Laser device and frequency control method

Abstract

To quickly start up a laser beam without degrading the frequency accuracy of the laser light. [Solution] The device comprises a variable light source unit that varies the frequency of the output laser light, a frequency adjustment unit that adjusts the frequency of the laser light, a semiconductor optical amplifier that amplifies the laser light output from the variable light source unit, and a control device that controls the operation of the variable light source unit. The control device includes a frequency control unit that controls the frequency of the variable light source unit to a predetermined range by supplying a control amount corresponding to the target frequency of the laser light to the frequency adjustment unit, an intensity control unit that controls the intensity of the laser light output from the semiconductor optical amplifier by controlling the current supplied to the semiconductor optical amplifier, and a correction unit that corrects the control amount according to the elapsed time since the start of current control to the semiconductor optical amplifier when increasing the intensity of the laser light output from the semiconductor optical amplifier.

Description

Technical Field

[0001] The present invention relates to a laser device and a frequency control method.

Background Art

[0002] As an invention for adjusting the intensity of laser light output from a wavelength-variable light source, for example, there is a wavelength-variable light source device disclosed in Patent Document 1. When setting the output optical power of the laser light to a predetermined power, this wavelength-variable light source device increases the target value of the optical output power stepwise by ΔP every time a predetermined time elapses, and passes a current through the gain element according to the increased target value. Further, when the optical output power reaches the final target value, this wavelength-variable light source device controls the current for driving the laser diode module so that the laser light has a desired wavelength.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the wavelength-variable light source device of Patent Document 1, when increasing the output optical power, the increase rate of the current is constant and the temperature change is also constant, so the influence on the temperature control of the laser diode module can be reduced. Further, according to this wavelength-variable light source device, since the wavelength of the laser light is controlled after the control of the output optical power is completed, the influence due to the heat generation of the gain element can be reduced and rapid convergence to a desired wavelength can be achieved. However, since the optical output power is increased stepwise until the target output optical power is reached, it takes time until the optical output power reaches the final target value.

[0005] The present invention has been made in view of the above, and aims to provide a technology for rapidly starting up a laser beam without degrading the frequency accuracy of the laser beam. [Means for solving the problem]

[0006] To solve the above-mentioned problems and achieve the objective, the laser device according to the present invention comprises a variable light source unit that varies the frequency of the output laser light, a frequency adjustment unit that adjusts the frequency of the laser light, a semiconductor optical amplifier that amplifies the laser light output from the variable light source unit, a temperature sensor that detects the temperature near the variable light source unit, a temperature controller that adjusts the temperature of the variable light source unit, and a control device that controls the operation of the variable light source unit. The control device comprises a temperature control unit that controls the temperature controller according to the temperature detected by the temperature sensor, a frequency control unit that controls the frequency of the variable light source unit to a predetermined range by supplying a control amount corresponding to the target frequency of the laser light to the frequency adjustment unit, an intensity control unit that controls the intensity of the laser light output from the semiconductor optical amplifier by controlling the current supplied to the semiconductor optical amplifier, and a correction unit that corrects the control amount according to the elapsed time since the start of current control to the semiconductor optical amplifier when increasing the intensity of the laser light output from the semiconductor optical amplifier.

[0007] In the laser device according to the present invention, the frequency adjustment unit includes a coarse adjustment unit that adjusts the frequency of the laser beam by being supplied with a coarse adjustment control amount, and a fine adjustment unit that adjusts the phase of the laser beam by being supplied with a fine adjustment control amount, and the frequency control unit may include a coarse adjustment control unit that supplies a coarse adjustment control amount corresponding to the target frequency to the coarse adjustment unit, and a fine adjustment control unit that supplies a fine adjustment control amount corresponding to the target frequency to the fine adjustment unit.

[0008] Furthermore, the laser device according to the present invention includes a first photodetector that outputs the intensity of laser light output from the variable light source unit, an optical filter having periodic transmission characteristics with respect to the wavelength of incident light and transmitting the laser light output from the variable light source unit with a transmittance corresponding to the transmission characteristics, a second photodetector that outputs the intensity of laser light transmitted through the optical filter, and a monitor value calculation unit that calculates a monitor value corresponding to the frequency of the laser light based on the laser light intensity acquired by the first photodetector and the second photodetector, respectively, and the fine-tuning control unit may supply a fine-tuning control amount corresponding to the difference between the monitor value and a target value corresponding to the target frequency to the fine-tuning unit.

[0009] Furthermore, in the laser device according to the present invention, the intensity control unit may stop supplying current to the semiconductor optical amplifier when changing the frequency of the laser light, and resume supplying current to the semiconductor optical amplifier after the frequency of the laser light output from the variable light source unit has been controlled to a predetermined range, and the correction unit may correct the control amount according to the elapsed time since the current supply to the semiconductor optical amplifier was stopped and the elapsed time since the current supply to the semiconductor optical amplifier was resumed.

[0010] Furthermore, in the laser device according to the present invention, the variable light source unit may have a variable frequency for the laser light by utilizing the Vernier effect.

[0011] Furthermore, the frequency control method according to the present invention includes a variable light source unit that varies the frequency of the output laser light, a frequency adjustment unit that adjusts the frequency of the laser light, a semiconductor optical amplifier that amplifies the laser light output from the variable light source unit, a first photodetector that outputs the intensity of the laser light output from the variable light source unit, an optical filter that has a periodic transmission characteristic with respect to the wavelength of incident light and transmits the laser light output from the variable light source unit with a transmittance corresponding to the said transmission characteristic, a second photodetector that outputs the intensity of the laser light that has passed through the optical filter, a temperature sensor that detects the temperature near the variable light source unit, a temperature controller that adjusts the temperature of the variable light source unit, and a control device that controls the operation of the variable light source unit. A frequency control method performed by the control device of a laser device comprising: a temperature control step of controlling the temperature controller according to the temperature detected by the temperature sensor; a frequency control step of controlling the frequency of the variable light source within a predetermined range by supplying a control amount corresponding to the target frequency of the laser light to the frequency adjustment unit; an intensity control step of controlling the intensity of the laser light output from the semiconductor optical amplifier by controlling the current supplied to the semiconductor optical amplifier; and a correction step of correcting the control amount according to the elapsed time since the start of current control to the semiconductor optical amplifier when increasing the intensity of the laser light output from the semiconductor optical amplifier.

