical amplifier, so that the number of ions at two levels involved in laser oscillation has a fixed relationship. To meet. Under this condition, if the intensity of the pumping light is further controlled so that the gain of an arbitrary optical signal, the power of the input light, or the power of the output light becomes a predetermined value, 3 levels including one remaining level are obtained. It is possible to uniquely determine the number of ions at one level. As a result, the gain profile can be uniquely fixed.

  In the above-described fourth method (second embodiment), all three levels are involved in laser oscillation, so that the numbers of ions at the three levels satisfy a certain relationship. Here, by imposing a condition that the total number of rare earth ions added to the amplification medium is constant, the number of ions at three levels is uniquely determined. As a result, the gain profile can be uniquely fixed.

  According to the present invention, it is possible to cause a plurality of laser oscillations.

  As described above, in the first to third methods, in the present invention, laser oscillation is performed in the optical amplifier, and at the same time, the gain of an arbitrary signal light is monitored, or laser oscillation is performed in the optical amplifier. In addition, the gain profile is controlled to be constant by monitoring the light amounts of the signal light and the laser oscillation light. In the above first to third methods, the following three signals can be used as specific monitor signals, but these are examples, and the present invention is not limited to these.

  (I) For at least one input signal light, a signal light power input to the amplification medium is partially branched, and an electric signal obtained by photoelectric conversion and a signal light power output from the amplification medium are partially branched. An electrical signal (hereinafter, referred to as a first monitoring method) that is calculated from a ratio with an electrical signal obtained by photoelectric conversion and is proportional to the gain of the signal light. The input at least one signal light may be a signal light to be transmitted, or may be a signal separately input as a monitor signal to the optical amplifier.

  (II) Part of the input signal light power is partially branched, and the electric signal obtained by photoelectric conversion and the part of the laser oscillation light in the resonator at the input end of the amplification medium are partly branched and this light is photoelectrically converted. An electric signal (hereinafter, referred to as a second monitoring method) which is a sum or a linear combination with an electric signal (a signal proportional to the power of laser oscillation light) obtained by the conversion.

  (III) Part of the output signal light power is partially split, and the electrical signal obtained by photoelectric conversion and the laser oscillation light in the resonator at the output end of the amplifying medium are partially split, and this light is converted into a photoelectric signal. An electric signal (hereinafter, referred to as a third monitoring method) which is a sum or a linear combination with an electric signal (a signal proportional to the power of laser oscillation light) obtained by the conversion.

  In the case of a method of performing control without using a monitor signal (the fourth method), two types of laser oscillation are performed by two types of optical resonators in an optical amplifier including an amplification medium. In this method, the wavelength of the oscillation light oscillated by the two types of optical resonators is selected from, for example, the following three types. In the present invention, in particular, two different wavelengths can be used.

  (A) The wavelength of the laser oscillation light is included in the range of an amplified spontaneous emission light (ASE) spectrum generated by stimulated emission from the amplification start level to the amplification end level (hereinafter, referred to as a first optical resonator). ).

  (B) The wavelength of the laser oscillation light is included in the range of the amplified spontaneous emission light (ASE) spectrum generated by stimulated emission from the amplification start level to the ground level (hereinafter, referred to as a second optical resonator). ).

  (C) The wavelength of the laser oscillation light is included in the range of the amplified spontaneous emission light (ASE) spectrum generated by stimulated emission from the amplification end level to the ground level (hereinafter, referred to as a third optical resonator). ).

  According to a first embodiment of the present invention, there is provided a first optical amplifier according to the above principle. An optical amplifier according to the present invention comprises: an amplification medium; an excitation unit for exciting the amplification medium; an optical resonator that oscillates laser light at at least one wavelength in the spectrum of ASE generated in the amplification medium; At least one light power selected from at least one predetermined wavelength range light selected from input light and at least one predetermined wavelength range light power selected from light output from the optical amplification medium And a control unit for controlling the excitation means based on a value obtained by the monitoring means.

  According to the first embodiment, a first control method according to the above principle is provided. The first control method includes, for example, a method using the optical amplifier according to the first embodiment. In the optical amplifier, the spontaneous emission light amplified in the amplification medium by the optical resonator in the amplification medium is output. Causing the laser to oscillate at at least one wavelength within the spectrum of the amplified amplified spontaneous emission light; and the power of light in at least one predetermined wavelength range selected from the light input to the optical amplification medium by the monitoring means. And monitoring at least one optical power selected from the power of light in at least one predetermined wavelength range selected from the light output from the optical amplifying medium, based on the value obtained by the monitoring means, A control unit controlling the excitation means to control a light amount of the excitation light source.

  According to the second embodiment, a second optical amplifier according to the above principle is provided. The optical amplifier of the present invention includes an amplification medium, an excitation unit for exciting the amplification medium, and an optical resonator that oscillates ASE generated in the amplification medium at a plurality of oscillation wavelengths.

  In order to obtain an optical resonator having the above-described oscillation wavelength, an optical bandpass filter for selecting a desired wavelength in the optical resonator, or a wavelength selecting element equivalent to this, is required. Further, it is preferable that some means for adjusting the loss at the laser oscillation wavelength in one round of the optical resonator, such as a variable optical attenuator and a fixed optical attenuator, is included. The element for adjusting the loss and the element for adjusting the wavelength can be included as a function in an optical branching unit (for example, a unit for separating or combining laser oscillation light) used in forming an optical resonator. is there.

  According to the second embodiment, a second control method according to the above principle is provided. The control method includes, for example, a method using the optical amplifier of the second embodiment, and includes laser-oscillating amplified spontaneous emission light generated in the amplification medium at a plurality of oscillation wavelengths.

  In the first and second embodiments, it is preferable that the monitoring unit includes an optical bandpass filter. In the first and second embodiments, the method, the monitoring method, and the resonator according to the above (1) to (3), (I) to (III), and (A) to (C) are provided. included.

  In the present invention, the rare earth ions to be added to the amplification medium may be one kind or a plurality of kinds.

  Hereinafter, the optical amplifier and the method of constant gain profile control according to the present invention will be described in more detail with reference to the drawings, but these are examples and the present invention is not limited thereto.

  The first embodiment of the present invention relates to an optical amplifier including an optical resonator having a loop formed between an output terminal and an input terminal of an optical amplifier. FIG. 4 shows an outline of the optical amplifier of the first embodiment, and FIG. 5 shows an outline of the optical amplifier of the second embodiment.

  The optical amplifier 400 (FIG. 4) according to the first embodiment is an optical amplifier including an optical resonator 402, a monitoring unit 404, and a control unit 420. The optical resonator 402 includes an amplification medium 410, an excitation unit 412 that excites the amplification medium 410, optical branching units 414 and 416, and a wavelength selection element 418. In addition, the monitoring unit 404 includes a power of light of at least one predetermined wavelength range selected from light input to the optical amplification medium and a power of at least one predetermined wavelength range selected from light output from the optical amplification medium. At least one optical power selected from the optical power is monitored. The control unit 420 controls the excitation unit 412 based on the value obtained from the monitoring unit. In the present embodiment, the monitoring unit 404 includes optical branching units 426 and 428 for inputting the monitored light to the control unit.

As the amplification medium 410, a rare-earth-doped optical fiber in which rare-earth element ions are added to the core and / or the clad can be suitably used. In particular, in the present invention, a thulium-doped optical fiber, an erbium-doped optical fiber, a holmium-doped optical fiber, or the like can be used. Specifically, an amplification optical fiber to which rare earth ions are added can be used as the amplification medium, which is made of quartz glass, bismuth-based glass, or a fluoride-based glass, ZBLAN, which hardly causes non-radiative transition as a host glass. Glass, In-Pb glass, tellurite glass, or the like. The rare earth ion may be any ion, but is preferably a thulium ion (Tm ³⁺ ), a holmium ion (Ho ³⁺ ), or an erbium ion (Er ³⁺ ). In the present invention, one or more of these ions can be added to the amplification medium.

  Excitation means 412 includes excitation light sources 422 and 424 for exciting the amplification medium, and multiplexers 436 and 438 for multiplexing light from the excitation light sources. This light source is generally used for exciting a rare earth doped optical fiber. For example, a semiconductor LD, an InGaAs strain quantum well LD, or the like is used. Specifically, for example, a solid-state laser such as an Nd-YLF laser, an Nd-YAG laser, a Ti sapphire laser, a semiconductor laser, or a fiber laser is used. In the optical amplifier shown in FIG. 4, the pumping light is bidirectionally pumped, but the present invention is not limited to this, and forward pumping and backward pumping may be used.

  The optical branching means is a melt-drawn fiber type (both branching type and wavelength division multiplexing type) dielectric multilayer film, a fiber grating or a circulator combined with a fiber grating, and reflects an input signal and / or a part of ASE. It is a device for taking out.

  The wavelength selection element included in the resonator system includes an optical filter such as a dielectric multilayer film and a fiber grating.

  In the present invention, a variable optical attenuator or the like can be introduced into the optical resonator. In the present invention, the optical resonator oscillates when the gain of the amplifying medium and the loss of one round of the resonance system coincide. However, by introducing a variable optical attenuator or the like, the gain of the amplifying medium and the round of the resonance system round. The loss relationship can be adjusted.

  As the multiplexer, an ordinary multiplexer such as a pump light / signal light multiplex coupler may be used.

  In the monitoring unit 404, the monitored light (hereinafter also referred to as a monitor signal) (first signal and second signal in FIG. 4) branched by the optical branching units 426 and 428 is input to the monitoring unit 419. The control unit 420 performs an operation based on the information from the monitoring unit, and the excitation unit 412 controls the excitation light based on this value. The monitoring unit 404 may include a photoelectric converter that converts the monitor signal split by the optical splitting units 426 and 428 into an electric signal. The photoelectric converter converts the monitor signal into an electric signal. In the present invention, the monitor signal or the electric signal is monitored.

