JP6510990B2 - Wavelength variable light source and driving method thereof - Google Patents

Description

  The present invention relates to a wavelength tunable light source and a method of driving the same.

  As a light source used for light absorption analysis or the like, an external resonator-type wavelength-tunable light source of which wavelength is selected by rotating a diffraction grating is known. For rotation of the diffraction grating, a step operation type actuator (for example, refer to Patent Document 1) or a MEMS (Micro Electro Mechanical Systems) actuator (for example, refer to Patent Document 2) is used. The step-motion actuator has a wide movable range, and can accurately stop at an arbitrary angle. On the other hand, the MEMS actuator has a high scan rate, and when it is used for absorption analysis etc., S / N can be improved in a short time by integration and averaging.

US Patent Specification 7466734 U.S. Patent Specification No. 8780347

  Since the step rate actuator has a low scan rate, it can not improve S / N in a short time as in the case of a MEMS actuator when it is used for absorption analysis or the like. On the other hand, since the MEMS actuator has a narrow movable range and can not accurately stop the diffraction grating at an arbitrary angle, it can not realize a wide wavelength range and high wavelength controllability like a step operation type actuator.

  An object of the present invention is to provide a wavelength tunable light source capable of enhancing a scan rate while maintaining a wide wavelength range and high wavelength controllability, and a method of driving the same.

  The variable-wavelength light source according to the present invention is a semiconductor laser that emits pulsed light and a diffraction grating that constitutes an external resonator together with the semiconductor laser, and the pulsed light emitted from the semiconductor laser is incident and is incident among the pulsed light. A diffraction grating for returning light of a wavelength according to an angle to a semiconductor laser, and a rotation drive unit for rotating the diffraction grating to change an incident angle, the rotation drive unit including a rotation shaft, and a step operation type A second actuator including a first actuator, a support, a movable part provided with a diffraction grating, and a connecting part rotatably connecting the movable part to the support; Is mounted on the rotating shaft such that the rotation axis of the movable part coincides with the central axis of the rotation shaft.

  In this wavelength tunable light source, a rotational drive unit for rotationally driving a diffraction grating that constitutes an external resonator includes a second actuator in addition to the first actuator that is a step operation type. The second actuator is rotatably connected to the support by a connection and includes a movable portion provided with a diffraction grating. Therefore, the scan rate can be increased by the second actuator while maintaining a wide wavelength range and high wavelength controllability by the first actuator. In addition, since the rotation axis of the movable part coincides with the central axis of the rotation shaft, the length of the external resonator is kept constant. This maintains the repeatability and stability of the wavelength.

  A method of driving a variable-wavelength light source according to the present invention is the method of driving a variable-wavelength light source described above, comprising the steps of: driving a first actuator; and driving a second actuator with the first actuator stopped. And.

  In this method of driving a variable wavelength light source, for example, when applied to absorption analysis, after performing coarse movement scan in a wide wavelength range by the first actuator, the wavelength range to be analyzed in more detail is narrowed down and the narrowed range is narrowed Fine movement scanning can be performed at high speed by the two actuators. This makes it possible to increase the accuracy of analysis in any wavelength range while maintaining a wide range of wavelength that can be analyzed.

  A method of driving a variable wavelength light source according to the present invention is the method of driving a variable wavelength light source described above, wherein a stepping motor is used as the first actuator, and the incident angle is changed by the first angle in one step. The actuator is driven at a first frequency and the second actuator is driven at a second frequency such that the incident angle increases or decreases with the second angle as the maximum amplitude, the first frequency and the second frequency being equal to each other, the first angle Where Δθ is the second angle is Δθ / 8.

  In this driving method of the wavelength variable light source, the unevenness of the angular velocity of the diffraction grating generated when the first actuator is used can be canceled by the second actuator. Thereby, the change speed of the wavelength of the light emitted from the variable wavelength light source can be made constant.

