JP6676389B2 - Tunable light source - Google Patents

Description

  The present invention relates to a tunable light source.

  Patent Literature 1 discloses that an optical gain medium that emits light, a wavelength selection element that selects a wavelength of light that is emitted from the optical resonator, and an optical gain medium that is provided inside an optical resonator that includes two mirrors. And a light intensity modulating element for modulating the light intensity of the above. In this wavelength swept light source, for example, a diffraction grating is used as a wavelength selection element, and the wavelength of emitted light is made variable by rotating the diffraction grating. Further, in this wavelength-swept light source, the spectral width of emitted light is made constant by synchronizing the driving of the light intensity modulation element and the wavelength selection element.

JP 2014-042010 A

  In a variable wavelength light source used for gas analysis and the like, it is required to keep a changing speed of a wavelength constant. However, in the above-described wavelength-swept light source, when the diffraction grating is rotated by using the step operation type actuator, the wavelength change speed fluctuates as the rotation angle fluctuates stepwise. If pulsed laser light is generated in this state, the amount of change in the wavelength of the laser light may vary between pulses even between adjacent pulses at the same time interval. For this reason, the absorption line width of the absorption curve obtained by gas analysis becomes unstable, and the accuracy of the analysis result cannot be improved.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength tunable light source capable of suppressing a change in a change speed of a wavelength.

  The wavelength tunable light source according to the present invention is a semiconductor laser that emits pulsed light, a laser driving unit that drives the semiconductor laser, and a diffraction grating that forms an external resonator together with the semiconductor laser, and a pulse emitted from the semiconductor laser. Light is incident, the diffraction grating that returns the light of the wavelength corresponding to the incident angle of the pulse light to the semiconductor laser, and the incident angle is changed by rotating the diffraction grating so that the angular velocity of the diffraction grating changes periodically. The step operation type rotary drive unit and the laser drive unit that drive the semiconductor laser so as to emit pulse light in synchronization with a change in angular velocity.

  In this wavelength tunable light source, the angular velocity of the diffraction grating periodically changes because a step operation type rotation drive unit is used for rotationally driving the diffraction grating that forms the external resonator together with the semiconductor laser. On the other hand, a semiconductor laser emits pulsed light in synchronization with a change in angular velocity. Thereby, the angular velocity at which the pulsed light is emitted can always be regarded as constant. Therefore, the wavelength change speed of the pulsed laser light generated from this pulsed light can always be regarded as constant. As a result, it is possible to suppress the fluctuation of the changing speed of the wavelength.

  Further, the angular velocity periodically changes between a first angular velocity and a second angular velocity larger than the first angular velocity, and the laser driving unit emits pulse light when the angular velocity is the first angular velocity. The semiconductor laser may be driven. In this case, since the first angular velocity is the minimum angular velocity, when the angular velocity is the first angular velocity, the incident angle is unlikely to change with time. Therefore, when the angular velocity is the first angular velocity, the semiconductor laser emits pulse light, so that the tolerance to jitter can be improved.

  A tunable light source according to the present invention includes a semiconductor laser that emits pulsed light, a laser driver that drives the semiconductor laser, a mirror that reflects pulsed light emitted from the semiconductor laser, and an external resonator together with the semiconductor laser. A pulsed light reflected by a mirror is incident, and a diffraction grating that returns light of a wavelength corresponding to the incident angle of the pulsed light to the semiconductor laser through the mirror, and the angular velocity of the mirror is periodic. A step operation type rotary drive unit that drives the mirror to change the incident angle by rotating the mirror so that the laser beam is emitted in synchronization with the change in the angular velocity. Drive.

  In this wavelength tunable light source, a step operation type rotation drive unit is used for rotationally driving a mirror disposed between a semiconductor laser and a diffraction grating which forms an external resonator together with the semiconductor laser. Changes periodically. On the other hand, a semiconductor laser emits pulsed light in synchronization with a change in angular velocity. Thereby, the angular velocity at which the pulsed light is emitted can always be regarded as constant. Therefore, the wavelength change speed of the pulsed laser light generated from this pulsed light can always be regarded as constant. As a result, it is possible to suppress the fluctuation of the changing speed of the wavelength.

