Optical modulator, laser interferometer, and spectroscopic apparatus

Abstract

To provide an optical modulator that can reduce a frequency of a signal to be subjected to computational processing in a demodulation circuit and can reduce cost of the demodulation circuit, a laser interferometer that includes the optical modulator and can be easily reduced in cost, and a spectroscopic apparatus that includes the laser interferometer.SOLUTION: An optical modulator is coupled to a demodulation circuit for demodulating a sample signal on the basis of a reference signal from a laser light reception signal including the sample signal and a modulation signal. The optical modulator comprises: a first optical modulation section that has a first vibration element vibrating at a first frequency and modulates a frequency of laser light; a second optical modulation section that has a second vibration element vibrating at a second frequency and modulates the frequency of laser light; a first signal oscillation section that generates a first signal using the first vibration element as source oscillation; a second signal oscillation section that generates a second signal using the second vibration element as source oscillation; and a reference signal generation section that generates the reference signal having a frequency lower than both the first frequency and the second frequency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical modulator, a laser interferometer, and a spectroscopic device.

Background Art

[0002] Patent Document 1 discloses a laser Doppler measurement device for grasping the movement of a moving object. In the laser Doppler measurement device, a laser beam is irradiated onto the object to be measured, and the movement of the object to be measured is measured based on the scattered laser beam that has undergone Doppler shift. Specifically, by the optical heterodyne interference method, the amount of shift in the frequency of the laser beam is obtained, and from this shift amount, the speed and displacement of the moving object are determined.

[0003] The laser Doppler measurement device described in Patent Document 1 includes a frequency shifter type optical modulator. This optical modulator includes a crystal AT oscillator that vibrates with thickness shear, and a diffraction grating including a plurality of grooves arranged in parallel in the displacement direction of the oscillator. This diffraction grating has grooves in a direction intersecting the vibration direction of the crystal AT oscillator. When the laser beam is irradiated onto the diffraction grating, the laser beam diffracts and the frequency of the laser beam shifts.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the thickness shear vibration has a high resonance frequency. Therefore, the frequency of the modulation signal superimposed on the laser light by the optical modulator described in Patent Document 1 also becomes high. Then, in the laser Doppler measurement device described in Patent Document 1, it is necessary to make the circuits that perform arithmetic processing on the modulation signal and the circuits that convert analog signals into digital signals compatible with high-frequency signals. As a result, the cost of these circuits increases. Therefore, it has become an issue to realize an optical modulator that can reduce the frequency of the signal processed arithmetically by the demodulation circuit and enable cost reduction of electronic components and the like used in the demodulation circuit.

Means for Solving the Problems

[0006] The optical modulator according to an application example of the present invention is an optical modulator connected to a demodulation circuit that demodulates a sample signal from a laser light reception signal including the sample signal added to the laser light by an object and the modulation signal added to the laser light, based on a reference signal, having a first vibration element that vibrates at a first frequency, and a first optical modulation unit that modulates the frequency of the incident laser light using the first vibration element; having a second vibration element that vibrates at a second frequency different from the first frequency, and a second optical modulation unit that modulates the frequency of the incident laser light using the second vibration element; a first signal oscillation unit that generates a first signal of the first frequency with the first vibration element as the source oscillation; a second signal oscillation unit that generates a second signal of the second frequency with the second vibration element as the source oscillation; a reference signal generation unit that generates the reference signal having a frequency lower than both the first frequency and the second frequency using the first signal and the second signal; and includes.

[0007] The laser interferometer according to an application example of the present invention is a laser light source that emits laser light; An optical modulator according to an application example of the present invention that guides the laser light through both the first optical modulation unit and the second optical modulation unit, and adds the modulation signal to the laser light. A light receiving element that detects a change in intensity of the laser light including the sample signal and the modulation signal, and outputs a laser light reception signal. A demodulation circuit that is connected to the optical modulator and demodulates the sample signal from the laser light reception signal based on the reference signal. Comprising.

[0008] A spectroscopic apparatus according to an application example of the present invention is A laser interferometer according to an application example of the present invention, A spectroscopic analysis unit that has a spectroscopic optical system including a moving mirror and generates spectroscopic spectrum information derived from a sample. Comprising The laser interferometer measures the displacement of the moving mirror. The spectroscopic analysis unit generates the spectroscopic spectrum information based on the measurement result of the displacement of the moving mirror by the laser interferometer.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the optical modulator, the laser interferometer, and the spectroscopic device of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0011] 1. First Embodiment First, the optical modulator and the laser interferometer according to the first embodiment will be described.

[0012] FIG. 1 is a functional block diagram showing a laser interferometer 1 according to the first embodiment. FIG. 2 is a schematic configuration diagram showing the optical modulator 100 and the interference optical system 50 shown in FIG. 1.

[0013] The laser interferometer 1 shown in FIG. 1 includes an interference optical system 50, an optical modulator 100, and a demodulation circuit 52.

[0014] The interference optical system 50 shown in FIG. 2 branches the laser light emitted from the laser light source 2 and makes it incident on the object 14 and the optical modulator 100, respectively. Then, the laser light returned from the object 14 and the optical modulator 100 is mixed and received by the light receiving element 10. In the light receiving element 10, the intensity change of the laser light including the sample signal (phase information added to the laser light, etc.) added by the object 14 and the modulation signal (frequency information added to the laser light, etc.) added by the optical modulator 100 is detected, and a laser light reception signal is output.

[0015] The demodulation circuit 52 shown in FIG. 1 has a preprocessing unit 53 and a demodulation processing unit 55. The preprocessing unit 53 performs electrical preprocessing on the laser light reception signal based on a reference signal. The demodulation processing unit 55 demodulates the sample signal from the laser light reception signal that has undergone preprocessing. Thereby, the displacement and speed of the object 14 can be measured.

[0016] In addition, the optical modulator 100 generates a reference signal having a frequency lower than the frequency (modulation frequency) of the modulation signal. By using this reference signal, the frequency of the signal processed by the demodulation circuit 52 can be reduced. That is, the frequency band that the demodulation circuit 52 should handle can be made lower than the modulation frequency. As a result, the specifications of the demodulation circuit 52 can be simplified, and the cost of electronic components and the like used in the demodulation circuit 52 can be reduced.

[0017] 1.1. Interference optical system The interference optical system 50 shown in FIG. 2 is a Michelson-type interference optical system. As shown in FIG. 2, the interference optical system 50 includes a laser light source 2, polarization beam splitters 41 and 42, and a light receiving element 10.

[0018] The laser light source 2 emits emitted light L1 (laser light) having a frequency f0. As the laser light source 2, a light source having a line width in the MHz band or less is preferably used. Specifically, gas lasers such as He-Ne lasers, DFB-LD (Distributed FeedBack - Laser Diode), FBG-LD (Fiber Bragg Grating attached Laser Diode), VCSEL (Vertical Cavity Surface Emitting Laser Diode), and semiconductor laser elements such as FP-LD (Fabry-Perot Laser Diode) can be mentioned.

[0019] The laser light source 2 is particularly preferably a semiconductor laser element. This makes it possible to particularly miniaturize the laser light source 2. Therefore, the laser interferometer 1 can be miniaturized.

