JP6389448B2 - Wavelength control method for tunable laser array - Google Patents

Description

  The present invention relates to a wavelength control method for a wavelength tunable laser array, and more particularly, to a wavelength control method for a wavelength tunable laser array that shortens the time from changing the wavelength of the wavelength tunable semiconductor laser to stabilizing the wavelength. About.

  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 SSG-DBR (SuperStructure Grafted Distributed Bragg Reflector Lesser). 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 (see Patent Documents 1 and 2).

  Further, the mesa adjacent to the TDA-DFB laser can be used in place of the heat compensation electrode without changing the laser structure itself, and the wavelength fluctuation at the time of switching the wavelength selective switch can be suppressed. In that case, a compensatory current is injected into the control layer of the adjacent LD, and the sum of the control layer current or power of the LD responsible for oscillation and the adjacent LD is made constant so that the locality at the time of switching is local. As a result, it is possible to suppress wavelength fluctuation (see Non-Patent Document 2).

  Further, as another method for suppressing the wavelength fluctuation, when a laser beam is output by switching from one laser in the TDA-DFB laser array to another laser in the TDA-DFB laser array, that is, the gain current is switched. In this case, a change in oscillation wavelength is suppressed by applying a current to the control electrode of the laser to which the laser beam is transferred in advance. In this case, thermal compensation is performed by previously applying the total value of the gain current and the control current to be applied to the switching destination laser to the control electrode of the switching destination laser, and as a result, wavelength variation is suppressed. (See Non-Patent Document 3 and Patent Document 3).

Japanese Patent No. 3168855 Japanese Patent No. 4850757 Japanese Unexamined Patent Publication No. 2011-198903

Nobuhiro Nuoya, Hiroyuki Ishii, Ryuzo Iga NTT Technology Journal Development of high-speed tunable distributed active DFB laser Makoto Shimozono, Nobuhiro Nuoya, Takuya Kanai, Hiroyuki Ishii 2013 IEICE Society Conference C-4-31 Makoto Shimozono, Nobuhiro Nuoya, Takuya Kanai, Hiroyuki Ishii 2014 IEICE General Conference C-4-20

  Here, the methods described in Patent Document 1 and Patent Document 2 have a problem that only a wavelength variable range of about 8 nm can be obtained, and a wide range of wavelengths cannot be selected. On the other hand, in the method described in Non-Patent Document 3, it is possible to select a wide range of wavelengths. However, when changing the wavelength in the method described in Non-Patent Document 3, it is necessary to perform thermal compensation after determining the laser to be switched to, which limits the wavelength selection of the transfer destination. Therefore, there is a problem in that it is extremely inconvenient in an application such as an optical packet switch that needs to select wavelengths flexibly at high speed.

  Further, when the wavelength is changed by performing thermal compensation, if a current is additionally applied to the control layer of the TDA-DFB laser other than the TDA-DFB laser that is responsible for oscillation, the result is a chip of the entire TDA-DFB laser array. As a result, the convergence wavelength (frequency) shifts as the temperature rises. That is, if the oscillation wavelength when laser oscillation is performed without performing thermal compensation is the target oscillation wavelength, a deviation occurs between the actual oscillation wavelength and the target oscillation wavelength. Then, in the wavelength selective switch, the changed transmission wavelength deviates from the center wavelength of the bandpass filter constituting the switch, and as a result, the wavelength change in the wavelength selective switch is longer than the change time that can be originally realized. There is a problem of becoming.

  In the wavelength selective switch capable of selecting a wide range of wavelengths, the present invention can perform thermal compensation in a wavelength tunable laser array even if a laser to be switched to is not determined in advance. An object of the present invention is to provide a wavelength control method for a tunable laser array.

  In order to achieve the above object, a first embodiment of the present invention includes a plurality of current control type wavelength tunable lasers having an active layer and a control layer to which a current can be applied independently, and the plurality of wavelength tunable lasers. A method for controlling the wavelength of a wavelength tunable laser array, wherein the output wavelength is variably controlled, wherein the first wavelength tunable laser is operated during operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers. The wavelength tunable laser is thermally compensated for all control layers of the tunable laser except for the control layer of the second tunable laser adjacent to the control layer of the first tunable laser. Applying a current of a value for performing thermal compensation when changing the wavelength within the variable wavelength range of the first wavelength tunable laser, and controlling the wavelength tunable laser other than the first and second wavelength tunable lasers Each layer has a Characterized in that it comprises applying an equal current.

  The second aspect of the present invention includes a plurality of current control type wavelength tunable lasers having an active layer and a control layer to which current can be independently applied, and tunable by changing output wavelengths of the plurality of wavelength tunable lasers. A method for controlling a wavelength of a wavelength tunable laser array, wherein all the wavelength tunable lasers other than the first tunable laser are operated during the operation of the first tunable laser among the plurality of tunable lasers. The wavelength tunable laser is thermally compensated for 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 thermal compensation when changing the wavelength within the variable wavelength range of the laser is applied, and the control layer of the wavelength tunable laser other than the first and second wavelength tunable lasers has the first And second tunable laser As the distance al away, characterized in that it comprises applying a significantly current values.

  According to a third aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array according to the first or second aspect, wherein the wavelength is changed within the oscillation wavelength range of the first wavelength tunable laser. And changing the current applied to the control layer of the first tunable laser and the current applied to the control layer of the second tunable laser, respectively, It is further characterized in that the total value of the current applied to the control electrode and the current applied to the control electrode of the second wavelength tunable laser becomes the same value before and after the wavelength change. .

  According to a fourth aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array according to the first or second aspect, wherein the oscillation is changed from the first wavelength tunable laser to the third wavelength tunable laser. In the control layer of the fourth wavelength tunable laser adjacent to the control layer of the third wavelength tunable laser, the heat when changing the wavelength within the variable wavelength range of the third wavelength tunable laser. A current having a value for performing compensation is applied, and the total value of the current applied to the control electrode of the third wavelength tunable laser and the current applied to the control electrode of the fourth wavelength tunable laser is an oscillation. The current applied to the control electrode of the first tunable laser and the current applied to the control electrode of the second tunable laser before switching are set to the same value as the first Other than the 3rd and 4th tunable lasers The control layer of the long-tunable laser is characterized in that it includes applying a uniform current, respectively.

