JP2011029378A - Optical transmitter, stabilized light source, and method for controlling laser diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a sudden temperature rise of a laser diode in an optical transmitter at the start of driving its laser diode instantaneously makes a wavelength that is greatly shifted from a desired wavelength to a longer wavelength side, thus interfering with the communication of the adjacent wavelength channel. <P>SOLUTION: In order to decrease deviation from the desired wavelength at the shutdown release time, a reference signal control section is set up for controlling the temperature of a laser diode to become lower compared to the target temperature for the non-shutdown state when the laser diode is in a shutdown state in an optical transmitter. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical transmitter, an optical stabilization light source, and a laser diode control method used for optical communication.

  As means for increasing the transmission speed in optical communication, there is wavelength division transmission (WDM) in which optical signals of a plurality of wavelengths are transmitted through a single optical fiber. Due to the demand for higher transmission speed, high-density wavelength division multiplexing (Dense WDM: DWDM) that transmits more optical signals at narrow wavelength intervals has also been realized. Since the wavelength interval of optical signals is narrow in DWDM, it is very important to improve the stability of the wavelength of optical signals in a transmitter. In the 1550 nm band DWDM transmitter, in order to cope with a wavelength interval of 0.8 nm, the center wavelength accuracy is required to be within ± 0.1 nm. In a DWDM transmitter having a wavelength interval of 0.4 nm or 0.2 nm, higher center wavelength accuracy is required.

  A laser diode (hereinafter referred to as LD) element used in an optical transmitter varies in wavelength of output light depending on the operating temperature of the LD. In a distributed feedback (DFB) LD, the wavelength increases as the temperature rises, and typically has a temperature dependency of about 0.1 nm / ° C. For this reason, in an optical transmitter compatible with DWDM, a temperature detection element and a thermoelectric element are incorporated in the LD module, and feedback control to the thermoelectric element (Automatic Temperature Control: ATC) is performed so that the detection temperature is constant. Thus, the temperature of the LD is kept constant, and the wavelength of the LD output light is controlled.

  The optical transmitter has a shutdown function (light emission stop function) that turns off the optical output of the LD based on a command from the system when a failure occurs on the transmission path. In the shutdown state, the LD drive current is reduced to zero or to the extent that the LD does not emit light, so that no optical signal is sent to the communication path. When canceling the shutdown state, the optical output of the LD is quickly turned on to resume the optical communication, so that the drive current starts to flow suddenly through the LD. At this time, the temperature of the LD changes rapidly, and the wavelength of the output light changes.

FIG. 8 is a block diagram showing a configuration of a conventional optical transmitter (hereinafter referred to as first conventional technology).
The LD 1 generates signal light according to the drive signal output from the LD driver 2. The thermoelectric element 3 adjusts the temperature of the LD 1, and the temperature detection element 4 detects the temperature of the LD 1. The reference signal generation unit 5 generates a reference signal corresponding to the target temperature that stabilizes the LD 1, and the error detection unit 6 compares the detection signal of the temperature detection element 4 with the reference signal of the reference signal generation unit 5 to obtain an error signal. Is generated. The temperature control unit 7 controls the temperature of the thermoelectric element 3 based on the error signal from the error detection unit 6. Since LD1 is installed in the vicinity of thermoelectric element 3, it is stabilized toward the target temperature. The reference signal control unit 8 controls the reference signal generation unit 5 so as to set a target temperature corresponding to a desired wavelength of the optical signal. The shutdown controller 9 turns off the drive current of the LD driver 2 when the shutdown signal (not shown) from the host system (not shown) is at a high level, and turns on the drive current of the LD driver 2 when it is at a low level. Control.

FIG. 9 is a timing chart showing the operation of the first prior art. 9A shows the optical shutdown signal, FIG. 9B shows the intensity of the optical output of the LD, FIG. 9C shows the temperature of the LD, and FIG. 9D shows the wavelength of the LD output light. Yes.
Before the time t0, it is a steady state before shutting down. At this time, the optical shutdown signal is at a low level, and the LD emits an optical signal with a constant output light intensity. The LD temperature is T0, and the wavelength of the output light is stabilized at λ0.
At time t0, when the optical shutdown signal becomes high level according to a command from the host system, the shutdown control unit 9 turns off the LD drive current of the LD driver 2. At this time, the amount of heat generated by the LD decreases due to a decrease in the LD drive current, and the temperature of the LD instantaneously decreases. However, this temperature drop is detected by the temperature detection element 4, and the temperature control unit 7 controls the drive current of the thermoelectric element 3 so that the temperature approaches T0, so the temperature of the LD returns to T0. During this time, no signal light is output from the LD 1.