[0020] The emitted light L1 is converted into linearly polarized light with an intensity ratio of P-polarization to S-polarization of, for example, 50:50 by passing through a wave plate (not shown). Thereafter, the emitted light L1 is split by a polarization beam splitter 41 into the emitted light L1a that is S-polarized and the emitted light L1b that is P-polarized.

[0021] The emitted light L1a is incident on the optical modulator 100, frequency-modulated, and a modulation signal is added thereto. Thereby, the reference light L2 is generated. The reference light L2 is converted into P-polarization by a wave plate (not shown) and is incident on the polarization beam splitter 42. Then, the reference light L2 passes through the polarization beam splitter 42 and is received by the light receiving element 10 via a rotator (not shown).

[0022] The emitted light L1b is converted into circular polarization by a wave plate (not shown), then is incident on the moving object 14, undergoes Doppler shift, and a sample signal is added thereto. Thereby, the object light L3 is generated. The object light L3 is converted into S-polarization by a wave plate (not shown) and is incident on the polarization beam splitter 42. Then, the object light L3 is reflected by the polarization beam splitter 42 and is received by the light receiving element 10 via a rotator (not shown).

[0023] The light receiving element 10 outputs a laser light reception signal by converting the intensity of the received light into an electrical signal.

[0024] In the laser interferometer 1 including the interference optical system 50 as described above, the phase information of the object 14 is obtained by the optical heterodyne interference method. Specifically, two lights (reference light L2 and object light L3) with slightly different frequencies are made to interfere, and the phase information is extracted from the obtained interference light. Then, the displacement of the object 14 is obtained from the phase information in a demodulation circuit 52 described later. According to the optical heterodyne interference method, when extracting the phase information from the interference light, it is less susceptible to the influence of disturbances, particularly stray light of frequencies that become noise, and high robustness is provided.

[0025] Note that the configuration of the interference optical system 50 is not limited to the above, and any optical element may be added. Also, what is received by the light receiving element 10 is the laser light emitted from the laser light source 2, and as long as it is laser light in which a modulation signal and a sample signal are superimposed as a result of modulation by the optical modulator 100 and the object 14 on its frequency and phase, it is not limited to the above interference light. Further, "demodulating the sample signal from the laser light reception signal" in this specification refers to demodulating the sample signal by performing various operations on the laser light reception signal.

[0026] 1.2. Optical Modulator The optical modulator 100 shown in Fig. 2 includes a first optical modulation unit 12, a first signal oscillation unit 511, a light guiding unit 15, a second optical modulation unit 13, a second signal oscillation unit 512, and a reference signal generation unit 54.

[0027] 1.2.1. First Optical Modulation Unit The first optical modulation unit 12 has a first vibration element 30 and modulates the frequency of the incident emitted light L1a (laser light) using the first vibration element 30. Thereby, the first optical modulation unit 12 generates the emitted light L1c.

[0028] Fig. 3 is a perspective view showing the first optical modulation unit 12 included in the optical modulator 100 shown in Fig. 1. Examples of the first optical modulation unit 12 shown in Fig. 3 include the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156.

[0029] Specifically, the first optical modulation unit 12 shown in Fig. 3 includes a first vibration element 30 and a diffraction grating 434 (first diffraction grating) provided on the first vibration element 30 for diffracting the incident emitted light L1a.

[0030] The first vibration element 30 has a first frequency f M1It vibrates. The first vibration element 30 is a vibrator that generates a periodic signal, such as a crystal oscillator, a ceramic oscillator, or an Si oscillator. Since these vibrators utilize the mechanical resonance phenomenon, they have a high Q value and excellent frequency stability. By modulating the frequency of the emitted light L1a using the first vibration element 30, the S / N ratio (signal-to-noise ratio) of the modulation signal can be increased.

[0031] Examples of crystal oscillators include crystal AT oscillators, SC-cut crystal oscillators, tuning fork type crystal oscillators, surface acoustic wave elements of crystal, etc. The oscillation frequency of a crystal oscillator is, for example, about 1 kHz to several 100 MHz.

[0032] A silicon oscillator is a vibrator comprising a single crystal silicon piece manufactured from a single crystal silicon substrate using MEMS technology and a piezoelectric film. MEMS (Micro Electro Mechanical Systems) is a micro electro mechanical system. Examples of the shape of the single crystal silicon piece include a cantilever beam shape such as a two-pronged tuning fork type or a three-pronged tuning fork type, and a double-cantilever beam shape. The oscillation frequency of a silicon oscillator is, for example, about 1 kHz to several 100 MHz.

[0033] A ceramic oscillator is a vibrator comprising a piezoelectric ceramic piece manufactured by firing piezoelectric ceramics and electrodes. Examples of piezoelectric ceramics include lead zirconate titanate (PZT), barium titanate (BTO), etc. The oscillation frequency of a ceramic oscillator is, for example, about several 100 kHz to several 10 MHz.

[0034] Among these, a crystal oscillator is preferably used for the first vibration element 30. Since the crystal itself is a piezoelectric material, a crystal oscillator has particularly high frequency stability.

[0035] The oscillation frequency (first frequency f M1 ) of the first vibration element 30 is not particularly limited, but is preferably 1 MHz or more and 100 MHz or less. In the frequency band within the above range, there are many vibrators with a high Q value of mechanical resonance. Therefore, the first frequency fM1 By setting it within the above range, the first frequency f of the first signal Ss1 output from the first signal oscillation unit 511 M1 can be stabilized.

[0036] The first vibration element 30 shown in FIG. 3 is a crystal AT oscillator that vibrates in a thickness-shear mode along the vibration direction 436 in the high-frequency region of the MHz band. Further, a diffraction grating 434 is provided on the first vibration element 30. The diffraction grating 434 has a plurality of linear grooves 432 extending in a direction intersecting the vibration direction 436. When the emitted light L1a is irradiated onto such a diffraction grating 434, even when the first vibration element 30 vibrates in a thickness-shear mode, the frequency of the emitted light L1a can be modulated to generate the emitted light L1c.

[0037] The first vibration element 30 has a front surface 4311 and a back surface 4312 that are in a front-back relationship with each other. The diffraction grating 434 is disposed on the front surface 4311. Further, a first electrode 437 for applying a potential to the first vibration element 30 and a pad 433 electrically connected to the first electrode 437 are provided on the front surface 4311. On the other hand, a second electrode 438 for applying a potential to the first vibration element 30 and a pad 435 electrically connected to the second electrode 438 are provided on the back surface 4312. The first electrode 437 and the second electrode 438 are arranged so as to overlap each other via the first vibration element 30 when the front surface 4311 is viewed in plan. Further, the pads 433 and 435 are arranged so as not to overlap each other via the first vibration element 30. When a voltage is applied between the first electrode 437 and the second electrode 438, thickness-shear vibration is induced in the portion where the first electrode 437 and the second electrode 438 overlap.

[0038] The diffraction grating 434 shown in FIG. 3 is disposed on the first electrode 437. That is, in FIG. 3, the diffraction grating 434 is constituted by a plurality of grooves 432 formed on the surface of the first electrode 437, and when the emitted light L1a is irradiated thereon, the emitted light L1c as diffracted light is emitted.

[0039] The diffraction grating 434 shown in FIG. 3 is, as an example, a blazed diffraction grating. A blazed diffraction grating refers to one in which the cross-sectional shape of the diffraction grating is serrated. Note that the shape of the diffraction grating 434 is not limited to this.