[0012] Furthermore, in the frequency control method according to the present invention, in the intensity control step, the supply of current to the semiconductor optical amplifier is stopped when the frequency of the laser light is changed, and the supply of current to the semiconductor optical amplifier is resumed after the frequency of the laser light output from the variable light source is controlled to a predetermined range, and in the correction step, the control amount is corrected according to the elapsed time since the supply of current to the semiconductor optical amplifier was stopped and the elapsed time since the supply of current to the semiconductor optical amplifier was resumed. [Effects of the Invention]

[0013] According to the present invention, it is possible to quickly start up a laser beam without degrading the frequency accuracy of the laser beam. [Brief explanation of the drawing]

[0014] [Figure 1] FIG. 1 is a schematic configuration diagram of a wavelength-variable laser device according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of a wavelength-variable light source unit. [Figure 3] FIG. 3 is a block diagram showing the configuration of a control device. [Figure 4] FIG. 4 is a diagram showing an example of a characteristic table. [Figure 5] FIG. 5 is a flowchart showing the flow of processing executed by a control unit. [Figure 6] FIG. 6 is a flowchart showing the flow of processing executed by a control unit. [Figure 7] FIG. 7 is a diagram showing an example of a correction table. [Figure 8A] FIG. 8A is a diagram showing the temporal change in the intensity of laser light output from a light source unit. [Figure 8B] FIG. 8B is a diagram showing the temporal change in the frequency of laser light output from a light source unit. [Figure 8C] FIG. 8C is a diagram showing the temporal change in the power supplied to a coarse adjustment unit. [Figure 8D] FIG. 8D is a diagram showing the temporal change in a target PD ratio. [Figure 8E] FIG. 8E is a diagram showing the temporal change in the temperature of a light source unit. [Figure 8F] FIG. 8F is a diagram showing the temporal change in the temperature of a planar lightwave circuit. [Figure 9] FIG. 9 is a flowchart showing the flow of processing executed by a control unit. [Figure 10] FIG. 10 is a diagram showing an example of a correction table. [Figure 11] FIG. 11 is a diagram showing an example of a correction table. [Figure 12A] FIG. 12A is a diagram showing the temporal change in the intensity of laser light output from a light source unit. [Figure 12B] FIG. 12B is a diagram showing the temporal change in the frequency of laser light output from a light source unit. [Figure 12C] FIG. 12C is a diagram showing the temporal change of the power supplied to the coarse adjustment unit. [Figure 12D] FIG. 12D is a diagram showing the temporal change of the target PD ratio. [Figure 12E] FIG. 12E is a diagram showing the temporal change of the temperature of the light source unit. [Figure 12F] FIG. 12F is a diagram showing the temporal change of the temperature of the planar optical waveguide circuit. [Figure 13] FIG. 13 is a schematic configuration diagram of a wavelength variable laser device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. Further, the drawings are schematic, and it should be noted that the dimensional relationships of each element may be different from the actual ones. There may also be parts where the dimensional relationships and ratios between the drawings are different from each other.

[0016] Also, in the figure, an orthogonal coordinate system of the X-axis, Y-axis, and Z-axis is appropriately shown, and the direction is explained thereby. In the space shown by the orthogonal coordinate system, the direction in which the X component increases is referred to as the +X direction, and the direction in which the X component decreases is referred to as the -X direction. Similarly, for the Y and Z components, they are defined as the +Y direction, -Y direction, +Z direction, and -Z direction. For convenience of explanation, the +Z direction may be referred to as the upward direction (above), the -Z direction may be referred to as the downward direction (below), and the Z-axis direction may be referred to as the vertical direction.

[0017] FIG. 1 is a schematic configuration diagram of a wavelength variable laser device 1 according to an embodiment of the present invention. The wavelength variable laser device 1 includes a modularized wavelength variable laser module 2 and a control device 3 that controls the operation of the wavelength variable laser module 2. In FIG. 1, the wavelength variable laser module 2 and the control device 3 are configured separately, but they may be modularized integrally.

[0018] The tunable laser module 2, under the control of the control device 3, variables the wavelength of the output laser light to one of several wavelengths and outputs laser light of that wavelength. In other words, the tunable laser module 2 variables the frequency of the output laser light to one of several frequencies and outputs laser light of that frequency. This tunable laser module 2 comprises a tunable light source unit 4, a semiconductor optical amplifier (SOA) 5, a planar lightwave circuit (PLC) 6, a photodetector 7, a temperature sensor 8, and a temperature controller 9. The tunable laser module 2 also includes a collimating lens 12, a beam splitter 13, and a photodiode (PD) PD14 for power monitoring.

[0019] Figure 2 shows the configuration of the tunable light source unit 4. The tunable light source unit 4 is a tunable laser that utilizes the Vernier effect, for example, and outputs laser light L1 under the control of the control device 3. This tunable light source unit 4 includes a light source unit 41 that varies the wavelength (frequency) 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. By locally heating the light source unit 41, it includes a coarse adjustment unit 42a and a fine adjustment unit 42b that change the wavelength (frequency) of the laser light L1 output from the light source unit 41. The coarse adjustment unit 42a and the fine adjustment unit 42b are examples of frequency adjustment units 42 that adjust the frequency of the laser light L1.

[0020] The light source unit 41 comprises a first waveguide section 43 and a second waveguide section 44, respectively, formed on a common base 11. Here, the base 11 is made of, for example, n-type InP. On the back surface of the base 11, an n-side electrode 45 is formed, which is made of, for example, AuGeNi and makes ohmic contact with the base 11.

[0021] The first waveguide section 43 has an embedded waveguide structure. This first waveguide section 43 comprises a waveguide section 431, a semiconductor laminated section 432, and a p-side electrode 433. The waveguide section 431 is formed to extend in the X direction within the semiconductor laminated section 432. The first waveguide section 43 also has a gain section 431a and a DBR (Distributed Bragg Reflector) type diffraction grating section 431b. Here, the gain section 431a is an active layer having a multiple quantum well structure made of InGaAsP and an optical confinement layer. The diffraction grating section 431b is composed of a sampling diffraction grating made of InGaAsP and InP.

[0022] The semiconductor stacked portion 432 is constructed by stacking InP-based semiconductor layers and has the function of a cladding portion relative to the waveguide portion 431. The p-side electrode 433 is positioned on the semiconductor stacked portion 432 along the gain portion 431a. A protective film (not shown) made of SiN is formed on the semiconductor stacked portion 432. The p-side electrode 433 is in contact with the semiconductor stacked portion 432 through an opening (not shown) formed in the protective film.

[0023] Furthermore, a microheater 421 is positioned on the protective film of the semiconductor stack 432, along the diffraction grating 431b. This microheater 421 generates heat in response to the power supplied from the control device 3, heating the diffraction grating 431b. The control device 3 controls the power supplied to the microheater 421, which changes the temperature of the diffraction grating 431b and thus its refractive index.

[0024] The second waveguide section 44 comprises a two-branch section 441, two arm sections 442 and 443, and a ring-shaped waveguide 444. The two-branch section 441 is composed of a 1x2 type branched waveguide including a 1x2 type multimode interference (MMI) waveguide 441a, with the two-port side connected to the two arm sections 442 and 443 respectively, and the one-port side connected to the first waveguide section 43. In other words, the two-branch section 441 integrates one end of the two arm sections 442 and 443, and optically couples them with the diffraction grating section 431b.

[0025] The arm sections 442 and 443 both extend in the X direction and are positioned to sandwich the ring-shaped waveguide 444. These arm sections 442 and 443 are optically coupled to the ring-shaped waveguide 444 with the same coupling coefficient κ. The value of κ is, for example, 0.2. The arm sections 442 and 443 and the ring-shaped waveguide 444 constitute a ring resonator filter RF1. The ring resonator filter RF1 and the bifurcated section 441 constitute a reflective mirror M1.

