JPWO2001003350A1 - WDM optical transmitter - Google Patents

Abstract

(57) [Abstract] The WDM optical transmitter of the present invention comprises a light source (1) that generates light whose wavelength changes depending on temperature and drive current, a temperature control unit (4) that controls the temperature of the light source so that the wavelength at the start of light emission is stable within a preset allowable range of the optical output wavelength, a drive current control unit (5) that controls the drive current to be supplied to the light source in accordance with the allowable range of the optical output wavelength, a wavelength control unit (3) that detects the optical output wavelength from the light source and controls the temperature of the light source based on the detection result to pull the optical output wavelength close to a predetermined target wavelength, and an operation control unit (6) that controls the start and stop of operation of each control unit at predetermined timings corresponding to the generation and stop of optical output, respectively.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to an optical transmitter used in a wavelength division multiplexing (WDM) optical transmission system.
In particular, channel fluctuations due to wavelength fluctuations in transient states when the device is turned on and off
WDM optical transmitter in which drive control is performed to avoid the occurrence of crosstalk between optical fibers
Background Technology In a WDM optical transmission system, each wavelength of multiple optical signals is wavelength-multiplexed according to the ITU (
International Telecommunication Union
The conventional optical fiber used in this WDM optical transmission system is
The transmitter uses automatic wavelength (frequency) control (hereafter referred to as automatic wavelength (frequency) control) to stabilize the wavelength of the output light.
In many cases, the AFC function is provided.
For example, the wavelength of the output light from a laser diode (LD) is detected and the result is
This is a function that keeps the wavelength of the output light constant by feeding back to the temperature control of the LD.
This has been achieved by using so-called wavelength lockers, etc. Figures 1 and 2 are block diagrams showing examples of the configuration of conventional WDM optical transmitters.
In the configuration example shown in Figure 1, the light emitted from the LD 100 is modulated by the external modulator 110.
The optical signal is modulated and output via the wavelength locker 120 and the optical filter 150.
In the wavelength locker 120, the wavelength detection unit 121 detects the external modulation
The wavelength of the optical signal from the detector 110 is detected, and the detection result is sent to the wavelength control circuit 122.
The wavelength control circuit 122 controls the wavelength of the output light to match the desired target wavelength.
A signal for controlling the temperature of the LD 100 is generated and sent to the temperature control circuit (ATC) 13.
0. In the temperature control circuit 130, the signal from the wavelength control circuit 122 and
The operating temperature of the LD 100 is controlled in accordance with the temperature monitor signal.
The drive current is controlled by the drive current control circuit 140.
During normal operation, the optical signal is transmitted with a constant channel spacing (e.g., 0.8 nm).
Furthermore, a bandpass filter (
By providing an optical filter 150 such as a BPF,
The occurrence of crosstalk between channels due to wavelength fluctuations is suppressed by hardware.
In the configuration example of FIG. 2, the wavelength locker 120 emits light from the rear surface of the LD 100.
The light output from the external modulator 110 is monitored to control the wavelength.
A switch 160 is provided to suppress the occurrence of crosstalk between channels due to wavelength fluctuations.
A modulator may also be used as the optical switch 160. However, in the conventional WDM optical transmitter described above,
In order to avoid the occurrence of stoke, optical filters and optical switches have been installed.
These optical filters and optical switches must be installed for each wavelength of light.
The overall configuration of the device becomes complicated, making it difficult to reduce the size and cost.
In addition, when using optical filters, there is a problem that many filters with different characteristics are used.
Furthermore, there was a drawback in that it was necessary to prepare an optical filter.
There is also the problem that loss increases when inserting a filter or optical switch.
The present invention was developed in consideration of the above circumstances, and aims to appropriately control the temperature and drive current of the light source.
By controlling the signal strength, it is possible to achieve a smooth transition between channels without using optical filters or optical switches.
An object of the present invention is to provide a WDM optical transmitter capable of suppressing the occurrence of crosstalk.
Disclosure of the Invention For this reason, the WDM optical transmitter of the present invention transmits multiple optical signals with different wavelengths.
In an optical transmitter used in a WDM optical transmission system that transmits wavelength-multiplexed signal light,
a light source that generates light whose wavelength changes depending on temperature and drive current;
based on the wavelength characteristics of the drive current and the interval between adjacent optical signal wavelengths.
The wavelength at the start of light emission of the light source is within the allowable range of the set optical output wavelength.
a temperature control means for controlling the temperature of the light source so that the temperature is stable within a range;
a drive current control means for controlling a drive current to be applied to the light source in accordance with the allowable range;
Detects the wavelength of light output from the light source and controls the temperature of the light source based on the detection result
and a wavelength control means for adjusting the optical output wavelength to a predetermined target wavelength.
start and stop of the control operations of the drive current control means and the wavelength control means,
Control at predetermined timings corresponding to when optical output is generated and when optical output is stopped.
and an operation control means for controlling the temperature of the light source during the transient state when the device is started and stopped.
The optical output wavelength fluctuates due to changes in the power consumption and drive current.
The temperature of the light source and the drive current are controlled by the temperature control so that the behavior remains within a preset tolerance range.
The temperature is controlled by a temperature control means, a drive current control means, and a wavelength control means.
The start and end of the control operations of the intensity control means, the drive current control means and the wavelength control means
By controlling the stop of the light filter at a predetermined timing by the operation control means,
This avoids the occurrence of crosstalk between channels without installing a filter or optical switch.
As a specific configuration of the above WDM optical transmitter, the operation control means controls the optical output generation.
When the temperature control is stabilized, the driving current
The control operation of the control means is started, and when the drive current control is stabilized, the control of the wavelength control means is started.
When the optical output is stopped, the control operation of the wavelength control means is stopped.
When the temperature of the light source is stabilized by the control operation of the temperature control means, the drive current control
The control operation of the means is stopped, the supply of drive current to the light source is stopped, and light emission stops.
It is preferable that the control operation of the temperature control means be stopped when the drive current control means is turned off. The drive current control means is an automatic power control means that controls the drive current supplied to the light source to a constant value.
The drive current is controlled so that the optical output power from the light source is constant.
Furthermore, automatic power control may be performed to control the
When control is performed, a differential amplification circuit configuration is provided.
