JP6816051B2 - Tunable laser device and wavelength control method for tunable laser device - Google Patents

Description

The present invention relates to a tunable laser apparatus and a wavelength control method for the tunable laser apparatus.

Conventionally, in a tunable laser apparatus, a technique for controlling the wavelength of the output laser light by using an optical filter having a periodic transmission characteristic with respect to the wavelength of the incident light is known (for example, Patent Document 1). reference).
The tunable laser apparatus described in Patent Document 1 includes a tunable light source unit that changes the wavelength of the output laser light, a first light receiving element that acquires the intensity of the laser light output from the tunable light source unit, and the like. It includes an optical filter such as etalon, a second light receiving element that acquires the intensity of laser light transmitted through the optical filter, and a control device (calculation circuit) that controls the operation of the tunable light source unit.
Here, the control device calculates a monitor value for controlling the wavelength of the laser light based on the intensity of the laser light acquired by the first and second light receiving elements, respectively. In addition, the control device uses the transmission characteristics of the optical filter at a predetermined temperature (hereinafter referred to as the reference temperature) to correspond to the target wavelength of the laser beam and set the target control target value of the monitor value. .. Then, the control device controls the operation of the tunable light source unit so that the monitor value matches the control target value.

Japanese Unexamined Patent Publication No. 2015-60961

By the way, the transmission characteristic of the optical filter shifts as a whole on the wavelength axis when the temperature of the optical filter deviates from the reference temperature. That is, when the control target value corresponding to the target wavelength of the laser beam is set by using the transmission characteristic at the reference temperature even though the temperature of the optical filter deviates from the reference temperature, the optical filter Since the transmission characteristics are shifted from the transmission characteristics at the reference temperature, the control target value does not correspond to the target wavelength of the laser beam. Therefore, if the operation of the tunable light source unit is controlled so that the monitor value matches the control target value, the wavelength of the laser beam is controlled to a wavelength deviated from the target wavelength.
Therefore, in the tunable laser apparatus described in Patent Document 1, the temperature of the optical filter is controlled to be constant by the temperature control apparatus. However, even if the temperature of the optical filter is controlled to be constant, the temperature of the optical filter unintentionally shifts from the reference temperature due to temperature variation inside the tunable laser device or heat inflow from the outside of the tunable laser device. It may shift. That is, there is a problem that it is difficult to accurately control the wavelength of the laser beam to the target wavelength.

The present invention has been made in view of the above, and an object of the present invention is to provide a wavelength tunable laser apparatus capable of accurately controlling the wavelength of a laser beam to a target wavelength, and a wavelength control method for the tunable laser apparatus. And.

In order to solve the above-mentioned problems and achieve the object, the wavelength-variable laser apparatus according to the present invention has a wavelength-variable light source unit that makes the wavelength of the output laser light variable, and the incident laser light wavelength. A first optical filter and a second optical filter having transmission characteristics whose characteristics change periodically, an optical branching portion that branches the laser light into three laser lights, and waveguides of the three laser lights, respectively. first optical waveguide, a second optical waveguide, and a third optical waveguide being guided by said first optical waveguide, the intensity of the spent first translucent light filters the laser beam a first light receiving element for outputting an electrical signal corresponding, being guided by the second optical waveguide, the output electric signals corresponding to the intensity of the laser light transmitted through the second optical filter The second light receiving element, the third light receiving element that outputs an electric signal corresponding to the intensity of the laser beam waveguideed by the third optical waveguide, the first light filter, and the second light. Temperature for adjusting the temperature of the filter, the first optical waveguide, the second optical waveguide, the third optical waveguide, the first light receiving element, the second light receiving element, and the third light receiving element. A controller and a control device for controlling the wavelength of the laser light output from the variable wavelength light source unit to a target wavelength are provided, and the first optical filter and the second optical filter have different temperature dependences. the transmission characteristics possess respectively, said control device, said third ratio of the output value of the electric signal output from the first light receiving element to the output value of the electrical signal output from the light receiving element and the first It is calculated as a monitor value, and the ratio of the output value of the electric signal output from the second light receiving element to the output value of the electric signal output from the third light receiving element is calculated as the second monitor value. The first control target value and the first control target value corresponding to the first monitor value, the second monitor value, the target wavelength of the laser light, and the target of the first monitor value and the second monitor value, respectively. The deviation of the temperature of the first optical filter and the second optical filter from the target temperature is determined based on the second control target value, and is output from the wavelength variable light source unit according to the deviation. It is characterized by controlling the wavelength of laser light .

Further, the wavelength tunable laser device according to the present invention, in the above invention, before Symbol control device includes a monitor value calculation unit for calculating a first monitor value and the second monitor value, the first control target a target value calculating unit for calculating the values and the second control target value based on said first monitor value and the first control target value, the wavelength of the laser light output from the wavelength-variable light source unit The operation of the temperature controller is controlled based on the wavelength control unit to be controlled, the second monitor value, and the second control target value, and the temperatures of the first optical filter and the second optical filter are controlled. It is characterized by including a temperature control unit for controlling the above.

Further, the wavelength tunable laser device according to the present invention, in the above invention, the control device, the first monitor value and the monitor value calculation unit for calculating a second monitor value, the first control target value and a target value calculator for calculating the second target control value, the second monitor value and based on said second control target value, the correction control target value by correcting the first control target value It is characterized by including a target value correction unit for generating the above, and a wavelength control unit for controlling the wavelength of the laser beam output from the tunable light source unit based on the first monitor value and the correction control target value. And.

Further, the wavelength tunable laser device according to the present invention, in the above-described invention, further comprising a temperature sensor for detecting the ambient temperature, wherein the control device, on the basis of the ambient temperature to control the operation of the temperature controller, It is characterized by including a temperature control unit that controls the temperature of the first optical filter and the second optical filter to a target temperature.

Further, in the tunable laser apparatus according to the present invention, in the above invention, the temperature controller has an installation surface on which a temperature control target is installed, and the first optical filter and the second optical filter are , The temperature controller is installed on the same installation surface.

Further, in the tunable laser apparatus according to the present invention, in the above invention, the first optical filter and the second optical filter are waveguide type optical filters.

Further, in the tunable laser apparatus according to the present invention, in the above invention, the first optical filter and the second optical filter have a core and a clad for propagating the laser light, and at least the core and the clad. A dopant is added to one of them, and at least one of the type and amount of the dopant to be added is different from each other.

Further, in the wavelength tunable laser apparatus according to the present invention, in the above invention, the first optical filter and the second optical filter are each composed of a planar light wave circuit, and are in the thickness direction of the planar light wave circuit. The layer structure is characterized by being composed of materials having different coefficients of thermal expansion.

The wavelength control method of the wavelength-variable laser apparatus according to the present invention includes a wavelength-variable light source unit that changes the wavelength of the output laser light and a transmission characteristic whose characteristics change periodically with respect to the incident wavelength of the laser light. A first optical filter and a second optical filter, respectively, an optical branching portion that branches the laser light into three laser lights, and a first optical waveguide that waveguides the three laser lights, respectively. an optical waveguide, and a third optical waveguide being guided by said first optical waveguide, a first for outputting an electric signal corresponding to the intensity of the laser light passed permeable said first optical filter a light receiving element, is guided by the second optical waveguide, a second light receiving element for outputting an electrical signal corresponding to the intensity of the laser light transmitted through the second optical filter, the third a third light receiving element for outputting an electrical signal corresponding to the intensity of the laser light guided by the optical waveguide, said first optical filter, before Symbol second optical filter, said first optical waveguide, A wavelength-variable laser including the second optical waveguide, the third optical waveguide, the first light receiving element, the second light receiving element, and a temperature controller for adjusting the temperature of the third light receiving element. In the wavelength control method of the apparatus, the first optical filter and the second optical filter have the transmission characteristics different from each other in temperature dependence, and the wavelength control method of the wavelength variable laser apparatus is the said. The monitor value calculation step for calculating the first monitor value and the second monitor value based on the intensity of the laser light acquired by the first light receiving element and the second light receiving element, respectively, and the target wavelength of the laser light The target value calculation step for calculating the first control target value and the second control target value, which are the targets of the first monitor value and the second monitor value, and the first monitor value and the first monitor value Based on the first control target value, a wavelength control step for controlling the wavelength of the laser light output from the wavelength variable light source unit, the second monitor value, and the second control target value. The deviation of the temperature of the first optical filter and the second optical filter from the target temperature is determined, the operation of the temperature controller is controlled according to the deviation, and the first optical filter and the second optical filter are controlled. It is characterized by including a temperature control step for controlling the temperature of the optical filter.

