JP2012169768A - Laser controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser controller capable of setting a suitable upper limit value of bias current according to the ambient temperature of a laser diode without depending on the individual laser diode even in the presence of manufacturing variations and time-related deterioration of the laser diodes.SOLUTION: The laser controller includes a laser diode 3, a current circuit 5 for supplying bias current to the laser diode 3, a current monitor section 9 for monitoring the bias current; a photo diode 11 for detecting an optical signal of the laser diode 3; an optical signal monitor section 13 for monitoring light intensity of the optical signal via the photo diode 11; and a control section 7 for performing APC control of the bias current. On the basis of the value of the bias current monitored by the current monitor section 9, the control section 7 calculates an upper limit value of the bias current used for the APC control and performs the APC control so that the bias current does not exceed the upper limit value.

Description

  The present invention relates to a laser control device that controls a laser diode.

  Patent Document 1 discloses an optical transmitter that can restore an optical output at an appropriate timing according to the ambient temperature when the optical output is automatically stopped. The optical transmitter of Patent Document 1 includes an LD (laser diode), an LD drive circuit, a monitor PD, an APC circuit that controls the drive current of the LD, a temperature monitor, and a controller. The controller monitors the bias current included in the drive current, controls the APC circuit to stop the optical signal when the monitored value of the bias current exceeds the shutdown threshold, and the value of the monitor signal immediately before the stop of the optical signal Is over the failure determination threshold value, the APC circuit is controlled so that the generation of the optical signal is restarted when the monitor value of the ambient temperature becomes lower than the recovery determination threshold value.

JP 2009-1111730 A JP 2009-296292 A JP 2000-022631 A

  When a failure occurs in the monitor PD for monitoring the light intensity of the LD or the light intensity monitor circuit, the light intensity of the LD is fed back from the monitor circuit to the APC circuit that controls the bias current of the LD. Therefore, when a suitable bias current is not supplied to the LD, an excessive bias current may be supplied to the LD. For this reason, it is conceivable to set an upper limit value for the bias current. However, when the LD is operating at a relatively low temperature, the light emission efficiency of the LD is relatively good. Therefore, when the bias current is supplied to the LD at this upper limit value, the LD is preset. The light intensity may exceed the upper limit (particularly the upper limit set by the standard). Therefore, it is conceivable to set a suitable upper limit value according to the temperature. However, in order to set the upper limit value according to the temperature, it is necessary to consider the manufacturing variation of the LD, the aging of each LD, etc., and therefore the ambient temperature of the LD regardless of the individual LD. Accordingly, it is difficult to set a suitable upper limit value of the bias current.

  Therefore, the object of the present invention has been made in view of the above matters, and even when there are manufacturing variations of laser diodes and aging deterioration, the ambient temperature of the laser diodes can be adjusted regardless of the individual laser diodes. Accordingly, it is an object of the present invention to provide a laser control device capable of setting a suitable upper limit value of the bias current.

  An optical transmitter according to the present invention includes a laser diode that generates an optical signal, a current circuit that supplies a drive current to the laser diode, and a current monitor that monitors a bias current included in the drive current supplied to the laser diode. Unit, a photodiode for detecting an optical signal generated by the laser diode, an optical signal monitoring unit for monitoring the optical intensity of the optical signal generated by the laser diode via the photodiode, and the optical signal A control unit that performs APC control of a bias current based on a monitor signal from the monitor unit, and the control unit uses a bias current value monitored by the current monitor unit to use a bias current for APC control. The APC control is performed so that the bias current does not exceed the upper limit value. And wherein the door. According to the laser control device of the present invention, the upper limit value (current Imax) of the bias current is calculated every time the ambient temperature of the laser diode changes. Therefore, even when there are manufacturing variations and aging deterioration of the laser diode, a suitable maximum value of the bias current can be set according to the ambient temperature of the laser diode without depending on the individual laser diodes.

  The optical transmission device according to the present invention further includes a temperature monitoring unit that monitors the ambient temperature of the laser diode, and the control unit is preset with a change in ambient temperature of the laser diode monitored by the temperature monitoring unit. Determining means for determining whether or not it is in the first range during the period, and calculating means for calculating the upper limit value when the determining means determines that the change is in the first range. Have. Therefore, the upper limit value of the bias current is calculated when the ambient temperature of the laser diode is stable.