  At time t1, when shutdown is canceled by a command from the host system and the optical shutdown signal becomes low level, the shutdown controller 9 turns on the LD drive current of the LD driver 2. At this time, since the LD drive current increases, the temperature of the LD instantaneously rises to T0 + ΔTh due to Joule heat. This temperature rise is detected by the temperature detection element 4, and the temperature controller 7 controls the drive current of the thermoelectric element 3 so that the temperature approaches T0. After the temperature of the LD falls to a temperature T0−ΔTc lower than T0, it returns to T0 with vibration. During this time, since the signal light is output from the LD1, as shown in FIG. 9D, when the shutdown is canceled, the wavelength of the LD output light suddenly rises to λ0 + Δλh, which is longer than λ0, and the temperature of the LD The LD output wavelength approaches the steady state λ0 while changing between λ0 + Δλh and λ0−Δλc as it changes.

  As a measure for improving wavelength fluctuation at the start of LD driving, which has been considered in the past, whether or not the time during which the temperature detected by the temperature detection element continuously stays within the convergence determination range has exceeded a predetermined time before the start of LD driving An optical transmitter (hereinafter referred to as the second prior art) that starts driving the LD on the condition that a predetermined time has been exceeded is shown. (See Patent Document 1)

  Furthermore, as another measure for improving the wavelength fluctuation at the start of the LD driving, which has been considered in the past, the LD driving is performed on the condition that the temperature of the LD is stable and the monitored wavelength is stabilized while the LD is weakly illuminated. A wavelength-stabilized light source and a control method (hereinafter referred to as third prior art) are shown. (See Patent Document 2)

JP 2006-140719 A JP 2003-298524 A

In the first prior art described above, since the LD temperature rapidly rises at the moment when the LD driving is started, the wavelength λ0 + Δλh which is greatly shifted from the desired wavelength λ0 to the long wavelength side instantaneously is obtained, and the wavelength interval is narrow. In some cases, the tolerance of the center wavelength accuracy is exceeded, and communication between adjacent wavelength channels may be disturbed.
In the second prior art described above, since the LD driving is started after the LD temperature is stabilized, the control is performed when the LD temperature is far from the target temperature, such as when the transmitter is turned on. Unstable behavior in which the LD wavelength is dragged by a transient temperature change can be improved. However, the phenomenon that the wavelength is greatly shifted to the longer wavelength side from the desired wavelength at the moment of starting the driving of the LD occurs as in the first prior art.

  In the third prior art described above, when the temperature of the LD is far from the target temperature, such as when the transmitter is turned on, an unstable behavior in which the LD wavelength is dragged by a transient temperature change based on control. Can be improved. However, the same phenomenon as in the first prior art in which the wavelength is greatly shifted to the longer wavelength side than the target wavelength at the moment of starting the LD drive is not improved. In addition, if the condition for starting the LD drive is that the monitored wavelength is stable while the LD is weakly emitted, light that is not intended for communication is emitted, and there is concern about the influence on adjacent channels and communication systems. The

  The present invention has been made to solve such problems, and an object of the present invention is to reduce wavelength fluctuation at the start of LD driving.

  An optical transmitter according to the present invention includes a laser diode, a laser driver that drives the laser diode, a temperature detection element that detects a temperature of the laser diode, a thermoelectric element that changes the temperature of the laser diode, and the thermoelectric sensor. A reference signal generation unit that generates a reference signal for setting the element to a reference temperature, and an error detection unit that generates an error signal according to a difference between a detection signal from the temperature detection element and a reference signal from the reference signal generation unit A temperature control unit that drives the thermoelectric element based on an error signal from the error detection unit to control the temperature of the laser diode to the reference temperature, and the reference temperature when the laser diode is in a shutdown state. When the shutdown state of the laser diode is released, the reference temperature is increased to An optical transmitter and a reference signal controlling unit for returning.