  ADVANTAGE OF THE INVENTION According to this invention, the fluctuation | variation of the changing speed of a wavelength can be suppressed.

1 is a configuration diagram of an absorption spectrometer using a variable wavelength light source according to the present embodiment. FIG. 2 is a configuration diagram of a variable wavelength light source according to the present embodiment. 4 is a timing chart of the wavelength tunable light source according to the embodiment. 5 is an example of a time waveform of a rotation amount and a light output in the present embodiment. 5 is an example of a time waveform of a rotation amount and a light output in a comparative embodiment. It is a lineblock diagram of a wavelength variable light source concerning a modification.

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

  FIG. 1 is a configuration diagram of an absorption spectrometer using a variable wavelength light source according to the present embodiment. FIG. 2 is a configuration diagram of the wavelength variable light source according to the present embodiment. As shown in FIG. 1, an absorption spectrometer 100 is a device for analyzing a gas component, and includes a wavelength variable light source 10, a rotation control unit 12, a gas cell 16, a lens 18, a detector 20, a lock An in-amplifier 22 and an oscilloscope 24 are provided.

  As shown in FIGS. 1 and 2, the variable wavelength light source 10 includes a semiconductor laser 1, a laser driver 2, a lens 3, a diffraction grating 4, a rotation driver 5, a lens 7, and a housing 8. And Note that the housing 8 is omitted in FIG.

  The semiconductor laser 1 has a first end 1a and a second end 1b facing each other. In the present embodiment, the semiconductor laser 1 is a quantum cascade laser (QCL). Since the quantum cascade laser has a structure in which a plurality of active layers having different center wavelengths are stacked in a stack, light of a broad band in the mid-infrared region can be emitted. The semiconductor laser 1 generates (turns on) the pulse light L1 when the drive current signal S2 is input (applied) from the laser drive unit 2, and emits the pulse light L1 from the first end 1a. The semiconductor laser 1 is not limited to a 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 enters the first end 1a from the outside is reduced to, for example, 5% or less. Reduced. The second end 1b includes a reflection control film (not shown) for obtaining an end face reflectance suitable for oscillation. As a result, the reflectance when light is emitted from the second end 1b to the outside is set to 50% to 90%.

  The laser driver 2 drives the semiconductor laser 1. The laser drive unit 2 receives a pulse-like movement command signal S1 output from the rotation control unit 12 as an external trigger, and outputs a pulse-like drive current signal S2 to the semiconductor laser 1 based on the input movement command signal S1. This is a laser drive power supply to output.

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

  The diffraction grating 4 is, for example, a blazed diffraction grating whose cross section is 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 4a having a high reflectance is provided. Accordingly, the diffraction grating 4 diffracts the light of the wavelength λ corresponding to the incident angle θ out of the incident pulse light L1 in the direction opposite to the incident direction, and returns the diffracted light L2 to the first end 1a. Is the angle between the optical axis A of the pulsed light L1 and the normal to the lattice plane.

If the grating period (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). Since the Littrow arrangement is used, the diffraction order m is 1. The angle of incidence and the angle of diffraction are equal.
mλ = 2d · sin θ (1)

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

  The rotation drive unit 5 is a step operation type actuator having a large rotation range, and drives the diffraction grating 4 to rotate. In the step operation type actuator, the minimum movement step (minimum rotation amount) is discrete. The rotation angle of the diffraction grating 4 by the rotation drive unit 5 is an angle between the optical axis A of the pulse light L1 and the normal to the grating surface, and is equal to the incident angle θ.

