JP6928853B2 - Wavelength control method for tunable laser device, tunable laser device and its calibration method - Google Patents

Description

The present invention relates to a wavelength control method for a tunable laser device, a tunable laser device, and a calibration method thereof.

Conventionally, in a tunable laser apparatus, there is known a technique for controlling the wavelength of laser light to be output by using a wavelength filter having periodic transmittance with respect to the wavelength of incident light (for example, Patent Document 1). reference).

The wavelength-variable laser apparatus described in Patent Document 1 includes a light source unit that changes the wavelength of the output laser light, a first detection unit that detects the intensity of the laser light output from the light source unit, an etalon, and the like. It includes a wavelength filter, a second detection unit that detects the intensity of laser light that has passed through the wavelength filter, and a control unit that controls the operation of the light source unit. The transmittance of the wavelength filter changes periodically with respect to the wavelength of light. As a result, the intensity of the laser light transmitted through the wavelength filter also changes periodically with respect to the wavelength, and this periodic characteristic is called a wavelength discrimination curve. Then, the control unit controls the wavelength of the laser light based on the wavelength discrimination curve formed by the intensity ratio of the laser light detected by the first and second detection units, respectively.

In the wavelength discrimination curve, the vicinity of the maximum value and the minimum value is a dead zone in which the change in the intensity ratio of the laser beam is small with respect to the change in wavelength and it is difficult to detect the change in wavelength, so that the accuracy of wavelength control is not good. .. Therefore, there is a technique for performing wavelength control using two wavelength filters having different wavelengths in the dead zone including the maximum value and the minimum value. FIG. 12 is a diagram showing a state in which wavelength control is performed using two wavelength filters. The horizontal axis of FIG. 12 is a display obtained by converting the wavelength of light into a frequency, and the vertical axis is the intensity ratio of the laser light detected by the first and second detection units, respectively. As shown in FIG. 12, by avoiding a dead zone including a maximum value and a minimum value of each wavelength filter, a lock point is set for one of the wavelength filters, and wavelength lock is performed at the lock point, thereby performing wavelength. The wavelength can be controlled accurately without using the dead zone of the filter.

Japanese Unexamined Patent Publication No. 2015-60961

However, when the wavelength is controlled by using two wavelength filters independently as described above, it is necessary to switch which wavelength filter is used for wavelength control, which complicates the control.

Further, when the temperature of the wavelength filter deviates, the periodic characteristics of the wavelength discrimination curve deviate in the wavelength axis direction, which makes it more difficult to switch to the optimum wavelength filter.

The present invention has been made in view of the above, and provides a wavelength control method for a tunable laser device, a tunable laser device, and a calibration method thereof, which can perform wavelength control accurately and easily. With the goal.

In order to solve the above-mentioned problems and achieve the object, the wavelength control method of the wavelength-variable laser apparatus according to the present invention includes a laser light emission step of emitting laser light having a variable wavelength from a light source unit and a wavelength of light. The first detection step of detecting the intensity of the laser light transmitted through the first wavelength filter having a transmittance that changes periodically with respect to the light as the first detection value, and the first wavelength filter with respect to the wavelength of the light. The second detection that detects the intensity of the laser light that has a transmittance that changes periodically with the same period and has passed through a second wavelength filter having a different peak wavelength of the transmittance from the first wavelength filter as a second detection value. A step, a first phase equivalent calculation step for calculating the first phase equivalent using a function for deriving one phase equivalent for the set of the first detected value and the second detected value, and a step. The second phase equivalent amount calculation step for calculating the second phase equivalent amount corresponding to the target wavelength, which is the target value for controlling the wavelength of the laser beam, and the position of the second phase equivalent amount and the first phase equivalent amount. It is characterized by including a phase difference calculation step of calculating a phase difference equivalent amount and a wavelength control step of controlling the wavelength of the laser light emitted from the light source unit according to the phase difference equivalent amount.

Further, the wavelength control method of the tunable laser apparatus according to the present invention is characterized in that the function is a function in which the phase equivalent amount periodically repeats a monotonous change according to the wavelength of the laser light.

