JP2008141366A - Optical amplification system for suppressing optical surge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplification system having optical surge suppressed and having a simple configuration, which is capable of reducing the amount of optical surge output at the time of rise of input light by switching a signal input to an output regularizing circuit when variance in input light power occurs. <P>SOLUTION: The optical amplification system for use in optical communication etc. which includes at least an optical amplification part, an input light power monitor, an input interruption detection circuit, an input interruption protection circuit, and a gain control means, is provided with: an output light power monitor, an electric signal switch, and the output regularizing circuit; and a control circuit in which the electric signal switch disposed between the output light power monitor and the output regularizing circuit performs switching from a signal output from the output power monitor to a pseudo output light power signal output from the input interruption detection circuit when the input interruption detection circuit detects an input light interruption. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical amplification system mainly used in optical communication and the like.

  Optical amplifiers are mainly used in optical communications, and play an important role in other fields such as measurement and analysis. Typical optical amplifiers include a Raman amplifier, a waveguide optical amplifier in which a rare earth is added to a glass waveguide, and an optical fiber amplifier in which a rare earth is added to an optical fiber.

  An optical amplification system configured to bring an optical amplification medium to which a rare earth element is added into an excited state with excitation light and amplify signal light by stimulated emission generated in the optical amplification medium is known.

  In the basic configuration of the optical amplification system, an output stabilization control circuit (hereinafter referred to as an ALC control circuit) is mounted in order to prevent the output variation due to aging of the optical amplifier and the environment. Also, when the input light of the optical amplifier is interrupted, it is in a strong excitation state, and when the input light recovers, a strong light pulse is generated, and there is a risk of damaging the optical elements in the subsequent stage and the optical amplifier itself (patent document) 1).

  For this reason, a normal optical amplifying system monitors the status of input light and, when the input light falls below a certain power level, determines whether the input light power has fallen below a predetermined value (input break detection). Circuit) and a protection circuit that suppresses or stops the drive current of the excitation light source when the input interruption detection circuit detects an input interruption (hereinafter referred to as an input interruption protection circuit).

  An optical amplification system used in optical communication is required to quickly operate normally when the input light recovers from a predetermined power or lower. 2A to 2D are explanatory diagrams showing optical characteristics of an optical amplification system having an input disconnection protection circuit. In particular, FIG. 2A shows the input optical power, FIG. 2B shows the output optical power, FIG. 2C shows the drive current of the pump LD, and FIG. 2D shows the output power. It is a figure which shows the electrical operation | movement of an ALC control circuit from a monitor.

  When the input light interruption state occurs as shown in FIG. 2A, the input interruption protection circuit operates and the output optical power becomes zero as shown in FIG. The ALC control circuit adjusts the pumping power according to the strength of the optical signal to make the output power constant. When the input light is interrupted, the ALC control circuit controls to increase the gain because the output light power is smaller than the set output light power value. When the input light is restored, the maximum drive current is passed through the pumping LD of the device that controls the gain of the optical amplifier. As a result, an abnormally high output optical power (hereinafter referred to as an optical surge) is output instantaneously.

As a method for suppressing an optical surge, it is known that the rise time of an optical signal is sufficiently longer than the relaxation time constant of an optical amplifier in an optical transmitter. However, since it takes time to start up the system, it cannot be used in optical communication. For this reason, a method for solving an optical surge in an optical amplification system that quickly operates normally has been proposed (see Patent Documents 3 to 5).
Japanese Patent Laid-Open No. 2002-141592 Japanese Patent No. 2651086 JP-A-7-240717 JP 2003-78485 A Japanese Patent Laid-Open No. 9-31095

  When the input optical power becomes very low, the ALC-controlled optical amplification system according to the prior art is controlled to keep the output optical power constant, and thus the gain is high. When the original input optical power is recovered from the low input optical power state, the optical amplifier system maintains a high gain, and thus the optical amplification system outputs an optical surge.

