JP3680402B2 - Optical amplifier - Google Patents

Description

[0001]
BACKGROUND 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 transmission system.
[0002]
[Prior art]
In order to construct a future multimedia network, an optical communication system with a larger capacity is required. Up to now, as multiplexing schemes that realize ultra-high capacity, time-division multiplexing (TDM), optical time-division multiplexing (OTDM), wavelength multiplexing (wavelength-) Research on division multiplexing (WDM) is being actively conducted. Among these, the WDM transmission system uses a wide gain band of an erbium (Er) -doped optical fiber amplifier (EDFA), and is a flexible optical wave network that performs cross-connection, branching / insertion at the optical level, or multiplexing of different services. It is expected as a means of realizing.
[0003]
In addition, the WDM system is advantageous compared to other systems when performing ultra-high capacity transmission using the existing 1.3 μm band zero-dispersion single mode fiber (SMF) network, which is currently most popular in the world. Conceivable. This is because the transmission speed per optical carrier is low (for example, 10 Gb / s), so that the chromatic dispersion tolerance and the optical input power tolerance limited by the nonlinear effect of the optical fiber can be set relatively large. It is.
[0004]
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 about 1530 nm to 1560 nm, but the gain is not necessarily constant with respect to the wavelength. FIG. 7 shows a typical spontaneous emission (Amplified Spontaneous Emission) spectrum of EDFA. The ASE spectrum almost reflects the small signal gain characteristics of the optical amplifier. As can be seen from the figure, there is a gain peak in the vicinity of 1530 nm (= 1.53 μm), and the characteristics are not flat with respect to the wavelength.
[0005]
As a method for reducing the wavelength dependence of the gain of EDFA, a method of adding both aluminum (Al) and Er is generally known (CG Atkins et al., Electron Lett., Vol. Pp910-911 (1989)). . Also, a method for optimizing the operating point of the EDFA (M. Suyama et al., OAA '93, MB5-1 (1993)) and a method for flattening the gain characteristics using an optical filter (H. Toba et al. al., IEEE Photon. Technol. Lett., Vol. 5, No. 2, p248 (1993)).
[0006]
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 light power as a parameter. In the non-saturated region, the ratio of Er ions in the inversion distribution state in the EDFA is large and corresponds to a state in which a constant gain is obtained regardless of the change in the output optical power. The saturation region is the ratio of Er ions in the inversion distribution state. Shows a state in which the gain decreases sharply as the output optical power increases.
[0007]
In order to change these two types of states, for example, the power of the excitation 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 inversion distribution state is large and unsaturated, while when the power of the pumping light is small with respect to the input power, The ratio of Er ions in the inversion distribution state decreases and becomes saturated.
[0008]
FIG. 10 shows an example of measuring the ASE band when a plurality of optical amplifiers placed in these two states are connected in cascade. From the figure, when the number of connected optical amplifiers increases, the decrease in bandwidth is small when operating in the non-saturation region, but the 3 dB bandwidth decreases rapidly when operating in the saturation region. You can see that
[0009]
FIG. 11 is a diagram showing the relationship between the gain and the wavelength when the ratio of inversion distribution of EDFA (N2 / NT) is used as a parameter. The parameter N2 / NT indicates the ratio of Er ions in the inversion distribution state to the total Er ions. When N2 / NT = 1, all Er ions transition to a higher energy level and a complete inversion distribution is obtained. It shows that it is obtained.
[0010]
Normally, the pumping power is controlled so as to obtain a constant optical output power (Po) (see FIG. 9). However, the power of the signal light input to the EDFA varies depending on use conditions and deterioration with time. If the optical output power is controlled to follow this change, the inversion distribution state shown in Fig. 11 will change, and the wavelength dependence of gain will change greatly, degrading the characteristics. I will let you.
[0011]
Therefore, for example, in a method of flattening the gain characteristic using an optical filter, a variable optical filter that can be controlled such as changing the characteristic of the optical filter according to the input optical power is required. The optical filter is difficult to realize, and even if it can be realized, there is a problem that the current technology becomes extremely expensive.
