Laser device and control method

Abstract

To provide a laser device in which an increase in size is suppressed.SOLUTION: A laser device includes: four wavelength variable light sources outputting first to fourth laser beams; a first filter part, the operation of which is switched between a first operation state where the first and second laser beams are output and a second operation where the first and second laser beams are not output when the first and second laser beams are input; a second filter part, the operation of which is switched between a third operation state where the third and fourth laser beams are output and a fourth operation state where the third and fourth laser beams are not output when the third and fourth laser beams are input; a third filter part which outputs the first and second laser beams when these laser beams are input from the first filter part and outputs the third and fourth laser beams when these laser beams are input from the second filter part; and a filter control part which achieves one of a fifth operation sate achieving the first and fourth operation states and a sixth operation state achieving the second and third operation states. An FSR of the first to third filter parts is 2 / (2n+1) times the laser beam frequency spacing when n is a non-negative integer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a technology for controlling the frequency of a laser beam in a wavelength-tunable light source capable of changing the frequency of the output laser beam by using a frequency filter having transmission characteristics in which the transmittance changes periodically with respect to the frequency of the input light. The technology for controlling the frequency of a laser beam to a desired frequency is also called frequency lock control, and is realized by feedback control based on the detection result of the power of the laser beam transmitted through the frequency filter. Specifically, the detection result of the power of the laser beam transmitted through the frequency filter is associated with the frequency of the laser beam by a frequency discrimination curve formed by the transmittance spectrum of the frequency filter, thereby detecting and controlling the frequency of the laser beam. Therefore, this type of wavelength-tunable light source is provided with a frequency monitor unit for detecting the frequency of the laser beam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-125587 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, as a light source for multicarrier transmission, there is a demand for a laser device that outputs multiple laser beams with different frequencies. In this type of laser device, it is desirable that the relative frequency interval between the laser beams be highly accurate. To maintain the frequency interval with high accuracy, it is preferable to monitor and control each frequency of the multiple laser beams using a common frequency monitor unit. This is because, when the frequencies of the multiple laser beams are monitored and controlled by individual frequency monitor units, if the frequency characteristics of the frequency monitor units change over time or due to external factors, the change may occur independently for each frequency monitor unit.

[0005] However, in a laser device equipped with multiple laser light sources that output laser light beams with different frequencies, attempting to monitor the frequencies of the multiple laser beams using a common frequency monitor can result in the following problems: The control unit that performs frequency locking control can only control one laser beam at a time, so the laser beams input to the frequency monitor at a time must be limited. In this case, a possible method would be to provide an optical switch for each laser element and use the optical switch to limit the laser beams input to the frequency monitor. However, this method requires as many optical switches as there are laser light sources, which could result in an increase in the size of the laser device and an increase in current consumption.

[0006] The present invention has been made in view of the above, and has an object to provide a laser device that is prevented from becoming large in size and a control method thereof. [Means for solving the problem]

[0007] One aspect of the present invention is a wavelength-tunable light source including four tunable light sources that output four laser beams having equal frequency intervals, the four laser beams being first, second, third, and fourth laser beams in order of decreasing frequency; a first input port, a second input port, a first output port, and a first operation switching unit, wherein when the first laser beam is input to the first input port and the second laser beam is input to the second input port, the first operation switching unit operates to output the first laser beam and the second laser beam from the first output port; and a second operating state in which the first laser light and the second laser light are not output to the outside, a third input port, a fourth input port, a second output port, and a second operation switching unit, wherein when the third laser light is input to the third input port and the fourth laser light is input to the fourth input port, the second operation switching unit operates to switch between a third operating state in which the third laser light and the fourth laser light are output from the second output port, and a fourth operating state in which the third laser light and the fourth laser light are not output to the outside. a third filter unit having a fifth input port, a sixth input port, a third output port, and a fourth output port, and when the first laser light and the second laser light are input to the first output port of the first filter unit, outputs the first laser light from one of the third output port and the fourth output port and outputs the second laser light from the other of the third output port and the fourth output port, and when the third laser light and the fourth laser light are input to the second output port of the second filter unit, outputs the third laser light from one of the third output port and the fourth output port and outputs the fourth laser light from the other of the third output port and the fourth output port; and a filter control unit that controls operations of the first operation switching unit and the second operation switching unit to achieve either a fifth operating state in which the first operation switching unit achieves the first operating state and the second operation switching unit achieves the fourth operating state, or a sixth operating state in which the first operation switching unit achieves the second operating state and the second operation switching unit achieves the third operating state,The FSR of the first filter unit, the second filter unit, and the third filter unit is a laser device that is 2 / (2n+1) times the frequency interval, where n is a non-negative integer.

[0008] At least one of the first filter section, the second filter section, and the third filter section may be a Mach-Zehnder interferometer.

[0009] At least one of the first operation switching unit and the second operation switching unit, which are the Mach-Zehnder interferometer, may be a heater provided in an arm of the Mach-Zehnder interferometer.

[0010] At least one of the first filter section, the second filter section, and the third filter section may be a ring resonator.

[0011] At least one of the first operation switching unit and the second operation switching unit, which are the ring resonator, may be a heater provided on a ring portion of the ring resonator.

[0012] The laser device may further include a monitor that monitors the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam output from the third filter.

[0013] The laser device may further include a frequency control unit that feedback-controls the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light based on the results monitored by the monitor unit.

