Laser device and control method thereof

Abstract

Provided is a laser device that: acquires a target frequency of a laser beam; detects a first intensity corresponding to the intensity of the laser beam after the laser beam has passed through a first frequency filter; detects a second intensity corresponding to the intensity of the laser beam after the laser beam has passed through a second frequency filter; detects the intensity of the laser beam; acquires a first ratio corresponding to the ratio of the first intensity with respect to the intensity of the laser beam and a second ratio corresponding to the ratio of the second intensity with respect to the intensity of the laser beam; sets, from one of the first ratio, the second ratio, a third ratio, which is the sum of the first ratio and the second ratio, and a fourth ratio, which is the difference between the first ratio and the second ratio, a monitor value corresponding to a frequency equivalent amount that corresponds to the frequency of the laser beam; acquires a target value corresponding to the target frequency on the basis of one of the first to fourth ratios; and adjusts a control amount so that the absolute value of the difference between the target value and the monitor value is decreased.

Description

[Technical Field]

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

[0002] In a laser device that can vary the frequency of output laser light, a technology is disclosed that controls the frequency of the laser light using two or more frequency filters with transmission characteristics in which the transmittance changes periodically with respect to the frequency of the input light (Patent Document 1).The two or more frequency filters are designed to be out of phase with each other.In this control, the transmitted light of the frequency filter that has the largest change in transmittance with respect to the change in frequency at the target frequency of the laser light is used for control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-140304 Summary of the Invention [Problem to be solved by the invention]

[0004] In a frequency filter whose transmission characteristics change periodically with frequency, the change in transmittance relative to frequency is small in the frequency bands near the extreme values ​​of the transmission characteristics, resulting in a decrease in control accuracy. Such frequency bands are also called dead bands.

[0005] The technology in Patent Document 1 is said to be able to suppress a decrease in control accuracy by setting two or more frequency filters so that they are out of phase with each other and selecting a frequency filter that is not in a dead band at the frequency of the control target.

[0006] However, even if the technology of Patent Document 1 is used, if the transmission characteristics of the frequency filter are shifted in the frequency axis direction (i.e., shifted horizontally) due to an unintended cause, the control target frequency may unintentionally overlap with the dead band of the selected frequency filter. This may result in a decrease in control accuracy. Possible unintended causes of this include temperature fluctuations and changes over time in the frequency filter.

[0007] The present invention has been made in view of the above, and has an object to provide a laser device and a control method thereof that can suppress a decrease in the accuracy of controlling the frequency of laser light. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention provides a laser unit including a light source unit that varies the frequency of laser light to be output, and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that is equivalent to the frequency of the laser light, and a control unit that controls the frequency of the laser light by supplying power corresponding to a control amount to the laser unit, wherein the monitor unit includes a first frequency filter and a second frequency filter that have transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and have phases that are relatively shifted, a first detection unit that detects a first intensity that corresponds to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second frequency filter that detects a first intensity that corresponds to the intensity of the laser light after the laser light has passed through the second frequency filter. and a second detection unit that detects a second intensity corresponding to the intensity of laser light, wherein the control unit obtains a target frequency that is a control target for the frequency of the laser light, obtains a first ratio corresponding to the ratio of the first intensity to the intensity of the laser light and a second ratio corresponding to the ratio of the second intensity to the intensity of the laser light, sets one of the first ratio, the second ratio, a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio as a monitor value that corresponds to the frequency of the laser light, obtains a target value that corresponds to the target frequency based on one of the first to fourth ratios, and controls the control variable so that the absolute value of the difference between the target value and the monitor value becomes small.

[0009] The control unit may calculate the first ratio or the second ratio by applying a correction coefficient to the first intensity, the second intensity, or the intensity of the laser light.

[0010] The control unit may convert the first intensity, the second intensity, and the intensity of the laser light into digital signals, and calculate the first ratio or the second ratio by digital calculation.

[0011] The transmittance of the first and second frequency filters may vary sinusoidally with frequency.

[0012] The control unit may calculate the first ratio or the second ratio by converting a frequency function indicating the transmission characteristics of the first frequency filter or the second frequency filter into a sine function of frequency from the first intensity or the second intensity and the intensity of the laser light.

[0013] The laser unit may be configured to vary the frequency of the laser light by utilizing the Vernier effect.

[0014] The control unit may control the frequency of the laser light by supplying power corresponding to the control amount to the laser unit.

[0015] The device may further include a temperature controller having an installation surface on which the light source unit, the first frequency filter, and the second frequency filter are installed, and the light source unit, the first frequency filter, and the second frequency filter may be installed on the same installation surface of the temperature controller.

[0016] The control unit may prioritize and select a ratio from the first to fourth ratios to be set as a monitor value corresponding to the frequency of the laser light based on a rate of change of the ratio relative to a frequency change at the target value.

[0017] The control unit may prioritize and select a ratio from the first to fourth ratios to be set as a monitor value corresponding to the frequency of the laser light based on the S / N of the ratio to the frequency change at the target value.

[0018] The control unit may prioritize and select a ratio from the first to fourth ratios to be set as a monitor value corresponding to the frequency of the laser light based on the rate of change of the ratio relative to the frequency change at the target value and the S / N.

[0019] The optical fiber may further include a temperature controller having an installation surface on which the light source unit and the first and second frequency filters are installed, and the control unit may correct the control temperature of the temperature controller, and the first ratio or second ratio, or the monitor value so as to offset horizontal or vertical deviations in the transmission characteristics of the first and second frequency filters.

[0020] The optical fiber may further include a temperature controller having an installation surface on which the light source unit and the first and second frequency filters are installed, and an environmental temperature sensor that detects the environmental temperature of the first and second frequency filters, and the control unit may correct the control temperature of the temperature controller, the first ratio or the second ratio, or the monitor value based on the environmental temperature detected by the environmental temperature sensor so as to offset changes in the transmission characteristics of the first and second frequency filters due to the environmental temperature.

[0021] One aspect of the present invention is a control method for a laser device having a light source unit that varies the frequency of an output laser beam, the control method including a first acquisition step of acquiring a target frequency that is a control target for the frequency of the laser beam, a first frequency filter and a second frequency filter having transmission characteristics in which the transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, detecting a first intensity corresponding to the intensity of the laser beam after the laser beam has passed through the first frequency filter, detecting a second intensity corresponding to the intensity of the laser beam after the laser beam has passed through the second frequency filter, and detecting the intensities of the laser beam; a setting step of setting a monitor value corresponding to a frequency equivalent amount equivalent to a frequency of the laser light from any one of the first ratio, the second ratio, a third ratio which is the sum of the first ratio and the second ratio, and a fourth ratio which is the difference between the first ratio and the second ratio; a third acquisition step of acquiring a target value equivalent to the target frequency based on any one of the first to fourth ratios; and an adjustment step of adjusting a control variable so that an absolute value of a difference between the target value and the monitor value becomes small. [Effects of the Invention]

[0022] The present invention provides an advantage in that it is possible to suppress a decrease in the accuracy of controlling the frequency of laser light. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing the configuration of a laser device according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of the light source unit. [Figure 3] FIG. 3 is a block diagram showing the configuration of the control unit according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing a frequency discrimination curve. [Figure 5] FIG. 5 is an explanatory diagram of the margin. [Figure 6] FIG. 6 is a diagram showing the relationship between φ and the margin. [Figure 7] FIG. 7 is a diagram showing temperature-dependent changes in the frequency discrimination curve in the comparative example. [Figure 8] FIG. 8 is a diagram showing the temperature-dependent change of the frequency discrimination curve in the embodiment. [Figure 9] FIG. 9 is a flowchart showing a control method performed by the control unit according to the first embodiment. [Figure 10] FIG. 10 is a flowchart showing a control method when performing correction according to the environmental temperature. [Figure 11] FIG. 11 is a flowchart showing a control method in the laser device of the fourth modified example. [Figure 12] FIG. 12 is a flowchart showing another example of the control method in the laser device of the fourth modified example. [Figure 13] FIG. 13 is a flowchart showing a part of a control method in a laser apparatus according to a further modification of the fourth modification. [Figure 14] FIG. 14 is a flowchart showing a part of a control method in a laser device according to a further modification of the fourth modification. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as an embodiment) 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 designated by the same reference numerals. Furthermore, the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. Furthermore, between drawings, there may be parts whose dimensional relationships and ratios differ. Furthermore, xyz coordinate axes are shown in the drawings as appropriate to explain directions.

[0025] (Embodiment 1) [Schematic configuration of laser device] FIG. 1 is a diagram showing the configuration of a laser device according to the first embodiment. The laser device 1 includes a modularized laser unit 2 and a control unit 3 that executes control steps for controlling the operation of the laser unit 2. In FIG. 1, the laser unit 2 and the control unit 3 are configured as separate units, but they may be integrated into a single module.

[0026] [Configuration of laser unit] The laser unit 2 varies the frequency of the output laser light to one of a plurality of frequencies under the control of the control unit 3, and outputs the laser light of that frequency. The laser unit 2 includes a light source unit 4, a semiconductor optical amplifier (SOA) 5, a planar lightwave circuit (PLC) 6, a photodetector unit 7, a temperature sensor 8, and a temperature controller 9. The planar lightwave circuit 6 and the photodetector unit 7 constitute a monitor unit 10.

[0027] FIG. 2 is a diagram showing the configuration of the light source unit. The light source unit 4 is, for example, a laser that utilizes the Vernier effect, and outputs laser light L1 under the control of the control unit 3. The light source unit 4 includes a laser main body unit 41 that changes the frequency of the output laser light L1, and a changing unit 42. The changing unit 42 has three microheaters that generate heat in response to the power supplied from the control unit 3, and changes the frequency of the laser light L1 output from the laser main body unit 41 by locally heating the laser main body unit 41.

[0028] The laser body 41 includes first and second waveguide sections 43 and 44 formed on a common base section B1. The base section B1 is made of, for example, n-type InP. An n-side electrode 45 made of, for example, AuGeNi is formed on the rear surface of the base section B1 and is in ohmic contact with the base section B1.

[0029] The first waveguide portion 43 has a buried waveguide structure and includes a waveguide portion 431, a semiconductor laminate portion 432, and a p-side electrode 433. The waveguide portion 431 is formed in the semiconductor laminate portion 432 so as to extend in the z direction. In addition, within the first waveguide portion 43, a gain portion 431a and a DBR (Distributed Bragg Reflector) type diffraction grating layer 431b are arranged.

