JP2011258703A - Control method of wavelength variable laser element and wavelength variable laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of a wavelength variable laser element and a wavelength variable laser device wherein power consumption can be reduced.SOLUTION: The control method of the wavelength variable laser element including a plurality of semiconductor laser elements which can change the laser oscillation wavelength by temperature adjustment and a semiconductor optical amplifier which amplifies laser beams inputted from the plurality of semiconductor laser elements, includes: an adjustment step of selecting the semiconductor laser element to be driven from the plurality of semiconductor laser elements in accordance with the wavelength of the laser beam to be outputted and adjusting the temperature of the selected semiconductor laser element to a prescribed temperature; and a current supply step of supplying a driving current of a current value corresponding to the prescribed temperature to the selected semiconductor laser element.

Description

  The present invention relates to a wavelength tunable laser element control method and a wavelength tunable laser apparatus.

  Conventionally, as an example of a wavelength tunable light source for DWDM (Dense Wavelength Division Multiplexing) optical communication, an integrated wavelength tunable laser element has been disclosed (see, for example, Patent Documents 1 and 2 and Non-Patent Documents 1 to 3). The tunable laser element disclosed in Patent Document 1 is a combination of a plurality of distributed feedback (DFB) semiconductor laser elements having different laser oscillation wavelengths and a multimode interference (MMI) optical coupling. And a semiconductor optical amplifier (SOA) integrated on a single substrate.

  This wavelength tunable laser element drives one DFB laser element selected from a plurality of DFB laser elements, and couples the laser beam output from the DFB laser element to a semiconductor optical amplifier with an optical combiner, thereby obtaining a desired light intensity. It is configured to amplify and output. Here, the laser oscillation wavelength of each DFB laser element can be changed by, for example, about 3 nm to 4 nm by adjusting the temperature of the DFB laser element. In addition, the wavelength interval of the laser oscillation wavelength of each DFB laser element is set to an interval that is changed by this temperature adjustment. Therefore, this wavelength tunable laser can output laser light having a desired wavelength in a continuous and wide wavelength range by selecting the DFB laser element to be driven and adjusting the temperature of the DFB laser to be driven.

JP 2005-317695 A JP 2008-103766 A

M. Bouda et al., Proc., OFC 2000, TuL1, 178. H. Oohashi et al., Tech. Dig., IPRM '2001, Nara, FBI-2, 575. K. Kudo et al., IEEE Phohtonics Technology Letters, 12 (2000), 242.

  By the way, with an increase in the wavelength tunable laser elements used in the DWDM optical communication system, a wavelength tunable laser element with lower power consumption is required in order to reduce power consumption in the entire system.

  The present invention has been made in view of the above, and an object thereof is to provide a wavelength tunable laser element control method and a wavelength tunable laser apparatus that can reduce power consumption.

  In order to solve the above-described problems and achieve the object, a method of controlling a wavelength tunable laser device according to the present invention includes a plurality of semiconductor laser devices capable of changing a laser oscillation wavelength by temperature adjustment, and the plurality of semiconductors. A method of controlling a wavelength tunable laser element comprising a semiconductor optical amplifier for amplifying laser light input from a laser element, wherein the semiconductor is driven from the plurality of semiconductor laser elements according to the wavelength of the laser light to be output An adjustment step of selecting a laser element and adjusting the selected semiconductor laser element to a predetermined temperature; and a current supply step of supplying a driving current having a current value corresponding to the predetermined temperature to the selected semiconductor laser element; , Including.

  The wavelength tunable laser device control method according to the present invention is the above invention, wherein, in the current supply step, the optical output intensity of the semiconductor optical amplifier is saturated with respect to the drive current of the selected semiconductor laser device. And the drive current supplied to the selected semiconductor laser element is controlled so as to be within a predetermined intensity range from the saturation light output intensity.

