Wavelength-tunable laser device and method for controlling wavelength-tunable laser device

Abstract

To provide a wavelength-tunable laser device and a method for controlling a wavelength-tunable laser device, which can prevent stabilization to a wavelength different from the original target wavelength and can maintain high wavelength discrimination efficiency of a wavelength discrimination unit used for stabilization.SOLUTION: A wavelength-tunable laser device according to the present invention uses an output signal from a first wavelength discrimination unit to perform wavelength control of a wavelength-tunable light source by a wavelength control unit so as to cancel out wavelength fluctuations, uses low-frequency components of an output signal from a second wavelength discrimination unit having higher wavelength discrimination efficiency than the first wavelength discrimination unit to control the operating point of the second wavelength discrimination unit by a filter control unit, and uses high-frequency components of the output signal from the second wavelength discrimination unit to perform wavelength control of the wavelength of the wavelength-tunable light source by the wavelength control unit so as to cancel out wavelength fluctuations.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wavelength tunable laser device and a method for controlling a wavelength tunable laser device. [Background technology]

[0002] Conventionally, in order to stabilize the wavelength of a wavelength-tunable light source, a method has been known in which two wavelength discrimination units with different wavelength discrimination efficiencies are used, the first wavelength discrimination unit is used to stabilize the wavelength, the discrimination characteristics of the second wavelength discrimination unit are controlled so that the wavelength discrimination efficiency for that wavelength is high, and then the second wavelength discrimination unit is used to stabilize the wavelength (Patent Documents 1 to 4, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-54714 [Patent Document 2] Patent No. 3766347 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-03591 [Patent Document 4] Japanese Patent Application Laid-Open No. 63-124481 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the conventional method, if the discrimination characteristics of the second wavelength discriminator change due to disturbance, the wavelength may be stabilized at a wavelength different from the original target wavelength. Also, with the conventional method, if the discrimination characteristics of the second wavelength discriminator change due to disturbance, the wavelength discrimination efficiency for the wavelength at that time may decrease.

[0005] The present invention has been made in view of the above-mentioned problems, and its object is to provide a wavelength-tunable laser device and a control method for a wavelength-tunable laser device that can prevent stabilization to a wavelength different from the original target wavelength and can maintain high wavelength discrimination efficiency of a wavelength discriminator used for stabilization. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the objectives, (1) A wavelength tunable laser device according to the present invention includes a wavelength tunable light source capable of arbitrarily selecting an oscillation wavelength, a first wavelength discriminator that receives a portion of output light from the wavelength tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, a second wavelength discriminator that receives another portion of output light from the wavelength tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and is designed to have a higher wavelength discrimination efficiency than the first wavelength discriminator, a filter control unit that performs filter control to control the wavelength discrimination characteristics of the second wavelength discriminator, a wavelength control unit that performs wavelength control of the wavelength of the wavelength tunable light source, and a setting instruction value that stores a setting instruction value according to a target wavelength, receives output signals from the first wavelength discriminator and the second wavelength discriminator, and controls the setting instruction value according to the target wavelength. The optical fiber optics system includes a controller that calculates a feedback signal based on an instruction value and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal, and a temperature adjustment element on which the wavelength-tunable light source, the first wavelength discriminator, and the second wavelength discriminator are mounted, wherein an output signal from the first wavelength discriminator is used to perform wavelength control of the wavelength-tunable light source by the wavelength control unit so as to cancel out wavelength fluctuations, a low-frequency component of the output signal from the second wavelength discriminator is used to perform filter control of the second wavelength discriminator by the filter control unit, and a high-frequency component of the output signal from the second wavelength discriminator is used to perform wavelength control of the wavelength-tunable light source by the wavelength control unit so as to cancel out wavelength fluctuations.

[0007] (2) The wavelength tunable laser device according to the present invention is characterized in that, in the invention (1) above, the wavelength control unit repeatedly and continuously performs wavelength control of the wavelength tunable light source using the output signal from the first wavelength discriminator, the filter control unit repeatedly and continuously performs filter control using the low-frequency component of the output signal from the second wavelength discriminator, and the wavelength control unit repeatedly and continuously performs wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

[0008] (3) The wavelength tunable laser device according to the present invention is characterized in that, in the invention (2) above, the wavelength control unit performs wavelength control to continuously sweep the oscillation wavelength using an output signal from the first wavelength discrimination unit.

[0009] (4) The wavelength tunable laser device according to the present invention is characterized in that, in the invention (1) above, the wavelength control of the wavelength tunable light source is performed by the wavelength control unit using the output signal from the first wavelength discrimination unit, the filter control is performed repeatedly and continuously by the filter control unit using the low-frequency component of the output signal from the second wavelength discrimination unit, and the wavelength control is performed repeatedly and continuously by the wavelength control unit using the high-frequency component of the output signal from the second wavelength discrimination unit.

[0010] (5) The wavelength tunable laser device according to the present invention is characterized in that, in the invention (1) above, the wavelength control unit repeatedly and continuously performs wavelength control of the wavelength tunable light source using the output signal from the first wavelength discriminator, the filter control unit performs the filter control one-off using the low-frequency component of the output signal from the second wavelength discriminator, and the wavelength control unit repeatedly and continuously performs the wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

[0011] (6) The wavelength tunable laser device according to the present invention is characterized in that, in the invention (1) above, the wavelength control of the wavelength tunable light source is performed by the wavelength control unit using the output signal from the first wavelength discriminator, the filter control is performed by the filter control unit using the low-frequency component of the output signal from the second wavelength discriminator, and the wavelength control is repeatedly and continuously performed by the wavelength control unit using the high-frequency component of the output signal from the second wavelength discriminator.

[0012] (7) A wavelength-tunable laser device according to the present invention includes a wavelength-tunable light source capable of arbitrarily selecting an oscillation wavelength, a first wavelength discrimination unit that receives a portion of output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, a second wavelength discrimination unit that receives another portion of output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and is designed to have a higher wavelength discrimination efficiency than the first wavelength discrimination unit, a filter control unit that performs filter control to control the wavelength discrimination characteristics of the second wavelength discrimination unit, a wavelength control unit that performs wavelength control of the wavelength of the wavelength-tunable light source, and a setting instruction value corresponding to a target wavelength that is stored and controls the first wavelength discrimination unit and the second wavelength discrimination unit. a controller that receives an output signal from the wavelength control unit, calculates a feedback signal based on the setting instruction value, and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal, and a temperature adjustment element on which the wavelength tunable light source, the first wavelength discriminator, and the second wavelength discriminator are mounted, wherein the wavelength control unit controls the wavelength of the wavelength tunable light source so as to cancel out wavelength fluctuations using the output signal from the first wavelength discriminator, and after the filter control unit controls the filter of the second wavelength discriminator, the wavelength control unit controls the wavelength of the wavelength tunable light source so as to cancel out wavelength fluctuations using the output signal from the second wavelength discriminator.