  The optical surge has a problem that the coupling part such as the optical fiber of the optical amplification system may be melted or the light receiving part that receives the optical surge may be destroyed. In some cases, this light surge is dangerous for the surrounding people.

  The width of the input optical power to the optical amplifier installed in the optical communication system is not so wide. JP-A-7-240717 and JP-A-9-331095 switch the gain of an optical amplifier in accordance with a plurality of input light conditions of an installed optical communication system. By setting the input light power value to be switched to a slightly lower power than normal input light, there is no extreme difference between the input light for gain switching and the input light at the time of recovery, and the optical surge can be kept low. it can.

  However, when the input signal changes abruptly, the response of the optical amplifying medium to the change in pumping light power is slow, which causes a problem that the output optical power cannot be kept constant. Therefore, the optical surge cannot be completely suppressed. . Furthermore, since it is necessary to prepare several setting values according to the input state, the circuit scale becomes large.

  Further, in Japanese Patent Application Laid-Open No. 2003-78485, since the light amount from the laser diode always emits auxiliary light, noise and errors may occur in the system at the subsequent stage.

  Simple configuration that can switch the signal input to the output stabilization circuit and reduce the amount of optical surge output at the rising edge of the input light when there is such a problem and fluctuations in the input optical power occur No optical amplification system has yet been obtained.

The present invention relates to an optical amplification system used for optical communication including at least an optical amplification unit, an input optical power monitor, an input interruption detection circuit, an input interruption protection circuit, and a gain control means.
An output optical power monitor, an electrical signal switch, and an output stabilization circuit, and when the input disconnection detection circuit detects an input light disconnection, an electrical signal switch disposed between the output optical power monitor and the output stabilization circuit, An optical amplification system comprising: a control circuit that switches a signal input to an output stabilizing circuit from a signal output from an output power monitor to a pseudo output optical power signal output from an input break detection circuit.

  In addition, the pseudo output optical power signal input to the output stabilization circuit when the input disconnection detection circuit determines that the input light disconnection is greater than the set output optical power value that is the optical output power determined by the output stabilization circuit, The optical amplification system is characterized in that the signal can obtain a large output optical power.

  The optical amplification system described above, wherein the output stabilization circuit is configured by a differential amplifier, and the differential amplifier is not electrically saturated by the pseudo output optical power signal when the input cutoff detection circuit detects an input cutoff. It is.

  Further, when the input interruption detection circuit detects the recovery of the input light, the electrical signal switching unit converts the signal input to the output stabilizing circuit from the pseudo output optical power signal output by the input interruption detection circuit to the output power monitor. The optical amplification system is characterized by having a delay time of 1 microsecond to 10 milliseconds for switching to the output signal.

  The present invention is a light with suppressed optical surge that can switch the signal input to the output stabilization circuit and reduce the amount of optical surge output when the input light rises when fluctuations in input optical power occur. An amplification system is provided.

  In the present invention, when the fluctuation of the input optical power occurs, the signal input to the output stabilizing circuit is switched, and the ALC control is performed so as to reduce the energy (pumping light) injected into the optical amplification fiber. It is possible to reduce the amount of light surge output at the time of rising of input light without changing the configuration of ALC control.

  First, the first of the present invention will be described in detail. In the optical amplification system, when the input interruption detection circuit detects the interruption of the input light in response to the signal from the input light monitor (hereinafter referred to as the input light interruption state), the signal from the input interruption detection circuit is received, An input disconnection protection circuit disposed between the output stabilizing circuit and the gain control means suppresses the drive current of the gain control means.

  At this time, the gain control means is in a standby state. The excitation LD that constitutes the gain control means stops emitting light. At the same time, an electrical signal switch placed between the output optical monitor and the output stabilization circuit receives the signal from the input disconnection detection circuit and converts the signal input to the output stabilization circuit to the output optical power from the output optical power monitor. The signal is switched to the pseudo output optical power signal from the input break detection circuit.

