JP2017005034A - Wavelength variable laser array and wavelength control method for wavelength variable laser array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce fluctuation in oscillation wavelength of a TDA-DFB laser and to reduce difference of the oscillation wavelength from a target oscillation wavelength even when thermal compensation of the TDA-DFB laser is performed.SOLUTION: A wavelength variable laser array which changes output wavelengths of a plurality of wavelength-variable lasers and performs variable control includes: a plurality of wavelength-variable lasers which have active layers and control layers that are formed on a board and can independently apply current, perform thermal compensation of the wavelength-variable lasers for the control layers of all wavelength-variable lasers other than a first wavelength-variable laser while the first wavelength-variable laser of the plurality of wavelength-variable lasers is in operation; a Peltier element formed on the board; a control unit which is connected to the Peltier element, obtains difference from the wavelength-variable laser between a real oscillation wavelength and a target oscillation wavelength, calculates a calibration value of chip temperature so as to lower the chip temperature of a wavelength variable laser array from the difference so that the real oscillation wavelength becomes the target oscillation wavelength, and applies current to the Peltier element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wavelength tunable laser array and a wavelength control method for the wavelength tunable laser array, and more specifically, calibrates a deviation between an actual oscillation wavelength and a target oscillation wavelength when the wavelength is changed in the wavelength tunable semiconductor laser. The present invention relates to a wavelength tunable laser array and a wavelength control method for the wavelength tunable laser array.

  The wavelength tunable laser is a useful light source used in a wide range of fields such as wavelength division multiplexing, optical measurement, optical frequency sweep type OCT, laser light spectroscopy, and photosensitivity measurement. Until now, various tunable lasers have been developed according to the required oscillation wavelength region, output intensity, wavelength stability, spectral line width, and the like. The wavelength tunable laser is classified into, for example, a gas laser, a liquid (pigment) laser, a solid-state laser, and a semiconductor laser when classified according to the type of laser oscillation medium.

  All types of tunable lasers are composed of a pump energy supply source (light, electricity, etc.), a gain (oscillation) medium, and a resonator. Among them, a wavelength tunable laser using a semiconductor as a gain medium is widely used in various fields because of low power consumption, small size, and easy handling. Therefore, many types of wavelength tunable semiconductor lasers have been developed so far. The figure of merit that determines the characteristics of a wavelength tunable semiconductor laser includes output, wavelength tunable width, mode stability, adjacent mode suppression ratio (SMSR), lifetime, and oscillation line width. Lasers with excellent characteristics in all performances are desirable, but usually it is difficult to satisfy all of them at the same time, so laser tuning is performed to improve performance according to usage. For example, a wavelength tunable semiconductor laser used in a wavelength selective switch is required to have a wide wavelength tunable width and capable of switching wavelengths at high speed.

  When a tunable semiconductor laser is used in high-density wavelength division multiplexing (DWDM), a necessary wavelength region cannot be usually covered only by a laser element of a single tunable semiconductor laser. Therefore, as a method for covering the necessary wavelength range, an attempt is made to provide two or more resonators having different free spectral ranges (FSRs) of the laser and widen the oscillation wavelength range using the vernier effect. Has been done. A typical example is an SSG-DBR (SuperStructure Grafted Distributed Bragg Reflector) laser. In this laser, two types of diffraction gratings having different FSRs are arranged before and after the gain medium, and a wide band is secured by changing the refractive index and changing the FSR value by applying a current thereto. Lasers using the vernier effect are characterized by being able to be controlled with a relatively small drive current. However, in principle, mode skipping occurs, and two diffraction gratings with different FSRs must be controlled simultaneously. There are two disadvantages that control is complicated because it must be done.

  As another attempt to cover the necessary wavelength range, there is a laser that expands the oscillation wavelength range by arranging lasers having different oscillation wavelength ranges in an array. One of them is a DFB laser array. A feature of the DFB laser array is that it oscillates in a wide wavelength range by arranging DFB lasers having different oscillation wavelength ranges in an array.

  A DFB laser array is an improved TFB (Tunable Distribution Amplification) DFB laser array. A feature of the TDA-DFB laser array is that it oscillates in a wide wavelength region of 40 nm or more without mode skipping. In the structure of the TDA-DFB laser array, active layers for obtaining gain and control layers for performing wavelength control are alternately arranged on both sides of the λ / 4 phase shifter. In order to avoid mode skipping, the unit length on both sides of the λ / 4 phase shifter is changed (see Non-Patent Document 1).