  In the optical transmission device according to the present invention, the control unit determines the ambient temperature of the laser diode monitored by the temperature monitoring unit when the determination unit determines that the change is in the first range. And storing means for storing the value in a storage device, wherein the determination means stores the value of the ambient temperature of the laser diode monitored by the temperature monitor after the upper limit value is calculated by the calculation means and the storage It is determined whether or not a difference from the value of the ambient temperature of the laser diode stored in the apparatus exceeds a second range, and when it is determined that the difference exceeds the second range, the change occurs in the period. It is determined again whether it is in the first range. Therefore, when the change in the ambient temperature of the laser diode exceeds the preset range, it is determined again whether or not the ambient temperature is stable. The upper limit value of the bias current can be calculated under the ambient temperature.

  In the optical transmission apparatus according to the present invention, the storage unit stores the value of the bias current monitored by the current monitor unit when the determination unit determines that the change is in the first range. The calculation means stores the upper limit value based on a bias current value stored in the storage device. Therefore, the upper limit value is calculated based on the value of the bias current supplied to the laser diode under a stable ambient temperature.

  According to the present invention, even when laser diode manufacturing variation or aging deterioration occurs, laser control that can set a suitable upper limit value of the bias current according to the ambient temperature of the laser diode without depending on individual laser diodes. An apparatus can be provided.

FIG. 1 is a diagram illustrating a configuration of a laser control apparatus according to the embodiment. FIG. 2 is a diagram illustrating a physical configuration of the control unit according to the embodiment. FIG. 3 is a flowchart for explaining the operation of the laser control apparatus according to the embodiment. FIG. 4 is a diagram showing the correlation between the bias current and the light intensity and how the correlation changes according to the temperature. FIG. 5 is a diagram schematically showing an example of the upper limit value of the bias current set according to the ambient temperature of the laser diode.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a diagram illustrating a configuration of a laser control apparatus 1 according to the embodiment. FIG. 2 is a diagram illustrating a physical configuration of the control unit 7. The laser control device 1 is mounted on, for example, an optical transmission device (not shown). As shown in FIG. 1, the laser control device 1 includes a laser diode 3, a current circuit 5, a control unit 7, a current monitor unit 9, a photodiode 11, an optical signal monitor unit 13, and a temperature monitor unit 15.

  The laser diode 3 generates an optical signal. The current circuit 5 supplies a drive current to the laser diode 3. The control unit 7 performs APC control of the bias current based on the monitor signal from the optical signal monitor unit 13. Based on the value of the bias current monitored by the current monitor unit 9, the control unit 7 calculates the upper limit value (hereinafter referred to as current value Imax) of the bias current used for APC control, and the bias current does not exceed the current Imax. APC control is performed as follows. The controller 7 calculates the current Imax by the method shown in the flowchart of FIG. The current monitor unit 9 monitors a bias current included in the drive current supplied to the laser diode 3. The current monitor unit 9 outputs a monitor signal indicating the monitoring result to the control unit 7. The photodiode 11 detects an optical signal generated by the laser diode 3. The optical signal monitor unit 13 monitors the light intensity of the optical signal generated by the laser diode 3 via the photodiode 11. The optical signal monitor unit 13 outputs a monitor signal indicating the monitoring result to the control unit 7. The temperature monitor unit 15 monitors the ambient temperature of the laser diode 3. The temperature monitoring unit 15 outputs a monitor signal indicating the monitoring result to the control unit 7.

  The control unit 7 physically has a computer device including a CPU 71, a ROM 72, a RAM 73, a storage device 7d, and the like shown in FIG. The CPU 71, ROM 72, RAM 73, and storage device 7d are connected to the bus 74. The CPU 71 loads the computer program (for example, a computer program for executing the processing of the flowchart shown in FIG. 3) stored in a memory such as the ROM 72 and the storage device 7d into the RAM 73, and executes the program for the current circuit 5. Control (in particular, APC control for the bias current supplied to the laser diode 3 and the processing shown in the flowchart of FIG. 3) is performed. The storage device 7d is a readable / writable memory (for example, a built-in memory of the laser control device 1 or a recording medium detachable from the laser control device 1), and executes various computer programs and computer programs. Stores various data necessary for.

