JP2023115762A - Wavelength variable laser device and control method of the wavelength variable laser device - Google Patents

Abstract

To provide a wavelength variable laser device and a control method of the wavelength variable laser device, in which a stability of a frequency of a laser beam output when continuously changing the frequency in a wide band is high.SOLUTION: In a wavelength variable laser device continuously sweeping a frequency of a laser beam output to an external part, a control part continuously sweeps the frequency of the laser beam while outputting the laser beam to the external part while oscillating a first wavelength variable laser element, sets the number of laser oscillation frequency of a second wavelength variable laser element to a first frequency during the sweeping to oscillate the laser, and an output of the laser beam to the external part is disconnected in order to be a stand-by state. In the case where it is determined that the frequency of the laser beam of the first wavelength variable laser element is appropriately matched to the first frequency, the output to the external part of the laser beam of the first wavelength variable laser element is disconnected, and the stand-by state of the second wavelength variable laser element is cancelled to output the laser beam of the second wavelength variable laser element to the external part as at least one step.SELECTED DRAWING: Figure 1

Description

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

As a light source for continuously changing the wavelength (or the frequency corresponding to the wavelength) of laser light over a wide band, a technology is known in which multiple wavelength tunable lasers with different wavelength tunable bands are provided and the wavelength tunable laser element that outputs the laser light is switched. (Patent Documents 1 and 2).

JP 2015-115411 A WO2006/089802

FMCW (Frequency Modulated Continuous Wave)-LiDAR light source, OCT (Optical Coherence Tomography) light source, OFDR (Optical Frequency Domain Reflectometry) light source, etc., have been requested to continuously change the frequency of laser light over a wide band. rising. However, with the known technique, the frequency of the output laser light may become unstable when switching the wavelength tunable laser element that outputs the laser light.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and provides a wavelength tunable laser device and control of the wavelength tunable laser device in which the frequency of output laser light is highly stable when the frequency is continuously varied over a wide band. It is to provide a method.

In order to solve the above-described problems and achieve the object, one aspect of the present invention provides a plurality of wavelength tunable laser elements including a first wavelength tunable laser element and a second wavelength tunable laser element capable of changing the laser oscillation frequency; and a control section, wherein the control section causes the first wavelength tunable laser element to oscillate to output the laser light to the outside. continuously sweeping the frequency of the laser light to the first frequency while outputting the second wavelength tunable laser element to the first frequency, and setting the laser oscillation frequency of the second wavelength tunable laser element to the first frequency during the sweep to cause laser oscillation; and when it is determined that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency, the first wavelength tunable laser element A wavelength for at least one step of cutting off the output of laser light to the outside, canceling the standby state of the second wavelength tunable laser element, and outputting the laser light of the second wavelength tunable laser element to the outside. It is a tunable laser device.

The control section may cause the first wavelength tunable laser element and the second wavelength tunable laser element to oscillate at a predetermined frequency based on control parameters stored in a storage section.

Let M be the number of wavelength tunable laser elements included in the plurality of wavelength tunable laser elements, and the controller cuts off the output of laser light from the first wavelength tunable laser element to the outside and the second wavelength tunable laser element. If the number of times the standby state of the device is released and the laser beam of the second wavelength tunable laser device is output to the outside is N, N≧M may be satisfied.

The wavelength tunable laser element may be capable of generating mode hopping in which the laser oscillation frequency changes discontinuously.

The frequency width for sweeping the frequency of the laser light of the first tunable laser element or the second tunable laser element is the frequency interval of the cavity mode of the first tunable laser element or the second tunable laser element. It may be smaller than three times.

A monitor unit for monitoring the frequency of the laser light is provided, and the control unit determines that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency means that the laser oscillation frequency is set to the first frequency using the monitoring section, and the monitored laser oscillation frequency and the swept wavelength tunable laser element It may be the case where it is determined that the current laser oscillation frequency substantially matches.

The monitor section includes a filter having a periodic response characteristic with respect to the frequency of light. The laser light of the element may be input from the other of said filters.

The monitor section may include a filter having a periodic response characteristic with respect to the frequency of light, and changing means for changing the frequency characteristic of the filter.

The monitor section may include a plurality of filters having periodic response characteristics with respect to the frequency of light and different frequency characteristics from each other.

The monitor section may be configured to monitor the frequency of the laser light by heterodyne detection.

A frequency for continuously sweeping the frequency of the laser light while oscillating the second wavelength tunable laser element and outputting the laser light to the outside, and continuously sweeping the frequency of the laser light from the first wavelength tunable laser element The width may be different from the frequency width for continuously sweeping the frequency of the laser light of the second wavelength tunable laser element.

One aspect of the present invention includes a plurality of wavelength tunable laser elements including a first wavelength tunable laser element and a second wavelength tunable laser element capable of changing the laser oscillation frequency, and a controller, and a laser beam to be output to the outside. wherein the control unit causes the first wavelength tunable laser element to oscillate to output laser light to the outside while changing the frequency of the laser light to the first 1 frequency is continuously swept, and during the sweep, the laser oscillation frequency of the second wavelength tunable laser element is set to the first frequency to cause laser oscillation, and the output of the laser light to the outside is cut off. and when it is determined that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency, the output of the laser light from the first wavelength tunable laser element to the outside is cut off. 1. A control method for a wavelength tunable laser device, wherein the step of canceling the standby state of the second wavelength tunable laser element and outputting the laser light of the second wavelength tunable laser element to the outside is performed at least once.