  The stabilized light source according to the present invention includes a laser diode, a laser driver that drives the laser diode, a temperature detection element that detects the temperature of the laser diode, a thermoelectric element that changes the temperature of the laser diode, A reference signal generation unit that generates a reference signal for setting the thermoelectric element to a reference temperature, and an error that generates an error signal according to a difference between a detection signal from the temperature detection element and a reference signal from the reference signal generation unit A detection unit, a temperature control unit that drives the thermoelectric element based on an error signal from the error detection unit to control the temperature of the laser diode to the reference temperature, and the laser diode is in a shutdown state, When the reference temperature is lowered and the shutdown state of the laser diode is released, the reference temperature is increased. Allowed by a stabilized light source and a reference signal controlling unit undone.

  Further, the temperature control method according to the present invention is a method for detecting a temperature of a laser diode and controlling the temperature of the laser diode based on a deviation between the temperature and a reference temperature. A first step of lowering the laser diode, a second step of causing the laser diode to emit light, and a third step of raising the reference temperature and returning it to the original level when the deviation becomes a predetermined value or less. This is a method for controlling a laser diode.

  In the optical transmitter, when the laser diode is in the shutdown state, the temperature of the laser diode is controlled to be lower than the target temperature when the laser diode is not in the shutdown state. Deviation from wavelength can be reduced.

It is a block diagram of the optical transmitter which concerns on Embodiment 1 of this invention. 3 is a timing chart of the optical transmitter according to the first embodiment of the present invention. 3 is a flowchart showing an operation sequence of the optical transmitter according to the first embodiment of the present invention. 3 is a timing chart of the optical transmitter according to the first embodiment of the present invention. It is a block diagram of the optical transmitter which concerns on Embodiment 2 of this invention. It is a block diagram of the optical transmitter which concerns on Embodiment 3 of this invention. It is a block diagram of the optical transmitter which concerns on Embodiment 4 of this invention. It is a block diagram of the optical transmitter which concerns on a 1st prior art. It is a timing chart of the optical transmitter which concerns on a 1st prior art.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of an optical transmitter according to the first embodiment. The LD 1 generates signal light according to the drive signal output from the LD driver 2. The thermoelectric element 3 provided close to the LD 1 adjusts the temperature of the LD 1 by absorbing heat from the LD 1 or radiating heat to the LD 1. A temperature detecting element 4 provided in the vicinity of the LD 1 detects the temperature of the LD 1.
The reference signal generator 5 generates a reference signal corresponding to the target temperature of the LD 1. The error detection unit 6 compares the detection signal of the temperature detection element 4 with the reference signal of the reference signal generation unit 5, and generates an error signal proportional to the difference between the target temperature and the detection temperature. The temperature control unit 7 controls the drive current of the thermoelectric element 3 based on the error signal from the error detection unit 6 so that the temperature of the LD 1 approaches the target temperature.

The reference signal control unit 8 will be described. The T0 calculator 81 calculates a temperature T0 at which the LD output light has a desired wavelength λ0 for communication with reference to a correspondence table of λ0 and T0 recorded in advance in the memory 82. Based on information (not shown) of the LD drive current value ILD, the ΔT0 calculation unit 83 shows a correspondence table between ILD and ΔT0 that is recorded in advance in the memory 84 with the temperature difference ΔT0 that decreases the target temperature from the temperature T0 in the shutdown state. Calculate with reference. Based on the error information from the error detection unit 6, the temperature stability determination unit 85 determines whether or not the temperature of the LD1 has converged to the target temperature.
Based on the information on whether or not the shutdown state is the shutdown state from the shutdown control unit 9, the target temperature change control unit 86 outputs the target temperature calculation unit 87 to the reference signal generation unit 5 with T0−ΔT0 as the target temperature in the shutdown state. To instruct. After the shutdown is canceled, the temperature stability determination unit 85 instructs the reference signal generation unit 5 to output T0 as the target temperature after determining that the LD temperature has stabilized.

The shutdown controller 9 is a shutdown signal (not shown) from a system (not shown).
Is in the high level, the LD driver 2 is instructed to turn off the LD drive current, and at the same time, the target temperature change control unit 86 of the reference signal control unit 8 is notified of the shutdown state. If the shutdown signal is at a low level, an instruction is given to turn on the LD drive current of the LD driver 2 so that the LD output light has a predetermined intensity, and at the same time, the target temperature change control unit 86 indicates that it is in the shutdown release state. To tell.