[0030] The gain section 431a is an active layer having a multiple quantum well structure made of InGaAsP and an optical confinement layer, and the diffraction grating layer 431b is composed of a sampled diffraction grating made of InGaAsP and InP.

[0031] The semiconductor laminated portion 432 is configured by laminating InP-based semiconductor layers, and has the function of a cladding portion for the waveguide portion 431, etc.

[0032] The p-side electrode 433 is disposed on the semiconductor laminate 432 along the gain portion 431a. A SiN protective film (not shown) is formed on the semiconductor laminate 432. The p-side electrode 433 is in contact with the semiconductor laminate 432 through an opening (not shown) formed in the SiN protective film.

[0033] Here, DBR heater 421, which is a microheater, is disposed on the SiN protective film of semiconductor laminate 432 so as to be aligned with diffraction grating layer 431b. DBR heater 421 generates heat in response to power supplied from control unit 3, heating diffraction grating layer 431b. Control of the power supplied to DBR heater 421 by control unit 3 changes the temperature of diffraction grating layer 431b, thereby changing its refractive index.

[0034] The second waveguide portion 44 includes a bifurcated portion 441 , two arm portions 442 and 443 , and a ring-shaped waveguide 444 .

[0035] The two-branching section 441 is configured by a 1×2 type branching waveguide including a 1×2 type multi-mode interference (MMI) waveguide 441a, and the two-port side is connected to each of the two arm sections 442 and 443, while the one-port side is connected to the first waveguide section 43. That is, by the two-branching section 441, one ends of the two arm sections 442 and 443 are integrated and optically coupled to the diffraction grating layer 431b.

[0036] The arm portions 442 and 443 both extend in the z direction and are arranged to sandwich the ring-shaped waveguide 444. These arm portions 442 and 443 are optically coupled to the ring-shaped waveguide 444 with the same coupling coefficient κ. The value of κ is, for example, 0.2. The arm portions 442 and 443 and the ring-shaped waveguide 444 form a ring resonator filter RF1. The ring resonator filter RF1 and the two-branch portion 441 form a reflecting mirror M.

[0037] Here, the RING heater 422, which is a microheater, is ring-shaped and is disposed on a SiN protective film (not shown) formed so as to cover the ring-shaped waveguide 444. The RING heater 422 generates heat in response to the power supplied from the control unit 3, thereby heating the ring-shaped waveguide 444. The control unit 3 controls the power supplied to the RING heater 422, thereby changing the temperature of the ring-shaped waveguide 444 and changing the refractive index thereof.

[0038] The two branching portions 441, the arm portions 442, 443, and the ring-shaped waveguide 444 all have a high mesa waveguide structure in which an optical waveguide layer 44a made of InGaAsP is sandwiched between cladding layers made of InP.

[0039] Here, the phase heater 423, which is a microheater, is disposed on a SiN protective film (not shown) on a part of the arm section 443. The region of the arm section 443 below the phase heater 423 functions as a phase adjustment section 445 that changes the phase of light. The phase heater 423 generates heat in response to the power supplied from the control section 3, and heats the phase adjustment section 445. Furthermore, the control section 3 controls the power supplied to the phase heater 423, thereby changing the temperature of the phase adjustment section 445 and changing the refractive index thereof.

[0040] The first and second waveguide sections 43 and 44 described above constitute an optical resonator C, which is made up of a diffraction grating layer 431b optically connected to each other and a reflecting mirror M. The gain section 431a and the phase adjustment section 445 are also disposed within the optical resonator C.

[0041] The diffraction grating layer 431b generates a first comb-shaped reflection spectrum having periodic reflection characteristics at predetermined frequency intervals, while the ring resonator filter RF1 generates a second comb-shaped reflection spectrum having periodic reflection characteristics at predetermined frequency intervals.

[0042] Here, the second comb-like reflection spectrum has a peak with a full width at half maximum that is narrower than the full width at half maximum of the peak of the first comb-like reflection spectrum, and has periodic reflection characteristics at a frequency interval different from the frequency interval of the first comb-like reflection spectrum.

[0043] To illustrate the characteristics of each comb-like reflection spectrum, the frequency interval (free spectral range: FSR) between peaks in the first comb-like reflection spectrum is 373 GHz. The full width at half maximum of each peak is 43 GHz. Meanwhile, the frequency interval (FSR) between peaks in the second comb-like reflection spectrum is 400 GHz. The full width at half maximum of each peak is 25 GHz. That is, the full width at half maximum of each peak in the second comb-like reflection spectrum (25 GHz) is narrower than the full width at half maximum of each peak in the first comb-like reflection spectrum (43 GHz).

[0044] In order to achieve laser oscillation, the light source unit 4 is configured to be able to superimpose one peak of the first comb-shaped reflection spectrum and one peak of the second comb-shaped reflection spectrum on the frequency axis. Such superimposition can be achieved by using at least one of the DBR heater 421 and the RING heater 422 to perform at least one of the following: heating the diffraction grating layer 431b with the DBR heater 421 to change the refractive index thereof by a thermo-optic effect, thereby moving and changing the first comb-shaped reflection spectrum as a whole on the frequency axis; or heating the ring-shaped waveguide 444 with the RING heater 422 to change the refractive index thereof, thereby moving and changing the second comb-shaped reflection spectrum as a whole on the frequency axis.

[0045] Meanwhile, in the light source unit 4, a resonator mode due to the optical resonator C exists. The resonator length of the optical resonator C in the light source unit 4 is set so that the resonator mode spacing (longitudinal mode spacing) is 25 GHz or less. With this setting, the resonator length of the optical resonator C is 1800 μm or more, and it is possible to expect a narrow linewidth of the oscillated laser light. The frequency of the resonator mode of the optical resonator C can be finely adjusted by heating the phase adjustment unit 445 using the phase heater 423 to change its refractive index and thereby move the frequency of the resonator mode overall on the frequency axis. In other words, the phase adjustment unit 445 is a part for actively controlling the optical path length of the optical resonator C.

[0046] The light source unit 4 is configured such that when the control unit 3 injects current from the n-side electrode 45 and the p-side electrode 433 into the gain unit 431a to cause the gain unit 431a to emit light, the light source unit 4 oscillates at a frequency at which the peaks of the spectral components of the first comb-like reflection spectrum, the peaks of the spectral components of the second comb-like reflection spectrum, and one of the resonator modes of the optical resonator C coincide, for example, at 193.4 THz, and outputs laser light L1.

[0047] The light source unit 4 can change the frequency of the laser light L1 by utilizing the Vernier effect. That is, when the DBR heater 421 is controlled by adjusting the power supplied from the control unit 3, the comb-shaped reflection spectrum shifts on the frequency axis. Similarly, when the RING heater 422 is controlled, the comb-shaped reflection spectrum shifts on the frequency axis. Similarly, when the Phase heater 423 is controlled, the spectrum shifts on the frequency axis.

[0048] For example, first, a state is created in which laser oscillation occurs at frequency f1, where the reflection peak of the DBR, the resonator mode of optical resonator C, and the reflection peak of the RING coincide. To achieve this state, the DBR heater 421 and the RING heater 422 each set the frequency positions at which the reflection spectra of the DBR and RING peak based on the power supplied. Furthermore, the phase heater 423 sets the frequency position at which the resonator mode peaks based on the power supplied. From the state in which laser oscillation occurs at frequency f1, the frequency at which the reflection peak of the DBR, the resonator mode of optical resonator C, and the reflection peak of the RING coincide can be set to frequency f2 by controlling each heater. The power supplied to each heater can be controlled using the current as a control variable. That is, the control unit 3 controls the frequency of the laser light L1 by supplying power corresponding to the current, which is the control variable, to the light source unit 4.

[0049] When changing the frequency of the laser light L1 from the first frequency to the second frequency, for example, first, the DBR heater 421 and the RING heater 422 are feedforward controlled so that the comb-like reflection spectra of the DBR and the RING overlap at the second frequency, and then the Phase heater 423 is feedback controlled so that one of the resonator modes coincides with the second frequency. However, the control method is not limited to this.

[0050] Returning to FIG. 1, the explanation will be continued. Although not specifically shown, the semiconductor optical amplifier 5 has a buried waveguide structure including an active core layer made of the same material and structure as the first waveguide section 43. However, the diffraction grating layer 431b is not provided. The semiconductor optical amplifier 5 is optically coupled to the light source section 4 by a spatial coupling optical system (not shown). The laser light L1 output from the light source section 4 is input to the semiconductor optical amplifier 5. When a current is supplied from the control section 3, the semiconductor optical amplifier 5 amplifies the laser light L1 and outputs it as laser light L2. The semiconductor optical amplifier 5 may be configured monolithically with the light source section 4 on the base section B1.

[0051] The planar lightwave circuit 6 is optically coupled to the arm unit 442 by a spatial coupling optical system (not shown). A portion of the laser light L3 generated by laser oscillation in the light source unit 4, similar to the laser light L1, is input to the planar lightwave circuit 6 via the arm unit 442. The laser light L3 has the same frequency as the laser light L1 and an intensity corresponding to the intensity of the laser light L1. The planar lightwave circuit 6 includes an optical branching unit 61, an optical waveguide 62, an optical waveguide 63 having a frequency filter 63a which is a ring resonator type optical filter, and an optical waveguide 64 having a frequency filter 64a which is also a ring resonator type optical filter. The frequency filter 63a is an example of a first frequency filter, and the frequency filter 64a is an example of a second frequency filter.

[0052] The optical branching unit 61 branches the input laser light L3 into three laser lights L4, L5, and L6. The optical waveguide 62 guides the laser light L4 to a PD (Photo Diode) 73 (described later) in the optical detection unit 7. The optical waveguide 63 guides the laser light L5 to a PD 71 (described later) in the optical detection unit 7. The optical waveguide 64 guides the laser light L6 to a PD 72 (described later) in the optical detection unit 7.

[0053] Here, the frequency filter 63a has a transmission characteristic in which the transmittance changes periodically with respect to the frequency of the input light, and transmits the laser light L5 at a transmittance according to the frequency of the laser light L5. The laser light L5 that has passed through the frequency filter 63a is input to the PD 71. In other words, the frequency filter 63a is a waveguide-type frequency filter. Note that an etalon filter or an MZI (Mach-Zehnder Interferometer) filter that has a transmission characteristic that changes periodically with respect to the frequency of the input light may also be used as the frequency filter 63a.