Further, in the wavelength control method of the wavelength variable laser device according to the present invention, in the above invention, the wavelength variable laser device further includes a temperature sensor for detecting the ambient temperature, and the wavelength control method of the wavelength variable laser device is described above. before performing the wavelength control step and the temperature control step, on the basis of the ambient temperature, the controls the operation of the temperature controller, the first light filter and the second temperature the target temperature of the optical filter It is characterized by further providing a rough adjustment step for controlling the temperature.

The wavelength control method of the wavelength-variable laser apparatus according to the present invention includes a wavelength-variable light source unit that changes the wavelength of the output laser light and a transmission characteristic whose characteristics change periodically with respect to the incident wavelength of the laser light. A first optical filter and a second optical filter, respectively, an optical branching portion that branches the laser light into three laser lights, and a first optical waveguide that waveguides the three laser lights, respectively. an optical waveguide, and a third optical waveguide being guided by said first optical waveguide, a first for outputting an electric signal corresponding to the intensity of the laser light passed permeable said first optical filter a light receiving element, is guided by the second optical waveguide, a second light receiving element for outputting an electrical signal corresponding to the intensity of the laser light transmitted through the second optical filter, the third A third light receiving element that outputs an electric signal corresponding to the intensity of the laser beam waveguided by the optical waveguide, the first optical filter, the second optical filter, the first optical waveguide, and the above. A wavelength-variable laser apparatus including a second optical waveguide, the third optical waveguide, the first light receiving element, the second light receiving element, and a temperature controller for adjusting the temperature of the third light receiving element. The first optical filter and the second optical filter have the transmission characteristics different from each other in temperature dependence, and the wavelength control method of the wavelength variable laser apparatus is the first. The monitor value calculation step for calculating the first monitor value and the second monitor value based on the intensity of the laser light acquired by the first light receiving element and the second light receiving element, respectively, and the target wavelength of the laser light, respectively. The target value calculation step for calculating the first control target value and the second control target value, which are the targets of the first monitor value and the second monitor value, and the second monitor value and the said Based on the second control target value, the target value correction step of correcting the first control target value to generate the correction control target value, and based on the first monitor value and the correction control target value, A wavelength control step of determining the deviation of the temperatures of the first optical filter and the second optical filter from the target temperature and controlling the wavelength of the laser light output from the wavelength variable light source unit according to the deviation. It is characterized by having.

Further, in the wavelength control method of a wavelength tunable laser device according to the present invention, in the above invention, the tunable laser apparatus further includes a temperature sensor for detecting the ambient temperature, the wavelength control method of the wavelength tunable laser device, before executing the target value correcting step, based on said ambient temperature to control the operation of the temperature controller, which controls the first optical filter and the temperature of the second optical filter to the target temperature It is characterized by further providing a rough step.

According to the wavelength tunable laser apparatus and the wavelength control method of the tunable laser apparatus according to the present invention, it is possible to accurately control the wavelength of the laser beam to the target wavelength.

FIG. 1 is a diagram showing a configuration of a tunable laser apparatus according to the first embodiment. FIG. 2 is a diagram showing a configuration of a tunable light source unit. FIG. 3 is a block diagram showing the configuration of the control device. FIG. 4 is a diagram showing transmission characteristic information stored in the storage unit. FIG. 5 is a diagram showing transmission characteristic information stored in the storage unit. FIG. 6 is a diagram showing wavelength power information stored in the storage unit. FIG. 7 is a flowchart showing a wavelength control method by the control device. FIG. 8 is a diagram illustrating a wavelength control method. FIG. 9 is a block diagram showing a configuration of a control device according to the second embodiment. FIG. 10 is a flowchart showing a wavelength control method by the control device. FIG. 11 is a diagram illustrating a wavelength control method. FIG. 12 is a diagram showing a modified example of the first and second embodiments.

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. In addition, the xyz coordinate axes are appropriately shown in the drawings, and the directions will be described thereby.

(Embodiment 1)
[Rough configuration of tunable laser device]
FIG. 1 is a diagram showing a configuration of a tunable laser apparatus 1 according to the first embodiment.
The tunable laser device 1 includes a modularized tunable laser module 2 and a control device 3 that controls the operation of the tunable laser module 2.
Although the tunable laser module 2 and the control device 3 are separately configured in FIG. 1, the members 2 and 3 may be integrally modularized.

[Structure of tunable laser module]
The tunable laser module 2 changes the wavelength of the output laser beam to a laser beam of any one of a plurality of wavelengths under the control of the control device 3, and outputs the laser beam of the one wavelength. The tunable laser module 2 includes a tunable light source unit 4, a semiconductor optical amplifier (SOA) 5, a planar lightwave circuit (PLC) 6, a light detection unit 7, and a temperature sensor 8. And a temperature controller 9.

FIG. 2 is a diagram showing the configuration of the tunable light source unit 4.
The tunable light source unit 4 is, for example, a tunable laser that utilizes the vernier effect, and outputs the laser beam L1 under the control of the control device 3. The wavelength variable light source unit 4 includes a light source unit 41 that changes the wavelength of the output laser light L1 and three microheaters 421 to 423 that generate heat according to the power supplied from the control device 3. A wavelength variable unit 42 that changes the wavelength of the laser beam L1 output from the light source unit 41 by locally heating the 41 is provided.

The light source unit 41 includes first and second waveguide units 43 and 44, which are formed on the common base portion B1, respectively. Here, the base B1 is made of, for example, an n-type InP. Then, on the back surface of the base portion B1, for example, AuGeNi is included, and an n-side electrode 45 that is in ohmic contact with the base portion B1 is formed.

The first waveguide section 43 has an embedded waveguide structure. The first waveguide section 43 includes a waveguide section 431, a semiconductor laminated section 432, and a p-side electrode 433.
The waveguide portion 431 is formed so as to extend in the z direction in the semiconductor laminated portion 432.
Further, a gain portion 431a and a DBR (Distributed Bragg Reflector) type diffraction grating layer 431b are arranged in the first waveguide section 43.
Here, the gain unit 431a is an active layer having a multiple quantum well structure made of InGaAsP and a light confinement layer. Further, the diffraction grating layer 431b is composed of a sampling diffraction grating composed of InGaAsP and InP.

The semiconductor laminated portion 432 is configured by laminating InP-based semiconductor layers, and has a function of a clad portion with respect to the waveguide portion 431.
The p-side electrode 433 is arranged on the semiconductor laminated portion 432 so as to be along the gain portion 431a. A SiN protective film (not shown) is formed on the semiconductor laminated portion 432. The p-side electrode 433 is in contact with the semiconductor laminated portion 432 via an opening (not shown) formed in the SiN protective film.
Here, the microheater 421 is arranged along the diffraction grating layer 431b on the SiN protective film of the semiconductor laminated portion 432. Then, the microheater 421 generates heat according to the electric power supplied from the control device 3, and heats the diffraction grating layer 431b. Further, by controlling the electric power supplied to the microheater 421 by the control device 3, the temperature of the diffraction grating layer 431b changes, and the refractive index thereof changes.

The second waveguide section 44 includes a two-branch section 441, two arm sections 442, 443, and a ring-shaped waveguide 444.
The two-branch portion 441 is composed of a 1 × 2 type bifurcated waveguide including a 1 × 2 type multi-mode interference type (MMI) waveguide 441a, and the two 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 1st waveguide section 43 side. That is, one end of the two arm portions 442 and 443 is integrated by the bifurcated portion 441 and optically coupled to the diffraction grating layer 431b.