FIG. 2 is a timing chart showing the operation of the optical transmitter according to the first embodiment. 2A shows the optical shutdown signal, FIG. 2B shows the intensity of the optical output of the LD, FIG. 2C shows the temperature of the LD, and FIG. 2D shows the wavelength of the LD output light. Yes. FIG. 3 is a flowchart showing an operation sequence of the optical transmitter shown in FIG.
Before the time t0, it is a steady state before shutting down. At this time, the optical shutdown signal is at a low level. The LD is controlled to a temperature T0, and emits LD output light at a desired output light intensity and wavelength λ0 for communication.

  At time t0, when the optical shutdown signal becomes high level by a shutdown command from the host system (step S1), the shutdown controller 9 turns off the LD drive current of the LD driver 2 (step S2). At the same time, the reference signal generator 5 instructs the target temperature to be lowered from T0 to T0−ΔT0 via the reference signal controller 8 (ΔT0 is a positive value) (step S3). The amount of heat generated by the LD decreases due to the shutdown, and the temperature of the LD instantaneously decreases. This temperature variation is detected by the temperature detection element 4, and the temperature controller 7 controls the drive current of the thermoelectric element 3 so as to bring the temperature of the LD closer to the new target temperature T0-ΔT0 (step S4). It waits for the temperature to converge to T0-ΔT0 (step S5). During the shutdown state, since the LD drive current is off, no signal light is output from LD1.

At time t1, when the optical shutdown signal becomes low level due to the shutdown release command from the host system (step S6), the shutdown controller 9 turns on the LD drive current of the LD driver 2 and starts the light emission of LD1 (step S6). S7). At this time, since the LD drive current increases rapidly, the temperature of the LD instantaneously rises to T0−ΔT0 + ΔTh due to Joule heat. The reference signal from the reference signal generator 5 remains at the target temperature T0−ΔT0. The temperature rise of the LD at this time is detected by the temperature detection element 4, and the temperature control unit 7 controls the drive current of the thermoelectric element 3 so that the temperature of the LD becomes T0−ΔT0 (step S8).
The temperature of the LD converges to T0-ΔT0 with vibration after dropping to a temperature T0-ΔT0-ΔTc lower than T0-ΔT0 (step S9). During this time, since the signal light is output from the LD1, as shown in FIG. 2D, when the shutdown is canceled, the wavelength of the LD output light becomes λ0−Δλ0 + Δλh, which is longer than the desired wavelength λ0. While varying between λ0−Δλ0 + Δλh and λ0−Δλ0−Δλc, the light converges to the target wavelength λ0−Δλ0 corresponding to the target temperature T0−ΔT0.

  Waiting for the LD temperature to converge to T0−ΔT0, the target temperature change control unit 86 of the reference signal control unit 8 instructs the target temperature calculation unit 87 to return the target temperature from T0−ΔT0 to T0 (time). t2) (Step S10). The target temperature is changed to T0 on condition that the temperature of the LD converges to T0−ΔT0 (that is, the error output from the error detection unit 6 stays within a predetermined range for a predetermined time). The temperature stability determination unit 85 makes a condition determination based on the error signal. The change of the target temperature to T0 may be made on the condition that a certain time has elapsed since the time from the time t1 until the temperature of the LD becomes stable. In this case, without using an error signal from the error detection unit 6, a target temperature change control unit 86 determines whether a predetermined time has elapsed by using a timer (not shown) built therein, and changes the target temperature.

  After time t2 when the target temperature is changed to T0, the temperature of the LD is detected by the temperature detection element 4, and the temperature control unit 7 controls the drive current of the thermoelectric element 3 so that the temperature approaches T0. Is controlled to a new target temperature T0 (step S11). When the shutdown state is entered again (S12), the process returns to the first step S1.

The temperature variation immediately after the shutdown is canceled is compared between the present embodiment and the first conventional optical transmitter.
In this embodiment, the temperature of the LD is set to T0−ΔT0 before the shutdown release where the LD does not emit light, and is set lower by ΔT0 than the first prior art. For this reason, the temperature T0−ΔT0 + ΔTh after the increase immediately after the shutdown release is lower by ΔT0 than the temperature T0 + ΔTh after the increase immediately after the shutdown release in the case of the first prior art. Accordingly, the temperature rise immediately after the shutdown is released with respect to the temperature T0 in the steady state where optical communication is performed is smaller by ΔT0 in the present embodiment.