[0054] Similarly, the frequency filter 64a has a transmission characteristic in which the transmittance changes periodically with respect to the frequency of the input light, and transmits the laser light L6 at a transmittance according to the frequency of the laser light L6. The laser light L6 that has passed through the frequency filter 64a is input to the PD 72. The frequency filter 64a may be an etalon filter or an MZI filter that has a transmission characteristic that changes periodically with respect to the frequency of the input light.

[0055] The transmission characteristics of the frequency filters 63a and 64a preferably have the same period. As will be described in detail later, the transmission characteristics of the frequency filters 63a and 64a are relatively out of phase with each other.

[0056] The light detection unit 7 includes PDs 71, 72, and 73, and executes a detection step. The PD 73 receives laser light L4 (which has the same frequency as the laser light L1 output from the light source unit 4 and has an intensity corresponding to the intensity of the laser light L1) and outputs an electrical signal corresponding to the intensity of the laser light L4 to the control unit 3. The PD 71 receives laser light L5 that has passed through the frequency filter 63a and outputs an electrical signal corresponding to the intensity of the laser light L5 to the control unit 3. The PD 72 receives laser light L6 that has passed through the frequency filter 64a and outputs an electrical signal corresponding to the intensity of the laser light L6 to the control unit 3. The electrical signals output from the PDs 71, 72, and 73 are used for frequency lock control by the control unit 3 (control for adjusting the frequency of the laser light L1 output from the light source unit 4 to a target frequency).

[0057] PD71 is an example of a first detector that detects a first intensity, which is the intensity of laser light L5, corresponding to the intensity of laser light L1 after passing through frequency filter 63a. PD72 is an example of a second detector that detects a second intensity, which is the intensity of laser light L6, corresponding to the intensity of laser light L1 after passing through frequency filter 64a. PD73 is an example of a third detector that detects a third intensity, which is the intensity of laser light L4, corresponding to the intensity of laser light L1.

[0058] The temperature sensor 8 is formed of, for example, a thermistor, and is placed on the installation surface 91 of the temperature controller 9 to detect the ambient temperature of the light source unit 4 and the planar lightwave circuit 6. Note that the temperature sensor 8 may be placed outside the temperature controller 9 to detect the temperature of the environment in which the laser device 1 is placed as the ambient temperature. The temperature sensor 8 outputs an electrical signal including information about the detected temperature to the control unit 3.

[0059] The temperature controller 9 is configured, for example, by a TEC (Thermo Electric Cooler) including a Peltier element. The light source unit 4, the semiconductor optical amplifier 5, the planar lightwave circuit 6, the photodetector unit 7, and the temperature sensor 8 are mounted on this temperature controller 9. The temperature controller 9 controls the temperatures of the light source unit 4, the semiconductor optical amplifier 5, the planar lightwave circuit 6, the photodetector unit 7, and the temperature sensor 8 according to the power supplied thereto. In this case, the control unit 3 controls the power supplied to the temperature controller 9 based on information about the temperature detected by the temperature sensor 8, mainly so that the light source unit 4 maintains a constant temperature. Controlling mainly so that the light source unit 4 maintains a constant temperature is preferable in terms of suppressing fluctuations in the frequency of the laser light L1 that depend on the operating conditions and the external environmental temperature.

[0060] In the case where the temperature controller 9 divides the installation surface 91 on which the light source unit 4, the semiconductor optical amplifier 5, the planar lightwave circuit 6, the photodetector unit 7, and the temperature sensor 8 are placed into two areas: a first area Ar1 on which the light source unit 4 and the semiconductor optical amplifier 5 are placed, and a second area Ar2 on which the planar lightwave circuit 6 and the photodetector unit 7 are placed, the temperature sensor 8 may be placed in the first area Ar1. In this case, the temperature sensor 8 may be placed close to the light source unit 4 or on the light source unit 4. Alternatively, the temperature sensor 8 may be placed in the second area Ar2 and close to the planar lightwave circuit 6.

[0061] [Configuration of the control unit] Next, the configuration of the control unit 3 will be described. Fig. 3 is a block diagram showing the configuration of the control unit. The control unit 3 is connected to a higher-level control device (not shown) equipped with a user interface, for example, and controls the operation of the light source unit 4 according to instructions from a user via the higher-level control device.

[0062] The following description will mainly focus on frequency lock control by the control unit 3, which is a main part of the present invention. For ease of explanation, Fig. 3 mainly illustrates the configuration of the control unit 3 that executes frequency lock control.

[0063] The control unit 3 includes analog-to-digital converters (ADC) 31, 32, 33, and 34, a calculation unit 35, a storage unit 36, and a current source 37.

[0064] The ADC 31 converts the analog electrical signal input from the PD 71 into a digital signal (voltage signal) and outputs it to the calculation unit 35. The ADC 32 converts the analog electrical signal input from the PD 72 into a digital signal (voltage signal) and outputs it to the calculation unit 35. The ADC 33 converts the analog electrical signal input from the PD 73 into a digital signal (voltage signal) and outputs it to the calculation unit 35. The ADC 34 converts the analog electrical signal input from the temperature sensor 8 into a digital signal (voltage signal) and outputs it to the calculation unit 35.

[0065] The calculation unit 35, which performs digital calculations, performs various types of calculations for the control executed by the control unit 3, and is configured, for example, by a CPU (Central Processing Unit) or FPGA (Field Programmable Gate Array). The storage unit 36 ​​has a portion configured, for example, by a ROM (Read Only Memory) in which various programs, data, etc. used by the calculation unit 35 to perform calculations are stored, and a portion configured, for example, by a RAM (Random Access Memory) used as a workspace when the calculation unit 35 performs calculations and for storing the results of the calculations of the calculation unit 35. The control function of the control unit 3 is realized by software using the functions of the calculation unit 35 and the storage unit 36.

[0066] The current source 37 supplies power to the light source unit 4 for controlling the frequency of the laser light L1 based on an instruction from the calculation unit 35. In this embodiment, the calculation unit 35 instructs the current source 37 on a current value as a control amount. The current source 37 supplies the light source unit 4 with a current of the instructed current value.

[0067] Next, the configuration of the calculation unit 35 will be described in detail. The calculation unit 35 includes, as functional units, a target frequency setting unit 351, a discrimination curve selection unit 352, a target value acquisition unit 353, a monitor value calculation unit 354, a difference acquisition unit 355, a PID control unit 356, and a DBR / RING power setting unit 357. These functional units are realized by the cooperation of software and hardware resources.

[0068] The target frequency setting unit 351 performs a first acquisition step of acquiring and setting a target frequency as a target value in controlling the frequency of the laser light L1, for example, in response to an instruction from a higher-level control device.

[0069] The discrimination curve selection unit 352 acquires the set target frequency and selects one of the first, second, third, and fourth frequency discrimination curves based on the target frequency. The first frequency discrimination curve corresponds to the transmission characteristics of the frequency filter 63a. The second frequency discrimination curve corresponds to the transmission characteristics of the frequency filter 64a. The third frequency discrimination curve is represented by the sum of the first and second frequency discrimination curves. The fourth frequency discrimination curve is represented by the difference between the first and second frequency discrimination curves.

[0070] When the first and second frequency discrimination curves, which are normalized so that the amplitude value varies between -1 and 1, vary sinusoidally with respect to the change in frequency, they can be expressed by sine functions (cosine functions) such as those shown in the following equations (1) and (2). Note that θ=2πf / F, where f is the frequency of light. F is the period or FSR (Free Spectral Range) of the discrimination curve, and is equal to the period of frequency filter 63a and frequency filter 64a. Furthermore, φ is the phase difference corresponding to the relative phase shift between frequency filter 63a and frequency filter 64a. sinθ (1) sin(θ+φ) (2)

[0071] The third and fourth frequency discrimination curves normalized so that the amplitude value varies between -1 and 1 are expressed by the following equations (3) and (4), where Δ=φ-π / 2. sin(θ+π / 4+Δ / 2) (3) sin(θ-π / 4+Δ / 2) (4)

[0072] FIG. 4 shows a first frequency discrimination curve C1, a second frequency discrimination curve C2, a third frequency discrimination curve C3, and a fourth frequency discrimination curve C4, normalized so that the amplitude value varies between −1 and 1. The horizontal axis represents frequency, normalized so that a half cycle of the discrimination curve is 1. The vertical axis represents ratios corresponding to the first ratio, the second ratio, the third ratio, and the fourth ratio for the first frequency discrimination curve C1, the second frequency discrimination curve C2, the third frequency discrimination curve C3, and the fourth frequency discrimination curve C4, respectively. Note that in FIG. 4, the phase shift φ is set to π / 2. Note that even if the phase shift φ between the first frequency discrimination curve and the second frequency discrimination curve is not π / 2, the phase shift between the third frequency discrimination curve and the fourth frequency discrimination curve will be π / 2 if the amplitudes of the first frequency discrimination curve and the second frequency discrimination curve are approximately equal.

[0073] The regions C11, C21, C31, and C41 are regions in the first to fourth frequency discrimination curves C1 to C4 where, unlike the dead zones, the rate of change of the ratio with respect to frequency is large and control accuracy can be improved. The regions C11, C21, C31, and C41 are set so as not to overlap with each other in terms of frequency.

[0074] Based on the target frequency, the discrimination curve selection unit 352 selects a frequency discrimination curve corresponding to one of the regions C11, C21, C31, and C41 that includes the target frequency. For example, if the target frequency is included in region C11, the discrimination curve selection unit 352 selects the first frequency discrimination curve C1. When selecting a frequency discrimination curve, it is preferable to select a frequency discrimination curve with a larger rate of change of the ratio relative to the frequency. In the case of FIG. 4, it is preferable to select, from among the multiple frequency discrimination curves, a frequency discrimination curve with a small absolute value of the ratio at the target frequency.

[0075] The target value acquiring unit 353 performs a third acquiring step of acquiring a target value by applying the target frequency to the frequency discrimination curve selected by the discrimination curve selecting unit 352. For example, in Fig. 4, when the target frequency is f_tgt, the target value R_tgt is acquired by applying the target frequency to the first frequency discrimination curve C1.

[0076] The monitor value calculation unit 354 performs a second acquisition step of acquiring the first ratio and the second ratio from the digital signals input from the ADCs 31, 32, and 33, and also performs a step of calculating the third ratio or the fourth ratio. Then, a setting step of setting one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value R_mon corresponding to the frequency of the laser light L1 is performed. The monitor value R_mon is an example of a frequency equivalent. While this example illustrates a case where the target frequency and the frequency of the laser light L1 are located in the same region (e.g., region C11), the monitor value R_mon and the target value R_tgt may be set on the same frequency discrimination curve.

