JPH07307704A - Optical amplifier - Google Patents

Abstract

PURPOSE:To automatically suppress an abnormal peak light output by automatically adjusting an optical input value switching from a fixed optical output to low gain corresponding to the optical input at the time of normal use. CONSTITUTION:The part of the input light 20 to an optical amplifier is received by the circuit 2-1 of a light receiving device. As for the converted electric signal, the modulation signal through a low-pass filter 3 and the maximum value of the value averaged by eliminating the influence of the abnormal peak of a front step are held in a peak hold circuit 4. A control switch offset value V 2 in which a signal fluctuation part is considered for this value is added in an addition circuit 5 and this value is set as the control switch value of the optical amplifier. When a signal optical input value becomes lower than this value, this is detected by a comparator 9, a switch signal is added to a switch SW 11 and the gain of the optical amplifier is lowered by switching the control of an exciting light source drive circuit 8 from an output constant control circuit 12 to a low gain setting 10. As a result, an abnormal peak output is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier used for optical communication or the like, and more particularly to an optical amplifier which is highly safe in handling and less dangerous.

[0002]

2. Description of the Related Art Generally, an optical amplifier used for optical communication or the like is controlled so that an optical output value does not change with respect to a slight change of a signal light input value, and an optical output becomes constant. Then, such control is performed by a method of detecting a part of the optical output and applying negative feedback to the excitation light source so that the optical output becomes constant. However, the optical input value and the optical output value described above are average values including a modulated main signal of about μ second, which is faster than the time constant of the gain fluctuation of the optical amplifier itself.

Further, the above-mentioned constant optical output control of the optical amplifier is carried out at a slow frequency such as a time constant (msec) of gain variation of the optical amplifier in order to avoid influence on the modulated main signal.

[0004]

In the conventional optical amplifier controlled as described above, when the optical input value becomes very low, feedback is applied so as to keep the optical output value constant. Is very high. If the optical input level shifts from such a low optical input state to the original optical input value and the transition of the optical input level is faster than the speed of the negative feedback control that keeps the optical output constant, the optical amplifier is high. Since the gain is maintained, the optical amplifier instantaneously outputs an abnormally high optical output.

Therefore, in the above-described optical amplifier according to the prior art, the abnormally high instantaneous (abnormal peak) optical output melts the coupling portion of the optical fiber or destroys the light receiver that receives this optical output. There is a problem that sometimes. In addition, this abnormal peak output may be dangerous to the surrounding people in some cases.

Generally, the width (dynamic range) of the optical input value to the optical amplifier installed in the optical communication system is not so wide. Therefore, if the optical amplifier can set the optical input value for switching the gain to a value slightly lower than the normal optical input according to the installed optical communication system, the optical input value for gain switching and the return It is possible to suppress an abnormal peak light output to a low level without causing an extreme difference from the light input value of.

However, in this switching of the optical amplifier according to the prior art, an operator must set an optical input value for gain switching by measuring an optical input in a normal use state for each communication system in which the optical amplifier is used. Therefore, there is a problem that the operator must perform complicated work.

An object of the present invention is to solve the above-mentioned problems of the prior art, and automatically adjust the optical input value for switching the gain of the optical amplifier to a low value in accordance with the optical input during normal use, and The abnormal peak optical output is suppressed by switching the gain of the optical amplifier to a low value without needing to do so, which causes the optical fiber to melt the coupling part of the optical fiber or destroy the optical receiver that receives this optical output. This is to provide an optical amplifier that can prevent such a situation and that does not pose a danger to people around.

[0009]

According to the present invention, the object is to detect an average light input value within a predetermined time, and hold the maximum value of the average light input value for a certain period of time.
This is achieved by setting an input value that is a certain level lower than the held value as a threshold value and reducing an amplifier gain when an optical input value below this threshold value is detected.