  The method of driving a variable wavelength light source according to the present invention is the method of driving a variable wavelength light source described above, wherein an ultrasonic motor is used as the first actuator, and the incident angle is changed by each first angle in one step. Assuming that one actuator is driven at a first frequency and the second actuator is driven at a second frequency such that the incident angle increases or decreases with the second angle as the maximum amplitude, and the first frequency is f, the second frequency is 2f If the first angle is Δθ, the second angle is Δθ / 16.

  In this driving method of the wavelength variable light source, the unevenness of the angular velocity of the diffraction grating generated when the first actuator is used can be canceled by the second actuator. Thereby, the change speed of the wavelength of the light emitted from the variable wavelength light source can be made constant.

  According to the present invention, the scan rate can be increased while maintaining a wide wavelength range and high wavelength controllability.

It is a block diagram of the absorption analyzer using the wavelength variable light source which concerns on this embodiment. It is a block diagram of the wavelength variable light source which concerns on this embodiment. It is a block diagram of a 2nd actuator. It is a graph of the light absorbency of methane obtained by coarse movement scan. It is a graph of the normalized absorbance of methane. It is a graph of the light absorbency of methane obtained by fine movement scan. It is a timing chart at the time of driving only the first actuator. It is a time waveform of the rotation amount in another driving method of a wavelength variable light source. It is a timing chart in the case of an ultrasonic motor. It is a time waveform of the amount of rotation in another drive method in the case of an ultrasonic motor. It is a figure for demonstrating the case where the rotating shaft is offset.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and redundant description will be omitted.

  FIG. 1 is a block diagram of an absorption analyzer using a variable wavelength light source according to the present embodiment. As shown in FIG. 1, the absorptiometry device 100 is a device for analyzing the component of the gas, and the wavelength variable light source 10, the rotation control unit 12, the gas cell 16, the lens 18, the detector 20, and the lock An in-amplifier 22 and an oscilloscope 24 are provided.

  FIG. 2 is a block diagram of the wavelength tunable light source according to the present embodiment. As shown in FIGS. 1 and 2, the variable wavelength light source 10 includes a semiconductor laser 1, a laser drive unit 2, a lens 3, a diffraction grating 4, a rotation drive unit 5, a lens 7, and a housing 8. And have. The housing 8 is omitted in FIG.

  The semiconductor laser 1 has a first end 1a and a second end 1b opposed to each other. In the present embodiment, the semiconductor laser 1 is a quantum cascade laser (QCL). The quantum cascade laser can emit broadband light in the mid-infrared region by having a structure in which a plurality of active layers having different central wavelengths are stacked in a stack. The semiconductor laser 1 generates (turns on) the pulsed light L1 by receiving (applying) the drive current signal S0 from the laser drive unit 2, and emits the pulsed light L1 from the first end 1a. The semiconductor laser 1 is not limited to the quantum cascade laser.

  The first end 1a includes a reflection reducing film (not shown). Thereby, the reflectance when light is emitted from the first end 1a to the outside is reduced to, for example, 5% or less, and the reflectance when light is incident from the outside to the first end 1a is, for example, 5% or less Reduced. The second end 1 b includes a reflection control film (not shown) for obtaining an end face reflectance suitable for oscillation. Thereby, the reflectance when light is emitted from the second end 1 b to the outside is set to 50% to 90%.

  The laser driver 2 drives the semiconductor laser 1. The laser drive unit 2 is a laser drive power supply that outputs a drive current signal S 0 to the semiconductor laser 1. The laser drive unit 2 may output a drive current signal S0 by using an external trigger as a signal input from another device (not shown). Drive current signal S0 is, for example, a pulse signal, and the duty ratio of drive current signal S0 is, for example, 1% to 10%.

  The lens 3 collimates the pulsed light L1 emitted from the first end 1a. The lens 3 is made of a material (for example, ZnSe) that is transparent at the oscillation wavelength. The lens 3 may be an aspheric lens to reduce spherical aberration. The lens 3 may be provided on both sides with a reflection reducing film that reduces the reflectance to, for example, 5% or less at the oscillation wavelength.

