JP2011176070A - Wavelength-variable laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength-variable laser device improving the precision of an adjustment of wavelength of the wavelength variable laser. <P>SOLUTION: A control timing of an electric current value is set to a phase adjustment signal 60, a same directional optical coupler filter adjustment signal 59, and a DBR (distribution Bragg reflector) type filter adjustment signal 61, in that order so that a target wavelength is provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wavelength tunable laser device.

  The transmission capacity of optical communication is rapidly increasing year by year, and wavelength division multiplexing (WDM) is being put to practical use as an inexpensive, high-speed, large-capacity technology that meets this demand. WDM is a technology that uses multiple monochromatic lights (several tens to 100 wavelengths) that differ in frequency by 50 GHz or 100 GHz at the same time and transmits different signals at each wavelength, and can increase the transmission capacity per fiber by several tens of times. Therefore, the cost of installing the fiber can be significantly reduced.

  Conventionally, a WDM light source requires various types of semiconductor lasers having different wavelengths and a modularized device (hereinafter abbreviated as a module) for driving the semiconductor laser. In order to manufacture a laser, it is necessary to produce a crystal for each wavelength, and it is also necessary to manufacture a module for each wavelength, which is problematic in terms of cost.

  On the other hand, a wavelength tunable module that can freely change the wavelength has been developed. Since this module has a variable light wavelength in the range of about 40 nm, it is only necessary to manufacture light emitting elements and modules of several wavelengths, and the module can be used at low cost. Yes. In this case, the wavelength tunable laser is required to have high wavelength accuracy (for example, <± 0.004 nm) and high spectral purity (for example, Side-Mode Suppression Ratio (SMSR)> 35 dB from the design of the transmission apparatus. The

Various systems have been studied as wavelength tunable lasers. As an example, a GCSR (Grating Assisted Codirectional Coupler Laser with Rear Sampled Grating Reflector) laser will be described with reference to Non-Patent Document 1. Fig. 1 shows the structure of the laser, and Fig. 2 shows the spectrum showing the operating principle of the laser.
In this laser, a distributed Bragg reflector (DBR) reflective filter 12, a phase adjustment region 13, a vertical directional optical coupler filter 14, and a gain region 15 are optically connected. The low refractive index is common to all regions of the distributed Bragg reflector (DBR) reflective filter 12, the phase adjustment region 13, and the vertical directional optical coupler filter 14 on the InP substrate 1 having the common terminal 11 on the back surface. The waveguide layer 2 and the high refractive index waveguide layer 3 are provided, and the region of the distributed Bragg reflector (DBR) reflective filter 12 is provided with the diffraction grating 5 on the high refractive index waveguide 3 and has the same vertical direction. The region of the optical coupler filter 14 includes a long-period diffraction grating 6 on the high refractive index waveguide 3, and each region on these semiconductor laminates includes a terminal 7 of the DBR reflector, a phase adjustment region Terminal 8, a directional optical coupler terminal 9, and a gain region terminal 10.

  As shown in FIG. 2, laser oscillation occurs in a longitudinal mode 34 in the vicinity of a wavelength at which the peak of the transmission spectrum 31 of the directional optical coupler filter and the reflection spectrum 32 of the DBR reflection filter coincide. The transmission spectrum 31 of the directional optical coupler filter and the reflection spectrum 32 of the DBR reflector can be adjusted by injecting current, respectively, and as a result, the wavelength of the laser oscillation 34 can be changed. Furthermore, by injecting current into the phase adjustment region and changing the refractive index, the wavelength at which the longitudinal mode of laser oscillation stands can be finely adjusted.

IEEE Photonics Technology Letters, Vol. 7, No. 7, July 1995, P697-699 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 8, NO. 6, NOVEMBER / DECEMBER 2002, P1349-1357

  As described above, it is essential to adjust the wavelength to the target wavelength and achieve a high SMSR, but it is necessary to adjust the three regions of the phase adjustment region, the directional coupler filter, and the DBR reflector with current. There is.

