JPH09214433A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the wavelength dependency of a signal gain for WDM transmission while output light power is kept constant through the use of an external power source by controlling oscillation light power so that input light power to a light amplifying medium is set to be constant from the detection result of input signal light power and oscillation light power. SOLUTION: An excitation light power control means 33 for keeping the signal light power of output from a light amplifier, an input signal light power detection means 21 and an oscillation light power detection means 26 are provided. Furthermore, an oscillation light power control means 29 for controlling oscillation light power so that input light power to the light amplifying medium becomes constant from the detection results of the input signal light power detection means 21 and the oscillation light power detection means 26 is provided. The oscillation light power of a wavelength different from input signal light is reduced or increased by quantity corresponding to the increase or reduced quantity of input signal light in an amplifying band, and input light power to the light amplifying medium is set to be constant. Thus, the specification of the wavelength of the amplifying gain can be set constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier suitable for collective amplification of a plurality of signal lights in a wavelength division multiplexing system.

[0002]

2. Description of the Related Art In order to construct a multimedia network in the future, an optical communication system with a larger capacity is required. Time-division multiplexing (T-Division Multiplexing: T) has been used as a multiplexing method for achieving an extremely large capacity.
DM) method, optical time-division multiplexing (Optical Time-Div)
ision Multiplexing: OTDM, Wavelength multiplexing
Researches on length-Division Multiplexing (WDM) system and the like are actively conducted. Among them, the WDM transmission system is an erbium (Er) -doped optical fiber amplifier (ED
It is expected to be used as a flexible lightwave network implementation method that utilizes the wide gain band of FA) to perform cross-connects, dropping / adding at the optical level, or multiplexing of different services.

Further, the WDM system is compared with other systems in the case of carrying out an ultra-high capacity transmission using an existing 1.3 μm band zero dispersion single mode fiber (SMF) network which is most popular in the world at present. Considered to be advantageous. This is because the transmission rate per each optical carrier is low (for example, 10 Gb / s), so that the chromatic dispersion allowable value and the allowable value of the optical input power limited by the nonlinear effect of the optical fiber can be set relatively large. Is.

In order to realize the WDM transmission system, an optical amplifier (EDFA) having a constant amplification gain over a wide band is required. The EDFA has an amplification band (gain band) over a range of 1530 nm to 1560 nm, but its gain is not always constant with respect to wavelength. Fig. 7 shows the typical spontaneous emission of EDFA (Amplified Spontaneous Emission: AS
E) Shows the spectrum. The ASE spectrum almost reflects the small-signal gain characteristic of the optical amplifier. As can be seen from the figure, there is a gain peak near 1530 nm (= 1.53 μm), and the characteristics are not flat with respect to wavelength.

As a method of reducing the wavelength dependence of the gain of the EDFA, a method of adding aluminum (Al) and Er together is generally known (CG Atkins et al., E
lectron Lett., Vol. pp910-911 (1989)). Also, ED
A method for optimizing the operating point of FA (M. Suyama et al., OA
A '93, MB5-1 (1993)) and a method of flattening the gain characteristic by using an optical filter (H. Toba et al., IEEE Photon.
Technol. Lett., Vol. 5, No. 2, p248 (1993)) has been proposed.

The band of the EDFA changes greatly when the relationship between the optical input power and the pumping light power is different. FIG. 8 is a diagram showing the relationship between the output optical power and the gain of the optical amplifier, and FIG. 9 is a diagram showing the relationship between the input optical power and the output optical power using the pumping optical power as a parameter. The unsaturated region is ED
In the FA, the proportion of Er ions in the population inversion state is large, which corresponds to a state in which a constant gain is obtained regardless of the change in output light power. In the saturation region, the proportion of Er ions in the population inversion state decreases, and the output It shows a state in which the gain sharply decreases with an increase in optical power.

In order to change these two types of states, for example, the power of pumping light may be changed. When the power of the pumping light is sufficient with respect to the input power, the ratio of Er ions in the population inversion state becomes large and the state becomes unsaturated,
On the other hand, when the power of the pumping light is smaller than the input power, the ratio of Er ions in the population inversion state decreases and the state becomes saturated.