The maximum drive current is limited to prevent excessive current from being supplied to the light source.
In addition, as a specific configuration of the temperature control means, the reference temperature that is the target of the control operation is
, given according to a reference voltage set inside the device, or
It may also be set according to an externally applied reference voltage. Furthermore, as an improvement to realize a higher output of the above-mentioned WDM optical transmitter,
The dynamic current control means adjusts the reference value that is the target of the control operation in response to a plurality of reference voltages.
The operation control means controls the temperature control means when light output is generated.
When the temperature control is stabilized, the control operation of the drive current control means is started.
When the drive current control is stabilized, the wavelength control means starts the control operation.
When the wavelength control is stabilized, the reference voltage of the drive current control means is increased step by step.
The reference voltage is switched to the reference level and then switched over each time the wavelength control stabilizes.
This may be repeated as follows. Alternatively, as another improvement to achieve higher output power in the above-mentioned WDM optical transmitter,
The operation control means starts the control operation of the temperature control means when the light output is generated, and the temperature
When the control of the driving current is stabilized, the control operation of the driving current control means is started, and then the driving current is set to the target value.
The optical output wave detected by the wavelength control means until it reaches the target reference value.
When the wavelength reaches the upper limit wavelength set within the allowable range, the control operation of the wavelength control means is started.
and suspends the control operation of the drive current control means, and
When the optical output wavelength is pulled to the vicinity of the target wavelength by the
The series of operations to restart the operation may be repeated. This improved configuration allows for control of the optical output wavelength within an acceptable range.
While this makes it possible to increase the driving current of the light source, it is possible to achieve high output of this device.
In addition, the specific configuration of the operation control means allows for the generation and stopping of optical output.
The timer operates in synchronization with the input of an alarm signal that indicates a preset time.
According to the timing, the temperature control means, the drive current control means, and the wavelength control means are controlled.
A timer is provided to output a signal that controls the start and end of the control operation.
In this configuration, temperature control is performed according to the timing based on the timer's timing operation.
The start and end of the control operations of the drive current control means and the wavelength control means are controlled.
Alternatively, another specific configuration of the operation control means is to control the control state of the temperature control means.
a temperature control alarm generating unit that generates a temperature control alarm signal indicating a state of the temperature control;
A drive current control alarm signal is generated to indicate the control state of the control means.
alarm generator, an external alarm signal that commands the start and stop of optical output, and a temperature control
The temperature control means, the drive current control means, and the drive alarm signal are outputted.
A system for controlling the start and end of each control operation of the dynamic current control means and the wavelength control means.
It is also possible to have a sequence unit. In such a configuration, the actual control state is determined based on each alarm signal generated inside the device.
This allows the operation timing of each component to be controlled. BEST MODE FOR CARRYING OUT THE INVENTION The WDM optical transmitter of the present invention will be described below with reference to the accompanying drawings. First, the laser diode used as the light source in the WDM optical transmitter will be
We will briefly explain the general characteristics of (LD). Figure 3 shows the relationship between the optical output power and drive current of the LD. Also, Figure 4 shows
, which shows the relationship between the optical output wavelength and the drive current of the LD. As shown in Figure 3, the LD operates when the drive current is equal to the threshold current Ith (e.g., 20 mA).
When the driving current Iop (for example, 100 mW) is exceeded, the optical output power increases rapidly.
A, etc.), the required optical output power can be obtained.
As shown in the figure, the optical output wavelength of the LD shifts to the longer wavelength side as the drive current increases.
In the figure, the rate (slope) of change in optical output wavelength with respect to drive current is 0.
01 nm/mA. This is due to the fact that the optical output wavelength of the LD fluctuates in response to changes in the drive current.
When the LD starts to emit light, the wavelength of the light output stabilizes at the target wavelength.
The output light crosses the wavelength of the channel (optical signal) that is being used, causing inter-channel crosstalk.
Also, when the LD stops emitting light, the light output is quenched.
There is a possibility that inter-channel crosstalk may occur during the time it takes for the LD to start emitting light. Therefore, there is a risk of inter-channel crosstalk occurring when the LD starts and stops emitting light.
In order to prevent this, it is necessary to limit the wavelength range in which the LD is allowed to emit light.
5 and 6 show the optical characteristics of the LD to avoid crosstalk between channels.
This is a diagram showing the allowable range of output wavelength. In Figure 5, the vertical axis represents wavelength, and the horizontal axis represents the change in the LD drive current from OFF to ON.
The wavelength fluctuation amount Δλ of the optical output when the laser is switched to the laser state is shown in FIG.
This corresponds to the amount of fluctuation ΔI of the driving current.
The state when the fluctuation amount is Δλ' is shown with wavelength on the horizontal axis. Here, the target wavelength of the optical output is λ₀, the wavelength of the adjacent channel on the shorter wavelength side is λ₋₁
, the wavelength of the adjacent channel on the longer wavelength side is λ₊₁In addition, dλ is the wavelength setting error.
and λ_modis the modulation band that represents the amount of wavelength fluctuation caused by modulating the output light.
This indicates the bandwidth and is determined according to the bit rate of the transmitted light. Target wavelength λ of the optical output₀Wavelength that does not cause inter-channel crosstalk
The range is λ₋₁+dλ+λ_modAbove, λ₊₁−dλ−λ_modIn the following range:
Considering the wavelength shift characteristics of the LD, the wavelength range λ within which the LD is allowed to emit light is_s
etThe allowable range λ of the optical output wavelength is the area enclosed by the thick line in FIG._set
can be expressed by the following equations (1) and (2): λ_set≧λ₋₁+dλ+λ_mod+Δλ…(1) λ_set≦λ₊₁−dλ−λ_mod...(2) Therefore, the wavelength at which the LD begins to emit light is λ₋₁+dλ+λ_modThat's all.
When the drive current Iop is stabilized at a value at which the required optical output power is obtained (wavelength locus),
The wavelength of the laser beam is within the above tolerance λ_setThe optical transmitter
By controlling the operation of
In the conventional optical transmission device described above, the tolerance range λ_set
Since the system did not have a function to control wavelengths, optical filters and optical switches had to be installed.