The arm portions 442 and 443 are all extended in the z direction and are arranged so as to sandwich the ring-shaped waveguide 444. These arm portions 442 and 443 are optically coupled to the ring-shaped waveguide 444 with the same coupling coefficient κ as the ring-shaped waveguide 444. The value of κ is, for example, 0.2. The arm portions 442 and 443 and the ring-shaped waveguide 444 form a ring resonator filter RF1. Further, the ring resonator filter RF1 and the bifurcated portion 441 form a reflection mirror M1.
Here, the microheater 422 is ring-shaped and is arranged on a SiN protective film (not shown) formed so as to cover the ring-shaped waveguide 444. Then, the microheater 422 generates heat according to the electric power supplied from the control device 3, and heats the ring-shaped waveguide 444. Further, by controlling the electric power supplied to the microheater 422 by the control device 3, the temperature of the ring-shaped waveguide 444 changes, and the refractive index thereof changes.

The above-mentioned two-branch portion 441, arm portion 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 by a clad layer made of InP. ..
Here, the microheater 423 is arranged on a part of the SiN protective film (not shown) of the arm portion 443. The region below the microheater 423 of the arm portion 443 functions as a phase adjusting portion 445 that changes the phase of light. Then, the microheater 423 generates heat according to the electric power supplied from the control device 3, and heats the phase adjusting unit 445. Further, by controlling the electric power supplied to the microheater 423 by the control device 3, the temperature of the phase adjusting unit 445 changes, and the refractive index thereof changes.

The first and second waveguides 43 and 44 described above constitute an optical resonator C1 composed of a diffraction grating layer 431b optically connected to each other and a reflection mirror M1. Further, the gain unit 431a and the phase adjusting unit 445 are arranged in the optical resonator C1.

The diffraction grating layer 431b generates a first comb-shaped reflection spectrum having a reflection characteristic that is substantially periodic at substantially predetermined wavelength intervals. On the other hand, the ring resonator filter RF1 generates a second comb-shaped reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals.
Here, the second comb-shaped reflection spectrum has a half-value full-width peak narrower than the half-value full-width of the peak of the first comb-shaped reflection spectrum, and has a wavelength interval different from the wavelength interval of the first comb-shaped reflection spectrum. It has a substantially periodic reflection characteristic. However, considering the wavelength dispersion of the refractive index, it should be noted that the spectral components are not strictly at equal wavelength intervals.

To exemplify the characteristics of each comb-shaped reflection spectrum, the wavelength interval (free spectrum region: FSR) between the peaks of the first comb-shaped reflection spectrum is 373 GHz in terms of the frequency of light. The full width at half maximum of each peak is 43 GHz in terms of light frequency. On the other hand, the wavelength interval (FSR) between the peaks of the second comb-shaped reflection spectrum is 400 GHz in terms of the frequency of light. The full width at half maximum of each peak is 25 GHz in terms of light frequency. That is, the full width at half maximum (25 GHz) of each peak of the second comb-shaped reflection spectrum is narrower than the full width at half maximum (43 GHz) of each peak of the first comb-shaped reflection spectrum.

In the tunable light source unit 4, in order to realize laser oscillation, one of the peaks of the first comb-shaped reflection spectrum and one of the peaks of the second comb-shaped reflection spectrum can be superposed on the wavelength axis. ing. In such superposition, at least one of the microheaters 421 and 422 is used to heat the diffraction grating layer 431b by the microheater 421, and the refractive index is changed by the thermooptical effect to change the refractive index of the first comb-shaped reflection spectrum. Is moved and changed as a whole on the wavelength axis, and the ring-shaped waveguide 444 is heated by the microheater 422 to change its refractive index to make the second comb-shaped reflection spectrum as a whole on the wavelength axis. It can be realized by performing at least one of moving to and changing.

On the other hand, in the tunable light source unit 4, there is a resonator mode by the optical resonator C1. In the tunable light source unit 4, the resonator length of the optical resonator C1 is set so that the interval between the resonator modes (longitudinal mode interval) is 25 GHz or less. In the case of this setting, the resonator length of the optical resonator C1 is 1800 μm or more, and it can be expected that the line width of the oscillating laser beam is narrowed. As for the wavelength of the resonator mode of the optical resonator C1, the phase adjusting unit 445 is heated by using the microheater 423 to change its refractive index, and the wavelength of the resonator mode is moved as a whole on the wavelength axis. This can be fine-tuned. That is, the phase adjusting unit 445 is a part for actively controlling the optical path length of the optical resonator C1.

When the control device 3 injects a current from the n-side electrode 45 and the p-side electrode 433 into the gain section 431a and causes the gain section 431a to emit light, the wavelength-variable light source unit 4 causes the spectrum component of the first comb-shaped reflection spectrum. The peak, the peak of the spectral component of the second comb-shaped reflection spectrum, and one of the resonator modes of the optical resonator C1 are configured to oscillate the laser at a matching wavelength, for example, 1550 nm, and output the laser beam L1. ..
Further, in the tunable light source unit 4, the wavelength of the laser beam L1 can be changed by utilizing the vernier effect. For example, when the diffraction grating layer 431b is heated by the microheater 421, the refractive index of the diffraction grating layer 431b increases due to the thermo-optical effect, and the first comb-shaped reflection spectrum of the diffraction grating layer 431b shifts to the long wave side as a whole. To do. As a result, the peak of the first comb-shaped reflection spectrum in the vicinity of 1550 nm is de-overlapping with the peak of the second comb-shaped reflection spectrum of the ring resonator filter RF1, and the second comb-shaped reflection existing on the long wave side is removed. It overlaps another peak in the spectrum (eg around 1556 nm). Further, by tuning the phase adjusting unit 445 to fine-tune the resonator mode and superimposing one of the resonator modes on the two comb-shaped reflection spectra, laser oscillation in the vicinity of 1556 nm can be realized. That is, in the tunable light source unit 4, the first and second comb-shaped reflection spectra are tuned by the microheater 421 for the diffraction grating layer 431b and the microheater 422 for the ring resonator filter RF1, respectively, to perform coarse adjustment and phase adjustment. By tuning the resonator length with the microheater 423 for the unit 445, a tunable operation for fine adjustment is realized.

Although not specifically shown, the semiconductor optical amplifier 5 has an embedded waveguide structure including an active core layer made of the same material and structure as the first waveguide 43. However, the diffraction grating layer 431b is not provided. The semiconductor optical amplifier 5 is optically coupled to the wavelength tunable light source unit 4 by a space-coupled optical system (not shown). Then, the laser beam L1 output from the tunable light source unit 4 is input to the semiconductor optical amplifier 5. Further, the semiconductor optical amplifier 5 amplifies the laser light L1 and outputs it as the laser light L2. The semiconductor optical amplifier 5 may be monolithically configured with the wavelength tunable light source unit 4 on the base portion B1.

The plane light wave circuit 6 is optically coupled to the arm portion 442 by a space-coupling optical system (not shown). Then, a part of the laser light L3 generated by the laser oscillation in the tunable light source unit 4 is input to the plane light wave circuit 6 via the arm unit 442 as in the laser light L1. The laser beam L3 has the same wavelength as the wavelength of the laser beam L1. The plane light wave circuit 6 includes an optical branching portion 61, an optical waveguide 62, an optical waveguide 63 having a ring resonator type optical filter 63a, and an optical waveguide 64 having a ring resonator type optical filter 64a.