[0014] The frequency control unit may provide a dither signal to the four wavelength-tunable light sources to oscillate the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light, and based on a result monitored by the monitor unit under the oscillation, may bring the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light closer to a peak frequency of a transmission spectrum of the third filter unit.

[0015] One aspect of the present invention is a method for controlling a laser device, the laser device having four wavelength-tunable light sources that output four laser beams having equal frequency intervals, the four laser beams being first, second, third, and fourth laser beams in order of decreasing frequency, a first input port, a second input port, a first output port, and a first operation switching unit, wherein when the first laser beam is input to the first input port and the second laser beam is input to the second input port, the first operation switching unit operates to output the first laser beam from the first output port. the third laser light and the fourth laser light are input to the fourth input port, and when the third laser light is input to the third input port and the fourth laser light is input to the fourth input port, the third operating state is output from the second output port by the action of the second operating switcher; a fourth operating state in which the first laser light and the second laser light are not output to the outside, a fifth input port, a sixth input port, a third output port, and a fourth output port, and when the first laser light and the second laser light are input to the first output port of the first filter unit, the first laser light is output from one of the third output port and the fourth output port, and the second laser light is output from the other of the third output port and the fourth output port, and the third laser light and the second laser light are output from the second output port of the second filter unit. a third filter unit that, when the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam are input, outputs the third laser beam from one of the third output port and the fourth output port, and outputs the fourth laser beam from the other of the third output port and the fourth output port; and a monitor unit that monitors the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam output from the third filter unit, wherein FSRs of the first filter unit, the second filter unit, and the third filter unit are 2 / (2n+1) times the frequency interval, where n is a non-negative integer,and controlling operations of the first operation switching unit and the second operation switching unit to realize one of a fifth operation state in which the first operation switching unit realizes the first operation state and the second operation switching unit realizes operation in the fourth operation state, and a sixth operation state in which the first operation switching unit realizes the second operation state and the second operation switching unit realizes the third operation state, and applying a dither signal to the four wavelength-tunable light sources to oscillate the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light, and feedback-controlling the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light based on the results monitored by the monitor unit under the oscillation. [Effects of the Invention]

[0016] According to the present invention, it is possible to realize a laser device and a control method thereof that are suppressed from becoming large in size. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a laser device according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of the variable wavelength light source shown in FIG. [Figure 3] FIG. 3 is a diagram showing a schematic configuration and an operating state of the optical filter shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the transmission spectra of the first to third filter sections in FIG. [Figure 5] FIG. 5 is a diagram showing a schematic configuration and an operating state of the optical filter shown in FIG. [Figure 6] FIG. 6 is a schematic diagram showing the transmission spectra of the first to third filter sections in FIG. [Figure 7] FIG. 7 is an explanatory diagram of an example of monitoring and feedback control of the frequency of laser light. [Figure 8] FIG. 8 is a flow diagram of an example of control executed by the control unit. [Figure 9] FIG. 9 is a diagram showing a schematic configuration and an operating state of an optical filter according to a modified example. [Figure 10] FIG. 10 is a diagram showing a schematic configuration and an operating state of an optical filter according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Furthermore, in the description of the drawings, identical parts are appropriately designated by the same reference numerals, and duplicate explanations are appropriately omitted. Furthermore, the drawings are schematic, and the dimensional relationships and ratios of each element may differ from the actual situation. Furthermore, the drawings may include parts whose dimensional relationships and ratios differ from each other.

[0019] (Embodiment) [Laser device configuration] Fig. 1 is a schematic diagram of a laser device according to an embodiment. Fig. 2 is a schematic diagram of the tunable light source shown in Fig. 1. The laser device 100 includes four tunable light sources 11 to 14, an optical filter 20, a monitor unit 30, a control unit 40, a DA conversion unit 50, and a thermoelectric element (TEC) 60. Hereinafter, the tunable light sources 11 to 14 may be referred to as tunable light sources #1 to #4.

[0020] The wavelength-variable light source 11 outputs laser lights L11 and L12 under the control of the control unit 40. The laser lights L11 and L12 have the same frequency. Similarly, the wavelength-variable light source 12 outputs laser lights L21 and L22 under the control of the control unit 40. The laser lights L21 and L22 have the same frequency. Similarly, the wavelength-variable light source 13 outputs laser lights L31 and L32 under the control of the control unit 40. The laser lights L31 and L32 have the same frequency. Similarly, the wavelength-variable light source 14 outputs laser lights L41 and L42 under the control of the control unit 40. The laser lights L41 and L42 have the same frequency. Note that the laser lights L12 to L42 are output to the outside of the laser device 100 and are supplied to, for example, an optical communication system.

[0021] If the frequencies of the laser lights L11, L21, L31, and L41 are f1, f2, f3, and f4, then f1 < f2 < f3 < f4, and f1 - f2 = f2 - f3 = f3 - f4 = Δf. That is, the laser lights L11, L21, L31, and L41 are four laser lights with equal frequency intervals between each other, and are an example of four laser lights that are the first laser light, the second laser light, the third laser light, and the fourth laser light from the lower frequency side.

[0022] The wavelength-variable light source 11 is a wavelength-variable light source that utilizes the Vernier effect and has a configuration as disclosed in Patent Document 1. Specifically, as shown in FIG. 2, the wavelength-variable light source 11 includes a DBR (Distributed Bragg Reflector) element 11a, a Gain section 11b, a Phase element 11c including a passive waveguide, a Ring element 11d, a heater 11e provided in the DBR element 11a, a heater 11f provided in the Phase element 11c, and a heater 11g provided in the Ring element 11d. Further, the wavelength-variable light source 11 is mounted on the TEC60.