  According to a fifth aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array of the first or second aspect, wherein oscillation is performed from the first wavelength tunable laser to a third wavelength tunable laser. Switching to a control layer of the fourth wavelength tunable laser adjacent to the control layer of the third wavelength tunable laser when changing the wavelength within the variable wavelength range of the third wavelength tunable laser. A current having a value for performing compensation is applied, and the total value of the current applied to the control electrode of the third wavelength tunable laser and the current applied to the control electrode of the fourth wavelength tunable laser is an oscillation. The current applied to the control electrode of the first tunable laser and the current applied to the control electrode of the second tunable laser before switching are set to the same value as the first 3rd and 4th wavelength tunable lasers The control layer of the tunable laser, the distance from the third and fourth tunable laser leaves, characterized in that it comprises applying a significantly current values.

  According to a sixth aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array according to the fifth aspect, wherein the value of the current applied to the control layer of the first wavelength tunable laser is determined by the thermal compensation. Is a value decreased by a calibration value for reducing wavelength fluctuations resulting from an increase in the chip temperature of the wavelength tunable laser array, and the calibration value is obtained in advance when the thermal compensation is performed and thermal compensation. The current value applied to the control layer of the second wavelength tunable laser is calculated from the relationship between the injection control current of the semiconductor laser versus the oscillation wavelength when the laser is not performed, and is a value increased by the calibration value. And

  According to a seventh aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array according to any one of the first to sixth aspects, wherein the wavelength tunable laser is a DBR laser. And

  According to an eighth aspect of the present invention, there is provided a method for controlling the wavelength of the wavelength tunable laser array according to any one of the first to sixth aspects, wherein the wavelength tunable laser is a TDA-DFB laser. It is characterized by.

  Since the present invention can statistically shorten the time until the wavelength is stabilized when the wavelength of the wavelength tunable laser constituting the wavelength tunable laser array is changed, such as an optical packet switch or an optical burst switch. It can also be applied as a wavelength tunable light source that is effective for high-speed switching applications.

It is a top view which shows the wavelength selective switch concerning Example 1 of this invention. In the wavelength selective switch of FIG. 1, it is a setting current when the laser array is not thermally compensated. In the wavelength selective switch of FIG. 1, it is a setting current when the thermal compensation of the laser array is performed by the method according to Example 1 of the present invention. It is a top view which shows the wavelength selective switch concerning Example 2 of this invention. In the wavelength selective switch of FIG. 4, it is a set current when the laser array is not thermally compensated. In the wavelength selective switch of FIG. 4, it is a setting current when the thermal compensation of the laser array is performed by the method according to Example 2 of the present invention. In the wavelength selective switch of FIG. 4, it is a setting current when the thermal compensation of the laser array is performed by the method according to the third embodiment of the present invention. In the wavelength selective switch of FIG. 4, it is a setting current when the thermal compensation of the laser array is performed by the method according to the fourth embodiment of the present invention. In the wavelength selective switch of FIG. 4, in order to change a wavelength by the 1st method or the 2nd method, it is a figure which shows the time change of the oscillation frequency when changing the value of the electric current applied to a control layer. is there. FIG. 5 is a diagram illustrating a relationship between a chip temperature and an oscillation wavelength of the laser array in FIG. 4. FIG. 5 is a diagram illustrating a relationship between a control current when performing wavelength control and a stabilized oscillation wavelength in any one TDA-DFB laser in the laser array of FIG. 4. FIG. 5 is a set current of the laser active layer and the laser control layer when the wavelength calibration of the present embodiment is performed in the laser array of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Example 1]
FIG. 1 is a top view showing a laser array 100 of wavelength selective switches according to a first embodiment of the present invention. The laser array 100 is a DBR laser array that is a current-controlled tunable laser, and includes a semiconductor substrate 110, laser active layers 111 to 116 provided on the semiconductor substrate 110, and a laser provided on the semiconductor substrate 110. And control layers 121 to 126. The laser active layer 111 and the laser control layer 121 form the DBR laser 101 on the semiconductor substrate 110. DBR lasers 102 to 106 are also formed on the semiconductor substrate 110 for the laser active layers 112 to 116 and the laser control layers 122 to 126, respectively. The DBR lasers 101 to 106 are arranged in parallel.

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

  The laser control layer 121 is applied with a current converted from a 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 122 to 126 are also applied with a current obtained by converting a signal from the control device 170 from the DA converters 152 to 156 through the amplifiers 192 to 196 and the electrodes 142 to 146, respectively, to change the refractive index. The wavelength of the output light is controlled.

  The laser array 100 includes an MMI (multimode interference) that is an optical coupler that combines the waveguides 161 to 166 that guide the output light from each DBR laser and the output light that is guided through the waveguides 161 to 166. ) A coupler 167, an SOA (semiconductor amplifier) 168 that adjusts the intensity of output light at the final stage, a waveguide 169 that guides and outputs the output light from the SOA 168, and an electrode 137 connected to the SOA 168. . The oscillation light of each DBR 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.

  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 DBR 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 DBR laser that is performing oscillation. In this case, only the current applied to the control layer of the first DBR laser (during oscillation) 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. If thermal compensation is used by applying a current to the control layer of the DBR laser No. 2, the wavelength drift can be reduced, and as a result, the time from when the wavelength is changed to when the wavelength is stabilized can be shortened.

  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 DBR laser that oscillates. The wavelength of the oscillation light is changed by switching the oscillation from one DBR laser to another third DBR laser. When switching the oscillation from the first DBR laser to the third DBR laser, not only the current applied to the control layer of the DBR laser but also the change of the current applied to the active layer is accompanied by each change compared to the first method. The amount of change in current of the DBR 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 this embodiment, by applying a current in advance to the control layers of all the DBR lasers in the DBR laser array so that the amount of heat generated in the DBR laser is constant before and after the wavelength change, The change is suppressed, and the refractive index change due to the temperature change is suppressed.

  In this embodiment, when changing the wavelength in the DBR laser array of the wavelength selective switch, when the wavelength value to be changed is not determined, the wavelength is changed by the first method, and the second In order to cope with the refractive index change due to temperature change in both cases when changing the wavelength by the method, thermal compensation of the DBR laser array is performed, the wavelength drift is reduced, and the time until the wavelength is stabilized is shortened .

  Specifically, in order to perform thermal compensation by changing the wavelength, a current is applied in advance to all control layers of the DBR laser other than the first DBR laser that oscillates, thereby relaxing the heat distribution in the chip.

