JP3458885B2 - Optical fiber amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier that collectively amplifies multi-wavelength signal light in a WDM optical transmission system.

[0002]

2. Description of the Related Art With the increase in capacity and speed of optical communication, research and development have been conducted on wavelength division multiplexing (WDM) transmission systems. In this WDM transmission system, one of the most important optical elements is an optical amplifier that collectively amplifies signal lights of multiple wavelengths. This optical amplifier is required to have a high gain and low noise and a flat gain spectrum in the signal light wavelength band. Conventionally, an amplifying optical fiber (EDF: Er- Optical Fiber Amplifier (EDFA: Er-Doped Fiber Amplifi)
er) is used.

Since this optical fiber amplifier is arranged at a predetermined distance by an optical fiber in an optical transmission system, the optical fiber is transmitted to the optical fiber amplifier at the next stage with sufficient intensity. The signal light output from the amplifier needs to have a predetermined intensity or higher. Therefore, conventionally, even if the intensity of the input signal light fluctuates, the intensity of the pump light supplied to the EDF, that is, the amplification factor is controlled in order to maintain the output signal light of the optical fiber amplifier at a constant intensity. ing. However, when the intensity of the signal light input to the EDF and the intensity of the pump light supplied to the EDF change, the state of population inversion in the EDF changes, which causes a problem that the flatness of the gain spectrum is impaired. .

The following techniques are known to solve this problem (S. Kinoshita, et al., OAA'96,
SaA5, 1996, JP-A-8-248455 and JP-A-8-250785). FIG. 13 is a configuration diagram of a conventional optical fiber amplification. In this optical fiber amplifier, a coupler 110, a front stage EDF 120, a coupler 111, a variable optical attenuator 130, a coupler 112 and a rear stage EDF 140 are cascaded in this order, and pumping light is supplied to the front stage EDF 120 by a pumping laser light source 121. Excitation light is supplied from the excitation laser light source 141 to the subsequent EDF 140.

A part of the signal light input to the front-stage EDF 120 is extracted by the coupler 110 and detected by the photodetector 122, and a part of the signal light output from the front-stage EDF 120 is extracted by the coupler 111. Based on the ratio of the intensities of the input signal light and the output signal light of the front-stage EDF 120 detected by the detector 123 and detected by the photodetectors 122 and 123, respectively, by the AGC circuit 124.
The intensity of the excitation light that is output from and is supplied to the front-stage EDF 120 is controlled.

Further, a part of the signal light output from the variable optical attenuator 130 (that is, the signal light input to the post-stage EDF 140) is extracted by the coupler 112 and detected by the photodetector 131, and the light detection thereof is performed. ALC circuit 1 based on the intensity of the signal light detected by the device 131
By 32, the insertion loss of the variable optical attenuator 130 is feedback-controlled. Also, the latter-stage EDF 140 is an APC.
Excitation light having a constant intensity is supplied from the excitation laser light source 141 controlled by the circuit 142.

By doing so, the front EDF 120
Amplifies the signal light with a constant gain, the variable optical attenuator 130 outputs a signal light with a constant intensity, and the post-stage EDF 140
Also amplifies the signal light with a constant gain, and the front EDF1
The variation of the population inversion of each of 20 and the latter-stage EDF 140, that is, the variation of the gain spectrum is eliminated.

[0008]

However, in the above-mentioned conventional example, two photodetectors 122 and 123 are required to keep the gain of the front EDF 120 constant, and the intensity of the input signal light of the rear EDF 140 is required. Required one photodetector 131, and in total three photodetectors were needed to maintain the flatness of the gain spectrum. In addition, JP-A-8-248455
Japanese Patent Laid-Open Publication No. 8-250785 and Japanese Patent Laid-Open Publication No. 8-250785 each disclose an optical fiber amplifier that uses a larger number of photodetectors to suppress fluctuations in the gain spectrum.

The present invention has been made in order to solve the above problems and uses a small number of photodetectors, and the output signal light intensity is constant even if the input signal light intensity varies, and the gain spectrum is increased. It is an object of the present invention to provide an optical fiber amplifier which does not fluctuate.

[0010]

An optical fiber amplifier according to a first aspect of the present invention comprises (1) a first pumping light source section for outputting pumping light, and (2) a pumping section output from the first pumping light source section. A first optical amplifier having an amplifying optical fiber that amplifies the signal light when light is supplied; and (3) a variable insertion loss that attenuates the signal light output from the first optical amplifier. Variable optical attenuator, (4) second pumping light source that outputs pumping light, (5)
When the pumping light output from the second pumping light source unit is being supplied, the signal light output from the optical attenuating unit is amplified and
If not, it is partially different from the amplifying optical fiber of the first optical amplifying section.
Second having an amplifying optical fiber to which a different additive is added
Based on the intensity of the signal light detected by the (7) input signal light detection unit, and (6) the input signal light detection unit that detects the intensity of the signal light input to the first light amplification unit Light fiber
An insertion loss control unit that controls the insertion loss of the variable optical attenuator unit to a predetermined value so that the gain deviation of the IVA amplifier is minimized ;
(8) and the output signal light detector for detecting the intensity of the signal light outputted from the second optical amplifying section, based on the intensity of the detected signal light (9) the output signal light detection unit, the signal light Strength of
And a pumping light controller that controls the intensity of the pumping light output from the second pumping light source unit so that?

According to this optical fiber amplifier, the input signal light is amplified by the first optical amplifying section having the amplifying optical fiber to which the pumping light output from the first pumping light source section is supplied, The insertion loss is attenuated by the variable optical attenuator that is variable, and the pumping light output from the second pumping light source unit is amplified and output by the second optical amplifier having an amplifying optical fiber to which the pumping light is supplied. Here, the insertion loss of the variable optical attenuator is controlled by the insertion loss controller based on the input signal light intensity detected by the input signal light detector (the intensity of the signal light input to the first optical amplifier). As a result, the gain flatness of the optical fiber amplifier is maintained. The intensity of the pumping light output from the second pumping light source unit is based on the output signal light intensity detected by the output signal light detecting unit (the intensity of the signal light output from the second optical amplifying unit). It is controlled by the pumping light controller, whereby the output signal light intensity of the optical fiber amplifier is maintained constant.

Here, the insertion loss control unit controls the insertion loss of the variable optical attenuating unit at a logarithmic level substantially linearly with the logarithmic value of the intensity of the signal light detected by the input signal light detection unit. It is suitable. In this way, the insertion loss of the variable optical attenuator is controlled by the insertion loss controller, so that the gain flatness of the optical fiber amplifier is maintained.