[0023] The DBR element 11a and the ring element 11d form a laser resonator. The DBR element 11a and the ring element 11d have comb-like reflection peaks with periodic frequency intervals. The DBR element 11a and the ring element 11d have different periods, allowing for coarse tuning of the frequency of the laser light L11 using a vernier method. The heater 11e heats the DBR element 11a, thereby changing the refractive index and shifting the comb-like reflection peak in the frequency axis direction. Similarly, the heater 11g heats the ring element 11d, thereby changing the refractive index and shifting the comb-like reflection peak in the frequency axis direction. The heating of the heaters 11e and 11g is controlled by the control unit 40.

[0024] The gain section 11b is disposed between the DBR element 11a and the ring element 11d, and emits light and exhibits an optical amplification effect when a current is supplied from the control section 40. As a result, laser oscillation occurs.

[0025] The phase element 11c is disposed between the DBR element 11a and the ring element 11d. The heater 11f heats the phase element 11c, thereby changing the refractive index and adjusting the optical length of the laser resonator. By adjusting the optical length of the laser resonator, the frequency of the resonator mode can be shifted in the frequency axis direction while being finely adjusted. The heating of the heater 11f is controlled by the control unit 40.

[0026] The wavelength-tunable light source 11 oscillates at a frequency where one of the comb-shaped reflection peaks of the DBR element 11a, one of the comb-shaped reflection peaks of the Ring element 11d, and the frequency of the resonator mode overlap. Furthermore, by changing these three overlapping frequencies, the frequencies of the laser beams L11 and L12 can be changed.

[0027] The configuration of the tunable light sources 12, 13, and 14 may be the same as that of the tunable light source 11. The tunable light sources 12, 13, and 14 are also individually mounted on TECs. The TECs are provided to stabilize the temperatures of the tunable light sources.

[0028] Returning to FIG. 1, the optical filter 20 receives the laser beams L11 to L41 and selectively outputs the laser beams L11 and L21 or the laser beams L31 and L41.

[0029] 3 is a diagram showing a schematic configuration and operating state of the optical filter 20. The optical filter 20 includes a first filter section 21, a second filter section 22, and a third filter section 23. In this embodiment, the first filter section 21, the second filter section 22, and the third filter section 23 are all Mach-Zehnder interferometers.

[0030] The first filter section 21 has a first input port P1, a second input port P2, and a first output port P3. A heater 21a serving as a first operation switching section is provided on one arm of the Mach-Zehnder interferometer of the first filter section 21. Note that an "x" in the figure indicates a terminated port.

[0031] The second filter section 22 has a third input port P4, a fourth input port P5, and a second output port P6. A heater 22a serving as a second operation switching section is provided on one arm of the Mach-Zehnder interferometer of the second filter section 22. Note that an "x" in the figure indicates a terminated port.

[0032] The third filter section 23 has a fifth input port P7, a sixth input port P8, a third output port P9, and a fourth output port P10. The fifth input port P7 is connected to the first output port P3 of the first filter section 21. The sixth input port P8 is connected to the second output port P6 of the second filter section 22. A heater 23a is provided on one arm of the Mach-Zehnder interferometer of the third filter section 23. In the drawing, white circles indicate the connection points of the ports.

[0033] The operation of the optical filter 20 will be described in detail later.

[0034] The monitor unit 30 monitors the laser beams L11 to L41 output from the optical filter 20. Specifically, the monitor unit 30 includes photodiodes (PD) 31 and 32 and analog-to-digital converters (ADC) 33 and 34. The photodiode (PD) 31 receives the laser beam L11 or L31 from the optical filter 20 and outputs an analog signal (current signal) corresponding to the power of the received laser beam. The ADC 33 receives the analog signal from the PD 31, converts it to a digital signal, and outputs it. The PD 32 receives the laser beam L21 or L41 from the optical filter 20 and outputs an analog signal (current signal) corresponding to the power of the received laser beam. The ADC 34 receives the analog signal from the PD 32, converts it to a digital signal, and outputs it.

[0035] The control unit 40 functions as a filter control unit (to be described later) and as a frequency control unit that feedback controls the frequencies of the laser beams L11 to L41 based on the results monitored by the monitor unit 30. The control unit 40 also controls the operation of the TEC 60 and other TECs.

[0036] The control unit 40 includes, as hardware, a calculation unit 41 and a storage unit 42. The calculation unit 41 includes a processor such as a CPU (Central Processing Unit) and performs various calculation processes for control. The storage unit 42 includes a storage unit such as a ROM that stores various programs and data used by the calculation unit to perform calculation processes. The storage unit 42 also includes a storage unit such as a RAM that is used as a workspace when the calculation unit performs calculation processes and for storing the results of the calculation processes of the calculation unit. The calculation unit 41 and the storage unit 42 are realized, for example, by a microcontroller.

[0037] Furthermore, the control unit 40 includes, as hardware, digital / analog converter (DAC) groups 43 to 46, and further includes components necessary for the control unit 40, such as a DC power supply and an input / output interface.

