JP5718034B2 - Wavelength tunable light source device and method for controlling wavelength tunable light source device - Google Patents

Description

  The present invention relates to a wavelength tunable light source device and a method for controlling the wavelength tunable light source device.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses a technique for performing coarse adjustment of the wavelength of a distributed feedback semiconductor laser by adjusting the temperature of the distributed feedback semiconductor laser, and finely adjusting the oscillation wavelength by a current injected into the distributed feedback semiconductor laser. Has been.

JP 2008-103766 A

  Incidentally, Patent Document 1 does not describe the contents related to the control at the time of starting the light source. In Patent Document 1, no consideration is given to the effect on the subsequent apparatus when changing the wavelength and when starting up.

  Therefore, an object of the present invention is to provide a wavelength tunable light source device and a wavelength tunable light source device control method capable of starting up or changing the wavelength while minimizing the influence on the subsequent device.

In order to solve the above-described problems, the present invention provides a wavelength tunable light source device that generates and outputs a laser beam having a desired wavelength, a laser diode whose emission wavelength varies with temperature, and a light output from the laser diode. Amplifying means for amplifying and transferring heat to and from the laser diode, and prior to starting the output of laser light, the temperature of the laser diode is a predetermined temperature corresponding to the target emission wavelength of the diode The temperature adjustment means that performs feedback control so as to become, and after the output of the laser light is started , the control constant of the temperature adjustment means is changed while the power of the laser light increases to the final target power. , and it controls the amplifying means by increasing the target value of the power of the laser beam stepwise, scan the power of the laser beam to the final target power A power control means for increasing a-up form, the control of the control means, when the power of the laser light becomes the final target power is the value before changing the control constant of the temperature adjustment means mentioned above changes And a wavelength control means for controlling the laser light so as to have a target wavelength.
According to such a configuration, it is possible to start up or change the wavelength while minimizing the influence on the subsequent apparatus.

According to another invention, in addition to the above-mentioned invention, the wavelength control means controls the laser light to have the target wavelength by controlling a driving current of the laser diode.
According to such a configuration, the wavelength can be set accurately.

According to another invention, in addition to the above-mentioned invention, the wavelength control means controls the laser light to have the target wavelength by controlling the temperature of the laser diode.
According to such a configuration, even if the deviation from the target wavelength is large after the control by the power control means, the target wavelength can be set.

In addition to the above invention, another invention is characterized in that a drive current is passed through the laser diode and the amplification means prior to the start of laser light output.
According to such a configuration, even when the laser diode and the amplification means generate heat, it is possible to promptly shift to a thermally stable state.

In addition to the above-mentioned invention, in another invention, a predetermined drive current at which the power of the laser beam output from the amplifying unit is equal to or lower than a level allowed for a subsequent apparatus is passed to the amplifying unit, and the power control In a state where the predetermined drive current is passed, the means controls the amplification means to increase the laser light stepwise to the final target power by using the power monitor value of the laser light output from the amplification means as an initial value. It is characterized by that.
According to such a configuration, the control can be quickly performed by setting the power monitor value to the initial value.

According to another aspect of the invention, in addition to the above-described invention, the wavelength control unit includes a power monitor value of a laser beam output from the amplification unit, and a laser beam output from the amplification unit and output through a wavelength filter. The wavelength control is performed based on the ratio to the power monitor value.
According to such a configuration, wavelength control can be accurately performed.

In addition to the above invention, another invention is characterized in that the temperature adjusting means adjusts the wavelength filter to a predetermined temperature prior to the start of laser beam output.
According to such a configuration, errors caused by the etalon filter can be minimized.

In addition to the above invention, another invention is different from a predetermined temperature at which the laser diode outputs the target wavelength when the laser light is controlled to the target wavelength by the wavelength control means. When the temperature is reached, the temperature is reset to the target temperature.
According to such a configuration, it is possible to prevent the temperature from greatly fluctuating and the wavelength of the laser light from fluctuating after wavelength locking.

According to another invention, in addition to the above invention, the output of the laser beam is started when power is turned on to the laser variable light source device.
According to such a configuration, laser light having a desired wavelength and power can be quickly output after the power is turned on.

In addition to the above invention, another invention is characterized in that the output of the laser light is started when the wavelength of the laser light outputted from the laser variable light source device is changed.
According to such a configuration, laser light having a desired wavelength and power can be quickly output when changing the wavelength.

The present invention further includes a laser diode whose emission wavelength varies depending on temperature, and an amplifying unit that amplifies light output from the laser diode and transfers heat to and from the laser diode. In the method of controlling a wavelength tunable light source device that generates and outputs a laser beam having a wavelength, prior to the start of laser beam output, the temperature of the laser diode is a predetermined temperature corresponding to the target emission wavelength of the diode After starting the output of the laser light and the temperature adjustment step for feedback control so that the power of the laser light increases to the final target power, after changing the control constant in the temperature adjustment step, The amplification means is controlled by increasing the target value of the laser light power stepwise, and the power of the laser light is adjusted to the final target power. When the power of the laser beam reaches the final target power by the power control step that increases stepwise until the power reaches the final target power, the control constant in the changed temperature adjustment step is set to the value before the change. And a wavelength control step for controlling the laser beam so as to have a target wavelength after returning.
According to such a configuration, it is possible to start up or change the wavelength while minimizing the influence on the subsequent apparatus.

  According to the present invention, it is possible to provide a wavelength tunable light source device and a wavelength tunable light source device control method capable of starting up or changing the wavelength while minimizing the influence on the subsequent device.