[0012]
[Problems to be solved by the invention]
When the conditions of the optical amplifier necessary for WDM transmission are rearranged again,
(1) The wavelength dependence of the amplification gain is small even if the input signal light power or the number of wavelength multiplexing changes.
  (2) The amplified optical power for each wavelength must be kept constant.
Is required. In FIG. 11, it can be seen that a flat gain characteristic is obtained for the wavelength band of 1540 to 1560 nm when the value of N2 / NT is near 0.7.
[0013]
Therefore, flat gain characteristics can be obtained if the operating state of the EDFA can always be maintained in this inverted distribution state. In order to realize such an operation, the EDFA may be controlled to have a constant gain. That is, N2 / NT can be kept at an arbitrary constant value by adjusting the pumping light power according to the change in the input light power so that the gain becomes constant. An example of such an experiment is shown in the literature (Technical Research Report of IEICE, OCS 94-66 PP31-36).
[0014]
However, if the power of the pumping light is controlled 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 problem, the above-mentioned document (Technical Research Report of IEICE, OCS 94-66 PP31-36) proposes to control the optical output using an optical attenuator. FIG. 12 shows the configuration of such an optical amplifier.
[0015]
In FIG. 12, the input signal light from the input port 1 and the excitation light from the excitation 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 driving current of the pumping LD 4 is controlled by an automatic fiber gain controller (AFGC) 10. The AFGC 10 controls the power of the pumping light so that the gain in the EDF 5 is constant based on the optical power of the ASE output from the EDF 5.
[0016]
Further, a part of the amplified signal light is branched by the optical coupler 8, and this branched light is converted into an electric signal by the photodetector 11, and the output signal level of the photodetector 11 becomes constant by the automatic power controller (APC) 12. Thus, the attenuation factor of the optical attenuator 7 is controlled.
[0017]
If an optical attenuator is used, the optical output can be adjusted regardless of the gain of the optical amplifier. Therefore, the composition and length of the EDFA 5 and the power of the pumping LD 4 are set so that the optical output is sufficiently higher than the desired optical output. A constant optical output can be obtained by adjusting the optical attenuator 7 installed at the output section of the optical amplifier performing the constant gain control. That is, the above (1) and (2) can be satisfied at the same time.
[0018]
However, when the optical attenuator 7 is used as shown in FIG. 12, the current technology is to reduce the maximum output optical power due to the use of the optical attenuator and to manufacture a variable attenuation factor type optical attenuator at low cost. There is a problem that is difficult.
[0019]
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 be a constant value (special Kohei 7-311212, Onaka et al., “Optical Amplifier”). In this case, a new light source is required instead of using an optical attenuator. In addition, the light source must have an oscillation wavelength within the amplification band of the EDFA and a wavelength somewhat distant from the WDM signal.
[0020]
The present invention has been made to solve the above-described problems. The wavelength dependence of the signal gain for WDM transmission is maintained while keeping the output optical power constant without newly inserting light using an external light source. An object of the present invention is to provide an optical amplifier with low performance.
[0021]
[Means for Solving the Problems]
The above problem is solved by the following configuration.
(Claim 1) In an optical amplifier having an optical amplification medium that has a predetermined amplification band and amplifies input signal light by pumping light and outputs the amplified signal light,SaidTo keep the signal light power of the output of the optical amplifier at a constant valueSaidExcitation light power control means for controlling the excitation light;SaidInput signal light power detecting means for detecting the power of the input signal light;
  At least two reflective elements are installed across the optical amplification medium, and the reflection by the reflective elements and theUsing an optical amplification mediumSaidAn oscillation means for oscillating light having a wavelength within a predetermined amplification band;SaidAn oscillation light power detection means for detecting the oscillation light power of the oscillation means;
  The one reflective element is a variable reflectance element, and the reflective variable element is a polarizer, a Faraday rotator, and the oscillation light. 100 % Reflecting elements are arranged in this order, the rotation angle of polarized light passing through the Faraday rotator is controlled using an electromagnet, and the signal light power of the output of the optical amplifier is set to a constant value by the excitation light power control means. After that, the pumping light power is kept constant,From the detection result of the input signal light power detection means and the oscillation light power detection means,SaidTo keep the input optical power to the optical amplifying medium constantSaidOscillation light power control means for controlling the oscillation light power is provided.