ADVANTAGE OF THE INVENTION According to this invention, when changing a frequency continuously in a wide band, it is effective in the stability of the frequency of the output laser beam being high.

FIG. 1 is a schematic configuration diagram of a wavelength tunable laser device according to Embodiment 1. FIG. FIG. 2 is a configuration diagram of an example of a wavelength tunable laser element. FIG. 3 is an explanatory diagram of adjustment of the laser oscillation frequency. FIG. 4 is a diagram of table data showing an example of the relationship between the laser oscillation frequency and the drive power for the first to third heaters. FIG. 5 is a configuration diagram of an example of the monitor unit. FIG. 6 is an explanatory diagram of an example of a frequency monitor. FIG. 7 is an explanatory diagram of an example of sweeping the frequency of laser light. FIG. 8 is a flowchart of an example of sweeping the frequency of laser light. FIG. 9 is a schematic configuration diagram of a wavelength tunable laser device according to Embodiment 2. FIG. FIG. 10 is a schematic configuration diagram of a wavelength tunable laser device according to Embodiment 3. FIG. FIG. 11 is an explanatory diagram of a plurality of discrimination curves. FIG. 12 is a diagram showing an example of a configuration for preparing a plurality of discrimination curves. FIG. 13 is a diagram showing another example of a configuration for preparing a plurality of discrimination curves. FIG. 14 is an explanatory diagram of an example in which two sweeps have different frequency widths. FIG. 15 is a configuration diagram of still another example of the monitor section.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment described below. In addition, in the description of the drawings, the same or corresponding elements are given the same reference numerals as appropriate.

(Embodiment 1)
FIG. 1 is a configuration diagram of a wavelength tunable laser device according to Embodiment 1. FIG. In FIG. 1, solid-line arrows indicate input/output of light, and dashed-line arrows indicate input/output of electrical signals and power. The wavelength tunable laser device 100 continuously sweeps the frequency of laser light to be output to the outside.

The wavelength tunable laser device 100 includes wavelength tunable laser elements 11 and 12 which are a plurality of wavelength tunable laser elements capable of changing the laser oscillation frequency, optical couplers 21 and 22, an output switching section 30, a monitor section 40, a control a portion 50; The wavelength tunable laser element 11 is an example of a first wavelength tunable laser element or a second wavelength tunable laser element, and the wavelength tunable laser element 12 is an example of a second wavelength tunable laser element or a first wavelength tunable laser element. That is, the multiple wavelength tunable laser elements include a first wavelength tunable laser element and a second wavelength tunable laser element.

FIG. 2 is a configuration diagram of an example of the wavelength tunable laser element 11. As shown in FIG. The wavelength tunable laser element 11 is a vernier type wavelength tunable laser element that includes a first reflection mirror 11a, a gain section 11b, a phase adjustment section 11c, and a second reflection mirror 11d. The first reflecting mirror 11a is a sampled grating-distributed Bragg reflector (SG-DBR) mirror whose reflection spectrum has periodic peaks with respect to frequency. The second reflecting mirror 11d is an SG-DBR mirror whose reflection spectrum has periodic peaks with respect to frequency at a period different from that of the first reflecting mirror 11a. A laser resonator is configured by the first reflecting mirror 11a and the second reflecting mirror 11d. The second reflecting mirror may be a reflecting mirror using a ring resonator filter as disclosed in JP-A-2016-178283.

The gain section 11b is arranged in the laser resonator and generates an optical gain by being supplied with driving power from the control section 50. As shown in FIG. The phase adjustment section 11c is a waveguide arranged within the laser resonator.

A first heater is provided in the first reflecting mirror 11a. The first heater heats the first reflecting mirror 11 a by being supplied with driving power from the control section 50 . This heating controls the reflection spectrum of the first reflecting mirror 11a. A second heater is provided on the second reflecting mirror 11d. The second heater heats the second reflecting mirror 11 d by being supplied with driving power from the control section 50 . This heating controls the reflection spectrum of the second reflecting mirror 11d. A third heater is provided in the phase adjustment unit 11c. The third heater heats the phase adjustment section 11 c by being supplied with drive power from the control section 50 . This heating adjusts the cavity length of the laser cavity. The frequency of the longitudinal mode (resonator mode) of the laser resonator can be controlled by adjusting the resonator length.

In the wavelength tunable laser element 11, the reflection peak of the first reflecting mirror 11a and the resonator mode of the laser resonator are adjusted by adjusting the drive power supplied to each of the first heater, the second heater, and the third heater. Laser oscillation is performed at a frequency substantially coincident with the reflection peak of the second reflecting mirror 11d, and laser light L1, which is CW (continuous wave) light, is output. That is, the first heater, the second heater, and the third heater constitute a plurality of control elements that control the laser oscillation frequency of the wavelength tunable laser element 11 by supplying drive power.

Returning to FIG. 1 , the wavelength tunable laser element 12 may have the same configuration as the wavelength tunable laser element 11 . The wavelength tunable laser element 12 outputs laser light L2 which is CW light.

The optical coupler 21 receives the laser light L1 output from the wavelength tunable laser element 11, splits the laser light L1 into the laser light L11 and the laser light L12, outputs the laser light L11 to the output switching unit 30, and outputs the laser light L12 is output to the monitor unit 40.

The optical coupler 22 receives the laser light L2 output from the wavelength tunable laser element 12, splits the laser light L2 into the laser light L21 and the laser light L22, outputs the laser light L21 to the output switching unit 30, and outputs the laser light L22 is output to the monitor unit 40.

