Laser device and control method therefor

Abstract

To shorten the frequency switching time of laser oscillation.SOLUTION: A laser device comprises: a laser light source unit having a first heater for heating a first frequency filter and a second heater for heating a second frequency filter, wherein the frequency of laser oscillation varies according to a vernier effect due to the first frequency filter and the second frequency filter; a temperature regulator; a temperature sensor; and a control unit. The control unit includes a power control unit that supplies power to each of the first and second heaters, and a temperature control unit that controls the temperature of the laser light source unit within a predetermined range on the basis of the temperature detected by the temperature sensor. The control unit acquires a target frequency of laser oscillation. The power control unit supplies correction power to each of the first and second heaters on the basis of: an initial setting value of an electrical characteristic of power set for each of the first and second heaters according to the target frequency, and a correction value determined for each of the first and second heaters on the basis of the temperature detected by the temperature sensor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laser device and a control method thereof. [Background technology]

[0002] In a laser device, a technique is known in which a frequency filter having a periodic response characteristic (transmission characteristic or reflection characteristic) with respect to the frequency of input light is used to change the frequency of laser oscillation according to the Vernier effect (see, for example, Patent Document 1). In Patent Document 1, the frequency filter is a sampled grating distributed reflectance region (SG-DR region), and laser oscillation occurs at a frequency where the reflection peaks of two SG-DR regions overlap. When changing the frequency of laser oscillation, the reflection peak wavelength (frequency) of the SG-DR region is changed by heating with a heater to change the temperature of the SG-DR region. This changes the frequency where the reflection peaks of the two SG-DR regions overlap, and laser oscillation occurs at the changed frequency. Such an overlap state of two frequency filters may be called a super mode. In addition, hereinafter, changing the frequency may be described as switching the frequency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5303581 Summary of the Invention [Problem to be solved by the invention]

[0004] Most of the heat emitted from the heater to heat the frequency filter is used to locally change the temperature of the frequency filter, and the thermal response of the frequency filter is completed in a time of several tens of μs. However, some of the heat emitted from the heater may also be used to change the temperature of the base on which the frequency filter is placed. In such a case, it may take several hundreds of ms or more until the thermal response of the base is completed. Therefore, even after the intended change in the response characteristics of the frequency filter is completed in several tens of μs by the heating of the heater, the temperature of the frequency filter may continue to change slowly for several hundreds of ms. As a result, the frequency of the super mode also continues to change slowly and is not stable. In such a state where the frequency of the super mode is not stable, it is difficult to start the constant frequency control that controls the laser oscillation frequency after the change to a constant frequency, or the SMSR (side mode suppression ratio) of the output laser light is deteriorated. Therefore, in the known technology, when switching the frequency of laser oscillation, it is necessary to wait until the temperature of the base is sufficiently stable and the frequency of the super mode is stabilized before starting the constant frequency control, which is a factor that limits the frequency switching time.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide a laser device capable of shortening the time required for switching the frequency of laser oscillation and a control method thereof. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention provides a laser light source unit having a first response characteristic in which a transmittance or a reflectance changes with respect to the frequency of input light, a first heater for heating the first frequency filter to change the first response characteristic, a second frequency filter having a second response characteristic in which a transmittance or a reflectance changes with respect to the frequency of input light and which is different from the first response characteristic, and a second heater for heating the second frequency filter to change the second response characteristic, the laser light source unit having a frequency of laser oscillation that changes in accordance with the Vernier effect of the first frequency filter and the second frequency filter, a temperature regulator thermally connected to the laser light source unit, and a temperature regulator provided in the laser light source unit or in the vicinity of the laser light source unit. and a control unit having a temperature sensor mounted on the heater, a power control unit that supplies power to each of the first heater and the second heater, and a temperature control unit that controls the temperature of the laser light source unit within a certain range by supplying a control amount to the temperature regulator in accordance with the temperature detected by the temperature sensor, wherein the control unit obtains a target frequency of the laser oscillation, and the power control unit supplies, to each of the first heater and the second heater, a correction power that is in accordance with an initial setting value of the electrical characteristics of the power that is set for each of the first heater and the second heater in accordance with the target frequency and a correction value for the initial setting value that is determined for each of the first heater and the second heater based on the temperature detected by the temperature sensor.

[0007] The control unit may determine the correction value based on correction coefficients set for the first heater and the second heater, respectively, and the temperature detected by the temperature sensor.

[0008] The control unit may determine the correction value based on the target frequency, a correction coefficient set for each frequency of the first heater and the second heater, and a temperature detected by the temperature sensor.

[0009] The initial set value and the correction value may be power values.

[0010] The initial set value and the correction value may be a current value or a voltage value.

[0011] If the control unit determines that a predetermined convergence condition is satisfied after changing the frequency of laser oscillation in the laser light source unit in accordance with the target frequency, it may terminate the supply of power in accordance with the initial setting value and the correction value.

[0012] The predetermined convergence condition may be that a difference between the temperature detected by the temperature sensor and a reference temperature is equal to or smaller than a predetermined value.

[0013] The predetermined convergence condition may be that the change over time in the temperature detected by the temperature sensor is equal to or smaller than a predetermined value.