It is a figure which shows the structural example of the wavelength variable light source device which concerns on 1st Embodiment of this invention. It is a flowchart for demonstrating operation | movement of 1st Embodiment. It is a timing chart for demonstrating operation | movement of 1st Embodiment. It is a figure for demonstrating a part of FIG. 3 (B) in detail. It is a figure for demonstrating the principle of the wavelength control in 1st Embodiment. It is a flowchart for demonstrating operation | movement of 2nd Embodiment. It is a figure for demonstrating the detail of the process of step S30 of FIG. It is a timing chart for demonstrating operation | movement of 2nd Embodiment. It is a flowchart for demonstrating operation | movement of 3rd Embodiment. It is a timing chart for explaining operation of a 3rd embodiment. It is a flowchart for demonstrating operation | movement of 4th Embodiment. It is a timing chart for explaining operation of a 4th embodiment. It is a flowchart for demonstrating operation | movement of 5th Embodiment. It is a timing chart for explaining operation of a 5th embodiment.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of First Embodiment FIG. 1 is a block diagram showing a configuration example of a wavelength tunable light source device according to the first embodiment of the present invention. As shown in this figure, the variable wavelength light source device 1 according to the first embodiment includes a variable wavelength light source 10 and a control circuit 30 as main components. The variable wavelength light source 10 outputs laser light having a predetermined wavelength and power in accordance with the control of the control circuit 30. The laser beam output from the wavelength tunable light source 10 is supplied to a subsequent apparatus (not shown). The control circuit 30 controls the wavelength tunable light source 10 to output laser light having a desired wavelength and power. The control circuit 30 is connected to a host device (not shown), and controls the wavelength tunable light source 10 in accordance with an instruction from the host device.

  The wavelength tunable light source 10 includes an LD module 11 having N (N ≧ 1) DFB-LDs (Distributed Feedback Laser Diodes) 11-1 to 11-N and an LD temperature monitor 12, and a temperature adjustment element. 13, an optical multiplexer 14, a gain element 15, an optical demultiplexer 16, a power monitor 17, an etalon filter 18, a wavelength monitor 19, an etalon filter temperature monitor 20, and a temperature adjustment element 21.

  On the other hand, the control circuit 30 includes a digital arithmetic unit 31, a DFB-LD current control circuit 32, a DFB-LD selection circuit 33, a DFB-LD current monitor circuit 34, an LD temperature control circuit 35, an LD temperature monitor circuit 36, and a gain element control. A circuit 37, a power monitor PD current monitor circuit 38, a wavelength monitor PD current monitor circuit 39, an etalon temperature control circuit 40, and an etalon temperature monitor circuit 41 are provided.

  Here, the DFB-LDs 11-1 to 11 -N, for example, cover the wavelength band corresponding to DWDM (Dense Wavelength Division Multiplexing) by, for example, twelve (N = 12) DFB-LDs. The LD temperature monitor 12 is constituted by, for example, a thermistor, detects the temperature of the DFB-LDs 11-1 to 11 -N, and notifies the LD temperature monitor circuit 36 of the temperature. The temperature adjustment element 13 is configured by, for example, a TEC (Thermo Electric Cooler) such as a Peltier element, and controls the temperature of the DFB-LDs 11-1 to 11 -N. Note that the DFB-LDs 11-1 to 11-N, the LD temperature monitor 12, and the temperature adjustment element 13 are provided on, for example, a single substrate having thermal conductivity. It becomes isothermal. Therefore, each of the DFB-LDs 11-1 to 11 -N is controlled to have substantially the same temperature by the control of the temperature adjusting element 13, and these temperatures are detected by the LD temperature monitor 12.

  The optical multiplexer 14 is a multiplexer having N input terminals and one output terminal, and combines the laser light output from any of the DFB-LDs 11-1 to 11 -N to the gain element 15. Supply. The gain element 15 is configured by, for example, a semiconductor optical amplifier (SOA), amplifies the laser beam output from the optical multiplexer 14 based on the control of the gain element control circuit 37, and the optical demultiplexer 16. To supply. The optical demultiplexer 16 outputs most of the laser light output from the gain element 15 as an optical output to a subsequent apparatus and supplies a part of the laser light to the power monitor 17 and the etalon filter 18 after being demultiplexed.

  The power monitor 17 is constituted by, for example, a photodiode, converts the laser light output from the optical demultiplexer 16 into an electric signal corresponding to the power, and supplies the electric signal to the power monitor PD current monitor circuit 38. . The etalon filter 18 as a wavelength filter is a filter having a periodic transmission characteristic with respect to the wavelength, and has, for example, a transmission characteristic corresponding to a plurality of wavelengths constituting the DWDM. Specifically, the etalon filter 18 has a transmission characteristic with a period of 50 GHz or 100 GHz as defined by ITU (International Telecommunication Union). Of course, these numbers are merely examples, and it is needless to say that any other interval may be used. The laser light transmitted through the etalon filter 18 is supplied to the wavelength monitor 19. The wavelength monitor 19 is configured by, for example, a photodiode, converts the laser light transmitted through the etalon filter 18 into an electrical signal corresponding to the power, and supplies the electrical signal to the wavelength monitor PD current monitor circuit 39.

  The temperature adjusting element 21 is configured by, for example, a TEC such as a Peltier element, and controls the temperature of the etalon filter 18 according to the control of the etalon temperature control circuit 40. The etalon filter 18, the etalon filter temperature monitor 20, and the temperature adjustment element 21 are provided on, for example, a single substrate having thermal conductivity, so that they are all thermally at substantially the same temperature.