  The control unit 7 has a plurality of functions. The control unit 7 has a plurality of functions based on the monitor signal input from the current monitor unit 9, the monitor signal input from the optical signal monitor unit 13, and the monitor signal input from the temperature monitor unit 15. Is a function realized by executing a computer program stored in a memory such as the ROM 72 and the storage device 7d. As such a plurality of functions, the control unit 7 particularly includes a determination unit 7a (determination unit), a calculation unit 7b (calculation unit), and a storage unit 7c (storage unit) shown in FIG.

  The determination unit 7a determines whether or not the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is within a first range in a preset period (hereinafter referred to as period T1) (the periphery of the laser diode 3). It is determined whether or not the temperature is stable.

  When the determination unit 7a determines that the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is in the first range (the ambient temperature of the laser diode 3 is stable) in the storage unit 7c. In addition, data indicating the value of the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is stored in the storage device 7d. When the determination unit 7a determines that the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is in the first range (the ambient temperature of the laser diode 3 is stable) in the storage unit 7c. In addition, data indicating the value of the bias current monitored by the current monitor unit 9 is stored in the storage device 7d.

  When the calculation unit 7b determines by the determination unit 7a that the change in the ambient temperature of the laser diode 3 monitored by the temperature monitor unit 15 is in the first range (the ambient temperature of the laser diode 3 is stable). Then, the current Imax is calculated. The calculation unit 7b calculates the current Imax based on the value of the bias current indicated by the data stored in the storage device 7d.

  The determination unit 7a further determines the ambient temperature value of the laser diode 3 monitored by the temperature monitor unit 15 after the current Imax is calculated by the calculation unit 7b and the ambient temperature of the laser diode 3 stored in the storage device 7d. It is determined whether or not the difference from the value exceeds the second range (whether or not the ambient temperature of the laser diode 3 has changed). The determination unit 7a includes a value of the ambient temperature of the laser diode 3 monitored by the temperature monitor unit 15 after the current Imax is calculated by the calculation unit 7b, and a value of the ambient temperature of the laser diode 3 stored in the storage device 7d. When the temperature difference exceeds the second range (the ambient temperature of the laser diode 3 has changed), the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is the first time period T1. It is determined again whether it is within the range (whether the ambient temperature after the change of the laser diode 3 is stable). The current Imax is calculated by the calculation unit 7b according to the ambient temperature of the laser diode 3, but an allowable upper limit value is set in advance for the current Imax.

  Next, the operation of the laser control apparatus 1 will be described with reference to FIG. FIG. 3 is a flowchart for explaining the operation of the laser control apparatus 1 according to the embodiment. The flowchart in FIG. 3 represents one specific example of a method for calculating the current Imax. First, the control unit 7 confirms that APC control is operating normally (step S1). That is, in step S1, the control unit 7 confirms that a preset light intensity is obtained for the laser diode 3 based on the monitor signal from the optical signal monitor unit 13. When it is confirmed in step S1 that the APC control is operating normally (step S1; Yes), the control unit 7 proceeds to step S2. When it is not confirmed in step S1 that the APC control is operating normally (step S1; No), the control unit 7 sets the current circuit 5 so that the drive current supplied to the laser diode 3 becomes zero. Control and exit.

  After step S1, the determination unit 7a determines whether or not the ambient temperature of the laser diode 3 is stabilized based on the monitor signal from the temperature monitor unit 15 (step S2). That is, in step S2, the determination unit 7a determines the change of the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 in the first range, for example, in a preset period T1, for example, 1 ms to 99 ms. It is determined whether the angle is 0.1 degree or less. The determination unit 7a determines that the ambient temperature of the laser diode 3 is stable when the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is within the first range in the period T1. The determination unit 7a continues to monitor the ambient temperature of the laser diode 3 based on the monitor signal from the temperature monitor unit 15 until it determines that the ambient temperature of the laser diode 3 is stable, but does not proceed to the subsequent step S3. .

  When the determination unit 7a determines that the ambient temperature of the laser diode 3 is stable in step S2, the storage unit 7c receives data indicating the current ambient temperature of the laser diode 3 (monitoring from the temperature monitoring unit 15) in step S3. Signal) is stored in the storage device 7d (step S3). If the determination unit 7a determines in step S2 that the ambient temperature of the laser diode 3 is stable, the storage unit 7c displays data indicating the current bias current value (monitoring from the current monitor unit 9) in step S4. Signal) is stored in the storage device 7d (step S4). In addition, the order of step S3 and step S4 is not restricted to the order shown in FIG. That is, step S4 may be executed after step S3, or step S3 may be executed after step S4.