[0022]
An interferometer is configured by installing two reflecting elements with the optical amplification medium interposed therebetween. If the wavelength of the oscillation light is within the amplification region of the amplification medium, the light having the wavelength is amplified by going back and forth between the two reflecting elements through the amplification medium and oscillates under a certain condition. Further, the value of the oscillation light power can be controlled to a predetermined value by using one reflection element as a variable reflectance element and controlling the reflectance of the variable reflectance element by the oscillation light power control means.
  Further, as the element with variable reflectivity, a polarizer, a Faraday rotator, and the oscillation light are used. 100 % Elements are arranged in this order, and the rotation angle of the polarized light passing through the Faraday rotator is controlled using an electromagnet, so that the excitation light power remains constant and the Faraday rotation is performed for the light incident on the polarizer. Through the child 100 % Of the polarization plane of light that is reflected by the element that reflects% and passes through the Faraday rotator and exits from the polarizer. 100 % Can be changed. As a result, it is possible to obtain an element with variable reflectivity as a whole.
  When the input signal light increases or decreases, if the pumping light power is controlled to keep the output signal light constant, the ratio of the inversion distribution in the optical amplifying medium changes, so that the wavelength characteristics of the amplification gain are not flat (see FIG. 11). For this reason, the oscillation light power control means reduces or increases the oscillation light power having a wavelength different from that of the input signal light in the amplification band by the increase or decrease of the input signal light, and the input light power to the optical amplification medium. By making the constant, the wavelength characteristic of the amplification gain can be made constant.
[0023]
(Claim 2) In an optical amplifier having an optical amplifying medium having a predetermined amplification band and amplifying input signal light by pumping light, the signal light power at the output of the optical amplifier is maintained at a constant value. Excitation light power control means for controlling the excitation light; input signal light power detection means for detecting the power of the input signal light;
  Oscillating means for oscillating light having a wavelength within the predetermined amplification band by using at least two reflecting elements sandwiched between the optical amplifying medium and utilizing the reflection by the reflecting element and the optical amplifying medium; An oscillation light power detection means for detecting the oscillation light power of the oscillation means;
  The one reflective element is an element with variable reflectivity, and the element with variable reflectivity includes an LN modulator and the oscillation light. 100 % Reflecting elements are arranged in this order, and the LN modulator is controlled using a bias voltage. After the pumping light power control means sets the signal light power of the output of the optical amplifier to a constant value, the pumping light power Oscillating optical power for controlling the oscillating optical power so that the input optical power to the optical amplifying medium is made constant based on the detection results of the input signal optical power detecting means and the oscillating optical power detecting means Control means.
  That is, as an element having a variable reflectance, an LN modulator and the oscillation light are 100 % Elements are arranged in this order, and the bias voltage of the LN modulator is changed to pass through the LN modulator. 100 The power of the light that is reflected by the% reflecting element and is emitted again through the LN modulator is 0 to 0. 100 % Can be changed freely. As a result, it is possible to obtain an element with variable reflectivity as a whole.
[0026]
(Claim 3)  Claim 1A storage means for storing a value necessary for the reflectance of the variable-reflectance element according to claim 1 in correspondence with the value of the power of the input signal light according to claim 1 is provided, and the value of the power of the input signal light Accordingly, the power of the oscillation light is adjusted using the value stored in the storage means. In this way, even when the input signal light fluctuates, the oscillation light power can be easily adjusted, the wavelength characteristic of the amplification gain can be flattened, and the output light power can be made constant.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a principle configuration diagram of an optical amplifier according to the present invention. In the present invention, as shown in the figure, an optical amplifier oscillates light having a wavelength different from the band of the WDM signal by adding an interferometer made of a reflection mirror or the like to the configuration of a normal optical amplifier. To change the inversion distribution state, and the optical amplifier conditions necessary for the WDM transmission described above,
(1) Less gain wavelength dependency
(2) Output optical power must be kept constant
Is to be satisfied at the same time.
