JP3557038B2 - Electric absorption type optical modulator drive circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electro-absorption optical modulator driving circuit for driving a semiconductor electro-absorption optical modulator used for optical communication.
[0002]
[Prior art]
The extinction ratio expressed in dB has a substantially linear relationship with the applied voltage in a semiconductor electro-absorption optical modulator. A laser beam of constant intensity is incident on the electro-absorption optical modulator, and a sinusoidal applied voltage is applied. In addition, a light pulse in the form of a transform limit can be generated. It is also possible to control the applied voltage by the transmission data and modulate the incident light by NRZ (non-return to zero) or RZ (return to zero).
[0003]
This electroabsorption type optical modulator has the advantage that the extinction ratio is large and the polarization dependence is small as compared with the LN modulator that has been widely used in the past. Also, due to the feature that the polarization dependency is small, application on the receiving side is considered to an optical DEMUX (demultiplexer) for extracting an optical signal of a desired channel from the time-division multiplexed optical signal.
[0004]
FIG. 8 shows an example of a conventional electric absorption type optical modulator driving circuit. The electric absorption type optical modulator driving circuit 101 includes a DC bias voltage source 102, an AC modulation voltage source 103, and a bias tee 104. The electroabsorption optical modulator 105 is driven by applying a voltage in a reverse bias region by the drive circuit 101 according to the purpose of use. In particular, since a large-amplitude modulation voltage is required for soliton pulse generation and optical DEMUX, the AC modulation voltage source 103 includes an amplifier 106 for increasing the amplitude of an AC signal.
[0005]
When such a conventional electro-absorption optical modulator driving circuit for driving an electro-absorption optical modulator is used, when the power of the driving circuit is turned on or off, the electro-absorption light modulator is turned off. The modulator was sometimes damaged.
[0006]
When a conventional electro-absorption type optical modulator drive circuit is used, and when one or more optical amplifiers are provided on the input side of the electro-absorption type optical modulator, when the power supply of the drive circuit is turned on and In some cases, the electroabsorption optical modulator may be damaged other than when the device is dropped.
[0007]
[Problems to be solved by the invention]
In a conventional electro-absorption type optical modulator drive circuit, the electro-absorption type optical modulator may be damaged when the power is turned on or when the power is turned off. Also, for an electro-absorption optical modulator having one or more optical amplifiers on the input side, the electro-absorption optical modulator may be damaged at times other than when the power is turned on and off.
[0008]
The present invention has been made in view of the above circumstances, and has a high reliability that can prevent the electroabsorption optical modulator from being damaged when the power supply of the drive circuit is turned on or when the power supply is turned off. It is an object of the present invention to provide an electro-absorption optical modulator driving circuit capable of realizing a high electro-absorption optical modulator.
[0009]
Further, the present invention can realize a highly reliable electro-absorption optical modulator that can prevent breakage of the electro-absorption optical modulator even when one or more optical amplifiers are provided on the input side. It is an object of the present invention to provide a type optical modulator driving circuit.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an electro-absorption optical modulator driving circuit for driving an electro-absorption optical modulator, wherein a DC bias voltage in a reverse bias direction of the electro-absorption optical modulator when an external power is supplied. A DC voltage source that generates an AC modulation voltage when an external power is supplied; the DC bias voltage generated by the DC voltage source; and the AC modulation generated by the AC voltage source. The voltage applied to the electro-absorption optical modulator is adjusted to a predetermined value by a bias tee applied to the electro-absorption optical modulator and a voltage applied to the electro-absorption optical modulator by the DC voltage source when the external power supply is started. Is connected to the bias tee, and when the external power supply is turned off, the AC voltage source is connected to the DC voltage source until the connection between the AC volt source and the bias tee is cut off. Ri, characterized in that the voltage applied to the electroabsorption optical modulator and means for holding a predetermined value or more.
[0011]
According to a second aspect of the present invention, in an electro-absorption optical modulator driving circuit for driving an electro-absorption optical modulator, when an external power is supplied, a direct current in a reverse bias direction of the electro-absorption optical modulator is provided. A DC voltage source for generating a bias voltage, an AC amplifier for amplifying an input AC modulation voltage when power is supplied, an AC amplifier power supply for supplying power to the AC amplifier when external power is supplied, When the DC bias voltage generated by the DC voltage source and the AC modulation voltage output from the AC amplifier are combined, a bias tee is applied to the electro-absorption optical modulator, and when the external power supply is started, Connecting the AC amplifier power supply to the AC amplifier after the voltage applied to the electroabsorption optical modulator by the DC voltage source exceeds a predetermined value, and turning off the external power supply Means for holding a voltage applied to the electro-absorption optical modulator by the DC voltage source to a predetermined value or more until the connection between the AC amplifier power supply and the AC amplifier is cut off. Features.