[0026] The two-branch section 441, the arm sections 442 and 443, and the ring-shaped waveguide 444 described above all have a high-mesa waveguide structure in which an optical waveguide layer 44a made of InGaAsP is sandwiched between cladding layers 44b made of InP.

[0027] A microheater 422 is provided on the ring-shaped waveguide 444. Specifically, the microheater 422 is ring-shaped and is positioned on a SiN protective film (not shown) that covers the ring-shaped waveguide 444. The microheater 422 generates heat in response to the power supplied from the control device 3, heating the ring-shaped waveguide 444. Furthermore, the temperature of the ring-shaped waveguide 444 changes, and its refractive index changes, by controlling the power supplied to the microheater 422 by the control device 3.

[0028] A microheater 423 is provided on a portion of the arm portion 443. Specifically, the microheater 423 is positioned on a SiN protective film (not shown) formed to cover the arm portion 443. The region of the arm portion 443 below the microheater 423 functions as a phase adjustment unit 445 that changes the phase of light. The microheater 423 generates heat in response to the power supplied from the control device 3, heating the phase adjustment unit 445. Furthermore, the temperature of the phase adjustment unit 445 changes, and its refractive index changes, by controlling the power supplied to the microheater 423 by the control device 3.

[0029] The first waveguide section 43 and the second waveguide section 44 described above constitute an optical resonator C1, which is composed of a diffraction grating section 431b and a reflection mirror M1 that are optically connected to each other. The gain section 431a and the phase adjustment section 445 are located within the optical resonator C1.

[0030] The diffraction grating 431b generates a first comb-like reflection spectrum having approximately periodic reflection characteristics at approximately predetermined wavelength intervals. On the other hand, the ring resonator filter RF1 generates a second comb-like reflection spectrum having approximately periodic reflection characteristics at approximately predetermined wavelength intervals. Here, the second comb-like reflection spectrum has a peak with a full width at half maximum that is narrower than the peak of the first comb-like reflection spectrum, and has approximately periodic reflection characteristics at wavelength intervals different from those of the first comb-like reflection spectrum. However, it should be noted that, considering the wavelength dispersion of the refractive index, the spectral components are not strictly at equiwavelength intervals.

[0031] To illustrate the characteristics of each comb-shaped reflection spectrum, the wavelength spacing between peaks (free spectral region: FSR) of the first comb-shaped reflection spectrum is 373 GHz in terms of light frequency. The full width at half maximum (FMAX) of each peak is 43 GHz in terms of light frequency. On the other hand, the wavelength spacing between peaks (FMAX) of the second comb-shaped reflection spectrum is 400 GHz in terms of light frequency. The full width at half maximum (FMAX) of each peak is 25 GHz in terms of light frequency. In other words, the FMAX of each peak in the second comb-shaped reflection spectrum (25 GHz) is narrower than the FMAX of each peak in the first comb-shaped reflection spectrum (43 GHz).

[0032] In the wavelength-tunable light source unit 4, in order to realize laser oscillation, one peak of the first comb-shaped reflection spectrum and one peak of the second comb-shaped reflection spectrum are configured to be superimposed on the wavelength axis. Such superposition can be achieved by using at least one of the microheaters 421 and 422 to heat the diffraction grating unit 431b with the microheater 421, thereby changing its refractive index by the thermo-optic effect and shifting the first comb-shaped reflection spectrum overall on the wavelength axis, and by heating the ring-shaped waveguide 444 with the microheater 422, thereby changing its refractive index and shifting the second comb-shaped reflection spectrum overall on the wavelength axis.

[0033] On the other hand, in the tunable light source unit 4, there are resonator modes provided 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 resonator modes (longitudinal mode interval) is 25 GHz or less. With this setting, the resonator length of the optical resonator C1 becomes 1800 μm or more, and a narrowing of the linewidth of the oscillating laser light can be expected. The wavelength of the resonator modes of the optical resonator C1 can be finely adjusted by heating the phase adjustment unit 445 using the microheater 423 to change its refractive index and shift the wavelength of the resonator modes along the wavelength axis. In other words, the phase adjustment unit 445 is a part for actively controlling the optical path length of the optical resonator C1.

[0034] The tunable light source unit 4 is configured such that, when the control device 3 injects current from the n-side electrode 45 and the p-side electrode 433 to the gain unit 431a and causes the gain unit 431a to emit light, it oscillates a laser at a wavelength where the peak of the spectral component of the first comb-shaped reflection spectrum, the peak of the spectral component of the second comb-shaped reflection spectrum, and one of the resonator modes of the optical resonator C1 coincide, for example, 1550 nm, and outputs laser light L1.

[0035] Furthermore, the wavelength-tunable light source unit 4 can change the wavelength of the laser light L1 by utilizing the Vernier effect. For example, when the diffraction grating unit 431b is heated by the microheater 421, the refractive index of the diffraction grating unit 431b increases due to the thermo-optic effect, and the first comb reflection spectrum of the diffraction grating unit 431b is shifted to the longer wave side overall. As a result, the peak of the first comb reflection spectrum around 1550 nm is no longer overlapped with the peak of the second comb reflection spectrum of the ring resonator filter RF1, and overlaps with another peak of the second comb reflection spectrum located on the longer wave side (for example, around 1556 nm). Furthermore, by tuning the phase adjustment unit 445 to fine-tune the resonator mode and superimposing one of the resonator modes onto the two comb reflection spectra, laser oscillation around 1556 nm can be achieved. In other words, in the wavelength-tunable light source unit 4, wavelength-tunable operation is realized by performing coarse tuning by tuning the first comb-shaped reflection spectrum and the second comb-shaped reflection spectrum, respectively, using a microheater 421 for the diffraction grating unit 431b and a microheater 422 for the ring resonator filter RF1, and then fine tuning by tuning the resonator length using a microheater 423 for the phase adjustment unit 445. Microheaters 421 and 422 are examples of the coarse tuning unit 42a, and microheater 423 is an example of the fine tuning unit 42b.

[0036] The semiconductor optical amplifier 5, although not shown in detail, has an embedded waveguide structure with an active core layer made of the same material and structure as the first waveguide section 43. However, it does not have a diffraction grating section 431b. This semiconductor optical amplifier 5 is optically coupled to the tunable light source section 4 by a spatial coupling optical system (not shown). The laser light L1 output from the tunable light source section 4 is input to the semiconductor optical amplifier 5. The semiconductor optical amplifier 5 amplifies the laser light L1 using power supplied from the control device 3 and outputs it as laser light L2. The semiconductor optical amplifier 5 may be monolithically configured with the tunable light source section 4 on the base section 11.

[0037] The collimating lens 12 makes the laser light L2, which has been amplified and output by the semiconductor optical amplifier 5, into parallel light. The focusing lens 18 focuses the laser beam L2, which has been made into parallel light by the collimating lens 12, onto an optical fiber (not shown) and optically couples it.