That is, specifically, the above-mentioned object is to eliminate the influence of a photodetector circuit for separating and receiving a part of the signal light input, a modulation signal of the output of the photodetector circuit, and an abnormal peak in the preceding stage. A low-pass filter, a peak hold circuit that holds a maximum value of averaged values of signals that have passed through the filter, and an adder circuit that adds a predetermined offset value to the value held in the peak hold circuit , A comparator for comparing the output value of the adder circuit with the output value of the photodetector circuit, and it is achieved by reducing the gain of the optical amplifier based on the comparison result by the comparator.

[0011]

According to the present invention, by including the above-mentioned means, the input value for gain switching for alleviating the abnormal peak can be automatically set on the circuit. This allows
It is possible to switch the gain of the optical amplifier to a low value and suppress the abnormal peak optical output without manpower, to melt the coupling part of the optical fiber by the optical output, or to destroy the optical receiver that receives this optical output. It can be prevented, and it is possible to prevent the surrounding people from being dangerous.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical amplifier according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical amplifier according to an embodiment of the present invention. In FIG. 1, 1-1,
1-2 is an optical coupler, 2-1, 2-2 is a light receiver circuit, 3 is a low-pass filter, 4 is a peak hold circuit, 5 is an adder circuit, 6 is a wavelength multiplexing module, 7 is an excitation light source, and 8 is Pumping light source drive circuit, 9 is a comparator, 10 is a low gain setting value, 1
Reference numeral 1 is a control method changeover switch, 12 is a constant output control circuit, and 13 is an amplification optical fiber.

An optical amplifier according to an embodiment of the present invention shown in FIG. 1 has a basic configuration for automatically setting an input value for switching to a low gain and a configuration for controlling an optical output at a constant level. . First, the configuration and operation for controlling the light output to be constant will be described.

In FIG. 1, a part of the signal light input 20 is
The main optical signal separated by the optical coupler 1-1 reaches the amplification optical fiber 13 through the wavelength multiplexing module 6.
The amplification optical fiber 13 is for amplifying the signal light input 20, and the pumping light from the pumping light source 7 is wavelength-multiplexed.
It is incident through the rule 6. A part of the optical signal (optical output) amplified by the amplified optical fiber 13 for amplification is
The light output 22 is separated by the optical coupler 1-2 at a specific ratio and is incident on the light receiver 2-2.

In the illustrated optical amplifier, the optical signal value input to the photodetector 2-2, that is, the optical signal value of the optical output 22 becomes a preset constant value in the normal output constant control operation state. And is controlled by the constant output control circuit 12. Therefore, the output signal of the light receiver 2-2 is negatively fed back to the excitation light source drive circuit 8 via the control method changeover switch (SW) 11.

As a result, the illustrated optical amplifier has the signal light input 2
When the level of 0 is low, the current of the pumping light source 7 is increased to control the amplification optical fiber 13 to a high pumping state, and when the level of the optical signal light input 20 is high, the reverse control is performed and the light receiver The gain is controlled so that the input to 2-2 is constant.

Next, a configuration for automatically setting an input value for switching the gain of the optical amplifier to a low gain and switching the gain according to the present invention will be described.

The signal light input separated by the optical coupler 1-1 enters the photodetector 2-1 and is converted into an electric signal. The signal light is several m, which is the gain fluctuation time constant of the amplification optical fiber.
It is modulated much faster than seconds. The signal light converted into electricity passes through the low-pass filter 3 so that only a slow fluctuation component having a gain fluctuation time constant of the amplification optical fiber or less is transmitted to the peak hold circuit 4.

The peak hold circuit 4 for holding the maximum value of the input signal holds the maximum value of the average values of the output signal of the low pass filter 3 within a predetermined time. In actual use, signal light having an intensity corresponding to the loss of the optical fiber in the installed communication system is input. Since the light level is controlled during normal operation, the maximum value of the light input can be usually regarded as the light output level during system operation.