  The second aspect of the present invention is characterized in that the pseudo output optical power signal input to the output stabilizing circuit is larger than the set output optical power value set by the output stabilizing circuit.

  The output stabilizing circuit compares the pseudo output optical power signal with the set output optical power value, and sends a signal to the gain control means so as to converge to the set output optical power value. At this time, the pseudo output optical power signal must satisfy [pseudo output optical power signal> set output optical power value]. In [Pseudo Output Optical Power Signal> Set Output Optical Power Value], the output stabilizing circuit performs ALC control so that the gain control means decreases the pumping LD current. When the input break detection circuit detects recovery of input light, the excitation LD current recovers from a small drive current to a large drive current. Therefore, supply of excess excitation light can be suppressed, and an optical surge of the optical amplifier can be suppressed.

  The third aspect of the present invention is characterized in that the output stabilizing circuit is an analog circuit using a differential amplifier. The differential amplifier receives a pseudo output optical power signal when the input light is interrupted. The pseudo output optical power signal is [pseudo output optical power signal> set output optical power value]. The signal output from the differential amplifier is always smaller than the set output optical power value. Therefore, the difference amplifier does not become electrically saturated.

  According to a fourth aspect of the present invention, when the input break detection circuit detects the recovery of the input light, the electrical signal switch outputs the signal input to the output stabilization circuit from the pseudo output optical power signal from the input break detection circuit. The output optical power signal from the optical power monitor is switched with a delay time of 1 microsecond to 10 milliseconds. When an optical amplifying medium to which rare earth is added is used as the optical amplifying unit, the response of the optical amplifying medium to the change in pumping light power is slow, so that it may be overexcited and cause an optical surge. By preparing a delay time in the control circuit, an optical surge in the optical amplification system can be suppressed.

  The optical amplifying unit can be composed of a WDM that combines signal light, an optical amplifying medium that has an amplifying function, an optical isolator that suppresses return light of output light, and the like. Optical components can be added to this configuration as necessary.

  As the optical amplification medium, quartz glass, quartz-based oxide glass, phosphate glass, bismuthate glass, tellurite glass, fluoride glass, phosphate crystal, oxide ceramics, and the like can be used.

  The shape of the optical amplification medium can be a planar waveguide, a flat plate shape, a slab shape, a fiber shape, or the like.

  FIG. 1 is a block diagram of an optical amplification system showing the basic configuration of the present invention. An optical amplification unit 101 that amplifies input light; an input optical power monitor 102 that monitors input light input to the optical amplification unit 101; an input break detection circuit 103 that determines input optical power from the input optical power monitor 102; An input cutoff protection circuit 107 that controls the gain control means 106 in response to a signal from the input cutoff detection circuit 103, an output optical power monitor 104 that monitors the output light of the optical amplifier 101, and an output of the output optical power monitor 104 An output stabilizing circuit 105 that keeps optical power constant, and an electric signal that switches the signal input to the output stabilizing circuit 105 in the input light interruption state from the output optical power monitor 104 to the pseudo output optical power signal of the input interruption detection circuit 103 The signal switch 108 is configured.

  When the input light to the optical amplification unit 101 is cut off, the input break protection circuit 107 receives a signal from the input break detection circuit 103 and suppresses the drive current of the gain control means 106. Then, the electric signal switch 108 is switched to (2), and the pseudo output optical power signal is input to the output stabilizing circuit 105. At this time, the pseudo output optical power signal is preferably larger than the set output optical power value of the output stabilization circuit 105. That is, the output stabilizing circuit 105 recognizes that the output optical power from the optical amplifying unit 101 is larger than the set value, and preferably performs ALC control so that the gain control means reduces the gain.