[0014] One aspect of the present invention is a laser light source unit having a first response characteristic in which a transmittance or a reflectance changes with respect to the frequency of input light, a first heater for heating the first frequency filter to change the first response characteristic, a second frequency filter having a second response characteristic in which a transmittance or a reflectance changes with respect to the frequency of input light, the second response characteristic being different from the first response characteristic, and a second heater for heating the second frequency filter to change the second response characteristic, the laser light source unit having a laser light source unit having a frequency of laser oscillation that changes in accordance with the Vernier effect of the first frequency filter and the second frequency filter, a temperature regulator thermally connected to the laser light source unit, and a temperature regulator provided in the laser light source unit or in the vicinity of the laser light source unit. and a temperature control unit that controls the temperature of the laser light source unit within a certain range by supplying a control amount to the temperature regulator in accordance with the temperature detected by the temperature sensor, the control method for a laser device comprising the steps of: acquiring a target frequency of the laser oscillation; acquiring the temperature detected by the temperature sensor; and supplying to each of the first heater and the second heater a correction power that corresponds to an initial setting value of the electrical characteristics of power set for each of the first heater and the second heater in accordance with the target frequency and a correction value for the initial setting value determined for each of the first heater and the second heater based on the acquired temperature. Effect of the Invention

[0015] According to the present invention, it is possible to reduce the time required for switching the frequency of laser oscillation. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a configuration of a laser device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating the laser oscillation frequency. [Diagram 3] FIG. 3 is a diagram illustrating the relationship between the heater power and the laser oscillation frequency. [Figure 4]FIG. 4 is a diagram showing an example of the relationship between heater power and supermode center frequency according to a known technique. [Diagram 5] FIG. 5 is a diagram showing an example of the relationship between heater power and supermode center frequency in the laser device according to the embodiment. [Figure 6] FIG. 6 is a flowchart illustrating an example of a control method performed by the control unit in the embodiment. [Figure 7] FIG. 7 is a flowchart showing another example of the control method performed by the control unit in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment described below. Furthermore, in the description of the drawings, the same parts are appropriately given the same reference numerals, and duplicated explanations are appropriately omitted. Moreover, the drawings are schematic, and the dimensional relationship of each element, the ratio of each element, and the like may differ from reality. Furthermore, between the drawings, there may be parts with mutually different dimensional relationships and ratios.

[0018] (Embodiment 1) 1 is a diagram showing the configuration of a laser device according to embodiment 1. The laser device 100 includes a laser light source unit 10, a control unit 20 that controls the operation of the laser light source unit 10, a temperature sensor 30, a frequency monitor unit 40, and a base unit 50.

[0019] [Laser light source configuration] The laser light source unit 10 is configured to output laser light L1 under the control of a control unit 20 described later. The laser light source unit 10 is a so-called variable wavelength light source, and the wavelength (frequency) of the laser light L1 is variable. The laser light L1 has a wavelength in a communication band such as the 1550 nm band. The wavelength of 1550 nm is equivalent to a frequency of approximately 193.4 THz.

[0020] The laser light source section 10 includes a first frequency filter 11, a phase section 12, a gain section 13, a second frequency filter 14, a semiconductor optical amplifier (SOA) 15, a first heater 11a, a second heater 14a, a third heater 12a, a first electrode 13a, and a second electrode 15a. The first frequency filter 11, the phase section 12, the gain section 13, the second frequency filter 14, and the SOA 15 have an optical waveguide structure monolithically integrated on a single common substrate, and are optically connected. The laser light source section 10 is, for example, a semiconductor laser element.

[0021] The first frequency filter 11 has a first response characteristic in which the transmittance or reflectance changes with the frequency of the input light. For example, the first frequency filter 11 has a comb-shaped reflection spectrum (one example of the first response characteristic) having a reflectance peak (reflection peak) that is periodic in frequency. The first frequency filter 11 has, for example, an SG-DR structure, a distributed feedback (DFB) mirror structure, or a ring resonator mirror structure.

[0022] The phase section 12 is optically connected to the first frequency filter 11. The phase section 12 is a passive optical waveguide element that transmits and outputs input light.

[0023] The gain section 13 is optically connected to the phase section 12. The gain section 13 is an active optical waveguide element that emits light including light having the frequency of the laser light L1 when power is supplied thereto and optically amplifies the light having the emitted frequency.

[0024] The second frequency filter 14 is optically connected to the gain section 13. The second frequency filter 14 has a second response characteristic whose transmittance or reflectance changes with respect to the frequency of the input light and is different from the first response characteristic. For example, the second frequency filter 14 has a comb-shaped reflection spectrum (an example of the second response characteristic) having frequency-periodic reflectance peaks (reflection peaks). However, the period of the reflection peaks of the second frequency filter 14 is different from the period of the first frequency filter. The second frequency filter 14 has, for example, an SG-DR structure, a distributed feedback mirror structure, or a ring resonator mirror structure.

[0025] The first frequency filter 11 and the second frequency filter sandwich the phase section 12 and the gain section 13 to form a laser resonator.

[0026] The SOA 15 is optically connected to the second frequency filter 14. The SOA 15 is an active optical waveguide element that amplifies light having the frequency of the laser light L1 when power is supplied to the SOA 15. The laser light L1 is output from the SOA 15 side.