  Examples of the step operation type actuator include an ultrasonic motor and a stepping motor. In the present embodiment, the rotation drive unit 5 is a stepping motor. The rotation drive unit 5 drives the diffraction grating 4 to rotate so that the angular velocity of the diffraction grating 4 changes periodically, and changes the incident angle θ. Details of the change in the angular velocity will be described later.

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

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

  The rotation control unit 12 outputs the movement command signal S1 to the rotation drive unit 5 to control the rotation of the rotation drive unit 5. The rotation control unit 12 branches the movement command signal S1 and outputs the signal to the laser driving unit 2.

  The gas cell 16 is a cylindrical container and has a gas inlet 16a and a gas outlet 16b. The gas cell 16 is configured such that a gas to be subjected to gas analysis flows inside the gas cell 16 along the axial direction. The gas cell 16 has a first window 16c at one end in the axial direction for allowing the laser light L3 to enter the gas cell 16, and a second window 16d for emitting the laser light L4 having passed through the gas to the outside of the gas cell 16 in the other axial direction. Has 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 electric signal S3. The detector 20 is, for example, a photodiode. Detector 20 outputs electric signal S3 to the lock-in amplifier.

  The lock-in amplifier 22 receives the electric signal S3 from the detector 20 and the drive current signal S2 from the laser driver 2 as a reference signal. The lock-in amplifier 22 removes unnecessary noise from the electric signal S3 based on the drive current signal S2, and outputs an electric signal S4 to the oscilloscope 24 as a signal indicating an optical output (intensity).

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

  The operation of the absorption spectrometer 100 will be described with reference to FIGS. FIG. 3 is a timing chart of the wavelength tunable light source according to the present embodiment. In this timing chart, (a) the movement command signal S1, (b) the rotation amount (that is, the change amount of the incident angle θ), (c) the angular velocity of the diffraction grating (the differential value of the rotation amount), and (d) the drive current signal S2, and (e) the optical output (ie, electrical signal S4) are shown.

  First, a movement command signal S1 is output from the rotation control unit 12 to the rotation drive unit 5 and the laser drive unit 2. The movement command signal S1 is, for example, a pulse signal having a frequency of 100 kHz (the cycle t is 0.010 msec). The movement command signal S1 is a rectangular wave signal having a duty ratio of, for example, 50% and repeating rising and falling every t / 2.

  As described above, in the present embodiment, the rotation drive unit 5 is a stepping motor. The rotation drive unit 5 rotates by a minimum movement step every time one pulse of the movement command signal S1 is input. The minimum moving step of the rotation drive unit 5 is, for example, 0.0025 deg. The rotation drive unit 5 rotates with the movement command signal S1 as a trigger. In the present embodiment, the rotation drive unit 5 rotates with the rising of the movement command signal S1 as a trigger. Accordingly, the diffraction grating 4 is driven to rotate so that the angular velocity of the diffraction grating 4 changes periodically, and the incident angle θ changes. The cycle of the change in the angular velocity is equal to the cycle t of the movement command signal S1.

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

  Due to such a change in the angular velocity, the amount of rotation changes in a stepwise manner. Here, the rotation amount monotonically increases. It should be noted that the monotonic increase means that there is no tendency to decrease, and means a monotonous increase in a broad sense. In FIG. 3B, the amount of rotation in an ideal case where the angular velocity does not change (the angular velocity is constant) is indicated by a chain line.

  The operation of the rotation drive unit 5 in an ideal case is a linear operation in direct proportion. Since the operation of the rotation drive unit 5 in the actual case is a step operation, the amount of rotation by the rotation drive unit 5 repeatedly becomes smaller or larger than the amount of rotation in the ideal case. After the rise of the movement command signal S1 and about t / 2 after the rise of the movement command signal S1, the rotation amount by the rotation drive unit 5 becomes equal to the rotation amount in an ideal case.