  When the input light to the optical amplifier 101 is recovered, the input break detection circuit 103 receives the signal from the input optical power monitor 102 and determines the input optical power. The input disconnection protection circuit 107 allows the signal from the output stabilization circuit 105 to be input to the gain control means 106. Further, the electric signal switch 108 is switched to (1) with a delay time of 1 microsecond to 10 milliseconds so that the signal from the output optical power monitor 104 is input to the output stabilizing circuit 105.

  The output stabilizing circuit 105 receives the signal from the output light power monitoring means 104 and performs ALC control. In the input light interruption state, the output stabilization circuit 105 receives the pseudo output optical power signal from the input interruption detection circuit 103 and performs ALC control so as to reduce the gain. When the input light is recovered, the gain is controlled from a small state to a large state.

  FIG. 4 is a block diagram illustrating the configuration of the output stabilization circuit 105. The output stabilizing circuit 105 includes an output setting circuit 401 that sets the output optical power, a difference amplifier 402 that makes a difference between the values of the output power monitor 104 and the output setting circuit 401, and an LD driver 403 that adds current to the gain control means.

  5A to 5E are explanatory diagrams showing the electrical operation of the output stabilizing circuit 105 when the input light is interrupted in the present invention. 5A shows a signal from the output power monitor 104 in FIG. 5, FIG. 5B shows a signal from the output setting circuit 401 in FIG. 4, and FIG. 5C shows a difference amplifier 402 in FIG. 5D is a diagram illustrating a signal input to the LD driver 403, and FIG. 5E is a diagram illustrating a signal input to the gain control means 106 in FIG. .

  6A to 6E are explanatory diagrams showing the electrical operation of the output stabilizing circuit when the input light is interrupted in the ALC control described in Japanese Patent No. 2651086. 6A shows a signal from the output power monitor, FIG. 6B shows a signal of the set light output power value, and FIG. 6C shows the output power monitor and the set light output of FIG. FIG. 6D is a diagram showing a signal input to a differential amplifier for comparing power value signals, FIG. 6D is a diagram showing a signal input to an LD driver for driving the excitation LD, and FIG. 6E is an input to the excitation LD. It is a figure which shows the signal to be performed.

  In the conventional ALC control, as shown in FIG. 6D, when the input light cut-off state is entered and the supply of the pumping light to the optical amplifying unit is stopped, the differential amplifier is electrically saturated. When the input light is restored, the excitation LD is given a maximum output current as shown in FIG. Then, the excitation light corresponding to the maximum output current is input to the optical amplifying unit and causes an optical surge. In the present invention, the pseudo ALC operation is performed by inputting the pseudo output optical power signal to the output stabilizing circuit as described in claim 3. As a result, the difference amplifier 402 is not electrically saturated. As shown in FIG. 5D, when the input light is interrupted, electrical saturation of the differential amplifier 402 is suppressed by the pseudo output optical power signal. Since there is no electrical saturation of the differential amplifier 402, the maximum output current is not continued. As a result, an optical surge can be efficiently suppressed.

  3A to 3D are explanatory views showing optical characteristics of an optical amplification system in which an optical surge is suppressed. In particular, FIG. 3A shows the input optical power, FIG. 3B shows the output optical power, and FIG. 3C shows the drive current value flowing through the gain control means when ALC control is performed. FIG. 3 (D) is a diagram showing a signal input to the output stabilization circuit. In the present invention, when the optical amplifier is in the input light interruption state, the pseudo output optical power signal is input to the output stabilizing circuit. As a result, when the input light is interrupted as shown in FIG. 3A, the ALC control receives the pseudo output optical power signal and controls the gain control means 106 to reduce the gain as shown in FIG. . Therefore, as shown in FIG. 3C, the excitation LD, which is a gain control means, is controlled to reduce the drive current. When the input optical power is recovered, the pump LD is changed from a control for reducing the drive current to a control for increasing it with a delay time of 1 microsecond to 10 milliseconds. Therefore, an optical surge having a huge optical peak, which has been a problem, does not occur.

  Hereinafter, an example explains.