[0028]
In the figure, a part of the optical output of this optical amplifier is branched out and converted into an electric signal by the output signal optical power detection means 32, and the output optical power of the pumping light source 23 is kept constant so that the extracted optical power is kept constant. To control. Thereby, constant control (Automatic Level Control; ALC) of the optical output is performed. . In addition, on the output side of the optical amplification medium (for example, EDF) 27, the optical power amplified by the interferometer and the noise component generated from the optical amplifier are removed, and only the signal component that is originally desired to be kept constant is selectively selected. A transmitting optical filter (for example, an optical bandpass filter) 31 is inserted.
[0029]
Since the ALC control is performed as described above, the output light power of the pumping light source 23 is adjusted to keep the light output constant even if the input light power changes. (For example, in FIG. 9, the operating point moves from point (a) to point (b)). For this reason, in the case of a WDM signal, the total power of each signal is only controlled to be constant. When the input signal light power changes, the value of N2 / NT is controlled by controlling the power of the excitation light source. Changes, the wavelength dependence of gain changes as shown in FIG.
[0030]
For this reason, an interferometer is formed by reflecting mirrors 25 and 30 with the EDF 27 interposed therebetween, and only light having a certain wavelength apart from the WDM signal is selectively selected from ASE light (spontaneously emitted light) generated in the EDFA. Oscillate. 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. Further, by controlling the optical power, the optical power in the EDF, that is, the input optical power can be kept constant without newly inserting light from the outside.
[0031]
As a result, the operating point returns from point (b) to point (a) in FIG. 9, so that the pumping light power becomes the original value, the value of N2 / NT does not change, and the wavelength dependence in the amplification band is eliminated. be able to. Specifically, by incorporating an element capable of controlling the optical power inside the interferometer and adjusting the optical power to intentionally oscillate, the value of N2 / NT resulting from the power adjustment of the excitation light source for ALC control The value of N2 / NT can be changed independently of the change in.
[0032]
Next, the configuration of the interferometer will be described. In FIG. 1, a specific wavelength λ_SThe optical couplers 24 and 28 capable of branching only the EDF 27 are arranged. Where λ_SIs a wavelength within the amplification band of the EDF 27, but is assumed to be far away from the wavelength of the WDM signal. Now tentatively λ_SIs 1530 nm, optical couplers 24 and 28 capable of selectively branching or multiplexing the wavelength of 1530 nm are used.
[0033]
The light of 1530 nm branched by the optical coupler 24 is reflected 100% by the mirror 25 attached to the tip of the optical coupler 24, is again combined with the WDM signal by the optical coupler 24, and is amplified when passing through the EDF 27. Demultiplexed by the coupler 28. The demultiplexed 1530 nm light is reflected by a variable reflectivity mirror 30 having a reflectivity γ (<1) and is multiplied by γ times, and is again combined with another signal by the optical coupler 28 and passes through the EDF 27. And return to the optical coupler 24 again. Reflection by the 1530 nm 100% reflection mirror 25 and the mirror 30 having a reflectance γ is repeated, and when the amplification exceeds the loss of this system, light of 1530 nm oscillates.
[0034]
The state of oscillation at that time is shown in FIG. Even if it is not light with a narrow spectrum as shown in the figure, it can be easily removed using an optical filter if the band of the light to oscillate is sufficiently far from the WDM signal band.
[0035]
Next, a method for controlling the power of oscillation light will be described. Using the fact that the relaxation time of Er in the EDF is relatively long (≈several tens of milliseconds), the power is controlled as a time average by oscillating or not oscillating light in a time shorter than the relaxation time. Like that. FIG. 3 shows an example of control of the oscillation light power.
[0036]
As the reflectivity γ of the reflectivity variable mirror 30 in FIG. 1 is gradually increased, the oscillation light does not gradually increase but suddenly oscillates at a certain point. For this reason, when it is desired to increase the power to oscillate, the oscillation interval is shortened as shown in FIG. Thereby, the average power in terms of time can be kept large and constant. On the other hand, when it is desired to reduce the oscillation power, the oscillation interval is made longer as shown in FIG. By doing so, the power can be kept small and constant on a time average basis.