  The digital arithmetic unit 31 controls each control circuit or selection circuit based on the monitor data supplied from each monitor circuit, controls the wavelength variable light source 10, and outputs laser light having a desired wavelength and power. The DFB-LD current control circuit 32 supplies a drive current to the DFB-LD selected by the DFB-LD selection circuit 33 based on the control of the digital arithmetic unit 31 and controls the drive current. The DFB-LD selection circuit 33 selects a DFB-LD corresponding to the wavelength to be output under the control of the digital arithmetic unit 31 and supplies a drive current from the DFB-LD current control circuit 32.

  The DFB-LD current monitor circuit 34 detects the current supplied to the DFB-LD selected by the DFB-LD selection circuit 33, converts it into digital data, and supplies it to the digital arithmetic unit 31. The LD temperature control circuit 35 controls the temperature adjustment element 13 and controls the temperature of the LD module 11 based on the control of the digital arithmetic device 31. The LD temperature monitor circuit 36 converts the electrical signal output from the LD temperature monitor 12 into digital data and supplies the digital data to the digital arithmetic unit 31.

  The gain element control circuit 37 controls the drive current of the gain element 15 based on the control of the digital arithmetic device 31 and controls the gain of the gain element 15. The power monitor PD current monitor circuit 38 converts the electrical signal output from the power monitor 17 into digital data and supplies the digital data to the digital arithmetic unit 31. The wavelength monitor PD current monitor circuit 39 converts the electrical signal output from the wavelength monitor 19 into digital data and supplies it to the digital arithmetic unit 31. The etalon temperature control circuit 40 controls the temperature adjustment element 21 and controls the temperature of the etalon filter 18. The etalon temperature monitor circuit 41 converts the electrical signal output from the etalon filter temperature monitor 20 into digital data and supplies the digital data to the digital arithmetic unit 31.

(B) Description of Operation of First Embodiment Hereinafter, an operation when the wavelength tunable light source device 1 shown in FIG. 1 is activated will be described with reference to a flowchart shown in FIG. The flowchart shown in FIG. 2 is a process executed when the wavelength tunable light source device 1 is powered on, for example, when the tunable light source device 1 is newly added to the system. When this flowchart is started, the following steps are executed.

  In step S <b> 10, the digital arithmetic device 31 starts temperature control of the LD module 11. Specifically, the digital arithmetic unit 31 detects the temperature of the LD module 11 based on the temperature-related data supplied from the LD temperature monitor circuit 36 (hereinafter referred to as “temperature data”), and sets the wavelength to be output. A difference value with the corresponding temperature is calculated, the LD temperature control circuit 35 is controlled based on the difference value, and control is started so that the LD module 11 reaches a desired temperature. The default value of the wavelength to be output can be stored in advance in a memory (not shown) built in the digital arithmetic unit 31, for example. In the present embodiment, the wavelength variation due to the temperature of the DFB-LDs 11-1 to 11-N is, for example, 100 pm / ° C., and thus it is necessary to perform temperature control so as to be within the allowable wavelength variation range. is there.

  As the details of the temperature control, for example, when the deviation of the temperature monitor value from the temperature target value is Err, this Err is given by the following equation (1), and the indicated value to the LD temperature control circuit 35 is as follows: (2). Kp and Ki are control constants for PI (Proportional Integral) control.

Err = temperature target value−temperature monitor value (1)
Indicated value to LD temperature control circuit = Kp × Err + ΣKi × Err (2)

  In step S <b> 11, the digital arithmetic device 31 starts temperature control of the etalon filter 18. Specifically, the digital arithmetic unit 31 detects the temperature of the etalon filter 18 based on the temperature data supplied from the etalon temperature monitor circuit 41, calculates a difference value from a predetermined temperature target value, Based on the difference value, the etalon temperature control circuit 40 is controlled so that the etalon filter 18 has a desired temperature. In the present embodiment, the variation of the transmission wavelength due to the temperature of the etalon filter 18 is, for example, 5 to 20 pm / ° C., so it is necessary to control the temperature so as to be within the allowable wavelength variation range. A detailed control method is performed by PI control as in the case of the LD module 11 described above.

  3A is a diagram showing a temporal change in the wavelength of the laser light output from the wavelength tunable light source device 1, and FIG. 3B is a time of the power of the laser light output from the wavelength tunable light source device 1. FIG. 3C is a diagram illustrating a control state of each unit. As shown in FIG. 3C, when the wavelength tunable light source device 1 is turned on at time T0, TEC1-ATC (Automatic Temperature Control), which is the control of TEC1 (temperature adjusting element 13), is performed by the process of step S10. ) Starts operation (ON), and TEC2-ATC, which is the control of TEC2 (temperature adjustment element 21), starts operation (ON) by the process of step S11.

  In the example of FIG. 3, the output wavelength is converged within Ftag ± F2th by T2 and within Ftag ± F1th by T4. Regarding the output optical power, it is assumed that it converges within Ptag ± P1th until T2 and below Poff−P2th until T3, and within Ptag ± P1th until T4.

  In step S12, the digital arithmetic unit 31 determines whether or not the temperatures of both the LD module 11 and the etalon filter 18 have reached the target temperature. If the target temperature has been reached (Yes in step S12), the process proceeds to step S13. In other cases (step S12: No), the same processing is repeated. In addition, you may make it determine with Yes, when entering into the predetermined range (for example, ± 1 degreeC) from target temperature.