  Each LD of the TDA-DFB laser array has a wavelength variable range of about 7 to 8 nm, and the wavelength region is shifted by about 7 to 8 nm for each LD. As a result, a wavelength variable region of 40 nm or more can be obtained. Therefore, if it is used in the range of the wavelength variable region of about 7 to 8 nm, it is possible to realize the wavelength variable operation using a single LD in the LD array, and when using in a wider wavelength variable range. The wavelength tunable range can be expanded by using a plurality of LDs in the LD array.

  In order to realize wavelength tunability using a TDA-DFB laser array as a wavelength selective switch, the current injected into the control layer of the TDA-DFB laser array is changed. When the control current requires a relatively large current of about several tens of mA, the wavelength change itself at the time of switching the wavelength selective switch occurs due to the carrier-plasma effect, so the wavelength changes in several ns from the time of switching the switch. However, when the current applied to the control layer of the TDA-DFB laser array changes, a local temperature change occurs. Due to wavelength fluctuations due to temperature changes, it takes about several ms from the time of switching until the wavelength stabilizes, causing a problem in high-speed response. In order to suppress such wavelength fluctuation due to heat, an electrode for heat compensation is introduced adjacent to the laser array, and a current complementary to the wavelength control current is applied to the electrode for heat compensation. The temperature change of the whole chip is suppressed, and as a result, the wavelength fluctuation has been suppressed (Patent Document 1).

  As another method for suppressing wavelength fluctuation, when switching laser light from one laser in the TDA-DFB laser array to another laser in the TDA-DFB laser array, that is, switching the gain current. The TDA-DFB laser array when the oscillating TDA-DFB laser is switched by applying a current in advance to the control electrode of the TDA-DFB laser other than the TDA-DFB laser that is oscillating. The variation of the chip temperature is suppressed, and the oscillation wavelength variation at the time of laser switching is suppressed (see Non-Patent Document 2).

Japanese Patent No. 4850757

Nobuhiro Nutani, Hiroyuki Ishii, Ryuzo Iga NTT Technology Journal Development of high-speed tunable distributed active DFB laser (2012 Vol.24 No.10 pp.48-52) Makoto Shimozono, Takuya Kanai, Hiroyuki Ishii Preliminary study of multi-channel switching using TDA-DFB laser array (2015 IEICE General Conference C-4-21)

  However, if a current is additionally applied to the control layer of a TDA-DFB laser other than the TDA-DFB laser that is responsible for oscillation, the chip temperature of the entire TDA-DFB laser array is increased as a result. Here, if the chip temperature of the entire TDA-DFB laser array is changed, the oscillation wavelength after convergence of the TDA-DFB laser array is shifted. Therefore, it is not possible to obtain an oscillation wavelength having the same value as the oscillation wavelength output when laser oscillation is performed without performing thermal compensation. That is, if the oscillation wavelength when laser oscillation is performed without performing thermal compensation is set as the target oscillation wavelength, a deviation occurs between the actual oscillation wavelength and the target oscillation wavelength. Then, in the wavelength selective switch, there arises a problem that the oscillation wavelength after the change is deviated from the center wavelength of the bandpass filter constituting the switch.

  The present invention has been made in view of such problems. The object of the present invention is to reduce fluctuations in the oscillation wavelength of the TDA-DFB laser and to perform thermal compensation of the TDA-DFB laser. These are a wavelength tunable laser array and a wavelength control method for the wavelength tunable laser array that can reduce the deviation of the oscillation wavelength from the target oscillation wavelength.

  In order to achieve such an object, a first aspect of the present invention is a wavelength tunable laser array that variably controls an output wavelength of a plurality of wavelength tunable lasers, and is formed on a substrate and independently. A plurality of current control type wavelength tunable lasers having an active layer and a control layer to which a current can be applied, wherein the first wavelength tunable laser is operated during the operation of the first wavelength tunable laser of the plurality of wavelength tunable lasers. The wavelength tunable laser is thermally compensated for the control layers of all the tunable lasers other than the tunable laser and a Peltier element provided on the substrate, and the actual wavelength from the tunable laser A current corresponding to a temperature calibration value for adjusting the temperature of the substrate, obtained from the difference between the actual oscillation wavelength and the target oscillation wavelength, is applied so that the oscillation wavelength becomes the target oscillation wavelength. Been That, characterized in that it comprises a Peltier device.

  Further, a second aspect of the present invention is the wavelength tunable laser array according to the first aspect, wherein the target oscillation wavelength is during operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers. It is an actual oscillation wavelength from the tunable laser when no current is applied to the control layers of all the tunable lasers other than the first tunable laser.