  In the present embodiment, the target temperature T0-ΔT0 of the LD before the shutdown release is lower by ΔT0 than the first prior art. The wavelength variation immediately after the shutdown is released has the same relationship as the temperature variation because the wavelength of the LD output light becomes longer as the LD temperature increases. Therefore, in the present embodiment, the wavelength λ0−Δλ0 + Δλh of the LD that has become longer after the shutdown is canceled is shorter by Δλ0 than the wavelength λ0 + Δλh of the first prior art LD. Δλ0 is a wavelength difference corresponding to the target temperature decrease ΔT0. As a result, the fluctuation in the direction of increasing the wavelength from the desired wavelength λ0 after the shutdown is canceled is smaller by Δλ0 in the present embodiment than in the first conventional technique.

A setting condition of the target temperature decrease range ΔT0 between time t0 and time t2 will be described.
In the process of convergence to the target temperature T0−ΔT0 after the shutdown is released (time t1 to t2), as shown in FIG. It converges while vibrating between ΔTc. In normal temperature control, | ΔTh |> | ΔTc |. If the thermal condition, temperature control parameter, and wavelength temperature coefficient of the LD are the same, the values of ΔTc and Δλc are equal in both cases of the present embodiment and the first prior art. The values of ΔTh and Δλh are the same in both cases of the present embodiment and the first prior art.

Therefore, the maximum value (absolute value) of the temperature fluctuation from T0 after the shutdown is canceled is ΔTh in the case of the first prior art, and in this embodiment, ΔTh−ΔT0 or ΔTc + ΔT0, whichever is greater (Max (ΔTh−ΔT0, ΔTc + ΔT0)). Therefore, if ΔT0 is set so as to satisfy the condition of 0 <ΔT0 <ΔTh−ΔTc (hereinafter referred to as the first wavelength variation suppression condition), ΔTh <Max (ΔTh−ΔT0, ΔTc + ΔT0), which is the first conventional technique. The technology has the effect of reducing temperature fluctuations and wavelength fluctuations after shutdown is canceled.
More preferably, when ΔT0 is set to satisfy ΔT0 = (ΔTh−ΔTc) / 2 (hereinafter referred to as a second wavelength variation suppression condition), the upper limit T0−ΔT0 + ΔTh of the temperature variation and the lower limit T0−ΔT0−ΔTc. Is equal to T0, the maximum temperature fluctuation can be suppressed to (ΔTh−ΔTc) / 2. At this time, the wavelength variation from λ0 after the shutdown is canceled is (Δλh−Δλc) / 2 and can be optimized.

In the above, the case where the process of converging from the raised temperature T0−ΔT0 + ΔTh after the shutdown release to the target temperature T0−ΔT0 converges while oscillating over the target temperature or the target wavelength is shown. Depending on the value of the control parameter or the like of the temperature controller 7, the target temperature or target wavelength may be approached monotonously. FIG. 4 shows a timing chart in this case. 4A shows the optical shutdown signal, and FIG. 4B shows the intensity of the LD output light. Since these are the same as FIG. 2A and FIG.
FIG. 4C and FIG. 4D show the LD temperature and the wavelength of the LD output light, respectively, when the temperature monotonously approaches the target temperature after a rapid temperature rise after the shutdown is canceled. Since the temperature of the LD does not go too far to the lower temperature side than the target temperature T0−ΔT0, ΔTc = 0 can be set in the above-described first or second wavelength variation suppression condition equation, and ΔT0 is 0 <ΔT0 <ΔTh−ΔTc. More preferably, if ΔT0 = ΔTh / 2 is set, wavelength fluctuation can be suppressed. If ΔTh is the same between the case where the temperature is accompanied by vibration and the case where the temperature monotonously approaches the target temperature, ΔT0 can be set larger than the case where the temperature vibrates when the temperature monotonously approaches the target temperature. The fluctuation can be suppressed more effectively.

  In general, when the temperature or the intensity of the LD output light is different, the temperature fluctuations ΔTh and ΔTc when the shutdown is canceled take different values. Therefore, the memory 84 referred to by the ΔT0 calculating unit 83 holds a correspondence table of ΔT0 with respect to the plurality of temperatures T0 and the LD drive current ILD, and suppresses the first or second wavelength variation at the plurality of temperatures / output light intensities. By setting ΔT0 that satisfies the condition, it is possible to more effectively suppress the wavelength fluctuation at the time of releasing the shutdown in a wide temperature / output light intensity range.

