JP7458196B2 - Laser device and its control method - Google Patents

Description

The present invention relates to a laser device and a control method thereof.

In a laser device that can vary the frequency of output laser light, a technology is disclosed that uses two or more frequency filters with transmission characteristics in which the transmittance changes periodically with respect to the frequency of the input light to control the frequency of the laser light (Patent Document 1). These 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 relative to the change in frequency at the target frequency of the laser light is used for control.

JP 2019-140304 Publication

A frequency filter having a transmission characteristic that changes periodically with respect to frequency has a small change in transmittance with respect to a change in frequency in a frequency band near the extreme value of the transmission characteristic, resulting in a decrease in control accuracy. Such a frequency band is also called a dead band.

In the technique of Patent Document 1, it is said that a decrease in control accuracy can be suppressed by setting two or more frequency filters to be out of phase with each other and selecting a frequency filter that is not in a dead zone at the control target frequency. .

However, even if the technology of Patent Document 1 is used, if the transmission characteristics of the frequency filter shift in the frequency axis direction due to an unintended cause, that is, a so-called lateral shift occurs, the control target frequency will be different from the dead band of the selected frequency filter. There is a risk that they may overlap. This may reduce control accuracy. Fluctuations in the temperature of the frequency filter can be considered as such an unintended cause.

The present invention has been made in view of the above, and an object of the present invention is to provide a laser device and a control method thereof that can suppress a decrease in control accuracy of the frequency of laser light.

In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a laser unit including a light source unit that varies the frequency of the output laser light, a monitor unit for acquiring a monitor value corresponding to a frequency equivalent amount 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, the monitor unit having a transmission characteristic in which the transmittance changes periodically with respect to the frequency of the input light and having a phase shift relative to the first frequency filter and a second frequency filter, a first detection unit 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 laser unit having a frequency equivalent amount equivalent to the frequency 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 the laser light, and the control unit acquires a target frequency that is a control target for the frequency of the laser light, acquires 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 corresponding to the frequency of the laser light, acquires a target value corresponding to the target frequency based on one of the first to fourth ratios, and controls the control amount so that the absolute value of the difference between the target value and the monitor value becomes small.

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 beam.

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

The transmittances of the first and second frequency filters may change sinusoidally with respect to changes in frequency.

The control unit converts a frequency function indicating a transmission characteristic of the first frequency filter or a transmission characteristic of the second frequency filter into a frequency sine function from the first intensity or the second intensity and the intensity of the laser beam. The first ratio or the second ratio may be calculated by converting the ratio into the following.

The laser section may have a variable frequency of the laser beam using a Vernier effect.

The control section may control the frequency of the laser beam by supplying power corresponding to the control amount to the laser section.

The temperature controller further includes a temperature controller having an installation surface on which the light source section, a first frequency filter, and a second frequency filter are installed, and the light source section, the first frequency filter, and the second frequency filter are connected to the temperature controller. may be installed on the same installation surface.

The control unit may set and select a ratio among the first to fourth ratios that has the largest change in ratio with respect to a frequency change in the target value as a monitor value corresponding to the frequency of the laser beam.

One aspect of the present invention is a method for controlling a laser device including a light source unit that makes the frequency of output laser light variable; , a first frequency filter and a second frequency filter having a transmission characteristic in which the transmittance changes periodically with respect to the frequency of input light, and whose phases are relatively shifted. detecting a first intensity corresponding to the intensity of the laser beam after passing through the first frequency filter; detecting a second intensity corresponding to the intensity of the laser beam after the laser beam passes through the second frequency filter; a detection step of detecting the intensity of the laser beam; a first ratio corresponding to the ratio of the first intensity to the intensity of the laser beam; and a second ratio corresponding to the ratio of the second intensity to the intensity of the laser beam. and a second obtaining step of obtaining the first ratio, the second ratio, the third ratio that is the sum of the first ratio and the second ratio, and the first ratio and the second ratio. a setting step of setting a monitor value corresponding to a frequency equivalent amount corresponding to the frequency of the laser beam from any one of the fourth ratios that is the difference between the ratios; a third acquisition step of acquiring a target value corresponding to the target frequency based on the target frequency; and an adjustment step of adjusting the control amount so that the absolute value of the difference between the target value and the monitor value becomes small. This is a method of controlling the device.

According to the present invention, it is possible to suppress a decrease in control accuracy of the frequency of laser light.

FIG. 1 is a diagram showing the configuration of a laser device according to the first embodiment. FIG. 2 is a diagram showing the configuration of the light source section. FIG. 3 is a block diagram showing the configuration of the control section according to the first embodiment. FIG. 4 is a diagram showing a frequency discrimination curve. FIG. 5 is an explanatory diagram of margin. FIG. 6 is a diagram showing the relationship between φ and margin. FIG. 7 is a diagram showing temperature-dependent changes in frequency discrimination curves in a comparative embodiment. FIG. 8 is a diagram showing temperature-dependent changes in the frequency discrimination curve in the embodiment. FIG. 9 is a flowchart showing a control method by the control unit according to the first embodiment.