A third aspect of the present invention is the wavelength tunable laser array according to the first or second aspect,
The thermal compensation is performed when the wavelength is changed within the variable wavelength range of the first wavelength tunable laser to the control layer of the second wavelength tunable laser adjacent to the control layer of the first wavelength tunable laser. A current having a value for performing the above is applied, and an equal current is applied to each of the control layers of the wavelength tunable lasers other than the first and second wavelength tunable lasers.

  According to a fourth aspect of the present invention, there is provided a plurality of current control type wavelength tunable lasers having an active layer and a control layer to which a current can be independently applied, and a Peltier element, and output wavelengths of the plurality of wavelength tunable lasers. Is a method of controlling the wavelength of the wavelength tunable laser array by changing the wavelength of the plurality of wavelength tunable lasers other than the first wavelength tunable laser during the operation of the first wavelength tunable laser. Performing the thermal compensation of the wavelength tunable laser for all control layers of the wavelength tunable laser, obtaining a difference between the actual oscillation wavelength from the wavelength tunable laser and the target oscillation wavelength, and calculating the actual oscillation wavelength. Calculating a chip temperature calibration value for adjusting the chip temperature of the wavelength tunable laser array from the difference so that the target oscillation wavelength becomes the target oscillation wavelength; The value of the current applied was characterized by and adjusting the die temperature of an amount corresponding the wavelength tunable laser array of the calibration value.

  Further, a fifth aspect of the present invention is the method according to the fourth aspect, wherein the target oscillation wavelength is the first wavelength during the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers. It is an actual oscillation wavelength from the wavelength tunable laser when no current is applied to the control layers of all the wavelength tunable lasers other than the wavelength tunable laser.

  According to a sixth aspect of the present invention, there is provided the method according to the fourth or fifth aspect, wherein the thermal compensation is performed by controlling a second wavelength tunable laser adjacent to the control layer of the first wavelength tunable laser. A current having a value for performing thermal compensation when changing the wavelength within the variable wavelength range of the first wavelength tunable laser is applied to the layer, and the wavelength tunable laser other than the first and second wavelength tunable lasers Each of the control layers is performed by applying an equal current to each control layer.

  The present invention corrects the wavelength shift (lengthening) caused by the temperature rise of the chip caused by the additional control current applied to shorten the switching time for the wavelength tunable laser constituting the wavelength tunable laser array. The laser can be operated at the correct wavelength. In addition, since the shift from the center wavelength can be reduced in high-speed switching applications such as a wavelength selective optical packet switch and an optical burst switch, it can be applied as an effective variable wavelength light source.

It is a top view showing a laser array concerning one embodiment of the present invention. It is a figure which shows the time change of an oscillation frequency when changing the value of the electric current applied to a control layer in order to change a wavelength. It is a figure which shows the relationship between the chip | tip temperature of a laser array of FIG. 1, and an oscillation wavelength. FIG. 3 shows the set currents of the laser active layer and the laser control layer when thermal compensation is performed by the method described in Non-Patent Document 2 in the laser array of FIG. It is a figure which shows the relationship between the control current at the time of changing a wavelength, and the oscillation wavelength after stabilization in arbitrary one TDA-DFB laser in the laser array of FIG.

[Laser array configuration]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a top view showing a laser array 100 of wavelength selective switches according to an embodiment of the present invention. The laser array 100 is a TDA-DFB laser array that is a current-controlled tunable laser, and includes a semiconductor substrate 110 and laser active layers 111a to 416a, 111b to 116b, and 111c to 116c provided on the semiconductor substrate 110. And laser control layers 121a to 126a, 121b to 126b, and 121c to 126c provided on the semiconductor substrate 110. The laser active layers 111 a to 111 c and the laser control layers 121 a to 121 c are provided on the substrate, and are alternately arranged on the semiconductor substrate 110 to form the TDA-DFB laser 101. The laser active layers 112a to 116a, 112b to 116b, 112c to 116c and the laser control layers 122a to 126a, 122b to 126b, 122c to 126c are also alternately arranged on the semiconductor substrate 110, and the TDA-DFB lasers 102 to 106 are used. Form. The TDA-DFB lasers 101 to 106 are arranged in parallel.