  In addition, a wavelength tunable laser device according to the present invention includes a plurality of semiconductor laser elements capable of changing a laser oscillation wavelength by temperature adjustment, and a semiconductor optical amplifier that amplifies laser light input from the plurality of semiconductor laser elements, The semiconductor laser element selected from the plurality of semiconductor laser elements is adjusted to a predetermined temperature according to the wavelength of the laser beam to be output, and the selected semiconductor laser element is driven with a current value corresponding to the predetermined temperature. And a control device for supplying current.

  Further, in the wavelength tunable laser device according to the present invention, in the above invention, the control device has a light output intensity of the semiconductor optical amplifier having a saturation characteristic with respect to a driving current of the selected semiconductor laser element, In addition, the drive current of the selected semiconductor laser element is controlled so as to be within a predetermined intensity range from the saturated light output intensity.

  According to the present invention, it is possible to realize a wavelength tunable laser element control method and a wavelength tunable laser apparatus that can reduce power consumption.

FIG. 1 is a schematic configuration diagram of a wavelength tunable laser device according to an embodiment. FIG. 2 is a schematic configuration diagram of the wavelength tunable laser element shown in FIG. FIG. 3 is a diagram for explaining the relationship between the drive current of the DFB laser element and the optical output intensity of the semiconductor optical amplifier. FIG. 4 is a diagram for explaining the setting of the drive current of the DFB laser element. FIG. 5 is a diagram illustrating an example of setting of wavelengths, temperatures, and drive currents of two DFB laser elements. FIG. 6 is a diagram showing the relationship among the wavelengths of the two DFB laser elements shown in FIG. 5, temperature, and driving current. FIG. 7 is a diagram illustrating power consumption of the wavelength tunable laser devices of the example and the comparative example.

  Embodiments of a wavelength tunable laser element control method and a wavelength tunable laser apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
FIG. 1 is a schematic configuration diagram of a wavelength tunable laser device according to an embodiment of the present invention. As shown in FIG. 1, the wavelength tunable laser device 100 includes a Peltier element 2 housed in a casing 1, a Peltier element 3 placed on the Peltier element 2, and a submount 4 on the Peltier element 3. The tunable laser element 5 and the thermistor 6 placed therethrough, the collimator lens 7 placed on the Peltier element 3, the beam splitter 8, the photodiode 9 and the etalon filter 10 placed on the Peltier element 2. And a photodiode 11, an optical isolator 12 accommodated in a protruding portion of the housing 1, a condenser lens 13, an optical fiber 14, and a control device 15.

  The wavelength tunable laser element 5 outputs laser light L having a predetermined wavelength. The thermistor 6 is disposed in the vicinity of the wavelength tunable laser element 5 and is used to monitor the temperature of the wavelength tunable laser element 5. The collimator lens 7 converts the laser light L output from the wavelength tunable laser element 5 into parallel light. The beam splitter 8 reflects a part of the light as reflected light RL while transmitting most of the laser light L (for example, 90% or more). The photodiode 9 is disposed so as to block a part of the optical path of the reflected light RL, receives a part of the reflected light RL, and outputs a current corresponding to the amount of received light. The etalon filter 10 has a transmission wavelength characteristic that periodically changes with respect to the wavelength, and transmits the reflected light RL that is not blocked by the photodiode 9 with a transmittance according to the wavelength. The photodiode 11 receives the reflected light RL transmitted through the etalon filter 10 and outputs a current corresponding to the amount of light received. The photodiode 9 is used for monitoring the intensity of the laser light L. The etalon filter 10 and the photodiode 11 are used to monitor the wavelength of the laser light L.

  The optical isolator 12 blocks the light returning from the optical fiber 14 side to the wavelength tunable laser element 5 while transmitting the laser light L that has passed through the beam splitter 8. The condenser lens 13 couples the laser light L transmitted through the optical isolator 12 to the optical fiber 14.

  The Peltier element 2 is used to cool the wavelength tunable laser element 5 and adjust the temperature of the etalon filter 10. The Peltier element 3 is used for temperature adjustment of the wavelength tunable laser element 5. The control device 15 measures the electrical resistance value of the thermistor 6, receives current from the photodiodes 9 and 11, and supplies drive current to the Peltier elements 2 and 3 and the wavelength tunable laser element 5.

