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 vibration element; a second vibration element; an optical modulation section that adds, using the first vibration element, the modulation signal to incident laser light; a first signal oscillation section that generates, using the first vibration element as source oscillation, a first signal having a first frequency; a second signal oscillation section that generates, using the second vibration element as source oscillation, a second signal having a second frequency; 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 apparatus.

Background Art

[0002] Patent Document 1 discloses a laser Doppler measurement apparatus for grasping the movement of a moving object. In the laser Doppler measurement apparatus, 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 received a 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 apparatus 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 diffraction grating is irradiated with a laser beam, 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 beam 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.

[0006] Therefore, there is a problem of realizing an optical modulator that can reduce the frequency of the signal processed by the demodulation circuit and enable cost reduction of electronic components and the like used in the demodulation circuit.

Means for Solving the Problems

[0007] The optical modulator according to the application example of the present invention is an optical modulator connected to a demodulation circuit that demodulates the sample signal based on a reference signal from a laser light reception signal including a sample signal added to the laser light by an object and a modulation signal added to the laser light, a first vibration element that vibrates at a first frequency, a second vibration element that vibrates at a second frequency different from the first frequency, an optical modulation unit that adds the modulation signal to the incident laser light using the first 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.

[0008] The laser interferometer according to the application example of the present invention is a laser light source that emits laser light, an optical modulator according to the application example of the present invention that adds the modulation signal to the laser light, A light-receiving element that detects a change in intensity of the laser beam including the sample signal and the modulation signal and outputs the laser beam reception signal; A demodulation circuit that is connected to the optical modulator and demodulates the sample signal from the laser beam reception signal based on the reference signal; and includes.

[0009] The 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; and includes 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 Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the optical modulator, laser interferometer, and spectroscopic device of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0012] 1. First Embodiment First, the optical modulator and laser interferometer according to the first embodiment will be described.

[0013] 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.

[0014] The laser interferometer 1 shown in FIG. 1 includes an interference optical system 50, an optical modulator 100, and a demodulation circuit 52.

[0015] 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. The light receiving element 10 detects 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, and outputs a laser light reception signal.

[0016] The demodulation circuit 52 shown in FIG. 1 includes 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 a sample signal from the preprocessed laser light reception signal. Thereby, the displacement and speed of the object 14 can be measured.

[0017] Also, 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. Thereby, 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.

[0018] 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, a collimating lens 3, an optical splitter 4, a half-wave plate 6, a quarter-wave plate 7, a quarter-wave plate 8, a polarizer 9, and a light receiving element 10.

[0019] The laser light source 2 emits emitted light L1 having a frequency f0. The light receiving element 10 converts the intensity of the received light into an electrical signal. The optical modulation unit 12 has an AOM 122 as will be described later. The AOM 122 is an acousto-optic modulator. The optical modulation unit 12 changes the frequency of the emitted light L1 and generates reference light L2 (laser light with a modulation signal superimposed) including a modulation signal. On the other hand, the emitted light L1 incident on the object 14 is reflected as object light L3 (laser light including a sample signal derived from the object 14) including a sample signal derived from the object 14.

[0020] Let the optical path connecting the optical splitter 4 and the laser light source 2 be the optical path 18. Let the optical path connecting the optical splitter 4 and the optical modulation unit 12 be the optical path 20. Let the optical path connecting the optical splitter 4 and the object 14 be the optical path 22. Let the optical path connecting the optical splitter 4 and the light receiving element 10 be the optical path 24. Note that the "optical path" in this specification refers to the path along which light travels, which is set between optical elements.

[0021] On the optical path 18, a half-wave plate 6 and a collimating lens 3 are arranged in this order from the optical splitter 4 side. On the optical path 20, a quarter-wave plate 8 is arranged. On the optical path 22, a quarter-wave plate 7 is arranged. On the optical path 24, an analyzer 9 is arranged.

[0022] The emitted light L1 emitted from the laser light source 2 passes through the optical path 18 and is split into two by the optical splitter 4. One of the split emitted lights L1, the first split light L1a, enters the optical modulation unit 12 through the optical path 20. Also, the other of the split emitted lights L1, the second split light L1b, enters the object 14 through the optical path 22. The reference light L2 generated by shifting the frequency in the optical modulation unit 12 enters the light receiving element 10 through the optical paths 20 and 24. The object light L3 generated by the reflection of the object 14 enters the light receiving element 10 through the optical paths 22 and 24.

[0023] In the laser interferometer 1 equipped with 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 the demodulation circuit 52 described later. According to the optical heterodyne interference method, when extracting the phase information from the interference light, it is less affected by external disturbances, especially stray light of the frequency that becomes noise, and high robustness is provided.

[0024] Hereinafter, each part of the interference optical system 50 will be further described. 1.1.1. Laser Light Source The laser light source 2 is a laser light source that emits an injection light L1 having coherence. As the laser light source 2, a light source with a line width of MHz band or less is preferably used. Specifically, gas lasers such as He-Ne lasers, DFB-LDs (Distributed FeedBack - Laser Diodes), FBG-LDs (Laser Diodes with Fiber Bragg Gratings), VCSELs (Vertical Cavity Surface Emitting Lasers), and semiconductor laser elements such as FP-LDs (Fabry-Perot Laser Diodes) can be mentioned.

[0025] The laser light source 2 is particularly preferably a semiconductor laser element. Thereby, it becomes possible to particularly miniaturize the laser light source 2. For this reason, the laser interferometer 1 can be miniaturized.

[0026] 1.1.2. Collimating lens The collimating lens 3 is an optical element disposed between the laser light source 2 and the optical splitter 4, and an aspherical lens can be mentioned as an example. The collimating lens 3 collimates the injection light L1 emitted from the laser light source 2. When the injection light L1 emitted from the laser light source 2 is sufficiently collimated, for example, when a gas laser such as a He-Ne laser is used as the laser light source 2, the collimating lens 3 may be omitted.

[0027] The collimated injection light L1 passes through the half-wave plate 6 and is converted into linearly polarized light with an intensity ratio of P-polarized light to S-polarized light of, for example, 50:50, and enters the optical splitter 4.

[0028] 1.1.3. Optical splitter The optical splitter 4 is a polarization beam splitter disposed between the laser light source 2 and the optical modulation unit 12, and between the laser light source 2 and the object 14. The optical splitter 4 has a function of transmitting P-polarized light and reflecting S-polarized light. By this function, the optical splitter 4 splits the emitted light L1 into a first split light L1a which is the reflected light at the optical splitter 4, and a second split light L1b which is the transmitted light of the optical splitter 4.