[0038] Each of the DAC groups 43 to 46 includes a plurality of DACs. The control unit 40 supplies current to the gain unit 11b, heaters 11e to 11g, and TEC 60 of the wavelength-tunable light source 11 through the DAC group 43. The control unit 40 also supplies current to the gain unit, heater, and TEC of the wavelength-tunable light source 12 through the DAC group 44. The control unit 40 also supplies current to the gain unit, heater, and TEC of the wavelength-tunable light source 13 through the DAC group 45. The control unit 40 also supplies current to the gain unit, heater, and TEC of the wavelength-tunable light source 14 through the DAC group 46.

[0039] Furthermore, the control unit 40 outputs a digital signal to the DA conversion unit 50. The DA conversion unit 50 includes DACs 51 to 53. The DACs 51 to 53 convert the input digital signal into an analog signal (current signal), respectively, and output the analog signal to the heaters 21 a to 23 a. That is, the control unit 40 supplies current to the heaters 21 a to 23 a via the DACs 51 to 53.

[0040] [Optical filter operation] Next, the operation of the optical filter 20 will be described with reference to FIGS. 3 to 6. First, the operation of the first filter section 21 switches between a first operating state and a second operating state. As shown in FIG. 3, the first operating state is a state in which, when laser light L11 is input to the first input port P1 of the first filter section 21 and laser light L21 is input to the second input port P2, laser light L11 and L12 are output from the first output port P3 as indicated by arrows R1 and R2 by the action of the heater 21a. Also, as shown in FIG. 5, the second operating state is a state in which, when laser light L11 is input to the first input port P1 of the first filter section 21 and laser light L21 is input to the second input port P2, laser light L11 and L12 are output to the terminal end as indicated by arrows R5 and R6 by the action of the heater 21a and are not output to the outside. The first operating state and the second operating state are switched depending on the degree to which the heater 21a heats the arm portion of the first filter unit 21 to change the refractive index of the waveguide that constitutes the arm portion. The switching between the first operating state and the second operating state is performed by the control unit 40 via the DA conversion unit 50.

[0041] The second filter unit 22 switches between a third operating state and a fourth operating state. As shown in Fig. 5, the third operating state is a state in which, when laser light L31 is input to the third input port P4 of the second filter unit 22 and laser light L41 is input to the fourth input port P5, the heater 22a operates to output the laser light L31 and L41 from the second output port P6 as indicated by arrows R7 and R8. As shown in Fig. 3, the fourth operating state is a state in which, when laser light L31 is input to the third input port P4 of the second filter unit 22 and laser light L41 is input to the fourth input port P5, the heater 22a operates to output the laser light L31 and L41 to the terminal end as indicated by arrows R3 and R4, but not to the outside. The third operating state and the fourth operating state are switched depending on the degree to which the heater 22a heats the arm portion of the second filter section 22 to change the refractive index of the waveguide that constitutes the arm portion. The switching between the third operating state and the fourth operating state is performed by the control section 40 via the DA conversion section 50.

[0042] Here, the control unit 40, which is a filter control unit, controls the operation of the heater 21a and the heater 22a to achieve either a fifth operating state in which the heater 21a as the first operation switching unit achieves the first operating state and the heater 22a as the second operation switching unit achieves the fourth operating state, or a sixth operating state in which the heater 21a achieves the second operating state and the heater 22a achieves the third operating state.

[0043] The fifth operating state is the state shown in Fig. 3. In the fifth operating state, in the third filter section 23, laser beams L11 and L21 are input from the first output port P3 of the first filter section 21 to the fifth input port P7. In this case, as indicated by arrows R1 and R2, the third filter section 23 outputs laser beam L11 from the third output port P9, which is one of the third output port P9 and the fourth output port P10, and outputs laser beam L21 from the other, the fourth output port P10.

[0044] The fifth operating state will now be described with reference to the transmission spectra of the first to third filter sections 21, 22, and 23 shown in FIG. 4. The FSR (Free Spectral Range) of the first to third filter sections 21, 22, and 23 is 2 / (2n+1) times the above-mentioned frequency interval Δf, where n is a non-negative integer. Note that in this embodiment, n is 0. As a result, in the fifth operating state, the transmission characteristics of the first filter section 21 from the first input port P1 to the first output port P3, as indicated by the curve C11, are characteristics that transmit the laser beam L11. Furthermore, the transmission characteristics of the first filter section 21 from the second input port P2 to the first output port P3, as indicated by the curve C21, are characteristics that transmit the laser beam L21. Furthermore, the transmission characteristics of the second filter section 22 from the third input port P4 to the second output port P6, as indicated by the curve C31, are characteristics that do not transmit the laser beam L31. Furthermore, the transmission characteristics of the second filter section 22 from the fourth input port P5 to the second output port P6, as indicated by a curve C41, are characteristics that do not transmit laser light L41. Furthermore, the transmission characteristics of the third filter section 23 from the fifth input port P7 to the third output port P9, as indicated by a curve C51, are characteristics that transmit laser light L11. Furthermore, the transmission characteristics of the third filter section 23 from the sixth input port P8 to the fourth output port P10, as indicated by a curve C61, are characteristics that transmit laser light L21. This achieves a fifth operating state.

[0045] 5. In the sixth operating state, the laser beams L31 and L41 are input from the second output port P6 of the second filter section 22 to the sixth input port P8 of the third filter section 23. In this case, as indicated by arrows R7 and R8, the third filter section 23 outputs the laser beam L31 from the third output port P9, which is one of the third output port P9 and the fourth output port P10, and outputs the laser beam L41 from the other, the fourth output port P10.