  First, in order to output a first wavelength in the DBR laser array of the wavelength selective switch, a current having a desired value is applied to the active layer and the control layer of the first DBR laser that is the DBR laser that performs oscillation. Next, in order to cope with the case where the wavelength is changed by the first method in the subsequent wavelength change in the DBR laser array, a desired current is applied to the control layer of the second DBR laser adjacent to the first DBR laser. Apply. When changing the wavelength within the variable wavelength range of the first DBR laser by applying a current to the control layer of the second DBR laser (wavelength change by the first method), the first DBR laser Since heat compensation can be performed, it is possible to shorten the time until the wavelength is stabilized after the wavelength is changed.

  Furthermore, the current value applied to the control layer of the DBR laser other than the first DBR laser and the second DBR laser is also set. This is to cope with the case where the wavelength is changed by the second method in the subsequent wavelength change in the DBR laser array. Here, the same current value is set in all control layers of the DBR lasers other than the first and second DBR lasers. By setting the same current value for each laser, heat in the chip that is biased only in the vicinity of the laser that oscillates can be distributed over a wide range, and thermal compensation for wavelength change can be performed. The first DBR laser When changing the wavelength by switching the oscillation to any other DBR laser other than the above (referred to as the third DBR laser) (the wavelength change by the second method described above), the wavelength is stabilized after changing the wavelength. It is possible to shorten the time until. It should be noted that the value of the applied current should be limited to a value that does not increase the frequency shift that converges.

  Next, the wavelength is changed in the DBR 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, the first oscillation is performed. The wavelength is changed by changing the current value applied to the control layer of the DBR laser. At this time, the current applied to the second DBR laser adjacent to the first DBR laser is also changed, and the current value applied to the control layer of the first DBR laser before the wavelength change and the second DBR laser are changed. The sum of the current value applied to the control layer of the first DBR laser after the wavelength change is the same as the sum of the current value applied to the control layer of the second DBR laser. To be. This is because a current is applied to the second DBR laser adjacent to the first DBR laser to perform thermal compensation for the wavelength change by the further first method. Note that the current value applied to the control layer of the DBR laser other than the first and second DBR lasers is the same as that 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, current is applied to the active layer and the control layer of the third DBR laser in order to oscillate by switching from the first DBR laser to the third DBR laser. . Further, a current is also applied to a control layer of a DBR laser (referred to as a fourth DBR laser) adjacent to the third DBR laser for performing thermal compensation.

  Here, a current having the same value as that of the current applied to the first DBR laser is applied to the active layer of the third DBR laser to be switched. The current value applied to the control layer of the fourth DBR laser is set to a value complementary to the current value of the control layer of the third DBR laser that oscillates, and the third DBR laser is heated. Used for compensation. Specifically, the sum of the current value applied to the control layer of the third DBR laser and the current value applied to the control layer of the fourth DBR laser is the current applied to the first DBR laser control layer in the channel 1. And the sum of the value and the current value applied to the control layer of the second DBR laser. This is to perform thermal compensation for wavelength change by the further first method. Further, a current is also applied to the control layer of the DBR laser other than the third DBR laser and the fourth DBR 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 DBR laser other than the first DBR laser and the second DBR laser in the channel 1.

  In the present embodiment, channel 1 and channel 2 are set so that the sum of all active layer currents and control currents is constant. This is because if the total value of the total currents of the channel 1 and the channel 2 changes, the oscillation temperature is not stable because the temperature of the chip is not stabilized and vibrates. In the present embodiment, the applied current is constant, but the applied power may be constant.

  By setting the current value applied to the control layer of the DBR laser in this way, 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 further switched to an arbitrary DBR laser. Sometimes, it is possible to shorten the time until the wavelength is stabilized after the wavelength is changed.

  Here, an example of wavelength control of the oscillation light of the conventional laser array and an example of wavelength control of the oscillation light of the laser array of the present embodiment will be described in comparison.

1. 2. Example of Wavelength Control of Oscillation Light of Conventional Laser Array FIG. 2 is a set current of the laser active layer and the laser control layer when the laser array is not subjected to thermal compensation in the laser array 100 of FIG. First, a current of 70 mA is applied to the laser active layer 111 of the DBR laser 101, and a current of 5 mA is applied to the laser control layer 121 of the DBR laser 101. The oscillation frequency of the DBR laser 101 at this time was 190.1 THz (channel 1).

  Next, the wavelength is changed in the DBR laser array 100 of the wavelength selective switch, but the wavelength is changed by the second method. The DBR laser selected here is the DBR laser 103. At this time, a current of 70 mA is applied to the laser active layer 113 of the DBR laser 103, and a current of 10 mA is applied to the laser control layer 123 of the DBR laser 103. The oscillation frequency of the DBR laser 103 at this time was 192.0 THz (channel 2).

  Here, the current application to the DBR laser 101 and the current application to the DBR laser 103 are switched every 1 ms, and the oscillation frequency of 190.1 Tz (channel 1) and the oscillation frequency of 192.0 THz (channel 2) are alternated. obtain. 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 20 μs.

2. Example of Wavelength Control of Oscillation Light of Laser Array of Example 1 FIG. 3 shows a laser active layer and a laser control layer when heat compensation is performed by the method according to Example 3 of the present invention in the laser array 100 of FIG. Set current.

  First, a current of 70 mA is applied to the laser active layer 111 of the DBR laser 101, and a current of 5 mA is applied to the laser control layer 121 of the DBR laser 101. At this time, in order to perform thermal compensation of each DBR laser, first, a current of 35 mA is applied to the laser control layer 122 of the adjacent DBR laser 102. This is a current required for performing thermal compensation when the wavelength is changed by the first method in the subsequent wavelength change in the DBR laser array. The oscillation frequency of the DBR laser 101 at this time was 190.1 THz (channel 1).

  Further, a current of 20 mA is applied in advance to the laser control layers 123 to 126 of the DBR lasers 103 to 106 other than the DBR lasers 101 and 102. This is to cope with the case where the wavelength is changed by the second method in the subsequent wavelength change in the DBR laser array. By setting the same current value in the laser control layers 123 to 126 in advance, heat in the chip that is biased only in the vicinity of the laser that oscillates is distributed over a wide range, and the heat distribution in the chip is relaxed in advance. And the thermal compensation for the wavelength change by the second method can be performed.