The optical fiber amplifier according to the second invention is
(1) A forward pumping light source unit and a backward pumping light source unit that respectively output pumping light, and (2) at least two different additives.
Consists of a type of amplifying optical fiber connected in series
The pumping light output from each of the forward pumping light source unit and the backward pumping light source unit, and an optical amplifying unit having an amplifying optical fiber that amplifies the signal light when being supplied from the forward direction and the backward direction, respectively, (3) Based on the intensity of the signal light detected by the input signal light detection unit that detects the intensity of the signal light input to the light amplification unit, and (4) the input signal light detection unit ,
Predetermined to minimize the gain deviation of the optical fiber amplifier
A forward pumping light control unit that controls the intensity of the pumping light output from the forward pumping light source unit to a value, and (5) an output signal light detection unit that detects the intensity of the signal light output from the light amplifying unit, ( 6) Based on the intensity of the signal light detected by the output signal light detector, the backward pumping light control that controls the intensity of the pumping light output from the backward pumping light source unit so that the intensity of the signal light becomes constant And a section.

According to this optical fiber amplifier, the input signal light is an amplifiable light in which the pumping light output from each of the forward pumping light source section and the backward pumping light source section is supplied from each of the forward and backward directions. It is amplified and output by the optical amplification section having a fiber. Here, the intensity of the pumping light output from the forward pumping light source unit is controlled by the forward pumping light control unit based on the input signal light intensity detected by the input signal light detecting unit, whereby the optical fiber amplifier Gain flatness is maintained. Further, the intensity of the pumping light output from the backward pumping light source unit is controlled by the backward pumping light control unit based on the output signal light intensity detected by the output signal light detecting unit, and thus the output of the optical fiber amplifier The signal light intensity is kept constant.

An optical fiber amplifier according to the third invention is
(1) a first pumping light source section for outputting pumping light; and (2) a first pumping light source section for amplifying signal light when the pumping light output from the first pumping light source section is supplied. 1) an optical amplification unit, (3) a forward pumping light source unit and a backward pumping light source unit that respectively output pumping light, and (4) a pumping light output from each of the forward pumping light source unit and the backward pumping light source unit. Is supplied from each of the front direction and the rear direction, the signal light output from the first optical amplification unit is amplified ,
At least part of which is different from the amplifying optical fiber of the optical amplifying section of 1.
Second having an amplifying optical fiber to which a different additive is added
Based on the signal light intensity detected by the (6) input signal light detection unit, and (5) the input signal light detection unit that detects the intensity of the signal light input to the first light amplification unit Light fiber
The forward pumping light controller that controls the intensity of the pumping light that is output from the forward pumping light source unit to a predetermined value so that the gain deviation of the IVA amplifier is minimized, and (7) that is output from the second optical amplifier unit. Output signal light detector for detecting the intensity of the signal light, and (8) the backward pumping light source so that the intensity of the signal light becomes constant based on the intensity of the signal light detected by the output signal light detector. And a backward pumping light controller that controls the intensity of the pumping light output from the unit.

According to this optical fiber amplifier, the input signal light is amplified by the first optical amplifying section having the amplifying optical fiber to which the pumping light output from the first pumping light source section is supplied, Subsequently, the pumping light output from each of the forward pumping light source unit and the backward pumping light source unit is amplified by the second optical amplifying unit having an amplifying optical fiber supplied from each of the forward direction and the backward direction, and output. To be done. Here, the intensity of the pumping light output from the forward pumping light source unit is based on the input signal light intensity detected by the input signal light detecting unit (the intensity of the signal light input to the first optical amplifying unit). It is controlled by the pumping light controller, which maintains the gain flatness of the optical fiber amplifier. In addition, the intensity of the pumping light output from the backward pumping light source unit is based on the output signal light intensity detected by the output signal light detecting unit (the intensity of the signal light output from the second optical amplifying unit). It is controlled by the pumping light controller, whereby the output signal light intensity of the optical fiber amplifier is maintained constant.

Here, the forward pumping light control unit controls the intensity of the pumping light output from the forward pumping light source unit substantially linearly with respect to the intensity of the signal light detected by the input signal light detecting unit. Is preferred. In this way, the intensity of the pumping light output from the forward pumping light source unit is controlled by the forward pumping light controller, so that the gain flatness of the optical fiber amplifier is maintained.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) First, the first embodiment will be described. FIG. 1 is a configuration diagram of an optical fiber amplifier according to the first embodiment.

This optical fiber amplifier amplifies the signal light (wavelength of 1.55 μm band) input to the connector 10 and outputs it to the connector 11. Between the connectors 10 and 11, an input signal light monitor is provided. Coupler 20, optical isolator 12, Al-doped EDF 30, WDM coupler 33, optical isolator 13, variable optical attenuator 40, P / Al co-doped EDF 50, Al-doped EDF 51, WDM coupler 53,
Optical isolator 14 and output signal light monitor coupler 6
0 are cascade-connected in this order via an optical fiber as required.

The input signal light monitor coupler 20 for inputting the signal light propagating from the connector 10 allows most of the signal light to pass through the optical isolator 12 as it is, and at the same time extracts a part of the signal light. The input signal is input to the photodetector 21. The optical isolator 12 receives the signal light propagating from the input signal light monitor coupler 20 as A
The light is allowed to pass to the l-added EDF 30 side, but not to the opposite direction. On the other hand, the input signal light monitor coupler 2
Input signal light detector 21 for detecting signal light reaching from 0
Outputs an input signal light intensity signal according to its intensity, and for example, a photodiode is preferably used.

The Al-added EDF 30 is obtained by adding 1.4 wt% of Al (aluminum) element to a silica-based amplifying optical fiber (EDF) to which Er (erbium) element is added by 500 wt.ppm. The 53 μm band absorption loss is 5.5 dB / m and the length is 8 m. This Al
When the pump light of constant intensity (wavelength 0.98 μm) output from the pumping laser light source 32 is supplied to the added EDF 30 via the WDM coupler 33, a population inversion occurs and the signal light is amplified. Further, the WDM coupler 33 passes the pumping light output from the pumping laser light source 32 to the Al-doped EDF 30 side, and also passes the signal light output from the Al-doped EDF 30 to the optical isolator 13 side.

The optical isolator 13 is a WDM coupler 33.
The signal light propagated from the optical path is transmitted to the variable optical attenuator 40 side, but the light is not transmitted in the opposite direction. The variable optical attenuator 40 for inputting the signal light that has passed through the optical isolator 13 attenuates the signal light with the insertion loss set by the insertion loss control circuit 70 and outputs the signal light. The insertion loss of the variable optical attenuator 40 is feedforward controlled based on the input signal light intensity signal output from the photodetector 21.

The P / Al co-doped EDF 50 to which the signal light output from the variable optical attenuator 40 is input is an EDF co-doped with 3.9 wt% P (phosphorus) element and 0.3 wt% Al element. There is a 1.53 μm band absorption loss of 4.5
The length is 5 m in dB / m. The Al-doped EDF 51 that receives the signal light output from the P / Al co-doped EDF 50 has the same composition as the Al-doped EDF 30 and has a length of 16 m. The P / Al co-doped EDF 50 and the Al-doped EDF 51 are both laser light sources for excitation 52
When the pumping light (wavelength: 1.48 μm) output from is supplied via the WDM coupler 53, a population inversion is generated and the signal light is amplified. Further, the WDM coupler 53 passes the pumping light output from the pumping laser light source 52 to the Al-doped EDF 51 side, and also passes the signal light output from the Al-doped EDF 51 to the optical isolator 14 side.