  Next, the wavelength variable laser element 5 will be specifically described. FIG. 2 is a schematic configuration diagram of the wavelength tunable laser element 5 shown in FIG. As shown in FIG. 2, the wavelength tunable laser element 5 includes a plurality of DFB laser elements 51 integrated on the same substrate, a plurality of optical waveguides 52 connected to the plurality of DFB laser elements 51, and a plurality of optical waveguides 52. For example, an MMI type optical combiner 53, an optical waveguide 54 connected to the optical combiner 53, a semiconductor optical amplifier 55 connected to the optical waveguide 54, and a bent waveguide 56 connected to the semiconductor optical amplifier 55. And. The control device 15 supplies a drive current to each of the plurality of DFB laser elements 51 and the semiconductor optical amplifier 55.

  The plurality of DFB laser elements 51 are composed of, for example, 12 DFB laser elements 51a. Each DFB laser element 51a has different laser oscillation wavelengths at the same temperature, but the laser oscillation wavelength can be changed by adjusting the temperature.

  Specifically, each DFB laser element 51a can change the laser oscillation wavelength within a range of about 3 nm to 4 nm, for example. Further, the laser oscillation wavelengths of the respective DFB laser elements 51a are designed to be arranged at intervals of about 3 nm to 4 nm at the same temperature. Thereby, the wavelength tunable laser element 5 can realize a wide wavelength tunable range from 1526 nm to 1563 nm, for example, when there are 12 DFB laser elements 51a.

  Next, the operation of the wavelength tunable laser device 100 and the method of controlling the wavelength tunable laser element 5 according to the present embodiment will be described with reference to FIGS.

  First, the DFB laser element 51a to be driven is selected from the plurality of DFB laser elements 51 according to the wavelength and light intensity of the laser light L to be output, the temperature and drive current of the selected DFB laser element 51a, and the semiconductor The drive current of the optical amplifier 55 is determined. This selection and determination is executed based on, for example, a table indicating the relationship between the temperature and drive current of each DFB laser element 51a and semiconductor optical amplifier 55 stored in the control device 15 based on an external command. be able to.

  Next, the control device 15 supplies the drive current to the Peltier elements 2 and 3 based on the determined temperature and drive current of the DFB laser element 51a and the drive current of the semiconductor optical amplifier 55, and selects the selected DFB laser element 51a. While adjusting the temperature, a drive current is supplied to the selected DFB laser element 51 a and the semiconductor optical amplifier 55. The DFB laser element 51a supplied with the drive current outputs laser light L having a desired wavelength.

  Of the plurality of optical waveguides 52, the optical waveguide connected to the selected DFB laser element 51 a guides the laser light L to the optical combiner 53. The optical combiner 53 guides the laser light L to the semiconductor optical amplifier 55 via the optical waveguide 54. The semiconductor optical amplifier 55 amplifies the input laser light L and outputs it to the bending waveguide 56. The bending waveguide 56 outputs the amplified laser beam L with an inclination of about 7 degrees with respect to the emission end face. In addition, it is desirable to adjust the inclination angle of the laser light L with respect to the emission end face in a range of 6 to 12 degrees. Thereby, the quantity of the light which returns to the several DFB laser element 51 side by the reflection in the output end surface among the laser beams L can be reduced.

  The laser light L output from the wavelength tunable laser element 5 sequentially passes through the collimator lens 7, the beam splitter 8, the optical isolator 12, and the condenser lens 13, is coupled to the optical fiber 14, and is output to the outside of the wavelength tunable laser device 100. Is done.

  Note that the control device 15 uses the temperature of the tunable laser element 5 monitored by the thermistor 6 and the light intensity and wavelength of the laser light L monitored by the photodiodes 9, 11 and the etalon filter 10. By adjusting the drive currents of the selected DFB laser element 51a and the semiconductor optical amplifier 55, feedback control is performed so that the light intensity and wavelength of the laser light L become constant.