By doing so, the wavelength becomes λ₋₁+dλ+λ_modLess than or equal to λ₊₁−dλ−λ
_modThe hardware prevents light that exceeds this level from being output to the outside.
In contrast, the WDM optical transmitter of the present invention controls the temperature and drive current of the LD.
By properly controlling the light, it is possible to achieve a high-speed transmission without using optical filters or optical switches.
This makes it possible to suppress the occurrence of inter-channel crosstalk. An embodiment of a WDM optical transmitter according to the present invention will now be described. Figure 7 is a block diagram showing the basic configuration of a WDM optical transmitter according to this embodiment.
In Figure 7, this device uses LD1 as a light source and the output light of LD1 as a main signal.
and a modulation unit 2 that splits the output light of the LD 1 to detect the wavelength and output the optical signal.
The wavelength is the target wavelength λ₀Wavelength control as a wavelength control means to control the wavelength to be constant
A temperature control unit (AFC) 3 controls the temperature of the LD 1 to control the optical output wavelength.
a temperature control unit (ATC) 4 for controlling the driving current of the LD 1;
The drive current control unit (ACC/APC) 5, the wavelength control unit 3, and the temperature control
and the drive current control unit 5.
and an operation control unit 6. In this case, part of the light output from the front face of the LD 1 is branched and fed to the wavelength control unit 3.
However, as in the case shown in FIG. 2, the output is sent from the rear of the LD1.
The light to be modulated may be sent to the wavelength control section 3.
A modulator may be provided outside the device. Figure 8 shows a first embodiment as a specific example of a WDM optical transmitter having the above basic configuration.
This is a diagram showing the configuration of the form. In the configuration example of Figure 8, light output from LD1 is sent to modulation unit 2, and
A part of this signal is branched off and sent to the AFC circuit 30 serving as the wavelength control unit 3.
The C circuit 30 has a configuration similar to that of a so-called wavelength locker.
Detection filter 31, photodiode (PD) 32, resistor 33, operational amplifier 3
The wavelength detection filter 31 is a filter that detects a wavelength.
An optical filter with different transmittance characteristics, which receives part of the output light from LD1.
The PD 32 photoelectrically converts the light transmitted through the wavelength detection filter 31 and receives it.
A current corresponding to the optical power is generated. This current corresponds to the optical output wavelength of the LD1.
The resistor 33 converts the current generated by the PD 32 into a voltage.
The connection point of the PD 32 and the resistor 33 is connected to the non-inverting input terminal of the amplifier 34.
and a predetermined reference voltage V_refis applied to the inverting input terminal, and the voltage level at the connection point
and the reference voltage V_refA signal corresponding to the difference is sent to the temperature control unit 4 via the switch 35.
The switch 35 functions as the operation control unit 6.
It operates on/off according to a signal from a timer (TIM) 61. The ATC circuit 40 includes a Peltier element 41 and a Peltier driver (PEL DRV) 4.
2, a switch 43, an operational amplifier 44, a variable resistor 45 and a thermistor 46
The Peltier element 41 is supplied with power from a Peltier driving unit 42 via a switch 43.
The device generates or absorbs heat depending on the current supplied to adjust the temperature of the LD1.
The Peltier device 42 generates a voltage corresponding to the output signal of the operational amplifier 44.
The switch 43 is turned on/off in response to a signal from the timer 61.
The operational amplifier 44 is connected to the positive and negative power supplies V₊, V₋connected in series between
The inverting input terminal is connected to a common connection point a of the variable resistor 45 and the thermistor 46.
The non-inverting input terminal is grounded, and a signal corresponding to the voltage level of the connection point a is transmitted to the
The variable resistor 45 controls the temperature of the LD 1 depending on its resistance value.
The thermistor 46 is a reference resistor that provides a reference value for temperature control.
The resistance value changes depending on the temperature, and the voltage level at the connection point a changes depending on the temperature of the LD1.
The switch 35 of the AFC circuit 30 is connected to the connection point a.
When the switch 35 is turned on, the operational amplifier 3
The output voltage of 4 is applied. The drive current control unit 5 is an automatic current control (
The ACC circuit 50 that realizes this is implemented by a transistor 51.
, resistors 52, 52', an operational amplifier 53, a switch 54 and a reference power supply
The collector terminal of the transistor 51 is connected to the LD1, and the emitter terminal of the transistor 52 is connected to the LD1.
The negative power supply V₋and the base terminal is connected to the op-amp.
The emitter terminal is connected to the output terminal of the operational amplifier 53.
The non-inverting input terminal of the operational amplifier 53 is also connected to the resistor 52'.
Negative power supply V₋The non-inverting input terminal is also pulled down to
When the switch 54 is turned on, the drive voltage
A current is supplied to the LD1, and the current value is controlled to be constant at Iop.
The current value Iop, which is the reference for controlling the ACC, is a reference voltage given by the power supply 55.
The required value is preset by the lens voltage. The timer 61 is activated by an externally provided light ON/OFF alarm signal (hereinafter referred to as P
The ON/OFF states of the switches 35, 43, and 54 are controlled in response to the WALM signal.
The optical transmitter outputs a control signal to switch between these modes at a predetermined timing, which will be described later. Next, the operation of the first embodiment will be described. Here, the operating conditions of the optical transmitter include, for example, the bit rate of the transmitted signal light,
The wavelength setting error dλ of each channel is 0.1 nm.
The wavelength interval of the light is 0.8 nm, and the modulation bandwidth λ_modWhen the value is set to 0.08 nm,
In order to avoid crosstalk between channels under the above operating conditions,
The allowable range λ of the optical output wavelength of LD1_setis expressed by the above-mentioned formulas (1) and (2).
By substituting specific values into the above, it can be expressed as the following formulas (1)' and (2)'.
. λ_set≧(λ₀-0.8)+0.1+0.08+Δλ =λ₀−0.62+Δλ…(1)’ λ_set≦(λ₀+0.8) -0.1-0.08 =λ₀+0.62 ... (2)' Figure 9 shows the tolerance range λ_set5. In FIG. 9, the drive current Iop [mA] is set to L to obtain the required optical output power.