The wavelength control method of the wavelength-variable laser apparatus according to the present invention is the first having a laser light emission step of emitting laser light having a variable wavelength from a light source unit and a transmission coefficient that periodically changes with respect to the wavelength of the light. It has a first detection step that detects the intensity of the laser light that has passed through the wavelength filter as the first detection value, and a transmission rate that periodically changes with respect to the wavelength of the light at the same period as the first wavelength filter. A second detection step of detecting the intensity of the laser beam transmitted through a second wavelength filter having a different peak wavelength of transmission from the first wavelength filter as a second detection value, the first detection value, and the second detection value. The first phase equivalent amount is calculated using a conversion table in which one phase equivalent amount corresponds to the set of, and the phase equivalent amount is set to repeat monotonous change periodically. The first phase equivalent amount calculation step, the second phase equivalent amount calculation step for calculating the second phase equivalent amount corresponding to the target wavelength which is the target value for controlling the wavelength of the laser light, and the second phase equivalent amount. A phase difference calculation step of calculating the phase difference equivalent amount between the first phase difference amount and the first phase difference equivalent amount, and a step of controlling the wavelength of the laser beam emitted from the light source unit according to the phase difference equivalent amount. It is characterized by including.

Further, the wavelength control method of the tunable laser apparatus according to the present invention is characterized in that, in the above invention, the conversion table is defined so that the phase equivalent amount periodically repeats monotonous and linear changes. do.

In the wavelength-variable laser apparatus according to the present invention, a light source unit that emits laser light having a variable wavelength, a first wavelength filter having a transmittance that changes periodically with respect to the wavelength of the light, and the first wavelength filter. It has a first detection unit that detects the intensity of the laser light that has passed through as a first detection value, and a transmission rate that periodically changes with respect to the wavelength of the light in a period equal to that of the first wavelength filter. A second wavelength filter having a different peak wavelength of transmission from the one wavelength filter, a second detection unit that detects the intensity of the laser beam transmitted through the second wavelength filter as a second detection value, the first detection value, and the first detection value. By inputting the set of the second detection values, the wavelength of the laser beam is controlled by using the storage unit that stores the function from which one phase equivalent amount is derived and the function stored in the storage unit. It is characterized in that it is provided with a light source control unit.

In the wavelength-variable laser apparatus according to the present invention, a light source unit that emits laser light having a variable wavelength, a first wavelength filter having a transmittance that changes periodically with respect to the wavelength of the light, and the first wavelength filter. It has a first detection unit that detects the intensity of the laser light that has passed through as a first detection value, and a transmission rate that periodically changes with respect to the wavelength of the light in a period equal to that of the first wavelength filter. A second wavelength filter having a different peak wavelength of transmission from the one wavelength filter, a second detection unit that detects the intensity of the laser beam transmitted through the second wavelength filter as a second detection value, the first detection value, and the first detection value. A light source that controls the wavelength of the laser beam by using a storage unit that stores a conversion table in which one phase equivalent amount corresponds to the set of the second detection values and the conversion table stored in the storage unit. The conversion table includes a control unit, and the conversion table is characterized in that the phase equivalent amount is set to repeat a monotonous change periodically.

Further, in the wavelength tunable laser apparatus according to the present invention, in the above invention, the first and second wavelength filters are configured so that the wavelengths in the dead zone are different from each other.

In the calibration method of the wavelength-variable laser apparatus according to the present invention, the first method has a laser light emission step of emitting laser light having a variable wavelength from a light source unit and a transmission coefficient that periodically changes with respect to the wavelength of the light. It has a first detection step that detects the intensity of the laser light that has passed through the wavelength filter as the first detection value, and a transmission rate that periodically changes with respect to the wavelength of the light at the same period as the first wavelength filter. A second detection step of detecting the intensity of the laser light transmitted through a second wavelength filter having a different peak wavelength of transmission from the first wavelength filter as a second detection value, the first detection value, and the second detection value. It is a conversion table in which one phase equivalent amount corresponds to the set of, and includes a conversion table creation step of creating a conversion table in which the phase equivalent amount periodically repeats monotonous changes.

According to the present invention, it is possible to realize an effect of realizing a wavelength control method of a tunable laser device, a tunable laser device, and a calibration method thereof, which can perform wavelength control accurately and easily.