[0040] FIG. 4 is a perspective view showing another configuration example of the first light modulation unit 12 included in the optical modulator 100 shown in FIG. 1. In FIG. 4, three axes orthogonal to each other, an A axis, a B axis, and a C axis, are set and indicated by arrows. The tip side of the arrow is defined as "plus", and the base end side of the arrow is defined as "minus".

[0041] The first vibration element 30 shown in FIG. 4 is a tuning fork type crystal oscillator. The first vibration element 30 shown in FIG. 4 has a vibration substrate having a base portion 401, a first vibration arm 402, and a second vibration arm 403. Since such a tuning fork type crystal oscillator has established manufacturing technology, it is easily available and has stable oscillation. Therefore, the tuning fork type crystal oscillator is suitable as the first vibration element 30. Further, the first light modulation unit 12 shown in FIG. 4 includes the first vibration element 30, electrodes 404, 405, and a light reflection portion 406 (first light reflection portion) provided on the first vibration element 30.

[0042] The base portion 401 is a portion extending along the A axis. The first vibration arm 402 is a portion extending from the end portion on the minus side of the A axis of the base portion 401 toward the plus side of the B axis. The second vibration arm 403 is a portion extending from the end portion on the plus side of the A axis of the base portion 401 toward the plus side of the B axis.

[0043] The electrode 404 is a conductive film provided on the side surface parallel to the A - B plane among the first vibration arm 402 and the second vibration arm 403. Although not shown in FIG. 4, the electrode 404 is provided on the side surfaces facing each other, and by applying voltages with different polarities to each other, the first vibration arm 402 and the second vibration arm 403 are driven.

[0044] The electrode 405 is a conductive film provided on the side surface of the first vibrating arm 402 and the second vibrating arm 403 that intersects the A-B plane. Although not shown in FIG. 4, the electrodes 405 are also provided on the side surfaces facing each other, and by applying voltages with different polarities to each other, the first vibrating arm 402 and the second vibrating arm 403 are driven.

[0045] The light reflection portion 406 is set on, for example, the side surface of the first vibrating arm 402 and the second vibrating arm 403 that intersects the A-B plane, and has a function of reflecting the emitted light L1a. Due to this function, since the light reflection portion 406 has a vibration component with a large amplitude in the incident direction of the incident emitted light L1a, the frequency of the emitted light L1a can be efficiently modulated to generate the emitted light L1c.

[0046] A crystal piece cut out from a crystal substrate is used for the tuning fork type crystal oscillator. Examples of the crystal substrate used for manufacturing the tuning fork type crystal oscillator include a crystal Z-cut flat plate. In FIG. 4, an X-axis parallel to the A-axis, a Y'-axis parallel to the B-axis, and a Z'-axis parallel to the C-axis are set. The crystal Z-cut flat plate is, for example, a substrate cut out from a single crystal of quartz such that the X-axis is the electrical axis, the Y'-axis is the mechanical axis, and the Z'-axis is the optical axis. Specifically, in the orthogonal coordinate system composed of the X-axis, Y'-axis, and Z'-axis, a substrate having a main surface inclined counterclockwise by about 1° to 5° around the X-axis with respect to the X-Y' plane composed of the X-axis and Y'-axis is cut out from the single crystal of quartz and is preferably used as the crystal substrate. Then, by etching such a crystal substrate, the crystal piece used for the first vibration element 30 shown in FIG. 4 is obtained.

[0047] 1.2.2. First signal oscillation section The first signal oscillation section 511 generates a first signal Ss1 with a first frequency f M1 using the first vibration element 30 as the source oscillation.

[0048] Examples of the first signal oscillation unit 511 include an oscillation circuit using an inverter, a Colpitts oscillation circuit, etc. These oscillation circuits operate with the fundamental wave oscillation of the first vibration element 30 as the source oscillation. Therefore, by using the first vibration element 30 with a high Q value of mechanical resonance, a first signal Ss1 with high frequency stability can be generated.

[0049] Note that the first vibration element 30 and the first signal oscillation unit 511 may be housed in one package.

[0050] 1.2.3. Light guiding unit The light guiding unit 15 shown in Fig. 2 is composed of a mirror 152. The mirror 152 reflects the emitted light L1c generated by the first light modulation unit 12 toward the second light modulation unit 13. By providing such a light guiding unit 15, the first light modulation unit 12 and the second light modulation unit 13 can be optically connected inside the optical modulator 100. Thereby, an optical modulator 100 with excellent workability such as alignment with other optical elements can be realized.

[0051] Note that the configuration of the light guiding unit 15 is not limited to the above. The light guiding unit 15 may have, for example, an optical waveguide or an optical fiber, or may have a prism.

[0052] 1.2.4. Second light modulation unit The second light modulation unit 13 shown in Fig. 2 has a second vibration element 31 and modulates the frequency of the incident emitted light L1c using the second vibration element 31. Thereby, the second light modulation unit 13 generates the reference light L2.

[0053] The configuration of the second light modulation unit 13 may be different from that of the first light modulation unit 12, but it is preferably the same. By making them the same, the modulation phase shift in the first light modulation unit 12 and the modulation phase shift in the second light modulation unit 13 can be made the same. Thereby, the S / N ratio of the modulation signal added by the optical modulator 100 to the emitted light L1a can be increased.

[0054] For example, when the oscillation frequency of the second oscillation element 31 is set with the oscillation frequency of the first oscillation element 30 being 1, it is preferably 0.01 or more and 100 or less, and more preferably 0.1 or more and 10 or less. This makes it particularly easy to align the modulation phase shift described above.

[0055] Also, the oscillation mode of the second oscillation element 31 may be different from that of the first oscillation element 30, but is preferably the same. This makes it easier to align the oscillation frequency and the modulation phase shift.

[0056] The configuration of the second optical modulation unit 13 is not particularly limited, and examples include the configuration shown in FIG. 3 and the configuration shown in FIG. 4. That is, the second optical modulation unit 13 may include a second diffraction grating similar to the diffraction grating 434 provided on the second oscillation element 31 and the second oscillation element 31. Further, the second optical modulation unit 13 may include a second optical reflection unit similar to the optical reflection unit 406 provided on the second oscillation element 31 and the second oscillation element 31.

[0057] The second oscillation element 31 oscillates at the second frequency f M2 Therefore, the reference light L2 includes a frequency component (difference frequency signal) corresponding to the difference between the first frequency f M1 and the second frequency f M2 as a modulation signal. By including such a difference frequency signal, the frequency when the laser light reception signal is arithmetic processed by the demodulation processing unit 55 can be lowered. That is, in the optical modulator 100, by modulating the frequency of the emitted light L1a via the two of the first optical modulation unit 12 and the second optical modulation unit 13, the frequency of the modulation signal can be lowered compared to the case where only one of them is passed through. That is, the frequency of the modulation signal included in the reference light L2 can be down-converted. In this specification, this is referred to as "optical down-conversion". Due to the optical down-conversion in the optical modulator 100, there is no need to perform down-conversion inside the demodulation circuit 52. As a result, the corresponding frequency of electronic components and the like constituting the demodulation circuit 52 can be lowered, and cost reduction can be achieved.