[0038] The beam splitter 13 reflects a portion of the laser light L2 (laser light L7) that has been optically amplified and output by the semiconductor optical amplifier 5. The PD 14 detects the intensity of the laser light L7 and outputs an electrical signal corresponding to the detected intensity to the control device 3.

[0039] The plane light wave circuit 6 is optically coupled to the arm section 442 by a spatial coupling optical system (not shown). A portion of the laser light L3 generated by the laser oscillation in the tunable light source section 4, similar to the laser light L1, is input to the plane light wave circuit 6 via the arm section 442. The laser light L3 has the same wavelength as the laser light L1. As shown in Figure 1, the plane light wave circuit 6 comprises an optical branching section 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.

[0040] The optical branching unit 61 branches the input laser beam L3 into three laser beams L4 to L6. The optical waveguide 62 guides the laser beam L4 to the PD (Photo Diode) 71 in the photodetector 7, which will be described later. The optical waveguide 63 guides the laser beam L5 to the PD 72 in the photodetector 7, which will be described later. Furthermore, the optical waveguide 64 guides the laser beam L6 to the PD 73 in the photodetector 7, which will be described later.

[0041] Here, the ring-resonator type optical filters 63a and 64a each have periodic transmission characteristics with respect to the wavelength of the incident light, and selectively transmit the laser light L5 and L6 with a transmittance corresponding to these transmission characteristics. The laser light L5 and L6 that have passed through the ring-resonator type optical filters 63a and 64a are then input to PD72 and 73, respectively. In other words, the ring-resonator type optical filters 63a and 64a correspond to the optical filters according to the present invention. For the sake of explanation, the ring-resonator type optical filters 63a and 64a will be referred to as optical filters 63a and 64a below. Note that the optical filters 63a and 64a have transmission characteristics in which their phases differ from each other in the range of 1 / 3 to 1 / 5 of one period.

[0042] As shown in Figure 1, the photodetector 7 includes PDs 71 to 73. PD 71 receives laser light L4 (identical to laser light L1 output from the tunable light source 4) and outputs an electrical signal to the control device 3 corresponding to the intensity of the laser light L4. PD 72 receives laser light L5 that has passed through the optical filter 63a and outputs an electrical signal to the control device 3 corresponding to the intensity of the laser light L5. PD 73 receives laser light L6 that has passed through the optical filter 64a and outputs an electrical signal to the control device 3 corresponding to the intensity of the laser light L6. The electrical signals output from PDs 71 to 73 are then used by the control device 3 for wavelength control to set the laser light L1 output from the tunable light source 4 to the target wavelength. In this embodiment, for the sake of explanation, the electrical signal output from PD 72 is used for wavelength control, out of the electrical signals output from PDs 72 and 73, respectively. PD71 is an example of a first photodetector, and PD72 and PD73 are examples of second photodetectors.

[0043] The temperature sensor 8 is composed of, for example, a thermistor and detects the ambient temperature of the tunable light source unit 4 and the planar light wave circuit 6. The temperature controller 9 is composed of, for example, a TEC (Thermo Electric Cooler) including a Peltier element. The tunable light source unit 4, semiconductor optical amplifier 5, planar light wave circuit 6, and photodetector 7 are mounted on the mounting surface 91 of the temperature controller 9. The temperature controller 9, under the control of the control device 3, adjusts the temperature of each component 4 to 7 to a predetermined reference temperature according to the power supplied from the control device 3.

[0044] Next, the configuration of the control device 3 will be described. Figure 3 is a block diagram showing the configuration of the control device 3. The control device 3 is connected to a higher-level control device (not shown) equipped with a user interface, for example, and controls the operation of the tunable laser module 2 according to instructions from the user via the higher-level control device. As shown in Figure 3, the control device 3 comprises a control unit 31 and a storage unit 32.

[0045] The control unit 31 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part based on the program stored in the ROM. The functions of the control unit 31 are realized as functional units when the CPU reads and executes the program from the ROM. The control unit 31 may also be equipped with an MPU (Micro Processing Unit) instead of a CPU. Furthermore, the control unit 31 may be composed of integrated circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0046] When the CPU executes a program, the control unit 31 realizes the correction unit 311, the coarse adjustment control unit 312, the fine adjustment control unit 313, the temperature control unit 314, the intensity control unit 315, and the monitor value calculation unit 316. The coarse adjustment control unit 312 and the fine adjustment control unit 313 are examples of frequency control units that control the frequency (wavelength) of the laser beam L1.

[0047] The coarse adjustment control unit 312 acquires the target frequency of the laser beam L1 from the higher-level control unit and sets the power to be supplied to the coarse adjustment unit 42a in order to output the laser beam L1 at the acquired target frequency. The coarse adjustment control unit 312 also corrects the set power according to the coarse adjustment unit correction amount supplied by the correction unit 311 and supplies the corrected power to the coarse adjustment unit 42a.

[0048] The monitor value calculation unit 316 acquires the electrical signal output from PD71 of the plane light wave circuit 6 and the electrical signal output from PD72 of the plane light wave circuit 6, and calculates the ratio of the output value of the electrical signal output from PD71 to the output value of the electrical signal output from PD72 as the PD ratio.

[0049] The fine-tuning control unit 313 obtains the target frequency of the laser beam L1 from the higher-level control unit. Based on the obtained target frequency and the characteristic table TB1 stored in the storage unit 32, the fine-tuning control unit 313 sets the target PD ratio. Figure 4 shows an example of the characteristic table TB1 stored in the storage unit 32. In the characteristic table TB1, multiple frequencies f1 to fn are associated with the respective target PD ratios when the frequency of the laser beam L1 is set to those frequencies f1 to fn. Based on the difference between the PD ratio calculated by the monitor value calculation unit 316 and the target PD ratio, the fine-tuning control unit 313 sets the power to be supplied to the fine-tuning unit 42b so that the target PD ratio is achieved. The fine-tuning control unit 313 also corrects the target PD ratio according to the fine-tuning unit correction amount supplied from the correction unit 311.

[0050] The correction unit 311 sets a coarse adjustment correction amount to correct the power set by the coarse adjustment control unit 312, based on the correction tables TB2 to TB4 stored in the memory unit 32. The correction unit 311 also sets a fine adjustment correction amount to correct the target PD ratio set by the fine adjustment control unit 313, based on the correction tables TB2 to TB4 stored in the memory unit 32. The correction tables TB2 to TB4 will be described later. The correction unit 311 outputs the set coarse adjustment correction amount to the coarse adjustment control unit 312 and the set fine adjustment correction amount to the fine adjustment control unit 313.

[0051] The temperature control unit 314 controls the temperature controller 9 so that the temperature detected by the temperature sensor 8 becomes the reference temperature. The temperature controller 9 cools or heats the installation surface 91 under control from the temperature control unit 314 so that the temperature of each component 4 to 7 becomes the reference temperature. The control of the temperature controller 9 by the temperature control unit 314 is an example of a temperature control step.