FIG. 1 is a block diagram schematically showing a configuration of a tunable laser apparatus according to an embodiment. FIG. 2 is a diagram for explaining a method of converting a current ratio into a phase. FIG. 3 is a diagram showing the relationship between the phase and the frequency shown in FIG. FIG. 4 is a diagram showing a state of coordinate transformation. FIG. 5 is a diagram showing the relationship between the phase and the frequency shown in FIG. FIG. 6 is a flowchart showing a wavelength control method by the control unit. FIG. 7 is a diagram showing the relationship between the phase and the frequency. FIG. 8 is a diagram showing an example of a conversion table. FIG. 9 is a diagram showing how the relationship between the phase and the frequency is corrected. FIG. 10 is a diagram showing another example of the conversion table. FIG. 11 is a diagram showing another example of the conversion table. FIG. 12 is a diagram showing a state in which wavelength control is performed using two wavelength filters.

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings. The present invention is not limited to the embodiments described below. Further, in the description of the drawings, the same parts are designated by the same reference numerals. In addition, the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, and the like may differ from reality. Further, even between the drawings, there may be parts having different dimensional relationships and ratios from each other.

(Embodiment)
[Structure of tunable laser device]
FIG. 1 is a block diagram schematically showing a configuration of a tunable laser apparatus according to an embodiment.
The tunable laser device 100 shown in FIG. 1 includes a tunable laser unit 200 and a control unit 300 that controls the operation of the tunable laser unit 200.
The tunable laser unit 200 and the control unit 300 may be integrally configured or may be configured as separate bodies.

[Structure of tunable laser unit]
The tunable laser unit 200 can change the wavelength of the laser light to be output under the control of the control unit 300. The tunable laser unit 200 includes a light source unit 210, an optical branching unit 220, a first wavelength filter 231 and a second wavelength filter 232, a first detection unit 241 and a second detection unit 242, and a third detection. A unit 243 and a section 243 are provided.

The light source unit 210 realizes a laser beam emitting step of emitting a laser beam having a variable wavelength. The light source unit 210 is, for example, a DBR (Distributed Bragg Reflector) or DFB (Distributed Feedback) laser device capable of controlling the oscillation wavelength of the emitted laser light, but the wavelength may be variable. There is no particular limitation.

The optical branching unit 220 branches the light input from the light source unit 210 into three parts. The optical branching portion 220 is an optical waveguide that branches the input light, but may be composed of an optical element such as a half mirror.

The first wavelength filter 231 and the second wavelength filter 232 have a transmittance that changes periodically with respect to the wavelength of light. The first wavelength filter 231 and the second wavelength filter 232 are, for example, a ring resonator type optical filter composed of a waveguide type optical filter. The first wavelength filter 231 and the second wavelength filter 232 each have a periodic transmission characteristic with respect to the wavelength of the incident light, and each of the laser light incident from the light source unit 210 has a transmittance corresponding to the transmission characteristic. To Penetrate. Further, the first wavelength filter 231 and the second wavelength filter 232 have different peak wavelengths of transmittance due to the difference in at least one of the type and amount of the dopant added to at least one of the core or the cladding. That is, the second wavelength filter 232 has a transmittance that periodically changes with respect to the wavelength of light with a period equal to that of the first wavelength filter 231 and has a different peak wavelength of transmittance from the first wavelength filter 231. Further, the first wavelength filter 231 and the second wavelength filter 232 may be etalon filters. Further, by providing three or more wavelength filters, the wavelength of the tunable laser unit 200 may be controlled by using three or more wavelength discrimination curves. When three or more wavelength discrimination curves are used, two of these discrimination curves may be selected, and the wavelength is controlled by calculating the sum, difference, product, quotient, etc. of a plurality of discrimination curves. You may.

The first detection unit 241 is composed of a photodiode or the like, and realizes a first detection step of detecting the intensity of the laser light transmitted through the first wavelength filter 231 as the first detection value.

The second detection unit 242 is composed of a photodiode or the like, and realizes a second detection step of detecting the intensity of the laser light transmitted through the second wavelength filter 232 as the second detection value.

The third detection unit 243 is composed of a photodiode or the like, and detects the intensity of the laser light emitted by the light source unit 210 as the third detection value.