The highest value of the averaged inputs held in the peak hold circuit 4 is input to the adder circuit 5,
The adder circuit 5 sets a value lower than this value by the offset setting voltage V2 as the signal light input value for gain switching.
The switching set value and the signal value from the light receiver 2-1 are input to the comparator 9 to determine the level relationship. Then, when the signal from the photodetector 2-1 becomes lower than the switching set value, the SW 11 receiving the signal sends the signal transmitted to the excitation light source drive circuit 8 from the signal of the constant output control circuit 12 to the low gain set value. Switch to 10 signals.

As a result, in the optical amplifier according to the embodiment of the present invention, the gain is controlled to be switched to a low value set in advance to the low gain setting value 10, and the signal light input level once lowered is changed to the gain switching value. Even if the normal level is instantaneously restored later, an abnormal peak output is not generated as the optical output 22 because the gain is low. Then, the illustrated optical amplifier can suppress the abnormal peak value of the optical output 22 to an increase of the offset amount with respect to the instantaneous recovery after the decrease of the signal light input 20.

Further, in the optical amplifier according to the above-described embodiment of the present invention, even when an abnormal peak output is generated during operation of the optical amplifier in the preceding stage, it is possible to reduce the peak hold value from being set to the abnormal peak. This can be prevented by the band-pass filter 3, and thus the malfunction of the optical amplifier can be prevented.

That is, in general, an abnormal peak signal has the highest peak value μ from the rise of the input signal.
A fast time of less than a second, after which the decay time constant is 0.0
It has the characteristic of decaying in about 7 msec. For this reason, if the pass band of the low-pass filter 3 is set to 1 kHz or less, the influence of the abnormal peak signal on the increase of the maximum value hold value is reduced to 1/1 of the peak value of the abnormal peak signal.
If the pass band of the low-pass filter 3 is set to 0.5 kHz or less, the influence can be suppressed to 1/20 or less of the peak value.

A reset switch SW1 is connected to the peak hold circuit 4, and the switch SW1 is connected to the reset switch SW1.
By using 1, the maximum value of the signal light input 20 held in the peak hold circuit 4 can be reset. As a result, it is possible to deal with a case where the level of the normal light input value is changed to be lower than the previous use value due to the change of the light level in the system, the change of the use place, or the like.

The offset value V2 is determined in consideration of the fluctuation of the input signal. For example, if there is a possibility that the level of the input fluctuation during normal operation may be lowered by 6 dB, the margin is considered by 3 dB. The offset value is set to a value 9 dB lower than the standard input level during normal operation. As a result, the signal light input value for switching the gain of the optical amplifier is set to a value 9 dB lower than the optical input during normal operation.

In this case, the illustrated optical amplifier causes the abnormal peak value of the optical output 22 to reach the worst value of 9 dB even if the size of the signal optical input 20 is instantly returned to the original value after the decrease of the signal optical input 20. Can be suppressed to increase.

FIG. 2 is a diagram showing an example in which the components for automatically switching the optical amplifier according to the embodiment of the present invention to a low gain are configured by analog circuits. 2, PD1 is a light receiver, LA1 is a log amplifier (logarithmic amplifier), A1 to A5 are operational amplifiers, and other reference numerals are the same as those in FIG.

FIG. 2 shows the photodetector circuit 2- in FIG.
1, the circuit configurations of the low pass filter 3, the peak hold circuit 4, the adder circuit 5, and the comparator 9 are shown in each block.

In FIG. 2, the voltage V1 applied to the photodetector PD1 is -5.2V, and the input light 21 separated by the optical coupler 1-1 is converted into an electric signal by the photodetector PD1. The band of the photodetector PD1 is 1 MHz. The operational amplifier A1 in the light receiver circuit 2-1 has a resistor R
1 (for example, 4.3 kΩ) is installed and the light receiver P
The output signal from D1 is amplified by the operational amplifier A1 and input to the log amplifier LA1.