[0013] (8) The wavelength tunable laser device according to the present invention is characterized in that, in any one of the inventions (1) to (7) above, the output signal from the first wavelength discrimination unit, the output signal from the second wavelength discrimination unit, and the feedback signal from the controller are digital signals or analog signals.

[0014] (9) The wavelength-tunable laser device according to the present invention is characterized in that, in any one of the above (1) to (7), the light input to the first wavelength discrimination unit and the second wavelength discrimination unit is at least a part of the forward light from the wavelength-tunable light source or at least a part of the backward light from the wavelength-tunable light source, which is branched into two by a light branching means, or at least a part of the forward light and at least a part of the backward light are respectively used.

[0015] (10) A method for controlling a wavelength-tunable laser device according to the present invention includes a wavelength-tunable light source capable of arbitrarily selecting an oscillation wavelength, a first wavelength discrimination unit that receives a portion of output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, a second wavelength discrimination unit that receives another portion of output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and is designed to have a higher wavelength discrimination efficiency than the first wavelength discrimination unit, a filter control unit that performs filter control to control the wavelength discrimination characteristics of the second wavelength discrimination unit, a wavelength control unit that performs wavelength control of the wavelength of the wavelength-tunable light source, and a control unit that stores a setting instruction value according to a target wavelength and discriminates output signals from the first wavelength discrimination unit and the second wavelength discrimination unit. a controller that receives an output signal from the first wavelength discriminator, calculates a feedback signal based on the setting instruction value, and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal, and a temperature adjustment element on which the wavelength tunable light source, the first wavelength discriminator, and the second wavelength discriminator are mounted, the method comprising: using an output signal from the first wavelength discriminator to perform wavelength control of the wavelength tunable light source by the wavelength control unit so as to cancel out wavelength fluctuations; and after performing filter control of the second wavelength discriminator by the filter control unit, using the output signal from the second wavelength discriminator to perform wavelength control of the wavelength tunable light source by the wavelength control unit so as to cancel out wavelength fluctuations.

[0016] (11) The control method for a wavelength-tunable laser device according to the present invention is characterized in that, in the invention (10) above, the wavelength control of the wavelength-tunable light source by the wavelength control unit using an output signal from the first wavelength discrimination unit is repeatedly and continuously performed, the filter control by the filter control unit using a low-frequency component of the output signal from the second wavelength discrimination unit is repeatedly and continuously performed, the wavelength control by the wavelength control unit using a high-frequency component of the output signal from the second wavelength discrimination unit is repeatedly and continuously performed, and wavelength control is performed by the wavelength control unit using the output signal from the first wavelength discrimination unit to continuously sweep the oscillation wavelength. [Effects of the Invention]

[0017] The wavelength tunable laser device and the method for controlling the wavelength tunable laser device according to the present invention have the advantage of being able to prevent stabilization at a wavelength different from the original target wavelength, and to maintain high wavelength discrimination efficiency of the wavelength discrimination section used for stabilization. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a wavelength tunable laser device according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing filter control using the low frequency component of the output signal from the second wavelength discriminator. [Figure 3] FIG. 3 is a flowchart showing a first example of wavelength stabilization control of the wavelength tunable laser device according to the first embodiment. [Figure 4] FIG. 4 is a flowchart showing a second example of wavelength stabilization control of the wavelength tunable laser device according to the first embodiment. [Figure 5] FIG. 5 is a flowchart showing a third example of wavelength stabilization control of the wavelength tunable laser device according to the first embodiment. [Figure 6] FIG. 6 is a flowchart showing a fourth example of wavelength stabilization control of the wavelength tunable laser device according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing a schematic configuration of a wavelength tunable laser device according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing an example of wavelength stabilization control of the wavelength tunable laser device according to the second embodiment. [Figure 9] 9(a) is a graph showing an example of wavelength control in which the target wavelength is swept from λ1 to λ2 using the output signal from the first wavelength discriminator, and FIG. 9(b) is a graph showing an example of wavelength control in which the output signal from the second wavelength discriminator is used during the sweep of the target wavelength. [Figure 10] FIG. 10 is a flowchart showing a first example of wavelength stabilization control of the wavelength tunable laser device according to the third embodiment. [Figure 11]FIG. 11 is a flowchart showing a second example of wavelength stabilization control of the wavelength tunable laser device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Embodiment 1) A wavelength tunable laser device and a method for controlling a wavelength tunable laser device according to a first embodiment of the present invention will be described below, although the present invention is not limited to this embodiment.

[0020] FIG. 1 is a diagram showing a schematic configuration of a wavelength tunable laser device 1 according to the first embodiment.

[0021] As shown in FIG. 1, the wavelength-tunable laser device 1 according to the first embodiment includes a wavelength-tunable light source 2, an optical branching means 3, a first wavelength discriminator 4, a second wavelength discriminator 5, a filter control unit 6, a wavelength control unit 7, a controller 8, a temperature adjustment element 9, a low-pass filter (LPF) 10, and a high-pass filter (HPF) 11.

[0022] The wavelength-tunable light source 2 can arbitrarily select the oscillation wavelength, and under the control of the wavelength control unit 7, tunable the wavelength of the output laser light to any one of a plurality of wavelengths, and outputs laser light of that wavelength.

[0023] The light branching means 3 branches the laser light output from the wavelength-tunable light source 2 into two laser lights. The configuration of the light branching means 3 is not particularly limited as long as it is configured to be able to branch the laser light output from the wavelength-tunable light source 2 into two laser lights. The two laser lights are an example of a part of the output light and another part of the output light from the wavelength-tunable light source 2.

[0024] The first wavelength discriminator 4 detects fluctuations in the oscillation wavelength of the wavelength-tunable light source 2 and outputs an output signal corresponding to the fluctuations in the oscillation wavelength to the controller 8. The first wavelength discriminator 4 is designed to receive one of the two laser beams branched by the optical branching means 3 and to output an electrical signal (output signal) corresponding to the intensity of the laser beam such that the intensity of the output signal has a periodic characteristic with respect to the wavelength. For example, the first wavelength discriminator 4 includes a first filter (not shown) having wavelength discrimination characteristics such as a transmission characteristic in which the transmittance changes periodically with respect to the wavelength of the input laser beam, and a first photodiode (not shown) to which the laser beam transmitted through the first filter is input. Note that the first filter may be an etalon filter or the like having a periodic transmission characteristic with respect to the wavelength of the input light.

[0025] The first filter section transmits one of the two laser beams branched by the optical branching means 3 at a transmittance according to the wavelength of the laser beam. The first photodiode receives the laser beam that has passed through the first filter section, and outputs an electric signal (output signal) according to the intensity of the laser beam to the controller 8.