An example of measuring the ASE band when a plurality of optical amplifiers placed in these two states are connected in cascade
Shown in 10. From the figure, when the number of connected optical amplifiers increases, the bandwidth decreases little when operating in the non-saturation region, but the 3 dB bandwidth decreases rapidly when operating in the saturation region. You can see that

FIG. 11 shows the proportion (N2) of the population inversion of the EDFA.
It is a figure which shows the relationship between gain and wavelength when / NT) is made into a parameter. Parameter N2 / NT indicates the ratio of Er ions in the population inversion state to all Er ions, and
In the case of 2 / NT = 1, it is shown that all Er ions transit to higher energy levels and a complete population inversion is obtained.

Normally, the pump power is controlled so that a constant optical output power (Po) is obtained (see FIG. 9).
The power of the signal light input to the DFA changes depending on usage conditions and deterioration with time. If control is performed so that the optical output power becomes constant following this change, the state of population inversion shown in Fig. 11 will change, and the wavelength dependence of gain will change significantly, degrading the characteristics. I will let you.

Therefore, for example, in the method of flattening the gain characteristic by using the optical filter, a variable optical filter capable of controlling such as changing the characteristic of the optical filter according to the input optical power is required. There is a problem that such an optical filter is difficult to realize, and even if it can be realized, the current technology is extremely expensive.

[0012]

The conditions of the optical amplifier required for WDM transmission are re-arranged as follows: (1) The wavelength dependence of the amplification gain is small even if the input signal light power or the number of wavelength division multiplexing changes (2) ) It is necessary to maintain the amplified optical power for each wavelength at a constant value. In FIG. 11, it can be seen that a flat gain characteristic is obtained in the wavelength band of 1540 to 1560 nm in the vicinity of the N2 / NT value of 0.7.

Therefore, if the operating state of the EDFA can always be maintained in this inverted population state, a flat gain characteristic can be obtained. In order to realize such an operation, the EDFA may be controlled so that the gain is constant. That is, when the pumping light power is adjusted according to the change in the input light power so that the gain becomes constant, N2 / NT can be maintained at an arbitrary constant value. Examples of such experiments are published in the Technical Report of IEICE Technical Report, OCS 94-66 PP31.
-36).

However, if the power of the pumping light is controlled in order to keep the gain constant, the above (1) can be realized, but the power of the pumping light cannot be adjusted to realize (2). In order to solve this point, the above-mentioned document (Technical research report of the Institute of Electronics, Information and Communication Engineers, OCS94-66 PP31-36) proposes to control the optical output by using an optical attenuator.
FIG. 12 shows the configuration of such an optical amplifier.

In FIG. 12, the input signal light from the input port 1 and the pump light from the pump LD 4 are added by the WDM coupler 3 and input to the EDF 5. The signal light amplified by the EDF 5 is output from the output port 9 via the optical isolator 6, the optical attenuator 7 and the optical coupler 8. The drive current of the pumping LD4 is the automatic fiber gain controller (AFG).
C) Controlled by 10. The AFGC 10 controls the power of the pumping light so that the gain in the EDF 5 becomes constant based on the optical power of the ASE output from the EDF 5.

Further, a part of the amplified signal light is branched by the optical coupler 8, and the branched light is converted into an electric signal by the photodetector 11, and the automatic power controller (APC).
At 12, the attenuation factor of the optical attenuator 7 is controlled so that the output signal level of the photo detector 11 becomes constant.

If an optical attenuator is used, the optical output can be adjusted independently of the gain of the optical amplifier. Therefore, the composition and length of the EDFA 5 and the pumping LD 4 of the EDFA 5 are adjusted so that an optical output sufficiently higher than a desired optical output can be obtained. A constant optical output can be obtained by setting the power and adjusting the optical attenuator 7 installed at the output part of the optical amplifier that performs constant gain control. That is, the above (1) and (2) can be satisfied at the same time.

However, when the optical attenuator 7 is used as shown in FIG. 12, the maximum output optical power is reduced due to the use of the optical attenuator and the variable attenuation rate type optical attenuator can be manufactured at low cost. However, there is a problem that it is difficult with the current technology.