  Subsequently, the drive current signal S2 is output from the laser driver 2 in synchronization with the movement command signal S1, and is input to the semiconductor laser 1 and the lock-in amplifier 22. The drive current signal S2 is a pulse signal output in synchronization with the rotation of the rotation drive unit 5 each time one pulse of the movement command signal S1 is input. The drive current signal S2 is output using the movement command signal S1 as a trigger, similarly to the rotation of the rotation drive unit 5. In the present embodiment, the drive current signal S2 rotates with the rising edge of the movement command signal S1 as a trigger. The frequency and cycle of the drive current signal S2 are equal to the frequency and cycle t of the movement command signal S1. The duty ratio of drive current signal S2 is, for example, 1 to 10%.

  When such a drive current signal S2 is input to the semiconductor laser 1, the pulse light L1 is generated when the angular velocity is ω1 in synchronization with the angular velocity change (with the same cycle t as the angular velocity change cycle). . The generated pulse light L1 is emitted from the first end 1a. For this reason, only when the pulsed light L1 is emitted, it can be considered that the rotation drive unit 5 rotates at a constant speed and the angular velocity is constant.

  After being collimated by the lens 3, the pulse light L 1 enters the diffraction grating 4. In the diffraction grating 4, light having a wavelength λ corresponding to the incident angle θ of the pulse light L1 is diffracted, and returns 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 oscillates when it reaches the threshold current, and is emitted from the second end 1b as laser light L3. After being collimated by the lens 7, the laser light L3 is 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 inside the gas cell 16 passes through the second window 16d and exits outside the gas cell 16. After being condensed by the lens 18, the laser light L 4 is received by the detector 20 and is converted into an electric signal S 3. An unnecessary noise component is removed from the electric signal S3 by the lock-in amplifier 22, and is converted into an electric signal S4.

  The electric signal S4 is output to the oscilloscope 24 as a signal indicating the optical output of the laser light L4. Since the electric signal S4 is output in synchronization with the drive current signal S2, the cycle of the electric signal S4 is equal to the cycle t, like the cycle of the drive current signal S2. When the electric signal S4 is analyzed by the oscilloscope 24, a gas analysis result is obtained.

  Next, a description will be given of the fact that the present embodiment can suppress a change in the wavelength change speed (non-uniformity of the wavelength change) as compared with the comparative embodiment. FIG. 4 is an example of a time waveform of the rotation amount and the light output in the present embodiment. FIG. 5 is an example of a time waveform of the rotation amount and the light output in the comparative embodiment. 4 and 5, the period t is 0.010 ms, and two periods are shown. In regions I, III, and V, the amount of change in the amount of rotation per unit time is small, and in regions II and IV, the amount of change in the amount of rotation per unit time is large. Therefore, when used for wavelength sweeping, the wavelength change is slow in the regions I, III, and V, and the wavelength change is fast in the regions II and IV.

  The comparative embodiment differs from the present embodiment only in that the timing at which the laser driver drives the quantum cascade laser is different. In the comparative embodiment, the quantum cascade laser emits pulsed light at a cycle shorter than the cycle of the change in the angular velocity. As a result, as shown in FIG. 5, pulsed laser light is generated in each of the regions I to V. Therefore, even between adjacent pulses at the same time interval, the amount of change in the wavelength of the laser light varies for each pulse. In particular, in the regions II and IV, since the amount of change in the amount of rotation per time is large, the amount of change in the wavelength of laser light between pulses is also large.

  In general industrial products, step-like unevenness in the angular velocity of a step operation type actuator is hardly noticeable and is often ignored. However, in the case of an external resonance type semiconductor laser, since the angular velocity of the diffraction grating is directly linked to the wavelength change speed, the wavelength change speed becomes uneven as described above. If pulsed laser light is generated in this state, the wavelength change amount of the laser light varies between pulses even between adjacent pulses at the same time interval. For this reason, the absorption line width of the absorption curve obtained by gas analysis becomes unstable, and the accuracy of the analysis result cannot be improved.