[0026] The second wavelength discriminator 5 receives the other of the two laser beams branched by the optical branching means 3 and is designed so that the intensity of an electrical signal (output signal) corresponding to the intensity of the laser beam has a periodic characteristic with respect to wavelength. The second wavelength discriminator 5 is also designed so that its wavelength discrimination characteristics can be controlled by the filter control unit 6 and have wavelength discrimination characteristics that provide higher wavelength discrimination efficiency than the first wavelength discriminator 4. Here, high wavelength discrimination efficiency means, for example, that the intensity of the electrical signal (output signal) changes more significantly with respect to a change in wavelength. High wavelength discrimination efficiency of the wavelength discriminator allows for detection of even smaller wavelength fluctuations. The second wavelength discriminator 5 includes, for example, a second filter unit (not shown) having wavelength discrimination characteristics such as a transmission characteristic in which transmittance periodically changes with respect to the wavelength of the input laser beam, and a second photodiode (not shown) to which the laser beam transmitted through the second filter unit is input. The second filter unit may be, for example, an etalon filter having a periodic transmission characteristic with respect to the wavelength of the input light.

[0027] The second filter unit is controlled by the filter control unit 6 to transmit the other laser light of the two laser lights branched by the light branching means 3 at a transmittance according to the wavelength of the laser light. The second photodiode receives the laser light that has passed through the second filter unit, and outputs an electrical signal (output signal) according to the intensity of the laser light to the controller 8 via a low-pass filter (LPF) 10 and a high-pass filter (HPF) 11. That is, of the electrical signal (output signal) output from the second wavelength discriminator 5, the low-frequency component (low-frequency signal) that has passed through the low-pass filter (LPF) 10 and the high-frequency component (high-frequency signal) that has passed through the high-pass filter (HPF) 11 are input to the controller 8.

[0028] Note that the electrical signal (output signal) input from the second wavelength discriminator 5 to the controller 8 is not limited to the acquisition method using the low-pass filter 10 and the high-pass filter 11, as long as it is possible to acquire low-frequency components (low-frequency signals) and high-frequency components (high-frequency signals). For example, the low-frequency components (low-frequency signals) and high-frequency components (high-frequency signals) of the electrical signal (output signal) output from the second wavelength discriminator 5 may be acquired by separating the signals using a bias tee or by applying a filter when calculating the feedback signal.

[0029] The laser light input to each of the first wavelength discriminator 4 and the second wavelength discriminator 5 may be either forward emitted light or rearward emitted light from the wavelength-tunable light source 2. Alternatively, at least a portion of one of the forward emitted light or rearward emitted light may be input to the first wavelength discriminator 4, and at least a portion of the other of the forward emitted light or rearward emitted light may be input to the second wavelength discriminator 5. The laser light output from the wavelength-tunable light source 2 and not input to the first wavelength discriminator 4 or the second wavelength discriminator 5 may be output to the outside of the wavelength-tunable laser device 1.

[0030] The filter control unit 6 performs filter control to control the wavelength discrimination characteristics of the second wavelength discriminator 5 by using the low frequency components of the output signal from the second wavelength discriminator 5 input to the controller 8. For example, the filter control unit 6 controls the transmittance of the second filter unit by heating the second filter unit using a heating means that generates heat in response to the supplied power.

[0031] The wavelength control unit 7 controls the wavelength of the laser light output from the wavelength-tunable light source 2. For example, the wavelength control unit 7 controls the wavelength of the laser light output from the wavelength-tunable light source 2 by locally heating the wavelength-tunable light source 2 using a heat generating means that generates heat in response to supplied power.

[0032] The controller 8 has a storage unit (not shown) that stores setting instruction values ​​corresponding to target wavelengths, and a calculation unit that receives electrical signals (output signals) from the first wavelength discriminator 4 and the second wavelength discriminator 5 and calculates a feedback signal based on the setting instruction values. Based on the calculated feedback signal, the controller 8 instructs the filter control unit 6 and the wavelength control unit 7 on control parameters, thereby controlling the filter control unit 6 and the wavelength control unit 7. For example, the controller 8 compares a target value set in advance for each wavelength with the output signal (monitor value) from the first wavelength discriminator 4, and outputs a feedback signal to the wavelength control unit 7 so as to reduce the difference.

[0033] The temperature adjustment element 9 is mounted with the wavelength-tunable light source 2, the optical branching means 3, the first wavelength discrimination unit 4, and the second wavelength discrimination unit 5. The temperature adjustment element 9 is configured with, for example, a TEC (Thermo Electric Cooler) including a Peltier element, and controls the temperatures of the wavelength-tunable light source 2, the optical branching means 3, the first wavelength discrimination unit 4, and the second wavelength discrimination unit 5 according to the power supplied.

[0034] In the wavelength-tunable laser device 1 according to the first embodiment, wavelength stabilization is performed by negative feedback control using a first wavelength discriminator 4 and a second wavelength discriminator 5, which have different wavelength discrimination efficiencies (wavelength discrimination characteristics), in response to fluctuations in the wavelength of the laser light output from the wavelength-tunable light source 2. Note that the various electrical signals (output signals) used for negative feedback control from the first wavelength discriminator 4, the second wavelength discriminator 5, and the controller 8 are digital signals or analog signals.

[0035] Specifically, in the wavelength-tunable laser device 1 according to the first embodiment, the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 so as to cancel out wavelength fluctuations by using the output signal from the first wavelength discriminator 4. Also, in the wavelength-tunable laser device 1 according to the first embodiment, the filter control unit 6 controls the operating point of the second wavelength discriminator 5 by using the low-frequency component of the output signal from the second wavelength discriminator 5 that has passed through a low-pass filter 10. Also, in the wavelength-tunable laser device 1 according to the first embodiment, the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 by using the high-frequency component of the output signal from the second wavelength discriminator 5 that has passed through a high-pass filter 11 so as to cancel out wavelength fluctuations. Also, since the second wavelength discriminator 5 has higher wavelength discrimination efficiency than the first wavelength discriminator 4, wavelength control is performed using the output signal from the second wavelength discriminator 5, thereby realizing more accurate wavelength stabilization control.

[0036] FIG. 2 is a diagram showing filter control using the low frequency components of the output signal from the second wavelength discriminator 5. In FIG.