Further, as shown in FIG. 13, a method has been proposed in which light is newly inserted from an external light source (probe LD) 17 and the power of light input to the EDF 18 is controlled to a constant value. (Japanese Patent Application No. 7-311212, Onaka et al., “Optical Amplifier”), but in this case, a new light source is needed instead of using an optical attenuator. Moreover, it must be a light source having an oscillation wavelength within the amplification band of the EDFA and having a wavelength separated from the WDM signal to some extent.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to maintain a constant output optical power without newly inserting light by using an external light source while maintaining a signal gain for WDM transmission. It is an object of the present invention to provide an optical amplifier having less wavelength dependence of the.

[0021]

The above problems can be solved by the following constitutions. (Claim 1) An optical amplifier having an optical amplification medium which has a predetermined amplification band and amplifies input signal light by pumping light and outputs the amplified signal light so that the signal light power output from the optical amplifier is maintained at a constant value. Pumping light power control means for controlling pumping light, input signal light power detecting means for detecting power of the input signal light, and oscillation of light having a wavelength within the predetermined amplification band by using the optical amplification medium The oscillating means, the oscillating light power detecting means for detecting the oscillating light power of the oscillating means, the input signal light power detecting means and the detection result of the oscillating light power detecting means, and the input light power to the optical amplifying medium. And an oscillating light power control means for controlling the oscillating light power so as to keep constant.

When the input signal light is increased or decreased, if the pumping light power is controlled to make the output signal light constant, the population inversion ratio in the optical amplification medium changes, so that the wavelength characteristic of the amplification gain is flat. It disappears (see Figure 11). Therefore, the oscillating light power control means decreases or increases the oscillating light power of a wavelength different from that of the input signal light in the amplification band by an amount corresponding to the increase or decrease of the input signal light, and the optical amplification medium. The wavelength characteristic of the amplification gain can be made constant by making the input optical power to the optical system constant.

(Claim 2) As the oscillating means, at least two reflecting elements for reflecting the oscillated light are arranged with the optical amplification medium interposed therebetween. An interferometer is constructed by placing two reflecting elements with an optical amplification medium interposed therebetween. If the wavelength of the oscillated light is within the amplification band of the amplification medium, the light of the wavelength is amplified by going back and forth between the two reflective elements through the amplification medium, and oscillates under a certain condition.

(Claim 3) One of the reflecting elements according to claim 2 is a variable reflectance element, and the oscillation light power control means according to claim 1 controls the reflectance of the variable reflectance element. As a result, the value of the oscillation light power can be controlled to a predetermined value.

(Claim 4) As a variable reflectance element according to claim 3, a polarizer, a Faraday rotator, and an element that reflects 100% of the oscillation light are arranged in this order, and polarized light passing through the Faraday rotator is arranged. By controlling the rotation angle of the light using an electromagnet, the light that enters the polarizer is reflected by the element that is 100% reflected through the Faraday rotator and is emitted again from the polarizer through the Faraday rotator. The polarization plane of can be changed from 0 to 180 degrees. As a result, it is possible to form an element having a variable reflectance as a whole.

(Claim 5) Storage means for storing a value necessary for the reflectance of the variable reflectance element according to claim 3 in correspondence with the power value of the input signal light according to claim 1. Is provided, and the power of the oscillation light is adjusted by using the value stored in the storage means according to the value of the power of the input signal light. With this configuration, even when the input signal light fluctuates, the oscillation light power can be easily adjusted, the wavelength characteristic of the amplification gain can be made flat, and the output light power can be made constant. .

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the principle of an optical amplifier according to the present invention. According to the present invention, as shown in the figure, a configuration in which an interferometer including a reflection mirror or the like is added to the configuration of a normal optical amplifier allows the optical amplifier to oscillate light having a wavelength different from the band of the WDM signal. To change the population inversion state to satisfy the above-mentioned conditions for the optical amplifier required for WDM transmission, (1) there is little wavelength dependence of gain, and (2) that the output optical power is maintained at a constant value. It is the one.