  Next, the wavelength is changed in the DBR laser array 100 of the wavelength selective switch, but the wavelength is changed by the second method. The DBR laser selected here is the DBR laser 103. First, a current of 70 mA is applied to the laser active layer 113 of the DBR laser 103, and a current of 10 mA is applied to the laser control layer 123 of the DBR laser 103. The oscillation frequency of the DBR laser 103 at this time was 192.0 THz (channel 2). Further, in order to cope with the case where the wavelength is changed by the first method in the wavelength change in the further DBR laser array, the DBR laser 103 is thermally compensated. In the thermal compensation, a current of 30 mA is applied to the control layer of the adjacent DBR laser 102, and this current value is complementary to the set value of the current applied to the control layer of the DBR laser 103 that performs oscillation. Must be set to a value. Specifically, the sum of the current value applied to the control layer 123 of the DBR laser 103 and the current value applied to the control layer 122 of the DBR laser 102 is the current applied to the control layer 121 of the DBR laser 101 in the channel 1. The value is set to be equal to the total value of the current value applied to the control layer 122 of the DBR laser 102.

  Next, a current of 20 mA is applied in advance to the laser control layers 121 and 124 to 126 of the DBR lasers 101 and 104 to 106 other than the DBR lasers 103 and 102. This is to cope with the case where the wavelength is changed by the second method in the wavelength change in the further DBR laser array.

  Here, the current application to the DBR laser 101 and the current application to the DBR laser 103 are switched every 1 ms, and the oscillation frequency of 190.1 Tz (channel 1) and the oscillation frequency of 192.0 THz (channel 2) are alternated. obtain. When the time within 10 GHz of the target frequency from the time of switching is defined as the switching time, the switching time is 10 μs in this control method.

  Therefore, the switching time can be significantly shortened by using the control method of the present invention. Although the case of six arrays has been described this time, it goes without saying that the present invention is effective even when the number of arrays is other than six.

[Example 2]
FIG. 4 is a top view showing the laser array 400 of the wavelength selective switch according to the second embodiment of the present invention. The laser array 400 is a TDA-DFB laser array that is a current-controlled tunable laser, and includes a semiconductor substrate 410 and laser active layers 411a to 416a, 411b to 416b, and 411c to 416c provided on the semiconductor substrate 410. And laser control layers 421a to 426a, 421b to 426b, and 421c to 426c provided on the semiconductor substrate 410. The laser active layers 411 a to 411 c and the laser control layers 421 a to 421 c are provided on the substrate, and are alternately arranged on the semiconductor substrate 410 to form the TDA-DFB laser 401. The laser active layers 412a to 416a, 412b to 416b, 412c to 416c and the laser control layers 422a to 426a, 422b to 426b, and 422c to 426c are also alternately arranged on the semiconductor substrate 410 and TDA-DFB lasers 402 to 406 are used. Form. The TDA-DFB lasers 401 to 406 are arranged in parallel.

  The laser array 400 includes electrodes 431 to 436 connected to the laser active layers 411a to 416a, 411b to 416b, and 411c to 416c, amplifiers 481 to 486 connected to the electrodes 431 to 436, and amplifiers 481 to 481, respectively. DA converters 471 to 476 connected to 486, respectively. The laser array 400 includes electrodes 441 to 446 connected to the laser control layers 421a to 426a, 421b to 426b, and 421c to 426c, amplifiers 491 to 496 connected to the electrodes 441 to 446, and amplifiers 491 to 491, respectively. DA converters 451 to 456 respectively connected to 496, and DA converters 471 to 476 and a control device 470 connected to DA converters 451 to 456. The laser active layers 411a to 411c oscillate laser light when a current converted from a signal from the control device 470 is applied from the DA converter 471 via the amplifier 481 and the electrode 431. The laser active layers 412a to 416c also oscillate laser light when the DA converters 472 to 476 are applied with currents converted from signals from the control device 470 via amplifiers 482 to 486 and electrodes 432 to 436, respectively.

  The laser control layers 421a to 421c are supplied with a current converted from the signal from the control device 470 from the DA converter 451 via the amplifier 491 and the electrode 441, and the wavelength of the output light is controlled by changing the refractive index. . The laser control layers 422a to 426c are also output by changing the refractive index by applying a current converted from the signal from the control device 470 from the DA converters 452 to 456 via the amplifiers 492 to 496 and the electrodes 442 to 446, respectively. The wavelength of light is controlled.

  The laser array 400 includes waveguides 461 to 466 that guide the output light from each TDA-DFB laser, and optical couplers that combine the output light guided through the waveguides 461 to 466. Mode interference) coupler 467, SOA (semiconductor amplifier) 468 for adjusting the intensity of output light at the final stage, waveguide 469 for guiding and outputting the output light from SOA 468, and electrode 437 connected to SOA 468 Is provided. The oscillation light of each TDA-DFB laser is combined into one by the MMI coupler 467 via the waveguides 461 to 466 arranged in the subsequent stage, and after passing through the SOA 468, is output from the waveguide 469 as output light. The SOA 468 is supplied with current from the outside via the electrode 437.

  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 this embodiment, 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 this embodiment, when changing the wavelength in the TDA-DFB laser array of the wavelength selective switch, when 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 method of 2, the TDA-DFB laser array is thermally compensated, the wavelength drift is reduced, and the wavelength is stabilized. Reduce time.

  Specifically, in order to perform thermal compensation by changing the wavelength, a current is applied in advance to all control layers of the TDA-DFB laser other than the first TDA-DFB laser that oscillates, and the heat distribution in the chip is determined. ease.

  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.

  Further, a current value applied to a control layer of a TDA-DFB laser other than the first TDA-DFB laser and the second TDA-DFB laser is also set. 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. It should be noted that the value of the applied current should be limited to a value that does not increase the frequency shift that converges.

  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 the present embodiment, channel 1 and channel 2 are set so that the sum of all active layer currents and control currents is constant. This is because if the total value of the total currents of the channel 1 and the channel 2 changes, the oscillation temperature is not stable because the temperature of the chip is not stabilized and vibrates. In the present embodiment, the applied current is constant, but the applied power may be constant.

  By setting the current value to be applied to the control layer of the TDA-DFB laser in this way, 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 any TDA-DFB can be distributed. Even when the channel is switched to the laser, it is possible to shorten the time from the change of the wavelength to the stabilization of the wavelength.

  Here, an example of wavelength control of the oscillation light of the conventional laser array and an example of wavelength control of the oscillation light of the laser array of the present embodiment will be described in comparison.