  Here, as an example, a case where wavelength control is performed with a target wavelength of 1551 nm is shown. The structure of the wavelength tunable laser will be described in detail in a later embodiment, but is an example in which a directional optical coupler filter, a phase adjustment region, a gain region, and a DBR reflector region are integrated from the light emitting direction. FIG. 3A shows an example of calculation of the dependence of the wavelength adjustment laser on the oscillation wavelength, optical output, and SMSR phase adjustment region refractive index change. This is a case where the wavelength of the directional optical coupler filter and the wavelength of the DBR reflector coincide with the target wavelength of 1551 nm. By adjusting the refractive index of the phase adjustment region, the target wavelength can be adjusted. At this time, the SMSR is 35 dB or more and the light output is maximized. FIG. 3B shows an example of calculation of the wavelength dependence of the oscillation wavelength, optical output, and SMSR of the tunable laser. This is a case where the DBR reflector wavelength matches the target wavelength of 1551 nm and the phase adjustment region refractive index change amount is -0.009. The target wavelength can be adjusted by adjusting the filter wavelength of the directional coupler. At this time, the SMSR is 35 dB or more and the light output is maximized. FIG. 3C shows an example of calculation of the oscillation wavelength of the tunable laser, the optical output, and the SMSR DBR reflector wavelength dependence. This is the case where the wavelength of the directional optical coupler filter matches the target wavelength of 1551 nm and the phase adjustment region refractive index change amount is -0.009. By adjusting the DBR reflector wavelength, the target wavelength can be adjusted. At this time, the SMSR is 35 dB or more and the light output is maximized.

  Thus, by adjusting the respective currents, it is possible to simultaneously achieve the oscillation wavelength and wavelength accuracy <± 0.004 nm and SMSR> 35 dB. However, this is a special case where the wavelength of the directional optical coupler filter and the wavelength of the DBR reflector coincide with the target wavelength of 1551 nm and the refractive index change amount of the phase adjustment region is -0.009. However, if any of these values deviates (assumed when the laser is operated for a long period of time), the control method that simultaneously achieves wavelength accuracy <0.004 nm and SMSR of 35 dB or more is unknown.

  An object of the present invention is to provide a wavelength tunable laser device with improved wavelength adjustment accuracy of the wavelength tunable laser.

  As means for solving the above-mentioned problems, a specific control method for adjusting the three regions by current is provided.

  One example is a tunable laser device described in the claims.

  ADVANTAGE OF THE INVENTION According to this invention, the wavelength tunable laser apparatus which improved the wavelength adjustment precision of a wavelength tunable laser can be provided.

It is a block diagram of the typical example (GCSR laser) of the conventional wavelength tunable laser. It is a figure which shows the principle of operation of a GCSR laser. This is the calculated value of the dependence of the GCSR laser wavelength, SMSR, and optical output on the phase adjustment region refractive index change. This is a calculated value of the wavelength dependence of GCSR laser wavelength, SMSR, and optical output center wavelength of the directional coupler filter. It is a calculated value of the DBR wavelength change dependency of the wavelength, SMSR, and optical output of the GCSR laser. 1 is a block diagram of Example 1. FIG. 3 is a table showing a control flow of the wavelength tunable laser of Example 1. 6 is a table showing a control flow of a wavelength tunable laser of Example 2. It is a block diagram of an optical transmitter. It is a block diagram of a wavelength variable laser. It is a block diagram of a wavelength variable laser. FIG. 8 shows the dependency of the laser wavelength, SMSR, and optical output on the phase adjustment region refractive index variation. FIG. 8 shows the dependence of the laser wavelength, SMSR, and optical output on the wavelength of the directional coupler filter center. FIG. 8 shows the dependence of the laser wavelength, SMSR, and optical output on the DBR wavelength change in FIG. FIG. 8 shows the dependence of the laser wavelength, SMSR, and optical output on the DBR wavelength change in FIG.

  Example 1 will be described with reference to FIGS. 4, 5, 7, 8 </ b> A, 8 </ b> B, and 9 </ b> A to 9 </ b> C.

  Example 1 is a wavelength tunable laser using a wavelength tunable laser using a 1.55 μm band laterally coupled co-directional optical coupler type wavelength filter (hereinafter referred to as “optical coupler type wavelength filter”) on an InP substrate. An optical transmitter as a device.

  FIG. 7 shows a configuration diagram of the optical transmitter, and FIG. 4 shows a block diagram of the optical transmitter in which FIG. 7 is simplified.

  The optical transmitter of the present embodiment includes an optical transmitter housing 81 and an interface board 82.

  Inside the optical transmitter housing 81, a submount 84 made of SiN on a Peltier element 97, which is a cooling element, and a lens 89 are provided.

  On the submount 84, a tunable laser 83, a lens 85, a beam splitter 86, a lens 87, an optical modulator 88 which is a Mach-Zehnder modulator, a line 91 for injecting current, a photodetector 92, an etalon 93, a beam A splitter 99, a photodetector 95, and a thermistor 94 are disposed.