Specifically, when the drive current is supplied to D1, the change in the optical output wavelength with respect to the drive current is
When the rate is, for example, 0.01 nm/mA, the wavelength change amount Δλ_OPis 0.01 x
The allowable range of the optical output wavelength at this time is λ_{set (o
p)}In this case, the laser light emitted from the LD1 begins to be emitted (
The allowable range of the optical output wavelength when the drive current is Ith is λ_set(th)Shown in
The range is as follows: Note that dλ in the figure_lock1and dλ_lock2is the wavelength of the AFC circuit 30
This indicates the pull-in range, and dλ_lock1is the long wavelength side, dλ_lock2
represents the wavelength pull-in range on the short wavelength side._lock1= dλ_lock
2An example is shown where λ = 0.8 nm. The above-mentioned optical output wavelength tolerance λ_setIn consideration of the above, the present optical transmitter
We will now explain the specific control method for operating the optical transmitter. First, start the optical transmitter and transmit the signal at wavelength λ₀Consider the case where an optical output of Figure 10 shows the control timing of each part at startup (top row) and the corresponding
The figure shows the change in optical output wavelength over time (bottom). As shown in Figure 10, the PWALM signal is used to start the device and begin emitting light.
When the signal is switched ON (time t₀), the timer 61 receives this and switches
This outputs a control signal to switch the Peltier driving unit 42 to ON.
The current from the Peltier element 41 is supplied to the ATC circuit 40 via the switch 43.
The control operation is started (ATC ON), and the temperature of the LD1 reaches the level of the variable resistor 45.
The temperature is automatically controlled to the required value set by the reference resistance.
The temperature setting is determined by the wavelength when the drive current is supplied to LD1 and light emission starts.
The tolerance of λ_set(th)It is predetermined to be within a certain time (t₁) has passed
When this occurs, the timer 61 outputs a control signal to switch the switch 54 ON.
This starts the control operation of the ACC circuit 50 (ACC ON), and
The supply of the driving current begins. When the threshold current Ith is supplied to the LD1,
Therefore, laser emission begins, and the light wavelength at this time is within the allowable range λ_set(th)Within
As the drive current increases, the optical output wavelength shifts to the longer wavelength side.
When the driving current reaches Iop, the driving current Iop is supplied to the ACC circuit 50.
Therefore, the optical wavelength is controlled to a constant value within the allowable range λ_set(op)This is within a sufficient time (t₂) has passed,
The timer 61 outputs a control signal to switch the switch 35 ON.
The control operation of the AFC circuit 30 is started (AFC ON) and the optical output wavelength is adjusted to the target wavelength.
wavelength λ₀The control operation of the AFC circuit 30 is specifically as follows:
Specifically, the output voltage of the operational amplifier 34 is input to the output terminal of the amplifier 34 via the switch 35 and the resistor 36.
When a voltage is applied to the connection point a between the variable resistor 45 and the thermistor 46,
The optical output wavelength shifted to the wavelength side is the target wavelength λ₀The temperature of LD1 is adjusted to approach
In this case, the temperature of the LD 1 is controlled by the AFC circuit 30 and the ATC
The AF is controlled by the AF circuit 40, but the relationship between the time constants of each control circuit, etc.
The temperature control by the C circuit 30 becomes the main control. As a result, the optical output wavelength of the LD 1 becomes
Target wavelength λ₀The output light is sent to the modulation section 2 and modulated.
After this, the signal is output externally. Next, let's consider the case where the optical output of the optical transmitter is stopped. Figure 11 shows the control timing of each part when the signal is stopped (top row) and the corresponding
The figure shows the change in optical output wavelength over time (bottom). As shown in Figure 11, the PWALM signal is turned OFF as a signal to stop optical output.
When it switches (time t₃), the timer 61 receiving this turns the switch 35 OFF.
This causes the control operation of the AFC circuit 30 to stop.
The temperature of the LD 1 is controlled by the ATC circuit 40, and the light
The output wavelength is within the allowable range λ corresponding to the drive current Iop._set(op)Shift inward
. And then, wait for a sufficient time for the optical output wavelength of LD1 to shift to the longer wavelength side and stabilize.
(t₄) has elapsed, the timer 61 controls the switch 54 to be turned OFF.
This causes the control operation of the ACC circuit 50 to be stopped (ACC
OFF), the drive current supplied to LD1 begins to decrease.
As a result, the optical output wavelength shifts to the shorter wavelength side, and the driving current becomes lower than the threshold current Ith.
When the wavelength becomes smaller, the laser stops emitting light.
Since the temperature control by the path 40 is maintained, the allowable range λ_set(th)Become inside
. As described above, according to the WDM optical transmitter of the first embodiment, the drive current of LD1
The optical output wavelength tolerance λ_setSet and start
AFC circuit 30, ATC circuit 40 and ACC circuit 5 during operation and stop
By switching the ON/OFF state of 0 at a predetermined timing,
Without the need for optical filters or optical switches, the crosstalk between channels can be reduced.
This makes it possible to reduce the size and cost of WDM optical transmitters.
This makes it possible to reduce costs and also reduces losses in optical filters and optical switches.
This eliminates loss and enables the optical transmitter to achieve higher output. Next, a second embodiment of the present invention will be described. Figure 12 shows an example of the configuration of a second embodiment of a WDM optical transmitter according to the present invention.
However, the same components as those in the first embodiment are denoted by the same reference numerals.
The same applies below. In Figure 12, the configuration of this device differs from that of the first embodiment in that the drive current
In the first embodiment, the control unit 5 is an ACC circuit 50 that controls the driving current to a constant value.
Instead, in the second embodiment, a constant optical output power is used.
An APC circuit 70 is provided to realize automatic power control (APC) that controls the drive current as follows:
The other configurations are the same as those in the first embodiment.
The APC circuit 70 is similar to the photodiode (PD) 71, resistors 72, 74, and 77.
, 78, a transistor 73, an operational amplifier 75, and a switch 76.
71 directly receives a part of the light output from the LD 1 and branched for the AFC circuit 30.
The resistor 72 generates a current according to the received light power.
The collector terminal of the transistor 73 is connected to the LD1.