  After step S3 and step S4, the calculation unit 7b calculates the current Imax (step S5). The current Imax is a value of the current bias current (the value of the bias current indicated by the data stored in the storage device 7d by the storage unit 7c in step S4) by a preset calculation method. It is a value calculated to a larger value. For example, the current Imax is a value about 1.1 times the current bias current value (the bias current value indicated by the data stored in the storage device 7d by the storage unit 7c in step S4). By the processing up to step S5, the upper limit value of the bias current can be calculated when the ambient temperature of the laser diode 3 is stable. Furthermore, the current Imax can be calculated based on the value of the bias current supplied to the laser diode 3 under a stable ambient temperature.

  In step S6, the determination unit 7a determines the ambient temperature value of the laser diode 3 monitored by the temperature monitoring unit 15 after step S5, and the ambient temperature value of the diode 3 stored in the storage device 7d in step S3. And the difference between the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 after step S5 and whether or not the difference exceeds a second range, for example, minus 2 degrees or more and plus 2 degrees or less. When it is determined that the difference between the ambient temperature value of the laser diode 3 stored in the storage device 7d in step S3 exceeds the second range, it is determined that the ambient temperature of the laser diode 3 has changed. Proceed again to S2 (step S6). Here, the determination unit 7a determines whether or not the change in the ambient temperature of the laser diode 3 monitored by the temperature monitoring unit 15 is in the first range in the period T1 (that is, whether the ambient temperature of the laser diode 3 has stabilized). No) is determined again, and the subsequent steps S3 to S6 are executed again.

  By the process in step S6, the upper limit value (current Imax) of the bias current can be calculated every time the ambient temperature of the laser diode 3 changes. Even if the change in the ambient temperature of the laser diode 3 exceeds the preset second range, it is determined again whether or not the ambient temperature has stabilized, so that the ambient temperature has changed. In addition, the upper limit value of the bias current can be calculated under the ambient temperature after the stable change.

  Next, with reference to FIG.4 and FIG.5, the effect | action and effect of the laser control apparatus 1 which concern on embodiment are demonstrated. FIG. 4 shows the characteristics of a general laser diode. The characteristics shown in FIG. 4 are the correlation between the bias current and the light intensity, and how the correlation changes depending on the temperature. The graphs L1, L2, and L3 are all graphs showing the correlation between the bias current and the light intensity, but the ambient temperatures of the laser diodes are different. A graph showing a correlation between the bias current and the light intensity when the ambient temperature of the laser diode is the lowest is a graph L1. A graph indicating a correlation between the bias current and the light intensity when the ambient temperature of the laser diode is the next lowest is a graph L2. A graph showing the correlation between the bias current and the light intensity when the ambient temperature of the laser diode is the highest is a graph L3. As shown in FIG. 4, the lower the ambient temperature of the laser diode, the higher the luminous efficiency of the laser diode, and the luminous efficiency deteriorates as the ambient temperature increases.

  In general, the bias current is adjusted by APC control so as to maintain the light intensity at a preset value e1. In addition, the upper limit value of the bias current is set to a value (current value i3) that is a certain amount larger than the current value (current value i2) required during high-temperature operation. However, when the laser diode is operating at a low temperature (for example, operating at a temperature at which the correlation shown in the graph L1 is realized), the light intensity e1 is obtained by the characteristics of the laser diode shown in FIG. Therefore, the current value i3 (upper limit value of the bias current) is excessive as compared with the current required for this (current value i1), and the light intensity becomes the value e2. The value e2 is larger than the set value e1 of the light intensity maintained by the APC control, and may exceed a permissible value in the standard of the light intensity, for example.

  Therefore, it is conceivable to change the upper limit value of the bias current according to the ambient temperature of the laser diode. However, when the upper limit value of the bias current is changed according to the ambient temperature of the laser diode, there is a manufacturing variation for each laser diode. Therefore, it is necessary to determine the upper limit value of the bias current according to the ambient temperature in consideration of the existence of such manufacturing variations, and also consider the increase of the bias current due to the aging of the laser diode which is difficult to predict. Must.