[0012]
Preferably, when the external power supply is started, the connection between the AC voltage source and the bias tee or the connection between the AC amplifier power supply and the AC amplifier is made with a delay provided by a circuit including a relay. It is characterized by.
[0013]
Preferably, when the external power supply is turned off, the DC bias voltage is held by a circuit including a capacitor.
The electro-absorption optical modulator is driven by applying a DC bias voltage and an AC modulation voltage in the reverse bias direction, and the extinction ratio of the electro-absorption optical modulator fluctuates according to the applied voltage. Modulates an optical signal incident on the optical modulator. Conventionally, when a power supply of a drive circuit is turned on or turned off, a cause of damage to the electro-absorption optical modulator is that a forward voltage is applied to the electro-absorption optical modulator when the power is turned on or off. It is thought that it is. That is, when the power supply of the drive circuit is turned on, the AC modulation voltage rises earlier than the DC bias voltage, and when the power supply of the drive circuit is turned off, the DC bias voltage falls earlier than the AC modulation voltage. A forward voltage is temporarily applied to the absorption type optical modulator, and the electroabsorption type optical modulator is damaged.
[0014]
Therefore, in the present invention (claims 1 and 2), when the power supply of the drive circuit is turned on, the DC bias voltage immediately rises, and the AC modulation voltage is applied such that the DC bias voltage in the reverse bias direction is equal to or more than a specific threshold value. By providing a control function to start up after that, it is possible to prevent a forward voltage from being applied to the electro-absorption optical modulator at any moment.
[0015]
Conversely, when the power supply of the drive circuit is turned off, the AC modulation voltage immediately falls, and the DC bias voltage has a function of charging the voltage in the reverse bias direction, and the DC bias voltage in the reverse bias direction gradually decreases. By doing so, it is possible to prevent a forward voltage from being applied to the electroabsorption optical modulator at any moment.
[0016]
According to a third aspect of the present invention, there is provided an electro-absorption optical modulator driving circuit for driving an electro-absorption optical modulator having an optical fiber amplifier on an input side, wherein the electro-absorption optical modulator is supplied when external power is supplied. A DC voltage source that generates a DC bias voltage in the reverse bias direction, an AC voltage source that generates an AC modulation voltage when external power is supplied, the DC bias voltage and the AC voltage generated by the DC voltage source. A bias tee applied to the electroabsorption optical modulator is combined with the AC modulation voltage generated by a source, and when it is detected that an optical signal incident on the electroabsorption optical modulator is interrupted, the AC Modulation voltage falls Protection means to prevent the power consumption in the electro-absorption optical modulator from increasing due to re-injection of optical signal And characterized in that:
[0017]
Preferably, it is possible to sense that the optical signal incident on the electroabsorption optical modulator is interrupted, to lower the AC modulation voltage, and then to reduce the DC bias voltage in the reverse bias direction.
[0018]
The power consumption in the electroabsorption optical modulator increases according to the magnitude of the applied voltage in the reverse bias direction and the magnitude of the light level of the optical signal incident on the electroabsorption optical modulator. Therefore, conventionally, when an optical signal having a large light level is incident on an electroabsorption optical modulator to which a voltage in a reverse bias direction is applied, the power consumption in the electroabsorption optical modulator becomes too large, and the electroabsorption optical modulator becomes too large. The absorber layer of the modulator is destroyed. A factor that causes an optical signal having a large optical level to enter the electroabsorption optical modulator is one or more optical amplifiers on the input side of the electroabsorption optical modulator. An optical amplifier is a device for compensating for optical loss due to transmission in an optical communication system. If an optical signal incident on the optical amplifier is interrupted for several ms or more, the optical signal re-entered for several ms thereafter is amplified. The rate increases. When this over-amplified optical signal is incident on the electro-absorption optical modulator, the power consumption in the electro-absorption optical modulator temporarily increases, and the electro-absorption optical modulator is increased. Is damaged. Due to the above factors, when one or more optical amplifiers are provided on the input side of the electro-absorption optical modulator, the possibility of breakage of the electro-absorption optical modulator increases.