  Although not shown in FIG. 7, the interface board 82 includes the laser current source 56 shown in FIG. 4, an external controller 57 having a look-up table (LUT), a temperature control circuit 64, and an optical modulator driver 66. Further, these elements may be mounted on another substrate and electrically connected via the interface substrate 82.

  The wavelength tunable laser 83, the lens 85, the beam splitter 86, the lens 87, and the optical waveguide 65 of the optical modulator 88 are arranged in this order in the first direction (left-right direction in the figure) so that the optical axes coincide. Accordingly, the light emitted from the wavelength tunable laser 83 passes through the lens 85 and enters the beam splitter 86. Most of the light is transmitted, collected by the lens 87, and incident on the optical waveguide 65 of the optical modulator 88. The incident light is modulated by a modulation operation based on the signal 67 to the optical modulator driver 66, and then is coupled to the optical fiber through the lens 51.

  The beam splitter 99 is arranged in the horizontal direction (vertical direction in the figure) of the beam splitter 86. Further, the beam splitter 99 is sandwiched between the etalon 93 and the photodetector 92 (left direction in the figure) and the photodetector 95 (right direction in the figure). Part of the light incident on the beam splitter 86 is incident on a wavelength locker including the beam splitter 99, the etalon 93, the photodetector 92, and the photodetector 95. The wavelength locker monitors the wavelength shift and light output with respect to the wavelength grid.

  Next, the configuration of the wavelength tunable laser will be described. FIG. 8A is a top view of the wavelength tunable laser.

  The wavelength tunable laser has a laterally coupled co-directional optical coupler type wavelength filter (hereinafter referred to as “optical coupler type wavelength filter”) 43, a phase adjustment region 44, a gain region 45, and a DBR reflection type filter 46 in the emission direction. Are connected in this order. The element end on the side coupling type co-directional optical coupler type wavelength filter 43 side is coated with HR (high reflection) coating with a dielectric multilayer film. When the half-value width of the laterally-coupled co-directional optical coupler-type wavelength filter 43 is w1, and the half-value width w2 of the DBR-type reflection filter 46, w1> w2. That is, the transmission band of the lateral coupling type co-directional optical coupler type wavelength filter 43 is a coarse filter wider than the reflection band of the DBR reflection type filter 46, and the reflection band of the DBR reflection type filter 46 is a direction coupling type. The narrow filter is narrower than the transmission band of the directional optical coupler type wavelength filter 43.

  FIG. 8B is a sectional view of the wavelength tunable laser. On the n-type InP substrate, a waveguide layer 137 that generates a gain by current injection and a waveguide layer 136 whose refractive index changes by current injection are formed. The waveguide layer 137 becomes a core layer of the gain region 45, and the waveguide layer 136 becomes a core layer of the optical coupler type wavelength filter 43, the phase adjustment region 44, and the DBR reflecting mirror 46. A diffraction grating 138 is formed in the DBR reflective filter 46. The light resonates and oscillates in the waveguide 42 constituted by the waveguide 136 and the waveguide 137 serving as the core layers. The oscillated light is emitted from the end face of the optical coupler type wavelength filter 43 side.

  Next, the wiring connection and the input / output relationship of the power supply and signals will be described.

  An external controller 57 having a look-up table (LUT) is connected to and controls the laser current source 56, the temperature control circuit 64, and the light modulator driver 66. The LUT defines a drive temperature corresponding to an initial target wavelength or an externally designated target wavelength. Furthermore, the LUT is supplied with the adjustment signal 59 for the directional coupler filter, the adjustment signal 60 for the phase domain, the current signal 61 for the gain domain, and the adjustment signal 62 for the DBR reflector type filter according to the target wavelength. The current value to be specified is specified.

  The external controller 57 outputs, to the temperature control circuit 64, the initial value for the target wavelength or the drive current value of the Peltier element 97 for the initial value as the control signal 101. The drive control circuit 64 starts temperature control to be an initial value based on the control signal 101. Then, the temperature control signal 72 from the thermistor 94 is input, and the feedback control using the control signal 73 to the Peltier element 97 as an output is performed to perform the temperature control that satisfies the drive condition suitable for the target wavelength.