The emitter terminal is connected to the negative power supply V₋is connected to the base terminal
is connected to the output terminal of the operational amplifier 75. The operational amplifier 75 has an inverting input terminal
A non-inverting input is connected to the common connection point between resistors 77 and 78 via a switch 76.
The power terminal is connected to the common junction between PD 71 and resistor 72. Resistor 77
, 78 are the ground terminal and the negative power supply V₋are connected in series between the
The divided voltage at
The operation of an optical transmitter equipped with the APC circuit 70 described above is performed according to the tolerance of the optical output wavelength.
Range λ_setThe setting of the first and second control circuits and the operation timing of each control circuit are basically the same.
The operation is the same as in the first embodiment, and the difference from the first embodiment is that
The driving current supplied to D1 is controlled to a constant current value Iop by the ACC circuit 50.
The APC circuit 70 adjusts the optical output power from the LD 1 to a desired level.
The only difference is that the APC circuit 70 is controlled to a constant value.
This is similar to the automatic power control generally performed in optical transmitters.
The optical power output from D1 is detected, and the optical power is input to each of resistors 77 and 78.
The level is constant depending on the predetermined reference voltage set according to the resistance value.
In this way, the drive current of LD1 is automatically controlled. In this way, according to the WDM optical transmitter of the second embodiment, the drive current control method
Even if ACC is replaced with APC, the same effect as in the first embodiment can be obtained.
It is possible. In the first and second embodiments described above, the basis for temperature control in the ATC circuit 40 is
In the above embodiment, the reference value is set by the resistance value of the variable resistor 45.
Instead of providing the variable resistor 45, an externally provided reference
Voltage V_REFmay be applied to the connection point a via a resistor R.
In this case, a configuration example corresponding to the first embodiment is shown in FIG. 13, and in the second embodiment,
An example configuration corresponding to this is shown in Figure 14. Next, a third embodiment of the present invention will be described. Figure 15 shows an example configuration of a third embodiment of a WDM optical transmitter according to the present invention.
In FIG. 15, this device has the same configuration as the second embodiment, except for the operational amplifier 75, etc.
Instead of the APC circuit 70 configured using
This applies an APC circuit 70' that configures an amplifier circuit. Specifically, the APC circuit 70' includes a PD 71, resistors 72, 77, 78, and 80.
, transistors 73 and 79, a switch 76, and a current source 81.
directly receives a portion of the light output from LD1 and generates an electric current according to the received light power.
The resistor 72 converts the current generated by the PD 71 into a voltage.
The collector terminal of the transistor 73 is connected to the LD1, and the emitter terminal is connected to the current source 81.
The base terminal is connected to the common terminal of the PD 71 and the resistor 72 via the switch 76.
The collector terminal of the transistor 79 is connected to a common node through a resistor 80.
The resistors 77 and 78 are connected to ground, and the emitter terminal is connected to a current source 81.
Ground terminal and negative power supply V₋The resistors 77 and 78 are connected in series between the
The base terminal of the transistor 79 is connected to the connection point.
The ON/OFF is switched according to the control signal from the timer 61, and the timer is turned ON.
This closes the APC loop and starts APC control.
This switches the control operation of the APC circuit 70' ON/OFF. An optical transmitter equipped with the APC circuit 70' as described above basically operates in the same manner as in the second embodiment.
The APC control operation operates in the same way as in the case of a general differential amplifier circuit.
The only difference is that the differential amplifier type APC circuit 70' is realized by a different path.
By using the current source 81, the upper limit of the drive current supplied to the LD 1 is set to the maximum current of the current source 81.
Flow Rate I_limitTherefore, an overcurrent to the LD1 can be prevented.
This has the advantage that: Next, a fourth embodiment of the present invention will be described. Figure 16 is a diagram showing an example of the configuration of a fourth embodiment of a WDM optical transmitter according to the present invention.
In FIG. 16, this device has the same configuration as the first embodiment, except that the ACC circuit 50
Instead, the ACC circuit 50' is applied to provide a reference for constant control of the drive current.
The voltage can be set in two stages to increase the drive current and maximize the maximum optical output power.
Specifically, the ACC circuit 50' has an increased power compared to the ACC circuit 50 used in the first embodiment.
The power supply 55 which provided a single reference voltage is now connected to resistors 56 to 58 and
The resistors 56 and 57 are connected to the ground terminal.
and the negative power supply V₋The resistor 58 is connected in series between the switch 5
9 is connected in parallel to the resistor 56. The resistors 56, 57 and the switch
The common connection point between the switches 59 is connected to the non-inverting input of the operational amplifier 53 via the switch 54.
17 is a diagram explaining the control operation of the ACC circuit 50' configured as described above.
In the ACC circuit 50', a control signal that switches the switch 54 ON is generated by the timer
The control operation is started when the signal is sent from 61. At this time, the switch 59
When the resistor 56 and the resistor 57 are in the OFF state, the voltage is divided by the first reference voltage.
The first reference voltage is applied to the operational amplifier 53 via the switch 54.
According to the lens voltage, the driving current is a current value I as shown in ACC1 in the upper part of FIG.
_op1At this time, the optical output wavelength of the LD 1 is controlled to be constant as shown in FIG.
As shown in the bottom row of 7, the wavelength shifts to the long wavelength side as the driving current increases.
Flow is I_op1When the tolerance λ_set(op)It becomes stable inside.
The control operation of the AFC circuit 30 starts in the same manner as in the control flow of the first embodiment described above.
The optical output wavelength is set to the target wavelength λ₀The optical output wavelength is pulled into λ by the AFC circuit 30.₀Sufficient time has passed for the
Then, a control signal for switching the switch 59 to the ON state is output from the timer 61.
As a result, the voltage divided by the resistors 56, 58 and 57 is
This second reference voltage is applied to the operational amplifier 53.
Therefore, the drive current is a current value I as shown in ACC2 in the upper part of FIG._OP2constant at
At this time, the optical output wavelength of the LD 1 is controlled to be
As the wavelength increases, the wavelength shifts to the long wavelength side, and the driving current increases._OP2When it reaches this number, the AFC
The control operation of the path 30 causes the optical output wavelength to be adjusted to the target wavelength λ₀As described above, according to the fourth embodiment, the reference voltage can be set in two stages.