  Examples of the control unit 420 include a difference signal generation circuit, a gain signal calculation circuit (division circuit), a combination thereof, a sum signal generation circuit and a linear combination calculation circuit. In the present invention, the monitoring unit and the control unit include a unit that performs the following control.

  (I) The monitoring means monitors the input and output power of at least one signal light, and the control section calculates the gain of the signal light from the value obtained by the monitoring means, and determines a predetermined value or The excitation means is controlled so as to match a value inputted from outside.

  (Ii) the monitoring unit monitors the power of the laser oscillation light in the optical resonator at the signal input end of the amplification medium and the power of the signal light incident on the amplification medium, and the control unit is obtained from the monitoring unit. Calculates the sum of the laser oscillation light power value and the signal light power value, or the value obtained by the linear combination of the laser oscillation light power value and the signal light power value, and agrees with a predetermined value or a value input from outside. The excitation means is controlled so that

  (Iii) The monitoring means simultaneously extracts a part of the laser oscillation light in the optical resonator and a part of the signal light incident on the amplification medium at the signal input end of the amplification medium and monitors the total power thereof. The control unit controls the excitation unit such that a value obtained by the monitoring unit matches a predetermined value or a value input from outside.

  (Iv) The monitoring means monitors the power of the laser oscillation light in the optical resonator at the signal output end of the amplification medium and the power of the signal light emitted from the amplification medium, and the control section is obtained by the monitoring means. Calculates the sum of the laser oscillation light power value and the signal light power value, or the value obtained by the linear combination of the laser oscillation light power value and the signal light power value, and agrees with a predetermined value or a value input from outside. The excitation means is controlled so that

  (V) The monitoring means simultaneously extracts a part of the laser oscillation light in the optical resonator and a part of the signal light emitted from the amplification medium at the signal output end of the amplification medium, and monitors the total power thereof. The control unit controls the excitation unit so that a value obtained by the monitoring unit matches a predetermined value or a value input from outside.

  In the first embodiment, it is preferable to provide isolators 430 and 432 as shown in FIG.

  In the present embodiment, various components, such as the components constituting the optical resonator and the control unit, can take various arrangements other than the arrangement shown in FIG.

  In the method of controlling the gain profile to be constant in the first embodiment, an input signal input to the optical amplifier and / or a part of the spontaneous emission light (ASE) amplified by the amplification medium in the optical amplifier is extracted. To oscillate. In addition, light to be monitored (hereinafter, also referred to as a monitor signal) (first signal and second signal in FIG. 4) is input to the monitoring unit 419. The control unit 420 performs an operation based on the information from the monitoring unit, and the excitation unit 412 controls the excitation light based on this value. In the present invention, a monitor signal or an electric signal obtained by converting the monitor signal is monitored.

  In the present invention, the above-described controls (i) to (v) are performed by the monitoring unit and the control unit.

  Hereinafter, a control method using the optical amplifier of the present invention (operation of the optical amplifier of the present invention) will be specifically described. In the following description, a single-pass configuration will be described, but the present invention can also use a double-pass configuration, a bidirectional optical amplifier configuration, and the like.

  First, the signal light enters from the left side in FIG. 4 and is partially branched by the optical branching element 426. The split signal light is input to the monitoring unit 419 as a first signal. Preferably, the first signal is an electrical signal. Therefore, in the present embodiment, it is preferable to convert the monitor signal light into an electric signal by using a photoelectric conversion element that converts the branched signal light into an electric signal. The signal light that has passed through the optical branching element 426 passes through the optical branching element 414, the isolator 432, and the multiplexer 436, and enters the amplification medium 410.

  The pumping light is incident from the front and the rear via the multiplexers 436 and 438. The amplified signal light is output after passing through the isolator 430 and the optical splitters 416 and 428. The optical splitter 428 splits a part of the output signal light in order to monitor a part of the signal light. The light split here is input to the monitoring unit 419 as a second signal. Preferably, the second signal is an electrical signal. Therefore, in the present embodiment, it is preferable to convert the branched signal light into an electric signal by using a photoelectric conversion element that converts the branched signal light into an electric signal.

  Here, the light to be monitored is WDM light having one or more wavelengths or light having a wavelength in an amplification band which is separately input to an optical amplifier. In the present invention, it is preferable that the signal is monitored by the monitoring means shown in the above (i) to (v).

  The first signal and the second signal are input to the control unit 420 via the monitoring unit 419, and the values such as the gain of these input signals are obtained, and the excitation is performed so that the values match the preset values. The current value of the light source is calculated, and the light amounts of the excitation light sources 422 and 424 are adjusted so as to have the current value. The control unit of the present invention performs the processes and controls described in (i) to (v) above.

  A part of the signal light and the ASE light emitted from the isolator 430 are extracted by the optical branching element 416, and injected into the amplification medium 410 again from the optical branching element 414 via the wavelength selecting element 418. In the present embodiment, an optical resonator is formed by a loop including at least the amplification medium 410, the pumping unit 412, the optical branching elements 414 and 416, and the wavelength selection element.

  The oscillation wavelength of the optical resonator makes the branching characteristics of the optical branching elements 414 and 416 have wavelength dependency, uses the function of the wavelength selection element 418, or uses both of them at the same time. It is specified by doing. At this oscillation wavelength, the optical resonator oscillates when the loss of one round of the optical resonator matches the gain of the amplification medium 410. If stable and stable oscillation is possible, the gain of the amplifying medium 410 at the oscillation wavelength selected by the wavelength selection element or the like does not change even if the excitation light source injects an excitation light amount exceeding the oscillation condition.

  As described above, the laser oscillation is caused by the optical resonator in the optical amplifier, and the light amount of the pumping light source is adjusted so that the gain profile becomes constant while monitoring by the monitoring means shown in (i) to (v). Adjust.

  A second embodiment of the present invention is an optical amplifier having a plurality of resonators and a method for controlling a gain profile of the amplifier to be constant.

  FIG. 5 schematically shows an optical amplifier according to the second embodiment. FIG. 5 shows an optical amplifier having two resonators. Hereinafter, description will be made based on this example. The optical amplifier 500 according to the present embodiment includes a first optical resonator 502 and a second optical resonator 504. The first optical resonator 502 includes an amplification medium 510, excitation means 512 for exciting the amplification medium 510, optical branching means 514, 516, and a wavelength selection element 518. The second optical resonator 504 includes an amplification medium 510, an excitation unit 512 for exciting the amplification medium 510, optical branching units 520 and 522, and a wavelength selection element 524.

  The excitation means 512 includes excitation light sources 526 and 528 for exciting the amplification medium, and multiplexers 530 and 532 for multiplexing light from the excitation light sources. In the optical amplifier shown in FIG. 5, the pumping light is bidirectional pumping, but the present invention is not limited to this, and forward pumping and backward pumping may be used.

  In the present embodiment, as shown in FIG. 5, an oscillation determination circuit 534 may be provided so that the two optical resonators can maintain the transmission state. The oscillation determination circuit forms an oscillation determination unit together with the optical branching elements 536 and 538 for extracting a part of the oscillation light from each optical resonator. For example, signal light is extracted to the oscillation determination circuit 534 by the optical branching elements 536 and 538, and a signal is input as an electric signal through a photoelectric conversion element or the like.

  Also in this embodiment, a variable optical attenuator or the like can be introduced into the optical resonator. In the present invention, the optical resonator oscillates when the gain of the amplifying medium and the loss of one round of the resonance system coincide. However, by introducing a variable optical attenuator or the like, the gain of the amplifying medium and the round of the resonance system round. The loss relationship can be adjusted.

  In the second embodiment, it is preferable to provide isolators 540 and 542 as shown in FIG.

  Note that, in the present embodiment, various components, such as the components constituting the optical resonator and the oscillation determination circuit, can be arranged in addition to the arrangement shown in FIG.

  The same elements as those described in the first embodiment can be used for each element of the present embodiment.

  Hereinafter, a control method (operation of the optical amplifier of the present invention) using the optical amplifier of the present embodiment will be specifically described. In the following description, a single-pass configuration will be described, but the present invention can also use a double-pass configuration, a bidirectional optical amplifier configuration, and the like.

  The signal light enters the amplification medium 510 via the optical splitters 514, 520, the isolator 540, and the multiplexer 530. The signal light emitted from the amplification medium 510 is emitted via the multiplexer 532, the isolator 542, and the optical branching elements 522, 516.

  In the present embodiment, it is preferable to include an oscillation determination circuit in order to maintain the first resonator and the second resonator in an oscillation state. The light in the first resonator is split by the optical splitter 538, and the split light is input to the oscillation determination circuit 534 as a monitor signal. The light in the second resonator is branched by the optical branching element 536, and the branched light is input to the oscillation determination circuit 534 as a monitor signal. Light as a monitor signal is preferably converted into an electric signal by a photoelectric conversion element or the like. The light amounts of the excitation light sources emitted from the excitation light sources 526 and 527 are controlled so that the two resonators oscillate in accordance with both monitor signals.

  In the first and second embodiments, it is preferable that the monitoring means include an optical band-pass filter so that the monitor signal passes therethrough.

  In the optical amplifier according to each of the embodiments described above, the propagation direction of the signal light in the amplification medium is not particularly specified, but the optical amplifier has the following configurations (a) to (c), and The light can take the propagation directions shown in these.

(A) An optical isolator is connected to both or both of the input side and the output side of the amplification medium. The signal light propagates in the amplification medium in only one direction (referred to as a single path in this specification).