[0077] The first ratio is the ratio of the first intensity detected by PD71 to the third intensity detected by PD73. Alternatively, the first ratio may be the ratio of the intensity obtained by applying a correction coefficient to the first intensity detected by PD71 to the intensity obtained by applying a correction coefficient to the third intensity detected by PD73. Alternatively, the first ratio may be a quantity equivalent to the ratio calculated using the intensity obtained by applying a correction coefficient to either the first intensity or the third intensity. Hereinafter, the first ratio may be referred to as PD1 / PD3.

[0078] The second ratio is the ratio of the second intensity detected by PD72 to the third intensity detected by PD73. Furthermore, as an equivalent to this ratio, the first ratio may be the ratio of the intensity obtained by applying a correction coefficient to the second intensity detected by PD72 to the intensity obtained by applying a correction coefficient to the third intensity detected by PD73. Furthermore, as an equivalent quantity to this ratio, the second ratio may be calculated using the intensity obtained by applying a correction coefficient to either the second intensity or the third intensity. Hereinafter, the second ratio may be referred to as PD2 / PD3.

[0079] The correction coefficients for the first intensity, the second intensity, or the third intensity are obtained in advance by experiments or the like, and are stored in the storage unit 36 ​​in the form of table data, relational expressions, or the like, and are read and used by the monitor value calculation unit 354 as appropriate. The correction coefficients may be determined, for example, according to the operating conditions of the laser device 1 or the temperature detected by the temperature sensor 8. The correction coefficients may also be determined so as to be suitable for application to a normalized frequency discrimination curve. The correction coefficients are applied to the first intensity, the second intensity, or the third intensity by, for example, addition, subtraction, multiplication, or division.

[0080] The third ratio is the sum of the first and second ratios. The fourth ratio is the difference between the first and second ratios. Thus, the third or fourth ratio may include a correction factor for the first intensity, the second intensity, or the third intensity.

[0081] The difference acquisition unit 355 calculates and acquires the difference between the target value R_tgt acquired by the target value acquisition unit 353 and the monitor value R_mon calculated by the monitor value calculation unit 354 .

[0082] The PID control unit 356 calculates a current instruction value based on the difference between the target value R_tgt and the monitor value R_mon, outputs the instruction value to the current source 37, and performs feedback control such as proportional-integral-derivative (PID) control or PI control. That is, the PID control unit 356 performs an adjustment step of adjusting the current value (control amount) so that the absolute value of the difference between the target value R_tgt and the monitor value R_mon becomes smaller.

[0083] The DBR / RING power setting unit 357 sets the power to be supplied to each of the DBR heater 421 and the RING heater 422 based on the target frequency set by the target frequency setting unit 351. The DBR / RING power setting unit 357 sets a current value based on the set power, and outputs an instruction for that current value to the current source 37, thereby performing feedforward control of the DBR heater 421 and the RING heater 422.

[0084] In the laser device 1 configured in this manner, the control target frequency is prevented from unintentionally overlapping with the dead band, and therefore, the decrease in the control accuracy of the frequency of the laser light can be suppressed.

[0085] Below, we will explain how unlikely it is that the control target frequency and the dead band will overlap when a lateral shift occurs by introducing a parameter called "margin." Margin is a parameter that serves as an evaluation index for the tolerance of the frequency monitor / control system to lateral shifts.

[0086] FIG. 5 is an explanatory diagram of the margin. FIG. 5 shows a fifth frequency discrimination curve C5 and a sixth frequency discrimination curve C6, which are sine functions normalized so that the amplitude value varies between −1 and 1. Regions C51 and C61 in the fifth and sixth frequency discrimination curves C5 and C6 are regions where, unlike the dead zone, the rate of change of the ratio with respect to frequency is large, enabling high control accuracy. Regions C51 and C61 are set so as not to overlap with each other in terms of frequency.

[0087] In Figure 5, the margin can be defined as the frequency difference between the point closest to the extreme value among the switching points of the two frequency discrimination curves and the center of the dead zone, i.e., the extreme value of the frequency discrimination curve (the minimum value in Figure 5). The larger the margin, the more it can be said that the frequency of laser light L1 can be monitored in a frequency region farther away from the dead zone, and therefore the higher the tolerance to lateral deviation. When frequency control is performed by switching between two frequency discrimination curves as shown in Figure 5, the margin is φ / 2.

[0088] FIG. 6 shows the relationship between φ and the margin. Line M1 shows the relationship between φ and the margin when the first and second frequency discrimination curves shown in equations (1) and (2) are used. Line M2 shows the relationship between φ and the margin when the first to third frequency discrimination curves shown in equations (1) to (3) are used. Line M2 overlaps with line M1 when φ is 90 degrees or less. Line M3 shows the relationship between φ and the margin when the first, second, and fourth frequency discrimination curves shown in equations (1), (2), and (4) are used. Line M3 overlaps with line M1 when φ is 90 degrees or more. Line M4 shows the relationship between φ and the margin when the first to fourth frequency discrimination curves shown in equations (1) to (4) are used. Line M4 overlaps with line M3 when φ is 60 degrees or less and with line M2 when φ is 120 degrees or more.

[0089] As shown in Figure 6, when the first to fourth frequency discrimination curves are used, the margin is high at all φ values, confirming that the frequency monitor / control system has high tolerance to lateral deviations.

[0090] 7 is a diagram showing temperature-dependent changes in the frequency discrimination curve in a comparative example, in which the laser device 1 performs frequency control using only the first and second frequency discrimination curves.

[0091] FIG. 7 shows a fifth frequency discrimination curve C5 and a sixth frequency discrimination curve C6, similar to FIG. 5 . However, the phase shift between the fifth frequency discrimination curve C5 and the sixth frequency discrimination curve C6 is π / 2. In region C51, points on the fifth frequency discrimination curve C5 corresponding to four exemplary target frequencies are indicated by solid white circles. Meanwhile, frequency discrimination curve C5A indicates a state in which the fifth frequency discrimination curve C5 has shifted laterally toward the positive frequency side due to temperature change, and frequency discrimination curve C5B indicates a state in which the fifth frequency discrimination curve C5 has shifted laterally toward the negative frequency side due to temperature change. Regions C5F, C5AF, and C5BF indicate the dead zones of the fifth frequency discrimination curve C5, the frequency discrimination curve C5A, and the frequency discrimination curve C5B, respectively.

[0092] When a lateral shift causes the frequency discrimination curve to be in the C5A state, the most negative point of the four target frequencies overlaps with the dead zone C5AF due to the lateral shift, as shown by the dashed white circle. Also, when a lateral shift causes the frequency discrimination curve to be in the C5B state, the most positive point of the four target frequencies overlaps with the dead zone C5BF due to the lateral shift, as shown by the dashed white circle. This indicates that the comparative configuration has low tolerance for lateral shift.

[0093] On the other hand, Fig. 8 is a diagram showing temperature-dependent changes in the frequency discrimination curve in this embodiment. Similar to Fig. 4, Fig. 8 shows first to fourth frequency discrimination curves C1 to C4. Here, in region C11, points on the first frequency discrimination curve C1 corresponding to three exemplary target frequencies are indicated by solid white circles. Meanwhile, frequency discrimination curve C1A shows a state in which the first frequency discrimination curve C1 has shifted laterally toward the positive frequency side due to temperature changes, and frequency discrimination curve C1B shows a state in which the first frequency discrimination curve C1 has shifted laterally toward the negative frequency side due to temperature changes. Regions C1F, C1AF, and C1BF show the dead zones of the first frequency discrimination curve C1, the frequency discrimination curve C1A, and the frequency discrimination curve C1B, respectively.

[0094] In the case of this embodiment, even if the frequency discrimination curve C1A is reached due to a lateral shift, none of the three target frequency points overlaps with the dead zone C1AF, as shown by the white dotted circles. Also, even if the frequency discrimination curve C1B is reached due to a lateral shift, none of the three target frequency points overlaps with the dead zone C1BF, as shown by the white dotted circles. This demonstrates that the embodiment has high tolerance to lateral shifts.

[0095] [Control Method] Next, a control method executed in the laser device 1 will be described with reference to the flowchart of FIG.

[0096] First, in step S101, the target frequency setting unit 351 sets a target frequency as a target value for the frequency of the laser light L1. Next, although not shown, the DBR / RING power setting unit 357 sets the power to be supplied to each of the DBR heater 421 and the RING heater 422 based on the target frequency set by the target frequency setting unit 351, and outputs to the current source 37 an instruction value for a current value corresponding to that power.

[0097] Next, in step S102, the discrimination curve selection unit 352 selects one of the first frequency discrimination curve, the second frequency discrimination curve, the third frequency discrimination curve, and the fourth frequency discrimination curve based on the target frequency. For example, from the first frequency discrimination curve, the second frequency discrimination curve, the third frequency discrimination curve, and the fourth frequency discrimination curve, the frequency discrimination curve that has the largest rate of change at the target frequency set in step S101 may be selected, or all of the frequency discrimination curves may be normalized so that the amplitude value varies between −1 and 1, and the frequency discrimination curve that has the smallest absolute value at the target frequency may be selected.

[0098] When the first frequency discrimination curve is selected (step S102, curve 1), in step S103, the target value acquisition unit 353 acquires and determines the target value R_tgt corresponding to the target frequency based on the first frequency discrimination curve. Subsequently, in step S104, the monitor value calculation unit 354 calculates and sets the monitor value R_mon corresponding to the frequency of the laser light L1 based on the first frequency discrimination curve. Thereafter, the flow proceeds to step S111.

[0099] When the second frequency discrimination curve is selected (step S102, curve 2), in step S105, the target value acquisition unit 353 acquires and determines the target value R_tgt corresponding to the target frequency based on the second frequency discrimination curve. Subsequently, in step S106, the monitor value calculation unit 354 calculates and sets the monitor value R_mon corresponding to the frequency of the laser light L1 based on the second frequency discrimination curve. Thereafter, the flow proceeds to step S111.

[0100] If the third frequency discrimination curve is selected (step S102, curve 3), in step S107, the target value acquisition unit 353 acquires and determines the target value R_tgt corresponding to the target frequency based on the third frequency discrimination curve. Subsequently, in step S108, the monitor value calculation unit 354 calculates and sets the monitor value R_mon corresponding to the frequency of the laser light L1 based on the third frequency discrimination curve. Thereafter, the flow proceeds to step S111.