  On the other hand, in the present embodiment, the laser driving unit 2 drives the semiconductor laser 1 so as to emit the pulse light L1 in synchronization with the movement command signal S1 (eventually, in synchronization with the change in the angular velocity). I do. Thus, the semiconductor laser 1 emits the pulse light L1 in synchronization with the change in the angular velocity. Therefore, the wavelength change speed of the pulsed laser light L3 generated from the pulsed light L1 can always be regarded as constant.

  The laser drive unit 2 is particularly suitable for the regions I, III, and V in which the amount of change in the amount of rotation per unit time is small, when the angular velocity is at the minimum value ω1 (low rotation period, when the bottom of the angular velocity time waveform is at the bottom). ), The semiconductor laser 1 is driven. Thereby, as shown in FIG. 4, the pulsed laser light L3 is generated when the angular velocity is ω1. FIG. 4 shows only the light output in the region III. When the angular velocity is ω1, the incident angle θ is unlikely to change with time, so that the tolerance to jitter can be improved.

Here, when the angular velocity is ω1, the case where the angular velocity can be regarded as ω1 is included. The range of angular velocities where the angular velocity can be considered as ω1 can be back calculated from the wave number accuracy to be achieved. For example, the number of steps of the diffraction grating 4 is 100 lines / mm, that is, the grating period d = 10 μm / lines, the minimum rotation amount of the rotation drive unit 5 is 0.0025 deg, and the wavelength of the laser beam L3 is 5 μm, that is, the wave number. Is set to 2000 cm ^−1, and a range in which the angular velocity can be regarded as ω1 is obtained by calculation when the wave number accuracy to be achieved is set to 1/100 of the minimum wave number increment.

In the above case, the initial angle of the diffraction grating 4 is 14.4775 deg, and the angle, wavelength, and wave number in the next step are 14.4800 deg, 5.0084 μm, and 1999.6211 cm ⁻¹ , respectively. Thus, the change in wavenumber (ie, the minimum wavenumber increment) is 0.3379 cm ⁻¹ , and the wavenumber accuracy to be achieved is one hundredth of this, 0.0034 cm ⁻¹ . Therefore, the upper limit of the allowable wavenumber 2000.0034Cm ^-1, the lower limit of the allowable wavenumber becomes 1999.9966cm ^-1.

  The lower limit of the allowable wavelength is 4.999999 μm, and the upper limit of the allowable wavelength is 5.00001 μm. At this time, the upper limit of the allowable angle is 14.47754 deg, and the lower limit of the allowable angle is 14.47749 deg. The difference between the upper limit and the lower limit of the allowable angle is 0.0500 mdeg. Therefore, the allowable angle error is 0.0250 mdeg.

  The frequency of the movement command signal S1 is 100 kHz, ω2 = 0.55 deg / ms. If the jitter amount of the laser drive unit 2 is 0.1 μs (corresponding to 1% of 0.010 msec in one cycle), the threshold value of the angular velocity that can be regarded as constant is 0.05 deg / ms. Therefore, the ratio of the threshold value of the angular velocity that can be regarded as constant to ω2 is 9.1%. That is, the range in which the angular velocity can be regarded as ω1 is about 10% or less of ω2.

  Even when the wavelength of the laser beam L3 takes another value, the range in which the angular velocity can be regarded as ω1 as long as the wave number accuracy to be achieved is set to 1/100 of the wave number increment of one step (ie, the minimum wave number increment). Does not change and is about 10% or less of ω2.

  As described above, in the wavelength tunable light source 10, the angular velocity of the diffraction grating 4 is used because the step operation type rotation drive unit 5 is used to rotationally drive the diffraction grating 4 that forms the external resonator E together with the semiconductor laser 1. Changes periodically. On the other hand, the semiconductor laser 1 emits the pulse light L1 in synchronization with the change in the angular velocity. Thus, the angular velocity at which the pulse light L1 is emitted can always be regarded as constant. Therefore, the wavelength change speed of the pulsed laser light L3 generated from the pulsed light L1 can always be regarded as constant. As a result, it is possible to suppress the fluctuation of the changing speed of the wavelength.