[0029] The first split light L1a which is the S-polarized light reflected by the optical splitter 4 is converted into circularly polarized light by the quarter-wave plate 8 and enters the optical modulation unit 12. The first split light L1a incident on the optical modulation unit 12 undergoes a frequency shift of f m [Hz] and is emitted as the reference light L2. Therefore, the reference light L2 includes a modulation signal with a modulation frequency (the first frequency f M ). That is, the frequency of the reference light L2 becomes f0 + f M . The reference light L2 is converted into P-polarized light when passing through the quarter-wave plate 8 again. The P-polarized light of the reference light L2 passes through the optical splitter 4 and the analyzer 9 and enters the light receiving element 10.

[0030] The second split light L1b which is the P-polarized light transmitted through the optical splitter 4 is converted into circularly polarized light by the quarter-wave plate 7 and enters the moving object 14. The second split light L1b incident on the object 14 undergoes a Doppler shift of f d [Hz] and is reflected as the object light L3. Therefore, the object light L3 includes a sample signal with a vibration frequency f d [Hz]. That is, the frequency of the object light L3 becomes f0 - f D . The object light L3 is converted into S-polarized light when passing through the quarter-wave plate 7 again. The S-polarized light of the object light L3 is reflected by the optical splitter 4, passes through the analyzer 9, and enters the light receiving element 10.

[0031] Since the emitted light L1 has coherence, the reference light L2 and the object light L3 enter the light receiving element 10 as interference light.

[0032] 1.1.4. Analyzer Since the S-polarized light and P-polarized light that are orthogonal to each other are independent of each other, simply superimposing them does not result in beats due to interference. Therefore, the light wave obtained by superimposing the S-polarized light and P-polarized light is passed through an analyzer 9 that is tilted by 45° with respect to both the S-polarized light and P-polarized light. By using the analyzer 9, it is possible to transmit the light of the components common to each other and cause interference. As a result, at the analyzer 9, the reference light L2 and the object light L3 interfere with each other, and interference light having a beat frequency of |f M -f D | is generated.

[0033] 1.1.5. Light receiving element When the interference light is incident on the light receiving element 10, the light receiving element 10 outputs a photocurrent (laser light reception signal) corresponding to the intensity of the interference light. By demodulating the sample signal from this laser light reception signal by a method described later, finally, the movement of the object 14, that is, the displacement and speed can be obtained. Examples of the light receiving element 10 include a photodiode and the like. Note that what is received by the light receiving element 10 is the laser light emitted from the laser light source 2, and it suffices that the frequency and phase thereof are laser light in which a modulation signal and a sample signal are superimposed as a result of being modulated by the optical modulation unit 12 and the object 14, and it is not limited to only the above-described interference light. In addition, "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.

[0034] 1.2. Optical modulator The optical modulator 100 shown in FIG. 1 includes a first vibrating element 30, an optical modulation unit 12, a first signal oscillation unit 511, a second vibrating element 31, a second signal oscillation unit 512, and a reference signal generation unit 54.

[0035] 1.2.1. First vibrating element The first vibrating element 30 has a first frequency f MIt vibrates. The first vibration element 30 is, for example, 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 inputting the first signal output from the first signal oscillation unit 511 with the first vibration element 30 as the source oscillation into the AOM 122, a modulation signal of the first frequency can be added to the first split light L1a in the AOM 122.

[0036] Examples of the crystal oscillator include a crystal AT oscillator, an SC-cut crystal oscillator, a tuning fork type crystal oscillator, a surface acoustic wave element of crystal, etc. The oscillation frequency of the crystal oscillator is, for example, about 1 kHz to several 100 MHz.

[0037] The silicon oscillator is a vibrator including 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 shape such as a two-pronged tuning fork type and a three-pronged tuning fork type, and a double-cantilever shape. The oscillation frequency of the silicon oscillator is, for example, about 1 kHz to several 100 MHz.

[0038] The ceramic oscillator is a vibrator including a piezoelectric ceramic piece manufactured by firing a piezoelectric ceramic and an electrode. Examples of the piezoelectric ceramic include lead zirconate titanate (PZT), barium titanate (BTO), etc. The oscillation frequency of the ceramic oscillator is, for example, about several 100 kHz to several 10 MHz.

[0039] Among these, a crystal oscillator is preferably used for the first vibration element 30. Since the crystal itself is a piezoelectric material, the crystal oscillator has particularly high frequency stability.

[0040] The oscillation frequency of the first vibration element 30 (the first frequency f M) is not particularly limited, but is preferably 1 MHz or more and 100 MHz or less. In the frequency band within this range, there are many oscillators with a high Q value of mechanical resonance. Therefore, by setting the first frequency f M within this range, the first frequency f M of the first signal Ss1 output from the first signal oscillation unit 511 can be stabilized.

[0041] 1.2.2. Optical modulation unit As described above, the optical modulation unit 12 shown in FIGS. 1 and 2 includes an AOM 122. When the periodic signal output with the first vibration element 30 as the source vibration is input to the AOM 122 and the first divided light L1a is irradiated to the AOM 122, a modulation signal of the first frequency f M is added to the first divided light L1a due to diffraction. When the AOM 122 is an element that transmits light, a reflecting plate (not shown) can be provided to return the first divided light L1a in the incident direction.

[0042] Note that, instead of the AOM 122, other frequency shifters may be used, or a phase shifter such as an electro-optical modulator (EOM) may be used.

[0043] 1.2.3. First signal oscillation unit The first signal oscillation unit 511 generates a first signal Ss1 of a first frequency f M using the first vibration element 30 as the source vibration.

[0044] 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 vibration. 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.

[0045] Note that the first vibration element 30 and the first signal oscillation unit 511 may be housed in one package. Examples of the first vibration element 30 and the first signal oscillation unit 511 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.

[0046] 1.2.4. Second Vibration Element The second vibration element 31 vibrates at the second frequency f C . The second vibration element 31 is, for example, an oscillator that generates a periodic signal such as a crystal oscillator, a ceramic oscillator, or an Si oscillator. Since these oscillators utilize a mechanical resonance phenomenon, they have a high Q value and excellent frequency stability.

[0047] 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.

[0048] The oscillation frequency of the second vibration element 31 (the second frequency f C ) is not particularly limited as long as it is different from the first frequency f M , but is preferably 1 MHz or more and 100 MHz or less. In the frequency band within the above range, there are many oscillators with a high Q value of mechanical resonance. Therefore, by setting the second frequency f C within the above range, the stabilization of the second frequency f C of the second signal Ss2 output from the second signal oscillation unit 512 can be achieved.