The optical isolator 14 is a WDM coupler 53.
The signal light propagated from the output signal light monitor coupler 6
Passes light to the 0 side, but does not pass light in the opposite direction. The output signal light monitor coupler 60 for inputting the signal light that has passed through the optical isolator 14 allows most of the signal light to pass through as it is and further outputs the signal light to the outside via the connector 11, while extracting a part of the signal light. The output signal is input to the photodetector 61. Output signal light detector 6 for detecting the signal light reaching from the output signal light monitor coupler 60
1 outputs an output signal light intensity signal corresponding to the intensity, and for example, a photodiode is preferably used. Then, the excitation light control circuit 71 feedback-controls the intensity of the excitation light output from the excitation laser light source 52 based on the output signal light intensity signal.

Further, the output signal light monitor coupler 60 is
The light input from the connector 11 side is input to the reflected light detector 62, and the reflected light detector 62 detects the light. The light input from the connector 11 to the output signal light monitor coupler 60 is reflected light of the signal light generated when the connector 11 is detached, and the reflected light detector 62 has a direct relationship with the present invention. There is no.

The optical fiber amplifier according to this embodiment operates as follows. Most of the signal light input from the connector 10 passes through the input signal light monitor coupler 20 and the optical isolator 12, and is input to the Al-doped EDF 30. The Al-added EDF 30 is a laser light source 32 for excitation.
Excitation light of constant intensity (wavelength 0.98 μm)
Are supplied to form an inverted distribution, and the signal light is input to the Al-doped EDF 30 and amplified. The amplified signal light passes through the WDM coupler 33 and the optical isolator 13 and is input to the variable optical attenuator 40.

On the other hand, a part of the signal light input from the connector 10 is taken out by the input signal light monitor coupler 20 and detected by the input signal light detector 21. An input signal light intensity signal corresponding to the detected intensity of the signal light is output from the input signal light detector 21 and input to the insertion loss control circuit 70. The insertion loss control circuit 70 controls the insertion loss of the variable optical attenuator 40 based on the input signal light intensity, and the signal light output from the variable optical attenuator 40 is
The intensity is such that the gain deviation of the optical fiber amplifier is minimized.

The signal light output from the variable optical attenuator 40 is P / Al co-doped EDF 50 and Al-doped EDF.
Input to 51 sequentially. The P / Al co-doped EDF 50 and the Al-doped EDF 51 are supplied with pumping light (wavelength 1.48 μm) output from the pumping laser light source 52 to form a population inversion, and the signal light is amplified. Then, the amplified signal light passes through the WDM coupler 53, the optical isolator 14, and the output signal light monitor coupler 60, and is output from the connector 11.

A part of the output signal light is taken out by the output signal light monitor coupler 60 and detected by the output signal light detector 61. An output signal light intensity signal corresponding to the intensity of the detected signal light is output from the output signal light detector 61,
It is input to the excitation light control circuit 71. Then, the pumping light control circuit 71 controls the intensity of the pumping light output from the pumping laser light source 52 based on the output signal light intensity, and the intensity of the signal light output from the optical fiber amplifier is maintained constant. To be done.

In this way, the intensity of the input signal light is detected by the input signal light detector 21, and the EDF (Al-added E) of the preceding stage is detected.
DF30) and subsequent EDF (P / Al co-added EDF50
And the Al-doped EDF 51), the insertion loss of the variable optical attenuator 40 is controlled by the insertion loss control circuit 70 based on the input signal light intensity to maintain the gain deviation of the optical fiber amplifier to a minimum. The intensity of the output signal light is detected by the output signal light detector 61, and the excitation laser light source 52
To EDF (P / Al co-added EDF50 and A
The pumping light intensity supplied to the 1-doped EDF 51) is controlled by the pumping light control circuit 71 based on the output signal light intensity so that the output signal light intensity of the optical fiber amplifier is maintained constant. Therefore, the optical fiber amplifier according to the present embodiment uses the two photodetectors (the input signal photodetector 21 and the output signal photodetector 61) to maintain both the gain flatness and the constant output signal light intensity. can do.

Next, the input signal light intensity and the variable optical attenuator 40
The relationship with the insertion loss of is explained. FIG. 2 is a graph showing the relationship between the input signal light intensity and the insertion loss of the variable optical attenuator 40 that minimizes the gain deviation of the optical fiber amplifier. Here, the input signal light has four wavelengths, and the respective wavelengths are 1543 nm, 1548 nm, 1552 nm and 1
It was 558 nm. The insertion loss of the variable optical attenuator 40 is manually adjusted so that the gain deviation of the four-wave input signal light in the optical fiber amplifier is minimized when the total intensity of the four-wave input signal light is changed. I adjusted it with. In this figure, the vertical axis represents the total input signal light intensity of four waves, and the horizontal axis represents the insertion loss of the variable optical attenuator 40 that minimizes the gain deviation in the optical fiber amplifier with respect to the input signal light intensity. is there. As can be seen from this figure, in the range where the total input signal light intensity of four waves is 10 dBm or less, in order to keep the gain deviation in the optical fiber amplifier to a minimum, the variable light is proportional to the total input signal light intensity of four waves. The insertion loss of the attenuator 40 may be changed.

Next, the insertion loss characteristic when a voltage control type variable optical attenuator 40 is used will be described. FIG. 3 is a graph showing the relationship between the control voltage applied to the variable optical attenuator 40 and the insertion loss. In the example of the voltage-controlled variable optical attenuator 40 shown in this figure, the insertion loss has a linear relationship with the control voltage.

Therefore, from FIG. 2 and FIG. 3, the insertion loss control circuit 70 converts the intensity of the input signal light taken out from the input signal light monitor coupler 20 and detected by the input signal light detector 21 into a logarithmic value. The control loss having a linear relationship with the logarithmic value may be output to control the insertion loss of the variable optical attenuator 40. By doing this,
The gain deviation of the optical fiber amplifier can be kept to a minimum.

Next, an example of a specific circuit of the insertion loss control circuit 70 will be described. FIG. 4 is a circuit diagram of the input signal photodetector 21 and the insertion loss control circuit 70. The insertion loss control circuit 70 converts the current signal output from the photodiode, which is the input signal photodetector 21, into a voltage signal by using the six-stage operational amplifiers Amp1 to Amp6, and further performs the logarithmic conversion of the voltage signal. The signal is amplified and the result is input to the variable optical attenuator 40.

The anode terminal of the photodiode, which is the input signal photodetector 21, is connected via a variable resistor VR1.
It is connected to a potential of 3.3V, a Vcc potential is applied to the cathode terminal, and a reverse bias voltage is applied to the input signal photodetector 21. The + input terminal of the operational amplifier Amp1 is connected to the anode terminal of the input signal photodetector 21,
The-input terminal is directly connected to its own output terminal. The-input terminal of the operational amplifier Amp2 is a resistor R
1 (resistance value 100Ω) is connected to the output terminal of the operational amplifier Amp1 and the anode terminal of the diode D, the + input terminal is applied with a potential of −3.3V, and the output terminal is connected to the diode D. It is connected to the cathode terminal of.