[0101] If the fourth frequency discrimination curve is selected (step S102, curve 4), in step S109, the target value acquisition unit 353 acquires and determines the target value R_tgt corresponding to the target frequency based on the fourth frequency discrimination curve. Subsequently, in step S110, the monitor value calculation unit 354 calculates and sets the monitor value R_mon corresponding to the frequency of the laser light L1 based on the fourth frequency discrimination curve. Thereafter, the flow proceeds to step S111.

[0102] Next, in step S111, the difference acquisition unit 355 calculates and acquires the difference between the target value R_tgt and the monitor value R_mon (target value R_tgt-monitor value R_mon).

[0103] Next, in step S112, the PID control unit 356 calculates a current instruction value that reduces the absolute value of the difference between the target value R_tgt and the monitor value R_mon.

[0104] Subsequently, in step S113, the PID control unit 356 outputs the calculated instruction value to the current source 37.

[0105] Next, in step S114, the PID control unit 356 determines whether the absolute value of the difference |target value R_tgt-monitor value R_mon| is within the target error. If it is determined that it is not within the target error (step S114, No), the control proceeds to step S115.

[0106] In step S115, the control unit 3 checks the discrimination curve selected by the discrimination curve selection unit 352. If it is confirmed that the first frequency discrimination curve has been selected (step S115, curve 1), the flow returns to step S104. If it is confirmed that the second frequency discrimination curve has been selected (step S115, curve 2), the flow returns to step S106. If it is confirmed that the third frequency discrimination curve has been selected (step S115, curve 3), the flow returns to step S108. If it is confirmed that the fourth frequency discrimination curve has been selected (step S115, curve 4), the flow returns to step S110.

[0107] On the other hand, in step S114, if the PID control unit 356 determines that |target value R_tgt-monitored value R_mon| is within the target error (step S114, Yes), the control ends.

[0108] As described above, in the laser device 1, the control target frequency is prevented from unintentionally overlapping with the dead band, and therefore, the decrease in the control accuracy of the frequency of the laser light can be suppressed.

[0109] Furthermore, in the laser device 1, four frequency discrimination curves are generated using two frequency filters 63a and 64a, which reduces the complexity of the configuration and control of the laser device compared to when the number of frequency filters is increased. Furthermore, since the detector that detects the intensity of the laser light is shared to some extent for the frequency discrimination curves, it is not necessary to switch the detector each time the frequency discrimination curve is switched. As a result, it is possible to prevent control from becoming unstable when the frequency discrimination curve is switched.

[0110] Furthermore, the laser device 1 can calculate the first or second ratio by applying a correction coefficient to the first intensity, the second intensity, or the third intensity. This allows the first or second ratio, as well as the third or fourth ratio, to be calculated depending on the operating conditions of the laser device 1, the temperature detected by the temperature sensor 8, and the appropriateness of fitting to the frequency discrimination curve. Specifically, depending on the temperature detected by the temperature sensor 8, a correction coefficient can be set to correct a horizontal deviation of the frequency filter that depends on temperature, or a correction coefficient can be set to correct a vertical deviation of the frequency filter that depends on temperature. Here, the vertical deviation of the frequency filter refers to a deviation in the transmission characteristics of the frequency filter along the transmittance axis. The vertical deviation can cause the target frequency to be out of control or an unachievable target value to be set. Furthermore, for example, if the transmission characteristics of the frequency filters 63a and 64a are not a sine function of frequency, the correction coefficient can be used to correct the first intensity, the second intensity, or the third intensity so that they fit to a frequency discrimination curve that is a sine function of frequency. In addition, when the temperature sensor 8 is placed in the first area Ar1, a second temperature sensor is placed separately from the temperature sensor 8 (first temperature sensor), and the power supplied to the temperature controller 9 is controlled based on information about the temperature detected by the temperature sensor 8, a correction coefficient may be set to correct at least one of the horizontal and vertical misalignments of the frequency filter based on information about the temperature detected by the second temperature sensor. In this case, the second temperature sensor may be placed in the second area Ar2, or may be placed closer to the planar lightwave circuit 6 than the light source unit 4. Alternatively, the second temperature sensor may be placed in a location different from the laser unit 2 (for example, outside the housing when the laser unit 2 is housed in the housing).

[0111] Furthermore, if the transmission characteristics of the frequency filters 63a and 64a are periodic functions that are not sinusoidal, a function for converting them to a sinusoidal function may be derived using a fast Fourier transform (FFT) and an inverse fast Fourier transform (IFFT). For example, the digital signals converted by the ADCs 31 and 32 may be accumulated for one or more periods, subjected to an FFT, and components other than the FSRs of the frequency filters 63a and 64a may be removed and then subjected to an IFFT to convert them to a sinusoidal function. The function thus derived is used for conversion to a sinusoidal function. Since the frequency transmission characteristics of an MZI filter can be treated as varying sinusoidally with respect to frequency, conversion to a sinusoidal function using an FFT and an IFFT is not necessary when using MZI filters as the frequency filters 63a and 64a. When using ring resonator filters as the frequency filters 63a and 64a, if the Q value of the frequency transmission characteristics of the filter is small, they can be treated as varying sinusoidally with respect to frequency.

[0112] Furthermore, in the laser device 1, a single temperature controller 9 controls the temperatures of both the light source unit 4 and the planar lightwave circuit 6, thereby achieving lower power consumption and lower costs than if a temperature controller were provided for each of the light source unit 4 and the planar lightwave circuit 6. However, if the control unit 3 mainly controls the power supplied to the temperature controller 9 so that the light source unit 4 maintains a constant temperature, or if the control unit 3 controls the oscillation frequency of the laser light output by the light source unit 4 by controlling the power supplied to the light source unit 4, temperature-dependent lateral deviation may easily occur in the frequency filters 63a, 64a of the planar lightwave circuit 6. In contrast, the laser device 1 has a configuration that is highly resistant to lateral deviation, making it suitable for suppressing a decrease in control accuracy.

[0113] Furthermore, in the laser device 1, the third ratio and the fourth ratio contain information on both the first ratio, which reflects the characteristics of the frequency filter 63a, and the second ratio, which reflects the characteristics of the frequency filter 64a. This means that if the voltage value of either the first ratio or the second ratio changes by even 1 bit relative to the frequency in the digital signals converted by the ADCs 31, 32, and 33, the change can be detected. In other words, even if the target value or the monitor value falls into the dead zone due to a lateral shift or the like, or if the phase shift φ is close to 0 or π, the change in the monitor value can be detected, and therefore frequency control can be performed.

[0114] Furthermore, in the laser device 1, the first ratio or the second ratio is calculated by applying a correction coefficient to the first intensity, the second intensity, or the third intensity, but the correction coefficient may be applied when the target value acquisition unit 353 acquires the target value from the target frequency. This correction coefficient is acquired in advance through experiments or the like and stored in the storage unit 36, and can be set according to the operating conditions of the laser device 1 and the temperature detected by the temperature sensor 8 or the second temperature sensor. Furthermore, when acquiring the target value from the target frequency, the target value may be acquired from the target frequency using a method similar to the method of converting a function other than a sine function into a sine function using FFT and IFFT.

[0115] Furthermore, in the laser device 1, the sum and difference calculations for calculating the third and fourth ratios are performed by digital calculations in the calculation unit 35, but the sum and difference calculations may also be performed by analog circuits. Using digital calculations makes it possible to reduce the number of elements used and the circuit size, and to achieve lower costs. Furthermore, using analog circuits makes it possible to prevent information loss due to quantization during digitization.

[0116] (Variation) Furthermore, the first modified example of the laser device 1 may further include a temperature sensor that detects the environmental temperature of the frequency filters 63 a and 64 a. Then, the calculation unit 35 may correct the control temperature and the first ratio or the second ratio of the temperature controller 9 based on the environmental temperature detected by the environmental temperature sensor so as to offset changes in the transmission characteristics of the frequency filters 63 a and 64 a due to the environmental temperature.

[0117] The environmental temperature sensor is constituted by, for example, a thermistor. The environmental temperature sensor may be placed at a position where it can detect the environmental temperature of the frequency filters 63a and 64a, and the position is not particularly limited. For example, if the laser unit 2 is housed in a housing, the environmental temperature sensor may be placed outside the housing, and may be provided in the control unit 3, for example. The environmental temperature sensor outputs an electrical signal containing information about the detected temperature to the ADC of the control unit 3. The ADC converts the analog electrical signal input from the environmental temperature sensor into a digital signal and outputs the digital signal to the calculation unit 35.

[0118] When the ambient temperature changes, even if the temperature controller 9 is controlled so that the light source unit 4 is at a constant temperature, the temperatures of the frequency filters 63a and 64a change, causing the first to fourth frequency discrimination curves to shift horizontally or vertically.

[0119] Similar vertical or horizontal misalignment can also occur due to other factors. Examples of such factors include changes in the heat generation (SOA heat generation) of the semiconductor optical amplifier 5 due to changes in the intensity of the laser light L2, and changes in the frequency filters 63a and 64a over time due to long-term use of the laser device 1. The frequency characteristics of the frequency filters 63a and 64a can change over time as the laser device 1 approaches the end of its product life after long-term use. Hereinafter, such unintended changes in the characteristics of the frequency filters 63a and 64a over a long period of time will be referred to as "deterioration." The following discussion will mainly focus on horizontal or vertical misalignment due to changes in environmental temperature and its correction, but horizontal or vertical misalignment due to other factors can also be corrected in the same way.

[0120] In a control method executed in the laser device 1 when horizontal or vertical deviation occurs due to a change in environmental temperature, the calculation unit 35 sets a temperature correction coefficient for correcting the target temperature of the ambient temperature of the light source unit 4 (the control target temperature of the temperature controller 9) based on the environmental temperature of the frequency filters 63a and 64a detected by the environmental temperature sensor. The frequency filters 63a and 64a are arranged in a state in which their temperature changes in response to the control of the temperature controller 9. As a result, correcting the target temperature changes the thermal effect of the temperature controller 9 on the frequency filters 63a and 64a, and therefore the temperatures of the frequency filters 63a and 64a also change. By setting the temperature correction coefficient so as to offset the change in the transmission characteristics of the frequency filters 63a and 64a due to the environmental temperature in response to this temperature change, it is possible to reduce the horizontal or vertical deviation of the first to fourth discrimination curves due to the environmental temperature. Here, "offsetting" does not necessarily mean completely canceling the horizontal or vertical deviation of the first to fourth discrimination curves due to the environmental temperature, but also includes so-called "subtraction," which means canceling so that the horizontal or vertical deviation is less than when the target temperature is not corrected. Furthermore, the application of the correction coefficient is, for example, application by any of the operations of addition, subtraction, multiplication, and division.