The output switching unit 30 receives the laser beams L11 and L21 and selectively outputs one of the laser beams L11 and L21. In Embodiment 1, the output switching unit 30 includes light blocking elements 31 and 32 and an optical coupler 33 . The light blocking element 31 receives the laser light L<b>11 and passes or blocks the laser light L<b>11 under the control of the control unit 50 . The light blocking element 32 receives the laser light L21 and passes or blocks the laser light L21 under the control of the control unit 50 . Here, the control unit 50 causes the light blocking element 32 to block the laser beam L21 while the light blocking element 31 allows the laser beam L11 to pass through, and The light blocking elements 31 and 32 are controlled so that the light blocking element 31 blocks the laser beam L11.

Light blocking elements 31 and 32 can be configured using, for example, semiconductor amplifiers. In this case, when the light blocking elements 31 and 32 block the laser light, the semiconductor optical amplifier is controlled to operate in reverse bias, and when the light blocking elements 31 and 32 allow the laser light to pass through, the semiconductor optical amplifier Controlled for forward bias operation. The light blocking elements 31 and 32 can also be configured using a Mach-Zehnder type optical switch or a 2×1 optical switch.

The optical coupler 33 outputs the laser light L11 that has passed through the light blocking element 31 or the laser light L21 that has passed through the light blocking element 32 to the outside of the wavelength tunable laser device 100 as the selected laser light L3.

The monitor unit 40 receives the laser beams L21 and L22. The laser beams L21 and L22 are used for monitoring the frequencies of the laser beams L11 and L12. The configuration of the monitor unit 40 will be detailed later.

The controller 50 controls power supplied to the gain sections of the wavelength tunable laser elements 11 and 12 and the first to third heaters. Also, it controls the operation of the light blocking elements 31 and 32 .

The control unit 50 includes an arithmetic unit, a storage unit, an input unit, an output unit, and a power supply unit. The calculation unit includes, for example, a CPU, and performs various calculation processes for control. The storage unit includes a storage unit such as a ROM that stores various programs and data used by the calculation unit to perform calculation processing, a work space when the calculation unit performs calculation processing, and the result of calculation processing of the calculation unit. and a storage unit such as a RAM used for storing the data, etc.

The input section receives an instruction signal from a host device of the wavelength tunable laser device 100 or the like, a current signal from the monitor section 40, or the like. Information contained in the received signal is stored in the storage unit. The input section comprises, for example, an analog-to-digital converter (ADC). The output unit receives the instruction signal generated by the arithmetic processing by the arithmetic unit, converts it into an appropriate instruction signal, and outputs it to the power supply unit, the light blocking elements 31 and 32, and the like. The output section comprises, for example, a digital-to-analog converter (DAC). The power supply unit supplies power to the wavelength tunable laser elements 11 and 12 based on the instruction signal.

(Adjustment of laser oscillation frequency)
Next, adjustment of the laser oscillation frequency will be described. FIG. 3 is an explanatory diagram of adjustment of the laser oscillation frequency. The upper stage shows the reflection spectrum of the first reflecting mirror, the middle stage shows the reflection spectrum of the second reflecting mirror, and the lower stage shows the spectrum of the resonator mode.

When the driving power supplied to the first heater is adjusted and controlled, the reflection spectrum of the first reflecting mirror shifts on the frequency axis from the shape indicated by the solid line to the shape indicated by the broken line as indicated by the thick arrow. Similarly, when the drive power supplied to the second heater is adjusted and controlled, the reflection spectrum of the second reflecting mirror shifts on the frequency axis from the shape indicated by the solid line to the shape indicated by the broken line. When the drive power supplied to the third heater is adjusted and controlled, the spectrum of the resonator mode shifts on the frequency axis from the shape indicated by the solid line to the shape indicated by the broken line.

In the state indicated by the solid line, the laser oscillates at the frequency fy at which the reflection peak of the first reflection mirror 11a, the resonator mode of the laser resonator, and the reflection peak of the second reflection mirror 11d coincide. To achieve this state, the first heater and the second heater respectively set the frequency positions at which the reflection spectra of the first reflecting mirror 11a and the second reflecting mirror 11d peak, based on the supplied power. Also, the third heater sets the frequency position at which the resonator mode peaks, based on the supplied power. When the state indicated by the dashed line is obtained by controlling the heaters, the wavelength at which the reflection peak of the first reflection mirror 11a, the resonator mode of the laser resonator, and the reflection peak of the second reflection mirror 11d coincide can be set to the frequency fx. The oscillation wave frequency can be changed to the frequency fx. By finely adjusting the drive power when controlling each heater, the laser oscillation frequency can be continuously (swept) finely adjusted while maintaining the match between the resonator mode and the two reflection peaks. It should be noted that the drive power to each heater can be controlled by the supplied current.

The relationship between the laser oscillation frequency of each of the wavelength tunable laser elements 11 and 12 and the driving power of the first to third heaters is stored in the storage unit of the control unit 50, and is referred to when setting the laser oscillation frequency. be done. FIG. 4 is a diagram of table data showing an example of the relationship between the laser oscillation frequency and the drive power for the first to third heaters. In FIG. 4 , “A” of “laser element” means setting for the wavelength tunable laser element 11 , and “B” means setting for the wavelength tunable laser element 12 . In the example shown in FIG. 4, when the laser oscillation frequency of the wavelength tunable laser element 11 is set to frequency f0, the drive powers of the first to third heaters are set to W1_0, W2_0 and W3_0, respectively. The drive power for the first to third heaters is an example of a control parameter that causes the wavelength tunable laser element to oscillate at a predetermined frequency.