  The laser array 100 includes electrodes 131 to 136 connected to the laser active layers 111a to 116a, 111b to 116b, and 111c to 116c, amplifiers 181 to 186 connected to the electrodes 131 to 136, and amplifiers 181 to 181, respectively. DA converters 171 to 176 connected to 186, respectively. The laser array 100 includes electrodes 141 to 146 connected to the laser control layers 121a to 126a, 121b to 126b, and 121c to 126c, amplifiers 191 to 196 connected to the electrodes 141 to 146, and amplifiers 191 to 191, respectively. DA converters 151 to 156 connected to 196, respectively, and a control device 170 connected to the DA converters 171 to 176 and the DA converters 151 to 156. The laser active layers 111 a to 111 c oscillate laser light when a current converted from a signal from the control device 170 is applied from the DA converter 171 through the amplifier 181 and the electrode 131. The laser active layers 112a to 116c also oscillate laser light when the DA converters 172 to 176 are applied with currents obtained by converting signals from the control device 170 via the amplifiers 182 to 186 and the electrodes 132 to 136, respectively.

  The laser control layers 121a to 121c are supplied with a current converted from the signal from the control device 170 from the DA converter 151 via the amplifier 191 and the electrode 141, and the wavelength of the output light is controlled by changing the refractive index. . The laser control layers 122a to 126c are also output from the DA converters 152 to 156 through the amplifiers 192 to 196 and the electrodes 142 to 146, respectively. The wavelength of light is controlled.

  The laser array 100 includes waveguides 161 to 166 that guide the output light from each TDA-DFB laser, and an optical coupler that combines the output lights that are guided through the waveguides 161 to 166. Mode interference) coupler 167, SOA (semiconductor amplifier) 168 that adjusts the intensity of output light at the final stage, waveguide 169 that guides and outputs the output light from SOA 168, and electrode 137 connected to SOA 168 Is provided. The oscillation light of each TDA-DFB laser is combined into one by the MMI coupler 167 via the waveguides 161 to 166 disposed in the subsequent stage, and after passing through the SOA 168, is output from the waveguide 169 as output light. The SOA 168 is supplied with current from the outside via the electrode 137.

  The laser array 100 includes a temperature detection device 157 and a Peltier element 158 provided on the semiconductor substrate 110, an electrode 147 connected to the temperature detection device 157, an electrode 148 connected to the Peltier element 158, an electrode 147, and And a control device 159 connected to 148.

[Thermal compensation of laser array]
Next, a method for controlling the wavelength of the oscillation light of the laser array of the wavelength selective switch in this embodiment will be described. When changing the wavelength in the TDA-DFB laser array of the wavelength selective switch, there are two types of methods depending on the wavelength range. The first method is a case where the wavelength is changed within the variable wavelength range of the first TDA-DFB laser that is performing oscillation. In this case, only the current applied to the control layer of the first TDA-DFB laser is changed. In this method, frequency fluctuations having a positive correlation with the amount of change in current applied to the control layer are observed. Therefore, when the amount of change in the control current is large, that is, when the wavelength is greatly changed, the time from the change of the wavelength to the stabilization of the wavelength is delayed, but this is the first TDA-DFB that oscillates. If thermal compensation is used by applying a current to the control layer of the second TDA-DFB laser adjacent to the laser, the wavelength drift can be reduced, resulting in a shorter time from changing the wavelength until the wavelength stabilizes. I can do it.

  The second method is a case where the amount of change in wavelength is relatively large, that is, a case where the wavelength is changed beyond the variable wavelength range of the first TDA-DFB laser that is oscillating. Switches the wavelength of the oscillation light by switching the oscillation from the first TDA-DFB laser to another third TDA-DFB laser. When the oscillation is switched from the first TDA-DFB laser to the third TDA-DFB laser, not only the current applied to the control layer of the TDA-DFB laser but also the change of the current applied to the active layer is accompanied. Compared with this method, the current change amount of each TDA-DFB laser is large, that is, the wavelength drift is also large. Therefore, as a result, the time from changing the wavelength to stabilizing the wavelength also increases. In this case, in Non-Patent Document 2, a current is applied in advance to the control layers of all TDA-DFB lasers in the TDA-DFB laser array so that the amount of heat generated in the TDA-DFB laser is constant before and after the wavelength change. Thus, the temperature change in the semiconductor substrate is suppressed, and the refractive index change due to the temperature change is suppressed.

  In Non-Patent Document 2, when changing the wavelength in the TDA-DFB laser array of the wavelength selective switch, if the wavelength value to be changed is not determined, the wavelength is changed by the first method, and In order to cope with the refractive index change due to temperature change in both cases when changing the wavelength by the second method, thermal compensation of the TDA-DFB laser array is performed, the wavelength drift is reduced, and the wavelength is stabilized. To shorten the time.

  Specifically, in order to perform thermal compensation by changing the wavelength, a current is additionally applied in advance to all control layers of the TDA-DFB laser other than the first TDA-DFB laser that oscillates. The heat distribution in the substrate (chip) is relaxed.