[0037] The vertical axis of FIG. 2 represents the filter output relative to the wavelength, and the horizontal axis of FIG. 2 represents the target wavelength (target wavelength). The filter output is, for example, the output voltage intensity of a photodiode. The dashed line graph in FIG. 2 represents the wavelength discrimination characteristic of the second wavelength discrimination unit 5 before fluctuation, and the solid line graph in FIG. 2 represents the wavelength discrimination characteristic of the second wavelength discrimination unit 5 after fluctuation. Point P0 in FIG. 2 is the operating point of the second wavelength discrimination unit 5 for obtaining a filter output signal in response to wavelength fluctuation in the wavelength discrimination characteristic before fluctuation. Point P1 in FIG. 2 is the operating point of the second wavelength discrimination unit 5 for obtaining a filter output signal in response to wavelength fluctuation in the wavelength discrimination characteristic after fluctuation. As can be seen from FIG. 2, the wavelength discrimination efficiency at point P1 in the wavelength discrimination characteristic after fluctuation is lower than the wavelength discrimination efficiency at point P0 in the wavelength discrimination characteristic before fluctuation. Therefore, if wavelength stabilization is attempted using the operating point of point P1 in the wavelength discrimination characteristic after fluctuation, stabilization control will be performed in a state where wavelength discrimination efficiency is low. Therefore, in the wavelength tunable laser device 1 according to the first embodiment, filter control is performed to control the operating point of the second wavelength discriminator 5 so that the operating point becomes an operating point at which higher wavelength discrimination efficiency can be obtained in the wavelength discrimination characteristics after the fluctuation. In the wavelength tunable laser device 1 according to the first embodiment, filter control is performed using the low-frequency components, taking advantage of the fact that the wavelength discrimination characteristics of the second wavelength discriminator 5 fluctuate relatively slowly and the fluctuation appears in the low-frequency components of the output signal from the second wavelength discriminator 5.

[0038] FIG. 3 is a flowchart showing a first example of wavelength stabilization control of the wavelength tunable laser device 1 according to the first embodiment.

[0039] First, in the wavelength-tunable laser device 1 according to the first embodiment, an oscillation wavelength is specified by the controller 8, and laser light is output from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S1). Next, in the wavelength-tunable laser device 1 according to the first embodiment, upon receiving one of the two laser beams branched by the optical branching unit 3, wavelength control is repeatedly and continuously performed using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 until the flow ends (step S2). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a preset threshold (step S3). If the controller 8 determines that the difference is not equal to or less than the preset threshold (No in step S3), it repeatedly performs the process of step S3 until the difference becomes equal to or less than the preset threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the preset threshold (Yes in step S3), the controller 8 proceeds to the next step in the flow. Next, in the wavelength-tunable laser device 1, the filter control unit 6 repeatedly and continuously performs filter control of the second wavelength discriminator 5 using the low-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S4). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S5). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S5), it repeatedly performs the process of step S5 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S5), it proceeds to the next step in the flow. Next, in the wavelength-tunable laser device 1 according to the first embodiment, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S6). Next, in the wavelength tunable laser device 1, the controller 8 determines whether or not to end a series of wavelength stabilization control flows (step S7).For example, in the wavelength tunable laser device 1 according to the first embodiment, the series of wavelength stabilization control flows is terminated when a predetermined condition set in advance is satisfied. For example, when the instructed oscillation wavelength changes, such as when switching the wavelength, the series of wavelength stabilization control flows is terminated. In the wavelength tunable laser device 1 according to the first embodiment, when the controller 8 determines not to terminate the flow (No in step S7), the process of step S7 is repeatedly executed until it is determined to terminate the flow. On the other hand, in the wavelength tunable laser device 1 according to the first embodiment, when the controller 8 determines to terminate the flow (Yes in step S7), the series of wavelength stabilization control flows is terminated.

[0040] In the wavelength-tunable laser device 1 according to the first embodiment, the wavelength discrimination characteristics of the second wavelength discriminator 5 are controlled using the low-frequency component of the output signal from the second wavelength discriminator 5, and wavelength control is performed using the high-frequency component of the output signal from the second wavelength discriminator 5, thereby preventing the wavelength from being stabilized at a wavelength different from the original target wavelength. Furthermore, in the wavelength-tunable laser device 1 according to the first embodiment, the wavelength discrimination efficiency of the wavelength discriminator used for stabilization can be maintained high. Furthermore, in the wavelength-tunable laser device 1 according to the first embodiment, low-frequency noise of the laser can be reduced by repeatedly and continuously performing wavelength control using the output signal (electrical signal) from the first wavelength discriminator 4 until the end of the flow.

[0041] FIG. 4 is a flowchart showing a second example of wavelength stabilization control of the wavelength tunable laser device 1 according to the first embodiment.

[0042] 4, the wavelength of the tunable light source 2 is controlled by the wavelength control unit 7 so as to cancel out the wavelength fluctuations using the output signal from the first wavelength discriminator 4, and then the wavelength control using the output signal from the first wavelength discriminator 4 is turned off (single execution). Then, in the second example of wavelength stabilization control, the filter control unit 6 repeatedly controls the filter of the second wavelength discriminator 5 (controls the operating point of the second wavelength discriminator 5) using the low-frequency components of the output signal from the second wavelength discriminator 5 that have passed through the low-pass filter 10 (continuous execution). Also, in the second example of wavelength stabilization control, the wavelength of the tunable light source 2 is repeatedly controlled by the wavelength control unit 7 so as to cancel out the wavelength fluctuations using the high-frequency components of the output signal from the second wavelength discriminator 5 that have passed through the high-pass filter 11 (continuous execution).

[0043] First, in the second example of wavelength stabilization control, the controller 8 instructs the oscillation wavelength, and laser light is output from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S11). Next, in the second example of wavelength stabilization control, one of the two laser lights branched by the optical branching unit 3 is received, and wavelength control is performed using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 (step S12). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a preset threshold (step S13). If the controller 8 determines that the difference is not equal to or less than the preset threshold (No in step S13), the process returns to step S12. On the other hand, if the controller 8 determines that the difference is equal to or less than the preset threshold (Yes in step S13), the process proceeds to the next step. Next, in a second example of wavelength stabilization control, the filter control unit 6 repeatedly and continuously performs filter control of the second wavelength discriminator 5 using the low-frequency components of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S14). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S15). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S15), the controller 8 repeatedly performs the process of step S15 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S15), the controller 8 proceeds to the next step in the flow. Next, in the second example of wavelength stabilization control, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency components of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S16). Next, in the second example of wavelength stabilization control, the controller 8 determines whether or not to end the series of wavelength stabilization control flows (step S17). For example, in the second example of wavelength stabilization control, when a predetermined condition set in advance is satisfied, the series of wavelength stabilization control flows ends.For example, when the specified oscillation wavelength changes, such as when switching wavelengths, the series of wavelength stabilization control flows is terminated. Then, in the second example of wavelength stabilization control, if the controller 8 determines not to terminate the flow (No in step S17), the process of step S17 is repeatedly executed until it is determined to terminate the flow. On the other hand, in the second example of wavelength stabilization control, if the controller 8 determines to terminate the flow (Yes in step S17), the series of wavelength stabilization control flows is terminated.

[0044] In the second example of wavelength stabilization control, it is possible to prevent the wavelength from being stabilized to a wavelength different from the original target wavelength. Furthermore, in the second example of wavelength stabilization control, by performing wavelength control using the output signal from the first wavelength discriminator 4 one-off, it is possible to reduce power consumption compared to when the wavelength control is repeatedly and continuously performed until the end of the flow.

[0045] FIG. 5 is a flowchart showing a third example of wavelength stabilization control of the wavelength tunable laser device 1 according to the first embodiment.

