JP5032451B2 - Wavelength tunable laser test method, wavelength tunable laser control method, and laser apparatus - Google Patents

Description

  The present invention relates to a tunable laser test method, a tunable laser control method, and a laser apparatus.

  Tunable lasers that can select a desired oscillation wavelength are known. For example, this tunable laser has two or more wavelength selectors such as a reflector having a periodic reflection spectrum peak and a gain region having a periodic gain peak, and the correlation between the respective periodic peaks. A desired oscillation wavelength is selected by controlling the relationship.

  In order to detect the correlation of each periodic peak, the oscillation state of the oscillation wavelength, optical spectrum, etc. is detected by using a measuring instrument such as a wavelength meter or an optical spectrum analyzer, and the optimum operating point corresponding to each channel. The wavelength selection information such as the lookup table is set, and the set temperature of the temperature control device (TEC) and the set current of the reflector are acquired based on the set wavelength selection information.

  This tunable laser can realize a desired oscillation wavelength by using a value read from a look-up table at the time of startup and wavelength switching. For example, the wavelength detection unit detects the output wavelength of the tunable laser.

  The tunable laser corrects the peak of the gain spectrum in the gain region by changing the temperature of the TEC when the detection result is different from the set value of the lookup table. This feedback loop is generally called a wavelength locker. By this operation, the output wavelength is kept constant.

  FIG. 1 is a diagram showing the relationship between the heater temperature and the oscillation wavelength of a reflector having a periodic reflection spectrum peak. In the tunable laser, the oscillation state is determined at a portion where the peaks of the reflector having the periodic reflection peak and the gain region having the periodic gain peak overlap. Therefore, the tunable laser has a jumping wavelength characteristic. In FIG. 1, a flat terrace portion indicates a stable oscillation wavelength of the tunable laser. That is, it can be said that the wavelength selection characteristic of the wavelength tunable laser that is the subject of the present invention has a characteristic in which the oscillation state occurs discontinuously.

  When the selected wavelength is λ2, the heater temperature needs to be set within the range A in FIG. In the lookup table, a heater current value corresponding to the optimum operating point a of the terrace is stored.

  Here, when the heater temperature is the optimum operating point a, the tunable laser can oscillate at the initial wavelength λ2. However, if the set value for realizing the initial wavelength deviates from the optimum operating point a due to the deterioration of the laser chip, the influence of the power source, etc., it can be said that oscillation is likely to occur at wavelengths other than λ2.

  For example, when the temperature of the TEC or the initial value of the drive current in the gain region is not given to the laser chip with high accuracy, there is a possibility of oscillation at a wavelength other than λ2. That is, there is a problem that it is easily affected by parameter variations.

  As a method for solving such a problem, a method of detecting a mode jump using a wavelength reader or an oscillation mode discriminator is known (for example, see Patent Document 1). In this document, an oscillation state such as an oscillation wavelength and an optical spectrum is detected by a wavelength detector. This wavelength detector is composed of an etalon having a periodic peak. Further, by using this wavelength detection unit, the parameter for controlling the positional relationship between the periodic peaks is changed in the increasing direction and the decreasing direction, respectively, and the boundary A1 and the boundary A2 are detected before and after the wavelength is largely changed. Even if the initial value of the drive current in the TEC temperature and the gain region is not accurately given to the laser chip by shifting the initial value with the average value of each boundary value as the optimum operating point a, the period is It is possible to control the positional relationship between typical peaks in an optimum state. Therefore, the possibility of oscillation at other wavelengths is reduced.

JP 2004-47638 A

  However, in the method of Patent Document 1, the wavelength detector may not be able to detect that the wavelength has changed significantly due to the wavelength interval of mode jump. For example, when the wavelength jumps in the same cycle as the cycle of the wavelength detection unit, there is a possibility that the same detection value is shown before and after the wavelength greatly changes. In this case, it becomes difficult to detect the boundary A1 or the boundary A2. In Patent Document 1, in order to solve this problem, a plurality of etalons having different wavelength ranges are combined. However, in this case, the cost increases due to an increase in the number of parts, the number of assembly steps, and the like. At the same time, miniaturization becomes difficult.

  An object of the present invention is to provide a test method for a wavelength tunable laser, a control method for a wavelength tunable laser, and a laser apparatus that can suppress an increase in the number of parts, the number of assembly steps, and the like and can detect an optimum operating point. Objective.

A test method for a wavelength tunable laser according to the present invention is a test method for a wavelength tunable laser having a plurality of wavelength selection units having different wavelength characteristic peaks in a resonator, and is based on an initial setting value. A first step of oscillating at a predetermined wavelength, a second step of detecting a discontinuous point of a gain state change of the wavelength tunable laser while changing the wavelength characteristics of the plurality of wavelength selecting units, and a discontinuous point are detected. viewed including a third step of calculating a stable operating point of the wavelength selection portion based on the time on this limit point a limit point of the oscillation state at a predetermined wavelength, a discontinuity point of a change in gain state of the second step In the detection, after detecting the discontinuous point of the gain state while changing the wavelength characteristic, the discontinuous point of the gain state is detected again while changing the wavelength characteristic with a change amount smaller than the change amount of the wavelength characteristic. It is characterized in that the further made.

  In the tunable laser testing method according to the present invention, since the discontinuity of the gain state is detected, the stable operating point of the wavelength selection characteristic can be determined without combining a plurality of etalons having different wavelength ranges. Can do. Thereby, increase of a number of parts, an assembly man-hour, etc. can be controlled. As a result, an increase in cost and an increase in size of the apparatus can be suppressed.

The oscillation state of the wavelength tunable laser may be generated discontinuously with respect to the change in the wavelength characteristics of the wavelength selection unit. The detection of the discontinuous point in the second step may be performed based on the detection of the discontinuous change in the output light intensity of the wavelength tunable laser or the voltage or current in the gain region of the wavelength tunable laser. The plurality of wavelength selection units may select wavelengths using the vernier effect.

The wavelength tunable laser has a semiconductor optical amplification region outside the resonator, and the detection of the discontinuous point in the second step is the light in the semiconductor optical amplification region when the semiconductor optical amplification region is biased in a state of absorbing light. This may be done by sensing the current. Detection of discontinuous points in the second step may be performed based on a differential value obtained by differentiating the amount of change in the gain state. In this case, the discontinuity of the gain state can be detected more accurately .

A method of controlling a wavelength tunable laser according to the present invention is a method of controlling a wavelength tunable laser including a plurality of wavelength selection units having different wavelength characteristic peaks in a resonator, and has a predetermined wavelength based on an initial setting value. A first step of causing the wavelength tunable laser to oscillate; a second step of detecting a discontinuous point of a gain state change of the wavelength tunable laser while changing the wavelength characteristic of the wavelength selection unit; and a point in time when the discontinuous point is detected. A third step of calculating a stable operating point of the wavelength selection unit based on the limit point of the oscillation state at a predetermined wavelength, and oscillating the wavelength tunable laser using the stable operating point obtained in the third step as a target value 4 and step, only contains the detection of discontinuities change in gain state of the second step, after detecting the discontinuous point of gain state while changing the wavelength characteristic, the variation of the wavelength characteristic While changing the wavelength characteristic in remote small variation, it is characterized in that is made by detecting a discontinuous point of gain state again.

  In the tunable laser control method according to the present invention, since the discontinuity of the gain state is detected, the stable operating point of the wavelength selection characteristic is determined without combining a plurality of etalons having different wavelength ranges. Can do. Thereby, increase of a number of parts, an assembly man-hour, etc. can be controlled. As a result, an increase in cost and an increase in size of the apparatus can be suppressed.