  Here, in the conventional wavelength tunable laser device, a constant driving current is supplied to the selected DFB laser element regardless of its temperature. On the other hand, in the wavelength tunable laser device 100 according to the present embodiment, the control device 15 supplies a drive current having a current value corresponding to the temperature to the selected DFB laser element 51a. As a result, the wavelength tunable laser device 100 consumes less power than the conventional wavelength tunable laser device.

  This will be specifically described below. FIG. 3 is a diagram for explaining the relationship between the driving current of the DFB laser element and the optical output intensity of the semiconductor optical amplifier. FIG. 3A shows the case where the temperature of the DFB laser element 51a is 10 ° C. 3 (b) shows the case where the temperature of the DFB laser element 51a is 50.degree. Note that the drive current of the semiconductor optical amplifier 55 is constant.

  As shown in FIGS. 3A and 3B, as the drive current of the DFB laser element 51a increases, the intensity of the laser beam output from the DFB laser element 51a and input to the semiconductor optical amplifier 55 increases. The light output intensity of the semiconductor optical amplifier 55 also increases. Here, the semiconductor optical amplifier 55 has a gain saturation characteristic with respect to the input light intensity. Therefore, the light output intensity of the semiconductor optical amplifier 55 also has a saturation characteristic with respect to the drive current of the DFB laser element 51a, as shown by the curves in FIGS. Note that having the saturation characteristic means that the light output intensity of the semiconductor optical amplifier 55 is not proportional to the drive current of the DFB laser element 51a, and the light output intensity is saturated.

  However, since the DFB laser element 51a has higher luminous efficiency when the temperature is lower, the light intensity of the laser beam output is higher when the temperature is lower even if the drive current is the same. Therefore, in FIGS. 3A and 3B, as can be seen from the fact that the light output intensity starts to saturate when the temperature is 10 ° C. at a current value smaller than that at 50 ° C., the DFB laser element. As the temperature of 51a is lower, the saturation characteristic of the optical output intensity of the semiconductor optical amplifier 55 becomes more prominent.

  Here, in FIGS. 3A and 3B, when the temperature of the DFB laser element 51a is 10 ° C., the saturation light output intensity of the semiconductor optical amplifier 55 is Pm1, and the DFB laser when the light output intensity is approximately Pm1. The drive current of the element 51a is Im1, and the light output intensity lower by 2 dB than Pm1 is Ps1, and the drive current of the DFB laser element 51a at that time is Is1. Similarly, the saturation light output intensity of the semiconductor optical amplifier 55 when the temperature of the DFB laser element is 50 ° C. is Pm2, and the driving current of the DFB laser element 51a when the light output intensity is approximately Pm2 is 2 dB from Im2 and Pm2. Assuming that the light output intensity is as low as Ps2, the drive current of the DFB laser element 51a at that time is Is2. As described above, since the light output intensity of the semiconductor optical amplifier 55 starts to saturate at a lower current value when the temperature of the DFB laser element 51a is lower, Im1 <Im2 and Is1 <Is2.

  As described above, in the conventional wavelength tunable laser device, the selected DFB laser element has a constant drive current regardless of its temperature, for example, from Is1 and Is2 as shown in FIGS. Ild2, which is a large current, was supplied.

  On the other hand, in the wavelength tunable laser device 100 according to the present embodiment, a drive current having a current value corresponding to the temperature is supplied to the selected DFB laser element 51a. Specifically, when the temperature of the selected DFB laser element 51a is 50 ° C., the drive current Ild2 is supplied. However, when the temperature is 10 ° C., the drive current Ild1 smaller than Ild2 and larger than Is1 is supplied. .