  The diffraction grating 4 is, for example, a blazed diffraction grating in which the cross section of the grating has a sawtooth shape. The pulse light L1 emitted from the first end 1a and collimated by the lens 3 enters the diffraction grating 4. On the grating surface of the diffraction grating 4, a reflective film 4 a with high reflectance is provided. Thereby, the diffraction grating 4 diffracts the light of the wavelength λ corresponding to the incident angle θ among the incident pulse light L1 in the direction opposite to the incident direction, and feeds it back to the first end 1a as the diffracted light L2. The incident angle θ is an angle formed by the optical axis A of the pulse light L1 and the normal to the lattice plane.

If the grating period (step interval) d of the diffraction grating 4 is determined, the incident angle θ with respect to the wavelength λ to be fed back is uniquely determined by the following equation (1). Because of the Littrow arrangement, the diffraction order m is 1. The incident angle and the diffraction angle are equal.
mλ = 2d · sin θ (1)

  The diffraction grating 4 and the second end 1 b of the semiconductor laser 1 in particular constitute a Littrow-type external resonator (EC: External Cavity) E. That is, the semiconductor laser 1 is an external resonant quantum cascade laser (EC-QCL), can realize a wide variable wavelength range, and can perform absorption analysis of a plurality of substances (in particular, organic substances). The diffraction grating 4 and the second end 1b multiply reflect the diffracted light L2 and amplify it. The diffraction grating 4 and the second end 1b emit the pulsed laser light L3 thus obtained from the second end 1b.

  The rotation drive unit 5 is a hybrid actuator including a first actuator 51 which is a step operation type and a second actuator 52 which is a MEMS actuator. The rotation drive unit 5 receives control signals S1 and S2 from the rotation control unit 12, and rotates the diffraction grating 4 based on the input control signals S1 and S2 to change the incident angle θ. The rotation angle of the diffraction grating 4 by the rotation drive unit 5 is an angle formed by the optical axis A of the pulse light L1 and the normal to the grating surface, and is equal to the incident angle θ.

  The first actuator 51 includes a rotating shaft 53 (see FIG. 3). The second actuator 52 is attached to the rotating shaft 53. The first actuator 51 is, for example, an ultrasonic motor and a stepping motor. In the present embodiment, the first actuator 51 is a stepping motor.

  FIG. 3 is a configuration diagram of the second actuator as viewed from the normal direction of the lattice plane. As shown in FIG. 3, the second actuator 52 includes a support 55, a movable part 56, and a pair of connecting parts 57. The support portion 55 is a frame whose outer contour has a rectangular shape. The movable portion 56 is a flat plate whose outer contour has a rectangular shape, and is disposed inside the support portion 55 at a distance from the support portion 55. The movable portion 56 is provided with the diffraction grating 4.

  The pair of connecting portions 57 rotatably connect the movable portion 56 to the support portion 55. In the present embodiment, the support portion 55, the movable portion 56, and the pair of connecting portions 57 are integrally formed, and are made of, for example, Si. The second actuator 52 is attached to the rotation shaft 53 such that the rotation axis R2 of the movable portion 56 coincides with the central axis R1 of the rotation shaft 53.

  The second actuator 52 sets the central axis of the pair of connecting portions 57 as the rotation axis R2 based on the control signal S2, and the movable portion 56 at a predetermined swing angle (about ± 15 ° at the maximum) and a predetermined frequency (for example, 1 kHz). By rotating the diffraction grating 4 (see FIG. 2). That is, the second actuator 52 increases or decreases the incident angle θ at a predetermined frequency with the predetermined swing angle as the maximum amplitude. The driving method of the second actuator 52 is an electromagnetic method, an electrostatic method, a piezoelectric method or the like.