The optical branching unit 61 branches the input laser beam L3 into three laser beams L4 to L6.
Then, the optical waveguide 62 guides the laser beam L4 to the PD (Photo Diode) 71 described later in the photodetector 7. Further, the optical waveguide 63 guides the laser beam L5 to the PD 72 described later in the photodetector 7. Further, the optical waveguide 64 guides the laser beam L6 to the PD73 described later in the photodetector 7.
Here, the ring resonator type optical filters 63a and 64a have periodic transmission characteristics with respect to the wavelength of the incident light, and selectively select the laser beams L5 and L6 with the transmittance according to the transmission characteristics. Transparent to. Then, the laser beams L5 and L6 that have passed through the ring resonator type optical filters 63a and 64a are input to the PD72 and 73, respectively. That is, the ring resonator type optical filters 63a and 64a are respectively composed of a waveguide type optical filter, and correspond to the first and second optical filters according to the present invention. Hereinafter, for convenience of description, the ring resonator type optical filter 63a will be referred to as a first optical filter 63a, and the ring resonator type optical filter 64a will be referred to as a second optical filter 64a.
The first and second optical filters 63a and 64a have the same transmission characteristics such that the phase difference is substantially "0" at the reference temperature (target temperature). Further, in the first and second optical filters 63a and 64a, quartz or quartz is used as the core material, and a dopant is added to at least one of the core and the cladding, and at least one of the type and the amount of the dopant to be added is added. Due to the difference, the temperature dependences have different transmission characteristics. Further, by adding materials having different coefficients of thermal expansion to the optical filter, the transmission characteristics having different temperature dependence may be obtained. For example, the first and second optical filters 63a and 64a are flat light wave circuits configured to overlap a plurality of layers, and the layer structure in the thickness direction (direction in which the plurality of layers overlap) of the flat light wave circuit is set. It is composed of a material having a different coefficient of thermal expansion for each optical filter. As a result, strain stress depending on the temperature is generated in the optical resonator portion, and the optical resonators have transmission characteristics different from each other. The point that the temperature dependence is different from each other will be described together with the description of the transmission characteristic information described later.

The light detection unit 7 includes PD71 to 73.
The PD71 receives the laser light L4 (same as the laser light L1 output from the tunable light source unit 4) and outputs an electric signal corresponding to the intensity of the laser light L4 to the control device 3.
The PD 72 receives the laser light L5 that has passed through the first optical filter 63a, and outputs an electric signal corresponding to the intensity of the laser light L5 to the control device 3. That is, the PD 72 corresponds to the first light receiving element according to the present invention.
The PD73 receives the laser light L6 that has passed through the second optical filter 64a, and outputs an electric signal corresponding to the intensity of the laser light L6 to the control device 3. That is, the PD73 corresponds to the second light receiving element according to the present invention.
The electrical signals output from the PDs 71 to 73 are used for wavelength lock control by the control device 3 (control for setting the laser beam L1 output from the wavelength tunable light source unit 4 to a target wavelength).

The temperature sensor 8 is composed of, for example, a thermistor or the like, and detects the ambient temperature of the plane light wave circuit 6. The temperature sensor 8 may be installed outside the temperature controller 9 and detect the temperature of the environment in which the tunable laser device 1 is arranged as the ambient temperature.
The temperature controller 9 is composed of, for example, a TEC (Thermo Electric Cooler) including a Peltier element or the like. A variable wavelength light source unit 4, a semiconductor optical amplifier 5, a plane light wave circuit 6, a photodetector unit 7, and a temperature sensor 8 are mounted on the temperature controller 9. Then, the temperature controller 9 adjusts the temperature of each of the members 4 to 8 according to the supplied electric power.
In the temperature controller 9, the installation surface 91 on which the respective members 4 to 8 are mounted is the first region Ar1 on which the wavelength variable light source unit 4 and the semiconductor optical amplifier 5 are mounted, the planar light wave circuit 6 and When the light detection unit 7 is divided into two regions of the second region Ar2 on which the light detection unit 7 is placed, the temperature sensor 8 is placed in the second region Ar2. That is, the temperature sensor 8 is arranged close to the plane light wave circuit 6.

[Control device configuration]
Next, the configuration of the control device 3 will be described.
FIG. 3 is a block diagram showing the configuration of the control device 3.
The control device 3 is connected to, for example, a higher-level control device (not shown) having a user interface, and controls the operation of the tunable laser module 2 according to an instruction from the user via the higher-level control device. ..
In the following, wavelength lock control by the control device 3 which is a main part of the present invention will be mainly described. Further, in FIG. 3, for convenience of explanation, only a configuration for executing wavelength lock control is shown as a configuration of the control device 3.
The control device 3 includes a control unit 31 and a storage unit 32.

The control unit 31 is configured by using a CPU or the like. The control unit 31 includes a monitor value calculation unit 311, a target value calculation unit 312, a wavelength control unit 313, and a temperature control unit 314.
The monitor value calculation unit 311 calculates the first and second monitor values for controlling the wavelength of the laser beam L1 based on the output values of the electric signals output from PD 71 to 73, respectively. Specifically, the monitor value calculation unit 311 describes the ratio of the output value of the electric signal output from the PD 72 to the output value of the electric signal output from the PD 71 as the first monitor value (hereinafter referred to as the first PD ratio). ). Further, the monitor value calculation unit 311 sets the ratio of the output value of the electric signal output from the PD73 to the output value of the electric signal output from the PD71 as the second monitor value (hereinafter referred to as the second PD ratio). calculate.

The target value calculation unit 312 controls the first control, which is the target of the first PD ratio, based on the target wavelength acquired from the upper control device (not shown) and the transmission characteristic information stored in the storage unit 32. The target value and the second control target value, which is the target of the second PD ratio, are calculated.
4 and 5 are diagrams showing the transmission characteristic information stored in the storage unit 32. In FIG. 5, the horizontal axis is the wavelength and the vertical axis is the PD ratio.
The transmission characteristic information is information indicating the transmission characteristics of the first and second optical filters 63a and 64a at the reference temperature (target temperature). More specifically, the transmission characteristic information is obtained when a plurality of wavelengths λ1 to λn [nm] and the wavelength of the laser beam L1 are set to the wavelengths λ1 to λn [nm] at the reference temperature (target temperature). A plurality of controls that serve as reference values for each first PD ratio (each second PD ratio), which is the ratio of the output value of the electric signal output from PD72 (PD73) to the output value of the electric signal output from PD71. The reference values Pd1 to Pdn are the information associated with each other. The first and second PD ratios are substantially proportional to the transmittances of the first and second optical filters 63a and 64a, respectively. Therefore, the transmission characteristic information shows the transmission characteristics (curve CL in FIG. 6) at the reference temperature (target temperature) of the first and second optical filters 63a and 64a.

Here, as described above, the transmission characteristics of the first and second optical filters 63a and 64a differ from each other in temperature dependence.
Specifically, the transmission characteristic (curve CL) of the first optical filter 63a is as shown by the curve CL1'in FIG. 5 when the temperature of the first optical filter 63a deviates from the reference temperature (target temperature). The whole shifts to the short wave side or the long wave side on the wavelength axis. Similarly, the transmission characteristic (curve CL) of the second optical filter 64a has a wavelength as shown by the curve CL2'in FIG. 5 when the temperature of the second optical filter 64a deviates from the reference temperature (target temperature). The whole shifts to the short wave side or the long wave side on the axis. Note that FIG. 5 illustrates a state of shifting to the long wave side. When the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature by the same temperature, the transmission characteristics of the first and second optical filters 63a and 64a are on the wavelength axis. Each shifts with a different amount of shift. That is, "transmission characteristics having different temperature dependences" means that "when the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature by the same temperature, the shift amounts on the wavelength axis are different from each other. It means "different transmission characteristics".

In the first embodiment, the first and second optical filters 63a and 64a are placed close to each other on the same installation surface 91 of the temperature controller 9, and the first and second optical filters 63a are placed close to each other. , 64a are composed of a waveguide type optical filter. As a result, the temperature ΔT (difference between the reference temperature (target temperature) and the temperature of the first optical filter 63a) deviating from the reference temperature (target temperature) of the first optical filter 63a and the reference temperature of the second optical filter 64a. The temperature ΔT (difference between the reference temperature (target temperature) and the temperature of the second optical filter 64a) deviating from (target temperature) is always substantially the same as each other (including ΔT = 0 ° C.).