  In step S13, the digital arithmetic unit 31 determines whether or not a light emission request is made from a higher-level device (not shown). If a light emission request is made (step S13: Yes), the process proceeds to step S14. In the case (step S13: No), the same processing is repeated. When the temperature of both the LD module 11 and the etalon filter 18 has not reached the target temperature, when a light emission request is made, the host device is notified that the request cannot be met. It may be.

  In step S14, the digital arithmetic unit 31 supplies predetermined control data to the DFB-LD current control circuit 32, and starts supplying a constant current to the DFB-LD selected by the DFB-LD selection circuit 33. To do. The DFB-LD selected by the DFB-LD selection circuit 33 can be determined based on the default wavelength previously stored in the memory by the user as described above. For example, the constant current is set to a value at which the noise level of the laser beam output from the DFB-LD is sufficiently low and the laser beam power is sufficiently obtained. In the example of FIG. 3C, DFB-CONST, which is control for supplying a constant current to the DFB-LD, is started (ON) at time T1.

  In step S <b> 15, the digital arithmetic unit 31 supplies predetermined control data to the gain element control circuit 37 and starts supplying a constant current to the gain element 15. As the constant current, for example, a current at which the power of the laser beam output from the gain element control circuit 37 is less than Poff [dBm] shown in FIG. In view of the existence of individual differences in the gain elements 15, it is desirable to set the current value to be less than Poff regardless of what individual is used. This is because if laser light of Poff or higher is output, it affects the subsequent apparatus. In the example of FIG. 3C, SOA-CONST that is a control for supplying a constant current to the gain element 15 is started (ON) at time T1. As a result, as shown in FIG. 3C, the power of the laser beam becomes a predetermined value less than Poff from time T1. In FIGS. 3A and 3B, hatched areas indicate prohibited areas, and it is necessary to perform control so that wavelength or power does not enter this range.

  In step S <b> 16, the digital arithmetic unit 31 detects the output optical power based on the data output from the power monitor PD current monitor circuit 38. In the example of FIG. 3B, the output optical power at time T1 is detected.

  In step S17, the digital arithmetic unit 31 sets the output optical power detected in step S16 as the initial value P0 of the optical power control in steps S19 to S21. In the example of FIG. 3B, the output optical power at time T1 is set as the initial value P0.

  In step S18, the digital arithmetic unit 31 detects whether or not a predetermined time has elapsed. When the predetermined time has elapsed (step S18: Yes), the process proceeds to step S19, and otherwise (step S18). : No), the same processing is repeated. Note that the predetermined time can be stored in a rewritable memory in the digital arithmetic unit 31, for example, and can be arbitrarily set by the user. In the example of FIG. 3B, if the time corresponding to (T2-T1) has elapsed, it is determined Yes at time T2, and the process proceeds to step S19.

  In step S19, the digital arithmetic unit 31 calculates the optical output power target value Pt at time T based on the following equation (3).

  Pt = ΔP / ΔT × (T−T2) + P0 (3)

  Here, ΔT and ΔP will be described. FIG. 4A is a diagram showing an increase in output optical power at times T2 to T3 shown in FIG. 3B, and FIG. 4B is an enlarged view of the vicinity of the rise of the straight line in FIG. FIG. The processes in steps S19 to S21 are repeated at a period of ΔT (for example, a period of several msec), and the optical output power target value is set so that the optical output power increases by ΔP. That is, in the processing of steps S19 to S21, the target value is set in a step shape indicated by a solid line, and the actual optical output power changes as indicated by a broken line.

  In step S20, the digital arithmetic unit 31 sets the output optical power target value calculated in step S19 as the target value of the output optical power control system. Specifically, the digital arithmetic unit 31 controls the current flowing through the gain element 15 by controlling the gain element control circuit 37 according to the output optical power target value. In FIG. 3C, the control (SOA-CONST) that starts a constant current to the gain element 15 started by the process of step S15 is stopped (OFF) at time T2, and the gain element 15 is controlled to output light. Control for increasing power (SOA-APC (Automatic Power Control)) is started (ON).

  As the details of the output optical power control, for example, when the deviation of the output optical power monitor value from the output optical power target value is Err, this Err is given by the following equation (4), and the gain element control circuit 37 The instruction value is given by the following equation (5). Kp and Ki are control constants for PI control.

Err = Output light power target value−Output light power monitor value (4)
Indicated value to gain element control circuit = Kp × Err + ΣKi × Err (5)

  In step S21, the digital arithmetic unit 31 refers to the output of the power monitor PD current monitor circuit 38, determines whether or not the output optical power is equal to the final target value Ptag, and if it is Ptag (step S21). In step S21: Yes, the process proceeds to step S22. In other cases (step S21: No), the same processing is repeated. The final output optical power target value can be stored in a rewritable memory in the digital arithmetic unit 31, for example, and can be arbitrarily set by the user. Instead of determining whether or not the output optical power is equal to the final target value Ptag, it is determined that the output optical power is equal to or higher than Ptag, or the output optical power is within a predetermined range ( For example, it may be determined that it is within Ptag ± P1th (range of FIG. 3B).

  In step S <b> 22, the digital arithmetic unit 31 starts wavelength control using a current for driving the DFB-LD. This will be specifically described. FIG. 5 is a diagram showing the relationship between the frequency of the optical output and the PD current ratio (wavelength monitor PD / power monitor PD), and the broken line in the figure shows the wavelength target value. The digital arithmetic unit 31 obtains a value obtained by dividing the data supplied from the wavelength monitor PD current monitor circuit 39 by the data supplied from the power monitor PD current monitor circuit 38 at the wavelength target value (FIG. 5). By controlling so as to be equal to the value of the intersection of the broken line and the solid line, the optical output can be controlled to have a desired wavelength. In the example of FIG. 3, wavelength control by current (DFB-AFC) is started (ON) from time T3, and the wavelength of the optical output converges to the target value Ftag around time T3.