[0027] The first heater 11a is provided so as to be thermally connected to the first frequency filter 11, and in this embodiment, is provided directly above the first frequency filter 11, on the side of the first frequency filter 11 opposite to the common substrate. When power is supplied to the first heater 11a, the first heater 11a locally heats the first frequency filter 11 to change the temperature of the first frequency filter 11, thereby changing the reflection spectrum of the first frequency filter 11.

[0028] The second heater 14a is provided so as to be thermally connected to the second frequency filter 14, and in this embodiment, is provided directly above the second frequency filter 14. When power is supplied to the second heater 14a, the second heater 14a locally heats the second frequency filter 14 to change the temperature of the second frequency filter 14, thereby changing the reflection spectrum of the second frequency filter 14.

[0029] The third heater 12a is provided so as to be thermally connected to the phase section 12, and in this embodiment, is provided directly above the phase section 12. When power is supplied to the third heater 12a, the third heater 12a locally heats the phase section 12 to change the temperature of the phase section 12, thereby changing the optical path length of the optical waveguide through which light propagates in the phase section 12. This changes the optical path length of the laser resonator.

[0030] The first heater 11a, the second heater 14a, and the third heater 12a are micro-heaters made of a metal such as titanium, but are not particularly limited thereto.

[0031] The first electrode 13a is provided so as to be in electrical contact with the gain section 13. The first electrode 13a is used to supply power to the gain section 13.

[0032] The second electrode 15a is provided so as to be in electrical contact with the SOA 15. The second electrode 15a is used to supply power to the SOA 15.

[0033] The first electrode 13a and the second electrode 15a are made of a metal material that makes ohmic contact with the semiconductor on which they are provided.

[0034] [Temperature sensor, frequency monitor, and base configuration] In this embodiment, the temperature sensor 30 is provided in the laser light source unit 10. The temperature sensor 30 is composed of, for example, a thermistor, and detects the temperature of the laser light source unit 10. The temperature sensor 30 outputs an electrical signal including information on the detected temperature to the control unit 20.

[0035] The frequency monitor 40 includes an optical waveguide 41 and photodetectors (PD) 42 and 43. The optical waveguide 41 includes a branching portion 41a, a first waveguide portion 41b, a second waveguide portion 41c, and a third frequency filter 41d.

[0036] The branching unit 41a receives the laser light L2 output from the first frequency filter 11 side of the laser light source unit 10, and branches the laser light L2 into two laser lights L3 and L4. The laser light L2 is a laser light generated by laser oscillation in the laser light source unit 10, similar to the laser light L1. The laser lights L2, L3, and L4 have the same frequency as the laser light L1, and have intensities corresponding to the intensity of the laser light L1.

[0037] The first waveguide 41b guides the laser beam L3 and outputs it to the PD 42. The second waveguide 41c guides the laser beam L4. The branching section 41a, the first waveguide 41b, and the second waveguide 41c are formed of an optical waveguide element such as a planar lightwave circuit (PLC) or a spatial optical system.

[0038] The third frequency filter 41d is provided in the middle of the second waveguide 41c. The third frequency filter 41d has a characteristic that the transmittance changes periodically with respect to the frequency of the input light, and transmits the laser light L4 with a transmittance according to the frequency of the laser light L4. The laser light L4 transmitted through the third frequency filter 41d is input to the PD 43. The third frequency filter 41d can be configured with a waveguide type frequency filter such as a ring resonator filter, an etalon filter, or an MZI (Mach-Zehnder Interferometer) filter.

[0039] The PD42 receives the laser light L3 and outputs an electrical signal corresponding to the intensity of the laser light L3 to the control unit 20. The PD42 receives the laser light L4 transmitted through the third frequency filter 41d and outputs an electrical signal corresponding to the intensity of the laser light L4 to the control unit 20. The electrical signals output from the PDs 42 and 43 are used for frequency lock control by the control unit 20 (control for setting the frequency of the laser light L1 output from the laser light source unit 10 to a target frequency).

[0040] The base unit 50 is mounted with the laser light source unit 10, the temperature sensor 30, and the frequency monitor unit 40 and is thermally connected to these. The base unit 50 is provided with a temperature regulator 51 such as a Peltier element. The temperature regulator 51 heats or cools the mounted elements including the laser light source unit 10 according to the supplied power, thereby controlling the temperatures of these elements.

[0041] [Control Unit Configuration] The control unit 20 is connected to a higher-level control device (not shown) equipped with, for example, a user interface, and controls the operation of the laser light source unit 10 according to instructions from a user via the higher-level control device.

[0042] The control unit 20 includes hardware such as a processor, a memory, and peripheral devices such as an input / output interface. The processor is, for example, a central processing unit (CPU), a digital signal processor (DSP), or a graphics processing unit (GPU), and performs various arithmetic processing for the functions realized by the control unit 20. The memory includes a portion configured, for example, of a read only memory (ROM), and a portion configured, for example, of a random access memory (RAM). The ROM stores various programs and data used by the processor to perform arithmetic processing. The RAM is used to store a working space when the processor performs arithmetic processing, results of the processor's arithmetic processing, and the like. The control unit 20 may include a computer-readable recording medium. The functions of the control unit 20 are realized by the cooperation of hardware and software, for example, by the processor executing a program read from the memory. The control unit 20 may also include an FPGA (Field Programmable Gate Array).