The laser device according to the present invention includes a wavelength tunable laser including a plurality of wavelength selection units having different wavelength characteristic peaks in a resonator, and a wavelength tunable laser that oscillates at a predetermined wavelength based on a predetermined setting value. The discontinuity detection unit detects the discontinuity of the change in the gain state of the wavelength tunable laser while changing the wavelength characteristics of the laser, and the limit of the oscillation state at the predetermined wavelength is the limit when the discontinuity is detected. Operating point calculating means for calculating a stable operating point of the wavelength selection unit based on the point, and a control unit for performing control to oscillate the wavelength tunable laser by the stable operating point obtained by the calculating means , the discontinuous inspection The output unit detects the discontinuous point of the gain state while changing the wavelength characteristic, and then detects the discontinuous point of the gain state again while changing the wavelength characteristic with a change amount smaller than the change amount of the wavelength characteristic. It is characterized in.

  In the laser apparatus according to the present invention, since the discontinuity of the gain state is detected, the stable operating point of the wavelength selection characteristic can be determined without combining a plurality of etalons having different wavelength ranges. Thereby, increase of a number of parts, an assembly man-hour, etc. can be controlled. As a result, an increase in cost and an increase in size of the apparatus can be suppressed.

  According to the present invention, it is possible to suppress an increase in the number of parts, the number of assembly steps, etc., and to detect an optimum operating point.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 2 is a schematic diagram showing the overall configuration of the wavelength tunable laser 10 and the laser apparatus 100 including the same according to the first embodiment of the present invention. As shown in FIG. 2, the laser device 100 includes a wavelength tunable laser 10, a temperature control device 20, an output detection unit 30, a wavelength detection unit 40, and a controller 50. The wavelength tunable laser 10 is disposed on the temperature control device 20. Next, details of each part will be described.

  The wavelength tunable laser 10 includes a CSG-DBR (Chirped Sampled Distributed Bragg Reflector) region 11, an SG-DFB (Sampled Distributed Distributed) region 12, and a semiconductor optically amplified (SOA: Sticulated) region 13. Have.

  The CSG-DBR region 11 includes an optical waveguide provided with a plurality of segments each provided with a first region having a diffraction grating and a second region connected to the first region and serving as a space portion. In the present embodiment, three segments are provided as an example. This optical waveguide is made of a semiconductor crystal whose absorption edge wavelength is shorter than the laser oscillation wavelength. In the CSG-DBR region 11, the lengths of the second regions are different. On the surface of the CSG-DBR region 11 above each segment, heaters 14a to 14c are provided, respectively.

  The SG-DFB region 12 includes an optical waveguide provided with a plurality of segments each provided with a first region having a diffraction grating and a second region connected to the first region and serving as a space portion. This optical waveguide is made of a semiconductor crystal having a gain with respect to laser oscillation at a target wavelength. Further, in the SG-DFB region 12, each second region has the same length. An electrode 15 is provided on the SG-DFB region 12.

  The CSG-DBR region 11 and the SG-DFB region 12 have wavelength peaks with different periods, respectively, and function as a wavelength selection unit. By changing the wavelength characteristics of the CSG-DBR region 11 and the SG-DFB region 12, a vernier effect is generated and an oscillation wavelength is selected.

  The SOA region 13 includes an optical waveguide made of a semiconductor crystal for gaining light or absorbing light by current control or voltage control. An electrode 16 is provided on the SOA region 13. The optical waveguides of the CSG-DBR region 11, the SG-DFB region 12, and the SOA region 13 are optically coupled to each other.

  The wavelength tunable laser 10 is mounted on the temperature control device 20. Further, a thermistor (not shown) for measuring the temperature of the temperature control device 20 is provided on the temperature control device 20.

  The output detection unit 30 includes a beam splitter 31 and a light receiving element 32. The beam splitter 31 is disposed so as to reflect a part of the laser light that has passed through the SOA region 13 and to give the reflected light to the light receiving element 32. The wavelength detector 40 includes a beam splitter 41, an etalon 42, and light receiving elements 43 and 44. The beam splitter 41 is arranged so that a part of the laser light emitted from the CSG-DBR region 11 side is reflected and given to the light receiving element 43, and the remaining laser light is transmitted and given to the light receiving element 44. The etalon 42 is disposed between the beam splitter 41 and the light receiving element 44.

  In FIG. 2, the wavelength detection unit 40 is disposed on the CSG-DBR region 11 side and the output detection unit 30 is disposed on the SOA region 13 side. However, the configuration is not limited thereto. For example, each detection part may be arrange | positioned reversely.

  The controller 50 includes a control unit such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), a power source, and the like. The ROM of the controller 50 stores control information, a control program, and the like for the wavelength tunable laser 10. The control information is recorded in the lookup table 51, for example. FIG. 3 shows an example of the lookup table 51.

As shown in FIG. 3, the lookup table 51 includes an initial setting value and a feedback control target value for each channel. Initial setting The value, the initial current value _I LD of the SG-DFB region 12, an initial current value _{I SOA} of the SOA region 13, an initial current value of the heater _{14a~14c Ia Heater} ~Ic Heater and the initial temperature value of the temperature control device 20 T _LD is included. The feedback control target value includes the feedback control target value Im1 of the output detection unit 30, the feedback control target value Im3 / Im2 of the wavelength detection unit 40, and the feedback control target values Pa _{Heater to} Pc _Heater of the heaters 14a to 14c. The feedback control target value Im1 indicates a target detection value of the light receiving element 32. The feedback control target value Im3 / Im2 indicates a target value obtained by dividing the detection value of the light receiving element 44 by the detection value of the light receiving element 43.

Next, the operation when the laser apparatus 100 is activated (cold start) will be described. This operation (cold start) is performed in a state where output light is not output from the laser device 100 by using the SOA region 13 as a shutter (dark tuning). First, the controller 50 refers to the lookup table 51 and obtains an initial current value I _LD , an initial current value I _SOA , initial current values Ia _{Heater to} Ic _Heater, and an initial temperature value T _LD corresponding to the set channel. .

Next, the controller 50 controls the temperature control device 20 so that the temperature of the temperature control device 20 becomes the initial temperature value _TLD . Thereby, the temperature of the wavelength tunable laser 10 is controlled to a constant temperature in the vicinity of the initial temperature value _TLD . As a result, the equivalent refractive index of the optical waveguide in the SG-DFB region 12 is controlled. Next, the controller 50 supplies a current having a magnitude of the initial current value I _LD to the electrode 15. Thereby, light is generated in the optical waveguide in the SG-DFB region 12. As a result, the light generated in the SG-DFB region 12 is repeatedly reflected and amplified in the optical waveguides in the CSG-DBR region 11 and the SG-DFB region 12 to cause laser oscillation.

Next, the controller 50 supplies currents having magnitudes of initial current values Ia _{Heater to} Ic _{Heater to} the heaters 14a to 14c, respectively. Thereby, the equivalent refractive index of the optical waveguide in the CSG-DBR region 11 is controlled to a predetermined value. Next, the controller 50 supplies a current having a magnitude of the initial current value _ISOA to the electrode 16. By the above control, the wavelength tunable laser 10 emits laser light to the outside with an initial wavelength corresponding to the set channel.

  Next, the controller 50 optimizes the power supplied to the heaters 14a to 14c. This optimization control will be described later. Thereafter, the controller 50 feedback-controls the supply current or voltage to the SOA region 13 so that the detection result of the light receiving element 32 becomes the feedback control target value Im1. Thereby, the intensity of the laser beam can be controlled within a specified range.

Next, the controller 50 feedback-controls the temperature of the temperature control device 20 so that the value obtained by dividing the detection result of the light receiving element 44 by the detection result of the light receiving element 43 becomes the feedback control target value Im3 / Im2. Thereby, the oscillation wavelength can be controlled within a specified range. Furthermore, the controller 50 performs feedback control so that the power supplied to the heaters 14a to 14c becomes the feedback control target values Pa _{Heater to} Pc _Heater , respectively. With the above operation, the wavelength tunable laser 10 oscillates at a desired wavelength.

  The power supply to the heaters 14a to 14c may be optimized while feedback controlling the current or voltage supplied to the SOA region 13 so that the detection result of the light receiving element 32 becomes the feedback control target value Im1. Or you may carry out, applying a fixed voltage to the SOA area | region 13 and absorbing light. In this case, the front end surface laser beam intensity can be detected using the SOA region 13.