(B) An optical circulator is connected to one side of the amplification medium, and a device having a mirror function of reflecting at least signal light is connected to the other end of the amplification medium. The signal light travels through the amplification medium after passing through the optical circulator and is amplified. Next, the signal light is turned by a mirror that reflects the signal light, travels in the opposite direction in the amplification medium, and is amplified. The amplified signal light passes through the circulator and exits (referred to as a double pass in this specification). In this case, considering the above-described first to third monitoring methods, an optical branching unit is provided for partially branching the signal light and extracting a monitor signal. It may be installed at each signal output port installed via a circulator. Further, the optical branching means can be provided between the optical circulator and the amplification medium. In this case, the input side monitor and the output side monitor can be distinguished by the direction of the coupling operation of the optical branching means itself.

(C) An optical circulator is connected to both of the amplification media. Two types of signal light having different traveling directions travel in opposite directions in the amplification medium in a state where they are simultaneously or temporally separated, and are amplified (hereinafter, referred to as a bidirectional optical amplifier). In this case, considering the above-described first to third monitoring methods, an optical branching unit is provided for partially branching out the signal light and extracting a monitor signal. The signal light may be set on the input side and the output side of the amplification medium based on one of the signal lights. Specifically, the optical branching means can be provided outside the circulator, between the circulator and the amplification medium.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Example 1)
The present embodiment is an example of the first embodiment of the present invention, and particularly is an example of an optical amplifier and a control method corresponding to the above (1).

  FIG. 6 is a configuration diagram for explaining the optical amplifier of the present invention. As shown in FIG. 6, the optical amplifier according to the present invention includes an optical resonator, monitoring means, and a control unit. The optical resonator divides a part of the signal light into an amplification medium 1306, excitation light sources 1314 and 1317 for exciting the amplification medium, a wavelength selection element 1305, a variable optical attenuator 1307, a wavelength selection element, and a variable optical attenuator. An optical branching element, a wavelength selecting element, and an optical branching element 1302 for multiplexing the signal light from the variable optical attenuator. The monitoring unit includes an optical splitter 1301 for splitting the first monitored signal light, an optical splitter 1311 for splitting the second monitored signal light, a controller 1316, and first and second monitored signal lights. And optical photoelectric conversion circuits 1313 and 1319 for converting the signal light to be monitored into an electric signal. The control unit includes excitation light drive circuits 1315 and 1318 for controlling the excitation light source. In this embodiment, an example of bidirectional pumping has been described, but the present invention is not limited to this, and forward pumping or backward pumping may be used.

The used amplification medium 1306 is ZBLAN glass, which is a kind of fluoride glass, to which Tm ions are added and the host glass is used. The added concentration of Tm ³⁺ was 6000 ppm. The length of the Tm-doped ZBLAN-based fluoride optical fiber was 5 m. As the excitation light sources 1314 and 1317, semiconductor lasers having an oscillation wavelength from 1400 to 1430 nm were used. The light splitting elements 1301 and 1311 in the portion for extracting the signal light to be monitored are devices of a type using a dielectric multilayer mirror and reflecting and extracting 1% of the incident signal light.

  As the signal light, 16 waves at 1480 nm to 1510 nm and 2 nm intervals were used. The optical bandpass filters 1312 and 1320 used had a center wavelength of 1480 nm and a full width at half maximum of a transmission band of 0.8 nm. As the photoelectric conversion circuits 1313 and 1319, InGaAs-PIN-PD was used. The optical branching elements 1302 and 1310 constituting the optical resonator have a pass loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1513 to 1516 nm.

  The wavelength selection element 1305 uses a dielectric multilayer film, and has a central wavelength of a transmission band of 1513 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. The variable optical attenuator 1307 was adjusted so that the loss at 1513 to 1516 nm in one round of the optical resonator was 18 dB. Variable optical attenuators are commonly used in optical amplifiers.

  The monitoring unit 1316 calculates a signal light gain from a ratio between the first monitor signal (the first electric signal in the present embodiment) and the second monitor signal (the second electric signal in the present embodiment). Including. More specifically, a differential signal generating circuit for generating a differential signal and a gain signal calculating circuit (division circuit) are included.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. First, the signal light enters from the left side in FIG. 6 and is partially branched by the optical branching element 1301. The branched signal light to be monitored enters the photoelectric conversion circuit 1313 via the optical bandpass filter 1312 and becomes a first electric signal. The signal light that has passed through the optical branching element 1301 passes through the optical branching element 1302, the isolator 1303, the pumping light / signal light multiplexing coupler 1304, and enters the amplification medium 1306.

  The pumping light is also incident from the rear through the pumping light / signal light multiplexing coupler 1308. The amplified signal light is output after passing through the isolator 1309 and the optical splitters 1310 and 1311. The optical branching element 1311 is for monitoring a part of the output signal light, and enters the photoelectric conversion circuit 1319 via the optical bandpass filter 1320 to become a second electric signal.

  Here, the signal light is WDM light having one or more wavelengths. The passing wavelengths of the two optical bandpass filters 1312 and 1320 are the same, and are adjusted to the wavelength of one specific channel of the WDM signal light.

  A part of the signal light and the ASE light emitted from the isolator 1309 are extracted by the optical branching element 1310, and injected into the amplification medium 1306 again from the optical branching element 1302 via the variable optical attenuator 1307 and the wavelength selection element 1305. Is done. Thereby, an optical resonator is formed.

  The oscillation wavelength of this optical resonator is specified by either giving wavelength dependency to the branching characteristics of the optical branching elements 1302 and 1310, using the function of the wavelength selection element 1305, or using both at the same time. Is selected. At the selected oscillation wavelength, the optical resonator oscillates when the loss of one round of the optical resonator matches the gain of the amplification medium 1306. If stable and stable oscillation is possible, the gain of the amplifying medium 1306 at the oscillation wavelength does not change even if the pumping light amount that exceeds the oscillation condition is injected.

  The first electric signal and the second electric signal described above are converted into gain signals by the division circuit 1316. The excitation light drive circuits 1315 and 1318 are adjusted by the gain signal so as to match a preset value, and the light amount of the excitation light source is controlled. The pumping light is injected into the amplification medium by the pumping light / signal light multiplexing couplers 1304 and 1308.

  FIG. 7 is a diagram for explaining a positional relationship of an optical branch element for forming an optical resonator. In FIG. 7, the same components as those in FIG. 6 are denoted by the same reference numerals as those in FIG. There are various cases in which the positions of the optical branching elements 1302 and 1310 for forming the optical resonator are different. The optical resonator includes a loop of an optical branching element 1302, an amplification medium 1306, an optical branching element 1310, a variable optical attenuator 1307, and a wavelength selecting element 1305. In this case, the insertion positions of the optical branching elements 1302 and 1301 and the pump light / signal light multiplexing coupler 1304 can be the positions A and B with the optical isolator 1303 interposed therebetween.

  In particular, when the passing loss of the optical isolator 1303 at the pump wavelength is high, the insertion position of the pump light / signal light multiplex coupler 1304 is desirably B. In the range of A and B, an appropriate position for inserting each element is determined by the loss of each branching means at the oscillation wavelength, the loss of the coupler, and the like, but the arrangement is not necessarily limited to the position shown in FIG. .

  Similarly, insertion positions of the optical branching elements 1311 and 1310 and the pumping / signal light multiplexing coupler 1317 can be at positions C and D. In general, the reverse blocking ratio of light of the optical isolator 1309 is often high in a wide wavelength range, and therefore, the insertion position of the pump light / signal light multiplex coupler 1317 is often desirably the position C. Regarding the optical branching elements 1311 and 1310 and the pumping / signal light multiplexing coupler 1317, an appropriate position can be determined in the range of C and D according to the loss of each branch portion at the oscillation wavelength, the loss of the coupler, and the like. However, the arrangement is not necessarily limited to the position shown in FIG.

  FIG. 8 is a diagram plotting the maximum value of the deviation of the gain profile when the input signal level is changed. That is, each input signal level is set to -25, -20, -15, -10 dBm / ch. -25 dBm / ch. FIG. 9 is a diagram in which the gain spectrum when the input is changed is plotted with the maximum value of the deviation from the reference spectrum, using the gain spectrum at step S as a reference.

  The excitation light amount was about 1.3 times the threshold value at which the optical resonator oscillates. The evaluation of the gain was measured by scanning a small signal probe light of -35 dBm. The dotted line in FIG. 8 shows the result when the gain is not controlled by the signal light to be monitored. The solid line in FIG. 8 is a plot of a value obtained when the signal light of 1480 nm is monitored and the control circuit is operated to perform control so that the gain at 1480 nm becomes constant. From FIG. 8, it has been clarified that the gain profile becomes constant by controlling.

(Example 2)
The present embodiment is an example of the optical amplifier represented by the above (1).
FIG. 9 is a configuration diagram for explaining a second embodiment of the optical amplifier of the present invention. The present embodiment is an example of an optical amplifier using a double-pass configuration, and particularly an example of a reflection-type optical amplifier.

  The optical resonator of this embodiment has the same configuration as that of the first embodiment. In this embodiment, a circulator 1503 is provided at the input end of the optical resonator, and a mirror 1508 is provided at the output side of the optical resonator. As shown in FIG. 9, the monitoring means of the optical amplifier according to the present embodiment is configured such that the optical branching element 1502 for extracting the second signal light is provided on the output end side of the circulator 1503 for extracting the amplified output signal. Except for this, the configuration is the same as that of the first embodiment. In this embodiment, an example of bidirectional pumping has been described, but the present invention is not limited to this, and forward pumping or backward pumping may be used.