[0049] 1.2.5. Second Signal Oscillation Unit The second signal oscillation unit 512 generates a second signal Ss2 having a second frequency f C using the second vibration element 31 as a source oscillation.

[0050] 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 with a high Q value of mechanical resonance, a second signal Ss2 with high frequency stability can be generated.

[0051] 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), etc.

[0052] 1.2.6. Reference signal generation unit FIG. 3 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.

[0053] The reference signal generation unit 54 shown in FIG. 3 multiplies a laser light reception signal including a modulation signal of the first frequency f M by a second signal Ss2 of the second frequency f C . Thereby, the frequency of the signal processed by the preprocessing unit 53 of the demodulation circuit 52 can be lowered. Also, 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 M and the second frequency f C . 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".

[0054] The reference signal generation unit 54 includes a first delay adjustment unit 541, a second delay adjustment unit 542, a multiplier 543, a low-pass filter 544, an A / D converter 545, and multiplication wirings 546, 547, 548. Note that the configuration of the reference signal generation unit 54 is not limited to this.

[0055] The first delay adjustment unit 541 and the second delay adjustment unit 542 adjust their respective delays 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.

[0056] The multiplier 543 multiplies the signal output from the first delay adjustment unit 541 and the signal output from the second delay adjustment unit 542. As a result of this multiplication, a signal with the frequency of the sum of the first frequency f M and the second frequency f C (sum frequency signal) and a signal with the frequency of the difference (difference frequency signal) are generated.

[0057] The low-pass filter 544 cuts the sum frequency signal from the signal of the multiplication result by the multiplier 543. Thereby, the difference frequency signal can be extracted and used as the reference signal SsL. Note that the low-pass filter 544 may be a band-pass filter.

[0058] The A / D converter 545 digitally converts the analog difference frequency signal. Thereby, a digital reference signal SsL is obtained. Note that the frequency of the analog reference signal SsL input to the A / D converter 545 is lower than the first frequency f M and the second frequency f C . Therefore, it is possible to lower the sampling frequency of the A / D converter 545, and the cost of the A / D converter 545 can be reduced. Note that the A / D converter 545 may be provided as necessary. For example, when the demodulation circuit 52 is composed of an analog circuit, it can be omitted.

[0059] The multiplication wiring 546 is a path for inputting the second signal Ss2 to the preprocessing unit 53. As a result, multiplication of the laser light reception signal and the second signal Ss2 becomes possible in the preprocessing unit 53, and the signal to be processed by arithmetic operations within the preprocessing unit 53 can be down-converted. Consequently, the operating frequency of electronic components such as the FPGA (programmable logic device), ASIC (application-specific integrated circuit), and microcomputer in which the preprocessing unit 53 is implemented can be lowered, and cost reduction can be achieved.

[0060] The multiplication wirings 547 and 548 are paths for inputting the reference signal SsL output from the A / D converter 545 to the demodulation processing unit 55. As a result, the signal to be processed by arithmetic operations in the demodulation processing unit 55 can be down-converted. Consequently, the operating frequency of the electronic components in which the demodulation processing unit 55 is implemented can be lowered, and cost reduction can be achieved.

[0061] Note that the frequency after down-conversion is the difference between the first frequency f M and the second frequency f C . When considering the sampling frequency of the A / D converter and the operating frequency of the FPGA, etc., the frequency of the difference between the first frequency f M and the second frequency f C is preferably in the kHz band. As an example, consider the case where the first frequency f M is 40.00 MHz and the second frequency f C is 39.95 MHz. In this case, the frequency f' M after down-conversion is 50 kHz. Also, in this case, the low-pass filters 532, 544, 555, and 556 are set to cut frequencies above 50 kHz.

[0062] Also, in this example, the first frequency f C is higher than the second frequency f M , but this relationship may be reversed. In this case, by reversing the positive and negative of the signal output from the demodulation circuit 52, the same value as in the above example can be obtained.

[0063] On the other hand, the frequency f' after down-conversion M affects the measurable velocity range and frequency range of the object 14 when measuring the displacement 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 M and the second frequency f C 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.

[0064] 1.3. Demodulation Circuit The demodulation circuit 52 shown in FIG. 3 includes a current-voltage converter 530, a preprocessing unit 53, and a demodulation processing unit 55.

[0065] 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.

[0066] 1.3.2. Preprocessing Unit The preprocessing unit 53 shown in FIG. 3 down-converts the laser light reception signal output from the current-voltage converter 530 and digitally converts it. In this specification, the operation performed by the preprocessing unit 53 is also referred to as "preprocessing".

[0067] The preprocessing unit 53 includes a multiplier 531, a low-pass filter 532, and an A / D converter 533.

[0068] The multiplier 531 multiplies the laser light reception signal output from the current-voltage converter 530 and the second signal Ss2 input via the multiplication wiring 546. As a result of this multiplication, a signal with the sum frequency of the laser light reception signal and the second signal Ss2 (sum frequency signal) and a signal with the difference frequency (difference frequency signal) are generated.

[0069] The low-pass filter 532 cuts the sum-frequency signal with respect to the signal of the multiplication result by the multiplier 531. Thereby, the difference-frequency signal can be extracted. Note that the low-pass filter 532 may be a band-pass filter.

[0070] The A / D converter 533 digitally converts the analog difference-frequency signal. Thereby, a digital difference-frequency signal is obtained, and this is used as the preprocessed signal S(t). Note that the A / D converter 533 may be provided as necessary. For example, when the demodulation processing unit 55 is composed of analog circuits, it can be omitted.

[0071] 1.3.3. Demodulation Processing Unit The demodulation processing unit 55 shown in FIG. 3 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.

[0072] The demodulation processing unit 55 shown in FIG. 3 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.

[0073] The preprocessed signal S(t) is divided 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.

[0074] 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.

[0075] The low-pass filter 555 and the low-pass filter 556 are filters that cut signals in the high-frequency band, respectively.

[0076] The divider 557 performs a division operation that divides the signal output from the low-pass filter 556 by the signal output from the low-pass filter 555.

[0077] 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.

[0078] 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. Further, if necessary, the speed of the object 14 is calculated.

[0079] 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.

[0080] 2. Second Embodiment Next, the optical modulator and the laser interferometer according to the second embodiment will be described.