  Further, the external controller 57 inputs the oscillation wavelength signal 58 to the laser current source 56. The oscillation wavelength signal 58 is generated by the laser current source 56 with respect to the terminals of the four elements (the optical coupler type wavelength filter 43, the phase adjustment region 44, the gain region 45, and the DBR reflector 46) included in the wavelength tunable laser 83. It is a signal which shows the electric current value supplied. Here, each signal transmitted to the terminal of the optical coupler type wavelength filter 43, the terminal of the phase adjustment region 44, the terminal of the gain region, and the DBR reflector filter adjustment terminal 46, the optical coupler type wavelength filter adjustment signal 59, the phase These are referred to as an adjustment signal 60, a gain current signal 61, and a DBR reflection type filter adjustment signal 62.

  The oscillation wavelength signal 58 supplies a current value specified for the LUT, or a wavelength locker output constituted by the wavelength detection of the photodetector 92 (detection signal 69) and the intensity output of the photodetector 95 (detection signal 70). The current value obtained from is supplied. Specifically, feedback control is performed in which the output is confirmed and adjusted again with a control signal for the laser current source 56 while minutely changing the amount of current.

  The laser current source 56 supplies the current of the current value determined by the initial value of the LUT or the control signal received from the external controller 57 to each terminal of the wavelength tunable laser 83.

  The optical modulator driver 66 mounted on the interface board 82 is connected to the Mach-Zehnder modulator 88 and the external controller 57. The optical modulator driver 66 receives an external control signal 100 via the external controller 57, and supplies a drive current to the Mach-Zehnder modulator 88.

  A method for controlling the optical transmitter according to the first embodiment will be described with reference to the control flow of FIG.

  Step 0: The oscillation wavelength signal 58 is input to the laser current source 56 from the external controller 57 having the LUT so that the initial target wavelength by driving the optical transmitter when the power is turned on or the target wavelength instructed from outside is set.

  Step 1: Start the laser. Based on the oscillation wavelength signal 58, the laser current source 56 sends the optical coupler type wavelength filter adjustment signal 59 to the terminal terminal 43 of the optical coupler type wavelength filter 43, the phase adjustment signal 60 to the terminal of the phase adjustment region 44, and the gain region 45. The gain current 61 and the DBR reflection filter adjustment signal 62 are input to the terminals of the DBR reflection filter 46 and the DBR reflection filter 46, respectively.

  Step 2: Adjust the oscillation wavelength to the target wavelength. The wavelength is monitored by monitoring the signal of the photodetector 92, and the phase adjustment signal 60 is input to the terminal of the phase adjustment region 44 so that the oscillation wavelength matches, and the wavelength is adjusted.

  Step 3: Adjust the transmission wavelength of the optical coupler type wavelength filter 43 to the target wavelength. By monitoring the signal of the photodetector 95, the optical coupler type wavelength filter adjustment signal 59 is input to the terminal of the optical coupler type wavelength filter 43 so that the optical output is maximized. Here, if the transmission wavelength of the directional optical coupler filter is adjusted to the target wavelength, the oscillation wavelength will deviate from the target wavelength, so the wavelength is monitored by simultaneously monitoring the signal of the photodetector 92, and the oscillation wavelength is The phase adjustment signal 60 is input to the terminal of the phase adjustment region 44 so as to match, and the wavelength and the optical output are adjusted.

  Step 4: Match the DBR reflector wavelength to the target wavelength. By monitoring the signal of the photodetector 95, the DBR reflection type filter adjustment signal 62 is inputted to the terminal of the DBR reflection type filter 46 so that the light output becomes maximum. Here, if the reflection wavelength of the DBR reflective filter is adjusted to the target wavelength, the oscillation wavelength will deviate from the target wavelength, so the wavelength is monitored by simultaneously monitoring the signal of the photodetector 92 so that the oscillation wavelength matches. A phase adjustment signal 60 is input to the phase adjustment region 44 to adjust the wavelength.

  Step 5: Steps 3 and 4 are alternately repeated until the target wavelength is changed.

  The principle of operation is as described in FIG. 2, and this laser oscillated in a single mode in a wide wavelength range from 1.5 μm to 1.57 μm by adjusting the oscillation wavelength by passing a current through each region.

  This optical transmitter achieved stable oscillation with wavelength accuracy of ± 0.004 nm and SMSR> 35 dB by the control shown in FIG.

  In the above configuration, the wavelength is controlled by controlling in order of (gain current signal 61), phase adjustment signal 60, optical coupler type wavelength filter adjustment signal 59, DBR reflection type filter adjustment signal 62 at the time of laser activation or wavelength change. Adjustment time is short. This is due to the following reason.