  Hereinafter, the above-described optimization control of the power supplied to the heaters 14a to 14c at the time of startup will be described.

  For the optimization control, it is necessary to obtain the position of the optimum operating point a in FIG. 1 and to control the heater temperature toward that position. Here, in order to obtain the optimum operating point a, it is necessary to obtain the boundaries A1 and A2. Further, it is necessary to actually change the operating point to the optimum operating point a. For these operations, it is necessary to control to change only the operating point without changing the oscillation wavelength (for example, λ2).

  In the CSG-DBR region 11 shown in FIG. 2, three heaters 14a to 14c are provided. The oscillation wavelength is realized by controlling the relationship between the heater temperatures and the average value of the heater temperatures. However, in order to change only the operating point while keeping the oscillation wavelength fixed, it is necessary to change the average value of the temperature of each heater while maintaining the temperature relationship of each heater. Hereinafter, all descriptions of changing the average temperature T are descriptions in a state in which the temperature relationship of each heater is maintained.

(When using rear end face laser light intensity)
First, the controller 50 changes the average temperature (hereinafter, average temperature T) of the heaters 14a to 14c. FIG. 4A shows the relationship between the average temperature T and the oscillation wavelength. FIG. 4B is a diagram showing the relationship between the average temperature T and the intensity of the laser light emitted from the CSG-DBR region 11 side (rear end surface side). The laser beam intensity on the rear end face side can be detected using the light receiving element 43.

  As shown in FIG. 4A, the oscillation wavelength increases rapidly as the average temperature T increases. The oscillation wavelength remains almost constant until the next stage wavelength. Further, as shown in FIG. 4B, the laser light intensity draws a downwardly convex curve in the temperature range where the oscillation wavelength is constant. The initial wavelength is λ2. Further, the initial average temperature T is set to a.

  The controller 50 gradually decreases the average temperature T by gradually reducing the power supplied to the heaters 14a to 14c. In this case, as shown in FIG. 4B, the intensity of the laser light increases. When the average temperature T is further decreased, the intensity of the laser beam is greatly decreased discontinuously. The average temperature T in this case is defined as temperature a1.

  Next, the controller 50 gradually increases the power supplied to the heaters 14a to 14c to gradually increase the average temperature T. In this case, as shown in FIG. 4 (b), the intensity of the laser beam gradually increases after it once decreases. When the average temperature T is further increased, the intensity of the laser light increases discontinuously. The average temperature T in this case is defined as temperature a2. The controller 50 determines the optimum average temperature T within the temperature range between the temperature a1 and the temperature a2. For example, the optimum average temperature T can be an average value of the temperature a1 and the temperature a2.

  Note that the controller 50 may determine the optimum average temperature T using the temperature obtained by differentiating the intensity of the laser beam emitted from the rear end surface. FIG. 4C is a diagram showing the relationship between the average temperature T and the differential value of the laser light intensity depending on the temperature. When the power supplied to the heaters 14a to 14c is gradually reduced to lower the average temperature T, the differential value of the laser light intensity also decreases. When the average temperature T is further decreased, the differential value of the laser light intensity becomes a positive value discontinuously from the negative value. The average temperature T in this case is defined as temperature a1.

  On the other hand, when the average temperature T is raised by gradually increasing the power supplied to the heaters 14a to 14c, the differential value of the laser light intensity also increases. When the average temperature T is further increased, the differential value of the laser light intensity becomes a negative value discontinuously from the positive value. The average temperature T in this case is defined as temperature a2. The controller 50 determines the optimum average temperature T within the temperature range between the temperature a1 and the temperature a2.

  As described above, the optimum average temperature of the heaters 14a to 14c can be determined by detecting the discontinuity (mode jump) of the gain state using the intensity of the laser light not passing through the etalon. In this case, it is not necessary to combine a plurality of etalons having different wavelength ranges. Thereby, increase of a number of parts, an assembly man-hour, etc. can be controlled. As a result, an increase in cost and an increase in size of the apparatus can be suppressed.

(When using front end face laser light intensity)
The optimum average temperature T may be determined using the laser beam intensity emitted from the SOA region 13 side (front end surface side). FIG. 5A is a diagram showing the relationship between the average temperature T and the oscillation wavelength. FIG. 5B is a diagram showing the relationship between the average temperature T and the intensity of the laser light emitted from the front end face side. The laser light intensity from the front end face side may be detected using the light receiving element 32 or may be detected using the SOA region 13.

  When detecting using the SOA region 13, it is possible to detect the discontinuity of the laser light intensity by detecting the gain state of the SOA region 13 while keeping the output light from the SOA region 13 constant. it can. Specifically, the gain state of the SOA region 13 can be detected by detecting the applied voltage or the supply current to the SOA region 13 while the output light from the SOA region 13 is held constant.

  Further, by using the SOA region 13 as a light receiving element, it is possible to detect a discontinuity in laser light intensity. Specifically, the detection current from the SOA region 13 can be detected in a state where the voltage applied to the SOA region 13 is kept constant with a reverse bias. Even if the voltage applied to the SOA region 13 is kept constant at 0 bias or forward bias, the detection current from the SOA region 13 can be detected as long as the SOA region 13 can absorb light. .

  As shown in FIG. 5B, in the temperature range where the oscillation wavelength is constant, the laser light intensity draws a convex curve upward. The controller 50 gradually decreases the average temperature T by gradually reducing the power supplied to the heaters 14a to 14c. In this case, as shown in FIG. 5B, the intensity of the laser beam decreases. When the average temperature T is further decreased, the intensity of the laser light increases discontinuously. The average temperature T in this case is defined as temperature a1.

  Next, the controller 50 gradually increases the power supplied to the heaters 14a to 14c to gradually increase the average temperature T. In this case, as shown in FIG. 5B, the intensity of the laser beam once increases and then gradually decreases. When the average temperature T is further increased, the intensity of the laser beam is greatly reduced discontinuously. The average temperature T in this case is defined as temperature a2. The controller 50 determines the optimum average temperature T within the temperature range between the temperature a1 and the temperature a2.

  The controller 50 may determine the optimum average temperature T by using the temperature obtained by differentiating the laser light intensity emitted from the front end surface. FIG.5 (c) is a figure which shows the relationship between the average value T and the differential value by the temperature of a laser beam intensity. When the average temperature T is lowered by gradually reducing the power supplied to the heaters 14a to 14c, the differential value of the laser light intensity increases. When the average temperature T is further decreased, the differential value of the laser beam intensity becomes discontinuously a negative value from the positive value. The average temperature T in this case is defined as temperature a1.

  On the other hand, when the average temperature T is increased by gradually increasing the power supplied to the heaters 14a to 14c, the differential value of the laser light intensity decreases. When the average temperature T is further increased, the differential value of the laser beam intensity becomes a positive value discontinuously from the negative value. The average temperature T in this case is defined as temperature a2. The controller 50 may determine the optimum average temperature T within a temperature range between the temperature a1 and the temperature a2.

  As described above, the optimum average temperature of the heaters 14a to 14c can be determined by detecting the discontinuity (mode jump) of the gain state using the differential value of the intensity of the laser light not passing through the etalon. In this case, it is not necessary to combine a plurality of etalons having different wavelength ranges. Thereby, increase of a number of parts, an assembly man-hour, etc. can be controlled. As a result, an increase in cost and an increase in size of the apparatus can be suppressed.

  In FIG. 4B and FIG. 5B, whether the convex curve is drawn up or down depends on the sharpness (peak width) of the wavelength peak of the CSG-DBR region 11 and the wavelength peak of the SG-DFB region 12. It changes according to the magnitude relationship with the sharpness (peak width).

(When using voltage applied to SG-DFB region)
The optimum average temperature T may be determined using a voltage applied when the SG-DFB region 12 is driven with a constant current. FIG. 6A is a diagram showing the relationship between the average temperature T and the oscillation wavelength. FIG. 6B is a diagram showing the relationship between the average temperature T and the voltage applied to the SG-DFB region 12. As shown in FIG. 6B, the applied voltage draws a downwardly convex curve in the temperature range where the oscillation wavelength is constant.