The log amplifier LA1 replaces the input signal in dB units and inputs the output to the low pass filter 3. The characteristics of this filter are that the connection resistance R2 (for example, 10 kΩ) to the operational amplifier A2 and the resistance R3 (for example, 10 kΩ).
kΩ), capacitance C1 (for example, 0.032 μF), capacitance C
By setting 2 (for example, 0.032 μF),
When the cutoff frequency is determined and has the values shown in parentheses, the cutoff frequency f = 0.5 kHz or less is passed. The low-pass filter applies a signal component in the high frequency range above the cutoff frequency of 12 dB /
Decrease with octave.

This low-pass filter 3 has 10d in the previous stage.
Even if an abnormal peak signal of about B is generated and this signal is input, the detection level passed through the low pass filter 3 is 1 dB.
It is possible to suppress the increase within. In addition, log amp L
The A1 and the low pass filter 3 may be arranged opposite to each other.

The signal passed through the low pass filter 3 is then input to the peak hold circuit 4. The peak hold circuit 4 includes diodes D1, D2, and D3, and is configured by connecting a capacitor C3 (for example, 0.1 μF) to the input stage of the operational amplifier A3. Then, feedback is applied through the resistor R5 (for example, 500 kΩ) to the diode D2.
Compensating for the leak current of the resistor R4 (for example, 20 kΩ)
The offset voltage of the operational amplifier A2 is compensated by applying feedback to the operational amplifier A2 at the previous stage via the.
The peak hold value is held in the capacitor C3 and is reset by short-circuiting the switch SW1.

The output of the peak hold circuit 4 is input to the adder circuit 5, and is input to the operational amplifier A4 via the resistor R6 (for example, 10 kΩ). To this input, an offset voltage V2 (for example, -1 V as -10 dB equivalent to normal signal light input) is input via a resistor R7 (for example, 10 kΩ). Since the operational amplifier A4 is operated as an adder circuit, the resistor R8 (10) having the same value as the resistor R7 is used.
Feedback is applied by kΩ). The output of the adder circuit 5 corresponds to the signal light input value for switching the gain of the optical amplifier.

The output of the adder circuit 5 is input to the comparator 9. The signal from the photodetector circuit 2-1 is input to the comparator 9 in the opposite polarity of the operational amplifier A5.
Compares the magnitude with the signal value from the adder circuit 5. Since the comparator 9 is an open loop, when the magnitude relationship between both inputs is reversed, the comparator 9 outputs a bipolar limit voltage. In this example, the output voltage V3 becomes a negative limit voltage during normal operation, and when the signal light input value falls below the input value for switching the gain of the optical amplifier, the output voltage V3 becomes a positive limit voltage.

The output voltage V3 of the comparator 9 is used to control the control method changeover switch 11 shown in FIG. 1 in accordance with the polarity of the limit voltage and switch the method of driving the excitation light source.

In the optical amplifier configured as described above, the offset voltage V2 is set to, for example, -6 dB corresponding to the normal signal light input, and the signal light input in the normal use state is -3 dBm. , The optical output is controlled to be constant at +10 dBm. And
When the level of the signal light input is reduced to −10 dBm with a pulse width of 10 ms, the optical amplifier is controlled to be switched to a constant gain state of, for example, 8 dB.

In this state, when the signal light input momentarily returns to the normal level of -3 dBm,
The optical amplifier will produce an abnormal peak output with an initial peak value of +5 dBm and a transient time constant of 70 μsec.
This abnormal peak output is lower than the normal light output, and it does not damage the receiver that receives this light output or pose a danger to people around. In addition, the optical amplifier having the above-mentioned configuration has a normal level of the output optical input of −3d
The slower the return to Bm, the smaller the abnormal peak output value becomes.

The circuit operation of the optical amplifier controlled to the constant gain state is restored for a time longer than the abnormal peak relaxation time,
The recovery of the signal light input value may be detected by setting a timer in a circuit similar to the setting of the switching value to the constant gain, and switching to the constant light output control.