In FIG. 9, an In-based fluoride optical fiber to which Tm ³⁺ was added at a concentration of 2000 ppm was used as the amplification medium 1526. The optical fiber length is 20 m. As an excitation light source, an InGaAs strained quantum well LD oscillating at 1030 nm was used. The optical amplifier according to the present embodiment includes a configuration for extracting a first electrical signal and a configuration for extracting a second electrical signal in order to extract a signal light to be monitored. A configuration for extracting a first electric signal includes an optical branching element 1501, an optical bandpass filter 1517, and a photoelectric conversion circuit 1519. The configuration for extracting the second electric signal includes an optical branching element 1502, an optical bandpass filter 1518, and a photoelectric conversion circuit 1520.

  Each of the light splitting elements 1501 and 1502 is a device that uses a dielectric multilayer mirror and reflects and extracts 1% of the incident signal light.

  As the signal light, 16 waves at 1460 nm to 1490 nm and 2 nm intervals were used. As the optical bandpass filters 1517 and 1518, those having a central wavelength of 1460 nm and a full width at half maximum of a transmission band of 0.8 nm were used. As the photoelectric conversion circuits 1519 and 1520, InGaAs-PIN-PD was used. The optical branching elements 1504 and 1507 that constitute the optical resonator have a pass loss of 0.2 dB or less at 1460 to 1490 nm and a branching ratio of 95% at 1493 to 1496 nm.

  The wavelength selection element 1510 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1493 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. The variable optical attenuator 1511 was adjusted so that the loss in the wavelength band of 1493 to 1496 nm in one round of the optical resonator was 20 dB.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. The signal light that has passed through the optical branching element 1501 enters the amplification medium 1526 via the circulator 1503, is reflected by the mirror 1508, passes through the amplification medium 1526 again, and is emitted through the circulator 1503 toward the optical branching element 1502. You.

  Here, the optical splitters 1501 and 1502 split a part of the signal light as the signal light to be monitored. From the branched signal light to be monitored, only necessary signal light components are extracted through optical band-pass filters 1517 and 1518 having the same passing wavelength, and are respectively incident on photoelectric conversion circuits 1519 and 1520 to be converted into electric signals. Is converted. The first and second electric signals are extracted as gain signals by the division circuit 1516. The excitation light drive circuits 1514 and 1515 are controlled by the gain signal so as to match the set value, and the excitation light amounts of the excitation light sources 1512 and 1513 are controlled. The pumping light is injected into the amplification medium by the pumping light / signal light multiplexing couplers 1505 and 1506.

  The optical resonator is configured by a loop including optical branching elements 1504 and 1507, a wavelength selection element 1510, a variable optical attenuator 1511, and an amplification medium 1526. Here, an isolator may be added from the optical branching element 1504 to the optical path connecting the optical branching element 1507 via the wavelength selecting element 1510 and the variable optical attenuator 1511 to define the traveling direction of oscillation light in the optical resonator. It is possible. Regardless of the presence or absence of the isolator, the gain of the amplification medium at the wavelength of the light that causes laser oscillation is fixed by the loss of one round of the optical resonator, and the gain of the monitored signal light at the extracted wavelength is divided by the dividing circuit 1516. , The gain profile as an amplifier is uniquely determined.

  FIG. 10 is a diagram for explaining an insertion position of an optical branching element when a double-pass configuration is used. Various positions other than those shown in FIG. 9 are possible for insertion positions of the respective optical branching elements constituting the monitoring unit, the optical resonator, and the excitation unit. In FIG. 10, the same reference numerals as in FIG. 9 are used for the same components as in FIG.

  A monitor circuit for the incident signal light (a combination of the optical branching element 1501, the optical bandpass filter 1517, and the photoelectric conversion circuit 1519) and a monitor circuit for the output signal light (the optical branching element 1502, the optical bandpass filter 1518, and the photoelectric conversion circuit 1520) Combination), a pump light circuit (a combination of the pump light / signal light multiplexing coupler 1505 and the pump light source 1512, and the pump light / signal light multiplex coupler 1506 and the pump light source 1513), and an optical resonator (the optical branching elements 1504 and 1507). The mutual positional relationship between the variable optical attenuator 1511 and the wavelength selection element 1510) will be described.

  When the optical splitters 1501 and 1502 are optical directional couplers, the optical splitter 1501 can be located at positions A and B, and the optical splitter 1502 can be located at positions D and B. On the other hand, the light splitting elements 1504 and 1507 can be combined with A and D, B and C, A and C, and D and C, respectively. On the other hand, the position of C is desirable for the pump light / signal light multiplex coupler 1506. The pumping light / signal light multiplexing coupler 1505 can have the positions A and D if the forward loss or the backward loss of the circulator 1503 at the pumping wavelength is sufficiently low, but the position B is desirable. The mutual positional relationship between the individual devices in each of the regions A to D can be freely set as long as the optical characteristics of each device are considered.

  FIG. 11 shows that each input signal level is from -25 to -10 dBm / ch. When changed to -25 dBm / ch. FIG. 11 is a diagram in which the maximum value of the deviation of the gain from the reference profile when the input is changed using the gain profile at the time of reference as a reference is plotted. The dotted line shows the characteristics when gain control is not performed at the wavelength of the signal light to be monitored, and the solid line shows the characteristics when gain control is performed. From FIG. 11, it has been clarified that the gain profile becomes constant by applying the control.

(Example 3)
The present embodiment is an example of the optical amplifier represented by the above (1).
FIG. 12 is a configuration diagram for explaining a third embodiment of the optical amplifier of the present invention, and is an example of a bidirectional optical amplifier. In this embodiment, the optical resonator, the monitoring unit, and the control unit have the same structure as in the first embodiment. In the present embodiment, as shown in FIG. 12, circulators 1702 and 1707 are provided at both ends of the optical resonator, and a first input signal and a second input signal are input to face the optical resonator. Although FIG. 12 shows an example of bidirectional pumping, the present invention is not limited to this, and forward pumping or backward pumping may be used.

As the amplification medium 1726, a tellurite-based optical fiber to which Tm ³⁺ was added at a concentration of 2000 ppm was used. The optical fiber length is 20 m. As the excitation light source 1715, an LD oscillating at 1400 nm was used, and as the excitation light source 1717, light generated from the LD oscillating at 1400 nm and the LD oscillating at 1600 nm was used.

  In this embodiment, the state of the gain profile is monitored using the signal light to be monitored, and the pump light source is controlled using the pump light driving circuits 1716 and 1718 to control the gain profile to be constant. Of these, two LDs oscillating at 1400 nm and 1600 nm connected to the excitation light driving circuit 1718 were fed back to control these excitation light sources. Extraction of the signal light to be monitored is performed by the optical branching elements 1701 and 1708, and for these, a fusion-stretched fiber coupler is used. This optical branching element is a device of a type that reflects and extracts 1% of the incident signal light.

  As the signal light, 16 waves at 1480 nm to 1510 nm and 2 nm intervals were used.

  As the optical bandpass filters 1711 and 1713, those having a center wavelength of 1510 nm and a full width at half maximum of a transmission band of 0.8 nm were used. As the photoelectric conversion circuits 1712 and 1714, InGaAs-PIN-PD was used. The optical branching elements 1703 and 1706 that constitute the optical resonator have a transmission loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1474 to 1477 nm.

  The wavelength selection element 1709 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1476 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. The variable optical attenuator 1710 was adjusted so that the loss at 1474 to 1477 nm in one round of the optical resonator was 20 dB.

  When the input signal level is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input is changed is observed at 1510 nm, and the value is 7 dB when the gain control is not performed, whereas the value is 0.3 dB when the gain control is performed. Met.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. The signal light having passed through the optical branch element 1701 enters the amplification medium 1726 via the circulator 1702. That is, the signal light passes through the optical branching element 1703 and the pumping light / signal light multiplexing coupler 1704, enters the amplification medium 1726, and is amplified. The backward pumping light is multiplexed by the pumping light / signal light multiplexing coupler 1705.

  The amplified signal light passes through the optical splitter 1706 and the circulator 1707, and is extracted through the optical splitter 1708. A part of the incident signal light is converted into an electric signal by the optical branching element 1701, the optical bandpass filter 1711, and the photoelectric conversion circuit 1712, and a part of the emitted signal light is converted into the optical branching element 1708 by the optical bandpassing element. The signal is converted into an electric signal by the filter 1713 and the photoelectric conversion circuit 1714.

  Each electric signal is converted to a gain signal by a division circuit 1720. With this gain signal, the amount of excitation light from the excitation light sources 715 and 717 is adjusted via the excitation light drive circuits 1716 and 1718 so as to match a preset value. As described above, the gain at the wavelength of the signal light to be monitored among the incident signal lights is controlled by the electric feedback.

  On the other hand, the optical resonator is configured by a loop including optical branching elements 1703 and 1706, a wavelength selecting element 1709, a variable optical attenuator 1710, and an amplification medium 1726.

  Here, an isolator may be added from the optical branching element 1703 to the optical path connecting the optical branching element 1706 via the wavelength selection element 1709 and the variable optical attenuator 1710 to define the traveling direction of the oscillation light in the optical resonator. It is possible. Regardless of the presence or absence of the isolator, the gain of the amplifying medium at the wavelength of the light causing laser oscillation is fixed by the loss of one round of the optical resonator, and the gain at the wavelength of the signal light to be monitored is divided by the division circuit 1720. Since the gain is fixed by the electric feedback system used, the gain profile of the amplifier is uniquely determined.

  FIG. 13 is a diagram for explaining the insertion positions of the respective optical branching elements constituting the monitoring means, the optical resonator, and the excitation means in the configuration shown in FIG. Various positions other than those shown in FIG. 12 are possible for the insertion positions of the optical branching elements constituting the monitor and the optical resonator. In FIG. 13, the same components as those in FIG. 12 are denoted by the same reference numerals as those in FIG.