  In the absorption spectrometer 100, gas analysis is performed by the pulsed laser light L3 generated by the variable wavelength light source 10. As described above, the laser light L3 is generated based on the pulse light L1 emitted when the angular velocity can be considered to be always constant. For this reason, in the laser beam L3, the wavelength change amount is always constant between adjacent pulses at the same time interval. Thereby, the absorption line width of the absorption curve obtained by gas analysis is stabilized, and the accuracy of the analysis result can be improved.

  Further, the angular velocity changes periodically between ω1 and ω2, and the laser driving unit 2 drives the semiconductor laser 1 so as to emit the pulse light L1 when the angular velocity is ω1. Since ω1 is the minimum angular velocity, when the angular velocity is ω1, the incident angle θ is unlikely to change with time. Therefore, when the angular velocity is ω1, the semiconductor laser 1 emits the pulse light L1, whereby the tolerance to jitter can be improved.

  As described above, the variable wavelength light source 10 according to the present embodiment has been described, but the present invention is not limited to this.

  FIG. 6 is a configuration diagram of a variable wavelength light source according to a modification. The wavelength tunable light source 10A further includes a mirror 30 that reflects the pulse light L1 emitted from the first end 1a and collimated by the lens 3. The pulse light L1 reflected by the mirror 30 is incident on the diffraction grating 4. The wavelength grating light source 10 (see FIG. 2) differs in that the diffraction grating 4 returns the diffracted light L2 to the first end 1a via the mirror 30 and the rotation driving unit 5 drives the mirror 30 to rotate. The main difference is that they are identical in other respects.

  In the variable-wavelength light source 10A, the angular speed of the mirror 30 changes periodically because the step-operation type rotation drive unit 5 is used to drive the mirror 30 to rotate. The rotation angle α of the mirror 30 by the rotation drive unit 5 is an angle between the optical axis A of the pulse light L1 and the normal to the reflection surface. It can be seen from the geometric relationship that the incident angle θ is correlated with the rotation angle α. Therefore, also in the wavelength tunable light source 10 </ b> A, similarly to the case of the wavelength tunable light source 10, it is possible to suppress the fluctuation of the wavelength change speed.

  Further, in the variable wavelength light source 10A, since the optical path length of the external resonator E can be increased by the configuration including the mirror 30, the wavelength resolution is improved. Further, from the above geometric relationship, by changing the rotation angle α of the mirror 30 by a predetermined amount, the diffraction angle (that is, the incident angle θ) can be changed twice as much as the change amount of the rotation angle α. That is, the amount of rotation of the rotation drive unit 5 required to change the diffraction angle can be reduced to 比較 compared with the case of the wavelength variable light source 10.

  As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and may be modified or applied to other matters without changing the gist described in each claim. There may be.

  In the wavelength tunable light sources 10 and 10A, the laser drive unit 2 drives the semiconductor laser 1 so as to emit the pulse light L1 in synchronization with the movement command signal S1 (and eventually in synchronization with the change in the angular velocity). The semiconductor laser 1 may be driven other than when the angular velocity is ω1. In other words, the laser drive unit 2 may drive the semiconductor laser 1 every time a predetermined time T (0 ≦ T <t) elapses from the rise of the movement command signal S1 if it is synchronized with the change in the angular velocity. If the laser beam L3 is instantaneous with respect to the change in the angular velocity, the angular velocity can be theoretically regarded as constant.

  For example, after about t / 2 has elapsed from the rise of the movement command signal S1, that is, when the angular velocity is ω2 (high-speed rotation period, at the top of the time waveform of the angular velocity), the laser driving unit 2 drives the semiconductor laser 1 It may be driven. As shown in FIG. 3D, when the angular velocity is ω2, the amount of change in the angular velocity is small, so that the jitter can be suppressed.