The-input terminal of the operational amplifier Amp3 is connected to the output terminal of the operational amplifier Amp2 via the resistor R2 (resistance value 1 kΩ), and the resistor R3 (resistance value 9
It is also connected to its own output terminal via kΩ), and a potential of −3.3 V is applied to the + input terminal. The + input terminal of the operational amplifier Amp4 is directly connected to the output terminal of the operational amplifier Amp3, and the − input terminal is directly connected to its own output terminal. The-input terminal of the operational amplifier Amp5 is connected to the output terminal of the operational amplifier Amp4 via the resistor R4 (resistance value 1 kΩ), and also the resistor R5.
It is also connected to its own output terminal via (resistance value 9 kΩ), and a potential of -3.3 V is applied to the + input terminal. The + input terminal of the operational amplifier Amp6 is the operational amplifier A
It is directly connected to the output terminal of mp5, and the-input terminal is directly connected to its own output terminal. Then, the voltage signal output to the output terminal of the operational amplifier Amp6 is
It becomes a control voltage for controlling the insertion loss of the variable optical attenuator 40.

According to the insertion loss control circuit 70, the potential of the anode terminal of the input signal photodetector 21, which represents the magnitude of the current output from the input signal photodetector 21, is impedance-matched by the operational amplifier Amp1 and the operational amplifier Amp1 is used. The voltage signal input to Amp2 is logarithmically converted by the operational amplifier Amp2 and the diode D, and the logarithmically converted voltage signal is amplified by the operational amplifiers Amp3 to Amp6. That is, the insertion loss control circuit 70 converts the intensity of the input signal light extracted from the input signal light monitor coupler 20 and detected by the input signal light detector 21 into a logarithmic value, and a linear relationship with the logarithmic value. It is possible to control the insertion loss of the variable optical attenuator 40 by outputting the control voltage at 1 to, and thus the gain deviation of the optical fiber amplifier can be kept to a minimum.

(Second Embodiment) Next, a second embodiment will be described. FIG. 5 is a configuration diagram of an optical fiber amplifier according to the second embodiment.

The optical fiber amplifier according to the present embodiment is the first
The main difference from the embodiment of
DF (Al-added EDF 30) and variable optical attenuator 40 are not provided, and EDF (P / Al-codoped E
DF50 and Al-doped EDF51) are supplied with excitation light not only from the rear direction but also from the front direction, and the intensity of the excitation light supplied from the front direction to the subsequent EDF is based on the input signal light intensity. It is a controlled point.

This optical fiber amplifier amplifies the signal light (wavelength 1.55 μm band) input to the connector 10 and outputs it to the connector 11. Between the connectors 10 and 11, an input signal light monitor is provided. Coupler 20, optical isolator 12, WDM coupler 55, P / Al co-doped EDF5
0, Al-doped EDF 51, WDM coupler 53, optical isolator 14, and output signal light monitor coupler 60 are cascaded in this order through an optical fiber as necessary.

The input signal light monitor coupler 20 for inputting the signal light propagating from the connector 10 allows most of the signal light to pass through as it is to be input to the optical isolator 12, and also extracts a part of the signal light. The input signal is input to the photodetector 21. The optical isolator 12 receives the signal light propagated from the input signal light monitor coupler 20 as W
Light is passed to the DM coupler 55 side, but light is not passed in the opposite direction. On the other hand, the coupler 20 for the input signal light monitor
Input signal light detector 21 for detecting signal light reaching from
Outputs an input signal light intensity signal according to its intensity, and for example, a photodiode is preferably used. The pumping light control circuit 72, which receives the input signal light intensity signal output from the input signal light detector 21, receives the pumping light (wavelength 1. The intensity of 48 μm) is feed-forward controlled.

The P / Al co-added EDF 50 and the Al-added EDF 51 each have the same composition as in the first embodiment, but in the present embodiment, the P / Al co-added EDF is used.
The length of 50 is 3 m, and the length of Al-added EDF 51 is 15 m. This P / Al co-added EDF 50 and A
The l-doped EDF 51 receives the pumping light (wavelength 1.48 μm) output from the pumping laser light source 54 in the WDM coupler 55.
Pumping light (wavelength 1.48 μm) supplied from the pumping laser light source 52 through the WD
When the light is supplied from the rearward direction through the M coupler 53, a population inversion occurs, and the signal light input from the WDM coupler 55 side is amplified.

Here, the WDM coupler 55 adds the pumping light output from the pumping laser light source 54 to the P / Al co-doped ED.
The signal light reaching from the optical isolator 12 side is passed to the P / Al co-doped EDF 50 side while being passed to the F50 side, and the WDM coupler 53 adds the pumping light output from the pumping laser light source 52 to the Al-doped EDF51
The signal light output from the Al-doped EDF 51 is passed to the optical isolator 14 side while being passed to the optical isolator 14 side.

The optical isolator 14 is a WDM coupler 53.
The signal light propagated from the output signal light monitor coupler 6
Passes light to the 0 side, but does not pass light in the opposite direction. The output signal light monitor coupler 60 for inputting the signal light that has passed through the optical isolator 14 allows most of the signal light to pass through as it is and further outputs the signal light to the outside via the connector 11, while extracting a part of the signal light. The output signal is input to the photodetector 61. Output signal light detector 6 for detecting the signal light reaching from the output signal light monitor coupler 60
1 outputs an output signal light intensity signal corresponding to the intensity, and for example, a photodiode is preferably used. Then, the excitation light control circuit 71 feedback-controls the intensity of the excitation light output from the excitation laser light source 52 based on the output signal light intensity signal.

The optical fiber amplifier according to this embodiment operates as follows. Most of the signal light input from the connector 10 passes through the input signal light monitor coupler 20, the optical isolator 12, and the WDM coupler 55, and is input to the P / Al-doped EDF 50. On the other hand, a part of the signal light input from the connector 10 is taken out by the input signal light monitor coupler 20 and detected by the input signal light detector 21. An input signal light intensity signal corresponding to the detected intensity of the signal light is output from the input signal light detector 21 and input to the pumping light control circuit 72. Then, the pumping light control circuit 72 makes the pumping laser light source 54 minimize the gain deviation of the optical fiber amplifier based on the input signal light intensity.
The intensity of the excitation light output from is controlled.

The P / Al co-doped EDF 50 and the Al-doped EDF 51 are supplied with pumping light (wavelength 1.48 μm) output from the pumping laser light sources 52 and 54, respectively, to form a population inversion distribution. When the light is input, the signal light is amplified. The amplified signal light is sent to the WDM coupler 53 and the optical isolator 14.
Then, the signal passes through the output signal light monitor coupler 60 and is output from the connector 11.