Below, a mode for carrying out the present invention (hereinafter, 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 given the same reference numerals. Furthermore, the drawings are schematic, and the dimensional relationships of each element, the ratios of each element, etc. may differ from reality. Furthermore, between the drawings, there may be parts with mutually different dimensional relationships and ratios. Furthermore, xyz coordinate axes are appropriately shown in the drawings to explain directions.

(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 section 2 and a control section 3 that executes a control step for controlling the operation of the laser section 2.
In addition, in FIG. 1, the laser section 2 and the control section 3 are configured as separate bodies, but they may be integrally modularized.

[Laser section configuration]
Under the control of the control section 3, the laser section 2 changes the frequency of the laser light it outputs to one of a plurality of frequencies, and outputs the laser light at that frequency. The laser section 2 includes a light source section 4, a semiconductor optical amplifier (SOA) 5, a planar lightwave circuit (PLC) 6, a photodetector section 7, a temperature sensor 8, and a temperature control section. A container 9 is provided. The planar light wave circuit 6 and the photodetector section 7 constitute a monitor section 10 .

FIG. 2 is a diagram showing the configuration of the light source section.
The light source section 4 is, for example, a laser that utilizes the Vernier effect, and outputs a laser beam L1 under the control of the control section 3. The light source section 4 includes a laser main body section 41 that makes the frequency of the output laser beam L1 variable, and a changing section 42. The changing unit 42 has three micro-heaters that generate heat according to the power supplied from the control unit 3, and locally heats the laser main body 41, thereby changing the laser beam L1 output from the laser main body 41. change the frequency of

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

The first waveguide section 43 has a buried waveguide structure. This first waveguide section 43 includes a waveguide section 431, a semiconductor stacked section 432, and a p-side electrode 433.
The waveguide section 431 is formed within the semiconductor laminated section 432 so as to extend in the z direction.
Further, within the first waveguide section 43, a gain section 431a and a DBR (Distributed Bragg Reflector) type diffraction grating layer 431b are arranged.

Here, the gain section 431a is an active layer having a multiple quantum well structure made of InGaAsP and an optical confinement layer. Further, the diffraction grating layer 431b is composed of a sampling diffraction grating made of InGaAsP and InP.

The semiconductor laminate section 432 is composed of a stack of InP-based semiconductor layers, and has the functions of a cladding section for the waveguide section 431.

The p-side electrode 433 is arranged on the semiconductor stack 432 along the gain section 431a. Note that an SiN protective film (not shown) is formed on the semiconductor laminated portion 432. The p-side electrode 433 is in contact with the semiconductor stack 432 through an opening (not shown) formed in the SiN protective film.

Here, the DBR heater 421, which is a micro-heater, is arranged on the SiN protective film of the semiconductor laminated portion 432 along the diffraction grating layer 431b. The DBR heater 421 generates heat according to the power supplied from the control unit 3, and heats the diffraction grating layer 431b. Further, by controlling the power supplied to the DBR heater 421 by the control unit 3, the temperature of the diffraction grating layer 431b changes, and its refractive index changes.

The second waveguide section 44 has two branch sections 441, two arm sections 442 and 443, and a ring-shaped waveguide 444.

The 2-branch section 441 is composed of a 1×2 branch waveguide including a 1×2 multimode interference (MMI) waveguide 441a, and the 2-port side is connected to each of the two arm portions 442 and 443. At the same time, the 1 port side is connected to the first waveguide section 43 side. That is, the two arm parts 442 and 443 are integrated at one end by the two-branch part 441 and are optically coupled to the diffraction grating layer 431b.

The arm portions 442 and 443 both extend in the z direction and are arranged to sandwich the ring-shaped waveguide 444 therebetween. 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 constitute a ring resonator filter RF1. Further, the ring resonator filter RF1 and the two-branch section 441 constitute a reflecting mirror M.

Here, the RING heater 422, which is a microheater, has a ring shape and is arranged on a SiN protective film (not shown) formed to cover the ring-shaped waveguide 444. The RING heater 422 generates heat in response to the power supplied from the control unit 3 and heats the ring waveguide 444. Further, by controlling the power supplied to the RING heater 422 by the control unit 3, the temperature of the ring-shaped waveguide 444 changes, and its refractive index changes.

The above-mentioned two-branch section 441, arm sections 442, 443, and 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. .

Here, the Phase heater 423, which is a micro-heater, is placed on a part of the SiN protective film (not shown) of the arm portion 443. A region of the arm section 443 below the Phase heater 423 functions as a phase adjustment section 445 that changes the phase of light. Then, the Phase heater 423 generates heat in accordance with the power supplied from the control section 3, and heats the phase adjustment section 445. Furthermore, by controlling the power supplied to the Phase heater 423 by the control unit 3, the temperature of the phase adjustment unit 445 changes, and its refractive index changes.

The first and second waveguide sections 43 and 44 described above constitute an optical resonator C constituted by a diffraction grating layer 431b and a reflection mirror M that are optically connected to each other. Further, the gain section 431a and the phase adjustment section 445 are arranged within the optical resonator C.