[0046] 5, the wavelength control unit 7 repeatedly controls the wavelength of the tunable light source 2 using the output signal from the first wavelength discriminator 4 to cancel out the wavelength fluctuation (continuous execution). Also, in the third example of wavelength stabilization control, the filter control unit 6 performs filter control of the second wavelength discriminator 5 (control of the operating point of the second wavelength discriminator 5) using the low-frequency component of the output signal from the second wavelength discriminator 5 that has passed through the low-pass filter 10, and then the control by the filter control unit 6 is turned off (single execution). And in the third example of wavelength stabilization control, the wavelength control unit 7 repeatedly controls the wavelength of the tunable light source 2 using the high-frequency component of the output signal from the second wavelength discriminator 5 that has passed through the high-pass filter 11 to cancel out the wavelength fluctuation (continuous execution).

[0047] First, in the third example of wavelength stabilization control, the controller 8 instructs the oscillation wavelength, and laser light is output from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S21). Next, in the third example of wavelength stabilization control, one of the two laser light beams branched by the optical branching unit 3 is received, and wavelength control using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 is repeatedly and continuously performed until the end of the flow (step S22). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S23). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S23), it repeatedly executes the process of step S23 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S23), the controller 8 proceeds to the next step in the flow. Next, in a third example of wavelength stabilization control, the filter control unit 6 performs a single filter control of the second wavelength discriminator 5 using the low-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 (step S24). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S25). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S25), the process returns to step S24. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S25), the process proceeds to the next step. Next, in the third example of wavelength stabilization control, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S26). Next, in the third example of wavelength stabilization control, the controller 8 determines whether to end the series of wavelength stabilization control flows (step S27). For example, in the third example of wavelength stabilization control, when a predetermined condition is satisfied, a series of wavelength stabilization control flows are terminated.For example, when the instructed oscillation wavelength changes, such as when switching wavelengths, the series of wavelength stabilization control flows is terminated. In the third example of wavelength stabilization control, if the controller 8 determines not to terminate the flow (No in step S27), the process of step S27 is repeatedly executed until it is determined to terminate the flow. On the other hand, in the third example of wavelength stabilization control, if the controller 8 determines to terminate the flow (Yes in step S27), the series of wavelength stabilization control flows is terminated.

[0048] In the third example of wavelength stabilization control, it is possible to prevent the wavelength from being stabilized to a wavelength different from the original target wavelength. Also, in the third example of wavelength stabilization control, by performing filter control using the low-frequency component of the output signal from the second wavelength discriminator 5 once, it is possible to reduce power consumption compared to when the filter control is repeatedly and continuously performed until the end of the flow. Also, in the third example of wavelength stabilization control, it is possible to reduce low-frequency noise of the laser by continuously performing wavelength control using the output signal (electrical signal) from the first wavelength discriminator 4.

[0049] FIG. 6 is a flowchart showing a fourth example of wavelength stabilization control of the wavelength tunable laser device 1 according to the first embodiment.

[0050] 6, the wavelength control unit 7 performs wavelength control of the wavelength-tunable light source 2 so as to cancel out wavelength fluctuations using the output signal from the first wavelength discriminator 4, and then the wavelength control using the output signal from the first wavelength discriminator 4 is turned off (single execution). Also, in the fourth example of wavelength stabilization control, the filter control unit 6 performs filter control of the second wavelength discriminator 5 (control of the operating point of the second wavelength discriminator 5) using the low-frequency components of the output signal from the second wavelength discriminator 5 that have passed through the low-pass filter 10, and then the control by the filter control unit 6 is turned off (single execution). And in the fourth example of wavelength stabilization control, the wavelength control unit 7 repeatedly performs wavelength control of the wavelength-tunable light source 2 so as to cancel out wavelength fluctuations using the high-frequency components of the output signal from the second wavelength discriminator 5 that have passed through the high-pass filter 11 (continuous execution).

[0051] First, in the fourth example of wavelength stabilization control, an oscillation wavelength is specified by the controller 8, and laser light is output from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S31). Next, in the fourth example of wavelength stabilization control, one of the two laser lights branched by the optical branching unit 3 is received, and wavelength control is performed using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 (step S32). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S33). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S33), the process returns to step S32. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S33), the process proceeds to the next step. Next, in a fourth example of wavelength stabilization control, the filter control unit 6 performs a single filter control of the second wavelength discriminator 5 using the low-frequency components of the output signal from the second wavelength discriminator 5 input to the controller 8 (step S34). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S35). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S35), the process returns to step S34. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S35), the process proceeds to the next step. Next, in the fourth example of wavelength stabilization control, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency components of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S36). Next, in the fourth example of wavelength stabilization control, the controller 8 determines whether to end a series of wavelength stabilization control flows (step S37). For example, in a fourth example of wavelength stabilization control, when a predetermined condition is satisfied, the series of wavelength stabilization control flows is terminated. For example, when the specified oscillation wavelength changes, such as when switching wavelengths, the series of wavelength stabilization control flows is terminated.In the fourth example of wavelength stabilization control, if the controller 8 determines not to end the flow (No in step S37), the process of step S37 is repeatedly executed until it is determined to end the flow. On the other hand, in the fourth example of wavelength stabilization control, if the controller 8 determines to end the flow (Yes in step S37), the series of wavelength stabilization control flows is ended.

[0052] In the fourth example of wavelength stabilization control, it is possible to prevent the wavelength from being stabilized to a wavelength different from the original target wavelength. Also, in the fourth example of wavelength stabilization control, by performing wavelength control using the output signal from the first wavelength discriminator 4 in a one-off manner, it is possible to reduce power consumption compared to when the wavelength control is repeatedly and continuously performed until the end of the flow. Furthermore, in the fourth example of wavelength stabilization control, by performing filter control in a one-off manner using the low-frequency component of the output signal from the second wavelength discriminator 5 in a one-off manner, it is possible to reduce power consumption compared to when the filter control is repeatedly and continuously performed until the end of the flow.

[0053] (Embodiment 2) A wavelength tunable laser device and a method for controlling a wavelength tunable laser device according to a second embodiment of the present invention will be described below. Note that in this embodiment, descriptions of the same configurations as those in the first embodiment will be omitted as appropriate.

[0054] FIG. 7 is a diagram showing a schematic configuration of a wavelength tunable laser device 1 according to the second embodiment.

[0055] 7, the wavelength tunable laser device 1 according to the second embodiment includes a wavelength tunable light source 2, an optical branching means 3, a first wavelength discriminator 4, a second wavelength discriminator 5, a filter control unit 6, a wavelength control unit 7, a controller 8, and a temperature adjustment element 9. That is, the wavelength tunable laser device 1 according to the second embodiment does not include the low pass filter (LPF) 10 and the high pass filter (HPF) 11 that are included in the wavelength tunable laser device 1 according to the first embodiment.