  The rotation drive unit 5 may be an ultrasonic motor. The ultrasonic motor is a piezoelectric actuator using a piezoelectric element, and operates by inverting the polarity of the voltage applied to the piezoelectric element every predetermined time in accordance with the rise and fall of the movement command signal S1. Accordingly, in the case of the ultrasonic motor, the cycle of the change in the angular velocity is の of the cycle of the movement command signal S1, and every time the movement command signal S1 is input for one pulse, the ultrasonic motor performs two steps of the stepping motor. Rotate with min as the minimum travel step. The cycle of the movement command signal S1 can be, for example, 50 kHz (the cycle t is 0.020 msec). The laser drive unit 2 may output the drive current signal S2 in synchronization with a change in the angular velocity by using, for example, the rise and fall of the movement command signal S1 as a trigger.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Laser drive part, 4 ... Diffraction grating, 5 ... Rotation drive part, 10 ... Wavelength variable light source, 30 ... Mirror, E ... External resonator, L1 ... Pulse light, L2 ... Diffraction light, L3 ... Laser light, θ: incident angle.

Claims (4)

A semiconductor laser that emits pulsed light,
A laser driver for driving the semiconductor laser,
A diffraction grating that forms an external resonator together with the semiconductor laser, wherein the pulsed light emitted from the semiconductor laser is incident, and light of a wavelength according to an incident angle of the pulsed light is fed back to the semiconductor laser. A diffraction grating;
A step operation type rotation drive unit that rotates the diffraction grating so as to periodically change the angular velocity of the diffraction grating to change the incident angle ,
The laser driving unit drives the semiconductor laser to emit the pulse light in synchronization with the change in the angular velocity ,
The angular velocity is periodically changing between a first angular velocity and a second angular velocity greater than the first angular velocity,
The variable wavelength light source, wherein the laser driving unit drives the semiconductor laser so as to emit the pulse light when the angular velocity is the first angular velocity . A semiconductor laser that emits pulsed light,
A laser driver for driving the semiconductor laser,
A mirror that reflects the pulsed light emitted from the semiconductor laser,
A diffraction grating that forms an external resonator together with the semiconductor laser, wherein the pulse light reflected by the mirror is incident, and a light having a wavelength according to an incident angle of the pulse light is transmitted through the mirror. A diffraction grating fed back to the semiconductor laser,
A step operation type rotation drive unit that drives the mirror to change the angle of incidence by rotating the mirror so that the angular velocity of the mirror changes periodically,
The laser driving unit drives the semiconductor laser to emit the pulse light in synchronization with the change in the angular velocity ,
The angular velocity is periodically changing between a first angular velocity and a second angular velocity greater than the first angular velocity,
The variable wavelength light source, wherein the laser driving unit drives the semiconductor laser so as to emit the pulse light when the angular velocity is the first angular velocity . A semiconductor laser that emits pulsed light,
A laser driver for driving the semiconductor laser,
A diffraction grating forming 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 fed back to the semiconductor laser. A diffraction grating;
A step operation type rotation drive unit that rotates the diffraction grating so as to periodically change the angular velocity of the diffraction grating to change the incident angle,
The wavelength tunable light source, wherein the laser driver drives the semiconductor laser so as to emit the pulsed light at the same cycle as the change in the angular velocity in synchronization with the change in the angular velocity. A semiconductor laser that emits pulsed light,
A laser driver for driving the semiconductor laser,
A mirror that reflects the pulsed light emitted from the semiconductor laser,
A diffraction grating that forms an external resonator together with the semiconductor laser, wherein the pulse light reflected by the mirror is incident, and a light having a wavelength according to an incident angle of the pulse light is transmitted through the mirror. A diffraction grating fed back to the semiconductor laser,
A step operation type rotation drive unit that drives the mirror to change the angle of incidence by rotating the mirror so that the angular velocity of the mirror changes periodically,
The wavelength tunable light source, wherein the laser driver drives the semiconductor laser so as to emit the pulsed light at the same cycle as the change in the angular velocity in synchronization with the change in the angular velocity.

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