In the figure, a part of the optical output of this optical amplifier is branched and taken out, converted into an electric signal by the output signal optical power detecting means 32, and the pumping light source 23 keeps the extracted optical power constant. Control the output light power. This allows constant control of the optical output (Automatic Level Control; A
LC). . An optical amplification medium (for example, EDF)
On the output side of 27, an optical filter (for example, an optical bandpass filter) that removes the optical power amplified by the interferometer and the noise component generated from the optical amplifier and selectively transmits only the signal component that is originally desired to be kept constant ) Insert 31.

Since the ALC control is performed as described above, even if the input light power changes, the output light power of the pumping light source 23 is adjusted to keep the light output at a constant value. (For example, in FIG.
In, the operating point moves from point (a) to point (b)). Therefore, as it is, in the case of the WDM signal, it is merely controlled so that the total power of each signal becomes constant, and when the input signal light power changes, the value of N2 / NT is controlled by controlling the power of the pumping light source. Changes, the wavelength dependence of gain changes as shown in FIG.

Therefore, the reflection mirror 2 is sandwiched by the EDF 27.
An interferometer is composed of 5 and 30 and selectively oscillates only the light of a certain wavelength apart from the WDM signal among the ASE light (spontaneous emission light) generated in the EDFA. By doing so, light with very strong power oscillates and is separated from the band of the WDM signal, so that it can be easily removed by a filter. Also, by controlling the optical power, without newly inserting light from the outside,
The optical power in the EDF, that is, the input optical power can be kept constant.

As a result, in FIG. 9, (b) to (a)
Since the operating point returns to the point, the pumping light power becomes the original value,
The value of N2 / NT does not change, and the wavelength dependence in the amplification band can be eliminated. Specifically, by incorporating an element capable of controlling the optical power inside the interferometer and adjusting the optical power to oscillate intentionally, the value of N2 / NT caused by the power adjustment of the excitation light source for ALC control It becomes possible to change the value of N2 / NT independently of the change of.

Next, the structure of the interferometer will be described. In FIG. 1, optical couplers 24 and 28 capable of branching only a specific wavelength λ _S are arranged with an EDF 27 interposed therebetween. However, λ _S is a wavelength within the amplification band of the EDF 27,
It is assumed that the wavelength is sufficiently far from the wavelength of the WDM signal.
Now, assuming that λ _S is 1530 nm, optical couplers 24 and 28 capable of selectively branching or multiplexing the wavelength of 1530 nm.
Is used.

The light of 1530 nm split by the optical coupler 24 is 100% by the mirror 25 attached at the end thereof.
The reflected light is combined with the WDM signal again by the optical coupler 24, amplified when passing through the EDF 27, and this time the optical coupler.
It is split by 28. The demultiplexed light of 1530 nm is reflected by the reflectance variable mirror 30 having the reflectance γ (<1) to be multiplied by γ, and is again combined with another signal by the optical coupler 28 to pass through the EDF 27. And is returned to the optical coupler 24 again. 1530 nm 100% reflection mirror 25 and a mirror 30 having a reflectance γ overlap each other, and when the amplification exceeds the loss of this system, light of 1530 nm oscillates.

The state of oscillation at that time is shown in FIG. Even if the light has a narrow spectrum as shown in the figure, if the band of the light to be oscillated is sufficiently far from the WDM signal band, it can be easily removed by using an optical filter.

Next, a method of controlling the power of the oscillation light will be described. Utilizing the fact that the relaxation time of Er in EDF is relatively long (≈ several tens of ms), light is oscillated or not oscillated in a time shorter than this relaxation time to control the power as a time average. To do so. FIG. 3 shows an example of controlling the power of oscillation light.

When the reflectance γ of the variable reflectance mirror 30 of FIG. 1 is gradually increased, the oscillated light does not gradually become stronger but suddenly oscillates at a certain point. For this reason, when it is desired to increase the oscillation power, the oscillation interval is shortened as shown in FIG. This makes it possible to keep the average power over time large and constant. on the other hand,
If you want to reduce the oscillation power, make the oscillation interval longer as shown in FIG. By doing so, the power can be kept small and constant over time.