The wavelength control unit 313 is based on the target wavelength acquired from the upper control device (not shown), the wavelength power information stored in the storage unit 32, the first control target value, and the first PD ratio. , The plurality of powers supplied to the microheaters 421 to 423 are changed, and the wavelength of the laser beam L1 is controlled to the target wavelength.
FIG. 6 is a diagram showing wavelength power information stored in the storage unit 32.
The wavelength power information includes a plurality of wavelengths λ1 to λn [nm] and a plurality of powers (initial power) supplied to the microheaters 421 to 423 to control the wavelength of the laser beam L1 to the wavelengths λ1 to λn [nm]. ) Is the information associated with each. In FIG. 6, for convenience of explanation, the total electric power supplied to the microheaters 421 to 423 is described as each electric power P1 to Pn [W].

The temperature control unit 314 controls the operation of the temperature controller 9 and controls the temperatures of the first and second optical filters 63a and 64a.
The storage unit 32 stores a program executed by the control unit 31, information necessary for processing of the control unit 31 (for example, transmission characteristic information, wavelength power information, etc.) and the like.

[Wavelength control method]
Next, the wavelength control method (wavelength lock control) by the control device 3 described above will be described.
FIG. 7 is a flowchart showing a wavelength control method by the control device 3.
First, the wavelength control unit 313 acquires the target wavelength input to the upper control device (not shown) via the user interface from the upper control device (step S1).
After step S1, the target value calculation unit 312 calculates the first and second control target values by referring to the transmission characteristic information stored in the storage unit 32 (step S2: target value calculation step). Specifically, the target value calculation unit 312 reads out the transmission characteristic information stored in the storage unit 32. Then, the target value calculation unit 312 receives a control reference value (for example, control reference) associated with the target wavelength (for example, wavelength λ1) acquired in step S1 among the plurality of control reference values Pd1 to Pdn in the transmission characteristic information. The value Pd1) is calculated as the first and second control target values.

After step S2, the wavelength control unit 313 refers to the wavelength power information stored in the storage unit 32, and sets each power (initial power) associated with the target wavelength acquired in step S1 to the microheaters 421 to 423. (Step S3).
After step S3, the temperature control unit 314 controls the operation of the temperature controller 9 based on the ambient temperature detected by the temperature sensor 8, and targets the temperatures of the first and second optical filters 63a and 64a. It is controlled to a temperature (reference temperature) (step S4: coarse adjustment step). For example, the temperature control unit 314 has the ambient temperature detected by the temperature sensor 8 and the total power supplied to the microheaters 421 to 423 in step S3 (in the wavelength power information, each power P1 to Pn [W]. Of these, the temperatures of the first and second optical filters 63a and 64a are estimated based on the power associated with the target wavelength acquired in step S1) and the like. Then, the temperature control unit 314 controls the operation of the temperature controller 9 so that the estimated temperatures of the first and second optical filters 63a and 64a become the target temperature (reference temperature). The temperature control unit 314 may control the operation of the temperature controller 9 so that the ambient temperature itself detected by the temperature sensor 8 becomes the target temperature (reference temperature).

After step S4, the monitor value calculation unit 311 uses the first PD ratio, which is the ratio of the output value of the electric signal output from PD72 to the output value of the electric signal output from PD71, and the electric signal output from PD71. The calculation with the second PD ratio, which is the ratio of the output value of the electric signal output from the PD73 to the output value of, is started (step S5: monitor value calculation step).
After step S5, the wavelength control unit 313 uses the microheater 421 so that the latest first PD ratio calculated after step S5 matches the first control target value calculated in step S2. Wavelength adjustment control for changing the power supplied to each of ~ 423 is executed (step S6: wavelength control step).

After step S6, the temperature control unit 314 determines whether or not the latest second PD ratio calculated after step S5 and the second control target value calculated in step S2 are the same. (Step S7).
When it is determined that the second PD ratio and the second control target value are the same (step S7: Yes), the control device 3 ends the wavelength lock control.
On the other hand, when it is determined that the second PD ratio and the second control target value are not the same (step S7: No), the temperature control unit 314 makes a second with respect to the second control target value. Temperature control is executed (step S8: temperature control step) in which the power supplied to the temperature controller 9 is changed (the temperature of the first and second optical filters 63a and 64a is changed) so that the PD ratios match. .. After that, the control device 3 returns to step S6 and executes the wavelength adjustment control.

FIG. 8 is a diagram illustrating a wavelength control method. Specifically, FIG. 8 is a diagram corresponding to FIG. 5, and the transmission characteristic information is shown by a curve CL. Further, the transmission characteristic of the first optical filter 63a in the state determined as "No" in step S7 is shown by the curve CL1', and the transmission characteristic of the second optical filter 64a in the state is shown by the curve CL2'. Shown.
When the temperature of the first optical filter 63a deviates from the reference temperature (target temperature), the transmission characteristic of the first optical filter 63a shifts entirely on the wavelength axis (shifts from the curve CL to the curve CL1'). That is, in step S6, although the temperature of the first optical filter 63a deviates from the reference temperature (target temperature) and the transmission characteristic of the first optical filter 63a is the curve CL1', the transmission characteristic information When the wavelength adjustment control is executed with the control reference value associated with the target wavelength TW in (curve CL) as the first control target value PDT, the wavelength of the laser beam L1 is the wavelength TW ′ deviated from the target wavelength TW. Will be controlled by.

Therefore, in the first embodiment, in step S7, by comparing the second PD ratio and the second control target value, the transmission characteristic of the first optical filter 63a is set to the reference temperature (target temperature). It is confirmed whether or not there is a shift from the transmission characteristics (whether or not the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature)).
Specifically, the transmission characteristics of the first and second optical filters 63a and 64a differ from each other in temperature dependence, as described above. Therefore, the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature), and the transmission characteristics of the first optical filter 63a shift from the transmission characteristics at the reference temperature (target temperature). If there is (when shifting from the curve CL to the curve CL1'), the transmission characteristic of the second optical filter 64a shifts by a shift amount different from the shift amount from the curve CL to the curve CL1'(curve). Shift from CL to curve CL2'). That is, in this case, the second PD ratio is not the second control target value PDT, which is the control reference value associated with the target wavelength TW in the transmission characteristic information (curve CL), but the shifted wavelength TW'. The PD ratio PDT2 is derived from the curve CL2'. Then, in step S8, the temperature of the first and second optical filters 63a and 64a is set as the reference temperature by executing the temperature control so that the second PD ratio matches the second control target value PDT. (Target temperature) is matched, and the transmission characteristic of the first optical filter 63a is returned from the curve CL1'to the curve CL at the reference temperature (target temperature) (see the arrow in FIG. 8). After that, in step S6, the wavelength of the laser beam L1 is controlled from the wavelength TW'to the target wavelength TW by executing the wavelength adjustment control again using the first control target value PDT.

The tunable laser device described in Patent Document 1 uses two optical filters as in the tunable laser device 1 according to the first embodiment. However, since the two optical filters are made of the same material, they have the same temperature dependence. That is, when the transmission characteristic of one optical filter shifts from the transmission characteristic at the reference temperature (target temperature), the transmission characteristic of the other optical filter also shifts by the same shift amount. Therefore, even if the temperatures of the two optical filters deviate from the reference temperature (target temperature) and the transmission characteristics of the other optical filter shift, the PD ratio according to the intensity of the laser light transmitted through the other optical filter remains. , Corresponds to the target wavelength of the laser beam and maintains a value substantially the same as the target control target value of the PD ratio. Therefore, in the wavelength-variable laser apparatus described in Patent Document 1, the PD ratio corresponding to the intensity of the laser light transmitted through the other optical filter and the target wavelength of the laser light correspond to each other, and the control target value that is the target of the PD ratio. Even when compared with, it is recognized that the transmission characteristics of one optical filter have shifted from the transmission characteristics at the reference temperature (target temperature) (the temperatures of the two optical filters have deviated from the reference temperature (target temperature)). Can not do it.