  As the details of the output light wavelength control, for example, the value obtained by dividing the data supplied from the wavelength monitor PD current monitor circuit 39 by the data supplied from the power monitor PD current monitor circuit 34 is set to the PD current ratio. When the monitor value is the PD current ratio target value and the deviation is Err, this Err is given by the following equation (6), and is an indication value to the DFB-LD current control circuit 32: Is given by the following equation (7). Kp and Ki are control constants for PI control. Here, δ is a conversion coefficient from the PD current ratio to the DFB-LD current circuit indication value.

Err = PD current ratio target value−PD current ratio monitor value (6)
Indicated value to DFB-LD current circuit = δ × (Kp × Err + ΣKi × Err) (7)

  As described above, in the first embodiment, the control of the temperature of the LD module 11 and the etalon filter 18 is started before the light emission request is made. By executing the above, it is possible to shorten the time until a laser beam having a desired power and wavelength is output after the request. Specifically, T2 to T4 can be realized in 1 second or less, for example.

  Further, in the first embodiment, as shown in FIG. 3, by setting a prohibited area and controlling the power and wavelength so as not to enter this area, it is possible to minimize the influence on the subsequent apparatus. It becomes possible.

  Further, in the first embodiment, the output light power is raised in a step shape as shown in FIG. 4B, so that the rate of change in temperature is made constant by making the rate of increase of current constant, and the temperature The influence on the control can be reduced. That is, when control is performed by simply setting the final target value of the output optical power to the target value of PI control, the output optical power increases rapidly at the start of control, and the power increase gradually decreases as it approaches the final target value. Become. In the case of such control, the flowing current changes in the same manner, so that the temperature change also changes rapidly at the beginning, and the change becomes slow as it approaches the final target value. On the other hand, in the case of the present application, since the output light power changes substantially linearly as shown in FIG. 4A, the temperature change also changes linearly and temperature control becomes easy.

  Furthermore, in the first embodiment, after the setting of the output optical power, the shift to the wavelength control by the current is made, so that the influence of the heat generation of the gain element 15 at the setting of the output optical power is reduced, and the desired wavelength is set. It is possible to converge quickly.

(C) Description of Second Embodiment Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as that of FIG. 1, but the processing executed in the digital arithmetic unit 31 is different. FIG. 6 is a flowchart for explaining the flow of processing executed in the second embodiment. In the flowchart shown in FIG. 6, portions corresponding to those in the flowchart shown in FIG. In the flowchart shown in FIG. 6, compared with the case of FIG. 2, the process of step S <b> 30 is added before step S <b> 10, and the process of step S <b> 31 is added between step S <b> 21 and step S <b> 22. Since the other processes are the same as those in the case of FIG. 2, the following description will focus on the processes in steps S30 and S31.

  For example, when the tunable light source device 1 is powered on, the process of FIG. 6 is started and the process of step S30 is executed.

  In step S <b> 30, the digital arithmetic device 31 calculates the shifted target temperature of the LD module 11. Specifically, since the gain element 15 is provided at a position close to the LD module 11, heat is transferred between them. For this reason, when the gain element 15 enters the operating state, the temperature of the LD module 11 rises due to the heat generated by the gain element 15. Therefore, in the second embodiment, as shown in FIG. 7, the control target value of the temperature of the LD module 11 is changed from the normal target temperature t0 (temperature corresponding to the desired wavelength) to Δt in the range of time T0 to T3. The temperature is changed to a lower temperature t1. Note that Δt can be a value corresponding to the temperature rise due to heat generation of the gain element 15.

  Since the processes in steps S10 to S21 are the same as those in the first embodiment, the description thereof will be omitted.

  When the control of the output optical power in steps S19 to S21 is completed, in step S31, the digital arithmetic unit 31 changes (restores) the temperature control target value of the LD module 11 from t1 to t0. As a result, the LD module 11 is stabilized at the temperature t0 corresponding to the desired wavelength. When the process of step S31 ends, the process proceeds to step S22, and wavelength control by current is started. The process of step S31 is inserted after step S21 in the example of FIG. 6, but may be inserted after step S18, for example, depending on the time constant of temperature control or the environment. It is also possible to change the temperature control target value of the LD module 11 from time to time according to the output light power monitor value or the current value of the gain element 15 during the loop of steps S19 to S21. According to such a method, it is possible to smoothly shift to the temperature control of the normal target temperature t0.

  FIG. 8 is a diagram for explaining the operation of the second embodiment. In the example of FIG. 8, since the temperature control is different from that of the first embodiment as compared with the case of FIG. 3, the behavior of the wavelength of FIG. It is the same.

  As described above, in the second embodiment, considering the heat generation of the gain element 15, the target temperature of the LD module 11 is set to the temperature t1 lower than the temperature t0 corresponding to the desired wavelength. Since overshoot from the target temperature due to heat generation of the gain element 15 can be prevented, the temperature of the LD module 11 can be brought close to the temperature t0 corresponding to the desired wavelength efficiently and quickly. As a method of determining t1 (Δt), it is desirable not only to increase the temperature by the gain element 15 but also to set the wavelength so as not to enter the prohibited region shown in FIG. Specifically, it is desirable that the wavelength be included in the range of + F2th and -F2th shown in FIG.