[0052] The intensity control unit 315 obtains the target intensity of the laser beam L2 from the higher-level control unit. The intensity control unit 315 also controls the power (current) supplied to the semiconductor optical amplifier 5 based on the intensity of the laser beam L7 detected by the PD14, performing feedback control (constant output control) so that the laser beam L2 reaches the target intensity.

[0053] Next, regarding the control method of the tunable laser device 1 by the control device 3, we will first explain the control method when increasing the intensity of the laser light L2. Figure 5 is a flowchart showing the flow of processing performed by the control unit 31 when increasing the intensity of the laser light L2 output from the semiconductor optical amplifier 5. It should be assumed that the control unit 31 obtains the target frequency of the laser light L1 and the target intensity of the laser light L2 from the higher-level control device before executing the processing shown in Figure 5.

[0054] First, the control unit 31 starts supplying power corresponding to the target intensity to the semiconductor optical amplifier 5 (step S101). Step S101 is an example of an intensity control step. After step S101, the control unit 31 enables the correction process and enables the start-up process to increase the intensity of the laser light L2 (step S102).

[0055] Next, the control unit 31 initializes the on-counter to 0 (step S103). The on-counter is a counter that increases by 1 at a predetermined period. This predetermined period is, for example, several milliseconds to several tens of milliseconds. After step S102, the control unit 31 starts counting with the on-counter (step S104).

[0056] Figure 6 is a flowchart showing the process flow in which the control unit 31 controls the controlled object. The control process in Figure 6 is performed as a separate task from the process in Figure 5. In the process in Figure 6, the control unit 31 determines, for example, whether control of the controlled object is set to be enabled by the higher-level device (step S201). If the control unit 31 determines that control of the controlled object is disabled (step S201: NO), it repeats the determination in step S201.

[0057] If control of the controlled object is enabled by the higher-level device (step S201: YES), the control unit 31 determines whether the correction process is enabled (step S202). If the correction process is disabled (step S202: NO), the control unit 31 sets the coarse adjustment correction amount and the fine adjustment correction amount to 0 (step S204) and moves the process to step S205.

[0058] If the correction process is enabled (step S202: YES), the control unit 31 sets the coarse adjustment correction amount and the fine adjustment correction amount, which are examples of correction amounts (step S203). The control unit 31 determines that the correction process is enabled after it is enabled in step S102 until it is disabled in step S106, which will be described later.

[0059] In step S203, if the startup process is enabled, the control unit 31 sets the coarse adjustment correction amount and the fine adjustment correction amount based on the on-counter value and the correction table TB2. Specifically, the control unit 31 first calculates the heat generation Qsoa in the optical ON state of the semiconductor optical amplifier 5. The heat generation Qsoa can be expressed by the following equation (1) using the drive voltage Vsoa of the semiconductor optical amplifier 5, the current Isoa of the semiconductor optical amplifier 5, and the optical output Psoa, which is the target intensity of the laser light L2 output from the semiconductor optical amplifier 5. Qsoa = Isoa * Vsoa - Psoa ... (1)

[0060] Here, the drive voltage Vsoa of the semiconductor optical amplifier 5 can be expressed by the following equation (2) using the current Isoa, the series resistance Rd of the semiconductor optical amplifier 5, and the rise voltage Vth of the semiconductor optical amplifier 5. Vsoa = Rd * Isoa + Vth ... (2)

[0061] Substituting equation (2) into equation (1), the heat generated Qsoa from the semiconductor optical amplifier 5 can be expressed by equation (3). Qsoa=Isoa*(Rd*Isoa+Vth)-Psoa ···(3)

[0062] Figure 7 shows an example of the correction table TB2. In the correction table TB2, the coarse adjustment correction amount per unit heat generation during the startup process and the fine adjustment correction amount per unit heat generation are associated with the value of the on-counter. The control unit 31 uses the result of multiplying the coarse adjustment correction amount per unit heat generation, which is associated with the value of the on-counter at step S203 in the correction table TB2, by the heat generation Qsoa as the coarse adjustment correction amount. The control unit 31 also uses the result of multiplying the result of multiplying the fine adjustment correction amount per unit heat generation, which is associated with the value of the on-counter at step S203 in the correction table TB2, by the heat generation Qsoa as the fine adjustment correction amount.

[0063] Next, the control unit 31 performs error calculation (step S205). Here, the control unit 31 calculates the difference between the result of correcting the target value of the power supplied to the coarse adjustment unit 42a in order to output the laser beam L1 of the target frequency using the coarse adjustment unit correction amount calculated in step S203, and the power supplied to the coarse adjustment unit 42a that is being monitored by the coarse adjustment control unit 312, as the coarse adjustment unit error. In addition, the control unit 31 calculates the difference between the result of correcting the target PD ratio using the fine adjustment unit correction amount calculated in step S203, and the PD ratio calculated from the electrical signal output from the plane light wave circuit 6, as the fine adjustment unit error.

[0064] After step S205, the control unit 31 sets the control variables, which are the coarse adjustment control amount and the fine adjustment control amount (step S206). Specifically, the control unit 31 sets the control amount at which the coarse adjustment error becomes zero as the coarse adjustment control amount, and sets the control amount at which the fine adjustment error becomes zero as the fine adjustment control amount. Step S206 is an example of a correction step.

[0065] Next, the control unit 31 outputs the control amount set in step S206 (step S207). Here, the control unit 31 outputs the power of the set coarse adjustment amount to the coarse adjustment unit 42a and the power of the set fine adjustment amount to the fine adjustment unit 42b. Step S207 is an example of a frequency control step. After step S207, the control unit 31 moves the processing flow to step S201.

[0066] Returning to Figure 5, after step S104, the control unit 31 determines whether the frequency of the laser beam L1 is converging to the target frequency while the process in Figure 6 is being repeated (step S105). Specifically, the control unit 31 determines whether the PD ratio calculated by the fine-tuning control unit 313 falls within a predetermined range from the target PD ratio corresponding to the target frequency obtained from the higher-level device. If the PD ratio calculated by the fine-tuning control unit 313 does not fall within a predetermined range from the target PD ratio corresponding to the target frequency (step S105: NO), the control unit 31 repeats the process in step S105. Here, even while the process in step S105 is being repeated, the process in Figure 6 is repeatedly executed as a task separate from the process in Figure 5. That is, a correction process based on the on-counter and the correction table TB2 is performed.

[0067] If the PD ratio calculated by the fine-tuning control unit 313 falls within a predetermined range from the target PD ratio corresponding to the target frequency (step S105: YES), the control unit 31 determines that the frequency of the laser beam L1 has converged to the target frequency, and then disables the correction process and the startup process (step S106). Here, when the correction process is disabled, in the process shown in Figure 6, which is executed repeatedly, after the determination in step S202, the coarse adjustment correction amount and the fine adjustment correction amount are set to 0 in step S204. As a result, the control unit 31 sets the power supplied to the coarse adjustment unit 42a to output the laser beam L1 at the target frequency as the coarse adjustment control amount. The control unit 31 also sets the power supplied to the fine adjustment unit 42b to achieve the target PD ratio based on the difference calculated in step S204, and sets the set power as the fine adjustment control amount. In other words, the control unit 42a and the fine adjustment unit 42b are controlled without correction by the coarse adjustment correction amount and the fine adjustment correction amount. After step S107, the control unit 31 stops the on-counter count (step S108).