[0056] In the wavelength-tunable laser device 1 according to the second embodiment, the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 so as to cancel out the wavelength fluctuations, using the output signal from the first wavelength discriminator 4. Then, in the wavelength-tunable laser device 1 according to the second embodiment, after the filter control unit 6 performs filter control of the second wavelength discriminator 5 (control of the operating point of the second wavelength discriminator 5), the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 so as to cancel out the wavelength fluctuations, using the output signal from the second wavelength discriminator 5.

[0057] FIG. 8 is a flowchart showing an example of wavelength stabilization control of the wavelength tunable laser device 1 according to the second embodiment.

[0058] First, in the wavelength-tunable laser device 1 according to the second embodiment, the controller 8 instructs the oscillation wavelength and outputs a laser beam from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S41). Next, in the wavelength-tunable laser device 1 according to the second embodiment, upon receiving one of the two laser beams branched by the optical branching unit 3, wavelength control is repeatedly and continuously performed using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 until the flow ends (step S42). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength and determines whether the difference therebetween is equal to or less than a preset threshold (step S43). If the controller 8 determines that the difference is not equal to or less than the preset threshold (No in step S43), it repeatedly executes the process of step S43 until the difference becomes equal to or less than the preset threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the preset threshold (Yes in step S43), the controller 8 proceeds to the next step in the flow. Next, in the wavelength tunable laser device 1 according to the second embodiment, the filter control unit 6 performs a single filter control of the second wavelength discriminator 5 using the output signal from the second wavelength discriminator 5 input to the controller 8 (step S44). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a preset threshold (step S45). If the controller 8 determines that the difference is not equal to or less than the preset threshold (No in step S45), the process returns to step S44. On the other hand, if the controller 8 determines that the difference is equal to or less than the preset threshold (Yes in step S45), the process proceeds to the next step. Next, in the wavelength tunable laser device 1 according to the second embodiment, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S46). Next, in the wavelength tunable laser device 1 according to the second embodiment, the controller 8 determines whether to end the series of wavelength stabilization control flows (step S47).For example, in the wavelength tunable laser device 1 according to the second embodiment, the series of wavelength stabilization control flows is terminated when a predetermined condition set in advance is satisfied. For example, when the specified oscillation wavelength changes, such as when switching the wavelength, the series of wavelength stabilization control flows is terminated. In the wavelength tunable laser device 1 according to the second embodiment, when the controller 8 determines not to terminate the flow (No in step S47), the process of step S47 is repeatedly executed until it is determined to terminate the flow. On the other hand, in the wavelength tunable laser device 1 according to the second embodiment, when the controller 8 determines to terminate the flow (Yes in step S47), the series of wavelength stabilization control flows is terminated.

[0059] The operating point of the second wavelength discriminator 5 is controlled by the filter control unit 6 so as to increase the wavelength discrimination efficiency. Here, the second wavelength discriminator 5 has a sufficiently high wavelength discrimination efficiency even if the operating point is not the point at which the wavelength discrimination efficiency is highest due to its high wavelength discrimination efficiency. Therefore, the operating point of the second wavelength discriminator 5 controlled by the filter control unit 6 does not have to be the optimal operating point. The second wavelength discriminator 5 has a higher wavelength discrimination efficiency than the first wavelength discriminator 4, and wavelength control is performed using the output signal from the second wavelength discriminator 5, thereby achieving highly efficient wavelength stability control.

[0060] In addition, in the wavelength tunable laser device 1 according to the second embodiment, low frequency noise of the laser can be reduced by repeatedly and continuously executing wavelength control using the output signal (electrical signal) from the first wavelength discriminator 4 until the end of the flow. Furthermore, in the wavelength tunable laser device 1 according to the second embodiment, by performing filter control using the output signal from the second wavelength discriminator 5 one-off, power consumption can be reduced compared to when the filter control is repeatedly and continuously executed until the end of the flow.

[0061] (Embodiment 3) A wavelength tunable laser device and a method for controlling a wavelength tunable laser device according to a third embodiment of the present invention will be described below. Note that in this embodiment, the same configurations as those in the first embodiment will not be described as appropriate.

[0062] The wavelength-tunable laser device 1 of embodiment 3, like the wavelength-tunable laser device 1 of embodiment 1 shown in Figure 1, includes a wavelength-tunable light source 2, an optical branching means 3, a first wavelength discriminator 4, a second wavelength discriminator 5, a filter control unit 6, a wavelength control unit 7, a controller 8, a temperature adjustment element 9, a low-pass filter (LPF) 10, and a high-pass filter (HPF) 11.

[0063] In the wavelength-tunable laser device 1 according to the third embodiment, the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 so as to cancel out the wavelength fluctuations, using the output signal from the first wavelength discriminator 4. Then, in the wavelength-tunable laser device 1 according to the third embodiment, after the filter control unit 6 performs filter control of the second wavelength discriminator 5 (control of the operating point of the second wavelength discriminator 5), the wavelength control unit 7 controls the wavelength of the wavelength-tunable light source 2 so as to cancel out the wavelength fluctuations, using the output signal from the second wavelength discriminator 5.

[0064] Furthermore, in the wavelength-tunable laser device 1 according to the third embodiment, the wavelength control unit 7 performs wavelength control to continuously sweep the oscillation wavelength of the laser light output from the wavelength-tunable light source 2 using the output signal from the first wavelength discriminator 4.

[0065] Fig. 9(a) is a graph showing an example of wavelength control in which the target wavelength is swept from λ1 to λ2 using the output signal from the first wavelength discriminator 4. Fig. 9(b) is a graph showing an example of wavelength control performed using the output signal from the second wavelength discriminator 5 while the target wavelength is being swept.

[0066] In the wavelength tunable laser device 1 according to the third embodiment, for example, as shown in Fig. 9(a), when the wavelength control unit 7 sweeps the target wavelength, which is the target value of the oscillation wavelength, from λ1 to λ2, the target value of the output signal of the first wavelength discriminator 4 is swept from T11 to T12. In addition, in accordance with the wavelength control by the wavelength control unit 7 to sweep the target wavelength, as shown in Fig. 9(b), the filter control unit 6 performs filter control of the second wavelength discriminator 5 using the low-frequency components of the output signal from the second wavelength discriminator 5 so that the second wavelength discriminator 5 is at its optimal operating point. During this time, the wavelength control unit 7 also performs wavelength control using the high-frequency components of the output signal from the second wavelength discriminator 5, so that the wavelength is stabilized even during the sweep of the target wavelength.

[0067] Fig. 10 is a flowchart showing a first example of wavelength stabilization control of the wavelength tunable laser device 1 according to embodiment 3. The first example of wavelength stabilization control of the wavelength tunable laser device 1 according to embodiment 3 shown in Fig. 10 shows a case where, as wavelength control for sweeping the target wavelength, a process for sweeping the target wavelength from λ1 to λ2 and a process for sweeping the target wavelength from λ2 to λ1 are repeatedly and continuously executed until the end of the flow.