[0121] Table 1 shows an example of the relationship between the ambient temperature and the temperature correction coefficient. These relationships are obtained, for example, during calibration, such as during manufacturing, shipping, or maintenance of the laser device 1. In Table 1, the temperature correction coefficient is represented as the LD offset temperature. In the example shown in Table 1, it is assumed that the ambient temperature varies from -5°C to 80°C. For example, the target temperature for the light source unit 4 is a predetermined value higher than 35°C and lower than 80°C. When the ambient temperature is 35°C, the LD offset temperature is 0°C. When the ambient temperature is -5°C, the LD offset temperature is ΔT1 [°C]. When the ambient temperature is 80°C, the LD offset temperature is ΔT2 [°C]. Both ΔT1 and ΔT2 are used for correction by being added to the target temperature. ΔT1 is, for example, a positive value, and ΔT2 is, for example, a negative value. This relationship is stored in the memory unit 36 ​​as first relationship information between the ambient temperature and the temperature correction coefficient. The first relationship information includes table data or a relational expression that associates the ambient temperature with the temperature correction coefficient. The LD offset temperature when the environmental temperature is a value other than -5°C, 35°C, or 80°C may be stored in the storage unit 36 ​​as table data or a relational expression, or may be calculated by interpolation from the LD offset temperatures when the environmental temperature is -5°C, 35°C, or 80°C. The environmental temperature when the LD offset temperature is 0°C may be referred to as the reference temperature below. In the case of Table 1, the reference temperature is 35°C.

[0122] [Table 1]

[0123] Similar measures can be taken when horizontal or vertical deviations occur due to changes in the SOA heat generation amount or deterioration of the frequency filters 63a and 64a. For deviations due to changes in the SOA heat generation amount, the temperature correction coefficient is determined by similarly defining the relationship between the SOA heat generation amount or the SOA current value (the value of the current supplied to the semiconductor optical amplifier 5) and the temperature correction coefficient. For deviations due to deterioration of the frequency filters 63a and 64a, the temperature correction coefficient is determined by similarly defining the relationship between some quantity reflecting the degree of deterioration and the temperature correction coefficient. The quantity reflecting the degree of deterioration may be, for example, the number of environmental temperature fluctuations, i.e., the cumulative number of times the temperature fluctuated beyond a predetermined range. Alternatively, the quantity reflecting the degree of deterioration may be time, i.e., the cumulative time during which the laser device 1 was operating under a predetermined operating condition. Alternatively, a predetermined function obtained by weighting quantities such as the number of environmental temperature fluctuations or the cumulative time during which the laser device 1 was operating under a predetermined operating condition may be used as a degradation function, and the output value of the degradation function may be used as the quantity reflecting the degree of degradation.

[0124] The temperature correction coefficients determined for each of the factors of the lateral or longitudinal deviation may be added together to be used as the final correction coefficient for the target temperature of the temperature controller 9 .

[0125] Furthermore, the discrimination curve shown in Fig. 4 may shift not only in the frequency axis direction but also in the ratio axis direction due to changes in the environmental temperature, etc. The occurrence of such a shift, also known as vertical shift, can cause a decrease in the accuracy of frequency locking.

[0126] Therefore, the calculation unit 35 may set a ratio correction coefficient according to the ambient temperature and correct the first ratio or the second ratio using the ratio correction coefficient. In this case, the storage unit 36 ​​stores second relationship information indicating the relationship between the ambient temperature and the ratio correction coefficient. The second relationship information includes table data or a relational expression in which the ambient temperature and the ratio correction coefficient are associated. The calculation unit 35 sets the ratio correction coefficient by referring to the storage unit 36. The ratio correction coefficient is set to offset the vertical deviation according to the ambient temperature. This prevents a decrease in frequency lock accuracy. For example, the ratio correction coefficient may be set based on a maximum or minimum point of the transmission characteristics of the frequency filter 63a or 64a. As a specific example, the ratio correction coefficient may be set so that a pole in the vertically shifted first or second frequency discrimination curve coincides with a pole in the first or second frequency discrimination curve at the reference temperature. This means that the amplitude of the vertically shifted frequency discrimination curve is adjusted to match the original frequency discrimination curve by applying the ratio correction coefficient. Note that the pole refers to a maximum or minimum point. Furthermore, the ratio correction coefficient is applied by, for example, addition, subtraction, multiplication, or division, but if the vertical deviation occurs in both the amplitude of the curve and the offset of the curve, the ratio correction coefficient is set as a combination of the amplitude correction coefficient and the offset correction coefficient. As a specific example, the ratio correction coefficient is set so that a pair of maximum and minimum values ​​of the vertically deviated first or second frequency discrimination curve matches a pair of maximum and minimum values ​​of the corresponding first or second frequency discrimination curve at the reference temperature.

[0127] Alternatively, the calculation unit 35 may set a ratio correction coefficient according to the SOA heat generation amount and correct the first ratio or the second ratio using the ratio correction coefficient. In this case, the storage unit 36 ​​stores third relationship information indicating the relationship between the SOA heat generation amount and the ratio correction coefficient. The third relationship information includes table data or a relational expression in which the SOA heat generation amount and the ratio correction coefficient are associated with each other. The calculation unit 35 sets the ratio correction coefficient by referring to the storage unit 36. The ratio correction coefficient is set to offset the vertical shift corresponding to the SOA heat generation amount. This prevents a decrease in frequency lock accuracy. For example, the ratio correction coefficient may be set based on the maximum or minimum point of the transmission characteristics of the frequency filter 63a or 64a. As a specific example, the ratio correction coefficient may be set so that the pole of the vertically shifted first or second frequency discrimination curve coincides with the pole of the first or second frequency discrimination curve for the reference SOA heat generation amount. This means that the amplitude of the vertically shifted frequency discrimination curve is adjusted to match the original frequency discrimination curve by applying the ratio correction coefficient. Here, the pole refers to a maximum or minimum point. The reference SOA calorific value is the SOA calorific value when the laser light L2 is at a reference intensity, and is obtained, for example, during calibration, such as when the laser device 1 is manufactured, shipped, or maintained. The ratio correction coefficient is applied by, for example, addition, subtraction, multiplication, or division. However, when vertical deviation occurs in both the amplitude of the curve and the offset of the curve, the ratio correction coefficient is set as a combination of the amplitude correction coefficient and the offset correction coefficient. As a specific example, the ratio correction coefficient is set so that a pair of maximum and minimum values ​​of the vertically shifted first or second frequency discrimination curve matches a pair of maximum and minimum values ​​of the corresponding first or second frequency discrimination curve in the reference SOA calorific value.

[0128] Alternatively, the calculation unit 35 may set a ratio correction coefficient according to an amount reflecting the degree of degradation and correct the first ratio or the second ratio using the ratio correction coefficient. In this case, the storage unit 36 ​​stores fourth relationship information indicating the relationship between the amount reflecting the degree of degradation and the ratio correction coefficient. The fourth relationship information includes table data or a relational expression in which the amount reflecting the degree of degradation corresponds to the ratio correction coefficient. The calculation unit 35 sets the ratio correction coefficient by referring to the storage unit 36. The ratio correction coefficient is set to offset the vertical shift caused by degradation of the frequency filters 63a and 64a. This prevents a decrease in frequency lock accuracy. For example, the ratio correction coefficient may be set based on the maximum or minimum point of the transmission characteristics of the frequency filter 63a or 64a. As a specific example, the ratio correction coefficient may be set so that a pole in the first or second frequency discrimination curve that has shifted vertically due to degradation coincides with a pole in the first or second frequency discrimination curve at the time of manufacturing the laser device 1. This means that the amplitude of the frequency discrimination curve that has shifted vertically due to deterioration is adjusted to match the original frequency discrimination curve by applying a ratio correction coefficient. Note that a pole refers to a maximum or minimum point. The ratio correction coefficient is applied by, for example, adding, subtracting, multiplying, or dividing. However, if the vertical shift occurs in both the amplitude of the curve and the offset of the curve, the ratio correction coefficient is set as a combination of an amplitude correction coefficient and an offset correction coefficient. Specifically, the ratio correction coefficient is set so that a pair of maximum and minimum values ​​of the vertically shifted first or second frequency discrimination curve matches a corresponding pair of maximum and minimum values ​​of the first or second frequency discrimination curve at the time of manufacturing the laser device 1.

[0129] Vertical deviations caused by a plurality of factors may be corrected simultaneously by sequentially applying the ratio correction coefficients determined for each factor of vertical deviation.

[0130] When both a temperature correction coefficient for offsetting horizontal deviation and a ratio correction coefficient for offsetting vertical deviation are set, setting the temperature correction coefficient after setting the ratio correction coefficient can more effectively suppress deterioration in frequency lock accuracy.

[0131] Fig. 10 is a flowchart showing a control method for performing correction according to the ambient temperature. The flowchart in Fig. 10 is obtained by adding steps S201 to S203 to the flowchart in Fig. 9, so the following will explain steps S201 to S203, and will omit explanation of steps S101 to S115.

[0132] 10, following step S101, in step S201, the control unit 3 acquires the ambient temperature. Then, in step S202, the control unit 3 acquires the target temperature. Then, in step S203, the control unit 3 sets correction coefficients, i.e., the temperature correction coefficient and the ratio correction coefficient. Then, control proceeds to step S102.

[0133] The modified example of the laser device 1 and the control method according to the flowchart of FIG. 10 are preferable because they allow frequency control at the reference temperature to be applied at all times, even if the ambient temperature changes, and this further increases the tolerance to lateral and vertical deviations caused by changes in the ambient temperature.

[0134] Furthermore, this modification and control method have the advantage that the third and fourth ratios obtained by calculating the first and second ratios can be optimally corrected without the need for individual correction coefficients. As a result, by simply correcting the first and second ratios, it is possible to achieve frequency control equivalent to that at the reference temperature, even when the environmental temperature changes.

[0135] Also, different correction coefficients may be set for the first ratio and the second ratio, thereby making it possible to perform optimal correction even if the influence of stray light, etc., differs between the first ratio and the second ratio.

[0136] Also, instead of applying the ratio correction coefficient to the first or second ratio, a monitor correction coefficient may be applied to the monitor value, which is set to offset the vertical deviation caused by the ambient temperature.