[Structure of control unit]
Next, the configuration of the control unit 300 will be described.
The control unit 300 controls the operation of the tunable laser unit 200 according to an instruction from the user. The control unit 300 includes a calculation unit 301, an input unit 302, and a storage unit 303.

The calculation unit 301 is configured by using a CPU or the like. The calculation unit 301 includes a first conversion unit 311, a second conversion unit 312, a third conversion unit 313, a first current ratio calculation unit 321 and a second current ratio calculation unit 322, and a phase calculation unit 330. A target phase calculation unit 340, a phase difference calculation unit 350, and a light source control unit 360 are provided.

The first conversion unit 311 performs A / D conversion processing on the first detection value (hereinafter referred to as PD1) input from the first detection unit 241 to convert it into a digital signal, and outputs this digital signal.

The second conversion unit 312 performs A / D conversion processing on the second detection value (hereinafter referred to as PD2) input from the second detection unit 242 to convert it into a digital signal, and outputs this digital signal.

The third conversion unit 313 performs A / D conversion processing on the third detection value (hereinafter referred to as PD3) input from the third detection unit 243 to convert it into a digital signal, and outputs this digital signal.

The first current ratio calculation unit 321 calculates the ratio (PD1 / PD3) of the output value of the digital signal output from the third conversion unit 313 to the digital signal output from the first conversion unit 311 as the first current ratio. ..

The second current ratio calculation unit 322 calculates the ratio (PD2 / PD3) of the output value of the digital signal output from the third conversion unit 313 to the digital signal output from the second conversion unit 312 as the second current ratio. ..

The phase calculation unit 330 sets the first current ratio calculated by the first current ratio calculation unit 321 and the second current ratio calculated by the second current ratio calculation unit 322 based on the function or conversion table read from the storage unit 303. The first phase equivalent amount calculation step for calculating the phase equivalent amount (first phase equivalent amount) determined based on the above is realized. The phase equivalent amount may be an amount that fluctuates in the range of 2π to 0, or a numerical range having an upper limit and a lower limit may be used as the phase equivalent amount.

FIG. 2 is a diagram for explaining a method of converting a current ratio into a phase. FIG. 2 shows a standardization in which the maximum values of the first current ratio and the second current ratio are 1, and the horizontal axis is the first current ratio and the vertical axis is the second current ratio with respect to an arbitrary frequency. The line L1 can be drawn. At this time, the first and second current ratios at a predetermined frequency are represented by the polar coordinate system as the point P1 as shown in FIG. 2, and the angle formed by the straight line passing through the origin and the point P1 and the horizontal axis is defined as the phase θ0. be able to. The phase θ0 is a variable calculated using the first detected value, the second detected value, and the third detected value.

FIG. 3 is a diagram showing the relationship between the phase and the frequency shown in FIG. The horizontal axis of FIG. 3 is the frequency. FIG. 3 shows the first current ratio and the second current ratio together with the phase θ0. The first current ratio and the second current ratio are standardized so that the maximum value is 1. _{The phase θ0 is a function that periodically changes between the minimum value θ0 Min} and the maximum value θ0 _Max shown on the vertical axis on the right side in FIG. 3 in the same period as the period of the transmittance of the first wavelength filter 231. I understand.

Subsequently, coordinate transformation is performed in order to transform the phase θ0 into a function that periodically repeats monotonous changes. FIG. 4 is a diagram showing a state of coordinate transformation. As shown in FIG. 4, the origin is shifted horizontally by ΔA and vertically by ΔB, and moved to a point Po (ΔA, ΔB) inside the line L1. This operation is equivalent to the operation of giving offsets to the values obtained by the first current ratio and the second current ratio, respectively. Then, in this coordinate system, the phase equivalent amount (hereinafter, also simply referred to as phase) θ1 can be defined from the angle formed by the straight line passing through the origin and the point P1 after movement and the line parallel to the horizontal axis.