(Structure of monitor section)
Next, the configuration of the monitor section 40 will be described. FIG. 5 is a configuration diagram of an example of the monitor unit. The monitor unit 40 includes an optical switch 41 , a filter 42 and a photodetector (PD) 43 .

The optical switch 41 selectively passes the laser beam L12 or the laser beam L22 as the laser beam L4 under the control of the control unit 50 . The filter 42 is an example of a filter having periodic response characteristics (transmission characteristics and reflection characteristics) with respect to the frequency of light. be. Such a filter 42 can be constructed using, for example, an etalon filter, a ring resonator filter, a Michelson interferometer, or the like. The filter 42 transmits the laser light L4 with a transmittance according to the frequency of the laser light L4. The laser light L4 after passing through the filter 42 is referred to as laser light L5.

The photodetector 43 has, for example, a photodiode, receives the laser beam L5, and outputs a current signal having a current value corresponding to the intensity of the received light to the control unit 50 .

The controller 50 monitors the frequency of the laser light L5 based on the correspondence between the value of the current signal (PD current value) from the photodetector 43 and the laser oscillation frequency. Such a correspondence relationship is obtained in advance by experiments or the like, and is stored in the storage unit as table data or relational expressions.

FIG. 6 is an explanatory diagram of an example of a frequency monitor. In FIG. 6, the horizontal axis indicates the frequency of light, and the vertical axis indicates the PD current value normalized by the maximum value. The curve shown in FIG. 6 has a shape corresponding to the transmission spectrum of filter 42 . Such curves are also called discrimination curves. In the case shown in FIG. 6, for example, when the PD current value is Ipd, the controller 50 determines that the frequency of the laser light L5 is 192.25 THz (approximately 1559 nm in terms of wavelength) based on the discrimination curve. .

Then, the controller 50 controls the drive power to the first to third heaters so that the PD current value corresponds to the desired laser oscillation frequency. Thereby, the laser oscillation frequency of the wavelength tunable laser element 12 can be feedback-controlled.

(Continuous sweep of laser light frequency)
Next, continuous sweeping of the frequency of the output laser light in the wavelength tunable laser device 100 will be described. FIG. 7 is an explanatory diagram of an example of sweeping the frequency of laser light. FIG. 7 shows a case where the frequency of the output laser light is continuously swept from frequency f1 (wavelength λ1) to a frequency smaller than frequency f3 (wavelength λ3). In the graph of FIG. 7, the horizontal axis is elapsed time, and the vertical axis is wavelength (frequency).

In this case, the controller 50 performs step A first. That is, the control unit 50 oscillates the wavelength tunable laser element 11 to output laser light to the outside, as indicated by the solid line l31 in the graph of FIG. 7A, while changing the frequency of the laser light from frequency f1 to , to frequency f2, which is an example of the first frequency. The sweep can be performed, for example, by continuously changing the driving power of the first to third heaters of the wavelength tunable laser element 11 until the frequency f2. Moreover, the control part 50 performs step B. FIG. That is, during this sweep, the control unit 50 sets the wavelength tunable laser element 12 to the frequency f2 to cause laser oscillation, as indicated by the dashed line l32', and cuts off the output of the laser light to the outside to wait. state. In steps A and B, the controller 50 controls the light blocking element 31 to pass the laser beam L11 and controls the light blocking element 32 to block the laser beam L21. As a result, the wavelength tunable laser device 100 continuously sweeps the frequency of the externally output laser light (laser light L3 (L11) in FIG. 1). In the case of such continuous sweep, the wavelength tunable laser element may be feedforward controlled. Further, for example, when the wavelength tunable laser element 12 is set to oscillate at the frequency f2, the wavelength tunable laser element 12 may be feedback-controlled so that the laser oscillation frequency becomes the frequency f2.

Subsequently, the control unit 50 performs step C. That is, when it is determined that the frequency of the laser light from the wavelength tunable laser element 11 substantially matches the frequency f2, the output of the laser light from the wavelength tunable laser element 11 to the outside is cut off, and the wavelength tunable laser element 12 is placed in a standby state. is released to output the laser light from the wavelength tunable laser device 12 to the outside. The determination that the frequency of the laser light from the wavelength tunable laser element 11 substantially matches the frequency f2 is made when the frequency of the laser light from the wavelength tunable laser element 11 completely matches the frequency f2, or when the wavelength tunable laser element 11 is performed when the frequency of the laser light reaches within a predetermined error range from the frequency f2.

Subsequently, the control unit 50 performs steps A to C for the second time. However, this time, as step A, the control unit 50 oscillates the wavelength tunable laser element 12 to output laser light to the outside, as indicated by the solid line l32 in the graph of FIG. The frequency of light is continuously swept from frequency f2 to frequency f3, which is another example of the first frequency. Further, in step B, the control unit 50 sets the wavelength tunable laser element 11 to the frequency f3 to cause laser oscillation during this sweep, as indicated by the dashed line l31', and outputs the laser light to the outside. is cut off and placed in a standby state. When the laser oscillation frequency is set in this manner, the frequency of the laser light output from the wavelength tunable laser element 11 becomes temporarily unstable, as shown by the spikes in the graph of FIG. 7(a). There is Such frequency instability phenomenon occurs due to mode hopping, for example, when the wavelength tunable laser element 11 is a wavelength tunable laser element that can cause mode hopping in which the laser oscillation frequency changes discontinuously. However, in step B, the laser light of the wavelength tunable laser element 11 is in a standby state by blocking the output to the outside, so that the laser light having an unstable frequency or an unintended frequency may be output to the outside. no.