  As described above, the optical transmitter according to the present embodiment lowers the target temperature from T0 corresponding to the desired wavelength to T0−ΔT0 in the shutdown state, thereby changing the wavelength variation from the steady state wavelength after the shutdown is canceled. Can be suppressed.

The optical transmitter according to the present embodiment can stabilize the wavelength not only when the shutdown is canceled but also when the driving of the LD is started after the optical transmitter is powered on. In this case, the wavelength variation at the start of light emission can be similarly suppressed by performing the same sequence from the step S1 when the power is turned on as a shutdown state. Further, even when the desired wavelength λ0 is changed for switching the wavelength channel of optical communication while the power is turned on, the same sequence as that in the shutdown state is performed from step S1 with the change of λ0. Wavelength variation at the start can be similarly suppressed.
In the present embodiment, the LD output light may be a modulated light modulated by a digital signal or an analog signal. In addition, it is possible to configure an optical transmitter system by using the optical transmitter according to the present embodiment as a wavelength-stabilized light source by using LD output light as continuous light and connecting an optical modulator at the subsequent stage.
These modifications can be similarly applied to other embodiments.

Embodiment 2. FIG.
The transmitter according to the second embodiment is the same as that of the first embodiment shown in FIG. 1 except for a part thereof, and the operation is also substantially the same as that of the first embodiment. Therefore, a different part from Embodiment 1 is demonstrated, a common part attaches | subjects the same code | symbol, and abbreviate | omits description. Since the internal configuration of the reference signal control unit 8 is the same as that of the first embodiment, the description thereof is omitted.
FIG. 5 is a block diagram illustrating a configuration of the optical transmitter according to the second embodiment. Unlike the first embodiment, the reference signal control unit 8 sets the target temperature based on the shutdown signal output from the LD driver 2.

Next, the operation will be described.
The operation is basically the same as in the first embodiment. The difference is that a shutdown signal indicating a shutdown state is input from the LD driver 2 to the reference signal control unit 8. When a host system (not shown) issues a shutdown signal to the LD driver 2, the LD driver 2 turns off the LD drive current. At the same time, the LD driver 2 sets the shutdown signal to a high level and outputs it to the reference signal control unit 8. When the host system issues a shutdown release signal to the LD driver 2, the LD driver 2 turns on the LD drive current and sets the shutdown signal to a low level.
The operation in which the reference signal control unit 8 sets the target temperature of the LD based on the shutdown signal is the same as that in the first embodiment.

  In the present embodiment, the same effect as in the first embodiment can be obtained. In addition, since the shutdown controller is not used, the circuit configuration can be simplified.

Embodiment 3 FIG.
The transmitter according to the third embodiment is the same as that of the second embodiment shown in FIG. 1 except for a part thereof, and the operation is also substantially the same as that of the second embodiment. Therefore, a different part from Embodiment 2 is demonstrated, a common part attaches | subjects the same code | symbol, and abbreviate | omits description. Since the internal configuration of the reference signal control unit 8 is the same as that of the second embodiment, the description thereof is omitted.
FIG. 6 is a block diagram illustrating a configuration of the optical transmitter according to the third embodiment. Unlike the second embodiment, the LD current monitor circuit 10 that detects the magnitude of the LD drive current of the LD driver 2 is provided, and the shutdown state is detected based on the monitor current value output from the LD current monitor circuit 10. .

Next, the operation will be described.
The operation is basically the same as in the second embodiment. The difference is that a shutdown signal for detecting a shutdown state is input from the LD current monitor circuit 10 to the reference signal control unit 8.
When the shutdown state is entered and the LD drive current is turned off, the LD current monitor circuit 10 detects this, sets the shutdown signal to high level, and outputs it to the reference signal control unit 8. When the shutdown is released and the LD drive current is turned on, this is detected by the LD current monitor circuit 10, and the shutdown signal is set to a low level and output to the reference signal control unit 8.
The operation in which the reference signal controller 8 sets the target temperature of the LD based on the shutdown signal is the same as that in the second embodiment.

  In the present embodiment, the same effect as in the second embodiment can be obtained. Further, in the configuration of the present embodiment, even when the light emission of the LD is stopped regardless of the shutdown command from the host system, the wavelength fluctuation at the start of the light emission can be suppressed.