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

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

To illustrate the characteristics of each comb-like reflection spectrum, the frequency interval (free spectral range: FSR) between peaks of the first comb-like reflection spectrum is 373 GHz. Further, the full width at half maximum of each peak is 43 GHz. On the other hand, the peak-to-peak frequency spacing (FSR) of the second comb-like reflection spectrum is 400 GHz. Further, the full width at half maximum of each peak is 25 GHz. That is, the full width at half maximum (25 GHz) of each peak in the second comb-like reflection spectrum is narrower than the full width at half maximum (43 GHz) of each peak in the first comb-like reflection spectrum.

The light source section 4 is configured such that one peak of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum can be superimposed on the frequency axis in order to realize laser oscillation. . Such superposition is achieved by using at least one of the DBR heater 421 and the RING heater 422 to heat the diffraction grating layer 431b with the DBR heater 421 and change its refractive index by the thermo-optic effect to form the first comb-shaped layer. The reflection spectrum is changed by moving the entire reflection spectrum on the frequency axis, and the ring-shaped waveguide 444 is heated by the RING heater 422 to change its refractive index to change the second comb-shaped reflection spectrum on the frequency axis. This can be achieved by performing at least one of the following: moving and changing the entire structure.

On the other hand, in the light source unit 4, there is a resonator mode due to the optical resonator C. In the light source unit 4, the resonator length of the optical resonator C is set so that the resonator mode interval (longitudinal mode interval) is 25 GHz or less. In this setting, the resonator length of the optical resonator C is 1800 μm or more, and it is expected that the line width of the oscillating laser light will be narrowed. 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 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.

When the light source section 4 injects current from the n-side electrode 45 and the p-side electrode 433 to the gain section 431a by the control section 3 and causes the gain section 431a to emit light, the peak of the spectral component of the first comb-shaped reflection spectrum, The peak of the spectral component of the second comb-shaped reflection spectrum and one of the resonator modes of the optical resonator C are configured to oscillate at a matching frequency, for example, 193.4 THz, and output the laser beam L1. .

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.

For example, first, a state is created in which the laser oscillates at a frequency f1 where the reflection peak of DBR, the resonator mode of optical resonator C, and the reflection peak of RING coincide. In order 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 reach their peaks, based on the supplied power. Furthermore, the Phase heater 423 sets a frequency position at which the resonator mode peaks based on the supplied power. From the state of laser oscillation at frequency f1, if the frequency at which the reflection peak of DBR, the resonator mode of optical resonator C, and the reflection peak of RING match by controlling each heater is frequency f2, then the frequency of laser beam L1 is the frequency Can be adjusted to f2. Note that the electric power supplied to each heater can be controlled using current as a control amount. That is, the control section 3 controls the frequency of the laser beam L1 by supplying the light source section 4 with electric power corresponding to the current, which is a control amount.

When changing the frequency of the laser beam L1 from the first frequency to the second frequency, for example, first feedforward control is performed on the DBR heater 421 and the RING heater 422 so that the comb-like reflection spectra of the DBR and RING overlap at the second frequency. Then, the Phase heater 423 is feedback-controlled so that one of the resonator modes matches the second frequency. However, the control method is not limited to this.

Returning to FIG. 1, the explanation will be continued. Although not specifically illustrated, 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. This 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. The semiconductor optical amplifier 5 amplifies the laser beam L1 and outputs the amplified laser beam L2. Note that the semiconductor optical amplifier 5 may be monolithically configured with the light source section 4 on the base section B1.

The planar lightwave circuit 6 is optically coupled to the arm portion 442 by a spatial coupling optical system (not shown). Similarly to the laser beam L1, a portion of the laser beam L3 generated by laser oscillation in the light source section 4 is input to the plane light wave circuit 6 via the arm section 442. Note that the laser beam L3 has the same frequency as the frequency of the laser beam L1, and has an intensity corresponding to the intensity of the laser beam L1. This planar light wave circuit 6 includes an optical branching section 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 having a frequency filter 64a which is a ring resonator type optical filter. A wave path 64. 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.

The optical branching unit 61 branches the input laser beam L3 into three laser beams L4, L5, and L6. The optical waveguide 62 guides the laser beam L4 to a PD (Photo Diode) 73 in the photodetector 7, which will be described later. The optical waveguide 63 guides the laser beam L5 to a PD 71 in the photodetector 7, which will be described later. The optical waveguide 64 guides the laser beam L6 to a PD 72 in the photodetector 7, which will be described later.

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 beam L5 with a transmittance that corresponds to the frequency of the laser beam L5. Then, the laser beam L5 that has passed through the frequency filter 63a is input to the PD 71. That is, the frequency filter 63a is a waveguide type frequency filter. Note that as the frequency filter 63a, an etalon filter or an MZI (Mach-Zehnder Interferometer) filter having periodic transmission characteristics with respect to the frequency of input light may be used.

Similarly, the frequency filter 64a has a transmission characteristic in which the transmittance changes periodically with respect to the frequency of input light, and transmits the laser beam L6 with a transmittance that corresponds to the frequency of the laser beam L6. Then, the laser beam L6 that has passed through the frequency filter 64a is input to the PD 72. As the frequency filter 64a, an etalon filter or an MZI filter having periodic transmission characteristics with respect to the frequency of input light may be used.

It is preferable that the transmission characteristics of the frequency filters 63a and 64a have the same period. Further, as will be described in detail later, the transmission characteristics of the frequency filters 63a and 64a are relatively out of phase.