[0019]
In the present invention (claim 3), in order to solve this problem, a control function is provided for lowering the AC modulation voltage when detecting that the optical signal incident on the electro-absorption optical modulator is interrupted. In response to the input of the optical signal over-amplified by the optical amplifier after the optical signal is cut off to the electro-absorption optical modulator, the power consumption in the electro-absorption optical modulator is prevented from increasing, and the electric absorption is prevented. Damage of the optical modulator can be prevented.
[0020]
According to a fourth aspect of the present invention, there is provided an electro-absorption optical modulator driving circuit for driving an electro-absorption optical modulator having an optical fiber amplifier on an input side, wherein the electro-absorption optical modulator is supplied when external power is supplied. A DC voltage source that generates a DC bias voltage in the reverse bias direction, an AC voltage source that generates an AC modulation voltage when external power is supplied, the DC bias voltage and the AC voltage generated by the DC voltage source. The AC modulation voltage generated by the source is adjusted, a bias tee applied to the electroabsorption optical modulator, and an absorption current flowing in the electroabsorption optical modulator are monitored, and the electroabsorption optical modulator is monitored. Means for lowering the AC modulation voltage when it is detected that the applied voltage is transferred in the forward direction.
[0021]
2. Description of the Related Art Conventionally, in an electroabsorption optical modulator, a forward voltage may be applied when an AC modulation voltage increases and a DC bias voltage in a reverse bias direction decreases. As described above, when a forward voltage is applied to the electroabsorption optical modulator, it causes damage. When the voltage applied to the electroabsorption optical modulator is transferred in the forward direction, the absorption current tends to flow in the reverse direction, so that the absorption current value decreases.
[0022]
In the present invention (claim 4), the absorption current monitor senses this phenomenon and provides a control function for lowering the AC modulation voltage, thereby preventing the forward voltage from being applied to the electroabsorption optical modulator. .
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the invention will be described with reference to the drawings.
(1st Embodiment)
The first embodiment is directed to a driving circuit that drives an electro-absorption optical modulator with a DC bias voltage and an AC modulation voltage. When a power supply of the driving circuit is started, the AC modulation voltage is slower than the DC bias voltage. When the power supply of the drive circuit is turned off, the AC modulation voltage immediately falls, and the DC bias voltage is maintained and gradually falls. The forward voltage is not applied even at an instant.
[0024]
FIG. 1 is a block diagram showing in principle the electro-absorption optical modulator drive circuit according to the present embodiment.
The electroabsorption optical modulator driving circuit 1 shown in FIG. 1 includes a DC bias voltage source 2, an AC modulation voltage source 3, a bias tee 4 for adjusting the DC bias voltage and the AC modulation voltage, and a rise / fall characteristic of the DC bias voltage. A control circuit 8a for adjusting and controlling ON / OFF of the AC modulation voltage source 3 is provided. The AC modulation voltage source 3 includes an AC amplifier 6 as necessary. The control circuit 8a detects a charging circuit 7 for charging a DC bias voltage, a switch 10a of an AC relay, and a charging voltage of the charging circuit 7, and performs DC bias voltage detection for controlling opening and closing of the switch 10a according to the detection result. It comprises a vessel 9.
[0025]
The control circuit 8a detects the DC bias voltage charged in the charging circuit 7 by the voltage detector 9, and when the voltage becomes equal to or higher than a predetermined threshold value in the reverse bias direction, that is, the predetermined bias voltage in the reverse bias direction. When it is detected that a DC bias voltage higher than the threshold value is applied to the electro-absorption optical modulator 5, the switch 10a is turned on and the AC modulation voltage source 3 is connected to the bias tee 4. The switch 10a is turned off to disconnect the AC modulation voltage source 3 from the bias tee 4. When the switch 10a is turned from the OFF state to the ON state, it is preferable to provide a predetermined delay from the sensing to the ON state, and when the switch 10a is turned from the ON state to the OFF state, it is preferable to immediately shut off the switch.
[0026]
In FIG. 1, when a power supply (not shown) of a drive circuit 1 rises, a charging circuit 7 is charged by a DC bias voltage source 2, and this charging voltage is applied to an electro-absorption optical modulator 5 from a bias tee 4. . When the charging voltage gradually increases and exceeds a predetermined threshold value in the reverse bias direction, after a predetermined delay is provided by the voltage detector 9, the switch 10a is closed, and the AC modulation voltage source 3 is connected to the bias tee 4. Connected to. Only at this point, the DC bias voltage and the AC modulation voltage are combined and applied to the electroabsorption optical modulator 5.