[0046] Here, the sixth operating state will be described with reference to the transmission spectra of the first to third filter sections 21, 22, and 23 shown in FIG. 6. In the sixth operating state, the transmission characteristics of the first filter section 21 from the first input port P1 to the first output port P3, as indicated by a curve C12, are such that the laser beam L11 is not transmitted. Furthermore, the transmission characteristics of the first filter section 21 from the second input port P2 to the first output port P3, as indicated by a curve C22, are such that the laser beam L21 is not transmitted. Furthermore, the transmission characteristics of the second filter section 22 from the third input port P4 to the second output port P6, as indicated by a curve C32, are such that the laser beam L31 is transmitted. Furthermore, the transmission characteristics of the second filter section 22 from the fourth input port P5 to the second output port P6, as indicated by a curve C42, are such that the laser beam L41 is transmitted. Furthermore, the transmission characteristics of the third filter section 23 from the fifth input port P7 to the third output port P9, as indicated by a curve C52, are characteristics that transmit laser light L31. Furthermore, the transmission characteristics of the third filter section 23 from the sixth input port P8 to the fourth output port P10, as indicated by a curve C62, are characteristics that transmit laser light L41. This achieves a sixth operating state.

[0047] As described above, the control unit 40 controls the operation of the heaters 21a and 22a to realize either the fifth operating state or the sixth operating state, thereby allowing two laser beams to be selectively output from the optical filter 20. This allows the laser device 100 to selectively output and monitor the frequencies of four laser beams L11 to L41 using one optical filter 20. According to such a laser device 100, the number of optical filters 20 is small relative to the number of wavelength-tunable light sources 11 to 14, and therefore, the size of the laser device 100 is prevented from increasing, and an increase in current consumption can also be prevented.

[0048] The heater 23a has a function of adjusting the inter-port transmission characteristics of the third filter section 23. That is, the heater 23a adjusts the inter-port transmission characteristics by adjusting the degree to which the refractive index of the waveguide constituting the arm section is changed by heating the arm section of the third filter section 23. Such adjustment is performed, for example, to correct the temperature characteristics of the third filter section 23, and is executed by the control section 40 via the DA conversion section 50.

[0049] [Feedback control by the control unit] Next, an example of a specific method for the control unit 40 to monitor and feedback control the frequencies of the laser beams L11 to L41 will be described.

[0050] 7 is an explanatory diagram of an example of monitoring and feedback control of the frequency of laser light. Curve C5 shows the frequency characteristics of an analog signal (hereinafter sometimes referred to as PD current) output from one of PDs 31 and 32 when one of laser lights L11 to L41 is input to monitor unit 30. The PD current changes with the same period as the FSR of first to third filter units 21 to 23, depending on the inter-port transmission characteristics of the optical filter.

[0051] When monitoring and feedback control of the frequencies of the laser beams L11 to L41 is performed, the control unit 40 oscillates the frequencies of the laser beams L11 to L41 by providing dither signals to the wavelength-tunable light sources 11 to 14. Such control of oscillating the frequencies of the laser beams L11 to L41 is also called dither control.

[0052] FIG. 7 shows a state in which the control unit 40 oscillates the frequency of the laser beams L11 to L41. In this case, the PD current behaves differently depending on the region of curve C5 in which the frequency oscillates. For example, in FIG. 7(a), the frequency oscillates with amplitude A1 in the region of curve C5 where the PD current increases with increasing frequency. In this case, the PD current oscillation (oscillation with amplitude A2) is in phase with the frequency oscillation. In FIG. 7(b), the frequency oscillates with amplitude A3 in the region of curve C5 where the PD current decreases with increasing frequency. In this case, the PD current oscillation (oscillation with amplitude A4) is in antiphase with the frequency oscillation. In FIG. 7(c), the frequency oscillates with amplitude A5 in the region including the maximum value of curve C5. In this case, the PD current oscillation (oscillation with amplitude A6) has a period half that of the frequency oscillation, its amplitude is relatively small, and the PD current approaches its maximum value.

[0053] Therefore, based on the monitoring result of the PD current monitored by the monitor unit 30 under the oscillation caused by the dither control, the control unit 40 can detect, for example, that when the PD current is at its maximum value, the frequency of the laser light corresponds to the maximum value of the PD current. Alternatively, by detecting whether the oscillation of the PD current is in phase with or out of phase with the oscillation of the frequency, the control unit 40 can detect whether the frequency of the laser light is higher or lower than the frequency corresponding to the maximum value of the PD current. Therefore, by controlling the frequency of the laser light output by the wavelength-tunable light source so that the PD current approaches its maximum value, the control unit 40 can perform feedback control so that the frequency of the laser light approaches a target frequency (the frequency corresponding to the maximum value of the PD current, which is the peak frequency of the transmission spectrum of the third filter unit 23). The feedback control can be performed, for example, by PI control or PID control.

[0054] 8 is a flow diagram of an example of control executed by the control unit. First, in step S101, the control unit 40 executes initial setting. This initial setting involves setting the target frequency of the laser light for the wavelength-tunable light sources 11 to 14 and applying a dither signal. The setting of the target frequency for the wavelength-tunable light sources 11 to 14 is achieved by supplying initially set power to the heaters provided in each wavelength-tunable light source in order to achieve the target frequency of the laser light.