By using such oscillated light, stronger light is oscillated when the input signal light power is weak, and weaker light is oscillated when the input signal light power is strong, so that it is within the amplification band of the EDF. It is possible to keep the total input power of a certain light constant.

That is, the input signal light power detecting means of FIG.
A part of the input signal light is branched and monitored by 21 and the amount of the reflectance γ of the mirror 30 is controlled earlier than the relaxation time of the EDF 27 depending on the strength of the input signal light power.
The power of the light input to F27 can always be kept constant as a whole. Further, by doing so, it becomes possible to correct the fluctuation of the power of the oscillated light due to the phase change due to the change of the ambient temperature.

The optical power to oscillate is controlled by the electronic circuit of the oscillation light power control means 29 after the monitor light is converted into an electric signal by the oscillation light power detection means 26, but the relaxation time of the EDFA is relatively long. It can be fully controlled by an electronic circuit.
This can be found in the bibliography (IEICE National Conference '92 Spring
c-318, pp 4-360), (GA Ball et al, IEEE J.Li
ghtwave., Vol.10, pp1338-1343 (1992)), (GA Ba
ll et al, Electron.Lett. Vol.29, No.18, pp 1623-16
25 (1993)).

However, the value of N2 / NT does not always become 0.7 only by keeping the input power to the EDF 27 constant, and it is important at what level the input power is kept constant. Keep the input power at a certain level and always keep N2
Unless /NT=0.7 is maintained, the wavelength dependence of gain cannot be eliminated.

This can be dealt with by finely operating the means for correcting the power of the oscillation light according to the power of the input signal light. For example, the optical amplifier is equipped with a control circuit using a microprocessor or memory, The optimum oscillation light power value may be stored in advance in the memory according to the input signal light power value, and the reflectance γ of the mirror 30 may be controlled according to the input signal light power based on this value. .

By performing such control, the value of N2 / NT can always be kept at 0.7 regardless of any change in the power of the input signal light, and as a result, the wavelength dependence of the gain can be eliminated. You can

Further, when the value of the input optical power of the WDM signal is approximately in the middle of the expected maximum value and the minimum value, the reflectance γ is adjusted so as to be in the middle of the controllable range. In this state, the parameters of the EDF 27 (Er ion concentration, EDF length, etc.) and the power of the pumping light source are selected so that the optical output of the optical amplifier has a predetermined power and the wavelength characteristic of gain is flat. (Of course, the maximum output of the pumping light source needs to have a surplus so that a predetermined optical output can be obtained even when the input signal light power reaches the minimum value.) In addition, the input signal light power or the wavelength multiplexing number Is increased, the pumping light power may be small, so that the number of Er in the population inversion state is decreased, the value of N2 / NT is decreased, and the gain on the short wavelength side is decreased. Therefore, the power of the light to be oscillated is reduced according to the increase of the input signal light power, and the value of N2 / NT may be controlled to be 0.7.

Next, a method of controlling the reflectance γ will be described. As a method of controlling the reflectance γ, a method of using interference, a method of using polarized light, etc. can be considered.
Each will be specifically described below.

As a "method of utilizing interference", there is a method of using an LN modulator. As shown in FIG. 4, the LN modulator
Light in the 1530 nm band is input from one side of the light source 34, passes through the LN modulator 34, and is reflected by the 100% reflection mirror attached to the other side. At this time, by changing the bias voltage of the LN modulator, it is possible to change the interfering phase in the LN modulator and arbitrarily control the power of the passing light by α (<1) times.

However, the light in the 1530 nm band is completely reflected by the mirror, passes through the LN modulator 34 again, and is attenuated by α ² times. That is, the reflectance can be freely controlled from 0 to 100% by changing the bias voltage of the LN modulator.

Although the LN modulator using the electro-optic effect has polarization dependency, it can be dealt with by inserting a polarizer in front of the LN modulator, and there is no problem with polarization of light to be oscillated. Next, there is a method of using an optical isolator as a “method of utilizing polarized light”. An optical isolator is a device that has a pair of entrance and exit ends, and allows light to pass only in a specified direction due to the non-reciprocity that light in the forward direction has low loss and light from the opposite direction has high loss. . FIG. 5 shows an example of the configuration.