[0068] Figure 8A shows the time variation of the intensity of the laser beam L2 when the processes shown in Figures 5 and 6 are performed, Figure 8B shows the time variation of the frequency of the laser beam L1 when the processes shown in Figures 5 and 6 are performed, and Figure 8C shows the time variation of the power supplied to the coarse adjustment unit 42a when the processes shown in Figures 5 and 6 are performed. Furthermore, Figure 8D shows the time variation of the target PD ratio when the processes shown in Figures 5 and 6 are performed, Figure 8E shows the time variation of the temperature of the light source unit 41 when the processes shown in Figures 5 and 6 are performed, and Figure 8F shows the time variation of the temperature of the plane light wave circuit 6 when the processes shown in Figures 5 and 6 are performed. In Figures 8A-8F, t0 is the time when the on-counter counting starts.

[0069] According to the process shown in Figures 5 and 6, increasing the intensity of the laser beam L2 first causes the temperature of the light source unit 41 to rise. Subsequently, the control unit 31 controls the temperature controller 9 to cool the light source unit 41 back to its original temperature, and the temperature of the plane light wave circuit 6 decreases during this cooling process. Based on the correction table TB2, the control unit 31 corrects the control amount in response to this temperature rise, controlling the power supplied to the coarse adjustment unit 42a as shown in Figure 8C, and controlling the target PD ratio as shown in Figure 8D. This correction allows power to be supplied to the coarse adjustment unit 42a and the fine adjustment unit 42b to suppress frequency changes due to temperature changes in the light source unit 41 and the plane light wave circuit 6, thereby controlling the frequency. As a result, the intensity of the laser beam L2 can be increased rapidly without degrading the frequency accuracy of the laser beam L2.

[0070] Next, we will explain the control method for changing the frequency of the laser beam L1. Figure 9 is a flowchart showing the processing flow executed by the control unit 31 when changing the frequency of the laser beam L1 output from the light source unit 41. It is assumed that the control unit 31 obtains the target frequency of the changed laser beam L1 and the target intensity of the laser beam L2 from the higher-level control device before executing the processing shown in Figure 9.

[0071] First, the control unit 31 stops supplying power to the semiconductor optical amplifier 5 and changes the target frequency of the laser beam L1 to the target frequency obtained from the higher-level device (step S301). After step S301, the control unit 31 initializes the on-counter to 0 and initializes the off-counter to 0 (step S302). Next, the control unit 31 enables the correction process, enables the frequency change process to change the frequency of the laser beam L1, starts the coarse adjustment control unit, and stops the fine adjustment control unit (step S303). After step S303, the control unit 31 starts counting the off-counter (step S304).

[0072] When the correction process is enabled in step S303, the control unit 31 executes the processes from step S203 onwards in the process shown in Figure 6. If the off-counter count has started, the frequency change process has been enabled, the coarse adjustment control has started, and the fine adjustment control has stopped, the control unit 31 sets the coarse adjustment correction amount in step S203 based on the value of the off-counter and the correction table TB3.

[0073] Figure 10 shows an example of the correction table TB3. In the correction table TB3, the value of the off-counter is associated with the coarse adjustment correction amount and the fine adjustment correction amount during the frequency change process. In step S301, the control unit 31 calculates the heat generated before the target frequency change using equation (3), and sets the calculation result as the heat generated Qsoa_s. The control unit 31 sets the coarse adjustment correction amount as the result of multiplying the coarse adjustment correction amount, which is associated with the value of the off-counter at the time of step S203 in the correction table TB3, by the heat generated Qsoa_s. Then, in step S206, the control unit 31 corrects the coarse adjustment control amount based on the set coarse adjustment correction amount and corrects the fine adjustment control amount based on the set fine adjustment correction amount. In step S207, the control unit 31 outputs the corrected coarse adjustment control amount to the coarse adjustment unit 42a and the corrected fine adjustment control amount to the fine adjustment unit 42b.

[0074] Returning to Figure 9, after step S304, the control unit 31 determines whether the frequency of the laser beam L1 is converging under the control of the coarse adjustment unit 42a while the process in Figure 6 is being repeated (step S305). Specifically, the control unit 31 determines whether the PD ratio calculated by the fine adjustment control unit 313 falls within a predetermined range from the target PD ratio with the corrected coarse adjustment control amount. If the PD ratio calculated by the fine adjustment control unit 313 does not fall within a predetermined range from the target PD ratio with the corrected coarse adjustment control amount (step S305: NO), the control unit 31 repeats the process in step S305. Here, even while the process in step S305 is being repeated, the process in Figure 6 is repeatedly executed as a task separate from the process in Figure 9.

[0075] If the PD ratio calculated by the fine-tuning control unit 313 falls within a predetermined range from the target PD ratio with the corrected coarse-tuning control amount (step S305: YES), the control unit 31 starts fine-tuning control (step S306). If the off-counter count has started, the frequency change process has been set to active, the coarse-tuning control has started, and the fine-tuning control has started, in step S203 the control unit 31 sets the coarse-tuning correction amount and the fine-tuning correction amount based on the value of the off-counter and the correction table TB3.

[0076] The control unit 31 sets the coarse adjustment correction amount, which is associated with the off-counter value at step S203 in the correction table TB3, as the result of multiplying the heat generation Qsoa_s by the coarse adjustment correction amount. The control unit 31 also sets the fine adjustment correction amount, which is associated with the off-counter value at step S203 in the correction table TB3, as the result of multiplying the heat generation Qsoa_s by the fine adjustment correction amount. Then, in step S206, the control unit 31 corrects the coarse adjustment control amount based on the set coarse adjustment correction amount and corrects the fine adjustment control amount based on the set fine adjustment correction amount. In step S207, the control unit 31 outputs the set coarse adjustment control amount to the coarse adjustment unit 42a and the set fine adjustment control amount to the fine adjustment unit 42b.

[0077] Returning to Figure 9, after step S306, while the process in Figure 6 is being repeated, the control unit 31 determines whether the frequency of the laser beam L1 is converging under the control of the fine adjustment unit 42b. Specifically, the control unit 31 determines whether the PD ratio calculated by the fine adjustment control unit 313 falls within a predetermined range from the target PD ratio with the corrected fine adjustment control amount. If the PD ratio calculated by the fine adjustment control unit 313 does not fall within a predetermined range from the target PD ratio with the corrected fine adjustment control amount (step S307: NO), the control unit 31 repeats the process in step S307. Here, even while the process in step S307 is being repeated, the process in Figure 6 is repeatedly executed as a task separate from the process in Figure 9.

[0078] If the PD ratio calculated by the fine-tuning control unit 313 falls within a predetermined range from the target PD ratio with the corrected coarse-tuning control amount (step S307: YES), the control unit 31 starts supplying power to the semiconductor optical amplifier 5 corresponding to the target intensity (step S308). Step S308 is an example of an intensity control step. After step S308, the control unit 31 starts counting on the on-counter (step S309).