A part of the output signal light is taken out by the output signal light monitor coupler 60 and detected by the output signal light detector 61. An output signal light intensity signal corresponding to the intensity of the detected signal light is output from the output signal light detector 61,
It is input to the excitation light control circuit 71. Then, the pumping light control circuit 71 controls the intensity of the pumping light output from the pumping laser light source 52 based on the output signal light intensity, and the intensity of the signal light output from the optical fiber amplifier is maintained constant. To be done.

As described above, the intensity of the input signal light is detected by the input signal light detector 21, and the P / Al co-doped EDF 50 and the Al-doped ED are output from the excitation laser light source 54.
The intensity of the pumping light supplied to F51 from the front direction is controlled by the pumping light control circuit 72 based on the intensity of the input signal light to maintain the gain deviation of the optical fiber amplifier to a minimum, and the intensity of the output signal light. Is detected by the output signal light detector 61, and the intensity of the excitation light output from the excitation laser light source 52 and supplied to the P / Al co-doped EDF 50 and the Al-doped EDF 51 from the rear is excited based on the output signal light intensity. It is controlled by the optical control circuit 71 to keep the output signal light intensity of the optical fiber amplifier constant. Therefore, the optical fiber amplifier according to this embodiment also has two photodetectors (the input signal photodetector 21 and the output signal photodetector 61).
Can be used to maintain both the gain flatness and the constant output signal light intensity.

Next, the relationship between the intensity of the input signal light and the intensity of the excitation light supplied by the excitation laser light source 54 will be described. FIG. 6 is a graph showing the relationship between the input signal light intensity and the forward pumping light intensity that minimizes the gain deviation of the optical fiber amplifier. Here, the input signal light has 8 wavelengths, and each wavelength is 2n from 1544 nm to 1558 nm.
It was m steps. Then, the sum of the intensities of the respective eight input signal lights is changed in the range from −26 dBm to −20 dBm, and the pump laser light source is set so that the gain deviation of the eight signal lights in the optical fiber amplifier is minimized. 54
From the front by P / Al co-added EDF50 and Al
The intensity of the excitation light supplied to the added EDF 51 was adjusted.
In this figure, the horizontal axis is the total input signal light intensity of eight waves, and the vertical axis is the pump light intensity with which the gain deviation in the optical fiber amplifier is minimum with respect to the input signal light intensity. As can be seen from this figure, in order to keep the gain deviation of the eight-wave signal light in the optical fiber amplifier to a minimum, the pumping laser light source 54 has a linear relationship with the total input signal light intensity of the eight waves. It suffices to change the intensity of the excitation light output from the.

Next, pumping light having an intensity that minimizes the gain deviation of the optical fiber amplifier is emitted from the front by the pumping laser light source 54 from the P / Al co-doped EDF 50 and Al-doped ED.
The output signal light spectrum when supplied to F51 will be described.

In FIG. 7A, the input signal light intensity is -26d.
FIG. 6 is an output signal light spectrum diagram when pump light is supplied so that the gain deviation of eight waves is minimized when Bm.
In this case, the intensity of the pumping light supplied from the pumping laser light source 54 to the P / Al co-doped EDF 50 and the Al-doped EDF 51 from the front is 0 mW, and the pumping laser light source 52 from the back to the P / Al co-doped EDF 51. The intensity of the excitation light supplied to the added EDF 50 and the Al-added EDF 51 is 4
It was 1 mW, and at this time, the gain of eight waves of the optical fiber amplifier became flat.

In FIG. 7B, the input signal light intensity is -20d.
FIG. 6 is an output signal light spectrum diagram when pump light is supplied so that the gain deviation of eight waves is minimized when Bm.
In this case, the intensity of the pumping light supplied from the pumping laser light source 54 to the P / Al co-doped EDF 50 and the Al-doped EDF 51 from the front is 35 mW, and the pumping laser light source 52 from the rear to the P / Al co-doped EDF 50. EDF50 added
The intensity of the pumping light supplied to the Al-doped EDF 51 was 0 mW, and at this time, the eight-wave gain of the optical fiber amplifier became flat.

As shown in FIGS. 7A and 7B, a flat gain spectrum is obtained in any case. However, the noise figure is -26 dB when the input signal light intensity is
When the input signal light intensity is -20 dBm (FIG. 7 (b)), it is 6.4 dB.
It is 2 dB, and it can be seen that the noise figure differs when the input signal light intensity differs.

When the signal light is to be amplified with a flat gain spectrum only by the Al-doped EDF 51, excluding the P / Al co-doped EDF 50 from the configuration of the optical fiber amplifier according to the second embodiment (FIG. 5). Is Al-added ED
It is necessary to shorten F51, and as a result, the input signal light intensity that gives the minimum gain deviation is substantially the same whether it is forward pumping or backward pumping. FIG. 8 is an output signal light spectrum diagram when the signal light is amplified only by the Al-doped EDF 51 except for the P / Al co-doped EDF 50 from the optical fiber amplifier according to the second embodiment. Al-added EDF
The length of 51 is 11 m, and the input signal light intensity is -20 d.
It is Bm. FIG. 8A is an output signal light spectrum diagram when the pumping laser light source 54 supplies pumping light with an intensity of 63 mW to the Al-doped EDF 51 only from the front direction, and FIG. 8B is a pumping laser light source. FIG. 5 is an output signal light spectrum diagram when the excitation light having an intensity of 63 mW is supplied to the Al-doped EDF 51 only from the rear direction by 52. As can be seen from these figures, a flat gain spectrum is obtained in any case.

(Third Embodiment) Next, a third embodiment will be described. FIG. 9 is a configuration diagram of an optical fiber amplifier according to the third embodiment. The optical fiber amplifier according to the present embodiment is different from the optical fiber amplifier according to the second embodiment mainly in that a front-stage EDF (Al-doped EDF 30) is further provided.

This optical fiber amplifier amplifies the signal light (wavelength 1.55 μm band) input to the connector 10 and outputs it to the connector 11. Between the connectors 10 and 11, an input signal light monitor is provided. Coupler 20, optical isolator 12, Al-doped EDF 30, WDM coupler 33, optical isolator 13, WDM coupler 55, P / Al co-doped EDF 50, Al-doped EDF 51, WDM coupler 53,
Optical isolator 14 and output signal light monitor coupler 6
0 are cascade-connected in this order via an optical fiber as required.

The input signal light monitor coupler 20 for inputting the signal light propagating from the connector 10 allows most of the signal light to pass through as it is to be input to the optical isolator 12, and at the same time extracts a part of the signal light. The input signal is input to the photodetector 21. The optical isolator 12 receives the signal light propagating from the input signal light monitor coupler 20 as A
The light is allowed to pass to the l-added EDF 30 side, but light is not passed in the opposite direction. On the other hand, the input signal light monitor coupler 2
Input signal light detector 21 for detecting signal light reaching from 0
Outputs an input signal light intensity signal according to its intensity, and for example, a photodiode is preferably used.