In the figure, the light in the 1530 nm band is first a polarizer.
It is linearly polarized by 37 and is incident on the Faraday rotator 38. At this time, the Faraday rotator 38 is designed so that the rotation angle of polarized light can be freely controlled. The light passing through the Faraday rotator is reflected by the 100% reflection mirror 39,
The light enters the Faraday rotator 38 again. At that time, since the polarization does not change due to reflection, the light passes through the Faraday rotator twice, and thus undergoes double rotation.

Therefore, for example, when the rotation angle of the Faraday rotator 38 is set to 45 °, the light passes through the Faraday rotator twice and receives 90 ° rotation, so that the light cannot pass through the polarizer. Light is blocked. If the Faraday rotator is adjusted so that the polarized light does not rotate even after passing through the rotator (so that it makes an integral multiple of 180 degrees in one pass), it will reflect and pass through the Faraday rotator twice. Since the polarized light does not rotate, the light also passes through without being blocked by the polarizer.

That is, by adjusting the rotation angle of polarized light in the Faraday rotator, it becomes possible to form an element having an arbitrary reflectance of 0% to 100%. It is the element length, the magnetic flux density, and the element constant that determine the rotation angle of the polarized light in the Faraday rotator 38. If the rotation angle of polarized light can be freely controlled, the above-described element can be configured. Therefore, it becomes possible to control the Faraday rotation angle by mounting the electromagnet 40 around the Faraday rotator 38 as shown in FIG. 5 and changing the current flowing through the electromagnet to change the magnetic field.

The above-mentioned control method has a reflectance of 0% to
This is related to the method of controlling freely between 100%, but the reflectance γ of the variable reflectance mirror (30 in Fig. 1) is 0%.
Even in the case of an element that has only the function of changing the two values (perfect transmission) and 100% (perfect reflection), it is possible to control the oscillation light power by controlling the oscillation interval as shown in FIG. It is possible.

Even if the above operation is performed, the optical output of the optical amplifier is always kept constant by ALC control.
However, since the total optical power of the WDM signal that is maintained is kept constant, the power of each optical signal naturally changes when the number of wavelength division multiplexing changes.

Therefore, in order to prevent the power of the optical output for each wavelength from changing even if the number of wavelength division multiplexing changes, a means for notifying the current number of wavelength division multiplexing to the optical amplifier is prepared, or A means for detecting the number of wavelength division multiplexes is required inside, but regarding these, the prior application (Japanese Patent Application No. 7-2147
It is possible by the means shown in 33).

FIG. 6 shows an embodiment of an optical amplifier using the present invention. This figure shows two pump LDs (4
7, 60) Shows the case of so-called bidirectional excitation used. Further, in the configuration shown in FIG.
Although 57 is installed on the exit end side, a similar optical amplifier can be constructed by replacing the position with the 100% reflection mirror 52 and installing it on the entrance end side. As a result, the optical input power to the EDF 55 can be controlled to a constant value without using a variable optical attenuator or a new light source, and the wavelength dependence of the gain of the optical amplifier can be reduced.

[0055]

As described above, according to the present invention, it is possible to realize an optical amplifier in which the wavelength dependence of the gain in the wavelength division multiplex transmission is small and the output optical power is kept constant without inserting light from the outside. It becomes possible.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of an optical amplifier of the present invention,

FIG. 2 is a diagram showing a state of oscillated light in the present invention,

FIG. 3 is a diagram for explaining a method of controlling oscillation light power in the present invention,

FIG. 4 is a configuration diagram (part 1) of an oscillation light power control element in an example,

FIG. 5 is a configuration diagram (part 2) of the oscillation light power control element in the example,

FIG. 6 is a configuration diagram of an optical amplifier according to an embodiment of the present invention,

FIG. 7 is a diagram showing a typical ASE spectrum,

FIG. 8 is a diagram showing an example of the relationship between gain and output optical power,

FIG. 9 is a diagram showing an example of the relationship between input optical power and output optical power,

FIG. 10 is a diagram showing the relationship between the 3 dB bandwidth of ASE and the number of optical amplifier stages,

FIG. 11 is a ratio of population inversion (N2 /
A diagram showing the relationship between gain and wavelength when NT) is used as a parameter,

FIG. 12 is a configuration diagram of an optical amplifier of a first conventional example,

FIG. 13 is a configuration diagram of a second conventional optical amplifier.