  First, in order to output the first wavelength in the TDA-DFB laser array of the wavelength selective switch, desired values are applied to the active layer and the control layer of the first TDA-DFB laser that is the TDA-DFB laser that performs oscillation. Apply a current of. Next, in order to cope with the case where the wavelength change is performed by the first method in the wavelength change in the subsequent TDA-DFB laser array, the second TDA-DFB laser adjacent to the first TDA-DFB laser is changed. A desired current is applied to the control layer. When the wavelength is changed within the variable wavelength range of the first TDA-DFB laser by applying a current to the control layer of the second TDA-DFB laser (the wavelength change by the first method), the first Therefore, it is possible to reduce the time until the wavelength is stabilized after the wavelength is changed.

  Furthermore, a current is also applied to a control layer of a TDA-DFB laser other than the first TDA-DFB laser and the second TDA-DFB laser. This is to cope with the case where the wavelength is changed by the second method in the subsequent wavelength change in the TDA-DFB laser array. Here, the same current value is set in all the control layers of the TDA-DFB lasers other than the first and second TDA-DFB lasers. By setting the same current value for each laser, the heat in the chip that is biased only in the vicinity of the laser that oscillates can be distributed over a wide range, and the heat compensation for the wavelength change can be performed. When changing the wavelength by switching the oscillation to any other TDA-DFB laser other than the DFB laser (referred to as the third TDA-DFB laser) (changing the wavelength by the second method), the wavelength is also changed. It is possible to shorten the time until the wavelength stabilizes after the first time.

  Next, the wavelength is changed in the TDA-DFB laser array of the wavelength selective switch to output the second value of the wavelength. At this time, when the wavelength is changed by the first method, oscillation is performed. The wavelength is changed by changing the current value applied to the control layer of one TDA-DFB laser. At this time, the current applied to the second TDA-DFB laser adjacent to the first TDA-DFB laser is also changed, and the current value applied to the control layer of the first TDA-DFB laser before the wavelength change. And the current value applied to the control layer of the second TDA-DFB laser is the sum of the current value applied to the control layer of the first TDA-DFB laser after the wavelength change and the control of the second TDA-DFB laser. The sum of the current values applied to the layers is the same. This is because a current is applied to the second TDA-DFB laser adjacent to the first TDA-DFB laser to perform thermal compensation for the wavelength change by the first method. Note that the current value applied to the control layer of the TDA-DFB laser other than the first and second TDA-DFB lasers is the same as before the wavelength change. This is to perform thermal compensation for wavelength change by the second method.

  On the other hand, when the wavelength is changed by the second method, the active layer and the control of the third TDA-DFB laser are used to oscillate by switching from the first TDA-DFB laser to the third TDA-DFB laser. Apply current to the layer. In addition, a current is also applied to a control layer of a TDA-DFB laser (referred to as a fourth TDA-DFB laser) adjacent to the third TDA-DFB laser for performing thermal compensation.

  Here, a current having the same value as the current applied to the first TDA-DFB laser is applied to the active layer of the third TDA-DFB laser to be switched. The current value applied to the control layer of the fourth TDA-DFB laser is set to a value complementary to the current value of the control layer of the third TDA-DFB laser that oscillates, A TDA-DFB laser is used for thermal compensation. Specifically, the sum of the current value applied to the control layer of the third TDA-DFB laser and the current value applied to the control layer of the fourth TDA-DFB laser is the first TDA-DFB laser in the channel 1. The current value applied to the control layer and the current value applied to the control layer of the second TDA-DFB laser are set to be the total value. This is to perform thermal compensation for wavelength change by the further first method. In addition, a current is also applied to a control layer of a TDA-DFB laser other than the third TDA-DFB laser and the fourth TDA-DFB laser. This is to perform thermal compensation for wavelength change by the second method. The applied current value is the same as the current value applied to the control layer of the TDA-DFB laser other than the first TDA-DFB laser and the second TDA-DFB laser in the channel 1.

  In Non-Patent Document 2, channel 1 and channel 2 are set so that the sum of all active layer currents and control current is constant. This is because if the total value of the total current of the channel 1 and the channel 2 changes, the chip temperature does not stabilize and the oscillation oscillates, so that the oscillation wavelength is not stable. Moreover, although the applied current is constant, the applied power may be constant.