[0058] The second vibration element 31 is a vibrator that generates a periodic signal, such as a crystal oscillator, a ceramic oscillator, or an Si oscillator. Since these vibrators utilize the mechanical resonance phenomenon, they have a high Q value and excellent frequency stability. By modulating the frequency of the emitted light L1c using the second vibration element 31, the signal-to-noise ratio (S / N ratio) of the modulation signal can be increased.

[0059] Among these, a crystal oscillator is preferably used for the second vibration element 31. Since the crystal itself is a piezoelectric material, the crystal oscillator has particularly high frequency stability.

[0060] The oscillation frequency (second frequency f M2 ) of the second vibration element 31 is not particularly limited, but is preferably 1 MHz or more and 100 MHz or less. In the frequency band within the above range, there are many vibrators with a high Q value of mechanical resonance. Therefore, by setting the second frequency f M2 within the above range, the stabilization of the second frequency f M2 of the second signal Ss2 output from the second signal oscillation unit 512 can be achieved.

[0061] 1.2.5. Second Signal Oscillation Unit The second signal oscillation unit 512 generates a second signal Ss2 having a second frequency f M2 using the second vibration element 31 as the source oscillation.

[0062] Examples of the second signal oscillation unit 512 include an oscillation circuit using an inverter, a Colpitts oscillation circuit, etc. These oscillation circuits operate with the fundamental wave oscillation of the second vibration element 31 as the source oscillation. Therefore, by using the second vibration element 31 having a high Q value of mechanical resonance, a second signal Ss2 with high frequency stability can be generated.

[0063] Note that the second vibration element 31 and the second signal oscillation unit 512 may be housed in one package. Examples of the second vibration element 31 and the second signal oscillation unit 512 housed in one package include a crystal oscillator (SPXO), a voltage-controlled crystal oscillator (VCXO), a temperature-compensated crystal oscillator (TCXO), a crystal oscillator with a thermostatic chamber (OCXO), and the like.

[0064] 1.2.6. Reference signal generation unit FIG. 5 is a block diagram showing an example of each circuit configuration of the reference signal generation unit 54 and the demodulation circuit 52 shown in FIG. 1.

[0065] The reference signal generation unit 54 shown in FIG. 5 multiplies a laser light reception signal including a modulation signal of the first frequency f M1 by a second signal Ss2 of the second frequency f M2 . Thereby, the frequency of the signal processed by the preprocessing unit 53 of the demodulation circuit 52 can be lowered. Further, the reference signal generation unit 54 multiplies the first signal Ss1 and the second signal Ss2, and generates a reference signal SsL having a frequency lower than the first frequency f M1 and the second frequency f M2 . That is, the reference signal SsL is generated using the first signal Ss1 and the second signal Ss2. Then, this reference signal SsL is input to the demodulation processing unit 55 of the demodulation circuit 52. Thereby, the frequency of the signal processed by the demodulation processing unit 55 can be lowered. In the following description, lowering the frequency of the signal to be processed is referred to as "down-conversion".

[0066] The reference signal generation unit 54 includes a first delay adjustment unit 541, a second delay adjustment unit 542, a multiplier 543, and a low-pass filter 544. Note that the configuration of the reference signal generation unit 54 is not limited to this.

[0067] The first delay adjustment unit 541 and the second delay adjustment unit 542 adjust the delays of each other in order to synchronize the phases between the first signal Ss1 output from the first signal oscillation unit 511 and the second signal Ss2 output from the second signal oscillation unit 512.

[0068] The multiplier 543 multiplies the signal output from the first delay adjuster 541 and the signal output from the second delay adjuster 542. As a result, as a multiplication result, a signal with the frequency of the sum of the first frequency and the second frequency (sum frequency signal) and a signal with the frequency of the difference (difference frequency signal) are generated.

[0069] The low-pass filter 544 cuts the sum frequency signal from the signal of the multiplication result by the multiplier 543. As a result, the difference frequency signal of frequency f M1 -f M2 can be extracted, and this is used as the reference signal SsL. By using the difference frequency signal as the reference signal SsL in this way, the frequency of the reference signal SsL input to the demodulation circuit 52 can be down-converted compared to the case where the first signal Ss1 and the second signal Ss2 are used as the reference signal as they are. That is, the frequency f M1 -f M2 can be made lower than both the first frequency f M1 and the second frequency f M2 . In this specification, this is referred to as "electrical down-conversion". Due to the electrical down-conversion in the optical modulator 100, there is no need to perform down-conversion inside the demodulation circuit 52. As a result, the corresponding frequency of the electronic components constituting the demodulation circuit 52 can be lowered, and cost reduction can be achieved. Note that the low-pass filter 544 may be a band-pass filter.

[0070] The frequency f' M after down-conversion is not particularly limited, but is preferably in the kHz band. As an example, consider the case where the first frequency f M1 is 4.97 MHz and the second frequency f M2 is 4.92 MHz. In this case, the frequency f' M after down-conversion is 50 kHz. Also, in this case, the low-pass filter 544 is set to cut frequencies above 50 kHz.

[0071] On the other hand, the frequency f' MWhen measuring the displacement of the object 14, it affects the measurable speed range and frequency range of the object 14. That is, when the frequency f' after down-conversion M is too low, these ranges may become narrow. Therefore, the difference between the first frequency f M1 and the second frequency f M2 is preferably 1 kHz or more and less than 1 MHz, and more preferably 10 kHz or more and 500 kHz or less. Thereby, while ensuring measurement performance suitable for a general measurement scene of the object 14, it is possible to reduce the cost of electronic components such as an A / D converter and an FPGA.

[0072] 1.3. Demodulation Circuit The demodulation circuit 52 shown in FIG. 5 includes a current-voltage converter 530, a preprocessing unit 53, and a demodulation processing unit 55.

[0073] 1.3.1. Current-Voltage Converter The current-voltage converter 530, also called a transimpedance amplifier (TIA), converts the photocurrent output from the light receiving element 10 into a voltage signal and outputs it as a laser light reception signal.

[0074] 1.3.2. Preprocessing Unit The preprocessing unit 53 shown in FIG. 5 digitally converts the laser light reception signal output from the current-voltage converter 530 and converts the sample signal (phase information etc. derived from the object 14) into a state where it can be demodulated by a known quadrature detection method. In this specification, the operation performed by the preprocessing unit 53 is also referred to as "preprocessing".

[0075] The preprocessing unit 53 shown in FIG. 5 includes an A / D converter 533, a band-pass filter 532, a phase adjustment unit 560, a first amplitude adjustment unit 534, a band-pass filter 536, an A / D converter 545, a multiplication wiring 574, a multiplier 537, a low-pass filter 538, a second amplitude adjustment unit 561, and an adder 562. Note that the configuration of the preprocessing unit 53 is not limited to this.

[0076] The laser light reception signal input to the preprocessing unit 53 is input to the A / D converter 533. The A / D converter 533 digitally converts the analog laser light reception signal. As a result, a digital laser light reception signal is obtained. By performing digital conversion immediately after the signal is input to the preprocessing unit 53, subsequent arithmetic processing can be performed by a digital circuit. This can reduce the cost of electronic components and the like on which the preprocessing unit 53 is mounted.

[0077] The signal output from the A / D converter 533 is split into two. One passes through the band-pass filter 532, the phase adjuster 560, and the first amplitude adjuster 534 and is input to the adder 562. The other passes through the band-pass filter 536, the multiplier 537, the low-pass filter 538, and the second amplitude adjuster 561 and is input to the adder 562.