  9A, 9B, and 9C show the oscillation wavelength, optical output, SMSR phase adjustment region refractive index change dependency, co-directional optical coupler filter center wavelength dependency, DBR wavelength change of the wavelength tunable laser of FIG. An example of dependency is shown. The range in which the wavelength can be continuously changed in the order of the phase adjustment region 44, the optical coupler type wavelength filter 43, and the DBR reflection type filter adjustment signal 46 becomes smaller. Considering the case where control is performed from the DBR reflective filter 46, if the deviation of the oscillation wavelength is small, adjustment may be possible in a very short time, but the oscillation wavelength exceeds the wavelength range that can be adjusted by the DBR reflective filter 46. In case of deviation, it is impossible to adjust to the target wavelength. In other words, since control without any policy is controlled by trial and error, a large amount of time may be consumed to reach the target wavelength. Therefore, the wavelength can be controlled with certainty by adjusting the range in which the wavelength can be continuously changed in the descending order, so that the wavelength can be reliably adjusted in a short time.

  Here, in the case where the laser light in FIG. 8 is output from the end face on the optical coupler-type wavelength filter 46 side, as shown in FIG. 9C, the light output becomes maximum under the condition that the SMSR is maximum. On the other hand, when the laser beam is output from the end surface of the laser shown in FIG. 8 on the DBR reflection filter 46 side, the light output is minimum under the condition that the SMSR is maximum. Therefore, if the light is output through the DBR reflective filter 46, the DBR reflection is applied to the terminal of the DBR reflective filter 46 so that the light output is minimized in Step 4 so that the light output is minimized. The mold filter adjustment signal 62 is input.

  Here, in step 3, while adjusting the optical coupler type wavelength filter adjustment signal 59, the phase adjustment signal 60 is instantaneously controlled every time the adjustment is made. At this time, it is easy to detect the maximum or minimum light output by superimposing a dither on the signal. Further, when the dither frequency of the optical coupler type wavelength filter adjustment signal 59 is f1 and the dither frequency of the phase adjustment signal 60 is f3, the optical coupler type wavelength filter adjustment signal is obtained by f1 <f3. While adjusting 59, the phase adjustment signal 60 can be instantaneously controlled each time it is adjusted.

  Here, in step 4, while adjusting the DBR reflection type filter adjustment signal 62, the phase adjustment signal 60 is instantaneously controlled every time the DBR reflection type filter adjustment signal 62 is adjusted. By superimposing a dither on the phase adjustment signal 60, it becomes easy to detect the maximum or minimum of the light output. Further, when the dither frequency of the DBR reflective filter adjustment signal 62 is f2 and the dither frequency of the phase adjustment signal 60 is f3, the DBR reflective filter adjustment signal 62 is adjusted by f2 <f3. However, the phase adjustment signal 60 can be instantaneously controlled every time adjustment is performed.

  In the above embodiment, the case of using the laterally coupled directional optical coupler type wavelength filter 46 is described. However, a laser using a vertical directional optical coupler filter may be used.

  In the first embodiment, the wavelength control is performed by the phase adjustment signal 60 in Step 2, and further, the signal of the photodetector 95 is monitored in Step 3, so that the light output is maximized so as to maximize the light output. Wavelength control and output control for inputting the coupler filter adjustment signal 59 are performed.

  However, the inventors of the present invention, through trial manufacture of the wavelength tunable laser 83 of Example 1, depending on the design conditions and the change over time, the optical output when the SMSR is the maximum in the wavelength change dependency of the DBR reflective filter. Has found that may not be the maximum. FIG. 10 shows the DBR wavelength change dependency of the wavelength, SMSR, and optical output of the laser shown in FIG.

  In such a case, the flow for feedback control of the current value to the phase adjustment signal 60 and the directional optical coupler filter adjustment signal 59 is changed, and the phase adjustment signal 60 and the directional optical coupler filter adjustment signal 59 are changed to the LUT. Only the feedback control by the DBR reflection type filter adjustment signal 62 is performed. This control can also achieve high wavelength accuracy and high SMSR at the same time.

  FIG. 6 shows a control flow.

  Specifically, when it is found in step 4 that no optical output peak is observed with respect to the DBR wavelength change, the control flow in FIG. 5 is changed, and new steps 5 and 6 are performed.

  In step 5, the DBR reflector adjustment signal 62 to the DBR reflector adjustment terminal 46 is controlled so as to match the target wavelength based on the signal of the wavelength locker comprising the photodetector 54 and the photodetector 55.

  In step 6, step 5 is repeated.