位相算出部３３０は、例えば式（１）で例示した式を用いて位相θ１を算出する。 FIG. 5 is a diagram showing the relationship between the phase and the frequency shown in FIG. The horizontal axis of FIG. 5 is the frequency standardized in one cycle of the first wavelength filter 231 as in FIG. FIG. 5 shows the first current ratio and the second current ratio together with the phase θ1 as in FIG. The phase θ1 is a function that periodically repeats a monotonous increase until _{the phase equivalent returns to the minimum value (θ1 Min} ) and the phase equivalent reaches the maximum value (θ1 _Max ) at frequencies f1, f2, f3, and f4. I understand. In this way, by appropriately selecting the points Po (ΔA, ΔB) inside the line L1, it is possible to define a function that periodically repeats a monotonous change with respect to a change in frequency. The phase θ1 shown in FIG. 5 can be calculated by the following equation (1), for example, when the phase shift of the transmission characteristics between the first wavelength filter 231 and the second wavelength filter 232 is π / 2.

The phase calculation unit 330 calculates the phase θ1 using, for example, the equation exemplified in the equation (1).

The target phase calculation unit 340 calculates the target phase (second phase equivalent amount), which is the phase equivalent amount corresponding to the target wavelength input from the input unit 302, based on the function or the conversion table read from the storage unit 303. The second phase equivalent amount calculation step is realized. Specifically, the target phase calculation unit 340 determines the theory of the first current ratio and the second current ratio from the transmittance of the frequency corresponding to the target wavelength in the wavelength discrimination curves of the first wavelength filter 231 and the second wavelength filter 232. The target phase is calculated by calculating the value and substituting it into the equation (1).

The phase difference calculation unit 350 realizes a phase difference calculation step of calculating the difference (phase difference equivalent amount) between the phase θ1 determined according to the first detection value and the second detection value and the target phase.

The light source control unit 360 controls the wavelength tunable laser unit 200. Specifically, the light source control unit 360 controls the wavelength of the laser light emitted from the light source unit 210 based on the phase difference calculated by the phase difference calculation unit 350.

The input unit 302 is connected to a button (not shown), a switch, a touch panel, a mouse, a keyboard, or the like, and receives a user's instruction input. The input unit 302 receives, for example, an instruction input of a target wavelength to be output to the tunable laser unit 200 by the user. Further, the input unit 302 may be configured to receive an instruction input of a target wavelength from a terminal outside the control unit 300 by wire or wireless communication.

The storage unit 303 stores a program or the like for the wavelength tunable laser device 100 to execute an operation. The storage unit 303 is configured by using a RAM (Random Access Memory), a ROM (Read Only Memory), an HDD (Hard Disk Drive), another recording medium, or the like. The storage unit 303 stores a function or a conversion table used by the calculation unit 301 for the calculation.

[Wavelength control method]
Next, the wavelength control method by the control unit 300 described above will be described.
FIG. 6 is a flowchart showing a wavelength control method by the control unit. FIG. 6 describes a wavelength control method after executing the laser beam emission step to the second detection step.
First, the calculation unit 301 determines whether or not the target wavelength λ has been input to the input unit 302 (step S1).

When the calculation unit 301 determines that the target wavelength λ has been input (step S1: Yes), the target phase calculation unit 340 calculates the target phase θ2 corresponding to the target wavelength λ (step S2: second phase equivalent amount). Calculation step). On the other hand, when the calculation unit 301 determines that the target wavelength λ has not been input (step S1: No), the process of step S1 is repeated.

Subsequently, the phase calculation unit 330 calculates the current phase θ1 (step S3: first phase equivalent amount calculation step). Specifically, the phase θ1 determined according to the first detected value, the second detected value, and the third detected value is calculated by using the function of the above-mentioned equation (1) or the conversion table.

Further, the phase difference calculation unit 350 calculates the phase difference Δθ = target phase θ2-phase θ1 (step S4: phase difference calculation step).

After that, the calculation unit 301 determines whether or not the phase difference Δθ is smaller than the threshold value (step S5).

When the calculation unit 301 determines that the phase difference Δθ is smaller than the threshold value (step S5: Yes), a series of processes is completed.

On the other hand, when the calculation unit 301 determines that the phase difference Δθ is equal to or greater than the threshold value (step S5: No), the light source control unit 360 calculates the wavelength control current so that the phase difference Δθ becomes smaller (step S5: No). Step S6). The wavelength control current is a current applied to control the wavelength of the light source unit 210, and the light source control unit 360 changes the amount of the wavelength control current applied to the laser light output by the light source unit 210. Control the wavelength of.