  A monitor circuit for the incident signal light (combination of the optical branch element 1701, the optical bandpass filter 1711, and the photoelectric conversion circuit 1712) and a monitor circuit for the output signal light (the optical branch element 1708, the optical bandpass filter 1713, and the photoelectric conversion circuit 1714) Combination), a pump light circuit (combination of the pump light / signal light multiplex coupler 1704 and the pump light source 1715, and the pump light / signal light multiplex coupler 1705 and the pump light source 1717), and an optical resonator (optical branching elements 1703 and 1706). Of the variable optical attenuator 1710 and the wavelength selection element 1709) will be described.

  The light branching element 1701 can be at the position of A or B. The optical branching element 1708 can be in the C or D position. On the other hand, the light splitters 1703 and 1706 can be combined with A and D, B and C, A and C, and B and C, respectively. On the other hand, the pumping light / signal light multiplexing coupler 1704 is at the position A or B, and the position B is preferable. The pumping light / signal light multiplexing coupler 1705 is at the position C or E, and the position C is preferable. The mutual positions of the individual devices in each of the regions A to E can be freely set as long as the optical characteristics of each device are considered.

(Example 4)
The present embodiment is an example of the optical amplifier represented by the above (2).
FIG. 14 is a configuration diagram for explaining a fourth embodiment of the optical amplifier of the present invention, and is a diagram showing a configuration of a single path. The optical amplifier according to the present embodiment monitors the optical resonator having the same configuration as that of the first embodiment and the sum of the total power of the signal input and the power of the light causing oscillation of the resonator at the input end of the amplification medium. And a controller for controlling the excitation light source. The monitoring means includes an optical branching element 1902 for extracting the signal input light and the light causing the oscillation of the optical resonator, a photoelectric conversion circuit 1910 for converting the power of the light into an electric signal, and an excitation light drive from the electric signal. A monitoring unit (for example, a differential signal generation circuit) 1915 for sending a signal to the circuits 1912 and 1914 is included. The control unit includes excitation light drive circuits 1912 and 1914 for controlling the excitation light sources 1911 and 1913.

  As the amplification medium 1916, a Zr-based fluoride optical fiber to which Er was added at a concentration of 2000 ppm was used. The optical fiber length is 7 m.

  As the excitation light sources 1911 and 1913, a polarization multiplexing type excitation unit in which LDs oscillating at 980 nm were arranged so that the polarizations were orthogonal to each other was used. In this embodiment, the state of the gain profile is monitored using the monitor signal light, and the gain profile is made constant by controlling the pump light source using the pump light driving circuits 1912 and 1914. In the control of this embodiment, feedback control is applied to all LDs (pumping light sources). However, the pumping light amount from the pumping light / signal light multiplexing coupler 1905 is always larger than the pumping light amount from the pumping light / signal light multiplexing coupler 1904. It was made to be 1.4 times.

  The portion from which the monitor signal light is extracted is composed of the optical branching element 1902 and the photoelectric conversion circuit 1910. The light branching element 1902 is a Parc-type coupler using a dielectric multilayer film as a filter, and has a branching ratio of 1% at 900 to 100 nm and 2500 to 3000 nm. As the signal light, 16 waves at 2 nm intervals from 2600 to 2630 nm were used. The photoelectric conversion circuit 1910 used PIN-PD.

  The optical branching elements 1901 and 1907 that constitute the optical resonator have a pass loss of 0.2 dB or less at 2600 to 2630 nm, and a branching ratio of 95% at 2610 to 2650 nm. The wavelength selection element 1908 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 2630 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. In the optical resonator, the variable optical attenuator 1909 was adjusted so that the loss at 2610 to 2650 nm in one round was 20 dB.

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 5 dB when gain control was not performed, whereas it was 0.2 dB when gain control was performed.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. Also in this embodiment, the configuration of the single path, the configuration of the double path, and the configuration of the bidirectional optical amplifier apply.

  The optical amplifier of this embodiment uses the optical resonator and the second monitoring method at the same time. In particular, in the present embodiment, in the second monitoring method, an optical branching element that partially branches the entire signal light and an optical branching element that partially branches the laser oscillation light in the resonator at the input end of the amplification medium are combined into one. It is characterized in that it is performed by an optical branching device. Based on the power of all the branched signal lights and the power of the laser oscillation light, these lights are incident on one photoelectric conversion element to be introduced at the same time and are converted into electric signals.

  The pumping light drive circuit is adjusted so that a difference signal component between the electric signal and a preset level becomes zero. The method of selecting the excitation light drive circuit is the same as in the above-described embodiment. The optical elements used are the same as those described in the above-described embodiment.

  The signal light enters the amplification medium via the optical splitters 1901 and 1902, the isolator 1903, and the excitation light / signal light multiplexing coupler 1904, and the signal light amplified in the amplification medium is excited light / signal light multiplexing coupler 1905. The light exits through an isolator 1906 and a light splitting element 1907. The optical resonator is configured by a loop including optical branch elements 1901 and 1907, a wavelength selection element 1908, a variable optical attenuator 1909, and an amplification medium 1916.

  The optical branching element 1902 has a function of extracting the oscillating light in the optical resonator and the total incident signal light at a specified ratio, respectively. The extracted monitor signal light is converted into an electric signal by the photoelectric conversion circuit 1910. You. This electric signal has a signal level proportional to the amount of light incident on the amplification medium 1916, and this level is compared with a predetermined level. The compared signal level is output as a difference signal by a difference signal generation circuit 1915 that generates the difference signal, and the excitation light drive circuit and the excitation light source are feedback-controlled by the difference signal.

  With this control, the light entering the incident end of the amplification medium 1916 always matches a predetermined value or a value set from outside. Needless to say, the insertion position of each optical branching unit has a degree of freedom. Reference numerals 1912 and 1914 denote excitation light driving circuits.

(Example 5)
FIG. 15 is a configuration diagram for explaining a fifth embodiment of the optical amplifier of the present invention, and is an example showing a single-path configuration.

  In the present embodiment, as shown in FIG. 15, an optical branching element 2002 for extracting the first monitored signal light at the input end side of the resonator, and converting the monitored signal light extracted therefrom into an electric signal Example 4 is the same as Example 4 except that a portion for extracting a signal light to be monitored including a photoelectric conversion circuit 2012 and an isolator 2011 between a variable optical attenuator 2010 and an optical branching element 2007 in an optical resonator are provided. Having a configuration.

As the amplification medium 2026, a Zr-based fluoride optical fiber to which Tm ³⁺ was added at a concentration of 6000 ppm was used. The optical fiber length is 7 m. The excitation light sources 2014 and 2016 are LDs oscillating at 1400 nm.

  In this embodiment, the state of the gain profile is monitored using the signal light to be monitored, and the gain profile is made constant by controlling the pump light source using the pump light driving circuits 2015 and 2017. In the control of this embodiment, feedback control was applied to all LDs oscillating at 1400 nm connected to the excitation light driving circuits 2015 and 2017. However, when the pumping light amount from the pumping light / signal light multiplexing coupler 2005 is P1 and the pumping light amount from the pumping light / signal light multiplexing coupler 2006 is P2, the relationship between the light amounts is controlled according to the following equation. .

P2 (mW) = 400t
P1 (mW) = 100t + 300
Where t is a real number from 0 to 1

  A fusion-stretched fiber coupler was used for the optical branch element 2002 for extracting the signal to be monitored and the 2004 for extracting the monitor signal. This is a fusion-stretched coupler having a branching ratio of 1% which is almost constant at 1470 to 1530 nm. However, the light splitting element 2002 splits only the light propagating from left to right in FIG. 15, and the light splitting element 1004 splits only the light propagating from right to left in FIG. As the signal light, 16 waves at 1480 nm to 1510 nm and 2 nm intervals were used.

  For the photoelectric conversion circuits 2012 and 2013, InGaAs-PIN-PD was used. The optical branching elements 2003 and 2007 constituting the optical resonator have a pass loss of 1 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1513 to 1517 nm.

  The wavelength selection element 2009 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1515 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. The optical resonator is adjusted by the variable optical attenuator 2010 so that the loss at 1515 nm in one round becomes 17 dB.

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 6 dB at 1515 nm when gain control was not performed, whereas it was 0.3 dB when gain control was performed. Note that reference numerals 2001, 2008, and 2011 denote optical isolators.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. This embodiment is different from the above-mentioned second monitoring method in that the optical branching element for partially branching the entire signal light and the optical branching element for partially branching the laser oscillation light in the resonator at the input end of the amplification medium are separated. By using these, each light is incident on another photoelectric conversion element, and is converted into an independent electric signal corresponding to the power of each light. The obtained electric signal is converted into an electric signal that is a component of a linear combination or a sum of the two by some electric means. The electric signal is taken out, and a difference signal component between the electric signal and a preset level becomes zero. The excitation light drive circuit is adjusted as described above. The method of selecting the excitation light drive circuit is the same as in the above-described embodiment. The optical elements used are the same as those described in the above-described embodiment.

  The signal light enters the amplifying medium 2026 via the isolator 2001, the optical splitters 2002 and 2003, and the multiplexing coupler for the pumping light / signal light 2005. The signal light amplified in the amplification medium 2026 is extracted through the pump light / signal light multiplexing coupler 2006, the optical branching element 2007, and the isolator 2008.

  The optical resonator includes a loop including optical branching elements 2003 and 2007, a wavelength selecting element 2009, a variable optical attenuator 2010, an isolator 2011, and an amplification medium 2026. The optical splitters 2002 and 2004 both operate as directional couplers. For this reason, the optical splitter 2004 splits and extracts only the laser oscillation light in the optical resonator traveling in the opposite direction to the signal light.