1. Example of Wavelength Control of Oscillation Light of Conventional Laser Array FIG. 5 shows set currents of the laser active layer and the laser control layer when the thermal compensation is not performed in the laser array 400 of FIG. First, an 80 mA current is applied to the laser active layer 413 of the TDA-DFB laser 403, and a 10 mA current is applied to the laser control layer 423 of the TDA-DFB laser 403. At this time, the oscillation frequency of the TDA-DFB laser 403 was 192.0 THz (channel 1).

  Next, the wavelength is changed in the TDA-DFB laser array 400 of the wavelength selective switch, but the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 405. At this time, a current of 80 mA is applied to the laser active layer 415 of the TDA-DFB laser 405, and a current of 15 mA is applied to the laser control layer 425 of the TDA-DFB laser 405. The oscillation frequency of the TDA-DFB laser 405 at this time was 193.3 THz (channel 2).

  Here, the current application to the TDA-DFB laser 403 and the current application to the TDA-DFB laser 405 are switched every 1 ms, and an oscillation frequency of 192.0 Tz (channel 1) and an oscillation frequency of 193.3 THz (channel 2). And get alternately. 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 50 μs.

2. Example of Wavelength Control of Oscillation Light of Laser Array of Example 2 FIG. 6 shows a laser active layer and a laser control layer when heat compensation is performed by the method according to Example 2 of the present invention in the laser array 400 of FIG. Set current.

  First, an 80 mA current is applied to the laser active layer 413 of the TDA-DFB laser 403, and a 10 mA current is applied to the laser control layer 423 of the TDA-DFB laser 403. 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 424 of the adjacent TDA-DFB laser 404. 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 404 at this time was 192.0 THz (channel 1).

  Further, a current of 10 mA is applied in advance to the laser control layers 421 to 422 and 425 to 426 of the TDA-DFB lasers 401 to 402 and 405 to 406 other than the TDA-DFB lasers 403 and 404. 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 the laser control layers 421 to 422 and 425 to 426 in advance, the heat in the chip that is biased only in the vicinity of 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, the wavelength is changed in the TDA-DFB laser array 400 of the wavelength selective switch, but the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 405. First, an 80 mA current is applied to the laser active layer 415 of the TDA-DFB laser 405, and a 15 mA current is applied to the laser control layer 425 of the TDA-DFB laser 405. The oscillation frequency of the TDA-DFB laser 405 at this time was 193.3 THz (channel 2). Further, thermal compensation of the TDA-DFB laser 405 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 424 of the adjacent TDA-DFB laser 404, and this current value is set to the set value of the current applied to the control layer of the TDA-DFB laser 405 that performs oscillation. 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 425 of the TDA-DFB laser 405 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is the control of the TDA-DFB laser 403 in the channel 1. The total value of the current value applied to the layer 423 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is set to be the same.

  Next, a current of 10 mA is applied in advance to the laser control layers 421 to 423 and 426 of the TDA-DFB lasers 401 to 403 and 406 other than the TDA-DFB lasers 405 and 404. 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.

  Here, the current application to the TDA-DFB laser 403 and the current application to the TDA-DFB laser 405 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). And get alternately. 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 40 μs.

  Therefore, the switching time can be significantly shortened by using the control method of the present invention. Although the case of six arrays has been described this time, it goes without saying that the present invention is effective even when the number of arrays is other than six.

[Example 3]
Also in this embodiment, 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 method of 2, the TDA-DFB laser array is thermally compensated, the wavelength drift is reduced, and the wavelength is stabilized. Reduce time.

  Specifically, in order to perform thermal compensation by changing the wavelength, a current is applied in advance to all control layers of the TDA-DFB laser other than the first TDA-DFB laser that oscillates, and the heat distribution in the chip is determined. ease.

  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.

  Further, a current value applied to a control layer of a TDA-DFB laser other than the first TDA-DFB laser and the second TDA-DFB laser is also set. 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. In the case of the present embodiment, the current value applied to the control layer of the TDA-DFB laser other than the first and second TDA-DFB lasers is the first TDA-DFB laser that is oscillating and the adjacent second TDA-DFB laser. Applied to the control layer of the TDA-DFB laser array as the distance from the first TDA-DFB laser and the second TDA-DFB laser increases so as to cancel out the thermal gradient from the pair with the TDA-DFB laser. The current value is increased in proportion to the distance away.

  In the chip, the closer to the TDA-DFB laser that oscillates, the higher the temperature of the chip. Therefore, as the distance from the TDA-DFB laser that oscillates becomes longer, the current applied to the laser control layer Increase the value to equalize the temperature in the chip. By setting the current value to be applied to the control layer of each TDA-DFB laser as in this embodiment, the heat in the chip that is biased only in the vicinity of the laser that oscillates is distributed over a wide range, and the heat for changing the wavelength When the wavelength can be changed by switching the oscillation to an arbitrary TDA-DFB laser other than the first TDA-DFB laser (referred to as a third TDA-DFB laser). Also in the wavelength change by the method, it is possible to shorten the time from the change of the wavelength to the stabilization of the wavelength.

  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, a third TDA-DFB laser is used to oscillate in a TDA-DFB laser (third TDA-DFB laser) other than the first TDA-DFB laser. A current is applied to the active layer and the control 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 current value applied to the control layer of the TDA-DFB laser array as the distance from the set of the third TDA-DFB laser that oscillates and the adjacent fourth TDA-DFB laser increases. Increase in proportion to the distance away.

  In the present embodiment, channel 1 and channel 2 are set so that the sum of all active layer currents and control currents is constant. This is because if the total value of the total currents of the channel 1 and the channel 2 changes, the oscillation temperature is not stable because the temperature of the chip is not stabilized and vibrates. In the present embodiment, the applied current is constant, but the applied power may be constant.

  By setting the current value to be applied to the control layer of the TDA-DFB laser in this way, 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 any TDA-DFB can be distributed. Even when the oscillation is switched to the laser, it is possible to shorten the time from the change of the wavelength to the stabilization of the wavelength.

  FIG. 7 shows set currents of the laser active layer and the laser control layer when the thermal compensation is performed by the method according to the third embodiment of the present invention in the laser array 400 of FIG.

  First, an 80 mA current is applied to the laser active layer 413 of the TDA-DFB laser 403, and a 10 mA current is applied to the laser control layer 423 of the TDA-DFB laser 403. 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 424 of the adjacent TDA-DFB laser 404. 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 404 at this time was 192.0 THz (channel 1).