[0027]
Therefore, when the power supply (not shown) of the drive circuit 1 rises, only the AC modulation voltage is not applied to the electroabsorption optical modulator 5, and the AC modulation voltage is applied only in the reverse bias direction. Since the DC bias voltage becomes sufficiently large, no forward voltage is applied to the electro-absorption optical modulator 5.
[0028]
On the other hand, in FIG. 1, when the power supply of the drive circuit 1 falls, the switch 10a is turned off by the control circuit 8a and the AC modulation voltage is immediately cut off, but the DC bias voltage is the voltage charged in the charging circuit 7. Gradually fall while being discharged by the electroabsorption optical modulator 5.
[0029]
Therefore, the DC bias voltage does not fall earlier than the AC modulation voltage, and no forward voltage is applied to the electro-absorption optical modulator 5.
(Second embodiment)
Next, a second embodiment will be described.
[0030]
The AC relay used for the switch of the AC modulation voltage in the first embodiment is relatively expensive because it requires a wide band, and the like, but an AC amplifier whose output immediately drops due to the cutoff of the power supply is used. Then, an inexpensive DC relay can be used. In this embodiment, an electric absorption type optical modulator driving circuit using a DC relay will be described.
[0031]
FIG. 2 is a block diagram showing in principle the electro-absorption optical modulator driving circuit according to the present embodiment.
The electroabsorption optical modulator driving circuit 1 of FIG. 2 is basically the same as that of the first embodiment, but replaces the AC relay 10a of FIG. It is inserted between the amplifiers 6.
[0032]
The control circuit 8a senses by the voltage detector 9 that the DC bias voltage in the reverse bias direction is applied to the electroabsorption optical modulator 5 by a predetermined threshold value or more, adds a delay by the relay 10b, and adds an AC amplifier. The power supply 11 is connected to the AC amplifier 6.
[0033]
According to the present embodiment, similarly to the first embodiment, a forward voltage is applied to the electro-absorption optical modulator 5 both when the power supply of the drive circuit 1 rises and when it falls. Not done.
[0034]
By the way, in addition to the first embodiment and the second embodiment, it is conceivable to use a sequential circuit based on a logic circuit as a circuit for controlling the order of rise and fall of the DC bias voltage and the AC modulation voltage. However, the power supply of the sequential circuit itself is shut down in an emergency such as a breaker cutoff or a power outage, so that the fall order cannot be controlled and cannot cope. On the other hand, when the charging circuit using the capacitor is provided in the first embodiment or the second embodiment, the charging function of the capacitor is not lost even if a power failure occurs, and the DC bias voltage is set to be smaller than the AC modulation voltage. Can be shut down late. That is, as a function capable of protecting against any situation, a mode using a capacitor in a charging circuit is excellent.
[0035]
(Third embodiment)
Next, a third embodiment will be described.
In the present embodiment, in an electroabsorption optical modulator having one or more optical amplifiers on the input side, when an optical signal incident on the electroabsorption optical modulator is interrupted, this is sensed and AC is detected. The modulation voltage is lowered to prevent the voltage applied to the electro-absorption optical modulator from drastically flowing in the reverse direction, and the optical signal over-amplified by the optical amplifier is re-entered to reduce the consumption in the electro-absorption optical modulator. A protection function for preventing an increase in power is provided.
[0036]
FIG. 3 is a block diagram showing a configuration of the electro-absorption optical modulator driving circuit according to the present embodiment.
3 includes a DC bias voltage source 2, an AC amplifier 6, an AC amplifier power supply 11, a bias tee 4 for adjusting the DC bias voltage and the AC modulation voltage, and a control circuit 8b. An optical amplifier 12 is connected to the input side of the electro-absorption optical modulator driving circuit 1.
[0037]
The control circuit 8b monitors an absorption current in the relay 10b and the electro-absorption optical modulator 5, and controls an ON / OFF of the relay 10b based on the absorption current value, and an attenuation for reducing the DC bias voltage. It comprises a vessel 14.
[0038]
The power consumption in the electroabsorption optical modulator 5 increases according to the magnitude of the light level of the optical signal incident on the electroabsorption optical modulator 5 and the magnitude of the applied reverse bias voltage. If the value of the absorption current decreases when a voltage is applied to the electro-absorption optical modulator 5, the optical signal incident on the electro-absorption optical modulator 5 is interrupted. Therefore, in the absorption current monitor circuit 13, when the absorption current value falls below a predetermined threshold value, it is determined that the optical signal incident on the electroabsorption optical modulator 5 has been interrupted, and the relay 10b controls the AC amplifier power supply 11 The control circuit 8b operates so as to cut off the supply of the voltage to the AC amplifier 6 from.