  The signal light for monitoring corresponding to the incident signal light, the monitor signal light, and the monitor light corresponding to the laser oscillation light extracted from the optical branching elements 2002 and 2004 are converted into electric signals by the photoelectric conversion circuits 2012 and 2013, respectively. , A sum signal generation circuit 2018 adds the two, and at the same time, compares the externally set level with the sum component to output a difference signal between the two.

  In the pump light drive circuits 2015 and 2017 and the pump light sources 2014 and 2016, feedback control is performed so that the difference signal becomes zero. Needless to say, the insertion position of each optical branching element has a degree of freedom.

(Example 6)
This embodiment is an example of the optical amplifier represented by the above (3).

  FIG. 16 is a configuration diagram for explaining a sixth embodiment of the optical amplifier of the present invention, and is an example showing a single-path configuration.

  In the present embodiment, at the input end of the amplification medium, the sum of the total power of the signal input and the power of the light causing oscillation of the resonator is monitored, and the pumping light source is controlled. As shown in FIG. 16, monitoring means and a control unit for monitoring the sum of the total power of the signal output and the power of the light causing oscillation of the resonator at the output end of the amplifying medium and controlling the excitation light source are provided as shown in FIG. , Except that it is provided between the isolator 2105 and the optical branching element 2107.

As the amplification medium 2116, a Zr-based fluoride optical fiber to which Tm ³⁺ was added at a concentration of 6000 ppm was used. The optical fiber length is 7 m. The excitation light sources 2110 and 2112 are LDs oscillating at 1400 nm.

  In this embodiment, the state of the gain profile is monitored using the monitor signal light, and the gain profile is made constant by controlling the pump light source using the pump light driving circuits 2111 and 2113.

  In the control of this embodiment, feedback control was applied to all LDs oscillating at 1400 nm connected to the excitation light drive circuits 2111 and 1113. However, when the pumping light amount from the pumping light / signal light multiplexing coupler 2103 is P1, and the pumping light amount from the pumping light / signal light multiplexing coupler 2104 is P2, the relationship between the light amounts is controlled according to the following equation. .

      P1 (mW) = 2 × P2 (mW)

  A fusion-stretched fiber coupler is used for the optical branching element 2106 of the monitor signal light extraction unit. This is a fusion-stretched coupler having a branching ratio of 1% which is almost constant at 1470 to 1530 nm. As the signal light, 16 waves at 1480 nm to 1510 nm and 2 nm intervals were used. As the photoelectric conversion circuit 2114, InGaAs-PIN-PD was used.

  The optical branching elements 2101 and 2107 constituting the optical resonator have a pass loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1513 to 1517 nm. The wavelength selection element 2108 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1515 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. In the optical resonator, the variable optical attenuator 2109 was adjusted so that the loss at 1515 nm in one round was 17 dB.

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 6 dB at 1515 nm when gain control was not performed, whereas it was 0.3 dB when gain control was performed.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. In this embodiment, the optical resonator and the third monitoring method are used simultaneously.

  The signal light enters the amplifying medium via the optical splitter 2101, the isolator 2102, and the pump / signal light multiplex coupler 2103. The amplified signal light is extracted via the pump light / signal light multiplexing coupler 2104, the isolator 2105, and the optical splitters 2106 and 2107.

  The optical resonator is configured by a loop including optical branching elements 2101 and 2107, a wavelength selecting element 2108, a variable optical attenuator 2109, and an amplification medium 2116. The optical splitting element 2106 is a type of splitting element that does not operate as an optical directional coupler, and splits all signal light and laser oscillation light simultaneously as a monitor component at a certain ratio. The monitor signal light extracted from the optical branch element 2106 is converted into an electric signal corresponding to the power of the monitor signal light by the photoelectric conversion circuit 2114, and the difference signal generation circuit 2115 compares the externally set level with the monitor component. The difference signal between the two is output.

  In the pumping light drive circuits 2111 and 2113 and the pumping light sources 2110 and 2112, feedback control is performed so that the difference signal becomes zero. Needless to say, the insertion position of each optical branching unit has a degree of freedom. Further, it is also possible to separately prepare an optical branching element for each of the laser oscillation component and the amplified signal component.

(Example 7)
The present embodiment is an example of the optical amplifier represented by the above (4).
FIG. 17 is a configuration diagram for explaining a seventh embodiment of the optical amplifier of the present invention, and is an example showing a single-path configuration.

  In this embodiment, the gain profile of the optical amplifier is controlled to be constant by two optical resonators. In this embodiment, since the same optical fiber is used for the two resonators, the concentration of the rare earth ions in the amplification medium in both resonators is the same. Accordingly, the condition that the total number of rare earth ions in the amplification medium in the resonator, which is required for controlling the gain profile using two resonators as described in (4) above, is satisfied.

As the amplification medium 2226, a Zr-based fluoride optical fiber to which Tm ³⁺ was added at a concentration of 6000 ppm was used. The optical fiber length is 7 m. The excitation light sources 2217 and 2219 are LDs oscillating at 1400 nm. In the control of the present invention, feedback control was applied to all LDs oscillating at 1400 nm connected to the excitation light driving circuits 2218 and 2220.

  The optical branching elements 2201 and 208 constituting the first optical resonator have a transmission loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1513 to 1517 nm. The wavelength selection element 2209 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1515 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. In the optical resonator, the variable optical attenuator 2212 was adjusted so that the loss at 1515 nm in one round was 17 dB.

  The optical branching elements 2202 and 2207 forming the second optical resonator have a pass loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1600 to 1800 nm. The wavelength selection element 2210 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1700 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. In the optical resonator, the variable optical attenuator 1213 was adjusted so that the loss at 1700 nm in one round was 16 dB.

  In this embodiment, there is a control portion for keeping the two optical resonators in the oscillation state at all times. The control unit has a monitor signal light extraction unit. The monitor signal light extraction unit includes optical branching elements 2215 and 2211 and photoelectric conversion circuits 2214 and 2216. The optical branching elements 2215 and 2211 are fusion-stretched type couplers that use a fusion-stretched fiber coupler and are almost constant at 1470-1750 nm and have a 1% branching ratio. As the photoelectric conversion circuits 2216 and 2214, InGaAs-PIN-PD was used. As the signal light, 16 waves at 1480 nm to 1510 nm and 2 nm intervals were used.

  The excitation light source was feedback-controlled using the oscillation determination circuit 2221 so that the first optical resonator and the second optical resonator were always in an oscillating state using the electric signals in the photoelectric conversion circuits 2214 and 2216.

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 6 dB when the control by the optical resonator was not performed, whereas it was 0.3 dB when the control was performed.

  Hereinafter, the operation of the optical amplifier of the present invention will be specifically described based on the configuration shown in FIG. The present embodiment is an example of an optical amplifier having two optical resonators, a first optical resonator and a second optical resonator. In the case of this embodiment, the pump light source only needs to keep the two optical resonators in the optical amplifier in a laser oscillation state. Therefore, in order to achieve this object, a function of monitoring each laser oscillation state (in FIG. 17, an optical branching unit 2211, a photoelectric conversion circuit 2216, an oscillation determination circuit 2221, an optical branching unit 2215, a photoelectric conversion circuit 2214, (Including an oscillation determination circuit 2221) can be incorporated in the optical amplifier. With this function, the state of laser oscillation can be monitored, and the pump light source can be adjusted so that both optical resonators always perform laser oscillation.

  In the optical amplifier described above, as shown in FIG. 17, it is possible to include variable attenuators 2212, 2213, etc. for making the loss of one round variable in the optical resonator.

  The signal light enters the amplifying medium 2226 via the optical splitters 2201 and 2202, the isolator 2203, and the pump light / signal light multiplex coupler 2204. The signal light emitted from the amplifying medium 2226 is emitted through the pump light / signal light multiplexing coupler 2205, the isolator 2206, and the optical branching elements 2207 and 2208.

  The optical resonator includes a first optical resonator including an optical branching element 2201, a wavelength selecting element 2209, a variable optical attenuator 2212, and optical branching elements 2215 and 2208, and optical branching elements 2202 and 2211 and a wavelength selecting element 2210. A variable optical attenuator 2213 and an optical branching element 2207.

  The optical splitter 2215 splits the light in the first resonator and inputs the split light to the photoelectric conversion circuit 2214. The obtained electric signal is input to the oscillation determination circuit 2221. The optical branching element 2211 is for branching light in the second resonator and inputting the light to the photoelectric conversion circuit 2216. The obtained electric signal is input to the oscillation determination circuit 2221. The excitation light drive circuits 2218 and 2220 control the amount of excitation light emitted from the excitation light sources 2217 and 2219 such that the two resonators oscillate in response to both electric signals. Needless to say, the insertion position of each optical branching element has a degree of freedom.

(Example 8)
FIG. 18 is a block diagram for explaining an eighth embodiment of the optical amplifier of the present invention, and shows a case where a single path is connected in two stages in series. First, the first optical amplifier will be described. The first optical amplifier 2301 is the same as that of the first embodiment shown in FIG. Therefore, the configuration and operation of the optical amplifier 1 are as described in the first embodiment.

  The second optical amplifier 2302 is the same as FIG. 14 (Example 4). Accordingly, each component of the amplifier will be described below, but will be described based on FIG.

As the amplification medium 1916, a Zr-based fluoride optical fiber to which Tm ³⁺ was added at a concentration of 6000 ppm was used. The optical fiber length is 7 m. As the excitation light sources 1911 and 1913, a polarization multiplexing type excitation unit in which LDs oscillating at 1400 nm were arranged so that the polarizations were orthogonal to each other was used. In the control using the monitor signal light, feedback control is applied to all LDs. However, the pump light amount from the pump light / signal light multiplex coupler 1905 is always twice as large as the pump light amount from the pump light / signal light multiplex coupler 1904. I tried to be.