Subsequently, the light source control unit 360 outputs the wavelength control current calculated based on the phase difference Δθ to the light source unit 210 (step S7: wavelength control step). After that, the calculation unit 301 repeats steps S3 to S5 to make the wavelength deviation from the target wavelength smaller than the threshold value. That is, the control unit 300 performs feedback control to make the wavelength deviation from the target wavelength smaller than the threshold value.

According to the embodiment described above, since the wavelength control is always performed using both the first detection value and the second detection value, it is not necessary to switch the wavelength filter used for the wavelength control. As a result, the control unit 300 can perform wavelength control accurately and easily.

Further, according to the embodiment, wavelength control is always performed using both the first detection value and the second detection value. That is, wavelength control is performed using both the wavelength discrimination curve of the first wavelength filter 231 and the wavelength discrimination curve of the second wavelength filter 232. Therefore, at a certain wavelength, even if one of the wavelength discrimination curve of the first wavelength filter 231 and the wavelength discrimination curve of the second wavelength filter 232 corresponds to the dead zone, the other is not the dead band, so that the wavelength discrimination curve It is prevented that wavelength control is performed using only the dead zone of. As a result, a certain degree of accuracy can be ensured in wavelength control at any wavelength. Further, even when the temperatures of the first wavelength filter 231 and the second wavelength filter 232 deviate from each other, the wavelength is measured by using both the wavelength discrimination curve of the first wavelength filter 231 and the wavelength discrimination curve of the second wavelength filter 232. Since the control is performed, a certain degree of accuracy can be ensured in the wavelength control.

(Modification example)
In the embodiment, an example in which the phase calculation unit 330 calculates the phase θ1 using the function shown in the equation (1) has been described, but the phase calculation unit 330 sets the first current ratio and the second current ratio to the phase θ1. The phase θ1 may be calculated using a conversion table that converts to.

FIG. 7 is a diagram showing the relationship between the phase and the frequency. The horizontal axis of FIG. 7 is the frequency standardized in one cycle of the first wavelength filter 231 as in FIG. FIG. 7 shows the first current ratio and the second current ratio together with the phase θ1 as in FIG. The phase θ1 is a function that periodically and linearly increases until the phase equivalent returns to the _{minimum value (θ1 Min ) at frequencies f5 and f7 and reaches the maximum value (θ1 Max).} Recognize.

The conversion table measures the wavelength of the laser light and the first detected value, the second detected value, and the third detected value while changing the wavelength of the laser light output by the light source unit 210, and the first current ratio at each frequency. And it can be created by finding the correspondence between the second current ratio and the phase θ1. At this time, as shown in FIG. 7, the first current ratio and the second current ratio are associated with the phase θ1 so that the phase θ1 repeats increasing periodically monotonously and linearly.

FIG. 8 is a diagram showing an example of a conversion table. The conversion table shown in FIG. 8 is created based on the measurement result and is stored in the storage unit 303 in advance. This conversion table is a conversion table in which one phase θ1 corresponds to a set of the first detected value and the second detected value, and the phase θ1 is defined to periodically and linearly increase in a monotonous manner. There is. The light source control unit 360 controls the wavelength output by the light source unit 210 by using this conversion table.

When the temperatures of the first wavelength filter 231 and the second wavelength filter 232 deviate from each other, the correspondence between the first current ratio and the second current ratio and the phase θ1 may be shifted according to the temperature deviation for reference. FIG. 9 is a diagram showing how the relationship between the phase and the frequency is corrected. As shown in FIG. 9, when the temperatures of the first wavelength filter 231 and the second wavelength filter 232 deviate, the wavelength axis direction corresponds to the temperature at which the first current ratio and the second current ratio shown in FIG. 7 deviate. Shift. Therefore, in order to correct this deviation, the phase θ1'in which the phase θ1 is shifted in the frequency axis direction may be used as the corrected phase equivalent amount. This correction enables control that corrects the temperature deviation. At this time, as the amount of shift (shift amount) in the frequency axis direction, for example, a thermistor was placed so as to measure the ambient temperature of the first wavelength filter 231 and the second wavelength filter 232, and the thermistor was measured. The shift amount may be controlled according to the temperature. Further, the shift amount with respect to the partial or total power consumption during the operation of the tunable laser apparatus 100 may be stored in advance in the storage unit 303, and the shift amount may be shifted based on the stored shift amount.