[0081] FIG. 4 is a functional block diagram showing the laser interferometer 1 according to the second embodiment. FIG. 5 is a schematic configuration diagram showing the optical modulator 100 and the interference optical system 50 shown in FIG. 4.

[0082] 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 each drawing representing the present embodiment, the same components as those in the above embodiment are denoted by the same reference numerals.

[0083] The second embodiment is the same as the first embodiment except that the configuration of the optical modulator 100 and the configuration of the preprocessing unit 53 are different.

[0084] 2.1. Optical modulator In the optical modulator 100 shown in FIG. 4, the optical modulation unit 12 has a first vibrating element 30 instead of the AOM 122. Then, in the optical modulation unit 12, as shown in FIG. 5, the frequency of the first split light L1a is modulated using the first vibrating element 30.

[0085] According to such a configuration, since the AOM 122 can be omitted, the optical modulator 100 can be made smaller, lighter, and consume less power.

[0086] In addition, by modulating the frequency of the first split light L1a using the first vibrating element 30, the modulation signal added to the reference light L2 and the first signal Ss1 output from the first signal oscillation unit 511 with the first vibrating element 30 as the source oscillation both originate from the vibration energy of the first vibrating element 30. Therefore, even if an external disturbance such as impact or noise is applied to the optical modulator 100 and the vibration of the first vibrating element 30 changes, both the modulation signal and the first signal Ss1 will change in the same way. Then, in the process of arithmetic processing in the demodulation circuit 52, the influence of both external disturbances can be canceled or reduced. As a result, a decrease in the signal-to-noise ratio (S / N ratio) of the sample signal demodulated by the demodulation circuit 52 can be suppressed.

[0087] 2.1.1. Optical modulation unit FIG. 6 is a perspective view showing the optical modulation unit 12 included in the optical modulator 100 according to the second embodiment.

[0088] Examples of the optical modulation unit 12 shown in FIG. 6 include the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156.

[0089] Specifically, the optical modulation unit 12 shown in FIG. 6 includes a first vibrating element 30 and a diffraction grating 434 provided on the first vibrating element 30 for diffracting the first split light L1a (split laser light).

[0090] The first vibration element 30 shown in Fig. 6 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 first split 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 first split light L1a can be modulated to generate the reference light L2.

[0091] 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, on the front surface 4311, 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 other hand, on the back surface 4312, 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. 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.

[0092] The diffraction grating 434 shown in Fig. 6 is disposed on the first electrode 437. That is, in Fig. 6, the diffraction grating 434 is constituted by a plurality of grooves 432 formed on the surface of the first electrode 437, and when the first split light L1a is irradiated thereon, the reference light L2 as diffracted light is emitted.

[0093] The diffraction grating 434 shown in Fig. 6 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.

[0094] FIG. 7 is a perspective view showing another configuration example of the optical modulation unit 12 shown in FIG. 6. In FIG. 7, 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".

[0095] The first vibration element 30 shown in FIG. 7 is a tuning fork type crystal oscillator. The first vibration element 30 shown in FIG. 7 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 optical modulation unit 12 shown in FIG. 7 includes the first vibration element 30, and electrodes 404, 405, and a light reflection portion 406 provided on the first vibration element 30.

[0096] 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.

[0097] The electrode 404 is a conductive film provided on a 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. 7, the electrode 404 is provided on 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.

[0098] The electrode 405 is a conductive film provided on a side surface intersecting the A-B plane among the first vibration arm 402 and the second vibration arm 403. Although not shown in FIG. 7, the electrode 405 is also provided on 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.

[0099] The light reflection unit 406 is set on a side surface that intersects, for example, the A-B surface among the first vibrating arm 402 and the second vibrating arm 403, and has a function of reflecting the first divided light L1a. Due to this function, since the light reflection unit 406 has a vibration component with a large amplitude in the incident direction of the incident first divided light L1a, it can efficiently modulate the frequency of the first divided light L1a and generate the reference light L2.

[0100] For the tuning fork type crystal oscillator, a crystal piece cut out from a crystal substrate is used. Examples of the crystal substrate used in the manufacture of the tuning fork type crystal oscillator include a crystal Z-cut flat plate. In FIG. 7, 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 crystal 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 crystal and is preferably used as the crystal substrate. Then, by etching such a crystal substrate, the crystal piece used for the first vibrating element 30 shown in FIG. 7 is obtained.

[0101] 2.1.2. Reference signal generation unit FIG. 8 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. 4.

[0102] The reference signal generation unit 54 shown in FIG. 8 includes a first delay adjustment unit 541, a second delay adjustment unit 542, a multiplier 543, a low-pass filter 544, an A / D converter 545, multiplication wirings 546, 547, 548, a multiplier 571, a band-pass filter 572, and multiplication wirings 573, 574. Note that the configuration of the reference signal generation unit 54 is not limited to this.

[0103] Multiplier 571 squares the signal output from the second delay adjuster 542. Let the signal output from multiplier 571 be the second signal Ss2'. The frequency of the second signal Ss2' is 2fc. Bandpass filter 572 allows only signals in a predetermined frequency band to pass through the signal output from multiplier 571. Multiplication wiring 573 is a path for inputting the signal output from bandpass filter 572 to preprocessing unit 53. Multiplication wiring 574 is a path for inputting the signal output from low-pass filter 544 to preprocessing unit 53.

[0104] 2.2. Demodulation Circuit The demodulation circuit 52 shown in Fig. 8 includes a current-voltage converter 530, a preprocessing unit 53, and a demodulation processing unit 55.

[0105] 2.2.1. Preprocessing Unit The preprocessing unit 53 shown in Fig. 8 down-converts the laser light reception signal output from the current-voltage converter 530, 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, and performs digital conversion.

[0106] The preprocessing unit 53 shown in Fig. 8 includes a multiplier 531, a low-pass filter 532, an A / D converter 533, a first amplitude adjustment unit 534, a multiplier 535, a low-pass filter 536, a multiplier 537, a low-pass filter 538, an A / D converter 539, a second amplitude adjustment unit 561, and an adder 562. Note that the configuration of the preprocessing unit 53 is not limited to this. For example, a delay adjustment unit may be provided at an arbitrary position.

[0107] The laser light reception signal input to the preprocessing unit 53 is split into two. One passes through the multiplier 531, the low-pass filter 532, the A / D converter 533, and the first amplitude adjustment unit 534 and is input to the adder 562. The other passes through the multiplier 535, the low-pass filter 536, the multiplier 537, the low-pass filter 538, the A / D converter 539, and the second amplitude adjustment unit 561 and is input to the adder 562.