  As shown in FIGS. 1 to 3, the first actuator 51 operates based on a control signal S 1 that is a movement command signal, and rotationally drives a second actuator 52 attached to the rotating shaft 53. Since the second actuator 52 is provided with the diffraction grating 4, the first actuator 51 rotationally drives the diffraction grating 4 together with the second actuator 52. Since the first actuator 51 is a step operation type, the minimum movement step (minimum rotation amount) is discrete. The minimum moving step of the first actuator 51 is, for example, 0.0025 °. The rotational speed of the first actuator 51 is about 0.5 rpm to several rpm, and the scan rate (the number of wavelength scans per second) is about 10 Hz at the maximum.

  The lens 7 collimates the laser beam L3 emitted from the second end 1b. The lens 7 is made of a material (for example, ZnSe) transparent at the oscillation wavelength. The lens 7 may be an aspheric lens to reduce spherical aberration. The lens 7 may be provided on both sides with a reflection reducing film that reduces the reflectance to, for example, 5% or less at the oscillation wavelength.

  The housing 8 accommodates the semiconductor laser 1, the lens 3, the diffraction grating 4, the rotational drive unit 5, and the lens 7 therein. The housing 8 has a window 8a. From the window 8a, the laser beam L3 emitted from the second end 1b and collimated by the lens 7 is emitted to the outside. The window 8a may be made of a material (for example, ZnSe) transparent at the oscillation wavelength, and reflection reduction films may be provided on both sides to reduce the reflectance to, for example, 5% or less at the oscillation wavelength.

  The rotation control unit 12 outputs control signals S1 and S2 to the rotation drive unit 5 to control the rotation of the rotation drive unit 5. Specifically, the rotation control unit 12 outputs the control signal S1 to the first actuator 51, and outputs the control signal S2 to the second actuator 52.

  The gas cell 16 is a cylindrical container and has a gas inlet 16a and an outlet 16b. The gas cell 16 is configured such that a gas to be subjected to gas analysis flows inside along the axial direction of the gas cell 16. The gas cell 16 has a first window 16c for causing the laser light L3 to be incident into the gas cell 16 at one end in the axial direction, and a second window 16d for emitting the laser light L4 having passed through the gas to the outside of the gas cell 16 Have at the end.

  The lens 18 condenses the laser light L4 and causes the detector 20 to receive the condensed light. The detector 20 receives the light collected by the lens 18 and converts the intensity of the received light into an electrical signal S3. The detector 20 is, for example, a photodiode. The detector 20 outputs the electrical signal S3 to the lock-in amplifier.

  The lock-in amplifier 22 receives the electric signal S3 from the detector 20 and also receives the drive current signal S0 from the laser drive unit 2 as a reference signal. The lock-in amplifier 22 removes unnecessary noise from the electrical signal S3 based on the drive current signal S0, and outputs the electrical signal S4 to the oscilloscope 24 as a signal indicating light output (intensity).

  The oscilloscope 24 receives the electrical signal S4 from the lock-in amplifier 22, and outputs, for example, a gas absorption line as an analysis result based on the electrical signal S4. The gas absorption line is a graph in which the horizontal axis represents time (wavelength) and the vertical axis represents light output.

  Subsequently, a method of driving the absorbance analyzer 100, specifically, a method of driving the variable wavelength light source 10 will be described. First, control signals S 1 and S 2 are output from the rotation control unit 12 and input to the rotation drive unit 5. Thus, the rotation drive unit 5 is driven. As a result, the diffraction grating 4 is rotationally driven by the rotation drive unit 5 to change the incident angle θ.

  At this time, first, in a state where the second actuator 52 is stopped, the first actuator 51 is driven so as to continuously change the incident angle θ (coarse scan). Subsequently, the first actuator 51 is driven such that the incident angle θ becomes a predetermined angle α. Next, in a state where the first actuator 51 is stopped, the second actuator 52 is driven so that the incident angle θ increases or decreases around the predetermined angle α (fine movement scan). That is, this driving method includes the steps of driving only the first actuator 51 of the rotation driving unit 5 and driving only the second actuator 52.

  At the time of coarse movement scan and fine movement scan, a drive current signal S 0 is output from the laser drive unit 2 and input to the semiconductor laser 1 and the lock-in amplifier 22. By inputting the drive current signal S0 to the semiconductor laser 1, the semiconductor laser 1 generates pulsed light L1. The generated pulse light L1 is emitted from the first end 1a.