  The controller 50 gradually decreases the average temperature T by gradually reducing the power supplied to the heaters 14a to 14c. In this case, the applied voltage to the SG-DFB region 12 increases as shown in FIG. When the average temperature T is further lowered, the applied voltage is greatly reduced discontinuously. The average temperature T in this case is defined as temperature a1.

  Next, the controller 50 gradually increases the power supplied to the heaters 14a to 14c to gradually increase the average temperature T. In this case, as shown in FIG. 6B, the applied voltage gradually increases after once decreasing. When the average temperature T is further increased, the applied voltage increases greatly discontinuously. The average temperature T in this case is defined as temperature a2. The controller 50 determines the optimum average temperature T within the temperature range between the temperature a1 and the temperature a2.

  The controller 50 may determine the optimum average temperature T using a voltage obtained by differentiating the voltage applied to the SG-DFB region 12 with respect to the temperature. FIG. 6C is a diagram showing the relationship between the average temperature T and the differential value depending on the temperature of the applied voltage. When the power supplied to the heaters 14a to 14c is gradually decreased to lower the average temperature T, the differential value of the applied voltage decreases. When the average temperature T is further lowered, the differential value of the applied voltage becomes a positive value discontinuously from the negative value. The average temperature T in this case is defined as temperature a1.

  On the other hand, when the average temperature T is raised by gradually increasing the power supplied to the heaters 14a to 14c, the differential value of the applied voltage increases. When the average temperature T is further increased, the differential value of the applied voltage becomes a negative value discontinuously from the positive value. The average temperature T in this case is defined as temperature a2. The controller 50 may determine the optimum average temperature T within a temperature range between the temperature a1 and the temperature a2.

  Note that a supply current when the SG-DFB region 12 is driven with a constant current may be used instead of an applied voltage when the SG-DFB region 12 is driven with a constant current. The applied voltage has a downwardly convex curve as shown in FIG. 6B, while the supply current has an upwardly convex curve. Even in this case, since the discontinuity occurs in the supply current, the optimum average temperature T can be determined.

  As described with reference to FIGS. 4 to 6, the heater is detected by detecting the discontinuity of the gain state using the laser light intensity, the voltage applied to the SG-DFB region 12, the supply current to the SG-DFB region 12, and the like. The optimum average temperature of 14a-14c can be detected.

The feedback control target values Pa _{Heater to} Pc _Heater are corrected with the electric power supplied to the heaters 14a to 14c necessary for giving the optimum average temperature T determined by the above means.

(When using injection current into CSG-DBR region)
In the above description, the equivalent refractive index of the optical waveguide of the CSG-DBR region 11 is changed by changing the temperature of the CSG-DBR region 11, but the CSG-DBR region 11 is injected by current injection into the CSG-DBR region 11. The equivalent refractive index of the optical waveguide may be changed. This is because the current density into the CSG-DBR region 11 changes the carrier density of the optical waveguide. In this case as well, similar to the heating by the heater, the injection current A to the CSG-DBR region 11 is increased or decreased to detect the laser beam intensity, the applied voltage to the SG-DFB region 12 or the discontinuous point of the supply current. Thus, the optimum injection current to the CSG-DBR region 11 can be determined.

  FIG. 7A is a diagram showing the relationship between the injection current A and the oscillation wavelength. FIG. 7B is a diagram showing the relationship between the injection current A and the intensity of the laser light emitted from the CSG-DBR region 11 side (rear end surface side). FIG. 7C is a diagram showing the relationship between the injection current A and the differential value of the laser beam intensity depending on the temperature. FIG. 7D is a diagram showing the relationship between the injection current A and the intensity of the laser beam emitted from the SG-DFB region 12 side (front end surface side). FIG. 7E is a diagram showing the relationship between the injection current A and the differential value of the laser beam intensity depending on the temperature. FIG. 7F shows the relationship between the injection current A and the voltage applied to the SG-DFB region 12. FIG. 7G is a diagram showing the relationship between the injection current A and the differential value depending on the temperature of the voltage applied to the SG-DFB region 12.

  As described with reference to FIG. 7, by detecting the discontinuity of the gain state such as the laser light intensity, the voltage applied to the SG-DFB region 12, the supply current to the SG-DFB region 12, the CSG-DBR region 11 is detected. The optimum injection current can be detected.

8 and 9 are flowcharts showing an example of control of the wavelength tunable laser 10. As shown in FIG. 8, first, the controller 50 refers to the look-up table 51, and sets the initial current value I _LD , the initial current value I _SOA , the initial current values Ia _{Heater to} Ic _Heater and the initial values corresponding to the set channel. A temperature value _TLD is acquired (step S1).

  Next, the controller 50 causes the wavelength tunable laser 10 to oscillate based on the initial setting value acquired in step S1 (step S2). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S3). Next, the controller 50 increases the power supplied to the heaters 14a to 14c, and adds the step value dT to the average temperature T of the heaters 14a to 14c (step S4).

  Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43, and stores the measured value in the variable M1 (step S5). Next, the controller 50 determines whether or not the absolute value of (M1-M0) is equal to or less than the threshold value Th (step S6). When it is determined in step S6 that | M1-M0 | is equal to or smaller than the threshold value Th, the controller 50 stores the value of the variable M1 in the variable M0 (step S7), and executes step S4 again.

If it is not determined in step S6 that | M1-M0 | is equal to or less than the threshold value Th, the controller 50 stores the average temperature T-dT / 2 in the variable T _high (step S8). Next, the controller 50 resets the average temperature T to an initial value (step S9).

  Next, as shown in FIG. 9, the controller 50 measures the intensity of the laser beam using the light receiving element 43, and stores the value in the variable M0 (step S10). Next, the controller 50 reduces the power supplied to the heaters 14a to 14c, and subtracts the step value dT from the average temperature T of the heaters 14a to 14c (step S11).

  Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S12). Next, the controller 50 determines whether or not the absolute value of (M1-M0) is equal to or less than the threshold value Th (step S13). When it is determined in step S13 that | M1-M0 | is equal to or smaller than the threshold value Th, the controller 50 stores the value of the variable M1 in the variable M0 (step S14), and executes step S11 again.

If it is not determined in step S13 that | M1-M0 | is equal to or less than the threshold value Th, the controller 50 stores the average temperature T + dT / 2 in the variable T _low (step S15). Next, the controller 50 stores T _low + (T _high −T _low ) × k (0 <k <1) in the variable T _opt as the optimum average temperature (step S16). Then, the controller 50, the average temperature T is to control the power to the heater 14a~14c such that _{T opt} (step S17). Thereafter, the controller 50 ends the execution of the flowchart.

  In this way, the optimum average temperature of the heaters 14a to 14c can be set by changing the average temperature with a constant step size and detecting the intensity change of the laser light emitted from the rear end face. Note that k may be a value that satisfies 0 <k <1, and may be 0.5, for example.

In the following embodiments, for example, the following consideration is given to the coefficient k employed when calculating the optimum value.
(1) In consideration of the fluctuation margin of the heater temperature, k = 0.5 may be set. In this case, the heater temperature is set at the center of the step range (range A in FIG. 1) of the wavelength tunable laser. Thereby, the point with the most margin can be selected with respect to the fluctuation of the heater control state.
(2) In consideration of the stability of the laser oscillation state, a value that can obtain a state in which the output light intensity is maximum (minimum at the rear monitor output) may be adopted. For example, as shown in FIG. 4B, the optical output intensity varies even within the step range of the wavelength tunable laser. In such a case, it can be said that the oscillation state is stable at the point where the light intensity in the resonator is the highest (FIG. 4B is the lowest value because it is the rear monitor output). When selecting such points, it is preferable to select k = about 0.7.