  As described above, the saturation characteristic is more remarkable when the temperature of the DFB laser element 51a is lower. Therefore, when the temperature of the DFB laser element 51a is low, the light output intensity of the semiconductor optical amplifier 55 is reduced even if the drive current is reduced. The amount of decrease is smaller. In the wavelength tunable laser device 100 according to the present embodiment, by using this characteristic, when the temperature of the DFB laser element 51a is low, the drive current supplied to the DFB laser element 51a is controlled to be small. The extra power consumption of the DFB laser element 51a is reduced to reduce the power consumption. As a result, the power consumption of the entire wavelength tunable laser device 100 is reduced.

  The setting of the drive current of the DFB laser element 51a will be described more specifically. FIG. 4 is a diagram for explaining setting of the drive current of the DFB laser element. As shown in FIG. 4, when the optical output intensity of the semiconductor optical amplifier 55 is P, P is a parameter of the temperature Tld of the DFB laser element 51a, the drive current Isoa of the semiconductor optical amplifier 55, and the drive current Ild of the DFB laser element 51a. As P = f (Tld, Isoa, Ild).

  In FIG. 4, the saturation optical output intensity of the semiconductor optical amplifier 55 is Pm, the driving current of the DFB laser element when the optical output intensity is approximately Pm, Imax, the optical output intensity lower by α [dB] than Pm, Ps, If the drive current of the DFB laser element 51a at that time is Imin, the range of Imin to Imax, which is the drive current corresponding to the light output intensity in the range of Pm to Ps, is within the appropriate drive current range of the DFB laser element 51a. is there.

  Note that P = f (Tld, Isoa, Ild) is obtained by measuring the light output intensity of the semiconductor optical amplifier 55 while changing Ild, with Tld, Isoa being constant, and having the saturation characteristic shown in FIG. It can be determined by obtaining the curve. Then, for each DFB laser element 51a, P = f (Tld, Isoa, Ild) is obtained for various values of Tld and Isoa, and Imin and Imax are obtained using this. As a result, an appropriate drive current range according to the use conditions can be obtained.

  The value of α [dB] is 2 dB in the present embodiment, but is not particularly limited as long as the semiconductor optical amplifier 55 has a saturation characteristic, and may be 3 dB, for example.

  Next, the setting of temperature and drive current will be described more specifically. FIG. 5 is a diagram illustrating an example of setting of wavelengths, temperatures Tld, and drive currents Ild of two DFB laser elements. FIG. 6 is a diagram showing the relationship between the wavelengths of the two DFB laser elements shown in FIG. 5, the temperature Tld, and the drive current Ild. 5 and 6 show DFB1 and DFB2, which are two DFB laser elements having adjacent laser oscillation wavelengths.

  In the example shown in FIGS. 5 and 6, the DFB 1 can change its laser oscillation wavelength from 1526.05 nm to 1529.553 nm by changing the temperature Tld from 11.77 ° C. to 46.38 ° C. Further, the DFB2 can change the laser oscillation wavelength from 1529.944 nm to 15333.073 nm by changing the temperature Tld from 15.56 ° C. to 46.57 ° C. Therefore, by using these two DFB1 and DFB2, the wavelength tunable range of the wavelength tunable laser element can be continuously changed from 1526.05 nm to 15333.073 nm.

  In the examples shown in FIGS. 5 and 6, the driving current Ild of DFB1 and DFB2 is set so that the optical output intensity of the semiconductor optical amplifier is lower by −2 dB than the saturated optical output intensity determined by the driving current Isoa. is doing. Further, the drive current Ild is set according to the temperature Tld of the DFB1 and DFB2, and specifically, when the temperature Tld is low, the drive current Ild is set small. As a result, excessive power consumption of the DFB laser element can be reduced, and a tunable laser device with low power consumption can be realized.

(Examples and comparative examples)
As an example of the present invention, 20 samples of a wavelength tunable laser apparatus having the same configuration as the embodiment shown in FIGS. 1 and 2 and having 12 DFB laser elements and having a wavelength tunable range from 1526 nm to 1563 nm Prepared. Then, under an external temperature of 75 ° C., the light output intensity of the laser light output from the wavelength tunable laser device is set to 20 mW, the laser light wavelength is changed from 1526 nm to 1563 nm, and the current consumption during operation is set. Was measured. In order to change the wavelength of the laser light from 1526 nm to 1563 nm, the DFB laser element to be operated was switched and the temperature was adjusted in the range of 10 ° C. to 50 ° C. The driving current of the DFB laser element is 100 mA to 200 mA so that the optical output intensity of the semiconductor amplifier at the adjusted temperature is -2 dB lower than the saturated optical output intensity according to the control method of the embodiment. Adjusted by range.