[0078] The band-pass filter 532 selectively passes the components of the signal output from the A / D converter 533 in a set frequency band. Thereby, the target frequency components can be extracted. Note that the band-pass filter 532 may be a low-pass filter.

[0079] The phase adjuster 560 shifts the phase of the signal output from the band-pass filter 532 by 90° and adjusts the phase delay. The first amplitude adjuster 534 adjusts the amplitude of the signal to match that of the second amplitude adjuster 561.

[0080] The band-pass filter 536 selectively passes the components of the signal output from the A / D converter 533 in a set frequency band. Thereby, the target frequency components can be extracted. Note that the band-pass filter 536 may be a low-pass filter.

[0081] The A / D converter 545 digitally converts the reference signal SsL output from the optical modulator 100.

[0082] The multiplier 537 multiplies the signal output from the band-pass filter 536 and the reference signal SsL input via the multiplication wiring 574. As a result, a sum-frequency signal having the frequency of the sum of the two signals and a difference-frequency signal having the frequency of the difference between the two signals are generated.

[0083] The low-pass filter 538 cuts the sum-frequency signal from the signal of the multiplication result by the multiplier 537. As a result, the difference-frequency signal can be extracted. Note that the low-pass filter 538 may be a band-pass filter.

[0084] The second amplitude adjustment unit 561 adjusts so that the amplitudes of the signals are aligned with those of the first amplitude adjustment unit 534.

[0085] The adder 562 adds the signal output from the first amplitude adjustment unit 534 and the signal output from the second amplitude adjustment unit 561. This addition result is used as the preprocessed signal S(t). Note that the A / D converters 533 and 545 may be provided as necessary. For example, they can be omitted if the demodulation circuit 52 is composed of analog circuits.

[0086] 1.3.3. Preprocessing Next, the preprocessing in the preprocessing unit 53 will be described. In the following description, as an example, a signal whose frequency changes in a sine wave shape is used as the modulation signal, and a system in which the displacement of the object 14 performs simple harmonic vibration in the optical axis direction will be described as an example.

[0087] The AC component I of the laser light reception signal input to the preprocessing unit 53 PD.AC is represented by the following formula (1).

[0088]

Equation

[0089] In the above formula (1), Φ M is the phase derived from the optical modulator 100, and X is given by the following formula (1a).

[0090]

Number

[0091] Φ S is the phase derived from the object 14, and Φ0 is the initial phase difference due to the optical path difference in the interference optical system 50.

[0092] In the first optical modulation unit 12 shown in FIG. 5, the frequency of the incident laser light is modulated using the first vibration element 30 that vibrates at the first frequency f M1 . Also, in the second optical modulation unit 13, the frequency of the incident laser light is modulated using the second vibration element 31 that vibrates at the second frequency f M2 . Therefore, the phase Φ M derived from the optical modulator 100 including these two optical modulation units is given by the following formula (1b).

[0093]

Number

[0094] In the above formula (1b), B is the modulation phase shift in the frequency modulation in the first optical modulation unit 12, C is the modulation phase shift in the frequency modulation in the second optical modulation unit 13, and t is time.

[0095] Let the first term on the right side of the above formula (1b) be α and the second term on the right side be β. Then, cosΦ M included in the above formula (1) is represented by the following formula (1c).

[0096]

Number

[0097] Also, sinΦ M included in the above formula (1) is represented by the following formula (1d).

[0098] [Number]

[0099] Then, the above formula (1) can be transformed as the following formula (1e).

[0100] [Number]

[0101] Here, it can be said that cosα, cosβ, sinα, and sinβ are trigonometric functions that change with time (α or β) and are trigonometric functions including the angular part. Such trigonometric functions can be expanded as the following formulas (1f-1), (1f-2), (1f-3), and (1f-4) by using the series representation of the Bessel function.

[0102] [Number]

[0103] Here, consider the case where the frequency passing through the band-pass filter 532 is set to the frequency (f’ M (= f M1 - f M2 )) after down-conversion, and the frequency passing through the band-pass filter 536 is set to twice the frequency after down-conversion (2f’ M ).

[0104] In this case, in the band-pass filter 532, the frequency components represented by the first, third, and fourth terms on the right side of the above (1e) are cut off. And the frequency component passing through the band-pass filter 532 is included in the component represented by the second term on the right side of the above formula (1e). Considering the frequency characteristics of the band-pass filter 532, the second term on the right side of the above formula (1e) can be expanded as the following formula (2) by using the above formulas (1f-3) and (1f-4).

[0105] [Number]

[0106] Of the two terms included in the right side of the above formula (2), the first term is the frequency component cut by the band-pass filter 532. That is, only the frequency component represented by the second term can pass through the band-pass filter 532. Therefore, the signal I passing through the band-pass filter 532 BPF1 is represented by the following formula (2a).

[0107]

Equation

[0108] In the phase adjuster 560, the phase of the signal I output from the band-pass filter 532 BPF1 is shifted by 90°. As a result, the signal I output from the phase adjuster 560 PS is represented by the following formula (3).

[0109]

Equation

[0110] On the other hand, in the band-pass filter 536, the frequency components represented by the second, third, and fourth terms on the right side of the above formula (1e) are cut. And the frequency components passing through the band-pass filter 536 are included in the component represented by the first term on the right side of the above formula (1e). Considering the frequency characteristics of the band-pass filter 536, the first term on the right side of the above formula (1e) can be expanded as the following formula (4) using the above formulas (1f-1) and (1f-2).

[0111]

Equation

[0112] Of the two terms included in the right side of the above formula (4), the first term is the frequency component cut by the band-pass filter 536. That is, only the frequency component represented by the second term can pass through the band-pass filter 536. Therefore, the signal I passing through the band-pass filter 536 BPF2 is represented by the following formula (4a).

[0113]

Equation

[0114] In the multiplier 537, the signal I output from the band-pass filter 536 BPF2 is multiplied by the reference signal SsL output from the A / D converter 545. The multiplication result I het is represented by the following formula (5).

[0115]

Equation

[0116] The multiplication result I het has its high-frequency components cut when passing through the low-pass filter 538. Then, the signal I output from the low-pass filter 538 LPF is represented by the following formula (6).

[0117]

Equation

[0118] After that, the signal I represented by the above formula (3) PS has its amplitude adjusted by being multiplied by J2(B)J2(C) in the first amplitude adjustment unit 534.

[0119] Also, the signal I represented by the above formula (6) LPF has its amplitude adjusted by being multiplied by 2J1(B)J1(C) in the second amplitude adjustment unit 561.

[0120] In the adder 562, the signal I with adjusted amplitude PS and the signal I with adjusted amplitude LPF are added together. As a result, the preprocessed signal S(t) is obtained. The preprocessed signal S(t) is represented by the following formula (7).

[0121]

Equation

[0122] In the above manner, the preprocessed signal S(t) is obtained. In the above formulas, each signal is represented by the frequency f' after down-conversion M . Therefore, according to this embodiment, the corresponding frequency of electronic components and the like constituting the demodulation circuit 52 can be lowered, and cost reduction can be achieved.