[0037]
Using such oscillation light, when the input signal light power is weak, stronger light is oscillated, and when the input signal light power is strong, the oscillation light is weakened so that the light within the amplification band of the EDF can be reduced. Make sure that the total input power is always kept constant.
[0038]
That is, a part of the input signal light is branched and monitored by the input signal light power detection means 21 in FIG. 1, and the amount of the reflectance γ of the mirror 30 is made to be less than the relaxation time of the EDF 27 depending on the strength of the input signal light power. By controlling quickly, the power of light input to the EDF 27 can be kept constant as a whole. In addition, by doing this, it is possible to correct the fluctuation of the oscillation light power by the phase change due to the ambient temperature change.
[0039]
The oscillating light power is controlled by an electronic circuit of the oscillating light power control means 29 after the monitor light is converted into an electrical signal by the oscillating light power detection means 26. Since the relaxation time of the EDFA is relatively long, Fully controllable. References (1) (National Conference of the Institute of Electronics, Information and Communication Engineers '92 Spring c-318, pp 4-360), (2) (GA Ball et al, IEEE J. Lightwave., Vol. 10, pp1338-1343) (1992)), (3) (GA Ball et al, Electron. Lett. Vol. 29, No. 18, pp 1623-1625 (1993)).
[0040]
However, just keeping the input power to the EDF 27 constant does not necessarily cause the value of N2 / NT to be 0.7, and what level the input power is kept constant is important. Unless the input power is kept at a certain level and always kept at N2 / NT = 0.7, the wavelength dependence in gain cannot be eliminated.
[0041]
This can be dealt with by finely operating the means for correcting the power of the oscillation light in accordance with the input signal light power. For example, a control circuit using a microprocessor, a memory or the like is mounted on the optical amplifier, and the memory is pre-loaded. The optimum value of the oscillation light power may be stored in accordance with the value of the input signal light power, and the reflectance γ of the mirror 30 may be controlled in accordance with the input signal light power based on this value.
[0042]
By performing such control, the value of N2 / NT can always be kept at 0.7 with respect to any change in the input signal light power, and as a result, the wavelength dependence in gain can be eliminated.
[0043]
Further, when the input optical power value of the WDM signal is approximately halfway between the maximum value and the minimum value of the assumed change, the reflectance γ is adjusted to be approximately 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 excitation light source are selected so that the optical output of the optical amplifier has a predetermined power and the wavelength characteristic of the gain becomes flat. (Of course, the maximum output of the pumping light source needs to have sufficient power to obtain a predetermined light output even when the input signal light power becomes the minimum value.)
Further, when the input signal light power or the number of multiplexed wavelengths increases, the pumping light power can be reduced, so that the number of Er in the inversion distribution state decreases and the value of N2 / NT decreases, and the short wavelength side. The gain decreases. Therefore, the power of the light to be oscillated is decreased according to the increase of the input signal light power, and the value of N2 / NT may be controlled to be 0.7.
[0044]
Next, a method for controlling the reflectance γ will be described. As a method for controlling the reflectance γ, (1) a method using interference, (2) a method using polarized light, and the like can be considered, and each will be described in detail below.
[0045]
{Circle around (1)} As a “method using interference”, there is a method using an LN modulator. As shown in FIG. 4, 1530 nm band light is input from one side of the LN modulator 34 and is reflected by a 100% reflecting mirror attached to the other side through the LN modulator 34. At this time, by changing the bias voltage of the LN modulator, the phase causing interference in the LN modulator can be changed, and the power of light passing therethrough can be arbitrarily controlled to α (<1) times.
[0046]
However, the 1530 nm band light is completely reflected by the mirror and passes through the LN modulator 34 again, so that α²Attenuated twice. That is, the reflectance can be freely controlled from 0 to 100% by changing the bias voltage of the LN modulator.
[0047]
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, (2) there is a method of using an optical isolator as a “method of using 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 predetermined direction due to the nonreciprocity that light in the forward direction is low loss and light from the reverse direction is high loss. . FIG. 5 shows an example of the configuration.