10 and 11 are flowcharts showing another example of the control of the wavelength tunable laser 10. As shown in FIG. 10, first, the controller 50 refers to the look-up table 51, and sets the initial current value I _LD , the initial current value I _SOA , the initial current values Ia _{Heater to} Ic _Heater and the initial values corresponding to the set channel. A temperature value _TLD is acquired (step S21).

  Next, the controller 50 causes the wavelength tunable laser 10 to oscillate based on the initial setting value acquired in step S21 (step S22). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S23). Next, the controller 50 increases the electric power supplied to the heaters 14a to 14c, and adds the step value dT / 2 to the average temperature T of the heaters 14a to 14c (step S24). Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S25). Next, the controller 50 stores the differential value (M1-M0) / (dT / 2) in the variable dM0 (step S26).

  Next, the controller 50 increases the electric power supplied to the heaters 14a to 14c, and adds the step value dT / 2 to the average temperature T of the heaters 14a to 14c (step S27). Next, the controller 50 measures the laser light intensity using the light receiving element 43, and stores the measured value in the variable M2 (step S28). Next, the controller 50 stores the differential value (M2-M1) / (dT / 2) in the variable dM1 (step S29).

Next, the controller 50 determines whether or not the absolute value of (dM1-dM0) is equal to or less than the threshold value Th (step S30). When it is determined in step S30 that | dM1-dM0 | is equal to or smaller than the threshold value Th, the controller 50 stores the value of the variable dM1 in the variable dM0, stores the value of the variable M2 in the variable M1, and sets the variable M1. Is stored in the variable M0 (step S31), and step S27 is executed again. If it is not determined in step S30 that | dM1-dM0 | is equal to or less than the threshold value Th, the controller 50 stores the average temperature T-dT / 2 in the variable T _high (step S32).

  Next, as shown in FIG. 11, the controller 50 resets the average temperature T to an initial value (step S33). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43, and stores the value in the variable M0 (step S34). Next, the controller 50 decreases the electric power supplied to the heaters 14a to 14c and subtracts the step value dT / 2 from the average temperature T of the heaters 14a to 14c (step S35). Next, the controller 50 measures the laser beam intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S36). Next, the controller 50 stores the differential value (M1-M0) / (− dT / 2) in the variable dM0 (step S37).

  Next, the controller 50 decreases the electric power supplied to the heaters 14a to 14c and subtracts the step value dT / 2 from the average temperature T of the heaters 14a to 14c (step S38). Next, the controller 50 measures the laser beam intensity using the light receiving element 43 and stores the measured value in the variable M2 (step S39). Next, the controller 50 stores the differential value (M2-M1) / (− dT / 2) in the variable dM1 (step S40).

  Next, the controller 50 determines whether or not the absolute value of (dM1-dM0) is equal to or less than the threshold value Th (step S41). When it is determined in step S41 that | dM1-dM0 | is equal to or less than the threshold value Th, the controller 50 stores the value of the variable dM1 in the variable dM0, stores the value of the variable M1 in the variable M0, and sets the variable M2 Is stored in the variable M1 (step S42), and step S38 is executed again.

If it is not determined in step S41 that | dM1-dM0 | is equal to or less than the threshold value Th, the controller 50 stores the average temperature T + dT / 2 in the variable T _low (step S43). Next, the controller 50 stores T _low + (T _high −T _low ) × k (0 <k <1) in the variable T _opt as the optimum average temperature (step S44). Then, the controller 50, the average temperature T is to control the power to the heater 14a~14c such that _{T opt} (step S45). Thereafter, the controller 50 ends the execution of the flowchart.

  Thus, the optimal average temperature of the heaters 14a to 14c can be set by using the differential value of the change in the gain state. Note that k may be a value that satisfies 0 <k <1, and may be 0.5, for example.

FIGS. 12 and 13 are flowcharts showing still another example of the control of the wavelength tunable laser 10. As shown in FIG. 12, first, the controller 50 refers to the look-up table 51, and sets the initial current value I _LD , the initial current value I _SOA , the initial current values Ia _{Heater to} Ic _Heater and the initial values corresponding to the set channel. A temperature value _TLD is acquired (step S51).

  Next, the controller 50 causes the wavelength tunable laser 10 to oscillate based on the initial setting value acquired in step S51 (step S52). Next, the controller 50 stores the initial value dT0 in the step value dT (step S53). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S54). Next, the controller 50 increases the electric power supplied to the heaters 14a to 14c, and adds the step value dT to the average temperature T of the heaters 14a to 14c (step S55).

  Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S56). Next, the controller 50 determines whether or not the absolute value of (M1-M0) is equal to or less than the threshold value Th0 (step S57). When it is determined in step S57 that | M1-M0 | is equal to or less than the threshold value Th0, the controller 50 stores the value of the variable M1 in the variable M0 (step S58), and executes step S55 again.

  If it is not determined in step S57 that | M1-M0 | is equal to or smaller than the threshold value Th0, the controller 50 determines whether or not the step value dT is equal to or larger than the threshold value Th1 (step S59). When it is determined in step S59 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 subtracts the step value dT from the average temperature T and multiplies the step value dT by k0 (0 <k0 <1). The value is stored in the step value dT (step S60), and step S55 is executed again.

If it is not determined in step S59 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 stores the average temperature T-dT / 2 in the variable T _high (step S61). Next, the controller 50 resets the average temperature T to an initial value (step S62).

  Next, as shown in FIG. 13, the controller 50 stores the initial value dT0 in the step value dT (step S63). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S64). Next, the controller 50 decreases the power supplied to the heaters 14a to 14c, and subtracts the step value dT from the average temperature T of the heaters 14a to 14c (step S65).

  Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S66). Next, the controller 50 determines whether or not the absolute value of (M1-M0) is equal to or less than the threshold value Th0 (step S67). When it is determined in step S67 that | M1-M0 | is equal to or smaller than the threshold value Th0, the controller 50 stores the value of the variable M1 in the variable M0 (step S68), and executes step S65 again.

  If it is not determined in step S67 that | M1-M0 | is equal to or smaller than the threshold value Th0, the controller 50 determines whether or not the step value dT is equal to or larger than the threshold value Th1 (step S69). When it is determined in step S69 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 adds the step value dT to the average temperature T and multiplies the step value dT by k0 (0 <k0 <1). The value is stored in the step value dT (step S70), and step S65 is executed again.

If it is not determined in step S69 that the step value dT is equal to or greater than the threshold value Th1, the average temperature T + dT / 2 is stored in the variable T _low (step S71). Next, the controller 50 stores T _low + (T _high −T _low ) × k1 (0 <k1 <1) as the optimum average temperature in the variable T _opt (step S72). Next, the controller 50 controls the power to the heaters 14a to 14c so that the average temperature T becomes T _opt (step S73). Thereafter, the controller 50 ends the execution of the flowchart.

  Thus, the optimum average temperature of the heaters 14a to 14c can be set by detecting the intensity change of the laser light emitted from the rear end face while gradually decreasing the step value dT. Note that k1 may be a value that satisfies 0 <k1 <1, and may be 0.5, for example.

14 and 15 are flowcharts showing still another example of the control of the wavelength tunable laser 10. As shown in FIG. 14, first, the controller 50 refers to the look-up table 51, and sets the initial current value I _LD , the initial current value I _SOA , the initial current values Ia _{Heater to} Ic _Heater and the initial values corresponding to the set channel. A temperature value _TLD is acquired (step S81).

  Next, the controller 50 causes the wavelength tunable laser 10 to oscillate based on the initial setting value acquired in step S81 (step S82). Next, the controller 50 stores the initial value dT0 in the step value dT (step S83). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S84).

  Next, the controller 50 increases the electric power supplied to the heaters 14a to 14c, and adds the step value dT / 2 to the average temperature T of the heaters 14a to 14c (step S85). Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S86). Next, the controller 50 stores the differential value (M1-M0) / (dT / 2) in the variable dM0 (step S87).

  Next, the controller 50 increases the electric power supplied to the heaters 14a to 14c, and adds the step value dT / 2 to the average temperature T of the heaters 14a to 14c (step S88). Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M2 (step S89). Next, the controller 50 stores the differential value (M2-M1) / (dT / 2) in the variable dM1 (step S90).