  The pulsed light L 1 is collimated by the lens 3 and then enters the diffraction grating 4. The diffraction grating 4 diffracts the light of the wavelength λ corresponding to the incident angle θ of the pulsed light L1, and feeds it back to the first end 1a as the diffracted light L2. The diffracted light L2 is multiply reflected between the diffraction grating 4 and the second end 1b and amplified. The diffracted light L2 is oscillated when reaching the threshold current, and is emitted as the laser light L3 from the second end 1b. The laser beam L3 is collimated by the lens 7 and then emitted to the outside of the housing 8 through the window 8a.

  The laser beam L3 emitted from the variable wavelength light source 10 enters the gas cell 16 through the first window 16c. The laser beam L4 that has passed through the gas in the gas cell 16 exits the gas cell 16 through the second window 16d. The laser beam L4 is condensed by the lens 18 and is then received by the detector 20 to be converted into an electric signal S3. The lock-in amplifier 22 removes an unnecessary noise component from the electrical signal S3 and converts it to an electrical signal S4.

  The electrical signal S4 is output to the oscilloscope 24 as a signal indicating the light output of the laser light L4. Since the electrical signal S4 is output in synchronization with the drive current signal S0, the cycle of the electrical signal S4 is the same as the cycle of the drive current signal S0. The electrical signal S4 is analyzed by the oscilloscope 24 to obtain an absorbance analysis result.

FIG. 4 is a graph of absorbance at a wave number of about 1300 cm ⁻¹ of methane (CH ₄ ) obtained by coarse movement scan. The scan rate was 1 Hz, and the absorbance was an average of 10 scans (10 seconds). FIG. 5 is a graph of absorbance (normalized absorbance) in the vicinity of a wave number of 1300 cm ^{−1 of} methane, which is referred to from a National Institute of Standards and Technology (NIST) database.

  It is considered that the closer to the graph of the normalized absorbance in FIG. 5, the higher the accuracy of the absorbance analysis. Compared with the graph of the normalized absorbance of FIG. 5, the graph of the absorbance of FIG. 4 has a dull shape at the peak portion in the center of the graph, and it can be seen that detailed information is not obtained for the peak portion. This is because the step-operation type first actuator 51 is not suitable for earning the number of scans, and it is difficult to increase S / N by integration and averaging.

FIG. 6 is a graph of absorbance at around 1300 cm ⁻¹ wavenumber of methane obtained by the fine movement scan. The predetermined angle α which is the center of the fine movement scan is an angle corresponding to the central wavelength of the peak obtained by the coarse movement scan. That is, by setting the incident angle θ to the predetermined angle α, the wavelength of the laser light L3 output from the variable wavelength light source 10 overlaps the central wavelength of the peak obtained by the coarse movement scan. In this state, the second actuator 52 was driven at a frequency of about 700 Hz with a swing angle of ± 2 °. Absorbance was an average value of 700 scans (one second).

  According to the comparison of FIGS. 4 to 6, according to the variable-wavelength light source 10, by performing the fine movement scan, it is possible to perform the mutual absorption analysis with more accuracy, and it is possible to measure the fine shape of the peak portion which could not be measured by the coarse movement scan. I understand. The method itself of increasing the number of integrations and increasing the S / N by high-speed scanning is also possible with a conventional external resonator-type wavelength-tunable light source using a MEMS actuator.

However, such a conventional tunable light source does not have a coarse movement mechanism like the first actuator 51. For this reason, the central wavelength can not be changed, and an analysis result as shown in FIG. 6 can be obtained only for an absorption peak in a limited range (for example, ± 50 cm ⁻¹ ). On the other hand, since the variable wavelength light source 10 includes the hybrid actuator, similar analysis results can be obtained not only for the peak near 1300 cm ⁻¹ but also for the peak near 1350 cm ⁻¹ , for example.