[0048]
In the figure, light in the 1530 nm band is first converted into linearly polarized light by a polarizer 37 and is incident on a Faraday rotator 38. At that time, the Faraday rotator 38 is configured so that the rotation angle of the polarized light can be freely controlled. The light that has passed through the Faraday rotator is reflected by the 100% reflection mirror 39 and is incident on the Faraday rotator 38 again. At that time, since the polarization does not change due to reflection, the light is rotated twice by passing through the Faraday rotator twice.
[0049]
Therefore, for example, when the rotation angle of the Faraday rotator 38 is set to 45 °, the light is rotated 90 ° by passing through the Faraday rotator twice and cannot pass through the polarizer, so that all the light is transmitted. Blocked. Also, if the Faraday rotator is adjusted so that the polarization does not rotate after passing through the rotator (so that it rotates by 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, it passes without being blocked by the polarizer.
[0050]
That is, by adjusting the rotation angle of polarized light in the Faraday rotator, it is possible to form an element having an arbitrary reflectance of 0% to 100%. In the Faraday rotator 38, the rotation angle of the polarized light is determined by the element length, the magnetic flux density, and the element constant. If the polarization rotation angle can be freely controlled, the above-described element can be configured. Therefore, the Faraday rotation angle can be controlled by attaching 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.
[0051]
The above-described control method relates to a method for freely controlling the reflectance between 0% and 100%. However, the reflectance γ of the reflectivity variable mirror (30 in FIG. 1) is set to 0% (complete transmission). ) And 100% (complete reflection), it is also possible to control the oscillation light power by controlling the oscillation interval as shown in FIG. .
[0052]
By the way, even if the above operation is performed, the optical output of the optical amplifier is always kept constant by the ALC control. However, the maintained optical output is such that the total power of the WDM signal is kept constant, and the power of each optical signal changes as a matter of course as the number of wavelength multiplexing changes.
[0053]
Therefore, in order not to change the power of the optical output for each wavelength even if the number of wavelength multiplexing changes, a means for notifying the current wavelength multiplexing number to the optical amplifier is prepared, or the wavelength is set inside the optical amplifier. A means for detecting the multiplex number is required, but these can be achieved by the means shown in the prior application (Japanese Patent Application No. 7-214733).
[0054]
FIG. 6 shows an embodiment of an optical amplifier using the present invention. This figure shows the case of so-called bidirectional excitation using two excitation LDs (47, 60) as excitation light sources. Further, in the configuration of the figure, the reflectivity variable mirror 57 is installed on the exit end side, but a similar optical amplifier can be configured even if the position is exchanged with the 100% reflection mirror 52 and installed on the entrance end side. be able to. As a result, the optical input power to the EDF 55 can be controlled to a constant value without using an optical variable attenuator or a new light source, and the wavelength dependence of the gain of the optical amplifier can be reduced.
[0055]
【The invention's effect】
As described above, according to the present invention, it is possible to realize an optical amplifier that has less wavelength dependency of gain in wavelength division multiplex transmission and maintains constant output optical power without inserting light from the outside. .
[Brief description of the drawings]
FIG. 1 is a principle configuration diagram of an optical amplifier according to the present invention;
FIG. 2 is a diagram showing a state of oscillation 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 (No. 1) of an oscillation light power control element in the embodiment;
FIG. 5 is a configuration diagram (No. 2) of an oscillation light power control element in the embodiment;
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 a relationship between an example gain and output optical power;
FIG. 9 is a diagram showing a relationship between input optical power and output optical power in an example;
FIG. 10 is a diagram showing a relationship between an ASE 3 dB bandwidth of one example and the number of optical amplifier stages;
FIG. 11 is a graph showing an inversion distribution ratio (N2 / NT) of an example EDFA as a parameter.
Figure showing the relationship between gain and wavelength when
FIG. 12 is a block diagram of a first conventional optical amplifier;
FIG. 13 is a configuration diagram of an optical amplifier of a second conventional example.