  On the other hand, as a comparative example, the 20 wavelength tunable laser apparatuses used in the example were subjected to an optical output intensity of 20 mW of laser light output from the wavelength tunable laser apparatus at an external temperature of 75 ° C., as in the example. The operation was performed by changing the wavelength of the laser beam from 1526 nm to 1563 nm, and the current consumption during operation was measured. However, unlike the example, the driving current of the DFB laser element was supplied at a constant 150 mA regardless of the temperature when any DFB laser element was operated.

  FIG. 7 is a diagram illustrating power consumption of the wavelength tunable laser devices of the example and the comparative example. FIG. 7 shows the average worst value when the wavelength of the laser light is changed from 1526 nm to 1563 nm. As shown in FIG. 7, in all the samples, power consumption of about 0.5 W lower than that in the comparative example was realized in the example.

  In the above embodiment, a DFB laser element is used as the semiconductor laser element. However, a distributed Bragg reflector (DBR) semiconductor laser element may be used. The number of semiconductor laser elements is not particularly limited, and can be set as appropriate according to the wavelength variable range desired to be realized in the wavelength tunable laser apparatus and the wavelength variable range of the semiconductor laser element that can be realized by temperature adjustment.

DESCRIPTION OF SYMBOLS 1 Case 2, 3 Peltier element 4 Submount 5 Wavelength variable laser element 6 Thermistor 7 Collimator lens 8 Beam splitter 9, 11 Photodiode 10 Etalon filter 12 Optical isolator 13 Condensing lens 14 Optical fiber 15 Control apparatus 51 Several DFB laser Element 51a DFB laser element 52, 54 Optical waveguide 53 Optical combiner 55 Semiconductor optical amplifier 56 Bending waveguide 100 Tunable laser device L Laser light

Claims (4)

A control method for a wavelength tunable laser element, comprising: a plurality of semiconductor laser elements capable of changing a laser oscillation wavelength by temperature adjustment; and a semiconductor optical amplifier that amplifies laser light input from the plurality of semiconductor laser elements. ,
An adjustment step of selecting a semiconductor laser element to be driven from the plurality of semiconductor laser elements according to the wavelength of the laser light to be output and adjusting the selected semiconductor laser element to a predetermined temperature;
A current supplying step of supplying a driving current having a current value corresponding to the predetermined temperature to the selected semiconductor laser element;
A method for controlling a wavelength tunable laser device, comprising:   In the current supply step, the optical output intensity of the semiconductor optical amplifier has a saturation characteristic with respect to the driving current of the selected semiconductor laser element, and is within a predetermined intensity range from the saturated optical output intensity. 2. The method of controlling a wavelength tunable laser element according to claim 1, wherein a drive current supplied to the selected semiconductor laser element is controlled. A plurality of semiconductor laser elements capable of changing the laser oscillation wavelength by adjusting the temperature;
A semiconductor optical amplifier for amplifying laser light input from the plurality of semiconductor laser elements;
A semiconductor laser element selected from the plurality of semiconductor laser elements is adjusted to a predetermined temperature according to the wavelength of the laser beam to be output, and a driving current having a current value corresponding to the predetermined temperature is applied to the selected semiconductor laser element. A control device for supplying,
A wavelength tunable laser device comprising:   The control device has a saturation characteristic with respect to the drive current of the selected semiconductor laser element, and the optical output intensity of the semiconductor optical amplifier is within a predetermined intensity range from the saturated light output intensity. 4. The wavelength tunable laser device according to claim 3, wherein a drive current of the selected semiconductor laser element is controlled.

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