  Subsequently, another driving method of the wavelength tunable light source according to the present embodiment will be described with reference to FIGS. 7 and 8. This driving method is different from the above-described driving method in that not only the first actuator 51 but also the second actuator 52 is driven in coarse movement scanning. Specifically, the first actuator 51 is driven at the frequency f so that the incident angle θ changes by Δθ in one step, and the second actuator 52 is increased or decreased such that the incident angle θ becomes Δθ / 8 as the maximum amplitude. Drive at frequency f.

  Here, after explaining the problem when only the first actuator 51 is driven in a state where the second actuator 52 is stopped, the reason for driving the first actuator 51 and the second actuator 52 as described above will be described. . FIG. 7 is a timing chart when only the first actuator is driven. In this timing chart, (a) movement command signal (ie, control signal S1), (b) rotation amount (ie, change amount of incident angle θ), and (c) angular velocity (differential value of rotation amount) of the diffraction grating It is shown.

  As shown in FIG. 7, the control signal S1 output from the rotation control unit 12 is a rectangular wave signal having a duty ratio of, for example, 50% and repeating rising and falling every t / 2. Control signal S1 is, for example, a pulse signal having a frequency of 100 kHz (period t of 0.010 msec).

  As described above, in the present embodiment, the first actuator 51 is a stepping motor. The first actuator 51 rotates by the minimum moving step every time one pulse of the control signal S1 is input. The first actuator 51 rotates with the control signal S1 as a trigger. In the present embodiment, the first actuator 51 rotates with the rising of the control signal S1 as a trigger. Thereby, the diffraction grating 4 is rotationally driven together with the second actuator 52 so that the angular velocity of the diffraction grating 4 changes periodically, and the incident angle θ changes. The period of change of the angular velocity is equal to the period t of the control signal S1.

  The angular velocity at the rise of the control signal S1 is the minimum value ω1. The angular velocity after a lapse of about t / 2 from the rise of the control signal S1 is the maximum value ω2. The time waveform of the angular velocity is sinusoidal, and changes continuously (smoothly) from the point where the angular velocity is ω1 to the point where the angular velocity is next ω1. In other words, the angular velocity changes periodically between ω1 and ω2.

  Due to this change in angular velocity, the amount of rotation changes in a step-like manner. Here, the amount of rotation monotonously increases. Note that monotonous increase means that it does not tend to decrease, and means monotonous increase in a broad sense. In FIG. 7B, the amount of rotation in the ideal case where the angular velocity does not change (the angular velocity is constant) is indicated by a one-dot chain line.

  The operation of the rotary drive 5 in the ideal case is a linear operation in direct proportion. Since the operation of the first actuator 51 is a step operation, the amount of rotation by the first actuator 51 repeatedly becomes smaller or larger than the amount of rotation in the ideal case. The amount of rotation by the first actuator 51 and the amount of rotation in the ideal case become equal after approximately t / 2 has elapsed from the rising of the control signal S1 and the rising of the control signal S1.

  Thus, when only the first actuator 51 is driven, unevenness occurs in the angular velocity of the diffraction grating 4 and the angular velocity of the diffraction grating 4 does not become constant. For this reason, when only the first actuator 51 is driven to perform wavelength sweeping, unevenness in the angular velocity of the diffraction grating 4 causes unevenness in the wavelength change rate. As a result, the absorption line width of the absorption curve obtained by the absorption analysis becomes unstable, and the accuracy of the analysis result can not be improved.

  FIG. 8 is a time waveform of the amount of rotation in another driving method of the wavelength tunable light source. The horizontal axis in FIG. 8 represents time, and the vertical axis represents the amount of rotation. In FIG. 8, the time waveform of the amount of rotation when only the first actuator 51 is driven at the frequency f (that is, the period 1 / f) is indicated by an alternate long and short dash line so that the incident angle θ changes by Δθ in one step. It is done. The time waveform of the amount of rotation when only the second actuator 52 is driven at the frequency f (that is, period 1 / f) is shown by a two-dot chain line so that the incident angle θ increases or decreases with Δθ / 8 as the maximum amplitude. There is. A composite waveform of the time waveform of the amount of rotation by the first actuator 51 and the time waveform of the amount of rotation by the second actuator 52 is indicated by a solid line.