[0137] 10, the position of the steps S201 to S203 is not limited to the above. By executing steps S201 to S203, the deviation of the frequency discrimination curve is corrected so that it coincides with the frequency discrimination curve at the reference temperature. Therefore, it is effective to perform such steps related to the correction of deviation before the step of calculating and setting the monitor value R_mon corresponding to the frequency of the laser light L1, which is step S104, S106, S108, or S110.

[0138] (Further variations) 9, it has been described that the frequency discrimination curve that has the largest rate of change at the target frequency may be selected from the first to fourth ratios, or the frequency discrimination curve that has the smallest absolute value at the target frequency after normalizing the amplitude of the frequency discrimination curve may be selected.In contrast to this, in the second modified example of the laser device 1, the control unit 3 may prioritize and select the ratio to be set as the monitor value corresponding to the frequency of the laser light from the first to fourth ratios based on the rate of change of the ratio with respect to the frequency change at the target value.

[0139] In addition, in the third variant of the laser device 1, the control unit 3 may prioritize and select a ratio from the first to fourth ratios to be set as a monitor value corresponding to the frequency of the laser light based on the S / N (signal-to-noise ratio) of the ratio to the frequency change at the target value.

[0140] That is, the laser beam L5 passing through the frequency filter 63a and the electrical signal output from the PD 71 to which the laser beam L5 is input may be subject to noise due to stray light or electrical noise, resulting in a deterioration in the S / N ratio. Similarly, the laser beam L6 passing through the frequency filter 64a and the electrical signal output from the PD 72 to which the laser beam L6 is input may be subject to noise due to stray light or electrical noise, resulting in a deterioration in the S / N ratio. Furthermore, the relative intensity of the laser beam L5 or the stray light relative to the laser beam L6 may change over time due to degradation, resulting in a deterioration in the S / N ratio. A deterioration in the S / N ratio may cause the frequency of the laser beam to fluctuate, resulting in a deterioration in frequency stability. Therefore, for example, by assigning a lower priority to frequency discrimination curves with a poor S / N ratio, even if the ratio has a large rate of change, the deterioration in the S / N ratio can be prevented or suppressed, thereby preventing or suppressing a deterioration in frequency stability.

[0141] In the fourth modification of the laser device 1, the control unit 3 may prioritize and select a ratio to be set as a monitor value corresponding to the frequency of the laser light from among the first to fourth ratios based on the rate of change of the ratio relative to the frequency change at the target value and the S / N ratio. This allows for the selection of a more appropriate frequency discrimination curve.

[0142] The prioritization method can be, for example, the highest priority for a frequency discrimination curve whose rate of change is greater than a first threshold related to the rate of change and whose S / N is higher than a second threshold related to the S / N, and the second highest priority for a frequency discrimination curve whose rate of change is equal to or less than the first threshold but whose S / N is higher than the second threshold. Alternatively, for example, a predetermined function obtained by weighting the parameters of rate of change and S / N may be used as an evaluation function, and prioritization may be performed in descending order of the value of the evaluation function. Such ranking rules can be set, for example, according to the required specifications for the laser device. The degree of S / N can be quantitatively evaluated by converting it into the range of fluctuation in the frequency of the laser light (frequency stability).

[0143] The prioritization of the above three types (change rate, S / N, S / N and change rate) is obtained, for example, during the manufacturing or shipping of the laser device 1 of the second to fourth modified examples, and is stored as table data or the like in the storage unit 36. The prioritization may also be rewritten during maintenance of the laser device 1 of the modified examples. The S / N can also be obtained by monitoring the electrical signal output from the PD 71 or the electrical signal output from the PD 72. It can also be obtained by measuring the frequency stability of the laser light L1.

[0144] Fig. 11 is a flowchart showing part of a control method for a laser apparatus according to the fourth modified example. This flowchart shows only the parts that replace steps S101 and S102 in the flowchart shown in Fig. 9. After returning in Fig. 11, steps S103 to S115 in Fig. 9 are carried out in the control flow.

[0145] In step S301, the target frequency setting unit 351 sets a target frequency as a target value of the frequency of the laser light L1.

[0146] Next, in step S302, the discrimination curve selection unit 352 acquires priority order information based on the "rate of change at the target frequency" from table data stored in the storage unit 36. Here, table data T1 stores priority order information based on the "rate of change at the target frequency." In table data T1, frequencies are associated with channel numbers (CH), and it is assumed here that the target frequency corresponds to channel n. In this case, for channel n, curve 4 (fourth frequency discrimination curve) has the highest priority, followed by curve 2 (second frequency discrimination curve), curve 3 (third frequency discrimination curve), and curve 1 (first frequency discrimination curve).

[0147] Next, in step S303, the discrimination curve selection unit 352 acquires the S / N of each curve at the target frequency from the storage unit 36. The relative intensity of stray light with respect to the laser light L5 or L6 may depend on the operating conditions and temperature of the laser device 1, and may also change over time. To take into account the effects of these dependencies and changes over time on the S / N, the current S / N of each curve may be estimated using not only the S / N acquired from the storage unit 36 ​​but also information such as the operating conditions, the temperature detected by the temperature sensor 8, the environmental temperature, and the degree of deterioration, and may be used in the subsequent steps. Here, the operating conditions specifically include the conditions of the power supplied to the DBR heater 421, the RING heater 422, and the Phase heater 423, the operating conditions of the semiconductor optical amplifier 5, etc.

[0148] Subsequently, in step S304, the discrimination curve selection unit 352 converts the degree of S / N into frequency stability.

[0149] Next, in step S305, the discrimination curve selection unit 352 determines whether the frequency stability of curve 4, which is the curve with the highest priority, is within the allowable range (or higher than a predetermined threshold). If it is within the allowable range (step S305, Yes), in step S306 the discrimination curve selection unit 352 selects curve 4, which is the curve with the highest priority, and returns. If it is not within the allowable range (step S305, No), the flow proceeds to step S307.

[0150] In step S307, the discrimination curve selection unit 352 determines whether the frequency stability of curve 2, which is the curve with the second highest priority, is within the allowable range. If it is within the allowable range (step S307, Yes), in step S308, the order of the curves with the first and second highest priority is swapped, and the process proceeds to step S306. In step S306, the discrimination curve selection unit 352 selects curve 2, which is the curve with the first highest priority after the swap, and returns.

[0151] If it is not within the allowable range (No at step S307), the flow proceeds to step S309, the calculation unit 35 transitions to an error state, and the flow ends.

[0152] The results of the priority change in step S308 may be overwritten in the storage unit 36.

[0153] Fig. 12 is a flowchart showing part of another example of the control method for the laser apparatus of the fourth modified example. In this flowchart, step S302 in the flowchart shown in Fig. 11 is replaced with steps S402a, S402b, and S402c. The other steps S301 and S301 to S309 are the same as in Fig. 11, so their explanation will be omitted.

[0154] In step S402a, the discrimination curve selection unit 352 acquires the control target value data of curve 1 and curve 2 around the target frequency (channel n) from table data T2 stored in the storage unit 36. The control target value data corresponds to the first ratio and the second ratio.

[0155] Next, in step S402b, the discrimination curve selection unit 352 calculates the rate of change of the control target value (ratio) for each of the four curves.

[0156] Next, in step S402c, the discrimination curve selection unit 352 assigns a higher priority to each curve the greater the rate of change, and then performs prioritization. Thereafter, steps S303 to S309 are executed as appropriate.

[0157] (Further modification of the fourth modification) In the fourth modification, the controller 3 may estimate the current S / N ratio of each curve using not only the S / N ratio acquired from the memory unit 36 ​​but also information such as operating conditions, the temperature detected by the temperature sensor 8, the ambient temperature, and the degree of deterioration, converting the S / N ratio into frequency stability and prioritizing the curves. In contrast, in a further modification of the fourth modification, the controller 3 may measure the current frequency stability of the laser beam L1, accurately evaluate the S / N ratio, and prioritize and select the first to fourth ratios. Using a measured value rather than an estimated value of frequency stability enables more appropriate S / N-based ranking and selection of frequency discrimination curves according to the required specifications. Furthermore, deterioration of frequency stability can be more reliably prevented or suppressed. The current frequency stability can be acquired by monitoring the degree of fluctuation in the electrical signals output from PD 71 and PD 72.

[0158] 13 and 14 are flowcharts showing a part of a control method for a laser apparatus according to a further modification of the fourth modification, in which priority is assigned based on the rate of change and S / N. The flowchart in FIG. 13 shows only the parts that are replaced by steps S101 and S102 of the flowchart shown in FIG. 9. After the return in FIG. 13, the control flow performs steps S104, S106, S108 or S110, and S111 to S113 of FIG. 9. FIG. 14 shows only the parts that are replaced by steps S114, S115, and "END" of the flowchart shown in FIG. 9.

[0159] First, referring to FIG. 13, in step S501, the target frequency setting unit 351 sets a target frequency as a target value of the frequency of the laser light L1.

[0160] Next, in step S502, the discrimination curve selection unit 352 acquires priority order information based on the "rate of change at the target frequency" from table data stored in the storage unit 36. Here, table data T3 stores priority order information based on the "rate of change at the target frequency." In table data T3, frequencies are associated with channel numbers (CH), and it is assumed here that the target frequency corresponds to channel n. In this case, for channel n, curve 4 (fourth frequency discrimination curve) has the highest priority, followed by curve 2 (second frequency discrimination curve), curve 3 (third frequency discrimination curve), and curve 1 (first frequency discrimination curve).

[0161] Subsequently, in step S503, the discrimination curve selection unit 352 selects curve 4, which is the curve with the highest priority, and returns.

[0162] 14, in step S514, the PID control unit 356 determines whether the absolute value of the difference, |target value R_tgt-monitor value R_mon|, is within the target error. If it is determined that it is within the target error (step S514, Yes), control proceeds to step S515. If it is determined that it is not within the target error (step S514, No), control proceeds to step S519, which will be described later.

[0163] In step S515, the discrimination curve selection unit 352 determines whether the frequency stability of curve 4, which is the curve with the highest priority, is within the allowable range (or higher than a predetermined threshold). If it is within the allowable range (step S515, Yes), the flow ends. If it is not within the allowable range (step S515, No), the flow proceeds to step S516.

[0164] In step S516, the discrimination curve selection unit 352 determines whether this step is being executed for the first time. If it is not the first time (step S516, No), the flow proceeds to step S517, where the calculation unit 35 transitions to an error state, and the flow ends.