[0039]
When the optical signal over-amplified by the optical amplifier 12 enters the electro-absorption optical modulator 5 after the optical signal is cut off, the electro-absorption optical modulator 5 receives only the DC bias voltage in the reverse bias direction. Since the voltage is applied, the power consumption does not increase so much, and the electroabsorption optical modulator 5 is not damaged.
[0040]
Further, in the present embodiment, in order to cope with a case where the over-amplification of the optical amplifier 12 is very large and the power consumption in the electro-absorption optical modulator is still too large just by lowering the AC modulation voltage, After the AC modulation voltage falls, a control to reduce the DC bias voltage in the reverse bias direction by the attenuator 14 is added. As a result, even for an over-amplified optical signal input from the optical amplifier 12, it is possible to prevent the power consumption in the electro-absorption optical modulator 5 from increasing, and to provide higher reliability. .
[0041]
When the applied voltage, which is the sum of the DC bias voltage and the AC modulation voltage in the reverse bias direction, is applied in the forward direction in the electroabsorption optical modulator 5, the flow of the absorption current is reversed, and the absorption current decreases. This phenomenon can be detected by the absorption current monitor 13 of the present embodiment. Therefore, by controlling the AC modulation voltage to fall before the applied voltage of the electroabsorption optical modulator 5 largely transfers in the forward direction, the electroabsorption optical modulator 5 receives only the DC bias voltage in the reverse bias direction. Such can be done. This can prevent a forward voltage from being applied to the electroabsorption optical modulator 5 and prevent breakage.
[0042]
(Fourth embodiment)
Next, a fourth embodiment will be described.
Spontaneous emission light (ASE) of an optical amplifier provided on the input side of the electro-absorption optical modulator always enters the electro-absorption optical modulator. When the ASE is large, the difference between the magnitude of the absorption current when the optical signal is incident and the magnitude of the absorption current when the optical signal is not incident is not so remarkable. It can be difficult to sense if you are disconnected. When the ASE of the optical amplifier is large as described above, instead of monitoring the absorption current, a clock component is extracted from the optical signal before entering the electro-absorption optical modulator, and the clock component is monitored. It is preferable or necessary to reliably sense that the optical signal has been interrupted. In the present embodiment, an electro-absorption optical modulator driving circuit that performs control based on the above-described clock component extraction will be described.
[0043]
FIG. 4 is a block diagram showing in principle the electro-absorption optical modulator drive circuit according to the present embodiment.
In this embodiment, an optical coupler 15 is inserted on the input side of the electro-absorption optical modulator 5 in the third embodiment, and a clock extraction circuit 16 is provided instead of the absorption current monitor 13 in FIG.
[0044]
The incident light before being incident on the electroabsorption optical modulator 5 is sent from the optical coupler 15 to the clock extracting circuit 16 to extract a clock component. At this time, if an optical signal is incident, a clock component can be extracted. However, if the optical signal is interrupted, a clock component cannot be extracted because only ASE exists. If it is detected that the optical signal has been cut off because the clock component could not be extracted, the relay 10b is turned off by the control circuit 8c, and the supply of the AC amplifier power supply 11 to the AC amplifier 6 is cut off. The DC bias voltage in the bias direction is reduced by the attenuator 14. As a result, it is possible to suppress an increase in power consumption in the electro-absorption optical modulator 5 with respect to the re-incident over-amplified optical signal and prevent the electro-absorption optical modulator 5 from being damaged.
[0045]
It should be noted that the ASE of the optical amplifier 12 on the input side of the electroabsorption optical modulator 5 has a large problem mainly on the receiving side where the optical signal level is low.
(Example of Circuit of Third Embodiment)
Next, an example of a specific circuit configuration of the electro-absorption optical modulator driving circuit according to the third embodiment will be described. Here, the function of delaying the application of the AC modulation voltage to the electroabsorption optical modulator 5, the charging function provided for the fall of the DC bias voltage, the function of lowering the AC modulation voltage from the absorption current monitor, and the like are described. This will be described based on a specific circuit example.
[0046]
FIG. 5 is an example of a circuit diagram of the electro-absorption optical modulator drive circuit according to the third embodiment. This electric absorption type optical modulator drive circuit includes four power supplies -VCC1, -VCC2, + VCC3 and -VCC4, an AC signal amplifier 6, a bias tee 4, a relay 10b, resistors R1 to R6, variable resistors VR1 and VR2. , Differential amplifiers IC1 and IC2, capacitors C1 to C4, diodes CD1 and CD2, Zener diodes Z1 and Z2, and transistors TR1 to TR4.