Therefore, in a certain wavelength tunable laser element, if the laser oscillation frequency at which mode hopping is likely to occur is known in advance, it is preferable not to perform continuous sweeping in the frequency range that includes that frequency, but instead to enter a standby state. For example, if the wavelength tunable laser element is a vernier type, mo-hop is likely to occur when the supermode changes.

Subsequently, the control unit 50 performs step C. That is, when it is determined that the frequency of the laser light from the wavelength tunable laser element 12 substantially coincides with the frequency f3, the output of the laser light from the wavelength tunable laser element 12 to the outside is cut off, and the wavelength tunable laser element 11 is placed in a standby state. is released to output the laser light from the wavelength tunable laser element 11 to the outside. Such steps A to C are repeated until the end frequency of the set continuous sweep.

The above steps A to C are performed at least once depending on the starting and ending frequencies of the continuous sweep.

In the wavelength tunable laser device 100 configured as described above, as shown in the graph of FIG. expensive.

Further, in the wavelength tunable laser device 100, the common monitor unit 40 is used to monitor the frequencies of the laser beams of the two wavelength tunable laser elements 11 and 12. can reduce the relative difference between the monitor values of the frequencies of

From the viewpoint of suppressing mode hopping, the frequency width for sweeping the frequency of the laser light of the wavelength tunable laser element 11 or 12 (the difference between the sweep start frequency and the sweep end frequency) is set to the resonance frequency of the wavelength tunable laser element 11 or 12 It is preferably less than three times the frequency spacing of the instrument modes. Also, the lower limit of the range is not particularly limited, but is, for example, one times the frequency interval of the resonator mode.

The operation of the wavelength tunable laser device 100 will be further described. FIG. 8 is a flowchart of an example of sweeping the frequency of laser light. In the flowchart shown in FIG. 8, the frequency of the laser light is continuously swept from frequency f1 to frequency f2 while the wavelength tunable laser element 11 (hereinafter referred to as LD(A)) outputs the laser light to the outside. The wavelength tunable laser element 12 (hereinafter referred to as LD(B) as appropriate) is in a standby state while oscillating at frequency f2, and the frequency of the laser light from LD(A) is approximately at frequency f2. It starts when it is determined that they match.

In this case, in step S101, the control unit 50 cuts off the output of the laser light from the LD(A) to the outside. Subsequently, in step S102, the control unit 50 cancels the blocking of the output of the laser light of LD(B) to the outside, and starts sweeping the laser light of LD(B).

Subsequently, in step S103, the control unit 50 changes the driving conditions of LD(A) so that the frequency target value of the laser oscillation frequency of LD(A) becomes f3, and further performs feedback control.

Subsequently, in step S104, the controller 50 determines whether the laser oscillation frequency of LD(A) has stabilized. Whether or not the laser oscillation frequency is stabilized is determined, for example, if the frequency of the laser light L22 (see FIGS. 1 and 5) monitored by the monitor unit 40 over a predetermined period of time or a predetermined number of times of monitoring is within a predetermined error range. or not.

When determining that the laser oscillation frequency is not stable (step S104, No), the control unit 50 executes step S104 again. If it is determined that the laser oscillation frequency has stabilized (step S104, Yes), the controller 50 executes step S105.

In step S105, the control unit 50 stores the frequency of the laser light L22 monitored using the monitor unit 40 as a switching threshold in the storage unit.

Subsequently, in step S106, the control unit 50 determines whether the error between the current frequency of the sweeping LD(B) and the switching threshold has fallen below a certain value. Step S106 is an example of a step of determining that the frequency of the laser light of LD(B) substantially matches the frequency f3.

If it is determined that the error is not within the certain value (step S106, No), the control unit 50 executes step S106 again. If it is determined that the error has fallen below the constant value, the control unit 50 executes step S107.

In step S107, the control unit 50 cuts off the output of the laser light from the LD (B) to the outside. Subsequently, in step S108, the control unit 50 cancels the blocking of the output of the laser light of LD(A) to the outside, and starts sweeping the laser light of LD(A).

In the flow shown in FIG. 8, when the control unit 50 determines that the frequency of the laser light of LD (B) substantially matches the frequency f3, LD (A) in a state where the laser oscillation frequency is set to the frequency f3. is monitored using the monitor unit 40, and it is determined that the monitored laser oscillation frequency (switching threshold value) and the current laser oscillation frequency of the wavelength tunable laser element being swept substantially match is. This more reliably suppresses the discontinuous change in the frequency of the laser light output when switching the sweeping wavelength tunable laser element.

Further, in the flow shown in FIG. 8, the number of wavelength tunable laser elements included in the plurality of wavelength tunable laser elements is M, and the controller 50 cuts off the output of the laser light from the first wavelength tunable laser element to the outside. , N≧M, where N is the number of times the second wavelength tunable laser device is released from the standby state and the laser beam of the second wavelength tunable laser device is output to the outside. Specifically, in the flow shown in FIG. 8, M is two and N is also two. In this way, when N≧M, the frequency of the laser light can be swept over a relatively wide band compared to the number of wavelength tunable laser elements.