[0165] On the other hand, if this is the first time (Yes in step S516), in step S518, the curves with the first and second priorities are swapped, and the process proceeds to step S519. In step S519, the discrimination curve selection unit 352 selects curve 2, which is the curve with the first priority after the swap. Next, in step S520, the target value acquisition unit 353 acquires and determines the target value R_tgt corresponding to the target frequency based on the selected curve 2. Thereafter, the flow returns to step S106 in accordance with the selected curve 2.

[0166] It should be noted that the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, 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-described embodiments, and various modifications are possible. [Explanation of symbols]

[0167] 1. Laser device 2 Laser section 3. Control Unit 4 Light source section 5. Semiconductor Optical Amplifier 6 Planar light wave circuit 7 Light detection unit 8 Temperature Sensor 9 Temperature Controller 10 Monitor section 31, 32, 33, 34 ADC 35 Arithmetic section 36 Memory section 37 Current source 41 Laser main body 42 Changes 43 First waveguide section 44 Second waveguide section 44a Optical waveguide layer 45 n-side electrode 61 Optical branching section 62, 63, 64 Optical waveguide 63a, 64a frequency filters 91 Installation surface 351 Target frequency setting unit 352 Discrimination curve selection section 353 Target value acquisition unit 354 Monitor value calculation unit 355 Difference acquisition part 356 PID control unit 357 DBR / RING power setting section 421 DBR heater 422 RING heater 423 Phase heater 431 Waveguide section 431a Gain section 431b Diffraction grating layer 432 Semiconductor laminate 433 p side electrode 441a waveguide 442, 443 Arm section 444 Ring-shaped waveguide 445 Phase Adjustment Unit Ar1 First area Ar2 Second Area B1 Base C optical cavity C1 First frequency discrimination curve C2 Second frequency discrimination curve C3 3rd frequency discrimination curve C4 4th frequency discrimination curve C5 5th frequency discrimination curve C6 6th frequency discrimination curve C5A, C5B frequency discrimination curve C11, C21, C31, C41, C51, C61, C1F, C1AF, C1BF, C5F, C5AF, C5BF area L1, L2, L3, L4, L5, L6 laser light M Reflective Mirror M1, M2, M3, M4 wire RF1 Ring Resonator Filter

Claims

1. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; The control unit acquiring a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; setting any one of the first ratio, the second ratio, a third ratio which is the sum of the first ratio and the second ratio, and a fourth ratio which is the difference between the first ratio and the second ratio as a monitor value corresponding to the frequency of the laser light; obtaining a target value corresponding to the target frequency based on any one of the first to fourth ratios; controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; In each of the frequency discrimination curves corresponding to the first to fourth ratios, regions that do not include maximum or minimum points where the slope with respect to frequency is zero and to which the target frequency is applied to obtain the target value are set so as not to overlap in frequency, thereby preventing a dead zone where the rate of change of the ratio with respect to a change in frequency is zero from being included in the region. Laser device.

2. The control unit calculates the first ratio or the second ratio by applying a correction coefficient to the first intensity, the second intensity, or the intensity of the laser light.

2. The laser device according to claim 1.

3. The control unit converts the first intensity, the second intensity, and the intensity of the laser light into digital signals, and calculates the first ratio or the second ratio by digital calculation.

3. The laser device according to claim 1 or 2.

4. The transmittance of the first and second frequency filters varies sinusoidally with frequency.

4. The laser device according to claim 1.

5. The control unit converts a frequency function indicating the transmission characteristics of the first frequency filter or the second frequency filter into a sine function of frequency from the first intensity, the second intensity, and the intensity of the laser light, to calculate the first ratio or the second ratio.

5. The laser device according to claim 1.

6. The laser unit utilizes the Vernier effect to change the frequency of the laser light.

6. The laser device according to claim 1.

7. the control unit controls the frequency of the laser light by supplying power corresponding to the control amount to the laser unit.

7. The laser device according to claim 1.

8. a temperature controller having an installation surface on which the light source unit, the first frequency filter, and the second frequency filter are installed, The light source unit, the first frequency filter, and the second frequency filter are The temperature controller is installed on the same installation surface.

8. The laser device according to claim 7.

9. The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on a rate of change of the ratio with respect to a frequency change at the target value. The laser device according to any one of claims 1 to 8.

10. The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on an S / N ratio of the ratio to the frequency change at the target value. The laser device according to any one of claims 1 to 8.

11. The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on a rate of change of the ratio relative to a frequency change at the target value and an S / N ratio. The laser device according to any one of claims 1 to 8.

12. a temperature controller having an installation surface on which the light source unit, the first frequency filter, and the second frequency filter are installed, The control unit corrects the control temperature of the temperature controller, the first ratio, the second ratio, or the monitor value so as to offset a horizontal or vertical deviation in the transmission characteristics of the first frequency filter and the second frequency filter. The laser device according to any one of claims 1 to 11.

13. a temperature controller having an installation surface on which the light source unit and the first and second frequency filters are installed, and an environmental temperature sensor that detects an environmental temperature of the first and second frequency filters, The control unit corrects the control temperature of the temperature controller, the first ratio, the second ratio, or the monitor value based on the environmental temperature detected by the environmental temperature sensor so as to offset changes in the transmission characteristics of the first frequency filter and the second frequency filter due to the environmental temperature. The laser device according to any one of claims 1 to 11.

14. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; The control unit a target frequency setting unit that acquires a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; a monitor value calculation unit capable of acquiring a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio; a discrimination curve selection unit that sets any one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value corresponding to the frequency of the laser light; a target value acquisition unit that acquires a target value corresponding to the target frequency based on any one of the first to fourth ratios, controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on a rate of change of the ratio with respect to a frequency change at the target value. Laser device.

15. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; The control unit a target frequency setting unit that acquires a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; a monitor value calculation unit capable of acquiring a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio; a discrimination curve selection unit that sets any one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value corresponding to the frequency of the laser light; a target value acquisition unit that acquires a target value corresponding to the target frequency based on any one of the first to fourth ratios, controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on an S / N ratio of the ratio to the frequency change at the target value. Laser device.

16. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; The control unit a target frequency setting unit that acquires a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; a monitor value calculation unit capable of acquiring a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio; a discrimination curve selection unit that sets any one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value corresponding to the frequency of the laser light; a target value acquisition unit that acquires a target value corresponding to the target frequency based on any one of the first to fourth ratios, controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; The control unit selects, from the first to fourth ratios, a ratio to be set as a monitor value corresponding to the frequency of the laser light, by prioritizing the ratio based on a rate of change of the ratio relative to a frequency change at the target value and an S / N ratio. Laser device.

17. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; a temperature controller having an installation surface on which the light source unit, the first frequency filter, and the second frequency filter are installed, The control unit a target frequency setting unit that acquires a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; a monitor value calculation unit capable of acquiring a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio; a discrimination curve selection unit that sets any one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value corresponding to the frequency of the laser light; a target value acquisition unit that acquires a target value corresponding to the target frequency based on any one of the first to fourth ratios, controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; The control unit corrects the control temperature of the temperature controller, the first ratio, the second ratio, or the monitor value so as to offset a horizontal or vertical deviation in the transmission characteristics of the first frequency filter and the second frequency filter. Laser device.

18. a laser unit including a light source unit that varies the frequency of an output laser beam and a monitor unit that acquires a monitor value corresponding to a frequency equivalent that corresponds to the frequency of the laser beam; a control unit that controls the frequency of the laser light by supplying a control amount to the laser unit; Equipped with the monitor unit includes at least a first frequency filter and a second frequency filter having transmission characteristics in which transmittance changes periodically with respect to the frequency of input light and having a phase that is relatively shifted, a first detector that detects a first intensity corresponding to the intensity of the laser light after the laser light has passed through the first frequency filter, and a second detector that detects a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; a temperature controller having an installation surface on which the light source unit and the first and second frequency filters are installed, and an environmental temperature sensor that detects an environmental temperature of the first and second frequency filters, The control unit a target frequency setting unit that acquires a target frequency that is a control target for the frequency of the laser light; obtaining a first ratio corresponding to a ratio of the first intensity to an intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to an intensity of the laser light; a monitor value calculation unit capable of acquiring a third ratio that is the sum of the first ratio and the second ratio, and a fourth ratio that is the difference between the first ratio and the second ratio; a discrimination curve selection unit that sets any one of the first ratio, the second ratio, the third ratio, and the fourth ratio as a monitor value corresponding to the frequency of the laser light; a target value acquisition unit that acquires a target value corresponding to the target frequency based on any one of the first to fourth ratios, controlling the controlled variable so that the absolute value of the difference between the target value and the monitored value becomes small; The control unit corrects the control temperature of the temperature controller, the first ratio, the second ratio, or the monitor value based on the environmental temperature detected by the environmental temperature sensor so as to offset changes in the transmission characteristics of the first frequency filter and the second frequency filter due to the environmental temperature. Laser device.

19. A method for controlling a laser device having a light source unit that can vary the frequency of an output laser beam, comprising: a first acquisition step of acquiring a target frequency that is a control target for the frequency of the laser light; a detection step of detecting a first intensity corresponding to the intensity of the laser light after the laser light has passed through a first frequency filter and a second frequency filter, the first and second frequency filters having transmission characteristics in which the transmittance changes periodically with respect to the frequency of the input light and having a phase that is relatively shifted, and detecting a second intensity corresponding to the intensity of the laser light after the laser light has passed through the second frequency filter; a second obtaining step of obtaining a first ratio corresponding to a ratio of the first intensity to the intensity of the laser light, and a second ratio corresponding to a ratio of the second intensity to the intensity of the laser light; a setting step of setting a monitor value corresponding to a frequency equivalent amount equivalent to the frequency of the laser light from any one of the first ratio, the second ratio, a third ratio which is the sum of the first ratio and the second ratio, and a fourth ratio which is the difference between the first ratio and the second ratio; a third obtaining step of obtaining a target value corresponding to the target frequency based on any one of the first to fourth ratios; an adjusting step of adjusting a control amount so that an absolute value of a difference between the target value and the monitor value becomes small; Including, In each of the frequency discrimination curves corresponding to the first to fourth ratios, regions that do not include maximum or minimum points where the slope with respect to frequency is zero and to which the target frequency is applied to obtain the target value are set so as not to overlap in frequency, thereby preventing a dead zone where the rate of change of the ratio with respect to a change in frequency is zero from being included in the region. A method for controlling a laser device.

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