[0108] The multiplier 531 multiplies one laser light reception signal and a second signal Ss2 input via the multiplication wiring 546. As a result of this multiplication, a signal with the frequency of the sum of the laser light reception signal and the second signal Ss2 (sum frequency signal) and a signal with the frequency of the difference (difference frequency signal) are generated as the multiplication result.

[0109] The low-pass filter 532 cuts the sum frequency signal from the signal of the multiplication result by the multiplier 531. As a result, the difference frequency signal can be extracted. Note that the low-pass filter 532 may be a band-pass filter.

[0110] The A / D converter 533 digitally converts the analog difference frequency signal. As a result, a digital difference frequency signal is obtained.

[0111] The first amplitude adjustment unit 534 adjusts so that the amplitudes of the signals are equalized with the second amplitude adjustment unit 561.

[0112] The multiplier 535 multiplies the other laser light reception signal and a second signal Ss2' input via the multiplication wiring 573. As a result of this multiplication, a signal with the frequency of the sum of the laser light reception signal and the second signal Ss2' (sum frequency signal) and a signal with the frequency of the difference (difference frequency signal) are generated as the multiplication result.

[0113] The low-pass filter 536 cuts the sum frequency signal from the signal of the multiplication result by the multiplier 535. As a result, the difference frequency signal can be extracted. Note that the low-pass filter 536 may be a band-pass filter.

[0114] The multiplier 537 multiplies the signal output from the low-pass filter 536 and a reference signal SsL input via the multiplication wiring 574. As a result of this multiplication, a signal with the frequency of the sum of the signal output from the low-pass filter 536 and the reference signal SsL (sum frequency signal) and a signal with the frequency of the difference (difference frequency signal) are generated as the multiplication result.

[0115] The low-pass filter 538 cuts the sum-frequency signal with respect to the signal of the multiplication result by the multiplier 537. Thereby, the difference-frequency signal can be extracted. Note that the low-pass filter 538 may be a band-pass filter.

[0116] The A / D converter 539 digitally converts the analog difference-frequency signal. Thereby, a digital difference-frequency signal is obtained.

[0117] The second amplitude adjustment unit 561 adjusts so that the amplitudes of the signals are equalized with the first amplitude adjustment unit 534.

[0118] 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 defined as the preprocessed signal S(t).

[0119] 2.2.2. 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 as a modulation signal is used, 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.

[0120] 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).

[0121]

Equation

[0122] In the above formula (1), A represents the amplitude. Also, Φ M is the phase derived from the optical modulation unit 12, and X is given by the following formula (1a).

[0123]

Equation

[0124] In the above formula (1a), 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.

[0125] In the optical modulation unit 12 shown in FIG. 8, the frequency of the incident laser light is modulated using the first vibration element 30 that vibrates at the first frequency f M . Therefore, Φ M is given by the following formula (1b).

[0126]

Equation

[0127] In the above formula (1b), B is the modulation phase shift in the frequency modulation in the optical modulation unit 12, and t is time.

[0128] In the multiplier 531, the AC component I PD.AC of the laser light reception signal and the second signal Ss2 input via the multiplication wiring 546 are multiplied. The multiplication result I het1 is given by the following formula (1c).

[0129]

Equation

[0130] As shown in the above formula (1c), the AC part I PD.AC of the laser light reception signal input to the preprocessing unit 53 shown in FIG. 8 is represented by a mathematical formula that includes a trigonometric function (cos) angle part and further includes a trigonometric function (sin) whose angle part changes with time. In this case, using the series representation of the Bessel function, the mathematical formula of the AC part I PD.AC of the laser light reception signal can be expanded.

[0131] And when the multiplication result I het1 in the multiplier 531 passes through the low-pass filter 532, the frequency component corresponding to the first-order term of the series representation can be extracted. As a result, the multiplication result I het1The signal I after passing through the low-pass filter 532 LPF1 is represented by the following formula (2).

[0132]

Equation

[0133] In the above formula (2), J1(B) is the coefficient of the first-order term when the Bessel function is expressed as a series. That is, the above formula (2) is the multiplication result I represented by the above formula (1c) het1 expanded using the series representation of the Bessel function and is the extracted first-order term.

[0134] Also, f’ M represents the frequency down-converted by the multiplication by the multiplier 531. That is, by passing the multiplication result through the low-pass filter 532, the difference frequency signal is extracted, so f’ M is defined by the following formula (2a).

[0135]

Equation

[0136] In the above formula (2a), f M is the frequency (first frequency) of the first signal Ss1, and f C is the frequency (second frequency) of the second signal Ss2. As can be seen from the above formula (2a), by multiplying the AC component I PD.AC and the second signal Ss2 in the multiplier 531, the frequency can be lowered by f c amount.

[0137] On the other hand, in the multiplier 535, the AC component I of the laser light reception signal PD.AC and the second signal Ss2’ input via the multiplication wiring 573 are multiplied. The multiplication result I het2 is given by the following formula (1d).

[0138]

Equation

[0139] Then, when the multiplication result I in the multiplier 535 het2 passes through the low-pass filter 536, the frequency component corresponding to the quadratic term in the series representation can be extracted. As a result, the multiplication result I het2 after passing through the low-pass filter 536 is the signal I LPF2 which is represented by the following formula (3).

[0140]

Equation

[0141] In the above formula (3), J2(B) is the coefficient of the quadratic term when the Bessel function is represented as a series. That is, the above formula (3) is the multiplication result I represented by the above formula (1d) het2 expanded using the series representation of the Bessel function and is the extracted quadratic term.

[0142] As described above, by providing the multipliers 531 and 535, the frequency of the AC component I PD.AC of the laser light reception signal can be down-converted to f’ M .

[0143] Also, in the multiplier 537, the signal I LPF2 after passing through the low-pass filter 536 is multiplied by the reference signal SsL. The signal I LPF3 after the multiplication result passes through the low-pass filter 538 is represented by the following formula (4).

[0144]

Equation

[0145] After that, the signal I LPF1 is amplitude-adjusted by multiplying -J2(B) in the first amplitude adjustment unit 534 after passing through the A / D converter 533.

[0146] Also, signal I LPF3 After passing through the A / D converter 539, its amplitude is adjusted by multiplying by 2J1(B) in the second amplitude adjustment unit 561.