  Next, the controller 50 determines whether or not the absolute value of (dM1-dM0) is equal to or less than a threshold value Th0 (step S91). When it is determined in step S91 that | dM1-dM0 | is equal to or less than the threshold value Th0, the controller 50 stores the value of the variable dM1 in the variable dM0, stores the value of the variable M2 in the variable M1, and sets the variable M1. Is stored in the variable M0 (step S92), and step S88 is executed again.

  If it is not determined in step S91 that | dM1-dM0 | is equal to or smaller than the threshold value Th0, the controller 50 determines whether or not the step value dT is equal to or larger than the threshold value Th1 (step S93). When it is determined in step S93 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 subtracts the step value dT from the average temperature T and multiplies the step value dT by k0 (0 <k0 <1). The value is stored in the step value dT (step S94), and step S85 is executed again.

When it is not determined in step S93 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 stores the average temperature T-dT / 2 in the variable T _high (step S95). Next, the controller 50 resets the average temperature T to an initial value (step S96).

  Next, as shown in FIG. 15, the controller 50 stores the initial value dT0 in the step value dT (step S97). Next, the controller 50 measures the intensity of the laser beam using the light receiving element 43 and stores the value in the variable M0 (step S98). Next, the controller 50 decreases the power supplied to the heaters 14a to 14c and subtracts the step value dT / 2 from the average temperature T of the heaters 14a to 14c (step S99). Next, the controller 50 measures the laser beam intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S100). Next, the controller 50 stores the differential value (M1-M0) / (− dT / 2) in the variable dM0 (step S101).

  Next, the controller 50 decreases the power supplied to the heaters 14a to 14c, and subtracts the step value dT / 2 from the average temperature T of the heaters 14a to 14c (step S102). Next, the controller 50 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M2 (step S103). Next, the controller 50 stores the differential value (M2-M1) / (− dT / 2) in the variable dM1 (step S104).

  Next, the controller 50 determines whether or not the absolute value of (dM1-dM0) is equal to or less than a threshold value Th0 (step S105). When it is determined in step S105 that | dM1-dM0 | is equal to or less than the threshold value Th0, the controller 50 stores the value of the variable dM1 in the variable dM0, stores the value of the variable M1 in the variable M0, and sets the variable M2 Is stored in the variable M1 (step S106), and step S102 is executed again.

  If it is not determined in step S105 that | dM1-dM0 | is equal to or smaller than the threshold value Th0, the controller 50 determines whether or not the step value dT is equal to or larger than the threshold value Th1 (step S107). When it is determined in step S107 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 adds the step value dT to the average temperature T and multiplies the step value dT by k0 (0 <k0 <1). The value is stored in the step value dT (step S108), and step S99 is executed again.

If it is not determined in step S107 that the step value dT is equal to or greater than the threshold value Th1, the controller 50 stores the average temperature T + dT / 2 in the variable T _low (step S109). Next, the controller 50 stores T _low + (T _high −T _low ) × k 1 (0 <k 1 <1) as the optimum average temperature in the variable T _opt (step S110). Next, the controller 50 controls the power to the heaters 14a to 14c so that the average temperature T becomes T _opt (step S111). Thereafter, the controller 50 ends the execution of the flowchart.

  Thus, the optimum average temperature of the heaters 14a to 14c can be set by detecting the laser beam intensity while gradually decreasing the step value dT. Note that k1 may be a value that satisfies 0 <k1 <1, and may be 0.5, for example.

  In the present embodiment, the optimum average temperature is detected at the time of start-up, but the optimum average temperature may be detected at the time of wavelength switching of the wavelength tunable laser 10 after temporarily stopping the output wavelength. Further, the above optimization may be performed after the laser apparatus 100 is installed in an actual operating environment. In this case, it is possible to correct a deviation between the test environment for acquiring the control information set in the lookup table 51 and the actual operating environment. Further, the detected optimum average temperature or the power supplied to the heater for giving the optimum average temperature may be recorded in the look-up table 51.

  In this embodiment, the discontinuous point of the gain state is detected by changing the equivalent refractive index of the optical waveguide in the CSG-DBR region 11, but the equivalent refractive index of the optical waveguide in the SG-DFB region 12 is changed. A discontinuous point in the gain state may be detected by changing. Also, discontinuous points of both the gain state change and the differential value of the gain state change may be detected. In this case, the accuracy of mode jump detection is improved.

  FIG. 16 is a schematic diagram showing an overall configuration of a laser apparatus 100a according to the second embodiment of the present invention. The laser device 100 a is different from the laser device 100 of FIG. 2 in that a wavelength tunable laser 10 a is provided instead of the wavelength tunable laser 10.

  As shown in FIG. 16, in the wavelength tunable laser 10a, an SG-DBR (Sampled Grafted Distributed Reflector) region 21, a PS (Phase Shift) region 22, a Gain region 23, an SG-DBR region 24, and an SOA region 13 are sequentially connected. Has a structured.

  The SG-DBR regions 21 and 24 include an optical waveguide provided with a plurality of segments each provided with a first region having a diffraction grating and a second region connected to the first region and serving as a space portion. This optical waveguide is made of a semiconductor crystal whose absorption edge wavelength is shorter than the laser oscillation wavelength. Moreover, in SG-DBR area | regions 21 and 24, the length of each 2nd area | region is equal. A heater 25 is provided on the SG-DBR region 21, and a heater 28 is provided on the SG-DBR region 24. The equivalent refractive index of the optical waveguide in the SG-DBR region 21 is controlled by temperature control by the heater 25. The equivalent refractive index of the optical waveguide in the SG-DBR region 24 is controlled by temperature control by the heater 28.

  The PS region 22 includes an optical waveguide made of a semiconductor crystal whose absorption edge wavelength is shorter than the laser oscillation wavelength. The electrode 26 is an electrode for supplying a current to the PS region 22. The Gain region 23 includes an optical waveguide having a gain with respect to laser oscillation at a target wavelength. The electrode 27 is an electrode for supplying a current to the Gain region 23.

  The SG-DBR region 21 and the SG-DBR region 24 have wavelength peaks with different periods, respectively, and function as a wavelength selection unit. The PS region 22 functions as a wavelength selection unit because the longitudinal mode can be controlled by phase adjustment. The oscillation wavelength is selected by changing the wavelength characteristics of the SG-DBR regions 21 and 24 and the PS region 22. The wavelength characteristics of the SG-DBR regions 21 and 24 can be controlled by at least one of the heaters 25 and 28 and the temperature control device 20.

  Also in the wavelength tunable laser 10a according to the present embodiment, the gain state of the wavelength tunable laser 10a is not changed while at least one wavelength characteristic of the SG-DBR regions 21 and 24 and the PS region 22 is changed at startup or wavelength switching. By detecting the continuity, the optimum temperature of the heaters 25 and 28 or the optimum current of the PS region 22 can be obtained.

  FIG. 17 is a schematic diagram showing an overall configuration of a laser apparatus 100b according to the third embodiment of the present invention. As shown in FIG. 17, the laser apparatus 100 b includes a PS-equipped Gain element 10 b including a Gain region 61 and a PS region 62. Further, a fixed etalon 67 and a liquid crystal mirror 66 are sequentially arranged on the PS region 62 side of the gain element with PS 10b. The fixed etalon 67 is an optical etalon having a periodic transmission wavelength peak. The liquid crystal mirror 66 is obtained by integrating a liquid crystal etalon on a mirror for forming a resonator with the end face of the gain region 61. Here, the liquid crystal etalon has an optical etalon structure in which a liquid crystal region capable of controlling the refractive index by voltage is sealed. In the liquid crystal mirror according to the present embodiment, the internal liquid crystal etalon has a wavelength peak different from that of the fixed etalon 67, and the peak of the reflection wavelength characteristic can be changed according to the applied voltage value.