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

The PD 71 is an example of a first detection unit that detects a first intensity that is the intensity of the laser beam L5 that corresponds to the intensity after the laser beam L1 passes through the frequency filter 63a. The PD 72 is an example of a second detection unit that detects a second intensity that is the intensity of the laser beam L6 that corresponds to the intensity after the laser beam L1 passes through the frequency filter 64a. The PD 73 is an example of a third detection unit that detects a third intensity that is the intensity of the laser beam L4 corresponding to the intensity of the laser beam L1.

The temperature sensor 8 is composed of, for example, a thermistor, is placed on the installation surface 91 of the temperature controller 9, and detects the ambient temperature of the light source section 4 and the planar light wave 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 on the detected temperature to the control unit 3.

The temperature controller 9 is composed of, for example, a TEC (Thermo Electric Cooler) including a Peltier element. A light source section 4 , a semiconductor optical amplifier 5 , a planar light wave circuit 6 , a photodetector section 7 , and a temperature sensor 8 are mounted on this temperature controller 9 . The temperature controller 9 then controls the temperatures of the light source section 4, semiconductor optical amplifier 5, planar light wave circuit 6, photodetector section 7, and temperature sensor 8 according to the supplied power. In this case, the control unit 3 controls the power supplied to the temperature controller 9 based on the temperature information detected by the temperature sensor 8 so that the light source unit 4 mainly maintains a constant temperature. It is preferable to control the temperature of the light source section 4 to be mainly constant in order to suppress fluctuations in the frequency of the laser beam L1 depending on operating conditions and external environmental temperature.

In addition, in the temperature controller 9, the temperature sensor 8 connects the light source section 4 and the installation surface 91 on which the light source section 4, the semiconductor optical amplifier 5, the planar light wave circuit 6, the light detection section 7, and the temperature sensor 8 are mounted. When divided into two areas, a first area Ar1 where the semiconductor optical amplifier 5 is placed and a second area Ar2 where the planar light wave circuit 6 and the photodetector 7 are placed, the first area It may be placed on Ar1. At this time, the temperature sensor 8 may be placed close to the light source section 4 or placed on the light source section 4 . Further, the temperature sensor 8 may be placed in the second area Ar2 and may be arranged close to the planar light wave circuit 6.

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

In the following, the frequency lock control by the control unit 3, which is a key part of the present invention, will be mainly explained. Also, for the sake of convenience, FIG. 3 mainly illustrates the configuration of the control unit 3 that executes the frequency lock control.

The control section 3 includes analog-to-digital converters (ADCs) 31, 32, 33, and 34, a calculation section 35, a storage section 36, and a current source 37.

The ADC 31 converts the analog electrical signal input from the PD 71 into a digital signal (voltage signal) and outputs the digital signal (voltage signal) 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 the digital signal (voltage signal) 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 the digital signal (voltage signal) to the arithmetic unit 35. The ADC 34 converts the analog electrical signal input from the temperature sensor 8 into a digital signal (voltage signal) and outputs the digital signal (voltage signal) to the calculation unit 35.

The calculation unit 35 that performs digital calculations performs various calculation processes for the control executed by the control unit 3, and is configured of, for example, a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array). The storage unit 36 includes a portion configured with a ROM (Read Only Memory), for example, in which various programs and data used by the calculation unit 35 to perform calculation processing, and a portion that stores various programs and data used by the calculation unit 35 to perform calculation processing. The computer 30 has a work space and a portion composed of, for example, RAM (Random Access Memory), which is used for storing the results of calculation processing by the calculation unit 35, etc. The control function of the control section 3 is realized in software by the functions of the calculation section 35 and the storage section 36.

The current source 37 supplies power for controlling the frequency of the laser beam L1 to the light source section 4 based on instructions from the calculation section 35. In this embodiment, the calculation unit 35 instructs the current source 37 to a current value as the control amount. The current source 37 supplies the light source section 4 with a current having a specified current value.

Next, the configuration of the calculation section 35 will be explained 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 section 357. These functional units are realized through cooperation between software and hardware resources.

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 beam L1, for example, based on an instruction from a higher-level control device.

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

The first and second frequency discrimination curves normalized so that the amplitude value varies between -1 and 1 can be expressed by sine functions (cosine functions) such as the following expressions (1) and (2) when they vary sinusoidally with respect to the change in frequency. Here, θ=2πf/F. f is the frequency of light. F is the period or FSR (Free Spectral Range) of the discrimination curve, and is equal to the periods of the frequency filters 63a and 64a. φ is the phase difference corresponding to the relative phase shift between the frequency filters 63a and 64a.
sinθ... (1)
sin(θ+φ) ... (2)

The third frequency discrimination curve and the fourth frequency discrimination curve, which are standardized so that the amplitude value changes between -1 and 1, are expressed by, for example, the following equations (3) and (4). Note that Δ=φ−π/2.
sin(θ+π/4+Δ/2)... (3)
sin(θ-π/4+Δ/2)... (4)

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, which are standardized so that the amplitude values vary between -1 and 1. FIG. The horizontal axis is the frequency, which is normalized by a half period of the discrimination curve. The vertical axis represents the first ratio, second ratio, third ratio, and fourth ratio for the first frequency discrimination curve C1, second frequency discrimination curve C2, third frequency discrimination curve C3, and fourth frequency discrimination curve C4, respectively. This is a corresponding ratio. 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, if the amplitudes of the first frequency discrimination curve and the second frequency discrimination curve are approximately equal, the third frequency discrimination curve The phase shift between this and the fourth frequency discrimination curve is π/2.