The Al-added EDF 30 has the same composition and length as those in the first embodiment. Excitation light (wavelength 0.98 μm) of a constant intensity output from the excitation laser light source 32 is transmitted to the Al-doped EDF 30 by WDM.
When supplied via the coupler 33, a population inversion is generated to amplify the signal light. Further, the WDM coupler 33 applies the pumping light output from the pumping laser light source 32 to the Al-doped EDF 30.
And the signal light output from the Al-doped EDF 30 is passed to the optical isolator 13 side.

The optical isolator 13 is a WDM coupler 33.
The signal light propagated from the WDM coupler 55 is passed to the WDM coupler 55 side, but the light is not passed in the opposite direction. The WDM coupler 55 allows the signal light reaching from the optical isolator 13 side to pass to the P / Al co-doped EDF 50 side,
The excitation light output from the excitation laser light source 54 is converted into P / Al.
Pass through the co-added EDF 50 side. The intensity of the excitation light (wavelength 1.48 μm) output from the excitation laser light source 54 is input by the excitation light control circuit 72 that inputs the input signal light intensity signal output from the input signal light detector 21. Feedforward control is performed based on the signal light intensity signal.

Each of the P / Al co-doped EDF 50 and the Al-doped EDF 51 has the same composition and length as in the case of the first embodiment. This P / Al co-added EDF50
And the Al-added EDF 51 has a laser light source 54 for excitation.
The pumping light (wavelength 1.48 μm) output from the pump is supplied from the front through the WDM coupler 55, and the pumping light (wavelength 1.48 μm) output from the pumping laser light source 52 is supplied.
m) is supplied from the rear side through the WDM coupler 53, a population inversion occurs, and the signal light input from the WDM coupler 55 side is amplified. The WDM coupler 53 passes the pumping light output from the pumping laser light source 52 to the Al-doped EDF 51 side, and also passes the signal light output from the Al-doped EDF 51 to the optical isolator 14 side.

The optical isolator 14 is a WDM coupler 53.
The signal light propagated from the output signal light monitor coupler 6
Passes light to the 0 side, but does not pass light in the opposite direction. The output signal light monitor coupler 60 for inputting the signal light that has passed through the optical isolator 14 allows most of the signal light to pass through as it is and further outputs the signal light to the outside via the connector 11, while extracting a part of the signal light. The output signal is input to the photodetector 61. Output signal light detector 6 for detecting the signal light reaching from the output signal light monitor coupler 60
1 outputs an output signal light intensity signal corresponding to the intensity, and for example, a photodiode is preferably used. Then, the excitation light control circuit 71 feedback-controls the intensity of the excitation light output from the excitation laser light source 52 based on the output signal light intensity signal.

The optical fiber amplifier according to this embodiment operates as follows. Most of the signal light input from the connector 10 passes through the input signal light monitor coupler 20 and the optical isolator 12, and is input to the Al-doped EDF 30. The Al-added EDF 30 is a laser light source 32 for excitation.
Excitation light of constant intensity (wavelength 0.98 μm)
Are supplied to form an inverted distribution, and the signal light is input to the Al-doped EDF 30 and amplified. The amplified signal light is sent to the WDM coupler 33 and the optical isolator 1.
3 and WDM coupler 55, and enters P / Al co-doped EDF 50.

On the other hand, a part of the signal light input from the connector 10 is taken out by the input signal light monitor coupler 20 and detected by the input signal light detector 21. An input signal light intensity signal corresponding to the detected intensity of the signal light is output from the input signal light detector 21 and input to the pumping light control circuit 72. Then, the pumping light control circuit 72 controls the strength of the pumping light output from the pumping laser light source 54 based on the input signal light intensity so that the gain deviation of the optical fiber amplifier is minimized.

The P / Al co-doped EDF 50 and the Al-doped EDF 51 are supplied with the pumping light (wavelength 1.48 μm) output from the pumping laser light sources 52 and 54, respectively, to form a population inversion. When the light is input, the signal light is amplified. The amplified signal light is sent to the WDM coupler 53 and the optical isolator 14.
Then, the signal passes through the output signal light monitor coupler 60 and is output from the connector 11.

A part of the output signal light is taken out by the output signal light monitor coupler 60 and detected by the output signal light detector 61. An output signal light intensity signal corresponding to the intensity of the detected signal light is output from the output signal light detector 61,
It is input to the excitation light control circuit 71. Then, the pumping light control circuit 71 controls the intensity of the pumping light output from the pumping laser light source 52 based on the output signal light intensity, and the intensity of the signal light output from the optical fiber amplifier is maintained constant. To be done.

In this way, the intensity of the input signal light is detected by the input signal light detector 21, and the P / Al co-doped EDF 50 and the Al-doped ED are outputted from the exciting laser light source 54.
The intensity of the pumping light supplied to F51 from the front direction is controlled by the pumping light control circuit 72 based on the intensity of the input signal light to maintain the gain deviation of the optical fiber amplifier to a minimum, and the intensity of the output signal light. Is detected by the output signal light detector 61, and the intensity of the excitation light output from the excitation laser light source 52 and supplied to the P / Al co-doped EDF 50 and the Al-doped EDF 51 from the rear is excited based on the output signal light intensity. It is controlled by the optical control circuit 71 to keep the output signal light intensity of the optical fiber amplifier constant. Therefore, the optical fiber amplifier according to this embodiment also has two photodetectors (the input signal photodetector 21 and the output signal photodetector 61).
Can be used to maintain both the gain flatness and the constant output signal light intensity.

Next, the relationship between the intensity of the input signal light and the intensity of the excitation light supplied by the excitation laser light source 54 will be described. FIG. 10 is a graph showing the relationship between the input signal light intensity and the forward pumping light intensity that minimizes the gain deviation of the optical fiber amplifier. Here, the input signal light has four wavelengths, and the respective wavelengths are 1544 nm, 1548 nm, and 1552 nm.
nm and 1558 nm. Then, the sum of the intensities of the four input signal lights is calculated from -17 dBm to -1.
The P / Al co-doped ED is changed from the front by the pumping laser light source 54 so that the gain deviation of the four-wave signal light in the optical fiber amplifier is minimized by changing the gain in the range of 0 dBm.
The intensity of the excitation light supplied to F50 and Al-added EDF51 was adjusted. In this figure, the horizontal axis is the total input signal light intensity of four waves, and the vertical axis is the pump light intensity with which the gain deviation in the optical fiber amplifier is minimum with respect to the input signal light intensity. As can be seen from this figure, in order to keep the gain deviation of the four-wave signal light in the optical fiber amplifier to a minimum, the pumping laser light source 54 should have a linear relationship with the total input signal light intensity of the four waves. It suffices to change the intensity of the excitation light output from the.

When a semiconductor laser light source is used as the excitation laser light source 54, the excitation laser light source 5
The intensity of the pumping light output from the
Since there is a linear relationship with the amount of current supplied to 4,
Therefore, if the current supplied to the pumping laser light source 54 is controlled with respect to the input signal light intensity as shown in FIG. 11, the gain deviation of the four-wave signal light in the optical fiber amplifier can be minimized. it can.