[0123] Here, a specific example will be described in the case where the first frequency f M1 is 4.97 MHz and the second frequency f M2 is 4.92 MHz. In this case, the frequency of the signal output from the band-pass filter 532 of the preprocessing unit 53 is 50 kHz, and the frequency of the signal output from the band-pass filter 536 is 100 kHz. Therefore, in this example, even if the first frequency f M1 and the second frequency f M2 are in the MHz band, it is possible to use electronic components and the like having a corresponding frequency in the kHz band.

[0124] 1.3.4. Demodulation Processing Unit The demodulation processing unit 55 shown in FIG. 5 performs demodulation processing on the preprocessed signal S(t) output from the preprocessing unit 53, demodulates the sample signal, and calculates the displacement, speed, etc. of the object 14. For the demodulation processing, for example, a known quadrature detection method is used.

[0125] The demodulation processing unit 55 shown in FIG. 5 is a digital circuit including a multiplier 551, a multiplier 552, a phase shifter 553, a low-pass filter 555, a low-pass filter 556, a divider 557, an arctangent calculator 558, and a signal output unit 559.

[0126] The preprocessed signal S(t) is split into two. One passes through the multiplier 551 and the low-pass filter 555 and is input to the divider 557. The other passes through the multiplier 552 and the low-pass filter 556 and is input to the divider 557.

[0127] The multiplier 551 multiplies one of the preprocessed signals S(t) and the reference signal SsL. The multiplier 552 multiplies the other preprocessed signal S(t) and the signal output from the phase shifter 553. The phase shifter 553 generates an output signal with the phase of the input reference signal SsL inverted without changing the amplitude.

[0128] The low-pass filter 555 and the low-pass filter 556 are filters that cut signals in the high-frequency band, respectively.

[0129] The divider 557 performs division to divide the signal output from the low-pass filter 556 by the signal output from the low-pass filter 555.

[0130] The arctangent calculator 558 calculates the phase as sample information derived from the object 14 by performing an arctangent operation on the signal output from the divider 557.

[0131] The signal output unit 559 performs phase connection such as unwrapping processing on the phase derived from the object 14 to calculate the displacement of the object 14. Also, if necessary, the speed of the object 14 is calculated.

[0132] Note that the circuit configuration of the demodulation processing unit 55 described above is an example and is not limited thereto. For example, the demodulation processing unit 55 is not limited to a digital circuit and may be an analog circuit. The analog circuit may include an F / V converter circuit or a ΔΣ counter circuit.

[0133] 1.3.5. Demodulation Processing In the demodulation processing unit 55 shown in FIG. 5, demodulation processing is performed on the preprocessed signal S(t) output from the preprocessing unit 53 to demodulate X in the above formula (7). X is Φ S -Φ0 is defined. When Φ0 is constant, Φ S (The phase derived from the object 14) change is required. In the above manner, the displacement, speed, etc. of the object 14 can be measured.

[0134] 2. Second Embodiment Next, an optical modulator and a laser interferometer according to the second embodiment will be described.

[0135] FIG. 6 is a schematic configuration diagram showing an optical modulator 100 and an interference optical system 50 included in the laser interferometer 1 according to the second embodiment.

[0136] Hereinafter, the second embodiment will be described. In the following description, the differences from the above embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 6, the same components as those in the above embodiment are denoted by the same reference numerals.

[0137] The second embodiment is the same as the first embodiment except that the configuration of the optical modulator 100 is different.

[0138] In the first embodiment, the light guide unit 15 is composed of the mirror 152. On the other hand, in this embodiment, the light guide unit 15 is composed of polarization beam splitters 154 and 156.

[0139] The emitted light L1 emitted from the laser light source 2 is split into two by the polarization beam splitter 41. One of the emitted lights L1a is converted into P-polarized light by a wavelength plate (not shown), then enters the optical modulator 100, and passes through the polarization beam splitter 154. The emitted light L1a emitted from the polarization beam splitter 154 is converted into circularly polarized light by a wavelength plate (not shown), and then frequency-modulated by the first optical modulation unit 12. As a result, the emitted light L1c with a modulation signal added is generated. This modulation signal is caused by the first vibration element 30 vibrating at the first frequency f M1 . The emitted light L1c is converted into S-polarized light by a wavelength plate (not shown), and then reflected by the polarization beam splitter 154. The emitted light L1c reflected by the polarization beam splitter 154 is reflected by the polarization beam splitter 156, and then converted into circularly polarized light by a wavelength plate (not shown). Then, it enters the second optical modulation unit 13 and is frequency-modulated. As a result, the reference light L2 with a modulation signal added is generated. This modulation signal is caused by the second vibration element 31 vibrating at the second frequency f M2 . As a result of the two frequency modulations, the modulation frequency added to the reference light L2 is lower than both the first frequency f M1 and the second frequency f M2 . Therefore, also in the optical modulator 100 according to the present embodiment, optical down-conversion is possible. Also in the second embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0140] 3. Third Embodiment Next, an optical modulator and a laser interferometer according to the third embodiment will be described.

[0141] FIG. 7 is a schematic configuration diagram showing the optical modulator 100 and the interference optical system 50 included in the laser interferometer 1 according to the third embodiment.

[0142] Hereinafter, the third embodiment will be described. In the following description, the description will focus on the differences from the above embodiments, and the description of the same matters will be omitted. In FIG. 7, the same components as those in the above embodiments are denoted by the same reference numerals.

[0143] The third embodiment is the same as the first embodiment except that the configuration of the optical modulator 100 and the configuration of the interference optical system 50 are different.

[0144] In the first embodiment, in the optical modulator 100, the first optical modulation unit 12 and the second optical modulation unit 13 are optically connected via the light guide unit 15. In contrast, in this embodiment, the light guide unit 15 is omitted, and polarization beam splitters 43 and 44 are added to the interference optical system 50.

[0145] Specifically, the emitted light L1 emitted from the laser light source 2 is split into two by the polarization beam splitter 41.

[0146] One of the emitted lights L1a is converted into circular polarization by a wavelength plate (not shown) and then frequency-modulated by the first optical modulation unit 12. As a result, a reference light L2a with a modulation signal added is generated. The modulation signal at this time is due to the first vibration element 30 vibrating at the first frequency f M1 After being converted into P-polarization by a wavelength plate (not shown), the reference light L2a passes through the polarization beam splitter 41 and the polarization beam splitter 43 and is received by the light receiving element 10.

[0147] The other emitted light L1b passes through the polarization beam splitter 42, is converted into circular polarization by a wavelength plate (not shown), then is incident on the moving object 14, undergoes Doppler shift, and a sample signal is added. As a result, an object light L3 is generated. The object light L3 is converted into S-polarization by a wavelength plate (not shown), then is reflected by the polarization beam splitter 42 and the polarization beam splitter 44. Then, after being converted into circular polarization by a wavelength plate (not shown), it is frequency-modulated by the second optical modulation unit 13. As a result, a reference light L2b including a modulation signal is generated. The modulation signal at this time is the second frequency f M2This is caused by the second vibrating element 31 that vibrates. Note that since this reference light L2b also includes a sample signal, it is also the object light L3. The reference light L2b (object light L3) is converted to P-polarized light by a wave plate (not shown) and then passes through the polarization beam splitter 44. Then, after being converted to S-polarized light by a wave plate (not shown), it is reflected by the polarization beam splitter 43 and received by the light receiving element 10.