[0147] In adder 562, the amplitude-adjusted signal I LPF1 and the amplitude-adjusted signal I LPF3 are added together. As a result, the preprocessed signal S(t) is obtained. The preprocessed signal S(t) is represented by the following formula (5).

[0148]

Equation

[0149] In the above manner, the preprocessed signal S(t) with its frequency down-converted is obtained.

[0150] Here, a specific example will be described when the first frequency f M is 4.97 MHz and the second frequency f C is 4.92 MHz. In this case, the frequency of the signal output from the low-pass filter 532 of the preprocessing unit 53 is 50 kHz, and the frequency of the signal output from the low-pass filter 536 is 100 kHz. Therefore, in this case, the low-pass filters 532, 538, 544, 555, and 556 are set to cut frequencies above 50 kHz, and the low-pass filter 536 is set to cut frequencies above 100 kHz. Also, the band-pass filter 572 is set to pass 9.84 MHz, which corresponds to twice the second frequency f C .

[0151] 2.2.3. Demodulation Processing Unit The demodulation processing unit 55 shown in FIG. 8 is the same as the demodulation processing unit 55 shown in FIG. 3. Demodulation processing is performed on the preprocessed signal S(t) output from the preprocessing unit 53 to demodulate X in the above formula (5). X is defined as Φ S - Φ0. Assuming that Φ0 is constant, Φ SA change in (the phase derived from the object 14) is required. As described above, the displacement, velocity, etc. of the object 14 can be measured.

[0152] 3. Modification of the Second Embodiment Next, a modulator and a laser interferometer according to a modification of the second embodiment will be described.

[0153] FIG. 9 is a block diagram showing an example of the circuit configurations of a reference signal generation unit 54 and a demodulation circuit 52 included in the laser interferometer 1 according to the modification of the second embodiment.

[0154] Hereinafter, the modification of the second embodiment will be described. In the following description, the differences from the second embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 9, the same components as those in FIG. 8 are denoted by the same reference numerals.

[0155] The modification of the second embodiment is the same as the second embodiment except that the configurations of the reference signal generation unit 54 and the preprocessing unit 53 are different. Hereinafter, the differences from the second embodiment will be listed.

[0156] In this modification, the second frequency is set to 2f which is twice that of the second embodiment. C For example, when the second frequency f of the second embodiment C is 4.92 MHz, in this modification, the second frequency 2f C is 9.84 MHz.

[0157] Also, in this modification, in the reference signal generation unit 54, a multiplier 571 for squaring the signal output from the second delay adjustment unit 542 is omitted. As a result, the number of components of the analog circuit can be reduced. Note that the second signal Ss2 is input to the preprocessing unit 53 via the multiplication wiring 573 at the same frequency (the second frequency 2f C ).

[0158] Furthermore, in this modified example, in the reference signal generation unit 54, a frequency divider 575 is provided in the middle of the multiplication wiring 546. The frequency divider 575 can reduce the input frequency to 1 / n (where n is an integer) and output it. In this modified example, the frequency divider 575 reduces the frequency to 1 / 2. As a result, the frequency of the second signal Ss2' output from the frequency divider 575 becomes fc.

[0159] Also, in this modified example, the position of the A / D converter 539 included in the preprocessing unit 53 is changed to be between the low-pass filter 536 and the multiplier 537. Similarly, the position of the A / D converter 545 included in the reference signal generation unit 54 is changed to be immediately after the low-pass filter 544 (between the low-pass filter 544 and the branch point where the signal output from the low-pass filter 544 is branched). Due to the above changes, the multiplier 537 included in the preprocessing unit 53 can be changed from analog to digital, and accordingly, the number of analog multipliers can be reduced. As a result, the probability of noise being mixed in the analog multiplier can be reduced, and a decrease in the S / N ratio of the preprocessed signal S(t) can be suppressed.

[0160] Here, as an example, consider the case where the first frequency f M is 4.97 MHz and the second frequency 2f C is 9.84 MHz. In this case, the frequency of the signal output from the low-pass filter 532 of the preprocessing unit 53 is 50 kHz, and the frequency of the signal output from the low-pass filter 536 is 100 kHz. Therefore, in this case, the low-pass filters 532, 538, 544, 555, 556 are set to cut frequencies above 50 kHz, and the low-pass filter 536 is set to cut frequencies above 100 kHz. Also, the band-pass filter 572 is set to pass the second frequency 2f C which is 9.84 MHz.

[0161] 4. Third Embodiment Next, an optical modulator and a laser interferometer according to the third embodiment will be described. FIG. 10 is a functional block diagram showing the laser interferometer 1 according to the third embodiment.

[0162] Hereinafter, the first 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. 10, the same components as those in FIG. 1 are denoted by the same reference numerals.

[0163] The third embodiment is the same as the first embodiment except that the configuration of the optical modulator 100 is different. The differences from the first embodiment will be listed below.

[0164] In the third embodiment, the optical modulator 100 shown in FIG. 10 includes a third vibration element 31A in addition to the first vibration element 30 and the second vibration element 31. Also, in the third embodiment, the optical modulator 100 includes a third signal oscillation unit 512A in addition to the first signal oscillation unit 511 and the second signal oscillation unit 512. Further, in the third embodiment, the optical modulator 100 includes a switching unit 56.

[0165] The third vibration element 31A 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.

[0166] The oscillation frequency (third frequency) of the third vibration element 31A 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 third frequency within the above range, the stabilization of the third frequency of the third signal Ss3 output from the third signal oscillation unit 512A can be achieved.

[0167] The switching unit 56 is configured to switch the connection destination in order to select the selection signal SsX input to the reference signal generation unit 54 from a plurality of signals (the second signal Ss2 or the third signal Ss3). Specifically, the second signal Ss2 output from the second signal oscillation unit 512 and the third signal Ss3 output from the third signal oscillation unit 512A are input to the switching unit 56. The switching unit 56 selects either the second signal Ss2 or the third signal Ss3 and inputs it to the reference signal generation unit 54 as the selection signal SsX. Note that the number of signals selected by the switching unit 56 is not limited to two, and may be three or more.

[0168] The reference signal generation unit 54 is the same as the reference signal generation unit 54 of the first embodiment, except that the selection signal SsX is used instead of the second signal Ss2 of the first embodiment. According to such a configuration, in the reference signal generation unit 54 and the preprocessing unit 53, the frequency f' after down-conversion M can be switched. Thereby, according to the vibration characteristics of the object 14, the optimal frequency f' M can be selected. As a result, the laser interferometer 1 capable of acquiring optimal measurement data according to the vibration characteristics of the object 14 can be realized. Specifically, in the case of the object 14 having a low vibration frequency (vibrating slowly), in order to accurately capture its vibration characteristics, it is necessary to secure a sufficient data measurement time. However, since there is an upper limit to the data length (the number of data points), when the sampling frequency of the demodulation circuit 52 is high, a sufficient data measurement time cannot be secured.