[0068] First, in the wavelength-tunable laser device 1 according to the third embodiment, the controller 8 instructs the oscillation wavelength and outputs a laser beam from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S51). Next, in the wavelength-tunable laser device 1 according to the third embodiment, upon receiving one of the two laser beams branched by the optical branching unit 3, wavelength control is repeatedly and continuously performed using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 until the flow ends (step S52). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S53). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S53), it repeatedly executes the process of step S53 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S53), the controller 8 proceeds to the next step in the flow. Next, in the wavelength tunable laser device 1, the filter control unit 6 repeatedly and continuously performs filter control of the second wavelength discriminator 5 using the low-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S54). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S55). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S55), the controller 8 repeatedly performs the process of step S55 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S55), the controller 8 proceeds to the next step in the flow. Next, in the wavelength tunable laser device 1 according to the third embodiment, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S56).

[0069] Next, in the wavelength tunable laser device 1, the wavelength control unit 7 uses the output signal from the first wavelength discriminator 4 input to the controller 8 to continuously sweep the oscillation wavelength. This involves repeatedly sweeping the target wavelength, which is the target value of the oscillation wavelength, from λ1 to λ2 and sweeping the target wavelength from λ2 to λ1 until the flow ends (step S57). For example, the wavelength control unit 7 periodically changes the target value of the output signal from the first wavelength discriminator 4 so that the target wavelength repeatedly changes between λ1 and λ2. Next, in the wavelength tunable laser device 1, the controller 8 determines whether to end the series of wavelength stabilization control flows (step S58). For example, in the wavelength tunable laser device 1 according to the third embodiment, the series of wavelength stabilization control flows ends when a predetermined condition is satisfied. For example, the series of wavelength stabilization control flows ends when the specified oscillation wavelength changes, such as when switching the wavelength. In the wavelength tunable laser device 1 according to the third embodiment, when the controller 8 determines not to end the flow (No in step S58), the process of step S58 is repeatedly executed until it is determined to end the flow. On the other hand, in the wavelength tunable laser device 1 according to the third embodiment, when the controller 8 determines to end the flow (Yes in step S58), the series of wavelength stabilization control flows is ended.

[0070] In the wavelength-tunable laser device 1 according to the third embodiment, even when wavelength sweeping is repeatedly and continuously performed until the end of the flow, it is possible to prevent the wavelength from being stabilized at a wavelength different from the original target wavelength, and it is possible to maintain high wavelength discrimination efficiency of the wavelength discrimination section used for stabilization.

[0071] Fig. 11 is a flowchart showing a second example of wavelength stabilization control of the wavelength tunable laser device 1 according to embodiment 3. The second example of wavelength stabilization control of the wavelength tunable laser device 1 according to embodiment 3 shown in Fig. 11 shows a case where, as wavelength control for sweeping the target wavelength, processing for sweeping the target wavelength from λ1 to λ2 is executed, and the sweeping is terminated when the target wavelength reaches λ2.

[0072] First, in the wavelength-tunable laser device 1 according to the third embodiment, an oscillation wavelength is specified by the controller 8, and laser light is output from the wavelength-tunable light source 2 under the control of the wavelength control unit 7 (step S61). Next, in the wavelength-tunable laser device 1 according to the third embodiment, upon receiving one of the two laser beams branched by the optical branching unit 3, wavelength control using an output signal (electrical signal) output from the first wavelength discriminator 4 to the controller 8 is repeatedly and continuously performed until the flow ends (step S62). Next, the controller 8 compares the output signal output from the first wavelength discriminator 4 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a preset threshold (step S63). If the controller 8 determines that the difference is not equal to or less than the preset threshold (No in step S63), it repeatedly performs the process of step S63 until the difference becomes equal to or less than the preset threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the preset threshold (Yes in step S53), the controller 8 proceeds to the next step in the flow. Next, in the wavelength-tunable laser device 1, the filter control unit 6 repeatedly and continuously performs filter control of the second wavelength discriminator 5 using the low-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S64). Next, the controller 8 compares the output signal from the second wavelength discriminator 5 with a target value previously set for each wavelength, and determines whether the difference therebetween is equal to or less than a predetermined threshold (step S65). If the controller 8 determines that the difference is not equal to or less than the predetermined threshold (No in step S65), it repeatedly performs the process of step S65 until the difference becomes equal to or less than the predetermined threshold. On the other hand, if the controller 8 determines that the difference is equal to or less than the predetermined threshold (Yes in step S65), it proceeds to the next step in the flow. Next, in the wavelength-tunable laser device 1 according to the third embodiment, the wavelength control unit 7 repeatedly and continuously performs wavelength control using the high-frequency component of the output signal from the second wavelength discriminator 5 input to the controller 8 until the end of the flow (step S66).

[0073] Next, in the wavelength tunable laser device 1 according to the third embodiment, the wavelength control unit 7 performs wavelength control using the output signal from the first wavelength discriminator 4 input to the controller 8, sweeping the target wavelength from λ1 to λ2 (step S67). For example, the wavelength control unit 7 changes the target value of the output signal from the first wavelength discriminator 4 in a stepwise manner so that the target wavelength is swept from λ1 to λ2. Next, the controller 8 determines whether the target wavelength has reached λ2 (step S68). If the controller 8 determines that the target wavelength has not reached λ2 (No in step S68), it repeats the process of step S68 until the target wavelength reaches λ2. On the other hand, if the controller 8 determines that the target wavelength has reached λ2 (Yes in step S68), the controller 8 proceeds to the next step. Next, in the wavelength tunable laser device 1 according to the third embodiment, the controller 8 determines whether to end the series of wavelength stabilization control flows (step S69). For example, in the wavelength tunable laser device 1 according to the third embodiment, the series of wavelength stabilization control flows end when a predetermined condition is satisfied. For example, when the instructed oscillation wavelength changes, such as when switching the wavelength, the series of wavelength stabilization control flows is terminated. In the wavelength tunable laser device 1 according to the third embodiment, if the controller 8 determines not to terminate the flow (No in step S69), the process of step S69 is repeatedly executed until it is determined to terminate the flow. On the other hand, in the wavelength tunable laser device 1 according to the third embodiment, if the controller 8 determines to terminate the flow (Yes in step S69), the series of wavelength stabilization control flows is terminated.