  As shown in FIG. 8, the unevenness of the angular velocity of the diffraction grating 4 which occurs when only the first actuator 51 is driven is canceled by the second actuator 52, and the composite waveform becomes a linear shape substantially proportional. Therefore, according to this driving method, the angular velocity of the diffraction grating 4 can be made substantially constant.

  Subsequently, a case where the first actuator 51 is an ultrasonic motor will be described with reference to FIGS. 9 and 10. FIG. 9 is a timing chart when only the first actuator is driven in the case of the ultrasonic motor. FIG. 10 is a time waveform of the amount of rotation in another driving method in the case of an ultrasonic motor. As shown in FIG. 9, the ultrasonic motor is a piezoelectric actuator using a piezoelectric element, and reverses the polarity of the voltage applied to the piezoelectric element at predetermined time intervals in accordance with rising and falling of the control signal S1. It works by. Therefore, in the case of the ultrasonic motor, the cycle of change in angular velocity is 1/2 of the cycle t of the control signal S1, and the ultrasonic motor has two steps of the stepping motor every time one control signal S1 is input. As a minimum move step.

  Therefore, in the case of an ultrasonic motor, as shown in FIG. 10, the first actuator 51 is driven at the frequency f so that the incident angle θ changes by Δθ in one step, and the incident angle θ is Δθ / 16. The second actuator 52 is driven at a frequency 2f so as to increase or decrease as the maximum amplitude. Thereby, the unevenness of the angular velocity of the diffraction grating 4 generated when only the first actuator 51 is driven is canceled by the second actuator 52, and the combined waveform becomes a linear shape substantially proportional. Therefore, according to this driving method, as in the case of the stepping motor, the angular velocity of the diffraction grating 4 can be made substantially constant.

  As described above, in the variable wavelength light source 10, the rotation drive unit 5 is a hybrid actuator having the first actuator 51 which is a step operation type and the second actuator 52 which is a MEMS actuator. Therefore, high speed scanning can be performed by the second actuator 52 while maintaining a wide wavelength range and high wavelength controllability by the first actuator 51.

  Further, a central axis R1 of the rotary shaft 53 of the first actuator 51 and a rotational axis R2 of the movable portion 56 of the second actuator 52 are coaxial. As shown in FIG. 11, when the central axis R1 and the rotation axis R2 are not coaxial but offset, the length LE of the external resonator E changes if the rotation angle of the first actuator 51 changes. Specifically, in FIG. 11B, the rotation angle of the first actuator 51 is larger and the length LE is shorter than in FIG. 11A.

  In FIG. 11, the second actuator 52 is in a stopped state, and the rotation angle of the second actuator 52 is 0 °. Thus, the length LE is uniquely determined by the rotation angle of the first actuator 51. However, in consideration of the rotation of the second actuator 52, the length LE varies due to the combination of the rotation angle of the first actuator 51 and the rotation angle of the second actuator 52. That is, there are a plurality of lengths LE with different mode orders with respect to the incident angle θ that achieves the desired wavelength.

  For example, the first actuator 51 is stopped at a predetermined rotation angle during coarse movement scanning for driving the first actuator 51 with the second actuator 52 stopped and the rotation angle of the second actuator 52 being 0 °. During fine movement scanning in which the second actuator 52 is rotated in a state, even if the incident angle θ is equal, the lengths LE are different from each other, and as a result of the mode order being different, the wavelengths may be different.

  As described above, as a result of the difference in the mode order between the coarse movement scan and the fine movement scan, the wavelength reproducibility and stability may be impaired. On the other hand, in the variable wavelength light source 10, the central axis R1 of the first actuator 51 and the rotation axis R2 of the second actuator 52 are coaxial. As a result, the length LE is uniquely determined with respect to the incident angle θ for achieving the desired wavelength, so that the reproducibility and the stability of the wavelength are maintained. If the length LE is uniquely determined with respect to the incident angle θ for achieving the desired wavelength, there is no problem even if the length LE changes according to the incident angle θ, but the length in the wavelength tunable light source 10 LE is kept constant for all incident angles θ.