By applying the ACC circuit 50', the optical output wavelength is controlled within the allowable range λ_setInside and Outside
Then, the drive current to LD1 is set to a current value I_OP2This can be increased to
This makes it possible to increase the optical output power of the LD, making it suitable for high-power WDM applications.
It is possible to provide an optical transmitter. In the fourth embodiment, the ACC reference voltage is set in two stages.
However, the present invention is not limited to this, and it is also possible to set three or more levels of reference voltage.
It is also possible to apply it to optical output wavelengths within the acceptable range λ_setRealizing control within the LD and driving
In addition to the above method, there is another method for increasing the current, for example, by using an AFC circuit.
There is also a method of switching the control state of the ACC circuit based on the optical output wavelength detected by the
Specifically, for example, in the configuration shown in FIG. 8, the operation of the AFC circuit 30
The optical output wavelength of the LD1 is detected based on the voltage level output from the amplifier 34.
and a function to temporarily stop the control operation of the ACC circuit 50 in response to the alarm.
and a function to maintain or resume the driving current at a constant level.
In this case, as shown in the lower part of FIG.
The optical output wavelength of 1 is within the tolerance range λ_setThe maximum wavelength λ is set near the upper limit of_MAXto
When this is reached (an alarm is issued), the control of the ACC circuit 50 is
The operation is temporarily stopped and the driving current is kept constant.
If the control operation of the C circuit 30 is started, the optical output wavelength will be set to the target wavelength λ₀Pulled into
The optical output wavelength is λ₀The wavelength detection of the AFC circuit 30 is performed when the wavelength is pulled into the vicinity.
Judging from the result (no alarm is issued), the suspended control of the ACC circuit 50
This increases the driving current of the LD, and the optical output wavelength shifts to the long wavelength side.
Then, the optical output wavelength shifts again to the maximum wavelength λ_MAXWhen it reaches ACC
The control operation of the circuit 50 is interrupted, and the same operation as above is repeated.
The current is the target current value I of the ACC circuit 50._limitWhen it reaches a constant value, A
The optical output wavelength is controlled by the control operation of the FC circuit 34 to λ₀By applying this method, even when high output power is required, the optical output wavelength
The tolerance of λ_setThe LD drive current can be set appropriately while achieving control within the
Although the case of the ACC circuit has been explained here, the same can be said for the APC circuit.
The same applies to the fifth embodiment of the present invention. Next, we will explain the fifth embodiment of the present invention. The WDM optical transmitter of the fifth embodiment displays the control states of temperature and drive current.
The alarm signals are generated internally by the device, and each alarm signal is sequenced.
The fifth embodiment is configured so that the timing of operation of each component is controlled by a dedicated control unit. Figure 19 shows an example of the configuration of a WDM optical transmitter according to the fifth embodiment. In Figure 19, this device is similar to the configuration of the first embodiment (see Figure 8), for example.
In place of the timer 61 used as the operation control unit 6, a sequence unit 62,
By providing a temperature control alarm generating unit 64 and a drive current control alarm generating unit 65,
The configuration of each part other than the above is the same as that of the first embodiment.
Therefore, the explanation will be omitted. The sequence unit 62 generates a light ON/OFF alarm that instructs the ON/OFF of the light output.
A PWALM signal is given from the outside, and the temperature control alarm generating unit 6
Temperature control alarm (ATC ALM) signal and drive current control alarm signal generated at 4
When the drive current control alarm (LDBI ALM) signal generated by the alarm generator 65 is input,
The level of each alarm signal is monitored to control the temperature and drive current of the LD1.
A signal to switch the state is generated. The temperature control alarm generator 64 includes, for example, an operational amplifier 64A, a resistor 64B,
64C, 64D, and comparators (COMP) 64E, 64F.
The non-inverting input terminal of the amplifier 64A is connected to the connection point a (ATC circuit 40) via a resistor 64C.
the common connection point between the variable resistor 45 and the thermistor 46, and
The input terminal is grounded via resistor 64B, and the output terminal and the inverting input terminal are connected
The comparator 64E is connected to the operational amplifier 64 through a resistor 64D.
The output signal from A is input, and the output level is set to a predetermined reference level ref
When it becomes lower than 1, it generates an ATC alarm signal.
is the output signal from the operational amplifier, and the output level is adjusted to a predetermined reference level.
When the level becomes higher than ref2 (> ref1), an ATC alarm signal is generated.
The ATC alarm signals output from the comparators 64E and 64F are as follows:
The reference levels ref1 and ref2 are input to the sequence unit 62.
is set in advance to correspond to the reference value for temperature control by the ATC circuit 40. The drive current control alarm generator 65 includes an operational amplifier 65A, resistors 65B, and
C, 65D, 65F, and a comparator (COMP) 65E.
5A has a non-inverting input terminal grounded via a resistor 65F and a resistor 65C.
One end of the resistor 52 of the ACC circuit 50 (negative power supply V₋side) and
The input terminal is connected to the other end of the resistor 52 (transistor 51 side) via the resistor 65B.
The output terminal and the inverting input terminal are connected via a resistor 65D.
The comparator 65E receives the output signal from the operational amplifier 65A and
When the output level becomes lower than a predetermined reference level ref3, the LD
This LDBI alarm signal is sent to the sequence unit 62.
The reference level ref3 is normally set by the ACC circuit 50.
This is preset to correspond to the drive current Iop, which is controlled to a constant value during use. Next, we will explain the operation of the optical transmitter configured as described above. Figure 20 shows the control timing of each part when the device is started and stopped (upper
) and the corresponding time change in optical output wavelength (bottom).
FIG. 21 is a flowchart showing the control operation of the sequence unit 62 at the time of startup.
FIG. 22 is a flowchart showing the control operation of the sequence unit 62 when the motor is stopped.
The allowable range of optical output wavelength λ_setis shown in FIG.
This is the same range as the above. First, let's consider the operation at startup. Step 101 in Figure 21 (S1 in the figure)
01, and so on), for example, when the power is turned on to this device,
At this time, the PWALM signal given to the sequence unit 62 from the outside is switched ON.
This power-on command instructs the generation of optical output.