(Embodiment 2)
FIG. 9 is a schematic configuration diagram of a wavelength tunable laser device according to Embodiment 2. FIG. The wavelength tunable laser device 100A replaces the optical couplers 21 and 22, the output switching unit 30, and the monitor unit 40 of the wavelength tunable laser device 100 shown in FIG. It has a configuration replaced with 40A.

The optical coupler 21A receives the laser light L1 output from the wavelength tunable laser element 11, splits the laser light L1 into the laser light L11 and the laser light L12, outputs the laser light L11 to the output switching unit 30A, and outputs the laser light L1 to the output switching unit 30A. L12 is output to the monitor section 40A.

The optical coupler 22A receives the laser light L2 output from the wavelength tunable laser element 12, splits the laser light L2 into the laser light L21 and the laser light L22, outputs the laser light L21 to the output switching unit 30, and outputs the laser light L22 is output to the monitor unit 40.

The output switching unit 30A has a 2×1 optical switch that receives the laser beams L11 and L21 and selectively outputs one of the laser beams L11 and L21 under the control of the control unit 50 . The output switching unit 30A can be configured using, for example, a Mach-Zehnder type optical switch.

The monitor section 40A includes a filter 42 and photodetectors 43A1 and 43A2. The filter 42 receives the laser light L12 from the wavelength tunable laser element 11 from one side, the first port 42a, and receives the laser light L22 from the wavelength tunable laser element 12 from the other side, the second port 42b. . A laser beam L13, which is the laser beam L12 after passing through the filter 42, is output from the second port 42b side. A laser beam L23, which is the laser beam L22 after passing through the filter 42, is output from the first port 42a side.

The optical coupler 21A receives the laser beam L23 and outputs it to the photodetector 43A2. The optical coupler 22A receives the laser beam 13 and outputs it to the photodetector 43A1.

The photodetector 43A1 receives the laser beam L13 and outputs a current signal having a current value corresponding to the received light intensity to the control unit 50 . The photodetector 43A2 receives the laser beam L23 and outputs a current signal having a current value corresponding to the received light intensity to the control unit 50 .

The controller 50 monitors the frequencies of the laser beams L13 and L23 based on the correspondence between the PD current values of the photodetectors 43A1 and 43A2 and the laser oscillation frequencies. Such a correspondence relationship is obtained in advance by experiments or the like, and is stored in the storage unit as table data or relational expressions.

In the wavelength tunable laser device 100A configured as described above, similarly to the wavelength tunable laser device 100, when the frequency is varied continuously over a wide band, the frequency of the output laser light is highly stable. Furthermore, in the wavelength tunable laser device 100A, the frequency of the laser light from the wavelength tunable laser element that is being transmitted and the frequency of the laser light from the wavelength tunable laser element that is in the standby state can be monitored at the same time. Sweeping the frequency and setting the frequency in the standby state can be performed separately and simultaneously for the light. This makes it possible to achieve a more accurate or continuous sweep.

(Embodiment 3)
FIG. 10 is a schematic configuration diagram of a wavelength tunable laser device according to Embodiment 3. FIG. The wavelength tunable laser apparatus 100B has a configuration in which the monitor section 40B of the wavelength tunable laser apparatus 100A shown in FIG. 9 is replaced with a monitor section 40B, and optical couplers 21B and 22B are added.

The monitor section 40B has a configuration obtained by adding photodetectors 43B1 and 43B2 to the monitor section 40A.

The optical coupler 21B transmits the laser beams L12 and L23, extracts the laser beam L14 which is a part of the laser beam L12, and outputs it to the photodetector 43B1. The optical coupler 22B transmits the laser beams L13 and L22, extracts the laser beam L24, which is a part of the laser beam L22, and outputs it to the photodetector 43B2.

The photodetector 43B1 receives the laser beam L14 and outputs a current signal having a current value corresponding to the received light intensity to the control unit 50 . The photodetector 43B2 receives the laser beam L24 and outputs a current signal having a current value corresponding to the intensity of the received light to the controller 50 .

The controller 50 monitors the frequency of the laser light L13 based on the correspondence relationship between the ratio of the PD current value of the photodetector 43A1 to the PD current value of the photodetector 43B1 (PD current ratio) and the laser oscillation frequency. Further, the controller 50 monitors the frequency of the laser light L23 based on the correspondence relationship between the ratio of the PD current value of the photodetector 43A2 to the PD current value of the photodetector 43B2 (PD current ratio) and the laser oscillation frequency. do. Such a correspondence relationship is obtained in advance by experiments or the like, and is stored in the storage unit as table data or relational expressions.

In the wavelength tunable laser device 100B configured as described above, similarly to the wavelength tunable laser device 100A, when the frequency is continuously varied over a wide band, the frequency of the output laser light is highly stable, and A more precise or continuous sweep can be achieved.

Further, the wavelength tunable laser device 100B monitors the frequency of the laser light based on the PD current ratio. For example, when the laser light intensity of the wavelength tunable laser element changes over time, the PD current value changes with the change in the laser light intensity. A decrease in monitor accuracy is suppressed.

(An example of the filter configuration of the monitor section)
In the example described with reference to FIG. 6, the controller 50 determines the frequency of the laser light based on the PD current value and the discrimination curve. Here, in the region indicated by the double-headed arrow Ar sandwiched between the two broken lines in FIG. Relatively high. However, outside the range of the double-headed arrow Ar, the slope of the discrimination curve is small, so the accuracy of frequency determination is relatively low. Such an out-of-range area is also called a dead zone or the like.