[0055] Next, in step S102, the control unit 40 controls the heater 21a to be in the ON state. This puts the first filter unit 21 into the first operating state. Next, in step S102, the control unit 40 controls the heater 22a to be in the OFF state. This puts the second filter unit 22 into the fourth operating state. Therefore, after step S103, the fifth operating state is realized, and laser light L11 and laser light L21 are output from the optical filter 20.

[0056] Next, in step S104, the control unit 40 acquires the monitoring result of the PD 31 in the monitor unit 30 (that is, the PD current from the PD 31 to which the laser light L11 is input).

[0057] Next, in step S105, the control unit 40 calculates a feedback value from the fluctuation of the PD current acquired in step S104 due to the dither. Here, the feedback value is the value of power to be supplied to the heater provided in the wavelength-tunable light source 11.

[0058] Next, in step S106, the control unit 40 performs feedback control of the wavelength-tunable light source 11 (#1) based on the calculation result in step S105. Specifically, the control unit 40 supplies power of the feedback value to the heater provided in the wavelength-tunable light source 11.

[0059] Next, in step S107, the control unit 40 acquires the monitoring result of the PD 32 in the monitor unit 30 (that is, the PD current from the PD 32 to which the laser light L2 is input).

[0060] Next, in step S108, the control unit 40 calculates a feedback value from the fluctuation of the PD current acquired in step S107 due to the dither. Here, the feedback value is the value of power supplied to the heater provided in the wavelength-tunable light source 12.

[0061] Subsequently, in step S109, the control unit 40 performs feedback control of the wavelength-tunable light source 12 (#2) based on the calculation result in step S108. Specifically, the control unit 40 supplies power of the feedback value to the heater provided in the wavelength-tunable light source 12.

[0062] Next, in step S110, the control unit 40 controls the heater 21a to be in the OFF state. This puts the first filter unit 21 into the second operating state. Next, in step S111, the control unit 40 controls the heater 22a to be in the ON state. This puts the second filter unit 22 into the third operating state. Therefore, after step S110, the sixth operating state is realized, and laser light L31 and laser light L41 are output from the optical filter 20.

[0063] Next, in step S112, the control unit 40 acquires the monitoring result of the PD 31 in the monitor unit 30 (that is, the PD current from the PD 31 to which the laser light L31 is input).

[0064] Next, in step S113, the control unit 40 calculates a feedback value from the fluctuation of the PD current acquired in step S112 due to the dither. Here, the feedback value is the value of power supplied to the heater provided in the wavelength-tunable light source 13.

[0065] Next, in step S114, the control unit 40 performs feedback control of the wavelength-tunable light source 13 (#3) based on the calculation result in step S113. Specifically, the control unit 40 supplies power of the feedback value to the heater provided in the wavelength-tunable light source 13.

[0066] Subsequently, in step S115, the control unit 40 acquires the monitoring result of the PD 32 in the monitor unit 30 (that is, the PD current from the PD 32 to which the laser light L41 is input).

[0067] Next, in step S116, the control unit 40 calculates a feedback value from the fluctuation of the PD current acquired in step S115 due to the dither. Here, the feedback value is the value of power supplied to the heater provided in the wavelength-tunable light source 14.

[0068] Next, in step S117, the control unit 40 performs feedback control of the wavelength-tunable light source 14 (#4) based on the calculation result in step S116. Specifically, the control unit 40 supplies power of the feedback value to the heater provided in the wavelength-tunable light source 14. Thereafter, the control returns to step S102, and the processing from step S102 onwards is repeated.

[0069] (Variation) In the above embodiment, the first to third filter sections 21 to 23 of the optical filter 20 are Mach-Zehnder interferometers, but the first to third filter sections are not limited to Mach-Zehnder interferometers.

[0070] 9 and 10 are diagrams showing a schematic configuration and operating state of an optical filter according to a modified example. This optical filter 20A can be used in place of the optical filter 20 in the laser device 100 shown in FIG. 1. This optical filter 20A includes a first filter section 21A, a second filter section 22A, and a third filter section 23A. In this embodiment, the first filter section 21A, the second filter section 22A, and the third filter section 23A are all ring resonators.

[0071] The first filter section 21A has a first input port P1A, a second input port P2A, and a first output port P3A. A heater 21Aa is provided in the ring section of the ring resonator of the first filter section 21A, serving as a first operation switching section. The "x" in the figure indicates a terminated port.

[0072] The second filter section 22A includes a third input port P4A, a fourth input port P5A, and a second output port P6A. A heater 22Aa is provided in the ring portion of the ring resonator of the second filter section 22A, serving as a second operation switching section. The "x" in the figure indicates a terminated port.

[0073] The third filter section 23A has a fifth input port P7A, a sixth input port P8A, a third output port P9A, and a fourth output port P10A. The fifth input port P7A is connected to the first output port P3A of the first filter section 21A. The sixth input port P8A is connected to the second output port P6A of the second filter section 22A. A heater 23Aa is provided in the ring portion of the ring resonator of the third filter section 23A. In the figure, white circles indicate the connection points of the ports.