One embodiment of the present invention described with reference to FIG.
Although the present invention has been described as being configured by an analog circuit, the present invention provides an A / D converter in the subsequent stage of the photodetector circuit 2-1 in FIG. 2 and processes the converted digital signal using a program. Thereby, the operation similar to the analog circuit can be realized by the digital circuit although the processing speed becomes slow.

Although the above-described embodiment of the present invention has been described as being applied to a fiber type optical amplifier, the present invention can also be applied to a semiconductor optical amplifier.

According to the above-described embodiment of the present invention, the maximum value of the average optical input value is held for a certain period of time, and the input value which is lower than the held value by a certain level is set as the threshold value. When the optical input value below the threshold value is detected, the gain of the amplifier is controlled to be decreased, so the optical input value for switching the gain of the optical amplifier to a low value is set according to the optical input during normal use. The gain can be automatically adjusted and the gain of the optical amplifier can be switched to a low value without requiring human intervention.

Therefore, according to the above-described embodiment of the present invention, the abnormal peak light output can be suppressed, and the optical output melts the coupling part of the optical fiber or receives the light output. It is possible to prevent the destruction, and it is also possible to prevent the surrounding people from being dangerous.

[0044]

As described above, according to the present invention, the abnormal peak light output of an optical amplifier used in a communication system or the like can be suppressed, and the optical output melts the coupling portion of the optical fiber, or (EN) Provided is a highly versatile and safe optical amplifier capable of preventing a receiver that receives an optical output from being destroyed, and also preventing danger to surrounding people. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical amplifier according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example in which a component for automatically switching to a low gain of an optical amplifier according to an embodiment of the present invention is configured by an analog circuit.

[Explanation of symbols]

 1-1, 1-2 Optical coupler 2-1, 2-2 Light receiver circuit 3 Low pass filter 4 Peak hold circuit 5 Adder circuit 6 Wavelength multiplexing module 7 Pumping light source 8 Pumping light source driving circuit 9 Comparator 10 Low gain setting Value 11 Control method change switch 12 Output constant control circuit 13 Optical fiber for amplification A1 to A5 Operational amplifier LA1 Log amplifier PD1 Light receiver

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H04B 10/17 10/16 H04L 25/03 D 9199-5K (72) Inventor Ichiro Yokota Yokohama, Kanagawa 216 Totsuka-cho, Totsuka-ku, Hitachi, Ltd.In the information and communications business division, Hitachi, Ltd. (72) Inventor Junya Kosaka 216, Totsuka-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture In-house information and communications division, Hitachi, Ltd. (72) Inventor Yoshiaki Sato Tokyo 1-1-6 Uchisaiwaicho, Chiyoda-ku, Nihon Telegraph and Telephone Corporation (72) Inventor Kazuo Aida 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. An average signal within a predetermined time in an optical amplifier in which the optical output is controlled to be constant without varying the optical output value with respect to a slight fluctuation of the signal light input value. The optical input value is detected, the average maximum value of the optical input value is held for a certain period of time, and the value that is lower than the held value by a certain level is set as a threshold value. An optical amplifier, which reduces the gain of the optical amplifier when a value is detected. 2. An optical amplifier in which an optical output value is controlled to be constant without varying the optical output value with respect to a slight fluctuation of the signal optical input value, and a part of the signal optical input is separated. A receiver circuit that receives light, a modulation signal of the output of the receiver circuit, a low-pass filter that removes the effect of an abnormal peak in the previous stage, and a peak that holds the maximum value of the averaged values of the signals that have passed through the filter. A hold circuit, an adder circuit that adds a predetermined offset value to the value held in the peak hold circuit, and a comparator that compares the output value of the adder circuit with the output value of the photodetector circuit An optical amplifier which reduces the gain of the optical amplifier based on a comparison result by the comparator.