(D) Description of Third Embodiment Next, a third embodiment of the present invention will be described. The configuration of the third embodiment is the same as that of FIG. 1, but the processing executed in the digital arithmetic unit 31 is different. FIG. 9 is a flowchart for explaining the flow of processing executed in the third embodiment. In the flowchart shown in FIG. 9, portions corresponding to those in the flowchart shown in FIG. In the flowchart shown in FIG. 9, the process of step S40 is added between the processes of step S21 and step S22 as compared with the case of FIG. Since the other processes are the same as those in FIG. 2, the operation will be described below with a focus on the process of step S <b> 40 with reference to FIG. 10 describing the operation of the third embodiment.

  For example, when the wavelength tunable light source device 1 is turned on, the process of FIG. 9 is started, and the same processes of steps S10 to S21 as described above are executed. As a result, the output light is increased to the power final target value. That is, the processing up to time T3 shown in FIG. 10 is the same as in the first embodiment.

  When the output light reaches the power final target value, in step S40, the digital arithmetic unit 31 determines whether or not a predetermined time has elapsed. If the predetermined time has elapsed (step S40: Yes), step S22 is performed. In other cases (step S40: No), the same processing is repeated. Here, as the predetermined time, as shown in FIG. 10, the time (= T3 ′) obtained by subtracting the time required for wavelength locking (= T4−T3 ′) from the maximum specified time for wavelength locking (= T4−T3). -T3) can be used. If the predetermined time has elapsed, the process proceeds to step S22, and wavelength lock (wavelength control) using current is executed.

  In the third embodiment, the wavelength lock control by the current is executed after the output light is delayed by a predetermined time (= T3'-T3) after the output light becomes equal to the power final target value. As described above, the temperature of the LD module 11 can be stabilized by taking a certain time from the completion of the control of the power of the output light to the execution of the wavelength lock. More specifically, when the gain element 15 generates heat by the output light power control in steps S19 to S21, and the wavelength control by the current is executed in a state where the LD module 11 has a temperature different from the target value, There is a possibility that the current flowing through the DFB-LD deviates from a predetermined range. Since the current flowing through the DFB-LD is set to an optimum value in consideration of noise and the like, the noise characteristics are degraded when wavelength locking is performed in such a state. However, in the third embodiment, by adding the process of step S40, the wavelength is controlled after the temperature is stabilized, so that the fluctuation range of the current flowing through the DFB-LD can be kept within an appropriate range.

  In addition, you may make it add the process of step S30 and step S31 shown in FIG. 6 to the process of FIG. According to such an embodiment, the temperature can be further stabilized.

(E) Description of Fourth Embodiment Next, a fourth embodiment of the present invention will be described. The configuration of the fourth embodiment is the same as that of FIG. 1, but the processing executed in the digital arithmetic unit 31 is different. FIG. 11 is a flowchart for explaining the flow of processing executed in the fourth embodiment. In the flowchart shown in FIG. 11, portions corresponding to those in the flowchart shown in FIG. In the flowchart shown in FIG. 11, compared with the case of FIG. 2, the processes of step S14 and step S15 are moved between step S11 and step S12 as step S114 and step S115. Since the other processes are the same as those in FIG. 2, the operation will be described below with a focus on the processes in steps S114 and S115 with reference to FIG. 12 for explaining the operation of the fourth embodiment.

  For example, when the wavelength tunable light source device 1 is turned on, the process of FIG. 11 is started, the processes of steps S10 and S11 are performed, and then the process of step S114 is performed.

  In step S <b> 114, the digital arithmetic unit 31 controls the DFB-LD current control circuit 32 and starts supplying a constant current to the DFB-LD selected by the DFB-LD selection circuit 33. Specifically, the data supplied from the DFB-LD current monitor circuit 34 is referred to, and the DFB-LD current control circuit 32 is controlled so that a constant current flows. As the constant current, the same value as in step S14 of the first embodiment can be used. In the example of FIG. 12C, DFB-ACC (Automatic Current Control), which is control for supplying a constant current to the DFB-LD, is started (ON) at time T0.

  As the details of the current control, for example, if the deviation of the current monitor value from the current target value is Err, this Err is given by the following equation (8), and is an indication value to the DFB-LD current control circuit 32: Is given by the following equation (9). Kp and Ki are control constants for PI control.

Err = current target value-current monitor value (8)
Indicated value to DFB-LD current control circuit = Kp × Err + ΣKi × Err (9)

  In step S 115, the digital arithmetic unit 31 supplies predetermined control data to the gain element control circuit 37 and starts supplying a constant current to the gain element 15. As the constant current, the same value as in step S15 of the first embodiment can be used. In the example of FIG. 12C, SOA-CONST, which is control for supplying a constant current to the gain element 15, is started (ON) at time T0. As a result, as shown in FIG. 12C, the laser beam power becomes a predetermined value equal to or less than Poff from time T0.

  In addition, since the process after step S12 is the same as that of the case of 1st Embodiment, the description is abbreviate | omitted.

  As described above, in the fourth embodiment, since the temperature control is performed in a state in which current is passed through the DFB-LD and the gain element 15 in advance, the LD module 11 is brought into a thermally stable state at an early stage. By doing so, the time required for startup can be shortened. Further, in addition to achieving the heat stable state at an early stage, the control delay of the DFB-LD and the gain element 15 can be shortened to shorten the time required for startup.