[0074] The optical filter 20A operates in the same manner as the optical filter 20. That is, the operation of the first filter unit 21A is switched between a first operating state and a second operating state. As shown in FIG. 9, the first operating state is a state in which, when laser light L11 is input to the first input port P1A of the first filter unit 21A and laser light L21 is input to the second input port P2A, laser light L11 and L12 are output from the first output port P3A as indicated by arrows R1A and R2A by the action of the heater 21Aa. Also, as shown in FIG. 10, the second operating state is a state in which, when laser light L11 is input to the first input port P1A of the first filter unit 21A and laser light L21 is input to the second input port P2A, laser light L11 and L12 are output to the terminal end as indicated by arrows R5A and R6A by the action of the heater 21Aa and are not output to the outside. The first operating state and the second operating state are switched depending on the degree to which the heater 21Aa heats the ring portion of the first filter unit 21A to change the refractive index of the waveguide that constitutes the ring portion. The switching between the first operating state and the second operating state is performed by the control unit 40 via the DA conversion unit 50.

[0075] The second filter unit 22A switches between a third operating state and a fourth operating state. As shown in Fig. 10, the third operating state is a state in which, when laser light L31 is input to the third input port P4A of the second filter unit 22A and laser light L41 is input to the fourth input port P5A, laser light L31 and L41 are output from the second output port P6A by the action of the heater 22Aa, as indicated by arrows R7A and R8A, respectively. As shown in Fig. 9, the fourth operating state is a state in which, when laser light L31 is input to the third input port P4A of the second filter unit 22A and laser light L41 is input to the fourth input port P5A, laser light L31 and L41 are output to the terminal end, as indicated by arrows R3A and R4A, respectively, by the action of the heater 22Aa, but are not output to the outside. The third operating state and the fourth operating state are switched depending on the degree to which the heater 22Aa heats the ring portion of the second filter unit 22 to change the refractive index of the waveguide that constitutes the ring portion. The switching between the third operating state and the fourth operating state is performed by the control unit 40 via the DA conversion unit 50.

[0076] Here, the control unit 40, which is a filter control unit, controls the operation of the heater 21Aa and the heater 22Aa to realize either a fifth operating state in which the heater 21Aa as the first operation switching unit realizes the first operating state and the heater 22Aa as the second operation switching unit realizes the fourth operating state, or a sixth operating state in which the heater 21Aa realizes the second operating state and the heater 22Aa realizes the third operating state.

[0077] The fifth operating state is the state shown in Fig. 9. In the fifth operating state, in the third filter section 23A, laser beams L11 and L21 are input from the first output port P3A of the first filter section 21A to the fifth input port P7A. In this case, as indicated by arrows R1A and R2A, the third filter section 23A outputs laser beam L11 from the third output port P9A, which is one of the third output port P9A and the fourth output port P10A, and outputs laser beam L21 from the other, the fourth output port P10A.

[0078] 10. In the sixth operating state, in the third filter section 23A, laser beams L31 and L41 are input from the second output port P6A of the second filter section 22A to the sixth input port P8A. In this case, as indicated by arrows R7A and R8A, the third filter section 23A outputs laser beam L31 from the third output port P9A, which is one of the third output port P9A and the fourth output port P10A, and outputs laser beam L41 from the other, the fourth output port P10A.

[0079] In the above embodiment, the first to third filter sections 21 to 23 of the optical filter 20 are all Mach-Zehnder interferometers, but at least one of the first to third filter sections 21 to 23 may be a Mach-Zehnder interferometer. In this case, the other filter sections may be ring resonators. Similarly, the first to third filter sections 21A to 23A of the optical filter 20A according to the above modification are all Mach-Zehnder interferometers, but at least one of the first to third filter sections 21A to 23A may be a ring resonator. In this case, the other filter sections may be Mach-Zehnder interferometers.

[0080] Furthermore, in the above embodiment, the third filter unit 23 outputs the laser light L11 from the third output port P9 and outputs the laser light L21 from the fourth output port P10 in the fifth operating state, but the third filter unit 23 may be configured to output the laser light L21 from the third output port P9 and output the laser light L11 from the fourth output port P10. Similarly, the third filter unit 23 may be configured to output the laser light L41 from the third output port P9 and output the laser light L31 from the fourth output port P10 in the sixth operating state.

[0081] Furthermore, in the above embodiment, the first and second operation switching units are heaters, but the first and second operation switching units are not particularly limited as long as they have the function of changing the refractive index of the waveguide.

[0082] Furthermore, in the above embodiment, the wavelength-tunable light sources 11 to 14 are wavelength-tunable light sources that utilize the Vernier effect, but the present invention is not limited to this.

[0083] Furthermore, the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Explanation of symbols]

[0084] 11, 12, 13, 14: Tunable wavelength light source 11a: DBR element 11b:Gain part 11c: Phase element 11d: Ring element 11e, 11f, 11g, 21a, 21Aa, 22a, 22Aa, 23a, 23Aa: Heater 20, 20A: Optical filter 21, 21A: First filter section 22, 22A: Second filter section 23, 23A: Third filter section 30: Monitor section 31, 32:PD 33, 34: ADC 40: Control section 41: Arithmetic section 42: Storage section 43, 44, 45, 46: DAC Group 50: DA conversion section 51, 52:DAC 60:TEC 100: Laser device A1, A2, A3, A4, A5, A6: Amplitude L11, L12, L21, L22, L31, L32, L41, L42: Laser light P1, P1A: First input port P2, P2A: Second input port P3, P3A: First output port P4, P4A: Third input port P5, P5A: 4th input port P6, P6A: Second output port P7, P7A: 5th input port P8, P8A: 6th input port P9, P9A: Third output port P10, P10A: 4th output port R1, R1A, R2A, R3, R3A, R4, R4A, R5, R5A, R6, R6A, R7, R7A, R8, R8A: Arrow