[Explanation of symbols]
1 is an input port, 2 is an optical isolator, 3 is a WDM coupler, 4 is an excitation LD, 5 is an EDF, 6 is an optical isolator, 7 is an optical attenuator, 8 is an optical coupler, 9 is an output port, 10 is an AFGC, 11 Is an optical detector, 12 is an APC, 13 is an optical isolator, 14 is a WDM coupler, 15 is an excitation LD, 16 is an optical coupler, 17 is a probe LD, 18 is an EDF, 19 is an optical isolator, 20 is an optical BPF, and 21 is an input signal. Optical power detection means, 22 is a WDM coupler, 23 is an excitation light source, 24 is an optical coupler, 25 is a 100% reflection mirror, 26 is an oscillation optical power detection means, 27 is an optical amplifying medium (EDF), 28 is an optical coupler, 29 Is an oscillation light power control means, 30 is a reflectivity mirror, 31 is an optical BPF, 32 is an output signal light power detection means, 33 is an excitation light power control means, 34 is an LN modulator, 35 is a voltage control circuit, 36 100% reflection mirror, 37 polarizer, 38 Faraday rotator, 39 100% reflection mirror, 40 electromagnet, 41 current control circuit, 43 optical coupler, 44 photodetector, 45 amplifier, 46 WDMMW 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 reflectivity 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 BPF, 64 is an optical coupler, 65 is a photodetector, 66 is an amplifier, 67 is A / D D / A converter, 68 is CPU, 69 is ROM, 70 is RAM
Indicates.

Claims (3)

In an optical amplifier having an optical amplification medium having a predetermined amplification band and amplifying input signal light by pumping light and outputting the amplified signal light,
And pumping light power control means for controlling the excitation light so as to maintain a constant value of power of signal light output of the optical amplifier,
An input signal light power detecting means for detecting the power of the input signal light,
At least two reflective elements is placed across the optical amplification medium, an oscillating means for the utilizing the reflection by the reflective element the light amplification medium to oscillate light having a wavelength in the predetermined within the amplification band,
And oscillation light power detecting means for detecting the oscillation light power of the oscillating means,
The one reflective element is a variable reflectivity element, and the variable reflectivity element includes a polarizer, a Faraday rotator, and an element that reflects 100 % of the oscillation light in this order, and a polarization that passes through the Faraday rotator. The rotation angle of the wave light is controlled using an electromagnet, and the signal light power of the output of the optical amplifier is set to a constant value by the control of the pumping light power control means, and the input light is kept constant while the pumping light power is kept constant. from the detection result of the signal light power detecting means and said oscillation light power detecting means, that the input light power to the optical amplifying medium is provided and the oscillation light power control means for controlling said oscillation light power so that a constant A characteristic optical amplifier. In an optical amplifier having an optical amplification medium that has a predetermined amplification band and amplifies input signal light by pumping light and outputs the amplified signal light,
Excitation light power control means for controlling the excitation light so as to keep the signal light power of the output of the optical amplifier at a constant value;
Input signal light power detecting means for detecting the power of the input signal light;
An oscillating means that oscillates light having a wavelength within the predetermined amplification band by using at least two reflecting elements and sandwiching the optical amplifying medium, using the reflecting element and the optical amplifying medium;
Oscillating light power detecting means for detecting the oscillating light power of the oscillating means;
The one reflective element is an element with variable reflectivity, and the element with variable reflectivity includes an LN modulator and the oscillation light. 100 % Reflecting elements are arranged in this order, the LN modulator is controlled using a bias voltage, and the signal light power of the output of the optical amplifier is set to a constant value by the control of the pumping light power control means, and then the pumping Oscillation for controlling the oscillation light power so that the input optical power to the optical amplifying medium is constant based on the detection results of the input signal light power detection means and the oscillation light power detection means while keeping the optical power constant. An optical amplifier comprising an optical power control means. A storage means for storing a value necessary for the reflectance of the variable-reflectance element according to claim 1 in correspondence with the value of the power of the input signal light according to claim 1 is provided, and the input signal light 2. The optical amplifier according to claim 1, wherein the power of the oscillation light is adjusted using a value stored in the storage means in accordance with a power value.

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