[0043] The control unit 20 includes, as functional units, a target frequency acquisition unit 21, a power control unit 22, a temperature acquisition unit 23, a correction unit 24, a monitor frequency calculation unit 25, and a temperature control unit 26. The target frequency acquisition unit 21 acquires information on a target value (target frequency) of the laser oscillation frequency for the laser light L1 from a higher-level control device. The power control unit 22 controls the power (heater power) supplied to the first heater 11a, the second heater 14a, and the third heater 12a. The temperature acquisition unit 23 acquires the temperature detected by the temperature sensor 30. The correction unit 24 calculates and determines a correction value related to the heater power. The monitor frequency calculation unit 25 monitors the frequency of the laser light L1 based on the information acquired from the frequency monitor unit 40. The temperature control unit 26 controls the power supplied to the temperature regulator 51 of the base unit 50 so that the temperature detected by the temperature sensor 30 is within a predetermined range. That is, the temperature control unit 26 functions as a temperature control unit that controls the temperature of the laser light source unit 10 within a predetermined range by supplying power to the temperature regulator 51 according to the temperature detected by the temperature sensor 30. Here, power is an example of a controlled amount as a physical amount supplied to the temperature regulator 51, but the controlled amount may be, for example, a current. Furthermore, the predetermined range is a range that is permissible as the temperature of the laser light source unit 10, and is within, for example, a range of ±0.1% from the set temperature of the laser light source unit 10. That is, it can be said that the laser light source unit 10 is controlled to an approximately constant temperature by the temperature regulator 51. The functions of these functional units will be described in detail later.

[0044] [Laser device operation] Next, a description will be given of the operation of the laser device 100. First, a basic operation of laser oscillation in the laser light source unit 10 will be described below, and then switching of the frequency of laser oscillation due to the Vernier effect will be described.

[0045] Fig. 2 is an explanatory diagram of the laser oscillation frequency. In Fig. 2, spectra S1 and S2 are comb-shaped reflection spectra of the first frequency filter 11 and the second frequency filter 14, respectively, and the vertical axis indicates the reflectance. Spectrum S3 indicates the position of the frequency of the longitudinal mode of the laser resonator. It is assumed that the frequency of the laser light L1 is f1 in state St1 and f2 in state St2.

[0046] First, an operation for realizing the state St1 will be described. First, the temperature control unit 26 of the control unit 20 controls the temperature of the laser light source unit 10 to be within a predetermined range. In this state, the power control unit 22 of the control unit 20 supplies a predetermined power (heater power) to the first heater 11a. The first heater 11a heats the first frequency filter 11 by being supplied with power, thereby changing the temperature of the first frequency filter 11. As a result, the spectrum S1 of the first frequency filter 11 moves on the frequency axis, and the frequency of one of the reflection peaks becomes f1. Similarly, the control unit 20 supplies a predetermined heater power to the second heater 14a. The second heater 14a heats the second frequency filter 14 by being supplied with power, thereby changing the temperature of the second frequency filter 14. As a result, the spectrum S2 of the second frequency filter 14 moves on the frequency axis, and the frequency of one of the reflection peaks becomes f1. Similarly, the control unit 20 supplies a predetermined heater power to the third heater 12a. When power is supplied to the third heater 12a, the third heater 12a heats the phase section 12 to change the temperature of the phase section 12. This causes the frequency of the longitudinal mode of the laser resonator to move on the frequency axis, and the frequency of one of the longitudinal modes becomes f1. As a result, at frequency f1, one of the reflection peaks of the first frequency filter 11, one of the reflection peaks of the second frequency filter 14, and one of the longitudinal modes overlap on the frequency axis. This forms a laser resonator in which the amount of feedback is maximized at frequency f1.

[0047] On the other hand, the control unit 20 supplies power to the gain unit 13. This causes the gain unit 13 to emit light. As a result, light of frequency f1 generated in the gain unit 13 is guided through the phase unit 12 and the gain unit 13, and laser oscillation occurs due to the optical amplification effect of the gain unit 13 and the effect of the laser resonator. The control unit 20 also supplies power to the SOA 15, which causes the SOA 15 to exhibit an optical amplification effect. As a result, the laser light output from the second frequency filter 14 by the above-mentioned laser oscillation is optically amplified by the SOA 15, and is output from the laser light source unit 10 as laser light L1. In this case, f1 can be said to be the center frequency of the supermode in state St1 (supermode center frequency).

[0048] Next, the switching of the frequency of laser oscillation due to the Vernier effect will be described. For example, it is assumed that the state of the laser light source unit 10 is shifted from state St1 to state St2, and the frequency of the laser light L1 is switched from f1 to f2. For the sake of simplicity, it is assumed that the frequency f2 coincides with one of the reflection peaks of the spectrum S1 of the first frequency filter 11 and one of the longitudinal modes. In this case, the control unit 20 changes the heater power supplied to the second heater 14a by the control in the power control unit 22. The second heater 14a changes the temperature of the second frequency filter 14 by changing the power supplied. As a result, the spectrum S2 of the second frequency filter 14 moves on the frequency axis, and the frequency of one of the reflection peaks becomes f2. As a result, at the frequency f1, one of the reflection peaks of the first frequency filter 11, one of the reflection peaks of the second frequency filter 14, and one of the longitudinal modes overlap on the frequency axis. As a result, a laser resonator is formed in which the amount of feedback is maximized at the frequency f2, and laser oscillation occurs at the frequency f2. In this case, f2 can be said to be the supermode center frequency in state St2.