[0079] When the on-counter starts counting, the frequency change process is enabled, the coarse adjustment control is started, and the fine adjustment control is started, the control unit 31 sets the coarse adjustment correction amount and the fine adjustment correction amount based on the on-counter value, the off-counter value, the correction table TB3, and the correction table TB4.

[0080] Figure 11 shows an example of the correction table TB4. In the correction table TB4, the on-counter value is associated with the coarse adjustment correction amount and fine adjustment correction amount during frequency change processing. When setting the coarse adjustment correction amount and fine adjustment correction amount based on the off-counter, the control unit 31 uses the result of multiplying the coarse adjustment correction amount associated with the off-counter value in the correction table TB3 at step S203 by the heat generation Qsoa_s as the coarse adjustment correction amount based on the off-counter. Furthermore, the control unit 31 uses the result of multiplying the fine adjustment correction amount associated with the off-counter value in the correction table TB3 at step S203 by the heat generation Qsoa_s as the fine adjustment correction amount based on the off-counter.

[0081] In setting the coarse adjustment correction amount and fine adjustment correction amount based on the on-counter, the control unit 31 calculates the heat generated in the optical on state after frequency change using equation (3), and the calculation result is defined as heat generation Qsoa_g. The control unit 31 uses the result of multiplying the coarse adjustment correction amount, which is associated with the on-counter value at step S203 in the correction table TB4, by the heat generation Qsoa_g as the coarse adjustment correction amount based on the on-counter. Furthermore, the control unit 31 uses the result of multiplying the result of the fine adjustment correction amount, which is associated with the on-counter value at step S203 in the correction table TB4, by the heat generation Qsoa_g as the fine adjustment correction amount based on the on-counter.

[0082] The control unit 31 corrects the coarse adjustment control amount based on the sum of the coarse adjustment correction amount based on the off-counter and the coarse adjustment correction amount based on the on-counter, and corrects the fine adjustment control amount based on the sum of the fine adjustment correction amount based on the off-counter and the fine adjustment correction amount based on the on-counter. The control unit 31 then outputs the corrected coarse adjustment control amount to the coarse adjustment unit 42a and the corrected fine adjustment control amount to the fine adjustment unit 42b.

[0083] Returning to Figure 9, after step S311, the control unit 31 determines whether the frequency of the laser beam L1 is converging to the target frequency while the process in Figure 6 is being repeated (step S310). Specifically, the control unit 31 determines whether the PD ratio calculated by the fine-tuning control unit 313 is within a predetermined range from the target PD ratio corresponding to the target frequency. If the PD ratio calculated by the fine-tuning control unit 313 is not within a predetermined range from the target PD ratio corresponding to the target frequency (step S310: NO), the control unit 31 repeats the process in step S310. While the process in step S310 is being repeated, the process in Figure 6 is repeatedly executed as a separate task from the process in Figure 9.

[0084] If the PD ratio calculated by the fine-tuning control unit 313 falls within a predetermined range from the target PD ratio corresponding to the target frequency (step S310: YES), the control unit 31 determines that the frequency of the laser beam L1 has converged to the target frequency, and then disables the correction process and frequency change process (step S311). Here, when the correction process is disabled, in the process shown in Figure 6, which is executed repeatedly, after the determination in step S202, the coarse adjustment correction amount and the fine adjustment correction amount are set to 0 in step S204. As a result, the control unit 31 sets the power supplied to the coarse adjustment unit 42a to output the laser beam L1 at the target frequency as the coarse adjustment control amount. The control unit 31 also sets the power supplied to the fine adjustment unit 42b to achieve the target PD ratio based on the difference calculated in step S204, and sets the set power as the fine adjustment control amount. That is, the coarse adjustment unit 42a and the fine adjustment unit 42b are controlled without correction by the coarse adjustment correction amount and the fine adjustment correction amount. After step S313, the control unit 31 stops the counting of the on-counter and the off-counter (step S312).

[0085] Figure 12A shows the time change in the intensity of the laser beam L2 when the processes shown in Figures 6 and 9 are performed, Figure 12B shows the time change in the frequency of the laser beam L1 when the processes shown in Figures 6 and 9 are performed, and Figure 12C shows the time change in the power supplied to the coarse adjustment unit 42a when the processes shown in Figures 6 and 9 are performed. Furthermore, Figure 12D shows the time change in the target PD ratio when the processes shown in Figures 6 and 9 are performed, Figure 12E shows the time change in the temperature of the light source unit 41 when the processes shown in Figures 6 and 9 are performed, and Figure 12F shows the time change in the temperature of the plane light wave circuit 6 when the processes shown in Figures 6 and 9 are performed. In Figures 12A-12F, t1 is the time when the off-counter starts counting, and t2 is the time when the on-counter starts counting.

[0086] According to the process shown in Figures 6 and 9, when the frequency of the laser beam L1 is changed, the intensity of the laser beam L2 is reduced, and first the temperature of the light source unit 41 decreases. Subsequently, the control unit 31 controls the temperature controller 9 to return the temperature of the light source unit 41 to its original temperature, and as the temperature controller 9 heats up, the temperature of the plane light wave circuit 6 rises. Based on the correction table TB3, the control unit 31 corrects the control amount in response to this temperature decrease, controls the power supplied to the coarse adjustment unit 42a as shown in Figure 12C, and controls the target PD ratio as shown in Figure 12D. This correction ensures that power is supplied to the coarse adjustment unit 42a and the fine adjustment unit 42b in a way that suppresses the frequency change due to the temperature change of the light source unit 41 and the plane light wave circuit 6, thereby suppressing the frequency change and allowing the laser beam L1 to be focused to the target frequency.

[0087] According to the process shown in Figures 6 and 9, increasing the intensity of the laser light L2 in step S308 first causes the temperature of the light source unit 41 to rise. Subsequently, the control unit 31 controls the temperature controller 9 to return the temperature of the light source unit 41 to its original temperature, and as the temperature controller 9 cools, the temperature of the plane light wave circuit 6 decreases. Based on the correction tables TB3 and TB4, the control unit 31 corrects the control amount in response to this temperature rise, controls the power supplied to the coarse adjustment unit 42a as shown in Figure 12C, and controls the target PD ratio as shown in Figure 12D. This correction allows power to be supplied to the coarse adjustment unit 42a and the fine adjustment unit 42b to suppress frequency changes due to temperature changes in the light source unit 41 and the plane light wave circuit 6, thereby controlling the frequency. As a result, the intensity of the laser light L2 can be increased rapidly without degrading the frequency accuracy of the laser light.

[0088] In the embodiment described above, the tunable laser device 1 is configured to include a two-branch section 441, two arm sections 442 and 443, and a ring-shaped waveguide 444, but it is not limited to this configuration. Figure 13 is a schematic diagram of a tunable laser device 1A according to a modified example of the present invention. The tunable laser module 2A includes a diffraction grating section 431c, a phase adjustment section 445a, optical demultiplexers 201 and 202, and an etalon filter 210. In the modified example, components that are the same as those in the embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0089] The diffraction grating section 431c is composed of a DBR type sampling diffraction grating made of InGaAsP and InP. A microheater 421a is positioned along the diffraction grating section 431c. The control device 3 can change the characteristics of the reflection spectrum by heating the waveguide of the diffraction grating section 431c by controlling the microheater 421a, and more specifically, can shift the reflection peak in the wavelength axis direction.