  In the present embodiment, the wavelength selection by the vernier effect is made possible by relatively changing the peak of the wavelength characteristics of the fixed etalon 67 and the liquid crystal mirror 66. The PS region 62 stably controls the longitudinal mode wavelength selected by superimposing the wavelength characteristics of the fixed etalon 67 and the liquid crystal mirror 66. In this embodiment, the liquid crystal mirror 66 and the fixed etalon 67 each function as a wavelength selection unit.

  The beam splitter 63 reflects a part of the laser light emitted from the gain region 61 side and gives it to the beam splitter 64. The beam splitter 64 supplies a part of the applied light to the light receiving element 44 and supplies the remaining light to the light receiving element 32. An etalon 65 is disposed between the beam splitter 64 and the light receiving element 44.

  The controller 50 can select the oscillation wavelength by controlling the voltage applied to the liquid crystal mirror 66 and the current supplied to the PS region 62. The controller 50 detects the intensity of the laser beam based on the detection result of the light receiving element 32 and detects the wavelength of the laser beam based on the detection result of the light receiving elements 43 and 44.

  Also in the gain element with PS 10b according to the present embodiment, the change in the gain state of the resonator laser is detected while changing the wavelength characteristic of at least one of the PS region 62 and the liquid crystal mirror 66 at the time of startup or wavelength switching. As a result, the optimum operating point of the wavelength selection characteristic of at least one of the PS region 62 and the liquid crystal mirror 66 can be obtained.

  The fourth embodiment shows an example in which the present invention is applied when the width of the terrace portion is known. Since the width of the terrace portion is known, in this embodiment, the optimum average temperature T is obtained by detecting the discontinuity of the gain state on either the high temperature side or the low temperature side. That is, referring to FIG. 1, when the range A is known, the optimum average temperature T can be obtained by acquiring one of the values of the boundary A1 and the boundary A2. This has an effect that the time required for boundary detection can be shortened as compared with the case where both the boundary A1 and the boundary A2 are acquired.

  FIG. 18 shows a specific flow. FIG. 18 shows a case where the present embodiment is applied to the laser apparatus of FIG. Steps S1 to S8 are the same as in FIG.

In the present embodiment, in step S9, the controller 50 calculates the optimum average temperature T based on the high temperature side boundary (T _high ) acquired in step S8. This calculation is executed by _obtaining T _opt = T _high −T _Width × k2 (0 <k2 <1). T _Width indicates the temperature range of the terrace, and is stored in the lookup table 51 in advance. As k2, 0.5 is selected when the center of T _Width is the point of the optimum average temperature.

In step S10, the controller 50 controls the power of the heater so that the average temperature T = T _opt . With the above operation, the average temperature T is optimized.

Note that T _Width recorded in the lookup table 51 is obtained in advance with high accuracy using a wavelength meter or the like. The terraces corresponding to the respective wavelengths may be different from each other, and in order to increase the accuracy of the optimum average temperature T, the magnitude of T _Width may be measured for all of them. Of course, when T _Width is prepared for each terrace, an operation of acquiring T _Width corresponding to a desired oscillation wavelength from the lookup table 51 is performed.

In addition, since the difference in the size of each terrace tends to occur at a constant ratio, the size T _Width of one terrace is measured, and the T _{Width of} another terrace based on the ratio is calculated from the value. Good. As the simplification of acquisition of T _Width, rather than measurements using such wavemeter, a method of determining the T _Width of each terrace from the design value of the laser chip. In addition to the method of obtaining T _Width for each laser chip, there is also a method of measuring T _Width from a representative chip in wafer units or lot units.

In the above description, the case of detecting the discontinuity (T _high ) on the _high temperature side has been described, but the same can be obtained by detecting the discontinuity (T _low ) on the _low temperature side. In this embodiment, the gain element with PS 10b corresponds to a wavelength tunable laser.

  In each of the above embodiments, the controller 50 corresponds to a discontinuity detection unit and an operating point setting unit.

  In the fifth embodiment, a method for determining the optimum operating point used for the optimization control of the power supplied to the heaters 14a to 14c, which has been performed in the control of the laser apparatus according to the first to fourth embodiments, is determined by calibration before shipping. Applied to the production process. According to the calibration of the present embodiment, the optimum target value of the power supplied to the heaters 14a to 14c can be obtained. In the first to fourth embodiments, the average temperature T of the heaters 14a to 14c is managed in order to determine the optimum operating point. In this embodiment, however, the power supplied to the heaters 14a to 14c is managed instead. Adopt the method. Hereinafter, the calibration method according to the present embodiment will be described.

  FIG. 19 is a schematic diagram showing an overall configuration of a calibration apparatus 200 according to the fifth embodiment of the present invention. The calibration apparatus 200 includes a lookup table 51, a controller 150, an external memory 152, and the like. The calibration device 200 is connected to the laser unit 300. Here, the laser unit 300 has a structure in which the wavelength tunable laser 10, the temperature control device 20, the output detection unit 30, and the wavelength detection unit 40 are accommodated in a laser package.

  In addition, each part of the said wavelength variable laser 10, the temperature control apparatus 20, the output detection part 30, and the wavelength detection part 40 is the same as FIG. The controller 150 includes a control unit such as a CPU, RAM, and ROM, a power source, and the like. According to the calibration method according to the present embodiment, a test for obtaining an optimal control value at each wavelength of the unit can be performed. Details will be described below.

20 and 21 are flowcharts showing an example of the calibration process of the laser unit 300. FIG. As shown in FIG. 20, first, the controller 150 refers to the lookup table 51, and acquires initial setting values of I _LD , I _SOA , Ia _{Heater to} Ic _Heater, and T _LD corresponding to the set channel wavelength. (Step S121).

  Next, the controller 150 oscillates the wavelength tunable laser 10 based on the initial setting value acquired in step S121 (step S122). Next, the controller 150 measures the laser light intensity using the light receiving element 43 and stores the value in the variable M0 (step S123). Next, the controller 150 increases the power supplied to each of the heaters 14a to 14c by the increment dP (step S124).

  Next, the controller 150 measures the laser light intensity using the light receiving element 43, and stores the measured value in the variable M1 (step S125). Next, the controller 150 calculates the absolute value | M1−M0 | and determines whether or not it exceeds the threshold Th (step S126).

If it is determined in step S126 that the absolute value | M1-M0 | does not exceed the threshold value Th, the controller 150 stores the value of the variable M1 in the variable M0 (step 127), and then executes step S124 again. To do. If it is determined in step S126 that the absolute value | M1-M0 | has exceeded the threshold value Th, the controller 150 determines the increment value dP from each power value of the heaters 14a to 14c supplied at that time. The value reduced by half is stored as Pa _{Heater-High to} Pc _Heater-High (step S128).

  Next, similarly to step S122, the controller 150 causes the wavelength tunable laser 10 to oscillate based on the initial setting value (step S129). Next, the controller 150 measures the laser light intensity using the light receiving element 43, and stores the value in the variable M0 (step S130). Next, the controller 150 decreases the power supplied to the heaters 14a to 14c by the increment dP (step S131).

  Next, the controller 150 measures the laser light intensity using the light receiving element 43 and stores the measured value in the variable M1 (step S132). Next, the controller 150 calculates an absolute value | M1−M0 | and determines whether or not the absolute value | M1−M0 | exceeds a threshold Th (step S133).

If it is determined in step S133 that the absolute value | M1-M0 | does not exceed the threshold value Th, the controller 150 stores the value of the variable M1 in the variable M0 (step 134), and executes step S131 again. . If it is determined in step S133 that the absolute value | M1-M0 | has exceeded the threshold value Th, the controller 150 determines the increment value dP from each power value of the heaters 14a to 14c supplied at that time. The value increased by half is stored as Pa _{Heater-Low to} Pc _Heater-Low (step S135).