According to the modification described above, since the phase θ1 changes linearly, the change in the phase equivalent amount is always constant with respect to the change in frequency, so that the wavelength can be controlled efficiently. As an example, when wavelength control is performed by the flowchart shown in FIG. 6, if the change in the phase equivalent amount is not constant with respect to the change in frequency, the number of times S3 to S7 are repeated may increase, but the change in frequency. On the other hand, when the change in the phase equivalent amount is constant, the number of times the control is repeated can be reduced.

Further, a conversion table for determining the phase equivalent amount may be created based on the first current ratio and the second current ratio. First, a simple calculation formula for converting the calculated values of the first current ratio and the second current ratio into the address of the storage unit 303 is prepared. Then, the corresponding phase equivalent amount is stored in the address of the storage unit 303. In this way, if the phase equivalent amount is stored in the storage unit 303, the storage unit 303 functions as a conversion table capable of referencing the phase equivalent amount with the minimum number of steps, so that the phase equivalent amount can be determined quickly. be able to.

10 and 11 are diagrams showing another example of the conversion table. In FIG. 10, the storage units 303 are arranged in a two-dimensional array, and each address is shown in decimal. FIG. 11 shows a numerical value corresponding to the phase stored at each address. As shown in FIG. 11, the phase equivalent amount may be stored in the storage unit 303 in a form that reflects the shape of the line L1 in the graph shown in FIG. In the examples shown in FIGS. 10 and 11, when a set of the first current ratio and the second current ratio is given, the address determined by the formula (first current ratio × 10 + second current ratio × 110) is referred to. By using the stored value as the phase equivalent amount, the storage unit 303 functions as a conversion table.

[Wavelength calibration method]
Next, the wavelength calibration method will be described.
In this wavelength calibration method, a conversion table in which one phase θ1 corresponds to a set of a first detection value and a second detection value in advance, and the phase θ1 periodically repeats a monotonous change is created. (Conversion table creation step). Specifically, measurement is performed in advance, a conversion table shown in FIG. 8 or FIG. 11 is created, and the created conversion table is stored in the storage unit 303.

According to this wavelength calibration method, since the conversion table created by performing the measurement using the first wavelength filter 231 and the second wavelength filter 232 is used, it is assumed that the peak wavelength of the transmittance of the wavelength filter varies. However, the wavelength can be appropriately controlled by using a conversion table according to each variation.

100 Wavelength variable laser device 200 Wavelength variable laser unit 300 Control unit 210 Light source unit 220 Light branch unit 231 First wavelength filter 232 Second wavelength filter 241 First detection unit 242 Second detection unit 243 Third detection unit 301 Calculation unit 302 Input Unit 303 Storage unit 311 1st conversion unit 312 2nd conversion unit 313 3rd conversion unit 321 1st current ratio calculation unit 322 2nd current ratio calculation unit 330 Phase calculation unit 340 Target phase calculation unit 350 Phase difference calculation unit 360 Light source control Department

Claims (8)