[0047]
In FIG. 5, first, when an external power supply (not shown) is applied to the drive circuit 1, the power supplies -VCC1, -VCC2, + VCC3, and -VCC4 rise. -VCC1 is the DC bias voltage source 2 in FIG. 3, and is applied as a DC bias voltage to the electroabsorption optical modulator 5 via the diode CD2, the transistor TR1, the resistor R1, and the bias tee 4 immediately after the power supply rises. You. The diode CD1 protects the DC bias voltage from becoming a forward voltage. With respect to this DC bias voltage value, the maximum voltage value is determined by the two Zener diodes Z1 and Z2, and the voltage value applied by the variable resistor VR1 is varied.
[0048]
As for the AC modulation voltage, when power is supplied to the AC amplifier 6, an AC signal is applied to the electro-absorption optical modulator 5 via the AC amplifier 6 and the bias tee 4. The + VCC3 power supply of the amplifier 6 is the AC amplifier power supply 11 of FIG. 3, and is shut off by the relay 10b when the power is turned on. In this relay 10b, in order for + VCC3 to flow to the amplifier 6, a predetermined voltage or more is applied to the base of the transistor TR3, and the transistor TR3 needs to be turned on. This base voltage is obtained by connecting a DC bias voltage determined by two Zener diodes Z1 and Z2 via a resistor R3, a resistor R4, and a capacitor C2.
[0049]
When the DC bias voltage has a predetermined value or more, a voltage is applied to the base of the transistor TR3 with a delay given by the time constant of the resistor R3 and the capacitor C2, the transistor TR3 is turned on, the relay 10b is activated, and + VCC3 is turned on. The AC modulation voltage is supplied to the AC amplifier 6 and applied to the electro-absorption optical modulator 5. In the relay 10b, the response speed is several milliseconds, and + VCC3 is applied to the amplifier 6 with a further delay. That is, when the drive circuit power supply is turned on, the DC bias voltage is immediately applied to the electro-absorption optical modulator 5, but the AC modulation voltage is applied after the DC bias voltage has a predetermined voltage value or more. The voltage is applied after the delay is given by the time constant of the resistor R3 and the capacitor C2 and the relay 10b, and the forward voltage is not applied.
[0050]
In FIG. 5, when the power supply of the drive circuit 1 is turned off, -VCC1, -VCC2, + VCC3 and -VCC4 simultaneously fall. When + VCC3 of the AC amplifier power supply 6 falls, the AC amplifier 6 is also turned OFF, so that the AC modulation voltage immediately falls. On the other hand, the DC bias voltage gradually decreases while the electric charge stored by the capacitor C1 is discharged to the electro-absorption optical modulator 5. The larger the charge capacity of the capacitor C1, the longer the DC bias voltage is applied to the electro-absorption optical modulator 5.
[0051]
That is, when the power supply falls, the AC modulation voltage immediately falls, and the DC bias voltage gradually decreases due to the charging function of the capacitor, so that the forward voltage is not applied to the electro-absorption optical modulator 5. Absent. Even if -VCC1, which is a DC bias voltage source, falls earlier than other VCCs, the base voltage of TR3 falls, relay 10b is turned off, and power supply to AC amplifier 6 is cut off. The AC modulation voltage falls. By selecting the charge capacity of the capacitor C1 so that the amount of charge of the DC bias voltage in the capacitor C1 is sufficient for the time until the AC modulation voltage falls, the electroabsorption optical modulator 5 is never forwarded. Directional voltage can be prevented from being applied.
[0052]
Incidentally, since the absorption current flowing in the electroabsorption optical modulator 5 is equal to the current flowing in the resistor R1, the current flowing in the resistor R1 can be read by the differential amplifier IC1 to monitor the absorption current. When the light incident on the electro-absorption type optical modulator 5 is cut off, the absorption current value becomes small, and when it becomes lower than a predetermined threshold value provided in the resistor R6, the variable resistor VR2, and -VCC4, the transistor TR4 is turned off. State. When the transistor TR4 is turned off, the power supply to the AC amplifier 6 is cut off, and the AC modulation voltage falls. By using the transistor TR4 to switch ON / OFF the power supply, it is possible to realize a faster fall of the AC modulation voltage as compared with a mechanical switching method such as a relay. A problem with such switching of the power supply on / off is that a large rush power supply at the time of power supply switching destroys the PN junction of the transistor, but a capacitor C3 is inserted in parallel between the PNs. By doing so, a large inrush current can be suppressed, and damage to TR4 can be prevented.