Claims

1. four wavelength-tunable light sources that output four laser beams having equal frequency intervals, the four laser beams being a first laser beam, a second laser beam, a third laser beam, and a fourth laser beam in order from the lowest frequency; a first filter unit having a first input port, a second input port, a first output port, and a first operation switching unit, wherein when the first laser light is input to the first input port and the second laser light is input to the second input port, the first operation switching unit switches its operation between a first operation state in which the first laser light and the second laser light are output from the first output port, and a second operation state in which the first laser light and the second laser light are not output to the outside; a second filter unit having a third input port, a fourth input port, a second output port, and a second operation switching unit, wherein when the third laser light is input to the third input port and the fourth laser light is input to the fourth input port, the second operation switching unit switches its operation between a third operation state in which the third laser light and the fourth laser light are output from the second output port, and a fourth operation state in which the third laser light and the fourth laser light are not output to the outside; a third filter unit having a fifth input port, a sixth input port, a third output port, and a fourth output port, and when the first laser light and the second laser light are input through the first output port of the first filter unit, outputs the first laser light from one of the third output port and the fourth output port and outputs the second laser light from the other of the third output port and the fourth output port, and when the third laser light and the fourth laser light are input through the second output port of the second filter unit, outputs the third laser light from one of the third output port and the fourth output port and outputs the fourth laser light from the other of the third output port and the fourth output port; a filter control unit that controls operations of the first operation switching unit and the second operation switching unit to realize one of a fifth operation state in which the first operation switching unit realizes the first operation state and the second operation switching unit realizes the fourth operation state, and a sixth operation state in which the first operation switching unit realizes the second operation state and the second operation switching unit realizes the third operation state; Equipped with The FSR of the first filter unit, the second filter unit, and the third filter unit is 2 / (2n+1) times the frequency interval, where n is a non-negative integer. Laser device.

2. At least one of the first filter section, the second filter section, and the third filter section is a Mach-Zehnder interferometer.

2. The laser device according to claim 1.

3. At least one of the first operation switching unit and the second operation switching unit, which are the Mach-Zehnder interferometer, is a heater provided in an arm portion of the Mach-Zehnder interferometer.

3. The laser device according to claim 2.

4. At least one of the first filter section, the second filter section, and the third filter section is a ring resonator.

2. The laser device according to claim 1.

5. At least one of the first operation switching unit and the second operation switching unit, which are the ring resonator, is a heater provided in a ring portion of the ring resonator.

5. The laser device according to claim 4.

6. a monitor unit that monitors the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam output from the third filter unit.

2. The laser device according to claim 1.

7. a frequency control unit that feedback-controls the frequencies of the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam based on the results monitored by the monitor unit.

7. The laser device according to claim 6.

8. The frequency control unit applies a dither signal to the four wavelength-variable light sources to oscillate the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light, and, based on a result monitored by the monitor unit under the oscillation, brings the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light closer to a peak frequency of a transmission spectrum of the third filter unit.

8. The laser device according to claim 7.

9. A method for controlling a laser device, comprising: The laser device includes: four wavelength-tunable light sources that output four laser beams having equal frequency intervals, the four laser beams being a first laser beam, a second laser beam, a third laser beam, and a fourth laser beam in order from the lowest frequency; a first filter unit having a first input port, a second input port, a first output port, and a first operation switching unit, wherein when the first laser light is input to the first input port and the second laser light is input to the second input port, the first operation switching unit switches its operation between a first operation state in which the first laser light and the second laser light are output from the first output port, and a second operation state in which the first laser light and the second laser light are not output to the outside; a second filter unit having a third input port, a fourth input port, a second output port, and a second operation switching unit, wherein when the third laser light is input to the third input port and the fourth laser light is input to the fourth input port, the second operation switching unit switches its operation between a third operation state in which the third laser light and the fourth laser light are output from the second output port, and a fourth operation state in which the third laser light and the fourth laser light are not output to the outside; a third filter unit having a fifth input port, a sixth input port, a third output port, and a fourth output port, and when the first laser light and the second laser light are input through the first output port of the first filter unit, outputs the first laser light from one of the third output port and the fourth output port and outputs the second laser light from the other of the third output port and the fourth output port, and when the third laser light and the fourth laser light are input through the second output port of the second filter unit, outputs the third laser light from one of the third output port and the fourth output port and outputs the fourth laser light from the other of the third output port and the fourth output port; a monitor unit that monitors the first laser light, the second laser light, the third laser light, and the fourth laser light output from the third filter unit; wherein the FSRs of the first filter unit, the second filter unit, and the third filter unit are 2 / (2n+1) times the frequency interval, where n is a non-negative integer; controlling operations of the first operation switching unit and the second operation switching unit to realize one of a fifth operation state in which the first operation switching unit realizes the first operation state and the second operation switching unit realizes the fourth operation state, and a sixth operation state in which the first operation switching unit realizes the second operation state and the second operation switching unit realizes the third operation state; applying a dither signal to the four wavelength-tunable light sources to oscillate the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light; Based on the results of monitoring by the monitor unit under the vibration, the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light are made to approach a peak frequency of a transmission spectrum of the third filter unit, thereby feedback-controlling the frequencies of the first laser light, the second laser light, the third laser light, and the fourth laser light. A method for controlling a laser device.

Images