Therefore, for example, as shown in FIG. 11, a plurality of discrimination curves C1 and C2 having mutually different phases are prepared, and when the frequency represented by point P1 is monitored, the discrimination curve C1 is used and the frequency represented by point P2 is used. If the discrimination curve C2 is used when monitoring the frequency at which the signal is detected, the determination accuracy can be relatively high regardless of the frequency.

FIG. 12 is a diagram showing an example of a configuration for preparing a plurality of discrimination curves. In the configuration shown in FIG. 12, the monitor section includes a filter 42 and a changing means 60 for changing the frequency characteristic of the filter 42. In the configuration shown in FIG. The changing means 60 is configured using a temperature control element such as a Peltier element or a stress applying element such as a piezo element. By changing the temperature of the filter 42 and the stress applied to the filter 42, the changing means 60 can change the frequency characteristic of the filter 42, for example, as shown by the discrimination curves C1 and C2 in FIG.

FIG. 13 is a diagram showing another example of a configuration for preparing a plurality of discrimination curves. In the configuration shown in FIG. 13, the monitor unit 40C has the configuration of the monitor unit 40 shown in FIG. It has a configuration with the addition of The filters 42C1 and 42C2 are examples of a plurality of filters having periodic response characteristics with respect to the frequency of light and different frequency characteristics from each other.

The optical switch 41 selectively passes the laser beam L12 or the laser beam L22 as the laser beam L4 under the control of the control unit 50 . The optical coupler 44C splits the laser beam L4 into a laser beam L41 and a laser beam L42. The filter 42C1 has characteristics like the discrimination curve C1 in FIG. 11, for example, and transmits the laser light L41 with a transmittance according to the frequency of the laser light L41. Laser light L41 after passing through filter 42C1 is referred to as laser light L51. The photodetector 43C1 receives the laser beam L51 and outputs a current signal having a current value corresponding to the received light intensity to the control unit 50 . The filter 42C2 has characteristics like the discrimination curve C2 in FIG. 11, for example, and transmits the laser light L42 with a transmittance according to the frequency of the laser light L42. Laser light L42 after passing through filter 42C2 is referred to as laser light L52. The photodetector 43C2 receives the laser beam L52 and outputs a current signal having a current value corresponding to the intensity of the received light to the control unit 50 .

The controller 50 monitors the frequency of the laser light L51 or L52 based on the correspondence between the PD current value from the photodetector 43C1 or 43C2 and the laser oscillation frequency. Such a correspondence relationship is obtained in advance by experiments or the like, and is stored in the storage unit as table data or relational expressions.

In the control unit 50, based on the correspondence between a calculated value (for example, a linear combination value) obtained by calculating the PD current value from the photodetector 43C1 and the PD current value from the photodetector 43C2 and the laser oscillation frequency, The frequencies of the laser beams L51 and L52 may be monitored. Since such a calculated value includes the effect of the discrimination curve of the filter that does not have a dead band with respect to the frequencies of the laser beams L51 and L52, the determination accuracy can be relatively high regardless of the frequency.

(Swept frequency width)
In the above embodiment, the frequency width Δf1 for continuously sweeping the frequency of the laser light from the wavelength tunable laser element 11 and the frequency width Δf2 for continuously sweeping the frequency of the laser light from the wavelength tunable laser element 12 may be the same. Good, but can be different.

FIG. 14 is an explanatory diagram of an example in which two sweeps have different frequency widths. As shown in FIG. 14A, in this example, the laser oscillation frequency of the wavelength tunable laser element 11 is continuously swept from frequency fa (wavelength λa) to frequency fb (wavelength λb), and Δf1=|fb −fa|. On the other hand, the laser oscillation frequency of the wavelength tunable laser element 12 is continuously swept from frequency fb (wavelength λb) to frequency fc (wavelength λc), and Δf2=|fc−fb|. Then, Δf2>Δf1. In this example, the wavelength tunable laser element that outputs laser light to the outside is switched at frequencies fa, fb, and fc.

In this case, as indicated by circles, triangles, and squares on the discrimination curve in FIG. 14(b), the switching frequencies are not in the dead zone, but are in the region where the wavelength determination accuracy is relatively high as indicated by the arrow Ar. By doing so, the frequency accuracy of the switching timing of the wavelength tunable laser element that outputs laser light to the outside can be made relatively high.

(Construction of still another example of the monitor section)
In the above embodiment, for example, the monitor section 40 is configured using the filter 42 having periodic response characteristics with respect to the frequency of light, but the configuration of the monitor section is not limited to this. For example, the monitor unit may be configured to monitor the frequency of the laser light by heterodyne detection, eg, as shown in FIG. 15 below.

FIG. 15 is a configuration diagram of still another example of the monitor section. The monitor section 40D includes an optical multiplexer 41D and a photodetector 43. As shown in FIG. The optical multiplexer 41D multiplexes the laser beams L12 and L22 and outputs the combined laser beam L6 to the photodetector 43 . The photodetector 43 receives the laser beam L6 and outputs a current signal having a current value corresponding to the received light intensity to the control unit 50 .

Here, the laser beam L6 contains a difference frequency component between the laser beams L12 and L22. The controller 50 detects the difference frequency component from the photodetector 43 and determines the frequency difference between the laser beams L12 and L22. Then, when the frequency difference falls within a predetermined range, it is determined that the frequency of the laser light L12 and the frequency of the laser light L22 substantially match.