[0049] As described above, the laser light source unit 10 changes the frequency of laser oscillation according to the Vernier effect of the first frequency filter 11 and the second frequency filter 14. When changing the frequency of the laser light L1 from f1 to f2, for example, first, one of the reflection peaks of the spectrum S1 and one of the reflection peaks of the spectrum S2 are overlapped, and the first heater 11a and the second heater 14a are feedforward controlled so that the supermode center frequency becomes f2. Then, based on the result of monitoring by the monitor frequency calculation unit 25, the third heater 12a is feedback controlled so that one of the longitudinal modes becomes f2. Hereinafter, such control that one of the longitudinal modes becomes the predetermined frequency while the supermode center frequency is the predetermined frequency may be called steady control. However, the control method is not limited to this.

[0050] 3 is an explanatory diagram of the relationship between heater power and laser oscillation frequency. The horizontal axis indicates the first heater power and the vertical axis indicates the second heater power supplied to the first heater 11a and the second heater 14a, respectively. Moreover, the region A11 to A20 indicates the band of the supermode center frequency realized by the combination of the first heater power and the second heater power.

[0051] For example, a certain combination of the first heater power and the second heater power results in a supermode center frequency of f3, which belongs to region A15. If the first heater power and the second heater power are increased from this state as indicated by the arrow p0 while maintaining a proportional relationship, the supermode center frequency can be switched to f4, which belongs to the same region A15 as f3 and is smaller than f3. For example, if the inclination angle of the arrow p0 with respect to the horizontal axis is θ, the amount by which the first heater power is changed is p0sinθ, and the amount by which the second heater power is changed is p0cosθ. In addition, when the supermode center frequency is switched from f4 to a frequency f5, which belongs to region A16, which is a lower frequency band than region A15, the first heater power and the second heater power can be changed as indicated by the arrows.

[0052] The relationship between the laser oscillation frequency and the heater power is stored as table data or the like in a storage unit of the control unit 20. The control unit 20 controls the first heater power and the second heater power so as to realize a desired supermode center frequency, for example, based on a frequency switching command from a higher-level control device.

[0053] (Behavior of supermode center frequency when switching laser oscillation frequency) Here, when the heater power is changed in order to switch the laser oscillation frequency, it may take some time for the supermode center frequency to stabilize, depending on how the change is made.

[0054] FIG. 4 is a diagram showing an example of the relationship between heater power and supermode center frequency according to a known technique. In FIG. 4, time t1 is the time at which the heater power starts to be changed to switch the laser oscillation frequency. Here, the heater power is the first heater power or the second heater power. The temperature is the temperature detected by the temperature sensor 30 and is related to the temperature of the laser light source unit 10.

[0055] As in the known art, when the heater power is suddenly increased in a short time (for example, tens of μs or less) as in region A1 to a desired value at time t1, that is, the heater power corresponding to the laser oscillation frequency after switching, as shown in curve C1, as described above, a part of the heat emitted from the heater with the increased heater power is used for the overall temperature change of the laser light source unit 10. As a result, the temperature shown in curve C2 in FIG. 4 also continues to change slowly for a time, for example, hundreds of ms or more, as in region A2, and accordingly, the supermode center frequency shown in curve C3 also continues to change slowly as shown in region A3. In this case, it is necessary to wait until time t2 after such a slow change in the supermode center frequency has converged before starting constant frequency control, which is a factor that limits the frequency switching time.

[0056] In contrast to this, FIG. 5 is a diagram showing an example of the relationship between the heater power and the supermode center frequency in the laser device 100 according to this embodiment.

[0057] In this embodiment, in order to switch the laser oscillation frequency, the heater power is changed as shown in region A4 to a desired value at time t1, that is, the heater power corresponding to the laser oscillation frequency after switching, as shown in curve C4. In this case, the temperature shown in curve C5 continues to change slowly for a period of time, such as several hundred ms or more, as shown in region A5, but the supermode center frequency shown in curve C6 is rapidly stabilized as shown in region A6. As a result, the constant frequency control can be started from time t3, which is before time t2 when the change in the supermode center frequency has converged, and the frequency switching time can be shortened.

[0058] Specifically, in this embodiment, the control unit 20 supplies correction power based on the target frequency of laser oscillation and the temperature detected by the temperature sensor 30 to each of the first heater 11a and the second heater 14a. The correction power corresponds to the initial set value of power set for each of the first heater 11a and the second heater 14a and a correction value for the initial set value. The correction value is determined for each of the first heater 11a and the second heater 14a based on the temperature detected by the temperature sensor 30.