[0169] On the other hand, in this embodiment, by reducing the sampling frequency of the demodulation circuit 52 by down-conversion, even with the same data length, a longer data measurement time can be secured. Therefore, for the object 14 with a low vibration frequency, measurement data of an appropriate length can be acquired.

[0170] As an example, when the frequency of the signal processed by the demodulation circuit 52 is set to 5 MHz without down-conversion, the sampling frequency of the demodulation circuit 52 needs to be about 100 MHz. Assuming that the upper limit value of the data length is 1 million points, the data measurement time can only be ensured for 10 milliseconds. In this case, for example, for the object 14 vibrating at a slow frequency of 100 Hz or less, it is difficult to accurately measure the vibration characteristics.

[0171] On the other hand, when the frequency of the vibration processed by the demodulation circuit 52 is down-converted to 1 kHz, the sampling frequency of the demodulation circuit 52 is only about 20 kHz. Therefore, a data measurement time of 50 seconds can be ensured. In this case, for example, even for the object 14 vibrating at a very slow frequency of about 1 Hz, the vibration characteristics can be accurately measured.

[0172] In Table 1 below, the first frequency f M is 4.97 MHz, and when the second frequency f C is changed in five steps, the frequency f' M after down-conversion, and examples of measurement objects (examples of vibration characteristics of measurable objects) are listed.

[0173]

Table 1

[0174] As shown in Table 1 above, by selecting one from a plurality of signals by the switching unit 56, the vibration characteristics of various objects 14 with different vibration frequencies can be measured by one laser interferometer 1. Thereby, a laser interferometer 1 that can be used for various applications can be realized.

[0175] 5. Fourth Embodiment Next, a spectroscopic apparatus according to the fourth embodiment will be described. FIG. 11 is a functional block diagram showing a spectroscopic apparatus 900 according to the fourth embodiment.

[0176] 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. 11, the same components as those in FIG. 1 are denoted by the same reference numerals.

[0177] The spectroscopic apparatus 900 shown in FIG. 11 includes the laser interferometer 1 according to each of the above embodiments and a spectroscopic analysis unit 910.

[0178] The spectroscopic analysis unit 910 receives the analysis light including the sample-derived signal generated by the action on the sample, and generates spectroscopic spectrum information derived from the sample. The spectroscopic analysis unit 910 shown in FIG. 11 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 interferometer. In the analysis interferometer, while changing the optical path length by moving the moving mirror 924, 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] Further, as described above, the laser interferometer 1 can be easily reduced in cost. Therefore, according to the above configuration, a spectroscopic apparatus 900 that can be easily reduced in cost and has excellent wave number resolution can be realized.

[0183] Note that the spectroscopic apparatus 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.

[0184] Further, the spectroscopic apparatus 900 can be applied to, for example, a white light interference shape measuring apparatus, an optical coherence tomography (OCT) imaging apparatus, etc. by using an element capable of acquiring a two-dimensional light intensity distribution as the analysis light receiving unit 926.

[0185] 6. Effects achieved by each of the above embodiments The optical modulator 100 according to each of the above embodiments and modification examples 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 a reference signal, and includes a first vibration element 30, a second vibration element 31, an optical modulation unit 12, a first signal oscillation unit 511, a second signal oscillation unit 512, and a reference signal generation unit 54. The first vibration element 30 vibrates at a first frequency f M The second vibration element 31 vibrates at a second frequency f M different from the first frequency f C The optical modulation unit 12 adds a modulation signal to the incident first split light L1a (laser light) using the first vibration element 30. The first signal oscillation unit 511 generates a first signal Ss1 having a first frequency f M with the first vibration element 30 as the source oscillation. The second signal oscillation unit 512 generates a second signal Ss2 having a second frequency f C with the second vibration element 31 as the source oscillation. The reference signal generation unit 54 uses the first signal Ss1 and the second signal Ss2 to generate the first frequency f M and the second frequency fC Generate a reference signal SsL having a frequency lower than both of them.

[0186] According to such a configuration, since the frequency of the signal processed by the demodulation circuit 52 can be lowered, the corresponding frequency required for electronic components and the like used in the demodulation circuit 52 can be lowered. Therefore, by having the above-described configuration, an optical modulator 100 that enables cost reduction of the connected demodulation circuit 52 can be realized.

[0187] Further, the optical modulation unit 12 may be provided on the first vibration element 30 and include a diffraction grating 434 that diffracts the incident first divided light L1a (laser light).

[0188] According to such a configuration, even if the first vibration element 30 is an element that vibrates in, for example, thickness shear, the frequency of the first divided light L1a can be modulated. Thereby, for example, an optical modulation unit 12 using a crystal AT oscillator having a high Q value of mechanical resonance can be realized.

[0189] Further, the optical modulation unit 12 may be provided on the first vibration element 30 and include an optical reflection unit 406 that reflects the incident first divided light L1a (laser light).

[0190] According to such a configuration, when the first divided light L1a is reflected, the frequency of the first divided light L1a can be modulated to generate the reference light L2.

[0191] Further, the first vibration element 30 and the second vibration element 31 are preferably crystal oscillators.

[0192] According to such a configuration, since the crystal itself is a piezoelectric material, the first vibration element 30 and the second vibration element 31 having particularly high frequency stability can be obtained.

[0193] Further, the first frequency f M and the second frequency f C are preferably in the range of 1 MHz or more and 100 MHz or less.

[0194] 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 M and the second frequency f C within the above range, the stabilization of the first frequency f M of the first signal Ss1 output from the first signal oscillation unit 511 and the stabilization of the second frequency f C of the second signal Ss2 output from the second signal oscillation unit 512 can be achieved.

[0195] Also, the optical modulator 100 according to each of the above embodiments and modification examples includes a third vibration element 31A, a third signal oscillation unit 512A, and a switching unit 56. The third vibration element 31A vibrates at a third frequency different from the first frequency f M and the second frequency f C . The third signal oscillation unit 512A generates a third signal Ss3 of the third frequency with the third vibration element 31A as the source oscillation. The switching unit 56 selects either the second signal Ss2 or the third signal Ss3 and inputs it to the reference signal generation unit 54. Then, the reference signal generation unit 54 uses the first signal Ss1 and the signal (selected signal SsX) selected in the switching unit 56 to generate a reference signal SsL having a frequency lower than both the first frequency f M and the frequency of the selected signal SsX.