An optical amplifying medium in which a rare earth is added to an optical fiber is obtained. 0.25 mol% of the optical amplifying fiber 704 is ErF ₃ to the core, a fluoride fiber doped with CeF ₃ 5.0 mol% Connect silica fiber fusion, using a fiber module encapsulated in a stainless steel metal package. The fluoride fiber length is 1.5 m.

  The configuration of Example 1 is shown in FIG. The input light having a wavelength of 1.55 μm input from the optical transmitter to the optical fiber 705 is branched by a 5/95 two-branch coupler 714, 5% to the input light power monitor PD 715 and 95% to the optical isolator 706. Entered. The input light input to the optical isolator 706 is combined with the pump light from the pump LD 701 having a wavelength of 0.98 μm by the WDM coupler 703 and input to the optical amplification fiber 704. The optical amplifying fiber 704 accumulates ions at the upper level by the excitation light, and outputs light having the same wavelength and phase as the input light by stimulated emission by the input signal light to amplify the light. The output light of the optical amplifying fiber 704 is branched by a 1/99 two-branch coupler 708, and 1% is input to the PD 710 which is an output signal light power monitor and 99% is input to the output fiber 709. The output fiber 709 outputs amplified signal light having a wavelength of 1.55 μm.

  At this time, the input optical power monitor PD 715 converts the input optical power into an electric signal and inputs it to the differential amplifier 717. The difference amplifier 717 subtracts the value converted into the electric signal from the value set in the reference power circuit 716 and inputs the result to the transistor 718. In the transistor 718, if the input value from the differential amplifier 717 [electric signal from the PD 715−reference power value] is a positive value, a drive current is given to the excitation LD 701, and if the input value is a negative value, the excitation LD 701 suppresses the drive current. Will work. That is, when the input optical power input to the optical fiber 705 is larger than the desired power, the feedback gain from the LD driver 713 is given to the pumping LD 701 to perform ALC control. When the power is smaller than the desired power, the feedback gain from the LD driver 713 is not given to the pumping LD 701, and the pumping LD 701 is controlled to be below the oscillation threshold.

  On the other hand, the optical power input to the output optical power monitor PD 710 is converted into an electrical signal and input to the differential amplifier 712. The difference amplifier 712 subtracts the predetermined value set by the reference power circuit 711 from the value converted into the electric signal, and the driver optical circuit 713 supplies the pumping LD 701 so that the output optical power held by the difference amplifier 712 becomes a desired optical power. Give negative feedback gain. That is, when the amplified optical power is smaller than the desired power, the pumping LD 701 increases the pumping light power to increase the optical gain in the optical amplification fiber 704. When the power is higher than the desired power, the power of the pumping light is reduced by the pumping LD 701 to reduce the optical gain in the optical amplification fiber 704.

  In the ALC control, when the input light interruption state occurs, the input value from the differential amplifier 712 becomes smaller than the desired power, and the pumping LD 701 is controlled to increase the pumping light power. However, when the input light is interrupted, the transistor 719 switches from the signal of the PD 710 to the pseudo output optical power signal, and the pseudo output optical power signal is input to the differential amplifier 712. At this time, the pseudo output optical power signal is input such that a value obtained by subtracting a predetermined value set by the reference power circuit 711 is larger than a desired value. The differential amplifier 712 receives the pseudo output optical power signal and tries to give a feedback gain so that the pumping light power is reduced by the pumping LD 701. However, the ALC control from the differential amplifier 712 is not performed on the excitation LD 701 by the input cutoff control.

  When the input light is recovered and the optical amplification system starts to drive again, the transistor 719 switches the signal from the pseudo output optical power signal to the PD 710, and the feedback gain from the differential amplifier 712 is input to the pump LD 701, and ALC control is performed. . At this time, the feedback gain given to the pumping LD 701 is given to the pumping LD 701 the same negative feedback gain as in the input light interruption state for 1 millisecond after the input light is recovered. And it switches to ALC control corresponding to the signal from PD710. The differential amplifier 712 controls the excitation LD 701 so that the gain is changed from a small state to a large state.