The control operation of the circuit 40 is started. At this time, the temperature of the LD 1 is
If the temperature deviates from the reference temperature of the ATC set according to
The output level of the operational amplifier 64A based on the reference
If the reference level of the comparator 64F is lower than the reference level ref1,
When the bell ref2 is higher than the bell ref1, an ATC alarm signal is issued and the sequence unit 62
The sequence unit 62 monitors the issuance of an ATC alarm signal and
As a result of the temperature control by the C circuit 40 (step 103), the temperature of the LD 1 reaches the reference temperature.
It waits until the ATC alarm signal is no longer issued (step 104). Then, when the ATC alarm signal is no longer issued, the sequence goes to step 105.
The ATC alarm mask (ATC ALM MSK) processing in the unit 62
At the same time as the start, in step 106, the switch 54 of the ACC circuit 50 is turned OFF.
A signal for switching from F to ON is output from the sequence unit 62, and the driving
However, the ATC alarm masking process is performed by the sequence section.
62, the ATC alarm signal is masked until a certain time has elapsed.
The masking process is performed for a certain period of time, which is the same as the control period of the AFC circuit 30 that is started later.
The optical output wavelength is adjusted to the target wavelength λ₀The time required for the temperature to stabilize in the vicinity is estimated.
When the control operation of the ACC circuit 50 is started in step 106, the drive current is increased.
As a result, the optical output wavelength shifts to the longer wavelength side (see the bottom of Figure 20).
When the drive current is controlled to a constant value Iop, the op- er
The output level of the amplifier 65A is the reference level ref3 of the comparator 65E.
When the voltage drops below 1 V, an LDBI alarm signal is generated and transmitted to the sequence unit 62.
The sequence unit 62 monitors the issuance of the LDBI alarm signal and
As a result of the constant control of the drive current by 0 (step 107), the drive current is kept at a current value Io
p and the LDBI alarm signal is not issued (step 108). When the LDBI alarm signal is not issued, in step 109, the AFC circuit 30
A signal to switch the switch 35 from OFF to ON is output from the sequence unit 62.
The target wavelength λ of the optical output wavelength is set by the AFC circuit 30.₀Pull-in control begins
At this time, the switch 35 is turned on, and the voltage level of the connection point a
The bell will change and an ATC alarm signal will be issued (step 110).
The issuance of this ATC alarm signal is ignored by the ATC alarm mask processing.
Therefore, there is no effect on the control operation of the sequence unit 62.
In 1, the temperature of the LD 1 is controlled by the control operation of the AFC circuit 30, and the optical output
The wavelength is the target wavelength λ₀If the vehicle is pulled in close to the target, an ATC alarm is generated in step 112.
The signal is then turned off.₀The transfer to
Then, in step 113, the ATC alarm mask process in the sequence unit 62 is canceled.
This completes the control operation at startup of the device. Next, consider stopping the optical output from the device.
As shown in FIG. 01, whether the PWALM signal has changed from ON to OFF is determined by the sequence.
When the PWALM signal is turned OFF, the AF
A signal that switches the switch 35 of the C circuit 30 from ON to OFF is sent to the sequence unit 6
2, and the control operation of the AFC circuit 30 is stopped.
The wavelength is the target wavelength λ₀At this time, the ATC circuit
Since the control operation of 40 is maintained, the temperature of LD1 is controlled to the reference temperature of ATC.
The voltage level at the connection point a changes due to the shift in the optical output wavelength.
Therefore, in step 203, an ATC alarm signal is issued and transmitted to the sequence unit 62.
The sequence unit 62 monitors the issuance of an ATC alarm signal and
As a result of the temperature control by the path 40 (step 204), the temperature of the LD 1 stabilizes at the reference temperature.
The ACC circuit is reset and the ATC alarm signal is awaited (step 205). When the ATC alarm signal is no longer being issued, the ACC circuit is reset in step 206.
A signal for switching the switch 54 of the line 50 from ON to OFF is sent from the sequence unit 62.
The drive current supplied to LD1 starts to decrease.
At step 207, the LDBI alarm signal is generated, and the drive current decreases.
The optical output wavelength shifts to the shorter wavelength side, and the drive current becomes zero and the optical output disappears.
This completes the control operation when the device is stopped. In this way, according to the fifth embodiment, the control states of the temperature and drive current are respectively
An alarm signal representing the alarm is generated inside the device and monitored by the sequence unit 62.
By using the control unit 6 instead of the timer, the same operation as in the first embodiment can be performed.
The same effect can be obtained. In addition, based on each alarm signal generated inside the device,
Since the operation timing of each part is controlled according to the actual control state,
Compared with the case where the 61 is used, the operation timing can be controlled more reliably.
In the fifth embodiment, the timer is added to the sequence unit in the first embodiment.
In the above, the case where the above is replaced with the above, etc., is explained, but similarly, the second to fourth embodiments can be replaced with the above.
This invention can be applied to various optical communication systems that use wavelength division multiplexing technology.
The device has great industrial applicability.

[Brief explanation of the drawings]

FIG. 1 is a block diagram showing an example of the configuration of a conventional WDM optical transmitter. FIG. 2 is a block diagram showing another example of the configuration of a conventional WDM optical transmitter. FIG. 3 is a diagram showing the relationship between the optical output power and drive current of a typical LD. FIG. 4 is a diagram showing the relationship between the optical output wavelength and drive current of a typical LD. FIG. 5 is a diagram showing the allowable range of the optical output wavelength of an LD to avoid inter-channel crosstalk. FIG. 6 is a diagram showing the state when the wavelength fluctuation amount in FIG. 5 is Δλ', with wavelength on the horizontal axis. FIG. 7 is a block diagram showing the basic configuration of a WDM optical transmitter according to the present invention. FIG. 8 is a diagram showing the configuration of a WDM optical transmitter according to a first embodiment. FIG. 9 is a diagram showing the allowable range λ _set of the optical output wavelength for the same embodiment. FIG. 10 is a diagram explaining the control operation at startup for the same embodiment. FIG. 11 is a diagram explaining the control operation at shutdown for the same embodiment. FIG. 12 is a diagram showing the configuration of a WDM optical transmitter according to a second embodiment. FIG. 13 is a diagram showing an example of the configuration corresponding to the first embodiment when the ATC reference value is provided externally. Fig. 14 is a diagram showing a configuration example corresponding to the second embodiment when the ATC reference value is provided externally. Fig. 15 is a diagram showing the configuration of a WDM optical transmitter of a third embodiment. Fig. 16 is a diagram showing the configuration of a WDM optical transmitter of a fourth embodiment. Fig. 17 is a diagram explaining the control operation of the ACC circuit in the above embodiment. Fig. 18 is a diagram explaining the operation of another specific example related to the above embodiment. Fig. 19 is a diagram showing the configuration of a WDM optical transmitter of a fifth embodiment. Fig. 20 is a diagram explaining the operation of the above embodiment. Fig. 21 is a flowchart showing the control operation of the sequence unit at start-up. Fig. 22 is a flowchart showing the control operation of the sequence unit at shutdown.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (13)

[Claims] Claim 1: A WDM optical fiber for transmitting wavelength-multiplexed signal light containing a plurality of optical signals with different wavelengths.