[0053]
The circuit including the transistor TR4 and the capacitor C3 also has a function of protecting the contact of the relay 10b when the relay 10b is turned on and power is supplied to the AC amplifier 6. That is, at the moment when the contact of the relay 10b is closed and turned on, the transistor TR4 is turned off by the capacitor C3, and thereafter, the capacitor C3 is charged and the transistor TR4 is gradually turned on. This operation suppresses an increase in the rush current and protects the contacts of the relay 10b.
[0054]
The transistor TR2 is turned on by being delayed by the time constant of the resistor R5 and the capacitor C4 inserted on the base side, so that the Zener diode Z1 cannot maintain the Zener voltage, and the DC bias voltage value is changed to the AC modulation voltage. It becomes smaller later. With the reduced DC bias voltage value, the value of the Zener diode Z2 is selected so that the transistor TR3 is not turned on, the transistor TR3 is also turned off, and the AC modulation voltage is slower than the DC bias voltage after re-input of the optical signal. Try to get up. Even if the optical signal over-amplified by the optical amplifier 12 re-enters, the transistor TR2 is not immediately turned off due to the time constant of the resistor R5 and the capacitor C4, and the DC bias voltage does not rise instantaneously. The time constant values of the resistor R5 and the capacitor C4 are set such that the DC bias voltage rises after the over-amplification of the optical amplifier 12 has stopped. When the optical amplifier 12 is an Er-doped fiber amplifier, the time constant of the resistor R5 and the capacitor C4 is desirably set to 1 ms or more.
[0055]
FIG. 6 shows the rising of the point A indicating the DC bias voltage and the point B indicating the power of the AC amplifier 6 for generating the AC modulation voltage when the power supply of the electro-absorption optical modulator driving circuit 1 in FIG. Shows the difference.
[0056]
FIG. 7 shows the difference between the fall of the point A indicating the DC bias voltage and the fall of the point B indicating the power supply of the AC amplifier 6 when the power supply of the electroabsorption optical modulator drive circuit 1 in FIG. I have.
[0057]
As shown in FIG. 7, when the power supply of the drive circuit 1 is turned on, the power supply of the AC amplifier 6 for generating the AC modulation voltage is controlled so as to start up later than the DC bias voltage, and as shown in FIG. When the power supply of the circuit 1 falls, the power supply of the AC amplifier 6 falls immediately, so that the AC modulation voltage falls immediately, and the DC bias voltage falls gradually by the charging function of the capacitor.
[0058]
From the above, the forward voltage is not applied to the electroabsorption optical modulator 5 even when the power supply of the drive circuit 1 is turned on and off, and the electroabsorption optical modulator 5 is damaged. I will not.
The present invention is not limited to the above-described embodiment, and can be implemented with various modifications within the technical scope thereof.
[0059]
【The invention's effect】
According to the present invention, even when the power supply of the drive circuit is turned on or off, control can be performed such that a forward voltage is not applied to the electroabsorption optical modulator instantaneously even when the power is turned off. Damage to the electroabsorption optical modulator due to application of a forward voltage to the optical modulator can be prevented.
[0060]
Further, according to the present invention, by detecting that the optical signal incident on the electro-absorption optical modulator has been interrupted, and by providing a control function for lowering the AC modulation voltage, the input side of the electro-absorption optical modulator is provided. Even when the optical signal over-amplified by the optical amplifier having one or more light beams re-enters the electro-absorption optical modulator, the power consumption in the electro-absorption optical modulator does not become too large, and Damage of the optical modulator can be prevented.
According to the present invention, an optical transmission device using a highly reliable electroabsorption optical modulator can be provided.
[Brief description of the drawings]
FIG. 1 is a principle block diagram showing a first embodiment of the present invention.
FIG. 2 is a principle block diagram showing a second embodiment of the present invention.
FIG. 3 is a principle block diagram showing a third embodiment of the present invention.
FIG. 4 is a principle block diagram showing a fourth embodiment of the present invention.
FIG. 5 is a circuit diagram showing a specific example of the third embodiment of the present invention.
6 is a waveform diagram showing a difference between a DC bias voltage and a rise of an AC amplifier power supply when the drive circuit power supply of FIG. 5 is started up.