Regions C11, C21, C31, and C41 are regions in the first to fourth frequency discrimination curves C1 to C4, in which the rate of change of the ratio to frequency is large, unlike the dead zone, and the control accuracy can be increased. The regions C11, C21, C31, and C41 are set so as not to overlap each other in terms of frequency.

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 in which the target frequency is included. For example, if the target frequency is included in region C11, the discrimination curve selection unit 352 selects the first frequency discrimination curve C1. In selecting a frequency discrimination curve, it is preferable to select a frequency discrimination curve in which the rate of change of the ratio with respect to the frequency is larger. In the case of FIG. 4, it is preferable to select, from among the multiple frequency discrimination curves, a frequency discrimination curve in which the absolute value of the ratio is small at the target frequency.

The target value acquisition unit 353 performs a third acquisition step of acquiring a target value by applying the target frequency to the frequency discrimination curve selected by the discrimination curve selection unit 352. For example, in FIG. 4, when the target frequency is f_tgt, the target value R_tgt is obtained by applying it to the first frequency discrimination curve C1.

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 is performed 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. The monitor value R_mon is an example of a frequency equivalent. Note that, although an example is shown in which the target frequency and the frequency of the laser light L1 are located in the same region (for example, region C11), the monitor value R_mon and the target value R_tgt may be set on the same frequency discrimination curve.

The first ratio is the ratio of the first intensity detected by the PD 71 to the third intensity detected by the PD 73. Furthermore, as something equivalent to the ratio, the first ratio may be a ratio of the intensity obtained by applying the correction coefficient to the first intensity detected by the PD 71 to the intensity obtained by applying the correction coefficient to the third intensity detected by the PD 73. Further, as the amount corresponding to the ratio, the first ratio may be a ratio calculated using an intensity obtained by applying a correction coefficient to either the first intensity or the third intensity. Below, the first ratio may be described as PD1/PD3.

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. Below, the second ratio may be referred to as PD2/PD3.

The correction coefficients for the first intensity, the second intensity, or the third intensity are obtained in advance through experiments or the like, and are stored in the storage unit 36 in the form of table data, relational expressions, etc., and are calculated by the monitor value calculation unit 354 as appropriate. Read and use. The correction coefficient may be determined depending on, for example, the operating conditions of the laser device 1, the temperature detected by the temperature sensor 8, or the like. Further, the correction coefficient may be determined to be suitable for fitting to a standardized frequency discrimination curve. The correction coefficient is applied to the first intensity, the second intensity, or the third intensity by, for example, addition, subtraction, multiplication, or division.

The third ratio is the sum of the first ratio and the second ratio. The fourth ratio is the difference between the first ratio and the second ratio. Accordingly, the third ratio or the fourth ratio may include a correction factor for the first intensity, the second intensity, or the third intensity.

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.

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 executes feedback control such as proportional-integral-derivative (PID) control or PI control. That is, the PID control unit 356 executes an adjustment step that adjusts 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.

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, outputs an instruction for the current value to the current source 37, and can perform feedforward control of the DBR heater 421 and the RING heater 422.

In the laser device 1 configured in this manner, it is possible to prevent the frequency of the control target from unintentionally overlapping the dead zone, and therefore it is possible to suppress a decrease in control accuracy of the frequency of the laser beam.

In the following, a parameter called "margin" will be introduced to explain how difficult it is for the control target frequency to overlap the dead zone when a lateral shift occurs. The margin is a parameter that serves as an evaluation index for the resistance of the frequency monitor/control system to lateral deviation.

FIG. 5 is an explanatory diagram of 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 values vary between -1 and 1. Regions C51 and C61 are regions in the fifth and sixth frequency discrimination curves C5 and C6, where, unlike the dead zone, the rate of change in the ratio to frequency is large and control accuracy can be increased. The regions C51 and C61 are set so as not to overlap each other in terms of frequency.

In Figure 5, the margin can be defined as the frequency difference between the switching point of the two frequency discrimination curves that is closest to the extreme value 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 the frequency of the laser light L1 can be monitored in a region farther away from the dead zone in frequency terms, and therefore the higher the tolerance to lateral deviation. Note that when frequency control is performed by switching between two frequency discrimination curves as in Figure 5, the margin is φ/2.

FIG. 6 is a diagram showing the relationship between φ and margin. A line M1 shows the relationship between φ and margin when two of the first and second frequency discrimination curves shown in equations (1) and (2) are used. A line M2 shows the relationship between φ and the margin when three of the first to third frequency discrimination curves shown in equations (1) to (3) are used. Line M2 overlaps line M1 when φ is 90 degrees or less. Line M3 shows the relationship between φ and margin when using three of the first, second, and fourth frequency discrimination curves shown in equations (1), (2), and (4). Line M3 overlaps line M1 when φ is 90 degrees or more. Line M4 shows the relationship between φ and margin when using the four first to fourth frequency discrimination curves shown in equations (1) to (4). Line M4 overlaps line M3 when φ is 60 degrees or less, and overlaps line M2 when φ is 120 degrees or less.