According to the first embodiment described above, the following effects are obtained.
In the tunable laser apparatus 1 according to the first embodiment, the transmission characteristics of the first and second optical filters 63a and 64a differ from each other in temperature dependence. Therefore, when the wavelength adjustment control (step S6) is executed based on the first control target value PDT corresponding to the target wavelength TW and the first PD ratio, the second control target wavelength TW corresponding to the target wavelength TW is executed. By comparing the control target value PDT with the second PD ratio, it is possible to determine whether or not the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature). Further, when the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature), the second PD ratio matches the second control target value PDT. By executing the temperature control (step S8), the temperatures of the first and second optical filters 63a and 64a can be matched with the reference temperature (target temperature). Then, by executing the wavelength adjustment control (step S6) again using the first control target value PDT, the wavelength of the laser beam L1 can be accurately controlled to the target wavelength TW.

Further, in the tunable laser apparatus 1 according to the first embodiment, before steps S6 to S8, the operation of the temperature controller 9 is controlled based on the ambient temperature detected by the temperature sensor 8, and the first step is performed. , The temperature of the second optical filters 63a and 64a is controlled to the target temperature (reference temperature) (step S4). Therefore, the temperatures of the first and second optical filters 63a and 64a are roughly adjusted to the target temperature (reference temperature) by executing step S4, and the first and second optical filters 63a and 64a are executed by executing steps S6 to S8. The temperature can be finely adjusted to the target temperature (reference temperature). That is, the temperatures of the first and second optical filters 63a and 64a can be efficiently matched with the target temperature (reference temperature).

Further, in the tunable laser apparatus 1 according to the first embodiment, the first and second optical filters 63a and 64a are installed close to the same installation surface 91 of the temperature controller 9. The first and second optical filters 63a and 64a are waveguide type optical filters. That is, by installing the flat first and second optical filters 63a and 64a having a small thickness dimension close to the same installation surface 91 of the temperature controller 9, the reference temperature in the first optical filter 63a ( The temperature ΔT deviating from the target temperature) and the temperature ΔT deviating from the reference temperature (target temperature) in the second optical filter 64a can be set to be substantially the same at all times.
In particular, in the first and second optical filters 63a and 64a, quartz or quartz is used as the core material, and a dopant is added to at least one of the core and the cladding, and at least one of the type and amount of the dopant to be added is added. different. Therefore, while making the temperature dependence of the transmission characteristics of the first and second optical filters 63a and 64a different from each other, the specific refractive index difference Δ between the core and the clad can be increased to reduce the size.

(Embodiment 2)
Next, the second embodiment will be described.
In the following description, the same components as those in the first embodiment will be designated by the same reference numerals, and detailed description thereof will be omitted or simplified.
FIG. 9 is a block diagram showing a configuration of the control device 3A according to the second embodiment. FIG. 10 is a flowchart showing a wavelength control method by the control device 3A.
In the wavelength tunable laser device 1A according to the second embodiment, the control device 3A that executes the wavelength lock control by a method different from that of the control device 3 is provided for the tunable laser device 1 described in the above-described first embodiment. It is adopted.
In the control device 3A, the functions of the wavelength control unit 313 and the temperature control unit 314 and the information stored in the storage unit 32 are different from those of the control device 3 described in the first embodiment described above. In the following, for convenience of explanation, the control unit (wavelength control unit and temperature control unit) and the storage unit according to the second embodiment will be referred to as a control unit 31A (wavelength control unit 313A and temperature control unit 314A) and a storage unit 32A, respectively. ..

The storage unit 32A stores a program executed by the control unit 31A, information necessary for processing by the control unit 31A, and the like. The storage unit 32A stores slope information and temperature dependence information as information necessary for the processing of the control unit 31A, in addition to the transmission characteristic information and wavelength power information described in the first embodiment described above.
The slope information is between the upper limit value UL (see FIG. 11) and the lower limit value LL (see FIG. 11) excluding the dead zone in the transmission characteristics (curve CL (see FIG. 11)) of the first and second optical filters 63a and 64a. This is information indicating the ratio of the fluctuation amount of the first and second PD ratios (inclination of the slope portion) to the fluctuation amount of the wavelength within the range of (hereinafter referred to as the slope portion). The "dead zone" is a portion corresponding to a peak or a valley in the transmission characteristics (curve CL) of the first and second optical filters 63a and 64a, and is the first and second parts with respect to the amount of wavelength fluctuation. It means a part where the fluctuation amount of the PD ratio is small.
The temperature dependence information is information indicating the temperature dependence relationship of the transmission characteristics of the first and second optical filters 63a and 64a. Specifically, the temperature-dependent information is the amount of wavelength shift in the transmission characteristics of the first optical filter 63a when the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature). This is information indicating the ratio (for example, double) of the wavelength shift amount Δλ2 (see FIG. 11) in the transmission characteristics of the second optical filter 64a to Δλ1 (see FIG. 11).

The control unit 31A employs a wavelength control unit 313A and a temperature control unit 314A having functions different from those of the wavelength control unit 313 and the temperature control unit 314 with respect to the control unit 31 described in the first embodiment described above. At the same time, the function of the target value correction unit 315 is added.
Hereinafter, the functions of the wavelength control unit 313A, the temperature control unit 314A, and the target value correction unit 315 will be described with reference to FIG.

In the wavelength control method by the control device 3A, as shown in FIG. 10, steps S6A to S8A are adopted instead of steps S6 to S8 with respect to the wavelength control method (FIG. 7) described in the first embodiment described above. The point is different. That is, the temperature control unit 314A according to the second embodiment is different in that only step S4 is executed with respect to the temperature control unit 314 described in the first embodiment described above. In the following, only steps S6A to S8A will be described.

Step S6A (wavelength control step) is executed after step S5.
Specifically, in the first loop (loop of steps S6A to S8A), the wavelength control unit 313A was calculated in step S6A in the same manner as in step S6 described in the above-described first embodiment. The wavelength adjustment control is executed so that the latest first PD ratio calculated after step S5 matches the first control target value. Further, in the second and subsequent loops (loops of steps S6A to S8A), the wavelength control unit 313A is calculated in step S6A after step S5 with respect to the correction control target value generated in step S8A described later. Wavelength adjustment control is executed so that the latest first PD ratio matches.

After step S6A, the target value correction unit 315 has the latest second PD ratio calculated after step S5 and the second PD calculated in step S2, similarly to step S7 described in the first embodiment described above. It is determined whether or not the control target value of 2 is the same (step S7A).
When it is determined that the second PD ratio and the second control target value are the same (step S7A: Yes), the control device 3A ends the wavelength lock control.

On the other hand, when it is determined that the second PD ratio and the second control target value are not the same (step S7A: No), the target value correction unit 315 performs the first control calculated in step S2. The target value is corrected to generate a correction control target value (step S8A: target value correction step).
Specifically, the target value correction unit 315 contains the transmission characteristic information and the temperature dependence information stored in the storage unit 32A, the latest first PD ratio PDT calculated after step S5 (see FIG. 11), and Based on the latest second PD ratio PDT2 (see FIG. 11) calculated after step S5, the wavelength shift amount Δλ1 (laser beam L1) in the transmission characteristics of the first optical filter 63a is performed by a predetermined calculation. The amount of wavelength shift from the target wavelength TW (see FIG. 11)) is calculated. Further, the target value correction unit 315 corrects the first control target value PDT calculated in step S2 based on the shift amount Δλ1 of the wavelength and the slope information stored in the storage unit 32A. The correction value CV (see FIG. 11) is calculated. Then, the target value correction unit 315 adds the correction value CV to the first control target value PDT calculated in step S2 to generate a correction control target value PDT'(see FIG. 11).
After this, the control device 3A returns to step S6A.