  The light branching element 1902 at the monitor signal light extraction portion is a bulk type coupler using a dielectric multilayer film as a filter. This means that the branching ratio at 1460 to 1530 nm is 1%. As the signal light, 16 waves at 1480 to 1510 nm and 2 nm intervals were used.

  The photoelectric conversion circuit 1910 used PIN-PD. The optical branching elements 1901 and 1907 that constitute the optical resonator have a pass loss of 0.2 dB or less at 1480 to 1510 nm and a branching ratio of 95% at 1470 to 1477 nm. The wavelength selection element 1908 uses a dielectric multilayer film, and has a center wavelength of a transmission band of 1475 nm, a loss of 0.5 dB, and a full width at half maximum of 0.8 nm. In the optical resonator, the variable optical attenuator 1909 was adjusted so that the loss at 1475 nm in one round was 15 dB.

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 10 dB when the gain control was not performed, whereas it was 0.3 dB when the gain control was performed.

  The optical amplifiers described in the second, third, fifth, sixth and seventh embodiments other than the first and fourth embodiments can be arbitrarily selected and connected in series. By connecting a plurality of optical fiber amplifiers in series, higher efficiency operation can be expected.

(Example 9)
FIG. 19 is a block diagram for explaining a ninth embodiment of the optical amplifier of the present invention, and shows a case where a single path is connected in two stages in series. The optical amplifier according to the present embodiment is obtained by inserting a gain equalizer 2402 and a variable optical attenuator 2403 into an intermediate portion (connection portion) of the two-stage optical amplifier described in the eighth embodiment.

  The gain equalizer 2402 uses a long-period fiber grating, and the variable optical attenuator 2403 has a flatness of loss at 1480 to 1510 nm of 0.1 dB or less.

  As described above, by using the gain equalizer 2402 and the variable optical attenuator 2403, the gain flatness at 1480 to 1510 nm is 30% in the eighth embodiment, but is 2% in the present embodiment. Was.

Here, the gain flatness is defined as follows.
(Gain flatness) = {(maximum gain in amplification band) − (minimum gain in same band)} / (minimum gain in same band)

  The level of each input signal is from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 10 dB when the gain control was not performed, whereas it was 0.3 dB when the gain control was performed.

  The first optical amplifier 2401 and the second optical amplifier 2404 can be arbitrarily selected from the optical amplifiers described in the first to seventh embodiments. The gain equalizer 2402 is inserted to flatten the gain profile, and the optical variable attenuator 2403 has a function of adjusting the amount of input signal to the second optical amplifier.

(Example 10)
FIG. 20 is a block diagram for explaining the tenth embodiment of the optical amplifier of the present invention, and shows a case where a single path is connected in two stages in series. The optical amplifier according to the present embodiment is obtained by inserting a gain equalizer 2502 and a variable optical attenuator 2503 in the middle of the two-stage optical amplifier described in the eighth embodiment. Further, the optical amplifier of this embodiment includes a control unit including an optical branching element 2504, an optical bandpass filter 2506, a photoelectric conversion circuit 2507, and a difference signal generation circuit 2508. The optical branch element 2404 is a bulk type device having a branch ratio of 1% at 1480 to 1510 nm. The optical bandpass filter 1506 is a device using a dielectric multilayer film having a transmission band having an intermediate wavelength of 1480 nm, a full width at half maximum of 0.8 nm, and a loss of 1 dB at the transmission center wavelength.

  The gain equalizer 2502 uses a long-period fiber grating. The variable optical attenuator 2503 has a loss flatness of 1 dB or less at 1480 to 1510 nm, and the attenuation is controlled by an external electric signal. it can.

  In this embodiment, the optical amplifier is controlled by monitoring the signal light of 1480 nm by the control unit and controlling the optical variable attenuator 2503 via the differential signal generation circuit 2508 of the control unit so that the value becomes constant. Feedback controlled. As a result, the level of the signal light incident on the second optical amplifier 2505 in each channel becomes constant.

  According to this example, the gain flatness at 1480 to 1510 nm was 30% in Example 8, whereas it was 2% in this example.

Here, the gain flatness is defined as follows.
(Gain flatness) = {(maximum gain in amplification band) − (minimum gain in same band)} / (minimum gain in same band)

  Further, each input signal level is changed from -25 to -10 dBm / ch. Was changed to For such a change of the signal, -25 dBm / ch. The gain profile at the time of was used as a reference. The maximum value of the deviation of the gain from the reference profile when the input was changed was 10 dB when the gain control was not performed, whereas it was 0.3 dB when the gain control was performed. Also, the level of each WDM light at the signal output portion of the optical amplifier of this embodiment was always kept at 3 dBm.

  As described in the tenth embodiment, the optical amplifier of the present invention can include a control unit for controlling the variable optical attenuator. The attenuation of the variable optical attenuator of such an optical amplifier can be adjusted by a control unit having a function of electrically adjusting based on the extracted monitor signal light.

  The first optical amplifier 2501 and the second optical amplifier 2505 can be arbitrarily selected from the optical amplifiers described in the first to seventh embodiments. Gain equalizer 2502 is inserted to flatten the gain profile. The optical splitter 2504 splits a part of the signal light. The optical bandpass filter 2506 extracts only an arbitrary one-channel signal, and the photoelectric conversion circuit 2507 converts the signal into an electric signal. A control signal is generated from the electric signal and a value preset in the difference signal generation circuit 2508, and the control signal controls the variable optical attenuator.

  Feedback control of the attenuation of the optical variable attenuator is performed so that the difference between the first optical amplifier 2501 and the second optical amplifier 2505 becomes small, preferably zero.

  In this embodiment, the input signal to the second optical amplifier has the same input level of each channel of the WDM signal.

(Example 11)
FIG. 21 is a configuration diagram for explaining an eleventh embodiment of the optical amplifier of the present invention, and is an example of an optical amplifier in which single paths are combined in multiple stages. In this embodiment, two optical amplifiers 2618 and 2619 are used. The present embodiment is an example in which an input signal input to an optical amplifier is divided into two bands in advance, each is amplified by another optical amplifier, and the amplified signal light is multiplexed again. In the figure, reference numeral 2602 denotes a first optical amplifier, 2603 denotes a gain equalizer, 2604 denotes a variable optical attenuator, 2605 denotes an optical branching element, 2606 denotes a second optical amplifier, 2607 denotes an optical bandpass filter, and 2608 and 2615. Denotes a photoelectric conversion circuit, and 2609 denotes a difference signal generation circuit.

  The optical amplifier 2618 is the same as that of the tenth embodiment. Therefore, the configuration and operation of the optical amplifier 2618 are as described in the tenth embodiment. Optical amplifier 2619 is described below.

  The third optical amplifier 2610 shown in the optical amplifier 2619 is the optical amplifier used in the first embodiment. The optical branching element 2613 has a wavelength of 1460 to 1490 nm, which is a bulk type device having a branching ratio of 1%. The optical bandpass filter 2614 is a device using a dielectric multilayer film having a transmission band having a center wavelength of 1460 nm, a full width at half maximum of 0.8 nm, and a loss of 1 dB at the transmission center wavelength.

  The gain equalizer 2611 uses a long-period fiber grating. The variable optical attenuator 2612 has a flatness of loss of 1 dB or less at 1460 to 1490 nm, and the amount of attenuation can be controlled by an external electric signal.

  In the control of the optical amplifier of this embodiment, the signal light of 1460 nm was monitored, and the variable optical attenuator 2612 was feedback-controlled via the differential signal generation circuit 2616 so that the value became constant. Thus, the level of the signal light emitted from the optical amplifier 2619 in each channel becomes constant.

  The signal light band splitter 2601 and the signal light band multiplexer 2617 multiplex and demultiplex the band of 1460 to 1476 nm and the band of 1480 to 1510 nm. The signal light is a 25-wave WDM including 9 waves arranged at 2 nm intervals at 1460 to 1476 nm and 16 waves arranged at 2 nm at 1480 to 1510 nm.

  The level of each input signal is from -25 to -10 dBm / ch. , The output light from the signal light multiplexer 2617 changes by 10 dB or more when no control is performed, whereas when the control is performed, all the signal light components fall to 5.0 to 5.2 dBm. Has entered.

(A) and (B) are schematic diagrams showing energy levels of Er ions and Pr ions, which greatly contribute to amplification, respectively. (A) and (B) are diagrams showing energy levels of Er ions and Tm ions, respectively. And the gain at a wavelength lambda ₁ constant in TDFA, a diagram showing the characteristics when adjusting the excitation quantity of TDFA. FIG. 2 is a configuration diagram for describing a configuration of a first embodiment of the optical amplifier of the present invention. FIG. 4 is a configuration diagram for describing a configuration of a second embodiment of the optical amplifier of the present invention. FIG. 2 is a configuration diagram for explaining an example of the first embodiment of the optical waveguide of the present invention. FIG. 7 is a diagram illustrating a positional relationship of an optical branching unit for configuring the optical resonator of the embodiment shown in FIG. FIG. 7 is a diagram plotting the maximum value of the deviation of the gain profile when each input signal level is changed in the first embodiment. FIG. 6 is a configuration diagram for explaining a second embodiment of the optical amplifier of the present invention. FIG. 9 is a diagram for explaining an insertion position of an optical branching element according to a second embodiment (a double-pass configuration). In the second embodiment, each input signal level is changed from -25 to 10 dBm / ch. FIG. 8 is a diagram in which the maximum value of the deviation of the gain profile when the value is changed to is plotted. FIG. 9 is a configuration diagram for explaining a third embodiment of the optical amplifier of the present invention. FIG. 14 is a diagram for explaining an insertion position of each optical branch element according to the third embodiment. FIG. 13 is a configuration diagram for explaining a fourth embodiment of the optical amplifier of the present invention. FIG. 13 is a configuration diagram for explaining a fifth embodiment of the optical amplifier of the present invention. FIG. 13 is a configuration diagram for explaining a sixth embodiment of the optical amplifier of the present invention. FIG. 14 is a configuration diagram for explaining a seventh embodiment of the optical amplifier of the present invention. FIG. 16 is a configuration diagram for explaining an eighth embodiment of the optical amplifier of the present invention. FIG. 14 is a configuration diagram for explaining a ninth embodiment of the optical amplifier of the present invention. FIG. 14 is a configuration diagram for explaining a tenth embodiment of the optical amplifier of the present invention. It is a block diagram for explaining an eleventh embodiment of the optical amplifier of the present invention.