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

Next, FIG. 7 is a diagram showing temperature-dependent changes in frequency discrimination curves in a comparative embodiment. The comparative form is a form in which frequency control is performed in the laser device 1 using only the first and second frequency discrimination curves.

In FIG. 7, similarly to FIG. 5, a fifth frequency discrimination curve C5 and a sixth frequency discrimination curve C6 are shown. However, the phase shift between the fifth frequency discrimination curve C5 and the sixth frequency discrimination curve C6 is set to π/2. Here, in the region C51, points on the fifth frequency discrimination curve C5 corresponding to four exemplary target frequencies are indicated by solid white circles. On the other hand, the frequency discrimination curve C5A shows a state in which the fifth frequency discrimination curve C5 shifts to the positive frequency side due to a temperature change, and the frequency discrimination curve C5B shows a state in which the fifth frequency discrimination curve C5 shifts to a negative frequency side due to a temperature change. It shows a state where it has shifted sideways. Regions C5F, C5AF, and C5BF indicate dead zones in the fifth frequency discrimination curve C5, frequency discrimination curve C5A, and frequency discrimination curve C5B, respectively.

When the state of the frequency discrimination curve C5A occurs due to the lateral shift, the most negative point among the four target frequencies overlaps with the dead zone C5AF due to the lateral shift, as shown by the white circle with a broken line. Further, when the state of the frequency discrimination curve C5B is reached due to the lateral shift, the most positive point among the four target frequencies overlaps with the dead zone C5BF, as shown by the white circle with a broken line. This indicates that the comparative form has low resistance to lateral slippage.

On the other hand, FIG. 8 is a diagram showing temperature-dependent changes in the frequency discrimination curve in the embodiment. In FIG. 8, the first to fourth frequency discrimination curves C1 to C4 are shown similarly to FIG. 4. Here, in the region C11, points on the first frequency discrimination curve C1 corresponding to three exemplary target frequencies are indicated by solid white circles. On the other hand, the frequency discrimination curve C1A shows a state in which the first frequency discrimination curve C1 shifts to the positive frequency side due to a temperature change, and the frequency discrimination curve C1B shows a state in which the first frequency discrimination curve C1 shifts to the negative frequency side due to a temperature change. It shows a state where it has shifted sideways. Regions C1F, C1AF, and C1BF indicate dead zones in the first frequency discrimination curve C1, frequency discrimination curve C1A, and frequency discrimination curve C1B, respectively.

In the case of the embodiment, even if the state of the frequency discrimination curve C1A is reached due to lateral shift, none of the points of the three target frequencies overlap with the dead zone C1AF, as shown by the broken white circle. Further, even when the state of the frequency discrimination curve C1B is reached due to lateral shift, none of the three target frequencies overlaps with the dead zone C1BF, as shown by the white circle with a broken line. This indicates that the embodiment has high resistance to lateral slippage.

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

First, in step S101, the target frequency setting unit 351 sets a target frequency as a target value of the frequency of the laser beam 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, An instruction value of a current value corresponding to the electric power is output to the current source 37.

Subsequently, 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. select. For example, from among 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 with the largest rate of change in the target frequency set in step S101 is selected. Alternatively, all frequency discrimination curves may be standardized so that the amplitude values vary between -1 and 1, and then the frequency discrimination curve whose absolute value is the smallest at the target frequency may be selected.

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. do. Subsequently, in step S104, the monitor value calculation unit 354 calculates and sets a monitor value R_mon corresponding to the frequency of the laser beam L1 based on the first frequency discrimination curve. The flow then proceeds to step S111.

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. do. Subsequently, in step S106, the monitor value calculation unit 354 calculates and sets a monitor value R_mon corresponding to the frequency of the laser beam L1 based on the second frequency discrimination curve. The flow then proceeds to step S111.

When 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. do. Subsequently, in step S108, the monitor value calculation unit 354 calculates and sets a monitor value R_mon corresponding to the frequency of the laser beam L1 based on the third frequency discrimination curve. The flow then proceeds to step S111.

When 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. Next, 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. The flow then proceeds to step S111.

Subsequently, 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).

Subsequently, in step S112, the PID control unit 356 calculates an instruction value of the current value such that the absolute value of the difference between the target value R_tgt and the monitor value R_mon becomes small.

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

Subsequently, 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 the error is not within the target error (step S114, No), control proceeds to step S115.

In step S115, the control unit 3 confirms 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.

On the other hand, if the PID control unit 356 determines in step S114 that |target value R_tgt−monitor value R_mon| is within the target error (step S113, Yes), the control ends.

As described above, in the laser device 1, the frequency of the control target is prevented from unintentionally overlapping with the dead zone, so it is possible to suppress the decrease in control accuracy of the frequency of the laser beam.