[0059] For example, the initial power setting value and the correction value may be based on table data such as Table 1 stored in the memory of the control unit 20. In Table 1, n is an integer equal to or greater than 3. "Frequency" is a target frequency, and is measured in terahertz, for example. "First heater power initial setting value" is an initial setting value of the power supplied to the first heater 11a, and is measured in watts, for example. "Second heater power initial setting value" is an initial setting value of the power supplied to the second heater 14a, and is measured in watts, for example. "First correction coefficient" is a correction coefficient for determining a correction value for the first heater power initial setting value, and is measured in watts / °C, for example. "Second correction coefficient" is a correction coefficient for determining a correction value for the second heater power initial setting value, and is measured in watts / °C, for example.

[0060] [Table 1]

[0061] If the power supplied to the first heater 11a is P1k and the power supplied to the second heater 14a is P2k when the frequency is fk (where k is any one of 1 to n), P1k and P2k are expressed by, for example, formulas (1) and (2). Note that T is the temperature detected by the temperature sensor 8, and T0 is a reference temperature. T0 is, for example, a target temperature of T when the laser light source unit 10 is in steady state control. Also, p1k is the first heater power initial setting value, which is equal to the power supplied to the first heater 11a when the laser light source unit 10 is in steady state control and the target frequency is fk. p2k is the second heater power initial setting value, which is equal to the power supplied to the second heater 14a when the laser light source unit 10 is in steady state control and the target frequency is fk. P1k = p1k + K1 × (T - T0) (1) P2k = p2k + K2 × (T - T0) (2)

[0062] The correction coefficients K1 and K2 can be set, for example, as follows: For example, it is assumed that when the temperature detected by the temperature sensor 8 changes by ΔT, the supermode center frequency changes by Δf. In this case, the formula (3) holds. Δf=(∂f / ∂T)ΔT (3)

[0063] In addition, if it is necessary to change the first heater power by Δpa and the second heater power by Δpb so that the coordinate point determined by the first heater power and the second heater power in FIG. 3 moves by Δp in the direction forming an angle θ with respect to the horizontal axis in order to change the supermode center frequency by Δf, then equation (4) holds. Furthermore, Δp is expressed by equations (5) and (6). Δf=(∂f / ∂p)Δp (4) Δpa=Δpsinθ (5) Δpb=Δp cosθ (6)

[0064] If equations (3) and (4) are set to cancel each other out, the change in frequency due to temperature change can be offset by the change in frequency due to power correction. In other words, equation (7) is set to hold. Then, the power Δp required for the offset (i.e., the power to be corrected) is expressed by equation (8). (∂f / ∂T)ΔT+(∂f / ∂p)Δp=0 ··· (7) Δp=-(∂f / ∂T) / (∂f / ∂p)ΔT ··· (8)

[0065] Therefore, equations (5) and (6) can be expressed as equations (9) and (10). Δpa=-(∂f / ∂T) / (∂f / ∂p)ΔTsinθ ··· (9) Δpb=-(∂f / ∂T) / (∂f / ∂p)ΔTcosθ ··· (10)

[0066] K1 and K2 can be set based on equations (9) and (10). K1 and K2 can also be set based on characteristics obtained by performing a calibration experiment in advance after fabricating the laser light source unit 10. Note that, in equations (7) to (8), the change in frequency due to temperature change is completely offset by the change in frequency due to power, but the correction coefficients K1 and K2 may be set so that the right side of equation (7) is not zero but is an allowable small value.

[0067] The storage unit of the control unit 20 stores table data such as Table 2 instead of table data such as Table 1, and the initial power value and correction value may be based on the table data such as Table 2. The difference between Table 1 and Table 2 is that the correction coefficients K1 and K2 in Table 1 are independent of the frequency, but the correction coefficients in Table 2 are set for each frequency. Specifically, the first correction coefficient and the second correction coefficient when the frequency is fk (where k is any value from 1 to n) are K1k and K2k, respectively. The power P1k supplied to the first heater 11a and the power P2k supplied to the second heater 14a when the frequency is fk can be set by replacing K1 and K2 in equations (1) and (2) with K1k and K2k, respectively. The correction coefficients K1k and K2k can be set by applying the above-mentioned equations (3) to (10) to each frequency fk. [Table 2]

[0068] If the correction coefficients K1 and K2 are values ​​independent of frequency, for example, if the relationship between the heater power and the frequency of the reflected peak is nonlinear, the correction coefficients may be too large or too small depending on the target frequency, resulting in over or under-correction and degradation of the SMSR. In contrast, by setting the correction coefficients for each frequency, it is possible to perform more appropriate correction for each target frequency.

[0069] (Control Flow) Fig. 6 is a flow chart showing an example of a control method by the control unit 20 in this embodiment. The flow shown in Fig. 6 is executed when changing the frequency of laser oscillation of the laser light source unit 10 from the current frequency to a target frequency. Note that the control by the temperature control unit 26 to keep the temperature of the laser light source unit 10 within a predetermined range is always executed in the background of the flow shown in Fig. 6.

[0070] First, the target frequency acquisition unit 21 receives information on the target frequency from a higher-level control device and acquires the target frequency (step S101).

[0071] Next, the correction unit 24 reads out and acquires the initial set power values ​​(first heater initial set value, second heater initial set value) corresponding to the target frequency from the storage unit. In response to this, the power control unit 22 controls the value of the power supplied to each of the first heater 11a and the second heater 14a to the initial set power value, and supplies the power to each of the first heater 11a and the second heater 14a (step S102).