[0090] The microheater 421a generates heat in response to the power supplied from the control device 3, heating the diffraction grating section 431c. Furthermore, by controlling the power supplied to the microheater 421a by the control device 3, the temperature of the diffraction grating section 431c changes, and its refractive index changes.

[0091] The phase adjustment unit 445a is used to adjust the resonator length of the optical resonator C1 by changing the refractive index. By adjusting the resonator length of the optical resonator C1, the wavelength of the resonator mode shifts in the wavelength axis direction. The phase adjustment unit 445a has a passive waveguide. The phase adjustment unit 445a is provided with a microheater 423. The microheater 423 changes the temperature of the phase adjustment unit 445a using power supplied from the control device 3, and changes the refractive index by utilizing the physical properties of the microheater.

[0092] The optical demultiplexer 201 transmits the laser light L2 output from the semiconductor optical amplifier 5 to the collimating lens 12 and reflects the remaining laser light L2 to the optical demultiplexer 202. The optical demultiplexer 201 is constructed using a beam splitter or the like. The optical demultiplexer 202 transmits a portion of the laser light input from the optical demultiplexer 201 to the PD 71, while reflecting the remaining laser light to the etalon filter 210. The optical demultiplexer 202 is constructed using a beam splitter or the like.

[0093] The etalon filter 210 has periodic transmission characteristics with respect to the frequency of light. The etalon filter 210 is mounted on a temperature controller 9, and its temperature can be changed by the temperature controller 9. The PD72 receives the laser light that has passed through the etalon filter 210 and outputs a current signal to the control device 3 corresponding to the intensity of the received laser light.

[0094] In the tunable laser device 1A, the control device 3 controls the microheaters 421, 421a, and 423, similar to the embodiment, thereby enabling a rapid increase in the intensity of the laser light L2 without degrading the frequency accuracy of the laser light L2. [Explanation of Symbols]

[0095] 1. Wavelength-tunable laser device 2-wavelength tunable laser module 3. Control device 4. Wavelength-tunable light source section 5. Semiconductor Optical Amplifier 6 Planar light wave circuit 7. Light detection unit 8. Temperature sensor 9 Temperature controller 12 Collimating lenses 13 Beam Splitter 14 PD 31 Control Unit 32 Storage section 41 Light source section 42 Frequency adjustment section 42a Coarse adjustment part 42b Fine adjustment part 43. First Waveguide Section 44 Second Waveguide Section 311 Correction Unit 312 Coarse adjustment control unit 313 Fine adjustment control section 314 Temperature Control Unit 315 Strength Control Unit 421-423 Microheater 431 Waveguide section 431a Gain section 431b Diffraction grating section 432 Semiconductor stacked section 433 p side electrode 441 2-way branch 441a Multimode Interferometric Waveguide 442, 443 Arm section 444 Ring-shaped waveguide 445 Phase adjustment section C1 optical resonator L1~L7 Laser light M1 Reflective Mirror

Claims

1. A variable light source unit that varies the frequency of the output laser light, A frequency adjustment unit for adjusting the frequency of the laser light, A semiconductor optical amplifier that amplifies the laser light output from the variable light source unit, A temperature sensor that detects the temperature near the variable light source unit, A temperature controller for adjusting the temperature of the variable light source unit, The system includes a control device for controlling the operation of the variable light source unit, The control device is A temperature control unit that controls the temperature controller according to the temperature detected by the temperature sensor, A frequency control unit controls the frequency of the variable light source within a predetermined range by supplying a control amount corresponding to the target frequency of the laser light to the frequency adjustment unit, An intensity control unit controls the current supplied to the semiconductor optical amplifier to control the intensity of the laser light output from the semiconductor optical amplifier, A correction unit that, when increasing the intensity of the laser light output from the semiconductor optical amplifier, corrects the control amount according to the elapsed time since the start of current control to the semiconductor optical amplifier, A laser device equipped with the following features.

2. The frequency adjustment unit is A coarse adjustment unit adjusts the frequency of the laser beam by supplying a coarse adjustment control amount, A fine-tuning unit that adjusts the phase of the laser beam by supplying a fine-tuning control amount, It has, The frequency control unit, A rough adjustment control unit that supplies a rough adjustment control amount corresponding to the target frequency to the rough adjustment unit, A fine-tuning control unit that supplies a fine-tuning control amount corresponding to the target frequency to the fine-tuning unit, The laser apparatus according to claim 1, comprising:

3. A first photodetector that outputs the intensity of the laser light output from the variable light source unit, An optical filter having periodic transmission characteristics with respect to the wavelength of incident light, which transmits laser light output from the variable light source unit with a transmittance corresponding to said transmission characteristics, A second photodetector that outputs the intensity of the laser light transmitted through the aforementioned optical filter, The system includes a monitor value calculation unit that calculates a monitor value corresponding to the frequency of the laser light based on the intensity of the laser light acquired by the first and second light-receiving elements, respectively. The fine-tuning control unit supplies a fine-tuning control amount to the fine-tuning unit that corresponds to the difference between the monitor value and the target value corresponding to the target frequency. The laser apparatus according to claim 2.

4. The strength control unit, When changing the frequency of the laser light, the current supply to the semiconductor optical amplifier is stopped. After the frequency of the laser light output from the variable light source is controlled to a predetermined range, the current supply to the semiconductor optical amplifier is resumed. The correction unit, The control amount is corrected according to the elapsed time since the current supply to the semiconductor optical amplifier was stopped and the elapsed time since the current supply to the semiconductor optical amplifier was restarted. The laser apparatus according to claim 1.

5. The variable light source unit utilizes the Vernier effect to make the frequency of the laser light variable. The laser apparatus according to claim 1.

6. A variable light source unit that varies the frequency of the output laser light, A frequency adjustment unit for adjusting the frequency of the laser light, A semiconductor optical amplifier that amplifies the laser light output from the variable light source unit, A temperature sensor that detects the temperature near the variable light source unit, A temperature controller for adjusting the temperature of the variable light source unit, A frequency control method performed by a control device for a laser apparatus comprising a control device for controlling the operation of the variable light source unit, A temperature control step in which the temperature controller is controlled according to the temperature detected by the temperature sensor, A frequency control step of controlling the frequency of the variable light source within a predetermined range by supplying a control amount corresponding to the target frequency of the laser light to the frequency adjustment unit, An intensity control step of controlling the current supplied to the semiconductor optical amplifier to control the intensity of the laser light output from the semiconductor optical amplifier, When increasing the intensity of the laser light output from the semiconductor optical amplifier, a correction step is performed to correct the control amount according to the elapsed time since the start of current control to the semiconductor optical amplifier, A frequency control method comprising the following:

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