In addition, in the laser device 1, four frequency discrimination curves are generated by the two frequency filters 63a and 64a, so the configuration and control of the laser device are complicated compared to the case where the number of frequency filters is increased. The increase in size is suppressed. Furthermore, since the detection section for detecting the intensity of laser light is shared to some extent with respect to the frequency discrimination curve, there is no need to switch the detection section every time the frequency discrimination curve is switched. As a result, control becomes unstable when switching the frequency discrimination curve.

Further, in the laser device 1, the first ratio or the second ratio can be calculated by applying a correction coefficient to the first intensity, the second intensity, or the third intensity. As a result, the first ratio or the second ratio, as well as the third ratio or the fourth ratio, are 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. can do. Specifically, according to the temperature detected by the temperature sensor 8, a correction coefficient is set to correct a horizontal shift of the frequency filter that depends on the temperature, or a correction coefficient is set to correct a vertical shift of the frequency filter that depends on the temperature. You can also set correction coefficients. Here, the vertical shift of the frequency filter means that the transmission characteristics of the frequency filter are shifted in the transmittance axis direction. Vertical deviation may cause the target frequency to be uncontrollable or to set an unattainable target value. For example, when the transmission characteristics of the frequency filters 63a and 64a are not a sine function of the frequency, the first intensity, the second intensity, or the third intensity can be adjusted to a frequency discrimination curve that is a sine function of the frequency using a correction coefficient. It may be corrected so that it applies to Note that the temperature sensor 8 is placed in the first area Ar1, and a second temperature sensor is placed separately from the temperature sensor 8 (first temperature sensor), and the temperature detected by the temperature sensor 8 is When controlling the power supplied to the temperature controller 9 based on the information, correction is made to correct at least one of the horizontal shift and the vertical shift of the frequency filter based on the temperature information detected by the second temperature sensor. A coefficient may also be set. At this time, the second temperature sensor may be placed in the second area Ar2, or may be placed closer to the planar light wave circuit 6 than the light source section 4. In addition, it may be placed in a location different from that of the laser section 2 (for example, if the laser section 2 is stored within a housing, it may be placed outside the housing).

In addition, when the transmission characteristics of the frequency filters 63a and 64a are periodic functions that are not sine functions of frequency, a function for converting into a sine function using fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) is used. You can guide and use it. For example, the digital signals converted by the ADCs 31 and 32 are accumulated for one period or more, subjected to FFT, components other than the FSR of the frequency filters 63a and 64a are removed, and IFFT is performed to convert the signals into a sine function. Using the function derived in this way, convert it into a sine function. Note that the frequency transmission characteristics of the MZI filter can be treated as changing sinusoidally with respect to changes in frequency, so when using the MZI filter as the frequency filters 63a and 64a, No conversion is required. When using ring resonator type filters as the frequency filters 63a and 64a, if the Q value of the frequency transmission characteristic of the filter is small, it can be treated as changing sinusoidally with respect to a change in frequency.

Furthermore, in the laser device 1, one temperature controller 9 controls the temperature of both the light source section 4 and the planar light wave circuit 6, so the light source section 4 and the planar light wave circuit 6 each have a temperature controller. Lower power consumption and lower costs can be achieved than if the device is installed. However, the control unit 3 mainly controls the power supplied to the temperature controller 9 so that the light source unit 4 has a constant temperature, and controls the power supplied to the light source unit 4 to control the output of the light source unit 4. When the oscillation frequency of the laser beam is controlled, temperature-dependent lateral deviation may easily occur in the frequency filters 63a and 64a of the planar light wave circuit 6. On the other hand, the laser device 1 has a configuration that is highly resistant to lateral shift, and is therefore suitable for suppressing a decrease in control accuracy.

Furthermore, in the laser device 1, the third ratio and the fourth ratio include 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 in the digital signals converted by the ADCs 31, 32, and 33, if the voltage value of either the first ratio or the second ratio changes by even 1 bit with respect to the frequency, that change can be detected. It means that. In other words, even if the target value or monitor value falls into a dead zone due to lateral shift, or if the phase shift φ is close to 0 or π, it is possible to detect changes in the monitor value, which means that frequency control can be performed. do.

Further, 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 target value acquisition unit 353 calculates the first ratio or the second ratio from the target frequency. A correction coefficient may be applied when obtaining the target value. This correction coefficient is obtained in advance through experiments and stored in the storage unit 36, and can be set depending on the operating conditions of the laser device 1 and the temperature detected by the temperature sensor 8 or the second temperature sensor. Can be done. Further, when obtaining the target value from the target frequency, the target value may be obtained from the target frequency using a method similar to the method of converting a non-sine function into a sine function using FFT and IFFT.

Further, in the laser device 1, the sum and difference calculations for calculating the third ratio and the fourth ratio are performed by digital calculations in the calculation unit 35, but the sum and difference calculations may also be performed by an analog circuit. . By using digital calculations, the number of elements used and circuit scale can be reduced, and cost reductions can be achieved. Furthermore, by using an analog circuit, it is possible to prevent information loss due to quantization during digitization.

Furthermore, the present invention is not limited to the above embodiments. The present invention also includes configurations in which the above-mentioned components are appropriately combined. Moreover, further effects and modifications can be easily derived by those skilled in the art. Accordingly, the broader aspects of the invention are not limited to the embodiments described above, but are capable of various modifications.