  The tunable laser thus produced oscillated in a single mode over a wide wavelength range from 1.5 μm to 1.57 μm.

  This optical transmitter achieved stable oscillation with wavelength accuracy of ± 0.004 nm and SMSR> 35 dB by the control shown in FIG.

43 ... Optical coupler type wavelength filter
44… Phase adjustment area
45… Gain area
46 ... DBR reflective filter
56 ... Laser current source
57… External controller
58 ... oscillation wavelength signal
59… Codirectional optical coupler filter adjustment signal
60 ... Phase adjustment signal
61 ... Gain current signal
62 ... DBR reflector type filter adjustment signal
64 ... Temperature control circuit
65: Optical waveguide
66 ... Optical modulator driver
67 ... Signal to optical modulator driver 66
69 ... Detection signal
70 ... Detection signal
81: Optical transmitter housing
82… Interface board
83 ... tunable laser
84… Submount
85 ... Lens
86… Beam splitter
87 ... Lens
88 ... Light modulator
89 ... Lens
91 ... Line for current injection
92 ... Photodetector
93 ... Etalon
95 ... Photodetector
94 ... Thermistor
97 ... Peltier element
99… Beam splitter
100 ... Control signal
101 ... Control signal
137 ... Waveguide layer that generates gain by current injection
136 ... Waveguide layer whose refractive index changes with current injection

Claims (9)

The gain region,
A first terminal provided in the gain region;
A first tunable filter with a half-value width w1,
A second terminal for supplying a current to the first tunable filter;
A second wavelength tunable filter with a half-value width w2,
A third terminal for supplying a current to the second tunable filter;
A phase adjustment region;
A fourth terminal for adjusting the phase of the phase adjustment region;
A tunable laser having:
It has a laser wavelength and a wavelength locker that detects optical output,
A wavelength tunable laser device that controls wavelengths in the order of the following steps 1 to 5.
Step 1. Individually input a predetermined current value to the first terminal, the second terminal, the third terminal, and the fourth terminal.
Step 2. Start control of the signal input to the fourth terminal based on the wavelength output of the wavelength locker.
Step 3. In parallel with the signal control to the fourth terminal started in Step 2, the signal input to the second terminal is controlled based on the optical output of the wavelength locker to determine the input current value. Then, the determined current value is input to the second terminal.
Step 4. Based on the light output of the wavelength locker in parallel with the signal control to the fourth terminal started in Step 2 and the signal input to the second terminal by the current value determined in Step 3 Control the signal input to the third terminal, determine the input current value, and input the determined current value to the second terminal.
Step 5. Repeat Step 3 and Step 4. In claim 1,
The determination of the current value based on the optical output signal of the wavelength locker used in the step 3 and the step 4 is to detect the peak of the optical output and to set the current value to maintain the peak of the optical output. Tunable laser device. In claim 1,
The wavelength tunable laser device, wherein the half width w1 and the half width w2 satisfy a relationship of w1> w2. In claim 1,
The wavelength tunable laser device, wherein an input signal to the first terminal, the second terminal, the third terminal, and the fourth terminal is a current value. In claim 1,
The wavelength locker includes an etalon, a first photodetector, and a second photodetector,
The first photodetector and the second photodetector are arranged so that a part of the laser output light is incident thereon,
A wavelength tunable laser device that monitors and outputs the maximum or minimum light output to the second photodetector. In claim 1,
In step 3 above,
A dither is superimposed on the input signal to the first terminal, and its frequency is f1,
When dither is superimposed on the input signal to the third terminal and its frequency is f3,
A wavelength tunable laser device satisfying f1 <f3. In claim 1,
In step 4 above,
A dither is superimposed on the input signal to the second terminal and its frequency is f2,
When dither is superimposed on the input signal to the third terminal and its frequency is f3,
A wavelength tunable laser device satisfying f1 <f3. In claim 2,
The wavelength tunable laser device, wherein the first wavelength tunable filter is an LGLC filter or a vertical co-directional coupler. In claim 2,
The wavelength tunable laser apparatus according to claim 4, wherein, in the step 4, when the peak cannot be detected by the light output from the wavelength locker, the steps 6 and 7 are performed instead of the steps 4 and 5.
Step 6. Based on the wavelength output by the wavelength locker in parallel with the signal control to the fourth terminal started in Step 2 and the signal input to the second terminal by the current value determined in Step 3 Control the signal input to the third terminal, determine the input current value, and input the determined current value to the second terminal.
Step 7. Repeat step 6 above.

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