  It should be noted that a current that is additionally applied to the control layer of the TDA-DFB laser other than the first and second (or third and fourth) TDA-DFB lasers does not have the same current value but oscillates. It suffices if the heat within the chip that is biased only in the vicinity can be set to be distributed over a wide range. For example, the value of the current applied to the control layer may be increased as the distance from the oscillating laser increases.

[Laser array temperature calibration]
In Non-Patent Document 2, by setting the current value applied to the control layer of each TDA-DFB laser in this way, heat can be applied not only to the vicinity of the laser that oscillates but also to the entire chip (semiconductor substrate). In addition, even when the oscillation is switched to an arbitrary TDA-DFB laser and the wavelength is changed, it is possible to shorten the time from the change of the wavelength to the stabilization of the wavelength.

  However, the oscillation wavelength when heat compensation is performed by increasing the overall chip temperature of the laser array 100 in order to shorten the time from when the wavelength is changed to when the wavelength is stabilized is the same as when oscillation compensation is not performed. May differ from oscillation wavelength. Assuming that the oscillation wavelength when the current is applied to the control layer of the TDA-DFB laser without performing thermal compensation is the target oscillation wavelength, the actual oscillation wavelength when performing thermal compensation, the target oscillation wavelength, Deviation occurs between the two. The deviation of the oscillation wavelength (oscillation frequency) will be described.

  First, the actual frequency variation of an arbitrary TDA-DFB laser when the wavelength (frequency) is changed by current injection will be described. FIG. 2 is a diagram showing temporal changes in the oscillation frequency when the value of the current applied to the control layer is changed in order to change the wavelength by the first method or the second method. In FIG. 2, the temporal change in the oscillation frequency is represented by a solid line 201, and the temporal change in the control current is represented by a one-dot chain line 202. The control current value before switching is indicated by A1, and the control current value after switching is indicated by A2. On the other hand, the oscillation frequency H1 before switching is changed as shown in FIG. 2 when the control current is switched from A1 to A2 (switching 211). At this time, first, it largely fluctuates to the high frequency side due to the carrier effect, exceeds the target oscillation frequency (oscillation frequency when heat compensation is not performed) H2, and becomes H3. At this time, a value ΔHmax corresponding to a difference (H3−H2) between the maximum frequency value and the target frequency value is referred to as a maximum frequency deviation. Thereafter, with the generation of heat, the frequency fluctuation gradually occurs on the low frequency side, and becomes stable at a constant oscillation frequency value H4. Here, finally, H4 may be lower than the target oscillation frequency value H2 after switching, and a value ΔHcon corresponding to the difference (H2−H4) between the target frequency after switching and the convergence frequency value is set to a convergence frequency shift. It is called.

  In the present invention, in order to reduce this convergence frequency shift, a Peltier element 158 is arranged on the chip of the laser array 100, the chip temperature is calibrated using the Peltier element 158, and a target oscillation frequency (wavelength) is obtained. Get. FIG. 3 is a diagram showing the relationship between the chip temperature of the laser array 100 and the oscillation wavelength. The oscillation wavelength of the laser array 100 changes to the longer wavelength side as the chip temperature rises. By applying a control current to all TDA-DFB lasers, the chip temperature is B1 in FIG. At this time, the value of the oscillation wavelength of the laser array 100 is I1. Here, in order to return the value of the oscillation wavelength of the laser array 100 to the target oscillation wavelength I2, the chip temperature of the laser array 100 must be lowered to B2. In order to lower the chip temperature of the laser array 100, the chip of the laser array 100 can be cooled by applying a voltage to the Peltier element 158 provided on the chip of the laser array 100. Therefore, by applying a voltage to the Peltier element 158 provided on the chip of the laser array 100, the chip temperature of the laser array 100 can be calibrated to B2 and controlled to oscillate a desired oscillation wavelength I2. . In this case, the control device 159 calculates the convergence frequency deviation ΔHcon. On the other hand, the chip temperature of the laser array 100 is detected by the temperature detection device 157 and transmitted to the control device 159. The control device 159 calculates a calibration value for the temperature at which the chip of the laser array 100 is adjusted (cooled) from the convergence frequency deviation ΔHcon and the chip temperature of the laser array 100. Next, in order for the Peltier element 158 to adjust (cool) the chip by the calculated adjustment (cooling) temperature, a current value to be applied to the Peltier element 158 corresponding to the adjustment (cooling) temperature was calculated and set. Above, the current set in the Peltier element 158 is applied to adjust (cool) the chip temperature.

  By calibrating the chip temperature and changing the wavelength by the first method and the second method as described above, it is possible to reduce the convergence frequency shift of the laser array 100.