[0148] When received by the light receiving element 10, the reference lights L2a and L2b and the object light L3 are received as interference light. Therefore, the interference light has a modulation signal with a modulation frequency lower than both the first frequency f M1 and the second frequency f. M2 Accordingly, the optical modulator 100 according to the present embodiment can also perform optical down-conversion. Even in the third embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0149] 4. Fourth Embodiment Next, a spectroscopic apparatus according to the fourth embodiment will be described. FIG. 8 is a functional block diagram showing a spectroscopic apparatus 900 according to the fourth embodiment.

[0150] Hereinafter, the fourth embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 8, the same components as those in FIG. 1 are denoted by the same reference numerals.

[0151] The spectroscopic apparatus 900 shown in FIG. 8 includes the laser interferometer 1 according to each of the above embodiments and a spectroscopic analysis unit 910.

[0152] The spectroscopic analysis unit 910 receives the analysis light including the sample-derived signal generated by the interaction with the sample, and generates spectroscopic spectrum information derived from the sample. The spectroscopic analysis unit 910 shown in FIG. 8 includes a spectroscopic optical system 920 and a calculation unit 930. The spectroscopic optical system 920 includes an analysis light source 922, a moving mirror 924, and an analysis light receiving unit 926. In the spectroscopic optical system 920, the analysis light emitted from the analysis light source 922 is irradiated onto the sample, and then incident on the analysis light interferometer. In the analysis light interferometer, while moving the moving mirror 924 to change the optical path length, the analysis light passing through the sample and the analysis light passing through the moving mirror 924 are interfered. Then, the interference light is received by the analysis light receiving unit 926, and an analysis light reception signal is acquired.

[0153] On the other hand, the laser interferometer 1 measures the displacement of the moving mirror 924 and outputs a mirror position signal. In the laser interferometer 1, since the displacement of the moving mirror 924 can be accurately measured, a highly accurate mirror position signal can be generated.

[0154] The calculation unit 930 generates a waveform (interferogram) representing the intensity of the interference light with respect to the optical path length in the spectroscopic optical system 920 based on the analysis light reception signal and the mirror position signal, and performs Fourier transform on this to generate spectroscopic spectrum information.

[0155] Therefore, the spectroscopic analysis unit 910 can generate highly accurate spectroscopic spectrum information based on the measurement result of the displacement of the moving mirror 924 by the laser interferometer 1.

[0156] Also, as described above, the laser interferometer 1 is easily cost-reduced. For this reason, according to the above configuration, a spectroscopic apparatus 900 that is easily cost-reduced and has excellent wavenumber resolution can be realized.

[0157] Note that the spectroscopic device 900 can be applied to FT-IR (Fourier transform infrared spectroscopy), FT-NIR (Fourier transform near-infrared spectroscopy), FT-VIS (Fourier transform visible spectroscopy), FT-UV (Fourier transform ultraviolet spectroscopy), FT-THz (Fourier transform terahertz spectroscopy), etc. by appropriately changing the type of analysis light and the like.

[0158] In addition, the spectroscopic device 900 can be applied to, for example, a white light interference shape measuring device, an optical coherence tomography (OCT) imaging device, etc. by using an element capable of acquiring a two-dimensional light intensity distribution as the analysis light receiving unit 926.

[0159] 5. Effects Exhibited by Each of the Above Embodiments The optical modulator 100 according to each of the above embodiments is an optical modulator connected to a demodulation circuit 52 that demodulates a sample signal from a laser light reception signal including the sample signal added to the object light L3 (laser light) by the object 14 and the modulation signal added to the reference light L2 (laser light) based on the reference signal SsL, and includes a first optical modulation unit 12, a second optical modulation unit 13, a first signal oscillation unit 511, a second signal oscillation unit 512, and a reference signal generation unit 54. The first optical modulation unit 12 has a first vibration element 30 that vibrates at a first frequency f M1 and uses the first vibration element 30 to modulate the frequency of the incident emitted light L1a (laser light). The second optical modulation unit 13 has a second vibration element 31 that vibrates at a second frequency f M1 different from the first frequency f M2 and uses the second vibration element 31 to modulate the frequency of the incident emitted light L1c (laser light) or the object light L3 (laser light). The first signal oscillation unit 511 generates a first signal Ss1 at the first frequency f M1 with the first vibration element 30 as the source oscillation. The second signal oscillation unit 512 generates a second signal Ss2 at the second frequency f M2 with the second vibration element 31 as the source oscillation. The reference signal generation unit 54 generates a reference signal SsL at a frequency lower than both the first frequency f M1 and the second frequency f M2 using the first signal Ss1 and the second signal Ss2.

[0160] According to such a configuration, since the frequency of the signal processed by the demodulation circuit 52 can be reduced, the corresponding frequency required for electronic components and the like used in the demodulation circuit 52 can be reduced. Therefore, by having the above-described configuration, an optical modulator 100 that enables cost reduction of the connected demodulation circuit 52 can be realized.

[0161] Further, the first optical modulation unit 12 may be provided on the first vibrating element 30 and include a diffraction grating 434 (first diffraction grating) that diffracts the incident emitted light L1a (laser light). Furthermore, the second optical modulation unit 13 may be provided on the second vibrating element 31 and include a second diffraction grating that diffracts the incident emitted light L1c (laser light) or the object light L3 (laser light).

[0162] According to such a configuration, even if the first vibrating element 30 and the second vibrating element 31 are elements that vibrate in, for example, thickness shear vibration, the frequency of the laser light can be modulated. Thereby, for example, the first optical modulation unit 12 and the second optical modulation unit 13 using a crystal AT oscillator having a high Q value of mechanical resonance can be realized.

[0163] Further, the first optical modulation unit 12 may be provided on the first vibrating element 30 and include a light reflection unit 406 (first light reflection unit) that reflects the incident emitted light L1a (laser light). Furthermore, the second optical modulation unit 13 may be provided on the second vibrating element 31 and include a second light reflection unit that reflects the incident emitted light L1c (laser light) or the object light L3 (laser light).

[0164] According to such a configuration, when the laser light is reflected, the frequency of the laser light can be modulated.

[0165] Further, the first vibrating element 30 and the second vibrating element 31 are preferably crystal oscillators.

[0166] According to such a configuration, since the crystal itself is a piezoelectric material, the first vibrating element 30 and the second vibrating element 31 having particularly high frequency stability can be obtained.

[0167] Also, the first frequency f M1 and the second frequency f M2 are preferably in the range of 1 MHz or more and 100 MHz or less.

[0168] In the frequency band within the above range, there are many oscillators with a high Q value of mechanical resonance. Therefore, by setting the first frequency f M1 and the second frequency f M2 within the above range, the stabilization of the first frequency f M1 of the first signal Ss1 output from the first signal oscillation unit 511 and the stabilization of the second frequency f M2 of the second signal Ss2 output from the second signal oscillation unit 512 can be achieved.

[0169] Also, the difference between the first frequency f M1 and the second frequency f M2 is preferably in the range of 1 kHz or more and less than 1 MHz.

[0170] Thereby, while ensuring measurement performance suitable for a general measurement scene of the object 14, cost reduction of the electronic components constituting the demodulation circuit 52 can be achieved.