Embodiment 4 FIG.
The transmitter according to the fourth embodiment is the same as that of the second embodiment shown in FIG. 1 except for a part thereof, and the operation is also substantially the same as that of the second embodiment. Therefore, a different part from Embodiment 2 is demonstrated, a common part attaches | subjects the same code | symbol, and abbreviate | omits description.
FIG. 7 is a block diagram illustrating a configuration of the optical transmitter according to the fourth embodiment. Unlike the second embodiment, a photodiode (hereinafter referred to as PD) 11 that converts the light output intensity of the LD 1 into a current and a PD current monitor circuit 12 that detects the magnitude of the current of the PD 11 are provided, and the PD current monitor circuit 12 The shutdown state is detected based on the monitor current value output from.

Next, the operation will be described.
The operation is basically the same as in the second embodiment. The difference is that a shutdown signal for detecting a shutdown state is input from the PD current monitor circuit 12 to the reference signal control unit 8.
When the shutdown state is entered and the light emission of the LD 1 stops, the PD current monitor circuit 12 detects a decrease in the current of the PD 11 and sets the shutdown signal to a high level and outputs it to the reference signal control unit 8. When the shutdown is released and the light emission of the LD 1 starts, the PD current monitor circuit 12 detects an increase in the current of the PD 11, sets the shutdown signal to a low level, and outputs it to the reference signal control unit 8.
The operation in which the reference signal controller 8 sets the target temperature of the LD based on the shutdown signal is the same as that in the second embodiment.

  In the present embodiment, the same effect as in the second embodiment can be obtained. Further, in the configuration of the present embodiment, even when the light emission of the LD is stopped regardless of the shutdown command from the host system, the wavelength fluctuation at the start of the light emission can be suppressed.

1 LD
2 LD Driver 3 Thermoelectric Element 4 Temperature Detection Element 5 Reference Signal Generation Unit 6 Error Detection Unit 7 Temperature Control Unit 8 Reference Signal Control Unit 9 Shutdown Control Unit 10 LD Current Monitor Circuit 11 PD
12 PD current monitor circuit

Claims (7)

A laser diode;
A laser driver for driving the laser diode;
A temperature detecting element for detecting the temperature of the laser diode;
A thermoelectric element for changing the temperature of the laser diode;
A reference signal generator for generating a reference signal for setting the thermoelectric element to a reference temperature;
An error detection unit that generates an error signal according to a difference between a detection signal from the temperature detection element and a reference signal from the reference signal generation unit;
A temperature controller that drives the thermoelectric element based on an error signal from the error detector to control the temperature of the laser diode to the reference temperature;
A light having a reference signal control unit that lowers the reference temperature when the laser diode is in a shutdown state and raises the reference temperature to restore the reference temperature when the shutdown state of the laser diode is released Transmitter. The optical transmitter according to claim 1, wherein the reference signal control unit changes the reference temperature based on a shutdown signal from a shutdown control unit that controls a shutdown state of the laser driver. The optical transmitter according to claim 1, wherein the reference signal control unit changes the reference temperature based on a shutdown signal from the laser driver. The optical transmitter according to claim 1, wherein the reference signal control unit changes the reference temperature based on a shutdown signal from a current monitor circuit that monitors a drive current of the laser diode. The optical transmitter according to claim 1, wherein the reference signal control unit changes the reference temperature based on a shutdown signal from a photodiode that monitors an optical output intensity of the laser diode. A laser diode;
A laser driver for driving the laser diode;
A temperature detecting element for detecting the temperature of the laser diode;
A thermoelectric element for changing the temperature of the laser diode;
A reference signal generator for generating a reference signal for setting the thermoelectric element to a reference temperature;
An error detection unit that generates an error signal according to a difference between a detection signal from the temperature detection element and a reference signal from the reference signal generation unit;
A temperature controller that drives the thermoelectric element based on an error signal from the error detector to control the temperature of the laser diode to the reference temperature;
A stable reference signal control unit that lowers the reference temperature when the laser diode is in a shutdown state and raises the reference temperature to restore the reference temperature when the shutdown state of the laser diode is released Light source. In the method of detecting the temperature of the laser diode and controlling the temperature of the laser diode based on the deviation between the temperature and the reference temperature,
A first step of lowering the reference temperature before light emission of the laser diode;
A second step of causing the laser diode to emit light;
A laser diode control method comprising: a third step of raising the reference temperature and returning it to the original temperature when the deviation becomes a certain value or less.

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