Explanation of reference numerals

400, 500 Optical amplifier 402, 502 Optical resonator 404, 504 Monitoring means 410, 510 Amplifying medium 412, 512 Exciting means 414, 416, 426, 428, 518, 524, 536, 538 Optical branching element 418 Wavelength selection element 419 Monitoring Unit 420 control unit 422, 526 pumping light source 426, 530, 532 multiplexer 430, 432, 540, 542 isolator 534 oscillation determination circuit 1305, 1908, 2009, 2108 wavelength selection element 1213, 1307, 1511, 1709, 1710, 1909 , 2010, 2109 Variable optical attenuator 1312, 1320, 1506, 1507, 1517, 1518 Optical bandpass filter 1316 Monitoring unit 1316 Arithmetic circuit 1316 Control unit 1503, 1702, 1707 Circulator 15 08 Mirror 1915, 2508 Difference signal generation circuit 2018 Sum signal generation circuit 2221 Oscillation determination circuit 2402 Gain equalizer 2601, 2617 Signal light band splitter

Claims (20)

  A rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which a rare-earth ion as a gain medium is added to a core and / or a clad; a pumping means for pumping the gain medium; An optical resonator that oscillates laser light at at least one wavelength in the spectrum, and a power of at least one predetermined wavelength range selected from light input to the optical amplifying medium and light output from the optical amplifying medium. Monitoring means for monitoring at least one light power selected from the power of light in at least one predetermined wavelength range; and a control unit for controlling the excitation means based on a value obtained from the monitoring means. The monitoring means is configured to control the laser oscillation light in the optical resonator at the signal input end of the amplification medium and the signal light incident on the amplification medium. And the control unit is obtained by the sum of the laser oscillation light power value and the signal light power value obtained by the monitoring means or by a linear combination of the laser oscillation light power value and the signal light power value. An optical amplifier which calculates a value and controls the pumping means so as to match a predetermined value or a value inputted from outside.   A rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which a rare-earth ion as a gain medium is added to a core and / or a clad; a pumping means for pumping the gain medium; An optical resonator that oscillates laser light at at least one wavelength in the spectrum, and a power of at least one predetermined wavelength range selected from light input to the optical amplifying medium and light output from the optical amplifying medium. Monitoring means for monitoring at least one light power selected from the power of light in at least one predetermined wavelength range; and a control unit for controlling the excitation means based on a value obtained from the monitoring means. The monitoring means is configured to detect a part of the laser oscillation light in the optical resonator at a signal input end of the amplification medium and a signal light incident on the amplification medium. And simultaneously monitoring the total power of the excitation means. The control means controls the excitation means so that a value obtained by the monitoring means coincides with a predetermined value or a value inputted from outside. An optical amplifier characterized in that the optical amplifier is controlled.   The oscillation wavelength of the optical resonator is located within a band of an amplified spontaneous emission light spectrum generated by stimulated emission of rare earth ions from an amplification start level to an amplification end level for amplifying the signal light. The optical amplifier according to claim 1 or 2, wherein:   The optical amplifier according to claim 3, wherein the oscillation wavelength is located on a short wavelength side of a signal light band.   The optical amplifier according to claim 3, wherein the oscillation wavelength is located on a long wavelength side of a signal light band.   The oscillation wavelength of the optical resonator is located within a band of an amplified spontaneous emission light spectrum generated by stimulated emission of a rare earth ion for amplifying the signal light from an amplification starting level to a ground level. The optical amplifier according to claim 1 or 2, wherein   The oscillation wavelength of the optical resonator is located within a band of an amplified spontaneous emission light spectrum generated by stimulated emission of rare earth ions for amplifying the signal light from an amplification end level to a ground level. The optical amplifier according to claim 1 or 2, wherein   The optical amplifier according to claim 1, wherein the oscillator further includes a band-pass filter.   The optical amplifier according to claim 1, further comprising a unit configured to change a loss in the resonator of the optical resonator.   10. The optical amplifier according to claim 1, further comprising an oscillation maintaining unit that monitors a laser oscillation state of each of the optical resonators and controls the excitation unit so that the oscillation state can be maintained.   A multi-stage optical amplifier, wherein a plurality of optical amplifiers selected from the optical amplifiers according to claim 1 are connected in series and / or in parallel.   It is characterized by further comprising one or more optical devices selected from a gain equalizer and a variable attenuator or an optical device having a combined function of a gain equalizer and a variable attenuator at a stage subsequent to the at least one optical amplifier. The optical amplifier according to claim 1.   A variable attenuator, or an optical device having a function in which a gain equalizer and a variable attenuator are combined, monitors the power of the signal light emitted from the optical device, and controls the light of the variable attenuator based on the power value. The optical amplifier according to claim 12, wherein the loss is adjusted.   When the amplification medium is a rare earth-doped optical fiber or a rare earth-doped optical waveguide to which thulium ions are added as ions for amplifying signal light, and the ground level having the lowest energy of the ions is counted as the first, the amplification is started. 14. The optical amplifier according to claim 1, wherein the level is the fourth level, and the final level of the amplification is the second level.   The optical amplifier according to claim 14, wherein an excitation wavelength of the excitation means is one or more wavelengths selected from a range of 630 to 720 nm, 740 to 830 nm, 1000 to 1100 nm, and 1320 to 1520 nm.   The excitation wavelength of the excitation means is one or more wavelengths selected from the range of 630 to 720 nm, 740 to 830 nm, 1000 to 1100 nm, 1320 to 1520 nm, and is selected from the range of 1000 to 1300 nm and 1520 to 2000 nm. 15. The optical amplifier according to claim 14, wherein the pump light having one or more wavelengths is input to an amplification medium at the same time.   The amplification medium is a rare-earth-doped optical fiber or a rare-earth-doped optical waveguide doped with holmium ions as ions for amplifying the signal light, and when the lowest energy ground level of the ions is counted as the first, the amplification is started. 14. The optical amplifier according to claim 1, wherein the level is a third level, and the final level of the amplification is a second level.   The amplification medium is a rare-earth-doped optical fiber or a rare-earth-doped optical waveguide to which erbium ions are added as ions for amplifying signal light, and when the lowest energy ground level of the ions is counted as the first, the amplification is started. 14. The optical amplifier according to claim 1, wherein the level is a third level, and the final level of the amplification is a second level. A rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which rare-earth ions serving as an amplification medium are added to a core and / or a clad; an excitation unit for exciting the amplification medium; an optical resonator for oscillating a laser; A control unit for controlling the pumping means based on the value obtained from the means, and a method for controlling the gain profile of the optical amplifier to be constant,
Causing laser oscillation in at least one wavelength within the spectrum of the amplified spontaneous emission light generated in the amplification medium of the amplified spontaneous emission light of the amplification medium by the optical resonator in the optical amplifier;
The power of light in at least one predetermined wavelength range selected from light input to the optical amplification medium by the monitoring means and the power of light in at least one predetermined wavelength range selected from light output from the optical amplification medium Monitoring at least one optical power selected from, based on the value obtained from the monitoring means, the control unit controls the excitation means to control the light amount of the excitation light source,
The monitoring means monitors the laser oscillation light in the optical resonator at the signal input end of the amplification medium and the power of the signal light incident on the amplification medium, and the control section controls the laser oscillation obtained by the monitoring means. Calculate the sum of the optical power value and the signal light power value, or the value obtained by the linear combination of the laser oscillation light power value and the signal light power value, so as to match a predetermined value or a value input from outside. A control method comprising controlling the excitation means. A rare-earth-doped optical fiber or a rare-earth-doped optical waveguide in which rare-earth ions serving as an amplification medium are added to a core and / or a clad; an excitation unit for exciting the amplification medium; an optical resonator for oscillating a laser; A control unit for controlling the pumping means based on the value obtained from the means, and a method for controlling the gain profile of the optical amplifier to be constant,
Causing laser oscillation in at least one wavelength within the spectrum of the amplified spontaneous emission light generated in the amplification medium of the amplified spontaneous emission light of the amplification medium by the optical resonator in the optical amplifier;
The power of light in at least one predetermined wavelength range selected from light input to the optical amplification medium by the monitoring means and the power of light in at least one predetermined wavelength range selected from light output from the optical amplification medium Monitoring at least one optical power selected from, based on the value obtained from the monitoring means, the control unit controls the excitation means to control the light amount of the excitation light source,
The monitoring means simultaneously extracts a part of the laser oscillation light in the optical resonator and a part of the optical signal incident on the amplification medium at the signal input end of the amplification medium, monitors the total power thereof, and A control unit controlling the excitation unit such that a value obtained by the monitoring unit matches a predetermined value or a value input from outside.

Images