an optical transmitter used in a DM optical transmission system, comprising: a light source that generates light whose wavelength changes depending on temperature and drive current; temperature control means that controls the temperature of the light source so that the wavelength at the start of light emission of the light source is stabilized within a predetermined allowable range of optical output wavelength that is set based on the wavelength characteristics of the light source to the drive current and the interval between adjacent optical signal wavelengths; drive current control means that controls the drive current to be supplied to the light source in accordance with the allowable range of optical output wavelength; wavelength control means that detects the wavelength of light output from the light source and controls the temperature of the light source based on the detection result to pull the optical output wavelength to near a predetermined target wavelength; and operation control means that controls the start and stop of each control operation of the temperature control means, drive current control means, and wavelength control means at predetermined timings that correspond to the generation and stop of optical output, respectively. 2. The WDM optical transmitter according to claim 1, wherein the optical output wavelength tolerance λ_setis the target wavelength of the optical output, λ₀and short wavelength
The optical signal wavelength adjacent to the side is λ₋₁and the optical signal wavelength adjacent to the long wavelength side is λ₋₁
The setting error of each optical signal wavelength is dλ, and the
The modulation bandwidth, which represents the amount of wavelength fluctuation, is λ_modand the driving current of the light source is
The wavelength variation according to the wavelength characteristics is Δλ, λ_set≧λ₋₁+dλ+λ_mod+Δλ λ_set≦λ₊₁−dλ−λ_mod A WDM optical transmitter characterized by being within a range that satisfies each of the conditional expressions. [Claim 3] In the WDM optical transmitting device described in claim 1, the operation control means starts the control operation of the temperature control means when optical output is generated, starts the control operation of the drive current control means when the temperature control stabilizes, starts the control operation of the wavelength control means when the drive current control stabilizes, and stops the control operation of the wavelength control means when optical output is stopped, stops the control operation of the drive current control means when the temperature of the light source is stabilized by the control operation of the temperature control means, and stops the control operation of the temperature control means when the supply of drive current to the light source is stopped and light emission stops. 4. The WDM optical transmitter according to claim 1, wherein said drive current control means performs automatic current control to keep the drive current supplied to said light source constant. 5. The WDM optical transmitter according to claim 1, wherein said drive current control means performs automatic power control to control the drive current so that the optical output power from said light source becomes constant. 6. The WDM optical transmitting apparatus according to claim 5, wherein said drive current control means comprises a circuit configuration of a differential amplification system. 7. The WDM optical transmitter according to claim 1, wherein the temperature control means provides a reference temperature, which is a target for control operation, according to a reference voltage set within the device. 8. The WDM optical transmitter according to claim 1, wherein the temperature control means sets a reference temperature, which is a target for control operation, in accordance with a reference voltage applied from outside the device. [Claim 9] A WDM optical transmitting device as described in claim 1, wherein the drive current control means is capable of setting a reference value as a target for control operation in stages according to a plurality of reference voltages, and the operation control means starts the control operation of the temperature control means when optical output is generated, starts the control operation of the drive current control means when the temperature control becomes stable, starts the control operation of the wavelength control means when the drive current control becomes stable, switches the reference voltage of the drive current control means to a larger level by one stage at a time when the wavelength control becomes stable, and sequentially repeats the switching of the reference voltage each time the wavelength control becomes stable. 10. The WDM optical transmitter according to claim 1, wherein said operation control means starts the control operation of said temperature control means when an optical output is generated, and starts the control operation of said drive current control means when the temperature control is stabilized, and then:
a wavelength control means for controlling a wavelength of a light beam emitted from the wavelength control means and a drive current ... 11. The WDM optical transmitter according to claim 1, wherein said operation control means comprises a timer that performs a timing operation in synchronization with an input of an alarm signal that instructs generation and stop of optical output, and outputs a signal that controls the start and end of each control operation of said temperature control means, said drive current control means, and said wavelength control means according to a predetermined timing.
Optical transmitter for use. [Claim 12] A WDM optical transmitting device as described in claim 1, wherein the operation control means is configured to include a temperature control alarm generating unit that generates a temperature control alarm signal indicating the control state of the temperature control means, a drive current control alarm generating unit that generates a drive current control alarm signal indicating the control state of the drive current control means, and a sequence unit that controls the start and end of each control operation of the temperature control means, the drive current control means and the wavelength control means based on an external alarm signal that instructs the generation and stop of optical output, the temperature control alarm signal and the drive current control alarm signal. [Claim 13] A WDM optical transmitting device as described in claim 12, wherein the temperature control alarm generating unit issues the temperature control alarm signal when the temperature of the light source is not controlled within a predetermined range, the drive current control alarm generating unit issues the drive current control alarm signal when the drive current to the light source does not reach a predetermined current value, and the sequence unit, when optical output is generated, starts the control operation of the temperature control means in response to input of the external alarm signal instructing the generation of optical output, starts the control operation of the drive current control means when the temperature control alarm signal is not issued, starts the control operation of the wavelength control means when the drive current control alarm signal is not issued, and, when optical output is stopped, stops the control operation of the wavelength control means in response to input of the external alarm signal instructing the stop of optical output, and stops the control operation of the drive current control means when the temperature control alarm signal is not issued.