  Further, current is applied to the laser control layers 421 to 422 and 425 to 426 of the TDA-DFB lasers 401 to 402 and 405 to 406 other than the TDA-DFB lasers 403 and 404. 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 applied current value increases the current value applied to the control layer of the TDA-DFB laser as the distance from the TDA-DFB laser 403 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases. To go. Specifically, the control layer 422 of the TDA-DFB laser 402 adjacent to the TDA-DFB laser 403 that oscillates (on the opposite side of the TDA-DFB laser 404), and the TDA-DFB laser 404 that performs thermal compensation (TDA- A current of 10 mA is applied to the control layer 425 of the TDA-DFB laser 405 adjacent to the opposite side of the DFB laser 403. Also, adjacent to the control layer 421 of the TDA-DFB laser 401 adjacent to the TDA-DFB laser 402 (opposite side of the TDA-DFB laser 403) and adjacent to the TDA-DFB laser 405 (opposite side of the TDA-DFB laser 404). A current of 20 mA is applied to the control layer 406 of the TDA-DFB laser 426. That is, as the distance from the TDA-DFB laser 403 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases, 10 mA and 20 mA are set so that the current applied to the control layer of the TDA-DFB laser increases. . By setting the current values in the laser control layers 421 to 422 and 425 to 426 as in the present embodiment, the heat in the chip that is biased only in the vicinity of the laser that oscillates is distributed over a wide range, and the heat distribution in the chip. Can be relaxed in advance, and thermal compensation for the change in wavelength by the second method can be performed.

  Next, the wavelength is changed in the TDA-DFB laser array 400 of the wavelength selective switch, but the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 405. First, an 80 mA current is applied to the laser active layer 415 of the TDA-DFB laser 405, and a 15 mA current is applied to the laser control layer 425 of the TDA-DFB laser 405. The oscillation frequency of the TDA-DFB laser 405 at this time was 193.3 THz (channel 2). Further, thermal compensation of the TDA-DFB laser 403 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 424 of the adjacent TDA-DFB laser 404, and this current value is set to the set value of the current applied to the control layer of the TDA-DFB laser 405 that performs oscillation. 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 425 of the TDA-DFB laser 405 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is the control of the TDA-DFB laser 403 in the channel 1. The total value of the current value applied to the layer 423 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is set to be the same.

  Next, a current is applied in advance to the laser control layers 421 to 423 and 426 of the TDA-DFB lasers 401 to 403 and 406 other than the TDA-DFB lasers 404 and 405, but the TDA-DFB laser 405 that oscillates and the thermal compensation are applied. As the distance from the TDA-DFB laser 404 that performs the operation increases, the value of the current applied to the control layer of the TDA-DFB laser is increased. Specifically, the control layer 426 of the TDA-DFB laser 406 adjacent to the TDA-DFB laser 405 that oscillates (on the opposite side of the TDA-DFB laser 404), and the TDA-DFB laser 404 that performs thermal compensation (TDA- A current of 10 mA is applied to the control layer 423 of the TDA-DFB laser 403 adjacent to the opposite side of the DFB laser 405. Further, a current of 20 mA is applied to the control layer 422 of the TDA-DFB laser 402 adjacent to the TDA-DFB laser 403 (on the opposite side of the TDA-DFB laser 404). Further, a current of 30 mA is applied to the control layer 421 of the TDA-DFB laser 401 adjacent to the TDA-DFB laser 402 (on the opposite side of the TDA-DFB laser 403). That is, as the distance from the set of the TDA-DFB laser 405 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases, the current applied to the control layer of the TDA-DFB laser increases as 10 mA, 20 mA, and 30 mA. Set as follows. By applying a current having such a setting value to the laser control layers 421 to 423 and 426 in advance, in order 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. It is.

  Here, the current application to the TDA-DFB laser 403 and the current application to the TDA-DFB laser 405 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). And get alternately. When the time within 10 GHz of the target frequency from the time of switching is defined as the switching time, the switching time is 28 μs in this control method.

  Therefore, the switching time can be significantly shortened by using the control method of the present invention. Although the case of six arrays has been described this time, it goes without saying that the present invention is effective even when the number of arrays is other than six.

[Example 4]
FIG. 8 shows set currents of the laser active layer and the laser control layer when the thermal compensation is performed by the method according to the fourth embodiment of the present invention in the laser array 400 of FIG.

  First, an 80 mA current is applied to the laser active layer 413 of the TDA-DFB laser 403, and a 10 mA current is applied to the laser control layer 423 of the TDA-DFB laser 403. 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 424 of the adjacent TDA-DFB laser 404. 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 404 at this time was 192.0 THz (channel 1).

  Further, current is applied to the laser control layers 421 to 422 and 425 to 426 of the TDA-DFB lasers 401 to 402 and 405 to 406 other than the TDA-DFB lasers 403 and 404. 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 applied current value increases the current value applied to the control layer of the TDA-DFB laser as the distance from the TDA-DFB laser 403 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases. To go. Specifically, the control layer 422 of the TDA-DFB laser 402 adjacent to the TDA-DFB laser 403 that oscillates (on the opposite side of the TDA-DFB laser 404), and the TDA-DFB laser 404 that performs thermal compensation (TDA- A current of 10 mA is applied to the control layer 425 of the TDA-DFB laser 405 adjacent to the opposite side of the DFB laser 403. Also, adjacent to the control layer 421 of the TDA-DFB laser 401 adjacent to the TDA-DFB laser 402 (opposite side of the TDA-DFB laser 403) and adjacent to the TDA-DFB laser 405 (opposite side of the TDA-DFB laser 404). A current of 20 mA is applied to the control layer 426 of the TDA-DFB laser 406. That is, as the distance from the TDA-DFB laser 403 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases, 10 mA and 40 mA are set so that the current applied to the control layer of the TDA-DFB laser increases. . By setting the current values in the laser control layers 421 to 422 and 425 to 426 as in the present embodiment, the heat in the chip that is biased only in the vicinity of the laser that oscillates is distributed over a wide range, and the heat distribution in the chip. Can be relaxed in advance, and thermal compensation for the change in wavelength by the second method can be performed.