In the monitor section 40D having such a configuration, it is not necessary to control an optical switch for selecting one of the laser beams L12 and L22, and the control can be omitted.

In addition, the present invention is not limited by the above-described embodiment. The present invention also includes a configuration obtained by appropriately combining the constituent elements of the above-described embodiments. Further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible.

11, 12: wavelength tunable laser element 11a: first reflecting mirror 11b: gain section 11c: phase adjusting section 11d: second reflecting mirror 13: laser light 21, 21A, 21B, 22, 22A, 22B, 33, 44C: light Couplers 30, 30A: Output switching units 31, 32: Optical blocking elements 40, 40A, 40B, 40C, 40D: Monitor unit 41: Optical switch 41D: Optical multiplexers 42, 42C1, 42C2: Filter 42a: First port 42b: Second port 43, 43A1, 43A2, 43B1, 43B2, 43C1, 43C2: photodetector 50: control unit 60: changing means 100, 100A, 100B: wavelength tunable laser device Ar: arrows C1, C2: discrimination curves L1, L11 , L12, L13, L14, L2, L21, L22, L23, L24, L3, L4, L41, L42, L5, L51, L52, L6: laser light l31, l32: solid line l31', l32': broken line

Claims (12)

a plurality of wavelength tunable laser elements including a first wavelength tunable laser element and a second wavelength tunable laser element capable of changing a laser oscillation frequency;
a control unit;
A wavelength tunable laser device that continuously sweeps the frequency of laser light to be output to the outside,
The control unit
continuously sweeping the frequency of the laser light to a first frequency while oscillating the first wavelength tunable laser element and outputting the laser light to the outside;
During the sweep, the laser oscillation frequency of the second wavelength tunable laser element is set to the first frequency to cause laser oscillation, and output of the laser light to the outside is cut off to enter a standby state;
When it is determined that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency, output of the laser light from the first wavelength tunable laser element to the outside is cut off and the second wavelength is selected. releasing the standby state of the tunable laser element and outputting the laser light of the second wavelength tunable laser element to the outside;
A tunable laser device that performs the step at least once. 2. The wavelength tunable laser according to claim 1, wherein the controller oscillates the first wavelength tunable laser element and the second wavelength tunable laser element at a predetermined frequency based on control parameters stored in a storage unit. Device. Let M be the number of wavelength tunable laser elements included in the plurality of wavelength tunable laser elements, and the controller cuts off the output of laser light from the first wavelength tunable laser element to the outside and the second wavelength tunable laser element. 3. The wavelength tunable laser device according to claim 1, wherein N≧M, where N is the number of times the device is released from the standby state and the laser beam of the second wavelength tunable laser device is output to the outside. The wavelength tunable laser device according to any one of claims 1 to 3, wherein the wavelength tunable laser element can generate a mode hop in which the laser oscillation frequency changes discontinuously. The frequency width for sweeping the frequency of the laser light of the first tunable laser element or the second tunable laser element is the frequency interval of the cavity mode of the first tunable laser element or the second tunable laser element. The wavelength tunable laser device according to any one of claims 1 to 4, which is smaller than three times. Equipped with a monitor unit for monitoring the frequency of the laser light,
When the control unit determines that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency, the second wavelength in a state where the laser oscillation frequency is set to the first frequency When the laser oscillation frequency of the tunable laser element is monitored using the monitor section, and it is determined that the monitored laser oscillation frequency substantially matches the current laser oscillation frequency of the swept wavelength tunable laser element. The wavelength tunable laser device according to any one of claims 1 to 5. The monitor section includes a filter having a periodic response characteristic with respect to the frequency of light. 7. The wavelength tunable laser device according to claim 6, wherein the laser light of the element is input from the other of said filters. 7. The wavelength tunable laser device according to claim 6, wherein said monitor unit comprises a filter having a periodic response characteristic with respect to the frequency of light, and changing means for changing the frequency characteristic of said filter. 7. The wavelength tunable laser device according to claim 6, wherein the monitor unit has a plurality of filters having periodic response characteristics with respect to the frequency of light and different frequency characteristics from each other. 7. The wavelength tunable laser device according to claim 6, wherein the monitor section is configured to monitor the frequency of the laser light by heterodyne detection. continuously sweeping the frequency of the laser light while oscillating the second wavelength tunable laser element and outputting the laser light to the outside;
The frequency width for continuously sweeping the frequency of the laser light from the first wavelength tunable laser element is different from the frequency width for continuously sweeping the frequency of the laser light from the second wavelength tunable laser element. 11. The wavelength tunable laser device according to any one of 10. a plurality of wavelength tunable laser elements including a first wavelength tunable laser element and a second wavelength tunable laser element capable of changing a laser oscillation frequency;
a control unit;
A control method for a wavelength tunable laser device that continuously sweeps the frequency of laser light to be output to the outside, comprising:
The control unit
continuously sweeping the frequency of the laser light to a first frequency while oscillating the first wavelength tunable laser element and outputting the laser light to the outside;
During the sweep, the laser oscillation frequency of the second wavelength tunable laser element is set to the first frequency to cause laser oscillation, and output of the laser light to the outside is cut off to enter a standby state;
When it is determined that the frequency of the laser light from the first wavelength tunable laser element substantially matches the first frequency, output of the laser light from the first wavelength tunable laser element to the outside is cut off and the second wavelength is selected. releasing the standby state of the tunable laser element and outputting the laser light of the second wavelength tunable laser element to the outside;
A method of controlling a tunable laser device, wherein the step is performed at least once.

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