[Explanation of symbols]

1 is an input port, 2 is an optical isolator, 3 is WDM
Coupler, 4 pump LD, 5 EDF, 6 optical isolator, 7 optical attenuator, 8 optical coupler, 9 output port, 10 AFGC, 11 photodetector,
12 is APC, 13 is optical isolator, 14 is WDM coupler, 15 is pump LD, 16 is optical coupler, 17 is probe LD, 18 is EDF, 19 is optical isolator, 20 is optical BPF, 21 is input signal optical power detection Means, 22 is WD
M coupler, 23 is excitation light source, 24 is optical coupler, 25 is 100
% Reflection mirror, 26 oscillation light power detection means, 27 optical amplification medium (EDF), 28 optical coupler, 29 oscillation light power control means, 30 variable reflectance mirror, 31 optical BP
F, 32 is output signal light power detection means, 33 is pumping light power control means, 34 is an LN modulator, 35 is a voltage control circuit, 36 is a 100% reflection mirror, 37 is a polarizer, 38 is a Faraday rotator, 39 Is a 100% reflection mirror, 40 is an electromagnet, 41 is a current control circuit, 43 is an optical coupler, 44 is a photodetector, 45 is an amplifier, 46 is a WDMW coupler,
47 is an excitation LD, 48 is a drive circuit, 49 is an optical isolator, 50 is an optical coupler, 51 is an optical coupler, 52 is a 100% reflection mirror, 53 is a photodetector, 54 is an amplifier,
55 is an EDF, 56 is an optical coupler, 57 is a variable reflectance mirror,
58 is a drive circuit, 59 is a WDM coupler, 60 is an excitation LD,
61 is a drive circuit, 62 is an optical isolator, 63 is an optical BP
F, 64 is an optical coupler, 65 is a photo detector, 66 is an amplifier, 67 is an A / D D / A converter, 68 is a CP
U, 69 is a ROM, and 70 is a RAM.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/07 H01S 3/131 3/10 H04B 9/00 E 3/131 H04J 14/00 14 / 02

Claims (5)

[Claims] 1. An optical amplifier having an optical amplification medium which has a predetermined amplification band and which amplifies input signal light by pumping light and outputs the amplified signal light so that the signal light power of the output of the optical amplifier is maintained at a constant value. Pumping light power control means for controlling the pumping light, input signal light power detecting means for detecting the power of the input signal light, and oscillation of light having a wavelength within the predetermined amplification band by using the optical amplification medium The oscillating means, the oscillating light power detecting means for detecting the oscillating light power of the oscillating means, the input signal light power detecting means and the detection result of the oscillating light power detecting means, and the input light power to the optical amplification medium. And an oscillating light power control means for controlling the oscillating light power so as to keep the optical power constant. 2. The optical amplifier according to claim 1, wherein the oscillating means is configured by installing at least two reflecting elements that reflect the oscillated light with the optical amplifying medium interposed therebetween. 3. The oscillation light power control means according to claim 2.
2. The optical amplifier according to claim 1, wherein one of the reflective elements according to claim 1 is a variable reflectance element, and the reflectance of the variable reflectance element is controlled. 4. The variable reflectance element according to claim 3,
A polarizer, a Faraday rotator, and an element that reflects 100% of the oscillation light are arranged in this order, and the rotation angle of the polarized light passing through the Faraday rotator is controlled by using an electromagnet. 1. The optical amplifier according to 1. 5. A storage means is provided for storing a value required as a reflectance of the variable reflectance element according to claim 3 in correspondence with a power value of the input signal light according to claim 1. The optical amplifier according to claim 1, wherein the power of the oscillation light is adjusted by using a value stored in the storage unit according to a value of the power of the input signal light.