Next, an example of a specific circuit of the pumping light control circuit 72 will be described. FIG. 12 shows an input signal light detector 21, a pumping light control circuit 72, and a pumping laser light source 54.
It is a circuit diagram of. The pumping light control circuit 72 converts the current signal output from the photodiode serving as the input signal photodetector 21 into a voltage signal and amplifies it by the four-stage operational amplifiers Amp11 to Amp14 and the npn-type transistor Tr. Based on the result, the semiconductor laser which is the excitation laser light source 54 is caused to emit light.

The anode terminal of the photodiode, which is the input signal photodetector 21, is grounded via the variable resistor VR2, the Vcc potential is applied to the cathode terminal, and the reverse bias voltage is applied to the input signal photodetector 21. Has been done. The + input terminal of the operational amplifier Amp11 is connected to the anode terminal of the input signal photodetector 21, and the − input terminal is directly connected to its own output terminal. Operational amplifier Amp1
The − input terminal of 2 is connected to the output terminal of the operational amplifier Amp11 via the resistor R11 (resistance value 1 kΩ) and also connected to its own output terminal via the resistor R12 (resistance value 3 kΩ), and the + input The terminal is grounded.
The + input terminal of the operational amplifier Amp13 is connected to the operational amplifier Am.
It is connected to the output terminal of p12, and the-input terminal is directly connected to its own output terminal. Operational amplifier Amp14
The − input terminal of is connected to the output terminal of the operational amplifier Amp13 via the resistor R13 (resistance value 1 kΩ) and is also connected to its own output terminal via the resistor R14 (resistance value 3 kΩ), and the + input terminal Is grounded.

The base terminal of the transistor Tr is connected to the operational amplifier Amp14 via the resistor R15 (resistance value 10Ω).
Of the resistor R16 (with a resistance value of 1.5).
Ω) to the anode terminal of the semiconductor laser light source that is the excitation laser light source 54. The cathode terminal of the excitation laser light source 54 is grounded.

According to this pumping light control circuit 72, the potential of the anode terminal of the input signal photodetector 21, which represents the magnitude of the current output from the input signal photodetector 21, is amplified by the operational amplifiers Amp11 to Amp14, A collector current having a linear relationship with the potential appearing at the output terminal of the operational amplifier Amp14 flows through the transistor Tr. That is, the excitation laser light source 54 is the input signal light detector 2
The pumping light having an intensity having a linear relationship with the intensity of the input signal light detected by 1 is output. Therefore, the pumping light control circuit 72 can control the intensity of the pumping light output from the pumping laser light source 54 so as to keep the gain deviation of the optical fiber amplifier at a minimum.

Further, in the optical fiber amplifier according to this embodiment, the P / Al co-doped EDF 50 and the Al-doped EDF are used.
The fluctuation of the noise characteristic due to the change of the population inversion of each 51 is reduced, and the noise figure is always maintained at a constant value of about 4.7 dB.

[0075]

As described above in detail, according to the optical fiber amplifier of the first invention, the input signal light is
The pumping light output from the first pumping light source unit is amplified by the first optical amplifying unit having the amplifying optical fiber to which the pumping light is supplied, and the insertion loss is attenuated by the variable optical attenuating unit that is variable,
The pumping light output from the second pumping light source unit is amplified and output by the second optical amplifying unit having the amplifying optical fiber to which the pumping light is supplied. Here, the insertion loss of the variable optical attenuator is controlled by the insertion loss controller based on the input signal light intensity detected by the input signal light detector (the intensity of the signal light input to the first optical amplifier). As a result, the gain flatness of the optical fiber amplifier is maintained. The intensity of the pumping light output from the second pumping light source unit is based on the output signal light intensity detected by the output signal light detecting unit (the intensity of the signal light output from the second optical amplifying unit). It is controlled by the pumping light controller, whereby the output signal light intensity of the optical fiber amplifier is maintained constant. Here, the insertion loss control unit
It is preferable to control the insertion loss of the variable optical attenuator substantially linearly with the logarithmic value of the intensity of the signal light detected by the input signal light detector. In this way, the insertion loss of the variable optical attenuator is controlled by the insertion loss controller, so that the gain flatness of the optical fiber amplifier is maintained.

Further, according to the optical fiber amplifier of the second invention, the input signal light is the pump light output from the forward pump light source section and the backward pump light source section from the backward pump light source section, respectively. It is amplified and output by the optical amplification section having the amplifying optical fiber being supplied.
Here, the intensity of the pumping light output from the forward pumping light source unit is controlled by the forward pumping light control unit based on the input signal light intensity detected by the input signal light detecting unit, whereby the optical fiber amplifier Gain flatness is maintained. In addition, the intensity of the pumping light output from the backward pumping light source unit is
Controlled by the backward pumping light controller based on the output signal light intensity detected by the output signal light detector, and
The output signal light intensity of the optical fiber amplifier is kept constant.

Further, according to the optical fiber amplifier of the third invention, the input signal light has a first amplifying optical fiber to which the pumping light output from the first pumping light source unit is supplied. A second light having an amplifiable optical fiber that is amplified by the optical amplification unit and is subsequently supplied with pumping light output from the forward pumping light source unit and the backward pumping light source unit, respectively. The signal is amplified by the amplifier and output. Here, the intensity of the pumping light output from the forward pumping light source unit is based on the input signal light intensity detected by the input signal light detecting unit (the intensity of the signal light input to the first optical amplifying unit). It is controlled by the pumping light controller, which maintains the gain flatness of the optical fiber amplifier. The intensity of the pumping light output from the backward pumping light source unit is the output signal light intensity detected by the output signal light detecting unit (the intensity of the signal light output from the second optical amplifying unit).
Is controlled by the backward pumping light control unit, and the output signal light intensity of the optical fiber amplifier is maintained constant.

In each of the optical fiber amplifiers according to the second and third aspects of the present invention, the forward pumping light control section pumps in a forward direction substantially linearly with respect to the intensity of the signal light detected by the input signal light detecting section. It is preferable to control the intensity of the excitation light output from the light source unit. In this way, the intensity of the pumping light output from the forward pumping light source unit is controlled by the forward pumping light controller, so that the gain flatness of the optical fiber amplifier is maintained.

As described above, in any of the optical fiber amplifiers according to the first to third inventions, only two photodetectors (input signal light detection unit and output signal light detection unit) are used. Even if the input signal light intensity varies, the output signal light intensity can be kept constant and the gain deviation can be kept to a minimum.

In particular, in the case of the optical fiber amplifiers according to the second and third aspects of the invention, since the variable optical attenuator having the mechanically movable portion is not used, high reliability can be obtained. Further, in the case of the optical fiber amplifier according to the third invention, it is possible to reduce the fluctuation of the noise characteristic due to the change of population inversion inside the amplifying optical fiber of the second optical amplification section.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical fiber amplifier according to a first embodiment.

FIG. 2 is a graph showing the relationship between the input signal light intensity and the insertion loss of the variable optical attenuator 40 that minimizes the gain deviation of the optical fiber amplifier.