  Next, the wavelength is changed in the TDA-DFB laser array 400 of the wavelength selective switch, but the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 405. First, an 80 mA current is applied to the laser active layer 415 of the TDA-DFB laser 405, and a 15 mA current is applied to the laser control layer 425 of the TDA-DFB laser 405. The oscillation frequency of the TDA-DFB laser 405 at this time was 193.3 THz (channel 2). Further, thermal compensation of the TDA-DFB laser 405 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 424 of the adjacent TDA-DFB laser 404, and this current value is set to the set value of the current applied to the control layer of the TDA-DFB laser 405 that performs oscillation. 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 425 of the TDA-DFB laser 405 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is the control of the TDA-DFB laser 403 in the channel 1. The total value of the current value applied to the layer 423 and the current value applied to the control layer 424 of the TDA-DFB laser 404 is set to be the same.

  Next, a current is applied in advance to the laser control layers 421 to 423 and 426 of the TDA-DFB lasers 401 to 403 and 406 other than the TDA-DFB lasers 404 and 405, but the TDA-DFB laser 405 that oscillates and the thermal compensation are applied. As the distance from the TDA-DFB laser 404 that performs the operation increases, the value of the current applied to the control layer of the TDA-DFB laser is increased. Specifically, the control layer 426 of the TDA-DFB laser 406 adjacent to the TDA-DFB laser 405 that oscillates (on the opposite side of the TDA-DFB laser 404), and the TDA-DFB laser 404 that performs thermal compensation (TDA- A current of 10 mA is applied to the control layer 423 of the TDA-DFB laser 403 adjacent to the opposite side of the DFB laser 405. Further, a current of 25 mA is applied to the control layer 422 of the TDA-DFB laser 402 adjacent to the TDA-DFB laser 403 (on the opposite side of the TDA-DFB laser 404). Further, a current of 55 mA is applied to the control layer 401 of the TDA-DFB laser 401 adjacent to the TDA-DFB laser 402 (on the opposite side of the TDA-DFB laser 403). That is, as the distance from the TDA-DFB laser 405 that performs oscillation and the TDA-DFB laser 404 that performs thermal compensation increases, the current applied to the control layer of the TDA-DFB laser increases to 10 mA, 25 mA, and 55 mA. Set. By applying a current having such a setting value to the laser control layers 421 to 423 and 426 in advance, in order 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. It is.

  Here, the current application to the TDA-DFB laser 403 and the current application to the TDA-DFB laser 405 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). And get alternately. 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 12 μs.

  Therefore, the switching time can be significantly shortened by using the control method of the present invention. Although the case of six arrays has been described this time, it goes without saying that the present invention is effective even when the number of arrays is other than six.

[Example 5]
In the first to fourth embodiments, by setting the current value applied to the control layer of each TDA-DFB laser, heat can be applied not only to the vicinity of the laser that oscillates but also to the entire chip (semiconductor substrate), Furthermore, 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 the thermal compensation is performed by increasing the entire chip temperature of the laser array 400 in order to shorten the time until the wavelength is stabilized after the wavelength is changed is the same as the case where the thermal 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. 9 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. 9, the temporal change in the oscillation frequency is represented by a solid line 901, and the temporal change in the control current is represented by a one-dot chain line 902. 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. 9 when the control current is switched from A1 to A2 (switching 911). 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 the convergence frequency deviation, the control current applied to the TDA-DFB laser of the laser array 400 is lowered by a desired value, and the convergence frequency deviation is calibrated to obtain a target oscillation frequency (wavelength). ) FIG. 10 is a diagram showing the relationship between the chip temperature of the laser array 400 and the oscillation wavelength. The oscillation wavelength of the laser array 400 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 400 is I1. Here, the value of the oscillation wavelength of the laser array 400 must be returned to the target oscillation wavelength I2. Therefore, the target oscillation wavelength I2 is controlled to oscillate by lowering the control current applied to the TDA-DFB laser of the laser array 400 by a desired value.

  By adjusting the control current applied to the TDA-DFB laser of the laser array 400 and changing the wavelength by the first method and the second method as described above, the convergence frequency shift of the laser array 400 is reduced. Can do.

  When the convergence value of the oscillation wavelength output from the laser array 400 is less than the target oscillation wavelength (when the oscillation frequency is higher than the target frequency), it is applied to the TDA-DFB laser of the laser array 400. The target oscillation wavelength can be obtained by increasing the control current by a desired value.

  Here, a specific example of calibration of the deviation of the convergence frequency of the oscillation light of the laser array of the present invention will be described. FIG. 11 is a diagram showing the relationship between the control current and the stabilized oscillation wavelength when performing wavelength control in any one TDA-DFB laser in the laser array 400. Here, a solid line 1101 indicates a case where a current is additionally applied to the control layer of each TDA-DFB laser in order to perform thermal compensation (Example 4), and a broken line 1102 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 without performing thermal compensation, the oscillation frequency is stabilized at J2 after a predetermined time has elapsed. On the other hand, when thermal compensation was performed by the method of Example 4 and a certain current value C1 was applied to the control layer of an arbitrary DFB laser, the oscillation frequency stabilized at J1 after a lapse of a certain time. When heat compensation is performed by the method of Example 4 and the control current value C1 is applied, the actual transmission frequency becomes the wavelength increased by the wavelength indicated by J1 due to the rise in chip temperature (the convergence frequency deviation is J2-J2 = ΔJ). Here, in order to obtain the oscillation frequency J2 by the method of the fourth embodiment (solid line 1101), the control current value must be C2. Accordingly, assuming that the current calibration value is C1−C2 = ΔC, the current applied to the control layer of the TDA-DFB laser that is oscillating is decreased by ΔC. As a result, the oscillation frequency is stabilized at J2 after a predetermined time has elapsed. Note that the decrease in the voltage applied to the control layer of the transmitting TDA-DFB laser is the increase in the voltage applied to the control layer of the control layer of the adjacent TDA-DFB laser.

  FIG. 12 shows set currents of the laser active layer and the laser control layer when the wavelength calibration of this embodiment is performed in the laser array 400 of FIG.

  First, a current is applied to the laser active layer 413 and the laser control layer 423 of the TDA-DFB laser 403, but the current applied to the laser active layer 413 remains 80 mA, and the current applied to the laser control layer 423 is 2 mA. Just lower it and change it to 8mA. At this time, the current applied to the adjacent laser control layer 424 in order to perform thermal compensation of each TDA-DFB laser is increased by 2 mA and changed to 37 mA. The current values applied to the other laser control layers 421, 422, 425, and 426 are the same as those in the fourth embodiment. The oscillation frequency of the TDA-DFB laser 404 at this time was 192.0 THz (channel 1).