  The driving method of the variable wavelength light source 10 includes the steps of driving only the first actuator 51 in the rotation driving unit 5 and driving only the second actuator 52. Thereby, in the absorption spectrometer 100, for example, after performing coarse movement scan in a wide wavelength range by the first actuator 51, the wavelength range to be analyzed in more detail is narrowed down, and the narrowed wavelength range is increased by the second actuator 52 at high speed. Fine movement scan can be performed. As a result, it is possible to increase the accuracy of analysis in any wavelength range while maintaining a wide analysis possible wavelength range.

  In another driving method of the variable wavelength light source 10, when the first actuator 51 is a stepping motor, the first actuator 51 is driven at the frequency f so that the incident angle θ changes by Δθ in one step during coarse movement scanning. At the same time, the second actuator 52 is driven at the frequency f so that the incident angle θ increases or decreases with Δθ / 8 as the maximum amplitude. When the first actuator 51 is an ultrasonic motor, the first actuator 51 is driven at the frequency f so that the incident angle θ changes by Δθ in one step during coarse movement scanning, and the incident angle θ is Δθ / The second actuator 52 is driven at a frequency 2f to increase or decrease 16 as the maximum amplitude.

  In this driving method, the second actuator 52 can cancel out the non-uniformity in angular velocity that occurs when the step-type first actuator 51 is used. Thereby, the fluctuation of the wavelength change rate of the laser light L3 is suppressed. As a result, the absorption line width of the absorption curve obtained by the absorption analysis is stabilized, and the accuracy of the analysis result can be improved.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Laser drive part, 4 ... Diffraction grating, 5 ... Rotation drive part, 10 ... Wavelength-variable light source, 51 ... 1st actuator, 52 ... 2nd actuator, 53 ... Rotation shaft, 55 ... Support part, 56: movable portion, 57: coupling portion, E: external resonator, L1: pulsed light, L2: diffracted light, R1: central axis, R2: rotation axis, θ: incident angle

Claims (4)

A semiconductor laser for emitting pulsed light;
A diffraction grating constituting an external resonator together with the semiconductor laser, wherein the pulse light emitted from the semiconductor laser is incident, and light of a wavelength according to an incident angle of the pulse light is returned to the semiconductor laser A diffraction grating,
And a rotational drive unit that rotates the diffraction grating to change the incident angle.
The rotational drive unit is
A first actuator including a rotating shaft and being step-operated,
A second actuator including a support portion, a movable portion provided with the diffraction grating, and a connecting portion rotatably connecting the movable portion to the support portion;
The variable wavelength light source according to claim 1, wherein the second actuator is attached to the rotating shaft such that a rotating shaft of the movable portion coincides with a central axis of the rotating shaft. The method of driving a variable wavelength light source according to claim 1,
Driving the first actuator;
Driving the second actuator in a state in which the first actuator is stopped. The method of driving a variable wavelength light source according to claim 1,
A stepping motor is used as the first actuator,
The first actuator is driven at a first frequency such that the incident angle changes by a first angle in one step, and the second actuator is increased or decreased such that the incident angle increases or decreases with a second angle. Drive at frequency
A method of driving a tunable light source, wherein the first frequency and the second frequency are equal to each other, and the first angle is Δθ, the second angle is Δθ / 8. The method of driving a variable wavelength light source according to claim 1,
An ultrasonic motor is used as the first actuator,
The first actuator is driven at a first frequency such that the incident angle changes by a first angle in one step, and the second actuator is increased or decreased such that the incident angle increases or decreases with a second angle. Drive at frequency
A driving method of a tunable light source, where the first frequency is f, the second frequency is 2f, and the first angle is Δθ, the second angle is Δθ / 16.

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