(F) Description of Fifth Embodiment Next, a fifth embodiment of the present invention will be described. The configuration of the fifth embodiment is the same as that of FIG. 1, but the processing executed in the digital arithmetic unit 31 is different. FIG. 13 is a flowchart for explaining the flow of processing executed in the fifth embodiment. In the flowchart shown in FIG. 13, the same reference numerals are given to the portions corresponding to those in the flowchart shown in FIG. Compared with the case of FIG. 11, the flowchart shown in FIG. 13 adds a process of step S120 between step S18 and step S19, and further adds a process of step S121 after step S21. The process of S22 is replaced with the process of step S122. Since the other processes are the same as those in FIG. 11, the operation will be described below centering on the processes in steps S120 to S122 with reference to FIG. 14 for explaining the operation of the fifth embodiment.

  For example, when the tunable light source device 1 is turned on, the process of FIG. 13 is started and the process of step S10 is executed. In addition, the process of step S10-step S18 is the same as that of the case of FIG.

  In step S120, the digital arithmetic unit 31 temporarily changes the values of Kp and Ki, which are temperature control constants of the LD module 11, to large values. Thus, even when a deviation occurs between the temperature target value of the LD module 11 and the monitor value due to the heat generation of the gain element 15 resulting from the processing of steps S19 to S21, the deviation is quickly eliminated. Can do. Since the processing in steps S19 to S21 is the same as that described above, the description thereof is omitted.

  In step S121, the digital arithmetic unit 31 changes the values of Kp and Ki, which are temperature control constants of the LD module 11, to the original values. Increasing the constant causes overshoot, hunting, and the like. However, by restoring the constant, it is possible to prevent these phenomena from occurring.

  In step S122, the temperature of the LD module 11 is controlled so that the wavelength of the output light becomes a desired wavelength. In the example of FIG. 14C, at time T3, TEC1-AFC (Automatic Frequency Control), which is wavelength control based on the temperature of the LD module 11, is started (ON), and the LD module 11 is maintained at a constant temperature. A certain TEC1-ATC is stopped (OFF). Further, DFB-ACC, which is a control for causing a constant current to flow through the DFB-LD, remains ON after time T3.

  As the details of the output light wavelength control by temperature, for example, the value obtained by dividing the data supplied from the wavelength monitor PD current monitor circuit 39 by the data supplied from the power monitor PD current monitor circuit 34 is PD. When the current ratio monitor value is the PD current ratio target value and the deviation is Err, this Err is given by the following equation (10), and is indicated to the LD temperature control circuit 35. Is given by the following equation (11). Kp and Ki are control constants for PI control. Note that δ ′ is a conversion coefficient from the PD current ratio to an instruction value for the LD temperature control circuit 35.

Err = PD current ratio target value−PD current ratio monitor value (10)
Indicated value to LD temperature control circuit = δ ′ × (Kp × Err + ΣKi × Err) (11)

  As described above, in the fifth embodiment of the present invention, the time constant of the PI control is temporarily increased during the output optical power control. Therefore, the temperature deviation caused by the heat generation of the gain element 15 Can be quickly converged. Further, in the fifth embodiment, after the output light power control is finished, the wavelength control is performed by the temperature, so that the wavelength control can be executed at the timing when the temperature is close to the steady state. The change in wavelength can be suppressed.

(G) Modified Embodiment Each of the above embodiments is an example, and there are various modified embodiments other than this. For example, in each of the above embodiments, the wavelength tunable light source device 1 is connected to the system and the above-described processing is executed when the power is turned on. However, the wavelength tunable light source device 1 is already connected to the system. In this case, the processing described above may be executed when the wavelength to be output is changed. In the case of changing the wavelength, the drive current of the gain element 15 is stopped or set to be equal to or less than Poff, and then the above-described processing may be executed.

  Further, in each of the above embodiments, when the temperature of the LD module 11 at the time when the wavelength control is started is different from the target temperature, the temperature may be reset to the target temperature. . According to such a configuration, a change in the drive current of the DFB-LD after wavelength locking can be suppressed as much as possible.

  Further, in each of the above embodiments, the rising slope of the output optical power shown in FIG. 4A is determined by the constraints of the subsequent apparatus, but for example, the characteristics of the gain element 15 are also considered. May be determined. Specifically, when the rise characteristic of the gain element 15 is stricter (slower) than the constraint condition of the subsequent apparatus, the slope may be determined according to the rise characteristic of the gain element 15.

  Further, in each of the above embodiments, the wavelength control is started after the output optical power becomes equal to the final target value. However, the wavelength control is started before the output optical power becomes equal to the final target value. It is also possible. According to such a configuration, it is possible to further reduce the time required for startup.

  In the above fifth embodiment, the control constant for PI control is temporarily increased. However, for example, the control constant may be temporarily shifted to PID control. According to such a configuration, it is possible to cope with a sudden change in the output value. In the fifth embodiment, the control constant for temperature control is temporarily increased. However, for example, the control constant for current control of the DFB-LD may be temporarily increased. Furthermore, although the temperature and current control methods have been described by taking PI control as an example, it goes without saying that other controls may be used.

  Further, in each of the embodiments described above, the output light is changed in a step shape as shown in FIG. 4, but the step interval can be made very coarse or finer. Specifically, the number of steps existing between times T2 and T3 can be set to only two or about 3 to 10, for example. Of course, it may be about several tens to several hundreds or more. In the example of FIG. 4, ΔP is always constant, but can be changed to some extent according to time or temperature, for example. Specifically, ΔP may be decreased when the temperature control deviation (Err) of the LD module 11 is increased, and may be increased in other cases.