  Next, the wavelength is changed in the TDA-DFB laser array 400 of the wavelength selective switch, but the wavelength is changed by the second method. The TDA-DFB laser selected here is the TDA-DFB laser 405 as in the fourth embodiment. First, a current is applied to the laser active layer 415 and the laser control layer 425 of the TDA-DFB laser 405, but the current applied to the laser active layer 415 remains 80 mA, and the current applied to the laser control layer 425 is 4 mA. Just lower it to 11mA. At this time, in order to perform thermal compensation of each TDA-DFB laser, the current applied to the adjacent laser control layer 424 is increased by 4 mA and changed to 34 mA. The current values applied to the other laser control layers 421, 422, 423, and 426 are the same as those in the fourth embodiment. The oscillation frequency of the TDA-DFB laser 405 at this time was 193.3 THz (channel 2).

  Using the wavelength control method of Example 4, the current application to the TDA-DFB laser 403 and the current application to the DFB laser 405 are switched every 1 ms, and an oscillation frequency (channel 1) of 192.0 THz and 193.3 THz The oscillation frequency is obtained alternately. Here, when the time within 10 GHz of the target frequency from the time of switching is defined as the switching time, the convergence frequency shift with respect to the target frequency in 1 ms after switching is 3 GHz. On the other hand, in this embodiment, when the current application to the TDA-DFB 403 and the current application to the TDA-DFB laser 405 are switched every 1 ms, the convergence frequency deviation with respect to the target frequency in 1 ms after the switching is 10 MHz. A significant reduction was achieved.

  Therefore, the wavelength calibration method of the wavelength tunable laser array of the present embodiment can realize a remarkable reduction in the convergence frequency shift. Although the case of six arrays has been described this time, it goes without saying that the present invention is effective even when the number of arrays is other than six.

100, 400 Laser array 101-106 DBR laser 401-406 TDA-DFB laser 110, 410 Semiconductor substrate 111a-116c, 411a-416c Laser active layer 121a-126c, 421a-426c Laser control layer 131-137, 141-146, 431-537, 441-446 Electrodes 141-146, 181-186, 441-446, 481-486 Amplifiers 151-156, 171-176, 451-456, 471-476 DA converters 161-166, 169, 461-466 469 Waveguide 167, 467 MMI coupler 168, 468 SOA
170, 470 control device

Claims (8)

Controls the wavelength of a wavelength tunable laser array that includes 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 variably controls the output wavelength of the plurality of wavelength tunable lasers A way to
During the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers, heat 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. Then, thermal compensation when changing the wavelength within the variable wavelength range of the first tunable laser is performed on the control layer of the second tunable laser adjacent to the control layer of the first tunable laser. And applying a current having a value for the same to the control layers of the wavelength tunable lasers other than the first and second wavelength tunable lasers, respectively. A method of controlling the wavelength. Controls the wavelength of a wavelength tunable laser array that includes 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 variably controls the output wavelength of the plurality of wavelength tunable lasers A way to
During the operation of the first wavelength tunable laser among the plurality of wavelength tunable lasers, heat 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. Then, thermal compensation when changing the wavelength within the variable wavelength range of the first tunable laser is performed on the control layer of the second tunable laser adjacent to the control layer of the first tunable laser. Current is applied to the control layer of the wavelength tunable laser other than the first and second wavelength tunable lasers, and the value increases as the distance from the first and second wavelength tunable lasers increases. A method for controlling the wavelength of the wavelength tunable laser array, comprising: applying a selected current.   The wavelength is changed within the range of the oscillation wavelength of the first wavelength tunable laser, and the current applied to the control layer of the first wavelength tunable laser and the control layer of the second wavelength tunable laser are applied. The total value of the current applied to the control electrode of the first tunable laser and the current applied to the control electrode of the second tunable laser is changed before and after the wavelength change. The method for controlling the wavelength of the wavelength tunable laser array according to claim 1, further comprising making the same value.   Switching the oscillation from the first wavelength tunable laser to the third wavelength tunable laser, wherein the third wavelength tunable laser has a control layer of a fourth wavelength tunable laser adjacent to the control layer of the third wavelength tunable laser; A current having a value for performing thermal compensation when changing the wavelength within the variable wavelength range of the tunable laser, and a current applied to the control electrode of the third tunable laser and the fourth wavelength The total value of the current applied to the control electrode of the tunable laser is applied to the control electrode of the first tunable laser and the control electrode of the second tunable laser before the oscillation is switched. And the same value as the sum of the currents to be applied, and applying equal currents to the control layers of the wavelength tunable lasers other than the third and fourth wavelength tunable lasers. Claim 1 or Method of controlling the wavelength of the tunable laser array according to.   Switching the oscillation from the first wavelength tunable laser to the third wavelength tunable laser, wherein the third wavelength tunable laser has a control layer of a fourth wavelength tunable laser adjacent to the control layer of the third wavelength tunable laser; A current having a value for performing thermal compensation when changing the wavelength within the variable wavelength range of the tunable laser, and a current applied to the control electrode of the third tunable laser and the fourth wavelength The total value of the current applied to the control electrode of the tunable laser is applied to the control electrode of the first tunable laser and the control electrode of the second tunable laser before the oscillation is switched. The control layer of the wavelength tunable laser other than the third and fourth wavelength tunable lasers has a distance from the third and fourth wavelength tunable lasers so as to be the same value as the total value with the current to be transmitted. The value increases as you move away Method of controlling the wavelength of the tunable laser array according to claim 1 or 2, characterized in that it comprises applying a Kushida current.   The value of the current applied to the control layer of the first wavelength tunable laser is a value reduced by a calibration value for reducing the wavelength variation caused as a result of an increase in the chip temperature of the wavelength tunable laser array due to the thermal compensation. The calibration value is calculated from the relationship between the injection control current of the semiconductor laser and the oscillation wavelength obtained in advance when the thermal compensation is performed and when the thermal compensation is not performed, and the control of the second wavelength tunable laser. 6. The method for controlling the wavelength of a wavelength tunable laser array according to claim 5, wherein a current value applied to the layer is a value increased by the calibration value.   7. The method for controlling the wavelength of a wavelength tunable laser array according to claim 1, wherein the wavelength tunable laser is a DBR laser.   The method for controlling the wavelength of the wavelength tunable laser array according to claim 1, wherein the wavelength tunable laser is a TAD-DFB laser.