  FIG. 5 schematically shows an example of the upper limit value of the bias current set according to the ambient temperature of the laser diode. The current value i31 is an upper limit value of the bias current when the ambient temperature of the laser diode is the lowest. The range indicated by reference numeral v1 in the figure indicates the variation in the upper limit value of the bias current associated with the manufacturing variation of the laser diode at this ambient temperature. The current value i32 is an upper limit value of the bias current when the ambient temperature of the laser diode is the next lowest. The range indicated by reference sign v2 in the figure indicates the variation in the upper limit value of the bias current associated with the manufacturing variation of the laser diode at this ambient temperature. Further, the current value i33 is an upper limit value of the bias current when the ambient temperature of the laser diode is the highest. The range indicated by reference sign v3 in the figure indicates the variation in the upper limit value of the bias current associated with the manufacturing variation of the laser diode at this ambient temperature.

  As shown in FIG. 5, the variation in the upper limit value of the bias current varies depending on the ambient temperature of the laser diode. Moreover, it is not easy to predict the variation in the upper limit value of the bias current due to the variation in the manufacturing of the laser diode. Furthermore, it is not easy to predict an increase in bias current due to aging of the laser diode. Therefore, in the past, considering the manufacturing variation of laser diodes and aging deterioration of individual laser diodes, etc., a suitable maximum current value is set according to the ambient temperature of the laser diodes without depending on the individual laser diodes. It is difficult to set.

  On the other hand, the laser control apparatus 1 according to the embodiment calculates the upper limit value (current Imax) of the bias current every time the ambient temperature of the laser diode 3 changes. Accordingly, even when manufacturing variations of the laser diode 3 and aging deterioration are involved, a suitable maximum value of the bias current can be set according to the ambient temperature of the laser diode 3 regardless of the characteristics of the individual laser diodes. Furthermore, the upper limit value of the bias current can be calculated when the ambient temperature of the laser diode 3 is stable. Furthermore, even if the change in the ambient temperature of the laser diode 3 exceeds a preset range, it is determined again whether the ambient temperature has stabilized, so even if the ambient temperature has changed. The upper limit value of the bias current can be calculated under the ambient temperature after the stable change.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  DESCRIPTION OF SYMBOLS 1 ... Laser control apparatus, 11 ... Photodiode, 13 ... Optical signal monitoring part, 15 ... Temperature monitoring part, 3 ... Laser diode, 5 ... Current circuit, 7 ... Control part, 71 ... CPU, 72 ... ROM, 73 ... RAM 74, bus, 7a, determination unit, 7b, calculation unit, 7c, storage unit, 7d, storage device, 9 ... current monitoring unit.

Claims (4)

A laser diode that generates an optical signal;
A current circuit for supplying a driving current to the laser diode;
A current monitoring unit for monitoring a bias current included in the drive current supplied to the laser diode;
A photodiode for detecting an optical signal generated by the laser diode;
An optical signal monitoring unit that monitors the optical intensity of the optical signal generated by the laser diode via the photodiode;
A controller that performs APC control of a bias current based on a monitor signal from the optical signal monitor;
With
The control unit calculates an upper limit value of a bias current used for APC control based on a bias current value monitored by the current monitoring unit, and performs APC control so that the bias current does not exceed the upper limit value. A laser control device characterized by that. A temperature monitor for monitoring the ambient temperature of the laser diode;
The controller is
Determination means for determining whether or not a change in ambient temperature of the laser diode monitored by the temperature monitoring unit is within a first range in a preset period;
Calculation means for calculating the upper limit value when the determination means determines that the change is in the first range;
The laser control device according to claim 1, comprising: The controller is
When the determination unit determines that the change is in the first range, the storage unit further stores a value of the ambient temperature of the laser diode monitored by the temperature monitor unit in a storage device;
The determination means includes a value of the ambient temperature of the laser diode monitored by the temperature monitor after the upper limit value is calculated by the calculation means, and a value of the ambient temperature of the laser diode stored in the storage device. It is determined whether or not the difference exceeds the second range, and when it is determined that the difference exceeds the second range, it is determined again whether or not the change is within the first range in the period. The laser control device according to claim 2. The storage means stores the value of the bias current monitored by the current monitor unit in the storage device when the determination means determines that the change is in the first range,
The laser control device according to claim 3, wherein the calculation unit calculates the upper limit value based on a value of a bias current stored in the storage device.

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