  Next, the configuration used for the measurement is shown in FIG. It was converted into an electrical signal by the O / E converter 803 from the optical amplification system 802 of the present invention, and the output waveform was observed by the oscilloscope 804. The oscilloscope 804 is configured to receive a trigger signal from the optical transmitter 801 and observe a relative delay between the input light and the output light waveform. The drive current supplied to the excitation LD 701 was also observed with the oscilloscope 804 at the same time. The oscillation threshold value of the excitation LD 701 was 35 mA, and the standby current was set to 34 mA.

  The result of the output response when the input light is turned on / off is shown in FIG. The recovery of gain was 1.8 microseconds, there was no overshoot of the drive current of the pump LD, and no optical surge occurred.

  The present invention can be used not only in a communication system in the field of optical communication but also in an application field of optical transmission such as evaluation and measurement.

It is a block diagram which shows the structure of this invention. It is a figure which shows each part signal in the conventional ALC control. It is explanatory drawing which showed the optical characteristic of the optical amplification system which suppressed the optical surge. 3 is a block diagram illustrating a configuration of an output stabilization circuit 105. FIG. It is explanatory drawing which showed the electrical operation | movement of the output stabilization circuit 105 at the time of an input light interruption state. It is the figure which showed the electrical operation | movement of the output stabilization circuit at the time of the input light interruption state in the existing ALC control. 1 is a diagram illustrating a configuration of Example 1. FIG. It is a figure explaining the offensive of the measurement system of Example 1. FIG. It is a figure which shows the measurement result of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical amplifier 102 which amplifies input light Input optical power monitor 103 Input interruption detection circuit 104 Output optical power monitor 105 Output stabilization circuit 106 Gain control means 107 Input interruption protection circuit 108 Electric signal switch 401 Output setting circuit 402 Difference amplifier 403 LD driver 701 Excitation LD
702 Optical fiber 703 WDM coupler 704 Optical amplification fiber 705 Optical fiber 706 Optical isolator 707 Optical isolator 708 Two-branch coupler 709 Output fiber 710 PD
711 Reference power circuit 712 Difference amplifier 713 Driver circuit 714 Two-branch coupler 715 PD
716 Reference power circuit 717 Difference amplifier 718 Transistor 719 Transistor 801 Optical transmitter 802 Optical amplification system 803 O / E converter 804 Oscilloscope

Claims (4)

About an optical amplification system used for optical communication including at least an optical amplification unit, an input optical power monitor, an input interruption detection circuit, an input interruption protection circuit, and a gain control means,
An output optical power monitor, an electrical signal switch, and an output stabilization circuit, and when the input disconnection detection circuit detects an input light disconnection, an electrical signal switch disposed between the output optical power monitor and the output stabilization circuit, An optical amplification system comprising: a control circuit that switches a signal input to an output stabilizing circuit from a signal output from an output power monitor to a pseudo output optical power signal output from an input disconnection detection circuit. When the input interruption detection circuit detects an input optical interruption, the pseudo output optical power signal that is input to the output stabilization circuit is larger than the set output optical power value that is the optical output power determined by the output stabilization circuit. The optical amplification system according to claim 1, wherein the optical amplification system is a signal capable of obtaining optical power. 3. The output stabilizing circuit includes a differential amplifier, and the differential amplifier is not electrically saturated by a pseudo output optical power signal when the input disconnection detection circuit detects an input optical disconnection. Optical amplification system. When the input break detection circuit detects recovery of input light, the electrical signal switch outputs the signal input to the output stabilization circuit from the pseudo output optical power signal output by the input break detection circuit. 4. The optical amplification system according to claim 1, wherein switching to a signal has a delay time of 1 microsecond to 10 milliseconds. 5.

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