FIG. 11 is a diagram illustrating a wavelength control method. Specifically, FIG. 11 is a diagram corresponding to FIG. 5, and the transmission characteristic information is shown by a curve CL. Further, the transmission characteristic of the first optical filter 63a in the state determined as "No" in step S7A is shown by the curve CL1', and the transmission characteristic of the second optical filter 64a in the state is shown by the curve CL2'. Shown.
In the first embodiment described above, in the control device 3, the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature), and the transmission characteristics of the first optical filter 63a are curved from the curve CL. When shifting to CL1', temperature control (step S8) was executed using the second PD ratio PDT2 and the second control target value PDT. That is, the control device 3 returns the transmission characteristic of the first optical filter 63a to the curve CL at the reference temperature (target temperature) by the temperature control, and executes the wavelength adjustment control (step S6) using the curve CL. Was there.
On the other hand, in the second embodiment, in the control device 3A, the temperatures of the first and second optical filters 63a and 64a deviate from the reference temperature (target temperature), and the transmission characteristics of the first optical filter 63a are curved. When the curve is shifted from CL to the curve CL1', the wavelength adjustment control (step S6A) is executed using the shifted curve CL1'. That is, the control device 3A calculates the wavelength shift amount Δλ1 from the transmission characteristic information, the temperature dependence information, and the latest first and second PD ratios PDT and PDT2, and also calculates the wavelength shift amount Δλ1 and the slope information. The correction value CV is calculated from the above, and the first control target value PDT is corrected by the correction value CV to generate the correction control target value PDT'(step S8A). Then, the control device 3A executes the wavelength adjustment control (step S6A) using the correction control target value PDT'. As a result, the wavelength of the laser beam L1 is controlled to the target wavelength TW.

Even when the wavelength adjustment control is executed using the shifted curve CL1'as in the second embodiment described above, the same effect as that of the first embodiment described above is obtained.
In the second embodiment, the wavelength adjustment control is executed using the transmission characteristic shifted by the temperature of the first and second optical filters 63a and 64a deviating from the reference temperature (target temperature), for example. Even when the first and second optical filters 63a and 64a deviate significantly from the reference temperature (target temperature) and temperature adjustment becomes difficult, the wavelength of the laser beam L1 can be controlled to the target wavelength TW. Further, in the first embodiment described above, since the temperatures of the first and second optical filters 63a and 64a are controlled in step S8, the time until the temperature change converges depends on these time constants. However, in the second embodiment, since the control for correcting the first control target value PDT is performed, the influence of the above-mentioned time constant can be reduced. Therefore, the time required for the wavelength of the laser beam L1 to converge to the target wavelength TW can be shortened.

(Other embodiments)
Although the embodiments for carrying out the present invention have been described so far, the present invention should not be limited only to the above-described first and second embodiments.
FIG. 12 is a diagram showing a modified example of the first and second embodiments.
In the above-described first and second embodiments, the transmission characteristics of the first and second optical filters 63a and 64a are designed so that the phase difference is substantially "0" at the reference temperature (target temperature). , Not limited to this. If the temperature dependence of the transmission characteristics of the first and second optical filters 63a and 64a is different from each other, the transmission characteristics of the first optical filter 63a at the reference temperature (target temperature) (curve CL1 (FIG. 12)). And the transmission characteristic of the second optical filter 64a (curve CL2 (FIG. 12)) may be designed to have a phase difference of, for example, π / 2. That is, by providing the phase difference in this way, the dead zone of the transmission characteristic (curve CL1) of the first optical filter 63a and the dead zone of the transmission characteristic (curve CL2) of the second optical filter 64a overlap each other. It will not be. Therefore, when the wavelength adjustment control (steps S8 and S8A) is executed, among the transmission characteristics (curves CL1 and CL2) of the first and second optical filters 63a and 64a, the target wavelength TW is not located in the dead zone. By using the characteristics, the wavelength of the laser beam L1 can be satisfactorily controlled to the target wavelength TW. Further, since the temperature dependence of the transmission characteristics of the first and second optical filters 63a and 64a is different from each other, the phase difference at the reference temperature (target temperature) is a desired phase difference (for example, π /) due to manufacturing error or the like. Even if it is not 2), the phase difference can be set to a desired phase difference (for example, π / 2) by controlling the temperatures of the first and second optical filters 63a and 64a. ..
Further, the number of optical filters is not limited to two, and may be three or more. At this time, if the temperature dependence of the transmission characteristics of the three or more optical filters is different from each other, the phase difference in the transmission characteristics of the three optical filters becomes approximately "0" at the reference temperature (target temperature). It may be designed, or may be designed to have a phase difference of, for example, π / N (N = number of optical filters).

In the above-described first and second embodiments, the ring resonator type optical filters 63a and 64a have been adopted as the first and second optical filters according to the present invention, but the present invention is not limited to this. Other optical filters such as etalon may be adopted as the first and second optical filters according to the present invention, as long as they are optical filters having periodic transmission characteristics with respect to the wavelength of incident light. Further, one of the first and second optical filters according to the present invention may be composed of a ring resonator type optical filter, and the other may be composed of an etalon.

In the above-described first and second embodiments, the positions where the first and second optical filters and the first and second light receiving elements according to the present invention are arranged are the positions described in the above-described first and second embodiments. Not limited to. For example, an optical branching section is provided in which the laser beam L1 output from the tunable light source unit 4 is branched into two laser beams and one laser beam is output to the semiconductor optical amplifier 5. Then, the first and second optical filters and the first and second light receiving elements according to the present invention may be arranged at positions that receive the other laser beam branched at the optical branching portion.

Further, the flow showing the wavelength control method by the control devices 3 and 3A is not limited to the order of processing in the flowcharts (FIGS. 7 and 10) described in the above-described first and second embodiments, and is changed within a consistent range. It doesn't matter. For example, in FIG. 7, steps S6 and steps S7 and S8 may be executed in parallel. It should be noted that the above-described first and second embodiments may be combined as appropriate. For example, in the first embodiment described above, instead of step S7, it is determined whether or not the difference between the second PD ratio and the second control target value is within a predetermined range, and it is determined that the difference is not within the range. In that case, step S8 may be executed, and if it is determined that the range is within the range, step S8A described in the above-described second embodiment may be executed.

1,1A Variable wavelength laser device 2 Variable wavelength laser module 3,3A Control device 4 Variable wavelength light source unit 5 Semiconductor optical amplifier 6 Plane optical wave circuit 7 Light detection unit 8 Temperature sensor 9 Temperature controller 31, 31A Control unit 32, 32A Storage Part 41 Light source part 42 Waveguide part 43 First waveguide part 44 Second waveguide part 45 n-side electrode 61 Optical branch part 62 Optical waveguide 63 Optical waveguide 63a Ring resonator type optical filter 63a (first optical filter )
64 Optical Waveguide 64a Ring Resonator Type Optical Filter 64a (Second Optical Filter)
71-73 PD
91 Installation surface 311 Monitor value calculation unit 312 Target value calculation unit 313, 313A Wavelength control unit 314, 314A Temperature control unit 315 Target value correction unit 421-423 Microheater 431 waveguide section 431a Gain section 431b Diffraction grating layer 432 Semiconductor lamination section 433 p-side electrode 441 2 branch part 441a Multimode interference type waveguide 442, 443 Arm part 444 Ring-shaped waveguide 445 Phase adjustment part Ar1 1st area Ar2 2nd area B1 Base C1 Optical resonator CL, CL1', CL2'curve CV correction value L1 to L6 laser light LL lower limit value M1 reflection mirror PDT 1st and 2nd control target values PDT'correction control target value PDT2 2nd PD ratio RF1 ring resonator filter TW target wavelength TW'wavelength UL upper limit Δλ1, Δλ2 Wavelength shift amount

Claims (12)