1 Laser device 2 Laser section 3 Control section 4 Light source section 5 Semiconductor optical amplifier 6 Planar light wave circuit 7 Photodetection section 8 Temperature sensor 9 Temperature controller 10 Monitor section 31, 32, 33, 34 ADC
35 Arithmetic section 36 Storage section 37 Current source 41 Laser main body section 42 Changing section 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 filter 91 Installation surface 351 Target frequency setting section 352 Discrimination curve selection section 353 Target value acquisition section 354 Monitor value calculation section 355 Difference acquisition section 356 PID control section 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 stack section 433 P-side electrode 441a Waveguides 442, 443 Arm section 444 Ring-shaped waveguide 445 Phase adjustment section Ar1 First region Ar2 Second region B1 Base C Optical resonator C1 First frequency discrimination curve C2 Second frequency discrimination curve C3 Third frequency discrimination curve C4 Fourth frequency discrimination curve C5 Fifth frequency discrimination curve C6 Sixth frequency discrimination curve C5A, C5B Frequency discrimination curve C11, C21, C31 , C41, C51, C61, C1F, C1AF, C1BF, C5F, C5AF, C5BF Regions L1, L2, L3, L4, L5, L6 Laser beam M Reflecting mirror M1, M2, M3, M4 Line RF1 Ring resonator filter

Claims (9)

a laser unit including a light source unit that makes the frequency of the laser beam to be output variable; and a monitor unit that acquires a monitor value corresponding to a frequency equivalent amount corresponding to the frequency of the laser beam;
a control unit that controls the frequency of the laser beam by supplying a control amount to the laser unit;
Equipped with
The monitor unit includes a first frequency filter and a first frequency filter, each having a transmission characteristic in which the transmittance changes periodically with respect to the frequency of input light, and whose phase is relatively shifted by an amount other than an integral multiple of π . a two-frequency filter; a first detection unit that detects a first intensity corresponding to the intensity of the laser beam after the laser beam has passed through the first frequency filter; At least a second detection unit that detects a second intensity corresponding to the intensity of the subsequent laser beam,
The control unit includes:
a target frequency setting unit that obtains a target frequency that is a control target for the frequency of the laser beam;
obtaining a first ratio corresponding to the ratio of the first intensity to the intensity of the laser beam, and a second ratio corresponding to the ratio of the second intensity to the intensity of the laser beam,
a monitor value calculation unit capable of obtaining 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 beam;
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,
A laser device that controls the control amount so that the absolute value of the difference between the target value and the monitor value becomes small. The laser according to claim 1, wherein the control unit converts the first intensity, the second intensity, and the intensity of the laser beam into digital signals, and calculates the first ratio or the second ratio by digital calculation. Device. The laser device according to claim 1 or 2 , wherein the transmittance of the first and second frequency filters changes sinusoidally with respect to a change in frequency. The control unit converts a frequency function indicating a transmission characteristic of the first frequency filter or a transmission characteristic of the second frequency filter into a sine function of the frequency from the first intensity, the second intensity, and the intensity of the laser beam. The laser device according to any one of claims 1 to 3 , wherein the first ratio or the second ratio is calculated by converting the ratio into . The laser device according to any one of claims 1 to 4 , wherein the laser section is configured to vary the frequency of the laser beam using a Vernier effect. The control unit controls the frequency of the laser beam by supplying power corresponding to the control amount to the laser unit.
A laser device according to any one of claims 1 to 5 . Further comprising a temperature controller having an installation surface on which the light source section, a first frequency filter, and a second frequency filter are installed,
The light source section, the first frequency filter, and the second frequency filter,
The laser device according to claim 6, wherein the laser device is installed on the same installation surface of the temperature controller. The laser device according to any one of claims 1 to 7, wherein the control unit sets and selects, among the first to fourth ratios, a ratio that has the largest change in ratio relative to a frequency change at the target value as a monitor value corresponding to the frequency of the laser light. A method for controlling a laser device including a light source section that makes the frequency of output laser light variable, the method comprising:
a first acquisition step of acquiring a target frequency that is a control target for the frequency of the laser beam;
Among the first frequency filter and the second frequency filter, the filter has a transmission characteristic in which the transmittance changes periodically with respect to the frequency of input light, and the phase is relatively shifted by an amount other than an integral multiple of π. , detecting a first intensity corresponding to the intensity of the laser beam after the laser beam passes through the first frequency filter, and detecting a first intensity corresponding to the intensity of the laser beam after the laser beam passes through the second frequency filter. a detection step of detecting a second intensity and detecting the intensity of the laser beam;
a second obtaining step of obtaining a first ratio corresponding to the ratio of the first intensity to the intensity of the laser beam, and a second ratio corresponding to the ratio of the second intensity to the intensity of the laser beam;
a third obtaining step of obtaining 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 setting step of setting a monitor value corresponding to a frequency equivalent amount corresponding to the frequency of the laser beam from any one of the first ratio, the second ratio, the third ratio, and the fourth ratio; ,
a third acquisition step of acquiring a target value corresponding to the target frequency based on any one of the first to fourth ratios;
an adjusting step of adjusting the control amount so that the absolute value of the difference between the target value and the monitor value becomes small;
Including a method of controlling a laser device.

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