FIG. 3 is a graph showing a relationship between a control voltage applied to the variable optical attenuator 40 and an insertion loss.

FIG. 4 is a circuit diagram of an input light monitor detector 21 and an insertion loss control circuit 70.

FIG. 5 is a configuration diagram of an optical fiber amplifier according to a second embodiment.

FIG. 6 is a graph showing the relationship between the input signal light intensity and the forward pumping light intensity that minimizes the gain deviation of the optical fiber amplifier.

FIG. 7 (a) is an output signal light spectrum diagram when pump light is supplied so that the gain deviation of eight waves is minimized when the input signal light intensity is −26 dBm, and FIG.
It is an output signal light spectrum figure when pumping light is supplied so that the gain deviation of eight waves may become the minimum when the input signal light intensity is -20 dBm.

FIG. 8 shows the optical fiber amplifier P according to the second embodiment.
FIG. 7 is an output signal light spectrum diagram in the case of amplifying signal light only by Al-added EDF 51 excluding / Al co-added EDF 50.

FIG. 9 is a configuration diagram of an optical fiber amplifier according to a third embodiment.

FIG. 10 is a graph showing the relationship between the input signal light intensity and the forward pumping light intensity that minimizes the gain deviation of the optical fiber amplifier.

FIG. 11 is a graph showing the relationship between the input signal light intensity and the current supplied to the excitation laser light source 54.

FIG. 12 is a circuit diagram of an input light monitor detector 21, an excitation light control circuit 72, and an excitation laser light source 54.

FIG. 13 is a configuration diagram of a conventional optical fiber amplification.

[Explanation of symbols]

10, 11 ... Connector, 12, 13, 14 ... Optical isolator, 20 ... Input signal light monitor coupler, 21 ... Input signal light detector, 30 ... Al-doped EDF, 32 ... Excitation laser light source, 33 ... WDM coupler, 40 ... Variable optical attenuator, 5
0 ... P / Al co-added EDF, 51 ... Al-added EDF, 5
2 ... Excitation laser light source, 53 ... WDM coupler, 54 ... Excitation laser light source, 55 ... WDM coupler, 60 ... Output signal light monitor coupler, 61 ... Output signal light detector, 62 ... Reflected light detector, 70 ... Insertion loss control circuit 71, 72 ... Excitation light control circuit.

Continuation of the front page (56) Reference JP-A-3-206427 (JP, A) JP-A-8-213675 (JP, A) JP-A-5-241209 (JP, A) JP-A-8-254723 (JP , A) JP 9-214034 (JP, A) JP 9-219696 (JP, A) JP 10-135546 (JP, A) JP 10-51057 (JP, A) JP 8-255940 (JP, A) JP-A-8-248455 (JP, A) Special Table 2000-513144 (JP, A) Yasushi Sugaya et al., IEICE Technical Report Vol. 95, No. 185 (OCS95-36), July 26, 1995, pp. 21-26 S. Kinoshita et al. , OSA Trends in Optics and Photonics, Vol. 5, Optical Amplifiers and Their Applications, December 25, 1996, pp. 49-52 (held July 13, 1996) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 3/00-3/30 H04B 10/00-10/28 JISST file (JOIS) WPI (DIALOG)

Claims (5)

(57) [Claims] 1. A first pumping light source section that outputs pumping light, and an amplifying optical fiber that amplifies signal light when the pumping light output from the first pumping light source section is supplied. A first optical amplifier, a variable optical attenuator with variable insertion loss that attenuates the signal light output from the first optical amplifier, a second pumping light source that outputs pumping light, When the pumping light output from the second pumping light source unit is supplied, the signal light output from the optical attenuating unit is amplified , and at least part of the amplification of the first optical amplifying unit is performed.
Second optical amplifying section having an amplifying optical fiber to which an additive different from that of the optical signal optical fiber is added, and an input signal light detecting section for detecting the intensity of the signal light input to the first optical amplifying section, Based on the intensity of the signal light detected by the input signal light detector , the gain deviation of the optical fiber amplifier is minimized.
An insertion loss control unit that controls the insertion loss of the variable optical attenuator to a predetermined value, and an output signal light detection unit that detects the intensity of the signal light output from the second optical amplification unit, The intensity of the excitation light output from the second excitation light source unit so that the intensity of the signal light is constant based on the intensity of the signal light detected by the output signal light detector. An optical fiber amplifier, comprising: 2. The insertion loss control unit controls the insertion loss of the variable optical attenuator at a logarithmic level in a substantially linear manner with respect to the logarithmic value of the intensity of the signal light detected by the input signal light detection unit. The optical fiber amplifier according to claim 1, wherein 3. A forward pumping light source section and a backward pumping light source section which respectively output pumping light, and at least two types of amplifying optical fibers having different additives.
Amplification that is configured to be connected in series and amplifies signal light when pumping light output from each of the forward pumping light source unit and the backward pumping light source unit is supplied from each of the forward direction and the backward direction. Based on the intensity of the signal light detected by the input signal light detection unit, and an optical signal amplification unit having an optical fiber, an input signal light detection unit for detecting the intensity of the signal light input to the optical amplification unit. , The gain deviation of the optical fiber amplifier is minimized
A forward pumping light control unit that controls the intensity of the pumping light output from the forward pumping light source unit to a predetermined value, and an output signal light that detects the intensity of the signal light output from the optical amplification unit. A pump that is output from the backward pumping light source unit so that the intensity of the signal light is constant based on the intensity of the signal light detected by the detector and the output signal light detector. An optical fiber amplifier, comprising: a backward pumping light controller that controls the intensity of light. 4. A first pumping light source section that outputs pumping light, and an amplifying optical fiber that amplifies the signal light when the pumping light output from the first pumping light source section is being supplied. No. 1 optical amplification unit, a forward pumping light source unit and a backward pumping light source unit that respectively output pumping light, and pumping light output from each of the forward pumping light source unit and the backward pumping light source unit is forward and backward. when being supplied from the rear direction, respectively, to amplify the signal light output from said first optical amplifier, the amplification of the first optical amplifying section
Additive with at least part of the optical fiber
A second optical amplifying section having an amplifying optical fiber, an input signal light detecting section for detecting the intensity of the signal light input to the first optical amplifying section, and an input signal light detecting section Based on the intensity of the signal light, the gain deviation of the optical fiber amplifier is minimized.
To detect the intensity of the signal light output from the second pumping light control unit and the forward pumping light control unit that controls the intensity of the pumping light output from the forward pumping light source unit to a predetermined value. the output signal light detection unit, from the based on the intensity of the detected the signal light by the output signal light detecting unit, the signal light as before <br/> SL-rear direction pump light source intensity is constant An optical fiber amplifier comprising: a backward pumping light controller that controls the intensity of the pumping light that is output. 5. The forward pumping light controller controls the intensity of the pumping light output from the forward pumping light source unit substantially linearly with respect to the intensity of the signal light detected by the input signal light detector. 5. The method according to claim 3 or claim 4, wherein
The optical fiber amplifier described.