[0196] According to such a configuration, the frequency f' M after down-conversion in the reference signal generation unit 54 can be switched. Thereby, an optimal frequency f' M can be selected according to the vibration characteristics of the object 14. As a result, the laser interferometer 1 capable of acquiring optimal measurement data according to the vibration characteristics of the object 14 can be realized.

[0197] In addition, the laser interferometer 1 according to each of the above embodiments and modified examples includes a laser light source 2, an optical modulator 100 according to each of the above embodiments and modified examples, a light receiving element 10, and a demodulation circuit 52. The laser light source 2 emits emitted light L1 (laser light). The optical modulator 100 adds a modulation signal to the first split light L1a (laser light). The light receiving element 10 detects the intensity change of the interference light (laser light) including the sample signal and the modulation signal, and outputs a laser light reception signal. The demodulation circuit 52 is connected to the optical modulator 100 and demodulates the sample signal from the laser light reception signal based on the reference signal SsL. According to such a configuration, the cost reduction of the laser interferometer 1 can be easily achieved.

[0198] In addition, the spectroscopic device 900 according to the embodiment includes the laser interferometer 1 according to each of the above embodiments and modified examples, 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.

[0199] As described above, the optical modulator, the laser interferometer, and the spectroscopic device of the present invention have been described based on the illustrated embodiments. However, the optical modulator, the laser interferometer, and the spectroscopic device of the present invention are not limited to the above embodiments and modified examples, and the configuration of each part may be replaced with any configuration, or any other configuration may be added.

[0200] In addition, in each of the above embodiments and modified examples, a Michelson-type interference optical system is used, but other types of interference optical systems may be used.

Description of Reference Numerals

[0201] 1…Laser interferometer, 2…Laser light source, 3…Collimating lens, 4…Optical splitter, 6…Half-wave plate, 7…Quarter-wave plate, 8…Quarter-wave plate, 9…Photodetector, 10…Light receiving element, 12…Optical modulation unit, 14…Object, 18…Optical path, 20…Optical path, 22…Optical path, 24…Optical path, 30…First vibration element, 31…Second vibration element, 31A…Third vibration element, 50…Interference optical system, 52…Demodulation circuit, 53…Preprocessing unit, 54…Reference signal generation unit, 55…Demodulation processing unit, 56…Switching unit, 100…Optical modulator, 122…AOM, 401…Base, 402…First vibrating arm, 403…Second vibrating arm, 404…Electrode, 405…Electrode, 406…Light reflecting part, 432…Groove, 433…Pad, 434…Diffraction grating, 435…Pad, 436…Vibration direction, 437…First electrode, 438…Second electrode, 511…First signal oscillation unit, 512…Second signal oscillation unit, 512A…Third signal oscillation unit, 530…Current-voltage converter, 531…Multiplier, 532…Low-pass filter, 533…A / D converter, 534…First amplitude adjustment unit, 535…Multiplier, 536…Low-pass filter, 537…Multiplier, 538…Low-pass filter, 539…A / D converter, 541…First delay adjustment unit, 542…Second delay adjustment unit, 543…Multiplier, 544…Low-pass filter, 545…A / D converter, 546…Multiplication wiring, 547…Multiplication wiring, 548…Multiplication wiring, 551…Multiplier, 552…Multiplier, 553…Phase shifter, 555…Low-pass filter, 556…Low-pass filter, 557…Divider, 558…Arctangent calculator, 559…Signal output unit, 561…Second amplitude adjustment unit, 562…Summer, 571…Multiplier, 572…Band-pass filter, 573…Multiplication wiring, 574…Multiplication wiring, 575…Frequency divider, 900…Spectroscopic device, 910…Spectroscopic analysis unit, 920…Spectroscopic optical system, 922…Analysis light source, 924…Moving mirror, 926…Analysis light receiving part, 930…Calculation unit, 4311…Surface, 4312…Back surface, L1…Emitted light, L1a…First divided light, L1b…Second divided light, L2…Reference light, L3…Object light, S(t)…Preprocessed signal, Ss1…First signal, Ss2…Second signal, Ss2’…Second signal, Ss3…Third signal, SsL…Reference signal, SsX…Selection signal

Claims

1. An optical modulator connected to a demodulation circuit that demodulates the sample signal based on a reference signal from a laser light reception signal including a sample signal added to the laser light and a modulation signal added to the laser light for an object, comprising: a first vibration element vibrating at a first frequency; a second vibration element vibrating at a second frequency different from the first frequency; an optical modulation unit that adds the modulation signal to the incident laser light using the first vibration element; a first signal oscillation unit that generates a first signal of the first frequency with the first vibration element as a source oscillation; a second signal oscillation unit that generates a second signal of the second frequency with the second vibration 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 optical modulator according to claim 1, wherein the optical modulation unit is provided in the first vibration element and includes a diffraction grating that diffracts the incident laser light.

3. The optical modulator according to claim 1, wherein the optical modulation unit is provided in the first vibration element and includes an optical reflection unit that reflects the incident laser light.

4. The optical modulator according to any one of claims 1 to 3, wherein the first vibration element and the second vibration 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. a third vibration element vibrating at a third frequency different from the first frequency and the second frequency; a third signal oscillation unit that generates a third signal of the third frequency with the third vibration element as a source oscillation; a switching unit that selects either the second signal or the third signal and inputs it to the reference signal generation unit; comprising: The reference signal generation unit generates the reference signal having a frequency lower than both the first frequency and the frequency of the signal selected in the switching unit using the first signal and the signal selected in the switching unit. The optical modulator according to any one of claims 1 to 3.

7. a laser light source that emits laser light; the optical modulator according to any one of claims 1 to 3 that 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 the laser light reception signal; A demodulation circuit connected to the optical modulator and demodulating the sample signal from the laser light reception signal based on the reference signal; A laser interferometer characterized by comprising the same. **Claim 8** The laser interferometer according to claim 7, A spectroscopic analysis unit having a spectroscopic optical system including a movable mirror and generating spectroscopic spectrum information derived from a sample; Comprising: The laser interferometer measures the displacement of the movable mirror, The spectroscopic analysis unit generates the spectroscopic spectrum information based on the measurement result of the displacement of the movable mirror by the laser interferometer. A spectroscopic apparatus characterized by this.

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