  When the convergence value of the oscillation wavelength output from the laser array 100 is less than the target oscillation wavelength (when the oscillation frequency is higher than the target frequency), a current is applied to the Peltier element 158, and the chip The target oscillation wavelength can be obtained by increasing the temperature.

[Example]
Here, a specific example (example) of wavelength control of the oscillation light of the laser array of the present invention will be described. First, a setting current in the case where thermal compensation of a TDA-DFB laser is performed by additionally applying a current to the laser control layer by the method described in Non-Patent Document 2 will be described.

  FIG. 4 shows set currents of the laser active layer and the laser control layer when the thermal compensation is performed by the method described in Non-Patent Document 2 in the laser array 100 of FIG.

  First, an 80 mA current is applied to the laser active layer 113 of the TDA-DFB laser 103, and a 10 mA current is applied to the laser control layer 123 of the TDA-DFB laser 103. At this time, in order to perform thermal compensation of each TDA-DFB laser, first, a current of 35 mA is applied to the laser control layer 124 of the adjacent TDA-DFB laser 104. This is a current necessary for performing thermal compensation when the wavelength is changed by the first method in the subsequent wavelength change in the TDA-DFB laser array. The oscillation frequency of the TDA-DFB laser 104 at this time was 192.0 THz (channel 1).

  Further, a current of 10 mA is applied in advance to the laser control layers 121 to 122 and 125 to 126 of the TDA-DFB lasers 101 to 102 and 105 to 106 other than the TDA-DFB lasers 103 and 104. This is to cope with the case where the wavelength is changed by the second method in the subsequent wavelength change in the TDA-DFB laser array. By setting the same current value in advance in the laser control layers 121 to 122 and 125 to 126, the heat in the chip that is biased only near the laser that oscillates is distributed over a wide range, and the heat distribution in the chip is relaxed in advance. Therefore, it is possible to perform thermal compensation for wavelength change by the second method.

  Next, although the wavelength is changed in the TDA-DFB laser array 100 of the wavelength selective switch, the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 105. First, a current of 80 mA is applied to the laser active layer 115 of the TDA-DFB laser 105, and a current of 15 mA is applied to the laser control layer 125 of the TDA-DFB laser 105. The oscillation frequency of the TDA-DFB laser 105 at this time was 193.3 THz (channel 2). Further, thermal compensation of the TDA-DFB laser 105 is performed to cope with the case where the wavelength is changed by the first method in the wavelength change in the further TDA-DFB laser array. In the thermal compensation, a current of 30 mA is applied to the control layer 124 of the adjacent TDA-DFB laser 104, and this current value is a set value of the current applied to the control layer of the TDA-DFB laser 105 that oscillates. On the other hand, it is necessary to set a complementary value. Specifically, the total value of the current value applied to the control layer 125 of the TDA-DFB laser 105 and the current value applied to the control layer 124 of the TDA-DFB laser 104 is the control of the TDA-DFB laser 103 in the channel 1. The total value of the current value applied to the layer 123 and the current value applied to the control layer 124 of the TDA-DFB laser 104 is set to be the same.

  Next, a current of 10 mA is applied in advance to the laser control layers 121 to 123 and 126 of the TDA-DFB lasers 101 to 103 and 106 other than the TDA-DFB lasers 105 and 104. This is to cope with the case where the wavelength is changed by the second method in the wavelength change in the further TDA-DFB laser array.

  Next, the chip temperature of the laser array 100 is calibrated. FIG. 5 is a diagram showing the relationship between the control current when changing the wavelength and the oscillation wavelength after stabilization in any one TDA-DFB laser in the laser array 100. Here, a solid line 501 indicates a case where a current is additionally applied to the control layer of each TDA-DFB laser in order to perform thermal compensation, and a broken line 502 indicates a case where thermal compensation is not performed.

  In this embodiment, when a certain current value C1 is applied to the control layer of an arbitrary DFB laser, if the thermal compensation is performed by the method described in Non-Patent Document 2, the oscillation frequency is set to B1 after a certain time has elapsed. Stable. On the other hand, when a certain current value C1 was applied to the control layer of an arbitrary DFB laser without performing thermal compensation, the oscillation frequency was stabilized at B2 after a predetermined time. The difference in the numerical values of the oscillation frequencies (frequency deviation: J1-J2) at this time was 2 GHz. At this time, a current is applied to the Peltier element to calculate a temperature for lowering the chip temperature of the laser array 100. Here, the frequency difference of 2 GHz corresponds to 0.16 nm in terms of a wavelength difference. Since the oscillation wavelength of the semiconductor laser shifts to a long wavelength (low frequency) of 0.1 nm when it rises by 1 ° C., a wavelength shift of 0.16 nm corresponds to an increase in temperature of 1.6 ° C. Therefore, a current is applied to the Peltier element so as to lower the set value of the Peltier element by 1.6 ° C. As a result, the oscillation frequency was B2. Therefore, in this example, the calibration temperature was 1.6 ° C.