FIG. 7 is a waveform chart showing a difference between a DC bias voltage and a fall of an AC amplifier power supply when the drive circuit power supply of FIG. 5 falls.
FIG. 8 is a diagram showing an example of a conventional electro-absorption optical modulator driving circuit.
[Explanation of symbols]
1 ... Electric absorption type optical modulator drive circuit
2: DC bias voltage source
3: AC modulation voltage source
4: Bias tee
5 ... Electric absorption type optical modulator
6 ... AC amplifier
7 ... Charging circuit
8a to 8c: control circuit
9 DC bias voltage detector
10a, 10b ... relay
11 AC power supply
12 ... Optical amplifier
13: Absorption current monitor
14 DC bias voltage attenuator
15 ... Optical coupler
16. Clock component extraction circuit
R1 to R6 ... resistance
VR1, VR2 ... variable resistance
TR1, TR4: Transistor
C1 to C4 ... capacitors
CD1, CD2 ... diode
Z1, Z2 ... Chenner diode
VCC1 to VCC4: Power supply
IC1, IC2 ... Differential amplifier

Claims (4)

In an electro-absorption optical modulator driving circuit that drives the electro-absorption optical modulator,
A DC voltage source that generates a DC bias voltage in a reverse bias direction of the electroabsorption optical modulator when an external power is supplied;
An AC voltage source that generates an AC modulation voltage when external power is supplied;
A bias tee that combines the DC bias voltage generated by the DC voltage source and the AC modulation voltage generated by the AC voltage source, and applies the voltage to the electro-absorption optical modulator;
At the time of startup of the external power supply, the AC voltage source is connected to the bias tee after the voltage applied to the electroabsorption optical modulator by the DC voltage source exceeds a predetermined value, and the external Means for holding the voltage applied to the electroabsorption optical modulator by the DC voltage source at a predetermined value or more until the connection between the AC voltage source and the bias tee is cut off when the power supply is turned off. An electric absorption type optical modulator driving circuit, comprising: In an electro-absorption optical modulator driving circuit that drives the electro-absorption optical modulator,
A DC voltage source that generates a DC bias voltage in a reverse bias direction of the electroabsorption optical modulator when an external power is supplied;
An AC amplifier that amplifies an input AC modulation voltage when power is supplied;
When an external power is supplied, an AC amplifier power supply for supplying power to the AC amplifier, the DC bias voltage generated by the DC voltage source and the AC modulation voltage output from the AC amplifier are combined, and the electric absorption is performed. Tee applied to the optical modulator, and
When the external power supply is started, the AC amplifier power supply is connected to the AC amplifier after the voltage applied to the electroabsorption optical modulator by the DC voltage source exceeds a predetermined value, and the external power supply is connected to the external power supply. Means for holding the voltage applied to the electroabsorption optical modulator by the DC voltage source at a predetermined value or more until the connection between the AC amplifier power supply and the AC amplifier is cut off when the power supply is turned off. An electric absorption type optical modulator driving circuit, comprising: In an electro-absorption optical modulator driving circuit that drives an electro-absorption optical modulator having an optical fiber amplifier on the input side,
A DC voltage source that generates a DC bias voltage in a reverse bias direction of the electroabsorption optical modulator when an external power is supplied;
An AC voltage source that generates an AC modulation voltage when external power is supplied;
A bias tee that combines the DC bias voltage generated by the DC voltage source and the AC modulation voltage generated by the AC voltage source, and applies the voltage to the electro-absorption optical modulator;
When it is detected that the optical signal incident on the electro-absorption optical modulator is interrupted , the power consumption in the electro-absorption optical modulator is increased by lowering the AC modulation voltage and re-entering the optical signal. A driving circuit for an electro-absorption optical modulator, comprising: a protection unit for preventing the light; In an electro-absorption optical modulator driving circuit that drives an electro-absorption optical modulator having an optical fiber amplifier on the input side,
A DC voltage source that generates a DC bias voltage in a reverse bias direction of the electroabsorption optical modulator when an external power is supplied;
An AC voltage source that generates an AC modulation voltage when external power is supplied;
A bias tee that combines the DC bias voltage generated by the DC voltage source and the AC modulation voltage generated by the AC voltage source, and applies the voltage to the electro-absorption optical modulator;
Means for monitoring an absorption current flowing in the electro-absorption optical modulator, and when the applied voltage to the electro-absorption optical modulator is sensed to be transferred in the forward direction, means for lowering the AC modulation voltage. An electro-absorption optical modulator driving circuit, characterized in that:

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