[0074] In the wavelength-tunable laser device 1 according to the third embodiment, even when the target wavelength is swept from λ1 to λ2, it is possible to prevent the wavelength from being stabilized at a wavelength different from the original target wavelength, and it is possible to maintain high wavelength discrimination efficiency of the wavelength discrimination section used for stabilization. [Explanation of symbols]

[0075] 1. Tunable wavelength laser device 2. Tunable wavelength light source 3 Optical branching means 4. First wavelength discrimination unit 5 Second wavelength discrimination unit 6 Filter control section 7 Wavelength control section 8 Controller 9 Temperature control element 10 Low-pass filter 11 High-pass filter

Claims

1. a wavelength-tunable light source capable of arbitrarily selecting an oscillation wavelength; a first wavelength discriminator that receives a portion of the output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light; a second wavelength discrimination unit that receives another output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and that is designed to have a higher wavelength discrimination efficiency than the first wavelength discrimination unit; a filter control unit that performs filter control for controlling wavelength discrimination characteristics of the second wavelength discriminator; a wavelength control unit that controls the wavelength of the wavelength-tunable light source; a controller that stores a setting instruction value corresponding to a target wavelength, receives output signals from the first wavelength discrimination unit and the second wavelength discrimination unit, calculates a feedback signal based on the setting instruction value, and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal; a temperature adjustment element on which the wavelength-tunable light source, the first wavelength discrimination unit, and the second wavelength discrimination unit are mounted; Equipped with using the output signal from the first wavelength discriminator, to perform wavelength control of the wavelength tunable light source by the wavelength controller so as to cancel out wavelength fluctuations; performing filter control of the second wavelength discriminator by the filter control unit using a low frequency component of the output signal from the second wavelength discriminator; using a high-frequency component of the output signal from the second wavelength discriminator, the wavelength control unit controls the wavelength of the tunable light source so as to cancel out wavelength fluctuations. A wavelength tunable laser device characterized by:

2. repeatedly and continuously performing wavelength control of the wavelength-tunable light source by the wavelength control unit using the output signal from the first wavelength discriminator; repeatedly and continuously executing the filter control by the filter control unit using the low-frequency component of the output signal from the second wavelength discriminator; the wavelength control unit repeatedly and continuously performs the wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

2. The wavelength tunable laser device according to claim 1.

3. the wavelength control unit performs wavelength control to continuously sweep the oscillation wavelength using the output signal from the first wavelength discrimination unit.

3. The wavelength tunable laser device according to claim 2.

4. performing a single wavelength control of the wavelength tunable light source by the wavelength control unit using the output signal from the first wavelength discriminator; repeatedly and continuously executing the filter control by the filter control unit using the low-frequency component of the output signal from the second wavelength discriminator; the wavelength control unit repeatedly and continuously performs the wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

2. The wavelength tunable laser device according to claim 1.

5. repeatedly and continuously performing wavelength control of the wavelength-tunable light source by the wavelength control unit using the output signal from the first wavelength discriminator; performing a single-shot filter control by the filter control unit using a low-frequency component of the output signal from the second wavelength discriminator; the wavelength control unit repeatedly and continuously performs the wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

2. The wavelength tunable laser device according to claim 1.

6. performing a single wavelength control of the wavelength tunable light source by the wavelength control unit using the output signal from the first wavelength discriminator; performing a single-shot filter control by the filter control unit using a low-frequency component of the output signal from the second wavelength discriminator; the wavelength control unit repeatedly and continuously performs the wavelength control using the high-frequency component of the output signal from the second wavelength discriminator.

2. The wavelength tunable laser device according to claim 1.

7. a wavelength-tunable light source capable of arbitrarily selecting an oscillation wavelength; a first wavelength discriminator that receives a portion of the output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light; a second wavelength discrimination unit that receives another output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and that is designed to have a higher wavelength discrimination efficiency than the first wavelength discrimination unit; a filter control unit that performs filter control for controlling wavelength discrimination characteristics of the second wavelength discriminator; a wavelength control unit that controls the wavelength of the wavelength-tunable light source; a controller that stores a setting instruction value corresponding to a target wavelength, receives output signals from the first wavelength discrimination unit and the second wavelength discrimination unit, calculates a feedback signal based on the setting instruction value, and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal; a temperature adjustment element on which the wavelength-tunable light source, the first wavelength discrimination unit, and the second wavelength discrimination unit are mounted; Equipped with using the output signal from the first wavelength discriminator, to perform wavelength control of the wavelength tunable light source by the wavelength controller so as to cancel out wavelength fluctuations; After the filter control of the second wavelength discriminator is performed by the filter control unit, using the output signal from the second wavelength discriminator, the wavelength control unit controls the wavelength of the tunable light source so as to cancel out wavelength fluctuations. A wavelength tunable laser device characterized by:

8. the output signal from the first wavelength discrimination unit, the output signal from the second wavelength discrimination unit, and the feedback signal from the controller are digital signals or analog signals; 8. The wavelength tunable laser device according to claim 1, wherein the wavelength tunable laser device is a laser diode.

9. The light input to the first wavelength discrimination unit and the second wavelength discrimination unit is obtained by splitting at least a part of forward light from the wavelength-tunable light source or backward light from the wavelength-tunable light source into two by a light splitter, or by splitting at least a part of the forward light and at least a part of the backward light, respectively.

8. The wavelength tunable laser device according to claim 1, wherein the wavelength tunable laser device is a laser diode.

10. a wavelength-tunable light source capable of arbitrarily selecting an oscillation wavelength; a first wavelength discriminator that receives a portion of the output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light; a second wavelength discrimination unit that receives another output light from the wavelength-tunable light source and outputs an output signal, the intensity of the output signal having a periodic characteristic with respect to the wavelength of the output light, and that is designed to have a higher wavelength discrimination efficiency than the first wavelength discrimination unit; a filter control unit that performs filter control for controlling wavelength discrimination characteristics of the second wavelength discriminator; a wavelength control unit that controls the wavelength of the wavelength-tunable light source; a controller that stores a setting instruction value corresponding to a target wavelength, receives output signals from the first wavelength discrimination unit and the second wavelength discrimination unit, calculates a feedback signal based on the setting instruction value, and instructs control parameters of the wavelength control unit and the filter control unit based on the feedback signal; a temperature adjustment element on which the wavelength-tunable light source, the first wavelength discrimination unit, and the second wavelength discrimination unit are mounted; A method for controlling a wavelength tunable laser device comprising: using the output signal from the first wavelength discriminator, to perform wavelength control of the wavelength tunable light source by the wavelength controller so as to cancel out wavelength fluctuations; After the filter control of the second wavelength discriminator is performed by the filter control unit, using the output signal from the second wavelength discriminator, the wavelength control unit controls the wavelength of the tunable light source so as to cancel out wavelength fluctuations.

2. A method for controlling a wavelength tunable laser device, comprising:

11. repeatedly and continuously performing wavelength control of the wavelength-tunable light source by the wavelength control unit using the output signal from the first wavelength discriminator; repeatedly and continuously executing the filter control by the filter control unit using the low-frequency component of the output signal from the second wavelength discriminator; repeatedly and continuously performing the wavelength control by the wavelength control unit using the high-frequency component of the output signal from the second wavelength discriminator; performing wavelength control by continuously sweeping the oscillation wavelength by the wavelength control unit using the output signal from the first wavelength discrimination unit; 11. The method for controlling a wavelength tunable laser device according to claim 10.

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