[0072] Next, the temperature acquisition unit 23 acquires the temperature detected by the temperature sensor 30 (step S103).

[0073] Next, the correction unit 24 reads out the correction coefficients (first correction coefficient, second correction coefficient) from the memory unit, and calculates and determines the correction values ​​corresponding to the initial set power values ​​(first heater initial set value, second heater initial set value) based on these correction coefficients and the temperature acquired by the temperature acquisition unit 23 (step S104).

[0074] Next, the correction unit 24 calculates and determines the power (the correction power to be supplied to each of the first heater 11a and the second heater 14a) according to the initial set power values ​​(first heater initial set value, second heater initial set value) and the correction value (step S105).

[0075] Next, the power control unit 22 controls the power supplied to each of the first heater 11a and the second heater 14a to the corrected power determined by the correction unit 24, and supplies the power to each of the first heater 11a and the second heater 14a (step S106). After that, the control returns to step S103, and the control unit 20 repeatedly executes steps S103 to S106.

[0076] In addition, when the above-mentioned formulas (1) and (2) are used in the control shown in Fig. 6, when the temperature T detected by the temperature sensor 30 stabilizes and becomes close to or equal to T0, the first heater power and the second heater power become very close to or equal to the values ​​without correction. Therefore, after changing the frequency of laser oscillation in the laser light source unit 10 according to the target frequency, when the control unit 20 determines that the temperature T detected by the temperature sensor satisfies a predetermined convergence condition, such as when the temperature T converges to T0, the control shown in Fig. 6 may be terminated, that is, the supply of power according to the initial setting value and the correction value may be terminated.

[0077] FIG. 7 is a flowchart showing another example of the control method by the control unit 20 in this embodiment, and is a flowchart for terminating the supply of power according to the initial set value and the correction value.

[0078] Steps S201 to S206 are the same as steps S101 to S106 in FIG. 6, and therefore a description thereof will be omitted.

[0079] Following step S206, the control unit 20 determines whether or not the temperature T detected by the temperature sensor satisfies a predetermined convergence condition (step S207).

[0080] Here, the convergence condition is, for example, that the difference between the temperature T detected by the temperature sensor 30 and the reference temperature T0 is equal to or less than a predetermined value. The predetermined value is, for example, a relatively small value that is permissible as the difference between T and T0 in steady-state control, for example, 0.01°C. Alternatively, the convergence condition may be that the change over time of the temperature T detected by the temperature sensor is equal to or less than a predetermined value. The change over time of the temperature T is an amount expressed, for example, in units of [°C / s]. If such a change over time is equal to or less than a predetermined value that allows the temperature to be determined to be stable, then the temperature T can be said to be stable.

[0081] When the control unit 20 determines that the temperature T satisfies the predetermined convergence condition (step S207, Yes), the control unit 20 ends the control shown in Fig. 7. After that, for example, the control unit 20 executes steady-state control, but since the control shown in Fig. 7 ends, the processing load of the control unit 20 during execution of the steady-state control is reduced, and power consumption can be reduced.

[0082] The convergence condition is not limited to the convergence condition related to the temperature T detected by the temperature sensor. For example, the control unit 20 may set the convergence condition to be a predetermined time, for example, time (t3-t1), elapsed from time t1 at which the heater power change for switching the laser oscillation frequency is started until the temperature T becomes stable, as shown in Fig. 5. The predetermined time may be obtained, for example, in a calibration experiment in advance, and stored in the storage unit of the control unit 20.

[0083] 6 and 7, the order of execution of each step is not limited to the above-mentioned order. For example, the temperature may be obtained before the target frequency is obtained.

[0084] In the above embodiment, the correction value is a correction value when the heater power is obtained by adding the initial set power value and the correction value, but the correction value is not limited to this. For example, the correction value may be a correction value that obtains the heater power when an operation other than addition (for example, an arithmetic operation other than addition) is performed on the initial set power value and the correction value.

[0085] In the above embodiment, the control unit stores a correction coefficient that is multiplied by (T-T0) to obtain a correction value, but the correction coefficient is not limited to this. For example, the correction coefficient may be a correction coefficient that is obtained by performing an operation other than addition (e.g., an arithmetic operation other than addition) on the correction coefficient and (T-T0).

[0086] Furthermore, in the above embodiment, the initial setting value and the correction value are power values, and the heater power is controlled and managed in accordance with these power values, but the initial setting value and the correction value may be electrical characteristic values ​​other than power values, such as current values ​​and voltage values, and the heater power may be controlled and managed in accordance with these electrical characteristic values.

[0087] In the above embodiment, the temperature sensor 30 is provided in the laser light source unit 10, but as long as it can detect a temperature reflecting the temperature of the laser light source unit 10, it may be provided in the vicinity of the laser light source unit 10. In addition, for example, when the laser light source unit 10 is mounted on a submount and is mounted on the base 50, the temperature sensor 30 may be provided on the submount.

[0088] Furthermore, in the above embodiment, the control unit 20 is mainly composed of digital circuits, but the control unit may be mainly composed of analog circuits.