  The calibration value of the chip temperature of the laser array 100 is set to 1.6 ° C., and a current is applied so as to lower the set value of the Peltier element by 1.6 ° C. Current application and current application to the TDA-DFB laser 105 are switched every 1 ms, and an oscillation frequency of 192.0 THz (channel 1) and an oscillation frequency of 193.3 THz (channel 2) are alternately obtained. When the time within 10 GHz of the target frequency from the time of switching is defined as the switching time, in this control method, the switching time is 38 μs, and the convergence frequency shift with respect to the target frequency in 1 ms after switching is 20 MHz, which is significant. We were able to reduce it.

  Because the oscillation wavelength of a wavelength tunable laser (TDA-DFB laser) can be changed quickly and accurately, the wavelength tunable applicable to applications that require high-speed wavelength switching, such as optical packet switches and optical burst switches. A laser can be realized.

DESCRIPTION OF SYMBOLS 100 Laser array 101-106 TDA-DFB laser 110 Semiconductor substrate 111a-116c Laser active layer 121a-126c Laser control layer 131-137, 141-148 Electrode 141-146, 181-186 Amplifier 151-156, 171-176 DA converter 157 Temperature detector 158 Peltier elements 161-166, 169 Waveguide 167 MMI coupler 168 SOA
159, 170 Controller

Claims (6)

A tunable laser array that variably controls the output wavelength of a plurality of tunable lasers,
A plurality of current control type tunable lasers formed on a substrate and having an active layer and a control layer to which current can be independently applied, during operation of the first tunable laser of the plurality of tunable lasers A wavelength tunable laser in which thermal compensation of the wavelength tunable laser is performed on the control layers of all the wavelength tunable lasers other than the first wavelength tunable laser;
A Peltier device provided on the substrate, which is obtained from a difference between the actual oscillation wavelength and the target oscillation wavelength so that an actual oscillation wavelength from the wavelength tunable laser becomes a target oscillation wavelength. And a Peltier element to which a current corresponding to a temperature calibration value for adjusting the temperature of the substrate is applied.   The target oscillation wavelength is such that no current is applied to the control layers of all the wavelength tunable lasers other than the first wavelength tunable laser during the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers. The tunable laser array according to claim 1, wherein the oscillating wavelength is an actual oscillation wavelength from the tunable laser.   The thermal compensation is performed when the wavelength is changed within the variable wavelength range of the first wavelength tunable laser to the control layer of the second wavelength tunable laser adjacent to the control layer of the first wavelength tunable laser. A current having a value for performing the above is applied, and a uniform current is applied to each of the control layers of the wavelength tunable lasers other than the first and second wavelength tunable lasers. Item 3. The wavelength tunable laser array according to Item 1 or 2. A wavelength tunable laser, comprising: a plurality of current control type wavelength tunable lasers having an active layer and a control layer to which current can be applied independently; and a Peltier element, and variably controlling the output wavelengths of the plurality of wavelength tunable lasers A method for controlling the wavelength of an array comprising:
Performing thermal compensation of the wavelength tunable laser to the control layers of all the wavelength tunable lasers other than the first wavelength tunable laser during the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers; ,
The difference between the actual oscillation wavelength from the wavelength tunable laser and the target oscillation wavelength is obtained, and the chip temperature of the wavelength tunable laser array is determined from the difference so that the actual oscillation wavelength becomes the target oscillation wavelength. Calculating a calibration value of the chip temperature for adjustment;
Applying a current having a value corresponding to the calibration value to the Peltier element, and adjusting a chip temperature of the wavelength tunable laser array by the calibration value. How to control.   The target oscillation wavelength is such that no current is applied to the control layers of all the wavelength tunable lasers other than the first wavelength tunable laser during the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers. 5. The method of claim 4, wherein the actual oscillation wavelength from the tunable laser is.   The thermal compensation is performed when the wavelength is changed within the variable wavelength range of the first wavelength tunable laser to the control layer of the second wavelength tunable laser adjacent to the control layer of the first wavelength tunable laser. A current having a value for performing the above is applied, and a uniform current is applied to each of the control layers of the wavelength tunable lasers other than the first and second wavelength tunable lasers. Item 6. The method according to Item 4 or 5.