Next, the controller 150
Pa _Heater-x = Pa _Heater-Low + (Pa _Heater-High- Pa _Heater-Low ) × k (0 <k <1)
Pb _Heater-x = Pb _Heater-Low + (Pb _Heater-High- Pb _Heater-Low ) × k (0 <k <1)
Pc _Heater-x = Pc _Heater-Low + (Pc _Heater-High- Pc _Heater-Low ) × k (0 <k <1)
Are calculated (step 136), and the calculation result is stored in the external memory 152 (step 137).

  The above steps are performed for each wavelength corresponding to the required channel, and as shown in FIG. 22, an optimum target value table for power control of the heaters 14a to 14c is generated. The user can stably realize a desired wavelength by controlling the laser apparatus based on the optimum target value table.

  In the calibration method according to the present embodiment, as in the first embodiment, the forward light intensity of the laser, the change in the gain state of the SOA region 13, the detection of the detection current using the SOA region, and the SG-DFB region 12 are performed. The gain state discontinuity may be detected using a change in the gain state of the laser beam. Further, the method for detecting the discontinuity of the gain state may be a method for detecting a change in the differential value of the gain state.

  Further, the calibration method according to the present embodiment can be similarly performed in a wavelength tunable laser of the type in which the refractive index of the SG-DBR region 11 is controlled by current. In that case, the injection current value into the SG-DBR region 11 may be controlled and calculated in the same manner as controlling the heater power in this embodiment.

  The calibration method of the present embodiment has been described for the laser device described in FIG. 19, but is also useful for the laser devices described in the second and third embodiments.

When the range of the terrace portion of the wavelength tunable laser (range A in FIG. 1) is known in advance, any one of the above-mentioned Pa _{Heater-High to} Pc _Heater-High or Pa _{Heater-Low to} Pc _Heater-Low Only one of them may be acquired, and an appropriate set value may be obtained by calculation based on this.

In most cases, heaters driven by Pa _{Heater-x to} Pc _Heater-x obtained by performing the calibration method are different from the heater temperature when the initial value is given. When it is considered that the change in the oscillation wavelength when Pa _{Heater-x to} Pc _Heater-x is given is more serious than when the initial values of the heaters 14a to 14c are given, control for correcting the wavelength is performed. It is also useful to do.

In this case, the calibration apparatus 200 drives the laser unit 300 using Pa _{Heater-x to} Pc _Heater-x as target values, and detects the output wavelength in that case with a wavelength meter (not shown). The calibration device 200 corrects the temperature value T _LD of the temperature control device 20 to realize the original target wavelength, and stores the temperature of the temperature control device 20 at that time in the external memory 152 as T _LD-x . When this operation is performed, an optimum target value table including the temperature value T _LD-x in addition to the optimum target values for the heaters 14a to 14c is generated.

It is a figure which shows the heater temperature of a reflector with the peak of a periodic reflection spectrum, and the relationship of an oscillation wavelength. 1 is a schematic diagram showing an overall configuration of a wavelength tunable laser and a laser apparatus including the same according to a first embodiment of the present invention. It is a figure which shows the example of a look-up table. It is a figure which shows the relationship between the temperature of a heater, and a rear end surface laser beam intensity | strength. It is a figure which shows the relationship between the temperature of a heater, and front end surface laser beam intensity | strength. It is a figure which shows the relationship between the temperature of a heater, and the applied voltage of a DFB area | region. It is a figure which shows the relationship between the supply current to a DBR area | region, and the change of a gain state. It is a figure which shows the flowchart which shows an example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows an example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the other example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the other example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the further another example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the further another example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the further another example of control of a wavelength variable laser. It is a figure which shows the flowchart which shows the further another example of control of a wavelength variable laser. It is a schematic diagram which shows the whole structure of the laser apparatus based on 2nd Example of this invention. It is a schematic diagram which shows the whole structure of the laser apparatus based on 3rd Example of this invention. It is a figure which shows the flowchart which shows an example of control of a wavelength variable laser. It is a schematic diagram which shows the whole structure of the calibration apparatus which concerns on 5th Example of this invention. It is a flowchart which shows an example of the calibration process of a laser unit. It is a flowchart which shows an example of the calibration process of a laser unit. It is a figure which shows the optimal target value of the electric power control of a heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor laser 11 CSG-DBR area | region 12 SG-DFB area | region 13 SOA area | region 14 Heater 20 Temperature control apparatus 30 Output detection part 40 Wavelength detection part 50 Controller 100 Laser apparatus 150 Controller 152 External memory 200 Calibration apparatus

Claims (8)

A test method for a wavelength tunable laser including a plurality of wavelength selection units having different wavelength characteristic peaks in a resonator,
A first step of causing the wavelength tunable laser to oscillate at a predetermined wavelength based on an initial setting value;
A second step of detecting a discontinuity point of a change in the gain state of the wavelength tunable laser while changing the wavelength characteristics of the plurality of wavelength selection units;
A third step of calculating a stable operating point of the wavelength selection unit based on the limit point when the discontinuous point is detected as a limit point of the oscillation state at the predetermined wavelength;
Only including,
In the detection of the discontinuous point of the gain state change in the second step, after detecting the discontinuous point of the gain state while changing the wavelength characteristic, the wavelength characteristic is changed with a change amount smaller than the change amount of the wavelength characteristic. A test method for a wavelength tunable laser, wherein the test is performed again by detecting discontinuous points in the gain state .   2. The test method of a wavelength tunable laser according to claim 1, wherein the oscillation state of the wavelength tunable laser is generated discontinuously with respect to a change in wavelength characteristics of the wavelength selection unit. The discontinuous point in the second step is detected based on detection of a discontinuous change in output light intensity of the wavelength tunable laser or a voltage or current in a gain region of the wavelength tunable laser. 2. A test method for a tunable laser according to 1.   The wavelength tunable laser testing method according to claim 1, wherein the plurality of wavelength selection units select a wavelength using a vernier effect. The wavelength tunable laser includes a semiconductor optical amplification region outside the resonator,
The discontinuous point detection in the second step is performed by detecting a photocurrent of the semiconductor optical amplification region when the semiconductor optical amplification region is biased to a state of absorbing light. Item 2. A test method for a wavelength tunable laser according to Item 1. 2. The tunable laser testing method according to claim 1, wherein the detection of the discontinuous point in the second step is performed based on a differential value obtained by differentiating the amount of change in the gain state. A method of controlling a wavelength tunable laser including a plurality of wavelength selection units having different wavelength characteristic peaks in a resonator,
A first step of causing the wavelength tunable laser to oscillate at a predetermined wavelength based on an initial setting value;
A second step of detecting a discontinuity in the change of the gain state of the wavelength tunable laser while changing the wavelength characteristic of the wavelength selection unit;
A third step of calculating a stable operating point of the wavelength selection unit based on the limit point when the discontinuous point is detected as a limit point of the oscillation state at the predetermined wavelength;
As the target value of the stable operating point obtained in the third step, seen including a fourth step of oscillating the tunable laser,
In the detection of the discontinuous point of the gain state change in the second step, after detecting the discontinuous point of the gain state while changing the wavelength characteristic, the wavelength characteristic is changed with a change amount smaller than the change amount of the wavelength characteristic. A method of controlling a wavelength tunable laser, wherein the control is performed by detecting a discontinuous point in the gain state again . A wavelength tunable laser including a plurality of wavelength selection units having different wavelength characteristic peaks in the resonator;
A discontinuous point detector that oscillates the wavelength tunable laser at a predetermined wavelength based on an initial setting value and detects a discontinuous point of a gain state change of the wavelength tunable laser while changing a wavelength characteristic of the wavelength selector. When,
An operating point calculating means for calculating a stable operating point of the wavelength selection unit based on the limit point, the time point when the discontinuous point is detected as a limit point of the oscillation state at the predetermined wavelength;
A control unit that performs control to oscillate the wavelength tunable laser according to the stable operating point obtained by the computing means ,
The discontinuous point detecting unit detects a discontinuous point in the gain state while changing the wavelength characteristic, and then again discontinues the gain state while changing the wavelength characteristic with a change amount smaller than the change amount in the wavelength characteristic. A laser device characterized by detecting a point .

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