A laser beam emission step that emits a laser beam having a variable wavelength from a light source unit,
A first detection step of detecting the intensity of the laser beam transmitted through the first wavelength filter having a transmittance that changes periodically with respect to the wavelength of light as a first detection value, and
The laser light that has passed through a second wavelength filter that has a transmittance that changes periodically with respect to the wavelength of the light at the same period as the first wavelength filter and has a different peak wavelength of transmittance from the first wavelength filter. The second detection step of detecting the intensity as the second detection value, and
A first phase equivalent calculation step for calculating the first phase equivalent using a function for which one phase equivalent is derived for the set of the first detected value and the second detected value, and
A second phase equivalent amount calculation step for calculating a second phase equivalent amount corresponding to a target wavelength, which is a target value for controlling the wavelength of the laser beam, and a second phase equivalent amount calculation step.
A phase difference calculation step for calculating the phase difference equivalent amount between the second phase equivalent amount and the first phase equivalent amount, and
A wavelength control step that controls the wavelength of the laser beam emitted from the light source unit according to the phase difference equivalent amount, and
A wavelength control method for a tunable laser apparatus, which comprises. The wavelength control method for a tunable laser apparatus according to claim 1, wherein the function is a function in which the phase equivalent amount periodically repeats monotonous changes according to the wavelength of the laser beam. A laser beam emission step that emits a laser beam having a variable wavelength from a light source unit,
A first detection step of detecting the intensity of the laser beam transmitted through the first wavelength filter having a transmittance that changes periodically with respect to the wavelength of light as a first detection value, and
The laser light that has passed through a second wavelength filter that has a transmittance that changes periodically with respect to the wavelength of the light at the same period as the first wavelength filter and has a different peak wavelength of transmittance from the first wavelength filter. The second detection step of detecting the intensity as the second detection value, and
A conversion table in which one phase equivalent amount corresponds to a set of the first detected value and the second detected value, and the phase equivalent amount is defined to periodically repeat a monotonous change. The first phase equivalent amount calculation step for calculating the first phase equivalent amount using
A second phase equivalent amount calculation step for calculating a second phase equivalent amount corresponding to a target wavelength, which is a target value for controlling the wavelength of the laser beam, and a second phase equivalent amount calculation step.
A phase difference calculation step for calculating the phase difference equivalent amount between the second phase equivalent amount and the first phase equivalent amount, and
A wavelength control step that controls the wavelength of the laser beam emitted from the light source unit according to the phase difference equivalent amount, and
A wavelength control method for a tunable laser apparatus, which comprises. The wavelength control method for a tunable laser apparatus according to claim 3, wherein the conversion table is defined so that the phase equivalent amount periodically repeats monotonous and linear changes. A light source unit that emits laser light with a variable wavelength,
A first wavelength filter with a transmittance that changes periodically with respect to the wavelength of light,
A first detection unit that detects the intensity of the laser beam that has passed through the first wavelength filter as the first detection value, and
A second wavelength filter having a transmittance that changes periodically with respect to the wavelength of light with a period equal to that of the first wavelength filter and having a different peak wavelength of transmittance from the first wavelength filter.
A second detection unit that detects the intensity of the laser beam that has passed through the second wavelength filter as a second detection value, and
A storage unit that stores a function from which one phase equivalent amount is derived by inputting a set of the first detected value and the second detected value, and a storage unit.
A light source control unit that controls the wavelength of the laser beam using the function stored in the storage unit, and a light source control unit.
A tunable laser device comprising. A light source unit that emits laser light with a variable wavelength,
A first wavelength filter with a transmittance that changes periodically with respect to the wavelength of light,
A first detection unit that detects the intensity of the laser beam that has passed through the first wavelength filter as the first detection value, and
A second wavelength filter having a transmittance that changes periodically with respect to the wavelength of light with a period equal to that of the first wavelength filter and having a different peak wavelength of transmittance from the first wavelength filter.
A second detection unit that detects the intensity of the laser beam that has passed through the second wavelength filter as a second detection value, and
A storage unit that stores a conversion table in which one phase equivalent amount corresponds to the set of the first detected value and the second detected value, and
Using the conversion table stored in the storage unit, a light source control unit that controls the wavelength of the laser beam and a light source control unit.
With
The conversion table is a tunable laser apparatus in which the phase equivalent amount is set to periodically repeat monotonous changes. The tunable laser apparatus according to claim 5 or 6, wherein the first and second wavelength filters are configured so that the wavelengths in the dead zone are different from each other. A laser beam emission step that emits a laser beam having a variable wavelength from a light source unit,
A first detection step of detecting the intensity of the laser beam transmitted through the first wavelength filter having a transmittance that changes periodically with respect to the wavelength of light as a first detection value, and
The laser light that has passed through a second wavelength filter that has a transmittance that changes periodically with respect to the wavelength of the light at the same period as the first wavelength filter and has a different peak wavelength of transmittance from the first wavelength filter. The second detection step of detecting the intensity as the second detection value, and
Creation of a conversion table for creating a conversion table in which one phase equivalent amount corresponds to a set of the first detected value and the second detected value, and the phase equivalent amount periodically repeats monotonous changes. Steps and
A method for calibrating a tunable laser device, which comprises.

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