[0089] In the above embodiment, the temperature at which the laser light source unit 10 is controlled by the temperature control unit 26 may vary depending on the target frequency. The relationship between the temperature at which the laser light source unit 10 is controlled and the target frequency is obtained, for example, by a preliminary experiment, and stored in the storage unit.

[0090] In the above embodiment, the first frequency filter 11 and the second frequency filter 14 are reflection filters, and the first and second response characteristics are reflection characteristics, but the present invention is not limited to this, and at least one of the first and second response characteristics may be a transmission characteristic. In this case, at least one of the first and second frequency filters is a transmission filter.

[0091] In addition, in the above embodiment, the temperature regulator 51 is thermally connected to the frequency monitor unit 40 so as to control the temperature of the frequency monitor unit 40, but the base unit 50 may be provided with a temperature regulator in addition to the temperature regulator 51, and the temperature regulator may control the temperature of the frequency monitor unit 40.

[0092] Furthermore, the present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0093] 10: Laser light source unit 11: First frequency filter 11a: First heater 12: Phase section 12a: 3rd heater 13: Gain section 13a: 1st electrode 14: Second frequency filter 14a: Second heater 15a: 2nd electrode 20: Control section 21: Target frequency acquisition unit 22: Power control section 23:Temperature acquisition section 24: Correction section 25: Monitor frequency calculation section 26: Temperature control unit 30: Temperature sensor 40: Frequency monitor section 41: Optical waveguide 41a: Branch 41b: 1st waveguide 41c: 2nd waveguide 41d: 3rd frequency filter 50: Base 51: Temperature controller 100: Laser device A1, A2, A3, A4, A5, A6, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20: Area C1, C2, C3, C4, C5, C6: Curve L1, L2, L3, L4: Laser light S1, S2: Spectrum St1, St2: Status

Claims

1. a laser light source unit including a first frequency filter having a first response characteristic in which a transmittance or a reflectance changes with respect to a frequency of input light, a first heater for heating the first frequency filter to change the first response characteristic, a second frequency filter having a second response characteristic in which a transmittance or a reflectance changes with respect to a frequency of input light, the second response characteristic being different from the first response characteristic, and a second heater for heating the second frequency filter to change the second response characteristic, wherein a frequency of laser oscillation changes in accordance with a Vernier effect caused by the first frequency filter and the second frequency filter; a temperature regulator thermally connected to the laser light source unit; a temperature sensor provided at or near the laser light source unit; a control unit including a power control unit that supplies power to each of the first heater and the second heater, and a temperature control unit that controls the temperature of the laser light source unit within a predetermined range by supplying a control amount corresponding to the temperature detected by the temperature sensor to the temperature regulator; Equipped with The control unit acquires a target frequency of the laser oscillation, The power control unit supplies, to each of the first heater and the second heater, a correction power according to an initial setting value of the electrical characteristic of the power set for each of the first heater and the second heater in accordance with the target frequency and a correction value for the initial setting value determined for each of the first heater and the second heater on the basis of a temperature detected by the temperature sensor. Laser device.

2. The control unit determines the correction value based on a correction coefficient set for each of the first heater and the second heater and a temperature detected by the temperature sensor.

2. The laser device according to claim 1.

3. The control unit determines the correction value based on the target frequency, a correction coefficient set for each frequency of the first heater and the second heater, and a temperature detected by the temperature sensor.

2. The laser device according to claim 1.

4. The initial set value and the correction value are power values.

2. The laser device according to claim 1.

5. The initial set value and the correction value are current values ​​or voltage values.

2. The laser device according to claim 1.

6. When the control unit determines that a predetermined convergence condition is satisfied after changing the frequency of the laser oscillation in the laser light source unit in accordance with the target frequency, the control unit ends the supply of power in accordance with the initial setting value and the correction value.

2. The laser device according to claim 1.

7. The predetermined convergence condition is that the difference between the temperature detected by the temperature sensor and a reference temperature is equal to or smaller than a predetermined value.

7. The laser device according to claim 6.

8. The predetermined convergence condition is that the change in temperature detected by the temperature sensor over time is equal to or less than a predetermined value.

7. The laser device according to claim 6.

9. a laser light source unit including a first frequency filter having a first response characteristic in which a transmittance or a reflectance changes with respect to a frequency of input light, a first heater for heating the first frequency filter to change the first response characteristic, a second frequency filter having a second response characteristic in which a transmittance or a reflectance changes with respect to a frequency of input light, the second response characteristic being different from the first response characteristic, and a second heater for heating the second frequency filter to change the second response characteristic, wherein a frequency of laser oscillation changes in accordance with a Vernier effect caused by the first frequency filter and the second frequency filter; a temperature regulator thermally connected to the laser light source unit; a temperature sensor provided at or near the laser light source unit; a temperature control unit that controls the temperature of the laser light source unit within a predetermined range by supplying a control amount corresponding to the temperature detected by the temperature sensor to the temperature regulator; A method for controlling a laser device comprising: obtaining a target frequency of the laser oscillation; acquiring a temperature detected by the temperature sensor; supplying, to each of the first heater and the second heater, a correction power according to an initial setting value of an electrical characteristic of power set for each of the first heater and the second heater in accordance with the target frequency and a correction value for the initial setting value determined for each of the first heater and the second heater on the basis of the acquired temperature; A method for controlling a laser device comprising:

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