A tunable light source unit that changes the wavelength of the output laser light,
A first optical filter and a second optical filter having transmission characteristics whose characteristics change periodically with respect to the wavelength of the incident laser light, respectively.
An optical branching portion that branches the laser beam into three laser beams,
A first optical waveguide, a second optical waveguide, and a third optical waveguide that guide the three laser beams, respectively.
Is guided by the first optical waveguide, a first light receiving element for outputting an electric signal corresponding to the intensity of the laser light passed permeable said first optical filter,
A second light receiving element that is guided by the second optical waveguide and outputs an electric signal corresponding to the intensity of the laser light that has passed through the second optical filter.
A third light receiving element that outputs an electric signal according to the intensity of the laser beam guided by the third optical waveguide, and a third light receiving element.
The first optical filter, the second optical filter, the optical branch, the first optical waveguide, the second optical waveguide, the third optical waveguide, the first light receiving element, the second light receiving element. And a temperature controller that adjusts the temperature of the third light receiving element,
A control device for controlling the wavelength of the laser light output from the tunable light source unit to a target wavelength is provided.
The first optical filter and the second optical filter are
The transmission characteristic temperature dependence is different from the possess respectively,
The control device is
The ratio of the output value of the electric signal output from the first light receiving element to the output value of the electric signal output from the third light receiving element is calculated as the first monitor value, and from the third light receiving element. The ratio of the output value of the electric signal output from the second light receiving element to the output value of the output electric signal is calculated as the second monitor value, and is also calculated.
The first control target value and the first control target value corresponding to the first monitor value, the second monitor value, and the target wavelength of the laser beam, and the target of the first monitor value and the second monitor value, respectively. The deviation of the temperature of the first optical filter and the second optical filter from the target temperature is determined based on the second control target value, and is output from the wavelength tunable light source unit according to the deviation. A tunable laser device characterized by controlling the wavelength of laser light . Before Symbol control device,
A monitor value calculation unit for calculating a first monitor value and the second monitor value,
A target value calculating unit for calculating a first target control value and the second control target value,
A wavelength control unit that controls the wavelength of the laser light output from the tunable light source unit based on the first monitor value and the first control target value.
A temperature control unit that controls the operation of the temperature controller based on the second monitor value and the second control target value, and controls the temperatures of the first optical filter and the second optical filter. The wavelength tunable laser apparatus according to claim 1, wherein the tunable laser apparatus is provided. The control device is
A monitor value calculation unit for calculating a first monitor value and the second monitor value,
A target value calculating unit for calculating a first target control value and the second control target value,
A target value correction unit that corrects the first control target value and generates a correction control target value based on the second monitor value and the second control target value.
The wavelength according to claim 1, further comprising a wavelength control unit that controls the wavelength of laser light output from the tunable light source unit based on the first monitor value and the correction control target value. Tunable laser device. Further comprising a temperature sensor for detecting the ambient temperature,
The control device is
The claim is characterized by comprising a temperature control unit that controls the operation of the temperature controller based on the ambient temperature and controls the temperature of the first optical filter and the second optical filter to a target temperature. The tunable laser apparatus according to any one of 1 to 3. The temperature controller
Has an installation surface on which the temperature control target is installed,
The first optical filter and the second optical filter are
The tunable laser apparatus according to claim 4, wherein the temperature controller is installed on the same installation surface of the temperature controller. The first optical filter and the second optical filter are
The tunable laser apparatus according to any one of claims 1 to 5, wherein the optical filter is a waveguide type. The first optical filter and the second optical filter are
The sixth aspect of the invention is characterized in that it has a core and a cladding that propagate the laser beam, a dopant is added to at least one of the core and the cladding, and at least one of the type and the amount of the dopant to be added is different from each other. The tunable laser device described. The first optical filter and the second optical filter are
The tunable laser apparatus according to claim 6, wherein each of the plane light wave circuits is formed, and the layer structure in the thickness direction of the plane light wave circuit is made of materials having different coefficients of thermal expansion. .. A wavelength-variable light source unit that changes the wavelength of the output laser light, and a first optical filter and a second optical filter that have transmission characteristics whose characteristics change periodically with respect to the wavelength of the incident laser light. , An optical branching portion that branches the laser beam into three laser beams, a first optical waveguide, a second optical waveguide, and a third optical waveguide that waveguide the three laser beams, respectively, and the first optical waveguide. is guided in the optical waveguide, a first light receiving element for outputting an electric signal corresponding to the intensity of the laser light passed permeable said first optical filter, guiding in said second optical waveguide To the intensity of the laser light waved by the second optical waveguide and the second light receiving element that outputs an electric signal corresponding to the intensity of the laser light that has passed through the second optical filter. a third light receiving element for outputting an electrical signal corresponding, the first optical filter, before Symbol second optical filter, the optical branching section, the first optical waveguide, the second optical waveguide, said first A method for controlling a wavelength of a wavelength-variable laser apparatus including an optical waveguide (3), the first light receiving element, the second light receiving element, and a temperature controller for adjusting the temperature of the third light receiving element .
The first optical filter and the second optical filter are
Each of the above-mentioned transmission characteristics having different temperature dependences
The wavelength control method of the tunable laser device is
A monitor value calculation step of calculating a first monitor value and a second monitor value based on the intensity of laser light acquired by the first light receiving element and the second light receiving element, respectively.
A target value calculation step corresponding to the target wavelength of the laser beam and calculating the first control target value and the second control target value which are the targets of the first monitor value and the second monitor value, respectively.
A wavelength control step for controlling the wavelength of the laser beam output from the tunable light source unit based on the first monitor value and the first control target value.
Based on the second monitor value and the second control target value, the deviation of the temperature of the first optical filter and the second optical filter from the target temperature is determined, and the temperature is determined according to the deviation. A wavelength control method for a wavelength variable laser apparatus, comprising: a temperature control step of controlling the operation of the controller and controlling the temperature of the first optical filter and the second optical filter. The tunable laser device is
Further equipped with a temperature sensor that detects the ambient temperature,
The wavelength control method of the tunable laser device is
Before executing the wavelength control step and the temperature control step, on the basis of the ambient temperature to control the operation of the temperature controller, the first optical filter and the temperature of the target of the second optical filter The wavelength control method for a wavelength variable laser apparatus according to claim 9, further comprising a coarse adjustment step for controlling the temperature. A wavelength-variable light source unit that changes the wavelength of the output laser light, and a first optical filter and a second optical filter that have transmission characteristics whose characteristics change periodically with respect to the wavelength of the incident laser light. , An optical branching portion that branches the laser beam into three laser beams, a first optical waveguide, a second optical waveguide, and a third optical waveguide that waveguide the three laser beams, respectively, and the first optical waveguide. is guided in the optical waveguide, a first light receiving element for outputting an electric signal corresponding to the intensity of the laser light passed permeable said first optical filter, guiding in said second optical waveguide To the intensity of the laser light waved by the second optical waveguide and the second light receiving element that outputs an electric signal corresponding to the intensity of the laser light that has passed through the second optical filter. A third light receiving element that outputs a corresponding electric signal, the first optical filter, the second optical filter, the optical branching portion, the first optical waveguide, the second optical waveguide, and the third. A method for controlling a wavelength of a variable wavelength laser apparatus including the optical waveguide, the first light receiving element, the second light receiving element, and a temperature controller for adjusting the temperature of the third light receiving element .
The first optical filter and the second optical filter are
Each of the above-mentioned transmission characteristics having different temperature dependences
The wavelength control method of the tunable laser device is
A monitor value calculation step of calculating a first monitor value and a second monitor value based on the intensity of laser light acquired by the first light receiving element and the second light receiving element, respectively.
A target value calculation step corresponding to the target wavelength of the laser beam and calculating the first control target value and the second control target value which are the targets of the first monitor value and the second monitor value, respectively.
A target value correction step of correcting the first control target value and generating a correction control target value based on the second monitor value and the second control target value, and
Based on the first monitor value and the correction control target value, the deviation of the temperature of the first optical filter and the second optical filter from the target temperature is determined, and the wavelength tunable light source is determined according to the deviation. A wavelength control method for a tunable laser device, which comprises a wavelength control step for controlling the wavelength of the laser light output from the unit. The tunable laser device is
Further comprising a temperature sensor for detecting the ambient temperature,
The wavelength control method of the tunable laser device is
Before executing the target value correcting step, based on said ambient temperature to control the operation of the temperature controller, which controls the first optical filter and the temperature of the second optical filter to the target temperature The wavelength control method for a tunable laser apparatus according to claim 11, further comprising a coarse adjustment step.

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