[0171] Also, the optical modulator 100 according to each of the above embodiments may include a light guide unit 15 that optically connects the first optical modulation unit 12 and the second optical modulation unit 13.

[0172] By providing such a light guide unit 15, the first optical modulation unit 12 and the second optical modulation unit 13 can be optically connected inside the optical modulator 100. Thereby, an optical modulator 100 excellent in workability such as alignment with other optical elements can be realized.

[0173] Also, the laser interferometer 1 according to each of the above embodiments includes a laser light source 2, a light modulator 100 according to each of the above embodiments, a light receiving element 10, and a demodulation circuit 52. The laser light source 2 emits emitted light L1 (laser light). The light modulator 100 guides the laser light so as to pass through both the first light modulation unit 12 and the second light modulation unit 13, and adds a modulation signal to the laser light. The light receiving element 10 detects a change in the intensity of interference light (laser light) including a sample signal and a modulation signal, and outputs a laser light reception signal. The demodulation circuit 52 is connected to the light modulator 100 and demodulates the sample signal from the laser light reception signal based on the reference signal SsL.

[0174] According to such a configuration, the frequency of the signal processed by the demodulation circuit 52 can be reduced, and a laser interferometer 1 that can be easily made low-cost can be obtained.

[0175] Also, the spectroscopic device 900 according to the above embodiment includes the laser interferometer 1 according to each of the above embodiments and a spectroscopic analysis unit 910. The spectroscopic analysis unit 910 has a spectroscopic optical system 920 including a movable mirror 924 and generates spectroscopic spectrum information derived from a sample. Then, the laser interferometer 1 measures the displacement of the movable mirror 924. Further, the spectroscopic analysis unit 910 generates spectroscopic spectrum information based on the measurement result of the displacement of the movable mirror 924 by the laser interferometer 1. According to such a configuration, the cost reduction of the spectroscopic device 900 can be easily achieved.

[0176] As described above, the light modulator, laser interferometer, and spectroscopic device of the present invention have been described based on the illustrated embodiments. However, the light modulator, laser interferometer, and spectroscopic device of the present invention are not limited to the above embodiments, and the configuration of each part may be replaced with any configuration, or any other configuration may be added.

[0177] Also, in each of the above embodiments, a Michelson-type interference optical system is used, but an interference optical system of another type may be used.

Description of Reference Numerals

[0178] 1… Laser interferometer, 2… Laser light source, 10… Light receiving element, 12… First optical modulator, 13… Second optical modulator, 14… Object, 15… Light guiding section, 30… First vibrating element, 31… Second vibrating element, 41… Polarizing beam splitter, 42… Polarizing beam splitter, 43… Polarizing beam splitter, 44… Polarizing beam splitter, 50… Interference optical system, 52… Demodulation circuit, 53… Pretreatment section, 54… Reference signal generation section, 55… Demodulation processing section, 100… Optical modulator, 152… Mirror, 154… Polarizing beam splitter, 156… Polarizing beam splitter, 401… Base, 402… First vibrating arm, 403… Second vibrating arm, 404… Electrode, 405… Electrode, 406… Light reflecting section, 432… Groove, 433… Pad, 434… Diffraction grating, 435… Pad, 436… Vibration direction, 437… First electrode, 438… Second electrode, 511… First signal oscillation section, 512… Second signal oscillation section, 530… Current-voltage converter, 532… Band-pass filter, 533… A / D converter, 534… First amplitude adjustment section, 536… Band-pass filter, 537… Multiplier, 538… Low-pass filter, 541… First delay adjustment section, 542… Second delay adjustment section, 543… Multiplier, 544… Low-pass filter, 545… A / D converter, 551… Multiplier, 552… Multiplier, 553… Phase shifter, 555… Low-pass filter, 556… Low-pass filter, 557… Divider, 558… Arctangent operation unit, 559… Signal output section, 560… Phase adjustment section, 561… Second amplitude adjustment section, 562… Summation unit, 574… Multiplication wiring, 900… Spectroscopic device, 910… Spectroscopic analysis section, 920… Spectroscopic optical system, 922… Analysis light light source, 924… Moving mirror, 926… Analysis light receiving section, 930… Calculation section, 4311… Surface, 4312… Back surface, L1… Emitted light, L1a… Emitted light, L1b… Emitted light, L1c… Emitted light, L2… Reference light, L2a… Reference light, L2b… Reference light, L3… Object light, Ss1… First signal, Ss2… Second signal, SsL… Reference signal, S(t)… Pretreated signal, f' M … Frequency, f M1 … First frequency, f M2 … Second frequency

Claims

1. An optical modulator connected to a demodulation circuit that demodulates a sample signal from a laser light reception signal including a sample signal added to laser light and a modulation signal added to the laser light based on a reference signal with respect to an object, A first optical modulation unit having a first vibrating element that vibrates at a first frequency, and using the first vibrating element to modulate the frequency of incident laser light; A second optical modulation unit having a second vibrating element that vibrates at a second frequency different from the first frequency, and using the second vibrating element to modulate the frequency of incident laser light; A first signal oscillation unit that generates a first signal of the first frequency with the first vibrating element as a source oscillation; A second signal oscillation unit that generates a second signal of the second frequency with the second vibrating element as a source oscillation; A reference signal generation unit that generates the reference signal having a frequency lower than both the first frequency and the second frequency using the first signal and the second signal; An optical modulator characterized by comprising the above.

2. The first optical modulation unit is provided on the first vibrating element and includes a first diffraction grating that diffracts incident laser light, The optical modulator according to claim 1, wherein the second optical modulation unit is provided on the second vibrating element and includes a second diffraction grating that diffracts incident laser light.

3. The first optical modulation unit is provided on the first vibrating element and includes a first optical reflection unit that reflects incident laser light, The optical modulator according to claim 1, wherein the second optical modulation unit is provided on the second vibrating element and includes a second optical reflection unit that reflects incident laser light.

4. The optical modulator according to any one of claims 1 to 3, wherein the first vibrating element and the second vibrating element are crystal oscillators.

5. The optical modulator according to any one of claims 1 to 3, wherein the first frequency and the second frequency are 1 MHz or more and 100 MHz or less.

6. The optical modulator according to any one of claims 1 to 3, wherein the difference between the first frequency and the second frequency is 1 kHz or more and less than 1 MHz.

7. The optical modulator according to any one of claims 1 to 3, further comprising a light guiding unit that optically connects the first optical modulation unit and the second optical modulation unit.

8. A laser light source that emits laser light, The optical modulator according to any one of claims 1 to 3, wherein the laser light is guided through both the first optical modulation unit and the second optical modulation unit, and the modulation signal is added to the laser light; A light receiving element that detects a change in intensity of the laser light including the sample signal and the modulation signal and outputs a laser light reception signal; A demodulation circuit that is connected to the optical modulator and demodulates the sample signal from the laser light reception signal based on the reference signal; A laser interferometer characterized by comprising:

9. The laser interferometer according to claim 8; A spectroscopic analysis unit that has a spectroscopic optical system including a moving mirror and generates spectroscopic spectrum information derived from a sample; Comprising: The laser interferometer measures the displacement of the moving mirror; The spectroscopic analysis unit generates the spectroscopic spectrum information based on a measurement result of the displacement of the moving mirror by the laser interferometer. A spectroscopic apparatus characterized by this.

Images