  In each of the above embodiments, the case where there are a plurality of DFB-LDs has been described as an example. However, the present invention can be applied even when the DFB-LD is a single unit.

  In each of the embodiments described above, two types of control, DFB-CONST and DFB-ACC, are provided for making the current of the DFB-LD constant. The DFB-CONST is a control for supplying a constant current to the DFB-LD by supplying predetermined data to the DFB-LD current control circuit 32. On the other hand, DFB-ACC is feedback control for controlling the DFB-LD current control circuit 32 while referring to data from the DFB-LD current monitor circuit 34. Of course, the latter has higher current control accuracy. Therefore, DFB-CONST and DFB-ACC shown in each embodiment can be replaced with each other. Of course, SOA-CONST and SOA-ACC can be replaced with each other. Further, although DFB-ACC has been described by taking PI control as an example, it goes without saying that other control methods may be used.

DESCRIPTION OF SYMBOLS 1 Wavelength variable light source device 11 LD module 11-1 to 11-N DFB-LD (laser diode)
12 LD temperature monitor 13 Temperature adjustment element (part of temperature adjustment means)
14 Optical multiplexer 15 Gain element (amplifying means)
16 Optical demultiplexer 17 Power monitor 18 Etalon filter (wavelength filter)
19 Wavelength monitor 20 Etalon filter temperature monitor 21 Temperature adjustment element (part of temperature adjustment means)
31 Digital computing device (part of power control means, part of wavelength control means)
32 DFB-LD current control circuit 33 DFB-LD selection circuit 34 DFB-LD monitor circuit 35 LD temperature control circuit 36 LD temperature monitor circuit 37 gain element control circuit 38 power monitor PD current monitor circuit (part of power control means)
39 Wavelength monitor PD current monitor circuit (part of wavelength control means)
40 Etalon temperature control circuit 41 Etalon temperature monitor circuit

Claims (11)

In a variable wavelength light source device that generates and outputs laser light of a desired wavelength,
A laser diode whose emission wavelength changes with temperature,
Amplifying means for amplifying the light output from the laser diode and transferring heat to and from the laser diode;
Prior to the start of output of laser light, temperature adjustment means for feedback control so that the temperature of the laser diode becomes a predetermined temperature corresponding to the target emission wavelength of the diode;
While starting the output of laser light, while the power of the laser light increases to the final target power, after changing the control constant of the temperature adjusting means, the target value of the laser light power is increased stepwise Power control means for controlling the amplification means to increase the power of the laser light stepwise to the final target power,
When the power of the laser beam becomes the final target power by the control of the control unit, the control constant of the changed temperature adjusting unit is returned to the value before the change, and then the laser beam is set to the target wavelength. Wavelength control means for controlling so that
A wavelength tunable light source device comprising:   The wavelength tunable light source device according to claim 1, wherein the wavelength control unit controls the laser light to have the target wavelength by controlling a driving current of the laser diode.   The wavelength tunable light source device according to claim 1, wherein the wavelength control unit controls the laser light to have the target wavelength by controlling a temperature of the laser diode. Prior to start of output laser light, the wavelength variable light source system according to any one of claims 1 to 3, wherein the communicating the driving current to the laser diode and the amplifier means. A predetermined drive current at which the power of the laser beam output from the amplifying unit is equal to or lower than a level allowed by a subsequent device is passed to the amplifying unit;
In a state where the predetermined drive current is passed, the power control means uses the power monitor value of the laser light output from the amplification means as an initial value, and controls the amplification means to step the laser light to the final target power. The tunable light source device according to claim 4 , wherein the wavelength tunable light source device is increased. The wavelength control unit performs wavelength control based on a ratio between a power monitor value of the laser beam output from the amplification unit and a power monitor value of the laser beam output from the amplification unit and output through the wavelength filter. tunable light source apparatus according to any one of claims 1 to 5, characterized in that. The wavelength tunable light source device according to claim 6 , wherein the temperature adjusting unit adjusts the wavelength filter to a predetermined temperature prior to the start of laser beam output. When the laser light is controlled to the target wavelength by the wavelength control means, if the laser diode is at a temperature different from a predetermined temperature for outputting the target wavelength, the temperature is set to the target temperature. The wavelength tunable light source device according to any one of claims 1 to 7 , wherein the wavelength tunable light source device is reset. The wavelength tunable light source device according to any one of claims 1 to 8 , wherein the output of the laser light is started when power is turned on to the laser variable light source device. When starting the output of the laser light, the wavelength tunable light source according to any one of claims 1 to 8, characterized in that it is time to change the wavelength of the laser light output from the laser variable light source system apparatus. A laser diode whose emission wavelength varies depending on temperature, and amplification means for amplifying the light output from the laser diode and transferring heat to and from the laser diode. In the control method of the wavelength tunable light source device that generates and outputs,
Prior to starting the output of laser light, a temperature adjustment step for feedback control so that the temperature of the laser diode becomes a predetermined temperature corresponding to the target emission wavelength of the diode;
While starting the output of laser light, while the power of the laser light increases to the final target power, after changing the control constant in the temperature adjustment step, the target value of the laser light power is increased stepwise A power control step for controlling the amplification means to increase the power of the laser light stepwise to a final target power;
When the power of the laser beam becomes the final target power by the control of the control step, the control constant in the changed temperature adjustment step is returned to the value before the change, and then the laser beam is set to the target wavelength. A wavelength control step for controlling so that
A method for controlling a wavelength tunable light source device, comprising:

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